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New Intravascular Stent Design with Larger Radial Stiffness to Anti-restenosis

Author: WangMing
Tutor: LuoYun
School: Shanghai Jiaotong University
Course: Mechanical Engineering
Keywords: intravascular stent structure design finite element method
CLC: TH778
Type: Master's thesis
Year: 2012
Downloads: 120
Quote: 0
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Abstract

Coronary artery disease has become the most common cause of death and disability. Stent implantation is the most important treatment due to its safety and reliability. However, its effectiveness in practical use is limited due to a serious disadvantage, restenosis. The reason of restenosis is convinced to be a multi-factor cause. The inflammation after stenting and excessive hyperplasia of injured arteries are commonly accepted as two principal factors. Thus, it is crucial for lowering the restenosis rate to reduce artery injury during implantation. Several mechanical factors in the stent design are considered to be involved in the development of restenosis.Properties and design of stents are regarded as a key factor influencing restenosis rate, which are difficult to research using conventional methods for the tiny dimension, complicated structure, expensive prototyping and testing of stents. Finite element method (FEM) is a widely accepted routine in the stent design and optimization. The whole deformation of balloon expandable stents is a typical nonlinear process. Therefore, simplified procedures were applied, typically omitting the process of stent crimping. In fact, plastic deformation and work hardening may occur in crimping, which may result in changes of material properties and affect the performance of stents. In this paper a complete deformation procedure of a typical stent was simulated using finite element method. Its mechanical performances were evaluated and compared with that using a simplified procedure (omitting the process of stent crimping). It was found that the crimping has a significant influence on the stent shape, stress distribution, recoil rate, radial stiffness and the maximum expandable diameter of stents.In order to improve the performances of stents and reduce the restenosis rate, in this paper a new design though based on asymmetric structures was proposed. A new stent was designed and analyzed according to the design though, centering on the increase of radial stiffness, the decrease of solid area and strut-thickness and the proper dogbone. The stent is composed of asymmetric quadrilateral cells. The whole deformation process was considered when simulated. It was found that the asymmetric quadrilateral cell has larger stiffness than the diamond, but it usually exists distortion when deforms. The distortion was restrained by the reasonable arrangement of the cell. In the same conditions (the material, radial stiffness, percent solid area), the strut-thickness of the stent with asymmetric quadrilateral cell is 50% of the control stents. The maximum stress was decreased by 12.3% with strengthening ring. The area ratio between the end cell and the middle cell of stents is the main factor to influence the dogbone.

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