镁合金支架植入兔腹主动脉后降解时间及血管内膜增生观察

【摘要】 目的 观察新型可降解镁合金支架——MPM植入兔腹主动脉后降解时间及血管内膜增生。方法 24只新西兰大白兔随机分为4组,每组6只,分别于距左肾动脉水平下1 cm腹主动脉处植入MPM支架各1枚。术后30、60、90、180 d分别复查腹主动脉造影,分离支架段血管进行观察。采用SPSS20.0软件对数据进行分析。结果 24只实验兔在随访期间存活良好。植入支架逐渐降解,180 d时基本降解;血管内膜增生,90 d时达峰值,整个降解过程血管通畅。结论 可降解镁合金支架MPM完全降解时间为182 d,可满足血管正性重塑。

     

镁合金支架植入兔腹主动脉后降解时间观察

【摘要】 目的 观察新型可降解镁合金支架——MPM植入兔腹主动脉后的降解时间,评估其对血管壁作用特性。方法 取新西兰大白兔12只,分为4组,每组3只。每只实验兔腹主动脉距肾动脉水平下1 cm处植入MPM支架1枚,术后30、60、90、180 d分别对一组实验兔行腹主动脉DSA检查,评估血管情况并分离支架段血管作病理学分析。结果 术后随访期间,12只实验兔均存活良好。病理检查显示30 d时支架形态完整,扩张完全;60 d时少部分支架支杆降解断裂,支撑力较前减弱;90 d时部分支架支杆断裂;180 d时支架几乎完全被吸收,血管内膜稍有增生。取标本肉眼观察,180 d时仅见少量残留支架。根据直线回归分析,计算出支架完全降解天数为182 d。结论 可降解镁合金支架MPM在兔主动脉中失去支撑作用的时间为182 d,可防止晚期血管再狭窄。

     

国产雷帕霉素洗脱支架和裸支架植入后血管再内皮化实验研究

目的 评价国产雷帕霉素洗脱支架与裸支架植入兔腹主动脉后不同时间血管再内皮化差异.方法 雄性新西兰大白兔24只,高脂喂养28 d后随机分为两组,分别于腹主动脉植入国产雷帕霉素洗脱支架Firebird(SES)和裸金属支架Mustang(BMS).每组分别于术后第3、7、14和28天各处死3只动物,经处理后以扫描电镜观察支架段血管内皮,应用图像处理系统分析支架植入段血管再内皮化程度.结果 支架植入术后第3天两组儿乎均无新生内皮,炎症反应较明显.术后第7、14和28天,SES组内皮覆盖程度明显低于BMS组(分别为15%±8%比53%±9%;49%±16%比83%±4%和73%±3%比93%±4%,P<0.05).结论 SES植入后靶血管出现明显的再内皮化延迟.     

可降解AZ３１镁合金支架在兔腹主动脉的降解性能研究

目的初步评价可降解AZ３１镁合金支架在兔主动脉的降解性能。方法将１２枚可降解AZ３１镁合金支架置入１２只新西兰大白兔腹主动脉中。分别于术后１个月（n＝３）、２个月（n＝３）、３个月（n＝３）及４个月（n＝３）处死动物。对支架段血管进行X线照相及病理检查。结果１２只实验兔在随访期存活良好。X线照相及病理显示１个月时支架形态完整,扩张完全;２个月时支架部分支杆降解断裂,失去支撑作用;３个月时大部分支架支杆降解,４个月时所有支架完全降解。支架在兔主动脉中完全降解所需时间为１０４．５d。结论可降解AZ３１镁合金支架在兔主动脉中２个月内失去支撑作用,延长支撑时间是未来的研究方向     

