Sterilizing with atmospheric plasma
Sterilization is a process by which materials and objects are freed from living microorganisms including their resting stages (e.g. spores). The state of the materials and objects achieved in this way is called “sterile”.
During the sterilization of materials (e.g. food, pharmaceuticals, liquids), objects, packaging, devices (e.g. vessels for the culture of microorganisms, endoscopes), all microorganisms contained or adhering to them, including their permanent forms (e.g. spores), are (ideally) killed and viruses, prions (infectious proteins), plasmids and other DNA fragments destroyed.
In practice, complete sterilization is not possible with 100% certainty. Therefore, a reduction of the number of reproductive microorganisms by a certain factor (in powers of ten) or a certain probability of complete sterilization, depending on the application, is required.
The sterilizing effect of atmospheric pressure plasmas has been scientifically proven in a large number of investigations. The effect is a complex interplay of many components that can be specifically balanced with suitable process control:
- In the near field the atmospheric plasma works by a combination of:Light (UV radiation)
- Electrons with high kinetic energies up to some keV
- Highly excited ions and short-lived oxygen species
- Electric fields
In secondary plasma, a highly reactive mixture of very different chemical species can be directed onto the surface:
- Nitrogen oxides
In addition, there is the efficient input of thermal energy into the near-surface layer.
Depending on the application, either a plasma system of pulsed arc discharge (PAA® technology), such as the PB3/PS2000, or the cold discharge of the PZ2 (PDD® technology) are suitable.
When using the PZ2, the effects of UV light (in the near field) and ROS (reactive oxygen species, especially ozone) and RNA (reactive nitrogen species) predominate. Very high electric fields can also be induced in the near field. The temperature input, on the other hand, is very low.
The PDD® technology, which forms the basis for the PZ2, is currently the most efficient ozone generator known.
Due to the high energy densities in the electric arc, a large amount of highly reactive species can be generated with the PB3. Depending on the composition of the input gas, the balance between ozone, nitrogen oxides or peroxides can be shifted. At the same time, a shock-like temperature increase can be triggered on the surface. Temperatures up to the decomposition limit of all organic and biological materials are reached and thus under suitable conditions almost perfect sterility is achieved.
Tpyical industrial products are packaging in the pharmaceutical sector, sterile goods, blister packaging, beverage filling, foodstuffs.
In most cases, virtually complete sterility is to be achieved in the industrial sector in a short cycle time (<1s), starting from a low level of contamination. Thus, pulsed arc discharge (PAA® technology) is the process of choice.
However, the extremely high generation rate of ROS (reactive oxygen species) of piezoelectric discharge (PDD® technology) with very low input power, high efficiency, compact design and maximum safety is often desired. Cavities are thus efficiently sterilized.
Resistant pathogens pose a considerable risk worldwide, especially in operative intensive care units, departments for burn injuries and neonatal units, but also in nursing wards for the elderly. Increasingly, methods are being sought that can kill multi-resistant pathogens in clinical practice without the use of antibiotics. The PZ2 has succeeded in effectively neutralising the methicillin-resistant Staphylococcus aureus (MRSA), which is classified as particularly critical.
Of course, the low-cost piezo technology also provides considerable added value for the user in the case of a large number of consumer products due to its germ-reducing and odour-reducing effect. Examples of this are: Cosmetic devices, everyday utensils, sports bags, shoes, freshness boxes.
PEEK implants have been firmly established in orthopaedics, especially in the area of the spine, for some time now. In the meantime, however, dental implants are increasingly being made of this high-performance plastic.
The reasons for this include the good mechanical properties, the biocompatibility and stability, the good sterilization resistance of the polymer and its X-ray transparency.
Positive effects of plasma
On the one hand, the plasma treatment destroys any microorganisms present on the surface. The germ-reducing effect of the plasma helps to reduce the risk of infection. At the same time, the “finely cleaned” surface increases the body’s tolerance to the foreign body implant. The second effect is based on the increase of the surface energy of the plastic, up to the so-called water wettability. As a result, the surface of the implant can be better wetted by the body’s own substances such as blood and other fluids, which promotes and accelerates the healing process.
Living tissue and medical application
The best studied area of plasma medicine is the treatment of wounds and inflamed skin areas. Since direct contact with living tissue is desired, only so-called cold plasma can be used. The cold plasma at atmospheric pressure works in a complex way: via UV rays, reactive compounds and electric fields. The interaction of these factors considerably slows down the growth of bacteria, which accelerates healing. In addition, plasma could stop the growth of caries-causing bacteria in tooth enamel or prevent inflammation of implants. We support basic research in this interesting field.
In technology, we have taken a decisive step by developing PDD® technology, the most efficient and effective comparable method. The basic technology is equally suitable for direct treatment of the wound via a gaseous plasma jet and for a two-dimensional barrier discharge onto the skin surface to be treated.
Despite the high efficacy on a large number of typical germs, including some multi-resistant pathogens that are increasingly in focus, the known side effects are comparatively weak. Of course, combination applications with actively added bioactive substances are also conceivable.
In detail, the transitions from medical therapy to cosmetics are fluent.