How to choose sterilization methods for medical and food silicone products

Those who have worked on projects in the medical or food industry know that only half of the product is qualified, and if the sterilization and disinfection processes are not done correctly, all the previous efforts will be in vain. Silicone parts are widely used in these two industries. This article discusses the common sterilization methods for silicone parts and the impact of each method on silicone.

First, distinguish two words: sterilization is the killing of all microorganisms, including spores, and the sterility requirements for medical devices refer to this level; Disinfection is the process of killing most pathogenic microorganisms and maintaining a daily cleanliness level. The requirements for silicone are completely different between the two.

Ethylene oxide sterilization (EO/EtO)

The most commonly used sterilization method for medical devices. After packaging, the product is placed in a sterilization cabinet and ethylene oxide gas penetrates the packaging to kill microorganisms.

The impact on silicone gel: Silicone gel will adsorb ethylene oxide, and after sterilization, it must be analyzed (ventilated) to release residual gases below a safe concentration. The analysis time ranges from a few hours to over ten days, depending on the thickness and formula of the silicone component.

Applicability: The vast majority of silicone components are compatible with EO sterilization, which is why it has become mainstream. The disadvantages are long cycle time, residue control requirements, and the fact that ethylene oxide itself is a flammable and toxic gas. The qualification requirements for sterilization service providers are high.

Radiation sterilization (gamma ray/electron beam)

Killing microorganisms with high-energy radiation does not require high temperatures or chemical gases.

The impact on silicone: Radiation can cause chain breakage and cross-linking on the molecular chains of silicone, leading to material hardening and discoloration (commonly yellowing). The higher the dosage, the more obvious it is. The performance changes of ordinary silicone after conventional sterilization doses of 25-40 kGy are usually acceptable, but the appearance changes of light colored transparent parts need to be evaluated. The formula optimized 'radiation resistant silicone' has less variation.

Applicability: Suitable for products that are not resistant to high temperatures, one-time mass sterilization, and assemblies with electronic components (sensitive components need to be evaluated). Fast speed and no residue are advantages.

High temperature and high pressure steam sterilization (wet heat sterilization, 121 ℃ or 134 ℃)

The most common sterilization method in hospital supply rooms. The main impact on silicone is repeated high temperatures: silicone itself has no problem with steam resistance and can withstand dozens of cycles, but each cycle accumulates a little compression permanent deformation and hardness change. The lifespan of seals and repeatedly used appliances should be evaluated based on the number of cycles.

Applicability: Standard sterilization method for reusable medical devices (surgical instrument accessories, silicone tubing). Disposable products are not applicable.

Dry heat sterilization: Higher temperatures (above 160 ℃) have a significant impact on the aging of silicone, and silicone components are generally not used.

Other methods

Hydrogen peroxide plasma sterilization (low temperature, increasingly used in hospitals): It has good compatibility with silica gel, but some silica gel formulas may adsorb hydrogen peroxide, and residual verification is needed.

Alcohol wiping disinfection: Daily disinfection, silicone is alcohol resistant, occasional wiping is not a problem, long-term repeated soaking may cause slight swelling of the surface and coating peeling (attention should be paid to parts with spraying).

The actual logic of selecting sterilization methods

Is the product disposable or reusable? Disposable (in vitro diagnostic consumables, disposable surgical accessories) should be treated with EO or irradiation, and sterilized by batches. Reusable instruments are designed and validated according to the sterilization method at the hospital end.

Sterilization validation should be done practically. It should not be a problem with silicone, but rather validated according to ISO 11135 (EO) and ISO 11137 (irradiation), including product performance testing and packaging integrity after sterilization.

The impact of sterilization on performance should be evaluated in the early stages of product development. The same silicone component, whether designed as a radiation resistant formula or a regular formula, has different costs; Should we leave time for EO analysis to affect delivery time.

The food industry is relatively simple: food contact with silicone involves cleaning and disinfection processes (dishwashers, chlorine containing cleaning agents, acid-base cleaning agents), which do not require sterile validation, but require testing for total migration according to food contact material standards. Long term exposure to fats and high temperature foods (such as baking molds) requires attention to oil and temperature resistance when selecting materials.

Sterilization is one of the barriers for silicone components to enter the medical food industry, and it is also a watershed in the capabilities of many factories. Have you ever undergone sterilization validation and can you cooperate with customers to provide sterilization compatibility data? Just ask to know if the other party has really done orders in this industry.