Data from: Collagen network strengthening following cyclic tensile loading

The bulk mechanical properties of tissues are highly tuned to the physiological loads they experience and reflect the hierarchical structure and mechanical properties of their constituent parts. A thorough understanding of the processes involved in tissue adaptation is required to develop multi-scale computational models of tissue remodelling. While extracellular matrix (ECM) remodelling is partly due to the changing cellular metabolic activity, there may also be mechanically directed changes in ECM nano/microscale organization which lead to mechanical tuning. The thermal and enzymatic stability of collagen, which is the principal load-bearing biopolymer in vertebrates, have been shown to be enhanced by force suggesting that collagen has an active role in ECM mechanical properties. Here, we ask how changes in the mechanical properties of a collagen-based material are reflected by alterations in the micro/nanoscale collagen network following cyclic loading. Surprisingly, we observed significantly higher tensile stiffness and ultimate tensile strength, roughly analogous to the effect of work hardening, in the absence of network realignment and alterations to the fibril area fraction. The data suggest that mechanical loading induces stabilizing changes internal to the fibrils themselves or in the fibril–fibril interactions. If such a cell-independent strengthening effect is operational in vivo, then it would be an important consideration in any multiscale computational approach to ECM growth and remodelling.

组织的宏观力学性能高度适配其所承受的生理载荷，同时也反映了其组成部分的层级结构与力学特性。若要构建组织重塑的多尺度计算模型，需深入理解组织适应性相关的过程。尽管细胞外基质（extracellular matrix, ECM）重塑部分源于细胞代谢活性的改变，但ECM的纳米/微观尺度组织结构也可能受力学调控，进而实现力学性能的调谐。作为脊椎动物主要的承重生物聚合物，胶原蛋白（collagen）的热稳定性与酶解稳定性已被证实可通过力学载荷得到增强，这表明胶原蛋白在ECM力学特性中发挥着主动调控作用。本研究旨在探究周期性载荷作用下，胶原基材料的力学性能变化如何通过其微观/纳米尺度胶原网络的结构改变得以体现。令人意外的是，在未观察到网络重排以及原纤维面积占比发生变化的情况下，我们检测到材料的拉伸刚度与极限抗拉强度均显著提升，其效果大致类似于加工硬化现象。上述实验数据表明，力学载荷可诱导原纤维内部或原纤维间相互作用产生稳定性变化。若此类不依赖细胞的强化效应在活体中真实存在，那么在针对ECM生长与重塑的各类多尺度计算研究中，该效应都将是一项关键的考量因素。