Plasma sterilization explained simply – Definition

Plasma sterilization is an innovative, fast, and highly effective low-temperature process (45 °C to 60 °C) for the residue-free elimination of germs and pathogenic microorganisms. It is typically used in pharmaceutical and medical fields and frequently in the packaging industry.

Advantages

The low-temperature process offers significant advantages—such as efficiency, gentleness on materials, sustainability, and workplace safety—over conventional sterilization methods such as steam (+100 °C) or ethylene oxide gas (toxic and leaves residues).

Due in particular to its thermolabile properties, which are beneficial for heat-sensitive instruments, dry plasma sterilization is suitable for materials sensitive to heat and moisture. These include, among others, surgical materials, plastics, dental instruments, cables, and aerospace materials.

Disadvantages

Plasma sterilization has fewer disadvantages and more limitations. For example, the items being treated must be completely dry and, when using low-pressure plasma, must also be vacuum-tight and plasma-resistant. Because the plasma treatment takes place in a vacuum chamber, even objects with complex geometries or cavities can be sterilized effectively—something that is not always possible without a reaction vessel.

plasma technology’s approach: Our plasma systems therefore use only low-pressure plasma for sterilization. This ensures efficient processing times, and thanks to the high durability of our products, our solutions are both efficient and cost-effective.

Applications for Materials and Products

Suitable products and materials for plasma sterilization or disinfection. Which products or materials can be disinfected or sterilized in low-pressure plasma?

Materials

In addition to various metals, polymers (plastics)—such as thermoplastics, thermosets, elastomers, TPU, and, in particular, silicones—can also be cleaned, disinfected, and sterilized using plasma. Glass, ceramics, and various textiles and membranes are also suitable for plasma sterilization and plasma disinfection.

In general, materials must be plasma- or vacuum-resistant in order to undergo plasma treatment. Materials that cause significant disruption to the vacuum or plasma due to heavy outgassing are therefore not suitable for treatment in low-pressure plasma.

Products

Typical products suitable for disinfection or sterilization in low-pressure plasma include those from the pharmaceutical, medical, and dental sectors, as well as the packaging industry. For low-pressure plasma sterilization, the products must be able to be placed inside the plasma chambers.

Fixed components, such as hospital interiors, cannot be treated with low-pressure plasma. Additionally, the plasma cannot reach products that are already packaged. In this case, the plasma sterilizes only the packaging, not the product itself.

Examples of products that can be successfully disinfected and sterilized in low-pressure plasma:

• Respiratory masks
• Safety goggles
• Surgical instruments
• Dental instruments
• Catheters and prostheses
• Endoscopes (thermolabile)
• PE, PP, and blister packaging

Even FFP3 respirators and other protective equipment for hospital staff, which are normally intended for single use, can be reprocessed for further use through plasma disinfection.

Process and Mechanism

Gas plasma sterilization is a gentle, dry, low-pressure process that oxidizes and completely destroys the cellular components of viable microorganisms. Since it is typically performed at temperatures between 37 °C and 60 °C, it is ideally suited for heat-sensitive materials.

Plasma Sterilization Process

Plasma has been proven to damage or inactivate all components of pathogens, such as bacteria, viruses, virions, prions, and fungi and their spores. This destroys, among other things, their cell walls, viral or spore coats, cell membranes, and the pathogens’ DNA genetic material. Furthermore, plasma removes contaminants and toxins from surfaces.

In a low-pressure process, the items to be sterilized (cleaned and dried) are placed in a sterilization chamber. When using low-pressure plasma, the chamber is evacuated to create a vacuum, and a process gas is introduced.

Due to the high penetrability of low-pressure plasma, even the smallest cavities and crevices are reached during plasma disinfection or sterilization. Depending on the process gas used and the selected treatment intensity and duration in the plasma atmosphere, products are both disinfected and sterilized.

How Plasma Sterilization Works

The scientifically proven sterilizing effect of plasma is the result of several factors.
The factors and how they work in detail:

High reactivity of the particles contained in the plasma
– The various reactive species contained in the plasma damage the organic molecules of living organisms, such as bacteria.
– Bacteria are killed by the oxides present in the plasma.

UV radiation generated in low-pressure plasma
– Ultraviolet radiation is a powerful disinfectant and damages the genetic material of pathogens, i.e., their DNA molecules.
– UV radiation affects living cells, such as bacteria, as well as viruses, which lack their own metabolism.
– Viruses are inactivated by the UV radiation present in the plasma.
– Bacteria are killed by the UV radiation present in the plasma.

