The boundary lubrication mechanism at the articulating surface of natural synovial joints has been the subject of much discussion in tribology. In this study, to elucidate the lubricating function of the superficial area of articular cartilage and synovial fluid (SF), cartilage specimens were processed with four different treatments: gentle and severe washing with detergent, incubation in NaCl solution, and trypsin digestion to selectively remove certain constituents from the cartilage surface. Subsequently, the frictional characteristics were examined in phosphate-buffered saline (PBS) and SF against glass. Angularly reciprocating sliding tests with a spherical glass probe and square articular cartilage specimens were performed at low contact loads in the mN range to extract the frictional behavior in the superficial area of the cartilage specimens. Meanwhile, the cartilage surface was observed to confirm the effects of treatments on the morphology of the cartilage surface using a fluorescence microscope and water-immersion methods. The coefficient of friction (COF) of the prepared cartilage specimens was varied from 0.05 to over 0.3 in PBS. However, a certain group of cartilage specimens exhibited a low COF of less than 0.1 with limited variation. For the low COF group of specimens, all four treatments increased the COF in PBS to different extents, and fluorescence microscopy revealed that the integrity of the cartilage surface was deteriorated by treatments. This means that the intact cartilage surface had lubricating constituents to maintain low friction, and the removal of such constituents resulted in the loss of the intrinsic boundary lubricity of the cartilage surface. The variation in the COF of the cartilage specimens was suppressed in SF because it had a clear boundary lubrication effect on the cartilage surface. The lubricating effect of SF could be confirmed even after degenerative treatment.

自然滑膜关节的关节表面的边界润滑机制一直是摩擦学中广泛讨论的主题。在本研究中，为了阐明关节软骨表面区域和滑液（SF）的润滑功能，对软骨标本进行了四种不同的处理：用洗涤剂温和和剧烈清洗、在氯化钠溶液中孵育以及胰蛋白酶消化以选择性去除来自软骨表面的某些成分。随后，检查了磷酸盐缓冲盐水 (PBS) 和 SF 与玻璃的摩擦特性。使用球形玻璃探针和方形关节软骨样本在 mN 范围内的低接触载荷下进行有角度往复滑动测试，以提取软骨样本表面区域的摩擦行为。同时，利用荧光显微镜和水浸法观察软骨表面，以确认治疗对软骨表面形态的影响。制备的软骨样本在 PBS 中的摩擦系数 (COF) 从 0.05 变化到超过 0.3。然而，某组软骨样本表现出低于 0.1 的低 COF，且变化有限。对于低COF组标本，所有四种处理均不同程度地增加了PBS中的COF，荧光显微镜显示软骨表面的完整性因处理而恶化。这意味着完整的软骨表面具有润滑成分以保持低摩擦，去除这些成分会导致软骨表面固有边界润滑性的丧失。 SF 抑制了软骨样本 COF 的变化，因为它对软骨表面具有明显的边界润滑作用。即使经过退变处理也能确认SF的润滑效果。