Bioprosthetic Heart Valve Leaflets Function Optimum And The Stent Modeling Manufacture Method Research

Prosthetic heart valve have become increasingly used in the treatment of cardiovalvular disease since their introduction in the early 1960s. These artificial heart valve may be either the mechanical heart valve or the bioprosthetic heart valve (BHV). The BHV that consists of valvular leaflets, supporting stent and sutural ring is a type of man- made heart valve. Valvular leaflets made by high molecular material of porcine or bovine pericardial can be opened or closed by ejected blood. Supporting stent not only act as supporting and bearing forces but also act as configuration function. The bioprosthetic heart valve is similar to human heart valve on flow field. Its flow pattern is central-like. Although its function is improved in antihemolysis and antithrombotic, the efficiencies in device design of the bioprosthetic heart valve is still not satisfied. The united manufacturing standard on the BHV stent hasn't been made. About the design and manufacture of the BHV, some problems have not been solven untill now. However, with the development of the flow field theory and the biomaterials theory, the research on the stress analysis on the BHV leaflet and the precision modeling on the BHV stent will give a great help to prolonging the lifetime of BHV.In order to reach the function of a human being's heart valve, the geometrical parametric model of bioprosthetic heart valve is established based on the heart anatomy. Based on the traditional design theory and the modern design method, we get the model of the BHV by analyzing natural shape of human valve. The wire stent of BHV is used instead of the muscle papillaris and the revolving curved surface is applied to valvular leaflets. The sutural ring of BHV replaces the annulus fibrosus. The stress distribution of curved surface with different shapes is analyzed based on Membrane theory. It is showed that the stress distribution of the spherical surface is comparatively reasonable. While the stress distribution of cylindrical surface is not uniform. The stress of the paraboloidal surface and the ellipsoid surface change in accordance with the change of coordinate points. Therefore, the stress distribution of the paraboloidal surface, the ellipsoid surface and spherical surface has been discussed in detail by the Finite Element method.The solid model of valvular leaflets, the supporting stent and the sutural ring of the BHV have been set up by Pro/ENGNEER software. We take turns to create the cylinder, sphere, paraboloid, ellipsoid surfaces and then make them to intersect with inverse conic surfaces to get satisfy boundary curves and important points. After constructing parametric models of BHV via Computer Aided Design, a series of accurate points are obtained. The stress distribution of leaflets with different shapes is analyzed by the Finite Element software.The finite element method is often applied to stress analysis, which is also crucial to the design of anti-fatigue and anti-calcification of bioprosthetic heart valve, however it has some disadvantages in modeling function. The Computer Aided Design software provides a convenient method to create the parametric model of the BHV and improve the accuracy of parametric models. The properties of material of the valve leaflet with the Finite Element model is defined and geometrical model of the valve leaflet with the Finite Element feature are established. After the valve leaflet with the Finite Element feature has been loaded, the result of the Finite Element analysis can be got. Not only the linear stress but also the non-linear stress of leaflets with different shapes, different thickness, different inclination and different properties of material are analyzed. It is showed that the maximal primary stress of the valve leaflet with elliptic sphere is low than that of the other valve leaflet and the stress distribution of the valve leaflet with elliptic sphere is comparatively reasonable. So, the ellipsoid surface should be applied in the design and machining of the BHV stent.Based on the result of the stress analysis on the BHV, we finished the design and the manufacture of the BHV stent. Firstly, the unfolded algorithm of the BHV stent is discussed in detail. The casting mould of two dimensions and the casting mould of three dimensions are designed by the Pro/ENGNEER software. The casting mould of two dimensions is worked by the wire cut electrical discharge machine and the BHV stent of two dimensions was got. Secondly, the graphite electrode of three dimensions is machined by the carving miller and the casting mould of three dimensions was got by electric spark machining method. And then we solve the problem of the elastic deformation of the valvular stent and gain the experimental data by compensative method. Finally, we obtained the finished production the BHV stent which is consistent with the theoretical design. The manufacture of the BHV stent was based on the stress analysis on the BHV leaflet, on the other hand the shape of the BHV leaflet depends on the manufacture of the BHV stent. The precision modeling and machining of the BHV stent is very useful to prolong the lifetime of the BHV and to improve clinical practice of the BHV.