The Rheology of Synovial Fluid and Some Potential Synthetic Lubricants for Degenerate Synovial Joints

A numerical study of non-Newtonian transient elastohydrodynamic lubrication of metal-on-metal hip prostheses

“…In the 1950's two material pairs were 28 investigated; metal-on-metal (MoM) [1] and metal-on-polymer [2]. In the latter case 29 the polymeric acetabular cup was initially made from polytetrafluoroethylene 30 (ptfe/teflon), a bearing material with the lowest known coefficient of friction, but it soon emerged that its wear resistance was inadequate and so an alternative polymer, 1 ultra high molecular weight polyethylene (UHMWPE) was adopted.…”

“…If hard-on-hard material pairs are used it is essential to minimize asperity interactions 28 and wear. The components are manufactured with high accuracy and the smallest 29 realistic roughness.…”

“…reason given for this assumption is that the shear-thinning effect was assumed to be 26 negligible when the shear rate was in a high range of between 10 5 and 10 7 s -1 , 27 governed by the range hip joints typically experience during walking cycles [21]. 28 There are limited numerical studies that investigate the rheology of joint synovial typically ranging from about (10 4 -10 5 ) mPas, at very low shear rates. Furthermore, 16 Cooke et al [28] drew attention to the considerable variation from one subject to 17 another, and even within one subject, depending upon the severity of arthritic In hip joint replacements mean shear rates (≈u/h) are typically in the range (10 6 -10 7 ) 25 1/s and under these circumstances the viscosity attains a near constant value which 26 differs little from that of water.…”

“…28 There are limited numerical studies that investigate the rheology of joint synovial typically ranging from about (10 4 -10 5 ) mPas, at very low shear rates. Furthermore, 16 Cooke et al [28] drew attention to the considerable variation from one subject to 17 another, and even within one subject, depending upon the severity of arthritic In hip joint replacements mean shear rates (≈u/h) are typically in the range (10 6 -10 7 ) 25 1/s and under these circumstances the viscosity attains a near constant value which 26 differs little from that of water. The values adopted for this very high shear rate 27 viscosity generally range from about (1-5) times that of water (0.692 mPas at 37°C).…”

“…The values adopted for this very high shear rate 27 viscosity generally range from about (1-5) times that of water (0.692 mPas at 37°C). 28 In this study the viscosity of synovial fluid at any point in the elastohydrodynamic The pressure variation across the lubricating film thickness was neglected due to the 12 very thin films considered. An average shear rate ( ) was adopted and calculated as 13 the ratio of relative surface velocity to film thickness.…”