The effects of degree of crosslinking on the fatigue crack initiation and propagation resistance of orthopedic-grade polyethylene.
Crosslinked ultrahigh molecular weight polyethylene (UHMWPE) has been recently approved by the Food and Drug Administration for use in orthopedic implants. The majority of commercially available UHMWPE orthopedic components are crosslinked using e-beam or gamma radiation. The level of crosslinking is controlled with radiation dose and free radicals are eliminated through heat treatments to prevent long-term degradation associated with chain scission or oxidation mechanisms. Laboratory studies have demonstrated a substantial improvement in the wear resistance of crosslinked UHMWPE. However, a concern about the resistance to fatigue damage remains in the clinical community, especially for tibial components that sustain high cyclic contact stresses. The objective of this study was to investigate both the initiation and propagation aspects of fatigue cracks in radiation crosslinked medical-grade UHMWPE. This work evaluated three levels of radiation, which induced three crosslink densities, on the fatigue crack propagation and total fatigue life behavior. Both as-received UHMWPE, as well as those that underwent an identical thermal history as the crosslinked UHMWPE were used as controls. Fractured crack propagation specimens were examined using scanning electron microscopy to elucidate fatigue fracture mechanisms. The results of this work indicated that a low crosslink density may optimize the fatigue resistance from both a crack initiation and propagation standpoint.
Baker
D A
DA
Department of Mechanical Engineering, University of California, Berkeley, California 94720.
Bellare
A
A
Pruitt
L
L
D000180:Acrylic Resins / Q000737:chemistry* / Q000528:radiation effects; D001672:Biocompatible Materials / Q000737:chemistry* / Q000528:radiation effects; D004868:Equipment Failure; D019544:Equipment Failure Analysis; D006358:Hot Temperature; D008855:Microscopy, Electron, Scanning; D009983:Orthopedic Equipment; D011095:Polyethylenes / Q000737:chemistry* / Q000528:radiation effects; D019736:Prostheses and Implants; D013314:Stress, Mechanical; D014961:X-Ray Diffraction
D000180:Acrylic Resins; D001672:Biocompatible Materials; C477624:GUR 1050 resin; D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene