Chemical incompatibility between polymerizing HEMA and rubber balloons used for selective endovascular treatment of intracranial aneurysms

Permanent selective occlusion by detachable balloons with parent vessel preservation is considered to be the endovascular treatment of choice of intracranial aneurysms. It has been proposed that replacement of contrast material within the balloon with a polymerizing substance will eliminate balloon deflation. Despite this solution, our clinical experience with polyisoprene rubber balloons shows that deflation can still occur when the balloons are filled with poly(2-hydroxyethyl methacrylate). Experimental data are presented that demonstrate the chemical incompatibility between hydroxyethyl methacrylate (HEMA) and polyisoprene rubber. The resulting degradation of the polyisoprene rubber accounts well for balloon failure. Thein vitro behaviour of silicone balloons and of a new HEMA sponge formulation to fill the balloons are compared.     

Properties of nylon 12 balloons after thermal and liquid carbon dioxide treatments

Critical design attributes of angioplasty balloons include the following: tear resistance, high burst pressures, controlled compliance, and high fatigue. Balloons must have tear resistance and high burst pressures because a calcified stenosis can be hard and nominal pressures of up to 16 atm can be used to expand the balloon. The inflated balloon diameter must be a function of the inflation pressure, thus compliance is predictable and controlled. Reliable compliance is necessary to prevent damage to vessel walls, which may be caused by over-inflation. Balloons are often inflated multiple times in a clinical setting and they must be highly resistant to fatigue. These design attributes are dependent on the mechanical properties and polymer morphology of the balloon. The effects of residual stresses on shrinkage, crystallite orientation, balloon compliance, and mechanical properties were studied for angioplasty nylon 12 balloons. Residual stresses of these balloons were relieved by oven heat treatment and liquid CO₂ exposure. Residual stresses were measured by quantifying shrinkage at 80 °C of excised balloon samples using a dynamic mechanical analyzer. Shrinkage was lower after oven heat treatment and liquid CO₂ exposure compared to the as-received balloons, in the axial and radial directions. As-received, oven heat treated, and liquid CO₂-exposed balloon samples exhibited similar thermal properties (T_g, T_m, X_t). Crystallite orientation was not observed in the balloon cylindrical body using X-ray scattering and polarized light microscopy, which may be due to balloon fabrication conditions. Significant differences were not observed between the stress–strain curves, balloon compliance, and average burst pressures of the as-received, oven heat treated, and liquid CO₂-exposed balloons.     

Novel paclitaxel-coated angioplasty balloon catheter based on cetylpyridinium salicylate: Preparation,characterization and simulated use in an in vitro vessel model

Drug-coated balloons (DCB), which have emerged as therapeutic alternative to drug-eluting stents in percutaneous cardiovascular intervention, are well described with regard to clinical efficiency and safety within a number of clinical studies. In vitro studies elucidating the correlation of coating method and composition with DCB performance are however rare but considered important for the understanding of DCB requirements and the improvement of established DCB. In this context, we evaluated the applicability of a pipetting, dip-coating, and spray-coating process for the establishment of DCB based on paclitaxel (PTX) and the ionic liquid cetylpyridinium salicylate (Cetpyrsal) as novel innovative additive in three different compositions. Among tested methods and compositions, the pipetting process with 50 wt.% PTX resulted in most promising coatings as drug load was less controllable by the other processes and higher PTX contents led to considerable drug crystallization, as visualized by electron microscopy, accelerating PTX loss during short-term elution. Applying these conditions, homogeneous coatings could be applied on balloon catheter, whose simulated use in an in vitro vessel model revealed percental drug losses of 36 and 28% during transit and percental drug transfers of 12 and 40% under expansion for coatings applied in expanded and folded balloon condition, respectively. In comparison to literature values, these results support the high potential of Cetpyrsal as novel DCB matrix regarding low drug loss and efficient drug transfer.     

