Encapsulation of BSA using a modified W/O/O emulsion solvent removal method

A systematic investigation of protein encapsulation in polylactic-co-glycolic-acid (PLGA) was carried out using the formation of a w/o/o emulsion followed by solvent removal. Various factors were studied, including composition of the suspension medium and the relative amounts of aqueous phase containing protein to polymer solution. High yields of microsphere fabrication were achieved by using silicon oil containing methylene chloride as a suspension medium instead of pure silicon oil, with minimal loss of polymer and protein drug (<2%). The amount of aqueous phase influenced the process and successful encapsulation was obtained if the volume ratios of aqueous phase to polymer solution were less than 5% (v/v) at a wide range of polymer concentration (2–15%?g?ml^?1). Protein encapsulation by this w/o/o emulsion and solvent removal method has a high yield of microsphere fabrication and protein encapsulation (98%). In addition, it provides an easy way to control the release rate of protein encapsulated in microspheres by modulating their porosity in fabrication process.     

乳化溶剂挥发法制备重组人血管内皮抑制素缓释微球

目的:制备重组人血管内皮抑制素(恩度)缓释微球,并对微球理化性质及体外释放行为进行初步考察。方法:采用乳化溶剂挥发法(W/O/O)制备恩度载药微球;对微球载药量、粒径、突释、体外释放速率及降解行为进行考察,同时利用凝胶电泳初步评价体外释放过程中恩度的完整性。结果:增加聚乳酸-羟基乙酸嵌段共聚物(PLGA)中羟基乙酸的比例、提高PLGA浓度、降低内水相体积、提高理论载药量均增加微球载药能力;降低内水相体积、提高分散速度均减小突释。增加PLGA中羟基乙酸的比例,30 d时累积释放可增加到65%。降解实验说明释放初期微球主要以扩散方式释放恩度,释放后期主要表现为微球的降解。凝胶电泳结果表明微球制备过程对蛋白质聚集性的影响不大。结论:用PLGA作为载体材料制备微球,可以延缓恩度的释放。     

W/O/W复乳溶剂蒸发法制备水溶性药物微球研究进展

介绍了W/O/W复乳溶剂蒸发法制备水溶性药物微球的基本步骤及存在问题,重点综述制备工艺的关键影响因素,并在此基础上阐述W/O/W复乳溶剂蒸发法技术的研究进展,提出该法在实际应用中存在的主要问题,并对其发展前景进行展望。     

Preparation of various metal-silicate micro-balloons using W/O/W emulsion

Micron-sized inorganic microparticles with hollow insides were prepared by interfacial reaction method, in which an ion exchange reaction between Na(+) and metal cations in internal and external aqueous phases, respectively, proceeded through the oil phase involving a cation carrier. The diameter of microballoons was approximately 10 microm and shell thickness was below 2 microm. The effects of preparation conditions against the formation of microballoons were examined. The factors examined were metal species in the external aqueous phase and the concentrations of metal chloride and cation carrier. The cross-section of microparticles formed was inspected by scanning electron microscope (SEM) and the inner space of some metal silicates was not hollow but filled-up. The increase of internal and external aqueous solution concentrations caused the increase of diameter and shell thickness of microballoons. Since the penetration of metal cation through the oil phase was promoted by the increase of carrier concentration, the formation of microballoons was completed in a short time of less than 30 min.     

Role of solvent/non-solvent ratio on microsphere formation using the solvent removal method

