Coupled theoretical and experimental methods to characterize heterogeneous, anisotropic, nonlinear materials: application to cardiovascular tissues

Abstract

The Generalized Anisotropic Inverse Mechanics (GAIM) method is able to provide general tissue characteristics in terms of stiffness, anisotropy strength, and preferred orientation. It allows for the computational dissection of samples, capturing regional differences within a single sample nondestructively. However, the linear assumption implicit in GAIM limited its utility, particularly in the case of cardiovascular soft tissues, which exhibit markedly nonlinear behavior when operating at physiologic strain levels. Therefore, GAIM was extended to consider large-deformation kinematics, a nonlinear closed-form structural model of planar fibrous tissue mechanics was utilized to describe the nonlinear behavior of a cardiovascular soft tissue (rat ventricle wall), and the partitioning method utilized by GAIM was replaced with a more robust partitioning scheme. Then, GAIM was applied in a stepwise fashion (NGAIM) in order to capture the full nonlinear kinetics of cardiovascular soft tissues. Finally, experiments characterizing the three-dimensional loading and failure of healthy porcine ascending aorta were discussed. The work presented in this thesis marks the development and use of novel theoretical and experimental approaches for the analysis of complex cardiovascular soft tissues. An analysis method was developed, NGAIM, that can be applied to examine regional mechanical differences in planar, nonlinear, anisotropic, heterogeneous, tissue samples from all over the body which yields full-field stress. Finally, a partnering was proposed which exploits the characterization capacity of NGAIM with the predictive capacity of the multiscale model to create full three-dimensional simulations of cardiovascular soft tissue behavior.