Full-field bulge test for planar anisotropic tissues: part II--a thin shell method for determining material parameters and comparison of two distributed fiber modeling approaches.

A thin shell method is presented to analyze the results of the bulge test presented in Part I of this paper. The method accounts for the effects of bending, which can be significant for thick tissues inflated from a planar state. We fit two commonly used hyperelastic distributed fiber constitutive models to the stretch-stress resultant data for human skin tissue calculated in Part I from the measured inflation pressure and deformed geometry of the tissue. To validate the method, the resulting parameters were implemented in a specimen-specific finite-element analysis. The method was capable of reproducing the experimentally measured pressure-stretch response of the tissue for a fully integrated distributed fiber model, but not for the pre-integrated distributed fiber models. The parameters obtained for the pre-integrated models significantly underestimated the anisotropic properties of the tissue. The thin shell method presented in this work has been applied to human skin tissues but is sufficiently general to be applied to analyze the inflation response of other planar tissues.