Structural Design And Biomechanical Numerical Analysis Of Body-fitted Stent In Stenotic Vessels

The average annual demand for vascular stents in China is more than 1 million pieces.Stent has the huge market demand and prominent bottlenecks.Acute/late malapposition has become a prevailing problem of the application,no matter for bare metal stent,drug-eluting stent,or bioabsorbable stent.In the research of stent application,one of the core issues is to study how to make the stent adhere to the vascular wall after it is implanted.That being said,the stent struts should be covered by the vascular intima without disturbing blood flow or causing any dangerous situation.As the existing methods of evaluating the apposition performance only consider the separation distance or fraction of non-contact area,which is rather unilateral and has deviations,a systematic evaluation standard is urgently needed to evaluate the apposition performance of the stent in the vascular lumen objectively and quantitatively.In order to solve the problem of vascular stent malapposition,a body-fitted stent design method in stenotic vessels was explored in this article.Its supporting performance and apposition performance in stenotic vessels with different calcification degrees of plaque were explored.A more comprehensive evaluation method for the apposition performance of the stent was established to evaluate the degree of stent malapposition.The research was divided into four parts: Firstly,a method for designing a bodyfitted stent structure was proposed.Two types of body-fitted stents were constructed based on the initial vascular model（Hereinafter referred to as Type A）and based on the deformed vascular model（Hereinafter referred to as Type B）respectively;Secondly,the finite element analysis was used to explore the crimping,expansion and recoiling process and mechanical performance of Type A and Type B stents in stenosis with different degrees of calcification of plaques.The results were compared with those of the traditional stent structure;Thirdly,a multi-dimension evaluation method of apposition was proposed based on separation distance,fraction of non-contact area,and residual volume.This method was used to evaluate the apposition performance of Type A and Type B stents in stenotic vessel models respectively with incompletely calcified plaque and fully calcified plaque;Finally,a real carotid stenosis artery model and a body-fitted stent based on the initial state of this vessel were constructed;the mechanical performance and apposition performance of the stent in the process of crimping,expansion and recoiling in the real stenotic vessels were explored.The support performance was evaluated from the residual stenosis rate.In the incompletely calcified plaques,the residual stenosis rates of traditional stent,Type A and Type B stents were 33.5%,32.1%,and 30.9%,respectively.While they were 36.2%,36.7%,and 36.7% respectively in fully calcified plaques.The apposition performance was evaluated from three aspects and all data listed below conforms to the order that incompletely calcified plaque model go first and fully calcified plaque model follows.In terms of the separation distance,Type A stent decreased by 21.6% and 21.9%respectively while Type B decreased by 21.1% and 18.6% respectively.As for the fractions of non-contact area,Type A stent decreased by 11.3% and 11.1%,while Type B decreased by 11.3% and 11.2% respectively.In terms of the residual volume,Type A stent decreased by 21.6% and 21.9%,while Type B decreased by 92.6% and 92.2%respectively.The difference between the body-fitted stent and the traditional stent in terms of separation distance and the fractions of non-contact area is about 20% and 10%respectively,which is not as obvious as that of the residual volume of about 90%.Therefore,it is not comprehensive to evaluate the apposition performance of intravascular stents only from separation distance or the area.The distance,area,and volume need to be considered comprehensively in order to ensure the apposition performance to be comparable between different lesions.The analysis results of each experiment showed that the body-fitted stents could support the vessels to the same extent as the traditional stent and feature better apposition performance,and they were effective in both incompletely calcified plaque and fully calcified plaque models.The evaluative method being established in this research for quantifying the stent apposition performance takes more geometric factors into consideration.It would be more comprehensive and sophisticated.