Research On Expansion And Fatigue Properties Of Medical Stent In Stenotic Tapered Vessels

Cardiovascular disease is the major cause of death from disease among residents.Because of its minimally invasive and high-efficiency,coronary stent implantation has become the first choice for treatment of coronary heart disease in China.After the stent is implanted in the patient,in-stent restenosis and stent fatigue fracture may occur,which seriously affects the long-term efficacy of medical stent implantation.In this paper,finite element software Abaqus was used to analyze the expansion behavior and fatigue life of stent in tapered vessels.Fe-safe fatigue analysis software was used to analyze the fatigue performance of the stent in vitro.The main research work and achievements of this dissertation are as follows:A stent-coupled expansion system was established to study stent expansion behavior in a Stenotic tapered vessel.The relation between stent length and lesion length on tissue stress was investigated.The effects of different stent materials,vessel tapering and materials,plaque shape and materials on the biomechanical behavior of stents and vascular tissue were analyzed.The results show that compared with the straight vessel,the stent implantation in the tapered vessel with the same stent length resulted in greater vessel and plaque stress,an increased stent recoil,and a decreased stent foreshortening.After the stent expansion,the maximal stress of plaque and vessel is located in the distal area.As the vessel tapering increased,the maximal stress of the vessels and plaques were increased.When stent length is equal to plaque length,the stress of the vascular tissue caused by stent expansion is minimal,and the axial shortening rate of the stent is minimal,indicating that the stent can cover the lesion.Therefore,when stent length is equal to lesion length,it may be the reasonable choice for straight and tapered vessels.Compared with the 316 L stainless steel stent,the cobalt-chromium alloy stent has a lower recoil rate and stronger resistance to deformation of vascular tissues.Compared to the stent expansion in vessels with hypocellular plaques,stents have greater recoil rate when expanded in vessels with calcified plaque.Compared with the low-sharpness model,stents implanted in vessels with high-sharpness plaques will result in greater plaque and vessel stress,whilesignificantly affecting the stent stress distribution.The fatigue performance of the stent in vitro was studied.The effects of different stent design,materials,thickness and stent tapering on the stent fatigue life were studied.The results show that the safety factor of the corner points of both ends of the Palmaz stent and the diamond-shaped holes is minimum,while the safety factors of excessive arcs at both ends of the S-shaped,M-shaped,and L-shaped stent,the supporting unit and the connecting unit are relatively minimum.When the thickness and outer diameter are the same,the fatigue life of the Palmaz stent is higher.Under the same conditions,the fatigue life of the L605 cobalt-chromium alloy stent is higher than that of the 316 L stainless steel stent.When the thickness of stent was changed,the position of fatigue failure did not change.When the thickness of stent was greater than 0.10 mm,the fatigue strength of the stent decreased with stent thickness increased.The tapered stent maintains a tapered shape after being expanded in vitro.Compared with both ends,the center of the tapered stent can withstand more pulsating cyclic loads.At the same time,the tapering of the stent has little effect on the fatigue performance of the stent.The fatigue performance of the stent in tapered vessels was studied.The effect of stent material and different vessel tapering on the the fatigue performance was analyzed.The results of the study indicated that the areas of maximum stress on the stent after expansion were concentrated in the corners of the diamond cells of the stent.When use the same design parameters of the stent,cobalt-chromium alloy material meet the requirements of the fatigue life better.When the vessel tapering is greater than 0.43 degree,the point at which the mean stress on the stent is maximal,resulting in minimal safety factor.The tapering of the vessel will affect the fatigue performance of the stent.When the tapering of the vessel is larger,the residual stress increased after the stent was implanted into the body.Under the pulsed blood flow,the stent is more prone to fatigue fracture.