Effect of different ratios of high and low molecular weight PLGA blend on the characteristics of pentamidine microcapsules

Two different PLGA samples (Resomer 502 and Resomer 506), either alone or in combinations, were used to prepare microcapsules. Microcapsules were prepared using a double emulsion solvent evaporation technique. The efficiency of encapsulation increased significantly when a mixture of 1 part Resomer 506 and 7 parts Resomer 502 was used to prepare the microcapsules. The efficiency of encapsulation of this batch was 23.7%, whereas the efficiency of encapsulations was only 13.9 and 9.8%, respectively, when the microcapsules were prepared with 100% Resomer 502 or 100% Resomer 506. In contrast, irrespective of the relative ratio of Resomer 502/Resomer 506, the median particle size of the microcapsules showed similar distribution pattern with the median size lies between 49 and 83 μm. The glass transition temperature (T_g) decreased significantly (44.6–25.5 °C) as the amount of Resomer 502 was increased in the formulation. The presence of Resomer 502 at lower concentration, along with Resomer 506, initially reduced the “burst effect.” However, incorporation of a higher amount of Resomer 502 increased the “burst effect.” Drug release from these microcapsules continued over 80 days. In conclusion, efficiency of encapsulation increased significantly when Resomer 506 was mixed with Resomer 502 at a ratio of 1:7. Blending of Resomer 502 with Resomer 506 reduced the glass transition temperature, which resulted in higher amount of drug release throughout the dissolution study.     

Factors influencing the properties and performance of microcapsules for immunoprotection of pancreatic islets

There are several approaches of immunoprotection of pancreatic islets for the purpose of successful allo- or xenotransplantation in the absence of immunosuppressive medication. Extravasculair approaches are either macroencapsulation (large numbers of islets together in one device) or microencapsulation. The latter approach is to envelop each individual islet in a semipermeable immunoprotective capsule. Quite promising results have been achieved with polylysine-alginate microencapsulated islet grafts in rodents, but clinical application is still restricted to a very small number of cases. Relevant considerations regard the following aspects. The biocompatibility of the microcapsules is influenced by the chemical composition of the materials applied and by mechanical factors related to the production process. With purified instead of crude alginates, the percentage of capsules with fibrotic overgrowth is reduced to approximately ten percent, and the remaining overgrowth is mainly explained by mechanical factors, i.e. inadequate encapsulation of individual islets. Even with purified alginates, however, the duration of encapsulated graft function is limited to a period of six to twenty weeks. Obviously, other factors than bioincompatibility play a role, which factors have to be identified. The limited duration of graft survival cannot be explained by rejection since, in rats, survival times of encapsulated isografts are similar, if not identical, to those of encapsulated allografts. An important factor is probably insufficient nutrition as a consequence of insufficient blood supply of the encapsulated and thus isolated islet. This also influences the functional performance of encapsulated islet grafts. Although normoglycemia can be readily obtained in streptozotocin diabetic rat recipients, glucose tolerance remains severely impaired, as a consequence of an insufficient increase of insulin levels in response to intravenous or oral glucose challenge. Important factors are the characteristics of the capsules applied in view of optimal diffusion kinetics, and the fact that an encapsulated islet graft can only be implanted in the peritoneal cavity because of its volume. Further studies should focus on finding a practically applicable method to reduce the barrier between encapsulated islets and the bloodstream, in order to improve both the functional performance and the survival of encapsulated islet grafts.     

四株海洋放线菌抗氧化活性初筛与微囊化包埋研究

海洋放线菌是新药研发的重要来源。通过DPPH自由基清除活性实验,从南海石珊瑚Diploriastrigosa共生放线菌中筛选有抗氧化潜力的活性菌株,然后采用生物相容性良好的海藻酸钠、黄原胶和壳聚糖作为囊材,利用挤压法制备包埋其中一株活性菌,测定微囊的粒径和包埋情况。结果表明,海洋放线菌ZJG4有较高的DPPH自由基清除活性（IC50=2．18mg／mL）,将其包埋后的微裳呈白色、球形,粒径在400～650／,m之间,具有良好的机械强度,包埋培养时间为4天。研究表明,微囊化包埋海洋放线菌培养制备工艺简单、条件温和,适合活生物细胞的包埋。     

超临界流体沉降技术制备微粒的研究进展

本文简单介绍超临界流体的特性,阐述超临界流体沉降技术的种类和特点,综述近几年在纳米粒、微球和微囊制备方面的最新研究进展。     

Effect of lecithins on BCG-alginate-PLL microcapsule particle size and stability upon storage

Alginate-PLL microcapsules containing BCG were prepared by emulsification/ internal gelation of an alginate solution dispersed within a vegetable oil containing lecithins as emulsifiers. The lecithins studied were soy bean lecithin at 0.1, 0.5, 1 and 2%concentration; and dried egg yolk lecithin at 0.1, 0.25, 0.5 and 1%. The microcapsule particle size showed a dependence upon the amount and type of lecithin added to the oil. Increasing the emulsifying agent concentration was found to reduce particle size, from 50.9mum obtained when lecithins were not used in the emulsification step, to 13.9mum obtained when 1% dried egg yolk lecithin was employed. The encapsulated BCG was identified by the Difco TB stain set K, followed by observation under optical microscopy. Once prepared, microcapsules were freeze-fried using 5%trehalose as cryoprotectant in order to preserve their stability upon storage. The stability of the microcapsules was assayed over 12 months at room temperature, finding that alginate-PLL microcapsules were stable up to 6 months. Moreover, in the case of microcapsules prepared with lecithins, a significant increase in particle size was observed, from 16.9mum at the beginning of the study to 25.2mum at 12 months storage.     