药物洗脱球囊抑制下肢动脉狭窄性病变的实验研究

【摘要】 目的 探讨新型药物洗脱球囊（DEB）在下肢动脉狭窄性病变（PAD）中可能具有的抑制管腔丢失、减少内膜增生作用。方法 以雄性新西兰纯种兔（体重2.5 ～ 3.0 kg）为实验对象，于兔腹主动脉近心端及远心端各植入Mustang裸支架1枚，模拟PAD模型，并分别用裸球囊（PTA组）及药物洗脱球囊（DEB组）在血管支架段行后扩张，术后28 d处死动物，收集腹主动脉支架标本，塑料包埋并行Masson染色，比较各组内膜增生程度，同时行DEB药物（紫杉醇）靶点β- 微管蛋白免疫组化检测。结果 形态学上，与PTA组比较，DEB组内膜增生及管腔狭窄率明显下降。同时β- 微管蛋白免疫组化检测显示，与PTA组相比，DEB组血管内膜β- 微管蛋白表达量显著增加。结论 动物实验初步显示，DEB具有潜在的有效地抑制管腔丢失、减少内膜增生作用，初步证实该新型DEB的优良性能，提示该新型DEB远期应用于临床治疗PAD的潜在可能性。     

可降解镁合金气管支架在兔气管狭窄模型中初步应用

【摘要】 目的 探讨可降解镁合金气管支架制备及其在气管狭窄动物模型中应用的安全性及可行性。方法 采用气管软骨环间横行切开气管,并用毛刷环形破坏气管黏膜方法制备兔气管狭窄模型30例。镁锌钇钕（Mg- Zn- Y- Nd）合金经热挤压和冷拉拔工艺制备出直径0.24 mm和0.28 mm两种丝材,通过单根丝一体化整体编织技术将两种合金丝编织成8 mm×20 mm气管裸支架各15枚,并检测其物理性能。透视下将两种支架分别植入气管狭窄模型兔气管内,并于术后3、7、15、30、60 d各处死两种支架3只兔,评价支架金属丝断裂、支架压缩、支架降解及气管黏膜肉芽组织增生情况。结果 两种镁合金支架支撑力均略大于镍钛（Ni- Ti）合金支架,丝材直径0.28 mm支架支撑力大于直径0.24 mm支架;丝材直径0.24 mm、0.28 mm支架平均扩张率分别为76.46%、84.66%;镁合金支架完全自膨性能略低于Ni- Ti合金支架。术后3 d支架结构完整,无坍塌;术后7 d支架结构基本完整,有部分丝材断裂,未见组织增生;术后15 d支架基本坍塌,大部分丝材断裂,未见组织增生;术后30 d支架完全降解,气管内壁光滑,未见组织增生;术后60 d气管内壁光滑,未见组织增生。结论 镁合金支架径向支撑力稍强于Ni- Ti合金支架,金属丝易断裂,但生物相容性良好,可降低肉芽组织增生。

     

辛伐他汀对兔股动脉球囊损伤后内膜增生和平滑肌细胞增殖的影响

【摘要】 目的 评价辛伐他汀对兔股动脉球囊损伤后血管狭窄和平滑肌细胞增殖的影响。方法 将24只雄性新西兰兔随机分为假手术组、动脉狭窄模型组和辛伐他汀组，每组8只。除假手术组外，其余两组行股动脉球囊损伤，辛伐他汀组给予辛伐他汀灌胃干预。术后第14天处死实验兔，取出血管标本，处理后行HE染色观察组织病理变化。计算机病理图像分析系统测量动脉管腔、内弹力层、外弹力层围绕面积，计算内膜、中膜面积和内膜/中膜面积比值，免疫组化法检测动脉壁增殖细胞核抗原（PCNA）表达，观察平滑肌细胞增殖情况。结果 与动脉狭窄模型组相比，辛伐他汀组血管管腔面积增加，但差异无统计学意义（P = 0.057），新生内膜面积显著减少（P = 0.006），内膜/中膜面积比值降低，但差异无统计学意义（P = 0.16），血管壁PCNA的阳性表达指数显著降低（P = 0.003）。结论 辛伐他汀可以显著抑制兔股动脉球囊损伤后内膜增生和平滑肌细胞增殖。

     

