Development of a PVA Hydrogel for Bioprosthetic Heart Valve Stent and Other Medical Applications

Polyvinyl alcohol (PVA) hydrogel (15%w/w) was processed by freezing and thawing from one through six thermal cycles to obtain wide range of mechanical properties. The materials were tested under uniaxial tension and results show that matching mechanical properties to that of porcine aortic root can be achieved. A fatigue machine for elastomer materials and tissues was built and fatigue test on PVA sample was carried out. The test results show that the PVA has good fatigue property. The stent prototype was designed and successfully made by mold casting method. Some potential medical applications are discussed.     

Nickel-free stainless steel avoids neointima formation following coronary stent implantation

SUS316L stainless steel and cobalt–chromium and platinum–chromium alloys are widely used platforms for coronary stents. These alloys also contain nickel (Ni), which reportedly induces allergic reactions in some subjects and is known to have various cellular effects. The effects of Ni on neointima formation after stent implantation remain unknown, however. We developed coronary stents made of Ni-free high-nitrogen austenitic stainless steel prepared using a N₂-gas pressurized electroslag remelting (P-ESR) process. Neointima formation and inflammatory responses following stent implantation in porcine coronary arteries were then compared between the Ni-free and SUS316L stainless steel stents. We found significantly less neointima formation and inflammation in arteries implanted with Ni-free stents, as compared to SUS316L stents. Notably, Ni²⁺ was eluted into the medium from SUS316L but not from Ni-free stainless steel. Mechanistically, Ni²⁺ increased levels of hypoxia inducible factor protein-1α (HIF-1α) and its target genes in cultured smooth muscle cells. HIF-1α and their target gene levels were also increased in the vascular wall at SUS316L stent sites but not at Ni-free stent sites. The Ni-free stainless steel coronary stent reduces neointima formation, in part by avoiding activation of inflammatory processes via the Ni-HIF pathway. The Ni-free-stainless steel stent is a promising new coronary stent platform.     

Tamibarotene-loaded citric acid-crosslinked alkali-treated collagen matrix as a coating material for a drug-eluting stent

Abstract

Tamibarotene-loaded biodegradable matrices with antithrombogenic and drug-releasing properties were prepared in a crosslinking reaction between amino groups of alkali-treated collagen (AlCol) and active ester groups of trisuccinimidyl citrate. The resulting matrices were characterized by their residual amino group concentrations, swelling ratios and thermal, antithrombogenic and drug-releasing properties. It was clarified that the addition of tamibarotene does not inhibit matrix formation. After immersion in water, the swelling ratio of a matrix became lower than that prior to immersion. Thermal analysis indicated that AlCol interacted with tamibarotene. The addition of tamibarotene to the matrix did not influence the antithrombogenic property of the resulting matrix. A matrix with a high crosslinking density had a prolonged tamibarotene elution time. These results demonstrate that tamibarotene-loaded matrices have great potential as a coating material for drug-eluting stents.     

无镍不锈钢冠脉支架力学行为的有限元模拟

以无镍不锈钢为支架材料,以冠脉支架结构为研究对象,对其压缩和扩张过程中的力学行为和柔顺性能进行了模拟计算,研究了支架压握并扩张后的轴向回弹率、径向回弹率以及不同端部网丝宽度支架的变形行为,计算出支架的弯矩-挠度曲线及支架的柔软度。结果表明,所研究的无镍不锈钢支架具有较小的轴向与径向回弹率,在变形过程中表现出良好的弹性弯曲变形性能。     

A three‐dimensional model describing stress‐temperature induced solid phase transformations: solution algorithm and boundary value problems

An always increasing knowledge on material properties as well as a progressively more sophisticated production technology make shape memory alloys (SMA) extremely interesting for the industrial world. At the same time, SMA devices are typically characterized by complex multi‐axial stress states as well as non‐homogeneous and non‐isothermal conditions both in space and time. This aspect suggests the finite element method as a useful tool to help and improve application design and realization. With this aim, we focus on a three‐dimensional macroscopic thermo‐mechanical model able to reproduce the most significant SMA features (Int. J. Numer. Methods Eng. 2002; 55 : 1255–1264), proposing a simple modification of such a model. However, the suggested modification allows the development of a time‐discrete solution algorithm, which is more effective and robust than the one previously discussed in the literature. We verify the computational tool ability to simulate realistic mechanical boundary value problems with prescribed temperature dependence, studying three SMA applications: a spring actuator, a self‐expanding stent, a coupling device for vacuum tightness. The effectiveness of the model to solve thermo‐mechanical coupled problems will be discussed in a forthcoming work. Copyright © 2004 John Wiley & Sons, Ltd.     