3D dosimetry study of 188Re liquid balloon for intravascular brachytherapy using bang polymer gel dosemeters

It has been suggested that the combination of intravascular brachytherapy and coronary stent implantation may result in further reduction of restenosis after percutaneous balloon angioplasty. The use of an angioplasty balloon filled with a 188Re liquid beta source for intravascular brachytherapy provides the advantages of accurate source positioning and uniform dose distribution to the coronary vessel wall. The effect of source edge and stent on the dose distribution of the target tissue may be clinically important. In BANG gels, the absorbed radiation produces free-radical chain polymerisation of acrylic monomers that are initially dissolved in the gel. The number of polymer particles is proportional to the absorbed dose. In this study, 3D dose distributions are presented for 188Re balloons, with and without stents, using a prototype He-Ne laser CT scanner and the proprietary BANG polymer gel dosemeters.     

Controlled Release of Antiproliferative Drugs From Polymeric Systems for Stent Applications and Local Cancer Treatment

Restenosis (re‐narrowing of the blood vessel wall) and cancer are two different pathologies that have drawn extensive research attention over the years. Antiproliferative drugs such as paclitaxel inhibit cell proliferation and are therefore effective in the treatment of cancer as well as neointimal hyperplasia, which is known to be the main cause of restenosis. Drug‐eluting stents (DES) significantly reduce the incidence of in‐stent restenosis (ISR), which was once considered a major adverse outcome of percutaneous coronary stent implantations. Localized release of antiproliferative drugs interferes with the pathological proliferation of vascular smooth muscle cells (VSMC), which is the main cause of ISR. Conventional approaches to treating cancer are mainly surgical excision, irradiation, and chemotherapy. In cancer therapy, surgical treatment is usually performed on patients with a resectable carcinoma. An integrated therapeutic approach, such as the addition of a delivery system loaded with an antiproliferative drug at the tumor resection site, is desirable. This will provide a high local concentration of a drug, that is, detrimental to malignant cells which may have survived surgery, thus preventing re‐growth and metastasis of the tumor. The present review describes recent advances in systems for controlled release of antiproliferative agents. It describes basic concepts in drug delivery systems and antiproliferative drugs and then focuses on both types of systems: stents with controlled release of antiproliferative agents, and drug‐eluting particles and implants for local cancer treatment. The last part of this article is dedicated to our novel drug‐eluting composite fiber structures, which can be used as basic stent elements as well as for local cancer treatment.     

Poly‐Lactic‐Acid for coating of endovascular stents: preliminary results in canine experimental av‐fistulae

Poly‐Lactic‐Acid (PLA) was evaluated for coating of vascular endoprostheses in the treatment of experimental arterio‐venous‐fistulae (AVF). Bilateral carotid – external jugular AVF were created in 5 adult dogs. 7 PLA coated nitinol stents were placed via a transfemoral approach covering 5 AVF. The contralateral AVF remained untreated. Angiography was performed immediately after stent placement, at weeks 1 and 3 and at months 3, 6 and 9. All grafts were removed and underwent histologic examination. In 2 cases the occlusion of the AVF was successful, while misplacement occurred in 3 cases. Occlusion of the parent vessel was disclosed in 3 cases. Histologic examination revealed a mild inflammatory reaction with the presence of macrophages. There was no foreign‐body reaction or fragmentation of the arterial vessel wall. PLA, which is a well‐known biodegradable material, showed a good mid‐term biocompatibility. Elastic mismatch of the non‐elastic coating and the self‐expandable nitinol stent caused misplacement. Frequent vessel‐occlusions were probably due to PLA‐filaments fraying into the vessel lumen. Using a different textile structure PLA might be a material suitable for coating endovascular stents.     

