Submission Abstract (max 120 words)In vitro buffers are frequently used to formulate model synovial fluids to investigate the role of individual constituents in synovial joint lubrication. This work examines how buffer choice affects protein film formation in static and rolling conditions. Solution pH dominates both the protein adsorption kinetics and the formation of tribofilms in static and rolling conditions respectively. Under static conditions, equilibrium adsorbed protein films from all buffers tested have similar properties although three distinct modes of adsorption, governed by the pH of the buffer, are observed. Films formed under rolling conditions are also pH dependent, with large irregular deposits formed in solutions with pH 7.4 or lower, The adsorption properties of proteins under static conditions only partially govern the lubrication properties of proteins.
AbstractSynovial fluid contains proteins which can participate in surface film formation and the lubrication of artificial joints. In laboratory experiments, model synovial fluids with a range of buffers are frequently used by various investigators. Buffer compositions with different pH, ionic strength and buffer chemistry may affect protein adsorption, and hence film formation. To clarify the role of buffers in protein film formations, the static adsorption of BSA in a selection of buffers is studied using a quartz crystal microbalance. Three distinct modes of adsorption are observed, but on reaching equilibrium, the adsorbed BSA layers have similar viscoelastic properties in all buffer solutions. The static adsorption results are compared with lubricants film formed in model rolling contacts. Films formed under rolling conditions are pH dependent. Thin, uniform films consistent with adsorbed films, and nonuniform films, with large irregular deposits are formed in high and low pH solutions respectively. The results show that the pH of the solution dominates both the adsorption kinetics of proteins under static conditions and the formation of tribofilms in rolling conditions. However, the adsorption properties of proteins under static conditions only partially govern the lubrication property of protein solutions.
A B S T R A C TA new test was developed to measure friction and wear of hip implant materials under reciprocating sliding conditions. The method requires a very small amount of lubricant (< 3 ml) which allows testing of human synovial fluid. Friction and wear of Cobalt Chromium Molybdenum (CoCrMo) material pairs were measured for a range of model and human synovial fluid samples. The initial development of the test assessed the effect of fluid volume and bovine calf serum (BCS) concentration on friction and wear. In a second series of tests human synovial fluid (HSF) was used. The wear scar size (depth and volume) on the disc was dependent on protein content and reduced significantly for increasing BCS concentration. The results showed that fluid volumes of < 1.5 ml were affected by evaporative loss effectively increasing the protein concentration resulting in anomalously lower wear. At the end of the test thick deposits were observed in and around the wear scars on the disc and ball; these were analysed by Infrared Reflection-Absorption Spectroscopy. The deposits were composed primarily of denatured proteins and similar IR spectra were obtained from the BCS and HSF tests. The analysis confirmed the importance of SF proteins in determining wear of CoCrMo couples.
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