Application of acid-catalyzed hydrolysis of dispersed organic solvent in developing new microencapsulation process technology

The aim of this study was to evaluate a new microencapsulation technology employing an acid-catalyzed solvent extraction method in conjunction to an emulsion-based microencapsulation process. Its process consisted of emulsifying a dispersed phase of poly(D,L-lactide-co-glycolide) and isopropyl formate in an aqueous phase. This step was followed by adding hydrochloric acid to the resulting oil-in-water emulsion, in order to initiate the hydrolysis of isopropyl formate dissolved in the aqueous phase. Its hydrolysis caused the liberation of water-soluble species, that is, isopropanol and formic acid. This event triggered continual solvent leaching out of emulsion droplets, thereby initiating microsphere solidification. This new processing worked well for encapsulation of progesterone and ketoprofen that were chosen as a nonionizable model drug and a weakly acidic one, respectively. Furthermore, the structural integrity of poly(D,L-lactide-co-glycolide) was retained during microencapsulation. The new microencapsulation technology, being conceptually different from previous approaches, might be useful in preparing various polymeric particles.     

Evaluation of sucrose esters as alternative surfactants in microencapsulation of proteins by the solvent evaporation method

Sucrose esters (SE) are surfactants with potential pharmaceutical applications because of their low toxicity, biocompatibility, and excellent biodegradability. The objective of the study was to investigate SE as alternative surfactants in stabilizing emulsions for the preparation of protein-loaded microparticles. To achieve this goal, using bovine serum albumin as model protein and 75/25 poly(d,1-lactide-co-glycolide) as polymer carrier, we have investigated the influence of the following formulation variables on particle characteristics: (1) SE concentration from 0.01% to 1% (wt/vol), (2) hydrophile-lipophile balance (HLB) value of SE from 6 to 15, and (3) the nature of emulsion stabilizer. The formulations were characterized using ATR-FTIR spectroscopy, bicinchoninic acid protein assay, optical microscopy and SDS-PAGE. Results showed that at 0.05% (wt/vol) surfactant concentration, SE with HLB of 6 to 15 provided discrete and spherical microparticles with the highest encapsulation efficiency compared with controls polyvinyl alcohol (PVA) and poloxamer 188. These results may be explained by the difference in critical micelle concentration, diffusion, and partition coefficient among the tested surfactants. HLB values were consistent with SE spectral data. The protein molecular weight was preserved after the encapsulation process. The effective SE concentration was far less (20-to 200-fold) than that is usually required for PVA in microencapsulation of proteins. However, the encapsulation efficiency was relatively lower (～13.5%). These preliminary results suggest that it may be desirable to optimize such formulations in vitro and in vivo for SE to be eventually used as altermative surfactants in the development of microparticulate systems for parenteral delivery of protein and gene medicines.     

The effect of electrostatic microencapsulation process on biological properties of tumour cells

Microencapsulation is one of the promising strategies to develop a three-dimensional in vivo tumour-mimic model in cancer research. Although previous studies have shown that tumour cells grow well during the microencapsulated culture, it is still not clear whether the electrostatic encapsulation process has an important effect on cellular characteristics. In this study, we investigated cellular response against non-physiological stress factors existing in the electrostatic microencapsulation process, such as the high-voltage electrostatic field, suspension and nutrition-free status. Our results showed that these non-physiological stress factors did not significantly induce cellular apoptosis, and did not affect cellular adhesion and viability. Furthermore, no change was found about invasion and drug resistance of the tumour cells. The normal endoplasmic reticulum function might play a role in maintaining biological properties during the electrostatic microencapsulation process.     

Synchronous microencapsulation of multiple components in silymarin into PLGA nanoparticles by an emulsification/solvent evaporation method

The development of polymeric carriers loaded with extracts suffers from the drawback not to be able to incorporate simultaneously various pharmacological compounds into the formulation. The aim of this study was therefore to achieve synchronous microencapsulation of multiple components of silymarin into poly (lactic-co-glycolic acid) nanoparticle, the most commonly used polymeric carrier with biodegradability and safety. The main strategy taken was to improve the overall entrapment efficiency and to reduce the escaping ratio of the components of different physicochemical properties. The optimized nanoparticles were spherical in morphology with a mean particle size of 150?±?5?nm. Under common preparative conditions, silybin and isosilybin were entrapped in high efficiency, whereas taxifolin, silychristin and silydianin, especially taxifolin, showed less entrapment because they were more hydrophilic. By changing the pH of the outer aqueous phase and saturating it with silymarin, the entrapment efficiency of taxifolin, silychristin and silydianin could be significantly improved to over 90%, the level similar to silybin and isosilybin, thereby achieving synchronous encapsulation. It could be concluded that synchronous encapsulation of multiple components of silymarin was achieved by optimizing the preparative variables.     