Lifting options for stratospheric aerosol geoengineering: advantages of tethered balloon systems

The Royal Society report 'Geoengineering the Climate' identified solar radiation management using albedo-enhancing aerosols injected into the stratosphere as the most affordable and effective option for geoengineering, but did not consider in any detail the options for delivery. This paper provides outline engineering analyses of the options, both for batch-delivery processes, following up on previous work for artillery shells, missiles, aircraft and free-flying balloons, as well as a more lengthy analysis of continuous-delivery systems that require a pipe connected to the ground and supported at a height of 20 km, either by a tower or by a tethered balloon. Towers are shown not to be practical, but a tethered balloon delivery system, with high-pressure pumping, appears to have much lower operating and capital costs than all other delivery options. Instead of transporting sulphuric acid mist precursors, such a system could also be used to transport slurries of high refractive index particles such as coated titanium dioxide. The use of such particles would allow useful experiments on opacity, coagulation and atmospheric chemistry at modest rates so as not to perturb regional or global climatic conditions, thus reducing scale-up risks. Criteria for particle choice are discussed, including the need to minimize or prevent ozone destruction. The paper estimates the time scales and relatively modest costs required if a tethered balloon system were to be introduced in a measured way with testing and development work proceeding over three decades, rather than in an emergency. The manufacture of a tether capable of sustaining the high tensions and internal pressures needed, as well as strong winds, is a significant challenge, as is the development of the necessary pumping and dispersion technologies. The greatest challenge may be the manufacture and launch of very large balloons, but means have been identified to significantly reduce the size of such balloons or aerostats.     

Cutting balloon angioplasty for resistant venous stenoses in hemodialysis patients

Purpose:  To report our initial experience of using cutting balloons angioplasty in the treatment of resistant venous stenoses of Brescia‐Cimino fistulas. Materials and Methods:  Forty‐eight patients with Brescia‐Cimino fistulas underwent percutaneous transluminal angioplasty (PTA) of 62 venous stenoses. Of these 48 patients, we encountered 8 venous stenoses (8/62, 12.9%) in 7 patients that were not successfully dilated with 6–8 mm high‐pressure balloons inflated up to 24 atm. In each of 8 stenoses, peripheral cutting balloons with diameters of 5–8 mm were employed to dilate resistant stenoses. Results:  The locations of stenoses were 3 at the surgical vein mobilization site ("swing point"), 4 at the cephalic vein downstream from the anastomosis, and 1 at the cephalic arch. The grade of stenosis after high‐pressure balloon angioplasty ranged from 57% to 87%(mean, 76%). Cutting balloons expanded completely in all stenoses and the residual stenosis after cutting balloon PTA ranged from 0% to 24%(mean, 7%). Residual stenosis was virtually nonexisistent at the 3 stenoses of "swing point." A focal rupture with a large hematoma occurred at the cephalic arch stenosis, which was treated by a stent placement. One minimal rupture that did not require any treatment occurred at the stenosis of downstream cephalic vein. No repeat angioplasty has been needed during follow‐up period (range, 74–249 days). Conclusion:  Our early experience demonstrated that when high‐pressure balloons fail to dilate stenoses of Brescia‐Cimino fistulas, peripheral cutting balloons with diameters of 5–8 mm can be effectively used to overcome the resistance of stenoses.     

Inorganic materials as drug delivery systems in coronary artery stenting

Recent studies proved coronary stent implantation to be superior over conventional angioplasty in the treatment of coronary artery disease. However, restenosis remains one of the most crucial problems in interventional cardiology. Inflammatory infiltrates and foreign body reactions can be found in the tissue surrounding the struts in stenting. Thrombogenesis, proliferation of α‐actin expressing cells (smooth muscle cells) and hyperplasia of the intima occur. In order to improve the biocompatibility of the stents, new stent designs and stent coatings have been developed. One advantage of stent coating is the combination of mechanical stability of the stent with the biocompatibility of the coating. The coatings are divided into active and passive coatings. Passive coatings improve the biocompatibility of the stent, while active coatings may suppress neointima proliferation by releasing anti‐inflammatory or antiproliferative substances. Immunosuppressive drugs (tacrolimus, sirolimus) and cytostatic drugs (paclitaxel) have been tested in several studies and showed promising results. However, it could also be demonstrated that polymer‐coated stents used as a matrix for drug release reduced the hyperplasia of the intima. However, after dissipation of the immunosuppressants or cytostatics, the presence of the polymer itself lead to a delayed inflammation and proliferation causing restenosis. Thus, efforts have been made to develop inorganic coatings that are suitable for drug loading. One promising approach is a new nanoporous alumina coating. Preliminary tests with this coating revealed favourable loading characteristics and sustained drug release in vivo. The present article provides an overview on different approaches for stent coatings.     

