On the Mechanical Behavior of Healthy and Aneurysmal Abdominal Aorta

Abdominal aortic aneurysm (AAA) is a pathological condition of the infrarenal aorta characterized by a local dilatation of the arterial wall. The main histopathologic features of an AAA are smooth muscle cell death and loss of elastin. The biomechanical behavior of AAAs has been widely studied to determine the rupture potential according to the principles of material failure. However, most prior approaches are limited by the use of data from uniaxial tensile testing and by the assumption of material isotropy, leading to inaccurate characterization of the 3D multiaxial mechanical response of the aneurysmal tissue. To date, the best data available on the behavior of human abdominal aorta (AA) and AAA to planar biaxial testing are the ones reported by Vande Geest et al. [1,2]. In a recent work [3], we considered a structurally motivated four-fiber family strain energy function (SEF) [4] to capture the biaxial behavior of the human AA and AAA from Vande Geest et al. [1,2]. We showed that this constitutive relation fits human data better than prior models and most importantly it captures the stiffening of the arterial wall related to both aging and aneurysmal development. These changes in mechanical behavior are mirrored by changes in the best-fit values of the parameters, with a progressive decrease of the isotropic part attributed to elastin and a parallel increase in values associated with the families of collagen fibers.