Department of Mechanical Engineering, McGill University, 817 Sherbrooke Street West, Montreal, H3A 0C3, Canada; Department of Biomedical Engineering, McGill University, 817 Sherbrooke Street West, Montreal, H3A 0C3, Canada.
Department of Mechanical Engineering, McGill University, 817 Sherbrooke Street West, Montreal, H3A 0C3, Canada.
J Mech Behav Biomed Mater. 2019 Nov;99:27-46. doi: 10.1016/j.jmbbm.2019.07.008. Epub 2019 Jul 15.
A layer-specific hyperelastic and viscoelastic characterization of human descending thoracic aortas was experimentally performed. Healthy aortas from twelve beating heart donors with an average age of 49.4 years, were received from Transplant Québec. Axial and circumferential strips were prepared from the specimens. They were dissected into intima, media and adventitia layers. Measurements of the opening angles were used to identify the circumferential residual stresses. Uniaxial tensile tests on axial and circumferential strips, together with the Gasser-Ogden-Holzapfel material model, were used to characterize the hyperelastic behaviour of the three aortic layers for each donor. Uniaxial harmonic excitations at different frequency, superimposed to initial stretch values, were used to characterize the viscoelastic behaviour. The storage modulus and the loss tangent were obtained for each layer in both directions; comparison to intact aortic wall was also performed. The generalized Maxwell model, within the framework of nonlinear viscoelasticity with internal variables, was used to obtain the constitutive material parameters. Results showed a positive correlation (p < 0.05 for circumferential media and adventitia) between stiffness and donor age for the three layers of the aorta in both axial and circumferential directions. A significant increase (around 50%) of the storage modulus (i.e. dynamic stiffness) was observed between the quasi-static value and loading at 1 Hz frequency, while further increase in frequency marginally affected its value. The loss tangent was only slightly influenced by the stretch value, which justified the use of the viscoelastic model adopted. Finally, similar loss tangent values were found for the three aortic layers.
采用实验方法对人体降主动脉的层特异性超弹性和粘弹性进行了表征。从来自 Transplan Québec 的 12 位年龄在 49.4 岁的健康心脏供体中获得了降主动脉样本。从样本中制备了轴向和周向条带。它们被解剖成内膜、中膜和外膜层。通过测量开口角度来识别周向残余应力。对轴向和周向条带进行单轴拉伸测试，并结合 Gasser-Ogden-Holzapfel 材料模型，用于表征每个供体的三个主动脉层的超弹性行为。在不同频率下对轴向和周向条带施加单轴谐波激励，叠加初始拉伸值，用于表征粘弹性行为。获得了每个层在两个方向上的储能模量和损耗角正切；也与完整的主动脉壁进行了比较。在具有内变量的非线性粘弹性框架内，使用广义 Maxwell 模型来获得本构材料参数。结果表明，在轴向和周向两个方向上，主动脉三层的刚度与供体年龄之间呈正相关（周向中膜和外膜的 p 值<0.05）。在准静态值和 1 Hz 频率下的加载之间观察到储能模量（即动态刚度）显著增加（约 50%），而频率的进一步增加对其值的影响很小。损耗角正切仅受拉伸值的轻微影响，这证明了所采用的粘弹性模型的合理性。最后，发现三个主动脉层的损耗角正切值相似。
