Mapping the friction coefficient of AISI 316L on UHMWPE lubricated with bovine serum to study the effect of loading and entrainment at high values of sliding-to-rolling ratio

From an experimental point of view, determining the lubrication regime established between contact surfaces of joint prosthesis using the theory of elastohydrodynamic lubrication is rather impractical due to the intrinsic hindrances to measure the thickness of the lubricant film at the contact area. This claim is supported by the results obtained by experts using optical interferometry to perform such measurements using synovial like fluids. Similarly, research has shown that the complex rheology of the synovial fluid complicates the direct application of EHL theory and plays an important role in the lubrication mechanisms at work in prosthetic devices. Since the natural response of all tribological systems is the frictional force, rather than trying to measure the thickness of the lubricant film to determine the lubrication regime, we measured the effect of loading and entrainment on the friction coefficient at the contact point of an AISI 316L stainless steel sphere loaded against an ultra-high molecular weight polyethylene disc, lubricated with fetal bovine serum solution, at high values of sliding-to-rolling ratio. Applying statistical analysis, we obtained a best-fit model that shows a smooth transition from mixed to full-film lubrication regime.