Deymier Alix C, An Yiran, Boyle John J, Schwartz Andrea G, Birman Victor, Genin Guy M, Thomopoulos Stavros, Barber Asa H
Dept. of Orthopedic Surgery, Columbia University, New York, NY, United States.
School of Engineering and Materials Science, Queen Mary University of London, UK.
Acta Biomater. 2017 Jul 1;56:25-35. doi: 10.1016/j.actbio.2017.01.037. Epub 2017 Jan 11.
The tendon-to-bone attachment (enthesis) is a complex hierarchical tissue that connects stiff bone to compliant tendon. The attachment site at the micrometer scale exhibits gradients in mineral content and collagen orientation, which likely act to minimize stress concentrations. The physiological micromechanics of the attachment thus define resultant performance, but difficulties in sample preparation and mechanical testing at this scale have restricted understanding of structure-mechanical function. Here, microscale beams from entheses of wild type mice and mice with mineral defects were prepared using cryo-focused ion beam milling and pulled to failure using a modified atomic force microscopy system. Micromechanical behavior of tendon-to-bone structures, including elastic modulus, strength, resilience, and toughness, were obtained. Results demonstrated considerably higher mechanical performance at the micrometer length scale compared to the millimeter tissue length scale, describing enthesis material properties without the influence of higher order structural effects such as defects. Micromechanical investigation revealed a decrease in strength in entheses with mineral defects. To further examine structure-mechanical function relationships, local deformation behavior along the tendon-to-bone attachment was determined using local image correlation. A high compliance zone near the mineralized gradient of the attachment was clearly identified and highlighted the lack of correlation between mineral distribution and strain on the low-mineral end of the attachment. This compliant region is proposed to act as an energy absorbing component, limiting catastrophic failure within the tendon-to-bone attachment through higher local deformation. This understanding of tendon-to-bone micromechanics demonstrates the critical role of micrometer scale features in the mechanics of the tissue.
The tendon-to-bone attachment (enthesis) is a complex hierarchical tissue with features at a numerous scales that dissipate stress concentrations between compliant tendon and stiff bone. At the micrometer scale, the enthesis exhibits gradients in collagen and mineral composition and organization. However, the physiological mechanics of the enthesis at this scale remained unknown due to difficulty in preparing and testing micrometer scale samples. This study is the first to measure the tensile mechanical properties of the enthesis at the micrometer scale. Results demonstrated considerably enhanced mechanical performance at the micrometer length scale compared to the millimeter tissue length scale and identified a high-compliance zone near the mineralized gradient of the attachment. This understanding of tendon-to-bone micromechanics demonstrates the critical role of micrometer scale features in the mechanics of the tissue.
肌腱与骨的附着处（附着点）是一种复杂的分层组织，它将坚硬的骨骼与柔顺的肌腱连接起来。在微米尺度下，附着部位在矿物质含量和胶原蛋白取向方面呈现出梯度变化，这可能起到了最小化应力集中的作用。因此，附着处的生理微观力学决定了最终的性能，但在此尺度下样品制备和力学测试的困难限制了对结构 - 力学功能的理解。在这里，使用低温聚焦离子束铣削技术制备了来自野生型小鼠和有矿物质缺陷小鼠附着点的微米尺度梁，并使用改进的原子力显微镜系统将其拉伸至破坏。获得了肌腱 - 骨结构的微观力学行为，包括弹性模量、强度、弹性和韧性。结果表明，与毫米级组织长度尺度相比，在微米长度尺度下力学性能显著更高，描述了附着点材料特性，而不受诸如缺陷等高阶结构效应的影响。微观力学研究揭示了有矿物质缺陷的附着点强度降低。为了进一步研究结构 - 力学功能关系，使用局部图像相关性确定了沿肌腱 - 骨附着处的局部变形行为。在附着点矿化梯度附近清晰地识别出一个高柔顺性区域，并突出了附着点低矿物质端矿物质分布与应变之间缺乏相关性。这个柔顺区域被认为起到能量吸收组件的作用，通过更高的局部变形限制肌腱 - 骨附着处内的灾难性破坏。对肌腱 - 骨微观力学的这种理解证明了微米尺度特征在组织力学中的关键作用。
肌腱 - 骨附着处（附着点）是一种复杂的分层组织，具有多种尺度的特征，可在柔顺的肌腱和坚硬的骨骼之间消散应力集中。在微米尺度下，附着点在胶原蛋白和矿物质组成及组织方面呈现出梯度变化。然而，由于制备和测试微米尺度样品存在困难，在此尺度下附着点的生理力学仍然未知。本研究首次在微米尺度下测量了附着点的拉伸力学性能。结果表明，与毫米级组织长度尺度相比，在微米长度尺度下力学性能显著增强，并在附着点矿化梯度附近识别出一个高柔顺性区域。对肌腱 - 骨微观力学的这种理解证明了微米尺度特征在组织力学中的关键作用。
