冠状动脉支架力学性能数值研究与优化设计

发布时间：2018-05-16 06:29

本文选题：血管支架 + 膨胀性　；参考：《大连理工大学》2011年博士论文

【摘要】：心血管病是威胁居民健康的重大疾病。据统计,国内每年死于心血管病的人数约为三百万,占总死亡人数的45%左右,每年用于心血管病的医疗费用超过1300亿元人民币。冠状动脉内支架植入术是治疗冠心病的一种有效手段,近年来越来越多地得到了广泛应用。冠脉支架的力学性能,是关系到支架术效果的关键因素之一。许多医务工作者和工程界的学者都在努力研究这一课题。本文利用有限元方法来研究冠脉支架的力学性能。论文的主要工作包括：针对冠脉裸支架结构,研究了有限元模型所采用的单元类型(高阶实体单元、低阶实体单元、壳单元、梁单元)和网格剖分密度对计算效率和精度的影响,模拟了冠脉裸支架全寿命内的变形过程所涉及到的力学性能。通过模拟支架生产过程中的压握变形、手术过程中的膨胀变形以及在冠状动脉内长期工作时的压缩变形,本文发现：压握过程对膨胀性能的影响较小,而膨胀程度对支架在工作状态下抵抗压缩载荷的径向支撑力具有较大的影响。另外,根据支架的膨胀性能曲线进行深入分析后得到了膨胀速度曲线,发现了膨胀速度曲线与支架的最佳膨胀范围的内在联系。本文对冠脉支架与球囊的接触问题进行了模拟,得到了比较准确的变形结果。在此基础上,提出了利用应变能来计算真实接触压力的方法。一般来说,通过接触分析所得到的球囊与支架间的接触压力,与实际情况下均匀一致的压力相比,误差往往比较大,这是由于支架金属丝比较细而只能在接触面上采用较粗的网格单元所导致的。根据功能原理,并且考虑到接触压力是驱动支架膨胀而产生应变能的唯一直接原因,本文利用支架应变能占全部应变能的百分比对膨胀载荷进行了修正,得到了支架与球囊之间真实而且均匀的接触压力,其结果与裸支架的膨胀曲线相互一致。这个方法可以作为验证接触分析结果正确性的依据。针对冠脉支架的纵向柔顺性,建立的悬臂梁弯曲模型,克服了三点载荷法和简支梁模型的缺陷,能够更准确、更全面地描述支架整体弯曲性能。以该模型为基础,本文详细研究了目标支架在较大弯曲曲率范围内的瞬时抗弯刚度情况,结果表明：在弯曲曲率较小的情况下,支架瞬时抗弯刚度一般表现为各向同性；而当弯曲曲率较大时,则出现非常明显的各向异性。此外,利用悬臂梁模型还发现,支架弯曲时还伴随发生了在弯曲平面外的侧向偏转以及绕支架中心轴的扭转变形。这两种附带变形是由支架弯曲变形而引起的,在一定程度上改变了支架的实际弯曲方向和曲率。这两种附带变形也正是瞬时弯曲刚度存在各向异性的证据。在优化设计工作中,利用ANSYS的APDL语言开发了适用于冠脉血管支架有限元分析的计算程序,该程序具有自动化运行、参数化建模、仝过程分析、鲁棒性计算及优化等特点,将此程序进一步加以完善后,即可作为专门用于血管支架力学性能模拟的软件。以此程序为基础,本文分别建立了描述支架膨胀综合性能和柔顺性能的数学模型,对目标支架的几何形状及尺寸进行了优化,改善了目标支架各项力学性能。以往在血管支架设计领域里采用的传统模式是对有限数量的设计方案分别进行数值模拟或实验分析,然后比较支架的力学性能结果并进行人工选优。本文的优化工作则将最优化理论拓展到血管支架的设计工作,有效地提高了血管支架优化设计工作的效率。
[Abstract]:Cardiovascular disease is a major disease that threatens the health of the residents. According to statistics, the number of people who die of cardiovascular disease annually is about three million, accounting for about 45% of the total death toll. The cost of medical treatment for cardiovascular diseases is more than 130 billion yuan per year. Coronary stent implantation is an effective means for the treatment of coronary heart disease. The mechanical properties of coronary stents are one of the key factors related to the effect of stenting. Many medical workers and engineering scholars are trying to study the subject. In this paper, the finite element method is used to study the mechanical properties of coronary stent.
The main work of the paper is as follows:
The effects of the element types (high order solid element, low order solid element, shell element, beam element) and mesh density on the calculation efficiency and accuracy are studied for the bare stent structure of the finite element model. The mechanical properties involved in the whole life of the coronary stents are simulated. In this paper, the compression deformation in the operation, the expansion deformation in the operation and the compression deformation in the long period of operation in the coronary artery are found in this paper. It is found that the influence of the compression process on the expansibility is small, and the expansion degree has a great influence on the radial support force against the compression load in the working state. In addition, the expansion performance curve of the support is based on the expansion performance. The expansion curve is obtained after in-depth analysis of the line, and the intrinsic relationship between the expansion speed curve and the optimum expansion range of the bracket is found.
In this paper, the contact problem between the coronary stents and the balloon was simulated and the result of a more accurate deformation was obtained. On this basis, the method of using the strain energy to calculate the real contact pressure was proposed. In general, the contact pressure between the balloon and the bracket obtained by the contact analysis is compared with the uniform pressure in the actual situation. The error is often relatively large, which is due to the finer metal wire of the bracket, which can only be caused by the use of a coarser mesh element on the contact surface. According to the function principle, the only direct reason for the strain energy generated by the expansion of the drive bracket is that the contact pressure is the percentage of the full strain energy to the expansion load. The charge is corrected and the actual and uniform contact pressure between the stent and the balloon is obtained. The result is consistent with the expansion curve of the bare scaffold. This method can be used as a basis to verify the correctness of the contact analysis results.
In view of the longitudinal flexibility of the coronary stent, a cantilever beam bending model has been established to overcome the defects of the three point load method and the simple supported beam model. It can describe the overall bending performance of the support more accurately and more comprehensively. Based on this model, the instantaneous flexural rigidity of the target bracket in a large curvature range is studied in detail, and the results are studied in detail. It is shown that the instantaneous bending stiffness of the bracket is usually isotropic when the bending curvature is small, and when the curvature of the bracket is large, there is a very obvious anisotropy. In addition, the cantilever beam model also shows that the lateral deflection outside the Wan Quping surface and the torsion around the center axis of the support are also accompanied by the cantilever beam model. The two incidental deformation is caused by the bending deformation of the bracket, which changes the actual bending direction and curvature of the bracket to a certain extent. The two incidental deformation is also the evidence of the anisotropy of the instantaneous bending stiffness.
In the optimization design, a program for the finite element analysis of coronary artery stents is developed using the APDL language of ANSYS. The program has the characteristics of automatic operation, parametric modeling, process analysis, robustness calculation and optimization. The program can be used as a special application for the mechanical performance of vascular stent. On the basis of this program, the mathematical model describing the comprehensive and compliant performance of the stent expansion is established in this paper. The geometry and size of the target support are optimized and the mechanical properties of the target support are improved. The traditional model used in the field of vascular stent design is a limited number of designs in the past. The numerical simulation and experimental analysis are carried out respectively, then the mechanical performance results of the support are compared and the artificial optimization is compared. The optimization work of this paper extends the optimization theory to the design work of the vascular scaffold, which effectively improves the efficiency of the optimization design of the vascular stent.

【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2011
【分类号】：R312

【引证文献】