曲尼司特对兔髂动脉损伤后内膜增殖及血管重构的影响

目的探讨曲尼司持对兔髂动脉球囊损伤后内膜增殖及血管重构的影响.方法 24只新西兰大白兔随机分为假手术组、对照组和用药组.用球囊导管对用药组和对照组兔行髂动脉损伤.用药组于术前3 d开始用曲尼司特(每天300 mg/kg),术后28 d取病变血管苏木精-伊红和弹力纤维染色并免疫组化检查,以计算机图像分析血管内膜、中膜厚度、管腔面积、平均动脉面积(外弹力膜内横截面积,EEL)的变化,计算增殖细胞核抗原(PCNA)增殖指数(PI).结果曲尼司特显著减少内膜厚度,增加血管腔面积和平均动脉面积,对中膜厚度无明显影响     

重视覆膜支架在外周血管病中的应用

自１９９１年Parieli率先应用覆膜支架治疗腹主动脉瘤以来，覆膜支架在主动脉病变中得到较广泛的应用，覆膜支架治疗巨大动脉瘤、假性动脉瘤、血管破裂／穿孔、动静脉瘘等病变取得了可喜的结果，在TIPS通道中覆膜支架的１年初次通畅率比裸支架高。目前覆膜支架应用于血管狭窄及闭塞性病变的研究尚少。覆膜支架植入后血管的长期畅通有待进一步观察。对于高度扭曲的血管植入覆膜支架存在困难和挑战。改进支架材料、覆膜结构和推送装置，开发具有自主知识产权的新支架，拓展覆膜支架的新用途，科学合理地应用支架是介入医师面临的重大课题。     

兔颈总动脉侧壁型动脉瘤模型制作的改进

【摘要】 目的 对兔颈总动脉侧壁型动脉瘤模型进行改进,以评价建模的成功率及支架植入后颈总动脉的通畅率。方法 取新西兰大白兔20只,饲养1周后行左侧颈内动脉结扎。1个月后行颈部3.0 T MRA检查评价颈动脉与椎动脉的变化情况。采用间断式外翻缝合法吻合静脉囊与颈总动脉,建立侧壁型动脉瘤。在植入覆膜支架前、术后即刻、3个月、6个月行血管造影。结果 20只实验兔均顺利行左侧颈内动脉结扎。MRI示结扎前右颈总动脉中段平均直径为（2.35 ± 0.08）mm,结扎后1个月右颈总动脉中段平均直径为（2.89 ± 0.22）mm ,与术前比较差异有显著统计学意义（P < 0.01）。MRA示17只兔右颈总动脉明显增粗,而双侧椎动脉略增粗;3只兔颈总动脉增粗不明显,而双侧椎动脉明显增粗。建立兔颈总动脉囊状动脉瘤模型17 只,术后均健康成活。DSA示覆膜支架植入前所有动脉瘤及右颈总动脉通畅,4个动脉瘤腔内有少量血栓形成,但无自发性完全闭塞。Willis或镁合金覆膜支架植入术后即刻造影示动脉瘤闭塞,右颈内动脉通畅。术后3个月DSA示16只兔右颈内动脉通畅,1只闭塞。术后6个月DSA示16只兔右颈内动脉通畅。动脉瘤模型的成功率为100%（17/17）,覆膜支架植入后右颈总动脉的通畅率为94.1%（16/17）。结论 兔颈总动脉侧壁型动脉瘤模型制作的改进提高了动脉瘤模型的成功率及覆膜支架植入后右颈总动脉的通畅率。
     

On the hydrogenation mechanism in magnesium I

The first time hydriding of spherical magnesium particles covered by a thin oxide layer and sieve-fractionated into narrow size distributions within the range 40–90 μm was followed by microgravimetry. The size distributions of the fractions were determined by semiautomatic image analysis. The hydridings were run at 402°C and 3 MPa hydrogen pressure after heating in helium. A dependence of the rate of hydriding on the heat treatment prior to reaction was observed and it is proposed that the heat treatment causes oxygen atoms to diffuse into the bulk metal and thereby break up the protective oxide layer. Based on the observed hydride propagation in the metal particles, a statistical model for the hydriding of a particle is applied to the hydriding curves for a series of samples. The data are found to be in fine agreement with the proposed model. It is concluded that care must be taken when generalizing results from the hydriding of magnesium powders.     

