Circumferential variations in passive and active mechanical properties of healthy and aneurysmal ascending aorta

Healthy and pathologic tissues of human ascending aorta (AA) were obtained from autopsy and surgical pathology. Each aortic ring was classified as a healthy (nondilated AA) or diseased (dilated AA) group. Within the diseased group, the samples were further sub-classified as tricuspid aortic valve (TAV), fused tricuspid aortic valve (fTAV) and congenital bicuspid aortic valve (BAV). Each aortic ring was sectioned into quadrants; anterior, posterior, inner curvature and outer curvature. Samples from each quadrant were processed for passive equi-biaxial tensile testing. Phenylephrine was used to contract vascular smooth muscle cells (VSMCs) for active equi-biaxial tensile testing. We observed local variations in stiffness in healthy, TAV, fTAV and BAV tissues. fTAV tissues were significantly stiffer than diseased TAV and BAV tissues and a different local remodeling between diseased fTAV and other diseased tissues exists. Also local variations of anisotropic properties in all groups exist and fTAV tissues are significantly more anisotropic than healthy tissues suggesting a change in microstructure. There was a significant increase in stiffness for tissues under active testing compared to tissues under passive testing. Moreover, we observed an increase of anisotropy for tissues under active testing.