Cardiovascular Biomechanics Laboratory, Department of Bioengineering and The McGowan Institute, University of Pittsburgh, Pittsburgh, Pennsylvania 15219, USA.
J Biomed Mater Res A. 2010 Jul;94(1):205-13. doi: 10.1002/jbm.a.32659.
Although bioprosthetic heart valves (BHV) remain the primary treatment modality for adult heart valve replacement, continued problems with durability remain. Several studies have implicated flexure as a major damage mode in porcine-derived heterograft biomaterials used in BHV fabrication. Although conventional accelerated wear testing can provide valuable insights into BHV damage phenomena, the constituent tissues are subjected to complex, time-varying deformation modes (i.e., tension and flexure) that do not allow for the control of the amount, direction, and location of flexure. Thus, in this study, customized fatigue testing devices were developed to subject circumferentially oriented porcine BHV tissue strips to controlled cyclic flexural loading. By using this approach, we were able to study layer-specific structural damage induced by cyclic flexural tensile and compressive stresses alone. Cycle levels of 10 x 10(6), 25 x 10(6), and 50 x 10(6) were used, with resulting changes in flexural stiffness and collagen structure assessed. Results indicated that flexural rigidity was markedly reduced after only 10 x 10(6) cycles, and progressively decayed at a lower rate with cycle number thereafter. Moreover, the against-curvature fatigue direction induced the most damage, suggesting that the ventricularis and fibrosa layers have low resistance to cyclic flexural compressive and tensile loads, respectively. The histological analyses indicated progressive collagen fiber delamination as early as 10 x 10(6) cycles but otherwise no change in gross collagen orientation. Our results underscore that porcine-derived heterograft biomaterials are very sensitive to flexural fatigue, with delamination of the tissue layers the primary underlying mechanism. This appears to be in contrast to pericardial BHV, wherein high tensile stresses are considered to be the major cause of structural failure. These findings point toward the need for the development of chemical fixation technologies that minimize flexure-induced damage to extend porcine heterograft biomaterial durability. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.
虽然生物假体心脏瓣膜（BHV）仍然是成人心脏瓣膜置换的主要治疗方式，但耐久性问题仍在继续。有几项研究表明，在用于 BHV 制造的猪源性异种移植物生物材料中，弯曲是主要的损伤模式。尽管传统的加速磨损测试可以为 BHV 损伤现象提供有价值的见解，但组成组织会受到复杂的、时变的变形模式（即张力和弯曲）的影响，这些模式无法控制弯曲的数量、方向和位置。因此，在这项研究中，开发了定制的疲劳测试设备，以使圆周取向的猪 BHV 组织条带承受受控的循环弯曲载荷。通过使用这种方法，我们能够单独研究由循环弯曲拉伸和压缩应力引起的层特异性结构损伤。使用了 10 x 10(6)、25 x 10(6)和 50 x 10(6)的循环水平，评估了弯曲刚度和胶原结构的变化。结果表明，仅在 10 x 10(6)个循环后，弯曲刚度就明显降低，此后随着循环次数的增加，降低速度逐渐降低。此外，与曲率相反的疲劳方向引起的损伤最大，这表明心室层和纤维层分别对循环弯曲压缩和拉伸载荷的抵抗力较低。组织学分析表明，早在 10 x 10(6)个循环时就发生了渐进性胶原纤维分层，但总体胶原方向没有变化。我们的结果强调，猪源性异种移植物生物材料对弯曲疲劳非常敏感，组织层的分层是主要的潜在机制。这似乎与心包 BHV 形成对比，在心包 BHV 中，高拉伸应力被认为是结构失效的主要原因。这些发现表明需要开发化学固定技术，以最大限度地减少弯曲引起的损伤，从而延长猪异种移植物生物材料的耐久性。（c）2010 年威利父子公司。J 生物医学材料研究，2010 年。
