Interactions Between Bilayers of Phospholipids Extracted from Human Osteoarthritic Synovial Fluid

Duncan Dowson, whom this issue commemorates, was a world leader in the field of biotribology, with prolific contributions both fluid-based and boundary lubrication biological tissues, particular articular cartilage, central biotribology due to its importance for joint homeostasis. Here we explore further cartilage lubrication, which has been attributed phospholipid (PL)-exposing layers at surface part. A force balance (SFB) unique sensitivity is used investigate normal frictional interactions formed by PLs extracted from osteoarthritic (OA) human synovial fluid (hSF). Our results reveal that vesicles OA-hSF lipids rupture spontaneously form bilayers on mica substrate (which, like in-vivo joints, negatively-charged) then undergo hemifusion quite low pressures SFB, large heterogeneity hSF lipids. Nanometric friction measurements coefficients mu = ca. 0.03 across hemi-fused bilayer these lipids, indicating residual hydration lipid-headgroup vs. interface. Addition calcium ions causes an increase 0.2, either calcium-bridging attraction lipid headgroups negatively-charged substrate, or shift slip plane more dissipative hydrophobic-tail suggest composition may be associated higher layers, thus connection greater wear degradation, exposed bilayers.