ADAPTIVE MULTIMODE LUBRICATION IN NATURAL SYNOVIAL JOINTS AND ARTIFICIAL JOINTS

To examine the lubrication mechanisms in both natural synovial joints and artificial joints with artificial cartilages, pendulum tests of pi g shoulder joints and simulator tests of sliding pairs of a stainless steel spherical component and natural articular cartilage or artificia l cartilage have been conducted.Firstly, it was shown in pendulum test s of pig shoulder joints that both concentration of hyaluronic acid or viscosity and adsorbed film formation of proteins and phospholipids e xerted a significant effect on frictional behaviour in swinging motion immediately after a loading of 100 N. Under a high load of 1 kN, low friction was observed under wide-ranging viscosity conditions, since a high load similar to body weight probably enhanced the squeeze film e ffect due to improved congruity. Next, frictional behaviour of sliding pairs in knee joint models, consisting of a stainless steel spherical surface and either specimens of pig tibial cartilage or polyvinylalco hol (PVA) hydrogel, was examined during walking in simulator tests. In these tests, the influences of lubricant viscosity and addition of pr otein on frictional behaviour were evaluated. For both compliant mater ials, the appropriate addition of gamma-globulin to sodium hyaluronate (HA) solution maintained low friction and protected rubbing surfaces under thin film conditions. These phenomena are discussed from the vie wpoint of adaptive multimode lubrication.