Articular cartilage maintains phenomenally low friction and strains in intact joints during articulation, yet after a century of study, the mechanisms underpinning cartilage’s in vivo functions remain uncertain. We recently re-introduced a unique benchtop testing system, the convergent stationary contact area (cSCA), to investigate frictions and strains in cartilage explants; the cSCA differs from other benchtop testing configurations by enabling sliding-induced hydrodynamic-driven fluid flows to influence interstitial hydration and lubrication during sliding. This study aimed to elucidate several points regarding cartilage tribomechanics and joint lubrication, including the following: (i) if the presence of putative lubricants alters the ability of sliding to drive tribological rehydration (i.e., sliding-driven compression recovery under loading); (ii) how lubricant presence influences the frictional behavior of articular cartilage when tested under physiologically representative sliding conditions (e.g., moderate-to-high hydration and fluid load support, low-to-moderate tissue strains, and fast sliding speeds); and (iii) interpreting these behaviors with respect to lubricant rheology at shear rates reflecting those found in cSCA tests and intact joints (> 10⁴ s⁻¹). We found that synovial fluid and hyaluronic acid solutions (i) were at most 3–10 × the viscosity of saline lubricants at physiological shear rates, (ii) substantially enhanced the rates of fluid and lubrication recovery during sliding, and (iii) minimized the amount of time the explants experienced detrimental ‘pathophysiological’ frictions by fostering tissue hydration recovery. Additionally, we show that when non-lubricating solutions and high sliding speeds are utilized, the cSCA can facilely replicate ‘semi-physiological’ strains and frictions, while the use of lubricant-containing baths fosters ‘physiologically consistent’ tribomechanical behaviors, improving the physiological relevance of long-term benchtop sliding tests.

关节软骨在关节运动期间保持了明显低的摩擦力和完整关节的应变，但是经过一个世纪的研究，支撑软骨体内功能的机制仍然不确定。我们最近重新引入了独特的台式测试系统，即收敛固定接触面积（cSCA），以研究软骨外植体中的摩擦和应变。cSCA与其他台式测试配置的不同之处在于，它使滑动引起的流体动力驱动的流体流能够影响滑动过程中的间隙水合作用和润滑。这项研究旨在阐明与软骨摩擦力学和关节润滑有关的几点，包括：（i）是否存在假定的润滑剂会改变滑动驱动摩擦学补液的能力（即在负载下滑动驱动的压缩恢复）；（ii）在生理上具有代表性的滑动条件下（例如，中等至高水合作用和流体负荷支持，低至中等组织应变和快速滑动速度）进行测试时，润滑剂的存在如何影响关节软骨的摩擦行为；（iii）在剪切速率下解释这些与润滑剂流变学有关的行为，以反映在cSCA测试和完整接头中发现的行为（> 10⁴  s ^-1）。我们发现滑液和透明质酸溶液（i）在生理剪切速率下至多为生理盐水粘度的3-10倍，（ii）大大提高了滑动过程中流体和润滑恢复的速率，并且（iii）最小化了外植体通过促进组织水化恢复而经历有害的“病理生理”摩擦的时间。此外，我们表明，当使用非润滑溶液和高滑动速度时，cSCA可以轻松复制“半生理”应变和摩擦，而使用含润滑剂的浴液则可以促进“生理一致”的摩擦力学行为，从而改善了生理学长期台式滑动测试的相关性。