Tissue-scale anisotropy and compressibility of tendon in semi-confined compression tests

In this study, porcine tendon tissue was tested with a dedicated semi-confined compression set-up that enables us to induce states of either fibrils in compression (mode I), tension (mode II) or at constant length (mode III), respectively. The results suggest that tendon tissue is compressible and demonstrates a significantly stiffer response in mode I than in mode III. This implies that the fibril direction remains the axis of transverse isotropy in compression and that it provides an anisotropic contribution to the tissue stress. These results, which are important for the development of constitutive models for tendon tissue, are discussed with respect to the hierarchical structure of the extracellular matrix.