Lipophilic NO-Driven Nanomotors as Drug Balloon Coating for the Treatment of Atherosclerosis

Drug-coated balloons (DCB) intervention is an important approach for the treatment of atherosclerosis (AS). However, this therapeutic approach has the drawbacks of poor drug retention and penetration at the lesion site. Here, a lipophilic drug-loaded nanomotor as a modified balloon coating for the treatment of AS is reported. First, a lipophilic nanomotor PMA-TPP/PTX loaded with drug PTX and lipophilic triphenylphosphine (TPP) compounds is synthesized. The PMA-TPP/PTX nanomotors use nitric oxide (NO) as the driving force, which is produced from the reaction between arginine on the motor substrate and excess reactive oxygen species (ROS) and inducible nitric oxide synthase (iNOS) in the AS microenvironment. The final in vitro and in vivo experimental results confirm that the introduction of the lipophilic drug-loaded nanomotor technology can greatly enhance the drug retention and permeability in atherosclerotic lesions. In particular, NO can also play an anti-AS role in improving endothelial cell function and reducing oxidative stress. The chemotherapeutic drug PTX loaded onto the nanomotors can inhibit cell division and proliferation, thereby exerting the effect of inhibiting vascular intimal hyperplasia, which is helpful for the multiple therapies of AS. Using nanomotor technology to solve cardiovascular diseases may be a promising research direction.     

The future of scientific ballooning

This paper gives a brief overview of the historical development of scientific balloons and their capabilities. Furthermore, a recent programme by NASA is introduced that aims to develop balloons capable of carrying payloads of several tonnes to above 99% of the Earth's atmosphere for up to 100 days. It is shown that the currently investigated balloons suffer from instabilities that can be minimized using a different design paradigm for the cutting patterns. Finally, a novel balloon design, similar to the topology of radiolarians, is introduced that is potentially superior to existing designs.     

A homogenized constrained mixture model of restenosis and vascular remodelling after balloon angioplasty

Restenosis is one of the main adverse effects of the treatment of atherosclerosis through balloon angioplasty or stenting. During the intervention, the arterial wall is overstretched, causing a cascade of cellular events and subsequent neointima formation. This mechanical stimulus and its mechanobiological effects can be reproduced in biomechanical simulations. The aim of these models is to predict the long-term outcome of these procedures, to help increase the understanding of restenosis formation and to allow for in silico optimization of the treatment. We propose a predictive finite-element model of restenosis, using the homogenized constrained mixture modelling framework designed to model growth and remodelling in soft tissues. We compare the results with clinical observations in human coronary arteries and experimental findings in non-human primate models. We also explore the model’s clinical relevance by testing its response to different balloon loads and to the use of drug-eluting balloons. The comparison of the results with experimental data shows the relevance of the model. We show its ability to predict both inward and outward remodelling as observed in vivo and we show the importance of an improved understanding of restenosis formation from a biomechanical point of view.     

压力容器端盖镀层条状凸起原因分析

采用宏、微观检测和电子探针等方法对压力容器端盖电镀表面条状凸起缺陷进行了分析。结果表明,镀层表面具有方向性的条状凸起与端盖钢板中的夹层有关,经机加工后局部露出表面的夹杂在镀锌过程中与酸或镀液发生反应,生成的产物使距表面很近的薄层向外膨胀并被镀层覆盖,形成镀层表面凸起。     

Production of novel epoxy micro-balloons

Epoxy micro-balloons are prepared by dropping and stirring of epoxy mixture in heated silicon oil. The mixture of epoxy, curing agent and blowing agent forms sphere particles, which are then blown via the function of blowing agent and simultaneously cured to form epoxy micro-balloons. Different ratio of epoxy and hardener will produce different types of epoxy micro-balloons. Schematic illustrations to produce the epoxy micro balloons are also proposed.     

