AZ31镁合金冠脉支架力学行为的有限元模拟

发布时间：2018-08-29 14:16

【摘要】：镁合金具有良好的生物相容性和可降解性,已被用于作为可降解冠脉支架材料进行研究,可降解镁合金支架有望成为新一代心血管支架。然而,与不锈钢材料相比,镁合金作为支架材料,抗拉强度低、屈服强度低、断后延伸率低、塑性变形能力差,使得镁合金支架存在径向回弹率大,径向支撑力低以及应力应变不均匀(应力集中)等问题。因而本文针对镁合金材料的力学性能特点,对镁合金支架结构进行优化设计,以弥补材料本身性能的不足。本文以有限元模拟为研究方法,采用AZ31镁合金为支架材料,对课题组自行开发的镁合金支架结构进行优化研究。通过改变支架结构单元的长度、丝宽、圆弧半径等结构参数,同时利用系统分析中的敏感性分析方法,对上述不同结构参数组合下支架的径向回弹率、径向支撑力以及应力应变分布进行参数敏感性研究。结果表明,参数是决定结构性能的重要因素,不同支架性能受不同结构参数影响的敏感性不同,通过模拟分析,对于径向回弹率而言,影响其性能的主要因素按影响力大小为长度变量、丝宽变量以及半径变量以及壁厚；对于支撑力而言,影响其性能的主要因素按影响力大小依次为长度变量、丝宽变量以及壁厚变量；对于最大主应变而言影响其性能的主要因素按影响力大小依次为长度变量、丝宽变量以及半径变量。在这些因素中,以长度因素和丝宽因素为甚,分别对支架的三个性能能产生较大影响。而改变半径对径向回弹率以及最大主应变的影响较大,对支撑力的影响较小；改变壁厚能够影响支架的支撑力性能和径向回弹率性能,对最大主应变的影响较小。这些变量对各自性能的影响力大小,对支架结构设计尤其是镁合金支架结构的设计尤为重要,可以在支架结构设计中作为参考。根据课题组支架的实际实验中发现,支架在变形过程中存在着变形不均匀性,主要是“之”字形支撑环在撑开时“V”形梁张的开角度存在差异。根据这种情况,我们对完整的支架和折叠球囊装配在一起的组合系统进行动态模拟分析,通过改变支架的结构、球囊的折翼的变化以及球囊的厚度的厚薄等变量,分别模拟支架在不同情况下的变形行为从模拟的结果看,球囊折翼的数量、支架与球囊的配合度、连接筋数量以及球囊自身厚度等情况对支架的扩张不均匀性有着重要的影响。具体来讲,支架与球囊的对称性越接近,支架的扩张越均匀,在实际可行的情况下,应采用球囊的折翼数量应与支架轴向最简单元的重复个数相同；球囊的厚度越小,支架的扩张越均匀,因此在选择球囊时,应尽量选择薄壁球囊进行扩张；同时,支架的连接筋分布越对称,连接筋越多,支架扩张越均匀,因此在支架连接筋的分布和数量选择上,应使连接筋的分布应尽量均匀,且不能过渡减少连接筋的数量,这些举措都有利于改善支架的对称不均匀性。
[Abstract]:Magnesium alloys with good biocompatibility and biodegradability have been used as biodegradable coronary stent materials. Biodegradable magnesium alloy stents are expected to become a new generation of cardiovascular stent. However, compared with stainless steel, magnesium alloy has low tensile strength, low yield strength, low elongation after fracture and poor plastic deformation. Low radial support and uneven stress and strain (stress concentration) and so on. Therefore, according to the mechanical properties of magnesium alloy, the structure of magnesium alloy scaffold is optimized to make up for the deficiency of the material itself. In this paper, AZ31 magnesium alloy was used as scaffold material to optimize the structure of magnesium alloy scaffold developed by our team. By changing the structural parameters such as length, wire width and arc radius of the support structure unit, and using the sensitivity analysis method in the system analysis, the radial springback rate of the support is obtained under the combination of the above different structural parameters. The parameter sensitivity of radial support force and stress-strain distribution was studied. The results show that the parameters are an important factor to determine the structure performance, and the sensitivity of different scaffolds is different by different structural parameters. Through simulation analysis, the radial springback rate is analyzed. The main factors influencing its performance are length variable, wire width variable, radius variable and wall thickness according to the influence. For the maximum principal strain, the main factors affecting its performance are the length variable, the wire width variable and the radius variable according to the order of influence. Among these factors, the length factor and the wire width factor have great influence on the three properties of the scaffold. However, changing radius has a great effect on the radial springback rate and the maximum principal strain, but has little effect on the supporting force, while changing the wall thickness can affect the support force performance and the radial springback performance of the support, but has little effect on the maximum principal strain. The influence of these variables on their performance is particularly important for the design of the scaffold structure, especially for the magnesium alloy scaffold, which can be used as a reference in the design of the scaffold structure. According to the experimental results of our group, it is found that there is inhomogeneity of deformation during the deformation of the bracket, which is mainly due to the difference in the opening angle of the "V" beam when the "zigzag" bracing ring is extended. According to this situation, we carry out dynamic simulation analysis of the complete scaffold and the composite system assembled with the folded balloon, by changing the structure of the scaffold, the change of the balloon wing and the thickness of the balloon, and so on. According to the simulation results, the number of the balloon flaps, the matching degree between the stent and the balloon, the number of connecting tendons and the thickness of the balloon have an important effect on the unevenness of the stent expansion. Specifically, the closer the symmetry between the stent and the balloon, the more uniform the stent's expansion. When practical, the number of folding wings of the balloon should be the same as the repeated number of the simplest elements in the axial direction of the stent; the thicker the balloon, the smaller the thickness of the balloon. The more uniform the stent is, the more uniform the stent expansion is, so the thin-walled balloon should be chosen to expand the stent, and the more symmetrical the connecting tendon distribution, the more uniform the stent expansion. Therefore, in the distribution and selection of the number of connecting bars, the distribution of the connecting tendons should be as uniform as possible, and the number of connections should not be reduced over time. These measures can help to improve the symmetrical heterogeneity of the scaffolds.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：R318.08

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