Chitosan microencapsulation of the dispersed phase of an O/W nanoemulsion to hydrochlorothiazide delivery

In view of biopharmaceutical limitations of hydrochlorothiazide (HCTZ), Trojan-type mucoadhesive systems were proposed, aiming to improve HCTZ pharmacological properties by modulating its release. Nanoemulsions were formed spontaneously by combining medium-chain triglycerides (Lipoid^® S75 and Pluronic^® F68) and high encapsulation efficiency was obtained. The mucoadhesive properties were provided by chitosan and microencapsulation of nanoemulsions in spray-dryer was successfully achieved by using Aerosil^® as wall material. The rapid redispersion of nanoemulsion in simulated fluids led to a fast and complete release of HCTZ in gastric medium. The pharmacodynamics of HCTZ was improved, extending the diuretic activity. Once a simple and low-energy method contributed to obtain stable mucoadhesive nanoemulsions, advantages in terms of production could also be achieved, allowing easy scaling up. This novel mucoadhesive Trojan particulate system of HCTZ showed to be a promising approach to overcome limitations in terms of absorption and consequently improve the therapeutic efficacy.     

Integrated optimization of fish oil microencapsulation process by spray drying

An integrated approach through coupling response surface method (RSM) and genetic algorithm (GA) was applied to optimize the spray dryer operational condition for production of fish oil microcapsules. The inlet drying air temperature, aspirator rate, and peristaltic pump rate were independent and encapsulation efficiency (EE) and exergy efficiency were dependent variables. RSM was applied to establish the relationship between the independent and dependent variables followed by integrating the developed models using three mathematical approaches and measure the fitness value of GA. Consequently, the optimal drying condition for microencapsulation of fish oil was: inlet drying air temperature?=?177.23°C, aspirator rate?=?63.93%, and peristaltic pump rate?=?14.04% yielding exergy efficiency of 8.10% and EE of 79.14%. The results of confirmation experiments for selected drying condition proved the capability of utilized approach for determination of sustainable and qualified process in fish oil microencapsulation by spray drying.     

PLGA微球的修饰及其应用

微球作为新型的药物载体系统已广泛用于临床研究,高分子化合物材料聚乳酸-羟基乙酸(pdy lactic-co-glycolic acid,PLGA)因其良好的生物相容性和生物可降解性备受关注。近年来,PLGA微球的研究一直是热门,针对其释放缺陷出现了很多复合修饰方法,主要包括环糊精、壳聚糖、聚乳酸、明胶、泊洛沙姆、聚乙烯亚胺等高分子材料的联用、针对末端基团进行化学修饰以及制备成核壳型微球,在保证包封率的情况下大大降低突释,改善药物释放曲线,从而在药物传递、基因治疗、影像诊断、组织工程等领域得到了广泛的应用。     

Production and characterization of polymer microspheres containing trace explosives using precision particle fabrication technology

Well characterized test materials are essential for validating the performance of current trace explosive detection systems. These test materials must replicate trace explosive contamination in the form of small particles with characteristic diameters in the micrometer range. In this work, Precision Particle Fabrication was used to fabricate monodisperse polymer microspheres that contain high explosives. Three high explosives were successfully incorporated into the microspheres. Ion mobility spectrometry confirmed that the encapsulation efficiency was typically greater than 50%, with some suspected loss to the aqueous phase during production. This study demonstrates that, with this technique, polymer microspheres containing explosives can be produced with sufficient encapsulation, along with tightly controlled particle size distributions at high production rates. These microspheres have proven to be a valuable test material for trace explosive detectors because of their highly precise size, shape and explosive composition.     

