Fluid-Structure Interaction Simulation And Optimization Of Transcatheter Aortic Valve

Valvular heart disease,particularly aortic valve disease,is an increasingly common cause of cardiovascular disease.For aortic valve disease,the valve replacement is the most effective therapy.Compared with conventional thoracotomy,interventional therapy,represented by transcatheter aortic valve Implantation(TAVI),can shorten the recovery period and reduce the impact of surgery on patients.However,the development of transcatheter aortic valve(TAV)is still not mature enough and perfect at present.Problems such as insufficient valvular life and stent slippage have not been overcome.By numerical analysis,research the deformation and stress distribution of TAV under physiological conditions,and then optimize the design of stent and bioprosthetic valve,play an important role in promoting the further development of TAVand TAVI.TAV analysis model consists of four parts:leaflets,stent,vessel and blood.The 3D geometric model was based on clinical data,and the mathematical model was a series of constitutive equations based on the different material properties.Segregated solution method was used to calcalute fluid-structure interaction(FSI).The 3D transient finite volume method under pressure-velocity coupling was derived in the fluid domain,and the finite element method under nonlinearity and geometric nonlinearity of the valve leaflets was described in the solid domain.Based on the study of the FSI theory of TAV,the two-way FSI analysis was set up.The deformation and stress state of the valve leaflets,stent and vessel wall were analyzed.During a complete cardiac cycle,it was found that the maximum deformations and stresses of the leaflets,stent and vessel wall all occurred at 0.28s.Deformation analysis showed that the valve leaflets were severe curling at the free edge,mainly affected by blood flow;and the stent and vascular wall were relatively small,mainly affected by radial support force.Stress analysis showed that the vulnerable positions of the valve were at the suture points,while the most vulnerabile position was at the suture point on the boundary between suture edge and free edge'of leaflets;the stress concentration positions of the stent were on the connecting pieces and the units rotation,at the same time these positions had large stress gradient between the inside and outside of stent,and also had strong stress fluctuation affected by blood flow;the weak positions of the vessel wall were at the junction between the roots of arotic sinus.Based on the analysis of the deformation and stress of each part of the traditional transcatheter aortic valve,a new aortic sinus-adapted stent model was established to prevent stent slipping and falling off.Through the FSI dynamics simulation,the TAVs with straight tube stent and aortic sinus-adapted stent were compared.The results showed that TAV with aortic sinus-adapted stent had better mechanical properties,more uniform and reasonable stress distribution,and less impact on the vascular wall,which accounts for the rationality of the new model.In this paper,a complete geometric model and mathematical model of TAV were established,and then the main stress concentration positions and deformation process were reseached through FSI analysis.On this basis,an aortic sinus-adapted stent was established,and the feasibility of it was verified through the simulation comparison.This study provides a theoretical basis for improving the durability of TAV.