Department of Aerospace Engineering and Engineering Mechanics, The University of Texas at Austin, Austin, TX 78712, USA.
Department of Biomedical Engineering, The University of Texas at Austin, Austin, TX 78712, USA.
Acta Biomater. 2021 Mar 15;123:154-166. doi: 10.1016/j.actbio.2020.12.006. Epub 2020 Dec 15.
The right ventricular myocardium, much like the rest of the right side of the heart, has been consistently understudied. Presently, little is known about its mechanics, its microstructure, and its constitutive behavior. In this work, we set out to provide the first data on the mechanics of the mature right ventricular myocardium in both simple shear and uniaxial loading and to compare these data to the mechanics of the left ventricular myocardium. To this end, we tested ovine tissue samples of the right and left ventricle under a comprehensive mechanical testing protocol that consisted of six simple shear modes and three tension/compression modes. After mechanical testing, we conducted a histology-based microstructural analysis on each right ventricular sample that yielded high resolution fiber distribution maps across the entire samples. Equipped with this detailed mechanical and histological data, we employed an inverse finite element framework to determine the optimal form and parameters for microstructure-based constitutive models. The results of our study show that right ventricular myocardium is less stiff then the left ventricular myocardium in the fiber direction, but similarly exhibits non-linear, anisotropic, and tension/compression asymmetric behavior with direction-dependent Poynting effect. In addition, we found that right ventricular myocardial fibers change angles transmurally and are dispersed within the sheet plane and normal to it. Through our inverse finite element analysis, we found that the Holzapfel model successfully fits these data, even when selectively informed by rudimentary microstructural information. And, we found that the inclusion of higher-fidelity microstructural data improved the Holzapfel model's predictive ability. Looking forward, this investigation is a critical step towards understanding the fundamental mechanical behavior of right ventricular myocardium and lays the groundwork for future whole-organ mechanical simulations.
右心室心肌与心脏右侧的其他部分一样，一直以来都被研究得不够充分。目前，人们对其力学特性、微观结构及其本构行为知之甚少。在这项工作中，我们旨在提供成熟的右心室心肌在纯剪切和单轴加载下的力学特性的首批数据，并将这些数据与左心室心肌的力学特性进行比较。为此，我们根据包括六种纯剪切模式和三种拉伸/压缩模式的综合力学测试方案，对右心室和左心室的绵羊组织样本进行了测试。在力学测试之后，我们对每个右心室样本进行了基于组织学的微观结构分析，得到了整个样本的高分辨率纤维分布图谱。有了这些详细的力学和组织学数据，我们采用了反有限元框架来确定基于微观结构的本构模型的最佳形式和参数。我们的研究结果表明，在纤维方向上，右心室心肌比左心室心肌的刚性小，但同样表现出非线性、各向异性和拉伸/压缩不对称行为，且具有方向依赖性的泊松效应。此外，我们发现右心室心肌纤维在穿壁方向上改变角度，并在片层平面内分散且垂直于它。通过我们的反有限元分析，我们发现 Holzapfel 模型成功地拟合了这些数据，即使是在仅使用基本微观结构信息的情况下。而且，我们发现包含更精确的微观结构数据可以提高 Holzapfel 模型的预测能力。展望未来，这项研究是理解右心室心肌基本力学特性的关键一步，为未来的整体器官力学模拟奠定了基础。
