The China International Medical Equipment Fair (CMEF) will take place in Shanghai from April 11-14, 2024. The fair is a leading global platform for medical and healthcare technology, providing a comprehensive showcase of technological advancements and solutions from the entire medical industry chain. CMEF is dedicated to industry trends, technological innovations and the promotion of future business opportunities and developments, contributing to the global progress of the medical industry.
Relyon plasma participates with its booth 5.2 K13 and presents its plasma devices for the treatment of surfaces as well as its components for integration into medical devices. Our plasma devices can disinfect, clean, modify and functionalize a wide range of surfaces in preparation for bonding, painting and printing. Our plasma components can also be used for disinfection in medical technology.
Relyon plasma takes part in the trade fair and presents its latest technology, the MediPlas system. The MediPlas system consists of the Reactor and the Driver. The Reactor is an ozone generator and can also emit hydrogen peroxide and nitrogen oxides, depending on the settings. The Reactor is based on cold atmospheric plasma (KAP) and can be integrated into applications as a component for sterilization and disinfection. The Driver is the driver for the ozone generator.
Visit us at our booth 5.2K13 at the CMEF in Shanghai and find out more about our products.
Product change notification for the power source PS2000 (19″)
We hereby inform you that the power source PS2000 (19″), which is used in conjunction with the PlasmaBrush PB3, has been further developed. The new version has a display on which the output values for plasma generation can be read. The display values appear one after the other in pairs with a display duration of 3 seconds each.
The article number has changed. Please take the new number into account for future orders.
Product designation
Old article number
New article number
Power source PS2000 (19″)
79120001
79120002
The change will take effect from 1st March, 2024. The old power sources will then no longer be available.
The device is completely downward compatible. In the event of a defect or replacement, devices with the article number 79120001 can be easily replaced by devices with the article number 79120002.
If you have any questions, please feel free to contact us at info-relyon@tdk.com at any time.
Product discontinuation plasmacell P300 as of 31 December 2023
We hereby inform that the the plasmacell P300 basic module incl. HMI with article number 1000608500, the plasmacell P300 module integrated suction with article number 1000608600 and the plasmacell P300 module compressor with article number 1000608700 will be discontinued on 31 December 2023.
The products can no longer be ordered from this point on. However, you can still obtain wear materials from us.
If you have any questions, please do not hesitate to contact us at any time via info@relyon-plasma.com.
Change of managing directors at relyon plasma GmbH
We would like to inform you that the management of relyon plasma GmbH has changed as of December 1, 2023. Dr. Stefan Nettesheim is resigning from his position as Managing Director and will support us in an advisory capacity as Senior Technology Manager.
Simona Lerach and Florian Freund will take over the new dual leadership of the management. They will continue the successful work of recent years and lead the company into a successful future together with you by providing new impetus.
We are delighted to have found industry-experienced successors in Ms. Lerach and Mr. Freund, who are ideally suited for this task. Both colleagues have been with the company for several years and, in our opinion, have the ideal wealth of experience to continue the positive development of relyon plasma GmbH as a medium-sized, technology-driven company.
In order to ensure a smooth transition, the handover from Dr. Nettesheim to Ms. Lerach and Mr. Freund has been prepared internally in the background for some time.
As before, our daily motivation remains to be your leading partner for plasma applications. The relyon plasma GmbH team you are familiar with will of course remain with you.
We look forward to continuing our dialog and, above all, to working with you in the future and will be happy to assist you.
Effective against bacteria, spores, fungi, and viruses, even when organized in biofilms. The high oxidation potential of peroxides and ozone, combined with the protein denaturation ability of nitric acids, leads to the perforation of protective cell membranes, acidification of biofilm pH values, partial oxidation of organic molecules (peptides, lipids), structural unfolding, and damage to RNA and DNA. Nitric acid can also nitrate aromatic amino acids like tyrosine and tryptophan. The synergistic effect of oxidation (ozone and peroxides) and denaturation enhances the overall disinfection capabilities of the mixture. Process control, such as temperature and dew point, plays a crucial role when a thin film of active substances condenses on the object to be sterilized.
Deodorization:
Effective in removing many volatile organic components with unpleasant odors from the air. However, it’s essential to be aware that partial oxidation may lead to potentially harmful byproducts, which should either be fully oxidized or absorbed by filters. An ideal approach is to capture the VOCs on a porous catalytically active adsorbent and subsequently degrade them using the Mediplas output.
Bleaching:
Swiftly fades organic colors, such as traces of tomato or coffee, cigarette condensate, etc. Moderate humidity can expedite the bleaching process.
Additional Applications:
Pest control
Plant protection
Fertilization
Cleaning of food or medical fluid systems
Water purification
MediPlas Output
MediPlas™: more than a simple ozone generator
Medical | Dental | Pharma | Packaging | Food
In essence, the chemistry of the plasma discharge is influenced by numerous parameters, of which only a subset can be adjusted independently. Extensive data has been gathered on this matter, though it won’t be expounded upon in this discussion. Nevertheless, for the prevalent practical scenario involving the utilization of air as the working gas, it is possible to streamline the most critical operational modes.
Typically, we can categorize the various modes of operation as follows:
Achieved when utilizing pure (dry) oxygen, obtained, for example, through pressure swing adsorption (PSA). Maximum concentration is reached by maintaining a cold reactor using the integrated Peltier cooler and keeping power density at a moderate level.
When compressed dry air is employed, the best ozone concentration is achieved at relatively low power density and optimal cooling. (For more detailed information, please refer to the comprehensive application note and consult the datasheets.)
High NOx Output:
This mode is activated when compressed dry air (CDA) is passed through the reactor while increasing the temperature and power density. In this case, ozone levels will start to decrease in favor of a rising concentration of various nitrous oxides with different oxidation states (NO2, N2O4, N2O5).
Peroxide Formation
Peroxides are generated in the presence of humidified input (water). These peroxides are highly reactive towards ozone and nitroxides, acting as precursors to higher oxidation states of nitrous oxides and acid formation.
Acid Formation:
Acidic species such as nitrous acid (HNO2) and nitric acid (HNO3) are formed in the presence of water and nitrous oxides.
We are moving even closer to our parent company TDK Electronics and will be integrated into its core structure. Therefore our e-mail addresses will change starting from calendar week 47/48.
However, relyon plasma GmbH will remain your reliable partner for plasma applications. Apart from the e-mail addresses, nothing will change for you in your contact with us – the usual contact persons will continue to be at your disposal.
The e-mail addresses of the individual colleagues are structured as follows: forename.surname@tdk.com
Our other e-mail addresses will change as follows:
We still have access to our old e-mail addresses for the time being and a forwarding service has also been set up. So don’t worry – your e-mails will reach us in any case.
Please feel free to pass this information to your colleagues. Apart from the e-mail addresses, nothing will change for you in your contact with us – the usual contact persons will continue to be available to you.
Dielectric barrier discharge flow reactors stand out as highly efficient technologies for ozone production using oxygen as their base. However, when employing ambient air, the chemistry becomes notably more intricate, involving multiple competing reaction pathways, resulting in a mixture of ozone combined with nitric oxide components, nitric acids, and peroxides. The process parameters that play a significant role in determining the output composition include:
We have developed a reactor tailored for typical flowrates ranging from 0 to 10 standard liters per minute (slm), incorporating integrated active Peltier cooling, which provides excellent control over the process temperature. The specially adapted driving circuit can finely adjust power density (via pulse-width modulation, PWM) and the amplitude of the excitation voltage. Additionally, the driver features a feedback signal that is proportional to the discharge intensity.
With the MediPlas components, constructing a robust, versatile ozone generation system becomes straightforward. Essentially, all you require is a DC power supply and a gas supply or an air pump.
From September 27-28, 2023, the User Group Atmospheric Pressure Plasma will again present innovative plasma applications at the 44. ak-adp workshop in cooperation with the National Center for Plasma Medicine e.V. and the Göttingen Health Campus. As part of this workshop, Dr. Stefan Nettesheim will give a presentation on the MediPlas™ system, which was developed for disinfection and sterilization, for example.
Wednesday, 27 September
1:00 p.m.
Opening of the workshop
1:10 p.m.
Cold plasma from wound healing to cancer – the role of the immune system
Influence of cold plasma on brain tumor cell growth – First results and perspectives
11:30 a.m.
In vivo mechanistic studies to elucidate plasma-induced microcirculation enhancement
12:00 p.m.
The patient room of the future as a real laboratory
12:30 p.m. Lunch
1:00 p.m.
Microbiological analyses and healing success after kINPen MED use in the context of plasma therapy of chronic wounds in patients with diabetes mellitus
1:30 p.m.
New procedure for peri-implantitis treatment – a multicenter pilot study
2:00 p.m.
Promising use of cold plasma in pilot studies on wound healing and rosacea
2:30 p.m. Finisher coffee
3:00 p.m.
General meeting of the NZPM
Participation fee
Incl. participant documents, regulars’ table and refreshments during breaks plus VAT 350.00 Euro.
Space Team Aachen uses the piezobrush® PZ3 for pretreatment with plasma in rocket development. In an application report, the student association provides insight into the work with the handheld device and the results achieved.
Motivation for the use of plasma
In the STAHR (Space Team Aachen Hybrid Rocket) project of Space Team Aachen e.V., a student experimental rocket with a self-developed hybrid engine is being constructed. The project is supervised by DLR (German Aerospace Center) within the framework of the STERN program. DLR’s STERN program (Student Experimental Rockets) offers aerospace engineering students at German universities the opportunity to plan and build their own rocket projects and launch them from the Esrange Space Center in northern Sweden. The rocket will launch in late 2024 and fly at speeds of up to Mach 1.4 to an altitude of at least 10 km. Almost all components will be developed in-house, from the flight computer to the engine and structural components.
The main elements of the rocket structure are the so-called body tubes. These are tubes made of carbon and glass-fiber reinforced plastic. Each rocket section consists of one tube. The individual sections are connected by aluminum interfaces glued into the tubes. The glued connection from the tube to the interface is a critical connection in the rocket. If it fails, the flight is a failure.
To achieve the best possible joint strength, suitable surface pretreatment of the bonding surfaces is essential. As part of a series of tensile shear tests in accordance with DIN 1465 at the Institute of Welding and Joining Technology (ISF) in Aachen, we first tested various pretreatments. Sandblasting on the aluminum interface and pretreatment with plasma on the carbon fiber-reinforced plastic (CFRP) proved to be the most suitable. For the plasma treatment, we used the piezobrush® PZ3 handheld plasma device at the institute. Its small form factor makes the device perfect for use inside the rocket’s carbon fiber tubes. It can also be taken anywhere in its carrying case, which is important for us since we work at different institutes in Aachen and thus need to be mobile.
Production of a section prototype
In order to experimentally validate the structure of the rocket, we made a prototype rocket section. The prototype consists of a carbon fiber reinforced tube bonded to two aluminum interfaces. This was the first time we used the piezobrush® PZ3 plasma handheld device on a real rocket component. Before surface treatment, we thoroughly cleaned all bonding surfaces with isopropanol. The pretreatment of the inside of the carbon fiber reinforced tube worked very well. The compact size of the unit made surface activation inside the tube possible in the first place.
Alternative pretreatment methods such as lasering would be difficult to implement due to the limited space. On the recommendation of Relyon Plasma, we used the device not only for surface activation of the carbon fiber-reinforced tube, but also for additional cleaning of the sandblasted surface of the aluminum interface. Here we initially had the problem that the device switched off the plasma after a few seconds. However, a quick look at the manual quickly remedied the situation: The shutdown is a protective function, which is activated if the device does not make contact with the component within five seconds. With this function in mind, further handling of the interface worked without a hitch. Results of the test series, for which we produced the prototype, are not yet available. These will be carried out at the end of August.
Due to the practical handling and the compact form factor, which is important for our application, we have firmly integrated the use of the piezobrush® PZ3 plasma handset into our production process.
About Space Team Aachen
Space Team Aachen is an association that offers interested students of RWTH and FH Aachen the opportunity to participate in pioneering space research. The growing team currently consists of more than 140 members. They are developing their own hybrid and liquid rocket engines. In addition, the highly motivated researchers also participate in international rocket competitions with their innovative developments. The team works closely with numerous renowned partners from science and industry.
Swiss Medtech Expo 2023
Information about the Swiss Medtech Expo
From 12 to 13 September, 2023, Swiss Medtech Expo will once again open its doors in Lucerne, Switzerland. The leading trade fair revolves entirely around the medical industry and is the third largest trade fair on the European medtech market. Around 170 medical device manufacturers, system and component suppliers, service providers and research and educational institutes will meet on site.
The show will focus on innovative materials, surfaces and coatings, miniaturization, regulatory affairs, smart design & engineering, out-of-the-box topics, smart manufacturing, additive manufacturing and smart products. The trade show and symposium, which will feature keynote presentations from science, technology and industry, will thus provide insight into the current state of medical knowledge. AM Expo and AMPA will also be held at the same time on the exhibition grounds.
The MediPlas system at trade fair
Relyon plasma will also be on site with its parent company TDK Electronics to present the MediPlas system. The system consists of two components, a reactor and a driver. When used, the reactor generates a high concentration of non-toxic gases that can be used to sterilize medical devices. The driver serves as a power source for the reactor. Please feel free to visit us at the Lucerne Exhibition Center in Hall 2, Booth F 2193a, and learn more about the wide range of applications for the MediPlas system.
You can find more information about the trade fair here.
3rd Chemistry World Conference
Presentration on the MediPlas® system: More than a simple ozone generator
From June 14-15, 2023, the 3rd Chemistry World Conference will be held in virtual format. The theme is “Modifying Chemistry with the Novelties that Accomplish Future Goals.” Special emphasis will be placed on the significant contribution of chemistry to the progress of humanity and to solving fundamental problems of today’s society. The prestigious group of participants includes business leaders, scientists, researchers, chemists, chemical engineers and academic experts.
Dr. Stefan Nettesheim, Managing Director of relyon plasma, will give a presentation on the MediPlas® system on the first day of the event. This will emphasize that the system is more than just a simple ozone generator.
Abstract to the presentation
With the help of the abstract, you can get an idea in advance of what content you can expect during the presentation:
Dielectric barrier discharge flow reactors are among the most efficient technologies for producing oxygen-based ozone. When ambient air is used, the chemistry becomes much more complex and involves many competing reaction pathways, resulting in a mixture of ozone with nitrogen oxide components, nitric acids and peroxides. The process parameters that determine to some degree the composition of the result are: Composition and humidity of the incoming gas, power density of the dielectric barrier discharge, amplitude of the electrical excitation, and process temperature.
We have developed a reactor for typical flow rates of 0-10 slm with integrated active Peltier cooling that provides high control over the process temperature. The custom driver circuit can adjust the power density (via PWM) and the amplitude of the excitation voltage. The driver also includes a feedback signal proportional to the discharge intensity. A well-defined output including very high ozone concentrations of more than 30,000 ppm can be achieved with very high stability.
However, for some sterilization and medical applications, we have shown that the sweet spot for germicide is not necessarily the operating point of highest ozone concentration, but that the nitric oxide species in combination with moisture and peroxides play a crucial role. The components described in this paper can be easily integrated into a wide variety of systems and can be specifically controlled to optimize the desired effects.
More information about the Chemistry World Conference can be found here.
Effective plasma pretreatment before bonding plastics
Plasma pretreatment significantly improves the quality of bonding results. The plasma technology used at Regiotape is based on the cold plasma principle. Here, electric arcs are generated by a piezoelectric direct discharge, which effectively processes and treats the surface to be treated. Surfaces functionalized by plasma exhibit a significant improvement in adhesion and can be used on a wide range of materials such as metals, plastics, glass, ceramics, wood and textiles. Depending on the material, plasma pretreatment can achieve an increase in adhesive strength of up to 132 percent.
Regiotape works with the piezobrush® PZ3 from relyon plasma in various areas. The company uses the handheld device to pre-treat customer materials, to improve adhesion and determine suitable adhesive tapes and adhesives, and to clean surfaces before bonding.
For this purpose, the Standard module for electrically non-conductive materials or the Nearfeld module for ectrically conductive materials are available for use depending on the production setup, customer requirements, treatment area and material.
Due to ever new surfaces being used in the automotive, aero, consumer and plastics sectors, the requirements with regard to processing and bonding have changed considerably in recent years. New plastic materials such as carbon, wood-plastic composite (WPC), various polyamides (PA) as well as low-energy materials (PE, PP etc.) are increasingly being combined with bonding technology for design and cost reasons. However, since the surfaces sometimes offer poor adhesion for the anchoring of the adhesive tapes and adhesives, the processing of the surface before bonding is decisive for the success of the bonding.
Here we learned from the company relyon plasma about a possibility that makes it possible to increase adhesion simply and significantly by means of plasma treatment. The low-voltage cold plasma devices from relyon plasma are ideal for conditioning critical surfaces and show excellent adhesion improvement on the surfaces mentioned and many others. We now use the plasma devices to process batch orders and to determine adhesion requirements on a wide variety of materials and are continually surprised by the positive results.
Efficient plasma pretreatment before bonding
An example shows the pretreatment with plasma of PA 6.6. A pretreatment with plasma achieved an adhesive strength improvement (adhesion of the 2K adhesive) of 60 percent.
Another example shows the plasma treatment on a carbon bicycle fork to increase the adhesion for a 2K adhesive used to insert the ball bearing shell. The piezobrush® PZ3 was used in conjunction with the Nearfield module for conductive surfaces. This plasma pretreatment increased the adhesion on the carbon mount by more than 50 percent.
About Regiotape
Regiotape GmbH is an outstanding supplier of adhesive tape solutions with more than 28 years of experience. The company places particular emphasis on innovative competence, customer orientation and technological know-how. In addition to a broad product portfolio consisting of over 1,200 different adhesive tapes, adhesives and occupational safety products, the adhesive specialist also offers services such as plasma pretreatment.
Industry Dialog for Sustainability – Plasma Technology in Best Practice Examples
From April 26-27, 2023, the user group atmospheric pressure plasma will again present innovative plasma applications for adhesion improvement at the 43. ak-adp workshop in Leipzig. A special focus will be on the topic of sustainability. As part of this workshop, Markus Mayer, application field engineer at relyon plasma, will give a presentation on the piezobrush® PZ3-i integration solution as part of the #ZukunftADP 2021 competition.
Wednesday, 26. April
1:00 p.m.
Opening of the workshop
1:15 p.m.
Plasma pretreatment for more sustainable production
1:45 p.m.
Evaluation of bio-based plastics and adhesives for lightweight construction
2:15 p.m.
Plasma chemical oxidation of magnesium components for use in optical equipment manufacturing
2:45 p.m. t.b.a.
3:15 p.m. Coffee break
4:00 p.m.
Plasma functionalization of natural fibers and biopolymer fibers for compounding.
4:30 p.m.
Plasma applications for agriculture: potentials and challenges
5:00 p.m.
Optical inspection of ultrathin SiOx coatings during production
5:00 p.m.
Industrial espionage and computer security – risks in a networked world – your data is certainly safe, isn’t it?!
7:00 p.m. Regulars’ table
Thursday, 27. April
9:00 a.m.
Competition #ZukunftADP – Review 2021
11:00 a.m. Coffee break
11:45 a.m.
Competition #ZukunftADP – Call for entries II
1:00 p.m. Lunch
2:00 p.m.
Special guided tour of parts of the museum focusing on “Surfaces of museum objects made of metal and their advantages/disadvantages in terms of preservation/restoration”
Participation fee
Incl. participant documents, evening program and refreshments during breaks plus VAT 300,00 Euro.
Application of the plasma bridge for grounding of conductive substrates
Autoren: Dariusz Korzec, Markus Hoffmann and Stefan Nettesheim
Datue: March 2023
Abstract
An atmospheric pressure plasma jet (APPJ) sustained by a pulsed atmospheric arc (PAA) transferred on an electrically conducting surface was operated with a mean power of 700 W, a pulse frequency of 60 kHz, and a gas mixture of N2 and H2 with up to 10% H2, flowing at 30 to 70 SLM. The plasmabrush® PB3 was used for this purpose. It was shown that the plasma bridge ignited between the grounded injector and electrically conducting and floating substrates can be used for electrical grounding. This allowed for arc transfer on such substrates.
The plasma bridge was stable for Argon flow through the injector from 3 to 10 SLM. Its length was between 5 and 15 mm. The plasma bridge current was 350 mA. The copper contact pads on an alumina electronic board were treated using the plasma bridge sustained by Ar injection for grounding. First, an oxide film of about 65 nm was grown by a compressed dry air (CDA) plasma jet. Then, this film was reduced at a speed of 4 cm2/s by forming gas 95/5 (95% of N2 and 5% of H2) plasma jet.
Introduction
The atmospheric pressure plasma jet (APPJ) in its numerous variations is a kind of cold atmospheric plasma (CAP) or atmospheric pressure plasma (APP) broadly used in research and industry. The low-temperature arc jet has a high potential for material processing due to its high local plasma density. The popular way of arc stabilization in low-temperature arc jets is a gas vortex. The physical, electrical, and material properties of such jets have been investigated. Many applications have been described, e.g., the modification of the surface of polymers for the improvement of adhesion, for example polyethylene, glass-fiber-reinforced polypropylene, or polydimethylsiloxane (PDMS). Furthermore, metal surfaces can be treated. Surface modification for the hydrophilic property of stainless steel treated by an atmospheric pressure N2-O2 plasma jet was demonstrated. Varnished or polymer-coated metal surfaces can also be successfully treated. A material increasingly interesting for surface treatment is glass. Other applications are oxidation and rapid annealing.
The plasma generator used in this study belongs to the pulsed atmospheric arc plasma jets (PAA-PJs). Its discriminating feature is the generation of the arc via HV pulses in the kHz range with voltages up to 15 kV for ignition and in the range of 500 V to 3000 V for sustaining the plasma. Recently, its physics was investigated by laser scattering techniques and optical spectroscopy. The influence of the pulse amplitude and frequency on PAA-PJ’s properties was examined.
Diffuse plasma mode
The PAA-PJ can be operated in diffuse or focused plasma mode. The broadest application of diffuse mode is the activation of different surfaces to increase the surface free energy (SFE) of polymers for the improvement of the paintability or gluing properties or for casting. The enhancement of the bonding properties of pressure-sensitive adhesives on coatings of white goods by means of atmospheric pressure plasma treatment has been demonstrated. Another example is the surface modification of carbon fibers. A strong increase of wetting, expressed as a decrease of the contact angle, resulting in the widening of printed electric contacts was observed after nitrogen plasma treatment of gas, PI, and PET before aerosol jet printing. The improvement of the mechanical shear strength of glued joints on PAA-PJ-treated aerosol-jet-printed pads has been documented. The suitability of the PAA-PJ for bacteria inactivation on temperature-sensitive surfaces was demonstrated on an example of geobacillus stearothermophilus spores.
The high energy density in the arc zone allows for the use of the PAA-PJ for coating processes. A 1.29 nm/s deposition rate of zinc oxide was demonstrated using a nebulized ZnCl2 solution sprayed into the downstream of the nitrogen plasma jet. The PAA-PJ can be used for low-density polyethylene coating, fluxing of printed circuit boards, coating wood with polyester or TiO2, and coating of bismuth oxide circular droplets.
Focused plasma mode
The term focused plasma mode is used for the operation of the PAA-PJ with the HV arc transferred from the grounded nozzle to a grounded, electrically conducting substrate. Under such conditions, a dense plasma is produced directly at the substrate surface. The transferred arc has been proven to be efficient for the cleaning, delubrication, oxide reduction, surface roughening, or depainting of metal surfaces. The mechanism of adhesion improvement is mainly chemical, but also, an increase in the surface roughness is involved. An additional advantage of the transferred arc is that no erosion of the nozzle occurs, and consequently, the lifetime of the nozzle can be prolonged by an order of magnitude. The applicability of this operation mode is limited by the need for the connection of the substrate to the electrical ground which is not always possible.
This study showed how an electrically floating surface charged up by a transferred arc can be grounded using a plasma bridge. Originally, the term plasma bridge referred to the low-pressure plasma used for the neutralization of an ion beam. However, in this study, it means the gaseous discharge ignited at atmospheric pressure in a gas with a low breakdown voltage such as argon for establishing a highly conductive electric connection between the substrate and the grounded gas injector. In this paper, the basic properties of such a plasma bridge are discussed. The reduction of oxidized copper contact pads distributed on a ceramic plate demonstrated the technological applicability of such a plasma bridge.
Conclusion on grounding of conductive substrates
If the PAA-PJ is used for the treatment of electrically conducting substrates, the transferred arc can be established only to electrically grounded surfaces. In some cases, the conducting surfaces, e.g., contacting pads of electronic boards, are constructed as electrically floating. In this study, it was shown that, for the grounding of floating electrodes, the plasma bridge ignited in argon can be used. The plasma bridge can be achieved by flooding of the contact pad by argon from an electrically conducting and grounded injector tube. The plasma bridge was ignited because, without grounding, the potential of the electrically floating substrate rose to many hundreds of volts, sufficient for gaseous breakdown in argon between the substrate and the injector. After ignition, the plasma bridge can be sustained even without the substrate between the injector and the HV arc.
The establishment of the plasma bridge was possible for argon flows between 3 and 10 SLM. The plasma bridge cannot be sustained for an argon flow below 3 SLM. At such low flows, the argon flux did not expand sufficiently to reach the substrate and allowed closing the electric gap between the biased substrate and the injector. The plasma bridge cannot be sustained for an argon flow over 10 SLM. The possible reason is the transition of the argon flow from laminar to turbulent, resulting in disruption of the argon bridge discharge.
Application example
The reduction of oxidized copper contact pads on alumina plates by forming gas 95/5 plasma was investigated as an application example. To achieve the grounding of the contact pads, the argon plasma bridge was used. The contact pads on the electronic board were made free from oxides without damage on the electrodes or on the solder stopping paint. Despite the non-conducting gaps between the contact pads, the plasma bridge was not extinguished during the entire duration of the electronic board treatment. The cuprous oxide film with a thickness of about 66 nm on an electric board with an area of 210 cm2 could be reduced within a 2 min process, reaching the processing speed of 4 cm2/s. For the typically much thinner native oxide, the process speed could be increased on order of magnitude.
Plasma cleaning – paint stripping and cleaning with plasma
Until now, atmospheric plasma treatment has been regarded more as a fine cleaning technique – i.e. plasma cleaning – that only acts on the immediate surface. A clean removal of large contaminations or thick layers was not possible until now. Read all about the topic in the following article: Plasma cleaning – paint stripping and cleaning with plasma.
Typically, thick layers (>1/100 mm) were always first removed mechanically, for example by grinding, sandblasting or brushing, and then post-cleaned. This creates large amounts of dust and can damage the product surface. Another well-established process is burning off with flame or hot air. Although this does not produce dust, it does produce a high emission of hazardous combustion gases, depending on the composition of the layer.
Wet-chemical processes with aggressive stains are also not harmless when used. Residues of the pickling can later lead to component corrosion and must therefore be completely removed after the process. Modern processes, such as laser cleaning or dry ice blasting, are not applicable in all cases and may be very cost-intensive. Dry ice blasting requires a continuous supply of CO2 abrasive. For the application of a cleaning process with atmospheric plasma, only a mains connection and compressed air are required.
Basic principle of plasma treatment
In order to effectively remove a layer from a surface, the best point of attack is in principle the interface between the two materials. If it is possible to focus the power of the removal mechanism precisely on this inner surface, the efficiency of the process is highest. In this case, it is not necessary to remove the entire layer thickness step by step, but the interface is stressed so much that the layer detaches. An atmospheric pressure plasma torch, whose voltage source generates a high voltage swing, can now be operated in such a way that an electrical breakdown occurs in an insulating or poorly conducting layer on a conductive material and a high energy is released in pulses at the transition from the insulating layer to the conductive substrate. With short pulses, a thermomechanical pressure wave is released at the interface and the layer is blasted free at a defined point. If the plasma flame is operated at a high pulse frequency and scanned over a surface, contiguous areas can be easily exposed.
Practical investigation and application
With this innovative process, it has been possible to effectively remove layers of paint more than one millimeter thick with a plasma jet. Only a very small amount of burn-off occurs and the product surface is hardly subjected to thermal stress or mechanically damaged. The result is a clean surface with a fine roughening that is ideally prepared for further processing steps. Bonding, contacting or coating are possible options here.
For the tests, the plasma system plasmabrush® PB3 was integrated into an XYZ axis unit (plasmacell 300) and operated in “ablation mode”. In this system, raster speeds of up to 800 mm/s are possible. The plasma ablation process can be automated or manual. This means that even difficult and angled areas can be easily reached. All conductive substrates are suitable, for example sheet metal, aluminum, steel, copper or conductive carbon fiber structures. The paint layer does not have to be conductive. Plasma blasting offers great application flexibility and can be used for the following coating systems, among others: Release agents, sizing, product residues, adhesive and glue deposits, polish residues, bitumen, waxes, paint layers, flux deposits. The areas of application are in production, maintenance and service in almost all industrial sectors.
Influence of non-thermal plasma systems and two favorable surface treatments
on the shear bond strength of PAEKs to composite resin
Authors: Dede, D. Ö., Ercan, U. K., Küçükekenci, A. S., Kahveci, Ç., Özdemir, G. D. & Bağış, B.
Publication: Influence of non-thermal plasma systems and two favorable surface treatments on the shear bond strength of PAEKs to composite resin, Journal of Adhesion Science and Technology, 2022, 36 (7), 748-761.
The polymers polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) are part of the polyaryletherketones (PAEK). They are of great interest for (dental) implants due to their biocompatibility and bone-like mechanical properties. However, the physical and chemical inertness of the substances also poses challenges in their processing.
The aim of this study therefore was to investigate the influences of non-thermal plasma (NTP) on the shear bond strength and surface roughness of PEEK and PEKK in composite resin. For this purpose, the polymers were partially pretreated by sandblasting or by etching using sulfuric acid.
In the study the NTP was generated based on two technologies: dielectric barrier discharge (DBD) and piezoelectric direct discharge (PDD). The piezobrush® PZ2 was used to generate PDD plasma.
Fig. 1: Generation of NTP based on dielectric barrier discharge (left) and piezoelectric direct discharge by the piezobrush® PZ2 (right).
The pre-treatment of a total of almost 300 PEEK and PEKK substrates (7 mm x 7 mm x 3 mm) were each divided into 9 different groups. These included a control group, pre-treatment of the substrates only by plasma (DBD and PDD), by sandblasting with silica-coated aluminium oxide particles and etching by highly concentrated sulphuric acid. Likewise, sandblasting and etching were each combined with one of the two methods for generating NTP (DBD and PDD).
The highest shear bond strength for PEEK was achieved on the substrates etched with sulphuric acid with a value of 20.29 ± 2.31 MPa (control group value: 8.54 ± 0.81 MPa). For PEKK, sandblasting was the most effective method. It increased the shear bond strength to 18.91 ± 1.09 MPa (control group value 8.68 ± 0.61). Treatment with the piezobrush® PZ2 resulted in an increase to 11.37 ± 0.53 MPa (PEEK) and 11.28 ± 1.11 MPa (PEKK). The plasma generated by DBD did not provide a significant increase. Furthermore, the combinations of sandblasting with plasma and etching with plasma also increased the shear bond strength values.
The surface roughness of PEEK and PEKK increased for both polymers only with sandblasting. They did not increase when treated with PDD and DBD. After etching, the surface roughness were even lower. It is striking that plasma treatment alone did not change the basic structure of the polymers, whereas sandblasting had a strong roughening effect. Etching tended to reverse these irregularities, with small cavities appearing after subsequent PDD treatment (cf. SEM images in Fig. 2, bottom right).
Fig. 2: SEM images of PEEK after surface treatments. (A) Control gr.; (B) DBD; (C) PDD; (D) Sandblasting; (E) Sandblasting + DBD; (F) Sandblasting + PDD; (G): Etching; (H): Etching + DBD; (I): Etching + PDD; For PEKK the results were similar.
With the already established methods of sandblasting and etching, good results can be achieved for increasing shear bond strength. However, their invasive and toxic properties are often critical for applications in the clinical field . Here plasma can provide a remedy. In this study, treatment with the piezobrush® PZ2 led to a significant increase in shear bond strength. Consumables can be dispensed with in the process.
Conclusion:
The study has shown that surface treatment of PAEKs with relyon plasma’s piezobrush® PZ2 prior to bonding to composite resin enables an increase in shear bond strength. Although already established methods achieve good results, activation by a compact hand-held device without the use of toxic consumables is quite promising.
Treatment with atmospheric pressure plasma
Effects of the treatment on the adhesive bonds of metal surfaces
Publication: Metal malzeme yüzeylerinin yapıştırma işlemlerinde atmosferik basınçlı plazma uygulamasının etkisi . Gazi Üniversitesi Mühendislik Mimarlık Fakültesi Dergisi, 38 (2), 665-678. DOI: 10.17341/gazimmfd.1025228
First published: https://dergipark.org.tr/tr/pub/gazimmfd/issue/72928/1025228
Summary
The following text summarises the Turkish study on the effect of atmospheric pressure plasma treatment on adhesive bonds of metal surfaces. The plasma treatments were carried out with the piezobrush® PZ2.
Atmospheric pressure plasma (APP) applications have come to the fore in many fields today. They can be applied quickly and stably to material surfaces and offer many advantages over plasma applications in vacuum. With APP, it is possible to improve the surface energies and adhesion behaviour of materials. In this study, the effect of atmospheric pressure plasma application on the adhesive bond strength of galvanised steels (H300LAD) and non-galvanised steels (H300LA) was investigated. Two different materials, two different adhesives and three different plasma application speeds were determined as experimental parameters. The results show that APP application improves the metal bonding process.
The contact angles of the test specimens made from galvanised and ungalvanised steel material were measured using water drops, and the relative surface tensions were determined using the ink test. These data were compared with those obtained after APP treatment and the effects of plasma treatment on the surface properties were studied. The test specimens produced with different plasma speeds and different adhesives were subjected to a tensile test. The data obtained were used to evaluate the effects of plasma treatment on the adhesive strength of the materials.
After APP treatment, an improvement in surface wettability of approximately 69% was achieved for the galvanised material and 34% for the non-galvanised steel material. In the experimental group (M1 Y2 V3), the adhesion strength increased 4.38 times after APP treatment, with the largest increase. The smallest increase in bond strength was achieved in the experimental group (M1 Y1 V1) with an increase of 1.74 times. While it is clear that bond strength increases with increasing plasma velocity, the most notable increase is the 39% increase in bond strength obtained by changing the velocity from V1 to V3 for galvanised steel.
Conclusion
It was found that the application of APP increases the surface energy of galvanised steel and non-galvanised steel, thereby improving the adhesion behaviour of metals. This difference can be further increased by varying experimental parameters. Furthermore, it was found that the plasma velocity changes the surface energy very effectively.
You can read the full publication in Turkish here.
The In-Vitro Activity of a Cold Atmospheric Plasma Device
against Bacteria and Biofilms Associated with Periodontal or Peri-Implant Diseases
Authors: Jungbauer G., FavaroL., MüllerS., Sculean A. & Eick S.
Publication: The In-Vitro Activity of a Cold Atmospheric Plasma Device Utilizing Ambient Air against Bacteria and Biofilms Associated with Periodontal or Peri-Implant Diseases, Antibiotics, 2022, 11(6), 752.
Conventionally, the biofilm that develops in periodontal and peri-implant diseases is removed mechanically and treated with the addition of antibiotics. Due to the generally high use of antibiotics, a search for alternative treatment methods is necessary, with cold atmospheric plasma (CAP) showing promising potential as a new treatment method.
The aim of the in-vitro study was to investigate the effect of CAP on log10-step reduction of colony forming units (CFU) for different planktonic bacterial species. A treatment of multispecies biofilms also took place. Furthermore, the adhesion of gingival fibroblasts to dentin and titanium samples before and after plasma treatment was considered.
In the study, the piezobrush® PZ3 with Module Nearfield from relyon plasma, which was originally developed for non-medical applications, was used to generate CAP. Figure 1 shows the experimental setup. The plasma generated by a combination of Piezoelectric Direct Discharge and Dielectric Barrier Discharge was efficiently transferred to the grounded substrate. It reached a temperature of about 50 °C with a power consumption limited to 8 W, and the treatment distance was 2 mm.
Figure 1. Experimental setup for the effect on planktonic bacteria and biofilms; DBD: Dielectric Barrier Discharge.
The bactericidal effect of CAP was investigated on a total of 11 bacterial species (including P. gingivalis, T. forsythia, and F. alocis). Treatment times were 10, 30, 60, and 120 s. Compared to the untreated samples, a reduction of ≥3 log10 CFU could be detected in 10 of 11 bacterial species already after 30 s, and after 120 s the detection threshold of CFU could be undercut by 8 of the 11 species.
Figure 2. (A) Colony forming units (CFU) counts, (B) mass and (C) metabolic activity of multispecies biofilms on dentin specimens and subsequent exposing of 30 s, 60 s and 120 s to cold plasma.
A strong influence on biofilms was also demonstrated by experiments with CAP. These were cultivated from the already investigated planktonic bacterial species. Figure 2 shows the test results on dentin. The number of CFU of the untreated biofilms was on average >8 log10, with a strong time-dependent decrease due to plasma treatment. After 120 s, a mean reduction of 2.43 log10 occurred. Biofilm mass did not change significantly by treatment, in contrast to metabolic activity. The latter was reduced by 95 % after 120 s of treatment. Analogously, similar results were obtained for titanium surfaces.
Figure 3. Gingival fibroblast counts per mm2 on (A) dentin and (B) titanium specimens after pretreatment of 120 s of cold plasma.
Adhesion of gingival fibroblasts was observed mainly on titanium. In Figure 3, a significant increase in fibroblast concentration from 800 to 1200 cells/mm2 can be seen after a treatment period of 120 s in contrast to dentin, which underlines the potential of CAP for the pretreatment of titanium implants.
Conclusion:
In summary, it is shown that CAP, in this study generated by the piezobrush® PZ3, can be used as an effective bactericide. CAP has a strong inhibitory effect on biofilms and can be used as a pretreatment of titanium implants to enable faster fusion with jawbone material. In particular, the significant increase in fibroblast concentration promotes faster wound healing. The possibilities of treating periodontal and peri-implant diseases with CAP have been demonstrated with the promising results of this study and form the foundation for further investigations.
Plasma-Oncology: Adjuvant therapy for head and neck cancer using cold atmospheric plasma
Authors: Xuran Li, Xiaoqing Rui, Danni Li, Yanhong Wang und Fei Tan
Publication: Plasma oncology: Adjuvant therapy for head and neck cancer using cold atmospheric plasma. Front. Oncol. 12:994172. doi: 10.3389/fonc.2022.994172
First published: https://www.frontiersin.org/articles/10.3389/fonc.2022.994172/full
Total recap
Summary of an interesting basic research publication on the potential use of plasma as adjuvant therapy in plasma-oncology for head and neck cancer:
More than half a million people are diagnosed with head and neck cancer (HNC) every year. In addition to the already classically established treatment methods, including surgery, chemotherapy and immunotherapy, an accompanying treatment with CAP (cold atmospheric plasma) will be investigated and made possible in the future.
Exemplary, CAP was generated by our piezobrush® PZ2 for the treatments in this study. As a partially ionized gas, CAP has already found widespread use in the medical field due to its ease of application. The plasma generation is based on piezoelectric direct discharge, whereby a temperature of 50 °C is not exceeded.
The publication also conducted an extensive literature review that drew on the effects of CAP as a way of treatment for HNC. Many of these studies report a positive effect of plasma on HNC, either at the microbiological level or by reducing patient symptoms.
Possible treatment can be either direct or indirect. In Figure 1, HNC cell structures in different media are directly plasma treated with CAP. An in vivo treatment could also be successfully performed. In indirect treatment, the reactive species generated by the CAP are transferred to a living recipient via an intermediate carrier.
The positive effect generated by the plasma occurs through an interplay of chemical and physical processes and is triggered, among other things, by charged particles and reactive oxygen and nitrogen species (ROS and RNS), which exert oxidative stresses on the tumor cells to be treated. Structural changes associated with this frequently lead to apoptosis and thus prevent further development of the tumor.
This is achieved by increased selectivity for diseased cells in contrast to neighboring healthy cells. In addition, CAP induces different DNA damage and causes mitochondrial dysfunction. Figure 2 explains the different influences on treated cancer cells in detail.
As a comprehensive therapy for the treatment of HNC (which includes thyroid cancer and melanoma, among others), CAP not only comes into question because of its dual-use capability, but also represents a complementary tool in the fight against carcinoma as an adjuvant therapy.
With its bactericidal effect, CAP can be used, for example, for postoperative treatment following the removal of tumor ulcers. Thus, it is possible to accelerate wound healing, reduce the use of pain-relieving drugs and increase a patient’s sense of well-being.
Relyon plasma will present its latest product developments at the booth of parent company TDK at electronica in Munich from November 15 to 18, 2022. The handheld piezobrush® PZ3, the compact plasma integration piezobrush® PZ3-i, the five modules and the MediPlasTM system will be on display in Hall A5 Booth 107. Almost at the same time, the disinfection and sterilization congress WFHSS will take place in Barcelona from November 16 to 19, 2022. Relyon plasma will also present the new high-performance ozone generator “MediPlas Reactor” and the drive unit “MediPlas Driver” at booth no. 15.
Cold atmospheric plasma solutions for manual and integrated applications
The use of plasma positively influences surface properties of materials that are of high importance for processing and end use. Users can thus significantly improve not only the quality of their work and production processes, but also of their products. The piezobrush® PZ3 is a compact handheld plasma device for easy and mobile use in laboratories, pre-development and small batch assembly. The integration solution piezobrush® PZ3-i is suitable for various applications such as printing, bonding and laminating. It can be easily integrated into existing or new production lines. There are currently five interchangeable modules for the piezobrush® PZ3 and piezobrush® PZ3-i.
Ozone generator for disinfection, sterilization and odor elimination
The latest innovation from relyon plasma is the MediPlas system, consisting of the plasma components MediPlas Reactor and MediPlas Driver. The MediPlas Reactor is a high-performance ozone generator. The MediPlas Driver is the associated driver and provides the necessary voltage power for ozone generation. The two plasma components can be integrated into systems in industry, medical technology, pharmaceuticals, packaging, automotive, food and beverage, and agriculture for disinfection, sterilization, and odor removal.
Visit us at electronica and WFHSS
Visit us at WFHSS and make an appointment with us!
Toshin Dental at the Dental Show in Tokyo
Our cooperation partner Toshin Dental will be at the Dental Show in Tokyo on October 22nd and 23rd. Among other things, the piezobrush® PZ3 from relyon plasma will be presented at the booth 1-024. The compact handheld plasma unit enables simple, efficient and mobile use of cold atmospheric pressure plasma for the surface treatment of plastics, metals and natural materials and can be used particularly well in dental technology. Plasma treatment activates, functionalizes and cleans surfaces.
Use of the piezobrush PZ3 in the dental technology
The application possibilities of cold atmospheric pressure plasma are widely spread. Not only in industry, but also in dental technology, the technology opens up many advantages. In particular, the compact piezobrush® PZ3 handheld plasma unit can be used in the dental laboratory and in implantology.
Technical data of the piezobrush PZ3:
Electrical connection: 110 -240 V / 50 – 60 Hz
Power consumption: max. 18 W
Weight: 110 g
Design: Hand-held unit with power supply, integrated fan
Loudness: 45 dBP
Treatment speed: 5 cm²/s
Typical treatment distance: 2 – 10 mm
Typical treatment width: 5 – 29 mm
Cold atmospheric plasma induces apoptosis in human colon and lung cancer cells
through modulating mitochondrial pathway
Authors: Yanhong Wang, Xinyu Mang, Xuran Li, Zhengyu Cai and Fei Tan
Publication:Cold atmospheric plasma induces apoptosis in human colon and lung cancer cells through modulating mitochondrial pathway, Frontiers in Cell and Developmental Biology, Front. Cell Dev. Biol., 26 July 2022, Sec. Cell Death and Survival
Summary of an interesting publication on basic research with our industrial product piezobrush® PZ2 for possible use in the medical field:
The treatment with cold atmospheric plasma (CAP) is an emerging and promising oncotherapy with significant potential. It has benefits that traditional treatment modalities lack. The aim of this study was to investigate the effect and mechanism of plasma-inhibited proliferation and plasma-induced apoptosis on HT29 human colon cancer cells and A549 lung cancer cells in vitro and in vivo.
Fig. 1: Image of the Piezobrush® PZ2 used in this study. (A, B) Contents and portability of the PZ2 kit. (C) Cellular treatment using the portable plasma device. (D) Close-up of the plasma nozzle in operational mode.
In this study, relyon plasma’s piezobrush® PZ2, a handheld CAP device based on piezoelectric direct discharge technology, was used to generate and deliver non-thermal plasma. With a maximum power consumption of 30 W, the CAP device generated cold active plasma with a nozzle temperature of <50 °C. The plasma nozzle was placed 10 mm above the treated surface. The treatment durations were 15, 30, 60 and 120 seconds (Figure 1C, D). To study the effect of PZ2 treatment on different tumor cells, direct plasma treatment was performed on the HT29 and A549 cells without covering them with the cell culture medium.
The CAP treatment inhibited the proliferation of HT29 colon cancer cells and A549 lung cancer cells. The analysis of the inhibitory effect of the CAP treatment was made with the Cell Counting Kit-8. The induced morphological changes at cellular and subcellular level were examined using transmission electron microscopy and tumor cell migration and invasion were performed using the Transwell migration and Matrigel invasion assay.
Fig. 2: Inhibition of cell proliferation by CAP treatment.
Fig. 3: Effect of CAP treatment on the migratory and invasive ability of HT29 and A549 cells.
In figure 2 optical images (A) show the damage to HT29 and A549 cells caused by the plasma treatment. The images (B and C) show the decreasing cell activity as the duration of treatment with CAP increases. The images and values above represent results from three independent experiments.
The HT29 (A) and A549 (B) cells were processed with the piezobrush® PZ2 for 30 and 60 seconds, incubated for 24 h before being subsequently subjected to the Transwell migration and Matrigel invasion assay. Representative images (left) and statistics (right) of the migration and invasion assay are shown above in figure 3. The scale bar corresponds to 200 μm. The experiments were performed in triplicate.
Plasma-induced apoptosis in HT29 and A549 cells was confirmed using AO/EB staining coupled with flow cytometry and production of apoptosis-related proteins such as cytochrome c, PARP, cleaved caspase-3 and caspase-9, Bcl-2 and Bax, was verified using Western blotting.
The results of the plasma treatment in in-vitro tests were tested in vivo using xenograft mice. The anticancer effect was confirmed and attributed to CAP-mediated apoptosis. Immunohistochemical analysis revealed that the expression of cleaved caspase-9, caspase-3, PARP and Bax was upregulated, while that of Bcl-2 was downregulated after CAP treatment. These results suggest that activation of mitochondrial signaling is involved during CAP-induced apoptosis of human colon and lung cancer cells in vitro and in vivo.
Summary of an interesting publication on basic research on the possible use of plasma in dermatology with exemplary application of the piezobrush® PZ3.
The applications of cold atmospheric plasma (CAP) have expanded in plasma medicine. As an emerging branch, plasma dermatology takes advantage of the beneficial complexity of plasma constituents, their technical versatility, and practical feasibility. The goal of this comprehensive review is to summarize recent advances in CAP-dominated skin therapy. The white paper focuses on three aspects: Plasma optimization of intact skin, clinically oriented dissection of CAP treatment of various skin diseases, and finally analysis of the safety aspects of treatment with CAP and suggestions for minimizing the potential risks.
RONS (reactive oxygen and nitrogen species) produced by the hierarchical reaction of CAP with ambient air play a key role in various biological and cellular processes. This enables the application of CAP in the medical field. Similarly, UV light and transient electric fields can find application in biomedicine. Plasma medicine is a newly coined term and stands for an interdisciplinary subject that combines physics, chemistry, life sciences and medicine. The applications of plasma medicine can be broadly divided into direct and indirect use. In a direct application, a living recipient is exposed to a gaseous plasma jet. In indirect treatment, the reactive species of the CAP are transmitted to a living recipient via an intermediate carrier.
Axial view of the piezobrush® PZ3 outlet
Sagittal view of the piezobrush® PZ3 body
Plasma dermatology has emerged as an attractive specialty in plasma medicine, in part because the skin is the largest and most superficial organ in the human body. This allows an easy plasma treatment. The original investigations of clinical randomized controlled trials (RCTs) on the use of CAP in dermatology focused primarily on chronic wounds. Several reviews on this topic already exist, highlighting the advantages and disadvantages.
Skin therapy using piezobrush® PZ3
Close-up of piezobrush® PZ3 in operating mode
The study concludes that conventional treatment methods have limitations and drawbacks in clinical dermatology. Cold atmospheric plasma offers excellent potential for treatment methods in clinical dermatology. The potential is due in part to its technical versatility, such as direct irradiation of superficial lesions, indirect treatment of deep and large lesions with plasma-activated media, and simultaneous treatment with CAP and other therapeutic methods. In addition to treating skin diseases, CAP can also optimize intact skin and enable transdermal drug delivery. Nevertheless, several challenges must first be overcome before this unique therapy can be applied in daily clinical practice.
Relyon plasma developed the MediPlasTM system based on DBD technology. The two coponents MediPlas Driver and MediPlas Reactor can be used in many fields of application such as industry or medical technology.
