Material Selection Requirements
Sterizability is a requirement for material selection in many medical devices. Common sterilization techniques include boiling water, disinfectants, dry heat, autoclaving (high pressure steam), ethylene oxide (ETO) and radiation. Each technique presents unique challenges and opportunities. Polycarbonate is one of the few plastics that can be sterilized with dry heat (120°C). However, it degrades a little each time imposing a limit on the number of times the sterilization can be repeated. ETO sterilization is done at moderate temperatures and is suitable for those materials that do not fare well in dry heat or autoclaving. Some plastics like nylons retain ethylene glycol and ethylene cholorohydrin (by-products of sterilization) and could release in human contact situation later which would be objectionable. General rule is not to use ETO if it can be autoclaved. Both ETO and gamma radiation can affect mechanical properties of plastics. Gamma radiation may cause some loss of optical properties and discoloration; and can also cause crosslinking. Crosslinking affects some material negatively (polypropylene, butyl rubbers etc.) and some positively (crosslinked polyethylene increased in flexural strength). |