The role of meso-scale structure on the mechanical response of soft musculoskeletal tissues

肌肉和肌腱是特别庞大的肌肉骨骼组织，具有明显的结构相似性：分层管状结构和沿首选方向的细长结构的主要单轴排列。这使得它们在结构上与身体其他组织不同。肌肉和肌腱组织对压缩载荷的反应与它们的拉伸行为相比，很少受到关注，尽管这两种组织在体内都处于压缩状态。申请人最近的工作揭示了这些组织的压缩响应具有特殊的各向异性，并表明细胞外基质结构的分层组织在稳定纤维样成分方面发挥了重要作用。这些观察结果有助于提高对这些组织中负荷转移的理解，并对建模和模拟具有指导意义。当前项目的目的是全面了解肌肉骨骼组织对多轴载荷的特殊反应的结构特征和机制。为此，详细研究了细胞外基质形成的中尺度结构对肌肉和肌腱组织力学行为的作用，重点研究了拉伸和压缩载荷响应之间的几种不对称。我们将在不同长度尺度上进行一套全面的专门实验，以确定多轴载荷下非线性组织和中观尺度材料的特性。组织切片将在不同的载荷下制备，并用于建立多尺度有限元模拟的计算机模型。基于非线性光学显微镜的原位实验，将细观结构的变化与组织尺度上施加的载荷联系起来。最后，实验结果以及从详细的有限元计算中获得的理解将用于定义一类适合表示肌肉骨骼组织的非线性各向异性行为的连续本构模型。

Muscle and tendon are particular bulky musculoskeletal tissues with a pronounced structural similarity: a hierarchical tubular architecture and a predominantly uniaxial alignment of elongated structures along a preferred direction. This distinguishes them in terms of structure from other tissues in the body. The response of muscle and tendon tissues to compressive loads has gained little attention compared to their tensile behaviour although both tissues are subjected to compressive states in-vivo. Recent work by the applicants revealed a particular anisotropy in the compressive response of these tissues and suggests an important role of the hierarchical organisation of extracellular matrix structures in stabilising the fibre-like components. These observations help improving the understanding of load transfer in these tissues and have implications for modelling and simulation.The aim of the current project is a comprehensive understanding of the structural features and mechanisms that govern the peculiar response of musculoskeletal tissues to multiaxial loads. To this end, the role of meso-scale structures formed by the extracellular matrix for the mechanical behaviour of muscle and tendon tissues is investigated in detail, with a focus on several asymmetries between the responses to tensile and compressive loads. A comprehensive set of dedicated experiments on different length-scales will be performed to determine non-linear tissue and meso-scale material properties under multiaxial loads. Histological tissue sections will be prepared under different loads and used to build computer models for multi-scale finite element simulations. In-situ experiments will be performed based on non-linear optical microscopy to connect the change of meso-structure with loads applied on tissue-scale. Finally, the experimental results together with the understanding gained from detailed finite element computations will be used to define a class of continuum constitutive models suitable to represent the non-linear anisotropic behaviour of musculoskeletal tissues.