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

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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.