ISO 11137
Gamma & E-Beam Sterilization for Medical Devices

ISO 11137 Gamma & E-Beam Sterilization for Medical Devices

Gamma and E-Beam sterilization are both radiation based sterilization techniques. While the former is performed by exposing the product to continuous Gamma rays, E-Beam sterilization utilizes Electron beams. Both methods are equally effective, but E-Beam is more powerful and hence the exposure time of the device is lesser. Reusable devices sterilized by these methods must undergo a "Quarterly Dose Audit" to ensure that they meet the established standards and sterilization levels. The frequency of these audits will become lesser as the years progress.

Neither method results in any radioactivity. In fact sterilization through irradiation is considered a "clean and efficient process" as it does not leave any residue on the device and no quarantine period is required once desired sterilization levels have been reached. Furthermore the rays can penetrate dense materials (especially so for Gamma) and closed package products with minimal rise in temperature and effect on the product material (unlike Steam and EtO/gas). E-Beam radiation displays certain limitations when penetrating dense materials (or) products with varying densities.

ISO 11137:

This International Standard specifies requirements for validation, process control and routine monitoring in the radiation sterilization of health care products. It applies to continuous and batch type gamma irradiators using the radionuclides 60 Co and 137 Cs, and to irradiators using a beam from electron or x-ray generator.

The ISO standard also provides information and guidance on equipment, irradiation compatible materials, Dose setting methods and dosimetric aspects for Gamma, E-Beam and X-Ray sterilization. For example the standard explains that all plastics can be classified as materials whose molecules either i) predominantly degrade with irradiation or ii) predominantly crosslink with irradiation. The latter types tend to have higher radiation stability.

Some specific guidelines for material selection are:

  • Aromatic materials are more stable than aliphatic materials
  • High levels of antioxidants help radiation stability. In general, the level of antioxidant should be doubled if the device is going to be radiation sterilized.
  • Most polypropylenes and polytetrafluoroethylene are unstable with irradiation and would need to be stabilized.
  • Phenolic antioxidants contained in most plastics are a cause of discoloration. Use of non-phenolic additives may eliminate the problem.
  • Elastic modulus of plastics is not significantly affected with a sterilizing dose of irradiation.
  • For a given polymer class, the lower the density the greater the radiation stability.