Department of Mechanical and Materials Engineering, Queen's University, 130 Stuart Street, Kingston, ON, K7L 3N6, Canada.
Department of Mechanical and Materials Engineering, Queen's University, 130 Stuart Street, Kingston, ON, K7L 3N6, Canada.
J Mech Behav Biomed Mater. 2021 Jun;118:104395. doi: 10.1016/j.jmbbm.2021.104395. Epub 2021 Mar 10.
This study characterizes the material properties of a viscoelastic, ex vivo porcine ascending aorta under dynamic-loading conditions via pulsatile flow. The deformation of the opaque vessel wall and the pulsatile flow field inside the vessel were recorded using ultrasound imaging. The internal pressure was extracted from the pulsatile flow results and, when coupled with the vessel-wall expansion, was used to calculate the instantaneous elastic modulus from a novel, time-resolved two-dimensional (i.e. axial and circumferential) stress model. The circumferential instantaneous elasticity obtained from the two-dimensional stress model was found to match the uniaxial tensile test for strains below 50%. The agreement in elasticity between the two stress states reveals that the two-dimensional stress model accurately resolves the circumferential stress of the viscoelastic aorta at physiological strains (8%-30%). At higher strains, results from pulsatile flow generated a more compliant response than the uniaxial measurements. Viscoelastic properties (storage modulus and loss factor) were also calculated using the two-dimensional stress model and compared to those obtained from uniaxial tests. While instantaneous elasticity matched between the cylindrical and uniaxial loading, the viscoelastic behaviour significantly diverged between stress states. The storage modulus obtained from the pulsatile flow data was dependent on mean Reynolds number, while the uniaxial storage modulus results exhibited a strong inverse dependency on the frequency. The loss factor for the pulsatile flow data increased alongside the frequency, while the uniaxial data indicated a constant loss factor over the entire frequency range. The results of the current study show that the two-dimensional stress model can accurately extract the material properties of the ex vivo porcine aorta.
本研究通过脉动流对粘弹性、离体猪升主动脉在动态载荷条件下的材料特性进行了描述。使用超声成像记录不透明血管壁的变形和血管内的脉动流场。从脉动流结果中提取内部压力，并将其与血管壁扩张结合使用，从一种新颖的、时变的二维（即轴向和周向）应力模型计算瞬时弹性模量。从二维应力模型获得的周向瞬时弹性在应变低于 50%时与单轴拉伸测试相匹配。两种应力状态下的弹性一致性表明，二维应力模型在生理应变（8%-30%）下准确地解析了粘弹性主动脉的周向应力。在较高的应变下，脉动流产生的响应比单轴测量更具弹性。还使用二维应力模型计算了粘弹性特性（存储模量和损耗因子），并将其与单轴测试获得的结果进行了比较。虽然圆柱形和单轴加载之间的瞬时弹性匹配，但两种应力状态下的粘弹性行为明显不同。从脉动流数据获得的存储模量取决于平均雷诺数，而单轴存储模量结果表现出与频率的强烈反比关系。脉动流数据的损耗因子随频率增加而增加，而单轴数据则表明在整个频率范围内损耗因子保持不变。本研究的结果表明，二维应力模型可以准确地提取离体猪升主动脉的材料特性。
