Department of Mechanical Engineering, Fu Foundation School of Engineering and Applied Science, Columbia University, New York, NY, USA; Division of Cardiac, Thoracic and Vascular Surgery, Section of Pediatric and Congenital Cardiac Surgery, New-York Presbyterian - Morgan Stanley Children's Hospital, Columbia University Medical Center, New York, NY, USA.
Department of Civil Engineering and Engineering Mechanics, Fu Foundation School of Engineering and Applied Science, Columbia University, New York, NY, USA.
Biomaterials. 2019 Dec;225:119493. doi: 10.1016/j.biomaterials.2019.119493. Epub 2019 Sep 17.
The native human heart valve leaflet contains a layered microstructure comprising a hierarchical arrangement of collagen, elastin, proteoglycans and various cell types. Here, we review the various experimental methods that have been employed to probe this intricate microstructure and which attempt to elucidate the mechanisms that govern the leaflet's mechanical properties. These methods include uniaxial, biaxial, and flexural tests, coupled with microstructural characterization techniques such as small angle X-ray scattering (SAXS), small angle light scattering (SALS), and polarized light microscopy. These experiments have revealed complex elastic and viscoelastic mechanisms that are highly directional and dependent upon loading conditions and biochemistry. Of all engineering materials, polymers and polymer-based composites are best able to mimic the tissue-level mechanical behavior of the native leaflet. This similarity to native tissue permits the fabrication of polymeric valves with physiological flow patterns, reducing the risk of thrombosis compared to mechanical valves and in some cases surpassing the in vivo durability of bioprosthetic valves. Earlier work on polymeric valves simply assumed the mechanical properties of the polymer material to be linear elastic, while more recent studies have considered the full hyperelastic stress-strain response. These material models have been incorporated into computational models for the optimization of valve geometry, with the goal of minimizing internal stresses and improving durability. The latter portion of this review recounts these developments in polymeric heart valves, with a focus on mechanical testing of polymers, valve geometry, and manufacturing methods.
天然人心脏瓣膜小叶包含分层微观结构,由胶原、弹性蛋白、糖胺聚糖和各种细胞类型的分层排列组成。在这里,我们回顾了各种已被用于探测这种错综复杂的微观结构的实验方法,并试图阐明控制小叶机械性能的机制。这些方法包括单轴、双轴和弯曲试验,以及微观结构表征技术,如小角 X 射线散射 (SAXS)、小角光散射 (SALS) 和偏光显微镜。这些实验揭示了复杂的弹性和粘弹性机制,这些机制具有高度的方向性,并取决于加载条件和生物化学。在所有工程材料中,聚合物和聚合物基复合材料最能模拟天然小叶的组织水平机械行为。这种与天然组织的相似性允许制造具有生理流动模式的聚合物瓣膜,与机械瓣膜相比,降低了血栓形成的风险,在某些情况下甚至超过了生物瓣的体内耐久性。早期关于聚合物瓣膜的工作简单地假设聚合物材料的机械性能为线弹性,而最近的研究已经考虑了全超弹性应力-应变响应。这些材料模型已被纳入瓣膜几何形状的优化计算模型中,目标是最小化内部应力并提高耐久性。本综述的后一部分回顾了聚合物心脏瓣膜的这些发展,重点介绍了聚合物的机械测试、瓣膜几何形状和制造方法。