Mechanical strength of aneurysmatic and dissected human thoracic aortas at different shear loading modes

Abstract

Rupture of aneurysms and acute dissection of the thoracic aorta are life-threatening events which affect tens of thousands of people per year. The underlying mechanisms remain unclear and the aortic wall is known to lose its structural integrity, which in turn affects its mechanical response to the loading conditions. Hence, research on such aortic diseases is an important area in biomechanics. The present study investigates the mechanical properties of aneurysmatic and dissected human thoracic aortas via triaxial shear and uniaxial tensile testing with a focus on the former. In particular, ultimate stress values from triaxial shear tests in different orientations regarding the aorta's orthotropic microstructure, and from uniaxial tensile tests in radial, circumferential and longitudinal directions were determined. In total, 16 human thoracic aortas were investigated from which it is evident that the aortic media has much stronger resistance to rupture under ‘out-of-plane’ than under ‘in-plane’ shear loadings. Under different shear loadings the aortic tissues revealed anisotropic failure properties with higher ultimate shear stresses and amounts of shear in the longitudinal than in the circumferential direction. Furthermore, the aortic media decreased its tensile strength as follows: circumferential direction > longitudinal direction > radial direction. Anisotropic and nonlinear tissue properties are apparent from the experimental data. The results clearly showed interspecimen differences influenced by the anamnesis of the donors such as aortic diseases or connective tissue disorders, e.g., dissected specimens exhibited on average a markedly lower mechanical strength than aneurysmatic specimens. The rupture data based on the combination of triaxial shear and uniaxial extension testing are unique and build a good basis for developing a 3D failure criterion of diseased human thoracic aortic media. This is a step forward to more realistic modeling of mechanically induced tissue failure i.e. rupture of aneurysms or progression of aortic dissections.

Acoustic scattering in a waveguide with a height discontinuity bridged by a membrane: a tailored Galerkin approach

“…Recently, we investigated the effect of residual stress on the critical pressure for dissection propagation in [13], which demonstrated that residual stress can elevate the critical pressure and thus lower the risk propagation. Gültekin et al [14] used a numerical phase-field approach and, after parameter fitting, found good agreement with experiments by Sommer et al [15] on shear-loading tests of both aneurysmatic and dissected human thoracic aortas that showed that the orthotropic media has significantly greater resistance to out-of-plane than to in-plane shear loading. Sommer et al also found that aortas with dissections had on average much less mechanical strength than aneurysmal specimens.…”

Biomechanical relevance of the microstructure in artery walls with a focus on passive and active components

“…For diseases such as aortic dissections much remains to be uncovered. In particular, we need to learn more about the mechanical properties and the embedded collagen fiber distribution, including that between aortic layers [58,72]. We need to better understand what actually triggers an aortic dissection and how to predict the propagation on the basis of a suitable fracture criterion.…”

A simplified method to account for wall motion in patient-specific blood flow simulations of aortic dissection: Comparison with fluid-structure interaction

“…tear propagation and rupture) necessitate the use of more advanced fluid-structure interaction (FSI) approaches to simulate the flow in this complex aortic condition. FSI couples CFD simulations with finite element modelling (FE) of the aortic wall; however, this method is subject to significant and additional modelling assumptions regarding the mechanical properties of the vessel, which are patient-specific and not known for the case of AD [13]. In addition, FSI models are difficult to setup and demand significant computational effort to be resolved.…”