Ethylene oxide sterilization: "It is a product-neutral process"

Many medical devices must be sterilized before use to prevent infections in patients. COMPAMED.de spoke with Patrick Radermacher of STERISYS, about the possibility of cold sterilization with ethylene oxide.

Mr. Radermacher, your company offers turnkey ethylene oxide sterilization systems for its customers. Can you explain the process?

Patrick Radermacher: Our clientele includes medical device manufacturers and sterilization service providers. We are experts in the design, construction, on-site installation, and commissioning of ethylene oxide sterilization systems. This process is one of two industrial sterilization processes. Between 50-55 percent of all medical devices produced in the world are sterilized using ethylene oxide gas. The other industrial process is radiation sterilization.

Ethylene oxide gas is introduced into a hermetically sealed chamber, which houses the ready-to-be-sterilized medical devices. The gas penetrates the different types of packaging and destroys most bacteria, viruses, and microbes (fungi) on the surfaces of the devices. This means cellular reproduction is disrupted at the microbiological level, thereby sterilizing the products.

After sterilization, the packaging for medical devices ensures safe handling at medical practices and hospitals, preventing the risk of contamination of the equipment as this would have catastrophic consequences for the patients. Non-sterile medical devices could lead to infections during treatment.

Does the gas sterilize both the outer layers of packaging and the package contents?

Radermacher: The primary packaging of medical devices contains a barrier or foil that is partly gas-permeable – the so-called Tyvek film.  The gas slowly works its way through the various cardboard layers, through the Tyvek film of the primary barrier, all the way to the medical devices. In doing so, both the medical devices and the complete packaging are sterilized.

What devices are sterilized with ethylene oxide? Are there exclusion criteria?

Radermacher:  Ethylene oxide sterilization is product neutral and does not cause changes to the physical and mechanical properties of the materials in medical devices. It is a so-called cold gas sterilization process (with temperatures typically between 45 and 55°C), which makes it ideal for the sterilization of so-called thermolabile and single-use medical devices. For obvious reasons, the latter cannot be disinfected using hot steam sterilization (at sterilization temperatures of about 130°C). The use of radiation sterilization (gamma or x-ray) is also limited, as this process adversely affects the physical and chemical properties of certain plastics during the sterilization process – for example, PVC becomes brittle after intensive irradiation.

You offer overpressure and vacuum sterilization systems. What is the difference?

Radermacher: More than 90 percent of globally produced devices that are sterilized with ethylene oxide undergo the vacuum sterilization process. It is a process that has continuously evolved over the past 50 to 60 years and is particularly suitable for a high throughput production. The products are packed in cardboard boxes and loaded onto a Euro-pallet. These are then containerized in 8 to 32 Euro-pallet sterilizers, i.e., sterilization chambers sized at up to 120 m³.  After this, the doors are tightly sealed, a vacuum is created inside the chamber, humidifying steam is added and the gas is introduced. After a validated gas exposure time, the devices are sterile, and the chamber is washed via successive vacuum and ventilation phases until the sterilization process is completed. The whole process of sterilization including the ethylene oxide gas dwell time happens under a vacuum – hence the name vacuum sterilization process. Higher gas concentrations are needed since a sterilization batch can include medical devices with different packaging types. This can be easily achieved with a high yield (90 percent ) ethylene oxide.

The so-called ethylene oxide overpressure sterilization process is particularly suitable for small to mid-sized sterilization batches of 500 to 7000 liters of chamber volume, or products that are mainly sterilized in their primary packaging, where the sterilization process can be easily integrated into the medical device manufacturer’s existing production flow. The sterilization cycle resembles the described vacuum sterilization process, except the gas holding phase during the sterilization cycle is held at an overpressure of 1.75 – 2.0 bar. The overpressure in the chamber produces a much more dynamic penetration behavior of the ethylene oxide into the products, which allows the use of a low concentration (for example, 7-15 percent) ethylene oxide gas mixture.  

What type of system and process should customers choose?

Radermacher: The choice of vacuum or overpressure sterilization process depends on several customer-specific product and process requirements and thus necessitates a case-by-case analysis. That said, the general rule is: If the client wants a sterilization volume of 500 to 7000 liters, we typically suggest the overpressure process. This applies if the dimensions of the sterilizer chamber are meant to be aligned with the dimensions and volumes of the medical devices that require sterilization. For larger volumes and pre-packaged products that are loaded onto pallets, we generally recommend the vacuum sterilization process.

You were one of the exhibitors at the last virtual MEDICA/COMPAMED trade fair. How did you like the format?

Radermacher: We have received "virtual" inquiries but from our point of view, you simply cannot compare things to the typical in-person trade fair event in Düsseldorf.  I think virtual trade fair visitors still have to get used to the new process. Hopefully, the next MEDICA/COMPAMED trade fair can take place in the usual format.