Significant material property differences between the porcine ascending aorta and aortic sinuses.

BACKGROUND AND AIM OF THE STUDY Valve-sparing aortic root replacement techniques have been developed to treat sinus of Valsalva aneurysms. Finite-element models have been used to investigate the effects of altering sinus geometry and aortic root modulus on leaflet stress and strain, which may relate to long-term valve competence. However, these studies have assumed the same material properties for the ascending aorta and aortic sinuses. The study aim was to compare the material properties of the ascending aorta and aortic sinuses in porcine roots. METHODS Square specimens, oriented in the longitudinal and circumferential directions, were excised from porcine ascending aorta and aortic sinuses. Specimens were subjected to equibiaxial mechanical stretch testing. Stress-strain data from the aortic sinuses were fitted to a Fung form strain energy function, whereas ascending aortic data were fitted to a Hookean form. Tissue stiffness was compared at 0.35 Green strain. RESULTS The ascending aorta demonstrated a relatively linear response, unlike the non-linear response of the aortic sinuses. The ascending aorta was stiffer in the circumferential than the longitudinal direction (304.74 +/- 86.47 versus 249.38 +/- 69.81 kPa, p = 0.003), as was the aortic sinus (436.97 +/- 176.30 versus 393.24 +/- 156.10 kPa, p = 0.015). Compared to the sinuses, the ascending aorta was significantly more compliant in both longitudinal (p = 0.001) and circumferential (p = 0.007) directions. CONCLUSION Both, the ascending aorta and aortic sinuses demonstrated anisotropy, with the circumferential direction stiffer than the longitudinal. However, the aortic sinuses were significantly stiffer than the ascending aorta. Finite-element modeling of the aortic root should incorporate such critical differences in the material properties.