A study of long-lived free radicals in gamma-irradiated medical grade polyethylene

Ultra-high molecular weight polyethylene (UHMWPE), used in orthopaedic impl ants, was irradiated with gamma rays at room temperature (23 degreesC) in a ir or vacuum, and it was then stored in the same environment for 2 yr at 23 degreesC, 37 degreesC, or 75 degreesC. ESR measurements showed decay as we ll as changes from alkyl to peroxy and polyenyl radicals in air due to reac tion with oxygen. In vacuum, on the other hand, radicals (primarily allyl) decayed without any observable transformation from one type to another. The residual concentrations obtained after 2 yr of post-sterilization storage at 23 degreesC, 37 degreesC, and 75 degreesC were found to be 15-20%, 10-15 %, and 2-10%, respectively. (C) 2001 Elsevier Science Ltd. All rights reser ved.