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

心脏瓣膜置换术是一种心脏直视手术，这意味着外科医生打开胸部和心脏以移除受损的瓣膜。在某些情况下，瓣膜可以在不打开胸腔的情况下更换，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。原因之一是假体的设计和材料选择。尽管双叶机械心脏瓣膜的性能令人满意，但仍存在与其性能相关的相当多的血流动力学并发症。本研究的具体目标是：目的1：设计并制作一种新型双叶机械心脏瓣膜。在这项研究中，提出了一种新的概念，设计和制造的双叶MHV。该型号在几个方面对传统瓣膜（如On-X和St. Jude）进行了设计改进：（1）铰链移动到两侧。这将在打开阶段消除瓣叶上的停滞点，从而降低铰链和瓣叶上血栓形成的风险。此外，瓣膜的3个孔口将血流分开，从而降低瓣膜效率，变成一个。（2）令人惊讶的是，所有类型的机械心脏瓣膜的支架（有效孔口或瓣环）都是圆形的，没有特别的原因。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，将显著改善传统设计和申报设计中双叶MHV的血液动力学，（3）支架可以设计为优化瓣叶的最小和最大张开角。这将控制瓣叶在闭合和打开阶段的动力学，从而最大限度地减少返流。在铰链的设计中，我们注意到它们在每次心跳时被血流有效地冲洗掉，这将降低铰链上形成血栓的风险。目标二：设计和制造价格合理、高保真和高质量的患病瓣膜合成手术培训模型，以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，重点是模拟脱垂二尖瓣重建手术和主动脉瓣修复主动脉瓣狭窄使用合成模型。所提出的合成模型是由水凝胶基聚合物，如聚乙烯醇。在脱垂二尖瓣重建手术的情况下，例如，实施诸如Edwards Lifesciences Myxo的瓣环成形术环以将患病瓣膜改革回到其原始形状。使用所提出的合成模型，模拟整个手术过程。这些模型将具有与预期病变组织相同的几何结构和机械特性。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术的选择。设计和制造合成生物材料制成的经皮瓣膜将是我在未来10年内的主要研究重点。经导管瓣膜为考虑传统瓣膜置换术风险的患者带来了巨大的希望，因为该技术允许临床医生通过导管输送瓣膜，无需传统的心脏直视手术。

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.