The wettability of the articular surface of cartilage depends on the condition of its surface active phospholipid overlay, which is structured as multi-bilayer. Based on a hypothesis that the surface of cartilage facilitates the almost frictionless lubrication of the joint, we examined the characteristics of this membrane surface entity in both its normal and degenerated conditions using a combination of atomic force microscopy, contact angle measurement, and friction test methods. The observations have led to the conclusions that (1) the acid–base equilibrium condition influences the lubrication effectiveness of the surface of cartilage and (2) the friction coefficient is significantly dependent on the hydrophobicity of the surface of the tissue, thereby confirming the hypothesis tested in this paper. Both wettability angle and interfacial energy were obtained for varying conditions of the cartilage surface both in its wet, dry and lipid-depleted conditions. The interfacial energy also increased with mole fraction of the lipid species reaching an asymptotic value after 0.6. Also, the friction coefficient was found to decrease to an asymptotic level as the wettability angle increased. The result reveal that the interfacial energy increased with pH till pH = 4.0, and then decreased from pH = 4.0 to reach equilibrium at pH = 7.0.

Purpose: The purpose of this paper is to study the sliding and the vibrating fretting tests mechanism of h‐BN micro‐particles when used as a lubricating grease‐2 additive.Design/methodology/approach: The fretting tests were conducted on steel/steel contacts using both vibrating fretting apparatus and the shaft‐sleeve slide fitted tester. The wear scars were characterized with profilometry. The tribological properties of grease‐2 compounded with h‐BN additive were also compared to those obtained for the commercial product Militec‐4.Findings: The experiment showed significant differences between the results obtained from the vibrating fretting and the shaft‐sleeve sliding fitted tests. Adding h‐BN to the lubricant leads to a better performance in the shaft‐sleeve slide regime than in the steel/steel vibrating test condition.Originality/value: The results of the experimental studies demonstrate the potential of h‐BN as an additive for preventing fretting sliding, and can very useful for further application of compound grease‐2 with h‐BN additive in industrial equipment.