No abstract

The effects of radiation sterilization on ultrahigh molecular weight polyethylene were explored by freeze fractures, electron spin resonance, absorption of aqueous media, density measurements, small-angle and wide-angle x-ray scatter, differential scanning calorimetry, infrared and ultraviolet-visible spectrometry, static and dynamic mechanical fatigue measurements, and standard environmental stress cracking measurements. The rate of fluid absorption increased significantly due to the appearance of carbonyl groups. As the fluids were absorbed, density increased and small-angle x-ray scatter (SAXS) intensity diminished slightly, as expected. Small changes in mechanical properties (e.g., tensile properties and dynamic spectrum) were always consistent with the cross-linking which occurs after irradiation; the only significant mechanical deterioration was in the fatigue properties. The nonspherulitic, inhibited crystallinity which characterized this material and which is responsible for its excellent static resistance to environmental stress cracking was not at all changed.

SynopsisUltrahigh molecular weight polyethylene is now extensively used in total joint replacements, and there is ample clinical evidence that this material wears at a significant rate in such applications.Six commercially available total hip replacements were subjected to an accurate simulation of clinical mechanical and chemical conditions, and the wear behavior of the polyethylene components was analyzed by friction coefficient measurements and scanning electron micrography of the wear surfaces. The results indicate that all of the proposed wear mechanisms excepting adhesive and abrasive wear may be eliminated. It is highly likely that abrasion fatigue and related phenomena are central to the wear process in many prostheses, but the wear process may be ultimately determined in many cases by the type of defects present in the manufactured material.

No abstract