表面宏微处理对塑料粘结NdFeB永磁性能的影响

本文研究了偶联剂处理ＮｄＦｅＢ磁粉及环氧树脂涂层对塑料粘结ＮｄＦｅＢ永磁体性能的影响，结果表明：（１）ＫＨ５５０包覆处理ＮｄＦｅＢ磁粉可改善Ｎｄ－ＦｅＢ磁粉的抗氧化性，提高塑料粘结ＮｄＦｅＢ的磁性能和压缩强度；（２）用偶联剂微观保护ＮｄＦｅＢ磁粉和环氧树脂涂层宏观保护相结合的办法可显著地提高塑料粘结ＮｄＦｅＢ永磁体的耐蚀性和抗高温氧化性     

新型自泳涂料后处理剂及工艺的研究

自泳涂料是一种新型的特殊乳胶涂料,使用时不仅涂装工艺简单、涂层均匀、不存在泳透力问题,而且具有成本低、无污染等特点,正在逐步推广应用于各个领域.针对目前自泳涂料多采用含铬后处理剂,不利于环境保护的缺陷,制得一种新型自泳涂料后处理剂,并通过试验研究了其配套性能的一系列影响因素,确定其使用工艺.根据自泳涂膜的各项性能测试结果表明,使用该后处理剂的漆膜外观平整,附着力优良,适用于自泳涂料的钝化处理.     

A study on the reconstruction of moderate contrast targets using the distorted born iterative method

Previous tomographic methods using ultrasound for reconstructing sound speed and attenuation images suffered from convergence issues for targets with moderate speed of sound contrast. Convergence problems can be overcome by the use of the multiple frequency, distorted Born iterative method (DBIM). The implementation of DBIM for measurement configurations in which receiver positions are fixed was studied, and a novel regularization scheme was developed. The regularization parameter needed to stabilize the inversion process initially was found through the Rayleigh quotient iteration, then relaxed according to the relative residual error between the measured and estimated scattered fields. The DBIM was successfully stabilized for both full and partial receiver angular coverage without a significant loss in spatial resolution. The effects of variable density in the reconstructions were briefly explored through simulations. The ability to reconstruct targets with moderate contrast was validated through experimental measurements. Speed of sound profiles for balloons filled with saline in a background of water were reconstructed using multiple frequency DBIM techniques. The mean squared error for speed of sound reconstructions of the balloon phantoms with 16.4% sound speed contrast was 1.1%.     

水难溶性药物的载体材料研究进展

水难溶性药物因其在水中溶解度小使得药物的临床应用受到限制.将水难溶性药物通过某些载体包裹,是对水难溶性药物进行增溶的一种行之有效的方法.综述了水难溶性药物载体材料的研究进展,并总结了各种载体材料的优缺点.针对普遍存在的增溶效果不理想的问题,指出了几种载体未来的发展方向.表面活性剂胶束因其自身的毒性而逐渐被其它载体材料取代.环糊精和聚合物胶束具有广阔的发展前景.尽管脂质体作为水难溶性药物载体存在不足之处,但其可用作水溶性药物的载体或者制备成主动靶向制剂(例如单克隆抗体导向的脂质体)、物理化学靶向制剂(例如磁靶向脂质体),仍具有巨大的研究价值和发展空间.     

Coating of polyurethane scaffolds with collagen: comparison of coating and cross-linking techniques

Collagen has been coated successfully onto numerous hydrophilic polymer scaffolds to improve cell adhesion. Due to the hydrophobic nature of thermoplastic polyurethane (TPU), coating with aqueous collagen solution is problematic for such scaffolds. This study facilitated the coating of TPU with collagen and compared cross-linking and coating techniques. Three different cross-linking methods were compared. Both thermal and glutaraldehyde methods showed proof of cross-linking; however glutaraldehyde seemed to be superior to the other methods. The use of human urine as a wetting agent and the chemical glutaraldehyde had no effect on a cytotoxicity test performed by means of a WST-1 assay with a fibroblastic cell line. Three different coating techniques for porous TPU scaffolds were also investigated: ultrasound, pressurized air and injection. Of these, injection performed best. This method facilitated a coating of 100% of the porous scaffolds examined, which was verified by staining, FTIR and SEM.