The Effect of Synovial Fluid Constituents on Boundary Lubrication of Superficial Area of Articular Cartilage

In this study, the complementary lubricating function of the superficial area of the articular cartilage and synovial fluid (SF) constituents was examined. The cartilage specimens underwent two different degenerative treatments: gentle washing with detergent to remove lipids and proteins absorbed onto the cartilage surface and incubation in a NaCl solution to remove lubricin from the surface. Sliding experiments with a glass probe and cartilage specimens were conducted at various speeds and low contact loads using lubricants containing SF constituents, such as phospholipids, proteins, and hyaluronic acid (HA). The treated cartilage surface and protein adsorption were observed using a fluorescence microscope and water immersion objectives to explore the underlying mechanisms of the difference in friction. The results showed that fresh SF exhibited low friction even after degenerative treatment. HA and phospholipids had no boundary lubrication effect, whereas the lubricant containing albumin and γ-globulin maintained a consistently low coefficient of friction, even after degenerative treatment. The significance of the interaction between albumin and γ-globulin should be emphasized.

Graphical abstract