The importance of good solvent concentration in the non-solvent mixture and the non-solvent viscosity on the ability to form microspheres using solvent removal process was investigated. The higher the viscosity of the polymer solutions, the higher the concentration of good solvent needed in the non-solvent mixture to produce microspheres. This finding was due to faster precipitation of the polymer phase. Also, the addition of a model drug, fluorescein isothiocyanate conjugated-labelled bovine serum albumin, to the polymer solution (10% poly-L-lactic acid:poly(fumaric-co-sebacic) anhydride in methylene chloride) resulted in an overall lower polymer solution viscosity (15.5 cP with fluorescein isothiocyanate conjugated-labelled bovine serum albumin as compared with 18.25 cP for blank polymer at 25°C). Additionally, the effect of good solvent concentration on non-solvent viscosity was evaluated, and the viscosity decreased as the concentration of good solvent increased. The effect of good solvent concentration on the non-solvent mixture on sphere formation was of great importance. Microspheres would not form when the good polymer solvent (methylene chloride) in the non-solvent phase was too low (below 175 ml for poly-L-lactic acid or 150 ml for poly(D,L-lactid-co-glycolid)) or was replaced by another good solvent such as ethyl acetate, even though the same viscosity was achieved. It was shown that the concentration of the good solvent in the non-solvent mixture was more of a controlling factor than the viscosity of the non-solvent mixture in microsphere formation and the findings support the conclusion that diffusion is the main controlling parameter in solvent removal.     

Role of solvent/non-solvent ratio on microsphere formation using the solvent removal method

The importance of good solvent concentration in the non-solvent mixture and the non-solvent viscosity on the ability to form microspheres using solvent removal process was investigated. The higher the viscosity of the polymer solutions, the higher the concentration of good solvent needed in the nonsolvent mixture to produce microspheres. This finding was due to faster precipitation of the polymer phase. Also, the addition of a model drug, fluorescein isothiocyanate conjugated-labelled bovine serum albumin, to the polymer solution (10% poly-L-lactic acid:poly(fumaric-co-sebacic) anhydride in methylene chloride) resulted in an overall lower polymer solution viscosity (15.5 cP with fluorescein isothiocyanate conjugated-labelled bovine serum albumin as compared with 18.25 cP for blank polymer at 25 degrees C). Additionally, the effect of good solvent concentration on non-solvent viscosity was evaluated, and the viscosity decreased as the concentration of good solvent increased. The effect of good solvent concentration on the non-solvent mixture on sphere formation was of great importance. Microspheres would not form when the good polymer solvent (methylene chloride) in the non-solvent phase was too low (below 175 ml for poly-L-lactic acid or 150 ml for poly(D,L-lactidco-glycolid)) or was replaced by another good solvent such as ethyl acetate, even though the same viscosity was achieved. It was shown that the concentration of the good solvent in the non-solvent mixture was more of a controlling factor than the viscosity of the non-solvent mixture in microsphere formation and the findings support the conclusion that diffusion is the main controlling parameter in solvent removal.     

Effects of salt addition on the microencapsulation of proteins using W/O/W double emulsion technique

The influence of co-encapsulation of stabilizing additives together with BSA on microsphere characteristics using the modified water-in-oil-in-water emulsion solvent evaporation (W/O/W) method was investigated. For this purpose, poly(L-lactide) microspheres containing bovine serum albumin (BSA) were prepared. The morphology, porosity, specific surface area, particle size, encapsulation efficiency and kinetics of drug release of protein loaded microspheres were analysed in relation to the influence of co-encapsulated stabilizing additives such as electrolytes. High salt concentrations in the internal (W1) aqueous phase, often necessary to stabilize protein or antigen solutions, led to an increase in particle size, particle size distribution, porosity and specific surface area. Bulk density and encapsulation efficiency decreased. The release profile was characterized by a high initial burst due to the highly porous structure. Addition of salt to the external or continuous water phase (W2), however, stabilized the encapsulation process and, therefore, resulted in improved microsphere characteristics as a dense morphology, a reduced initial burst release, a drastically increased bulk density and encapsulation efficiency. Analysis of the specific surface area (BET) showed that the addition of salt to W2, regardless of the salt concentration in the W1 phase, decreased the surface area of the microspheres approximately 23-fold. Microsphere properties were influenced by salts additions through the osmotic pressure gradients between the two aqueous phases and the water flux during microsphere formation. Release profiles and encapsulation efficiencies correlated well with the porosity and the surface area of microspheres. Furthermore, the influence of a low molecular weight drug and different time-points of salt addition to W2 on microsphere characteristics were studied by encapsulation of acid orange 63 (AO63), confirming the results obtained with BSA. This study suggests that modification of the external water phase by adding salts is a simple and efficient method to encapsulate stabilized protein solution, with high encapsulation efficiency and good microsphere characteristics.     