Nonhalogenated solvent-based solvent evaporation process useful in preparation of PLGA microspheres

The objective of this study was to develop an isopropyl formate-based evaporation process useful in producing poly-D,L-lactide-co-glycolide microspheres. Surprisingly, the evaporating tendency of isopropyl formate was comparable to that of methylene chloride and far better than that of ethyl acetate. After optimization of the isopropyl formate-based process, progesterone was encapsulated into microspheres. Under our conditions, its encapsulation efficiency ranged from 75.1% to 92.6%. Even though all microspheres took spherical geometry, their external and internal morphologies were greatly influenced by progesterone payloads. A GC analysis demonstrated that residual isopropyl formate in various microspheres was 1.8% to 4.0%. Interestingly, progesterone underwent polymorphic transition during the microencapsulation process – the β form was present in microspheres with lower progesterone payloads, whereas the α form predominated over the β one at higher progesterone loads. In terms of human safety and environmental toxicity, isopropyl formate might have an edge over halogenated organic solvents for solvent evaporation.     

Development of new reverse micellar microencapsulation technique to load water-soluble drug into PLGA microspheres

The objective of this study was to develop a new reverse micelle-based microencapsulation technique to load tetracycline hydrochloride into PLGA microspheres. To do so, a reverse micellar system was formulated to dissolve tetracycline hydrochloride and water in ethyl formate with the aid of cetyltrimethylammonium bromide. The resultant micellar solution was used to dissolve 0.3 to 0.75 g of PLGA, and microspheres were prepared following a modified solvent quenching technique. As a control experiment, the drug was encapsulated into PLGA microspheres via a conventional methylene chloride-based emulsion procedure. The microspheres were then characterized with regard to drug loading efficiency, their size distribution and morphology. The reverse micellar procedure led to the formation of free-flowing, spherical microspheres with the size mode of 88 microm. When PLGA microspheres were prepared following the conventional methylene chloride-based procedure, most of tetracycline hydrochloride leached to the aqueous external phase: A maximal loading efficiency observed our experimental conditions was below 5%. Their surfaces had numerous pores, while their internal architecture was honey-combed. In sharp contrast, the new reverse micellar encapsulation technique permitted the attainment of a maximal loading efficiency of 63.19 +/- 0.64%. Also, the microspheres had smooth and pore-free surfaces, and hollow cavities were absent from their internal matrices. The results of this study demonstrated that PLGA microspheres could be successfully prepared following the new reverse micellar encapsulation technique.     

乳酸羟乙醇酸共聚物微球中蛋白包封率的测定

目的:寻求一种合适的方法测定蛋白在乳酸羟乙醇酸共聚物(PLGA)微球中的包封率。方法:采用复乳 溶剂挥发法制备 BSA的PLGA微球,应用考马斯亮蓝法测定总蛋白浓度,根据文献报道的7种不同方法进行包封率测定。结果:不同的测定方法对 PLGA微球中真实的药物包封率的反映程度不同,相互间差异很大。结论:以水解法测定BSA在PLGA微球中包封率的方法提取 最完全。水解法中,又以乙腈作溶剂、再用氢氧化钠水解两步提取法最为简便、快速、准确。     

The necessity for the coating of perfluorodecalin-filled poly(lactide-co-glycolide) microcapsules in the presence of physiological cholate concentrations: Tetronic-908 as an exemplary polymeric surfactant

Recently, we demonstrated that biodegradable poly(lactide-co-glycolide) (PLGA) micro- and nanocapsules with a liquid content of perfluorodecalin are principally useful for the development of artificial oxygen carriers. In order to solve a decisive and well-known problem with PLGA microcapsules, i.e. the spontaneous agglomeration of the capsules after depletion of the emulsifying agent (i.e. cholate), coating with the ABA block copolymer, Tetronic-908 was studied. After Tetronic-908 treatment at concentrations that were harmless to cultured cells, the clustering of the microcapsules was prevented, the adsorption of opsonins was decreased and the attachment to cells was inhibited, but the oxygen transport capacity of PLGA microcapsules was even increased. The present data clearly show that perfluorodecalin-filled PLGA microcapsules must be coated before decreasing the emulsifying agent cholate to physiological concentrations, in order to develop a solution that has the capabilities to function as a potential artificial oxygen carrier suspension.     

