Characterization of Mechanical Properties of an Inhomogeneous Soft Tissue Using Hyper-viscoelastic Modeling and Inverse Finite Element Method

Characterization of mechanical properties of soft tissues using hyper-viscoelastic models has been of special attention in medical fields such as medical diagnosis. In most of these studies, only one single tissue has been analyzed and therefore, in cases that the lower tissue does not function well, generalization of obtained results for a tissue will not be suitable for other tissues. In the current study, mechanical properties of chicken chest and sheep liver, two different study cases, have been determined at the same time using an indentation test. To determine the properties of the obtained model, inverse finite element method (IFEM) has been employed. Moreover, an optimization algorithm has been used for minimizing the differences of force-time curves that are obtained from indentation test and finite element analysis. By separating the force-time curve to two hyperelastic and viscoelastic parts, the parameters of each part have been determined individually using a separate inverse finite element method. This procedure results in reducing the computation time. Eventually, the parameters of viscoelastic and hyperelastic models have been determined by nonlinear root mean square error of 0.0695 and 0.0315, respectively. Comparison of the curves obtained from finite element analyses and those obtained from experiments shows the validity and capability of the employed method.