Biomechanical Properties of Ascending Thoracic Aortic Aneurysms and Mathematical Characterization

To properly understand the natural history of ascending thoracic aortic aneurysms (ATAA) and better assess their risk of rupture, stress analyses asking for biaxial biomechanical data of the tissue are necessary, but information on this matter is restricted in the literature. The present study addressed the role of ATAA on the biomechanical response of vessel wall. Degenerafive ATAA were excised from patients during graft replacement and non-aneurysmal age-matched vessels during autopsy. Uniaxial tensile-tests were conducted on circumferential (CIRC) and longitudinal (LONG) tissue strips. The experimental recordings were reduced by a Fung-type strain-energy function that was found to be appropriate for characterization of the vessel's biomechanical response. The material parameters and rupture properties disclosed that ATAA and non-aneurysmal aorta were anisotropic, i.e. stronger and stiffer in the CIRC direction. ATAA had no influence on tissue strength, but caused stiffening and extensibility reduction. Our findings may serve as input data for the implementation of finite element models to be used as improved surgical intervention criteria.