Sterilization

Sterilization is a critical process for medical devices that come into contact with sterile body tissues or the vascular system. It involves validated methods to achieve a defined sterility assurance level (SAL), typically 10⁻⁶, meaning the probability of a viable microorganism being present is less than one in a million.

Common sterilization methods:

1. Ethylene Oxide (EtO) Sterilization
- Low-temperature process (37-63°C)
- Suitable for heat-sensitive materials
- Penetrates packaging and device lumens
- Regulated by ISO 11135
- Requires aeration to remove residuals
- Environmental concerns due to emissions

2. Gamma Radiation Sterilization
- Uses Cobalt-60 isotope radiation
- Room temperature process
- Excellent material penetration
- Suitable for sealed, final packages
- Regulated by ISO 11137-1, 11137-2
- Can affect polymer properties

3. E-beam (Electron Beam) Sterilization
- Uses accelerated electrons
- Faster than gamma radiation
- Lower penetration depth
- Regulated by ISO 11137-1, 11137-2
- More precise dose control
- Growing popularity for sustainability

4. Steam Sterilization (Autoclave)
- High temperature (121-134°C) with saturated steam
- Most economical method
- Limited to heat-stable materials
- Regulated by ISO 17665
- Common for reusable surgical instruments
- Short cycle times

Sterility Assurance Level (SAL):
The probability of a single viable microorganism occurring on a product after sterilization:
- SAL 10⁻⁶ - Standard for most medical devices
- SAL 10⁻³ - Low-temperature sterilization, some Class I devices

Validation requirements:
Manufacturers must demonstrate:
- Installation Qualification (IQ)
- Operational Qualification (OQ)
- Performance Qualification (PQ)
- Routine monitoring and revalidation
- Bioburden testing before sterilization
- Sterility testing after sterilization

Key standards:
- ISO 11135 - EtO sterilization
- ISO 11137 (parts 1-3) - Radiation sterilization
- ISO 17665 (parts 1-3) - Steam sterilization
- ISO 11138 - Biological indicators
- ISO 11737 - Microbiological methods

Regulatory considerations:
- Must be validated according to ISO standards
- Part of Quality Management System (ISO 13485)
- Included in Design History File (DHF)
- Critical for Class II and III sterile devices
- Requires stability testing post-sterilization