Dielectric Barrier Discharge Technology
The big advantage of the DBD technology (dielectric barrier discharge technology) is the easy establishment of non-equilibrium plasma conditions. With the DBD technology it can be established in a much simpler way than with other technologies. Microdischarges distributed over a surface with a lifespan of only a few nanoseconds pump hot electrons into the gas phase while the total process remains “cold” (far from thermodynamical equilibrium). Therefore, new species can be generated with high efficiency. High yield ozone generation is the most important process for many applications in water and air treatment.
Plasma components based on DBD technology
MediPlas® Reactor
Relyon plasma developed two components based on DBD technology. The MediPlas Reactor is a high-yield atmospheric DBD ozone generator with active cooling and humidity tolerance. Appliances with the MediPlas Reactor can reduce the concentration of pathogens in contact with contaminated surfaces such as medical equipment, masks and tubing.
MediPlas Driver
The MediPlas Driver can drive customer specific DBD-assemblies with up to 300 pF capacity and an atmospheric air gap up to 2 mm distance from the ground electrode. Each MediPlas Driver can feed three MediPlas Reactor blocks.
Application of DBD technology
The are many fields of application for the DBD technology. It can be used in industry, medical technology, for treating water and air quality and much more. The tecnology is suitable for integration into everyday objects such as cupboards, vacuum cleaners, ventilation systems or waste bins. Because of the space-saving units the field of application is very broad. DBD technology offers unprecedented configuration options for operation in various media such as gas or at a liquid or solid interface within a wide range of pressure, energy-density and temperature.
Typical DBD configurations can be designed in planar or cylindrical geometries and can be operated under forced flow, jet-like or under diffusion or convection conditions. The basic principle an be scaled over a very wide range. The voltage amplitude, frequency and power of the AC source can easily be adapted to the needs of the application.
coffee machine cleaner with plasma technology
plasma technology steriliser
vacuum cleaner with plasma technology
room air purifier with plasma technology
plasma atomizer for fresh and clean air
air purifier with plasma technology for pure and clean air
filter module with plasma technology
Advantages
Advantages of the DBD technology:
High concentration with use of air and oxygen
Materials are „medical grade“
Small, compact and easy to integrate
Intern cooling systeme
Wide range of applications (cabinets, waste systems, lockers, etc.)
Easy way to reduce odours, germs, viruses, moulds, pesticides and fungicides
Very environmentally friendly – no auxiliary materials such as chemicals or additives necessary
White paper: Lifetime of the Standard Module
Plasma expert Dr. Dariusz Korzec and his team have extensively tested the lifetime of the Module Standard. This module can be used for the entire piezobrush® product range from relyon plasma, including the piezobrush® PZ3handheld deviceand the compact plasma integration piezobrush® PZ3-i for production lines.
Summary of the endurance test
The subject of the study is the investigation of the long-term durability of Standard Modules. For the endurance test, 10 piezobrush® PZ3 devices were used in combination with the Standard Modules, which are equipped with a polybutylene terephthalate (PBT) plasma liner. The modules were in operation for 37 weeks – more than 6000 hours. They were paused only briefly in between to measure the electrical parameters and the activation area.
The core of the Standard Module is the CeraPlas® F. The high voltage generated with it leads to the ignition of the Piezoelectric Direct Discharge (PDD). A gas flow was maintained around the CeraPlas F. In the case of the piezobrush® PZ3, ambient air was used for this, in the case of the piezobrush® PZ3-i either compressed dry air (CDA) or nitrogen.
Structure of the Standard module consisting of the CeraPlas® F high-voltage generator, a plasma liner, a heat-shrinkable sleeve and electrical contacts
In the test performed, a continuous test cabinet was equipped with 10 holders for Standard Modules operated without substrates. All piezobrush® PZ3 handheld devices were set to continuous operation.
Every two weeks, all tested modules were removed from the piezobrush® PZ3, inspected for damage or wear, measured electrically, and also the activation area was measured. The latter is done with the help of the activation image recording system (AIR). In the first step of this procedure, the substrates made of high-density polyethylene (HDPE) were statically activated with the same piezobrush® PZ3. Three substrates were then treated with each standard module. The distance between the nozzle edge and the substrate was 4.0 mm and the treatment time was 10 seconds.
After treatment, each substrate was positioned on the base of the AIR system and the AIR procedure was performed. The activation area was visualized with two drops of a 58 mN/m test ink applied to the plasma-treated surface with a small brush immediately after the plasma treatment. The observed behavior of the test ink means that the substrate had a higher surface energy than 58 mN/m. Otherwise, the test ink would not wet the HDPE substrate.
The most important evaluation parameter is the average of the mean values of the activation areas determined per module. In the example, it was 612.7 mm2. Another important global parameter is the standard deviation of the module-related mean values of the activation area. In the present example, it was 13.19 mm2, which corresponds to 2.2%. This parameter provides information about the reproducibility of the activation performance from piece to piece. This parameter should be particularly low in the present case.
Several factors influence the accuracy of the activation area determination:
Aging of the test ink: A test ink that has been stored in air for a long time changes its properties and shows a significantly smaller activation area than a fresh test ink.
Different HDPE properties: The properties of HDPE substrates vary from supplier to supplier and batch to batch.
The influence of surface pretreatment: Various preparation procedures for the HDPE surface prior to plasma treatment are known.
The following measures have been taken to minimize the undesirable influences:
To avoid the influence of aging of the test ink on the activation surface results, the test ink bottle was always stored sealed before it was used to apply the ink. In addition, for each series of measurements, a fresh test ink bottle was opened and labeled with an opening date.
Only the “natural” HDPE from a single supplier was used for the study. The substrates of some batches had different surface properties on both sides, as one side was sometimes glossy and sometimes matte. However, the difference in activation area depending on the side of the substrate was not statistically significant. The substrates used were also not completely flat, but had a concave and a convex side. Therefore, for equal test conditions, each substrate was positioned with the convex side up.
To avoid the influence of solvents and water on the results, no wet treatment of the substrates was performed. To remove dust particles and sawdust residues, the surfaces were wiped dry with paper towels.
The activation area varied with the duration of the endurance test. During the first 2000 hours, the activation area decreased slightly. From about 2000 hours onwards, an increase was observed. The maximum value, reached after 6000 hours, was 26% higher than the minimum value.
The activation areas on the HDPE substrates were visualized using a 58 mN/m test ink.
The test system, linked to a database, was used to measure and store the electrical parameters of the CeraPlas® F of the modules tested. Each time the activation range was determined with the AIR system, the module was plugged into the electronic docking station and the excitation frequency, input voltage and current were automatically measured. Impedance was selected to monitor the change in module characteristics over time. There was a clear trend: a slight increase during the first 2000 hours and a monotonic decrease of 19% overall between 2000 and 6000 hours of operation. This trend was opposite to that of the activation area, which first slightly decreased and then increased.
Conclusion on the lifetime of Standard Module
All modules passed the 6000 hours of the endurance test without significant performance degradation. During the test, the activation area varied between 500 and 600 mm2. The input impedance of the CeraPlas® F decreased over 2000 h with the endurance test time. After 6000 h, it was 19% below the maximum value of 5800 mΩ. Both the increase in activation area and the decrease in input impedance of the CeraPlas® F can be explained by the loosening of the shrink sleeve, which resulted in less mechanical damping of the CeraPlas® F vibrations.
Plasma pre-treatment in marking printing of PTFE fabric
piezobrush® PZ3-i beta test report
A leading company in the development, production and distribution of tool solutions for surface finishing uses the new piezobrush® PZ3-i in combination with the KEYENCE MK-G1000SA continuous inkjet printer to mark PTFE fabrics safely and effectively. Pre-treatment with the compact plasma integration unit increases the surface energy of the fabric material in the print area. This makes it possible to achieve a clear and abrasion-resistant marking print of a DataMatrix code using continuous inkjet.
Test procedure
To check the effectiveness of the plasma pre-treatment, the PTFE fabric was placed and manually aligned on a conveyor belt with a predefined conveying speed. The plasma module was activated with the signal input of the optical sensor and the passing fabric was pretreated. Here, the Module Standard was rotated by 45° to the conveying direction in order to better adapt the effective treatment area to the printing area.
New feature: Angle of rotation amounts for the piezobrush® PZ3-i
Figure 1: The treatment angles can be easily adjusted on the piezobrush® PZ3-i.
The effective area was visualised using test ink, as shown in figure 3. Downstream, at a distance of about 120 mm, the fabric in the central effective area of the plasma was marked with an individual (numerically ascending) 12 mm wide Data Matrix Code (DMC for short) and the corresponding number using an inkjet. This marking was carried out using the KEYENCE MK-G1000SA continuous inkjet printer and the KEYENCE MK-13 ink type (highly adhesive black ink).
Figure 2: Set-up with piezobrush® PZ3-i and KEYENCE MK-G1000SA continuous inkjet printer
Figure 3: Visualised print area
Figure 4: Effective area of the plasma treatment
To validate the effectiveness of the plasma pre-treatment more precisely, a total of five different fabrics were tested. For all of them, the surface energy was less than 30 mN/m without pre-treatment and between 38 – 42 mN/m after plasma treatment. The validation of the surface energy was carried out using test inks.
In the following, the plasma-pretreated areas on the material samples are shown on the left and the untreated areas with applied test ink are shown on the right:
Results and discussion
Handling and experience report on the marking process:
The printing process of 1500 tissue samples could successfully be carried out in the beta test of the piezobrush® PZ3-i. The trigger signal for the further clocking of the code and start time of the plasma and printer unit was able to identify all tissue types without any further configuration being necessary.
The process speed was 35 mm/s, while the distance between substrate and piezobrush® PZ3-i module was 2 to 3 mm. Dry compressed air was used as the process gas, the inlet pressure here was set to 1.2 bar. This corresponds to a gas flow of 10 l/min. With a plasma power of 100% and a rotation angle of the module of 45° (see fig. 1 and 2), a treatment width of 15 mm could be achieved (see fig. 3 and 4).
Print results:
During the printing process, the plasma pre-treatment was absolutely necessary. Without increasing the surface energy to at least 38 mN/m, bonding of the printer ink was not possible. The printed image then appeared faded, was not abrasion-resistant and the DMC used could not be read.
The following illustration shows the print image without plasma pre-treatment in the upper half of the image and with pre-treatment in the lower half:
Conclusion
Only by using a plasma pre-treatment is it possible to reliably mark the examined PTFE fabrics by means of continuous inkjet printing. This can be easily integrated into the process sequence using the piezobrush® PZ3-i from relyon plasma. This ensures good readability of the printed DataMatrix code as well as its fatigue strength even under difficult conditions such as friction and temperature. Traceability and reliable processes in the subsequent process steps are thus ensured by pre-treatment with the piezobrush® PZ3-i in the marking print.
piezobrush® PZ3-i webinar
Finally, the time has come: For the start of series production of our compact plasma integration piezobrush® PZ3-i for new and existing production lines, we would like to present the device and its easy handling to you. Guest speakers will be beta testers and partners who have already extensively tested the device in advance and will report on their experiences with the new plasma solution. The piezobrush® PZ3-i webinar is aimed at interested parties from industry and medicine.
The piezobrush® PZ3-i – energy efficient and compact
With the piezobrush® PZ3-i, we are introducing a unique plasma solution that is not yet available on the market. The topic of environmental friendliness is increasingly coming into focus when it comes to pretreating various materials and increasing adhesion. Thanks to its low power consumption of 18 W and high activation performance, the piezobrush® PZ3-i is designed to be particularly energy-efficient and also has a very low consumption of process gases. In addition, it replaces environmentally harmful methods such as the use of chemical primers or flaming processes.
The integration solution relies on a compact design with a weight of just 380 g and is suitable even for small installation spaces thanks to the separability of the module carrier and driver unit. However, applications where larger treatment widths are required are also taken into account: Thanks to the modular design, several individual units can be lined up.
Webinar about the industry standard of the future
In the free webinar, you will receive important tips on how to set up the plasma integration as well as initial experience reports from our beta testers and partners who have tested the device in advance in various application fields in the areas of bonding, printing and laminating.
The German webinar will take place in the morning. So that you know in advance what to expect, we have created an agenda with all the presentation points for you.
You can watch the German-language webinar here:
Agenda of the English webinar
For the English-language webinar in the afternoon, we have also created an overview of the different presentations.
Watch the video recording of the English webinar:
If you have any questions about the event or about plasma in general, please feel free to contact us at any time:
We are already looking forward to welcoming you virtually in Regensburg in June!
You can download the press release for the webinar here.
Bonding of electronics enclosure
ZENSO is a contractor specializing in Medical Device design and development and has been using the piezobrush® PZ3 for this purpose for some time. A user feedback:
Confronted with an adhesion problem between a medical-grade SEBS elastomer and a tried and tested adhesive, we first looked into primers and secondly tested several different adhesives. None of the trialed products increased the bond strength in a significant way.
We found relyon plasma while investigating surface treatments and the various devices currently available on the market. After discussing the case with them, we chose to rent the piezobrush® PZ3 for our investigation. The small size of the piezobrush® PZ3 range was also of interest to us. The results were immediate and very convincing.
Where all other options had failed, the piezobrush® PZ3 managed to increase adhesion to a good level at the lowest setting of 30% (exposure time of 7 seconds over a 12×9 mm area). Increasing the power resulted in even higher bond strength, with the highest setting yielding an impressive bond. We decided to also trial the piezobrush® PZ3 on a 2-part IP65 rated electronics enclosure. Although we achieve sufficient bond strength in this case, the adhesive is a specialty product that we would like to change. Again, the results were impressive.
The decision to buy the piezobrush® PZ3 was a no-brainer. Its performance is excellent, it is well built, easy to use and its design is ergonomic and thoughtful (e.g., changing the screen orientation to landscape is very handy while using the pen horizontally). Furthermore, the people at relyon plasma are very knowledgeable, helpful, and friendly.
ZENSO Electronics, www.zenso.be
The piezobrush® PZ3 has been designed as a compact plasma handheld device for use in laboratories, predevelopment and assembly of small series.
Use of plasma for bonding, activation and etching
Inola Kopic, Lukas Hiendlmeier, Fulvia Del Luca and George Al Boustani from the Chair of Neuroelectronics at the Technical University of Munich (TUM) have investigated three different possible applications for the handheld piezobrush® PZ3 and the associated Modules Standard and Nearfield. These include adhesive bonding between glass and polydimethylsiloxane (PDMS), surface activation of polyimide (PI) and etching of parylene-C.
All measurements took place under normal laboratory conditions (p = 1.3 bar; T = 25 °C; r.l. = %) and the plasma treatment under a fume bonnet.
The piezobrush® PZ3 has far exceeded our expectations. It can be used in a wide range of applications, such as plasma bonding of microfluidics made of PDMS, produced via soft lithography processes, or for etching thin-film material (e.g. parylene) and stands out above all due to its performance and easy handling compared to other plasma devices. We are thrilled and can recommend the device to everyone.Inola Kopic, Chair of Neuroelectronics at TUM
Bonding PDMS to glass
A standard process for the production of microfluidics is soft lithography with silicone (PDMS). Here, the channels are moulded from a so-called master mould and then closed by bonding to another surface. Usually, the PDMS is bonded to glass via plasma. In this process, OH groups are induced on the PDMS and glass surfaces and then brought into contact with each other. Stable Si-O-Si bonds are formed with the elimination of water molecules, which ideally prevents the PDMS from being removed.
The aim of this investigation was therefore to test whether plasma treatment with the piezobrush® PZ3 handheld device changes the surface sufficiently for the bond between glass and PDMS to form.
Fig. 1. Representation of a microfluidic channel
For the investigation, a microfluidic structure was softlithographically imprinted with 1.5 mm thick PDMS (see figure 1). The structure was then bonded to a 1 mm thick glass plate. Both surfaces (approx. 2 cm2) were treated for 1 min at 100% power. The PDMS was placed on the glass and lightly pressed on. Subsequently, the microfluidic was placed on the glass and pressed on. To check the adhesion, an attempt was also made to remove the PDMS from the glass pane with tweezers. Video 1 clearly shows that the bond between polymer and glass is so stable that only small pieces can be broken out, but the PDMS layer cannot be removed from glass.
Video 1. Tearing out PDMS bonded to glass
Surface activation of polyimide films
In addition to the bonding of microfluidic structures made of PDMS on glass, the hydrophilicity of PI films before and after plasma treatment was also investigated. In microfabrication, surfaces are often modified to make them more hydrophilic. Hydrophilic surfaces are advantageous, for example, in centrifugal coating or in subsequent ink printing processes, as the liquid can be better distributed on the surface.
One indicator for checking whether a surface is hydrophilic or hydrophobic (water-repellent) is the contact angle (CA). For this, a drop of a liquid (for example water) is placed on the surface to be tested and the angle formed between the drop and the substrate is measured. If the angle is > 90°, the surface is said to be hydrophobic. If, on the other hand, the angle is < 90°, the surface is hydrophilic. This method was used by the TUM team to characterize the substrate. Two cleaned 75 µm thick PI films were used as substrates. One of these foils was then additionally treated with plasma (1 min at 100 % power). Using a contact angle measuring device from Dataphysics, a drop of the test liquid, in this case ultrapure water, was applied to the surfaces and the contact angle on both foils was then measured. The result can be seen in Figure 2 and Figure 3.
Fig. 2. Contact angle measurement of a water drop on PI film before plasma treatment (CA = 52.6 °)
Fig. 3. Contact angle measurement of a water drop on PI film after plasma treatment (CA = 20.7 °).
It is clearly visible that the contact angle (CA) on both surfaces is < 90°. This in turn means that both substrate surfaces are hydrophilic. However, it is astonishing that the contact angle on the treated substrate decreases significantly (CA = 20.7 °) already after a one-minute application with piezobrush® PZ3 and thus the surface becomes more hydrophilic.
Etching Parylene-C
Parylene has found wide acceptance as a coating material in the microelectronics and medical industries. In this context, removal in delimited areas is of particular interest. One method for this is etching with oxygen plasma. To check whether the piezobrush® PZ3 is suitable for etching parylene-C, a series of tests was carried out. For this purpose, a 1 mm thick glass substrate coated with 5 µm parylene-C was masked with Kapton tape and treated for a duration of 20 min (corresponds to 4×5 min) at 100 % power with the handheld plasma device. Subsequently, the difference in thickness of the parylene layer between the etched area and the area protected by the tape was measured using a profilometer (Keyence VK250).
Figure 4 shows the result after plasma treatment. The lower picture shows the difference in height between the glass substrate and the parylene layer. The plasma device was able to etch away the entire 5 µm thick layer within 20 min. Thus, the device is even suitable for etching parylene layers in the µm range.
Fig. 4. image of the parylene layer (upper image, left half of the picture) on glass (upper image, right half of the picture).
Conclusion
In conclusion, it can be said that the plasma handheld device can be used in a wide variety of areas, be it microfluidics, electronics or microfabrication, and that despite its compact size, it is possible to achieve excellent results compared to conventional plasma systems.
New nickel-plated A250, A350 and A450 nozzles
The surface of the A250, A350 and A450 nozzles used in conjunction with the plasmabrush® PB3 will be nickel-plated in the future. This will prevent the formation of a loosely attached copper oxide layer which leads to a nozzle improvement. Our investigations showed no change in the process parameters current, voltage, power, plasma and nozzle temperature, activation area and service life due to the nickel plating.
Fig. 1. Comparison of the new nickel-plated copper nozzles (see above) and the old copper nozzles (see below). Left: nozzle A250, middle: nozzle A350, right: nozzle A450.
The example of nozzle A250 shows that the surface of the nickel-plated nozzles is intact even after a duration of more than 390 hours (see below). This prevents contamination of the samples by oxide residues.
Fig. 2. Nickel-plated A250 nozzle after running for more than 390 hours.
The nozzles have new article numbers:
Product designation
Old article number
New article number
plasmabrush® PB3 nozzle A250
1000242500
1000242501
plasmabrush® PB3 nozzle A350
1000600700
1000600701
plasmabrush® PB3 nozzle A450
78707200
78707201
Tab. 1. The new nickel-plated copper nozzles, which will be offered starting in February.
The change will take effect from 01 February 2021. Orders placed before this date will not be affected. The previous nozzle models will only be available on special request from 01 February 2021.
Instead of the usual gifts for our loyal customers and partners during the Christmas season, we decided to donate the budget for this purpose to a charitable organization this year. We issued the corresponding donation this week to “Rengschburger Herzen e.V.”, which supports people who are in need without any fault of their own.
“Spenden statt Schenken” (“Donate, don’t buy presents”) is the German name of the charity campaign.
The charitable association from Regensburg has set itself the goal of offering quick and simple help to those who need it most. The “Rengschburger Herzen” help and support the socially weak, the homeless, the elderly, families with children, single parents, and home residents, providing support in an undiplomatic manner.
The entire association acts selflessly, which means that every euro received goes 1:1 to those in need. Within about three years, the association around initiator Arno Birkenfelder has built up a network of supporters that has accomplished a lot of good. For example, when the food banks, the “Strohhalm” and other facilities were closed at the beginning of the Corona pandemic, several tons of food were promptly given out on fixed dates to people in need who suddenly had no place to go.
This is an effort that the entire relyon plasma team would like to support with the donation. “Instead of giving our customers and partners a Christmas present, we would like to give them the feeling of having done something good,” as Managing Directors Klaus Forster and Dr. Stefan Nettesheim explained their joint decision.
Dr. Stefan Nettesheim is a guest on the Fusion & Plasma Podcast
The CEO of relyon plasma GmbH was a guest on the Fusion & Plasma Podcast last week and talked to Adam Kit (University of Helsinki) about the future of plasma technology in the medical industry, among other things.
The interesting conversation, in which Dr. Stefan Nettesheim also talks about current research projects, is now available to listen to online on Spotify: Listen now.
A Novel Computer-Controlled Maskless Fabrication Process for Pneumatic Soft Actuators
Authors: Tinsley, L. J. & Harris, R. A.
Publication: A Novel Computer-Controlled Maskless Fabrication Process for Pneumatic Soft Actuators, Actuators, 2020, 9(4), 136.
Soft robots use compliant and elastic materials throughout their structure. The inherent properties of the constituent materials result in fundamentally different behaviour compared to their rigid counterparts. Currently, template-based, and additive manufacturing techniques are commonly used for the fabrication of pneumatic soft actuators. While the complexity of the actuators increases, the limitations of these processes become obvious. With moulding, the geometry is limited, and personalization of individual parts is complex. Fabrication techniques based on 3D-printing make the use of different materials possible, but there are limitations in resolution, speed, materials, and scalability. To tackle this task Tinsley and Harris used computer-controlled localised plasma treatment with the piezobrush® PZ2-i to selectively modify the chemical behaviour of silicone and PET to produce pneumatic soft actuators.
For this process a manufacturing platform was generated, by placing the piezobrush® PZ2-i in a 3-axis actuation platform. The bonding was carried out between the silicone Ecoflex 00-50 and a PET sheet. With their difference in stiffness, this material combination is well suited for soft actuators with bending properties.
Fig. 1. Plasma treatment platform.
For the bonding process both, the silicone Ecoflex and PET were selectively treated by plasma. The PET sheets were then immersed in a 1% solution of 3-aminopropyltriethoxysilane (APTES). Afterwards the two materials were aligned and placed into contact to enable the bonding.
Two actuators were produced by this method to test their properties. Neither actuator failed upon inflation to 16 kPa and 63 kPa, but rather the deformation of the Ecoflex indicated a state close to failure. Via the specific design different inflation levels could be reached of the different chambers (see Fig. 2). The tested simple designs show the robust nature and the designed selectivity of the bonding, but this approach allows the production of actuators as well of much higher complexibility.
Fig. 2. Two actuators were produced and tested by inflation.
In the here presented work, a novel fabrication method for pneumatic soft actuators based on plasma treatment was investigated. Advantages of this approach are that it is digitally driven, like 3D-printing processes, but being much faster and applicable to a wider range or materials. Although this method is currently not suited for actuators requiring feature sizes below 1 mm, it can make the fabrication of larger actuators easier than with conventional methods.
Discontinuation of piezobrush® PZ2 and piezobrush® PZ2-i
As of 30.11.2021 we will discontinue the handheld piezobrush® PZ2. The successor model piezobrush® PZ3 with the associated interchangeable modules Standard and Nearfield is available immediately. We will also discontinue the piezobrush® PZ2-i as of 30.11.2021. The new integration solution piezobrush® PZ3-i is expected to be available in the first half of 2022.
The new product generation offers customers a lot of different advantages:
piezobrush® PZ2 vs. piezobrush® PZ3
The piezobrush® PZ3 is designed as successor of the piezobrush® PZ2. The table gives an overview of the respective advantages of the two devices.
Electrical connection
Power consumption
Plasma power
Weight
Sound level
Plasma temperature
Treatment speed
Typical treatment distance
Max. treatment width
Standard modules
Special modules
Operating mode with inert gas
110-240 V / 50-60 Hz
max. 15 W
max. 8.0 W
110 g
45 dB
< 50 °C
5 cm²/s
2 – 10 mm
29 mm
Standard, Nearfield
expected to be available from July 2022
not yet possible
If you have questions about the discontinuation get in contact with us.
On Shear Bond Strength Of Adhesive Resin Cement To Zirconia
Authors: Mahrous, A.; Radwan, M. M. & Emad, B.
Publication: Effect Of Non-Thermal Air Plasma Treatment On Shear Bond Strength Of Adhesive Resin Cement To Zirconia, Egyptian Dental Journal, 2018, 64, 2879-2888.
Zirconia is among the main materials used for dental applications. One common application is to bond it with cement as adhesive. In this study, the effect of sandblasting and cold atmospheric plasma on the surface roughness and shear bonding strength was investigated.
The zirconia plates were divided into four groups. One remained untreated and functions as control group. The second group was treated with the conventional method of sandblasting the surface. For this, 50 μm alumina was applied. The third group was treated with cold atmospheric plasma, using the piezobrush® PZ2 from relyon plasma. The fourth group was first sandblasted and then treated with plasma.
Figure 1: Surface roughness of the four samples measured with scanning electron microscopy.
The surface roughness was measured with scanning electron microscopy. As expected, the sandblasting increases the roughness significantly, as it is mainly applied to increase the surface area. The plasma treatment, however, had almost no impact on the surface roughness. The aim of the plasma treatment is not the surface area increasement, but rather the increased wettability due to finecleaning and activation of the surface.
Figure 2: Shear bond strength of the cement on zirconia.
The effect of the bonding was investigated by measuring the shear bond strength. The untreated control samples had a low shear bond strength. By increasing the surface area with sandblasting, its value could be increased. This is of course accompanied with an increased roughness. Although the plasma treatment did not change the roughness, the shear bond strength was significantly increased. The best value could be achieved by the combination of the two methods, where first the surface area was increased by sandblasting and in a second step the surface wettability was enhanced by the plasma treatment.
In this study, the effect of sandblasting and cold atmospheric plasma on the shear bond strength of adhesive resin cement to zirconia was investigated. Both methods showed a positive effect of the shear bond strength. The best results could be achieved by combining the two methods.
of Alkali-Treated Ceria-Stabilised Zirconia/Alumina Nanocomposite (NANOZR)
Authors: Takao, S.; Komasa, S.; Agariguchi, A.; Kusumoto, T.; Pezzotti, G. & Okazaki, J.
Publication: Effects of Plasma Treatment on the Bioactivity of Alkali-Treated Ceria-Stabilised Zirconia/Alumina Nanocomposite (NANOZR), International Journal of Molecular Sciences, 2020, 21.
Zirconia ceramics such as ceria-stabilized zirconia/alumina nanocomposites (nano-ZR) are applied as implant materials due to their excellent mechanical properties. However, surface treatment is required to obtain sufficient biocompatibility. In the present study, the material surface functionalization with plasma was explored and the initial adhesion of rat bone marrow mesenchymal stem cells, their osteogenic differentiation, and production of hard tissue, on plasma-treated alkali-modified nano-ZR was assessed.
Figure 1. SEM and SPM measurements did not reveal any changes in surface structure and roughness due to the plasma treatment. In contrast, the water contact angle decreases from 63° to 0°. XPS measurements show that the carbon content on the surface decreases, while the oxygen and zirconium content increases.
In this work the piezobrush® PZ2 from relyon plasma was applied for modifying the surface properties of nano-ZR probes with cold atmospheric plasma. The surface properties were assessed. Furthermore, in vitro and in vivo studies were performed. The surface structure of implants is well-defined. Therefore, it is immanent important that a pre-treatment of dental implants prior to immersion does only alter the biocompatibility, while keeping the mechanic properties, such as roughness, unchanged. The surface properties were investigated with scanning electron microscopy (SEM), scanning probe microscopy (SPM), contact angle measurement and x-ray photoelectron spectroscopy (XPS). No changes could be found between the reference and the plasma-treated probe with SEM and SPM. This showed that the surface roughness remains constant, and the macroscopic surface structure is not impacted. With contact angle measurement, however, a completely different picture emerges. The initial contact angle of 63° could be reduced to 0°, indicating superhydrophilicity. This can be explained by the XPS-data. The carbon amount on the surface is decreased, while the oxide and zirconia peak increases. This indicates a removal of carbonous impurities revealing the zirconia.
Figure 2. Fluorescence microscopy was used to investigate the proportion and morphology of rBMMSCs and HUVECs on untreated and treated zirconia samples.
With fluorescence measurements the cell adhesion of rat bone marrow mesenchymal stem cells (rBMMSCs) and human umbilical vein endothelial cells (HUVECs) was analysed in vitro. The cell-substance interactions are one of the first events to occur between the implant material and the body when the implant is processed during implantation. Not only the number of cells adhered to the implant surface could be increased with the cold plasma treatment, furthermore an elongation of the cells could be observed. These results indicate that changes in surface structure are linked with initial adhesion and proliferation of various cells. Observation of the response of HUVECs to the material surface after implant surgery is important in wound healing considerations.
Figure 3. 3D macro-CT images show an increased proportion of bone mass (green) for the plasma-treated zirconia implants (red).
In vivo experiments were performed by implanting the plasma-treated and control implants in the rat femur. After eight weeks, further investigations were carried out. With three-dimensional macro-CT the increased amount of bone (green) around the zirconia implant (red) becomes obvious. Quantitatively, this was evaluated by the ratio of bone mass to total mass (BV/TV), the average trabecular number (Tb.N), the average trabecular thickness (Tb.Th), and the trabecular separation (Tb.Sp). Except for the last one, all these values were determined to be significantly higher for the plasma treated samples. All these measured parameters indicate a more stable integration of the implant eight weeks after implantation by the plasma treatment.
Figure 4. Histological sections of untreated (left) and treated zirconium implants.
The new bone formation was further investigated by histological sections. Not only the bone area ratio (BA), but as well the bone-to-implant contact (BIC) was increased by the plasma treatment. Both of them are indications for the quality of osseointegration.
In this publication the effects of treating nano-ZR implants with cold atmospheric plasma were investigated. While the plasma treatment does not affect the roughness of the implant, superhydrophilicity could be achieved. In in vitro and in vivo studies, a faster and better protein, cell, and bone adhesion could be measured, from which can be concluded that atmospheric plasma treatment is useful as a prosthetic treatment option for patients allergic to metal.
The treatment of a polymer surface using an atmospheric pressure plasma jet (APPJ) causes a local increase of the surface free energy (SFE). The plasma-treated zone can be visualized with the use of a test ink and quantitatively evaluated. However, the inked area is shrinking with time. The shrinkage characteristics are collected using activation image recording (AIR). The recording is conducted by a digital camera. The physical mechanisms of activation area shrinkage are discussed. The error sources are analyzed and methods of error reduction are proposed. The standard deviation of the activation area is less than 3%. Three polymers, acrylonitrile butadiene styrene (ABS), high-density polyethylene (HDPE), and polyoxymethylene (POM), are examined as a test substrate material. Due to a wide variation range of SFE and a small hydrophobic recovery, HDPE is chosen. Since the chemical mixtures tend to temporal changes of the stoichiometry, the pure formamide test ink with 58 mN/m is selected. The method is tested for the characterization of five different types of discharge: (i) pulsed arc APPJ with the power of about 700 W; (ii) piezoelectric direct discharge APPJ; (iii) piezoelectric driven needle corona in ambient air; (iv) piezoelectric driven plasma needle in argon; and (v) piezoelectric driven dielectric barrier discharge (DBD). For piezoelectrically driven discharges, the power was either 4.5 W or 8 W. It is shown how the AIR method can be used to solve different engineering problems.
1. Introduction
The non-equilibrium atmospheric pressure plasma (APP) is broadly used for polymer surface treatment [1,2,3], especially for the improvement of adhesion [4]. Even though it is a long-known technology, the surface treatment of polymers remains the focus of current research. The application examples are the improvement of adhesion on composites of polymers with natural materials [5] or applications in medical sciences, for example, tailoring of the cell growth [6].
Due to its excellent chemical and mechanical properties, polyethylene (PE) is a widely used engineering material. Its drawback is its low surface free energy (SFE) of 31–37 mJ/m2 [7,8]. The APP is frequently used to increase the SFE of PE, to allow printing, varnishing, coating, or gluing on its surface. Examples of studies focussing on this subject include the application of dielectric barrier discharge (DBD) for the treatment of high-density polyethylene (HDPE) [9] or ultrahigh-modulus polyethylene (UHMPE) fibers [10].
A very versatile method of APP generation involves using atmospheric pressure plasma jets (APPJ) [11,12]. There exist a large number of gaseous discharge architectures used for such processing tools [13]. The APPJs are also used to increase the SFE of polymers [14,15] and, consequently, to improve the adhesion of glues and molds [5], or printability [16]. There is increasing interest in biomedical applications of cold APPJs [17].
The mechanisms of the surface modification by atmospheric pressure plasma jets (APPJ) are still not completely understood [18]. Different types of APPJ are used for the treatment of PE, for example, the high voltage blown arc [14,19], the capacitive, cold APPJ [20], DBD driven APPJ [21], or piezoelectric direct discharge (PDD) [22]. Several gases are used for APPJ treatment of PE, for example, Argon [23,24] or compressed dried air (CDA) [19]. APPJ improves adhesion to PE in 3D bio-printed structures [25] or modifies the surface properties of shoulder implants made of ultra-high molecular weight polyethylene (UHMWPE) [26]. Compared with traditional polymer surfaces activation methods, such as flaming [27,28] or corona treatment [29–33], the APPJs allow the achievement of locally much higher values of surface free energy.
The diversity of APPJ physics and chemistry makes it difficult to evaluate and compare the efficiency of different APPJs using conventional plasma plume diagnostic techniques, such as electrostatic probe diagnostics [34], dielectric probes [35], optical emission spectroscopy [36,37], absorption spectroscopy between VUV to MIR [38], electron density measurements by millimeter wave interferometry or by IR heterodyne interferometry [39], high-speed photography [40,41], or calorimetric probe [42].
A pragmatic approach for comparative plasma source evaluation is to establish a model process and define a measurable process parameter, for example, deposition rate, etch rate, or activation speed. In this work, the activation area reached after some predefined treatment time on the polymer surface is proposed as such a comparative parameter. To determine the activation area, a novel activation image recording (AIR) technique is developed. The test inks are investigated in a wide range of the SFE and the optimum ink is selected. Three polymers, acrylonitrile butadiene styrene (ABS), high-density polyethylene (HDPE), and polyoxymethylene (POM) are examined as materials for test substrates. The tests with HDPE show its suitability for AIR.
This study aims to demonstrate that AIR is suitable for the comparison of APPJs belonging to different power classes. On the one hand, the low power (8 W) room temperature PDD type of plasma is used [22]. On the other hand, the powerful (700 W) pulsed atmospheric arc (PAA) type of APPJ is applied [43]. The suitability for different types of APPJ discharges and different gas mixtures should also be evaluated.
2. Materials and Methods
2.1. Atmospheric Pressure Plasma Sources
In this study, the activation area was produced using atmospheric pressure plasma (APP) sources with seven discharge configurations, marked with A to G, illustrated in Figure 1. The typical operation parameters for all configurations are summarized in Table 1.
Table 1. Discharge configurations and default operating parameters. Distance means the distance between the substrate and the orifice of the nozzle for A, the tip of the CeraPlas™ for B and C, the tip of the needle electrode for E, F, and the outer surface of the dielectric barrier for G.
In configuration A, the pulsed atmospheric arc (PAA) was used for plasma generation. Its operation principle is explained in detail in [43]. As an example, the plasmabrush® PB3 of Relyon Plasma GmbH with A450 nozzle was used. This APPJ is an industrial device designed for the high-speed treatment and allows control of the plasma ON-time in the ms range.
The configurations B,C, and D are all based on the piezoelectric direct discharge (PDD), described in detail in [22], but representing different technical solutions. The configurations B and C were used in the commercial hand-held devices piezobrush® PZ2 and piezobrush® PZ3 of Relyon Plasma GmbH, respectively. Both applied the piezoelectric transformer CeraPlas™ F [44] for high voltage generation. The main differences between B and C in the physical sense are the different air flows (see Table 1). For some experiments, the PDD was generated using the CeraPlas™ HF (discharge configuration D) [45], which is smaller than CeraPlas™ F. Consequently, its maximum operation power was lower and the operation frequency was higher (compare the operation parameters in Table 1).
In configuration E, a needle corona [46] was supplied with high voltage (HV) from the CeraPlas™ F over a plasma bridge [47]. This HV causes an atmospheric air corona discharge on the tip of the needle electrode.
The configuration F, referred to as a plasma needle [48], consisted of the same needle electrode as in configuration E, but was operated in a gas flow of different gas mixtures [47]. In this study, the results obtained with argon as a plasma gas are presented. The discharge configuration G produced a dielectric barrier discharge (DBD) with an active electrode being the HV tip of the CeraPlas™ F. Configurations E, F and G are realized technically as replaceable modules for piezobrush® PZ3 [47].
Figure 2a shows a generic setup for substrate surface activation, with the distance d between the treated surface and the plasma source. The meaning of this distance differs depending on the configuration. The plasma source reference position for configuration A is the tip of the copper nozzle A450 of the plasmabrush® PB3. For configurations B, C, and D, this reference is the tip of the piezoelectric transformer CeraPlas™ , for configurations E and F, the tip of the needle powered piezoelectrically, and for configuration G, the outer surface of the dielectric barrier.
Figure 2. Experimental setup. (a) Generic setup for activation of the polymer substrate surface. The meaning of d depends on configuration A–G as defined in Table 1. (b) Picture of setup for AIR.
2.2. Visualization of the Activation Area
The activated zone on the surface of the polymer substrate produced using one of the discharge configurations listed in Table 1 can be visualized by spreading a test ink over the substrate surface. The properly chosen value of the test ink (see Section 2.4.3) assures that the ink is wetting only the activated surfaces and rolls off the non-treated surface areas.
The plasma source was positioned at a given distance from the substrate surface and the power was switched on for a short predefined time. Figure 3 shows the shapes of the visualized activation area produced using discharge configuration A, C and G. As can be expected, the rotationally symmetric configuration A produces a rotationally symmetric activation zone. The difference between pictures A1 and A2 is in treatment time, which is 100 ms and 3 s, respectively. In the case of A2, the treatment time is so long, that the thermal damage in the center of the activation zone occurs, resulting in the reduction of the SFE.
Figure 3. The shapes of the activation area visualized by the 58 mN/m test ink on the HDPE substrate for configurations A, C and G. The sizes of the substrates seen in pictures for A and C are 50 mm × 50 mm. The treatment times are 100 ms, 3 s, 10 s, 1 s and 20 s for A1, A2, C1, C2, and G1−3 respectively.
The pictures C1 and C2 show the activation zones produced in configuration C. The activation zone visualized in picture C1 was produced by a 10 s treatment at a distance of 4 mm. The kidney-like shape was caused by the shape of the discharge itself, following the rectangular geometry of the CeraPlas™ F HV tip. The image in C2 was obtained at the much larger distance of 10 mm and the shorter treatment time of 1 s, resulting in the splitting of the activation zone into two small sub-zones. The activation images produced using configurations B and D are very similar to the image for configuration C because they were also generated by the piezoelectric device of CeraPlas™ type.
The pictures G1, G2 and G3 show the activation areas produced in configuration G. The characteristic four-folded shape in G2 is caused by the four fixtures used to keep the quartz dielectric barrier cup. The pictures G1 and G3 demonstrate how the tilting of the plasma handheld instrument affects the shape of the activation area. The tilting was performed in the direction perpendicular to the narrow and to the wide sides of the CeraPlas™ F, respectively.
The circular activation areas related to the rotationally symmetric needle electrodes of configuration E and F are not shown in Figure 3.
2.3. Activation Image Recording
The shape of the activation area provides interesting information about the character of the plasma source used for the activation. However, for quantitative evaluation of the plasma source performance, some reference value must be defined. In this study, the area of the activation visualized by the test ink is such a value. To increase the accuracy and repeatability of the evaluation of the test ink patches, the automated method of ink patch area determination was introduced. Since the area of the ink patches changes over time (see Section 3.1.1) the pictures of the ink patch were taken in short intervals with a digital camera (see Figure 2b). The contour of the ink patch was automatically recognized and the number of pixels was counted. By comparison with the number of pixels of the known area of the entire substrate, the actual area of the test ink patch was calculated. The algorithm applied in the activation image recording (AIR) the method has some limitations. The image recognition was optimized for dark blue ink on a white substrate. If the test ink was of another color or was too pale, errors in recognition of the ink patch boundary could occur. Such errors are also possible if the substrate was dark or if the illumination of the ink patch was weak or not time-stable. In the case of splitting of the activation area into more than one patch, as shown in C2 in Figure 3, the largest sub-patch was selected for evaluation. The not inked areas within the ink patch, such as the inner circle shown in A2 in Figure 3, were not subtracted.
2.4. Test Inks
2.4.1. Formamide Based Test Inks
Different liquid mixtures were used for the production of test inks suitable for the determination of the SFE of solid surfaces. The test inks defined in a number of standards [49] and gauging the surface energies from 31 to 58 mN/m were mixed with formamide and 2-ethoxyethanol (alternative names: ethylene glycol monoethyl ether or ethyl Cellosolve—registered trademark of Union Carbide Corp.). The dependence of the gauged SFE on the volume percentage of formamide in the test ink mixture is shown in Figure 4a. For gauging the test inks in the SFE in the range from 58 to 72 mN/m, the mixtures of formamide with DI water were used. The linear approximation of the SFE on the volume percentage of fomamide in a formamid–water mixture is also shown in Figure 4a.
Figure 4. Determination of the SFE by use of the test inks. (a) The SFE gauged by the test ink consisting of formamide mixed with 2-ethoxyethanol (blue curve, according to [49]) and formamide mixed with water (red line, linear approximation) as a function of formamide volume percentage; (b) The typical radial distribution of the SFE after HDPE treatment in configuration C. The SFE levels for water and formamide test inks, and for the levels sufficient for printing on HDEP, are depicted with dashed lines.
2.4.2. SFE Radial Distribution
Since the chemically active species causing the surface activation were not distributed homogeneously across the plasma plume of an APPJ, the SFE also varies across the activated zone. Consequently, applying the test inks gauged with different SFEs, different sizes of the activation zone were obtained. Figure 4b shows the radial distribution of the SFE on an intensively treated HDPE. The size of the visualized activation zone almost doubled if the test ink 46 mN/m was taken instead of the pure water-based test ink 72 mN/m. On the one hand, the relative accuracy of the AIR method improves with the size of the activation zone. On the other hand, a too low SFE of the test ink results in large visualized areas even for poor activation. The SFE value of 58 mN/m is a good compromise between these two extremes. The intensive treatment means that a large part of the activation area reaches the saturation value of 72 mN/m. For weak treatment, the SFE distribution curve could be below the 58 mN/m resulting in no visualized activation area. The SFE distributions reaching just over the 58 mN/m line would be not suitable, because the visualized area would be very sensitive to any random influences and the results would be unreproducible. The assumption for the validity of the AIR method is that the treatment time is long enough to assure the intensive treatment.
2.4.3. Aging of Test Ink
Since the 2-ethoxyethanol is more volatile than the formamide, the stoichiometry, and consequently the SFE gauged by test ink mixed from formamide and 2-ethoxyethanol, can increase over time. It corresponds to the movement to the right along the blue line in Figure 4. This test ink will show a smaller activation area than the not aged test ink. No such change of composition is exhibited by the 58 mN/m test ink, because it is made of 100% formamide. The pure formamide has a surface tension of 58.2 mN/m but the commercially available inks are specified with some tolerance, typically ±0.5 mN/m. No sensitivity to stoichiometry was an important reason for the selection of this specific ink as a standard for this study.
Despite using the test ink consisting of a single liquid chemical, strong differences in the visualization result can be observed when older formamide test inks are used. The activated areas visualized with test ink from vials differing in age by more than 2 years differ by more than 25%. On the other hand, the results obtained with fresh ink from different vials are very reproducible with the relative standard deviation of visualized areas of less than 3%.
The other origin of the instability of formamide based test inks is their hygroscopicity [50]. When absorbing moisture from humid air, the test ink dyne number shifts in the direction of higher values causing a decrease of the visualized surface. It corresponds to the movement to the left along the red line in Figure 4.
To avoid the aging of the ink, only fresh ink vials were used and the vial remained open only for a short time of ink application.
2.4.4. Environmental Influences
It is known that environmental conditions, such as air temperature, relative humidity and pressure, have a significant influence on the wetting properties of liquids on polymer surfaces. The liquid temperature has a significant influence on its surface tension. The temperature coefficient of surface tension is −0.1514 and −0.0842 mN/(K·m) for water and formamide, respectively. Consequently, a variation of temperature of more than 10 K would cause the change of the calibration number of the formamide test ink.
It is documented in the literature that the increase of the pressure causes an increase of the contact angle [51], which manifests in a decrease in the activation area. The humidity influences both the surface tension of the liquid water–air interface [52] and the water contact angle on the solid surface [53].
To evaluate the influence of the environmental factors on the activation area results, these conditions are logged in during the test ink patch evaluation. The temperature, humidity, and pressure sensors are placed at a distance of 10 cm from the optical axis of the digital camera (see Figure 2b).
2.5. Substrates
The substrates used in this study are made of three pristine polymers: acrylonitrile butadiene styrene (ABS), high-density polyethylene (HDPE), and polyoxymethylene (POM) and are delivered by Rocholl GmbH, Germany. It is known that additives, such as stabilizers, have a strong influence on the surface properties of polymers [54]. For test substrates, the “natural” HDPE without additives were used. For plasma treatment and activation area evaluation the substrates with sizes 100 mm ×50 mm ×2 mm or 50 mm ×50 mm ×2 mm were used. The second one was assumed if no explicit information was included. For plasma treatment, the substrates were fixed on a solid block of HDPE with sizes 100 mm ×100 mm ×10 mm. Only the substrates treated in discharge configuration G were placed on a grounded metal plate.
According to the standard [49], the substrates were preconditioned after delivery at least 40 h under 23 ◦C and 50% humidity. No cleaning procedure was applied. All substrates were treated with plasma and exposed to the test ink at temperature 23 ◦C ± 2 K and a relative humidity of 50% ±5%.
3. Results and Discussion
The results consist of two parts. In the first part, different influences on the visualized activation area are analyzed and the definition of the activation area, as used for the evaluation plasma sources’ performance, is proposed. In the second, the proposed definition of the activation area is implemented to evaluate different types of APP sources.
3.1. Activation Area Determination
3.1.1. Shrinkage of the Test Ink Patch
As Section 2.3 stated, the activated area wetted with test ink decreases significantly with time. The strongest change is observed within a few seconds after application of the test ink. The stable value is reached within minutes. The dependence of the visualized activated area on time elapsing after an ink application, as shown in Figure 5a, will be called shrinkage characteristics.
Figure 5. Shrinkage characteristics of the 58 mN/m test ink patch (a) taken for 3 min on HDPE, and (b) taken 17 s on three substrate materials: ABS, HDPE and POM. The discharge configuration C was used.
In this example, the shrinkage speed of the test ink patch decreases with time. In the first second, the ink patch area decreases by 8%. At 7 s after wetting, the shrinkage speed is about 1.4% per second. At 2 min after wetting, it is only 0.11%/s. As a reference time for the AIR method, the time of 10 s with shrinkage speed of 0.8%/s is set. It is a compromise between a large error in the surface determination for very short times and the influence of material and environmental factors for very long times.
The activation area visualized after 10 s of shrinking corresponds, not exactly, to 58 mN/m. Due to the water absorption in the ink after 10 s, the ink shows the wetting of surfaces with higher surface free energy than 58 mN/m. The value for t =0 s would correspond to exactly 58 mN/m because the test ink has this property immediately after application only. The application recipes for the commercial test inks prescribe that the evaluation of the ink wetting should be conducted within 2 s after application, accepting the disadvantage of the very fast-changing of the ink wetting properties in this time range.
3.1.2. Selection of Substrate Material
The selection of the substrate material has a strong influence on the accuracy and activation area range of the AIR method. On the one hand, it is important that the selected material should have the SFE without plasma treatment far below the value of 58 mN/m. On the other hand, the maximum SFE reachable after the plasma treatment should be significantly higher than 58 mN/m.
