Fluid Structure Interaction Simulation Of The Bioprosthetic Heart Valve Based On Hyperelastic Constitutive Model

Bioprosthetic heart valve replacement is the main treatment for aortic valve stenosis and insufficiency.Clinical statistics show that the proportion of elderly patients with valvular heart disease is larger than young people.Under aging trend,the demand for artificial aortic valve is bringing a great challenge to the quality and quantity of the existing products.Data of the aortic valve under physiological conditions are difficult to obtain.The use of computational fluid mechanics has been of great importance in the development of bioprothetic heart valves including mechanical valves,biological valves and tissue valves.Based on the histological structure and mechanical properties of primary aortic valve leaves and artificial valve materials,a geometric model of aortic valve with inhomogeneous thickness was established,and the incompressibility,nonlinearity,anisotropy and superelastic response under physiological conditions of the aortic valve leaves were established by using the hyperelastic constitutive model.The subprogram of the constitutive equation of the material is written in Fortran language.Then a specimen with different fiber angles are simulated at varied loading rates.The stress and strain curves obtained by the subprogram calculation based on the hyperelastic constitutive are analyzed,and the anisotropy and the insensitivity to the loading rate are verified.The thickness of the arterial wall is optimized according to the clinical statistical data,and the geometric model of the blood is modified and the integral geometric model of the aortic valve fluid solid coupling system is formed.Arterial wall was simplified as incompressible isotropic and the blood flow through the aorta is assumed to be a constant temperature and viscosity Newtonian flow.There is constraint of no sliding,continuity of velocity and force on the convective solid coupling boundary;the left ventricular blood pressure measured under physiological conditions was used as loading.The results of fluid structure interaction of aortic valve were analyzed from deformation and stress,focusing on the similarities and differences between aortic side and left ventricle side.The pretension steps of the arterial wall were added before the fluid solid coupling simulation.Three pretension forces of 10N,100N and 1000N were used to simulate the influence of the size of pretension on the mechanical properties of the leaflets.When the pretension is 1000N,the maximum principal stress and the maximum shear stress distribution of the leaves during the whole process are compared with the no pretension.The stress distribution cloud maps are basically the same,the stress concentration areas are at the intersection of the stitched edge and the free edge.In addition,two surface stress data of the aorta side and left ventricle under four cases of 0N,100N,500N and 1000N showed that the maximum and minimum stress on the two sides of the aortic valve was different between non pretension and pretension cases,but as the pretension forces increased from 100N to 1000N,there is no difference.In this paper,a more accurate model of the aortic valve fluid solid interaction simulation was established from three aspects including the leaflets with non-uniform thickness and the arterial wall that conforms to the clinical actual thickness for the geometric model;the hyperelastic material model of the valve leaves;the introduction of pretension process of the arterial wall in the boundary condition.The deformation and stress of the leaflets were analyzed respectively,special focus was put on the stress differences in the same surface.It provides some insights into better understanding of the biomechanical properties of artificial aortic valves.