Evaluating ascending aortic aneurysm tissue toughness: Dependence on collagen and elastin contents

Ascending thoracic aortic aneurysms (ATAAs) can lead to a dissection or rupture of the aorta, causing death or disability of the patients. Surgical interventions used to treat this disease are associated with risks of mortality and morbidity. Several studies have investigated the rupture mechanisms of ATAAs; however, underlying reasons behind aortic rupture (failure) have not been fully elucidated and further investigations are necessary. The rupture of pathological aortic tissue is a local phenomenon resulting from defects or tears in the vessel wall. In this work, the toughness-based rupture properties of ATAAs have been examined. The toughness, biaxial tensile properties, and histological properties of aneurysmal and control human ascending thoracic aortas (ATAs) were characterized from four quadrants of surgically excised aortic rings. The aneurysmal tissue population included aortas from patients with bicuspid aortic valves (BAV) and tricuspid aortic valves (TAV). The toughness, incremental modulus, and thickness properties of the aortas were determined and compared regionally. Additionally, to further explore the rupture propensity of ATAAs, the inter-correlation of the toughness properties with histological characteristics have been explored. We found no correlation between toughness and incremental modulus. However, toughness decreased significantly with the amount of collagen. In the outer curvature, there was an increase in incremental modulus with collagen+elastin content, but a decrease in toughness. These results suggest tissue remodeling could affect toughness and stiffness differently in ascending aortic aneurysms.