Abstract
Ultra-High Molecular Weight Polyethylene (UHMWPE) is widely used as a bearing material in artificial joints. However, UHMWPE wear particles are considered to be a major factor in long-term osteolysis and loosening of implants. Many researchers have reported that the volume and size of particles were critical factors in macrophage activation, with particles in the size range of 0.1-1 gm being the most biological active. To minimize the amount of wear of UHMWPE, and to enlarge the size of UHMWPE wear particles, a counterface material of Co-28Cr-6Mo alloy was processed using micro slurry-jet erosion (MSE). The slurry used in this analysis consisted of alumina particles mixed with water, which was then combined with compressed air within an injection nozzle. The slurry was ejected onto the Co-Cr-Mo alloy at a high speed to process a superfine surface. Four types of Co-28Cr-6Mo alloy surface profiles were prepared; M-1, M-2, and M-3 were processed by MSE. The feed rate of injection nozzle for processing of M-1 was 1mm/s. That for M-2 was 2 mm/s to reduce the MSE effect in comparison to for M-1. M-1 was lapped with nano-diamond to reduce the asperity on the surface, and the processed surface was represented for M-3. The conventional artificial joint surface was represented by G-1, which had a 10 nm surface roughness, as a control surface. A pin-on-disc wear tester capable of multidirectional motions was used to test if MSE processing was the most appropriate for artificial joints. It was found that the processed surface reduced the amount of UHMWPE wear, which would ensure the long-term durability of artificial joints. A scanning electron microscope was used to measure the size of the UHMWPE wear particles. A significant difference was not observed in the aspect ratio of the wear debris, and many wear particles greater than or equal to 1.0 gm in size were observed.
