Anisotropic hyperelastic properties of porcine pericardium under equibiaxial loading: implications for aortic valve design

This study characterized the anisotropic hyperelastic mechanics of native porcine pericardium and investigated how experimentally derived tissue constitutive models influence fluid-structure interaction simulations of bioprosthetic aortic valves. Fresh pericardium from nine 51-week-old Landrace pigs was subjected to equibiaxial tensile testing under physiological-like hydrated conditions. The tissue showed nonlinear, direction-dependent mechanical behaviour, with the circumferential direction resisting deformation more strongly than the radial direction at higher loads. At approximately 0.48 MPa maximum applied stress, mean circumferential strain was 0.0696 ± 0.0102 compared with 0.1060 ± 0.0297 in the radial direction, a significant directional difference, while the two directions behaved similarly at approximately 50% of maximum stress. Experimental data were fitted using ten anisotropic hyperelastic constitutive models. The Fung, Holzapfel 2005, and four-fiber-family formulations showed strong performance according to the authors’ evaluation index, while the authors noted that rankings based only on coefficient of determination were not sufficient to identify the most predictive formulation. Holzapfel 2005 and four-fiber-family models were ultimately selected for bioprosthetic aortic valve FSI simulations because their explicit fiber-reinforced formulations allowed tissue architecture to be represented directly. Both models predicted global valve performance consistent with normal aortic valve function, including peak velocities of 1.77 and 1.94 m/s, respectively, but produced differences in leaflet motion, jet structure, pressure recovery, and local wall shear stress. Overall, the study demonstrates the importance of experimentally grounded biaxial characterization when selecting constitutive models for bioprosthetic heart valve design and computational hemodynamic assessment.