Basic Study of Lubrication in Artificial Joints with Compliant Materials

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Friction and lubrication of compliant materials (Siliconrubber, Poly-urehtane and Polyvinylalcohol-hydrogel) versus hard and smooth mateials (Stainless steel, Alumina ceramic and Quartz glass) were measured with a pin-on disk friction testing apparatus. The results shows that start up friction with hydrophobic materials were higher than that with hydrophilic materials. After start up, friction with compliant materials was low and the effect of surface roughness on friction was measured. The start up friction was dependent on standstill time with load and constituents of synovial fluid as lubricant.In the measurement of fluid pressure with a hip joint simulator for lubrication in walking, most of impusive load at heel strike was supported by the fluid pressure. According to the measured frictional torque, sockets of hydrophobic materials result higher friction than the socket of hydrophilic materials in general through the walking cycles. Frictional coefficient was low at high loading due to squeeze film effect in hip joints.Socket of high water content Polyvinylalcohol-Hydrogel resulted high frictional coefficient under high contact pressure due to adhesion between the mating surfaces, and friction decreased with a decrease of contact pressure. When such material is used for an artificial joint, good lubrication condition must be maintained for long term application.