The progression of local cartilage surface damage toward early stage osteoarthritis (OA) likely depends on the severity of the damage and its impact on the local lubrication and stress distribution in the surrounding tissue. It is difficult to study the local responses using traditional methods; in situ microtribological methods are being pursued here as a means to elucidate the mechanical aspects of OA progression. While decades of research have been dedicated to the macrotribological properties of articular cartilage, the microscale response is unclear. An experimental study of healthy cartilage microtribology was undertaken to assess the physiological relevance of a microscale friction probe. Normal forces were on the order of 50 mN. Sliding speed varied from 0 to 5 mm/s, and two probes radii, 0.8 and 3.2 mm, were used in the study. In situ measurements of the indentation depth into the cartilage enabled calculations of contact area, effective elastic modulus, elastic and fluid normal force contributions, and the interfacial friction coefficient. This work resulted in the following findings: (1) at high sliding speed (V = 1–5 mm/s), the friction coefficient was low (μ = 0.025) and insensitive to probe radius (0.8–3.2 mm) despite the fourfold difference in the resulting contact areas; (2) the contact area was a strong function of the probe radius and sliding speed; (3) the friction coefficient was proportional to contact area when sliding speed varied from 0.05 to 5 mm/s; (4) the fluid load support was greater than 85% for all sliding conditions (0% fluid support when V = 0) and was insensitive to both probe radius and sliding speed. The findings were consistent with the adhesive theory of friction; as speed increased, increased effective hardness reduced the area of solid–solid contact which subsequently reduced the friction force. Where the severity of the sliding conditions dominates the wear and degradation of typical engineering tribomaterials, the results suggest that joint motion is actually beneficial for maintaining low matrix stresses, low contact areas, and effective lubrication for the fluid-saturated porous cartilage tissue. Further, the results demonstrated effective pressurization and lubrication beneath single asperity microscale contacts. With carefully designed experimental conditions, local friction probes can facilitate more fundamental studies of cartilage lubrication, friction and wear, and potentially add important insights into the mechanical mechanisms of OA.

中文翻译：

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软骨微摩擦学的原位研究：速度和接触面积的作用。

局部软骨表面损伤向早期骨关节炎 (OA) 的进展可能取决于损伤的严重程度及其对周围组织局部润滑和应力分布的影响。使用传统方法很难研究当地的反应；这里正在寻求原位微摩擦学方法作为阐明 OA 进展的机械方面的一种手段。虽然数十年的研究一直致力于关节软骨的宏观摩擦学特性，但微观响应尚不清楚。进行了健康软骨微摩擦学的实验研究，以评估微型摩擦探针的生理相关性。法向力约为 50 mN。滑动速度从 0 到 5 毫米/秒不等，研究中使用了两个探针半径，0.8 和 3.2 毫米。软骨压痕深度的原位测量能够计算接触面积、有效弹性模量、弹性和流体法向力贡献以及界面摩擦系数。这项工作导致了以下发现：（1）在高滑动速度（V  = 1–5 mm/s），摩擦系数很低（μ = 0.025）并且对探针半径（0.8–3.2 mm）不敏感，尽管所产生的接触面积有四倍的差异；(2)接触面积是探针半径和滑动速度的强函数；(3)滑动速度在0.05~5mm/s范围内，摩擦系数与接触面积成正比；(4) 在所有滑动条件下流体载荷支撑大于 85%（当V 为0% 流体支撑时） = 0) 并且对探针半径和滑动速度都不敏感。研究结果与摩擦的粘附理论一致；随着速度的增加，有效硬度的增加减少了固-固接触面积，从而降低了摩擦力。在滑动条件的严重程度决定了典型工程摩擦材料的磨损和退化的情况下，结果表明关节运动实际上有利于保持低基质应力、低接触面积和流体饱和多孔软骨组织的有效润滑。此外，结果证明了在单个粗糙微尺度接触下的有效加压和润滑。通过精心设计的实验条件，局部摩擦探头可以促进软骨润滑、摩擦和磨损的更基础研究，