Wang Qiang, McGoron Anthony J, Bianco Richard, Kato Yasushi, Pinchuk Leonard, Schoephoerster Richard T
Department of Biomedical Engineering, Florida International University, Miami, USA.
J Heart Valve Dis. 2010 Jul;19(4):499-505.
A novel trileaflet polymer valve, which is a composite design of a biostable and biocompatible polymer poly(styrene-block-isobutylene-block-styrene) (SIBS) with an embedded reinforcement polyethylene terephthalate (PET) fabric, is being developed with the intention of providing a valve that has low thrombogenicity, high durability and favorable hemodynamic performance. The study aim was to investigate the biocompatibility and performance of this SIBS valve prototype under physiological loading conditions similar to humans, using a large-animal model.
Four SIBS valves (two with surface modification using dimyristoyl phosphatidylcholine, DMPC), and two commercial Magna tissue valves, were implanted into sheep. Hemodynamic and blood chemistry measurements were performed periodically during the postoperative period. The explanted SIBS valves were extensively evaluated using macroscopic, histological, radiographical and scanning electron microscopy/energy-dispersive spectroscopy analysis.
Three animals, one with the DMPC-coated SIBS valve, and two with the Magna valves, reached the end of the study in satisfactory clinical condition, and were euthanized after 20 weeks. The other three animals (two with SIBS valves, one with a DMPC-coated SIBS valve) died at 6, 6.5, and 10 weeks due either to material failure or myocardial infarction. The explanted valves exhibited stent deformation and cracks on the leaflets, which exposed the underlying PET fabric and resulted in severe blood and tissue reactions. Extrinsic calcification was identified on the leaflets, and was associated with the regions of surface cracks.
The SIBS valve failed in animal testing because of material failure and calcification. The physical properties of SIBS must be improved in order to provide the structural integrity required for long-term in-vivo use in the form of a heart valve.
一种新型三叶聚合物瓣膜正在研发中，它是由生物稳定且生物相容的聚合物聚（苯乙烯 - 嵌段 - 异丁烯 - 嵌段 - 苯乙烯）（SIBS）与嵌入的增强聚酯纤维（PET）织物组成的复合设计，旨在提供一种具有低血栓形成性、高耐久性和良好血流动力学性能的瓣膜。本研究的目的是使用大型动物模型，在类似于人体的生理负荷条件下，研究这种SIBS瓣膜原型的生物相容性和性能。
将四个SIBS瓣膜（两个使用二肉豆蔻酰磷脂酰胆碱（DMPC）进行表面改性）和两个商业Magna组织瓣膜植入绵羊体内。术后定期进行血流动力学和血液化学测量。对取出的SIBS瓣膜进行宏观、组织学、放射学以及扫描电子显微镜/能谱分析等广泛评估。
三只动物，一只植入DMPC涂层的SIBS瓣膜，两只植入Magna瓣膜，在临床状况良好的情况下完成了研究，并在20周后实施安乐死。另外三只动物（两只植入SIBS瓣膜，一只植入DMPC涂层的SIBS瓣膜）在6周、6.5周和10周时因材料故障或心肌梗死死亡。取出的瓣膜显示出支架变形和瓣叶上的裂缝，这些裂缝暴露了下面的PET织物，并导致严重的血液和组织反应。在瓣叶上发现了外部钙化，并与表面裂缝区域相关。
SIBS瓣膜在动物试验中失败是由于材料故障和钙化。必须改善SIBS的物理性能，以提供作为心脏瓣膜长期体内使用所需的结构完整性。