Doxycycline delivery from PLGA microspheres prepared by a modified solvent removal method

We report on the development of a modified solvent removal method for the encapsulation of hydrophilic drugs within poly(lactic-co-glycolic acid) (PLGA). Using a water/oil/oil double emulsion, hydrophilic doxycycline was encapsulated within PLGA spheres with particle diameters ranging from approximately 600?nm to 19?μm. Encapsulation efficiencies of up to 74% were achieved for theoretical loadings from 1% to 10% (w/w), with biphasic release over 85 days with nearly complete release at the end of this time course. About 1% salt was added to the formulations to examine its effects on doxycycline release; salt modulated release only by increasing the magnitude of initial release without altering kinetics. Fourier transform infrared spectroscopy indicated no characteristic differences between doxycycline-loaded and control spheres. Differential scanning calorimetry and X-ray diffraction suggest that there may be a molecular dispersion of the doxycycline within the spheres and the doxycycline may be in an amorphous state, which could explain the slow, prolonged release of the drug.     

Doxycycline delivery from PLGA microspheres prepared by a modified solvent removal method

We report on the development of a modified solvent removal method for the encapsulation of hydrophilic drugs within poly(lactic-co-glycolic acid) (PLGA). Using a water/oil/oil double emulsion, hydrophilic doxycycline was encapsulated within PLGA spheres with particle diameters ranging from approximately 600?nm to 19?µm. Encapsulation efficiencies of up to 74% were achieved for theoretical loadings from 1% to 10% (w/w), with biphasic release over 85 days with nearly complete release at the end of this time course. About 1% salt was added to the formulations to examine its effects on doxycycline release; salt modulated release only by increasing the magnitude of initial release without altering kinetics. Fourier transform infrared spectroscopy indicated no characteristic differences between doxycycline-loaded and control spheres. Differential scanning calorimetry and X-ray diffraction suggest that there may be a molecular dispersion of the doxycycline within the spheres and the doxycycline may be in an amorphous state, which could explain the slow, prolonged release of the drug.     

Microencapsulation of insulin using a W/O/W double emulsion followed by complex coacervation to provide protection in the gastrointestinal tract

Abstract

Microcapsules containing insulin were prepared using a combination of a W/O/W double emulsion and complex coacervation between WPI (used as a hydrophilic emulsifier) and CMC or SA with further spray drying of the microcapsules in order to provide protection in the gastrointestinal tract. The microcapsules prepared exhibited high encapsulation efficiency and showed the typical structure of a double emulsion. After spray drying of these microcapsules, the integrity of the W/O/W double emulsion was maintained and the biological residual activity remained high when using the combination of 180?°C inlet air temperature and 70?°C outlet air temperature. The microcapsules exhibited low solubility at pH 2 and high solubility at pH 7 so they might protect insulin at acid pH values in the stomach and release it at intestinal pH values. The microcapsules developed in this study seem to be a promising oral delivery vehicle for insulin or other therapeutic proteins.     

Preparation of silica microspheres encapsulating phase-change material by sol-gel method in O/W emulsion

Spherical silica microcapsules containing phase-change material (PCM) were prepared by the sol-gel method in O/W emulsion. This is the first time that inorganic encapsulation of PCM with core/shell structure has been studied. The results of this synthesis revealed that micron size (4 - 8 microm) silica microspheres encapsulating n-pentadecane can be successfully created from acidic solutions ([H+] > or = 1.44 N) by using cationic surfactants as the emulsifiers. The identification of the mechanisms for the formation of silica shell at the oil-water interface indicates that it should be the charge-controlled mechanism through S+X-I+ (positively charged surfactant-halide ion-positively charged silica species) electrostatic interactions or the reaction rates-controlled mechanism working on cationic emulsifiers.     