Thermogravimetric analysis of the relationship among calcium magnesium acetate,calcium acetate and magnesium acetate

Thermal decomposition characteristic of calcium magnesium acetate (CMA), calcium acetate (CA) and magnesium acetate (MA) are investigated through thermogravimetric (TG) analysis at the heating rates of 5 K min⁻¹, 7.5 K min⁻¹, 10 K min⁻¹ and 15 K min⁻¹. After dehydration, the evaporation of carboxylic radical and carbon dioxide of CMA and CA exist in two separate segments, but for MA, this occurs together in just one segment without clear borderline. The curves of calculated CMA (C-CMA) and the deduced characteristic parameters illustrate the different characteristic of CA and MA from the corresponding components in CMA which may be the reason for the different performances of these sorbents in SO₂ and NO_x reduction. Also, the kinetic parameters of activation energy and reaction order of the three sorbents are calculated through Vyazovkin method and Avrami theory, respectively.     

Long-term cycling of the magnesium hydrogen system

Magnesium powder with a grain size of approximately 50γm was hydrogenated for 30 min and dehydrogenated the same time at 390°C, 515 times. A moderate loss in hydrogen storage capacity was observed and was ascribed to a measured decrease in reaction kinetics as the cycle number increased. The time for maximum hydrogen absorption was found to depend significantly on cycle number while the time for maximum desorption was found to be virtually independent of cycle number.     

Hydrogenation properties of pure magnesium and magnesium–aluminium thin films

We have studied the hydrogenation/dehydrogenation behaviour of multilayered stacks of Pd/Mg/Pd and Pd–Fe(Ti)–Mg–Al–Mg–Fe(Ti)–Pd grown by electron beam physical vapour deposition. The palladium coating was deposited at both sides of the structure to ensure a fast dissociation rate and good transport properties for hydrogen as well as to avoid oxidation of magnesium either from atmosphere as from the substrate surface. Fe and Ti layers were included in the stack composition in order to assess their possible catalyst effect as well as to prevent the formation of Mg_xPd_y intermetallics during the thermal treatments. We have studied the structure evolution after thermal treatments as well as after the hydrogenation and dehydrogenation processes using XRD. We have also followed the reactions kinetics by resistometry and differential scanning calorimetry. The nanostructured Mg films have been hydrogenated at temperature as low as 50 °C in few minutes. Adding aluminium to magnesium has improved its hydrogenation capacity. We have also observed that the formation of an Mg_xAl_y intermetallic before hydrogenation improves the storage capacity. We have confirmed that titanium is a better catalyst for the hydrogenation/dehydrogenation of the Mg films.     

Interaction of zirconia with magnesium hydride and its influence on the hydrogen storage behavior of magnesium hydride

This study demonstrates how zirconia additive transforms to zirconium hydride and substantially lowers the dehydrogenation temperature of magnesium hydride. We prepared MgH₂+xZrO₂ (x = 0.125 and 0.5) powder samples reacted for 15 min, 1 h, 5 h, 10 h, 15 h, 20 h and 25 h, and monitored the phase changes at each stage of the reaction. Differential scanning calorimetry (DSC) study provides the first crucial evidence regarding the chemical transformation of zirconia. Subsequently, detailed additional sample testing by X-ray diffraction (XRD), energy dispersive x-ray spectroscopy and confocal Raman microscopy provide strong supports that low temperature dehydrogenation of magnesium hydride is a result of formation of an active in situ product (zirconium hydride). This observation is validated by the negative Gibbs free energy values obtained for the formation of zirconium hydride over a broad working temperature range of 0–600 °C. Scanning electron microscopy (SEM) results prove the high dispersion of tiny nanoparticles all across the surface after the chemical interaction between MgH₂ and ZrO₂ and atomic force microscopy (AFM) study further proves that objects with grain sizes of ～10 nm are abundant throughout the scanned surfaces. These observations reiterate that better metal oxide additives interact with MgH₂ and results to the evolution of highly active insitu nanocatalysts.     

