A comparison of the effects of gamma-irradiation and ethylene oxide sterilization on the properties of compression moulded poly-d,l-lactide

Compression moulded specimens from two batches of poly-d,l-lactide, of different molecular weights, have been subjected to gamma-radiation and to ethylene oxide (ETO) exposure to establish the effects of sterilizing procedures on potential orthopaedic implants. Materials were exposed to between zero and 10 Mrad, and up to three standard ETO cycles. Tensile properties, dynamic mechanical behaviour, fracture toughness and hydrolytic degradation rates were measured. Molecular weight change was determined by size exclusion chromatography and solution viscosity. Calculated radiochemical yields suggest that the primary effects of irradiation are random chain scission. A clear relationship between properties and molecular weight was established and is used to interpret the relative effects of the two sterilization procedures. With gamma-irradiation scission processes cause a fall in molecular weight in both batches whereas ETO only significantly affected the lower molecular weight batch. It is thought that the ETO effects are determined by moisture diffusion rates which are molecular weight dependent, and therefore property changes with the higher molecular weight material are more limited.