INFLUENCE OF STERILIZATION BY GAMMA-IRRADIATION AND OF THERMAL ANNEALING ON CREEP OF HYDROXYAPATITE-REINFORCED POLYETHYLENE COMPOSITES

Sterilization of medical devices by gamma (gamma)-irradiation is commo n. The effect of irradiation on a bone replacement material, HAPEX(TM) (hydroxyapatite-reinforced polyethylene composite), was investigated. Unfilled and hydroxyapatite-filled polyethylene at 0.20 and 0.40 fill er volume fractions were gamma-irradiated at 2.5 Mrad, and the modifie d properties were studied by differential scanning calorimetery, isoch ronous experiments, and creep tests. The effect of thermal annealing o f the samples from 140 degrees C also was examined. The results sugges t that both irradiation and annealing increase creep resistance of the materials. These are associated with the formation of crosslinks and an increase in crystallinity, respectively. (C) 1998 John Wiley & Sons , Inc.