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

点击翻译按钮获取中文摘要

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.