Application of new zirconia/alumina composite ceramics to bearing surfaces of artificial joint prostheses

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We have investigated the biocompatibitity, phase stability and wear properties of Ce-TZP/Al_2O_3 nanocomposite1. Biocompatibility test: We implanted cylinder specimens of CeTZP/Al_2O_3 and Alumina into paraspinal muscles of male Wistar rats. The biocompatibility of CeTZP/Al_2O_3 was almost the same as that of Alumina. For both of ceramics, moderate soft tissue responses were noted at 1 week, and thereafter macrophages and lymphocytes decreased gradually. At 24 weeks, stable encapsulating membranes with some fibrocytes and almost no inflammatory cells were observed for both of ceramics. There were no significant differences of the membrane thickness between CeTZP/ Al_2O_3 nanocomposite and Alumina2. Aging test: Test specimens of CeTZP/AI2O3 and YTZP were kept under various aging conditions (rabbit tibiae, 62°C saline or autoclave). The surface of the specimens was examined after the aging treatments by thin-film X-ray diffraction, and the volumetric fraction of the monoclinic phase was determined. Although Y-TZP showed remarkable phase transformation under in vitro conditions, almost no change m the monoclinic rate was observed for Ce-TZP/Al_2O_3 under all conditions3. Wear test : In water lubrication ( contact pressure ;11.3MPa), the average wear rate of the pin was 2.12±0.37× 10^<-7>mm^3/Nm for Alumina and 0.55±0.04× 10^<-7>mm^3/Nm for Ce-TZP/Al_2O_3. In 30 vol% serum lubrication ( contact pressure ;50 Mpa), there were no remarkable differences in the wear rates of Ce-TZP/Al_2O_3 nonocomposite, Y-TZP and alumina specimens without aging (36 h autoclave). However, the wear rates of Y-TZP with aging were much higher than that of Ce-TZP/Al_2O_3 nonocomposite with agingThe present results suggest that this ceramic is very promising as a bearing component in artificial joint