Department of Mechanical Engineering, Boston University, Boston, MA, United States.
Department of Mechanical Engineering, Boston University, Boston, MA, United States; Department of Biomedical Engineering, Boston University, Boston, MA, United States.
J Mech Behav Biomed Mater. 2018 Jan;77:745-753. doi: 10.1016/j.jmbbm.2017.08.002. Epub 2017 Aug 5.
The complex three-dimensional elastin network is a major load-bearing extracellular matrix (ECM) component of an artery. Despite the reported anisotropic behavior of arterial elastin network, it is usually treated as an isotropic material in constitutive models. Our recent multiphoton microscopy study reported a relatively uniform elastin fiber orientation distribution in porcine thoracic aorta when imaging from the intima side (Chow et al., 2014). However it is questionable whether the fiber orientation distribution obtained from a small depth is representative of the elastin network structure in the arterial wall, especially when developing structure-based constitutive models. To date, the structural basis for the anisotropic mechanical behavior of elastin is still not fully understood. In this study, we examined the transmural variation in elastin fiber orientation distribution in porcine thoracic aorta and its association with elastin anisotropy. Using multi-photon microscopy, we observed that the elastin fibers orientation changes from a relatively uniform distribution in regions close to the luminal surface to a more circumferential distribution in regions that dominate the media, then to a longitudinal distribution in regions close to the outer media. Planar biaxial tensile test was performed to characterize the anisotropic behavior of elastin network. A new structure-based constitutive model of elastin network was developed to incorporate the transmural variation in fiber orientation distribution. The new model well captures the anisotropic mechanical behavior of elastin network under both equi- and nonequi-biaxial loading and showed improvements in both fitting and predicting capabilities when compared to a model that only considers the fiber orientation distribution from the intima side. We submit that the transmural variation in fiber orientation distribution is important in characterizing the anisotropic mechanical behavior of elastin network and should be considered in constitutive modeling of an artery.
复杂的三维弹性蛋白网络是动脉的主要承重细胞外基质 (ECM) 成分。尽管已有研究报道动脉弹性蛋白网络具有各向异性行为，但在本构模型中通常将其视为各向同性材料。我们最近的多光子显微镜研究报告称，当从内膜侧成像时，猪胸主动脉中的弹性纤维取向分布相对均匀（Chow 等人，2014 年）。然而，从较小深度获得的纤维取向分布是否代表动脉壁中弹性蛋白网络结构尚不确定，特别是在开发基于结构的本构模型时。迄今为止，弹性蛋白各向异性力学行为的结构基础仍不完全清楚。在这项研究中，我们检查了猪胸主动脉中弹性纤维取向分布的跨壁变化及其与弹性蛋白各向异性的关系。使用多光子显微镜，我们观察到弹性纤维取向从靠近腔表面的区域的相对均匀分布到主导中膜的区域的更周向分布，然后到靠近外膜的区域的纵向分布发生变化。进行平面双向拉伸试验以表征弹性蛋白网络的各向异性行为。开发了一种新的基于结构的弹性蛋白网络本构模型，以纳入纤维取向分布的跨壁变化。与仅考虑内膜侧纤维取向分布的模型相比，新模型很好地捕捉了弹性蛋白网络在等双轴和非等双轴加载下的各向异性力学行为，并且在拟合和预测能力方面都有所提高。我们认为，纤维取向分布的跨壁变化对于表征弹性蛋白网络的各向异性力学行为很重要，在动脉的本构建模中应予以考虑。