Leukotriene B4-loaded microspheres as a new approach to enhance antimicrobial responses in Histoplasma capsulatum-infected mice

Histoplasmosis is a pulmonary disease characterised by chronic granulomatous and suppurative inflammatory reactions caused by Histoplasma capsulatum. Regarding new therapies to control fungal infections, the aim of this study was to investigate whether pulmonary administration of leukotriene B₄ (LTB₄)-loaded microspheres (MS) could confer protection to 5-lipoxygenase knockout (5-LO^−/−) mice infected by H. capsulatum. In this study, MS containing LTB₄ were administered intranasally to mice infected by H. capsulatum. On Day 14 after the infection, fungal recovery from the lungs and histology were evaluated and inflammatory cytokines were measured. Pulmonary administration of LTB₄-loaded MS was able to reduce fungal recovery from infected lungs. Production of important inflammatory cytokines related to host defence was augmented following MS administration to the lungs. Lung histology also showed that infected mice presented a clear reduction in the fungal burden following the pulmonary release of LTB₄ from MS. Our study provides evidence that the proposed biodegradable microparticulate system, which can release LTB₄ to the lungs, can be employed as therapy, enhancing the antimicrobial activity of host cells during histoplasmosis.     

Kinetics of solvent extraction/evaporation process for PLGA microparticle fabrication

Organic solvent extraction/evaporation from an o/w-dispersion has been widely used for the fabrication of PLGA microparticles. The purpose of this work was to elucidate the kinetics of the solvent extraction/evaporation process. A mathematical diffusion model was developed and applied to predict the duration of the solvent extraction. As the diffusion coefficient, D(p), plays a major role in the modeled process, a new and experimentally simple method for estimating D(p) was developed. Both the experimental method and the mathematical model were validated through PLGA microparticle fabrication experiments. For microparticles of mode diameters of 2 and 20 microm, the solvent was extracted in approximately 10 s. Sufficient hardening of the microparticles required, however, the evaporation of solvent from the extraction phase. Residual solvent in extraction phase exerted a strong effect on the morphology of the final product as demonstrated by scanning electron microscopy. Only if most solvent was removed from the aqueous extraction phase, a powdery product of individual microparticles was obtained. At residual organic solvent concentration of above 0.2% in the extraction phase, the microparticles strongly aggregated during collection on a membrane filter and final drying. The presented methods may be useful for better controlling microparticle fabrication processes by solvent extraction/evaporation.     

Study of a microencapsulation process of a virucide agent by a solvent evaporation technique

Abstract

A highly water-soluble virucide agent was microencapsulated by a water/oil/water emulsification-solvent evaporation method. An aqueous drug solution was emulsified into a solution of polymer in methylene chloride, followed by emulsification of the primary emulsion in an external aqueous phase. Microcapsules were formed after solvent evaporation, the solidification of the microcapsule walls was followed by an optical method. The influence of stirring speed was analysed to find the optimal hydrodynamic conditions with respect to the process yield, corresponding to the weight of obtained microcapsules per litre of water/oil/water emulsion, the initial virucide agent content and the drug release kinetics. The optimal conditions were obtained for the complete suspension speed. The improvement of the microencapsulation process was attempted by increasing the concentration of the primary emulsion and by the reuse of the external aqueous phase after removal of the microcapsules.     

Enhanced oral bioavailability of salmeterol by loaded PLGA microspheres: preparation,in vitro,and in vivo evaluation

The objective of the current study was to prepare microspheres of salmeterol (SM) using poly (lactide-co-glycolide) (PLGA) and assess its viability to enhance the oral bioavailability. Microspheres of SM were prepared by oil-in-water emulsion-solvent evaporation method. The formulations were characterized in encapsulation efficiency, particle size, zeta potential, and in vitro release. The prepared microspheres were found to be spherical in shape with smooth surface. The size of microspheres ranged from 14.7 to 16.5?µm. The polydispersity index (PDI) was 0.12?±?0.05 and the zeta potential was ?33.2?±?1.4?mV. In vitro release profile, SM was graduated released from the microspheres as time lapsed, suggesting that SM was well entrapped in SM-loaded PLGA microspheres. The model that fitted best for SM released from the microspheres was Higuchi equation. In vivo study, SM-loaded PLGA microspheres are thought to have the potential to maintain SM concentration within target ranges for a long time, decreasing side effects caused by concentration fluctuation, ensuring the efficiency of treatment and improving patient compliance by reducing dosing frequency.     

