Modeling the Propagation of Aortic Dissection

Abstract: Aortic dissection is a diseased condition of the aorta in which there is an initial tear to the intimal layer propagating in the radial direction initially then causing delamination of the arterial layers creating a false lumen. It is estimated to effect 30 individuals in one million per year. The dissection is fatal when it ruptures, and 90 % of the patients die within three months if not diagnosed. This study presents the first steps towards modeling the propagation of aortic dissection. The aorta was treated as a three-layered fiber-reinforced composite structure, and the Tsai-Wu failure criterion was employed to obtain the 3-D failure surface for the healthy and dissected human aortic media. To be able to obtain Tsai-Wu coefficients, uniaxial tensile tests in the axial, circumferential, and radial direction, and additionally in-plane (axial-circumferential plane) and out-of-plane shear tests in different orientations were performed on human aortic medias. To our knowledge the combination of applied tests and performingof out-of-plane shear tests on aortic tissues is novel. The results showed that the aortic media was the weakest in radial direction under tensile loading. Furthermore, the media was much stronger under out-of-plane shear loading than under in-plane shear loading. In order to consider influences of stress coupling between axial and circumferential directions, an optimal specimen geometry was designed for biaxial tensile testing by the help of finite element analyses. A cruciform geometry with a reduced cross-section in the biaxially loaded zone was found to fit our purposes the best. The preparation protocol to achieve this geometry is currently under investigation. For aortic tissues, all compressive strengths and some biaxial tensile strengths needed to be assumed since they are yet not possible to obtain from mechanical tests. Finally, failure surfaces described by the Tsai-Wu criterion were plotted in 2-D using the analyzed experimental data, with different assumptions in compressive and biaxial tensile strengths.