The formamide based test inks are “blind” on the polar component of activation on some plastics; an example is a popular polymer PVC (polyvinyl chloride) [55]. Such materials can be excluded as a standard for plasma sources’ evaluation. Another group of materials, not suitable for this purpose, is that exhibiting a strong hydrophobic recovery [56,57]. The materials that significantly lose their hydrophilicity obtained by plasma treatment after minutes are, for example, thermoplastic polyurethane (TPU) [58] or polydimethylsiloxane (PDMS) elastomer [59]. A comparatively weak hydrophobic recovery exhibits polyethylene (PE), especially if treated with oxygen-containing plasmas [60]. Its native contact angle with deionized water is about 90◦ and the SFE of the HDPE substrates used in this study is 36 mN/m. The measurements conducted in our lab with the use of a Krüss droplet test instrument show that the SFE of 66 mN/m and the contact angle of 34◦ reached after brief plasma treatment remains unchanged after 4 h in ambient air. The contact angle increases in 100 days by 7◦, which is much less than for many common polymers. For a change of activation area with storage time after treatment — see Section 3.1.6. Our measurements on ABS substrates plasma-treated in configuration A also show no measurable hydrophobic recovery 4 h after the plasma treatment.
Due to the wide range of SFE after plasma activation and low hydrophobic recovery,the ABS, POM and HDPE are suitable substrate materials for the AIR method. To select the best material among these three, the shrinkage characteristics for these materials were collected. The results are shown in Figure 5b. Two disadvantages of POM can be stated. First, the activation area of POM is much lower than that of ABS and HDPE, causing the reduced resolution of the AIR technique. The second is the speed of variation of the activation area. The ratio of starting area to the area after 10 s of shrinking is 2.07 for POM, compared with 1.35 and 1.25 for ABS and HDPE, respectively.
The possible explanation of the strong variation of the shrinkage characteristics for POM can be its strong water absorption reaching up to 0.5% of water in comparison with HDPE, absorbing only up to 0.01% of water. In the case of POM, the water from the substrate can be absorbed by the hygroscopic formamide, increasing the gauged surface free energy and consequently decreasing the visualized activation area.
The high sensitivity on plasma activation makes ABS advantageous as a reference substrate for the evaluation of weak plasma sources. The well-defined pure water test ink with 72 mN/m can be used in combination with ABS substrate. The red curve in Figure 6a shows the activation area on the ABS surface generated in configuration G as a function of the SFE value of the test ink. The curve shows that, after only a 10 s treatment, a very small variation of the activation area of 7% is observed when changing the SFE of the activation area definition from 46 to 72 mN/m. The consequence is the reduced range of activation area available for the AIR method. A small difference between strongly and weakly activated areas can be expected. In contrast to ABS, the HDPE substrates show a very strong variation of the activation area with SFE value of the test ink, more than doubling, when the SFE value of the test ink decreases from 72 to 46 mN/m. A similar difference is observed for HDPE activated in configuration C (see Figure 6b). This outstanding range of the activation area on HDPE was an important reason for the selection of HDPE as a standard material for the AIR method.
Figure 6. The visualized activation area on a substrate surface as a function of SFE calibration of the test ink. (a) Discharge configuration G was used with the treatment time of 20 s on HDPE and 10 s on ABS; (b) Discharge configuration C was used for 10 s treatment on HDPE.
3.1.3. Ink Patch Shrinkage Mechanism
In this section, results are presented that support the thesis that the increase in water concentration in the formamide test ink layer is the main reason for the ink patch shrinkage. During the collection of shrinkage characteristics, the relative humidity in the substrate vicinity was raised intentionally by about 10% for 5 s. During this time, a strong increase in the shrinkage speed can be observed (slope line 2 in Figure 7a). This result confirms the shrinkage mechanism based on the increase of water content in the ink. A significantly smaller shrinkage speed after exposure to higher humidity (slope line 3 in Figure 7a) than before exposure (slope line 1) can be explained by this effect. Since during the exposure of the ink to air with higher humidity, a higher concentration of water in ink is reached, after establishing the previous value of humidity, the shrinkage speed is lower because the concentration gradient of water in the air and the ink is lower.
Figure 7. Shrinkage characteristics of the 58 mN/m test ink patch on HDPE plasma-treated in configuration C. (a) The segment showing the influence of increased air humidity; (b) The influence of the different amounts of applied ink.
The amount of applied test ink has a significant influence on the shrinkage characteristics. In Figure 7b, the curves for the increasing amount of ink, given in droplets (1 droplet≈8 μL), are shown. The strongest variation of the shrinkage characteristics is for the smallest amount of ink. This correlates with the scenario of humidity penetration from the ambient air into the test ink. The larger the amount of the ink, the lower the water concentration and, consequently, the smaller the SFE change gauged by the test ink. This scenario is also in agreement with the observation that the difference between curves for one and two droplets is much larger than between the curves for two and three droplets.
The differences for the 10 s point are in the range of 10%, which is significant for the AIR method. To minimize the error resulting from this effect, the amount of ink should be proportional to the activation area, to keep the thickness of the ink film constant. The pragmatic rule for the experiments in this study is that the activation areas below 300 mm2 are visualized with a single ink droplet, and, for activation areas larger than 300 mm2, with two droplets.
3.1.4. Influence of Ink SFE Value on Shrinkage Characteristics
Figure 8 shows the relative (all values of one curve are divided by its maximum value) shrinkage characteristics for the test inks in the range from 46 to 72 mN/m. They correspond to the activation area points from the plot in Figure 6b. The variation of the shrinkage characteristics from 46 to 58 mN/m, shown in Figure 8a, increases with increasing gauged SFE value, which correlates with an increase in the volume percentage of the formamide in the 2-ethoxyethylene/formamide test ink. In this case, the hygroscopic properties of the the formamide can explain this tendency. The higher volume percentage of the formamide in the test ink, the faster the absorption of the water from humid air in hygroscopic formamide and, consequently, the stronger the change of the gauged SFE. However, a geometrical effect can also play an important role. With the increasing total area of the ink patch, accompanying the test ink SFE value reduction, the same linear shift of the patch boundary during shrinking results in less relative area change.
Figure 8. Comparison of relative shrinkage curves for test inks produced as mixtures of formamide with (a) 2-ethoxyethylene, and (b) water. The HDPE substrate was treated in configuration C.
Figure 8b shows the shrinkage characteristics recorded for the mixture of formamide with water. A shrinkage mechanism different to that described earlier must be considered for an explanation of these curves, because the presence of water in the mixtures excludes a strong change due to water absorption. The faster evaporation of formamide than water could be speculated, but the shrinkage characteristics for test ink gauged with 72 mN/m (100% water) require different explanations most probably based on an interaction between water and the activated HDPE surface.
3.1.5. Renewed Ink Application
For a better understanding of the mechanisms of the ink patch shrinkage, the shrinkage characteristics were collected after renewed test ink application on the same patch. This experiment should show whether the origin of the shrinkage is related to the change of substrate surface properties or ink properties. In Figure 9a, the shrinkage characteristics for the fresh ink patch and the same ink patch refreshed two, four, and six times by the new test ink are shown. It can be observed that the starting points of all four shrinkage characteristics are quite close to each other. This means that the application of fresh ink causes gouging of the starting value of the visualized surface, which allows the conclusion that no substantial change in the activation area between taking two subsequent characteristics occurs. The conclusion of this experiment is that the changes in the test ink properties themselves are responsible for the shrinkage of the test ink patch.
Figure 9. Shrinkage characteristics of the 58 mN/m test ink patches (a) directly after first ink application, after 1, 3 and 5 ink re-applications and (b) after 1, 3 and 5 ink wiping and renewed application. Treatment conducted in configuration D with the power of 4.5 W at the distance of 5 mm.
To ensure that the shrinkage characteristics start with test ink without water admixture, the series of shrinkage characteristics were collected for fresh ink applied on the activated area after the removal of the previously applied ink. The test ink was removed by dabbing off with cellulose tissue. In Figure 9b, three such characteristics are shown for inking after one, three, and five ink removal/application cycles. It can be observed that the starting point of all characteristics is roughly at the same level, confirming the thesis that no change of the 58 mN/m activation area occurs. The observable change is the shift of the asymptotes to which the characteristics converge. They decrease with the number of whippings and re-applications of the test ink. The possible explanation of such behavior is the decrease of the maximum SFE on the HDPE surface after each wiping of the test ink. It is known that PCT (physical contact treatment), for example by the use of cellulose tissues, causes strong hydrophobic recovery. It was documented for PS, COP and PDMS in [61] that mechanical rubbing the activated surfaces causes the hydrophobic recovery. The ink removal with tissue from the HDPE surface can partially affect the layer of activation and cause the reduction of the SFE values. The flatter surface distribution of SFE results in a larger area decrease by a small change of the SFE gauged by the test ink.
3.1.6. Hydrophobic Recovery
Typically, the hydrophobic recovery refers to the decrease of the SFE during long-term storage. For example, on oxygen-plasma treated polyethylene surfaces, a strong hydrophobic recovery is described [62]. The surface free energy of 46 mJ/m−2 reached LDPE after corona treatment decreases after 22 days of exposition to air, down to the SFE of 36 mJ/m−2 [63], compared with the SFE for non-treated LDPE of 31 mJ/m−2.
In this study, the hydrophobic recovery refers to the reduction of the visualized activation area as a function of storage time. Figure 10 shows such a dependence for HDPE surface treated in configuration D. No hydrophobic recovery is stated in the time scale of the AIR measurement.
Figure 10. Influence of the storage time on the activation area. The plasma treatment of HDPE substrates was conducted in configuration D and visualized with the 58 mN/m test ink.
Despite the hydrophobic recovery documented for HDPE, no significant reduction of the activation area can be observed after storage of the activated substrates over an extended period. The results in Figure 10 document the changes over 300 h. The trend line shows in this time a decrease of 3 % of the activation area per 100 h. This result is not contradictory to the previously reported hydrophobic recovery results because those are related mainly to the decrease of the maximum value of the SFE reached after plasma treatment. Since the SFE of 58 mN/m used as a threshold for visualization in this work, which is much less than the maximum value of SFE obtained after treatment in configuration D, reaching the SFE of up to 72 mN/m (see Figure 6), the contour with 58 mN/m does not have to be affected much by the decline of the maximum SFE.
3.2. Characterization of Plasma Sources
To demonstrate the plausibility of the results collected with the AIR method, typical examples of operational characteristics of different APPS are presented and discussed. These are the dependence of the activation area (58 mN/m test ink on HDPE) on the treatment time and the distance from the plasma source.
3.2.1. Dependence on Treatment Time
Fricke et al. [64] showed that the width, defined by the use of the profiles of the contact angle, of the activation area produced on the surface of polyethylene with APPJ non-linearly increases with treatment time and shows a tendency to saturate for very long treatment times. A similar behavior is observed for activation areas generated for both the PDD type plasma jets (see Figure 11a) and the PAA based plasma jets (see Figure 11b).
Figure 11. Dependence of activation area (58 mN/m, HDPE) on the treatment time. The plasma treatment is performed in configurations (a) B and C, and (b) A, operated at conditions from Table 1, respectively. The area of thermally induced loss of glossiness is included for comparison.
The two curves in Figure 11a show the dependences of the activation area on the treatment time for configurations B and C, respectively. The main difference between the operating conditions of these two configurations is different airflow. Configuration B is equipped with a stronger fan. The reduced dilution of the chemically active species in configuration C results in a higher activation efficiency, which is documented by a 17% increase in the activation area.
Configuration A is operated with power two orders of magnitude higher than that of B and C. The consequence is a much higher plasma temperature, which ranges from a few hundred ◦C in the diffuse plasma zone, to several thousand ◦C in the arc zone. This thermal difference causes a major difference in plasma chemistry. While the PDD produces ozone and active oxygen as the main chemical species, almost no ozone and high concentrations of nitrogen oxides, such as nitric oxide (NO) and nitrogen dioxide (NO2), are measured in gaseous products of the PAA plasma jet. Despite this difference, the PAA based plasma tools very efficiently activate the HDPE surface, with maximum SFE reaching 68 mN/m, corresponding to the contact angle of DI water of 35◦. With such maximum value of SFE, the formamide gauged for 58 mN/m can be used for the quantitative evaluation of such a plasma jet.
The treatment area for configuration A was determined as a function of the treatment time and is visualized in Figure 11b. Even for the shortest pulse of 50 ms, an activation area of 63 mm2 is determined. For plasma switched on longer than 50 ms, not only the activation area can be visualized by test ink, but also a glossy HDPE surface becomes visibly mat. Such surface changes can be explained by a preferential material abrasion of low molecular weight materials, which produces changes in surface topography [65]. An interesting point on the time scale is the cross-over of the mat area curve and the activation area curve, occurring at 470 ms. For treatment times longer than 0.5 s a partial melting in the center of the activation area can be observed. The picture of the molten zone in the middle of the mat zone on the HDPE substrate is shown in Figure 12. Such molten areas have much lower SFE compared with a non-molten surface. For treatment times longer than 2 s, the molten zone becomes not wettable with formamide 20–30 s after the ink application. Such a case of partial wetting is shown in Figure 3, picture A2. After the reference time of 10 s, the molten zones were wettable. Consequently, the points for 3 and 5 s are included in the plot.
Figure 12. The picture of the HDPE substrate taken after treatment in configuration A operated at conditions from Table 1. The treatment time is 3 s.
3.2.2. Influence of the Substrate Distance
A further physical factor strongly affecting the activation area is the distance between the plasma source and the substrate. For plasma sources in configurations B and D, the activation area decreases with the distance increasing over 5 mm (see Figure 13a). This can be explained by increasing the dilution of the chemically active species and weaker electric fields enhancing the activation. The activation area for configuration B is roughly twice as high as that for configuration D because its operating power is higher by a factor of two. It can be also observed that the treatment with configuration B is possible at a larger distance of about 15 mm than for D, decaying at about 12 mm.
Figure 13. Dependence of the activation area (58 mN/m, HDPE) on distance for (a) configuration B and D, and (b) configuration E and F.
Much longer activation zones show the plasmas generated in configuration E operated in ambient air and F operated in argon flow. The activation area of both configurations is represented by red and blue lines in Figure 13b, respectively. The points of decay (zero points of the fitting lines) are 21 and 26 mm, respectively, compared with 15 mm for configuration B. Configuration E is operated without airflow. Consequently, the reason for the elongation of the plasma zone can be the more focussed electric field produced by the needle electrode. The even longer plasma jet in configuration F is caused by the argon flow. It contains long-living activated species, which can be transferred over a longer distance. It also allows us to sustain plasma at much lower electric fields, due to its lower break-down voltage. These tendencies are in agreement with well known results for other types of cold APPJs [66] and confirm the plausibility of the AIR results.
4. Conclusions and Outlook
A novel method for the evaluation of the activation area produced on polymer surfaces by atmospheric pressure plasma jets is proposed. The activation image recording (AIR) with a digital camera is used for the collection of shrinkage characteristics of activation zones wetted by the test ink.
This study demonstrates that AIR can be used as a diagnostic technique for the performance evaluation of atmospheric pressure discharges at different working conditions. It is also shown that it is suitable for the comparison of strongly different types of APPJs. HDPE is selected as the best suitable material for test substrates thanks to: (i) its wide range of SFE achieved after APPJ treatment; (ii) low hydrophobic recovery; (iii) availability as a polymer without additives; (iv) moderate cost; and (v) high popularity as a reference material for plasma studies.
For activation area visualization, the test ink gauged for 58 mN/m (pure formamide liquid) is selected because: (i) the influence of changes of the proportion of two liquids with different volatility can be avoided; (ii) the SFE value is almost in the middle between the SFE of non-treated HDPE (35 mN/m) and the maximum achievable SFE of (72 mN/m); and (iii) formamide is defined as a component of the test inks in several important international standards.
The reference time on shrinkage characteristics is 10 s after distribution of the test ink on the HDPE surface. It is a compromise between a large absolute error in the area determination for a very short reference time and the influence of material and environmental factors and increasing relative error for a very long reference time.
The optimal treatment time should be selected depending on the kind of discharge and scales inversely proportional with plasma power. For example, to achieve a good resolution of the AIR results for the 700 W plasma device, the plasma treatment time in the ms range is needed. For PDD and other CeraPlas™ driven discharges, the treatment time of 10 or 20 s is optimal.
It is shown that the hydrophobic recovery, defined as change of the activation area with storage time after HDPE treatment with CeraPlas™ based device, is very slow: 3% per 100 h.
The origin of the short-term changes is in the temporal variations of the test ink properties. The most probable reasons for such variations are: (i) the change of stoichiometry of the two-component test ink due to different evaporation speeds of the components; (ii) the absorption of water from air humidity in the pure formamide test ink.
To achieve exact, statistically sound and reproducible results with the AIR method, some assumptions and rules of handling must be fulfilled.
The AIR results are valid only for intensive discharges, when 72 mN/m saturation on a large part of the activation area on HDPE is reached;
the treatment time should not exceed the limit for the thermal damage of the HDPE surface;
only a fresh test ink should be used, and the test ink vial should be opened only for a short time of ink application;
the amount of the test ink should be adjusted to the size of the activation area; and
the AIR measurements should be conducted at room temperature and medium humidity.
Even though the physical and chemical mechanisms of the test ink patch shrinkage are not explained in detail, the shrinkage characteristics are successfully used for solving engineering problems during the development and evaluation of the novel plasma tools. Using AIR, the authors approached the following engineering tasks:
determination of the optimum operating conditions for the maximum surface activation speed;
investigation of the influence of the constructional changes on the APPJ performance;
determination of equivalent working point for plasma tool replacing a different one;
the investigation of the performance changes of the APPJ in course of an endurance test; and
the analysis of the influence of the type of discharge on the hydrophobic recovery.
The results of this study show that further work on this subject is needed. Among others, the physical–chemical mechanisms of the time-dependent shrinkage of the test ink patches should be investigated in more detail. The experimental development could also further improve the accuracy of the AIR technique. One example is the automation of the test ink application, allowing us to dose an exact amount of the liquid and to determine exactly the starting point for the ink patch shrinkage process.
Author Contributions: Conceptualization, D.K. and T.A.; methodology, D.K.; software, T.A.; validation, E.B.; formal analysis, E.B.; investigation, D.K.; resources, S.N.; data curation, T.A.; writing—original draft preparation, D.K.; writing—review and editing, D.K. and E.B.; visualization, D.K. and T.A.; supervision, S.N.; project administration, D.K.; funding acquisition, S.N. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data can be obtained on request from the first author. Acknowledgments: Thanks to Bernd Grundmann for practical advice and all kinds of mechanical machining in the course of the study. All CeraPlas™ devices are provided by TDK Electronics GmbH, Deutschlandsberg. Conflicts of Interest: The authors declare no conflict of interest.
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Trade show Bondexpo
Product launch of the compact plasma integration piezobrush® PZ3-i
Relyon plasma from Regensburg, a subsidiary of TDK Electronics AG, is presenting the innovative plasma system piezobrush® PZ3-i at Bondexpo in Stuttgart, the International Trade Show for Adhesive Bonding Technology. Based on PDD® technology, this compact integration solution is suitable for a wide range of surface applications.
Regensburg/Stuttgart.Bondexpo opens its doors from October 5-8, 2021, after being cancelled last year. Relyon plasma will present the compact integration solution piezobrush® PZ3-i for the first time in hall 5 at booth 5505. Cold pressure plasma is used to optimally prepare hydrophobic surfaces for bonding by increasing the surface energy and to enable a stable adhesion process.
Piezobrush® PZ3-i – Plasma as the industry standard of the future
The highlight of this year’s trade show appearance is the presentation of the compact integration solution piezobrush® PZ3-i for the first time ever. The cold plasma device is designed for integration into existing production lines and is therefore compact, safe, and efficient. Thus, it is ideally suited for pre-treatment prior to gluing, printing, and laminating. Due to its compact and robust housing, it is easy and uncomplicated to implement the piezobrush® PZ3-i in inline systems. In addition, comprehensive process control is possible in automated production processes, ensuring traceability. The device is intuitive to operate and can be serviced without tools.
Bild 1. piezobrush®PZ3-i consisting of driver housing and module mount.
Flexible treatment widths due to modularity
With an average treatment width of 5 – 29 mm (CDA), the piezobrush® PZ3-i is very well suited for the pre-treatment of adhesive grooves or for printing on low-energy materials. With other process gases such as nitrogen, treatment widths of up to 50 mm are possible. For many applications, however, even larger treatment widths are required. Due to the modular design, the individual units can be easily arranged in a row to achieve larger treatment widths that can be individually adapted to the application.
Bild 2. Linking of several piezobrush® PZ3-i single units for larger treatment widths.
The piezobrush® PZ3-i with PDD® technology generates highly effective cold plasma. Based on the experience with the predecessor model piezobrush® PZ2-i, which is already in use at many customer sites, the piezobrush® PZ3-i was developed according to user needs to close the gap between handheld devices and high-performance inline devices. For example, the company IKA®-Werke GmbH & Co. KG uses the predecessor to glue autoclavable pipettes.
Up to now, high-performance systems have been used for automated plasma processes. These are optimized for high process speeds, but this is associated with relatively high demands on process accuracy and control. Especially with temperature-sensitive substrates, overheating of the sample must be avoided. The piezobrush® PZ3-i, on the other hand, simplifies the use of plasma due to the low plasma temperature of less than 50 °C, the supply with low-voltage cables and an occupational safety due to contact safety and low emissions. This opens new application possibilities: With the piezobrush® PZ3-i, it is now possible to achieve optimal and reproducible adhesion results with little effort.
Bild 3. Use of the predecessor model piezobrush® PZ2-i for bonding polypropylene (PP). source: IKA®-Werke GmbH & Co. KG
Use cases at the booth
Relyon plasma is looking forward to welcoming interested visitors at the booth. They can experience the new development piezobrush® PZ3-i, the handheld device piezobrush® PZ3 as well as the PAA® technology in action directly on-site and ask the experts application questions. In addition, trade show visitors can also bring their own substrates so that they can see the benefits of plasma treatment for themselves.
Technical data of the piezobrush® PZ3-i:
Supply voltage
24 V DC
Power consumption
Max. 18 W
Design
Integration unit with gas connection
Weight
380 g
Plasma temperature
< 50°C
Treatment distance
2 – 10 mm
Treatment width
5 – 29 mm (CDA) 5 – 50 mm (nitrogen)
Tabelle 1. Overview of the technical data of the compact plasma integration piezobrush® PZ3-i
Effect of Plasma Treatment on Titanium Surface on the Tissue Surrounding Implant Material
Abstract:
Authors: Tsujita, H.; Nishizaki, H.; Miyake, A.; Takao, S. & Komasa, S.
Publication: Effect of Plasma Treatment on Titanium Surface on the Tissue Surrounding Implant Material, International Journal of Molecular Sciences, 2021, 22.
The effect of cold atmospheric plasma on a titanium surface was investigated via SEM, XPS, contact angle, cell morphology and ROS. Furthermore, the implants were implanted in a rat femur for in vivo analysis. After eight weeks the hard tissue integration was investigated via CT analysis and histological analysis.
Both, the in vitro and the in vivo analysis show an altered titanium surface, resulting in a better wettability and thus an increased amount of new bone formation in the tissue surrounding the implant.
Fig. 1. The study design is shown. Experiments can be divided into two areas. One is to confirm how the atmospheric pressure plasma treatment on titaniumsurface affects thematerial surface. The other is an in vivo analysis using rat femur. Eight weeks after implantation the rat was euthanized and the femur was removed together with the implant and CT analysis and histological analysis were performed.
Total recap:
The effect of surface modification of titanium implants on bone formation is the object of several investigations. Especially cold atmospheric plasma treatment shows promising results. While most investigations focus on in vitro investigations, this work from Tsujita et al. links the surface characterization with investigations of hard tissue integration in vivo.
Titan implants were treated with cold atmospheric plasma generated by the piezobrush® PZ2 for 30 seconds at a distance of 10 mm. The process gas was generated by the device from the ambient air.
The surface properties were investigated by SEM, XPS and contact angle analysis. The SEM analysis revealed that the plasma treatment did not change the surface structure. The effect of the plasma is based on surface manipulation in atomic scale, which results in a reduced carbon load on the surface, as shown with XPS. The water contact angle was before the treatment 32°, after the plasma treatment the implant was superhydrophilic.
Fig. 2. SEM image of plasma treated (a,c) and untreated (b,d) titanium screws.
The tissue integration of implants is strongly dependent on the cell adhesion behavior. Therefore, the adhesion of RBMC cells was investigated. While the cells on the untreated titanium (Fig. 3 b,d) have an oval shape, the cells on the treated titanium (Fig. 3 a,c) are enlarged and filamentous pseudopodia were acquired.
Fig. 3. SEM images of RBMC cells on titanium plates. Left: plasma-treated, right: untreated.
Additional to the in vitro experiments, plasma-treated and untreated titanium implants were implanted in the rat femur. After eight weeks of healing, the implant was further investigated. In figure 4, you see a three-dimensional computer tomography picture of the implant. It is clearly obvious that the amount of new bone formation is for the treated implant higher (Fig. 4 a) than for the untreated implant (Fig. 4 b).
Fig. 4. Three-dimensional computer tomography of the plasma-treated (a) and untreated (b) implant eight weeks after implantation.
From quantitative histomorphometric analysis (fig. 5), both, the bone area ratio (BA), and the bone-to-implant contact (BIC) could be determined. Both values are strongly enhanced for the plasma treated implants. In combination with the histopathological image of the bone tissue around the implant and the fluorescent labelled dynamic tissue morphometry, a early enhanced osseointegration and formation of hard tissue could be confirmed.
Fig. 5. Quantitative histomorphometric analysis of bone area ratio (BA) and bone-to-implant contact (BIC).
Early osseointegration is important to achieve initial stability after implant placement. In the investigation, control and experimental groups included untreated screws and those irradiated with atmospheric-pressure plasma using the piezobrush, respectively. The femurs of rats were used for in vivo experiments. Micro-CT analysis showed that more new bone was formed in the test group than in the control group. Similar results were shown in histological analysis. Thus, titanium screw, treated with atmospheric-pressure plasma, could induce high hard tissue differentiation even at the in vivo level.
The Case Study of KIT describes the fabrication of elastic and chemically inert gaskets made of PTFE and PDMS films with piezobrush® PZ3
Elastic and chemically highly inert flat gasket sheets are to be developed. For this, PTFE film of 50 μm thickness with a soft acrylic adhesive on one side is to be glued to a soft (40 Shore A) PDMS film with a thickness of 1 mm. As both materials have very low surface energies, it is hard to find an adhesive which bonds those materials together in a stable manner and is also elastic enough to keep the overall elasticity of the gasket.
Preliminary bonding experiments using double-sided adhesive tape
Preliminary tests used double-sided adhesive tape (3MTM High Performance Double Coated Tape 9088-200) to bond the PTFE film and the PDMS film together (Fig. 1).
Fig. 1: Preliminary bonding experiments with double-sided adhesive tape.
First tests failed, because the double-sided adhesive tape did not adhere well to the PDMS film. Using a primer based on heptane and a thin film of cyanoacrylate glue on the PDMS led to a surface with a higher energy; and the adhesion of the double-sided adhesive tape was improved. However, the flexibility of the gasket was reduced because of the stiffness of the cyanoacrylate glue.
Bonding experiments with the piezobrush® PZ3 device
First, the PDMS film surface was treated with piezobrush® PZ3 plasma (1 min at 100% power); and the PTFE film was subsequently bonded with its soft acrylic adhesive side (Fig. 2, Fig. 5 sample A). The adhesion between the films was very good and not affected by deformation of the gasket, i.e., the elastic properties were also maintained. Hence, using double-sided adhesive tape or cyanoacrylate as intermediate layer is no longer required.
Fig. 2: piezobrush® PZ3 plasma treatment of PDMS and subsequent bonding to the acrylic adhesive side of the PTFE film.
In a second experiment, both PDMS and pure PTFE surfaces were treated with piezobrush® PZ3 plasma and subsequently bonded by means of double-sided adhesive tape (Fig. 3, Fig. 5 samples B and C). This also worked well, provided the force to peel the films apart is not too strong. A similar approach using cyanoacrylate instead of the adhesive tape failed, as the plasma treatment did not improve the adhesion properties of this glue.
Fig. 3: piezobrush® PZ3 plasma treatment of PDMS and PTFE films and subsequent bonding via double-sided adhesive tape.
Finally, two PDMS films were surface treated with the piezobrush® PZ3 plasma and subsequently bonded with double-sided adhesive tape (Fig. 4, Fig. 5 samples D). Again, very good adhesion of the bonded films was obtained.
Fig. 4: piezobrush® PZ3 plasma treatment of two PDMS films and subsequent bonding via double-sided adhesive tape
Fig. 6: PDMS sheet with bonded samples A–D. Samples A, B, C: PTFE, Sample D: PDMS; further details see text. Left: Top view, right: bottom view showing the wetted adhesive surfaces.
Conclusion
It is commonly known that plasma treatment leads to surface activation resulting in better wetting and adhesive properties. The piezobrush® PZ3 device led to excellent results and is still easy and effortless to handle. Piezobrush® PZ3 plasma treatment of low energy surfaces, such as PDMS and PTFE, allowed subsequent bonding with simple double-sided adhesive tape with only little effort; and the resulting gaskets met the requirements regarding elasticity and chemical inertness.
Trade show IDS – Handheld plasma device for the dental lab and plasma components for system integration
Relyon plasma from Regensburg, a subsidiary of TDK Electronics, is presenting the piezobrush® PZ3 handheld plasma device for use in dental laboratories at IDS – International Dental Show. Moreover, the innovative implaPrep concept for demonstrating integration components for plasma activation of dental implants is introduced live.
Regensburg/Cologne. After being cancelled in spring 2021, the world’s leading trade fair for the dental community, IDS, will open its doors in Cologne from September 22-25, 2021, to present innovations and market trends to the professional audience. Relyon plasma will exhibit in hall 11.1 at booth H 48 J49 to present the benefits of plasma in the dental laboratory and implantology. On the one hand, the focus will be on the plasma handheld piezobrush® PZ3, which is primarily used in the dental laboratory for preparing prosthetics prior to bonding and color individualization. On the other hand, the focus of the trade show booth is on the implaPrep concept, which enables the plasma treatment of implants directly before implantation in order to obtain superhydrophilic implants and thus create the best possible conditions for rapid osseointegration.
Handheld cold plasma device piezobrush® PZ3 in the dental laboratory
Plasma technology has already been in use in dental laboratories for years as low-pressure plasma – however, these systems are usually very complex and expensive. With the introduction of the plasma handheld piezobrush® PZ3 last year, relyon plasma has succeeded in establishing an equally highly efficient, user-friendly plasma treatment in a compact handheld format and for a fraction of the cost.
The application focus here is on the treatment of prosthetics and veneers prior to color individualization. Due to the increased surface energy, the ceramics stain, for example, is dispersed much better on the surface, which leads to an even and aesthetically attractive result. In addition, more stain can be applied within one working step; this leads to a reduction in the number of firings required and thus also shortens the processing time.
Color individualisation of prosthetics without and with plasma treatment
Another application is the bonding of high-performance plastics such as PEEK with composite or PMMA. In addition to the surface activation, the surface is also cleaned of organic impurities at the same time, which improves the distribution of the adhesive and enables it to bond immediately with the correct bonding partners. This results in much more stable bonds between the bonding partners, such as the prosthetic and abutment, which ultimately increases the service life of the bond and thus patient/client satisfaction.
Plasma activation of implants with the implaPrep concept
Currently, the implaPrep concept is a prototype setup that allows titanium implants to be lifted from a hydrophobic to a superhydrophilic state by a 50-second plasma treatment. This property is based on structurally neutral plasma fine cleaning and electrochemical excitation by the plasma, thus creating the basis for optimized biocompatibility and acceptance by the surrounding living tissue. The underlying increased surface energy improves the initial attachment of osteoblasts, which subsequently leads to increased bone regeneration after implantation.
Implant without and with plasma treatment
This process was scientifically investigated and validated during the development phase of the plasma driver and the plasma reactor integrated in the implaPrep concept. Now it is time to collaborate with a partner from the dental industry to integrate these components developed in accordance with ISO 13485 into an existing system or to jointly establish a stand-alone device for the plasma activation of implants. Within the framework of the IDS, relyon plasma is looking for a development partner in order to transfer the device from prototype status to a series device. From now on, the focus will be on system integration, medical device approval and the subsequent establishment of an international sales network.
During a personal visit at the booth, both devices can be tested directly on site with own materials, implants and applications to get a hands-on impression of the plasma technology.
Inactivation of Listeria monocytogenes and Salmonella on Stainless Steel
by a Piezoelectric Cold Atmospheric Plasma Generator
Abstract
The group of Alexandros Stratakos recently investigated the effect of piezoelectric cold atmospheric plasma on the foodborne pathogens L. monocytogenes and Salmonella on stainless steel surfaces.
Authors: Gonzalez-Gonzalez, C. R.; Hindle, B. J.; Saad, S. & Stratakos, A. C.
Publicaton: Inactivation of Listeria monocytogenes and Salmonella on Stainless Steel by a Piezoelectric Cold Atmospheric Plasma Generator, Applied Sciences, 2021, 11.
In food processing, decontamination of the food contact surfaces is indispensable. One commonly used material in this context is stainless steel. I a recent work by the group of Alexandros Stratakos from the University of the West of England this issue was addressed by the use of piezoelectric cold atmospheric plasma.
For this investigation, stainless steel 304 plates were thoroughly cleaned and covered with the Gram-positive Listeria monocytogenes and Gram-negative Salmonella. Half of the samples were protein-soiled with Bovine serum albumin (BSA) to simulate real-life conditions. Cold atmospheric plasma was generated with the piezobrush® PZ2 from relyon plasma at distances of 10 mm and 20 mm. The log reduction up to a treatment time of 300 seconds were determined and fitted according to the Weibull + tail model.
Fig. 1. Effect of treatment time on inactivation of L. monocytogenes with a distance of (a) 10 and (b) 20 mm. Models were fitted using a Weibull + tail inactivation curve.
The effect of cold atmospheric plasma is based on the reactive oxygen and nitrogen species (RONS), which act independently or in synergy through different mechanisms with the cell. One of the major effects is the oxidative damage of the membrane, structural proteins, and DNA, which ultimately lead to cell inactivation. The pathogenic bacteria covered with BSA experience a protective effect of serum albumin on the bacterial cells against the reactive species generated by the cold atmospheric plasma. Since the inactivation was tested on dried cells, no biofilms were allowed to form.
Fig. 2. Effect of treatment time on inactivation of Salmonella with a distance of (a) 10 and (b) 20 mm. Models were fitted using a Weibull + tail inactivation curve.
In this study the effect of cold atmospheric plasma on foodborne pathogens L. monocytogenes and Salmonella inoculated on stainless-steel was determined. The cold atmospheric plasma treatment was able to significantly reduce the levels of both pathogens. The log reduction is time dependent. Protein-soiled coupons showed a protective effect to cold plasma inactivation achieving lower reductions compared to clean stainless-steel coupons for both L. monocytogenes and Salmonella. Longer distances from the plasma source decreased the decontamination efficiency of CAP; however, the difference in pathogen reduction was less pronounced at longer exposure times.
Conclusion
This study demonstrates the capacity of cold atmospheric plasma device piezobrush® PZ2 to effectively reduce the levels of both foodborne pathogens on stainless-steel surfaces and the potential to adopt this technology by the food industry as a disinfection process of surfaces to reduce cross-contamination and thus increase safety.
We use the piezobrush PZ3 handheld unit within our R&D. Especially in the area of surface treatment of complex 3D bodies, we were able to quickly achieve success in coating barrier lacquers that would not have been possible without increasing the surface tension.Arthur Reiners - R&D / laboratory manager
The compactness and ease of use of the piezobrush PZ3 in particular convinced the developers in R&D. “What is helpful about the hand-held device is the simple and uncomplicated operation,” says Arthur Reiners, laboratory manager at Sihl.
About Sihl GmbH
Sihl stands as a strong partner at the side of future-oriented industries and creates innovative solutions through high-quality coatings. More than 350 employees in the Sihl Group contribute to the success of customers from a wide range of industries in almost every country in the world. From automotive to tourism, from packaging and labels to printing and logistics, customers trust the high-quality coatings and technological know-how. As a specialist for future-proof products, Sihl enables innovative trends and promotes sustainable results.
Dynamic Contact Angle Measuring and Tensiometer (DCAT)
Measuring Imaginary Dynamic Contact Angles on Dental Implants
Author: Dr. Sebastian Schaubach, DataPhysics Instruments GmbH Date: 05/25/2021
Summary
The tensiometers of the DCAT series with their dedicated software from DataPhysics Instruments are able to determine imaginary contact angles reliably and reproducibly. This is a precious extension of the dynamic contact angle measuring method as it opens up the possibility to easily study hyperhydrophilic materials and, notably, to quantitatively distinguish the results also in cases where conventional methods always yield contact angles of 0°. Researchers in the development of dental implants and other bio-compatible materials will benefit from this feature, just as everybody working in the field of “hyperhydrophilicity” who wants to reliably quantify hydrophilicity differences between very hydorphilic materials.
Introduction
The water contact angle is an important parameter to characterize the wettability of a material and to classify it as hydrophilic or hydrophobic. On materials which are very hydrophilic, water spreads completely over the surface, and a contact angle of 0° is reached. If such very hydrophilic surfaces are sought after, as for example in the development of bio-compatible materials, the question arises if it is possible to distinguish between materials which all possess a 0° water contact angle? How to identify amongst them the one with the very best hydrophilicity? The answer is: this becomes possible with so-called imaginary contact angles. To the best of our knowledge, the DCAT tensiometers from DataPhysics Instruments are the only measuring systems which feature a reliable and reproducible imaginary contact angle determination in their software. In the following the application of the method will be presented at the example of dental implants.
Fig. 1. The surface of dental implants is very hydrophilic. Thus, water spreads on it, which conventionally means the contact angle is 0°. However, imaginary contact angles allow further discrimination.
Technique and Method
A tensiometer of the DCAT series from DataPhysics Instruments is a universal measuring system for the force-based study of interfacial parameters and phenomena. With the software module DCATS 32 and suitable sample holders it can be used for dynamic contact angle measuring on various solids, like implants, plates, films, powders, fibre bundles and even single fibres. This is particularly useful for studying hydrophilic samples: When optical contour analysis reaches its limits, one still obtains reliable and accurate results measuring dynamic contact angles with a DCAT thanks to its precise weighing system.
Fig. 2. Dynamic contact angle is formed when the solid sample dipped in or pulled out of the test liquid with known surface tension.
For measuring dynamic contact angles the solid sample is attached to the instrument’s balance via a holder and then dipped into and pulled out off a test liquid with a known surface tension γ (see Fig. 2 left). The measured weight m of the liquid lamella that contacts the sample at the contact line of length L is related to the sought contact angle θ according to the equation
where g is the gravity constant. In order to eliminate the buoyancy effect of the sample the measured weight is extrapolated to zero immersion height h before calculating the advancing contact angle θadv or the receding contact angle θrec for dipping in and pulling out, respectively (cp. Fig. 2 right).
From equation (1), it theoretically should not be bigger than 1 (for which θ is 0°). However, in practice, measurements of very hydrophilic surfaces do yield values of X > 1, in particular for rough surfaces where an additional force is generated during wetting by the capillarity of the porous surface (Fig. 3)
Fig. 3. Non-equilibrium model of meniscus-dependent filling to a complete wetting state on a rough surface.
Now, instead of assigning a contact angle of 0° in all those cases, the DataPhysics Instruments tensiometer software calculates the imaginary contact angle, i.e., the complex number fulfilling equation (1). This opens up the possibility to still distinguish between very hydrophilic materials, like the dental implants studied in this application note.
Experiment
In this application note the advancing and receding contact angles of three different titanium-based dental implants from Nobel Biocare® were determined with a DCAT 25.
Therefore, measurements were carried out on three identical samples per implant, which were taken out of the packaging with as little contact as possible and then analysed without further cleaning or treatment. Afterwards, one of the used samples of implant 3 was plasma treated with the handheld device piezobrush® PZ3 from relyon plasma (metallic: nearfield module) and measured again. Plasma is widely used to increase the hydrophilicity of various materials.
In a preliminary test the surface tension of the water, which was later used as ‘known test liquid’, was measured using a Wilhelmy plate in order to ensure its purity (γ = 72.8 mN/m).
For the dynamic contact angle measuring an implant sample was attached to the sample holder. The method “Dynamic CA” was selected in the software and the sample diameter was typed in (implant 1: 5.5 mm, implant 2: 3.0 mm, implant 3: 4.3 mm). As the implants are slightly tapered, with the tip being a little smaller than the given diameter, the immersion depth was set to 5 mm. Then the measurement was started, and the instrument automatically dipped the sample into the water and pulled it out again, whereafter the software calculated the dynamic contact angles.
Results
Fig. 4 shows the advancing (red) and the receding (green) contact angles determined for the studied dental implants. For all implants there were only minor deviations between the measurements of the three examined samples, which results in small error bars (± 2.9° max. for CAadv of implant 3).
Fig. 4. Dynamic contact angles (red: advancing, green: receding) for the three different implants and for one plasma treated sample of implant 3.
As can be seen in Fig. 4, both of the advancing CA and receding CA of implant 1 and implant 2 are imaginary values, indicating that these two kinds of surfaces are hyperhydrophilic materials and possess extremely high wetting rates.
Besides, an extremely fast spreading of water on the surfaces was observed during the samples dipping in the water (Fig. 1), which is consistent with the results of CA measurement. Furthermore, implant 1 shows higher imaginary CAs than implant 2, indicating that more extra force at implant 1 was detected during the wetting process caused by extra spreading and capillary forces. Thus Implant 1 is much more hyperhydrophilic than implant 2.
Interestingly, as Fig.4 shown, the advancing CAs of implant 3 are normal CAs with higher than 90o, and around 41o of the CA after the surface was treated with piezobrush® PZ3. This indicates that the wettability of its original surface is not hydrophilic and the wetting rate is extremely low that can be neglect.
Besides, no spreading of water on the surface of implant 3 was observed during dipping in. However, the receding CAs of all samples are the imaginary CAs, which indicates an extra force was detected during the pulling out process caused by the extra spreading and capillary forces. Besides, the CA of the plasma treated implant 3 surface is lower than the untreated surface, indicating that the surfaces has become more hydrophilic after surface treatments.
Therefore, the advancing and receding water contact angles on implant 1 and 2 as well as the receding contact angle on implant 3 are imaginary contact angles. That means conventionally values of 0° would have been obtained in all those cases. The DataPhysics Instruments software, however, determined the imaginary contact angles which permits a further discrimination.
Literature
[1] Hyperhydrophilic rough surfaces and imaginary contact angles; H. P. Jennissen; Mat.-wiss. u. Werkstofftech. 2012, 43, 743-750; DOI: 10.1002/mawe.201200961
relyon plasma @ Bondexpo
The 14th Bondexpo – International Trade Fair for Bonding Technology – will open its doors in Stuttgart from 5 to 8 October 2021. We are very pleased that relyon plasma is represented at Bondexpo 2021 with its own booth. Bondexpo convinces with a clear and consistent focus on the process chain of joining/bonding by means of gluing, moulding, sealing and foaming. In addition, visitors will gain an in-depth insight into the current and future challenges in joining and bonding the broadest range of materials.
The Motek will take place in parallel at the Stuttgart Exhibition Centre. Motek is the world’s leading event in the fields of production and assembly automation, feed technology and material flow, streamlining through handling technology, and industrial handling. As such, Motek is the only trade fair to clearly focus on all aspects of mechanical engineering and automation and on the presentation of entire process chains.
Experience our innovative plasma technology up close in hall 5 at booth 5505. Two products from the piezobrush® family are unique here: the piezobrush® PZ3 handheld plasma unit and the brand-new, clever inline solution piezobrush® PZ3-i with new nozzle modules. We will also show you our plasmatool as well as our plasmacell in Stuttgart. You can try out our plasma systems directly on-site with your own materials and case studies. You are welcome to contact us in advance at info@relyon-plasma.com.
Visit us at booth 6415
Visit us at Bondexpo and get a free entrance ticket for the exhibition!
Thermographic investigations on the pretreatment of polypropylene
Motivation and objective
As part of the beta test campaign for the piezobrush® PZ3 device from relyon plasma GmbH, the SKZ conducted investigations on the adhesion enhancement of a 2C epoxy adhesive on a low-energy and thus difficult-to-bond plastic polypropylene (PP). In addition to the piezobrush® PZ3 and the predecessor model PZ2 (both based on “piezoelectric direct discharge” (PDD) plasma technology), a conventional atmospheric pressure plasma system with rotating nozzle (ADP) was used. Furthermore, the plasma pretreatment process was monitored by thermography to investigate the influence of the pretreatment type on the temperature rise of the substrate.
Materials and methods
Extruded PP sheets (MEPOLEN PP-H, BEN Kunststoffe Vertriebs-GmbH) with a thickness of 2 mm were used as substrates. After cleaning the PP substrates in an ultrasonic bath for 5 min and subsequent airing for 15 min in an automated pretreatment stand with integrated motorized axes, the plates were pretreated with the three different devices (PZ2, PZ3 and ADP) (cf. Figure 1a). A thermal camera from Optris GmbH with a frame rate of 80 Hz, which was also installed, recorded thermograms during pretreatment, which were evaluated with respect to their temperature distribution via a line profile (red line) 2.0 cm away (cf. Figure 1b). Both the thermal camera and the individual pretreatment units were permanently installed, and the defined treatment speed was realized using the axis-controlled sample table method. The treatment distance between the substrate and the two piezobrush units was chosen based on the recommendations of the unit manufacturer, which were 3.0 mm, 6.0 mm and 9.0 mm. Figure 2 shows the optically detectable plasma exit area. It can be clearly seen here that the active area of the plasma protrudes approximately 12 mm from the nozzle opening on both devices. For the ADP, the nozzle spacing was 8.0 mm. The treatment speeds varied between 0.5 mm/s and 20.0 mm/s. In order to determine suitable pretreatment parameters for the adhesion tests, contact angle measurements were carried out to determine the surface free energy (SFE) on the pretreated substrates according to DIN EN ISO 19403-2 using a Drop Shape Analyzer DSA30 from KRÜSS GmbH. The test liquids used were Diiodomethane and deionized water (both p.a. purity) were used as test liquids. Five droplets per test liquid were deposited during each measurement. The evaluation of the measurement data was performed according to the Owens-Wendt-Rabel-Kaelble method (OWRK). The most promising pretreatment parameters in terms of their SFE were then used for the strength tests.
Figure 1: Pretreatment of a PP sheet in the automated pretreatment stand with the piezobrush® PZ3 and simultaneous recording of thermograms with an integrated thermocamera (a). b: Exemplary representation of a thermogram after pretreatment with piezobrush® PZ3 and the evaluation line (red) 2.0 cm away from the nozzle center.Figure 2: Representation of the emerging plasma of the two piezobrush devices (PZ2 and PZ3). The area of the plasma visible to the eye can be seen up to a distance of 12 mm from the nozzle on both devices.
Tensile tests were carried out using the LUMiFrac adhesion analyzer from LUM GmbH based on CAT technology. The adhesive used was the 2C epoxy adhesive DELO-DUOPOX® AD840 from DELO Industrie Klebstoffe GmbH & Co. KGaA was used. The bonds were produced between the plastic specimen and a metal adapter. For this purpose, the stainless steel screw-in adapter V2A-D10 with a diameter of 10.0 mm was previously ground and cleaned with isopropanol. Before applying the adhesive, approx. 5 to 20 glass beads (Ø = 80 to 100 μm) were placed on the joining surface to ensure a constant adhesive layer thickness. A sufficient amount of adhesive was then applied so that the entire bonding surface could be filled by increasing the contact pressure, but the adhesive did not flow out several millimeters laterally. Six tensile test specimens were made for each specimen-adhesive combination. Curing took place at a constant contact pressure of 1.0 N under standard climate conditions (23 °C, 50 % humidity) for seven days. Figure 3 on the left shows the schematic structure of the specimen for the tensile test. The stainless steel screw-in adapter (gray) and a copper weight (green) are connected to the plastic (blue) via an adhesive layer (orange). The test setup is shown in Figure 3 on the right. For testing, the assembly is rota-ted so that the centrifugal force on the test plunger is increased at 5.0 N/s. If the test punch breaks at a certain load, a sensor (red) detects the impact. The tensile strength can then be determined via the speed at impact and fracture surface. The fracture type of the LUMiFrac specimens was then classified according to DIN EN ISO 10365.
Figure 3: Design of the specimen for tensile testing (left) and schematic representation of the test arrangement in the LUMiFrac adhesion analyzer (right).
Contact angle measurements
Looking at the results of the contact angle measurements in Figure 4, it can be clearly seen that the SFE of the PP substrate increases after pretreatment with the PZ2 (a – c) and the PZ3 (d – f) as a function of the treatment distance (a, d: 3.0 mm; b, e: 6.0 mm; c, f: 9.0 mm) compared to the untreated condition (reference). While the PP reference has a SFE of 31.7 mN/m with hardly any polar component (0.6 mN/m), the SFE increases continuously with decreasing treatment distance and lower treatment speed. A steady increase in the polar fraction can be observed, with the disperse fraction remaining at a constant level (about 35 mN/m). When comparing the PZ2 with the PZ3, it is noticeable that higher values for the SFE of the substrate are achieved with the PZ3 at the same treatment distance and speed. While it was not possible to achieve an SFE of more than 50 mN/m with the PZ2 for the selected parameters, an increase in the SFE to almost 60 mN/m was recorded with the PZ3. It is also noticeable that pretreatment at a treatment distance of 9.0 mm results in only a slight increase in the SFE of the substrate, irrespective of the version of the piezobrush. Although the active plasma region extends about 12 mm out from the plasma nozzle in both devices as shown in Figure 2, the decreasing energy input into the substrate with increasing distance seems to be the reason for the lower surface activation. In addition, the low standard deviations of the determined SFE indicate a homogeneous pretreatment with the piezobrush devices. An improvement in the wettability of the PP substrate could thus be achieved by means of PDD plasma.
