Towards the Next Generation of Heart Valve Prostheses; the Engineering Aspects

心脏瓣膜置换术是一种开放的心脏手术，意味着外科医生打开胸腔和心脏，移除受损的瓣膜。在某些情况下，不需要打开胸腔就可以替换瓣膜，这被称为微创手术。虽然心脏瓣膜置换术是最常见的心血管外科手术之一，但手术结果和瓣膜的整体性能往往很难预测。其中一个原因是假体的设计和材料的选择。尽管双叶机械心脏瓣膜的性能令人满意，但仍有相当大的血液动力学并发症与其性能相关。本研究的具体目标是：**目标1：新型双叶机械心脏瓣膜的设计与制造。**在本研究中，提出了一种设计与制造双叶机械心脏瓣膜的新概念。该型号在以下几个方面对传统阀门(如ON-X和St.Jude)进行了设计改进：(1)铰链向两侧移动。这将在打开阶段消除传单上的停滞点，从而降低铰链和传单上形成血栓的风险。(2)令人惊讶的是，所有类型的机械瓣膜支架(有效的瓣口或瓣环)都是无缘无故的圆形。我们的初步计算研究表明，支架的椭圆度约为10%，这似乎是可以接受的，在传统设计和拟议设计中，将显著改善双叶MHV的血流动力学。(3)支架的设计可以优化叶的最小和最大张开角度。这将控制小叶在关闭和打开阶段的动态，从而最大限度地减少返流。在铰链的设计中，我们注意到它们有效地被每次心跳上的血流冲洗掉，这将降低铰链上血栓形成的风险。**目标2：设计和制造负担得起的、高保真的、高质量的病变瓣膜的合成外科训练模型，以模拟所有可能的手术方案，如脱垂的二尖瓣重建手术和主动脉瓣关闭不全的主动脉瓣修补术。此外，这些合成模型将成为设计和制造下一代人工瓣膜的基础，这是我的长期目标。**在这项研究中，重点是使用合成模型模拟二尖瓣脱垂重建术和主动脉瓣关闭不全修复术。建议的合成模型是由水凝胶为基础的聚合物，如聚乙烯醇。例如，在脱垂的二尖瓣重建术中，实施了像Edwards Lifesciences Myxo这样的瓣环成形术，以将患病的瓣膜重塑到其原始形状。利用所提出的综合模型，对整个手术过程进行了模拟。这些模型将具有与预期病变组织相同的几何和机械性能。**我的长期目标是使用和推进心血管工程和技术，以扩大使用微创技术进行心脏瓣膜置换的选择。在未来10年内，由合成生物材料制成的经皮瓣膜的设计和制造将是我研究的主要重点。对于传统瓣膜置换风险的患者来说，经导管瓣膜置换术前景看好，因为这项技术允许临床医生通过导管输送瓣膜，从而消除了传统的心脏直视手术的需要。

Heart valve replacement is an open heart operation which means the surgeon opens the chest and heart to remove the damaged valve. In some cases, the valve can be replaced without opening the chest which is called minimally invasive surgery. While heart valve replacement is among the most common cardiovascular surgical procedures, the surgical outcome and the overall performance of the valve is often difficult to predict. One of the reasons is the design and choice of material for construction of the prostheses. Although bileaflet mechanical heart valves perform satisfactorily, there are still considerable hemodynamic complications associated with their performance. The specific goals of the proposed research are: **Objective 1: The design and fabrication of a novel bileaflet mechanical heart valve.**In this study, a novel concept for the design and fabrication of bileaflet MHVs is proposed. This model is a design improvement on conventional valves such as On-X and St. Jude in several ways: (1) the hinges are moved to the sides. This would eliminate the stagnant points on the leaflets in the opening phase and thus, lowers the risk of thrombus formation on hinges and leaflets. Also the 3 orifices of the valve dividing the blood stream and thus decreasing the valve efficiency become one, (2) surprisingly, the stent (effective orifice or annulus) of all types of mechanical heart valves is circular for no particular reason. Our preliminary computational studies show that an ovality of around 10% of the stent, which seems to be acceptable, will significantly improve the hemodynamics of bileaflet MHVs in both conventional designs and the proposed design, and (3) the stent can be designed such that to optimize the minimum and maximum opening angles of leaflets. This will control the dynamics of leaflets in both the closing and the opening phases and thus minimizes the regurgitation flow. In the design of the hinges, we notice that they are effectively washed out by blood stream on each heart beat which will lower the risk of thrombus formation on hinges.**Objective 2: The design and manufacture of affordable, high fidelity, and high quality synthetic surgical training models of diseased valves to simulate all possible surgical options such as prolapse mitral valve reconstructive surgeries and aortic valve repair for aortic insufficiencies. Also, these synthetic models will be the basis for the design and fabrication of the next generation of prosthetic valves which are my long term goals. **In this study, the focus is on the simulation of the prolapse mitral valve reconstructive surgeries and aortic valve repair for aortic insufficiencies using synthetic models. The proposed synthetic models are made of hydrogel-based polymers such as polyvinyl alcohol. In the case of the prolapse mitral valve reconstructive surgery, for instance, an annuloplasty ring such as Edwards Lifesciences Myxo is implemented to reform the diseased valve back to its original shape. Using the proposed synthetic models, the entire surgical procedure is simulated. These models will have the same geometry and mechanical properties to that of the intended diseased tissue.**My long term goals are to use and advance cardiovascular engineering and technology in order to expand options for heart valve replacement using minimally invasive techniques. Design and fabrication of percutaneous valves made of synthetic biomaterials will be the main focus of my research within the next 10 years. Transcatheter valves hold great promise for patients considered risk for conventional valve replacement as this technology allows clinicians to deliver valves via a catheter, eliminating the need for traditional open heart surgery.