Xiang Shen

BALLOON-EXPANDABLE STENTS EXPANSION IN TAPERED VESSELS AND THEIR INTERACTIONS

In-stent restenosis (ISR) after stent implantation, especially in tapered vessels, remains an obstacle in the long-term benefits of stenting. In the present study, a finite element method (FEM) was employed to investigate the expansion process of balloon-expandable stents in tapered vessels (the TV model) and their interactions. For comparison, a numerical model of the same stent deployment in a straight vessel was also investigated. Results showed that in the TV model, the peak tissue stresses took place at the distal end of the tapered vessel. The node displacements of the stents proximal and distal ends remained consistent before the stent contacted the tapered vessel, while the proximal end was larger than the distal end after the stent contacted the tapered vessel. The regions of maximum stresses in the stent after expansion were concentrated in the corners of the diamond cells of the stents proximal end. The investigation provided some interpretations of the clinical observations in tapered vessels and also provided stent design proposals for tapered vessels. The FEM quantified the mechanical properties of stents in tapered vessels, and can help clinicians select appropriate stents, assist designers in pretests and create new stents made especially for tapered vessels.

ASSESSMENT OF CORONARY STENT DEPLOYMENT IN TAPERED ARTERIES: IMPACT OF ARTERIAL TAPERING

Coronary stents are used to prop open blocked arteries in order to restore normal blood flow. A major setback in this technology is in-stent restenosis (ISR), which gravely limits the clinical success of stents, especially in tapered vessels. The present study used the finite element method to study the effects of arterial tapering on the biomechanical behavior of both stents and vessels during stent deployment inside tapered arteries. The effect of arterial tapering was demonstrated by a combination of corresponding tapered arteries with various tapering angles, including a straight artery case for comparison. Results indicated that an increase of vessel tapering led to an increase in stent radial recoil, stent tapering following expansion, and von Mises stresses on vessels. However, an increase of vessel tapering also led to a decrease in stent foreshortening. The analysis provides suggestions for clinical application in tapered vessels. The finite element method evaluated mechanical stent behavior in tapered vessels, and can help designers to optimize the design of stents for tapered vessels.

Effect of different expansion strategies on coronary stent deployment in a tapered artery

BACKGROUND Vascular stenting has been widely used to treat vessel stenosis. However, long-term successes of the procedure are often compromised by late stent thrombosis (ST) and in-stent restenosis (ISR), especially in tapered arteries. OBJECTIVE The aim of this study was to choose a reasonable expansion strategy for tapered arteries. METHODS A balloon-expandable coronary stent deployment in a tapered vessel was numerically studied fol-lowing three strategies: (i) selecting the proximal diameter of the tapered vessel as the reference diameter to expand the stent, (ii) selecting the middle diameter of the tapered vessel as the reference diameter to expand the stent, and (iii) selecting the distal diameter of the tapered vessel as the reference diameter to expand the stent. RESULTS Computational results showed that the first expansion strategy resulted in the maximum vessel stress and the best stent apposition, while the third strategy resulted in the minimal vessel stress and the worst stent appo-sition. Meanwhile, the second expansion strategy achieved a trade-off between the first and third strategies, leading to acceptable vessel stress and stent apposition. CONCLUSIONS The second expansion strategy is the most reasonable choice for tapered vessels, and it should be considered when implanting a stent.

FLEXIBILITY BEHAVIOR OF CORONARY STENTS: THE ROLE OF LINKER INVESTIGATED WITH NUMERICAL SIMULATION

Flexibility is a vital property of stents and different stent structures lead to different flexibility behaviors. In this study, the finite element analysis was adopted and a virtual bending deformation was imposed to quantify the effects of linker pattern, linker number, bending direction and linker location on flexibility. Stent performance indicators, including stress distribution, deformation patterns and bending stiffness, were examined. Results indicate that higher levels of stresses are found on the linker struts, associated with much larger deformation. The linker number plays the most significant role in flexibility, and simply decreasing linker number could result in a sharp increase in flexibility and a decrease in stress. The linker pattern has great impact on stent flexibility, especially on the behavior of self-contact. Stents with different linker patterns could respond differently in the course of bending, and the stent with an offset peak-to-peak linker pattern is the best choice. It is a...

