Elucidation of Adaptive Multimode Lubrication Mechanism in Natural Synovial Joints from Hierarchic and Microscopic Viewpoints

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The object of this research is to elucidate the adaptive multimode lubrication mechanism in natural synovial joints from the hierarchic and microscopic viewpoints.The systematic investigation was performed to clarify the adaptive multimode lubrication mechanism in natural synovial joints. Experimental evaluation of fluid film formation in knee joint model in simulator and numerical analysis showed the important role of elastohydrodynamic lubrication during walking. In friction tests of pig shoulder joints by pendulum method, the influence of hyaluronate concentration on frictional behavior under high and low load conditions was clarified in related to removal of adsorbed films or addition of phospholipid or proteins. The boundary lubrication by adsorbed film composed of phospholipids, proteins and glycoproteins was clearly shown by an increase in friction after removal of adsorbed film. Addition of liposome of phospholipid liposome and gamma-globulin was effective in lowering of fricti … More on. Reciprocating tests of sliding pair of articular cartilage and Langmuir-Blodgett film formed on glass plate indicated the superiority of mixed film of phospholipid and protein to phospholipid film. The protecteive effect by mixed adsorbed film was confirmed in in-vivo tests. The atomic force microscopy (AFM) was applied to observe the changes in articular cartilage surfaces at different friction levels during rubbing process. The corresponding force-distance curves at several friction levels were examined. These results indicated that lubricating roles of adsorbed film and gel film changes with progressive wear process. The tribological property of polyvinyl-alcohol (PVA) hydrogel specimen as artificial cartilage was compared with that of natural articular cartilage to clarify the difference between both materials. The three-dimensional numerical analysis was planned to examine the influence of shearing stimulation on chondrocyte in articular cartilage which was found in continuous shearing test to monolayer of cultured chondrocyte in cone/plate viscometer inducing the remarkable increase in interleukin 6 (IL-6). Less