Wan W K, Campbell G, Zhang Z F, Hui A J, Boughner D R
Department of Chemical and Biochemical Engineering, University of Western Ontario, London, Ontario, Canada.
J Biomed Mater Res. 2002;63(6):854-61. doi: 10.1002/jbm.10333.
Although bioprosthetic heart valves offer the benefits of a natural opening and closing, better hemodynamics, and avoidance of life-long anticoagulant therapy, they nevertheless tend to fail in 10-15 years from tears and calcification. Several authors, including the present ones, have identified the rigid stent as a factor contributing to these failures. The ultimate solution is an artificial heart valve that has mechanical properties that allow it to move in conformity with the aortic root during the cardiac cycle, has superior hemodynamics, is nonthrombogenic, will last more than 20 years, and mitigates the need for anticoagulants. We have identified a polymer, polyvinyl alcohol (PVA) hydrogel, that has mechanical properties similar to soft tissue. The purpose of this research is to match the tensile properties of PVA to the porcine aortic root and to fabricate a stent prototype for a bioprosthetic heart valve with the use of the PVA hydrogel. Specimens of 15% w/w PVA were prepared by processing through 1-6 cycles of freezing (-20 degrees C) at 0.2 degrees C/min freeze rate and thawing (+20 degrees C) at different thawing rates (0.2 degrees C/min and 1 degrees C/min), for different holding times (1 and 6 h) at -20 degrees C. Subsequently tensile tests and stress-relaxation tests were conducted on the specimens. The different holding times at -20 degrees C demonstrated no difference in the result. The slower thawing rate improved the tensile properties but did not produce significant changes on the stress-relaxation properties. The nonlinear stress-strain curve for the PVA after the fourth freeze-thaw cycle matched the porcine aortic root within the physiological pressure range. The stress-relaxation curve for PVA also approximated the shape of the aortic root. The complex geometry of an artificial heart valve stent was successfully injection molded. These results, in combination with other preliminary findings for biocompatibility and fatigue behavior, suggest that PVA hydrogel is a promising biomaterial for implants, catheters, and artificial skin.
尽管生物人工心脏瓣膜具有自然开合、更好的血液动力学以及避免终身抗凝治疗等优点，但它们仍倾向于在10至15年内因撕裂和钙化而失效。包括本文作者在内的几位作者已确定刚性支架是导致这些失效的一个因素。最终的解决方案是一种人工心脏瓣膜，其机械性能使其能够在心动周期中与主动脉根部协同运动，具有优异的血液动力学性能，不产生血栓，使用寿命超过20年，并减少对抗凝剂的需求。我们已经确定了一种聚合物，聚乙烯醇（PVA）水凝胶，其机械性能与软组织相似。本研究的目的是使PVA的拉伸性能与猪主动脉根部相匹配，并使用PVA水凝胶制造生物人工心脏瓣膜的支架原型。通过以0.2℃/min的冷冻速率在-20℃下冷冻1至6个循环，并在不同的解冻速率（0.2℃/min和1℃/min）下解冻（+20℃），在-20℃下保持不同的时间（1小时和6小时），制备了15% w/w PVA的样品。随后对样品进行了拉伸试验和应力松弛试验。在-20℃下不同的保持时间在结果上没有差异。较慢的解冻速率改善了拉伸性能，但对应力松弛性能没有产生显著变化。第四个冻融循环后PVA的非线性应力-应变曲线在生理压力范围内与猪主动脉根部相匹配。PVA的应力松弛曲线也近似于主动脉根部的形状。成功注塑了人工心脏瓣膜支架的复杂几何形状。这些结果，结合生物相容性和疲劳行为的其他初步发现，表明PVA水凝胶是一种用于植入物、导管和人工皮肤的有前途的生物材料。