Figure 4: Plot of the SFE (divided into polar and disperse fraction) of the PP substrate after pretreatment with the PZ2 (a – c) and PZ3 (d – f) at different treatment rates and intervals.
Tensile tests using LUMiFrac
In order to investigate the influence of the substrate pretreatment on the bond strength, bondings were carried out on selected treatment parameters. In addition to reference samples (untreated PP), samples were also pretreated with the PZ2 and PZ3 at a treatment distance of 3.0 mm, since the greatest increase in SFE values was achieved here compared to the untreated reference. The treatment speeds selected were 1.5 mm/s and 10.0 mm/s for PZ2 and 1.5 mm/s, 5.0 mm/s and 10.0 mm/s for PZ3. In addition, a conventional atmospheric pressure plasma system with a rotary nozzle served as a comparison method. The parameters selected here (treatment distance: 8.0 mm or treatment speed: 150.0 mm/s) for optimum bond strength resulted from preliminary tests with the PP substrate and adhesive used. The results of the tensile strength tests using Adhesion Analyzer are shown in Figure 5. It can be clearly seen that with all pretreatment methods a significant increase in bond strength is achieved compared to the untreated PP. With a PZ3 pretreatment at a treatment speed of 1.5 mm/s, the tensile strength of the bonded joint can even be increased from about 1.0 MPa in the base state to up to 4.5 MPa after pretreatment. There is also a change in the fracture pattern: while the reference specimens show an adhesive failure (AF), a partially cohesive joint failure (CSF) occurs after the pretreatment described (cf. Figure 6). Furthermore, it is noticeable that the bond strength increases with decreasing treatment speed for PZ2 and PZ3 and that the fracture pattern changes from AF to CSF. In addition, the results suggest an increased bond strength at the same treatment speed (1.5 mm/s) by using PZ3 compared to PZ2. Thus, for the selected adhesive-substrate combination, a correlation can be made between the increased SFE after pretreatment and the improved bond strength. When comparing the PDD plasma technology with a conventional ADP from a rotary nozzle, an equivalent increase in bond strength can be achieved with optimum parameter selection.
Figure 5: Adhesive and tensile strength of the PP substrate. In addition to reference specimens, pre-treated substrates (PZ2, PZ3, ADP) were also investigated at different treatment speeds. The fracture types differ between adhesive failure (AF) and cohesive joint failure (CSF).Figure 6: Illustration of a LUMiFrac specimen showing adhesive failure (AF) of the bond after tensile testing (a) as well as cohesive bond failure (CSF) and AF (mixed fracture) (b).
Thermography during pre-treatment
In order to investigate how much the temperature change on the PP substrates is during the pretreatment with the PZ2 and PZ3, the process was monitored with a thermocamera. Figure 7 shows three thermograms each at treatment speeds of 1.5 mm/s, 5.0 mm/s and 10.0 mm/s during the pre-treatment process with the PZ2 (a – c) and PZ3 (d – f). The treatment distance was set to a constant 3.0 mm here. Looking at the thermograms, it is noticeable that the temperature load decreases with increasing treatment speed, as expected. It can also be seen that pre-treatment with PZ3 causes a greater temperature increase at the same treatment speed than its predecessor PZ2. Nevertheless, the surface temperatures of the substrate remain below 55 °C even at very slow treatment speeds (e.g. 1.5 mm/s). This is again illustrated in the graphical plot of temperature versus pixel coordinate along the evaluation line in Figure 8. While the maximum temperature for treatment with the PZ2 does not exceed 35 °C, a treatment speed of 1.5 mm/s with the PZ3 results in a maximum temperature of approx. 53 °C. However, at the treatment speeds of 10.0 to 20.0 mm/s recommended by the manufacturer, no temperatures above 35 °C can be detected even with the PZ3.
Figure 7: Plot of individual thermograms after pretreatment with the PZ2 (a – c) and PZ3 (d – f) at a treatment distance of 3.0 mm and different treatment speeds of 1.5 mm/s (a, d), 5.0 mm/s (b, e) and 10.0 mm/s (c, f).Figure 8: Graphical representation of the temperature distribution over the pixel coordinate along the evaluation line (cf. Figure 1) after pretreatment for PZ2 (a) and PZ3 (b) at different treatment speeds and a treatment distance of 3.0 mm.
Conclusion
In summary, it can be said that surface modification by means of PDD technology of the non-polar plastic PP is very possible. By pretreating PP with the PZ2 or PZ3, the surface energy (especially the polar fraction) can be increased when suitable treatment parameters are selected, and a significant increase in adhesive strength can be achieved compared to the untreated PP substrate. It could also be shown for the selected adhesive-substrate combination that a pretreatment with the PZ3 achieved a comparable strength increase as a pretreatment with a conventional ADP system with rotating nozzle at a higher treatment speed. Another advantage of the PDD technology is the treatment of the substrate with cold-active plasma. Thermographic images showed that the temperature of the substrate did not rise above 55 °C even at low treatment speeds and short distances. This is particularly crucial for temperature-sensitive materials such as plastics. Thus, even films can be pretreated with the piezobrush devices without any problems and without damage. A disadvantage is the need for a lower treatment speed due to the lower power of the devices compared to conventional atmospheric plasma systems. Furthermore, it could be shown by means of thermography that treatment with the PZ3 is somewhat more energy-intensive compared to the PZ2, but in return achieves a significant increase in SFE and adhesive strength compared to its predecessor version PZ2.
Joining of different plastics for detailed eye models
eyecre.at from Ötztal has been producing detailed eye models for surgery training since 2012. The goal is to create an artificial eye that feels like a real one, but has a long shelf life and can be adapted to customer requirements. Therefore, the joining of different plastics is particularly important – at this point, the piezobrush® PZ3 handheld plasma device is used to ensure robustness and high quality.
To ensure the robustness of our artificial eyes, we wanted to find the best solution for treating our products.
The best solution was relyon plasma, the world’s smallest handheld plasma device with PDD technology.David Ortner - CEO eyecre.at
Since we purchased the piezobrush® PZ3, our product quality and efficiency have increased significantly.
Many thanks to relyon plasma GmbH!David Ortner - CEO eyecre.at
About eyecre.at
It all started small, when the CEO, David Ortner, recognized that there was room for improvement after years of experience in doctor training and wetlabs. In a field where the alternatives were limited, he realized it was possible to create a product that could solve most of the existing issues with artificial eye production, while still providing the essential innovations for ophthalmic doctors and companies. Today, Eyecre.at GmbH produces the best solutions available on the market. The market superiority yields from many years of experience in the ophthalmic wetlab equipment sector, and products tailored to customers’ needs, domestically manufactured, and continuously developed.
Multi-Device Piezoelectric Direct Discharge for Large Area Plasma Treatment
Authors: Dariusz Korzec *, Florian Hoppenthaler, Anatoly Shestakov, Dominik Burger, Andrej Shapiro, Thomas Andres, Simona Lerach and Stefan Nettesheim First published: MDPI – https://www.mdpi.com/2571-6182/4/2/19/pdf
Abstract
The piezoelectric cold plasma generators (PCPG) allow for production of the piezoelectric direct discharge (PDD), which is a kind of cold atmospheric pressure plasma (APP). The subjects of this study are different arrays of multi-device PCPGs for large-area treatment of planar substrates. Two limiting factors are crucial for design of such arrays: (i) the parasitic coupling between PCPGs resulting in minimum allowed distance between devices, and (ii) the homogeneity of large area treatment, requiring an overlap of the activation zones resulting from each PCPG. The first limitation is investigated by the use of electric measurements. The minimum distance for operation of 4 cm between two PCPGs is determined by measurement of the energy coupling from an active PCPG to a passive one. The capacitive probe is used to evaluate the interference between signals generated by two neighboring PCPGs. The second limitation is examined by activation image recording (AIR). Two application examples illustrate the compromising these two limiting factors: the treatment of large area planar substrates by PCPG array, and the pretreatment of silicon wafers with an array of CPG driven dielectric barrier discharges (DBD).
1. Introduction
The upscaling of plasma systems has long been a concern of researchers [1–3]. Cold atmospheric pressure plasma jets (APPJ) are very important tools for surface processing [4–7]. Typically, the APPJs produce plasma small in size, from a few millimeters to a few centimeters. To up-scale the size of the treated substrate, different discharge architectures are applied based on the multiplication of a single plasma source. One example of such a methodology is the matrix of micro-hollow cathode discharges (MHCD) [8,9]. The arrays of atmospheric pressure plasma jets (APPJs) are subject of a number of papers [6,10–13]. Such array sources powered with frequency in the kHz range, based on dielectric barrier discharge (DBD) are described in [14,15].Recently, the operation of piezoelectric direct discharge (PDD) [16,17] as an APPJwas characterized [18,19]. The resonant piezoelectric transformers (RPT) [20] used for generation of the PDD, can be used in arrays for the increase of the treatment area and speed. One approach is to build a multichannel RPT, as described in [21,22]. The disadvantage of such a solution is the technological complexity and the limitation to a specific task. More flexibility allows an approach based on modularity: arranging many single PDDgenerators in an array. Such an approach was demonstrated for six separate RPTs for a high power plasma generator [23]. The system for an arbitrary number of parallel-connected piezoelectric cold plasma generators (PCPGs) [24] is described in [25]. The problem faced by Plasma 2021, 4282 by practical realizations is the electrodynamic and acoustic interference of the PCPGspositioned close to each other. To avoid such interferences, a minimum distance between the PCPGs must be kept. On the other hand, for the homogeneous treatment of a broad moving substrate PCPG activation traces are needed with distances, which are smaller, than the activation width of a single PCPG. This width can be influenced either by the operating parameter such as PCPG power, distance between the PCPG and the substrate, the substrate movement speed and gas mixture, or by definition of the activation, e.g., reaching of some threshold value of the surface free energy. In this work, the activation image recording (AIR) system is used for the evaluation of the activation area. The minimum distance for different types of PCPG is investigated by measurement of energy coupling from an active PCPG to a passive PCPG placed at some distance from the active one. The AIR experiments are used to determine the minimum required distance between PCPG traces for different device configurations. The resulting system architectures and following application examples are described and discussed.
2. Experimental Details
For all experiments presented in this study, two types of PCPGs were used: the CeraPlas™ F and CeraPlas™HF. Their physical operation principle and the method of parameter control is described in [26]. Two discharge configurations were used. The first was the PDD. The second was the PDD-powered dielectric barrier discharge (DBD) [17].
2.1. Energy Transfer Measurement
The electric field generated by one PCPG can induce the electromechanical oscillations of another PCPG positioned in the vicinity of the first one, providing the resonance frequencies of both devices are very similar. This effect was used in this study for determining the minimum safe distance between two PCPGs working in an array of PDD devices. For this purpose, two PCPGs of CeraPlas™ HF type were positioned with their high voltage sides face-to-face. The first of them was not movable. The second one can be moved linearly by the micrometric manipulator to set the exact distance between the tips of the PCPGs.Figure 1a shows the setup used for evaluation of the energy coupling between twoPCPGs. A sinusoidal signal generator was used to generate the input signal of the first PCPG. The input terminals of the second PCPG were not powered but bridged by aRout=10 kΩresistor. They were used as output terminals of the measurement setup. On input and output, the current and voltage were measured. For current measurements, the current probe Tektronix TCP202 was used. The voltage was measured by the use of the Tektronix P6015A voltage probe. Both probes were connected to the Tektronix DPO3034phosphor oscilloscope (5 M record length; 2.5 GS/s sample rate).
2.2. Capacitive Probe Measurement
The high voltage tip of the PCPG was made of PZT ceramics and was not equipped with any electrically conducting electrode. Consequently, the direct voltage measurement of the PCPG output voltage was impossible. However, during operation, the PCPG produces a strong alternating electric field causing the plasma ignition. This field can be evaluated by the use of the large area capacitive probe. The details about this method and the signal interpretation were described in detail in [19]. The voltages measured by such probe are proportional to the kHz voltage on the tip of the PCPG. The proportionality factor is inthe10−3range. In this study, the capacitive large area probe was used to investigate the operation of a couple of PCPG working at a close distance from each other, as shown in figure 1b.
Figure 1.The setup for electric characterization by use of: (a) energy transfer efficiency between two PCPGs, and(b) capacitive probe measurement.
2.3. Activation Area Determination
To determine the activation area of a PCPG, the device was positioned to assure a required distance between the PCPG tip and the substrate surface, typically 4.5 mm. The substrate used for evaluation is the HDPE plate 2 mm×50 mm×100 mm. The usual treatment time is 10 s for open PDD and 20 s for the PDD-powered DBD. The test ink was used for visualization of the activated zone. To avoid the aging effect due to stoichiometry changes of multi-liquid test ink, the 58 mN/m test ink (Fa. Ahlbrandt)consisting of pure formamide is used. The additional advantage of the value 58 mN/m was that it assures a high dynamic range of the evaluation method, because it was positioned in the middle between the surface energy value of non-treated HDPE (36 mN/m) and the maximum reachable value for a plasma-treated surface, of 72 mN/m.It can be observed that, after covering the activated surface with test ink, the ink spot area decreased within seconds. The pictures of the ink spots were taken in short intervals using a digital camera. The contour of the ink spot was automatically recognized and the ink spot area was calculated from the pixel count using specialized software. The system used for this purpose was the Activation Image Recording (AIR) of relyon plasma GmbH. From the collected shrinkage curve, showing the activation area as a function of time, the point after 10 s of shrinking was selected as a reference value. The AIR method is described in detail in [19].
3. Results and Discussion
3.1. Interferences between PCPGs
Three types of interferences between two PCPGs working in small distance from each other can be observed. The first one occurred, if the PCPGs operated at high power are very close to each other, with a tip-to-tip distance of less than 30 mm. In such a case, the spark discharge between the PCPGs can be observed which disrupts the regular operation of both PCPGs. Working for a long time in such a mode can cause damage to the devices. The second one is based on the acoustic energy transfer between the PCPGs [27]. Since the condition of acoustic impedance matching are not fulfilled in our setup, only a small part of the energy coupled in the PCPG can be transferred acoustically to another PCPG. Nevertheless, the acoustic noise, depending on the control drive used, can be observed for the tip-to-tip distance up to 8 cm. The most probable reason for the acoustic noise is the beat between the ultrasonic frequencies of both PCPGs. The operation frequencies of the PCPGs are very similar, but not identical. The reasons for this difference can be related either to the device characteristics or to the operating conditions. The most important device-related influence has the length of the PCPG and its electric parameters. They have a production process-related statistical distribution, which causes the differences in the resonant frequencies. The operation-related difference in frequency is caused by the PCPGcontrol system. To keep the power of the PCPG constant, the frequency was varied. This control mechanism was described in detail in [26]. The overlapping of two signals with operation frequencies f1 and f2 generated by two neighboring PCPGs respectively, results in a beat frequency fb[28] given as:
fb=|f2−f1|
The fb is typically in the small kHz range and is audible. It is especially loud, if some acoustic resonances in the holder and connections of the PCPG are excited. The source of acoustic noise can also be the excitation of transversal resonances in the PCPG itself. Since the transversal sound velocity in hard PZT is a factor two lower than the longitudinal one, and the first harmonic frequency can be excited, the transversal resonance frequency is a quarter of the second harmonic frequency of the PCPG. For CeraPlas™ Fit is 50 kHz/4 = 12.5 kHz. This was a high pitch sound, which was frequently audible if two PCPGs are operated close to each other. Such noise is strong enough to exclude many attractive applications of the PCPG arrays. The third type of interference was by the electric fields of the both PCPGs and will be investigated in more detail in the following sections. It is effective even if the PCPG oscillation amplitude is too weak to cause the spark discharge or the loud noise.
3.2. Coupling Efficiency
The active PCPG, as described in Section 2.1, is operated with the input voltage of1 V. The voltage transformation ratio for PCPG was about 1000, resulting in an output voltage of the active PCPG in the range of 1000 V, which is not sufficient to cause a gaseous breakdown at the PCPG tip. Consequently, the electric coupling between the active and passive PCPG is purely capacitive, with no losses for the discharge. Since no parasitic discharge between PCPGs can ignite, the measurement can be conducted starting from very small distances between the PCPGs. Figure 2a shows the voltage induced in the passive PCPG as a function of this distance. The output voltage for distance below 3 mm is larger than the corresponding input voltage. The reason can be the higher oscillation quality of the second PCPG, compared with the first one. The difference in oscillation resonance quality can be caused by the different input impedance of the first PCPG and the load of the second one. The output voltage decreases rapidly with increasing distance and vanishes for the distance larger than 3 cm. The coupling efficiency, defined as the output-to-input power ratio, is decaying for the distance of more than 3 cm, as shown in Figure 2b. However, it reaches the maximum value of 80.4% at the distance of 2.4 mm. Further increase of the coupling efficiency can be achieved by precise adjustment of the load resistor. With decreasing coupling efficiency, the resonance frequency of the active PCPG is increasing, reaching its non-loaded frequency by a distance of about 15 mm (see Figure 2b). The practical conclusion from this investigation is that the CeraPlas™HF devices placed in distances larger than 3 cm will not cause the electric interference between them.
Figure 2.The energy coupling from active to passive PCPG (see Figure 1a) as a function of distance between the PCPG tips.(a) Voltages on the low voltage sides of the PCPGs. (b) The coupling efficiency and the resonance frequency of the active PCPG determined with 10 kΩload on the low voltage side of the passive PCPG. Both PCPGs used are of CeraPlas™ HF type. The signal on input of the active PCPG was sinusoidal with amplitude of 1
3.3. Overlapping of Emitted Signals
A typical signal measured by a capacitive probe for PCPG of CeraPlas™ F-type operated with 8 W power in the tip-to-probe distance of 30 mm is shown in Figure 3a. It can be interpreted as an overlap of a more-or-less sinusoidal signal and short non-periodic pulses being a response on micro-discharges. The frequency of the sinusoidal componentcorresponds to the second harmonic of the PCPG oscillation. The positive and negativemicro-discharge responses are different. Typically, the positive (anodic) peaks have a highermagnitude than the negative (cathodic) ones. Such asymmetry is due to the difference in the physics of the positive and negative streamers.
Figure 3.The probe voltage measured for: (a) single PCPG, and (b) two PCPGs placed parallel at a tip-to-tip distance of60 mm, operated with the input power of 8.0 W and the CDA flow of 8 SLM each. The distance between the PCPG tip and the probe surface is 30 mm
Figure 3b shows the probe voltage measured when two PCPG placed in the tip-to-tip distance of 60 mm are operated in front of the probe. At this distance no field interference between the PCPGs can be observed. The two signals are not coherent in phase. In curve in Figure 3b during the time corresponding to one cycle of the PCPG second-harmonic oscillation, two cathodic and two anodic micro-discharge peaks can be observed. The phase shift between the two independently oscillating PCPGs results in a shift of the micro-discharge peaks in respect to the maximum of the sinusoidal curve. Due to slightly different oscillation frequencies of the both PCPGs, the phase difference of the two signals is not constant in time. Consequently, in another voltage excerpts, the signals with 0◦or 180◦phase difference can be found. Examples of voltage curves for such phase shifts are shown in Figure 4a,b respectively. When comparing the curves for a single PCPG in Figure 3a and for two PCPGs working in phase (phase difference of 0◦) as shown in Figure 4a, it can be seen that the signal components related to the PCPG oscillations are added. The amplitude for the singlePCPG is about 15 V. For two PCPGs working in phase, it is doubled to about 30 V. The cathodic and anodic micro-discharge peaks occur at about the same place as a single PCPG signal, but the number of micro-discharges doubles—in the shown examples eight instead of four anodic micro-discharges and 10 instead of five cathodic micro-discharges. When comparing the curves for a single PCPG in Figure 3a and for two PCPGsworking with a phase shift of 180◦as shown in Figure 4b it can be seen, that the signal components related to the PCPG oscillation are compensating each other on the capacitive probe. The occurrence of the anodic micro-discharges of one PCPG is overlapping with the cathodic signals of another PCPG.
Figure 4.The probe voltage measured by capacitive probe for two concurrently working PCPGs with phase shift of (a) 0◦and (b) 180◦. The input power and CDA flow of the PCPGs is 8.0 W and 8 SLM respectively. The distance between PCPGs is 60 mm.
Such independence of the voltages for a couple of PCPGs of CeraPlas™ F type can be observed for tip-to-tip distances down to 40 mm. It can be concluded that at such sufficient distances, the PCPGs run independently and do not influence each other.
3.4. Surface Activation
The most important parameter of a plasma system used for surface activation is the activation rate, defined as the activated area per time unit. In case of static treatment, the activation rateηactcan be expressed as the ratio of the activated area Sact to the activation time ttreat :
(2)
The activation image of a single PCPG operated statically with the power of 8 W generated on the HDPE substrate is shown in Figure 5a. The kidney shape of this image results from the structure of the PDD shown in the picture included in the upper-right corner of the figure. The Equation (2) yields for ttreat=10 s and Sact=400 mm2 the activation rate of 40 mm2/s. In case of the treatment with the relative speed vtreat between the substrate and the PCPG, the Equation (2) can be rewritten as:
(3)
where wact is the width of the activation strip. The rotational asymmetry causes the activation resulting in moving substrates de-pends on the movement direction. Figure 5b illustrates this dependence. Two curves represent the interaction length of a point on the substrate with the activation zone of PCPG moving relatively to the substrate surface. The position of the treated substrate point is defined on the axis perpendicular to the motion direction. The line with red bullets shows the result for substrate movement along the x-axis accordingly to the axis orientation shown in Figure 5a. The full width at half maximum (FWHM) of about 22.5 mm by such movement direction is by 40% larger than the FWHM for movement along the y-axis of16 mm.
Figure 5.The activated zone produced on a HDPE substrate by CeraPlas™F module operated 10 s with the power of 8 W.(a) The image achieved statically by use of 58 mJ/m2test ink. (b) The interaction length of the activation zone with thesingle point of the substrate for movement of the substrate along thexandyaxis of the ink image. The arrows show themovement direction with respect to the activation image. The point position is defined on the axis perpendicular to themovement direction. For both curves, the full widths at half maximum (FWHM) is depicted
Assuming the same interaction time of 10 s by linear movement of the PCPG (the treatment time for the static treatment) the speeds of 1.6 and 2.25 mm/s for y and x-direction respectively are achieved. The activation rate calculated by use of Equation (3) is in both cases the same: 1.6 mm/s×22.5 mm = 2.25 mm/s×16 mm = 36 mm2/s.This difference in the activation profile has practical implications for the design of PCPG arrays, allowing either faster activation on narrower substrates or slower activation on wider substrates. Using the results of the electric measurements the minimum distance between PCPGs assuring no interferences between these devices is dmin=40 mm, as depicted with red arrows in Figure 6a. To reach a homogeneous treatment when moving in y-direction, two rows of PCPGs are sufficient as illustrated in Figure 6a. For movement along the x-axis, at least three rows of PCPGs would be needed. The size of the activation image depends strongly on the treatment time. Consequently, the width and length of the activation image varies as well. The curve with red triangles in Figure 6b illustrates the increase of the activation width Lx as a function of treatment time. A similar curve can be plot for Ly of the activation image, as defined in Figure 5a. Assuming the motion of the substrate in they direction, the speed vy of this movement can be determined, by which the mean interaction time is equivalent to the static treatment time ttreat:
(4)
Taking into account the decrease of the activation length with decreasing treatment time, the dependence of the treatment speed is calculated and plotted in Figure 6b as the curve with blue circles. From this curve, it can be seen that the activation rate can be increased by an increase of the linear speed in the considered activation time range. It can also be shown, that if the PCPG movement speed vy would be higher than some limiting value the two rows of PCPG would be not enough to assure a homogeneous treatment. The treatment strips would not overlap anymore. The black arrows in Figure 6b show that the treatment width would be below 20 cm, if the treatment speed would exceed 6.3 mm/s.The estimation in this example is valid for HDPE and surface energy of 58 mN/m. In many practical examples, less demanding materials are used and lower surface energies are required, resulting in a larger activation image for a shorter treatment time. Consequently, much higher treatment speed, in the range of tens of cm per second, can be achieved.
Figure 6.Determination of the CeraPlas™F module array geometry. (a) The position of the CeraPlas™F modules fulfillingthe conditions of no interference and homogeneous treatment. (b) The width of the image of the activation area achieved ona HDPE substrate treated with piezobrush®PZ3 operated with power of 8 W and the equivalent treatment spee
3.5. Realization Examples
3.5.1. Treatment of Substrates on a Belt Conveyor
In this example, the modules equipped with PCPG of CeraPlas™F type are used toarrange an array for treatment of substrates moved on a belt conveyor with a width of 20 cm.The substrates placed on a belt conveyor should be treated by PDD plasma. Using the PCPG configuration from Figure 6a the 10 PCPGs are sufficient to cover such treatmentwidth. The maximum treatment speed of the substrates transferred by a belt conveyor islimited by the maximum PCPG power of 8 W. The only means of treatment rate scaling isto use a larger number of PCPG in series. In our case, four two-row arrays of 10 PCPGseach are applied (see Figure 7) allowing to increase the maximum speed of homogeneoustreatment from 6.3 mm/s to about 25 mm/s.
Figure 7.The plasma system consisting of 40 PCPGs organized into four units of 10 PCPG modules is shown underoperation. The input power and CDA flow of each PCPG is 8.0 W and 7 SLM respectively
The typical operating parameters of this system are the PCPG power of 480 W andthe compressed dry air (CDA) consumption of 280 SLM. With these parameters, theozone production rate is 3.2 g/h. The CeraPlas™ drives are supplied with 24 V DC froma common power supply. The entire system consists of input, treatment, and outputchambers. Those are separated from each other and from the outside environment withsilicon rubber curtains, which minimize the outflow of oxidizing species to the environmentand keep their concentration in the treatment chamber high. The most important measurefor avoiding the outflow of oxidizing species is the extraction system attached to the inputand output chambers. The exhaust flow of the extraction system is adjusted to the gasintake of the PCPG modules. The PCPG modules are fed with CDA by means of thegas distribution system, with common gas manifold and mass flow controller. The beltconveyor transfers the substrates through the system. The adjustable vertical position ofthe PCPG module rows allows for the treatment of objects with very different sizes.
3.5.2. Precleaning of 6-Inch Silicon Wafers
The example presented in Section 3.5.1 refers to the treatment of electrically non-conducting or weak conducting substrates. If the substrate material is electrically-conductive, the PDD exists in a spark mode, with total energy focused on a small spot. It is disadvantageous if we aim for a large homogeneous area of treatment. The precleaning of highly-dopped silicon wafers described in this section is such a case with high treatment homogeneity requirement. The plasma focusing can be avoided by the application of a dielectric barrier discharge powered by the PDD. Different configurations of the PDD-powered DBDs are described in [17]. The DBD configuration used in this example is known in the literature as floating electrode dielectric barrier discharge (FE-DBD) [29,30]. In such configuration, the substrate (in our case the silicon wafer) plays the role of the DBD passive electrode (Figure 8a). The DBD plasma is generated by the use of a coupling electrode which is biased from the PCPG (CeraPlas™F) over a plasma bridge. The kHz oscillation of the coupling electrode is transferred capacitively to the air gap between the dielectric barrier and the surface of the silicon wafer. The DBD is sustained under the entire bottom surface of the coupling electrode, as shown schematically in Figure 8a).
Figure 8.The modular treatment unit with 12 CeraPlas™F plasma sources organized in 4 sub-units and the power and gascontrol unit. (a) Plasma generation principle. (b) Picture of the system.
The size of the coupling electrode results from a compromise between two opposing tendencies. With increasing diameter of the coupling electrode, (i) the treatment width increases allowing higher activation rate but (ii) the efficiency of the DBD decreases resulting in the decrease of the activation rate. The reason for the second effect is the decrease of the oscillation voltage of the coupling electrode due to increasing the load capacity of the PCPG. Since the power of the PCPG is controlled by frequency, current and voltage, the increase of capacity resulting in increase of the blind current results in the decrease of voltage, causing less energetic micro-discharges in the DBD. Concluding, there exists an optimum diameter of the coupling electrode and it is, for the given shape and dielectric barrier, about 16 mm. Figure 8b shows the realization of a system moving across a six-inch wafer assuring the homogeneous treatment. In Figure 9, schematically, the traces of 9 PCPGs produced by this system are drawn. This realization required the minimum PCPG tip-to-tip distance of 9 cm, which is assured when the red circles with the diameter of 9 cm are not overlapping. This tip-to-tip distance is larger than for example in Section 3.5.1 because the control driver of older type was applied, causing an audible noise for tip-to-tip distance up to 8 cm. The reason for such behavior was the swiping of a larger frequency range with a larger frequency step. In the currently used CeraPlas™ drive the multiparameter control is used. The input power ofthe piezoelectric transformer is controlled by changes of the input current, input voltage andthe input signal frequency, resulting in moderate, non-periodic variations of the frequency.
Figure 9.The traces of 9 PCPG-powered DBDs, each with width of 16.6 mm. The 6-inch wafer is treated in two sweepswith 8.3 mm offset: back and forth represented by blue and orange dot-dash-lines respectively. The black circles show theposition of the coupling electrodes. The red dashed line circles visualize the minimum allowed tip-to-tip distance betweenthe PCPGs.
4. Conclusions
The influence of the distance between an active and a passive PCPG on energy cou-pling between them is investigated. The minimum distance for safe operation is determined.It is 30 mm for the CeraPlas™HF, 40 mm for the CeraPlas™F powered by new type Cer-aPlas™driver, and 90 mm for CeraPlas™F powered by old type driver. The geometriccriteria for homogeneous treatment with an array of PCPGs are investigated. Since themaximum activation width for CeraPlas™F, defined as reaching the free surface energyof 58 mN/m on HDPE, is 25 mm, at least two rows of devices with overlapping activa-tion patterns are needed to assure the treatment homogeneity, if the distance betweenthe PCPGs is 40 mm. The activation width is decreasing with treatment speed. If somelimiting speed value is exceeded, an additional row of PCPGs must be added to assure thehomogeneous activation. The modularity concept and the calculation of the PCPG matrixlayout is illustrated by two applications: the treatment of planar 8-inch substrates on a beltconveyor and the precleaning of 6-inch silicon wafers.
Author Contributions: Conceptualization, S.N., D.K., D.B., F.H., A.S. (Anatoly Shestakov), A.S.(Andrej Shapiro), and T.A.; Data curation, F.H., A.S. (Andrej Shapiro), T.A., and D.K.; Formalanalysis, A.S. (Anatoly Shestakov) and D.K.; Funding acquisition, S.N. and S.L.; Investigation, A.S.(Anatoly Shestakov), D.K., A.S. (Andrej Shapiro), F.H., and D.B.; Methodology, D.K. and A.S. (AnatolyShestakov); Project administration, S.L., A.S. (Andrej Shapiro), and F.H.; Resources, A.S. (AndrejShapiro), F.H., D.B., and T.A.; Supervision, S.L.; Validation, S.N., D.K., and F.H.; Visualization, D.K.,A.S. (Andrej Shapiro), and F.H.; Writing—original draft, D.K.; Writing—review & editing, D.K., S.L.,F.H. All authors have read and agreed to the published version of the manuscript Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data can be obtained on request from the first author Acknowledgments: The PCPGs used in this study: CeraPlas™ F and CeraPlas™HF are provided by TDK Electronics GmbH. The authors thanks Jonas Wagner for electrical assembling of the multi-PCPGplasma devices. Conflicts of Interest: The authors declare no conflict of interest
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Atmospheric pressure plasma in solar thermal technology
GREENoneTEC Solarindustrie GmbH from St. Veit in Austria uses plasma technology in the production of solar thermal collectors. The high-performance plasma system plasmabrush® PB3 is integrated into the automated surface pre-treatment of glass before bonding is integrated into the automated system. Günter Unterweger from the work preparation department reports below on his experiences with atmospheric pressure plasma in solar thermal technology.
We currently use two devices of the plasmabrush® PB3 technology to increase the surface tension and thus process-safe bonding. In our automated production line, we use this technology to treat the bonding areas of the glass surface of our solar thermal collectors immediately before bonding. In the second step, the glass is placed on the aluminum collector frame, which has already been provided with 2-component adhesive. After that, the solar thermal collector passes through a 20-minute conveyor-system for the curing of the adhesive system for the curing of the adhesive.Günter Unterweger - GREENoneTEC
https://youtu.be/cUUVf0c4MsU
Why relyon plasma?
GREENoneTEC chose reylon plasma because of the best price-performance ratio. In addition, the plasmabrush® PB3 technology could be integrated into our automated system very easily and without complications.
Due to the compactness of the plasmabrush® PB3 technology, the treatment of the bonding surfaces to increase the surface tension can also be very easily integrated into an automated system. This increases the process reliability for bonding many times over.
The surface tension is significantly higher with plasmabrush® PB3 technology than with treatment using a glass washing machine.
Surface tension after glass washing machine: 44-48 mN/m
Surface tension after plasma treatment: 66-72 mN/m
We are considering using the plasmabrush® PB3 technology also for the pre-treatment of bare aluminum profiles, which we currently clean in a time-consuming manner with stainless steel brushes.
About GREENoneTec
As the world’s largest thermal flat-plate collector manufacturer, GREENoneTEC has an annual production capacity of over 1.6 million m² of collector area. We offer the highest product quality with excellent delivery performance and reliability on eight highly automated robot production lines, we offer the highest product quality with excellent delivery performance and reliability – naturally Made in Austria, certified according to ISO 9001 and ISO 14001 and with 30 years of experience in the solar industry.
Surface Energy Analysis of Dental Implants after Plasma Activation
with the piezobrush® PZ3 with the DataPhysics Instruments OCA-PDDS
Today, DataPhysics Instruments stands for high-performance, high-quality and innovative solutions in the field of surface and interface metrology worldwide. In collaboration with relyon plasma, the surface energy analysis of dental implants with and without plasma treatment is being investigated.
The surface treatments of dental implants have attracted more and more attention due to its important utilization in the optimization of implants wetting behavior. Studies have shown that the initial attachment of osteoblasts is improved by increasing the surface energy, which subsequently leads to increased new bone formation after implantation. Thus, various surface treatment devices have appeared and the plasma handheld device piezobrush® PZ3 is widely used in dental laboratories. The surface energy is a vital parameter to verify a successful pretreatment or cleaning process of implant surface. Furthermore, the knowledge of the surface energy facilitates an estimation of the wetting behaviour and adhesive properties of the implants for further processing. However, the surface energy analysis of micro-structured samples (Fig. 1) is still a big challenge, because the available test areas are very small and it require to dose small drops so that the drops don’t touch or wet beyond the edge of the test surface.
Fig.1 The droplet between the screw threads of a dental implant
To meet this issue, DataPhysics Instruments offers the picolitre dosing system (PDDS) for dosing the extra-small droplets (down to 30 picolitres). Integrated in the contact angle measuring system OCA 200, a fast and reliable surface energy analysis of implants is guaranteed.
Technique and Method
The optical contact angle measuring and contour analysis systems OCA 200 (Fig. 2) is special for microscopic and macroscopic structures. In combination with the high-performance camera even smallest drops of highly volatile liquids can be monitored. In addition, the electrically driven sample table makes it possible to position micro-structured samples with highest precision and exceptional speed for fast automated measuring procedures. Especially, when it combines with the picolitre dosing system PDDS (Fig. 3), the contact angle measurement on even smaller structures can be analysed, such as the mesh structure of a coronary stent or on single fibres (see application notes of PDDS). Therefore, OCA 200-PDDS allows to generate a single drop that is small enough to fit between the screw threads of a dental implant for its contact angle measurement.
Fig. 2. The optical contact angle measuring and contour analysis systems OCA 200, DataPhysics Instruments.
Furthermore, the surface energy (SFE) of a solid is evaluated by contact angle measurements with at least two different test liquids, whose surface tensions including their dispersive and polar parts are known. These dispersive and polar parts are used to calculate the interfacial tension σSL between the solid and a liquid based on a suitable model. Very often, the Owens, Wendt, Rabel and Kaelble model (OWRK-model) is used, which considers the geometric mean of the dispersive and polar parts of the liquid’s surface tension sL and of the solid’s surface energy ss (equation 1):
Substituting this expression in the Young equation, the polar and the dispersive part of the solid’s surface energy can be determined from the regression line in a suitable plot.
Hence, the OCA 200 with PDDS is an ideal technique for the surface energy analysis of dental implants.
For the plasma activation the piezobrush® PZ3 is used. This handheld device uses a piezoelectric element to transform the low input voltage to a high voltage output to create cold atmospheric plasma. A plasma treatment has the effect of surface activation and fine cleaning, which typically both have impact on the surface energy and on its partition in a polar and unpolar fraction.
Experiment
In this note, one ceramic dental implant and two metallic dental implants were used as samples for the measurement. The packaging was removed from dental implants with as little contact as possible and the surface energy of them was analysed firstly without any further cleaning and treatment. In a second step the dental implants were treated with the plasma handheld device piezobrush® PZ3 from relyon plasma, using the Module Standard for the ceramic implant and the Module Nearfield for the titanium dental implant. Cold atmospheric pressure plasma with a temperature of less than 50°C is used for surface pre-treatment of dental implants to increase the surface energy and thus the osseointegration.
The surface energies for untreated and plasma treated implats were determined indirectly via contact angle measurements by the use of two test liquids with known properties. DataPhysics Instruments recommends using diiodomethane, ethylene glycol, thiodiglycol and water as standard test liquids for the determination of the surface energy. However, the viscosity of thiodiglycol is too high for dispensing drops with the PDDS. Note that, in any case, it is important to make sure that the selected test liquids do not chemically react with the substrate to be analysed. Thus, water and diiodomethane were chosen in this note.
The samples were fixed and orientated vertically with plasticine on the sample stage of the analyzing system OCA 200-PDDS (Fig. 3).
Fig. 3 Picolitre dosing system PDDS , Data Physics Instruments.
To ensure proper contact angle measurement with unhindered wetting, the PDDS had to be controlled so that it generated test liquid drops with wetting areas smaller than the screw threads of the dental implants. One single droplet was disposed between the screw threads of the dental implants each time. To ensure the accuracy and reproducibility of the result, each liquid was tested three-fold. After automatic evaluation with the SCA 21 software module, the average CA values and SFE of the three samples were obtained.
Results
Wettability is of major importance for all kinds of surface treatments. To have a deep understanding of the wettability difference between the original and treated dental implant surfaces, the contact angle and surface energy measurements of water and diiodomethane on these surfaces were carried out.
Fig. 4 The contact angle measurements on the untreated and treated implant surfaces.
Fig. 5 Surface energy of the untreated and treated implant surfaces with the polar and dispersive components
The contact angle values of treated implants surfaces are lower than of the untreated surfaces, indicating the surfaces become more hydrophilic after surface treatments (Fig. 5). Using the contact angle values, the surface energy of all implants has been calculated according to OWRK (Eq. 1). Fig. 5 illustrates the respective results together with the polar and dispersive components of the SFE. The total and polar components SFE of all treated implant surfaces increased compared to their untreated surfaces, especially, that of treated metallic implant1 and ceramic implants increased significantly. As known, higher surface energies implicate more polar as well as cleaner surfaces. Therefore, the finest organic impurities that are invisible to the human eye, could be simultaneously removed from the dental prosthesis after activating the surface, which are benefcial for further processing.
Summary
The optical contact angle measuring and contour analysis system OCA 200 in combination with the picolitre dosing system PDDS from DataPhysics Instruments provides a simple and reliable method to determine the surface energy of dental implants before and after surface treatment with a piezobrush® PZ3 from relyon plasma.
This techinique broadens the way to study the surface energy of the micro-structured samples, which is also of great importance for improving industrial treatments like painting, cleaning, coating or conglutination.
Plasma in the medical sector
Relyon plasma from Regensburg, a subsidiary of TDK Electronics, presents the versatile application possibilities of atmospheric pressure plasma within the webinar series “Plasma in the medical sector”. Starting with the production of medical products, through the dental industry to direct use in medicine and skin treatment.
Regensburg. Due to the numerous trade fair postponements in medicine, as well as in dental and medical technology, relyon plasma is organising the new webinar series “Plasma in the medical sector”. Customers and interested parties with be presented with all the latest news on the topic of plasma in medical production, dental industry and implantology as well as medicine. Participation in the webinars is free of charge.
Plasma in the production of medical devices
The webinar series will kick off on 20 May 2021 with the webinar “Plasma in the production of medical devices”. Here, plasma experts and users from production will explain how plasma is used for process and quality optimisation in the manufacturing of medical devices. Particularly noteworthy is the fact that atmospheric pressure plasma can be used regardless of the number of pieces. For example, there is the piezobrush® PZ3 handheld plasma unit for use in the laboratory or prototype production as well as the plasmabrush® PB3 high-performance plasma system for high quantities and production speeds.
Plasma in the dental laboratory and implantology
On 24 June 2021, the webinar will focus on the dental industry. Here, dental technicians and implantologists will show how atmospheric pressure plasma is used in the dental laboratory and in implantology. In the dental laboratory, the piezobrush® PZ3 handheld plasma device is mainly used to improve adhesion processes or to create a uniform colour image during colour individualisation. In implantology, the focus is on increasing the wettability of implants through cold plasma pre-treatment. The increased surface energy improves the initial accumulation of osteoblasts, which subsequently leads to increased new bone formation after implantation. Bone regeneration can be improved by surface activation with plasma, which leads to increased and accelerated osseointegration.
Plasma in medicine
The third webinar in the series deals with the topic of plasma in medicine and gives an outlook on the areas in which plasma is already being used and the current state of research. One topic is skin treatment with cold atmospheric pressure plasma, which accelerates wound healing. Furthermore, the speakers will discuss the disinfecting effect of atmospheric pressure plasma. For example, surfaces can be disinfected and even made sterile by special plasma reactors. In this way, plasma contributes to patient protection and the high quality of medical treatments.
Authors: Dariusz Korzec, Simona Lerach and Stefan Nettesheim
Abstract
The piezobrush® PZ3, powered by the CeraPlasTM F-type piezoelectric transformer (PT), is used to generate an atmosphere with a high concentration of chemically active species and ions. In this document, we evaluate the potential of piezobrush® PZ3 and piezoelectric direct discharge (PDD) for virus inactivation.
1 Introduction
Severe acute respiratory syndrome (SARS) viruses are known to be transmitted by inhalable respiratory droplets in aerosols.2–4 They can also be deposited on surfaces, where, depending on the material, they can survive even for several days.5,6 These facts need to be considered when developing an efficient method for their inactivation. The method prescribed by the US Centers for Disease Control and Prevention (CDC) for disinfecting surfaces is to use different chemical disinfectants.7 The chemical disinfectants achieve a 5-log reduction of bacterial contaminants in five minutes.8 Sodium hypochlorite, ethyl alcohol,9 isopropanol and benzalkonium chloride10 are effective against Corona virus. Povidone-iodine has been shown to be active against human coronaviruses 229E and OC43.11 It has been observed that the SARS coronavirus is inactivated completely by 70% ethanol and povidone-iodine with an exposure time of one minute, and by 2.5% glutaraldehyde with an exposure time of five minutes.12 The other method of disinfection is using UV radiation.13 Its maximum bactericidal effect occurs at the wavelength range of 240–280 nm. Microorganism inactivation is the result of the destruction of nucleic acid through the induction of thymine dimers. The application of UV radiation in the healthcare environment (i.e., operating rooms, isolation rooms, and biological safety cabinets) is limited to the destruction of airborne organisms or inactivation of microorganisms on surfaces.
Unlike disinfection, sterilization destroys all microorganisms on the surface of an article or in a fluid to prevent disease transmission associated with the use of that item.7 The probability of microorganism survival is described using the sterility assurance level (SAL), which should be less than 10−6 for sterilization. For high-level disinfection and sterilization of semi-critical and critical medical devices, respectively – critical medical devices being those with contact to sterile body tissues or fluids – the sterilization procedures do not need to be altered for patients with known or suspected SARS. The most common sterilization methods mean that SAL < 10−6 can be achieved, including high temperature methods such as steam sterilization or flash sterilization, and low temperature methods, including ethylene oxide (EtO), peracetic acid, steam-formaldehyde, and ozone sterilization (SAL < 10−6 reported in14). The only plasma-based sterilization method prescribed by CDC uses hydrogen peroxide gas plasma, which requires the vacuum system and a process time of about one hour. Nevertheless, gas plasma sterilization is a promising method which is potentially effective against all microorganisms including prions.15,16 This statement also holds for cold atmospheric pressure plasmas.17 Sterilization effect of atmospheric pressure non-thermal air plasma are reported on dental instruments, for example.18
Recently, a number of reports have documented a significant reduction in and deactivation of different types of virus through the use of cold atmospheric plasma (CAP). The term CAP is used here for two types of atmospheric pressure plasma (APP): the dielectric barrier discharge (DBD) and the atmospheric pressure plasma jet (APPJ).19 N2 gas plasma (under pressure of 0.5 atm, 1.5 kpps = kilo-pulses per s) is not only virucidal for the influenza virus itself but also influences its viral components.20 For F viruses and adenoviruses, plasma of this kind is inducing changes in viral surface morphology, protein, and genomic RNA.21
The airborne and waterborne MS2 bacteriophages were exposed to atmospheric pressure cold plasma produced by DBD working in the 20–28 W power range. The airborne viruses were applied from MS2 viral suspension using a Collison nebulizer. A comparison of the survival rate of airborne MS2 for different gas mixtures – 2% O2 in Ar, 2% O2 in He and room air – shows that the air plasma assures the lowest survival rates, being lower than the rate for argon gas mixture by a factor of four at moderate power levels and a treatment time of 0.12 s. The survival percentage decreases rapidly with increasing plasma power. The waterborne MS2 requires a much longer treatment time in the range of few minutes to achieve a comparable reduction of viral survival.22 Terrier et al.23 have recorded a reduction of 6.5, 3.8 and 4log(10) TCID50/mL in the titrate of the hPIV-3, RSV, and influenza virus A (H5N2) suspensions, respectively, after treatment using cold oxygen plasma. Active oxygen seems to be a crucial species for the inactivation of viruses.
Bactericidal activity was proven for piezoelectric direct discharge (PDD).24 However, PDD has properties which make it very promising for virus inactivation. It operates with air, resulting in a broad spectrum of reactive oxygen species (ROS) and reactive nitrogen species (RNS) generated by such plasma. It generates large amounts of ozone (see section 2.2), which itself is used for virus decontamination. Furthermore, the negative ions produced in piezobrushR PZ3 can also be applied for virus inactivation (see section 5). Using specialized nozzles, different discharge architectures can be realized in a single plasma tool. In this document, we discuss the virucidal aspects of the piezobrushR PZ3 and other CeraPlasTM based devices.
2 Importance of ozone
The gaseous discharge in atmospheric air produces a large number of chemically active and excited species.25 They play a crucial role in all chemical reactions between plasma and the micro-organisms, so it is advantageous to maximize their concentrations. Most of them do not live long, which makes quantitative analysis quite difficult. One comparatively stable product of cold air plasma is ozone, which itself has primary importance due to its inactivation of microorganisms. In the next sections, we will take a closer look at the importance and generation of ozone.
2.1 Disinfection by ozone
Ozone can be applied for disinfection purposes either in gas or as ozonated water.26 To achieve results comparable with those for chemical disinfectants, much longer treatment times are needed using ozone at moderate concentrations in air. For the strain of Escherichia coli, death rates in excess of 99.99% were achieved after 480 minutes of exposure to ozone at a concentration of 20 ppm.27 However, the advantage of ozone is that it is generated “on the spot”, removing the need to store, transport, or handle hazardous substances.26
More rapid decontamination is possible at higher ozone concentrations. Ozone levels of 300 ppm and higher were found to be effective for disinfecting surfaces contaminated with E. coli and Staphylococcus aureus within seconds.28
Among 12 representative viruses, mostly human pathogens, the surrogate for SARS virus, murine coronavirus (MCV), is susceptible to ozone gas (peak ozone gas concentration: 20– 25 ppm) plus high (> 90%) relative humidity, resulting in > 3LOG10 inactivation.29
Both plasma- and ozone-induced depolarization of the mitochondrial membrane is observed, which is sufficient to trigger apoptosis or necrosis.30
Figure 1: Setup for measurement of ozone concentration for pure gas mixtures.
2.2 Characterization of ozone production
In the piezobrush® PZ3 the air flow is produced using a fan, which makes it difficult to determine the air flow exactly. To obtain exact values, the measurements of ozone concentration have been conducted for CeraPlasTM F, embedded in the experimental setup shown schematically in figure 1. The PT can be operated in CDA or in a mixture of nitrogen and oxygen. The CDA flow is controlled by a needle valve and MFM of FESTO. The nitrogen and oxygen flow are controlled by use of MFC of MKS.
The UV absorption spectroscopy is frequently used due to the high accuracy in a broad range of ozone concentration.31,32 For the ozone concentration measurements presented here, a desktop instrument based on this principle, the Ozone Analyzer Model UV-100 by ECO Sensors, Inc., is used, allowing ozone concentration measurement in the range from 0.01 to 1000 ppm (volume).
The ozone concentration can be measured directly but is not a suitable value for characterizing PT efficiency because the result strongly depends on air flow. A more suitable value for this purpose is the production rate, defined as mass of ozone produced per time unit.
Knowing the air flow fgas, the production rate of ozoneRprod can be calculated from the ozone concentration NO3 using the following equation:
where VA is the molar volume and MO3 – the molar mass of ozone (48 g/mol).