High kinetic energy of ions and electrons
– The plasma particles strike the surfaces of the products at high speed, mechanically dislodging existing contaminants and pathogens (sputtering effects).
– Regardless of the nature of the particles—whether living or not—they can be mechanically dislodged, transferred into the gas phase, and removed from the treatment chamber via constant gas transport.
– The charged particles destroy bonds in the cell membranes and thus also penetrate the viral envelopes of enveloped viruses (for information: The SARS-CoV-2 virus is an enveloped virus).

The fine vacuum present in the low-pressure plasma
– The fine vacuum and the temperature increase upon contact with the high-energy plasma species cause the organisms of the pathogens to dry out.

Plasma Disinfection

Plasma disinfection reduces the number of disease-causing microorganisms so that an object no longer poses a risk of infection. These are methods for the targeted, but not complete, killing and inactivation of disease-causing (pathogenic) microorganisms. Disinfected objects are therefore not 100% germ-free, but rather have a reduced or low microbial load. Effective disinfection achieves a KRINKO guideline of approximately 84 to 99.9%. Depending on the process gas used and the selected treatment intensity and duration in the plasma atmosphere, products are both disinfected and sterilized.

Difference from Plasma Cleaning

Plasma cleaning generally refers to the removal of unwanted contaminants and microorganisms without killing or inactivating the latter. In medical settings, cleaning can be performed, for example, using cleaning agents, wipes, or vacuum cleaners.

In the context of plasma, the mechanical removal of microorganisms through sputtering effects corresponds to simple cleaning. Simple cleaning achieves a germ reduction of approximately 50–80%. Plasma disinfection therefore achieves a significantly higher germ reduction than plasma cleaning.

Difference from Plasma Sterilization

The key difference between plasma disinfection and plasma sterilization lies in the (percentage) reduction in the microbial count, which is significantly reduced by disinfection (84 to 99.9%) and completely eliminated without residue by sterilization (100%). Sterile products are therefore free of viable microorganisms, such as bacteria, fungi, or spores. Prions, viruses, and virions must also be inactivated.

Plasma disinfection can be applied to living tissue, e.g., for wound treatment with cold plasma (below 40 °C), and performed on-site.
Plasma sterilization is typically performed in an optimized low-pressure plasma system with appropriate processing times and process gases.

Suitable Plasma Systems and Process Gases

The selection of the appropriate plasma system and process gas depends primarily on the product to be treated. Product quantities, the scheduled timing of disinfection or sterilization, and the desired outcome must also be taken into account.

Suitable plasma systems for sterilization with low-pressure plasma:
If a sterilization process is to be integrated into production, large-volume production systems are the ideal choice. Production systems are adapted to the specific requirements of the products to be sterilized and tailored to existing manufacturing processes. The plasma systems can also be equipped with a pass-through function.

Suitable low-pressure plasma systems for plasma disinfection:
For more mobile on-site use, such as disinfection after the first use of smaller products, small laboratory systems are certainly better suited.

Suitable process gases include various noble gases as well as hydrogen, nitrogen, and oxygen. Mixtures of different gases are also possible. The selection of the process gas depends on the product to be sterilized or disinfected. However, the desired effect of the plasma process is also a factor in the selection.

PlasmaKlient Research Project

PlasmaKlient was a funded research project (KMU-innovativ by the BMBF, now BMFTR) conducted in collaboration with Furtwangen University and plasma technology GmbH. From 2019 to 2022, research was conducted on a novel plasma technology designed to improve the environmental friendliness of plasma etching processes by eliminating the release of HFC emissions.

Problem Statement and Necessity

Global emissions of perfluorocarbons (also known as PFCs, F-gases) are a major contributor to climate change due to their extremely high global warming potential and long atmospheric lifetime. Their use was promoted over 35 years ago as an alternative to ozone-depleting CFC compounds in air conditioning and refrigeration systems, sprays, foams, and insulation materials, as well as fire extinguishing agents.

At the latest since the 2016 Kigali Climate Conference, where 150 countries agreed to a drastic reduction in consumption, climate-damaging perfluorinated hydrocarbons have also been regulated. For industrialized nations, a phased reduction of 85 percent by 2036 was agreed upon, while developing and emerging economies committed to reduction targets of 80 and 85 percent, respectively, by 2047. On the surface, these targets are primarily linked to the rapidly growing demand for air conditioning units, for which natural alternative refrigerants such as ammonia, CO2, or propane are already available today. However, the requirements apply equally to industrial production processes.

Dry or plasma etching processes

Conventional dry or plasma etching processes used in semiconductor and printed circuit board manufacturing employ and release significant quantities of fluorinated greenhouse gases. The substances used as etching gases include:

• tetrafluoromethane (CF₄),
• hexafluoroethane (C₂F₆),
• perfluoropropane (C₃F₈), or
• perfluorobutadiene (C₄F₆).

