Biological Fluid Mechanics Research Laboratory, Biomedical Engineering Faculty, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran.
Department of Surgery, Faculty of Medicine, Université Laval and Centre de Recherche du CHU, Quebec, Canada.
Artif Organs. 2020 Mar;44(3):278-287. doi: 10.1111/aor.13552. Epub 2019 Sep 1.
Bioprosthetic heart valves still have poor long-term durability due to calcification and mechanical failure. The function and performance of bioprostheses is known to depend on the collagen architecture and mechanical behavior of the target tissue. So it is necessary to select an appropriate tissue for such prostheses. In this study, porcine, equine, and bovine pericardia were compared histologically and mechanically. The specimens were analyzed under light microscopy. The planar biaxial tests were performed on the tissue samples by applying synchronic loads along the axial (fiber direction) and perpendicular directions. The measured biaxial data were then fitted into both the modified Mooney-Rivlin model and the anisotropic four parameter Fung-type model. The modified Mooney-Rivlin model was applied to the modeling of the bovine, equine, and porcine pericardia using finite element analysis. The equine pericardium illustrated a wavy collagen bundle architecture similar to bovine pericardium, whereas the collagen bundles in the porcine pericardium were thinner and structured. Wavy pericardia may be preferable candidates for transcutaneous aortic valves because they are less likely to be delaminated during crimping. Based on the biaxial tensile test, the specimens indicated some degree of anisotropy; the anisotropy rates of the equine specimens were almost identical, and higher than the other two specimens. In general, porcine pericardium appeared stiffer, based on the greater strain energy magnitude and the average slope of the stress-stretch curves. Moreover, it was less distensible (due to lower areal strain) than the other two pericardial tissues. Furthermore, the porcine model induced localized high stress regions during the systolic and diastolic phases of the cardiac cycle. However, increased mechanical stress on the bioprosthetic leaflets may cause tissue degeneration and reduce the long-term durability of the valve. Based on our observations, the pericardial specimens behaved as anisotropic and nonlinear tissues-well-characterized by both the modified Mooney-Rivlin and the Fung-type models. The results indicate that, compared to bovine pericardium, equine tissue is mechanically and histologically more appropriate for manufacturing heart valve prostheses. The results of this study can be used in the design and manufacture of bioprosthetic heart valves.
生物心脏瓣膜仍然存在较差的长期耐久性，这是由于钙化和机械故障导致的。生物假体的功能和性能已知取决于目标组织的胶原结构和机械性能。因此，有必要为这种假体选择合适的组织。在这项研究中，比较了猪、马和牛的心包膜组织的组织学和力学性能。在光镜下分析标本。通过沿轴向（纤维方向）和垂直方向同步施加负载，对组织样本进行平面双向拉伸测试。然后，将测量的双向数据拟合到改进的 Mooney-Rivlin 模型和各向异性四参数 Fung 型模型中。使用有限元分析，将改进的 Mooney-Rivlin 模型应用于牛、马和猪的心包膜建模。马的心包膜显示出类似于牛的心包膜的波浪形胶原束结构，而猪的心包膜中的胶原束更薄且结构更复杂。波浪形的心包膜可能是经皮主动脉瓣的较好候选物，因为它们在卷曲过程中不太可能分层。基于双向拉伸试验，这些样本显示出一定程度的各向异性；马样本的各向异性率几乎相同，高于其他两种样本。一般来说，基于更大的应变能大小和应力-应变曲线的平均斜率，猪心包表现出更高的刚性。此外，它比其他两种心包组织的可扩展性更小（由于面积应变较小）。此外，猪模型在心脏周期的收缩和舒张阶段会引起局部高应力区域。然而，生物假体瓣叶上的机械应力增加可能导致组织退化，降低瓣膜的长期耐久性。根据我们的观察，心包标本表现为各向异性和非线性组织，这两种特性都可以通过改进的 Mooney-Rivlin 和 Fung 型模型很好地描述。结果表明，与牛心包相比，马组织在机械和组织学上更适合制造心脏瓣膜假体。本研究的结果可用于生物心脏瓣膜的设计和制造。
