Cross-scale interactions between mineral and collagen for tendon-bone attachment

描述（由申请人提供）：撕裂的肌腱和韧带通常需要手术修复其骨性附着点。这些修复中的很大一部分结果不佳;例如，高达94%的手术肩袖修复失败。这些失败的根源是连接两种材料的根本挑战，肌腱和骨，具有截然不同的机械性能。肌腱-骨的自然插入涉及许多机制，这些机制产生了坚固和坚韧的附着。不幸的是，这种组织随着年龄的增长而退化，并且在愈合中不会再生。我们的总体目标是开发肌腱-骨插入的多尺度模型，这将导致（1）组织韧性指标，可以指导临床决策， 老年患者;（2）为将来的组织工程外科移植物奠定基础。基于我们以前的工作，我们假设增韧和强化机制存在于几个长度尺度上，并且这些机制在肌腱和骨之间的组织的顺应性区域中最明显，该区域在愈合环境中不会再生。我们将描述硬化，强化和增韧机制，有助于这种弹性跨尺度的自然和病理肌腱骨插入作为年龄的函数。这项工作涉及三个目标：（1）在纳米级，将使用透射电子显微镜电子能量损失光谱法获得元素空间图，以确定插入物上的矿物质和胶原分布。将对单个矿化胶原纤维进行机械测试;我们最近对哺乳动物胶原纤维进行了此类测试。计算机模拟实验将确定和量化矿化胶原纤维韧性的变形机制。(2)在微观尺度上，同步加速器X射线衍射、拉曼光谱和偏振光显微镜将用于确定矿物质含量和胶原蛋白取向的分布。将使用共聚焦显微镜安装的测试框架，以微米分辨率检查肌腱-骨插入的力学。在计算机模拟中，将使用非线性均匀化方法将目标1中的矿化胶原纤维力学纳入矿化和交联胶原纤维连接网络的本构模型中。(3)在毫米尺度上，肌腱和肌腱的3D交叉几何形状 骨将使用相衬X射线计算机断层扫描来确定，肌腱-骨插入的力学将使用组织水平拉伸试验来确定。将肌腱-骨几何结构与微尺度组织模型相结合的计算机模拟实验将产生肌腱-骨插入韧性机制的假设。力学场将传递到分层模型水平，以评价胶原纤维对预测的生理和病理肌腱-骨插入载荷的反应。总之，这些模型和数据形成了未来组织工程工作的基础，并努力确定肌腱-骨组织健康的临床有用指标。

DESCRIPTION (provided by applicant): Torn tendons and ligaments often require surgical repair to their bony insertions. A large percentage of these repairs have poor outcomes; for example, up to 94% of surgical rotator cuff repairs fail. At the root of these failures is the fundamental challenge of attaching two materials, tendon and bone, with vastly different mechanical properties. The natural tendon-to-bone insertion involves a number of mechanisms that create a strong and tough attachment. Unfortunately, this tissue degrades with age, and is not regenerated in healing. Our overall goal is to develop a multiscale model of the tendon-to-bone insertion that will lead to (1) tissue toughness metrics that can guide clinical decisions for elderly patients, and (2) foundations for future tissue- engineered surgical grafts. Based on our previous work, we hypothesize that toughening and strengthening mechanisms exist across several length scales, and that these are most pronounced in a the compliant region of tissue between tendon and bone that does not regrow in the healing setting. We will characterize the stiffening, strengthening, and toughening mechanisms that contribute to this resilience across scales in natural and pathologic tendon-to-bone insertions as a function of age. The work involves three aims: (1) At the nanoscale, elemental spatial maps will be acquired using transmission electron microscopy electron energy loss spectroscopy to determine mineral and collagen distributions across the insertion. Individual mineralized collagen fibrils will be mechanically tested; we have recently performed such tests on mammalian collagen fibrils. In silico experiments will identify and quantify deformation mechanisms underlying the toughness of mineralized collagen fibrils. (2) At the microscale, synchrotron X-ray diffraction, Raman spectroscopy, and polarized light microscopy will be used to determine the distributions of mineral content and collagen orientation. Mechanics of the tendon-to-bone insertion will be examined with micrometer resolution using a confocal microscope-mounted testing frame. In silico, nonlinear homogenization methods will be used to incorporate mineralized collagen fiber mechanics from Aim 1 into constitutive models of connected networks of mineralized and cross-linked collagen fibers. (3) At the millimeter scale, the 3D inter-digitation geometry of tendon and bone will be determined using phase contrast X-ray computed tomography and the mechanics of the tendon-to-bone insertion will be determined using tissue level tensile tests. In silico experiments combining tendon-to-bone geometry with microscale tissue models will produce hypotheses of mechanisms underlying tendon-to-bone insertion toughness. Mechanical fields will be passed down hierarchical model levels to evaluate collagen fibril response to predicted physiologic and pathologic tendon-to-bone insertion loading. Together, these models and data form the foundation of future tissue engineering efforts and efforts to identify clinically useful metrics of tendon-to-bone tissue health.