Mechanical Behavior Research And Design Optimization Of Coronary Stent

Cardiovascular diseases are one of the principal causes of death of human being. They are often related to atherosclerosis, which lead to a narrowing or even blocking of the artery walls and resulting in a reduction of blood flow through the artery. Coronary stents are widely used in clinic and the vascular intervention market of coronary stents has increased rapidly because of their high initial success rate, minimal invasive nature and improved long-term effectiveness. In order to meet the specific needs of coronary stent development of cardiovascular diseases treatment, the aim of this paper is to suggest a potential design optimization method for reducing a risk of vascular in-stent restenosis, through optimization studies to improve stent expanding properties, fatigue life and drug release effect by using computer aided design (CAD). The main contributions of this thesis can be summarized as follows:1. Finite element analysis of coronary stent dilation and in-stent blood flow is every complex, especially for the build of in-stent blood flow model. In this study an integrative FEA model was built for stent dilation, in-stent blood flow, the interaction between blood flow and stent and artery tissue, and stent fatigue life analysis to ensure the reliability of FEA results. The properties of stent expanding, hemodynamics in stented artery and stent fatigue life were analyzed using this integrative model. Furthermore, the flexibility of coronary stent was studied, from which, the importance of link strut for stent flexibility was indicated.2. With regard to the problem of coronary stent design concerning the function between design objiectives and design variable, which is quite complex and can not be described directly, kriging surrogate model was presented to optimize coronary stent. An improved optimization method was proposed to translate the complex problem of stent design into a pure mathematical optimization problem.Subsequently, the optimizations to improve stent properties as flows were discussed in details:(1) The optimization improve mechanical behaviors of stent dilation, in which the geometries of stent were seleted as the design variables, was discussed in details. The dogboning effect was eliminated by the way of stent design. The influence of stent design on dogboning was posted.(2) The optimization to improve mechanical behaviors of stent dilation? in which the length of bloon was seleted as the design variable, was discussed in details. The dogboning effect was eliminated by the way of balloon design. The influence of the length of balloon on dogboning was posted.(3) The optimization to improve stent fatigue life, in which the stent geometries were seleted to be the design variables, was also discussed in details. The fatigue life of stent was improved. The characteristic of diamond stent fatigue life was expatiated.Finally, to meet the needs of multiple performance indicators in the design of coronary stents, a multi-objective optimization to improve stent expansion performance and fatigue life was carried out using kriging surrogate model. Moreover, another multi-objective optimization to improve stent combination property was also studied.The results suggested that the performances of stent were significantly improved after optimization. The propesed adaptive optimization method can effectively improve stent properties and provide an new way of stent design.3. Drug release of DES in stented artery is a nolinear and complex process. The drug release analysis and optimization for drug-eluting stents in the arterial wall are studied.The Finite Element Method (FEM) is here used to analyze the process of drug release in the vessels for DES. The effects of diffusion coefficients and the thickness of coating for drug release were discussted based on FEA results. Kriging surrogate model is used to build an approximate function relationship between the drug distribution and the coating parameters, replacing the expensive FEM reanalysis of drug release in the optimization process. The diffusion coefficients and the coating thickness are selected as design variables. An adaptive optimization approach based on kriging surrogate model is proposed to optimize the lifetime of the drug in artery wall. The results demonstrate that the optimized design can efficiently improve the efficacy of drug deposition and penetration into the arterial walls, providing a new way of DES design.