Research On Mechanical Behavior Of Coronary Stent In Tapered Vessels

Stent implantation is an important method to treat coronary artery disease caused by vascular stenosis.However,in-stent restenosis has seriously hampered its efficacy.The dynamic bending of the vessel-stent coupling system and the change of the hemodynamic environment can affect the occurrence and development of the restenosis during stent service.Therefore,it is very important to study the bending deformation and hemodynamics of the vessel-stent coupling system during the service of stent.Because of the complexity of blood vessels and stents,numerical simulation is often used to study the bending behavior and hemodynamics of stent after implantation.However,most of the existing studies idealize the vascular model as a cylindrical tube,but physiological anatomy shows that most of the blood vessels are gradually shrinking.This simplification will bring errors to the results,so it is difficult to fully explain the mechanism of the restenosis in the stent.Therefore,this dissertation studied the flexural and hemodynamic behavior of the coronary stent in the tapered vessels,and aimed to provide a theoretical basis for the structural design and clinical selection of the tapered vessels.The main research contents and results are as follows:(1)The purpose of this chapter was to study flexural behavior of stents in vitro.The influence of the design parameters of the stent linker unit on the deformation modes,stress distribution and bending stiffness was investigated.The results showed that the number of the linker had the greatest influence on the flexibility.By simply increasing the number of linker,stent flexibility can be greatly reduced.The layout of the linker affected the bending stiffness of the bracket.The bending direction affected the bending stiffness,the compliance difference was mainly in the plastic deformation stage.The contiguous or hetero direction of the adjacent two groups of linker units can change the stent flexibility.(2)The purpose of this chapter was to study flexural behavior of vessel-stent coupling system in vivo.First,the simulation of stent implantation was carried out to obtain the vessel-stent coupling model after the stent implantation.On this basis,the bending behavior model of the tapered vessel-circular stent and the tapered vessel-tapered stent coupling system was established.In order to facilitate comparison and analysis,the bending behavior model of cylindrical vessel-cylindrical stents coupling system was also established.The results showed that: the taper characteristics of blood vessels can result in uneven stress distribution of the vessel and stent.The cylindrical stent turned into a cone,and the distal end of the vessel was damaged seriously.The implantion of a tapered stent into the tapered vessel can relieve the damage of the distal end of the vessel.After bending,the longitudinal deformation of the linker unit in the central position was bent.After the bending deformation of the vessel-stent coupling system,the vessels were straighten along with stress concentration at both ends of the stent parts.With the increase of the cone degree,the vseel straightening and stress concentration in the proximal end were relieved,while the distal end straightening and stress concentration were more serious.The vseel straightening and stress concentration in the distal end were relieved with the existence of a tapered stent in the tapered vessel.(3)The purpose of this chapter was to study the hemodynamics of tapered vessels.The formation and growth mechanism of plaque in the tapered vessel was analyzed,and the local hemodynamic analysis was performed on the vascular models implanted with stents.The results were as follws.The characteristics of tapered affected the local hemodynamic parameter distribution of normal vessel.With the increase of the taper of the vessel,the velocity of flow increased,the average time of wall shear stress decreased,the oscillatory shear factor increased.Vortex occured in the plaque terminal area,which made the plaque terminal area be the high-risk area of endometrial hyperplasia.The narrow part of the wall shear stress was much higher than that of other parts.After the stent implantion,positions near the stent became the blood stagnation zone and low wall shear stress zone.With the increase of the taper of the vessel,the time averaged wall shear stress decreased and the possibility of in-stent restenosis increased.The implantation of tapered stent in a tapered vessel can improve the distribution of the corresponding local hemodynamic parameters.