甲苯咪唑水包油型口服乳剂的药物释放

目的：对水包油（Ｏ／Ｗ）型甲苯咪唑乳剂的体外释药行为进行研究。方法：采用动态透析法。结果：甲苯咪唑的溶解度及其从油相扩散至水相的过程是药物释放的限速步骤。结论：与片剂相比,乳剂和混悬剂中甲苯咪唑的释放表现出明显的缓释作用     

In vitro microbicidal activity of W/O/W multiple emulsion for vaginal administration

The microbicidal activity of a W/O/W multiple emulsion destined for vaginal application, containing lactic acid in the internal aqueous phase, octadecylamine (ODA) in the oily phase and benzalkonium chloride (CBZ) in the external aqueous phase was evaluated against three microbial strains: Escherichia coli, Staphylococcus aureus and Candida albicans. The results were different depending on the procedure used. Interpretable results were obtained if only a gentle agitation was used just after the introduction of the microbial suspension to the product. This suggested that vigorous agitation lead to a variable fraction of CBZ or ODA entrapped in the micelles of ethylene and propylene oxide copolymer (COE).     

An enhanced process for encapsulating aspirin in ethyl cellulose microcapsules by solvent evaporation in an O/W emulsion

An enhanced process for microencapsulating aspirin in ethylcellulose was demonstrated using an oil-in-water emulsification/solvent evaporation technique. Methylene chloride (CH2Cl2) was used as the dispersed medium and water as the dispersing medium. The recovered weight, particle size distribution, aspirin loading efficiency, and the aspirin release rate of microcapsules were analysed. The addition of appropriate amounts of non-solvent (n-heptane) prior to the emulsification increases the recovered weight, but decreases the size of the formed microcapsules. The addition of non-solvent also changes the microcapsule characteristics, resulting in a coarser surface and an increased release rate. Increasing the polymer (ethylcellulose) concentration in the dispersed phase increases the size of the microcapsules, the recovered weight, and loading efficiency, but decreases the release rate. The release rate follows first-order kinetics during the first 12h, suggesting a monolithic system with aspirin uniformly distributed in the microcapsule.     

An enhanced process for encapsulating aspirin in ethyl cellulose microcapsules by solvent evaporation in an O/W emulsion

An enhanced process for microencapsulating aspirin in ethylcellulose was demonstrated using an oil-in-water emulsification/solvent evaporation technique. Methylene chloride (CH2Cl2) was used as the dispersed medium and water as the dispersing medium. The recovered weight, particle size distribution, aspirin loading efficiency, and the aspirin release rate of microcapsules were analysed. The addition of appropriate amounts of non-solvent (n-heptane) prior to the emulsification increases the recovered weight, but decreases the size of the formed microcapsules. The addition of non-solvent also changes the microcapsule characteristics, resulting in a coarser surface and an increased release rate. Increasing the polymer (ethylcellulose) concentration in the dispersed phase increases the size of the microcapsules, the recovered weight, and loading efficiency, but decreases the release rate. The release rate follows first-order kinetics during the first 12 h, suggesting a monolithic system with aspirin uniformly distributed in the microcapsule.     

W/O/W型薄荷油复乳的制备及其性质初步研究

目的制备薄荷油W/O/W型复乳,并对其性质进行初步研究。方法采用二步法制备薄荷油W/O/W型复乳,对其物理性质如:外观、显微形态、乳剂类型、粘度、表面张力、相变温度、物理稳定性等方面进行初步研究。结果薄荷油W/O/W型复乳外观呈白色、外相能被曙红指示液染色、室温下的粘度为15.2 mPa.S,表面张力为30×10-3N.m-1,相变温度为84℃。结论二步法制备薄荷油W/O/W型复乳物理稳定性较好。     

Preparation and characterization of quercetin-loaded polymethyl methacrylate microcapsules using a polyol-in-oil-in-polyol emulsion solvent evaporation method