2.2.1 Ozone concentration vs. CDA flow
The concentration of ozone as a function of CDA flow is visualized as a blue plot in figure 2. According to the fitting curve of this plot, the ozone concentration decreases almost inversely proportional to the CDA flow. The higher the flow, the stronger the dilution grade of ozone, and the lower the expected activation efficiency. To maximize the activation efficiency, the ozone concentration must be maximized by minimizing the air flow. The limiting factor regarding minimization of the air flow is the PT cooling requirements, which are dependent on the power coupled in the system.
Using the ozone concentrations from the blue plot and the equation (1), the production rates are calculated and visualized as a red plot in figure 2. For gas flow higher than 5 SLM, only a small variation in the production rate is observed. With gas flow decreasing below 5 SLM, the ozone production rate decreases. This effect can be explained by
Figure 2: Concentration and production rate of ozone as a function of CDA flow.
the increasing temperature of the PT due to insufficient air cooling. The increasing temperature causes a decrease in the quality of the mechanical oscillation and consequently, of the voltage step-up ratio of the PT, which is well documented in the literature.33 The flows below 3 SLM are not investigated, to avoid the risk of PT thermal damage such as unsoldering of the electric connections, local depolarization of the PZT, or a mechanical break in the PT.
2.2.2 Influence of power on ozone production rate
In figure 3, the production rate as a function of the input power of the CeraPlasTM F is displayed for a CDA flow of 8 SLM. The production rate increases in power in the entire power range investigated. It reaches the maximum value of 73 mg/h for 8 W. This trend
Figure 3: Ozone production rate as a function of the input power of the CeraPlasTM F.
follows that of the electric field produced by the tip of the PT and of the mean value of the number of micro-discharges per cycle as a function of power. Since the micro-discharges are responsible for generating chemically active species, a correlation with not only the ozone production rate but also, the inactivation efficacy for viruses is to be expected.
The increase in the ozone production rate is faster for power values below 5 W, and slows down for higher values, which can be interpreted as a loss of ozone production efficiency (production rate per energy unit). This effect can be explained by the increasing temperature of the PT tip and resulting loss of the PT voltage gain ratio. An additional mechanism to be considered is the enhanced decomposition of the ozone with increasing temperature.34
2.2.3 Ozone concentration vs. oxygen percentage
Figure 4: Concentration of ozone as a function of oxygen percentage in the nitrogenoxygen gas mixture. Total gas flow: 6 SLM. PT power: 8.3 W.
The concentration of ozone can be increased when oxygen gas mixtures with a higher oxygen percentage than that in air are used. Figure 4 demonstrates the increase in ozone concentration with the increasing percentage of oxygen in the nitrogen-oxygen gas mixture. As is to be expected, the ozone concentration for pure nitrogen is measured as equal to zero. The maximum value of 485 ppm is achieved for pure oxygen. This value is higher by a factor of four than for 20% of oxygen in a nitrogen-oxygen gas mixture, which is close to the air stoichiometry.
Figure 5: Concentration and production rate of ozone as a function of oxygen flow.
2.2.4 Ozone concentration vs. oxygen flow
The values of ozone concentration displayed are always collected 60 seconds after switching the plasma on. For shorter times, the value shown by the ozone gauge is not yet stable. For longer times the ozone values start to decrease slightly, which can be related to the increase in PT temperature. The maximum value of 852 ppm has been achieved for the oxygen flow of 3 SLM. The ozone concentration increases with decreasing oxygen flow. Furthermore, for oxygen, the PT operation was not investigated at flows below 3 SLM, so as to avoid thermal damage to the PT.
The ozone production rate changes only slightly with oxygen flow, reaching the maximum value of 254 mg/h for 6 SLM and minimum value of 233 mg/h for 3 SLM. These values are about four times higher than the production rate in CDA or ambient air.
3 Atmospheric pressure plasma jets
The atmospheric pressure plasma jets (APPJs) constitute the largest family of cold atmospheric plasma (CAP) devices used for inactivation of microorganisms. The plasma needle and the kINPen are reviewed here as examples of tools for virus inactivation.
3.1 Plasma needle
An important version of an APPJ is the plasma needle, developed for surface treatment of biological materials.35 It is a small device consisting of a needle electrode with a diameter of 0.3 mm, separated from the cylindrical grounded electrode by a dielectric barrier. It typically works with He or other noble gases. Standard operating parameters are the flow of 2 SLM and the rf (13.56 MHz) power of 0.5-2 W. It was used for the treatment of cultured cells36,37 – especially for bacterial inactivation38 – treatment of dental cavities,39,40 deactivation of Escherichia coli 41 and Streptococcus mutans bacteria.42 The treatment of mammalian cells (reattachment and apoptosis achieved) 43,44 – was also conducted invivo.45,46
3.2 The kINPen
A representative example of APPJs for biomedical applications is the kINPen.47 Similarly to the plasma needle, it consists of a pin-type electrode with a diameter of 1 mm surrounded by a quartz capillary with an inn diameter of 1.6 mm and an outer grounded electrode. It is also used with noble gases, typically Argon. The voltage of the 1.1 MHz signal supplied ranges from 2 to 6 kV. The coupled power is 2–3 W. Thanks to the very low thermal load of less than 150 mW, it is very suitable for tissue studies,48 such as in risk assessments of the application of a plasma jet in dermatology.49 It was tested for blood coagulation,50 for wound healing,51 and for destruction of malignant melanoma,52 colon cancer cells,53 and pancreatic cancer cells in vitro and in vivo.54 It shows antimicrobial properties.55 However, kINPen is designed for the very low power level needed for the treatment of living tissue, not for the effective inactivation of viruses.
3.3 Multi-gas nozzle as an APPJ
The function of the plasma needle, the kINPen, and other types of APPJs can be fulfilled by the piezobrushR PZ3 device operated with the multi-gas nozzle. It can be operated in the power range and with gas mixtures typical of the plasma needle and kINPen.
Figure 6: Operation principle of the CeraPlasTM PZ2 multi-gas nozzle.
The structure of the multi-gas nozzle used with piezobrush® PZ2 is explained in figure 6. A similar solution will be implemented for the piezobrush® PZ3. The basic operation principle of the multi-gas nozzle is the ignition of plasma on the tip of a needle electrode. The electromagnetic power needed for plasma generation is coupled to the needle electrode from the PT via a narrow air gap. To avoid thermal damage, the PT must be cooled by gas flow, which is why the regular air flow is sustained in the piezobrushR PZ2 using the holes in the needle holder (see figure 6). The piezobrushR PZ2 air flow is separated from the plasma chamber into which the process gas is flowing. Consequently, the plasma on the needle electrode tip is ignited in the gas supplied through the silicon rubber gas pipe. The type and shape of the plasma mainly depend on the shape of the needle electrode tip and the electrical properties of the objects in its vicinity.
3.4 Production of plasma-activated water
The investigation of aqueous-phase chemistry and bactericidal effects from air discharge plasma in contact with water shows evidence of the formation of peroxynitrite through a pseudo-second-order post-discharge reaction of H2O2 and HNO2.56 The plasma-activated water (PAW) shows virucidal properties, as shown by using SDBD discharge (Ar with 1% air) on the example of bacteriophages T4, Φ174, and MS2.57
The piezobrushR PZ2 with needle nozzle was also applied to generate PAW. Glemser used it for mutation of microorganisms in water solutions.58 1 mL of culture was placed in a Petri dish and the multi-gas nozzle of the piezobrushR PZ2 was moved evenly over the spread-out cell solution for the assigned duration at a distance of a few millimeters.
4 Dielectric barrier discharge
Two types of dielectric barrier discharge (DBD) are the focus of research interest for medical purposes: the floating electrode DBD (FE-DBD)59 and the surface micro-discharges (SMD).60 These are subject of the following sections.
Figure 7: Operation principle of the FE-DBD nozzle.
The characteristic property of the FE-DBD is that the second electrode of the DBD discharge is the treated object (e.g., biological substrate, tissue, body of a living being).59 The structure of the FE-DBD is shown in figure 7. The applications are focused on physical and biological mechanisms of direct plasma interaction with living tissue.61 The toxicity of the cold plasma treatment for the wound on live pig skin tissue is one example.62 Applications in dentistry and oncology are alo known.63 Living tissue sterilization64 including open wounds (live rat model)65 and sterilization of Escherichia coli 66 are claimed to have been successful.
The operation principle of the near-field nozzle (NFN), which is used with piezobrush®PZ3 for the treatment of electrically conducting substrates, is identical to that of the FE-DBD. When operating with reduced power, it is suitable for live tissue treatment.
Figure 8: Operation principle of the SMD nozzle.
4.2 Surface micro-discharge
The surface micro-discharge (SMD) is one of surface dielectric barrier discharges (SDBDs).67,68 The structure of the SMD is shown in figure 8. At a low power level it can be used for the treatment of biomolecular films.69 SMD was applied in plasma treatment of onychomycosis,70 in cancer research,71–74 in in vivo skin treatment,75 and in the preventive medicine for nosocomial infections.76,77 The links between antimicrobial effects and plasma chemistry were studied,78 and the efficacy of plasma in regard to spores79 and bacterial decontamination (Escherichia coli) investigated.80 The realization of a specialized SMD-nozzle for piezobrush® PZ3 is being considered.
5 Negative atmospheric ions
A number of researchers are emphasizing the high importance of negative air ions (NAI) in regard to the inactivation of bacteria. Negative ions generators reduce airborne transmission of viruses.81 Negative ions can originate from different types of corona discharge.65,82
– Hagbom et al.83 used an ionizer operating at 200,000 eV and the very low current of 80 µA, generating NAI attaching to the airborne particles or aerosol droplets. The latter, negatively charged, are electrostatically attracted to a positively charged collector plate. By using such an instrument they achieved the effective prevention of the airborne transmission of the influenza A virus infection (strain Panama 99) between animals, and the inactivation of virus (>97%) using NAI.
The piezobrush® PZ3 operated with the standard nozzle generates the piezoelectric direct discharge (PDD)84 and produces chemically active species and ions of both polarities. However, the selective production of negative ions with concentrations exceeding 107cm−3 is demonstrated with special nozzle module. The generation of negative ions is measured using the CeraPlasTM HF, but it works for CeraPlasTM F as well.
5.1 Setup for NAI measurement
Figure 9 shows the setup for the generation and measurement of negative ions. Here, the standard package CeraPlasTM HF PT was applied, powered by the CeraPlasTM drive. The AlphaLab Inc. air ion counter was used to measure negative and positive ion concentrations. The distance between the tip of the CeraPlasTM HF element and the wind shield of
Figure 9: Setup for measurement of ion concentration in air flow.
the ion counter in the configuration as shown in the picture was 15 cm. The CeraPlasTM package was positioned in a PMMA tube with an inner diameter of 100 mm. Air flow in the PMMA tube was established using the ebmpapst 4414M fan, whose air flow rate is typically 100 m3/h = 1670 NLM. To remove the positive ions from the air flow, an electrostatic filter shaped like an aluminum cylinder is applied, with a diameter of 32 mm and length of 40 mm. The cylinder is grounded over two serially connected diodes with 900 V reverse voltage, oriented with cathodes to the ground (see figure 9).
5.2 NAI concentration
First, the experiments without the needle electrode were conducted. The negative ion concentration of 8.4 × 106 cm−3 was achieved with PT input power of 4 W. At the same
Figure 10: The ion and ozone concentration as a function of power emitted from the ion source with the needle electrode.
time, the concentration of positive ions is more than 200 times lower. With decreasing PT input power, both negative ion concentration and negative ion selectivity decrease. With PT input power of 2 W, the negative ion concentration is 3.8 × 106 cm−3. The positive ion concentration is lower by a factor of 20.
In the configuration discussed above, it was not possible to reduce the ozone concentration sufficiently without reducing the negative ion concentration. To overcome this obstacle, a special nozzle construction was developed with a needle electrode permanently attached to the CeraPlasTM tip using an electrically conducting silicon rubber glue, as demonstrated in figure 9. The results obtained using this special nozzle are summarized in figure 10.
Furthermore, this setup makes it possible to achieve a negative ion concentration that is higher than 107 cm−3 and two orders of magnitude higher than the positive ion concentration. However, the main advantage of the needle solution is the very moderate ozone concentration, below 0.2 ppm. With PT input power reduced to 1 W, the ozone concentration is less than 0.02 ppm, but the high concentration of negative ions of 1.3×107 cm−3 is still reached. Although poor selectivity is the price to pay for this, a good compromise can be found between 2 and 3 W of PT input power.
Figure 11: The modular treatment unit with 8 radially oriented CeraPlasTM F plasma sources.
6 Modular disinfecting units
Typically, the sources of atmospheric pressure plasma produce plasma in small sizes, from millimeters to a few centimeters. To up-scale the size of the treated substrate, different discharge architectures are applied based on the multiplication of a single plasma source.
One example of such a methodology is the matrix of micro-hollow cathode discharges (MHCD). Their use for inactivation of microorganisms was demonstrated using the example of yeast spores. They required 90 seconds for the inactivation of a surface of 1 cm2 that was contaminated with spores.85,86 The arrays of APPJs are described in a number of papers.87–89 In this section, the examples of modular plasma tools applying the CeraPlasTM modules are described.
Figure 12: The single CeraPlasTM HF module during the PDD treatment of thread conveyed spool-to-spool.
6.1 For threads and fibers
The treatment of continuous threads and ribbons of different sizes can be performed in a plasma system consisting of a number of CeraPlasTM modules distributed along the plasma source axis. Treatment speeds from a few centimeters to few tens of centimeters per second can be reached, depending on the type of substrate, number of CeraPlasTM units, and expected disinfection result. Figure 11 shows the implementation of the axial substrate movement concept for 8 CeraPlasTM HF modules. The CeraPlasTM HF modules are distributed in axial steps of 40 mm and an angular position varying by 135◦ from position to position. The modules are fixed on four carrier plates oriented perpendicularly to the direction of the substrate motion. The radial position of the CeraPlasTM module can be varied and fixed to adapt to different sizes/shapes of the substrate. The picture of a single CeraPlasTM HF module operated in front of a thread is shown in figure 12. Currently the CeraPlasTM F modules are used in modular systems, allowing treatment widths of more than 25 mm.
Figure 13: The belt conveyor treatment units with 10 to 80 CeraPlasTM F modules.
Table 1: Parameter estimations for different numbers of CeraPlasTM F devices.
Despite its versatility and efficiency, the power of the handheld piezobrush® PZ3 is limited. The only means of power scaling when using the most powerful PT in the world, the CeraPlasTM F, is to use a larger number of them. The great advantage of the modularity is the simplicity of scaling. The typical values can be assumed for each CeraPlasTM F-based module, and the specifications for any number of modules can be estimated.
Figure 13 shows four variants of the plasma system for treatment of goods on a belt conveyor with 10, 30, 60 and 80 CeraPlasTM F plasma modules, respectively. The plasma modules are organized in rows, ten modules in each row. The operating parameters of these systems are summarized in table 1. The architecture of each system is similar. The CeraPlasTM drives are supplied with 24 V DC from a common power supply. The ACDC converter of the power supply is dimensioned according to the number of PT modules used. The entire system consists of input, treatment, and output chambers. Those are separated from each other and from the outside environment with silicon rubber curtains, which minimize the outflow of ozone to the environment and keep the ozone concentration in the treatment chamber high. The most important measure for avoiding the outflow of ozone is the extraction system attached to the input and output chambers. The exhaust flow of the extraction system is adjusted to the gas intake of the PT modules. The PT modules are fed with compressed dry air (CDA) or other gases, such as oxygen, by means of the gas distribution system, with common gas manifold and mass flow controllers configured according to the number of modules and the needs of the process. The belt conveyor transfers the objects to be disinfected through the system. Thanks to the adjustable vertical position of the PT module rows, objects of very different shapes and sizes can be treated.
7 Conclusion
The handheld piezobrush® PZ3 has properties which make it a very versatile device for virus inactivation. It is especially useful for research in this field, because it allows for different plasma species. The ozone production rate for 8 W power and air is 80 mg/h, allowing ozone concentrations of >100 ppm to be achieved. Negative ions can be produced by means of a specialized nozzle, reaching concentrations of 107 ions per cubic centimeter.
The concept enables easy replacement of the nozzles, ensuring that the piezobrush® PZ3 is highly versatile and therefore easy to implement as a research tool. Different plasma types used in the field of virus inactivation: APPJ, DBD, FE-DBD, SMD, and others can be retrofitted using the specialized nozzles. The production of PAW using plasma needle and multi-gas nozzle is also demonstrated.
Based on the CeraPlasTM F piezoelectric transformer, a device was built which allows ozone concentrations of up to 1000 ppm in flow to be achieved, which would suffice to kill and decompose the most resistant viruses. By blowing the plasma gas of a CeraPlasTM Fbased device into a closed chamber or bag, conditions could be achieved which are not only sufficient for disinfection, but also for sterilization.
Thanks to its modularity, the disinfection processes developed with the piezobrush® PZ3 can be easily upscaled in size and speed.
Acknowledgments
The authors thanks Andrej Shapiro for the mockup of the modular system. We also acknowledge the contribution of Daniel Neuwirth to the measurements of the negative ion concentration.
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Plasma in the dental practice
The dental practice Dr. Reichermeier & Dr. Hardt from Regen uses piezobrush® PZ3 plasma in the dental practice on the one hand for the mounting of dental prostheses such as crowns, bridges and veneers and on the other hand for the treatment of implant surfaces.
In the dental practice of Dr. Reichermeier & Dr. Hardt, we have been using the piezobrush PZ3 handheld device from relyon plasma since March 2021. The surface cleaning and the associated significantly improved wettability of the surfaces are clearly evident in daily use.Dr. Reichermeier - Dentists Regen
Treatment of implant surfaces
The two videos below clearly show the difference in the wettability of the implants. While the implant without plasma is super hydrophobic, the plasma treated implant is super hydrophilic. The surface is wetted with PRGF (activated patient’s own platelets) for tissue stimulation and accelerated regeneration.
Without plasma treatment
After plasma treatment
We observed that the sterile titanium surface of implants appears many times more hydrophilic after plasma treatment than the untreated titanium implant. Blood wets the surface immediately after contact in the surgical area. We were able to integrate the simple and short plasma irradiation into the respective workflows without any problems.Dr. Reichermeier
Mounting of dental prostheses – crowns, bridges, veneers
We treat the respective ceramic or metal surface with plasma before the fixed insertion of the denture. In this way, we establish better wetting and flow behavior of the different materials. The aim is to achieve an even better bond between the tooth and the material and thus to further increase the longevity of the restorations.
If you want more information about plasma in dental practice, please contact us.
Plasma and UV-light surface modification of Titanium Surfaces
Effects of Surface Modification on Adsorption Behavior of Cell and Protein on Titanium Surface by Using Quartz Crystal Microbalance System
Abstract
The effect of plasma and UV-light treatment of titanium surfaces on the adsorption behaviour of cells and proteins was investigated. With SEM and SPM images show that the microstructure remains unaffected. Meanwhile, the surface composition changes according to XPS measurements from a high amount of carbonous material to a more blank titanium surface. Along this the surface wettability is strongly increased. With a quartz crystal microbalance the adsorption behaviour of cells was investigated, indicating an intermediate effect on the biocompatibility for the UV-treated samples, and a strong effect for the plasma-treated samples.
Authors: Matsumoto, T.; Tashiro, Y.; Komasa, S.; Miyake, A.; Komasa, Y. & Okazaki, J. Publication: Effects of Surface Modification on Adsorption Behavior of Cell and Protein on Titanium Surface by Using Quartz Crystal Microbalance System, Materials, 2021, 14.
In a recent publication Matsumoto et al. compared the effect of ultraviolet light and atmospheric plasma on the adsorption behavior of cells and proteins on a titanium surface. Titanium and its alloys is the most commonly used material for dental implants. The osseointegration is critical for the successful clinical outcome, which can take several months after implantation. Especially the primary stability is based on the speed of adsorption. In this investigation the deposition of albumin, fibronectin, and rat bone marrow (RBM) cells on titanium disks was monitored with a quartz crystal microbalance. The titanium plates were prepared in three different ways: As a reference an untreated plate was used. The other fraction was treated with UV-light (HL-2000 HybriLinker; Funakoshi, Tokyo, Japan) for 15 min. The third fraction was treated with cold atmospheric plasma (piezobrush® PZ2, relyon plasma, Germany) for 30 s at 10 mm distance. These samples were characterized with SEM, XPS and contact angle measurements. Furthermore, the samples were exposed to the proteins while the adsorped mass was monitored with a QCM (Affinix QNµ; Initium Co., Ltd., Tokyo, Japan).
Attachment of RBM cells to titanium. Left: Untreated, center: UV treatment and right: plasma treated.
The SEM and SPM images show that there is no significant change in the surface microstructure by the pre-treating with UV-radiation and cold plasma. Especially the surface roughness is for all three samples very comparable. This indicates that no structural changes are introduced to the surface. The XPS however, shows a shift in the elemental composition. Especially the oxygen contribution is increased by the UV- and plasma treatment compared to the bare probe. Meanwhile the carbon content is lowered for the treated samples. This trend is very pronounced for the plasma treated samples. A similar tendency can be found for the contact angle measurement. The water contact angle of the untreated sample indicates with 90.6 ° an hydrophobic behaviour. It could be lowered with UV to 7.2 ° and with plasma to complete wetting (0 °). The hydrophilicity of the treated samples was attributed to the removal of carbon compounds via the pre-treatments.
Fig: Changes in the adsorption over time of rat bone marrow (RBM) cells on (blue) untreated, (red) UV-treated, and (yellow) plasma-treated Ti-QCM sensors.
The measurements with the QCM show for all investigated cell types the fastest adsorption for the plasma treated samples, followed by the UV-treated and the untreated samples. The same is true for the total adsorbed weight after 60 minutes. A similar trend can be seen for the mineralization, where the calcium deposition on RBM cells seeded on the untreated, UV-treated and plasma-treated titanium disks was determined after 21 and 28 days. As an other indication for the osseointegration the ROS accumulation was monitored. The same trend as for the other measurements could be found here.
Fig.: Amount of calcium deposited 21and 28 days after incubation of the culture on untreated, UV-treated, and plasma-treated Ti disks.
The effectiveness of UV-radiation and cold atmospheric plasma for hydrophilizing implant surfaces was evaluated by simulating the initial hard-tissue-formation behavior of the tissue surrounding the implant material. The surface morphology remains unchanged upon treatment, however, the wettability is highly increased by both methods. The plasma-treated titanium surface showed the lowest contact angle, which enabled the highest adsorption of albumin, fibronectin, and RBM cells. While the performance of the UV-treated and plasma-treated samples were generally similar, the plasma-treated samples showed the highest amounts of F-actin, filopodia, and lamellipodia, the highest ALP activity, the highest amount of calciumprecipitation, and the lowest ROS value of all sample types.
Due to the numerous trade fair postponements in medicine as well as in dental and medical technology, relyon plasma is organizing a new webinar series on plasma in the medical industry in order to present customers and interested parties with all the latest news on plasma in medical production, dental industry and implantology as well as medicine.
May 20, 2021 – Plasma in the production of medical devices June 24, 2021 – Plasma in dental laboratory and implantology July 29, 2021 – Plasma in medicine
Plasma in medicine
In the webinar, plasma experts and physicians explain how atmospheric pressure plasma is used in medicine for disinfection, sterilization and skin treatment .
Time
Topic
Speaker
04:00 – 04:05
Welcome and introduction
Simona Lerach – relyon plasma GmbH
04:05 – 04:35
Cold atmospheric pressure plasma devices in medicine – discharge types, regulatory challenges and development trends
Cold atmospheric pressure plasma devices in medicine – discharge types, regulatory challenges and development trends – Dr. Torsten Gerling
Since about ten years, cold atmospheric pressure plasma sources (CAP) are on the market as medical devices. The number of companies providing CAPs depends on the definition of CAP itself and sums up to around three to five depending on literature. The uniqueness of CAP is the local generation of an effective cocktail, which was proven antimicrobial under lab conditions as well as inducing wound healing tracer signals. Here the existence of multiple different technologies on the market comes into play to extract the maximum usability of CAP for different treatment conditions due to different cocktail compositions depending on the discharge type and therefore device. The challenge to apply high voltage based devices under highly regulated safety restrictions as well as future trends of development will be discussed together with present and upcoming medical devices. The presentations aims to communicate an overview of the state of the art as well as motivate people to take part in the plasma medicine field.
Cold plasma applied as a disinfection method – Dr. Stefan Nettesheim
In the webinar Dr. Stefan Nettesheim discuss how temperature stable and chemically resistant germs can be killed with high efficacy by practical application of cold non-equilibrium plasma. Therefore he will present different concepts starting with the handheld device up to the integration kit.
The webinars take place via the GoToMeeting platform and participation is free of charge.
Skin Therapy Using Cold Atmospheric Plasma – Prof. Fei Tan
Cold atmospheric plasma (CAP)-based plasma medicine is an emerging interdisciplinary field exemplified by its potentials in several medical and surgical specialties. In addition, our recent study has demonstrated CAP’s multimodal effect for multi-tissue regeneration. One of the most intensively studied specialties of plasma medicine is dermatology, partially because skin is the largest and most superficial organ in the human body, which makes plasma treatment relatively easy. Here, we present the first relevant review that is comprehensive, up-to-date, disease-specific, and bridging the gap between biotechnology and clinical practice.
Plasma in the dental laboratory and implantology
In the webinar, dental technicians and implantologists explain live in which process steps plasma is used in the dental industry and how the patient benefits from the use of plasma technology.
Time
Topic
Speaker
04:00 – 04:05
Welcome and introduction
Simona Lerach – relyon plasma GmbH
04:05 – 04:35
Cold plasma in dental technology
Moataz Bayadse – University Medical Center Mainz
04:35 – 05:05
Investigation of plasma effects on implants
Dr. Sebastian Schaubach – dataPhysics Instruments
05:05 – 05:30
Case Study: Plasma treatment at the dentist
Florian Freund – relyon plasma GmbH
05:30
Questions and Answers
All
Cold plasma in dental technology – Moataz Bayadse – University of Mainz
This lecture describes the introduction of cold plasma and its diverse indications in dentistry. The benefits of cold plasma application can be observed in various fields of study like dental surgery, dental prosthetics, hygiene and sterilization. Aim of this lecture is to give an overview about potential clinical applications of cold plasma in dentistry and show in vitro data on the promising potential of activation of dental materials.
Investigation of plasma effects on challenging surfaces – a case study on medical implants – Dr. Sebastian Schaubach – DataPhysics Instruments
To characterize the surface chemical properties of a material, contact angle measurements and calculated surface free energies have proven to be reliable parameters over many years. For example, the effect of plasma treatment on a wide variety of surfaces can be quantified. But what do you do if the surface to be characterized is very finely structured or exceeds the measurement capabilities of classical optical contact angle measurement? In our webinar we would like to show you how special picoliter dispensing systems can be used to measure the contact angle on plasma-needled dental implants with a very fine structure. Furthermore, we will show you the concept of imaginary contact angles with which hyperhydrophilic surfaces can also be quantitatively investigated with regard to wettability.
Plasma treatment at the dentist – Florian Freund – relyon plasma GmbH
While the cold plasma handheld piezobrush is already being used in dentistry on healing caps, implants and protheses of various materials, the new relyon plasma implaPrep concept is designed especially for the safe and reproducible treatment of titanium implants. A prototype of this new device will be presented along with different use cases of cold plasma in the dental office including the experiences of Dr. Reichermeier in Regen, Germany and Dr. Schweiger in Füssen, Germany.
Plasma in the production of medical devices
In the webinar, experts from plasma and production technology will use practical examples to explain how plasma technology is used in the production of medical products for process and quality optimization.
Introduction to the topic of plasma in medical technology
In medical technology, particularly high demands are placed on the properties of the materials used. This is often at the expense of processability, especially with regard to adhesion processes such as bonding and printing. However, it is precisely these processes that have become indispensable in modern production and are only possible through pre-treatment. Classically, toxic primers are often used here, but increasingly cold atmospheric pressure plasma is also being used for surface activation.
Cold atmospheric pressure plasma is a partially charged gas that has two main effects on surfaces. Firstly, it is able to remove organic impurities from surfaces through fine cleaning. Secondly, plastics in particular can be functionalised so that they wet better and adhesion-controlled subsequent processes are thus possible. These processes take place at the atomic level without changing the optical and bulk properties.
The most common method of plasma treatment is based on PAA® technology, in which plasma is ignited via a pulsed arc and transferred to the surface by a jet. With this method, there are a variety of applications that are also particularly relevant in the medical technology industry, especially when it comes to a high degree of line speed and automation.
Optimizing production processes in medical technology with cold PDD® plasma
The quality of adhesion processes such as bonding, sealing or printing has a decisive impact on the further processing, quality and durability of medical products. The materials used, such as special plastics, are often difficult to wet and usually cannot do without appropriate pre-treatment. Piezo Direct Discharge or PDD® technology provides a cold, atmospheric plasma with which the functional surfaces of a wide variety of materials can be activated either manually or automatically. This allows easy and cost-effective optimization of the subsequent adhesion process without the need for harmful wet chemistry or safety-critical flame treatment. The application areas and advantages of this technology will be demonstrated using various practical application examples.
If you have any questions about the event or about plasma in general, please feel free to contact us at any time:
We are already looking forward to welcoming you virtually in Regensburg!
Self-sterile surfaces through covalent grafting
DeBogy Molecular Inc. is a Michigan early-stage company that uses transformative technology to permanently modify surfaces to eliminate viruses and germs on contact. Permanent self-sterile surfaces are created by covalently grafting biocidal molecules onto numerous substrates. The aim of the plasma treatment is to activate the surfaces and thus optimally prepare them for the grafting process.
Thanks to the plasma technology of relyon plasma GmbH, DeBogy as a young US start-up company was able to activate numerous substrates for pre-treatment with a cost-effective technology. The handheld plasma devices piezobrush® PZ2 and its successor piezobrush® PZ3 are used for this purpose. Zoe Durand - Co founder and VP Marketing - DeBogy Molecular Inc.
Another setup shows the use of the piezobrush® PZ2 for argon plasma activation using the Multigas nozzle.
The image below shows a comparison of the contact angles before and after plasma treatment. The drop on the left untreated side of the substrate is very round and therefore wets the surface poorly. The three drops on the right plasma-treated side, on the other hand, are much flatter and wider, which indicates increased surface wettability.
Plasma treatment can achieve uniform wetting of the surface, so that the surface is subsequently also uniformly grafted by biocidal molecules and permanently self-sterile.
Not only did we obtain full satisfaction with relyon plasma products, but the customer and technical service was outstanding. Prior to each purchase, Corinna Little from relyon plasma provided thoughtful and valuable advice, ample technical information and followed-up on a regular basis. relyon plasma has far exceeded our expectations.Houssam Bouloussa - Co-Founder & VP operations - DeBogy Molecular Inc.
We at relyon plasma are always excited to work with partners like DeBogy Molecular, that are on the driving innovation and change in our industry.
Landmark study by DeBogy Molecular
In a Landmark study published in June 2022, DeBogy Molecular shows that bacteria and fatal infections after implantation can be dramatically reduced when implants have been prepared through plasma activation and grafting.
Surface treatment of powder-coated aluminium profiles
When bonding powder-coated aluminium profiles, adhesion complications can occur, which can be reduced by prior surface treatment. In this application report, Oliver Ehrengruber of Winterhalder Selbstklebetechnik GmbH reports on three different approaches that were tested to improve adhesion through surface activation and enable bonding of the powder-coated aluminum profile.
Application
The test dealt with a stand in which a fabric tape is applied to powder-coated aluminium profiles to reduce noise when folding. Due to a change in the formulation of the coating powder, the adhesion on the surface had decreased and the fabric tape no longer stuck as strongly as before.
Solution approaches
Three solution approaches were tested:
Wet chemical pre-treatment of the aluminium profiles with primer/adhesion promoter
Physical pre-treatment (flame treatment) with pyrosil gas
The wet chemical pre-treatment of the aluminium profiles with primer/adhesion promoter is ruled out due to the solvent load, which represents a health hazard, as well as possible soiling/streaks outside the bonding surface at the customer.
Customer conclusion on 2.:
The advantages of the physical pre-treatment, the so-called flame treatment, with pyrosil gas are the good increase of the surface energy and the simple application. However, the potential danger posed by the open gas flame in production has attracted negative attention.
Customer conclusion on 3.:
With the physical pre-treatment based on atmospheric pressure plasma with the piezobrush® PZ3, a very good increase in surface energy is possible. With the simple and safe application, this approach is the favorite of the test.
The piezobrush® PZ3 in use on the powder-coated aluminium profile.
Conclusion
As a compact handheld plasma device, the piezobrush® PZ3 is the winner of this test due to its ease of use. The adhesion of the powder-coated aluminium profile was significantly improved and the bonding of the stand with the fabric tape was now perfectly possible. Without the use of chemicals or gases, any (health) hazard is eliminated. With the piezobrush PZ3, a safe and environmentally friendly surface treatment and thus an activation of the surface energy is possible.
One of the most common applications of cold atmospheric pressure plasma is the activation of polyolefines, such as polypropylene (PP) prior to an adhesive process. Bednarik et al. performed a comparative study on the influence and effectiveness of cold atmospheric pressure plasma and β– -radiation on the wetting contact angle, free surface energy, its polar component and the adhesive properties.
Fig.: Setup of the plasma treatment.
For the investigation, two systems were applied to activate the PP surface, for the cold plasma activation the piezobrush® PZ3 (relyon plasma, Germany) and for the β– -radiation (accelerated electrons) a Rhodotron high-voltage accelerator (Tongeren, Belgium), which presented the maximum energy of 10 MeV was applied. Different power settings respectively dose settings were applied. The surface energy could be increased for all dose/power settings compared to the reference, with the highest values of the surface energy of 54.4 mN/m achieved with the plasma treatment. Especially the polar fraction could be increased with both pre-treatments.
Fig.: Surface energies determined for different energy entries.
The origin of this polar component was determined with FTIR-measurements, where a great difference between the spectra could be determined in the region of 1850 – 1600 cm-1, which confirms the formation of carbonyl functional groups in the PP polymer chain. Additionally, in the signal in the spectral range of 3600 – 3100 cm-1 was enhanced via the treatments, indicating the formation of hydroxyl functional groups.
Fig.: Infrared spectra of (a) PP, untreated, (b) PP, after plasma treatment (8 W), and (c) PP, after β¯ radiation treatment (99 kGy).
Load bearing capacity of bonded joints
For most applications the most important value of adhesive bonding, is the load bearing capacity of bonded joints. This parameter was determined by measuring the shear strength of the bond with tensile test. The surface treated by both aforementioned methods, i.e., cold plasma and β- radiation, displayed a significant increase of the bond’s strength for every type of tested adhesive, i.e., cyanoacrylate-, acrylate-, and epoxide-based. The strength of the adhesive bond connecting the virgin materials was taken as a reference point.
Fig.: Load-bearing of adhered joints for two-component acrylate adhesive (depending on plasma power and radiation dose).
Summary
In this work the effects of β–radiation and cold plasma on PP were investigated. Both methods had a positive effect on both the wetting and the surface energy of the tested material. The adhesive properties of the polymer specimens were significantly improved by both β− radiation and cold plasma treatment. The results proved, that β− radiation is on the similar level of effectiveness as plasma treatment, as far as improvements of adhesive bond’s strength and adhesiveness of PP are concerned. This is especially astonishing, taking into account the different sizes of the devices: The piezobrush PZ3 is a handheld device, while the β− radiation system is an almost room filling highly specialized device.
The dental laboratory Till-Jung from Augsburg, Germany, has been using the piezobrush® PZ3 in the dental laboratory for 2 months and since then they do not want to miss it anymore. In this case study plasma is used at various stages in the dental laboratory to optimize and improve processes such as the glazing of ceramic or zirconium crowns or veneering with resin.
Glazing of ceramic or zirconium crowns
After a short plasma cleaning of the surface of ceramic or zirconium crowns with the plasma device prior to stain glazing, the glaze masses take on a completely different appearance. I experience that the painted layers literally nestle into any surface texture and no longer repell due to surface tension.Rosi Jung - Zahntechnik Till-Jung
Trial bridge without prior plasma treatment. After firing, the ceramic shades collapsed and flowed off into the cervical area.The sample bridge was cleaned and treated with plasma. After firing, the shade is homogeneously distributed and has a beautiful gloss.
The colors thus remain more stable in place and no longer bleed. Even during pre-drying in the firing chamber, there is no unwanted drift of the glaze into the cervical area. The colors remain in their positioned place.
I can therefore work considerably more precisely and save myself a second glaze firing. I like the result very much.Rosi Jung - Zahntechnik Till-Jung
Plasma cleaning prior to veneering
Secondly, the piezobrush® PZ3 is used for plasma cleaning of the veneering surfaces of the blasted metal outer telescopic crowns before veneering with opaquer. Immediately after blasting, the surface is cleaned with compressed air and subsequently briefly conditioned with the piezobrush® PZ3. Primer is then applied and the veneering resin is layered on.
During shearing tests, not only I but also my co-workers had the distinct feeling of a considerably more aggressive adhesion after surface cleaning with the plasma device. This is actually quite logical when the plasma jet removes atoms that form an impurity layer on the surfaces and the plastic primer thus has more contact with the targeted metal structure.Horst Till - Zahntechnik Till-Jung
In addition, implant abutment adhesive bases are also enhanced with the plasma jet to improve the adhesion of crowns and abutments.
Conclusion
We work with the piezobrush® every day. For us, it closes a tricky gap in the dental production chain and gives a good feeling of increased safety.Horst Till - Zahntechnik Till-Jung
If you would like to learn more about plasma in the dental laboratory, please contact us.
KIOTO Photovoltaics GmbH from St. Veit in Austria has been using plasma in solar technology for years. Here, the plasma high-performance system plasmabrush® PB3 is integrated into the automated system for surface pre-treatment before bonding. Philipp Pollheimer from maintenance reports on his experiences with atmospheric pressure plasma in solar technology.
We currently use the plasmabrush® PB3 technology in both photovoltaic plants. We use it to pre-treat the adhesive surface of our solar junction boxes. In the second step, a 2-component adhesive is applied and the junction box is attached to the back of our photovoltaic modules.Philipp Pollheimer - KIOTO Photovoltaics GmbH
Chemical agents replaced by plasma
Pre-treatment with the plasmabrush® PB3 cleans and activates the bonding surface, thus ensuring optimum bonding adhesion. Previously, a similar adhesion result was achieved with chemical agents. However, we wanted to improve the safety of our employees and also reduce the burden on the environment to a certain extent.
Therefore, after some failures with other manufacturers, we decided to use this system from relyon plasma. We have discovered that this system is very easy to integrate into an automated system. This system has now been running for years in St.Veit without any problems. For this reason, the same system from relyon plasma was selected for the new system to be purchased in Wies in 2020.Philipp Pollheimer - KIOTO Photovoltaics GmbH
About KIOTO Photovoltaics GmbH
As a producer of high-quality photovoltaic modules with “Made in Austria” quality, KIOTO Photovoltaics GmbH is the market leader in Austria, but beyond that, the modules are also distributed throughout Europe. In 2005 KIOTO SOLAR finally started with the production of photovoltaic modules. Since then, around 1,600 modules leave the production line every day.
Plasma treatment of electrodes
for environmental and biomedical applications
Jiri Navratil – R&D Engineer for Aerosol Jet Printing at University of West Bohemia in Pilsen reports on his experiences with the different plasma systems of relyon plasma for the plasma treatment of electrodes for environmental and biomedical applications.
At the University of West Bohemia the plasma system plasmabrush® PB3 is integrated into the Aerosol Jet Printing System. The plasmabrush® PB3 is the high power system suitable for a very fast treatment of larger areas – in this case mostly PET, polyimide or other thin film substrates. However University of West Bohemia is also working with smart textiles or small scale fragile substrates. Glass, ceramic or silicon samples can be easily blown away by the plasmabrush® PB3 system without proper fixation. Thus the smaller piezobrush® PZ2 system as a handy tool for the laboratory is used whenever only a few seconds of plasma treatment is needed prior to the deposition of liquid material. The piezobrush® PZ2 is a plug-and-play system, ready to use in seconds. No special substrate fixation is required since the gas flow is much lower than with the plasmabrush® PB3 device.
Last year we also got the piezobrush® PZ3 for testing and found out that the information display and especially build-in timer helps us a lot to achieve proper and homogenous treatment of each substrate.Jiri Navratil – R&D Engineer for Aerosol Jet Printing at the West Bohemian University
piezobrush® PZ3 vs. piezobrush® PZ2
Countdown function piezobrush® PZ3
Module Nearfield piezobrush® PZ3
Carbon allotropes with rationalized nanointerfaces and nanolinks for environmental and biomedical applications
The applications introduced in this case study are part of the project called CARAT. This stands for carbon allotropes with rationalized nanointerfaces and nanolinks for environmental and biomedical applications. In one case the substrates are treated in different ways, e.g. with plasma, to achieve the lowest contact resistance between multiwall carbon nanotubes and golden or copper electrodes on silicon substrate. The carbon nanotubes are printed on the substrate by Aerosol Jet system. Plasma treatment increases the surface energy and thus improves the printing result.
Gold and copper electrode system for contact resistance measurement on silicon substrate.
Plasma treating of the substrate.
Glass substrate with golden electrodes for OECT transistor.
The other use case is in the field of organic electrochemical transistors (OECT) development. Here a PEDOT (organic conductive polymer) channel needs to be printed with a width of 200 µm and in as low and homogenous a thickness as possible. This can be achieved with the plasma pre-treatment which improves the surface energy of the substrates.
Plasma treating of OECT electrodes.
Aerosol Jet printed PEDOT channel with a width of 200 µm on a plasma treated substrate.
After PEDOT channel printing, the reservoir is made by dispensing of dielectric material. It is necessary for the ionic liquid which is dispensed into the reservoir in the next step. Here the plasma treatment again helps to improve adhesion and wetting angle of the used dielectric and ionic liquid.
Reservoir printed by dispenser on OECT before ionic liquid deposition.
Certification according to DIN EN ISO 13485
Relyon plasma successfully certified according to DIN EN ISO 13485 and DIN EN ISO 9001
Relyon plasma from Regensburg, a subsidiary of TDK Electronics, successfully obtained DIN EN ISO 13485 and DIN EN ISO 9001 certifications at the end of 2020. TÜV SÜD thus certifies the company’s quality management system for medical devices for the very first time.
Regensburg. In line with the new corporate goals, relyon plasma has converted its quality management system to the requirements of ISO 13485 in recent months and successfully implemented the adaptations. Following the positive audit by TÜV SÜD, relyon plasma GmbH has now received certification in accordance with DIN EN ISO 13485:2016 in addition to certification in accordance with DIN EN ISO 9001:2015.
From industrial supplier to medical device manufacturer
Founded in 2002 as Reinhausen Plasma, relyon plasma GmbH focused on the development of plasma technology for industrial customers. However, with the implementation of Piezoelectric Direct Discharge technology, the customer base has increasingly expanded in the direction of medical technology and subsequently also to medical devices. In order to meet the requirements of both customers and the regulations, the company decided in 2019 to be certified according to DIN EN ISO 13485 in addition to DIN EN ISO 9001. The EN ISO 13485 standard “Medical devices: Quality Management Systems – Requirements for Regulatory Purposes” deals with the requirements that manufacturers and suppliers of medical devices must fulfill when developing, implementing and maintaining management systems for the medical device industry.
Managing Director relyon plasma GmbH: Dr. Stefan Nettesheim
Dr. Stefan Nettesheim, Managing Director of relyon plasma GmbH, comments on the company’s development: “For many years we have been supplying industry, universities and research institutes with first-class atmospheric plasma systems for surface treatment. Now we are expanding our portfolio on this technological basis specifically for dental and medical technology. Our entire process chain, from development and production to service, has been certified conforming to ISO 13485. In accordance with this quality standard, we now offer our cold plasma modules for integration in medical applications.”
Quality management system for medical devices
After the new quality management manual was completed in November 2019, relyon plasma GmbH has used the year 2020 for the fully comprehensive implementation of the requirements of ISO 13485, taking into account ISO 9001. The certification places high demands on exact compliance with all process steps, with particular attention being paid to consistent and complete documentation and risk management. Therefore, the complete organization from design and development, production, installation, maintenance up to sales underwent structural adjustments. From now on, the improved documentation will ensure long-term qualified personnel deployment as well as modern production technology.
Focussing on the customer
Thanks to this certification from independent TÜV SÜD Product Service GmbH, not only customers from the medical technology sector can be sure that the quality management system and in particular the development meet the high regulatory requirements. This covers all areas from application technology in dental and medical technology to sales and service of plasma systems for surface treatment and activation, including equipment for decontamination in dental and medical technology.
“Our medical technology customers thus benefit from our many years of expert knowledge and have access to compliant products of the highest quality for integration into their own applications,” says Dr. Stefan Nettesheim, summarizing the advantages for customers.
Furthermore, relyon plasma continues to focus on innovation, which is now sustainably supported by the backbone of the consistent application of the management system.
Quality management team relyon plasma (from left to right): Andreas Ammon , Katharina Bayer, Geri Richter
Piezoelectric Direct Discharge – Devices and Applications
Authors: Dariusz Korzec, Florian Hoppenthaler and Stefan Nettesheim
Date: December 2020
Abstract
The piezoelectric direct discharge (PDD) is a comparatively new type of atmospheric pressure gaseous discharge for production of cold plasma. The generation of such discharge is possible using the piezoelectric cold plasma generator (PCPG) which comprises the resonant piezoelectric transformer (RPT) with voltage transformation ratio of more than 1000, allowing for reaching the output voltage >10 kV at low input voltage, typically below 25 V. As ionization gas for the PDD, either air or various gas mixtures are used. Despite some similarities with corona discharge and dielectric barrier discharge, the ignition of micro-discharges directly at the ceramic surface makes PDD unique in its physics and application potential. The PDD is used directly, in open discharge structures, mainly for treatment of electrically nonconducting surfaces. It is also applied as a plasma bridge to bias different excitation electrodes, applicable for a broad range of substrate materials. In this review, the most important architectures of the PDD based discharges are presented. The operation principle, the main operational characteristics and the example applications, exploiting the specific properties of the discharge configurations, are discussed. Due to the moderate power achievable by PCPG, of typically less than 10 W, the focus of this review is on applications involving thermally sensitive materials, including food, organic tissues, and liquids.
Introduction
The low temperature or cold atmospheric pressure plasmas (APP) are versatile tools in a large number of human activities. Their applications are ranging from improvement of industrial production processes, to numerous applications in biology, genetics, and medicine. The increasing demand on a compact, affordable, and flexible plasma tools motivated the development of a new family of piezoelectric cold plasma generators (PCPG) based on the resonant piezoelectric transformer (RPT) principle. The use of PCPG to produce the piezoelectric direct discharge (PDD) is the focus point of this review. The operation power range of 3 to 10 W makes PCPGs especially suitable for implementation in compact desktop instruments or in handheld atmospheric pressure plasma jets (APPJ). The low temperature of the produced plasma gases, only a few K higher than the ambient temperature, makes the treatment of fruits, seeds, and tissues feasible. The high achievable ozone concentration allows for application for disinfection and sterilization. These are only a few of the strongly diverging application field examples. In this review, different configurations of PCPG driven devices are classified, and their operation principles are explained. The suitability of these configurations for specific classes of applications is discussed and illustrated with practical application examples. The authors hope that this review will inspire completely new fascinating approaches and application fields, not yet revealed.
Three generations of the PDD based piezo-brushes
Conclusion and Outlook
This review shows the use of three types of PCPG for generation of the PDD. Based on the PCPG, several handheld, versatile plasma tools were developed, allowing the treatment of wide range of thermally sensitive substrates such as implants, fruits, or liquids. This versatility is achieved by using different excitation structures, such as DBD, APPJ, FE-DBD, SMD, or plasma needle, all powered by the same PCPG. PCPG is able to produce a high ozone concentration in air or in oxygen. The ozone concentrations of 250 in air and 800 ppm in oxygen, and the production rates of 80 mg/h and 250 mg/h, respectively, are achieved. For evaluation of the activation performance of the different discharge configurations, the activation area on LDPE substrates visualized by use of 58 mN/m test inks is used. For both: open nozzle and DBD nozzle operation the activation results correlate with the number of micro-discharges per PCPG oscillation cycle. The correlation between the specific discharge architecture and its optimal processing targets is discussed. Specifically, three configurations of PCPG driven DBD discharges are evaluated on the basis of activation area. The best results were achieved with single DBD with the excitation electrode driven over the plasma bridge. The second best is the configuration with the double DBD driven directly by the PCPG. The weakest results were achieved with double DBD with the excitation electrode driven over the plasma bridge. The needle electrode powered by PCPG over the plasma bridge is able to produce plasma in different gases, reaching the activation results comparable with the open PDD. The generation of piezoelectric direct discharge is a considerably new discipline in the atmospheric pressure plasma world. Consequently, many interesting questions are still not answered. Some examples of scientifically challenging subjects are:
Physics of the PDD plasma bridge, especially its temporal development, and electric parameter determining its power coupling capacity.
Influence of humidity on the PDD properties, chemistry, and microbiocidal activity.
Control of the PDD chemistry by shaping the excitation signal, for example by pulse width modulation.
Bonding optical fibers and aluminum components by using plasma entirely without the use of chemicals
The NETWORK GROUP s.r.o. uses the piezobrush® PZ3 handheld plasma device to improve the bonding process of optical fibers and aluminum components. This conversion now is possible by replacing chemicals through plasma.
