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

心脏瓣膜置换术是一种开胸手术，即外科医生打开胸腔和心脏，取出受损的瓣膜。在某些情况下，可以在不打开胸腔的情况下更换瓣膜，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通常难以预测。其中一个原因是假肢的设计和材料的选择。虽然双肢机械心脏瓣膜的表现令人满意，但仍有相当多的血流动力学并发症与它们的表现相关。本研究的具体目标是：**目的1：设计和制造一种新型双肢机械心脏瓣膜。**在本研究中，提出了一种设计和制造双片mhv的新概念。这种模型在设计上对on - x和St. Jude等传统阀门进行了改进，从几个方面进行了改进：(1)铰链移到了两侧。这样可以在打开阶段消除小叶上的停滞点，从而降低铰链和小叶上血栓形成的风险。而且瓣膜的3个孔将血流分开，从而降低了瓣膜的效率，(2)令人惊讶的是，所有类型的机械心脏瓣膜的支架（有效孔或环）都是圆形的，没有特别的原因。我们的初步计算研究表明，在常规设计和提出的设计中，大约10%的椭圆度将显著改善双小叶mhv的血流动力学，这似乎是可以接受的，并且(3)可以设计支架以优化小叶的最小和最大开口角度。这将在关闭和打开阶段控制小叶的动态，从而最小化反流。在铰链的设计中，我们注意到它们在每次心脏跳动时都被血流有效地冲洗掉，这将降低铰链上血栓形成的风险。**目的2：设计和制造经济、高保真、高质量的病变瓣膜合成手术训练模型，模拟所有可能的手术选择，如脱垂二尖瓣重建手术和主动脉瓣修复主动脉功能不全。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。**本研究的重点是使用合成模型模拟二尖瓣脱垂重建手术和主动脉瓣修复主动脉功能不全。提出的合成模型是由水凝胶基聚合物如聚乙烯醇制成的。例如，在二尖瓣脱垂重建手术中，使用Edwards Lifesciences Myxo等环形成形术环将患病的二尖瓣恢复到原来的形状。利用所提出的综合模型，模拟了整个手术过程。这些模型将具有与预期病变组织相同的几何形状和机械特性。**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。人工合成生物材料经皮瓣膜的设计与制造将是我未来10年的主要研究方向。经导管瓣膜对于那些被认为存在传统瓣膜置换术风险的患者来说具有很大的前景，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内直视手术的需要。

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.