Mechanical Performance Analysis And Robust Multi-Objective Optimization Of Tapered Vascular Stent

Cardiovascular disease is the disease with the highest mortality rate.Vascular stent implantation is an effective method for the treatment of cardiovascular disease because of its rapid efficacy,small trauma and high safety.However,in-stent restenosis will affect the long-term efficacy of the stent.Stents with insufficient radial stiffness and vessel injury caused by stents during vessel torsion are all factors leading to restenosis.Therefore,it is important to study stents radial support and torsion performance and to carry out multi-objective optimization design.However,current studies mostly focus on straight stents,but tapered stents are more suitable for human tapered vessels and have better therapeutic effect on cardiovascular disease.Therefore,this paper studies the radial compression deformation,torsional deformation behavior and robust multi-objective optimization of tapered stents,and provides theoretical basis for the design and clinical selection of tapered stents.The main research results of this paper are summarized as follows:(1)Systematic research on the radial support performance of the tapered stent.The effects of different link shapes,numbers,stent tapering and dimensional parameters and stent materials on the radial stiffness of the stent were studied.It has been found that the shape,number,length and width of the link have little effect on the radial stiffness of the stent.Compared to cylindrical stents,tapered stents reduced have radial stiffness.The stent materials have a great influence on its radial stiffness.The L605 cobalt-chromium alloy stent has the highest radial stiffness,and the 316 L stainless steel stent is the second.The WE43 magnesium alloy stent has the worst radial stiffness.In addition,as the stent thickness,the strut width increases,and the strut length decrease,the radial stiffness of the stent increases.Therefore,if the radial support performance of the stent needs to be optimized,these parameters should be taken into consideration.(2)Systematic research on the torsional performance of the tapered stent.Firstly,the torsional performance of the stent unit and the whole was studied.It was found that the difference between the two was very large,and the whole stent model was choosen for finite element analysis.Secondly,the influence of the link shape and number on the stent torsional performance was studied.The results show that the link number has a significant influence on the stent torsional performance,while the influence of the link shape is small.In addition,the tapered stent has better torsional performance than a cylindrical stent.The torsional performances of stents with different materials are significantly different.The torsional performance of WE43 magnesium alloy stent is the best,followed by 316 L stainless steel stent.The torsion performance of L605 cobalt-chromium alloy stent is the worst.Finally,the influence of stent dimensional parameters on its torsional performance was studied.The results show that the stent initial diameter,thickness,strut length and width are the key parameters determining the torsion performance of the stent,while the link length and width have little effect on the torsional performance of the stent.(3)Three commonly used in stent optimization surrogate model techniques including response surface method,radial basis function neural network and Kriging were constructed and compared.First,the three surrogate models werect briefly introduced.Secondly,the construction process of the surrogate model was determined.The stent thickness,taper,the strut length and width were selected as design variables.The 30 sets of samples were determined using the optimal Latin hypercube technique.The performance of each sample point was obtained through the finite element model.The three surrogate models of each performance were constructed.Finally,the accuracy of the three surrogate models was compared.The results show that the Kriging model has higher precision when the finite element model of the stent performance includes more components and the interaction between components and components is larger.(4)Multi-objective robust optimization for tapered vascular stents was studied.The stent thickness,taper,the strut length,and width were determined as design variables,and the stent axial shortening rate and radial recoiling rate of the stent were determined as constrains.The stent radial stiffness,axial stiffness,flexibility metric and twist metric were determined as objectives.The relationship between design variables and stent performances was studied based on the Kriging surrogate model,and the trade off between them was determined.The NSGA-II algorithm was used to optimize the multi-objective design of the stent,and a stent with better comprehensive mechanical performances was obtained.The effect of noise factors on the optimization results was taken into consideration.Multi-objective robust optimization of the stent based on Monte Carlo simulation and 6? quality analysis technology were carried out.The reliability of the stent performances was greatly increased after the robust optimization.