These have a global warming potential 7,390 times (CF₄) to 12,200 times (C₂F₆) that of CO₂.

From a technological perspective, plasma etching plays a crucial role in printed circuit board and semiconductor manufacturing, given the increasingly complex circuit structures and growing demands on the quality of contact and bonding surfaces. For example, the process is used for back-etching circuit layers in multilayer PCB assemblies, surface activation and patterning, or cleaning through-holes for via formation.

In semiconductor manufacturing, it is used, for example, for substrate patterning as well as for cleaning CVD coating systems. Alternative, HFC-free process gases that offer adequate etch rates, process stability, and processing results, or cleaning systems that ensure effective and energy-efficient removal of the highly stable fluorinated compounds from the process exhaust air, are not yet available. Consequently, there is a significant risk that the absolutely necessary reductions in HFC emissions for the printed circuit board and semiconductor industries will soon become a very concrete problem—not only in Europe, but worldwide.

Objectives of PlasmaKlient

To significantly improve the environmental sustainability of plasma etching processes and thereby ensure their long-term viability, PlasmaKlient researched a novel process and system concept and demonstrated its implementation using printed circuit board applications as an example. The research objective was to be achieved through a multi-stage, hermetically sealed, closed-loop plasma process in which the following process steps are directly interconnected:

• Process stage 1: Generation of reactive fluorine from a target.
• Process stage 2: Transfer of the fluorine into a stably regulated, highly abrasive process atmosphere in the so-called etching stage.
• Process stage 3: Chemical recombination of the unused fluorine residues and recycling of the products back to the initial target.

Results

Using a reference application from the printed circuit board manufacturing industry, we were able to make plasma etching more environmentally friendly. We demonstrated that efficient, HFC-emission-free etching processes are possible in a low-pressure plasma system without compromising the functionality of the printed circuit boards.

The success of PlasmaKlient laid the foundation for making another plasma technology process environmentally and climate-friendly in the future, thereby contributing to innovation and sustainability

PlasmaWood Research Project

The PlasmaWood research project was funded by the BMBF (Federal Ministry of Education and Research—now BMFTR) as part of the “KMU-innovativ: Resource and Energy Efficiency” funding program. The central focus of the project was the sustainable treatment of wooden facades using low-pressure plasma to make them more weather-resistant and durable.

Project Management by Jörg Eisenlohr

Under the leadership of Jörg Eisenlohr (Managing Director of plasma technology GmbH), the research project was carried out from October 1, 2021, to March 31, 2024. Approximately €700,000 was allocated to the government funding program “Tapping the Potential of Wood as a Renewable, CO2-Neutral Building Material.”

Low-Pressure Plasma Technology as a Key Factor

Low-pressure plasma technology has led to the development of an environmentally friendly process designed for the sustainable production of weather-resistant wood facades. Wood is one of the oldest building materials in human history, but it is rarely used in modern construction. The main reason is its lack of resistance to external influences, as well as the need for regular and costly surface treatment, which is why plaster facades (87%) are the preferred choice.

PlasmaWood aimed to create new process solutions to make wooden facades higher quality, more weather-resistant, and thus more cost-effective. Plasma coatings, in particular, are known for making material surfaces more dirt- and water-repellent or for preventing rust formation. In this research project, (low-pressure) plasma technology was applied to wood for the first time to investigate whether new potential for sustainable residential and commercial construction could be unlocked.

Testing Procedure Using a Plasma System

In the first step, small standard samples were examined and tested on a laboratory scale. The initial findings were positive. Coatings applied using low-pressure plasma improved both adhesion and stability on the wood samples.

In the next step, a pilot plant was developed and set up to test the positive plasma effects on larger wood samples. Furthermore, research was conducted to determine whether fungal decomposition could be prevented, and additional additives (biocidal additives) for pest control were tested

Successful Wood Preservation Treatment

The test results were positive. Targeted plasma treatments for wood facade elements made them more robust and weather-resistant.

The key benefits include:

• More weather-resistant and durable wood facades
• Lower maintenance costs for outdoor wood surfaces
• Energy savings compared to conventional facade designs
• CO₂-storing wood as a new alternative to common building materials
• More options for future prefabricated wood buildings in the construction industry

The Future with PlasmaWood

Based on successful research findings, plasma-treated wood elements are suitable as sustainable building materials. However, further fine-tuning and optimization are still needed to make PlasmaWood more economically viable and cost-effective.

Plasma treatments are therefore beneficial for many wood elements when it comes to durability and sustainability. To apply them cost-effectively in industry, similar to green hydrogen, further improvements are still needed.
We at plasma technology GmbH continue to conduct research on this topic to establish wood as a climate-friendly, resource-conserving, and economical element in the construction industry.