Estimation of Fully Three-Dimensional Properties of Passive Soft Tissues: A Coupled Inverse model-experimental Study

Prof. Michael Sacks (University of Texas at Austin)

Friday 27th May, 2016 14:00-15:00 Maths 203


Knowledge of the three-dimensional (3-D) mechanical behavior of soft tissues is essential to understand many areas of physiology and pathophysiology, and to develop suitable biomaterials for replacement. Despite the significant progress made in the two-dimensional experimentation and modeling of soft tissues, there remains a substantial need to obtain and model their full three-dimensional form. Currently, there remains no current method to quantify the full 3D mechanical behavior. Our aim in the present work is, based on a-priori kinematical analyses, to obtain an optimal set of deformation modes using a custom built triaxial device, to obtain new experimental data on the bulk 3-D mechanical behavior of cubic samples of passive myocardium. Second, we developed an inverse finite element model based on an anisotropic pseudoelastic energy function and accurately estimate the parameters involved. The energy function in our model is assumed to be locally orthotropic which is consistent with the (histologically-quantified) myofiber-collagen fibers arrangement.  A significant feature of our inverse model is that it is able to incorporate the histologically-measured spatial variation of local preferred material directions throughout the myocardium sample. In this connection, a series of finite element simulations were carried out to investigate how this variation influences the values of the estimated energy parameters in our model. We also conduct a comparative study of alternative sets of energy parameters to find an optimal set of parameters that are sufficient to capture the mechanical behavior observed in the experiment. Finally, we run additional experiments for some combined deformation modes and use the data to evaluate the descriptive capacity of our model.


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