title: 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 >longitudinaldirection> 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.
authors.affiliation: Institute of Biomechanics, Graz University of Technology, Austria.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Sommer
authors.affiliation: Institute of Biomechanics, Graz University of Technology, Austria.
authors.forename: Selda
authors.initials: S
authors.lastname: Sherifova
authors.affiliation: University Clinic of Cardiac Surgery, Medical University Graz, Austria.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Oberwalder
authors.affiliation: University Clinic of Cardiac Surgery, Medical University Graz, Austria.
authors.forename: Otto E
authors.initials: OE
authors.lastname: Dapunt
authors.affiliation: Department of Cardiothoracic Surgery, NYU Langone Medical Center, New York, NY, USA.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Ursomanno
authors.affiliation: Division of Cardiothoracic Surgery, University of Texas Medical Branch, Galveston, TX, USA.
authors.forename: Abe
authors.initials: A
authors.lastname: DeAnda
authors.affiliation: Departments of Mathematics and Biomedical Engineering, University of North Carolina, Chapel Hill, NC, USA.
authors.forename: Boyce E
authors.initials: BE
authors.lastname: Griffith
authors.affiliation: Institute of Biomechanics, Graz University of Technology, Austria. Electronic address: holzapfel@tugraz.at.
authors.forename: Gerhard A
authors.initials: GA
authors.lastname: Holzapfel
mesh_terms: D000784:Aortic Dissection / Q000473:pathology* / Q000503:physiopathology*; D016880:Anisotropy; D001013:Aorta, Thoracic / Q000293:injuries* / Q000473:pathology / Q000503:physiopathology; D017545:Aortic Aneurysm, Thoracic / Q000473:pathology* / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D033081:Shear Strength; D013314:Stress, Mechanical
keywords: Aortic aneurysm; Aortic dissection; Connective tissue disorder; Thoracic aorta; Ultimate stress