Materials sensitive to the sterilization sequence mainly include polycarbonate (PC), polyvinyl chloride (PVC), silicone, porous or hygroscopic materials, and some modified plastics. Their performance may significantly decrease due to improper sterilization sequence.
1. Easily hydrolyzed materials: Polycarbonate (PC)
Sensitive sequence: S → G (Steam → Gamma)
Reason: After steam sterilization, the material's moisture content increases, making it prone to hydrolysis during subsequent gamma irradiation, leading to molecular chain breakage, a sharp drop in impact strength, and yellowing (ΔE > 3).
Optimization suggestions: Avoid steam sterilization followed by irradiation; if this is necessary, add 4–6 hours of drying at 120°C before G, and control the transport time to < 2 hours.
2. Heat-Sensitive Material: Polyvinyl Chloride (PVC)
Sensitivity Sequence: S → EO or Continuous High-Temperature Steam
Reason: PVC softens and deforms easily under high temperature and humidity, and residual moisture hinders EO gas penetration, reducing sterilization effectiveness.
Optimization Recommendation: Prioritize the EO → S sequence, ensuring dryness before steam treatment; control the cooling rate after steam sterilization to prevent deformation.
Example: In the testing of infusion bag components, using G → EO instead of S sterilization successfully prevented structural collapse.
3. Swelling-Sensitive Material: Silicone
Sensitivity Sequence: S → EO or High-Dose EO
Reason: After steam sterilization, the microporous structure of silicone expands, making it prone to swelling and precipitation of small molecules upon contact with EO, affecting sealing and biocompatibility.
Optimization Recommendations: Use a low dose of EO (450 mg/L) and ensure thorough drying before EO; the recommended sequence is G → EO → S to reduce cumulative damage to the silicone.
Practical Case: After three cycles of G→EO→S, the hardness change of the breathing mask sealing ring was <8%, with no precipitation.
4. Porous or Closed-Structure Materials
Sensitive Sequence: S → EO
Reason: Residual moisture after steam sterilization hinders EO gas diffusion, leading to incomplete sterilization (false negatives), especially in closed structures such as catheters and valves.
Optimization Recommendations: EO must be applied before S to ensure gas sterilization is completed in a dry environment; if steam is required, vacuum drying should be performed before S.
Recommended Institution: Wuhan Institute of Pharmaceutical and Medical Device Testing provides porous device penetration validation services and supports ATP testing and microbial challenge testing.
5. Modified Plastics (e.g., radiation-resistant PC, toughened PBT)
Sensitivity Order: G → S → G (Double irradiation + high temperature)
Reason: Although radiation-resistant, high-temperature steam accelerates free radical reactions, leading to aging phenomena such as yellowing, fogging, and embrittlement.
Optimization Recommendations: Control total irradiation dose < 50 kGy; check moisture content before each G treatment to ensure < 0.05%.
