EAGER: Slick Yet Stuck? Using Adhesion to Expose the Conditions of the Buried Cartilage Interface

在动物王国中，已经进化出了显著的粘附机制，帮助跳蛛粘附着陆，章鱼捕获猎物，壁虎在垂直表面上爬行，以及攀缘鱼抓住光滑的生物污染的岩石。在每一个不同的和充分研究的情况下，粘附和生存之间有很强的联系，以推动进化过程。这个研究小组最近发现，软骨，一种以极低的粘附摩擦而闻名的材料，会产生极强的粘附应力-与壁虎，章鱼和鲶鱼的粘附应力相当。这一发现是矛盾的，因为摩擦力和粘附力从根本上是联系在一起的。此外，与其他强粘附的自然例子不同，强关节粘附没有明显的进化压力。软骨同时表现出“超润滑性”和“超粘附性”的事实违反了关于软骨润滑的长期假设，同时揭示了关于不寻常的潜在力学的关键线索。EARLY探索性研究（EAGER）项目旨在解决“软骨润滑-粘附”悖论。 其结果将：（1）阐明关节中如何产生拉力以及这对关节润滑意味着什么;（2）提供对生物粘附的原创见解，同时揭示生物灵感和材料发现的新方向;（3）深入了解“关节破裂”的原因和后果，这是一种常见的、临床上重要的且知之甚少的现象。 如果将对软骨功能力学的理解浓缩到一个单一的框架中，它将为保护、治疗或替换受损关节提供实质性改进的策略。该项目将使用新颖的界面张力测量来量化界面渗透性，实验分离粘附的贡献（见于壁虎）和吸力（见于粘扣鱼）机制，并系统地评估软骨摩擦力和附着力之间的交叉点。 使用微力显微镜，梁位移从正常和摩擦力将量化的实验压头。 将从牛关节中获得软骨样本（骨软骨核心）。 制定了三个目标。 第一个将通过改变拔出前的停留时间来系统地改变组织间液损失，从而隔离渗出对粘附、抽吸和界面间隙的影响。 第二个目标是通过消除吸力的影响，使用准静态拔出率进行拔出试验，从而隔离和量化粘合力。 第三个目标是量化界面性质（例如滑动摩擦、有效接触模量、平衡模量和流体载荷分数），这将对吸力产生不同的影响（取决于半径）和附着力（与半径无关）该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Remarkable adhesive mechanisms have evolved across the animal kingdom to help jumping spiders stick a landing, octopi catch prey, geckos locomote on vertical surfaces, and clingfish grip slippery, bio-fouled rocks. In each of these distinct and well-studied cases, there were strong connections between adhesion and survival to drive the evolutionary process. This research team has recently discovered that cartilage, a material well-known for exceptionally low adhesive friction, generates exceptionally strong adhesive stresses -- comparable to those of the gecko, octopus, and clingfish. This finding is paradoxical, because friction and adhesion are fundamentally linked. Additionally, unlike other natural examples of strong adhesion, there is no obvious evolutionary pressure for strong joint adhesion. The fact that cartilage simultaneously exhibits both "super-lubricity" and "super-adhesion" violates long-standing assumptions about cartilage lubrication while exposing critical clues about the unusual underlying mechanics. This EArly-Concept Grant for Exploratory Research (EAGER) project seeks to resolve this "cartilage lubrication-adhesion" paradox. The results will: (1) clarify how tensile forces are generated in the joint and what that implies about joint lubrication; (2) provide original insights into bio-adhesion while exposing new directions for bio-inspiration and materials discovery; (3) lend insight into the causes and consequences of "joint cracking", a common, clinically important, and poorly understood phenomenon. If the understanding of cartilage functional mechanics are condensed into a single framework, it will inform substantially improved strategies to protect, treat, or replace compromised joints.The project will use novel interfacial tension measurements to quantify interfacial permeability, experimentally separate the contributions from adhesion (seen in the gecko) and suction (seen in the clingfish) mechanisms, and systematically assess the intersection between cartilage friction and adhesion across length scales. Using micro force microscopy, beam displacements from normal and friction forces will be quantified on an experimental indenter. Cartilage samples (osteochondral cores) will be obtained from bovine joints. Three aims have been developed. The first will isolate the effect of exudation on adhesion, suction, and interfacial gaps by varying the dwell time prior to pull-off to systematically vary interstitial fluid loss. The second aim will isolate and quantify adhesive forces by eliminating the contribution of suction, using quasistatic rates for the pull-off tests. The third aim will quantify the interfacial properties (e.g. sliding friction, effective contact modulus, equilibrium modulus, and fluid load fraction) across length scales by using varying probe radii, which will have varying effects on suction forces (dependent on radius) and adhesion forces (independent of radius).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.