Plastic behaviour of polyelectrolyte microcapsules derived from colloid templates

The deformability and osmotic properties of hollow microcapsules were studied by means of the micropipette video microscopic technique. The microcapsules were prepared by consecutive multiple adsorption of the polyanion, poly (styrene sulphonate), and the polycation, poly(allylamine hydrochloride), onto melamine formaldehyde resin latex of 5mum diameter, which was decomposed after completing the coating by transferring to hydrochloric acid of pH1.1. The polyelectrolyte microcapsules reacted to micropipette suction with plastic deformation. If lipids are added to the polyelectrolyte layers, the capsules cannot be visibly deformed by micropipette suction up to 104 N/m2. However, plastic shrinking was observed if the stress was generated by the osmotic pressure of a sucrose solution of 106 N/m2.     

Drug-loaded polyelectrolyte microcapsules for sustained targeting of cancer cells

In this review we will overview novel nanotechnological nanocarrier systems for cancer therapy focusing on recent development in polyelectrolyte capsules for targeted delivery of antineoplastic drugs against cancer cells. Biodegradable polyelectrolyte microcapsules (PMCs) are supramolecular assemblies of particular interest for therapeutic purposes, as they can be enzymatically degraded into viable cells, under physiological conditions. Incorporation of small bioactive molecules into nano-to-microscale delivery systems may increase drug's bioavailability and therapeutic efficacy at single cell level giving desirable targeted therapy. Layer-by-layer (LbL) self-assembled PMCs are efficient microcarriers that maximize drug's exposure enhancing antitumor activity of neoplastic drug in cancer cells. They can be envisaged as novel multifunctional carriers for resistant or relapsed patients or for reducing dose escalation in clinical settings.     

Mechanical strength of single microcapsules determined by a novel micromanipulation technique

A micromanipulation technique has been developed to measure the bursting force of single dry microcapsules coated onto a surface, such as those normally used in carbonless copying paper. For measuring the bursting force of a given microcapsule, a single fine probe with a flat end about 10mum in diameter was used to squeeze the microcapsule against a flat surface until it burst. The force being imposed on the microcapsule was measured by a transducer connected to the probe. The bursting force and diameter of single dry microcapsules in two samples, different in size and wall thickness, were measured by this technique. The bursting force of the microcapsules in one sample ranged from 50 to 220muN and the diameter from 1.3 to 7.0mum, whilst the bursting force in the other was from 20 to 175muN and the diameter from 0.7 to 3.7mum. This technique makes it possible to compare the mechanical strength of microcapsules made of different formulations, and to infer information about microcapsule mechanical properties.     

The relation between narrow-dispersed microcapsules and surfactants

Electric ink display is one of the prospect technologies in paper-like display. In this paper, electric ink microcapsules are prepared by means of an in situ polymerization and complex coacervation. In order to obtain the microcapsules in a uniform size distribution, this study focused on the inter-facial tension between tetrachloroethylene and water solution, the dispersion of the core droplets and the microencapsulation with different kind of surfactants. By measuring the inter-facial tensions between water and tetrachloroethylene, it is found that urea-formaldehyde (UF) pre-polymer presents certain surface activity due to the inter-facial tension descending from 43?mN?m^?1 to 35?mN?m^?1. Because the surface activity of pre-polymer is not valid, the water-soluble emulsifiers can occupy on the surface of the droplets and prevent the UF resin depositing there. The analysis of the size distribution shows that the UF microcapsules are multi-dispersed. Furthermore, the influence of anionic surfactant of SDS on the size distribution of the core droplets is also investigated. The average diameters of the core droplets prepared with 0.005?wt% and 0.012?wt% SDS are?～50?µm and 28?µm, respectively. That reveals the existence of SDS not only decreases the droplet diameters, but also makes the size distribution centralized. Because the surface of the core droplets is charged due to the absorption of SDS anionic, the Gelatin and Gum Arabic (GA) coacervating layer is easy to form there. The size of the GA microcapsules prepared with 0.003?wt% SDS is?～65?µm. Finally; the responsive behaviour of the microcapsules to electric field is also investigated.     

正交试验优选白藜芦醇微囊处方

目的：优选白藜芦醇微囊的处方。方法：采用滴制法制备白藜芦醇微囊,以海藻酸钠黏度、海藻酸钠与白藜芦醇质量比、海藻酸钠质量分数、氯化钙质量分数为考察因素,以白藜芦醇载药量和包封率的综合评分为评价指标,采用正交试验优选白藜芦醇微囊处方。结果：最优处方为海藻酸钠黏度为380cps、海藻酸钠与白藜芦醇的质量比为0．5：1、海藻酸钠质量分数为2．0％、氯化钙质量分数为3．0％。结论：所选白藜芦醇微囊处方合理,制得的白藜芦醇微囊裁药量和包封率较高。