The Lubricating Activity of Phospholipids on Charged and Neutral Surfaces

Abstract

In this paper, the amphoteric character of cartilage surface is used to study friction between charged (+/+), (−/−), and uncharged (±/±) biological surfaces. The surface of the bovine articular cartilage at varying pH solutions is either charged positively or negatively. When examining the coefficient of friction of the (cartilage/cartilage) pair, depending on the pH, we observe surfaces charged positively, negatively, and without charge. The uncharged surface refers to the iso-electric point (IEP) and shows greater friction than the charged surfaces of the cartilage. The measurement of surface energy versus. pH of the spherical lipid bi-layer will reveal the amphoteric nature of the membrane surface. The friction coefficient of the (cartilage/cartilage) pair and the surface energy of the spherical lipid bi-layer versus pH are expressed by a bell-shaped curve. This is an interesting case that confirms the fact that the phospholipid bi-layer is embedded on the surface cartilage. This experimental confirmation of negative surface cartilage is insufficiently highlighted in the literature on natural lubrication.