Study On The Mechanical Behavior Of Pulmonary Valve Stent For The Treatment Of Tetralogy Of Fallot

Tetralogy of Fallot is a kind of congenital heart disease.The treatment methods include radical operation and palliative operation.There will be delayed stenosis and /or reflux after operation.Transcatheter pulmonary valve replacement is often used to reconstruct the pulmonary valve in the right ventricular outflow tract or valved conduit.However,the interventional valves are difficult to fix and need to be replaced many times after operation.Therefore,it is necessary to explore a more appropriate treatment method to achieve long-term curative effect.In the current research on the mechanical behavior of pulmonary valve stents,the emphasis is to understand the stress distribution and the possibility of stent fracture.There are few mechanical studies on the comparison of different configurations of pulmonary valve stents.This paper proposes a treatment method for infant valve implantation: implant a surgical valve right during thoracotomy;use a balloon for expansion in the long term as the second treatment;in the third treatment,use valve-in-valve when the bioprosthetic valve is close to damage and reaches the stenosis limit,then the primary valve stent will become the stent segment of the new interventional valve after being expanded again.According to the mechanical characteristics and simulation process of the support,the numerical theory based on the elastic-plastic mechanics problem was expounded and deduced.Then,based on the conceptual design,the 3D model of the stent was established by UG.ABAQUS and Hypermesh were used to establish the corresponding finite element analysis model for the mechanical properties of the pulmonary valve stent.In view of whether the stent design can meet the mechanical and dimensional requirements of children’s growth and adult intervention,the von Mises stress,equivalent plastic strain,expansion and fatigue analysis were evaluated to verify the design and treatment of the stent.After that,how the structural design affects the mechanical properties of the stent was discussed,and eight supports were designed,which had different characteristics in connection length,thickness and grid structure.The twice expansion process and radial compression test were simulated by finite element method,focusing on the maximum stress and strain,distribution frequency of stress and strain,elastic rebound rate,conical degree,radial rebound rate and radial stress.The main conclusions are as follows:(1)The stress and plastic strain of the stent after loading and free rebound are within the safety range,and can maintain the new shape after deformation,and there is no fatigue failure during service,which verifies it can meet the mechanical and geometric requirements of children’s growth and adult intervention.(2)The maximum stress and plastic strain always appear at the grid junction of the stents.(3)The increase of grid density can reduce the conical degree,but there are too many cross points,so the stress distribution is uneven and there are too many stress concentration points.The grid density is inversely proportional to the radial support strength,so it is necessary to control a certain grid density,and at the same time,it is necessary to ensure that the strength of the expansion process will not be insufficient due to the low density.(4)The length of the connecting segment has little effect on the elastic rebound rate and conical degree.The increase of the length of the connecting segment will reduce the overall stress,but also reduce the supportive capability.The length of the connection segment can be adjusted according to the grid density.When the grid density is high,the length of the connection can be shortened.(5)We cannot have both elastic rebound rate and conical degree,so we should balance the two.The elastic recovery rate increases with the increase of thickness and grid density,but the conical degree is on the contrary.(6)Grid symmetric configuration is not desirable,because the proximal and distal ends of the stent should have different designs to better adapt to blood vessels and sew artificial valves,and symmetric configuration cannot provide appropriate radial force.(7)In a reasonable range,the thickness is the least influential factor.When the radial force is reduced due to other design requirements,the performance of the bracket can be balanced by increasing the thickness,but it should not exceed 0.5mm.This paper makes a new contribution to the treatment of tetralogy of Fallot and the design of stents,and provides a theoretical basis and reference data for the mechanical behavior analysis of stents.