Biaxial mechanical properties of porcine ascending aortic wall tissue

BACKGROUND AND AIM OF THE STUDY: Biaxial mechanical properties have been reported for porcine aortic valve leaflets, but not for the aortic root wall. These data are important for understanding the relationship between tissue material properties and function, providing a baseline for diseased tissue, and for providing a basis for numerical models of aortic mechanics. The study aim was to determine the biaxial material properties of porcine aortic root wall tissue. METHODS: Tissue samples (20 mm x 20 mm) were obtained from the aortic root walls of 18 pigs (anterior and posterior samples from each pig) and tested with a custom-built biaxial tensile testing apparatus. The data were fitted to the strain energy formulation: W = ?[a(long)E11(2) + a(circ)Ecc(2) + 2a(int)E11Ecc], where W is the strain energy, E11 = longitudinal strain, Ecc = circumferential strain, along, a(circ), and aint are the constants that were determined, and represent the longitudinal and circumferential elastic moduli, and interaction between the two axes, respectively. RESULTS: The root wall tissue was less stiff in the longitudinal direction (along = 115.8 +/- 8.4 kPa) than the circumferential direction (a(circ) = 169.9.3 +/- 7.4 kPa). As expected, there was mechanical interaction between the two axes (a(int) = 45.7 +/- 3.4 kPa). Additionally, anterior tissue samples were less stiff than posterior samples. All tissue samples exhibited a linear stress-strain relationship up to 40% strain, in contrast to aortic leaflet tissue, which was highly non-linear. CONCLUSION: These results demonstrated that the porcine aortic root wall tissue is an anisotropic material with linear elastic properties, in contrast to leaflet tissue. Additionally, the data suggest that a finite element model using an isotropic material as a basis for the aorta is insufficient for a physiologically accurate representation.