Abstract：
The friction of solids is primarily understood through the adhesive interactions between the surfaces. As a result, slick materials tend to be nonstick (e.g., Teflon), and sticky materials tend to produce high friction (e.g., tires and tape). Paradoxically, cartilage, the slippery bearing material of human joints, is also among the stickiest of known materials. This study aims to elucidate this apparent paradox. Cartilage is a biphasic material, and the most cited explanation is that both friction and adhesion increase as load transfers from the pressurized interstitial fluid to the solid matrix over time. In other words, cartilage is slippery and sticky under different times and conditions. This study challenges this explanation, demonstrating the strong adhesion of cartilage under high and low interstitial hydration conditions. Additionally, we find that cartilage clings to itself (a porous material) and Teflon (a nonstick material), as well as other surfaces. We conclude that the unusually strong interfacial tension produced by cartilage reflects suction (like a clingfish) rather than adhesion (like a gecko). This finding is surprising given its unusually large roughness, which typically allows for easy interfacial flow and defeats suction. The results provide compelling evidence that cartilage, like a clingfish, conforms to opposing surfaces and effectively seals submerged contacts. Further, we argue that interfacial sealing is itself a critical function, enabling cartilage to retain hydration, load support, and lubrication across long periods of inactivity.
摘要：
固体的摩擦主要通过表面之间的粘合剂相互作用来理解。因此,光滑的材料往往不粘(例如，Teflon),和粘性材料往往会产生高摩擦(例如，轮胎和胶带)。矛盾的是,软骨，人体关节的滑动轴承材料，也是已知材料中最粘的。本研究旨在阐明这一明显的悖论。软骨是一种双相材料，最多引用的解释是，随着载荷从加压的间质液转移到固体基质，摩擦和粘附力都会增加。换句话说,软骨在不同的时间和条件下是光滑和粘的。这项研究挑战了这种解释，证明软骨在高和低间质水合条件下的强粘附性。此外,我们发现软骨附着在自身（多孔材料）和特氟龙（不粘材料）上，以及其他表面。我们得出的结论是，软骨产生的异常强的界面张力反映了吸力（像粘鱼）而不是粘附（像壁虎）。鉴于其异常大的粗糙度，这一发现令人惊讶，这通常允许容易的界面流动和失败的吸力。结果提供了令人信服的证据表明软骨，像一条粘鱼，符合相对的表面和有效地密封浸没的接触。Further,我们认为界面密封本身是一个关键的功能，使软骨保持水合，负载支撑,和长期不活动的润滑。
