Biaxial mechanical properties of the native and glutaraldehyde-treated aortic valve cusp: Part II - A structural constitutive model

We have formulated the first constitutive model to describe the complete me asured planar biaxial stress-strain relationship of the native and glutaral dehyde-treated aortic valve cusp using a structurally guided approach. When applied to native, zero-pressure fixed, and low-pressure fixed cusps, only three parameters were needed to simulate fully the highly anisotropic, and nonlinear in-plane biaxial mechanical behavior. Differences in the behavio r of the native and zero- and low-pressure fixed cusps were found to be pri marily due to changes in the effective fiber stress-strain behavior Further , the model was able to account for the effects of small (<10 deg) misalign ments in the cuspal specimens with respect to the biaxial test axes that in creased the accuracy of the model material parameters. Although based upon a simplified cuspal structure, the model underscored the role of the angula r orientation of the fibers that completely accounted for extreme mechanica l anisotropy and pronounced axial coupling. Knowledge of the mechanics of t he aortic cusp derived from this model may aid in the understanding of fati gue damage in bioprosthetic heart valves and, potentially, lay the groundwo rk for the design of tissue-engineered scaffolds for replacement heart valv es. [S0148-0731(00)00504-5].