Elucidation of Adaptive Multimode Lubrication Mechanism and Self-Organization in Natural Synovial Joints

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The object of this research is to elucidate the adaptive multimode lubrication mechanism in natural synovial joints in relation to the self-organization 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 phospholipid liposome and γ-globulin was effective … More in lowering of friction. 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 change 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 based on finite element method was conducted to examine the influence of compressive stimulation on chondrocyte in articular cartilage. The morphology and distribution of chondrocytes in articular cartilage were investigated by confocal laser scanning microscopy (CLSM) to construct the three-dimensional model. It was noticed that the local strain near surface had larger value than average one immediately after compressive loading and recovered to the average level. This local high strain has the possibility to have a remarkable effect on the chondrocyte located in those zones. The changes in strain were observed by CLSM. Less