Effects of Metal Material Stent Design Parameters on Longitudinal Stent Strength

The longitudinal stent deformation (LSD) was usually caused by the external force in the blood vessel. The effects of metal material stent design parameters on the longitudinal stent strength (LSS) were studied using finite element method (FEA). A longitudinal stent compression model was developed and a rigid surface was used to compress the stent after stent deployment in coronary arteries. Results showed that the connector length, the strut amplitude and the curvature radius at the crown junctions influenced the LSS hardly. However, the number of connector played the most significant role in the LSS, and increasing the number of connectors can substantially improve the LSS, and the LSS of stent with four connectors was nearly three times than that of the stent with two connectors. For the shape of connector, the LSS of the S-stent, M-stent and L-stent were successively increased. With regard to the L-stent, increasing the width of connector can improve the LSS. Reasonably changing stent design parameters can effectively strengthen the LSS. Conclusions obtained from this paper can help surgeons to select appropriate stents and designers to optimize the stent design to reduce the LSD.

The Influence of Arterial Wall Thickness on Stainless Steel Material Stent Expansion in Tapered Arteries

The implantation of an intravascular stent has become a common and widely used minimally invasive treatment for coronary heart disease. But in-stent restenosis (ISR) after stent implantation, especially in tapered vessels, limits the clinical success of stents. In this study, the finite element method (FEM) has been carried out to study the effects of vessel wall thickness on 316L stainless steel stent deployment in tapered arteries. The influence of arterial wall thickness was demonstrated by combination of varied wall thickness and constant wall thickness case. Results indicated that compared to a vessel model with varied thickness from proximal end to distal end, a vessel model with constant thickness had higher vessel wall stress induced by stent expansion. Thus the injury level of vessel wall during stent expansion was overestimated. Numerical simulation results from this study are beneficial to construct a reasonable and accurate expansion model of stent in tapered vessels. The FEM can quantify mechanical properties of stents in tapered vessels, and can compare different modeling strategies for vessel wall thickness, and assist designers to develop new stents especially for tapered vessels.

Expansion Performance of Novel Balloon-Expandable Stent for Tapered Vessel

In-stent restenosis still remains an obsession to cardiologist, especially in tapered vessels. In this paper, we designed a novel balloon-expandable stent for tapered vessel and proposed a finite element method (FEM) to study the expansion of the novel stent. The effect of stent design parameters on stent tapering and foreshortening were also researched. Results show that the radial displacement of stent proximal end was always larger than that of stent distal end during stent expansion, and the stent had a tapered shape as a whole after expansion. The degree of stent tapering observed increased with the expansion pressure increase. Besides, increasing the gradient of ring amplitude not only could increase the tapering degree of stent after expansion, but also could decrease stent foreshortening, improving the positioning accuracy after stent implantation. In conclusion, FEM can quantify expansion performance of novel balloon-expandable stents and help designers to devise and assess new stent designs for tapered vessel.

Experimental Studies of the Longitudinal Flexibility of Balloon-Expandable Coronary Stents

Stents are medical devices used in cardiovascular intervention for unblocking the diseased arteries and restoring blood flow. A setup for the measurement of the longitudinal flexibility of a coronary stent was developed based on machine vision technology. A crimped stent made by medical stainless steel thin-walled tube was tested with the setup. The results show that the bending deformation of stent includes two phases: the elastic deformation phase and the plastic deformation phase. The bending angle changed very little with the increase of bending moment during the elastic deformation. However, the bending angle changed significantly when a small moment was applied during the plastic deformation. In conclusion, the experimental setup can be used to study and compare flexibility of different design kinds of coronary stents and provides a convenient tool for designers to improve bending characteristics of new stents.

Effect of Material and Work Status of Vascular Stents on Flexibility Property of Stents

Flexibility is an important mechanical property of stent. The primary aim of this investigation is to evaluate the effect of material and work status of vascular stent on the flexibility of stent using finite element method (FEM). Uniform bending moment was applied to unit models of stents with the help of multipoint constraint element. The results show that the flexibility of biodegradable pure iron stent is better than one of stainless steel stent. Among three work statuses of stents, the flexibility of expanded stent is the worst, while the flexibility of crimped stent is the best. In conclusion, FEM can quantify stent mechanical behaviors related to flexibility and help surgeons to select favorable stents and help designers to pretest and improve flexibility of new stents.

Research on Constructing Surrogate Model of Coronary Stent Mechanical Property

Coronary stents are small tube-like structures expanded into stenotic arteries to restore blood flow perfusion to the downstream tissues. In this paper, based on the finite element analysis (FEA), both the response surface model (RSM) and radial basis function neural network (RBFNN) are used to construct the surrogate model for stent recoil performance. Precision between these two surrogate models are compared. The results show that the surrogate model with RBFNN is more reliable and efficient.