Previously, the NETWORK GROUP used chemicals to enable the bonding of aluminum substrates and optical fibers. Since they have been using the piezobrush® PZ3, this step in the process has become unnecessary.
We can omit the chemical treatment of the surface to achieve the same results. The benefits are in the reduction of chemicals used in the process with the same quality of bonding.Jakub Somer, R&D engineer Networkgroup
Results of the treated surfaces with bonded optical fibers passed testing procedures to achieve long life of sensing elements.
About Network Group s.r.o.
NETWORK GROUP, s.r.o., is a Czech company operating in the field of data cable distribution, printed circuit board assembly, and fiber optic sensor development and production.
Learn more about the topic
If you would like to learn more about replacing chemicals through plasma or the case study, please contact us.
Due to the relocation of the IDS, the world’s leading international trade fair for the dental industry, relyon plasma organized webinars to present the topic of plasma in dentistry.
Plasma in the dental lab
Agenda: plasma in the dental lab
Topic
Referent
04:00 p.m.
Introduction
Dr. Stefan Nettesheim Managing director relyon plasma GmbH
04:10 p.m.
Introduction plasma handheld device piezobrush® PZ3 in the dental lab
Corinna Little Application engineer relyon plasma GmbH
04:30 p.m.
Live Applications from the dental lab: Over 7 years of plasma experience in dental technology
Alexander Weber Highfield Laboratory
05:00 p.m.
Presentation of research projects
Dr. Eva Brandes relyon plasma GmbH
05:20 p.m.
Questions and answers
All
Plasma and implants
Agenda: plasma and implants
Topic
Referent
04:00 p.m.
Introduction
Dr. Stefan Nettesheim Managing director relyon plasma GmbH
04:10 p.m.
The implaPrep concept for plasma activation of dental implants
Florian Freund Head of research and development relyon plasma GmbH
04:30 p.m.
Increasing the surface energy of implants in a dental office. Benefits and practical guidance.
Jan Willem Vaartjes Vice-president of the Royal Dutch Association of Dentists (KNMT)
Wetting analyses and topographic characterization of cold-plasma-modified dental implants
Marius Behnecke Osnabrück University of Applied Sciences
05:30 p.m.
Bioactivation of implants by cold plasma – a new way in dental implantology?
Univ.-Prof. Dr. Dr. Ralf Smeets University Medical Center Hamburg-Eppendorf
05:50 p.m.
Questions and answers
All
Lectures
Increasing the surface energy of implants in a dental office
Jan Willem Vaartjes
In the lecture “Increasing the surface energy of implants” Jan Willem Vaartjes reports on advantages and shows practical applications of plasma treatment: “Since 2017 we started with different methods to activate the implants to create a super hydrophilic surface. What do we know from the literature? What are the different methods and what did we learn. Since implants are already successful, does it really make a difference? In this presentation, I will try to answer these questions and also try to shed some light on future developments. “
Multimodal Therapy Using Cold Atmospheric Plasma for Multi-tissue Regeneration
Prof. Fei Tan
Cold atmospheric plasma (CAP) is an emerging biomedical technology exemplified by its antimicrobial and anti-neoplastic potentials. On the other hand, acidic fibroblast growth factor (aFGF) has been a long-standing potent mitogen for cells from various origins. In this study, we are the first to develop a multimodal treatment combining the aforementioned physicochemical and pharmacological treatments and investigated their individual and combined effects on wound healing, angiogenesis, neurogenesis, and osteogenesis.
Bioactivation of implants by cold plasma
Univ.-Prof. Dr. Dr. Ralf Smeets
Univ.-Prof. Dr. Dr. Ralf Smeets explains the comparison of the effects of cold plasma activation of implant surfaces with a chair-side procedure in practice. Data collected regarding changes in physicochemical surface properties such as topography, roughness, surface chemistry and wettability) as well as cell responses such as cell attachment, morphology, viability, proliferation and cytotoxicity of murine osteoblast progenitor cells under standardized conditions in vitro will be presented.
Furthermore, relevant points regarding “purification” in the sense of removal of carbon metabolites, increase of surface energy and wettability of implant surfaces will be discussed. As an outlook, questions such as whether cold plasma activation could optimize osseointegration and/or peri-implant soft tissue attachment or whether cold plasma devices could be helpful tools for the dentist/implantologist in complex cases such as immediate loading or compromised patients will be addressed.
Questions?
If you have any questions about about plasma in dentistry industry or plasma in general, please feel free to contact us at any time:
We are already looking forward to welcoming you at our IDS booth in September in Cologne!
Dental webinar
Cold atmospheric plasma in the dental laboratory and for implant activation
Relyon plasma from Regensburg, a subsidiary of TDK Electronics, will present the piezobrush® PZ3 handheld plasma device for use in dental laboratories and the implaPrep concept for plasma activation of dental implants at different webinars.
Regensburg. Due to the postponement of the IDS, the world’s leading international trade fair for the dental industry, relyon plasma will be hosting webinars to present all the latest plasma innovations in the dental industry to all customers and interested parties. Webinars will be held on March 10, 2021 to showcase the “Handheld plasma device piezobrush® PZ3 in the dental laboratory” and on March 11, 2021 presenting “Plasma activation of implants with the implaPrep concept”. Both webinars are going to begin with an introduction of plasma in the dental industry – devices, applications, and modes of operation. In addition, experts from dental laboratories and implantology will present real-life application examples during the webinar. The webinars are going to close with the presentation of different research projects and an outlook on future opportunities of plasma in the dental industry. Participation in the webinars is free of charge.
Handheld plasma device piezobrush® PZ3 in the dental laboratory
The plasma handheld device piezobrush® PZ3 is widely used in dental laboratories. Cold atmospheric pressure plasma with a temperature of less than 50°C is used for surface pre-treatment of dental prosthesis. Plasma activation increases the surface energy and thus the wettability of the denture. This is particularly important when, for example, high-performance materials such as PEEK are bonded with composite or if PMMA or ceramics parts are coated. In addition to activating the surface, the finest organic impurities, which are invisible to the human eye, are simultaneously removed from the dental prosthesis.
Plasma activation of implants with the implaPrep concept
The functionalization of medical and dental implants serves to optimize the wetting behavior. Materials used in medical technology, such as zirconia ceramics or titanium and stainless steel, but also PEEK, Teflon, silicone and highly filled polymers, can be effectively optimized in their wetting behavior by plasma pre-treatment. This property is the basis for biocompatibility and acceptance by the surrounding living tissue. By increasing the surface energy the initial attachment of osteoblasts is improved, which subsequently leads to increased new bone formation after implantation. Thus, surface activation with plasma can improve bone regeneration, leading to increased and accelerated osseointegration. This is particularly important in complex cases, immediate loading, or compromised patients.
Activation of the implant surfaces with implaPrep is a supportive procedure that is used by an implant dentist, oral surgeon, or oral and maxillofacial surgeon prior to the insertion of the implants into the jawbone. The material and surface structure specified by the manufacturer is not changed by this process.
Surface activation is achieved by an atmospheric dielectric barrier discharge on the implant, which removes microscopic carbon-based adsorbates from the surface, increasing surface energy and improving implant wettability. This enhances the interactions of proteins and cells with the implant surface at a molecular level.
Registration The relyon plasma team is looking forward to welcoming you to the webinars and to attending the IDS at the new date from 22 to 25 September in Cologne.
We are very pleased that the University of Stuttgart is using our handheld plasma device piezobrush® PZ3 in 3D printing in two different departments. On the one hand, the handheld device is used in the field of optical design and simulation for surface activation and plasma cleaning of substrates for 3D printing. On the other hand the piezobrush® PZ3 is used in the 4th Institute of Physics for the pre-treatment of glass substrates for 3D printing of microoptics.
Plasma activation in 3D printing
Using the new piezobrush® PZ3 from relyon plasma, glass substrates for 3D printing of micro-optics made of different polymers can be excellently activated at the 4th Institute of Physics at the University of Stuttgart, so that they adhere more reliably to surfaces and can also be used for more robust applications. Claudia Imiolczyk - 4th Institute of Physics - University of Stuttgart
90 degree lens at the fibre optic endFreeform hologram at the fibre optic endLens with spherical aberration at the glass fibre end
In addition to the activation of ITO-coated glass plates with the “Module Nearfield”, the “Module Standard” is used for the advantageous activation of the end surfaces of glass fibers to be printed, since here small areas (125 µm) can be selectively held in the plasma. At the same time, the application of plasma technology serves to clean these end surfaces, resulting in optimized wavefronts in contrast to simple propanol cleaning.Claudia Imiolczyk - 4th Institute of Physics - University of Stuttgart
Plasma cleaning of glass substrates
The plasma technology of relyon plasma is used at the Institute for Technical Optics at the University of Stuttgart for the simple and user-friendly cleaning of substrates for micro-3D-printing to improve the adhesion of the printed parts. The compact design is particularly useful for activating the end surfaces of optical glass fibers, as these cannot be easily treated in equipment with a plasma chamber.Dr. Simon Thiele - Institute for Technical Optics at the University of Stuttgart
Further information about piezobrush® PZ3 in 3D printing can be found at the overview page.
Improved bonding quality of possible PEEK/PEEK joints in components for (dental) implants is the motivation for this work. In the course of the investigations at the Osnabrück University of Applied Sciences, the Marius Behnecke compared different pre-treatment methods for improving adhesion: a conventional grinding process, low-pressure plasma treatment and plasma treatment with the piezobrush® PZ3 handheld device. It was observed that both plasma treatments were superior to grinding. In the numerous analysis methods used, the manual plasma treatment with the piezobrush® PZ3 was comparable to that in the low-pressure chamber. This makes the PDD® plasma (“Piezo Direct Discharge”) of the piezobrush® PZ3 a highly efficient and flexible alternative to conventional low-pressure plasma processes.
Execution of experiments
A 0.6 mm thick PEEK film with the trade name evonik VESTAKEEP 4000g serves as substrate material. The dimensions of the samples here are 60 x 100 mm. First, the surfaces are cleaned with isopropanol and then placed in an ultrasonic bath for one minute. After wiping three times with a 1:1 mixture of isopropanol and n-heptane, the samples are fed to the various pre-treatments. The three investigated modifications are:
This is followed by the adhesive application of methyl methacrylate-based Weicon RK-7300 with an adhesive layer thickness of 0.25 mm on 5 mm width and curing for 24 h at 30°C.
Tensile shear tests
The quality of the adhesive bond is measured by tensile shear tests according to DIN 1465. Only the sample geometry deviates from the standard, the adhesive surface is DIN-compliant. The test speed on the ZwickRoell tensile machine is 1 mm/s. The tensile shear strength is significantly increased by all three pre-treatment methods compared to the untreated reference (see Fig. 1). Grinding leads to the greatest dispersion of the results. In contrast, treatment in the low-pressure plasma chamber (LP plasma, “low pressure”) results in the lowest standard deviation. This, as well as the plasma treatment with the PDD plasma of the piezobrush® PZ3, leads to a noticeable increase in the tensile force, since the respective standard deviations do not overlap with those of the reference sample. Overall, it can be seen that the manual pre-treatment with the piezobrush® PZ3 achieves tensile shear strengths comparable to low pressure plasma treatment. Both plasma treatments are superior to the grinding of the substrates.
Fig. 1: Tensile shear tests of the bonded joint on differently pre-treated PEEK films for dental applications.
Contact angle measurement
Fig. 2: Contact angle measurement of different test fluids before and after grinding, low pressure and piezobrush® PZ3 plasma on PEEK films.
To better understand the results of the tensile tests, the surface is characterized before and after the different pre-treatments. For this purpose, contact angle measurements are performed with five different liquids: water, diiodomethane, formamide, ethylene glycol and glycerol. The evaluation is carried out according to two different methods:
Owens-Wendt-Rabel and Kaelble method (OWRK method): division of the free surface energy into polar and disperse fractions
Berger method: Determination of an acidity parameter to characterize the acidic or basic properties of the surface
The contact angles of the five test liquids are each determined using the “Sessile Drop” method (resting drop) on the OCA20 from the manufacturer DataPhysics Instruments GmbH (Filderstadt, Germany).
All modifications lead to a reduction of the contact angles and thus to a better wettability compared to the reference (see Fig. 2). Again, the results of the ground sample show the highest scattering. Both the plasma treatment in the low-pressure chamber and the plasma treatment with the piezobrush® PZ3 handheld device significantly reduce the contact angle of all test liquids. Here, the low-pressure plasma (LP plasma) has the greatest influence on the contact angle of the test liquids.
Surface energy
From the results of the contact angle measurement, the surface energy is now determined according to the OWRK method. The evaluation was performed using SCA20 software from the manufacturer dataphysics (Filderstadt, Germany). Grinding the surface leads to a lower total energy, but with higher polar fractions (see Fig. 3). Both the plasma treatment in low pressure and the plasma treatment with the piezobrush® PZ3 handheld unit lead to significantly increased surface energies on the plasma-modified PEEK substrate with strongly increased polar fractions. The low-pressure plasma generates slightly higher polar fractions, while the disperse fractions are at the same level for both plasma technologies.
Fig. 3: Surface energy after grinding, low pressure and piezobrush® PZ3 plasma treatment compared to untreated PEEK film.
Acidity of the surfaces
Fig. 4: Acidity parameters of the different pre-treatments compared to the untreated PEEK film
Also based on the contact angle measurements, the acidity parameters of the different samples are now determined. The evaluation is based on Berger, E. J., J. Adhes. Sci. and Techno. 5, 373 – 391 (1990). The unmodified PEEK substrate has a slightly acidic character, as the positive value in Fig. 4 shows. Grinding of the surface seems to promote this behavior, but the method is not suitable for strongly varying roughness. Acidity is reduced both by low-pressure plasma treatment and by treatment with the piezobrush® PZ3. In the latter case, the PDD plasma even produces a surface with basic properties.
Scanning electron and atomic force microscopy
In order to assess the surface quality of the various samples, they are examined under a scanning electron microscope. The images are taken using the AURIGA cross-beam scanning electron microscope from Carl Zeiss AG (Oberkochen, Germany).
Fig. 5: Scanning electron microscope images (5000x magnification) of the untreated PEEK film (top left), after grinding (top right) and after plasma treatments in the low-pressure chamber (bottom left) and with the piezobrush® PZ3 (bottom right)
Fig. 5 clearly shows that at five thousand times magnification there is hardly any change in the plasma-treated surfaces, in contrast to the sample after the grinding process.
Fig. 6: Scanning electron microscope images (20000x magnification) of the untreated PEEK film (left), after low-pressure plasma treatment (middle) and after treatment with the piezobrush® PZ3 (right)
At a magnification of twenty thousand times, a change in the structure of the PEEK surface after the plasma processes can be seen. Here the surface condition is very similar after treatment with low-pressure plasma and with the piezobrush® PZ3.
The extent to which the topography of the samples differs can be determined using atomic force microscopy. Here, the ground sample cannot be measured due to the high surface roughness. The untreated surface of the PEEK film and the respective surfaces after the plasma treatments are measured using the contact mode of the Easyscan2 atomic force microscope from Nanosurf AG (Liestal, Switzerland).
Fig. 7: Atomic force microscopic images of the untreated PEEK film (left), after low-pressure plasma treatment (center) and after treatment with the piezobrush® PZ3 (right)
The surface topography of the untreated sample shown on the left in Fig. 7 has a surface roughness Sa= 6.7 nm. After treatment of the PEEK film in low-pressure plasma, this value increases to Sa= 7.4 nm and is thus comparable to that after treatment with the piezobrush® PZ3 with Sa= 7.1 nm.
Conclusion
On the PEEK surface under investigation (evonik VESTAKEEP), plasma treatments lead to improved adhesion, even compared with mechanical grinding of the surface. Even by high-resolution scanning electron microscopy, only a nanostructuring of the surface can be detected. The micro- and macroscopic topography is not affected, in contrast to mechanical surface treatment, i.e. grinding. The method of contact angle measurement shows comparable results after low-pressure plasma treatment and treatment with the piezobrush® PZ3 for surface energy and acidity parameters. For both plasma processes a treatment time of one minute was chosen in each case. The plasma power of the low-pressure chamber is 100 W, that of the piezobrush® PZ3 can be quantified to the 5 W input power of the piezoelectric transformer CeraPlas™. While the chamber for the low-pressure plasma has to be pumped out and ventilated after the process, the atmospheric plasma of the piezobrush® PZ3 does not require an external gas supply due to the integrated fan. This makes the handheld unit a highly efficient, cost-effective and flexible alternative for plasma treatment of components, for example in dental technology.
Cold plasma in disinfection technology
We are very happy that Dr. Stefan Nettesheim from relyon plasma will give a presentation on the subject of cold plasma in disinfection technology at VDI.TECHNIK.TALK.ONLINE.
Subject
“Cold Plasma in Disinfection Technology – Effect mechanisms and outlook”.
Date
10.12. 2020, 17:30 – 19:00 o’clock
Speaker
Dr. Stefan Nettesheim, Managing Director, relyon plasma GmbH in Regensburg
Content
Plasmas and the reactive oxygen species (ROS) generated in the plasma reduce the concentration of pathogens on contact with contaminated surfaces. Bacteria, viruses, fungi and prions as well as toxins and other organic contaminants can be rapidly degraded. Even complete sterilization is possible with intensive exposure. Moisture and the interaction with the biological interface play a major role. Plasma disinfection does not require expensive vacuum systems or toxic chemicals, which makes the process cost-effective and environmentally friendly.
Stefan Nettesheim studied physics at the University of Konstanz and the TU Berlin and received his doctorate in the group of Prof. Gerhard Ertl (Nobel Prize for Chemistry 2007) at the Fritz Haber Institute of the MPG in Berlin. After postdoctoral positions at the Faculty of Chemistry in San Sebastian in Spain and the ETH Zurich, he moved to industry, to the Packaging Technology Division (SIG) in Switzerland.
At Sachsenring AG in Zwickau and Schunk Kohlenstofftechnik he was involved in fuel cell development and has been managing director at relyon plasma GmbH in Regensburg since 2011.
In the group for Marine Metrology of the Leibniz Institute for Baltic Sea Research the assembly of cables belongs to daily business. For this purpose, an optimal preparation of the cable sheath, which usually consists of polyethylene (PE) or polyurethane (PUR), is essential for the casting with insulating casting resin. This sealing is intended to protect the cables permanently from water penetration in underwater applications.
Without prior plasma treatment, insufficient bonding occurs during potting, which means that the waterproofing and thus the required quality is not given.
The Leibniz Institute for Baltic Sea Research Warnemünde (IOW) is a non-university marine research institute. In its four departments, the basic disciplines of marine research are represented. Its research programme is directed towards coastal and marginal seas with a special focus on the Baltic Sea ecosystem. In addition to its research activities, the IOW pursues a transfer concept and operates research infrastructures for the scientific community. The IOW is a member of the Leibniz Association (WGL). Its institutional budget is jointly funded by the Federal Government and the Länder. The IOW is a foundation under public law.
Technology for kids
We are very happy that we support the association TfK – Technology for Kids e.V. for the second time this year.
Since 2010, the non-profit association TfK has been realizing projects in which children deal with technical topics and become enthusiastic about technology and craftsmanship, especially by “doing it yourself”. This is particularly important in order to actively counteract the lack of skilled workers, as studies have shown that the decision to take up a technical profession is already made in childhood. Our membership fee is used to make this offer possible at Regensburg schools. Only in this way can we promote early on that young people are interested in and decide for a technical profession in the future.
If you would like more information, please visit the website or contact the TfK team directly.
Pre-treatment of plastic films with piezobrush® PZ3
for the creation of intelligent polymer surfaces by e-grafting
The Institute of Polymer Nanotechnology (INKA) at the University of Applied Sciences and Arts Northwestern Switzerland (FHNW) is investigating the functionalization of plastic surfaces by means of structuring and chemical modification. Dr. Sonja Neuhaus, together with her two project team members Nika Petelinsek and Dr. Alok Goel, investigated the pre-treatment of plastic films with the piezobrush® PZ3 during the beta test phase. The motivation for this is the project on “Immobilization of enzymes with electron beam assisted grafting (e-grafting) for intelligent polymer surfaces”.
Here, aqueous, functional polymer solvents are to optimally wet different polymer surfaces. The wettability of the solvents should not be changed by the addition of surfactants, as this would have a negative effect on the function of the enzymes. In order to be able to functionalize as many different substrates as possible, the piezobrush® PZ3 is used to increase the surface energies of plastic films that are difficult to wet. The tests showed that the piezobrush® PZ3 is very well suited to significantly improve the wettability of small-format samples of the following materials: Polyethylene terephthalate (PET), Polymethyl methacrylate (PMMA), Polypropylene (PP) and Polyethylene (PE). Especially the flexibility and mobility of the plasma handheld device convinced the researchers, as they can transfer the samples directly into the e-grafting process without delays.
Motivation and objectives
The project “Immobilization of enzymes with electron beam assisted grafting (e-grafting) for intelligent polymer surfaces”, funded by the Swiss National Science Foundation (SNSF), provides the context for the investigations with the piezobrush® PZ3. E-grafting could become a revolutionary technology in surface functionalization by using low energy electron beam emitters. Electrons break chemical bonds and are thus the initial trigger for new covalent bonds between substrate and the graft materials.
Fig. 1: e-grafting of functional polymers on the surface of a plastic film. The grafted layer provides an ideal environment for the immobilization of enzymes while maintaining their activity.
For the immobilization of enzymes on plastic surfaces, a favorable environment for enzymes is to be created by grafted layers. The researchers are also investigating whether enzymes can be bound directly to the surface by e-grafting.
The e-grafting method is extremely attractive due to its energy efficiency, the possibility to irradiate in air and the complete absence of organic solvents or toxic ingredients. Additionally, only the surface is modified without affecting the bulk of the material. The potential of intelligent surfaces is huge, but has only been partially tapped to date. Especially decisive for the consumer is the possibility to make processes and products more informative and safer.
For the e-grafting process aqueous solvents of functional polymers are used. These often do not sufficiently wet the mostly hydrophobic polymer films. The problem can basically be solved by adding isopropanol or surfactants to lower the surface tension of the coating solvents. In the current project, however, surfactants are undesirable, as they can negatively influence the function of the enzymes. In order to be able to functionalize a large number of substrates nevertheless, a series of experiments to increase the surface energy is being carried out within the framework of this beta test. The overall objective is to improve the wettability of the functional polymer solvents by plasma treatment of the substrates with the piezobrush® PZ3.
Validation and analysis methods
Four film substrates are treated with the piezobrush® PZ3: Polyethylene terephthalate (PET), Polymethyl methacrylate (PMMA) and the two Polyolefins Polypropylene (PP) and Polyethylene (PE). The samples each have a format of 4 cm x 4 cm. After cleaning with isopropanol, the samples are treated for 30 s, 60 s or 90 s. The contact angles of water, diiodomethane and ethylene glycol are then determined with a Krüss DSA at five sites per sample. The contact angle measurement is performed shortly after the treatment (i.e. after 0.5 h) and after 3 and 6 hours. New samples are used for each measurement to prevent cross-contamination by the test liquids. The surface free energy is calculated with the method of Owens-Wendt-Rabel and Kaelble (OWRK). For a phenomenological evaluation, the researchers compare the wettability of polymer films before and after the plasma treatment. For this purpose, a small amount of solution is applied to the film with a squeegee and the wetting is qualitatively evaluated.
Results and discussion
The water contact angles of the untreated samples are between 80° (PET) and 96° (PE), which explains the poor wettability with aqueous solvents. The treatment with the piezobrush® PZ3 leads to a significant reduction of the contact angles (Fig. 2). The difference before and after the treatment is particularly evident for PET with a contact angle of about 40°. For all films the hydrophilic wettability regime can be achieved. The treatment duration plays a subordinate role here; however, in principle, lower contact angles are achieved with longer treatment duration.
Fig 2: Contact angle of water on PET, PMMA, PP and PE measured immediately after treatment with the piezobrush® PZ3 compared to the untreated reference. The treatment duration was varied (30, 60 and 90 s).
With the contact angles of ethylene glycol and diiodomethane the surface energy and its components are calculated (Fig. 3). With 30 mN/m (polyolefins) to 40 mN/m (PET) the untreated materials have low surface energies. The polar fraction is negligible in all cases. Treatment with the piezobrush® PZ3 can increase the surface energy for PET to the maximum value of 59 mN/m, for PMMA and PE to around 50 mN/m and for PP to 43 mN/m. The polar component increases massively for all materials and is practically the only one responsible for the increase in total surface energy. Here, too, only a slight dependence on the duration of treatment is apparent. For PP, the surface energy can be slightly increased with increasing treatment duration.
Fig. 3: Total free surface energy (green) as a function of treatment time with the piezobrush® PZ3 for PET, PMMA, PP and PE. The dispersive (orange) and polar (red) components of the free surface energy are also shown.
The strongly improved wettability can also be observed phenomenologically when applying polymer solvents (Fig. 4). By masking during pre-treatment, certain areas can be selectively activated. These areas are then much better wettable, as shown by the example of a PP film with different mask geometries (Fig. 5). Only the treated areas are wetted by the colored aqueous solvents.
Fig. 4: Colored water drops on PMMA. The area on the left was pre-treated with piezobrush® PZ3, the area on the right was not treated.Fig. 5: Selective wetting of PP films produced by masking during plasma treatment with the piezobrush® PZ3
Activated surfaces are often subject to aging phenomena such as the so-called “hydrophobic recovery”. To define the time window for further processing, the surface energy is additionally determined 3 and 6 hours after plasma treatment. It was found that no major changes in surface energy occur during this period (Fig. 6). Only for PP a significant increase occurred unexpectedly after six hours, which cannot be explained from today’s point of view.
Fig. 6: Surface free energy of PET, PMMA, PP and PE as a function of time after treatment. Shown are the total surface free energy (green) and its disperse (orange) and polar (red) components.
Conclusion and outlook
In the researchers’ opinion, the piezobrush® PZ3 is very well suited to significantly improve the wettability of small-format PP, PE, PMMA and PET samples. The piezobrush® PZ3 fully met the expectations of Dr. Neuhaus’ team and convinced them with its easy handling. The group will use the piezobrush® PZ3 to pre-treat the samples prior to coating by means of e-grafting: “The great flexibility and mobility of the piezobrush® PZ3 allows us to carry out the pre-treatment directly at the electron beam emitter, so we do not lose any time due to long distances”.
Whitepaper piezobrush® PZ3
Operation Principle and Characteristics
Authors: Dariusz Korzec, Florian Hoppenthaler, Thomas Andres, Dominik Burger, Andrea Werkmann, Stefan Nettesheim, and Markus Puff Date: October 2020
Outline whitepaper piezobrush® PZ3
The subject of this whitepaper is the atmospheric pressure plasma jet piezobrush® PZ3, developed by relyon plasma GmbH in Regensburg, Germany, on the base of the CeraPlas® F and CeraPlas® drive – both products of TDK Electronics GmbH & Co OG in Deutschlandsberg, Austria. The main task of the piezobrush® PZ3 is the plasma treatment of different materials for increase of the surface energy. The increased surface energy enhances the wettability, the adhesion of glues, casting compounds and sealings or improves the printability in wide range of industries. The treatment rate in the range of few square centimeters per second makes the piezobrush® PZ3 predestined for small-scale works mainly in the laboratory, workshop, and small-scale production. The low thermal load makes it possible to apply the piezobrush® PZ3 in combination with specialized nozzles on biomaterials and tissues.
The objective of this document is the technical presentation of the piezobrush® PZ3 addressed to potential technical sales and users. The document contains a short explanation of the working principles, comparison to other plasma tools, typical applications, technical and performance data. The comparison was made with the predecessor device piezobrush® PZ2. The presented information should help in deciding the specific applications the device can be used for. The measurement of Ozone concentration, electric field and activation area have been used for the quantitative characterization of the piezobrush® PZ3. The piezobrush® PZ3 whitepaper Part II and III deal with principles, performance characterization, and application examples of specialized nozzles.
The stem cell is the foundation of regenerative medicine and tissue engineering. Regulating specific stem cell fate, such as cell attachment, proliferation, differentiation, and even death, undergoes continuous development. Cold atmospheric plasma (CAP), the core technology of plasma medicine, is attracting tremendous attention due to its ability and versatility to manipulate various types of cells, including stem cells. Specifically, the direct and indirect applications of CAP in controlling cell fate are best exemplified by upfront irradiation of the stem cells and modification of the stem cell niche, respectively. This review will describe the recent advances in various CAP strategies, both direct and indirect, and their influence on the fate of healthy and cancer stem cells. Particular emphasis will be placed on the mechanism of connecting the physical and chemical cues carried by the plasma and biological changes presented by the cells, especially at the transcriptomic level. The ultimate goal is to exploit CAP’s potential in regenerative medicine.
Cold atmospheric plasma
In physics, plasma is the so-called fourth state of matter consisting of roughly equal numbers of positively and negatively charged particles. It could be produced typically at very high temperature or at low pressures and acquired either naturally or artificially. Cold atmospheric plasma (CAP) is a partially ionized gas generated at atmospheric pressure and operates under room temperature. This term is sometimes interchangeable with low-temperature plasma (LTP), non-thermal atmospheric plasma (NTAP), and non-equilibrium atmospheric plasma (NAP). Various technologies have been used to generate atmospheric plasma (Fig. 1), including, but are not limited to, pulsed atmospheric arc (PAA) technology (Fig. 1a) and piezoelectric direct discharge (PDD) technology (Fig. 1b), each with distinct advantages and disadvantages. A detailed comparison between these two technologies and their medical applicability can be found in Table 1.
Fig. 1 Schematics of atmospheric plasma generated using different technologies. a Pulsed atmospheric arc (PAA) technology. (1) High voltage cable, (2) gas inlet, (3) inner electrode (anode), (4) electrical arc, (5) nozzle (cathode), and (6) down-stream plasma. b Piezoelectric direct discharge (PDD) technology. (1) air inlet, (2) open piezoelectric transformer, (3) plasma generator, and (4) down-stream plasma
PAA technology
PDD technology
Mechanism
Based on the ignition of an electric arc between two electrodes by means of pulsed high voltage; gas flow is ionized as it passes close to the arc, which creates a plasma jet of highly reactive gaseous species
Based on the direct electrical discharge at an open piezoelectric transformer; this dissociates and ionizes the surrounding process gas, which is typically ambient air
Pros
High process speed; adjustable plasma temperature; long-term stability
Very compact; high efficiency; ambient temperature
Cons
Requires automation; need to avoid undesired thermal over-treatment; operate at high power consumption,
Relatively low power output; potential electrical hazard to user due to proximity
Medical applicability
Indirect applications: cell or tissue-resident niche; surgical implant
Direct applications: cells, tissues, and animal or human organs
The key components of CAP include reactive oxygen and nitrogen species (RONS), ions and electrons, and UV photons [1]. The composition and concentration of these components can be tuned and programmed for various applications, especially biomedical ones. In order for CAP to directly influence living recipients, such as cells, the plasma-derived reactive species need to pass various non-biological and biological phases (Fig. 2). Once the atmospheric plasma exits the nozzle and forms a jet, it contains reactive species including H2O2, O3, OH, and NOx. Then, they react with the extracellular fluid to form further reactive species including H3O+, NO2−, NO3−, O2−, ONOO−, and OOH−. Neutral diffusion of these RONS finally triggers intracellular events.
Fig. 2 Hierarchical delivery of plasma-derived reactive species towards stem cells and stem cell niche. (A) Atmospheric plasma phase, and its main components. (B) Plasma jet, and the reactive species contained in its plume. If CAP is used as an indirect approach to activate a stem cell niche, the entire process occurs when plasma jet interacts with the solid interface of a niche. However, if CAP is used to directly stimulate a living recipient, it propagates through a liquid phase first. (C) Liquid interface, and various RONS created upon diffusion through it. (D) The biological effect of plasma penetrates across various levels
Plasma medicine
Plasma medicine is an emerging interdisciplinary field incorporating physics, chemistry, life science, and medicine. It has infiltrated several medical specialties with promising clinical or preclinical potentials [2]. In dermatology, CAP can functionally promote wound healing and cosmetically achieve skin rejuvenation [3]. In microbiology, applications of CAP are exemplified by eradication of microbial biofilm and disinfection of contaminated tissue [4]. In oncology, CAP induces senescence, detachment, apoptosis, and necrosis of tumour cells, demonstrating not only cancer selectivity but also synergy with existing anti-cancer treatment [5].
In addition to these direct plasma treatments on the living tissue, indirect treatments of the biological environment or the niche around the tissues or cells also have attracted extensive research. One example is surface modification of an artificial cell niche, e.g. tissue engineered scaffold or surgical implants (Fig. 3). The other modern example is the plasma-activated medium (PAM) [6]. PAM is inspired by the scientific basis of plasma-liquid interactions in which the reactive chemistry of CAP is transferred and retained prior to a chain of biological events. It can potentially be injected to treat deep cancers or cancers that have spread over large areas. Whether used directly or indirectly, CAP is at the heart of advancing plasma medicine.
Fig. 3 Interfacial modification of an artificial stem cell niche using CAP. Image was taken when using a handheld plasma device based on piezoelectric direct discharge (PDD) technology. The gaseous plasma jet can be seen exiting the nozzle and spreading over the target surface
Stem cell niche and control of stem cell fate
Stem cells are revolutionizing modern medicine mainly because of their clinical potential to promote the relief, repair, and regrowth response of diseased or damaged tissue. Stem cells exert these regenerative functions through their dynamic interaction with the surrounding microenvironment or the niche in which they reside [7]. The resultant homeostasis determines the fate of stem cells, either survival or death (Fig. 4). Therefore, possible fate options of stem cells include, but are not limited to, attachment (anchoring to the niche), proliferation (self-renewal), differentiation (lineage specification), and death (active, programmed, or passive, accidental) [8].
Fig. 4 The influence of plasma treatment on the survival and death of stem cells. The box in the middle depicts the two main strategies of plasma treatment, directly on the cells and indirectly on the cell niche; the box on the left highlights the main events during stem cell survival, whereas the box on the right covers the main forms of stem cell death
Conventional methods of controlling the fate of stem cells are mostly physical and chemical modulation of the stem cell niche. Adjustable physical and mechanical stimuli include strain, shear stress, matrix rigidity, and topography [9] whereas the tuneable chemical cues include exogenous growth factors, cytokines, and various small molecules [10]. Recent advances in biomaterial research have attempted to partially or entirely replace the stem cell microenvironment with engineered synthetic materials [11]. This has evolved from simple two-dimensional (2D) cultures to complex three-dimensional (3D) scaffolds. No matter the approach, as mentioned above, is applied, their effects are considered ‘indirect’ as they universally target the niche in which stem cells inhabit.
In comparison, CAP is a unique technology to regulate and direct stem cell fate due to its excellent versatility. Not only can CAP indirectly control cell fate by modifying the cell-resident niche, it can also directly influence cell fate by stimulating stem cells in close contact (Fig. 4). This mini-review presents an up-to-date view of the versatility of CAP in controlling stem cell fate, highlighting a novel strategy for regenerative medicine and other applications.
Enhancing stem cell attachment using CAP
The cell-niche adhesion is crucial for stem cell survival and is dynamically adapted. CAP has recently been proven capable of improving stem cell’s attachment to the natural niche and artificial extracellular matrix (ECM). This enhancement is mostly indirect, as CAP modifies the cell-facing niche or ECM (Table 2).
Table 2 Enhancing stem cell attachment and promoting stem cell proliferation using CAP. (ASCs adipose-derived stem cells, ECM extracellular matrix, ESCs embryonic stem cells, HA hydroxyapatite, HSCs haematopoietic stem cells, MSCs mesenchymal stem cells, NO nitric oxide, NSCs neural stem cells, NT neurotrophin, PCL polycaprolactone, PS polystyrene, PSCs pluripotent stem cells, PU polyurethane, USSCs unrestricted somatic stem cells)
Due to its intrinsic mechanism, CAP is well known to introduce chemical changes to the cell culture surface. One of the essential parameters of surface chemistry is surface energy, which is commonly reflected by wettability. Ueda et al. discovered that human pluripotent stem cells (PSCs) adhered poorly to hydrophobic cell culture dishes [12]. However, after turning the surface hydrophilic using CAP treatment, the chemically modified polystyrene (PS) surface could support optimal PSC attachment and long-term self-renewal. Unlike the traditional understanding that CAP solely induces chemical modification, a new theory by Yang et al. suggesting that CAP also alters other surface properties has gained popularity [13]. In their work, CAP treatment of the polymeric substrate also changed the topography and elasticity at the nanoscale level. The predominant mechanical effect enhanced the adhesion and spreading of human mesenchymal stem cells (MSCs) through good focal adhesions.
In addition to the 2D surfaces (e.g. laboratory cell culture system), 3D interfaces (e.g. tissue engineering scaffold) are also conveniently processable using CAP. The extent of enhancement depends on several factors including, but are not limited to, plasma parameters, type of stem cells, and the scale of the scaffold. Firstly, the quantity of bone marrow-derived MSCs (BM-MSCs) attached to CAP-treated gelatin scaffolds was significantly increased compared to untreated specimens [14]. Also, among the three types of working gas used (nitrogen, oxygen, and air), nitrogen plasma provided the best MSC attachment, owing to the N-containing functional groups generated on the surface. Secondly, surface modification of polyurethane (PU) scaffold using CAP led to increased cell attachment [15]. However, the increments were substantially different for human embryonic stem cells (ESCs) and rat postnatal neural stem cells (NSCs). Finally, Sankar et al. subjected polycaprolactone (PCL) fibrous scaffolds with nano-, micro-, and multiscale to CAP treatment. They discovered that the nanofibers demonstrated most remarkable MSC adhesion, spreading, and elongation [16].
The relevant research priority has shifted in the last several years; the emerging applications use genetically modified stem cells. In the study performed by Schendzielorz et al., CAP-assisted hydrophilization of cochlear implant electrode array surfaces enabled firm colonization of human adipose-derived stem cells (ASCs) that are known to secrete neurotrophins [17]. This long-term delivery of neurotrophic factors has profound clinical potential for treating inner ear diseases and neurotology conditions.
In summary, CAP can enhance stem cell attachment to their adjacent environment, mostly by activating the support surfaces. The mechanism of enhanced cell attachment is most likely due to the improved physicochemical changes of the surface, which enhance the expression of adhesion molecules, thus leading to favourable cell attachment.
Promoting stem cell proliferation using CAP
The continued self-renewal and proliferation drives the functionality of stem cells in regenerative medicine. CAP can accelerate the growth of stem cells while maintaining their stemness. This improvement in cell proliferation is achieved through either indirect stimulation of cell-resident niche or direct exposure of stem cells (Table 2).
On the one hand, CAP can speed up cell growth by activating the cell-niche interface, regardless of the interface material. These materials range from regular cell culture plastic, such as PS [18], bioceramic, such as hydroxyapatite (HA) [20], to ECM-based protein, such as gelatin [19]. However, CAP-induced optimization of the surface chemistry seems to be the central cause for the cellular benefit. Biazar and colleagues demonstrated better proliferation of unrestricted somatic stem cells (USSCs) on the PS surfaces treated with oxygen or argon CAP than on the untreated samples [18]. Also, oxygen plasma provided more significant advantage than argon plasma, not just because of higher ensuing hydrophilicity, but also partially due to topographical changes, i.e. larger surface nano-roughness. In Prasertsung’s study, the proliferation of BM-MSCs was significantly higher on the CAP-treated gelatin films than on the unmodified ones [19]. This observation was confirmed by shorter population doubling time and a higher growth rate of cells. Furthermore, the optimal water contact angle, a marker for hydrophilicity and surface energy, was observed at 27 to 32 degrees. Tan et al. concurred with these results and further explored their cellular and genetic mechanism [20]. In order to ascertain the actual growth rate of human MSCs on the HA samples, flow cytometry was used to analyse the dynamic distribution of cell cycle phases. It was suggested that the favourable cell proliferation on plasma-activated surfaces was a result of faster progression of the cell cycle, likely mediated by preferential expression of focal adhesion kinase (FAK). This was one of the first studies revealing CAP-regulated biological benefits at a large-scale transcriptomic level.
On the other hand, CAP can enhance cell proliferation by irradiating the stem cells in situ. This possibility was exemplified by a series of step-wise investigations conducted by Park and her team [21,22,23]. In 2016, they showed that helium-based CAP increased proliferation of ASCs by nearly 60% after 3 days of incubation, compared with untreated cells [21]. Plasma-exposed ASCs maintained cellular stemness and their ability to differentiate into adipocytes, without demonstrating cellular senescence. In addition, Akt, ERK1/2, and their downstream NF-κB were all activated in ASCs after plasma exposure. These results collectively showed that nitric oxide (NO) rather than reactive oxygen species (ROS) is responsible for the increased proliferation of ASCs following CAP exposure. In 2019, Park et al. extended their stem cell choice from ASCs to various mesoderm-derived human adult stem cells [22]. They discovered that CAP increased proliferation of BM-MSCs and haematopoietic stem cells (HSCs) by almost twofold. Furthermore, CAP treatment of these stem cells also activated expression of stem cell-specific surface markers, such as CD44 and CD105, and common pluripotent genes for stemness, such as Oct4, Sox2, and Nanog. This year, the South Korean research group took the relevant work one step further by exploring the epigenetic mechanism by which CAP activates the proliferation of stem cells [23]. After examining the entire genome expression profiles of ASCs, they found that CAP upregulated genes for cytokines, chemokines, and growth factors, but downregulated the genes of intrinsic apoptotic pathways. Once again, plasma-induced epigenetic modifications at both mRNA and protein levels mainly relied on the NO generated from CAP.
In brief summary, CAP can promote stem cell proliferation directly and indirectly. These are realized by either exposing the stem cells to plasma or activating the cell-niche interface. The mechanism of accelerated cell proliferation is a result of multilevel events, including faster cell cycle at the cellular level, activated stem cell-specific markers at the protein level, and advantageous deregulation of genes at the transcriptomic level.
Inducing stem cell differentiation using CAP
One of the defining features of stem cells is their capability to differentiate into various types of more specialized cells. This process usually involves a switch from proliferation to specialization, as well as alterations in cellular morphology, function, and fate. CAP can induce and/or boost the lineage-specific differentiation of stem cells into hard tissues or soft tissues, through direct and/or indirect non-thermal treatment (Fig. 4). Cell differentiation induced by CAP-assisted coating deposition and drug delivery has been discussed elsewhere and, therefore, will not be discussed here.
CAP can induce differentiation of stem cells into hard tissues, such as bone, cartilage, and teeth, mostly through modifying cell-resident, tissue-engineered scaffolds (Table 3). Wang et al. achieved the osteogenic differentiation of BM-MSCs in a series of studies [24,25,26]. Firstly, they surface-modified HA/chitosan scaffolds [24]. A careful investigation found more total and adhesion-mediated protein (e.g. fibronectin and vitronectin) adsorption on the scaffold surfaces, which likely contributed to the enhanced late-stage osteogenic differentiation. Secondly, they combined the micro-scale architecture offered by 3D printed poly(lactic acid) (PLA) scaffolds with the nanoscale roughness and chemical modification provided by CAP, significantly promoting in vitro bone regeneration [25]. Lastly, they studied the cellular infiltration and drug loading in plasma-treated core-shell nanofibers [26]. CAP modification not only increased the pore size of the scaffold resulting in more calcium deposition, but also contributed to significant variations in drug release profiles. Like BM-MSCs, ASCs can also adapt to plasma modification of the scaffolds. Waser-Althaus et al. discovered that the degrees of osteogenic differentiation of ASCs on CAP-treated polyetheretherketone (PEEK) surface depended on plasma power and process gas [27].
Table 3 Inducing and enhancing tissue-specific differentiation from stem cells using CAP. (ASCs adipose-derived stem cells, BM-MSCs bone marrow-derived mesenchymal stem cells, CJMSCs conjunctiva-derived mesenchymal stem cells, MPJs micro-plasma jets, NO nitric oxide, NSCs neural stem cells, PCL polycaprolactone, PDL-MSCs periodontal ligament-isolated mesenchymal stem cells, PEEK polyetheretherketone, PLA poly(lactic acid), PU polyurethane, RONS reactive oxygen and nitrogen species)
Moreover, Griffin et al. examined the role of CAP in guiding ASCs towards both osteogenic and chondrogenic differentiations [28, 29]. On the one hand, ASCs could be differentiated preferentially towards osteogenic and chondrogenic lineages on amine (NH2) and carboxyl (COOH) modified scaffolds using CAP, respectively [28]. This chemical group-dependent plasma polymerization method has significant potential for selective stem cell therapy in the regeneration of bone and cartilage. On the other hand, ASCs on the argon CAP-treated polyurethane (PU) scaffolds showed upregulated expression of bone makers (e.g. alkaline phosphatase, collagen I, and osteocalcin) and cartilage markers (e.g. aggrecan and collagen II) [29]. Upon implantation onto the chick chorioallantoic membrane, plasma-treated scaffolds supported higher expression of vascular endothelial growth factor (VEGF) and laminin. These satisfactory in vitro and in vivo results proved CAP to be a simple but efficient tool that can promote ASC skeletal differentiation. Last but not least, CAP can directly induce osteogenic differentiation of stem cells from an unusual source, such as human mesenchymal stem cells isolated from periodontal ligament (PDL-MSCs), expanding its potential for future dental applications [30].
CAP can also induce differentiation of stem cells into forming soft tissues, such as nerves, mostly through directly irradiating NSCs (Table 3). In a series of studies, Xiong et al. achieved neuronal differentiation using murine immortalized neural stem cell line (C17.2-NSCs) and primary rat NSCs in a series of studies [31,32,33]. Initially, they applied microplasma jets (MPJs), a unique form of CAP, to direct in vitro differentiation of NSCs into the neuronal lineage, with longer neurites and cell bodies constituting a mature neuronal network [31, 32]. The neuronal differentiation rate was around 75% using this one-step approach, which was much higher compared to the standard chemical method. The differentiated NSCs matured and produced mostly cholinergic and motor neuronal progeny. Their preliminary investigation suggested NO to be the main factor in such fate choice. Then, they deepened the investigation of the mechanism of enhanced and directed differentiation of NSCs by CAP, especially the possible signalling pathways stimulated by NO [33]. The exogenous NO in the plasma and the increased synthesis of intracellular NO by inducible nitric oxide synthase (iNOS) after plasma stimulation could be the underlying contributors. Collectively, the extracellular and intracellular NO downregulated Notch1 and Id2 and upregulated Ngn2 and Ascl1, thereby activating downstream NeuroD expression. As a supplement to the above study, Jang et al. conducted additional upstream and downstream investigations [34]. Specifically, RONS from the plasma phase interacted with reactive species in the extracellular liquid phase to form NO. The extracellular NO reversibly inhibited mitochondrial complex IV, while cytosolic hydrogen peroxide acted as an intracellular messenger to initiate the Trk/Ras/EKR signalling pathway. Thus, this study elucidated the mechanism connecting physicochemical signals from the CAP cascade to the intracellular neuronal differentiation signalling pathway, offering insights into developing of a novel plasma-based treatment for neurological diseases.
Transplantation of pancreatic islet-forming stem cells is a promising therapeutic method for treating diabetes mellitus. However, finding a readily available stem cell source and cell carrier is technically challenging. An interesting work by Nadri et al. combined conjunctiva-derived mesenchymal stem cells (CJMSCs) and PCL scaffold [35]. CAP-treated scaffold supported enhanced differentiation of CJMSCs into insulin-producing cells, with significantly higher insulin release in vitro.
In summary, CAP can induce and/or enhance differentiation of stem cells into various tissues, such as bone, cartilage, and nerve. Again, these could be achieved by either direct exposure or indirect modification. The underlying mechanism of CAP-induced cell differentiation is likely far more complicated than those of CAP-assisted cell attachment and proliferation. But it should be traced back to the complex recipe of RONS generated using highly tunable but sophisticated plasma parameters. Since stem cell attachment, proliferation, and differentiation are a dynamic and seamless chain of events, CAP has the potential to be used as a one-step streamlining tool to facilitate stem cell survival during their fate choices.
Stimulating cancer stem cell death using CAP
In contrast to cell survival, controlled cell death could also be desired when determining stem cell fate, especially for cancer stem cells. Cancer stem cells (CSCs) are a small subpopulation of cells within tumours, likely initiating cancer recurrence and metastasis. They are capable of self-renewal, differentiation, and tumourigenicity when transplanted into a live host [36]. CSCs are resistant to conventional treatments, such as chemotherapy and radiotherapy. Therefore, efforts are increasing to develop novel anti-cancer treatment modalities targeting the CSCs. CAP proves a promising candidate for such a clinical purpose. The exertion of anti-CSCs using CAP is genuinely versatile, including direct irradiation of cells with or without adjuvant agent [37], plasma-stimulated macrophages [38], and plasma-activated medium (PAM) [39, 40] (Fig. 4).
Although plasma alone can eliminate cancer cells in many preclinical studies using various malignancy models, it has also demonstrated synergy with conventional chemotherapy medications [41]. Adhikari et al. combined CAP with nanotechnology, i.e. silymarin nanoemulsion (SN), for treating melanoma [37]. Co-treatment by SN and CAP increased the cellular toxicity for both melanoma cells and CSCs in a time-dependent manner in vitro and also decreased tumour weight and size in vivo. The p53-mediated apoptosis in these cells was likely activated through inhibition of the HGF/c-MET downstream pathway. Thus, CAP oncotherapy supplemented by SN serves as a new treatment approach for melanoma.