Projected economics of a new magnesium production process and their impact on the cost of magnesium hydrides

In this paper, the benefit per cost ratio for the production of one ton of magnesium is used as a parameter to calculate its market value as a function of the discount rate. Compared to the conventional (chemical) method, the study shows that a cheaper magnesium metal could be produced from sea water using solar energy along with the preferential precipitation technique.Magnesium, among other metals, forms a number of attractive hydrides. The cost of these hydrides is directly proportional to the price of the magnesium metal.The economic impact of using this cheaper magnesium on the cost of hydrides and hydrogen is considered. An estimate of their prices is given.     

Combustion of magnesium particles in oxygen-inert atmospheres

The combustion mechanism of laser-ignited magnesium particles in the 100 ν-size range was studied by cinemicrography of burning particles and by scanning electron micrography of quenched samples. Burning was investigated in room-temperature, atmospheric-pressure, oxygen-argon atmospheres, with oxygen mass fractions ranging from 0.03 to unity. Certain observations also were made for burning in air, for burning at pressures between 1/5 and 2 atm, for burning at ambient temperatures up to roughly 500°C, for burning in atmospheres with water concentrations of roughly 2%, and for burning in carbon dioxide. Prompt and delayed types of ignition were identified. Combustion was found to involve an extended gas-phase reaction zone, surface accumulation of solid oxide, jetting, spinning, and fragmentation. Regular burning, with little accumulation of oxide within the particle, also was observed but only in dilute atmospheres. Except in very dilute atmospheres, buildup of surface oxide was found to produce extinction earlier than expected, either by enhancing the burning rate or by preventing combustion from going to completion. A number of different extinction modes were observed. Burning time was measured as a function of initial flame diameter. Ratios of flame to particle diameters also were estimated. A simplified theoretical model was developed for describing the quasi-steady combustion. Theory and experiment agree in most but not all respects. The theory suggests the occurrence of a homogenous magnesium-oxygen reaction followed later by condensation of the oxide. The fact that the oxide which condenses on the particle surface is solid rather than liquid, is reasoned to influence the combustion mechanism significantly.     

Theoretical study on the reaction of magnesium with water in the gas-phase

The reaction of magnesium with water is of interest for propulsion and hydrogen generation. Reaction mechanism of Mg with water was investigated by ab initio quantum chemical methods. The geometries and frequencies of all reactants, products, intermediates and transition states were calculated at the B3LYP/6-311G++(3df, 2p) level. Energies at a higher level of accuracy were obtained at G2M (CC2) level using the B3LYP-optimized geometries. The Mg and water firstly formed an atom-molecule adduct Mg⋅₂OH, and then either formed MgOH + H by a H-dissociation process or formed HMgOH by the process of H-migration from one to the other side of the adduct molecule. The barrier heights of two processes are 48.28 kcal/mol and 32.51 kcal/mol. The rate constants were calculated by using the variational transition state theory with the zero-curvature tunneling correction in a temperature range of 1000-5000 K. The results showed that H-migration process was dominant in the studied temperature range and the branch ratio of H-dissociation process appeared bigger at higher temperature.     

Open-circuit potential—time transient of the magnesium anode

On interrupting polarisation, the magnesium anode exhibits a negative overshoot in potential followed by a slow recovery to a steady state value. A mod     

Electrochemical insertion of magnesium in open-ended vanadium oxide nanotubes

Vanadium oxide nanotubes were obtained as the main product in a sol–gel reaction followed by hydrothermal treatment from V₂O₅ precursors and octadecylamine. The tubes consist of concentric shells of highly crystalline vanadium oxide separated by alternation organic amine layers. The vanadium oxide nanotubes are redox-active and can electrochemically insert magnesium reversibly. The electrochemical insertion magnesium properties of vanadium oxide nanotubes were studied by electrochemical impedance (EIS) and cyclic voltammogram.