冠脉血管支架介入耦合系统力学行为数值模拟研究

针对冠脉支架植入术后引起的血管内再狭窄问题,开展了冠脉支架介入耦合系统力学行为的数值模拟研究。基于Ogden非线性弹性理论,构建了冠脉血管和动脉粥样硬化斑块的超弹性本构模型。通过非线性有限元法,建立了冠脉支架与狭窄血管的耦合作用模型,研究了冠脉支架在经历压握收缩、压握卸载、球囊扩张与球囊收缩等介入过程后的体内扩张性能,分析了冠脉支架的介入对狭窄血管损伤及再狭窄的力学影响因素。对比分析了S型支架和N型支架介入后狭窄冠脉血管的生物力学响应,数值计算结果表明：狭窄冠脉血管在支架支撑体波峰处存在较高的应力梯度,而且由于2种支架联接筋结构的类似性,血管内膜与斑块的应力分布规律一致。但是,N型支架的径向回弹率与轴向短缩率均小于S型支架,导致了更高的狭窄血管壁面峰值应力和应力梯度,更易于引起冠脉血管损伤造成血管内再狭窄。综上,该文提出的冠脉支架介入耦合系统力学模型,对于优化支架结构、抑制冠脉血管再狭窄问题,提供了重要的理论依据和临床参考。     

制备方法对高分子载药涂层结构和体外释放动力学的影响

分别采用浸涂法和喷涂法在316L不锈钢基体表面制备含雷帕霉素的丙烯酸树脂缓释涂层,并使用FTIR、SEM及DSC对涂层中雷帕霉素的物化状态进行了测试和分析,测试了上述两种方法制备的药物洗脱支架的体外药物释放动力学曲线,并分析了两种制备方法之间的差异.结果表明上述两种方法制备的含药涂层药物分布状态存在一定差异,药物释放速率有所不同,以浸涂法制备的含药涂层释放速率更快.     

Principles of treating enlarging pseudoaneurysm in a dialysis arteriovenous graft

The arteriovenous graft (AVG) is one of the major types of permanent vascular access used to provide hemodialysis. Complications encountered with AVG use include stenosis, infection, thrombosis, and pseudoaneurysm formation. Venous outflow stenosis along with frequent needle cannulation at the same site can lead to breakdown of the graft material, resulting in pseudoaneurysm formation. In the following case, we illustrate common management principles used to treat pseudoaneurysms. While stent‐grafts have been utilized for pseudoaneurysm repair, stent‐graft usage is not always optimal. Surgical management may be an ideal choice of treatment. The role of educating the dialysis staff and patients is essential to identify and minimize the risk of pseudoaneurysm formation.     

输尿管支架表面化学接枝镀铜涂层及其性能

采用聚多巴胺接枝化学镀铜方法在316L不锈钢表面制备载铜聚多巴胺涂层,使用扫描电镜、原子力显微镜、X射线光电子能谱、电感耦合等离子体质谱仪等手段表征其表面形貌、成分和铜离子释放量并将其与细菌和细胞共培养,研究了涂层的抗感染、抗结石性能和生物相容性。结果表明,载铜涂层的厚度为27 nm,分布均匀,其中的铜以Cu、CuO和Cu₂O的形式存在。将涂层在人工尿液中浸泡14 d,铜离子每天的释放量接近。将涂层分别与大肠杆菌和金黄色葡萄球菌培养24 h后,抗菌率为96.2%和95.9%。在金黄色葡萄球菌悬液中浸泡30 d后在涂层表面沉积的钙离子和镁离子含量分别为48.7 mg/L和235.3 mg/L,明显低于对照组。细胞增殖实验的结果表明,这种涂层无细胞毒性。     

Macro- and microscale variables regulate stent haemodynamics,fibrin deposition and thrombomodulin expression

Drug eluting stents are associated with late stent thrombosis (LST), delayed healing and prolonged exposure of stent struts to blood flow. Using macroscale disturbed and undisturbed fluid flow waveforms, we numerically and experimentally determined the effects of microscale model strut geometries upon the generation of prothrombotic conditions that are mediated by flow perturbations. Rectangular cross-sectional stent strut geometries of varying heights and corresponding streamlined versions were studied in the presence of disturbed and undisturbed bulk fluid flow. Numerical simulations and particle flow visualization experiments demonstrated that the interaction of bulk fluid flow and stent struts regulated the generation, size and dynamics of the peristrut flow recirculation zones. In the absence of endothelial cells, deposition of thrombin-generated fibrin occurred primarily in the recirculation zones. When endothelium was present, peristrut expression of anticoagulant thrombomodulin (TM) was dependent on strut height and geometry. Thinner and streamlined strut geometries reduced peristrut flow recirculation zones decreasing prothrombotic fibrin deposition and increasing endothelial anticoagulant TM expression. The studies define physical and functional consequences of macro- and microscale variables that relate to thrombogenicity associated with the most current stent designs, and particularly to LST.