Microstructure-informed viscoelasticity for the ascending thoracic aortic wall in the healthy and aneurysmal state

A microstructure-informed viscoelastic characterization of the wall of the ascending thoracic aorta in healthy and aneurysmal human donors under finite strains is presented. Planar biaxial quasi-static and stress-relaxation tests were conducted on six different regional specimens extending from the aortic root to the aortic arch. The samples were obtained from four aneurysmal and four healthy donors. The collagen architecture was quantified by second-harmonic generation imaging. The measured microstructural features were integrated into a thermodynamically consistent constitutive framework with distinct isotropic and anisotropic contributions to the elastic and viscous response. This allows for the analysis of orientation-dependent dissipation at finite strains for a discrete number of representative collagen fibers. The model successfully captured specimen-specific responses and provided a parameter set directly linked to collagen organization. This enabled the identification of regional and pathological differences that cannot be inferred solely from macroscopic behavior. Complementary convergence and sensitivity analyses established practical numerical guidelines for spatial and temporal discretization to ensure efficient implementation. Additionally, this study provides a donor-specific parameter set for this viscoelastic model, which can be used for the in silico assessment of dynamic phenomena of the aortic wall. This is relevant for disease progression and the virtual long-term evaluation of surgical interventions.