Like direct irradiation of CSCs, indirect CAP treatments, such as co-culture of cancer cells with plasma-activated macrophages, also provide an equivalent anti-cancer function. Kaushik et al. demonstrated a tumour-suppressive role for CAP-stimulated macrophages in solid metastatic cancers that are mediated by epithelial-mesenchymal transition (EMT) [38]. EMT contributes to many malignant behaviours of cancer cells and CSCs, including anti-apoptotic, motile, invasive, and stem-like features. CAP could induce M1/M2 macrophage polarization, with M1 to a greater extent. These M1-polarized macrophages delayed the EMT process in glioma cells, attenuating CSCs maintenance. Therefore, CAP acted as an immune-modulating oncotherapy upregulating pro-inflammatory anti-tumourigenic M1 macrophages.
One of the recent advances of CAP oncotherapy is the usage of PAM, a plasma-treated solution in which the reactive chemistry of gaseous CAP is transferred and retained. Ikeda et al. discovered that PAM selectively induces apoptotic death of cancer cells but not healthy cells. Also, PAM killed both CSCs and non-CSC endometrioid carcinoma and gastric cancer cells [39]. When tested in a mouse xenograft model, PAM also had an anti-cancer effect on CSCs. Therefore, these in vitro and in vivo results supported PAM as a new modality of oncotherapy, targeting various cancer cells, including CSCs. Similar to CSCs, residual undifferentiated human induced PSCs, intended for regenerative medicine and cell transplantation therapy, might also demonstrate tumourigenic potential. Thus, selective elimination of undifferentiated stem cells from a population of differentiated cells before their transplantation is clinically important. Matsumoto et al. achieved this by inducing external oxidative stress using CAP [40]. Undifferentiated PSCs were more sensitive to PAM than PSC-derived differentiated cells. Gene expression and protein assay suggested that hydrogen peroxide and various RONS in PAM was one of the mechanisms underlying PAM-induced selective cell death.
In summary, CAP is a multimodal treatment to suppress or eliminate cancer stem cells and stem cells with tumourigenic potential. Due to the versatility of CAP, the mechanism of plasma-induced CSCs elimination is strategy-dependent.
Concluding remarks and future directions
How to control stem cell fate is the key question while maximizing its clinical potential in regenerative medicine and cell transplantation therapy. It is difficult for a single technology to regulate all fate options of stem cells, considering the temporal and spatial complexity of cellular events, such as cell attachment, proliferation, differentiation, and death. Cold atmospheric plasma is a promising strategy due to its excellent versatility. Its direct applications, such as irradiating stem cells in close contact, and its indirect applications, such as modifying stem cell niche, have already gained preclinical interests. However, several challenges remain unsolved before this unique tool can be used widely in clinical applications.
Firstly, extensive research is required to elucidate the mechanism of how physicochemical changes induced by plasma are translated into biological benefits. Secondly, although CAP can regulate individual stages of stem cell fate, controlling the transition from one stage to another and balancing the extent of each stage demands further testing. Lastly, CAP-assisted enhancement in stem cell survival and CAP-induced death in cancer stem cells will need to be cell-specific and tissue-specific, thereby providing a customizable therapy based on the exact clinical requirement.
In summary, the innovative applications of CAP in regulating stem cell fate establishes a new frontier in plasma medicine, likely helping to form a next-generation therapy in regenerative medicine.
Availability of data and materials
The datasets during and/or analysed during the current study are available from the corresponding author on reasonable request.
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Enhanced Osseointegration and Bio-Decontamination of Nanostructured Titanium
Alkali-treated titanate layer with nanonetwork structures (TNS) is a promising surface for improving osseointegration capacity in implants. Nevertheless, there is a risk of device failure as a result of insufficient resistance to biofilm contamination. This study tested whether treatment using a handheld non-thermal plasma device could efficiently eliminate biofilm contamination without destroying the surface nanostructure while re-establishing a surface that promoted new bone generation. TNS specimens were treated by a piezoelectric direct discharge (PDD) plasma generator. The effect of decontamination was performed utilizing Staphylococcus aureus. The evaluation of initial cell attachment with adhesion images, alkaline phosphatase activity, extracellular matrix mineralization, and expression of genes related to osteogenesis was performed using rat bone marrow mesenchymal stem cells, and the bone response were evaluated in vivo using a rat femur model. Nanotopography and surface roughness did not significantly differ before and after plasma treatments. Cell and bone formation activity were improved by TNS plasma treatment. Furthermore, plasma treatment effectively eliminated biofilm contamination from the surface. These results suggested that this plasma treatment may be a promising approach for the treatment of nanomaterials immediately before implantation and a therapeutic strategy for peri-implantitis.
1. Introduction
Titanium is one of the most prevalently applied materials for orthopedic and dental implants owing to its excellent mechanical properties, corrosion resistance, and biocompatibility [1,2]. Nevertheless, titanium implant utilization is limited by the risk of peri-implant infections, prolonged osseointegration healing time, and inadequate osteoconductive properties, particularly in patients with osteoporosis [3]. The clinical long-term success rates of titanium-based implants are 89.23% and 82.94% after 10- and 16-year follow-up periods, respectively [4]. To further increase the clinical long-term success rate of implants, the promotion of early osseointegration, long-term stability of the bone-implant interface, and reduced peri-implantitis are required [2,5,6]. The physical and chemical characteristics of the implant surface play a crucial role in early-stage bone formation around implants [7].
Owing to the susceptibility of the passive oxide layer and its electroconductivity, implant surface modifications, such as sandblasting [8], acid-etching [9], oxidation [10], and calcium phosphate deposition (alone or in combination) [11,12], have been undertaken over the past three decades to transform the roughness, micro- and nano-scale features, and chemical composition of the implant surface; these modifications can impart high levels of biocompatibility and promote early bone formation around the implants [13,14,15].
Our previous research shows that a homogeneous, hydrophilic sodium titanate layer with nanonetwork structures (TNS) is generated on the titanium surface after high-concentration alkaline treatment [16]. TNS has higher roughness and hydrophilicity compared to Ti and is, therefore, more compatible with the protein and cell attachment, as well as hydroxyapatite formation; these factors result in excellent osteogenic activity [17]. Nevertheless, several challenges must still be resolved before their clinical application. More specifically, alkali-treated titanium with nanostructures is still inadequate in terms of resistance to the bacterial attachment and biofilm formation that can eventually cause peri-implantitis [18], and more promptly, osseointegration is still a requirement in the early stage of implantation.
Plasma is one of the four fundamental states of matter and is defined as a neutral ionized gas constituted of particles in permanent interaction, which include photons, electrons, positive and negative ions, atoms, free radicals, and excited or non-excited molecules. Plasma could be obtained at atmospheric pressure by several techniques such as Radio-frequency (RF) plasmas [19], Dielectric barrier discharges (DBD) plasmas [20], Corona discharge plasmas [21], Gliding arc discharge plasmas [22,23]. As a consequence of reactive oxygen and nitrogen species (RONS) production, plasma treatment has been used to remove contamination and impart hydrophilicity to implant surfaces, which, in turn, promotes protein and cell adhesion [24,25]. According to Lee et al., plasma treatment decreases bacterial attachment by carbon-cleaning the implant surface, thereby reducing the risk of implant infection [26]. The RONS generated by plasma treatment could decontaminate and inhibit biofilm recolonization on the implant surface without destroying the elaborate surface geometry of the implant, while also promoting osteoblast attachment and differentiation [23,25,27,28]. Plasma treatment is non-toxic, low temperature, safe, and has high treatment efficiency, making it more suitable for clinical applications than other sterilization methods. The use of a handheld, nonthermal, atmospheric plasma device that utilizes piezoelectric technology has recently been focused on medical applications. As it has a higher processing efficiency and is more environmentally friendly than UV, laser, and other types of plasma treatment, the nonthermal atmospheric plasma device is very convenient for immediate treatment prior to implantation. Simultaneously, this nonthermal atmospheric plasma, which could eliminate biofilm while re-established surface characteristics that are promotive for bone regeneration, are particularly suitable for the treatment of peri-implantitis [29].
In the present study, we hypothesized that nonthermal atmospheric plasma treatment could change the chemical components on the implant surface and preserve the roughness of the nanostructured surface established by alkali treatment, thereby promoting osseointegration and decontamination. To prove this hypothesis, we investigated the effect of plasma treatment on biofilm formation, cell adhesion, and osseointegration in the early stage of implantation through in vivo and in vitro experiments. Staphylococcus aureus was utilized to illustrate the effect of plasma treatment on decontamination. Plasma treatment of TNS effectively changed the chemical composition on the sample surface, which further improved implant hydrophilicity and facilitated cell attachment and osteogenic differentiation, while decontaminating the biofilm without destroying the TNS surface nanomorphology. Plasma treatment has potential clinical applications, such as immediate treatment before implantation and the therapeutic treatment of peri-implantitis.
2. Results
2.1. Surface Characterization
Scanning electron microscopy (SEM), which has made a significant contribution to the observation and characterization of nanomorphology, was utilized to survey the surface topography of TNS and plasma-TNS samples. SEM micrographs showed that the nanoporous network structure within an average diameter of 50–100 nm was well-interconnected and homogeneous on the titanium surface after alkali treatment. As shown in Figure 1, the nanoporous structure of the sample surface did not change significantly after plasma treatment. The effect of plasma treatment on the surface measured by atomic force microscopy (AFM) demonstrated similar nanotopographies on the surfaces of TNS and plasma-TNS samples (Figure 1). Furthermore, the values of surface roughness (Ra and Rz) measured by AFM indicated that there was no significant difference between TNS and plasma-TNS samples (Table 1). Hydrophilicity analysis of the surface of TNS and plasma-TNS samples showed that the TNS surface exhibited hydrophilic properties with a contact angle of approximately 9°. Notably, a significant change in wettability was recognized on the surface of plasma-TNS samples with a contact angle of <3°, which exhibited super-hydrophilic characteristics (Figure 1E).
Figure 1. Scanning electron micrographs of (A) Titanate layer with nanonetwork structures (TNS) and (B) plasma-TNS; Scanning probe micrographs and a typical surface profile of (C,F) TNS and (D,G) plasma-TNS. (E) The measurement of the contact angle on the surface of TNS and plasma-TNS. Data shown are the means ±SD (n = 3). *** p < 0.001.
Group
Parameter Ra (nm)
Parameter Rz (nm)
TNS
24.71 ± 7.14
218.93 ± 89.48
Plasma-TNS
27.16 ± 5.01
233.90 ± 19.79
Table 1. Roughness values of the TNS and plasma-TNS. Data shown are the means ±SD (n = 3).
The chemical composition and chemical bonding on TNS and plasma-TNS surfaces were investigated by X-ray photoelectron spectroscopy (XPS). Wide-survey XPS spectra of the specimens revealed that the surface chemical composition contained the characteristic peaks of Ti, O, C, N, and Na. To further investigate the changes in chemical composition and chemical bonding after plasma treatment, high-energy-resolution spectra for C1s, O1s, N1s, and Ti2p were obtained. Ti 2p3/2 and Ti 2p1/2 components were shown at 458.5 eV and 464.2 eV, respectively, with a 5.7 eV spin-orbital splitting value consistent with the Ti4+ valence state. The Na1s spectra from TNS and plasma-TNS samples did not significantly differ, indicating that both sample types were covered by titanite. This was consistent with the findings of previous studies [30]. The presence of carbon contamination on all surfaces was obvious, which was also consistent with previous studies [31]. Notably, the carbon ratio on the sample surface significantly decreased after plasma treatment. Figure 2 shows the ratio of N/Ti to O/Ti on the surface of TNS and plasma-TNS samples. The ratios indicated the notable increase of O and N content on the surface of plasma-treated samples.
Figure 2. XPS analysis on the surface of TNS and plasma-TNS presented as the mean calculated from the random location of three samples: (A) oxygen/titanium ratio, (B) carbon/titanium ratio, (C) nitrogen/titanium ratio, (D) Wide-survey XPS spectra of the specimens, (E) high-resolution spectra of carbon 1 s, (F) high-resolution spectra of nitrogen 1 s, and high-resolution spectra of oxygen 1 s on the surface of (G) TNS and (H) plasma-TNS, respectively.
High-energy-resolution spectra of the N1s peak before and after plasma treatment are shown in Figure 2F. The distinct spectra observed on plasma-treated samples were exhibited at a binding energy of 406.8 eV, corresponding to NOx (nitrate) species [32,33]. In contrast, few of these spectra were found on the surface of untreated samples. Figure 2 also shows the high-resolution oxygen 1s spectra from the surface of TNS and plasma-TNS samples. According to Moulder et al. [32], the deconvolution of the O1s peak reveals three different oxygen atom states. The component located at the binding energy of 530.3 eV (O1) corresponds to oxygen O2− in the TiO2 lattice structure; the component at 531.4 eV (O2) is often related to -OH groups; the component at 532.7 eV (O3) is typically associated with NOx or H2O groups [34].
XPS spectra of the TNS surface showed that most of the oxygen was bonded in the form of an oxide (O1), and the proportion of -OH bonds was smaller (Figure 2G). This generally indicates that oxygen atoms are more likely to form TiO2 on the sample surface. In contrast to the TNS surface, a large number of O2 components were observed on the surface of plasma-TNS samples. These were related to the -OH group and caused by the interaction of energetic reactive oxygen species between the plasma and the material surface. As a result, the material surface hydrophilicity was significantly improved, consistent with the contact angle measurement results. The important O3 component typically associated with NOx groups was detected on the surface of plasma-TNS samples; this was due to the Reactive Nitrogen Species (RNS) dominating the gas-phase chemistry during plasma treatment [35,36].
2.2. Biofilm Decontamination
In order to assess the efficiency of decontamination by plasma treatment, Staphylococcus aureus (S. aureus) culture was incubated on the surface of TNS for 24 h and allowed to develop into a biofilm. The surfaces were then exposed to plasma treatment. The results of inactivation demonstrate that plasma treatment could significantly decrease the S. aureus viability (Figure 3).
Figure 3. Effect of plasma treatment on decontamination. Data shown are the means ±SD (n = 3). *** p < 0.001.
2.3. Determination of Intracellular Reactive Oxygen Species (ROS)
Furthermore, as shown in Figure 4, the level of intracellular ROS on the surface of TNS was significantly higher than that on the surface of plasma-TNS samples after incubation for 24 h, while there was no significant difference in the number of adhered cells between both types of surface.
Figure 4. Determination of intracellular reactive oxygen species of rat bone marrow mesenchymal stem cells attached to the TNS and plasma-TNS disks. Data shown are the means ±SD (n = 3). * p < 0.05.
2.4. Cell Adhesion and Morphology
After 24 h of incubation, cell morphology staining using phalloidin and DAPI showed that the cells adhered to plasma-treated surfaces had a higher cell area than those adhered to untreated surfaces (Figure 5A–E). The increase in initial cell adhesion and the changes in cell morphology likely contributed to the super-hydrophilicity of the surface produced by the plasma treatment [37] in accordance with the hydrophilicity analysis results. Moreover, the CellTiter-Blue® Cell Viability Assay was used to evaluate the adhesion of rat bone marrow mesenchymal stem cells (rBMMSCs) to TNS and plasma-TNS samples. The results showed higher numbers of cells adhered to the surface of plasma-TNS samples at 1, 3, and 6 h (Figure 5F).
Figure 5. Morphological analysis of rBMMSCs attached to the (A,C) TNS and (B,D) plasma-TNS disks, (E) cell area, values were presented as mean ±SD of three representative images measured as per the surface of three samples in each group, (F) cell adhesion on TNS and plasma-TNS disks at 37 °C. Data shown are the means ±SD (n = 3). *** p < 0.001; ** p < 0.01.
2.5. Osteogenic Activity of Rat Bone Marrow Mesenchymal Stem Cells (rBMMSCs)
ALP activity, which is a biochemical marker of osteoblast activity and cell phenotype in the early stage of cell differentiation and bone formation, was higher at seven and 14 days in the plasma-TNS group than in the TNS group (Figure 6A). Compared to the TNS group, the plasma-TNS group showed higher calcium deposition (a marker of extracellular matrix mineralization) at 21 and 28 days (Figure 6B). Gene expression of the bone morphogenetic protein (BMP) and osteocalcin (OCN), which are representative osteogenic differentiation products, were significantly higher in cells grown on plasma-TNS than in those cultured on TNS samples (Figure 6C,D). These results indicated that the differentiation activity of rBMMSCs was significantly promoted by surfaces treated with plasma.
Figure 6. (A) Alkaline phosphatase activity, (B) calcium deposition, (C) bone morphogenetic protein 2 (BMP-2) and (D) osteocalcin (OCN) in cells grown on sample disks. Data shown are the means ±SD (n = 3). *** p < 0.001; ** p < 0.01; * p < 0.05.
2.6. Evaluation of the Bone Morphogenesis Around the Implant In Vivo
Bone formation activity around the TNS implant and the plasma-TNS implant was evaluated using a rat femur model. More trabecular microarchitecture was observed in the region of the plasma-TNS surface than in that of the TNS surface (Figure 7). Furthermore, the ratio of bone volume to total volume (BV/TV), mean trabecular number (Tb.N), and mean trabecular thickness (Tb.Th) were significantly higher in the plasma-TNS samples, indicating that the plasma-treated implants promoted osteogenesis activity (p < 0.01). Mean trabecular separation (Tb.Sp) was lower in the plasma-TNS implant than in the TNS implant (p < 0.01).
Figure 7. Reconstructed three-dimensional microcomputed tomography transverse slices of rat femurs containing TNS (A) and plasma-TNS (B) implants. The implant, cortical bone, and cancellous bone are shown in red, blue, and green, respectively. (C) Bone volume to total volume ratio (BV/TV), (D) mean trabecular number (Tb.N), (E) mean trabecular separation (Tb.Sp), and (F) mean trabecular thickness (Tb.Th) around implants after eight weeks. Data shown are the means ± SD (n = 3). *** p < 0.001; ** p <0.01.
Furthermore, a longitudinal section was used to evaluate new bone formation around the implant. As shown in Figure 8, newly formed bone was observed around the plasma-TNS implant than the TNS implant. Quantitatively, the histomorphometric analysis showed that bone area ratio (BA) and bone-implant contact (BIC) were significantly higher around the plasma-TNS implants than around the TNS implants (Figure 8E,F). In addition, the newly formed bone around the implant was labeled with oxytetracycline hydrochloride (blue) at one week, alizarin red S (red) at four weeks, and calcein (green) at eight weeks. The labeled bone area between the implant interface and the labeled bone area at weeks 1, 4, and 8 was significantly higher in plasma-TNS implants than in TNS implants (Figure 8G–I).
Figure 8. Villanueva staining of bone tissues around (A) TNS and (B) plasma-TNS implants. Fluorescence labeling of new bone and mineralization around (C) TNS and (D) plasma-TNS implants. (E) Bone area ratio (BA) and (F) bone-implant contact (BIC) of TNS and plasma-TNS implants. Fluorescently labeled bone area (LBA) after (G) one week, (H) four weeks, and (I) eight weeks. Data shown are the means ±SD (n = 3). *** p < 0.001; ** p < 0.01; * p < 0.05.
3. Discussion
The surface morphology and chemical composition on the surface with nanostructures of titanium play a crucial role in mimic natural bone tissue and soft tissues to promote the bone healing process, which has been widely reported in the literature [15]. According to our previous experiments, the homogeneous nanoporous structures on the titanium surface generated by alkali treatment enhanced osseointegration, contributing to its excellent hydrophilicity and roughness compared with pure titanium [16,17]. Nevertheless, the resistance of nanostructured surfaces to biofilm is still insufficient, which could give rise to peri-implantitis, and more promptly, osseointegration, which is still a requirement in the early stage of implantation. In the present study, non-thermal atmospheric pressure plasma was employed to modify the nanostructured surface, and the effect of promotion of osteogenic activity and decontamination were evaluated comprehensively.
According to the nanotopographies observed by SEM and AFM, the sample surfaces revealed similar homogeneous nanoporous network structure whether treated by plasma or not, which indicated that plasma treatment does not destroy the geometry of the nanostructure on the sample surface and could thereby preserve the positive effect of the nanostructure on osseointegration. Additionally, XPS analysis confirmed that the chemical composition on the sample surface changed significantly after plasma treatment. Compared with the surface of TNS, a large number of polar oxygen groups (such as hydroxyl, carbonyl, and carboxyl groups) are formed after plasma treatment, which could enhance their hydrophilicity [35]. This is consistent with the analysis of the contact angle experiment, which determines that the hydrophilicity of the plasma-TNS surface has been further improved. Simultaneously, the increase of NOx after plasma treatment was also demonstrated by XPS analysis and may be due to the excessive gas-phase RNS produced by the plasma [38].
Moreover, the decrease of carbon and the formation of RONS were observed after plasma treatment, and were considered to be related to the effectiveness of the decontamination and the inhibition of early bacteria attachment and biofilm formation [39,40,41,42]. During plasma decontamination, bacteria are directly exposed to the plume of plasma that consists of abounding RONS, which induce membrane alterations and enzyme inhibition, prompt changes in membrane transport proteins, leading to the accumulation of more RONS, ultimately resulting in physiological dysfunction and cell death [43,44]. In addition, the results of the decontamination experiment showed that the plasma treatment applied to the biofilm-contaminated nanostructured surface could effectively eliminate the biofilm without destroying the nanostructure of the surface. Moreover, Lee et al. demonstrated that plasma treatment could decrease the carbon contamination to form a hydrophilic surface, thereby improving resistance to bacterial attachment and inhibiting the recolonization of biofilms, which would be highly beneficial from a clinical perspective [26].
According to the results of the cell adhesion experiment, plasma treatment did not induce cell apoptosis and even promoted cell attachment in the early stage of incubation [45]. Cell morphology analysis revealed higher cell areas on surfaces subjected to plasma treatment, which are likely to contribute to the increased hydrophilic character of plasma-treated samples [46]. Furthermore, the enhancement of osteogenic differentiation ability of cells was demonstrated by the results of ALP activity, calcium deposition, and bone morphogenetic protein 2 and osteocalcin gene expression. Simultaneously, animal experiments also revealed that plasma treatment contributed to the promotion of new bone generation and osseointegration comprehensively. According to the micro-CT, histological section, and fluorescent labeling analyses, plasma treatment had a significant positive effect on the promotion of osteogenesis. Notably, plasma treatment generated surfaces that strongly promoted new bone tissue formation at weeks 1 and 4 post-implantation, contributing to osteogenesis and confirming implant stability. These qualities play a decisive role in implantation success at the early stage of implantation, and our results thus support future research avenues utilizing and exploiting these promising qualities.
The results of XPS analysis revealed that plasma treatment significantly changed the chemical composition on the surface and led to an increase of polar oxygen groups (such as hydroxyl, carboxyl groups, etc.). Furthermore, we prefer to investigate the influences of these increased oxygen functional groups on the cells attached to the plasma-treated surface. Research on stem cell biology in recent decades has focused on that excessive intracellular ROS accumulation could damage proteins, lipids, DNA, and eventually lead to cell apoptosis [47,48], simultaneously, have clarified a variety of anti-oxidant and anti-stress mechanisms of stem cells [49,50]. Nevertheless, there is increasing evidence to support the opinion that intracellular ROS in redox homeostasis plays a critical part in maintaining stem cell self-renewal under some circumstances [51]. Indeed, stem cells are located in a state characterized by low levels of intracellular ROS, which are crucial to the regulation of the potential for self-renewal and stemness, while high levels of intracellular ROS effectively inhibit the ability of stem cells to self-renewal and differentiation [52,53,54]. Moreover, according to Ueno et al. reported, titanium surface pre-treated with UV light significantly reduced intracellular ROS and the expression of inflammatory cytokines, so that preventing the oxidative stress-induced DNA damage and promoting cell adhesion and spread [55]. Consequently, investigation of the link between intracellular ROS levels and altered chemical properties after plasma treatment may give insights into the mechanism by which plasma treatment promotes the osseointegration in the early stage of implantation. As the results have shown, cells attached to the plasma-treated surface exhibit a lower level of intracellular ROS compared with those on the untreated surface, while the increasing osteogenic activity. Recently, Gómez-Puerto et al. have demonstrated that oxygen functional groups could induce phosphorylation of forkhead box O3 (FOXO3) at serine 294, which was mediated by MAPK8 kinase, and its translocation to the nucleus. Simultaneously, activation of FOXO3 results in the downregulation of intracellular ROS through the activation of autophagy to maintain redox homeostasis during osteoblastic differentiation [56]. Furthermore, the overexpression of the FOXO3 gene in osteoblasts could decrease oxidative stress and osteoblast apoptosis, and increased bone formation rate [57]. We hypothesized that the oxygen functional groups on the plasma-treated surface might activate phosphorylation of FOXO3 to downregulate the oxidative stress state, which seems to be one of the possible mechanisms of the enhanced osteogenic activity after plasma treatment. Further experiments will be performed in the future to confirm whether the better osteogenic activity observed in the plasma-TNS group is due to the decrease of intracellular ROS induced by oxygen functional groups-mediated the phosphorylation of FOXO3.
In summary, it was demonstrated that plasma treatment could remarkably contribute to the enhancement of osteogenic activity and decontamination of the surface. Through the evaluation of the surface characteristics and biofilm decontamination, we confirmed that plasma treatment could eliminate the contamination without destroying the beneficial nanostructure of the surface. Following the results of osteogenic activity experiment both in vitro and in vivo, we also verified that the surface after plasma treatment is highly beneficial for the enhancement of osteoblast differentiation and early osteogenic activity. Additionally, owing to the excellent effect of simultaneous re-establishment of a highly hydrophilic surface suitable for osseointegration and elimination of the biofilm, and the clinically friendly advantages of plasma treatment, such as handheld, smooth operation, low cost, the wide-spread application of plasma is expected to be favorable either as a treatment immediately before implantation or as a therapeutic strategy for peri-implantitis. Furthermore, this study demonstrated that the roughness of nanostructured surface was not changed by plasma treatment, which could be of great significance for the combined application of this plasma treatment and other materials with the nanostructure. In future experiments, we will also establish an infection animal model and comprehensively evaluate the efficiency of plasma treatment on infected implants, as a novel therapeutic strategy for peri-implantitis.
4. Materials and Methods
4.1. Sample Preparation
Pure grade 2 titanium disks (15 mm in diameter and 1 mm in thickness) and titanium screw implants (1.2 mm in external diameter and 12 mm in length) were prepared by mechanical processing (Daido Steel, Osaka, Japan) to evaluate surface characteristics and for the animal study, respectively. The disks were then polished with incremental SiC abrasive papers (800#, 1000#, and 1500#). All samples were ultrasonically rinsed with acetone, ethanol, and deionized water (10 min each) and dried at room temperature overnight. All samples were immersed in a 10 M NaOH solution at 30 °C for 24 h, washed with ion-exchanged water (200 mL) several times until the conductivity of the solution reached 5 μS/cm3, and then dried at room temperature overnight to establish porous, homogeneous, and uniform nanonetwork structures (TNS) on the titanium surface.
4.2. TNS Plasma Treatment
Plasma treatment was performed using a non-thermal atmospheric pressure handheld plasma device (piezobrush® PZ2, Relyon Plasma GmbH, Regensburg, Germany) that utilized piezoelectric direct discharge technology. Half of the samples were treated at room temperature with plasma-induced by active gas at atmospheric pressure for 30 s. The distance between the jet exit and samples was set to 5 mm to ensure that the samples were wholly immersed in the plasma plume emerging from the nozzle. Plasma-treated TNS was tested in the experimental group, while the control group was untreated.
4.3. Surface Characterization
TNS and plasma-TNS surface topography were evaluated by SEM (S-4800, Shimadzu, Kyoto, Japan) with 10 kV accelerating voltage. AFM (SPM-9600, Shimadzu Co., Tokyo, Japan) was utilized to assay the mean average surface roughness (Ra), mean peak-to-valley height (Rz), surface profiles and three-dimensional surface topography of the samples. The sample chemical composition was determined by XPS (Kratos Axis Ultra, Shimadzu, Japan). Sample surface wettability was evaluated using a contact angle measurement system (VSA 2500 XE; AST Products, Billerica, MA, USA).
4.4. Biofilm Decontamination
S. aureus culture was prepared from a single colony inoculated into 5 mL of Tryptic soy broth (TSB) medium and incubated for 16 h at 37 °C. One milliliter of bacterial suspension, which was adjusted to a concentration of 1 × 105 CFU/mL by adding fresh TSB medium, was added to the surface of TNS, resulting in biofilm formation after 24 h of incubation. Then, the bacterial suspension was removed, and samples were prepared for subsequent plasma treatment by rinsing with phosphate buffer saline (PBS) solution to remove nonadherent bacteria. Following the plasma treatment, samples were transferred into a sterile test tube containing 5 mL of TSB medium and vortexed for 2 min to dislodge the formed biofilm. The quantification of bacteria contained in the solution was performed by the plate-counting method [58].
4.5. Cell Culture
The rBMMSCs were obtained from the femurs of 8-week-old Sprague-Dawley rats (SHIMIZU Laboratory Supplies Co., Kyoto, Japan). Cells were cultured in growth medium containing minimal essential medium (Nacalai Tesque Inc., Tokyo, Japan), 10% fetal bovine serum (Nacalai Tesque Inc.), and antibiotic-antimycotic mixed stock solution (Nacalai Tesque Inc.) in a 5% CO2 humidified incubator at 37°C. The medium was changed every 3 days.
4.6. Cell Morphology
After 24 h of incubation, samples were washed with PBS, fixed by incubating with 4% paraformaldehyde solution for 20 min, permeabilized with 0.2% (v/v) Triton X-100 for 30 min, incubated with Blocking One reagent (Nacalai Tesque, Kyoto, Japan) for 30 min, and then stained with Alexa Fluor 488-phalloidin (Invitrogen/Life Technologies) and DAPI at 37 °C in the dark for 1 h. A confocal laser scanning microscope (LSM700; Carl Zeiss) was used to evaluate the F-actin and cell nuclei of adherent cells. A total of 30 cells randomly were selected from three representative images measured in per surface of three samples in each group, according to the recent report. And ImageJ software was used to the fluorescent image analysis.
4.7. Cell Adhesion
The rBMMSCs were seeded onto the specimens at an initial density of 4 × 104 cells/cm2 and allowed to attach for 1, 3, 6, and 24 h. Following incubation at 37°C, the nonadherent cells were removed by washing with PBS (Nacalai Tesque, Inc.) and cultured with 300 μL of diluted CellTiter-Blue® Reagent (50 μL CellTiter-Blue® Reagent diluted in 250 μL PBS). After an additional 1 h of incubation, the fluorescence intensity was measured with a microplate reader (SpectraMax M5; Molecular Devices, Sunnyvale, CA, USA) according to the manufacturer’s protocol.
4.8. Determination of Intracellular ROS
Generation of intracellular ROS was analyzed by utilizing the oxidation-sensitive fluorescent probe 2’,7’-dichlorofluorescein diacetate (DCFH-DA, Sigma, St. Louis, MO, USA). Following incubation for 24 h, the cells washed with PBS, and incubated with 10 mM DCFH-DA for 30 min at 37 °C. Then, cells were washed twice with PBS, detached with 50 µL trypsin (0.25%), and diluted with 50 µL PBS. Fluorescence was then measured at excitation/emission wavelength of 485/528 nm using a fluorescence microplate reader, according to the manufacturer’s instruction.
4.9. Alkaline Phosphatase (ALP) Activity
In order to evaluate ALP activity, 4 × 104 cells were seeded on specimens and cultured in α-MEM containing 10% fetal bovine serum, antibiotic-antifungal agent, 10 mM glycerophosphate (Wako Pure Chemical Industries, Osaka, Japan), and 10 nM dexamethasone (Nacalai Tesque). The differentiation medium was changed every 3 days. Following 7 or 14 days of incubation, samples were washed with PBS, and cells that had attached to the sample surface were dissolved with 300 μL of 0.2% Triton X-100. ALP activity was evaluated by an alkaline phosphatase luminometric enzyme-linked immunosorbent assay (ELISA) kit (Sigma-Aldrich) in accordance with the manufacturer’s instructions. A PicoGreen dsDNA analysis kit (Invitrogen/Life Technologies) was utilized to evaluate the DNA content. The amount of ALP was normalized to the amount of DNA in each cell lysate.
4.10. Extracellular Matrix Mineralization
Following 21 or 28 days of incubation, calcium deposition in the extracellular matrix was measured after dissolution with 10% formic acid. Calcium content was quantified and calculated using a Calcium E-test Kit (Wako Pure Chemical Industrials Ltd.) according to the manufacturer’s instructions.
4.11. Osteogenesis-Related Gene Expression
Expression of osteogenesis-related genes was assessed using a real-time TaqMan RT-PCR assay (Life Technologies, Carlsbad, CA, USA). Total RNA was extracted using a RNeasy Mini Kit (Qiagen, Venlo, the Netherlands), and 10-μL aliquots of each RNA sample were reverse transcribed into cDNA utilizing a Prime Script RT Reagent kit (TaKaRa Bio, Shiga, Japan). The mRNA levels of osteogenesis-related genes for bone morphogenetic protein 2 (Bmp 2) and bone gamma-carboxy glutamic acid-containing protein (OCN) were investigated using a Step One TM Plus RT-PCR System (Life Technologies). Relative gene expression levels in each group were normalized to that of the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) housekeeping gene.
4.12. Animal Model and Surgical Procedures
The animal experiment was performed according to the ethical principles of the National Animal Care Guidelines and was approved by the Medical Ethics Committee of Osaka Dental University, Japan (approval no. 19-06002, 16 August 2019). Eight-week-old male Sprague-Dawley rats (Shimizu Laboratory Supplies Co., Kyoto, Japan) weighing 180–200 g were used in this study. The rats were randomly divided into two groups, with eight rats in each group. Surgical procedures used in this study were previously described [59]. After general anesthesia and surgical cleaning, a 10-mm longitudinal incision was made along the medial side of the knee joint of the right hind leg. The patella and extensor mechanism were then dislocated to expose the distal femur. A 1.2-mm hole was drilled into the intercondylar notch using a dental burr with sterilized saline irrigation. Screws were implanted into the prepared channels, the knee joint was restored, and the incision was sutured. Gentamicin (1 mg/kg) and buprenorphine (0.05 mg/kg) were injected for 3 days after surgery to prevent post-surgical infection and decrease postoperative pain.
4.13. Sequential Fluorescent Labeling and Microcomputed Tomography
Polychrome sequential labeling of bone via intraperitoneal injection of fluorescent dyes was employed to determine the process and characteristics of new bone formation and mineralization after implantation according to the following timetable: rats were injected with 25 mg/kg oxytetracycline hydrochloride (Sigma-Aldrich, USA) at 1 week after implantation, with 30 mg/kg alizarin red S (011-01192, Wako, JP) at 4 weeks, and with 20 mg/kg calcein (340-00433, Wako, Japan) at 8 weeks. Rats were then anesthetized and euthanized at 8 weeks, and the right femurs including the implants were placed in a saline solution immediately after dissection and scanned with an SMX-130CT microcomputed tomography (micro-CT) scanner (Shimadzu) operated at 90kV and 40 μA with a copper filter. Three-dimensional reconstruction models were obtained using morphometric software (TRI/3D-BON; Ratoc System Engineering, Tokyo, Japan). The region of interest was defined as 2 mm below the highest point of the growth plate and extending 500 μm around each implant. The bone volume fraction (BV/TV), mean trabecular number (Tb.N), mean trabecular thickness (Tb.Th), and mean trabecular separation (Tb.Sp) were quantified to assess bone regeneration.
4.14. Histology of Sequentially Labeled Sections
After the micro-CT scan, implanted femurs collected at 8 weeks were stained utilizing the Villanueva method to evaluate bone generation. All histomorphometric and fluorescence characteristics of the sections were analyzed using a BZ-9000 digital cold illumination microscope (Keyence Co., Osaka, Japan) and a laser scanning microscope (Carl Zeiss, Oberkochen, Germany), respectively.The excitation and emission wavelengths were 351/460 nm for oxytetracycline hydrochloride (blue), 543/617 nm for alizarin red S (red), and 488 nm/517 nm for calcein (green), respectively. Bone area, BIC, and labeled bone area were assessed utilizing ImageJ software in a 200× field around the implant.
4.15. Statistical Analysis
All data were expressed as the mean ± standard deviation. Each experiment was repeated three times, and all results were compared in SPSS 26.0 by Student’s t-test; P< 0.05 was considered statistically significant.
5. Conclusions
Plasma treatment of titanium surfaces with nanonetwork effectively changed the chemical composition of the sample surface, which further improved implant hydrophilicity and facilitated cell attachment and extension; significantly accelerated new bone generation and improved osseointegration in the early stage of implantation. Furthermore, the plasma treatment efficiently decontaminated the implant surface while preserving the nanoscale morphology of the TNS surface and generated a surface beneficial to osteogenesis at the same time, which could be used as a novel approach for immediate treatment before implantation or as the therapeutic method of peri-implantitis. Moreover, the elucidation of the effect on cell adhesion, differentiation, and decontamination by plasma treatment has imparted meaningful advice for future research and the development of plasma-based therapeutic strategies.
Author Contributions
A.A., T.S. and S.K. conceived and designed the experiments; Y.Z. performed the experiments; S.K., H.N. and Y.Z. analyzed the data; J.O. contributed reagents/materials/analysis tools; Y.Z. wrote the paper. All authors have read and agreed to the published version of the manuscript.
Funding
This study was supported by a grant from the Japan Society for the Promotion of Science (19K19146 and 18K09713) and Osaka Dental University Research Funds (20–08).
Acknowledgments
We thank Tohru Sekino and Hisataka Nishida from Osaka University for preparing the TNS and providing helpful suggestions. We are grateful to Akinori Agariguchi from Osaka Dental University for beneficial advice. We also grateful Yasuyuki Kobayashi from the Osaka Research Institute of Industrial Science and Technology Morinomiya Center for helpful suggestions. We also thank the members of the Department of Removable Prosthodontics and Occlusion and the Department of Periodontology for their advice and assistance.
Conflicts of Interest
The authors declare no conflict of interest.
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Assessment of wettability, surface morphology and tensile strength of the adhesive bond with epoxy adhesive
In the beta test phase Oliver Beier and Andreas Pfuch of INNOVENT e.V. Technologieentwicklung in Jena have investigated the plasma activation of various plastics after treatment with the piezobrush® PZ3 and the module “Standard”. They report in the case study about their expierences.
Different methods were used to analyze the plasma activation. For all three materials under investigation, polypropylene (PP), polycarbonate (PC) and polytetrafluoroethylene (PTFE), improved wettability was demonstrated already after one treatment at a speed of 20 mm/s. The method used here for was measuring the contact angle of water droplets. In the atomic force microscope (AFM) an increased roughness of the surfaces after treatment with the piezobrush® PZ3 was determined. The improved wettability and the nano roughening of the surface after treatment with piezobrush® PZ3 lead to a significant improvement in the adhesion of PP and PTFE. Adhesion tests of adhesive bonds with the epoxy adhesive DP460 from 3M on PP and PTFE showed a significant increase in tensile strength of the previously plasma activated samples compared to the untreated samples.
Assessing wettability with water contact measurements
To evaluate the effect of plasma activation and its different parameter sets, 10 drops of distilled water with a volume of 1 µl are deposited on each sample. With the contact angle measuring instrument OCA 20 from DataPhysics GmbH their contact angles with the surface are determined. The lower the contact angle, the higher the wettability. A total of six different parameter sets were performed on all samples. Thereby the most important parameters are treatment speed, distance between plasma module and substrate and number of treatment passes (P). The speed is set to a constant 20 mm/s in all experiments by means of an automatic traversing unit. The treatment distances are selected to be 2 and 4 mm and for these one, two and four passes are tested with the piezobrush® PZ3. In all tests, the passes are scanned over the surface at a spacing of 3 mm.
Figures 1 to 3 show that the wettability on all three types of plastics is increased by treatment with the piezobrush® PZ3. Already one pass (1 P) achieves very good results, which can only be slightly improved by further passes (2 and 4 P).
Measurement of surface roughness with the atomic force microscope
The analysis of the surface morphology also shows that just one pass with the piezobrush® PZ3 changes the plastic surfaces. In these tests, a distance of 4 mm between module and substrate is used at a speed of 20 mm/s. With the atomic force microscope MFP3D from Asylum Research, the reference samples as well as the samples treated with the piezobrush® PZ3 are measured and the roughness of the surfaces is determined. As the number of passes increases, the roughening in the nm range also increases, as can be seen in Figures 4 to 6.
Adhesion tests of an adhesive bond between plastic and steel with epoxy adhesive
For the last series of tests with the most application-related aspects, the three plastics PP, PC and PTFE are joined with a steel die using 3M’s epoxy adhesive DP460. The adhesive bond is not stressed. After a curing time of 2 hours at 65°C, the tensile strength is determined according to DIN EN ISO 4624. For this purpose, 10 samples each are subjected to an adhesive tensile test with the test system Inspekt table 50 kN by Hegewald and Peschke. While the tensile strength of the plasma-treated samples is in the order of magnitude of the reference in the PC (see Fig. 8), a significant improvement of the adhesive bond is shown for both PP and PTFE, even after only one pass with the piezobrush® (see Fig. 7 and 9).
Summary of the results
Investigations of plasma activation of various plastics PP, PC and PTFE with the piezobrush® PZ3 show that even a single pass over the surfaces at a speed of 20 mm/s produces a significant and reproducible improvement in wettability. In addition, the surfaces are roughened in the nm range. In the final tests of the tensile strength of the adhesive bond with epoxy adhesive it becomes clear that both the improved wettability and the increased roughness are typically necessary but not always sufficient criteria for an improved bond. Although pre-treatment with piezobrush® PZ3 does not show any improvement in tensile strength for PC and the selected epoxy adhesive, it does show an improvement for the corresponding joints with PP and PTFE.
Overall, the beta testers from INNOVENT attest the piezobrush® PZ3 a clearly structured and intuitive program structure. Moreover switching between the two modules “Standard” and “Nearfield” is easy and safe. Last but not least there are good and homogeneous treatment results for the plasma parameters investigated.
Reliable adhesive joints in medical technology
Rimkus Medizintechnik has been active in the field of biomedicine and medical technology for many years. The current focus is on telemetry for obstetrics. All medical devices comply with the international standard DIN EN ISO 13485 and require consistently high manufacturing quality. Often the housing parts of medical devices are made of plastic and silicone, which on the one hand serve to protect the electronics inside and on the other hand to fulfill the function of the device. However, in joining technology, it is usually very demanding to produce durable and reliable adhesive joints between silicone and plastic parts. In order to guarantee strong adhesive joints between silicone and plastic, cold atmospheric pressure plasma from the plasma handheld device piezobrush® PZ2 is used in production at Rimkus Medizintechnik.
Housing components to be bonded: The silicone part on the left is to be connected to the plastic housing part on the right to serve as a pressure chamber.
Application example: Assembly of housing parts
The housing of a sensor for uterine contractions serves as an example. In this case the housing material is Bayblend, a mixture of the plastics ABS and PC. A silicone part made of Silpuran serves as a pressure chamber for measuring the absolute pressure. For this purpose, a firm bonding with the housing is necessary. First the parts are cleaned with isopropanol. Then the plasma treatment with the piezobrush® PZ2 takes place.
The silicone part is then glued into the opening using RTV mounting adhesive 118Q from Momentive and the excess adhesive is removed. After 24 hours the adhesive joints between silicone and plastic are stable.
Now the interior components are mounted and the upper and lower parts of the housing are connected and sealed with a silicone ring. After cleaning the bonding surfaces with isopropanol, plasma treatment with the piezobrush® PZ2 is performed.
Then the silicone ring is connected to the housing with mounting adhesive. This construction serves primarily to allow the built-in Li-Po battery to gently open the housing in the event of damage and subsequent inflation, instead of bursting it open as would be the case for a screw connection.
Housing before and after complete assembly and connection and sealing with a silicone ring.
Good arguments for cold plasma
We have tried various methods for the pre-treatment of the plastic surface: primer, gas flame, other plasma generators. Primers were not easy to handle and damage the surface next to the bonding area. The gas flame is difficult to dose. Other plasma generators produced plasma that is too hot and require additional infrastructure. The piezobrush system generates cold plasma and it’s handling is very flexible. The adhesive joints produced with it resulted in sufficient strength for our purposes.Martin Patsch - Rimkus Medizintechnik
About Rimkus Medizintechnik
Rimkus Medizintechnik has been active in the biomedical field since 1986. Computer-aided systems and mobile measurement technology are the special fields of expertise. After 30 years in medical technology, the current focus is on telemetry for obstetrics. In 1999, Rimkus Medizintechnik was the first company to launch a telemetry system on the market which, using waterproof transducers, could record the fetal heart rate and contractions completely wirelessly, even in water, and transmit them by radio.
Cold plasma ensures high quality of medical products in the production process
IKA Group is a leading company in laboratory, analysis, and process technology, specializing in mixing, heating, distilling and crushing applications among others. As part of this expertise, IKA Group produces pipettes in Staufen that have to be autoclavable to meet high hygiene standards. During production, relyon plasma’s innovative PDD Technology® is used for bonding polypropylene to ensure the high quality of the medical products.
The pipette housing components are made of polypropylene (PP). A grey cover is glued to the white body with acrylic adhesive. Pre-cleaning the plastic surface with isopropanol alone cannot guarantee that the adhesive bond will survive the autoclaving process at 121°C without damage. Therefore an activation of the polypropylene is necessary to ensure the required quality of the bond.
Plasma activation prior to bonding polypropylene
The activation of the plastic material is carried out during pipette production by cold plasma with the piezobrush® PZ2-i. The piezobrush® PZ2-i is permanently integrated into the production line. The plasma activation allows the bonding of polypropylene directly after the surface pre-treatment without any delay. The discharged plasma is highly effective and barely exceeds room temperature. Therefore a temperature induced over-treatment of the plastic surface can be excluded, even if the line should come to a halt. Thus, this atmospheric treatment with cold plasma from the piezobrush® PZ2-i differs from other conventional pre-treatment methods such as flame treatment or the use of wet chemical primers.
Innovative plasma technology
The use of the piezobrush® PZ2-i with its innovative cold plasma technology ensures simple and reliable quality of the adhesive bond during pipette production. In addition, this type of surface treatment offers process and quality reliability as well as a safe work environment. The ozone produced can be extracted by a simple suction device. Due to the high efficiency and the correspondingly low power consumption and temperature of the plasma, there is no danger to employees, even in case of accidental contact. With conventional plasma jet systems, such as the plasmabrush® PB3, on the other hand, the operator has to ensure that the system is protected against contact by means of a barrier or enclosure.
Plasma treatment with piezobrush® PZ2-i
Plasma handheld device for feasibility test
The piezobrush® PZ3 handheld device is suitable for testing whether cold plasma provides the desired process improvement for a specific application. This is ideal for initial feasibility tests as well as for the production of small series. Thanks to its integrated fan, it does not require the use of external gases. In addition, the piezobrush® PZ3 has various process modes that allow the determination of reproducible parameter sets. Afterwards, the piezobrush® PZ2-i can easily be used for automated production. Both systems are also available as rental units.
Further informationen
Are you interested in further information on the use of plasma technology in production? Get in touch with us.
The plasmabrush® PB3 high-performance plasma system is known for its robustness, the equally compact design and the long service life. Only the electrode and the nozzle are wearing parts of the atmospheric pressure plasma system. Between these two components the electric arc is stabilized by raising the process gas into the plasma state. In the following report the lifetime of the plasmabrush® PB3 A250 nozzle is investigated.
By choosing the right nozzle, a process can be optimally adapted to the respective application. The A250 nozzle is the optimal choice for low potential and temperature-sensitive plasma applications. The nozzle is connected to ground potential and thus serves as the cathode for the DC voltage pulses of the system. Due to the special geometry of the nozzle, the arc, which is responsible for the discharge, is enclosed within the nozzle geometry, so that the direct discharges are located inside the nozzle. In contrast, the emerging plasma beam consists only of secondary plasma. With the so-called secondary plasma, highly reactive species are transferred without charge carriers leading to a high potential of the nozzle. This makes this nozzle particularly suitable for applications in electronics industry.
A further advantage of the design of the A250 nozzle results from its burning behaviour. The plasma is generated by high voltage flashovers. As already described, the nozzle is a wear part within the system. For the user, the nozzles can be exchanged without tools in a very short time.
Bruning behaviour
With an air flow of 35 standard litres per minute (slm), the discharge is distributed over the entire inside of the nozzle. As a result, the burning behaviour remains constant. For a longer lifetime of the nozzle the flow dynamics can be optimized by a suitable air flow.
Firing pattern of nozzle A250 after different operating hours
The figure above shows the burning pattern of the escaping secondary plasma of the nozzle after 0, 500 and 1000 operating hours. Here it becomes clear that although the nozzle material gradually oxidizes, the focal image, which is decisive for the process, hardly changes during the operating time.
Temperature
In addition to the visual evaluation of the process, a constant behaviour over time can be shown via temperature. The following figure shows the measurement setup for temperature measurement. It is clear that the temperature at a distance of 8 mm is constantly at approx. 300 °C.
The temperature of the nozzle is measured at 8 mm intervals. The temperature is around 300 °C over the entire measuring time.
Measurement setup
In summary, the A250 nozzle can be described as a low potential and relatively cold plasma nozzle with a long service life of 1000 h. The plasma properties remain constant over the entire period and do not require any readjustment in the process.