Flavonoids and related compounds exhibit a wide range of useful pharmacological properties but present challenges related to their stability and solubility in commonly available solvents. In this study, polymethyl methacrylate (PMMA) microcapsules were prepared using a novel polyol-in-oil-in-polyol (P/O/P) emulsion solvent evaporation method as a means of stabilizing the flavonoids, using quercetin as a model flavonoid drug. The morphology of the microcapsules was evaluated using a scanning electron microscope, revealing a spherical shape with a smooth surface. The cross-section image of the PMMA microcapsules prepared with an amphiphilic polymer in the inner polyol phase showed that the microcapsule was filled with several submicron microspheres. The mean diameter varied from 1.03+/-0.12 microm to 2.39+/-0.42 microm, and the encapsulation efficiency ranged from 12.7% to 26.9%. When free quercetin was stored at 42 degrees C, the residual quercetin content gradually decreased to 18% over 28 days as a result of oxidation. However, when encapsulated in PMMA microcapsules with an amphiphilic polymer in the inner polyol phase, the residual quercetin content decreased to just 82%. In-vitro release studies indicated a sustained release pattern throughout the 36-h study. The release kinetics of the microcapsules with an amphiphilic polymer followed a diffusion-controlled mechanism and the microcapsule without amphiphilic polymer followed an anomalous diffusion behaviour. This study suggests that the novel P/O/P emulsion solvent evaporation method can be applied to the encapsulation of flavonoids.     

Preparation of soft microcapsules containing multiple core materials with interfacial dehydration reaction using the (W/O)/W emulsion

The soft microcapsules containing eucalyptus oil, ubiquinone and the fine water droplets could be prepared with interfacial dehydration reaction between hydroxy methyl cellulose and tannic acid using the water-in-oil-in-water type multiple (W/O)/W emulsion. The diameters of the microcapsules and the content and the microencapsulation efficiency of the core materials were significantly affected by the revolution velocity (Nr₁) to form the (W/O) emulsion and the revolution velocity (Nr₂) to form the (W/O)/W emulsion and the lecithin concentration. The mean diameters of the inner water droplets and those of the microcapsules were proportional to Nr₁^?1.25 and Nr₁^?0.11 for the revolution velocity (Nr₁), respectively. With increasing the revolution velocity (Nr₁), the content and the microencapsulation efficiency of the inner water droplets increased, while those of the oil phase decreased. The mean diameters of the microcapsules were proportional to Nr₂^?1.1. The content and the microencapsulation efficiency of the inner water droplets and those of the oil phase decreased with the revolution velocity (Nr₁) and increased with the lecithin concentration.     

Poly (epsilon-caprolactone) microparticles containing Levobunolol HCl prepared by a multiple emulsion (W/O/W) solvent evaporation technique: effects of some formulation parameters on microparticle characteristics

The aim of this study was to prepare poly (epsilon-caprolactone) (PCL) microparticles of Levobunolol HC1 (L-HC1) for use as an anti-glaucomatous drug to the eye. The double emulsion (W/O/W) solvent evaporation technique was used for encapsulating L-HC1 as a hydrophilic drug. The study examined the impact of different factors including the pH and volume of the external aqueous phase, the concentration of polyvinylalcohol (PVA) and Pluronic F68 (PF68) used as stabilizers and drug/polymer ratios on the characteristics of the microparticles. Scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were used to identify the physical state of the drug and polymer. The zeta potential of the particles was also identified. Entrapment efficiency was found to be highest with a 0.5% PVA concentration and 100 mL volume of external aqueous phase at pH 12. The high efficiency was due to a reduction in the degree of drug ionization. The microparticles were spherical and appropriately sized for ophthalmic application. Drug release from the microparticles appears to consist of two components, with an initial rapid release followed by a slower stage. Drug release was slower when the microparticle was incorporated into the thermally reversible gel (Pluronic F127) in comparison to drug release from the free drug incorporated into the gel and drug release from the free microparticle.     

Branched oligoester microspheres fabricated by a rapid emulsion solvent extraction method

Methyl formate was used as the solvent of biodegradable oligoesters for the fabrication of microspheres with encapsulated bovine serum albumin (BSA). The procedure of dispersion of the double emulsion of the w/o/w type and its dilution and solvent extraction is very rapid, taking only several minutes. A higher yield and better encapsulation efficiency were obtained with copolymers of DL-lactic acid with mannitol than with pure linear poly DL-lactic acid. The procedure was accelerated, and yields and encapsulation efficacy were enhanced by the addition of 5% methyl formate to the external water phase. The microspheres were smaller than 100mum. No benefits were obtained from the addition of wetting agents or other additives to the intermediate (oligoesteric) phase. Further development should concentrate particularly on hydrodynamic conditions and optimization of the composition of the external phase.