基于形状记忆合金和可降解聚合物的渐扩张式血管支架研究

发布时间：2018-05-14 10:22

本文选题：形状记忆合金 + 可降解聚合物　；参考：《上海交通大学》2013年硕士论文

【摘要】：心血管疾病是人类的第一大杀手，而血管支架置入术是目前针对这一疾病最为有效的治疗手段，但限制这一治疗技术的主要原因是支架内再狭窄：即由于血管在支架植入后的过度增生而造成血管内部管腔再次狭窄。尽管影响支架内再狭窄的因素有很多，如支架结构、患者的个体差异、是否患有糖尿病、以及是否具有吸烟习惯等，但其主要成因之一即为在血管支架在植入过程中球囊快速扩张而造成的血管壁的撕裂损伤而引起的后续免疫反应，以及平滑肌过度迁移增殖反应。因此，如果能够在支架置入过程中甚至置入后，尽量减少支架扩张对于周围血管组织的刺激及损伤是降低血管支架内再狭窄的有效手段。在渐进扩张式血管支架设计过程中，如何实现渐进扩张原理，同时又不过多的增加支架结构的复杂程度是设计的关键所在。本研究中提出了基于形状记忆合金和可降解聚合物的渐进扩张式血管支架设计。由于形状记忆合金超弹性特性使其可以满足作为支架材料可以承受较大应变量这一要求。同时，经过变形后的形状记忆合金在置入后会由于其内部存储的变形能，逐渐向外扩张以进一步恢复其原有形状。在复合了由可降解聚合物制成的支架限制单元后，支架的扩张速度不仅取决于其压握程度，还受到限制单元的限制。通过调节支架扩张力和限制单元的限制作用以使的支架能够在血管壁可以接受的速度渐进扩张。本文首先通过实验的方法测定了形状记忆合金和可降解聚合物的材料特性。其中，形状记忆合金的材料参数通过单轴拉伸的方式获得，并采用静态降解的方式，对可降解聚合物在静态降解过程中的材料特性进行了初步的研究。实验发现，可降解聚合物在静态降解过程中，其弹性模量基本无变化，，但延展率随着降解时间的推移逐渐变小，即随着降解时间的推移材料逐渐变脆、变硬。文中进一步探讨了基于两种不同结构的自扩张镍钛合金支架的渐扩张式血管支架设计方案，讨论了在不同情况下血管支架渐进扩张的实现方式及各自的优缺点，并最终选择圆管切割型设计方案。同时，通过对镍钛合金的热处理，采用放大的支架单元的形式对渐扩张支架的设计原理进行了相应的验证。进而，为了更为方便的对支架的扩张状态及结果进行相应的调整，利用有限元方法建立了包含支架从最初的设计过程到体内置入的模拟过程。数值模拟结果表明，支架的初期扩张量可以很方便的通过改变限制单元的长度和厚度进行调节和控制。
[Abstract]:Cardiovascular disease is the first killer of human beings, and stent implantation is the most effective treatment for this disease. However, the main reason for limiting this treatment technique is stent restenosis, that is, the re-stenosis of intravascular lumen due to excessive proliferation of blood vessels after stent implantation. Although there are many factors affecting restenosis in stents, such as stenting structure, individual differences in patients, diabetes mellitus, and smoking habits, etc. However, one of the main causes is the subsequent immune response caused by the rapid balloon dilation of vascular stents and the proliferation of smooth muscle. Therefore, it is an effective way to reduce the restenosis of stent by minimizing the stimulation and injury of stent dilatation to the surrounding vascular tissue, if the stent can be inserted during or even after implantation. How to realize the principle of progressive expansion while not increasing the complexity of stent structure is the key to the design of progressive dilation stent. In this study, a progressive dilatation stent design based on shape memory alloy and degradable polymer was proposed. Because of the superelastic properties of shape memory alloy, it can be used as scaffold material to withstand large strain. At the same time, the shape memory alloy after deformation will gradually expand outward to further restore its original shape because of the deformation energy stored inside. The expansion speed of the scaffold is not only dependent on its grip degree, but also limited by the limiting unit after recombination of the scaffold which is made of degradable polymer. By adjusting the dilatation force and limiting effect of the limiting unit, the stent can expand gradually at an acceptable rate on the vascular wall. In this paper, the properties of shape memory alloys and degradable polymers were measured experimentally. Among them, the material parameters of shape memory alloy were obtained by uniaxial tensile method, and the properties of degradable polymers in the static degradation process were studied by static degradation method. It was found that the elastic modulus of degradable polymers remained unchanged in the static degradation process, but the elongation rate decreased with the degradation time, that is, the materials became brittle and hardened with the degradation time. In this paper, we further discuss the design scheme of gradually expanding vascular stent based on two different structures of self-expanding Ni-Ti alloy stent, and discuss the realization of progressive dilatation of vascular stent under different conditions and their respective advantages and disadvantages. And the final choice of circular pipe cutting design. At the same time, the design principle of the expanding stent was verified by the heat treatment of Ni Ti alloy and the form of enlarged support unit. Furthermore, in order to adjust the expansion state and the results of the scaffold more conveniently, the simulation process including the initial design process and the internal placement of the scaffold was established by using the finite element method. Numerical simulation results show that the initial expansion of the support can be easily adjusted and controlled by changing the length and thickness of the limiting unit.
【学位授予单位】：上海交通大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：R318.11

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