Plasma in lightweight construction
In lightweight construction, it is particularly important that not only the materials but also the connections between the individual components are weight-optimized. Therefore, structural bonding is particularly suitable for the joining technology. This is because, unlike screws and rivets, they contribute only marginally to the overall weight. In order to make these bondings particularly durable and resilient, also for safety reasons, plasma in lightweight construction is often used to optimize processes and quality.
For this reason, the piezobrush® PZ2 handheld plasma device is also used by capricorn COMPOSITE GmbH.
capricorn COMPOSITE are not only experts for the development and production of fibre composite components. They also use high-quality prepreg-autoclave technology to produce serial and prototype parts for the automotive industry, motor sports, medical engineering and aviation.
The piezobrush® PZ2 is mainly used for structural bonding of lightweight components. From a technical point of view, the very simple and flexible application is particularly outstanding. In lightweight construction, a previous plasma treatment results in a significant improvement in the adhesion of the pretreated surfaces. This is especially important for materials with low surface energy.
Today everyone can improve product quality with plasma
The easy, safe and environmentally friendly way for start-ups and small businesses
Published: ISGATECH DICHT! 2.2020 – plasma technology for start‐ups Author: Andrea Werkmann
MACHINERY AND PLANTS INTERDISCIPLINARY INDUSTRIES – The use of plasma technology to optimize adhesion processes is state of the art in industry. However, since conventional plasma systems rely either on cost-intensive vacuum chambers (low-pressure plasma) or a relatively high degree of automation (atmospheric-pressure plasma), smaller companies or start-ups can benefit less from the advantages of the technology. This is where a further developed system based on PDD (Piezoelectric Direct Discharge) Technology® can help today.
For a start-up company, the use of a conventional industrial plasma system is generally hardly conceivable, but thanks to relyon plasma’s piezo technology, professional adhesive joints are possible without major investments. Technologically, the plasma generation is based on the discharge of the piezoelectric transformer CeraPlas™ from TDK Electronics AG, which is built into the cold plasma handheld device piezobrush®. This enables highly efficient plasma generation at a power consumption of only 18 W. Different surfaces must be activated with the appropriate accessories to achieve a good result in the end: With the module Standard (Fig. 1, left) non-conductive materials can be treated like plastic, while the module Nearfield (Fig. 1, right) is used for the treatment of conductive materials like metals
For special geometries, the piezobrush® PZ2 can also be equipped with a multi-gas nozzle, whose needle insert allows treatment in narrow grooves and the injection of other process gases. In addition to the handheld device, cold plasma technology is also available in the piezobrush® PZ2-i integration unit. The external process control of this unit allows easy integration into traversing units or existing dosing systems. All this paves the way for plasma technology to be used for everything from prototypes to small series and even larger quantities.
Advantages of the technology
All in all, the advantages of plasma treatment are obvious: materials such as plastics and composites, which could otherwise only be securely bonded, sealed or encapsulated by pre-treatment with toxic and environmentally harmful chemical primers, can now be optimally processed further thanks to short plasma pre-treatment without evaporation time. The highly reactive molecules in the plasma gas functionalize the surfaces, thereby increasing wettability and creating anchor groups in the uppermost atomic layers, which in turn form an optimized bond with adhesive, sealing or casting compounds. The effect of the cold plasma on the substrate surface can be compared with the high performance systems: Compared to conventional systems with about 100 times the power consumption, the piezobrush® can achieve similar actuation results on a variety of plastics at a process speed that is only 10 times faster (about 20 mm/s).
The plasma handheld device also offers many advantages in terms of occupational safety. In large industrial plants, plasma pre-treatments are typically carried out directly in-line. When operating these high-performance systems, however, a number of occupational safety issues have to be taken into account: Due to the risks of electric shock and hot surfaces, the systems have to be installed in such a way that they cannot be touched. The generation of process exhaust gases also requires an adequate extraction system. With regard to process safety, a relative speed between plasma generator and substrate must be set. If the line speed is reduced, thermal damage or over-treatment of temperature-sensitive materials can occur. The piezobrush® is different: Since the type of plasma generated in the handheld device hardly exceeds room temperature, no heat loss occurs during this plasma treatment. This, together with the low input power, allows easy and safe handling of the handheld device. Both the risks for the operator and those of over-treatment or thermal damage to substrates are reduced to a minimum.
Predestined for prototype construction and small series
This makes cold plasma technology an alternative for prototype construction and small series production, replacing dubious wet chemical primers without the high investment and integration costs of conventional plasma systems. The handy cold plasma technology is already being used in professional 3D printing, for example at Creabis GmbH (Fig. 2), for structural bonding of larger polyamide-based components in prototype construction. For example, the interior door paneling of a small electric vehicle produced by a German start-up of Creabis was printed from unfilled PA12 by selective laser sintering (SLS) in four individual parts. These are then activated with plasma and dotted with cyanoacrylate (superglue). About 1 hour later, while the plasma activation of the parts is still continuing, they were finally structurally bonded with a 2K adhesive. The use of the piezobrush® PZ2 thus opens up possibilities for the company that were previously unthinkable when bonding individual parts.
Another practical example is the start-up ACT (Animal Care Technologies GmbH), whose team developed the Colicheck. This device is applied as a cuff to a horse’s leg and can detect and report early symptoms of colic. Due to the conditions of use, the cuff has to be very robust and well bonded. With plasma technology, professional adhesive joints can be achieved for the housing and only by using the piezobrush® PZ2 has the company succeeded in producing a reliable and durable adhesive joint for the plastic housing parts. Both the ABS material of the plastic shells and the TPE intermediate ring show an almost undetachable bond with the polymer adhesive used due to the plasma treatment.
Conclusion and outlook
The simple and safe use of cold plasma in the piezobrush®PZ2 has been further developed with the successor model piezobrush®PZ3 (Fig. 3) – for example with integrated tools for process control, such as: acoustic feedback, power settings and various modes for controlling the treatment time. The new system can be operated with various interchangeable modules for treating different materials. Ultimately, however, more and more powerful systems are available that enable start-ups and small companies to improve their processes economically and technologically simply by using proven plasma technology, thus further enhancing the quality of their products.
Would you also like to use plasma technology for start‐ups?
If you too would like to use plasma technology for start‐ups, please contact us. You can test the piezobrush® PZ3 easily and quickly directly at your site without any financial risk.
SITA Messtechnik GmbH develops, produces and sells fluorescence measurement technology for the cleanliness control of parts. In the following user report Mr. Stefan Büttner and Mr. Lutz Freudenberg have investigated the efficiency and effect of plasma cleaning of stainless steel sheets by means of fluorescence measurement.
Preparation
First, stainless steel plates were cleaned for 15 minutes in an ultrasonic bath at 60° C with the alkaline cleaner SurTec 151 (3 mass %) and then thoroughly rinsed with demineralized water and dried with hot air. Afterwards, a drop of Fuchs Anticorrit MRK 4 oil was applied to the clean surfaces and rubbed with a laboratory cloth.
The metal sheet was then scanned in SITA FluoScan 3D (a test bench for automated cleanliness control) using fluorescence measurement to investigate the distribution of the oil on the sheet. The fluorescence measurement is a layer thickness sensitive measurement and records the fluorescence intensity in RFU (relative fluorescence unit). The lower the measured value in RFU, the cleaner the surface.
Plasma treatment
The aim of the plasma treatment is to clean the stainless steel sheet by removing the oil film and thereby optimising the surface for subsequent processes such as bonding, varnishing or printing. For this purpose the plasma handheld device piezobrush® PZ3 is used.
This was attached to the traveling axis of the SITA FluoScan 3D so that the plasma treatment could be carried out automatically. The piezobrush® PZ3 was moved over the test plate by a programmed travel path, with the plasma switched on at a constant travel speed and at a constant distance to the surface.
In order to make the influence of the speed clear, the treatment was first carried out at 2.5 mm/s and in the second place at half the treatment time, correspondingly at a speed of 5 mm/s. The effect of plasma cleaning was subsequently examined by a renewed fluorescence measurement on the plasma-treated metal sheets.
Summary
It can be clearly shown that the two areas that were cleaned with plasma are much cleaner than the rest of the metal sheet. It is also clear that more thorough cleaning can be achieved by a longer treatment time.
Figure 1: Results of the fluorescence measurement on the uncleaned stainless steel sheetFigure 2: Results of the fluorescence measurement on the plasma cleaned stainless steel sheet
By suitable selection of the parameters of plasma cleaning with the help of fluorescence measurement to control and optimize the cleaning effect, an optimal cleaning effect can be achieved with high economic efficiency.
In the cleaning of metal parts, plasma cleaning shows its strengths especially in the field of ultra-fine cleaning and the selective cleaning of functional surfaces before cleanliness-critical processes or for high-quality products.
The effect of the plasma is clearly visible in the results of the fluorescence measurement. As expected, a longer treatment duration results in a better cleaning effect.
About SITA Messtechnik GmbH
SITA Messtechnik GmbH develops, produces and sells devices for measuring the dynamic surface tension of liquids for controlling the surfactant concentration, fully automated foam tester for analysing the foaming behaviour of liquids, fluorescence measuring technique for controlling the cleanliness of parts and for monitoring the contamination level in process liquids as well as devices for testing the wettability by measuring the contact angle. The measuring devices are robust and very easy to operate with. They are used in research, development and manufacturing laboratories of the chemical industry for analysis and quality assurance tasks and in the field of surface technology/parts cleaning for monitoring and controlling processes.
Cold plasma in electronics industry – the new plasma handheld device piezobrush® PZ3
Whether for bonding or marking of plastic components, wire bonding processes on metallic contact pads or the production of energy storage devices: Adhesion plays a decisive role for product quality and process stability in many areas of the electronics industry. Plasma is increasingly being used in the electronics industry to optimally prepare the surfaces of a wide variety of materials for such adhesion processes. This technology enables selective treatment of functional surfaces on plastics, metals or composites to improve a number of subsequent processes. While conventional atmospheric pressure plasma systems must be permanently integrated into systems with appropriate gas supply, extraction and safety concepts, the cold plasma handheld device piezobrush® PZ3 offers the possibility of uncomplicated and manual optimization of surfaces.
Improved adhesion processes on housing parts
A wide variety of materials and material combinations are used to enclose electronic assemblies and devices, such as aluminium, standard plastics like ABS, PC, PA or PP, but also fibre-reinforced composites. In addition to creating a functional interface and, in the end user area, an attractive appearance, the housing serves primarily to protect the electronics from external influences and contamination. Accordingly, a solid bonding of housing parts is of extreme importance for the quality of the entire product. The surfaces of the typically used housing materials are often repellent to dirt and humidity, but also to adhesives, printing inks or varnishes. In many cases this leads to insufficient adhesion of the bonding of housings or to inferior quality of labelling or design elements. These problems are primarily due to the insufficient wettability of the used materials. By treating the surfaces with cold atmospheric pressure plasma, the wettability can be improved in a targeted manner. This can be demonstrated by analysing the contact angle between a test liquid, such as water, and the plastic surface: The smaller the contact angle, the flatter the drop and the better the wettability (see figure).
High wettability is a necessary parameter for an optimized subsequent process such as bonding. Thanks to the compact and inexpensive Piezo Direct Discharge (PDD) technology® used in the piezobrush® PZ3 handheld device, start-ups and smaller companies can now afford to improve the surface properties of housing parts using plasma. For example, this is used at Animal Care Technologies GmbH to securely bond the two parts of the housing of the specially developed Colicheck. The Colicheck is applied as a cuff to the horse’s leg to track the horse’s state of health and detect and report early symptoms of colic. As a leg cuff the housing of the Colicheck has to be very robust and well bonded. With the plasma technology of relyon plasma, professional adhesive joints can be achieved for the housing.
„Only through the use of the relyon plasma piezobrush PZ2 have we succeeded in producing a reliable and durable bond between our plastic housing parts. Both the ABS material of the plastic shells and the TPE intermediate ring show an almost inseparable bond with the used polymer adhesive due to the plasma treatment. Without the plasma treatment with the piezobrush, a sufficient adhesive bond for our quality claim would be impossible.“, said Doris Hoffmann of Animal Care Technologies GmbH.
Cold plasma technology
Conventional plasma systems work either in the low-pressure range and are accordingly designed as chambers which are equipped with components, pumped off and emptied again after plasma treatment. Alternatively, there are also inline-capable plasma solutions under atmospheric pressure, which, however, require integration efforts, such as the installation of a suction unit and the implementation of a process control to prevent over-treatment or temperature damage of substrates such as plastics. In addition, direct contact with the plasma flame can endanger the health of employees.
The piezobrush® PZ3 plasma handheld device is much easier to handle. The plasma discharge generated here using PDD Technology® does not involve significant heat loss and therefore requires only 18 W of power. This makes the piezobrush® in manual operation harmless for the operator and also for temperature-sensitive materials, such as thin plastic foils. Also with regard to the purchase costs, the piezobrush® represents much lower hurdles compared to conventional systems and is therefore also suitable for start-ups or small series.
The reason for the compactness and efficiency of the piezobrush® PZ3 lies in its pluggable exchangeable modules: The heart of the piezobrush® PZ3 is the CeraPlas piezoelectric plasma generator from TDK. The approx. 7 cm long component transforms a small input voltage highly efficiently by several dimensions so that a cold plasma can be ignited under room conditions without the addition of special gases. This plasma does not exceed a temperature of 50°C and is a mixture of highly reactive ions, radicals and neutral particles. The oxygen-based reagents in particular are particularly effective for the functionalization of plastics. By treating typically hydrophobic plastics with the piezobrush® PZ3 and the module Standard, these oxygen species accumulate as polar end groups on the molecules of the surface. These act here as functional “anchors”, which can form stable bonds to adhesives or inks, for example (see figure).
The piezobrush PZ3 can also be used for ultra-fine cleaning of metals or semiconductors. However, this is only possible by using the module “Nearfield” for conductive substrates. Blickfeld GmbH, for example, uses the piezobrush® to flexibly and easily modify the surface properties of various materials, such as semiconductor components. In this way, they are optimized for subsequent processes. The company has developed its own LiDAR technology based on patented silicon MEMS mirrors and commercially available components.
Process optimization in joining technology
The cold plasma technology of the piezobrush® PZ3 can improve processes not only for housings and components. The handheld device is also used in joining technology. For example, the insulating sheathing of cables is often a challenge, not only during assembly, but also during marking. A wide variety of plastics are used here, whose surfaces have a repellent effect on adhesives or printing inks. Typical materials are for example PE, PVC, PC, PTFE (Teflon®) or PI (Kapton®). Adhesion problems can occur in processes such as bonding, encapsulation or overmoulding of connectors, which may only become noticeable under temperature or alternating loads. These problems can occur on the cable sheathing side, but also on the connector material side. This is minimized by plasma pre-treatment of the corresponding surfaces.
Even when marking the cable sheathing, e.g. by means of inkjet printing processes, the printed images on these special materials may be of inferior quality and the marking may be rubbed off when the cable is wrapped. An example print on a PTFE substrate shows that even on this highly repellent material, a standard inkjet ink adheres much better to the plasma-treated side of the test coupon (see figure).
Not only for liquid binding partners such as adhesives or inks, a pre-treatment with the piezobrush® of the surface to be wetted can provide a decisive increase in adhesion. In the field of wire bonding, the company TPT Wire Bonder GmbH & Co. KG was able to more than double the shear force value of wire bonding on the contact surfaces of batteries by treating them with the piezobrush® and the associated module “Nearfield” (see figure).
Plasma-supported production processes for energy storage systems
Apart from improved contacting of batteries, some processes can also be optimized in the production of other energy storage devices using cold atmospheric pressure plasma. For example, plasma technology helps to improve the wetting of bipolar plates with liquid electrolytes, as used in fuel cells. In principle, the piezobrush® PZ3 handheld device can be used to selectively modify the wetting properties of surfaces. Especially for energy storage systems with liquid electrolytes there is still a lot of research potential in the area of internal structure. As far as the external area of such cells is concerned, the quality of the housing is once again a key factor: These must meet the highest requirements in terms of robustness and tightness, a requirement that can be easily met with the help of cold plasma technology.
Summary
In the presented selection of applications of the piezobrush® PZ3 for plasma in electronics industry, the wide range of possible uses for its compact cold plasma technology becomes clear: From adhesion processes, such as bonding or printing on standard but also special materials, to applications in wire bonding, to research and development projects, such as in the field of energy storage. The easy handling and intuitive operation make the piezobrush® PZ3 the ideal tool for plasma pre-treatment from pre-development to the production of small series.
Surface tension and pre-treatment – effects of plasma
Students of the degree course in plastics and elastomer technology at the University of Applied Sciences Würzburg-Schweinfurt (FHWS) examined the effects of the plasma handheld device piezobrush® PZ2 on various plastics as part of the internship “Measurement of surface tension and pre-treatment” under the direction of Prof. Dr.-Ing. J. Leiber. The surface energies of the samples before and after the treatment were evaluated using test inks as well as contact angle measurements.
One group of students compared the small 18 W handheld piezobrush® PZ2 with a laboratory corona system (dose: 5000 Ws/m2): Comparably good results were achieved on polypropylene (PP), although the corona system required a shorter treatment time for this. [1] Another group of students also achieved a significant increase in surface energy on PP, but also on PP/EPDM and ABS substrates. [2] The easy handling of the piezobrush® PZ2 was praised and suggestions for process control were given. In their own experiments, the students learned that distance and speed of treatment are important process parameters in plasma processes.
Analysis methods
During the internship the students used two methods for the determination of the surface energy: The analysis based on test inks and contact angle measurements. In comparison, the test inks are easier to handle, but less accurate than contact angle measurements with three test liquids. In the latter method, drops of the respective test liquid are deposited on the surface and then their contact angle is measured. The surface energy determined by this method can thus be broken down into its polar and disperse fractions, the sum of which gives the total value of the surface energy.
Results and conclusion
Overall, the students observed that the surface energies of the examined plastics could be significantly increased by treatment with the piezobrush® PZ2. Due to the functionalization of the surface by the addition of oxygen groups, the increase is mainly visible in the polar fraction of the surface energy, as shown in the visualization of the results [2] in figure 1.
Fig. 1: Surface energy determined by contact angle measurement as the sum of the disperse and polar fractions on various plastics before and after treatment with the piezobrush® PZ2
These results were achieved at a process speed of 20 mm/s and a distance of 5 mm between substrate and nozzle outlet of the piezobrush PZ2. Using a laboratory corona system, comparable results can be achieved on PP at 170 mm/s. [1] By working with the piezobrush PZ2 handheld unit, the students were able to impressively demonstrate the influence of treatment speed and working distance on their increase in surface energy: For reproducible results, they recommend the installation of the piezobrush PZ2 handheld device in a fixture that can maintain defined distances and constant speeds. [2] Overall, the students draw a positive conclusion: “However, for use in practical training it is advantageous to have such a compact device. Here it can be shown in a simple way how a corona treatment works, what needs to be taken into account and what effect it has. In addition, such a hand-held device is also very suitable for mobile purposes, e.g. lectures or for small workshops at home” [2].
Sources:
[1] R. Knaub, M. Deininger, M. Jampolski, S. Taumann, J.
Ketterer, J. Keller (2019), Praktikumsbericht „Messung der Oberflächenspannung
und Vorbehandlung“ im Modul „Analytik und Oberflächen der Kunststoffe“ des
Studienganges Kunststoff- und Elastomertechnik an der Hochschule für angewandte
Wissenschaften Würzburg-Schweinfurt
[2] A. Schäder, G. Fischer, C. Zier, F. Schneider, S. Götz,
D. Gärtig (2019), Praktikumsbericht „Messung der Oberflächenspannung und
Vorbehandlung“ im Modul „Analytik und Oberflächen der Kunststoffe“ des
Studienganges Kunststoff- und Elastomertechnik an der Hochschule für angewandte
Wissenschaften Würzburg-Schweinfurt
relyon plasma presents the world’s smallest plasma handheld device piezobrush® PZ3 with PDD® technology
Relyon plasma based in Regensburg, Germany, a subsidiary of TDK Electronics, presents the world’s smallest and highly effective plasma handheld device piezobrush® PZ3 with PDD® technology. It is used for the simple, efficient and mobile utilization of cold atmospheric pressure plasma for surface treatment of plastics, metals and natural materials. The plasma treatment activates, functionalizes and cleans surfaces. This significantly improves the quality of subsequent processes such as bonding, printing, varnishing or coating.
Regensburg. The piezobrush® PZ3 is a compact plasma handheld device for easy and mobile use in laboratories, pre-development and assembly of small series. With a maximum power consumption of 18 W, the Piezoelectric Direct Discharge (PDD®) technology is used to generate cold active plasma at a temperature of less than 50 °C. The use of plasma has a positive effect on the surface properties of materials which are of vital importance for processing and end use. Users can thus significantly improve not only their workflow and production processes, but also their products.
PDD® Technology enables mobile handheld devices
The heart of the piezobrush® PZ3 is the TDK CeraPlas™ plasma generator, a high-voltage discharge component for plasma generation. It transforms a low input voltage in such a way that very high electric field strengths are generated, which dissociate and ionize the surrounding air. Only the compact design of the PDD® technology makes it possible to integrate atmospheric pressure plasma into such a handheld device.
Increased performance of the device
In general, all materials can be treated with atmospheric pressure plasma from the piezobrush® PZ3, since there is hardly any temperature impact on the material during surface treatment with atmospheric pressure plasma. This virtually eliminates the risk of over-treatment of materials such as plastics. However, different surfaces have to be activated with the appropriate accessories to achieve a good end result. Two modules are currently available for the piezobrush® PZ3.
The module Nearfield on the other hand is designed for the treatment of conductive materials such as metals, CFRP, indium tin oxide or conductive plastics.
Non-conductive materials such as plastics, glass, ceramics or natural materials such as organic fibers, textiles and leather show very good results after plasma treatment with the module Standard.
The increased maximum power compared to the previous model allows a treatment speed of 5 cm²/s and a treatment width of up to 29 mm. Even on materials that are very difficult to treat such as high-density polyethylene (HDPE) a surface energy of 72 mN/m can be achieved after plasma treatment.
In comparison to the previous model piezobrush® PZ2, the piezobrush® PZ3 also has an integrated process control of the plasma treatment. The device is equipped with various functions – such as a stopwatch to measure the time, a countdown function to set the time with automatic switch-off function or a power setting by adjusting the plasma intensity. The control is easy and intuitive via the integrated display.
piezobrush® PZ3 offers various application possibilities
Due to its compact design, the piezobrush® PZ3 can be used in a wide range of applications. In a lot of cases, surfaces are functionalized, for example, before bonding with plasma, whereby the following bonds show a significant improvement in the adhesive force. Plasma treatment also improves the adhesion of printing inks and varnishes on the surface, which significantly increases the print quality, as the surface is optimally wetted by the ink and an even print image is created. A further field of application is a plasma pretreatment that removes the finest impurities so that deviations between different material batches can be compensated and a consistently high level of quality is maintained.
The piezobrush® PZ3 will be available on the market from May 2020. In order to test and validate individual processes and applications, samples can be treated in the relyon plasma application laboratory. In addition, relyon plasma offers a loan of the plasma handheld device so that it can be directly included and tested in the respective process.
The complete press release can be downloaded here.
Webinar
On 7 May 2020 relyon plasma presented the device in a webinar. You can watch the webinar recording by clicking the link below.
Atmospheric pressure plasma for process improvement in wire bonding
Atmospheric pressure plasma is used in wire bonding as a selective fine cleaning step to remove contamination and residues from the contact surfaces. In general, strong bonds between wire and substrate can only be achieved on clean contact surfaces (bond pads). Thus, plasma treatment has a considerable effect on the quality and consequently the reliability of the entire component. Together with TPT Wire Bonder from Karlsfeld and the joint partner Axend Pte Ltd., relyon plasma has investigated the effects of cold atmospheric pressure plasma on wire bonding with gold wire.
Regensburg / Karlsfeld. Ideally, wire bonding is applied to clean metal surfaces (bond pads) of semiconductor components or carrier materials. In practice, however, there are often contaminations on the surface, which can result in non-stick on pad (NSOP) or so-called “lifts” (elevations of the bonds). Both cases lead to failures, downtimes and quality defects in production. For this reason, atmospheric pressure plasma is used in this process for selective fine cleaning prior to wire bonding, which avoids NSOPs as well as lifts and increases quality.
Investigation of the ball shear strength before and after plasma treatment
A test circuit board of ENEPIG surface (“Electroless Nickel Electroless Palladium Immersion Gold”) was treated on one side with the atmospheric pressure plasma high performance system plasmabrush® PB3 at a distance of 20 mm for 0.5 seconds with a compressed air plasma. Subsequently, 60 bond connections (30 balls and wedges) were applied to the untreated and plasma-treated test circuit board with the TPT HB16 Wedge & Ball Bonder. The plasma pre-treatment is intended to create a stronger connection between the bond pads and the wire.
In visual comparison, the ball bonds on the untreated and plasma treated ENEPIG surfaces seem to be firm and there are no problems with the Bond-Stick during wire bonding process. In order to measure the difference between the plasma pre-treated and the untreated ball bonds, a shear test is performed with the XYZTEC Condor Sigma Bond Tester, which shows a significant difference in quality between the two test series. An average shear strength of 60.89 gf is measured for the 30 samples without plasma pre-treatment before the ball bond is completely detached from the ENEPIG surface. Only a barely visible imprint of the sheared wire contact remains on the bond pad, a typical feature for the failure of the intermetallic bond between gold wire and ENEPIG surface.
Investigation of the ball shear strength on untreated and plasma pre-treated ENEPIG surface
In contrast, the bonds on the plasma pre-treated surfaces show a completely different behaviour in the shear tests with an average shear strength of 68.34 gf: The fracture pattern shows a sheared ball bond, leaving wire material on the surface. The shear strength of the bonds on the plasma pre-treated surface is therefore only limited by the shear strength of the wire itself. The results show that the intermetallic bond between the ENEPIG surface and the gold wire can be improved by plasma pretreatment to such an extent that it is significantly stronger than the strength of the gold wire material.
Wire pull test for wedge bonds before and after plasma treatment
For wedge bonds a wire pull test is performed with the XYZTEC Condor Sigma Bond Tester. Inconsistent test results occur with wedges applied without prior plasma treatment, proving that the bond is not ideal although it doesn’t seem critical. All in all, most wedges applied without plasma pre-treatment show so-called lifts, which indicate a weak intermetallic wedge bond.
Wire pull tests of bonds on untreated and plasma pretreated ENEPIG surface
In case of wedges applied to the plasma pre-treated surface, no failure in the wedge area occurs. All fracture patterns that appear are either within the wire itself or directly in front of the bond point (span or neck break), indicating that the bonds of both the ball and wedge are strong and therefore the wire only breaks in the area between the two bonds.
The results clearly show that surface treatment with atmospheric pressure plasma leads to significant improvements in both ball and wedge bonding, as clearly demonstrated in ball shear and wire pull tests.
The paper deals with the surface activation of low energy surfaces. It shows how surfaces of plastics such as polypropylene, PTFE or silicone can be effectively treated with cold atmospheric pressure plasma to achieve good wettability and thus optimize the adhesive strength of an acrylate-based adhesive.
Introduction
On the one hand, low-energy surfaces have the positive property of repelling dirt and allowing water to roll off. However, these plastics are typically very difficult to print or glue.
All surfaces have a characteristic polarity and surface tension. The surface energy is an important basis for the selection of the appropriate adhesive. Besides roughness and cleanness, the surface energy determines the maximum achievable adhesive strength of the adhesive. As a basic rule can be stated: The surface energy of the adhesive needs to be lower than the one of the materials to be bonded (substrate). Acrylate-based adhesives are polar and therefore have relatively high surface energy. Acrylate-based adhesives achieve an ideal final adhesion on polar substrates (e.g. glass or metals) with a high surface energy.
More critical is the use of acrylate-based adhesives for materials with low surface energy (non-polar substrates) such as silicone, PTFE and polypropylene. Easier than using a new adhesive formulation for each substrate would be to raise the surface to a sufficient level of surface energy, e.g. with an atmospheric plasma treatment.
Materials and methods
Three very widely used low-energy polymers were selected for the experiments:
A simple hand-held cold plasma system piezobrush® PZ2 has been used for cold surface treatment. For comparison, a treatment of the surface with a typical atmospheric pulsed plasma jet plasmabrush® PB3 was also investigated. Air and forming gas (N2:H2 = 95:5) was used as process gas.
A first indication of the surface energy can be obtained with test inks which are applied to the sample. The samples were each exposed up to half of the plasma process. Figure 1 shows a significant increase in surface energy for all samples.
Abbildung 1) Effect of a cold atmospheric plasma treatment (duration 3 s) in the upper part of each sample. (A) Polypropylene with air, (B) PTFE with air, (C) PTFE with forming gas, (D) silicone elastomer with forming gas, (E) silicone elastomer with air.
Adhesive forces were measured in a peel test with a tractor at a defined pull-off speed. During the tensile test, the adhesive tape first peels off the untreated and afterwards of the plasma treated surface. In all tensile tests a sudden increase in adhesion is observed, which correlates on the sample with the transition from the untreated (low-energy) to the treated (high-energy) surface.
Abbildung 2) Tensile test with a tape coated with acrylate. The originally very low adhesion force is multiplexed.
Polypropylene, a widely used thermoplastic polymer, is physiologically harmless and biologically inert and therefore very suitable for applications in food and pharmaceutical industries. Because of its low surface energy, polypropylene is difficult to print or bond. Therefore, the treatment of the surface, e.g. with corona systems, on an industrial scale is applied. [1,2,3,4].
For polypropylene, a surface energy of approx. 58 mN/m is achieved with cold treatment using piezobrush® PZ2 starting at 31 mN/m after a short treatment period. The peel test results in a doubling of the adhesion for an acrylate-based adhesive tape.
Silicone elastomers are used in various areas due to their excellent mechanical properties, their resistance to UV light and their chemical resistance even at elevated temperatures. The disadvantage of silicone elastomers is the problematic bonding with other materials due to the low surface energy.
The effect caused by the cold discharge of the piezobrush® PZ2 with forming gas is only slightly more significant than that of using air. In both cases, complete water wettability is achieved.
It is a known fact that silicones with hydrophilic surface properties can be obtained by plasma treatment, but this effect is not permanent over a long period of time. [5,6,7,8].
Abbildung 3) The surface energy of cold plasma activated silicone is noticeably decreasing on a time scale of hours. This decrease has an exponential course and, depending on the type of silicone, a half-life of a few minutes to a few days.
PTFE is very inert. Its chemical resistance ensures a long service life and good compatibility in the medical technology sector. PTFE is one of the few plastics that can be steam sterilized in an autoclave at 130 °C, but it is difficult to wet and very difficult to bond. The contact angle with water is 126°. It is known that under certain conditions PTFE can be treated with plasma to increase the surface energy. [9,10,11,12].
Summary
All investigated low energy plastic surfaces (polypropylene, silicone and Teflon) can be activated very well with the cold discharge of the piezobrush® PZ2 and show a significant increase of the surface energy. For PTFE, forming gas (nitrogen/hydrogen) is far more effective than air.
Literature
Martina Lindner, Norbert Rodler, Marius Jesdinszki, Markus Schmid, and Sven Sangerlaub. Surface energy of corona treated PP, PE and PET films, its alteration as function of storage time and the effect of various corona dosages on their bond strength after lamination. Journal of Applied Polymer Science, 135(11):45842, 2018.
Igor Novák and Ivan Chodák. Adhesion of poly(propylene) modified by corona discharge. Die Angewandte Makromolekulare Chemie, 260:47-51, 1998.
J. Skalný, M. Luknáarová, and D. Dindošová. AC corona – discharge treatment of polypropylene foils effects of gaseous atmosphere. Czech. J. Phys B, B38:329-337, 1988.
Mark Strobel, Viv Jones, Christopher S. Lyons, Michael Ulsh, Mark J. Kushner, Rajesh Dorai, and Melvyn C. Branch. A comparison of corona-treated and flame-treated polypropylene films. Plasmas and Polymers, 8:61-95, 2003.
Emmanuel P. Everaert, Henny C. Van Der Mei, Joop De Vries, and Henk J. Busscher. Hydrophobic recovery of repeatedly plasma-treated silicone rubber. part 1. Storage in air. Journal of Adhesion Science and Technology, 9(9):1263-1278, 1995.
Jongsoo Kim, Manoj K. Chaudhury, Michael J. Owen, and Tor Orbeck. The mechanisms of hydrophobic recovery of polydimethylsiloxane elastomers exposed to partial electrical discharges. Journal of Colloid and Interface Science, 244:200-207, 2001.
Jongsoo Kim, Manoj K. Chaudhury, and Michael J. Owen. Modeling hydrophobic recovery and electrically discharged polydimethylsiloxane elastomers. Journal of Colloid and Interface Science, 293:364-375, 2006.
Elidiane C. Rangel, Giovana Z. Gadioli, and Nilson C. Cruz. Investigations on the stability of plasma modified silicon surfaces. Plasma and Polymers, 9(1):35-48, 2004.
P. Favia, A. Milella, L. Iacobelli, and Riccardo d’Agostino. Plasma Pretreatments and Treatments on Polytetrauoroethylene for Reducing the Hydrophobic Recovery, chapter 20, pages 271-280. John Wiley & Sons, Ltd, 2005.
Shinya Ishikawa, Ken Yukimura, Koichi Matsunaga, and Toshiro Maruyama. Surface modification of poly(tetrauoroethylene) film using dielectric barrier discharge of intermittent pulse voltage. Japanese Journal of Applied Physics, 39(9R):5223-5228, 2000.
Ulla König, Mirko Nitschke, Anke Menning, Grit Eberth, Matin Pilz, Christine Arnhold, Frank Simon, Gudrun Adams, and Carsten Werner. Durable surface modification of poly(tetrauoroethylene) by low pressure H2O plasma treatment followed by acrylic acid graft polymerization. Colloids and Surfaces B: Biointerfaces, 24(1):63- 71, 2002.
Akira Takeuchi, Takahiro Kurahashi, and Kyosuke Takeda. Effect of microwave plasma surface treatment for improved adhesion strength of direct copper plating on polytetrauoroethylene (PTFE). In Conference Proceedings of IPC APEX EXPO, pages 1-7, April 2009.
More about surface activation of low energy surfaces
We are looking forward to starting a new decade of innovative plasma technology together with you and the next generation of our piezobrush® handheld device. We invite you as our valued partners to the product launch of our new piezobrush® PZ3 in Regensburg on May 7, 2020. Following this event, an exclusive sales partner meeting will take place on May 8, 2020.
At the launch event, beta testers from various industries will report on the practical use of the piezobrush® PZ3. You will also have the opportunity to experience the device yourself and to discuss your current use cases with our application engineers.
At the subsequent sales partner meeting you will receive product-specific training from our application engineers, plasma experts, and developers. Furthermore, we would like to plan marketing and sales activities for 2020 together with you in order to be able to support you in the best possible way in the new year.
Where: relyon plasma GmbH – 93055 Regensburg, Osterhofener Str. 6, Germany Accomodation: ACHAT Premium Regensburg, We have arranged a hotel contingent for you with the keyword: relyon plasma
Register now
Registration form
Please note that the number of participants is limited. Therefore we ask you for early registration. A detailed conference program and the program of the evening event will be published at the end of March. If you have any questions regarding the event, please feel free to get in touch with us.
We are looking forward to starting a new decade of innovative plasma technology together with you and the next generation of our piezobrush® handheld device. We invite you to visit us in Regensburg on May 7, 2020 for the product launch of our new piezobrush® PZ3.
At this event, beta testers from various industries will report on the practical use of the piezobrush® PZ3. You will also have the opportunity to experience the device yourself and to discuss your individual use cases with our application engineers.
Save the date in your calendar today: When: May, 7th 2020 Conference program: 9.30 a.m. – 05.00 p.m. Evening event: 6.00 – 11.00 p.m. Where: relyon plasma GmbH – 93055 Regensburg, Osterhofener Str. 6 Accommodation: ACHAT Premium Regensburg, We have arranged a hotel contingent for you with the keyword: relyon plasma
Register now for the product launch piezobrush® PZ3
With the form below you can register for our launch event:
Registration form
Please note that the number of participants is limited. Therefore we ask you for early registration. A detailed conference program and the program of the evening event will be published at the end of March.
If you have any questions regarding the event, please feel free to get in touch with us: info@relyon-plasma.com
Visit to Kunststoff-Zentrum SKZ in Würzburg
At the beginning of the year, our colleague Corinna Little had the pleasure of visiting the Kunststoff-Zentrum SKZ in Würzburg, where she was shown the extensive equipment of the laboratories by the team of the Joining and Surface Technology Research Department. In addition to the numerous analytical methods for surface characterization such as contact angle measurement or scanning electron microscopy with EDX (element analysis), the experts at SKZ have various mechanical testing methods at their disposal, including tensile, compression and bending tests. Extensive ageing tests can also be carried out at the Würzburg site using climate and temperature chambers.
In the field of surface pre-treatment, all common processes are represented in the laboratory, from flame treatment and various lasers to low-pressure and atmospheric-pressure plasmas and corona. We are happy to extend this wide portfolio with our cold plasma technology in the piezobrush handheld unit.
The Kunststoff-Zentrum SKZ offers different interesting workshops in the next weeks:
On Thursday, March 5, 2020, the Working Group Hygiene Regensburg will organize the first Innovation Day: Hygiene 4.0 in Regensburg. As part of this Working Group we are happy to be co-organizer of the event.
Hygiene protects and saves lives. Against the background of increasing and newly developing antibiotic resistance, the prevention and treatment of nosocomial infections is of particular relevance to health care. In addition to early, rapid and precise diagnosis, it is important to exploit prevention potentials as fully as possible by avoiding or reducing bacterial exposure. Materials and surfaces, antiseptic coating processes of hygienically relevant surfaces as well as easy-to-clean or sterilizable constructions of medical devices and equipment play an essential role in this context.
At the Innovation Day, among other things, updates on transmission control and clarification of outbreaks of pathogens will be given and various methods for reducing the germ load in the clinical environment will be presented. In addition, the conference with industrial exhibition offers an excellent opportunity for trade exhibitors for interdisciplinary exchange with experts from research, industry and application.
Impressions
Agenda Hygiene 4.0
09:00
Registration
09:30
Welcome
Dr. Thomas Diefenthal, BioPark Regensburg GmbH
09:45
Welcome
Bürgermeister Jürgen Huber, Stadt Regensburg
10:00
Keynote
Prof. Dr. Johannes Hübner, Infektiologie, Klinikum der Universität München
10:45
Transmission control of germs
Prof. Dr. Wulf Schneider, Klinikhygiene, Universitätsklinikum Regensburg
11:15
Applications of the Whole Genome Sequencing: Clarification of outbreaks caused by pathogens
Prof. Dr. Karsten Nöckler, Abteilung Biologische Sicherheit, Bundesinstitut für Risikobewertung
11:45
Lunch
01:00
Antiseptic stewardship – Resistances towards biocidal active substances and their clinical significance
Prof. Dr. Günter Kampf, Institut für Hygiene und Umweltmedizin, Universität Greifswald
01:30
Management of hygienically relevant areas in medical facilities
Prof. Dr. Clemens Bulitta, Institut für Medizintechnik, Ostbayerische Technische Hochschule, Amberg-Weiden
02:00
Reduction of the microbial surface exposure in hospitals
Prof. Dr. Wolfgang Bäumler, Klinik und Poliklinik für Dermatologie, Universitätsklinikum Regensburg
02:30
Implementation challenges of antimicrobial surfaces in medical devices using the example of implant coatings
Thomas Paulin, aap Implantate AG
03:00
Coffe break
03:30
Hygiene by design – Design principles for medical technology products
Markus Mutterer, designaffairs GmbH
04:00
Preparation of medical devices – Ambition and reality
Christian Trenkler, GLP MEDICAL GmbH
04:30
Technology-supported monitoring & Visualization of factors influencing the pathogen transmission
Please note that due to the new situation regarding the spread of the corona virus, MedtecLIVE will be postponed to a date in 2020, which is still to be determined.
Plasma in medical technology
From March 31 – April 2, 2020, MedtecLIVE – THE event for the manufacturing of medical technology opens its doors in Nuremberg. We are very happy to present once again this year at the joint stand with Biopark Regensburg in Hall 10.0, Stand: 10.0-344, how versatile plasma technology can be used in medical technology.
In the foreground of our participation is the plasma hand-held device piezobrush PZ2, which has been used in medical and dental technology for many years. The piezobrush combines the sterilizing effect of atmospheric plasma with a highly efficient increase of surface energy.
Overall, surface treatment with plasma technology offers decisive advantages for many fields of application in biotechnology, pharmacology and medical technology – and also in dentistry. The acceleration of wound healing is particularly noteworthy here.
About MedtecLIVE
MedtecLIVE was created from the events Medtec Europe and MT-CONNECT and entered the market at its first event in 2019 as THE European trade fair for medical technology. MedtecLIVE’s concept aims to link all players in the medical technology industry, from classic suppliers to manufacturers.
The exhibition with a top-class supporting program ranging from special areas to specialist lectures in the exhibition forums will be rounded off by the parallel and freely accessible MedTech Summit Congress and the B2B Matchmaking event “Partnering”. The close intermeshing of the exhibition and the high-caliber accompanying program will ensure an overall event that has become an innovation hub and a unique networking platform for participants from all over Europe and beyond.
Visit us at booth 10.0-344
Visit us at MedtecLIVE and get a free entrance ticket for the exhibition.
Please note that WIN EURASIA will be postponed to 18 – 21 June 2020, due to the new situation regarding the spread of the corona virus.
WIN EURASIA
From June 18 to 21, 2020 relyon plasma will be represented together with its Turkish partner FCB ARGE at the WIN EURASIA – World of industry 2020 in the Tüyap Fair Convention and Congress Center in Istanbul. In hall 14, booth K113, relyon plasma’s plasma solutions for surface treatment will be presented and can be tested directly on site.
About WIN EURASIA 2020
At this year’s World of industry EURASIA six trade fairs come together:
CeMAT EURASIA
IAMD EURASIA
Industrial Energy Systems EURASIA
Metalworking EURASIA
SurfaceTechnology EURASIA
Welding EURASIA
Exhibitors and visitors will have a unique opportunity to showcase and experience the 360 Degree Manufacturing Industry. From sheet metal processing to metal forming technologies; automation services to electric and electronic equipment, hydraulic & pneumatic services to intralogistics, World o findustry EURASIA 2020 will bring all the ecosystem needed for the future’s factories.
Plasma in industrial printing
Ritzi Industriedrucktechnik GmbH accompanies customers from medical technology, automotive and building services engineering sectors from the development stage right through to the finished print product. The common printing processes screen, digital and pad printing are used. In industrial printing, plasma is used to optimise the surface properties before printing in order to increase the adhesion of ink and accordingly the print quality.
On the difficult plastic PEI (polyetherimide), we were able to achieve outstanding adhesion properties with the piezobrush and all this even inline. The production process could be streamlined and significantly accelerated.Marius Ritzi - Ritzi Industriedrucktechnik GmbH
Do you want to have further information on our piezobrush PZ2?
Wire bonding is a method used to interconnect integrated circuits or semiconductors to other components or the housing by means of thin wires (bonding wire). For this process it is of vital importance that the contact surfaces are free of impurities and residues. For this reason, atmospheric pressure plasma is used for fine cleaning prior to wire bonding to achieve better connections and thus increase quality and productivity.
Wire bonding
Ideally, wire bonding takes place on clean metal surfaces of the semiconductor component or carrier material. In practice, however, contaminations of the surface frequently occur, which can lead to non-stick on pad (NSOP) or so-called “lifts”. Both cases lead to production failures, downtimes and quality defects. By means of a selective plasma treatment prior to the bonding process both NSOPS and lifts can be avoided and thus the quality can be increased.
Another application is in adhesive processes on solder resist. This is applied before soldering in order to prevent the surfaces coated with it from being wetted with solder on the printed circuit board. However, such areas are often to be coated, glued or potted in a further step, which is difficult because the surface has very poor wetting properties. The solder resist can be activated by a plasma treatment, so that coating, gluing or potting of circuit boards is possible without any problems.
Flux
A flux is a substance added during soldering which improves the wetting of the workpiece by the solder and removes the oxides on the surfaces by chemical reaction. However, these are often corrosive, corroding or harmful to health and should be removed from the surface after soldering. Therefore the parts are cleaned after soldering with the plasmabrush.
Selective fine cleaning and activation
Atmospheric pressure plasma offers the possibility to remove organic as well as oxidic impurities from the decisive surfaces in the existing process and to make repellent layers either completely or selectively wettable. In contrast to low-pressure plasma, the jet of an atmospheric pressure plasma system can be easily integrated into the production line without significantly increasing cycle times. This makes this technology a cost-effective and attractive way to improve quality.
Gen-Plus aims to promote new innovations in the field of formulation and technology concepts for the pharmaceutical industry.This includes solid and semisolid dosage forms as well as patches and thin films. The range is from the early idea to the medicinal product samples (for clinical trials) under GMP conditions. The plasma handheld piezobrush PZ2 is used for the plasma treatment of films made of polyethylene and polypropylene.
Gen-Plus develops transdermal patches. We upload various substances on thin films. We used the piezobrush to explore improvements in adding these materials to our film products. The corona treatment done by the piezobrush enabled a better adhesion of the substances to the film. The piezobrush was easy to use and practical in a R&D lab environment.Juraj Jerkovic - Gen-Plus GmbH & Co. KG
Are you interested in further information about our piezobrush PZ2?
The Max Planck Institute for Astronomy – MPIA was founded in 1967, and it is one of roughly 80 institutes of the Max Planck Society, Germany’s largest organizations for basic research. The MPIA deals with the following questions, for example: How do stars and planets form? What can we learn about planets orbiting stars other than the Sun? How do galaxies form, and how have they changed in the course of cosmic history?
The engineering department also uses our plasma hand-held device piezobrush PZ2. Ralf-Rainer Rohloff describes the application as follows:
We use the plasma device to activate adhesive surfaces made of CFRP and glass/glass-ceramic since conventional firing systems can cause temperature damages on the components.Ralf-Rainer Rohloff, Max-Planck-Institut für Astronomie
You want to have more information about our piezobrush PZ2?
At MEDICA, the world forum for medicine, which takes place from 18 to 21 November 2019 in Düsseldorf, relyon plasma will present its solutions for the medical and healthcare sector for the first time at the TDK Stand C42 in Hall 9.
As a highlight, we present the plasma handheld piezobrush PZ2, which has been used for years in the manufacture of medical devices, e.g. before bonding plastic components.
Learn more about plasma technology in medical and dental technology and discover new opportunities in the market.
About MEDICA
MEDICA is the world’s largest event for the medical sector. For more than 40 years it has been firmly established on every expert’s calendar. There are many reasons why MEDICA is so unique. Firstly, the event is the largest medical trade fair in the world – it attracted more than 5,100 exhibitors from 70 countries in 17 halls. Furthermore, each year, leading individuals from the fields of business, research, and politics grace this top-class event with their presence — naturally alongside tens of thousands of national and international experts and decision-makers from the sector, such as yourself. An extensive exhibition and an ambitious program — which together present the entire spectrum of innovations for outpatient and clinical care — await you in Düsseldorf.
Atmospheric pressure plasma in electronics production
From November 12 – 15, 2019 productronica – the world’s leading trade fair for the development and manufacture of electronics – will open its doors at Messe München. We will present some application examples for atmospheric pressure plasma at productronica 2019.
Together with our partner Bridge S. r. l. we are represented in hall B2 at booth 428 at F & K DELVOTEC Bondtechnik GmbH. At the booth our high performance plasma system plasmabrush PB3 was integrated into the Cobocell 4.0. Plasma is used for fine cleaning before bonding. In addition, atmospheric pressure plasma offers different applications for increased productivity and quality also in the line production of electronic assemblies.
Wire bonding
Ideally, wire bonding takes place on clean metal surfaces of the semiconductor component or carrier material. In practice, however, contaminations of the surface frequently occur, which can lead to non-stick on pad (NSOP) or so-called “lifts”. Both cases lead to production failures, downtimes and quality defects. By a previous selective plasma treatment both NSOPS and lifts can be avoided and thus the quality can be increased.
Solder resist
Another application is in adhesive processes on solder resist. This is applied before soldering in order to prevent the surfaces coated with it from being wetted with solder on the printed circuit board. However, such areas are often to be coated, glued or potted in a further step, which is difficult because the surface has very poor wetting properties. The solder resist can be activated by a plasma treatment, so that coating, gluing or potting of circuit boards is possible without any problems.
Flux
A flux is a substance added during soldering which improves the wetting of the workpiece by the solder and removes the oxides on the surfaces by chemical reaction. However, these are often corrosive, corroding or harmful to health and should be removed from the surface after soldering. Therefore the parts are cleaned after soldering with the plasmabrush.
Selective fine cleaning and activation
Atmospheric pressure plasma offers the possibility to remove organic as well as oxidic impurities from the decisive surfaces in the existing process and to make repellent layers either completely or selectively wettable. In contrast to low-pressure plasma, the jet of an atmospheric pressure plasma system can be easily integrated into the production line without significantly increasing cycle times. This makes this technology a cost-effective and attractive way to improve quality.
Plasma and adhesive
Our partner John P. Kummer GmbH will also be demonstrating the interaction of plasma activation with various adhesives and adhesive tapes at Stand 301 in Hall A4. The piezobrush® PZ2 will be demonstrated and tested live on the stand.
Discover plasma in electronics production at productronica 2019!