Sommer Gerhard, Sherifova Selda, Oberwalder Peter J, Dapunt Otto E, Ursomanno Patricia A, DeAnda Abe, Griffith Boyce E, Holzapfel Gerhard A
Institute of Biomechanics, Graz University of Technology, Austria.
University Clinic of Cardiac Surgery, Medical University Graz, Austria.
J Biomech. 2016 Aug 16;49(12):2374-82. doi: 10.1016/j.jbiomech.2016.02.042. Epub 2016 Feb 26.
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.
动脉瘤破裂和胸主动脉急性夹层是危及生命的事件，每年影响数万人。其潜在机制尚不清楚，已知主动脉壁会失去其结构完整性，进而影响其对加载条件的力学响应。因此，对此类主动脉疾病的研究是生物力学中的一个重要领域。本研究通过三轴剪切和单轴拉伸试验研究了动脉瘤性和夹层性人类胸主动脉的力学性能，重点是前者。特别是，确定了关于主动脉正交各向异性微观结构在不同方向上的三轴剪切试验的极限应力值，以及在径向、周向和纵向的单轴拉伸试验的极限应力值。总共研究了16个人类胸主动脉，从中可以明显看出，主动脉中膜在“面外”剪切载荷下比在“面内”剪切载荷下具有更强的抗破裂能力。在不同的剪切载荷下，主动脉组织呈现各向异性破坏特性，纵向的极限剪切应力和剪切量高于周向。此外，主动脉中膜的拉伸强度按以下顺序降低：周向＞纵向＞径向。从实验数据中可以明显看出各向异性和非线性组织特性。结果清楚地表明，受供体病史（如主动脉疾病或结缔组织疾病）影响，样本间存在差异，例如，夹层样本的平均力学强度明显低于动脉瘤样本。基于三轴剪切和单轴拉伸试验相结合的破裂数据是独一无二的，为建立患病人类胸主动脉中膜的三维破坏准则奠定了良好基础。这是朝着更真实地模拟机械诱导的组织破坏（即动脉瘤破裂或主动脉夹层进展）迈出的一步。
