Design And Performance Study Of Candy-plug NiTi Alloy Stent Graft Based On Finite Element Analysis

Aortic dissection is a major disease that threatens human health and is one of the major aortic diseases in China.Traditional open surgery has the disadvantages of high trauma and high risk.Thoracic endovascular aortic repair(TEVAR)is widely used in the treatment of aortic dissection with its minimally invasive treatment.However,after aortic endovascular repair,the continuous regurgitation of the distal aorta is easy to induce the expansion or even rupture of the false lumen.The Candy-plug technique effectively solves the problem of distal regurgitation.With the deepening of the research,the problem of intimal damage and secondary implantation of the occluder after the implantation of the Candy-plug stent gradually emerged.In this study,the design of the Candy-plug NiTi alloy vascular stent combined with the "three-zone selection"and the"occlusion device1' was innovatively proposed for the distal regurgitation of TEVAR.Using finite element simulation analysis and in vitro experimental verification,this study provides a solution to effectively solve the problem of intimal injury and secondary implantation of occluder caused by Candy-plug stent implantation.Through the mechanical simulation of the stent structure,the direct displacement model and the two-step displacement simulation scheme are closer to the force state of the stent graft.The change in structural parameters affects the support force of the support greater than the maximum stress.The influence of wire diameter,wave height,stent shape,period number,ring diameter and bending radius on the radial support force is gradually weakened.The wire diameter is positively correlated with the radial support force,and the period number,height are negatively correlated with the radial support force.In relation to the relationship,the support force of the M-type stent is better than that of the Z-screw-type stent and the Z-type stent.The radial support force is the largest at the bending radius of 0.8 mm.With the increase of the diameter of the stent,the radial support force of the stent decreases first and then increases.The degree of influence of wave height,period number,stent shape,wire diameter,bending radius and ring diameter on the maximum stress gradually decreases.Ring diameter and wire diameter are positively correlated with maximum stress but wave height,period number and bending radius are negatively correlated with maximum stress.The Z-type stent has the best stress state.Within the scope of this study,the influence of structural parameters on the support force of the stent is greater than the maximum stress.The radial support force test experiment has a high degree of agreement with the simulation experiment,which verifies the accuracy of the simulation experiment results.Hemodynamic simulation suggests that the introduction of the occlude device has a significant blocking effect on distal reflux.After the first one stent was implanted,the proximal rupture is completely blocked.However,the pressure difference between the true and false lumen at the distal end increases,the value of TAWSS is high and secondary flow occurs,which may induce further expansion or even rupture of the false lumen;after the stent is implanted,the pressure difference between the true and false lumen drops and the false lumen is implanted.The value of RRT increased significantly and the thrombotic effect is significant.At the same time,the blood flow velocity in the false lumen decreased,the blood reflux phenomenon is significant,and the occlude device plays a good blocking role,reaching the expectation of blocking the distal reflux.Through the in vitro experiments,the glycerol solution with a volume fraction of 45%can effectively simulate the viscosity characteristics of the blood,which provides a basis for the preparation of simulated blood;the shape of the new Candy-plug stent recovered well after implantation,effectively preventing the appearance of endoleak and stent movement;the design of the occlude head has obvious sealing effect on the simulated blood,and the hemodynamic simulation is verified.The conclusion ensures the accuracy of the simulation analysis.