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

描述(申请人提供)：撕裂的肌腱和韧带经常需要手术修复他们的骨附着点。其中很大比例的修复效果不佳；例如，高达94%的外科肩袖修复失败。这些失败的根源在于连接肌腱和骨骼这两种材料的根本挑战，这两种材料的机械性能截然不同。肌腱到骨骼的自然插入涉及许多机制，这些机制产生了坚固而坚韧的附着物。不幸的是，这种组织会随着年龄的增长而退化，而且在愈合过程中不会再生。我们的总体目标是开发肌腱到骨骼植入的多尺度模型，该模型将导致(1)能够指导临床决策的组织韧性指标 老年患者；(2)未来组织工程外科移植物的基础。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的尺度上，并且这些机制在肌腱和骨之间的顺应性区域最明显，该区域在愈合环境中不会再生。我们将描述在自然的和病理性的肌腱到骨的植入中，随着年龄的变化，有助于这种跨尺度弹性的僵硬、强化和增韧机制。这项工作涉及三个目标：(1)在纳米尺度上，将使用透射电子显微镜电子能量损失谱来获得元素空间图，以确定矿物和胶原在种植体上的分布。个别矿化的胶原纤维将进行机械测试；我们最近在哺乳动物胶原纤维上进行了这样的测试。在硅胶原实验中，我们将识别和量化矿化胶原纤维韧性的变形机制。(2)在微观尺度上，采用同步辐射X射线衍射仪、拉曼光谱和偏光显微镜等手段来测定矿物含量和胶原蛋白的取向分布。肌腱到骨骼插入的机制将使用安装在共焦显微镜上的测试框架以微米级的分辨率进行检查。在硅胶中，将使用非线性均化方法将AIM 1中的矿化胶原纤维机理合并到矿化和交联型胶原纤维的连接网络的本构模型中。(3)在毫米尺度上，肌腱和肌腱的3D交指几何形状 骨骼将使用相位对比X射线计算机断层扫描来确定，肌腱到骨骼的插入机制将通过组织水平拉伸测试来确定。在计算机实验中，将肌腱到骨骼的几何学与微观组织模型相结合，将产生肌腱到骨骼插入韧性的机制假说。机械场将向下传递分层模型水平，以评估胶原纤维对预测的生理性和病理性肌腱到骨插入载荷的响应。总之，这些模型和数据构成了未来组织工程工作的基础，并努力确定肌腱到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.