The role of denatured synovial fluid proteins in the lubrication of artificial joints

• Published in: Biotribology (Oxford) 2019-03, Vol.17, p.49-63
• Main Authors: Stevenson, H., Jaggard, M., Akhbari, P., Vaghela, U., Gupte, C., Cann, P.
• Format: Article
• Language: English
• Subjects: Artificial hip joints, β-sheet fibrils; CoCrMo; Friction; Human synovial fluid; Wear
• ISSN: 2352-5738; 2352-5738
• DOI: 10.1016/j.biotri.2019.03.003

CoCrMo ball-on-flat wear tests were carried out with 25 wt% bovine calf serum (25BCS) and human synovial fluid (HSF) to investigate artificial joint lubricating mechanisms. Post-test the wear scar on the disc was measured and surface deposits in and around the rubbed region were analysed by Micro InfraRed Reflection Absorption Spectroscopy (Micro-IRRAS). In most tests the HSF samples gave higher wear than the 25BCS solution; in some cases, up to 77%. After rinsing a similar pattern of surface deposits was observed in and around the wear scar for both the model and HSF. Micro-IRRAS showed the deposits were primarily denatured proteins with an increased β-sheet content. In some cases, trans-alkyl chain/carbonyl components were also present and these were assigned to lipids. Thioflavin T fluorescent imaging also indicated aggregated non-native β-sheet fibrils were present in the deposits and their presence was associated with lower wear. The formation of insoluble, denatured protein films is thought to be the primary lubrication mechanism contributing to surface protection during rubbing. From this and earlier work we suggest inlet shear induces denaturing of proteins resulting in the formation of non-native β-sheet aggregates. This material is entrained into the contact region where it forms the lubricating film. Patient synovial fluid chemistry appears to influence wear, at least in the bench test, and thus could contributes to increased risk of failure, or success, with metal-metal hips. Finally using 25BCS as a reference screening fluid gives an overly optimistic view of wear in these systems. •CoCrMo wear tests were carried out with model (25BCS) and human synovial fluids.•Surface films formed during the tests were examined to understand their role in the lubrication process.•Human synovial fluid gave higher wear (up to 77% increase), compared to 25BCS which is the standard screening fluid.•Protein-rich deposits are formed around the wear scar. For some HSF samples lipids were also detected.•Synovial fluid proteins shear-denature to form insoluble aggregates with an increased non-native β-sheet content.•ThT fluorescence imaging confirms the formation of non-native β-sheet aggregates with an amyloid-type fibril structure.