| Summary: | 博士 === 國立陽明大學 === 醫學工程研究所 === 96 === Patients suffering from serious arthritis may require artificial joint replacement surgeries. When compared to the articulation of articular cartilages, the artificial joint undergoes a boundary lubrication in which a thin layer of synovial fluid molecules was formed between the artificial joint materials. Therefore, a larger wear rate was observed in the artificial joint system. Many researchers have devoted themselves to modifying the artificial joint materials in order to reduce the wear phenomena. Therefore, we previously proposed that a modification of the lubrication by adding effective lubricating molecules may help to reduce the wear of artificial joint. However, with this previous study outcome still lacked a fundamentally understanding of the artificial joint lubrication mechanism under synovial fluid.
Hence, we investigated the boundary lubrication behaviors of synovial fluid molecules, such as albumin, globulin, hyaluronic acid, and lipid as well as retrieved synovial fluids in this study. We obtained the tribological behaviors of the single molecule as well as multiple molecules on the surfaces of artificial joint materials by experiments. The analysis platform was established to perform the composition and properties measurement of the synovial fluid molecules. Both the clinical retrieved synovial fluid and pure chemicals of the synovial compositions were tested in the friction tests. The correlations between the friction characteristics and synovial compositions were summarized. The measurement of friction coefficient of a single biomolecule showed that phospholipids led to a smaller friction coefficient. The friction coefficient of globulin was much higher than those of the others. The friction coefficient of albumin solution increased with increasing concentrations. The addition of phospholipids in the albumin solution led to an increase of friction coefficient. The friction coefficient of globulin solution decreased with increasing concentrations. The addition of phospholipids in the globulin solution led to a reduction of friction coefficient.
Furthermore, studies were carried out to investigate the effect of tribological and thermal process induced conformational change of human serum albumin on the friction characteristics. Albumin acted as an interfacial molecule in the boundary lubrication regime. The results indicated that a decrease of ��-helix content and an unfolding of the secondary structure of albumin were possibly induced by the friction heat during UHMWPE-metal articulation process. The conformational change of albumin affected the frictional characteristics of polyethylene and cartilages. A model describing the frictional features of the conformational change of albumin on the hydrophilic cartilage and the hydrophobic UHMWPE was also proposed.
Key words: artificial joint replacement, boundary lubrication, synovial fluid molecules, wear, albumin, globulin, hyaluronic acid, lipid, tribological behaviors, friction coefficient, conformational change
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