Water-free microencapsulation of proteins within PLGA microparticles by spray drying using PEG-assisted protein solubilization technique in organic solvent

Poly(d,l-lactic-co-glycolic acid) (PLGA) microparticles encapsulating therapeutic proteins were prepared under a water-free formulation condition. Bovine serum albumin (BSA) and recombinant human growth hormone (rhGH) were homogeneously solubilized as nano-scale complexes in methylene chloride phase by using polyethylene glycol (PEG) as a complex-forming agent. The organic phase containing dissolved PLGA and PEG/protein complexes was directly spray dried to obtain PLGA microparticles encapsulating proteins. They exhibited sustained release profiles of BSA and rhGH up to 30 days with reduced initial bursts. The released protein molecules from the microparticles maintained structural integrity without aggregation, suggesting that the current single-step protein microencapsulation method without using water could be potentially applied for sustained delivery of a wide range of therapeutic protein drugs that are not soluble in organic solvents.     

Microagglomeration of pulverized pharmaceutical powders using the Wurster process I.: Preparation of highly drug-incorporated, subsieve-sized core particles for subsequent microencapsulation by film-coating

A novel agglomeration process of pulverized pharmaceutical powders into subsieve-sized agglomerates (microagglomeration) was designed for manufacturing highly drug-incorporated core particles for subsequent microencapsulation by film-coating. The microagglomeration of pulverized phenacetin powder, whose mass median diameter was 9 μm, was performed by spraying an aqueous colloidal dispersion of acrylic polymer, Eudragit® RS30D, as a binding/coating agent using a spouted bed assisted with a draft tube (the Wurster process), and the effect of process variables was examined. An appropriate spray liquid flow rate made it possible to produce microagglomerates of 20–50 μm with 60% yield. However, 10% of the product still survived as particles smaller than 10 μm even at the elevated liquid flow rate. In contrast, the survived particles smaller than 10 μm tended to be predominantly reduced to 2%, while coarse agglomerates larger than 53 μm were not excessively produced, by additionally setting a fixed bed of glass beads in the spouted bed apparatus. The length of the draft tube influenced compaction of the agglomerates as well as their surface-smoothening. Equipping the fixed bed of the glass beads and the long draft tube in the spouted bed allowed us to prepare microagglomerates of 20–50 μm at yield of 55% applicable as highly drug-incorporated, free-flowing, surface-smoothed, narrowly size-distributed core particles for subsequent microencapsulation by film-coating.     

bFGF-PLGA缓释微球及其体外释药性能研究

目的以bFGF为缓释药物、PLGA为药物载体制备bFGF-PLGA缓释微球,观察微球表面形态,检测微球物理性能和体外释药行为。方法采用W1/O/W2复乳溶剂挥发法制作微球;通过扫描电镜观察微球的表面形态结构;利用ELISA法测试微球中药物的载药量和包封率,并对微球中药物的体外释放行为进行研究。结果微球表面圆滑均匀,平均粒径(0.75±0.08)μm,载药量[(59.9±1.9)×10-3]%,包封率为(79.9±2.8)%;在为期45 d的体外释放试验中,bFGF累积释放率达到80%。结论bFGF-PLGA微球能够稳定地在较长时间释放药物bFGF,验证了PL-GA微球作为bFGF控制释放载体的可行性。     

微囊化大鼠胰岛与睾丸Sertoli细胞联合移植的实验研究

目的 应用细胞微囊化方法、病理技术研究微囊化大鼠胰岛细胞与睾丸Sertoli细胞联合移植对糖尿病小鼠的血糖影响及Sertoli细胞对共移植的胰岛细胞的免疫豁免作用.方法 将30只小鼠随机分为2组,每组15只.Ⅰ组为胰岛细胞微囊化移植组,Ⅱ组为胰岛细胞与睾丸Sertoli细胞联合微囊化移植组,建立糖尿病模型后,2组均采用...