New paradigms for relating the microstructure of cartilage to its large scale mechanics: The Roles of Rigidity-Percolation and Double Gel Network Structure in Non-Linear Response

将软骨微观结构与其大规模力学联系起来的新范例：刚性渗透和双凝胶网络结构在非线性响应中的作用

基本信息

批准号：
1536463
负责人：
Itai Cohen
金额：
$ 34.81万
依托单位：
Cornell University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2015
资助国家：
美国
起止时间：
2015-08-01 至 2019-07-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1536463&HistoricalAwards=false
关键词：
New paradigms relating microstructure cartilage

项目摘要

Cartilage, the smooth tissue that coats bones in joints, is a remarkable material that can last decades and outperform any man-made substance in its unique combination of material properties. There are several aspects of cartilage's microstructure that contribute to its longevity. First, the matrix that gives rise to these mechanical properties is comprised of two interpenetrating polymer networks, a design that has recently been shown to inhibit crack formation. Second, the mechanical properties of cartilage change with depth such that energy damping occurs almost entirely in a thin region near its surface. The PIs have recently developed a theoretical model that explains how variations in the concentration of the polymer networks lead to this localization of energy absorption to the tissue surface. This project uses an array of experimental techniques to test this model and extend its applicability to extreme deformations where cartilage can be damaged. By chemically treating the tissue to remove essential molecular components and testing the tissue response in their absence, the PIs will determine which elements of the matrix are essential for generating cartilage's unique combination of mechanical properties. A better understanding of the macromolecular origins of cartilage mechanical properties will give insight into how diseases such as arthritis develop, guide approaches to tissue repair therapies, and more broadly, provide mechanical design criteria for fabrication of robust materials that can endure extreme loading.Articular cartilage has unique material properties that enable it to endure millions of loading cycles per year while protecting underlying tissues. The structural and compositional origins of its compressive properties have been known for decades. However, there is no equivalent understanding of the underlying mechanisms associated with its shear behavior. Recently the investigators introduced a rigidity percolation theory, previously established to explain the properties of reconstituted polymer networks, to explain the linear response of cartilage shear mechanics. This theory is that the observed orders of magnitude variation in the shear modulus of cartilage arises from small concentration differences of matrix constituents that are poised near a rigidity percolation threshold. Furthermore, the theory makes novel predictions about molecular mechanisms of non-linear shear behavior and gives new insight into mechanical changes that occur from biochemical and mechanical damage. This project will test these predictions and determining if rigidity percolation can be used as a new paradigm for the macromolecular origins of the mechanical shear properties of articular cartilage. Specifically, using chemical and mechanical degradation techniques, predictions made by the model about the critical extracellular matrix elements that give rise to cartilage's macroscale mechanical properties will be tested. Finally, this project will extend the applicability of the model to describe how the microscopic structure of cartilage is altered when it is sheared beyond the linear regime.

软骨是覆盖关节骨骼的光滑组织，是一种非凡的材料，可以持续数十年，并且以其独特的材料特性组合优于任何人造物质。软骨的微观结构有几个方面有助于其寿命。首先，产生这些机械性能的基体由两个互穿聚合物网络组成，这种设计最近被证明可以抑制裂纹形成。其次，软骨的机械性能随深度而变化，因此能量阻尼几乎完全发生在其表面附近的薄区域。 PI 最近开发了一个理论模型，该模型解释了聚合物网络浓度的变化如何导致能量吸收局部化到组织表面。该项目使用一系列实验技术来测试该模型，并将其适用性扩展到软骨可能受损的极端变形。通过对组织进行化学处理以去除必需的分子成分，并在没有这些成分的情况下测试组织的反应，PI 将确定基质中的哪些元素对于生成软骨的独特机械性能组合至关重要。更好地了解软骨机械特性的大分子起源，将有助于深入了解关节炎等疾病的发展过程，指导组织修复治疗方法，更广泛地说，为制造可承受极端载荷的坚固材料提供机械设计标准。关节软骨具有独特的材料特性，使其能够承受每年数百万次的负载循环，同时保护下面的组织。其压缩特性的结构和成分起源几十年来一直为人所知。然而，对其剪切行为相关的潜在机制还没有同等的理解。最近，研究人员引入了刚性渗流理论，该理论先前是为了解释重构聚合物网络的特性而建立的，以解释软骨剪切力学的线性响应。该理论认为，观察到的软骨剪切模量的数量级变化是由接近刚性渗透阈值的基质成分的微小浓度差异引起的。此外，该理论对非线性剪切行为的分子机制做出了新颖的预测，并对生化和机械损伤引起的机械变化提供了新的见解。该项目将测试这些预测，并确定刚性渗透是否可以用作关节软骨机械剪切特性的大分子起源的新范例。具体来说，使用化学和机械降解技术，将测试模型对产生软骨宏观机械性能的关键细胞外基质元素所做的预测。最后，该项目将扩展模型的适用性，以描述当软骨被剪切超出线性状态时，软骨的微观结构如何改变。