發(fā)布時(shí)間：2018-08-29 14:16

【摘要】：鎂合金具有良好的生物相容性和可降解性,已被用于作為可降解冠脈支架材料進(jìn)行研究,可降解鎂合金支架有望成為新一代心血管支架。然而,與不銹鋼材料相比,鎂合金作為支架材料,抗拉強(qiáng)度低、屈服強(qiáng)度低、斷后延伸率低、塑性變形能力差,使得鎂合金支架存在徑向回彈率大,徑向支撐力低以及應(yīng)力應(yīng)變不均勻(應(yīng)力集中)等問題。因而本文針對鎂合金材料的力學(xué)性能特點(diǎn),對鎂合金支架結(jié)構(gòu)進(jìn)行優(yōu)化設(shè)計(jì),以彌補(bǔ)材料本身性能的不足。本文以有限元模擬為研究方法,采用AZ31鎂合金為支架材料,對課題組自行開發(fā)的鎂合金支架結(jié)構(gòu)進(jìn)行優(yōu)化研究。通過改變支架結(jié)構(gòu)單元的長度、絲寬、圓弧半徑等結(jié)構(gòu)參數(shù),同時(shí)利用系統(tǒng)分析中的敏感性分析方法,對上述不同結(jié)構(gòu)參數(shù)組合下支架的徑向回彈率、徑向支撐力以及應(yīng)力應(yīng)變分布進(jìn)行參數(shù)敏感性研究。結(jié)果表明,參數(shù)是決定結(jié)構(gòu)性能的重要因素,不同支架性能受不同結(jié)構(gòu)參數(shù)影響的敏感性不同,通過模擬分析,對于徑向回彈率而言,影響其性能的主要因素按影響力大小為長度變量、絲寬變量以及半徑變量以及壁厚；對于支撐力而言,影響其性能的主要因素按影響力大小依次為長度變量、絲寬變量以及壁厚變量；對于最大主應(yīng)變而言影響其性能的主要因素按影響力大小依次為長度變量、絲寬變量以及半徑變量。在這些因素中,以長度因素和絲寬因素為甚,分別對支架的三個(gè)性能能產(chǎn)生較大影響。而改變半徑對徑向回彈率以及最大主應(yīng)變的影響較大,對支撐力的影響較小；改變壁厚能夠影響支架的支撐力性能和徑向回彈率性能,對最大主應(yīng)變的影響較小。這些變量對各自性能的影響力大小,對支架結(jié)構(gòu)設(shè)計(jì)尤其是鎂合金支架結(jié)構(gòu)的設(shè)計(jì)尤為重要,可以在支架結(jié)構(gòu)設(shè)計(jì)中作為參考。 根據(jù)課題組支架的實(shí)際實(shí)驗(yàn)中發(fā)現(xiàn),支架在變形過程中存在著變形不均勻性,主要是“之”字形支撐環(huán)在撐開時(shí)“V”形梁張的開角度存在差異。根據(jù)這種情況,我們對完整的支架和折疊球囊裝配在一起的組合系統(tǒng)進(jìn)行動(dòng)態(tài)模擬分析,通過改變支架的結(jié)構(gòu)、球囊的折翼的變化以及球囊的厚度的厚薄等變量,分別模擬支架在不同情況下的變形行為從模擬的結(jié)果看,球囊折翼的數(shù)量、支架與球囊的配合度、連接筋數(shù)量以及球囊自身厚度等情況對支架的擴(kuò)張不均勻性有著重要的影響。具體來講,支架與球囊的對稱性越接近,支架的擴(kuò)張?jiān)骄鶆?在實(shí)際可行的情況下,應(yīng)采用球囊的折翼數(shù)量應(yīng)與支架軸向最簡單元的重復(fù)個(gè)數(shù)相同；球囊的厚度越小,支架的擴(kuò)張?jiān)骄鶆?因此在選擇球囊時(shí),應(yīng)盡量選擇薄壁球囊進(jìn)行擴(kuò)張；同時(shí),支架的連接筋分布越對稱,連接筋越多,支架擴(kuò)張?jiān)骄鶆?因此在支架連接筋的分布和數(shù)量選擇上,應(yīng)使連接筋的分布應(yīng)盡量均勻,且不能過渡減少連接筋的數(shù)量,這些舉措都有利于改善支架的對稱不均勻性。
[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.
【學(xué)位授予單位】：南京理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2012
【分類號】：R318.08

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本文編號：2211451