Salt Effects in Mucin Lubrication

Abstract

Animal joints are lubricated by two complementary mechanisms. Weeping lubrication carries most of the joint load hydrostatically, leaving only a small fraction of the total to be carried by rubbing of the solid “skeletons” of the two cartilages. This rubbing is, in turn, lubricated by the synovial mucin; i.e., by long chain polymer molecules dissolved in the joint fluid. There is good evidence that the mucin molecules adsorb to the surfaces and provide boundary lubrication. In this paper we examine further this adsorption processs using a bearing whose two surfaces are rubber and glass, respectively. It is found that the lubricating ability of the mucin is good if it is applied to the bearing in a solution with about physiological salt concentration. At higher salt concentrations the lubrication is comparatively poor, while at zero salt concentration it is very bad indeed. If, on the other hand, the mucin is applied at physiological salt concentration, and then the salt and unadsorbed mucin are washed away with distilled water the lubrication remains good, and has, on occasion, even improved. Once the mucin has been adsorbed the entire range of salt concentration can be explored, with the lubrication becoming worse at high salt concentration and then recovering in greater or lesser degree when the salt is washed off. It seems, then, that the salt concentration affects lubrication in two ways. It can upset the adsorption of the lubricating film, and it can change the lubricating effectiveness of the film once it is adsorbed.

Influence of frequency and amplitude on the mucus viscoelasticity of the novel mechano-acoustic Frequencer™

“…Moreover, there is a minimum in WA for both S1 and S2 at a concentration of NaCl of 0.5 gL −1 . Mc Cutchen and Wilkins observed the same trend for the mucus lubricating ability on glass [44]. We therefore speculate that high ionic strengths lead to a saturation of the negative charges of both glass and mucin's molecular chains and that the physiological NaCl concentration may be the optimum to obtain the minimum WA in vitro.…”