In the medical device industry, "sterility" is an uncompromising baseline. Whether it's pacemaker leads implanted inside the body or respiratory masks that come into contact with the skin, all medical silicone rubber products must undergo rigorous sterilization before leaving the factory. However, different sterilization methods can affect the physical, chemical, and biological properties of silicone rubber to varying degrees. The challenge lies in ensuring sterility while preserving material performance—a delicate balancing act.

1. Main Sterilization Methods and Mechanisms

Ethylene Oxide (EtO)

Mechanism: Alkylation damages microbial DNA.

Advantages: Strong penetration suitable for complex packaging and heat-sensitive devices.

Impact on Silicone Rubber:

Possible EtO residue or by-products (e.g., ethylene glycol), requiring thorough aeration.

Repeated treatments may cause slight cross-linking, leading to minor increases in hardness.

Widely used for sterilizing silicone rubber, especially implantable devices.

Gamma Ray Irradiation (γ-ray)

Mechanism: High-energy rays damage microbial nucleic acids.

Advantages: Cold sterilization, allows batch processing without residues.

Impact on Silicone Rubber:

High doses (>25 kGy) might lead to main chain scission or oxidation, reducing tensile strength and causing surface stickiness.

Addition-cured silicone rubbers are more radiation-resistant than peroxide-cured types.

Doses should be controlled ≤25 kGy, and antioxidants (like carbon black) can be added.

Electron Beam (E-beam)

Mechanism: Similar to gamma rays but with shallower penetration depth.

Advantages: Fast, no radioactive source.

Impact: Similar to gamma rays but with less thermal effect due to shorter exposure time, making it suitable for thin-walled products.

Steam Sterilization (Autoclave)

Mechanism: 121–134°C saturated steam denatures proteins.

Advantages: Environmentally friendly and cost-effective.

Impact on Silicone Rubber:

Medical silicone rubber can withstand hundreds of cycles (e.g., baby bottle nipples).

Long-term high temperature and humidity may accelerate hydrolysis, particularly if catalyst residues are present.

Not suitable for devices containing electronic components.

Low-Temperature Plasma (e.g., Hydrogen Peroxide Plasma)

Mechanism: Reactive radicals kill microorganisms.

Advantages: Low temperature (<50°C), no toxic residues.

Impact: Minimal damage to silicone rubber but poor penetration, suitable only for surface sterilization.

2. Key Performance Evaluation Metrics

Post-sterilization testing should include:

Physical Properties: Changes in hardness, tensile strength, and elongation at break ≤15%.

Chemical Properties: Extractables and residual monomers comply with ISO 10993-17.

Biological Properties: No worsening of cytotoxicity or sensitization.

Appearance: No yellowing, exudation, or sticky surfaces.

3. Selection Recommendations

Device Type  Recommended Sterilization Method      Reason

Implantable catheters, prostheses   EtO or low-dose γ-ray      Balances sterility and material stability

Disposable breathing masks    γ-ray or E-beam Efficient for large batches

Reusable silicone nipples   Steam sterilization      Safe and usable at home

Flexible patches with electronic sensors Low-temperature plasma  Avoids thermal/radiation damage

4. Frontier Trends

Sterilization Compatibility Design: Development of high-purity silicone formulations with low catalyst residue.

Online Monitoring: Embedding indicator labels to provide real-time feedback on sterilization effectiveness.

Green Sterilization: Promoting environmentally friendly alternatives like hydrogen peroxide and ozone.

Conclusion

A small silicone tube must traverse the "last mile" of sterility from production to clinical use. Each sterilization process tests the limits of the material. Through deep understanding of the interaction between sterilization and materials, engineers ensure that when these items enter the human body, they are not only sterile but also maintain their life-preserving flexibility and reliability. Because sterility is never just about killing bacteria—it’s about respecting the wholeness of life itself.



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