The Abdominal Aortic Aneurysm Walls: Structural, Mechanical and Constitutive Approaches

An abdominal aortic aneurysm (AAA) is a progressive disease with dynamic structure alteration and following mechanical response to loading. Material constitutive models used to describe AAAs’ walls’ behaviour are highly complicated. Despite the availability of many models, the issue of selecting the most appropriate is still under consideration, especially for patient-specific FEM modelling. Moreover, the problem becomes more complex if it is taken into consideration the severity of AAAs. In the presented study, the severity of AAA was evaluated based on histological imaging of the taken sample. The progressive three-stage model of development was utilised. The mechanical behaviour of the AAAs’ walls was assessed on uniaxial tensile tests. Three of the most popular constitutive models, Holzapfel et al. from 2000 (Holzapfel et al. in J Elasticity 61:1–48, 2000), Raghavan and Vorp from 2000 (Raghavan and Vorp in J Biomech 33:475–482, 2000) and Yeoh’s model proposed by Polzer et al. (Med Eng Phys 35:1282–1289, 2013) were fitted to experimental data for AAAs in different stages of disease severity. According to the findings, models cover the initial stiffness, crucial for wall stress computations, with varying effectiveness. For all of the most popular models, the coefficients of determination (R2) evaluated the goodness of fitting were over 98%, despite the quality of fitting the first part of the Cauchy stress-stretch ratio relationships.