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This study aims to determine the effect of progressive loss of the surface active phospholipids on the characteristics, and hence tribological function of articular cartilage. In accordance to Hill's hypothesis, 3-7 lipid bilayers at pH 7.4 operate as the solid lubricant in the cartilage-cartilage interface during physiological function. These bilayers are known to be depleted during cartilage degeneration. This study models this loss of phospholipid bilayers, studying experimentally both wet and dry cartilage surfaces, measuring surface wettability, and friction coefficient under a constant stress of 1.2 MPa. The results demonstrate that the friction coefficient increases gradually with loss of the phospholipid bilayers, and gains in value with decrease in wettability. [ABSTRACT FROM AUTHOR]

Purpose |!|#8211; 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 |!|#8211; 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 |!|#8211; 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 |!|#8211; 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. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the influence of pH on interfacial energy distributed over the phospholipids-bilayer surface model and the effect of hydrophobicity on coefficient of friction (f) were investigated by using microelectrophoresis. An important clinical implication of deficiency in hydrophobicity is the loss of phospholipids that is readily observed in osteoarthritis joints. This paper establishes the influence of pH on interfacial energy upon an increase f, which might be associated with a decrease of hydrophobicity of the articular surface. [Copyright &y& Elsevier]