Mines Saint-Étienne, Univ Lyon, Univ Jean Monnet, INSERM, U1059 SAINBIOSE, Centre CIS, 42023, Saint-Étienne, France.
Biomech Model Mechanobiol. 2019 Oct;18(5):1507-1528. doi: 10.1007/s10237-019-01161-1. Epub 2019 May 7.
Abdominal aortic aneurysm is a prevalent cardiovascular disease with high mortality rates. The mechanical response of the arterial wall relies on the organizational and structural behavior of its microstructural components, and thus, a detailed understanding of the microscopic mechanical response of the arterial wall layers at loads ranging up to rupture is necessary to improve diagnostic techniques and possibly treatments. Following the common notion that adventitia is the ultimate barrier at loads close to rupture, in the present study, a finite element model of adventitial collagen network was developed to study the mechanical state at the fiber level under uniaxial loading. Image stacks of the rabbit carotid adventitial tissue at rest and under uniaxial tension obtained using multi-photon microscopy were used in this study, as well as the force-displacement curves obtained from previously published experiments. Morphological parameters like fiber orientation distribution, waviness, and volume fraction were extracted for one sample from the confocal image stacks. An inverse random sampling approach combined with a random walk algorithm was employed to reconstruct the collagen network for numerical simulation. The model was then verified using experimental stress-stretch curves. The model shows the remarkable capacity of collagen fibers to uncrimp and reorient in the loading direction. These results further show that at high stretches, collagen network behaves in a highly non-affine manner, which was quantified for each sample. A comprehensive parameter study to understand the relationship between structural parameters and their influence on mechanical behavior is presented. Through this study, the model was used to conclude important structure-function relationships that control the mechanical response. Our results also show that at loads close to rupture, the probability of failure occurring at the fiber level is up to 2%. Uncertainties in usually employed rupture risk indicators and the stochastic nature of the event of rupture combined with limited knowledge on the microscopic determinants motivate the development of such an analysis. Moreover, this study will advance the study of coupling microscopic mechanisms to rupture of the artery as a whole.
腹主动脉瘤是一种常见的心血管疾病，死亡率很高。动脉壁的力学响应依赖于其微观结构成分的组织和结构行为，因此，需要详细了解动脉壁层在直至破裂的范围内的微观力学响应，以改进诊断技术并可能改进治疗方法。根据接近破裂时的负载最终由外膜来承担的常见观点，本研究中，开发了一种外膜胶原网络的有限元模型，以研究单轴加载下纤维水平的力学状态。本研究使用多光子显微镜获取的兔颈动脉外膜组织在静止和单轴拉伸下的图像堆栈，以及从先前发表的实验中获得的力-位移曲线。从共聚焦图像堆栈中提取一个样本的形态参数，如纤维方向分布、波纹度和体积分数。采用反向随机抽样方法与随机游走算法相结合，对胶原网络进行数值模拟重构。然后使用实验的应力-应变曲线对模型进行验证。模型显示了胶原纤维在加载方向上解缠和重新取向的显著能力。这些结果进一步表明，在高拉伸时，胶原网络表现出高度的非仿射行为，对每个样本都进行了量化。进行了全面的参数研究，以了解结构参数之间的关系及其对力学行为的影响。通过这项研究，模型被用于得出控制力学响应的重要结构-功能关系。我们的结果还表明，在接近破裂的负载下，纤维水平发生故障的概率高达 2%。通常使用的破裂风险指标的不确定性以及破裂事件的随机性质，加上对微观决定因素的了解有限，这促使进行了这样的分析。此外，这项研究将推进将微观机制与整个动脉破裂相耦合的研究。
