Elucidation of Adaptive Multimode Lubrication, Deterioration and Restoration 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 and to clarify its relation to degradation and restoration.The systematic investigation was performed to elucidate the adaptive multimode lubrication 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. Impact tests of synovia and articular cartilage exhibited the existence of protecting film of proteins, particularly gamma-globulin after testing and impact-induced electrical phenomena of cartilage. 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 effect of added proteins. The boundary lubrication by adsorbed film composed of phospholipids and proteins was clearly shown by an increase in friction after removal of adsorbed film. Addition of liposome of phospholipid and protein was effective in lowering of friction. Reciprocating tests of sliding pair of articular cartilage and Langmuir-Biodgett film formed on glass plate indicated the superiority of mixed film of phospholipid and protein to phospholipid film.The continuous shearing to monolayr of cultured chondrocyte in cone/plate viscometer showed the remarkable increase in interleukin 6 (IL-6). This suggests that the shearing stimulation due to inferior lubrication plays an important role in deterioration and restoration in osteoarthritis.