Research On Structural Design And Mechanical Behavior Of Balloon-Expandable Stents For Tapered Vessels

Vascular stenting is a widely-used approach for the treatment of cardiovascular coronary stenosis because of the minimally invasive associated surgery and high efficiency.However in-stent restenosis(ISR)after stent implantation,especially in tapered vessel,remains an obstacle in the long-term benefits of stenting.In this dissertation we designed a novel balloon-expandable stent for the special physiological structure of tapered vessels from the structural design of medical vascular stent.And then we utilized the finite element analysis to analyze the critical mechanical behavior of the stent for tapered vessels in vitro expansion,the expansion in the tapered vessel,the longitudinal deformation and other key mechanical behavior.The main contents and achievements of this dissertation are as follows:(1)The purpose of this chapter was to study the structural design of balloon-expandable stents for tapered vessels.Changing the parameter values of the height and width of the support in the whole stent would obtain a novel balloon-expandable stent with tapered characteristics after expansion,that is,from the proximal end of the stent to the distal end of the stent,the height gradient of each of the two adjacent supports was decreased and the width gradient of the support was increased.(2)The purpose of this chapter was to study the expansion behavior of the novel balloon-expandable stent for tapered vessels in vitro.The effects of design parameters(support height gradient and width gradient)and the material of the stent(316L stainless steel and L605)on the expansion behavior of the stent for tapered vessels were studied.The results showed that the effect of the support width gradient on the expansion of the balloon-expandable stent for tapered vessels was greater than that of the support width gradient.The maximum taper of the stent for tapered vessels was proportional to the support height gradient and width gradient.The shortening of the stent for tapered vessels was inversely proportional to the support height gradient and width gradient of the stent.(3)The purpose of this chapter was to study the expansion behavior of the novel balloon-expandable stent expand in the tapered vessels,and mainly to study the effects of taper of the tapered vessels and the material on the stent expansion.In order to explain thenecessity of studying the expansion behavior of stent in the tapered vessels,the expansion behavior of cylindrical stents in circular vessels and tapered vessels was compared and analyzed.The results showed the cylindrical stent had good adaptability to the circular vessels,but for the tapered vessels,the peak tissue stresses took place at the distal end of the tapered vessels,and caused greater damage to the vascular wall.In the analysis of the effects of taper of tapered vessel on the stent for tapered vessels expansion behavior,four different taper vascular models were established for comparison.The results showed when the taper of the stent was different from the taper of the blood vessel,the lower axial shortening of the stent and the lower damage rate of the stent to the vessel wall.(4)The purpose of this chapter is to study the effects of the main design parameters of the stent(the height gradient and width gradient of the support),material(316L stainless steel and L605)and the external force on longitudinal deformation behavior of novel balloon-expandable stent for tapered vessels.The results showed that the height gradient and the width gradient of the support had little effect on the longitudinal stent strength.The results also showed that the longitudinal strength of the first end of the proximal and the distal end is smaller than the second end and the third end.The proximal and distal end is more likely to occur longitudinal deformation,and the results of this study were consistent with the effect of the cylindrical stent structural parameters on the longitudinal stent deformation.This dissertation provides a scientific basis and theoretical guidance for the structural design optimization of new stents for tepaered vessels.