Importance of adaptive multimode lubrication mechanism in natural and artificial joints

Abstract

The healthy natural synovial joints maintain excellent load-carrying capacity and lubricating properties with extremely low friction and minimum wear even under heavily loaded conditions. The superior lubricating performance appears to be actualized by not single lubrication mode but the synergistic combination of various modes depending on the severity of operating conditions. This mechanism is called adaptive multimode lubrication and the application of this good working lubrication mechanism to artificial joints with soft layer is expected to contribute to remarkable improvement in longevity of joint prostheses. However, some of detailed mechanisms in natural synovial joints have not yet been clarified. In this article, the effectiveness of biphasic lubrication in natural synovial joints was examined by biphasic finite element analysis under both the on–off loading (migrating contact) and the continuous loading (continuous contact) to cartilage. Then, the method to suppress the gradual rising in friction for articular cartilage under the continuous loading is discussed. Finally, the effectiveness of fibre reinforcement in hydrogel artificial cartilage was examined in walking simulator test.