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The knee meniscus is a soft fibrous tissue with a high incidence of injury in older populations. The objective of this study was to determine the effect of age on the failure behavior of human knee meniscus when applying uniaxial tensile loads parallel or perpendicular to the primary circumferential fiber orientation. Two age groups were tested: under 40 and over 65 years old. We paired high-speed video with digital image correlation to quantify for the first time the planar strains occurring in the tear region at precise time points, including at ultimate tensile stress, when the tissue begins losing load-bearing capacity. On average, older meniscus specimens loaded parallel to the fiber axis had approximately one-third less ultimate tensile strain and absorbed 60% less energy to failure within the tear region than younger specimens (p 0.05). Older specimens also had significantly reduced strength and material toughness when loaded perpendicular to the fibers (p 0.05). These age-related changes indicate a loss of collagen fiber extensibility and weakening of the non-fibrous matrix with age. In addition, we found that when loaded perpendicular to the circumferential fibers, tears propagated near the planes of maximum tensile stress and strain. Whereas when loaded parallel to the circumferential fibers, tears propagated oblique to the loading axis, closer to the planes of maximum shear stress and strain. Our experimental results can assist the selection of valid failure criteria for meniscus, and provide insight into the effect of age on the failure mechanisms of soft fibrous tissue.

Achilles tendinopathy remains one of the most prevalent overuse injuries in elite as well as recreational athletes. Regardless of the fact that the aetiology of tendinopathy has not been fully understood, therapeutic mechanical loading programs have emerged as being the treatment of choice. In this light, mechanical properties of the tendon and their response to changes in loading or unloading have been the subject of many previous investigations. One of these properties often investigated is strain, a measure of relative deformation. By means of a systematic review, an overview was given of research in this field, with a primary objective to list the methods used and secondary aim to synthesize data on strain mapping in the Achilles tendon. Following the guidelines of the PRISMA statement, 47 articles were found appropriate for qualitative assessment. Achilles tendon strain has been investigated across a variety of contexts, including the response to exercise, walking, unloading, ageing, hormonal changes and weight. Only three studies investigated the effect of the presence of tendinopathy on strain. Ultrasound was the most often used imaging modality to measure or estimate strain. Further methodological parameters, e.g. the location of measurement, differed greatly between all different studies. Nearly all studies considered global strain. Some studies investigated the transverse strain response of the Achilles tendon. Recently, however, the role of local - intratendinous - strain distribution has been found to be of critical importance and further studies should focus on imaging modalities to investigate these local changes.

Transcatheter aortic valve replacement (TAVR) is a safe and effective treatment option for patients deemed at high and intermediate risk for surgical aortic valve replacement. Similar to surgical aortic valves (SAVs), transcatheter aortic valves (TAVs) undergo calcification and mechanical wear over time. However, to date, there have been limited publications on the long-term durability of TAV devices. To assess longevity and mechanical strength of TAVs in comparison to surgical bioprosthetic valves, three-dimensional deformation analysis and strain measurement of the leaflets become an inevitable part of the evaluation. The goal of this study was to measure and compare leaflet displacement and strain of two commonly used TAVs in a side-by-side comparison with a commonly used SAV using a high-resolution digital image correlation (DIC) system. 26-mm Edwards SAPIEN 3, 26-mm Medtronic CoreValve, and 25-mm Carpentier-Edwards PERIMOUNT Magna surgical bioprosthesis were examined in a custom-made valve testing apparatus. A time-varying, spatially uniform pressure was applied to the leaflets at different loading rates. GOM ARAMIS(®) software was used to map leaflet displacement and strain fields during loading and unloading. High displacement regions were found to be at the leaflet belly region of the three bioprosthetic valves. In addition, the frame of the surgical bioprosthesis was found to be remarkably flexible, in contrary to CoreValve and SAPIEN 3 in which the stent was nearly rigid under a similar loading condition. The experimental DIC measurements can be used to characterize the anisotropic materiel behavior of the bioprosthetic heart valve leaflets and validate heart valve computational simulations.