: This paper presents the investigation of biomechanical behaviour of sheep heart fibre using uniaxial tests in various samples. Non-linear Finite Element models (FEA) that are utilised in understanding mechanisms of different diseases may not be developed without the accurate material properties. This paper presents uniaxial mechanical testing data of the sheep heart fibre. The mechanical uniaxial data of the heart fibre was then used in fitting four constitutive models including the Fung model, Polynomial (Anisotropic), Holzapfel (2005) model, Holzapfel (2000) model and the Four-fibre Family model. Even though the constitutive models for soft tissues including heart myocardium have been presented over several decades, there is still a need for accurate material parameters from reliable hyperelastic constitutive models. Therefore, the aim of this research paper is to select five hyperelastic constitutive models and fit experimental data in the uniaxial experimental data of the sheep heart fibre. A fitting algorithm was made used to optimally fitting and determination of the material parameters based on selected hyperelastic constitutive model. In this study, the evaluation index (EI) was used to measure the performance and capability of each selected anisotropic hyperelatic model. It was observed that the best predictive capability of the mechanical behaviour of sheep heart fibre the Polynomial (anisotropic) model has the EI of 100 and this means that it is the best performance when compared to all the other models.

The function of the omasum is incompletely understood; however, the omasum plays an important role in the transport of appropriately sized feed particles from the reticulorumen to the abomasum, oesophageal groove closure, fermentation of ingesta, and absorption of water, volatile fatty acids, and minerals. The aim of this study is to evaluate the suitable hyperelastic anisotropic model based on biomechanical properties of sheep omasum. The results show that all five (5) hyperelastic models may be suitable for the evaluation of sheep omasum. The average coefficient of determination (R2) of Fung, Polynomial (Anisotropic), Holzapfel (2000), Holzapfel (2005) and Four-Fiber-Family hyperelastic models were found to be 0.79 ± 0.19, 0.95 ± 0.05, 0.92 ± 0.07, 0.93 ± 0.05 and 0.94 ± 0.03, respectively. Also, it was found that the best hyperelastic model for fitting uniaxial data of the sheep omasum was Polynomial (Anisotropic) with EI of 100.0 followed by the Four-Fiber-Family model with EI of 96.18.

When immobile or neuropathic patients are supported by beds or chairs, their soft tissues undergo deformations that can cause pressure ulcers. Current support surfaces that redistribute under-body pressures at vulnerable body sites have not succeeded in reducing pressure ulcer prevalence. Here we show that adding a supporting lateral pressure can counteract the deformations induced by under-body pressure, and that this 'pressure equalisation' approach is a more effective way to reduce ulcer-inducing deformations than current approaches based on redistributing under-body pressure. A finite element model of the seated pelvis predicts that applying a lateral pressure to the soft tissue reduces peak von Mises stress in the deep tissue by a factor of 2.4 relative to a standard cushion (from 113 kPa to 47 kPa)-a greater effect than that achieved by using a more conformable cushion, which reduced von Mises stress to 75 kPa. Combining both a conformable cushion and lateral pressure reduced peak von Mises stresses to 25 kPa. The ratio of peak lateral pressure to peak under-body pressure was shown to regulate deep tissue stress better than underbody pressure alone. By optimising the magnitude and position of lateral pressure, tissue deformations can be reduced to that induced when suspended in a fluid. Our results explain the lack of efficacy in current support surfaces and suggest a new approach to designing and evaluating support surfaces: ensuring sufficient lateral pressure is applied to counteract under-body pressure.

Availability of biaxial mechanical data for heart myocardia remains high in demand for the development of accurate and detailed computational models. The aim of this study is to study the regional difference of wall mechanics using rat heart in the left ventricle (LV), septal wall (STW) and right ventricle (RV). This was achieved by conducting a biaxial test on three rat heart myocardia (i.e LV, RV and STW). Fung, Choi-Vito, Polynomial (Anistropic), Four-Fiber family, Holzapfel (2000) and Holzapfel (2005) hyperelastic models were selected and fitted on the bixial data of the LV, RV and STW. The best hyperelastic model was the selected based on evaluation index (EI) determined from the coefficient of determination (R2). All the six models were then compared in all three rat heart myocardia. The results show that the Polynomial (Anisotropic) model outperforms the other five models in all myocardial tissues with EI’s above 90 % goodness of fit. The Four-fiber-family and the two Holzapfel models perform equally in the LV and STW myocardial tissue between 50 and 70 % goodness of fit. The Fung and Choi-Vito models yielded poor goodness of fit in the LV and STW myocardial tissues. Parameter fitting is useful method in advancing reliable data to be used in the development of accurate computational models.

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