Lubrication of animal joints. iii. the effect of certain chemical alterations of the cartilage and lubricant

The coefficient of friction of dog ankle joints measured in vitro was found to be greatly affected by certain enzymatic treatments of bovine synovial mucin. Testicular hyaluronidase had no effect on its lubricating action even though it abolished the viscosity. By contrast, tryptic digestion destroyed the ability of the mucin to lubricate without reducing the viscosity. These observations indicate that a protein moiety is an intrinsic component of the mucin molecule; and that, together with an only partly polymerized hyaluronate, it is responsible for the mucin's function as a lubricant. The protein may serve as a prosthetic group for adsorption of the mucin onto the surface of the cartilage. Sodium heparin inhibited lubrication by the mucin. In mucin-free buffers, the pH and molarity of the lubricant bath altered both the friction and deformability of the cartilage. The change in friction was not consistently related to the change in deformability. The amphoteric effect of pH on the friction raises the possibility that electrostatic surface effects contribute to adhesive friction. Formalin made the cartilage rigid and increased the coefficient of friction. It did not, however, have much effect on the lubricating action of the mucin. A small number of pathological human synovial fluids were studied and found to lubricate as well or better than healthy bovine material.