Gamma and ethylene oxide (EO) sterilization are two widely used, versatile and effective methods in medical device manufacturing. Deciding whether a medical device is better suited for gamma or EO sterilization starts with a material evaluation of the medical device and associated packaging. Gamma and EO methods implement distinct scientific mechanisms and reactions to result in sterility. Alec Respecki, Packaging Engineer II, explains how each material interacts with sterilization agents and how to choose the best sterilization method.
What is Gamma Sterilization?
Gamma sterilization eliminates microorganisms using high-energy gamma rays. This sterilization technique exposes the packaged medical device to high-energy photons generated from the decay of a radioisotope known as Cobalt 60. The exposure disrupts the cellular structure of bacteria, fungi, etc. preventing them from multiplying.
Advantages of Gamma Sterilization
- Compatible with most packaging materials, including non-porous film and foil pouches
- Relatively fast cycle times
- Excellent penetration through a wide variety of packaging
The advantages of gamma sterilization make it the ideal choice for moisture-sensitive medical devices that require non-porous packaging materials. For example, a product such as a sterile wound dressing or cleansing pad must retain its moisture until point-of-use.
Disadvantages of Gamma Sterilization
- Cannot be used for electronic medical devices with a battery since the radiation can cause the battery to explode.
- Not suited for some medical devices with plastic polymers due to:
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- Radiation-induced degradation causing discoloration/yellowing of plastics
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- Cross-linking—affecting the molecular structure (long-chain molecules) of the plastics making them brittle or rigid
- Can increase seal strength values via chemical changes in adhesives during the sterilization process
- Requires an expensive and limited resource, Cobalt 60
- Routine dose audits require real product each fiscal quarter for bioburden and sterility testing.
Gamma Sterilization Takeaways
If a medical device contains technology, gamma sterilization may not be an option—radiation can damage or destroy batteries and circuitry. These devices must instead use EO sterilization or other methods such as X-ray or E-beam.
For devices consisting of plastic polymers, gamma sterilization can pose problems as well. Gamma radiation drives oxidation in many plastics, which can discolor or degrade both device materials and packaging. Gamma exposure can also cause cross-linking, changing the plastic’s molecular structure. This stiffens or weakens flexible packaging and polymer components, increasing the risk of cracking or failure.
Adhesives may be affected as well. Radiation-induced chemical changes at the seal interface can increase seal strength, making packages harder to open. In a surgical setting, this can compromise aseptic technique or cause drops due to excessive opening force.
Despite these risks, gamma sterilization offers excellent penetration, speed, and versatility. Issues can be mitigated through careful material selection, thoughtful device design, and post-sterilization validation testing.
What is EO Sterilization?
Ethylene Oxide (EO) gas effectively kills microorganisms by denaturing proteins and chemically breaking bonds with free radicals. Unlike gamma sterilization, EO sterilization must have packaging with a porous or breathable component like Tyvek® or medical grade paper. The breathable component must comprise a portion of the packaging so the EO gas can penetrate the sterile barrier system and adequately contact the medical device.
Advantages of EO Sterilization
- Ideal sterilization method for devices that contain electronics, circuit boards and batteries, which do not react to EO
- Highly effective for textile products and sutures, maintaining the soft, spongy nature of fabrics and threads.
Disadvantages of EO Sterilization
- Highly flammable and explosive
- Exposure to EO can be carcinogenic, requiring stringent practices and oversight
- Longer cycle times
- Packaging must have a porous component
- EO residuals are possible, requiring additional processing time for off-gassing
Ethylene Oxide Sterilization Takeaways
Despite the strict handling and exposure controls required at EO sterilization facilities, EO is often a suitable option for medical device sterilization.
When gamma sterilization is not feasible, EO becomes the primary alternative. For example, a medical drill containing a lithium-ion battery cannot undergo gamma sterilization, making EO the logical choice. To meet EO’s porosity requirements, Tyvek or medical-grade paper must be incorporated into the packaging.
Key Takeaways
Evaluating the device and packaging materials is the key to determining which sterilization method is best for your project. For porous packaging materials and electronic devices, EO is a good option. For non-porous packaging materials and devices without a battery, gamma is a safe choice. Devices without sensitivities, such as those made entirely out of metal, allow greater flexibility in selecting a sterilization method. Metals are generally nonreactive, so most sterilization modes are viable. Overall, let the materials guide the way.
The jury is still out on the environmental, sustainability and human health concerns that are unique to sterilization. As always, industry partnering, collaboration and bold experimentation can lead to previously unimaginable breakthroughs.