Characterizing the Inhomogeneity of Aorta Mechanical Properties and its Effect on the Prediction of Injury

Traumatic aortic rupture (TAR) is one of the most significant causes of motor-vehicle fatalities with the majority of injuries occurring in the peri-isthmus region. Despite the fact that TAR accounts for 20% of the total automobile fatalities, there is uncertainty regarding its etiology and underlying mechanisms. Finite element (FE) models are essential for calculating the strains and stresses in aorta during car accidents leading to TAR and assessing the risk of injury and/or failure. Current FE models of the thorax generally consist of simplistic material models for the aorta with the assumptions of isotropy and homogeneity. In order to develop reliable FE models, suitable constitutive relationships are needed which account for the rate dependency, nonlinearity, inhomogeneity, and anisotropy of the aortic tissue. The objectives of this study were twofold. The first objective was to investigate the inhomogeneity of porcine descending thoracic aorta (DTA) using a custom-made nano-indentation test setup. The second objective was to investigate the risk of aortic failure in car accidents by implementing the inhomogeneity of aorta in the Global Human Body Model (GHBM). Changes in stress and strain distributions and the effect of aortic inhomogeneity were evaluated in frontal chest impacts. The results from nanoindentations in the axial orientation showed that distal sections are stiffer than the proximal ones and the medial quadrant shows the least stiff behavior. Results from FE simulations suggest that implementing the inhomogeneity of the aortic tissue had the most influence on the isthmus and ATA regions.