Preparation of multi-phase microspheres of poly(D,L-lactic acid) and poly(D,L-lactic-co-glycolic acid) containing a W/O emulsion by a multiple emulsion solvent evaporation technique.

Multi-phase microspheres of poly(D,L-lactic acid) (PLA) or poly(D,L-lactic-co-glycolic acid) (PLGA) containing a water-in-oil (W/O) emulsion were prepared by a multiple emulsion solvent evaporation technique. Acetonitrile was used as the solvent for the polymers and light mineral oil as the dispersion medium for the encapsulation procedure. Process and formulation parameters to optimize the microencapsulation of a W/O emulsion containing water-soluble drugs were investigated. Drug loading efficiencies of 80-100 per cent were obtained under specific preparative conditions. The drug loading efficiency in the microspheres was dependent upon the ratio of the W/O emulsion to polymer and the concentration of surfactant in the mineral oil. Compared to conventional microspheres, in which fine drug particles are homogeneously dispersed in the polymer beads, the multi-phase microspheres permit the higher encapsulation efficiency of water-soluble drugs and eliminate partitioning into the polymer-acetonitrile phase which results in low encapsulation efficiency with conventional solvent evaporation techniques.     

PLGA microspheres with high drug loading and high encapsulation efficiency prepared by a novel solvent evaporation technique

PLGA microspheres with high drug loading and high encapsulation efficiency were fabricated by a novel solvent evaporation process-in-situ S/O/W process. Insulin was dissolved in DMSO and dispersed into DCM to form fine particles due to an anti-solvent effect. The in-situ formed suspension was then added into an aqueous phase and emulsified. Microspheres were formed following the evaporation of organic solvents. The experimental results showed that the modified S/O/W process could encapsulate more than 90%(w/w) insulin in the microspheres with a drug loading of over 15% and the initial burst was much less than microspheres made by a W1/O/W2 process. Compared with a traditional water-in-oil-in-water (W1/O/W2) process, the in-situ S/O/W process does not require high solubility of the encapsulated drug in water and, because no special pre-treatment is needed to reduce the particle size of the drug, it is superior to an ordinary S/O/W process. The in-situ S/O/W process is particularly applicable to encapsulate peptides and low molecular weight proteins.     

Dissolution,Stability, and Morphological Properties of Conventional and Multiphase Poly(DL-Lactic-Co-Glycolic Acid) Microspheres Containing Water-Soluble Compounds

Multiphase microspheres of poly(DL-lactic-co-glycolic acid) (PLGA) containing water-soluble compounds were prepared by a multiple-emulsion solvent evaporation technique. These compounds were dissolved in the aqueous phase of a W/O emulsion with soybean oil as the oil phase. This emulsion was dispersed throughout the matrix of the microsphere. The morphological properties of the multiphase microspheres during in vitro dissolution studies were compared to those of conventional microspheres prepared from the same polymer. Drug release from the multiphase microspheres was characterized by an initial uniform release for the first 20 days followed by a more rapid phase of drug release. Chlorpheniramine maleate (CPM) and brilliant blue (BB) were the soluble model compounds investigated. The release rates of these agents from the multiphase microspheres were independent of the drug content in the microspheres. The release profiles from the conventional microspheres showed a lag time of 10 and 16 days for the CPM and BB, respectively. The dissolution rate of the model soluble compounds from the conventional microspheres increased as the loading in the microspheres increased. No differences in the degradation rate of the PLGA from the multiphase and the conventional microspheres were seen during the dissolution studies.     

Selection of the solvent system for the preparation of poly(d,l-lactic-co-glycolic acid) microspheres containing tumor necrosis factor-alpha (TNF-α)

Dichloromethane (DCM) and acetonitrile (ACN) are the most commonly used solvents for polylactic acid (PLA) or poly(lactic-co-glycolic acid) (PLGA). In order to select a suitable solvent system for the preparation of PLGA microspheres containing tumor necrosis factor-alpha (TNF-α), the stability of TNF-α when mixed with DCM and ACN under various phase conditions was investigated. When the TNF-α solution was emulsified into DCM to form a W/O emulsion prior to solvent evaporation using the W/O/W technique, a significant loss in activity of TNF-α was found. When the TNF-α was dispersed as a dry powder in the DCM phase, the protein was inactivated due to immediate hydration under the conditions of the solid/O/W system. Since TNF-α also was inactivated in a buffered saline containing ACN, the stability of the protein in microspheres prepared from an anhydrous solvent system was studied using ACN as the polymer solvent. Multiphase microspheres prepared by an anhydrous multiple emulsion process had a significantly higher loading efficiency of intact TNF-α than conventional matrix-type microspheres prepared by an anhydrous method using TNF-α powder and ACN.     

Preparation and in vitro characterization of gelatin microspheres containing Levodopa for nasal administration

The dissolution properties of twomodel compounds, brilliant blue and tumour necrosis factor (TNF-alpha), from poly(D,L- .lactic-co-glycolic acid) (PLGA) multiphasemicrospheres wereinvestigated. In addition, the invivo releaseof TNF-alpha from the microspheres, in mice, was studied. The microspheres were prepared by an anhydrous multiple emulsion solvent evaporation method. Multiphase microspheres containing brilliant blue exhibited athree phase release profile in vitro, and displayed a significantly lower level of dye released during the initial phase compared to conventional matrix-type microspheres. Slow release of the dye was observed during the second phase, which was followed by a disintegration of the polymer wall during the third phase of the release process. In vitro dissolution profiles of TNF-alpha were calculated by compensation for the simultaneous degradation of the protein in the dissolution medium. The initial burst release of TNF-alpha was significantly reduced with the multiphase microspheres. The three phase release profile, as seen with the dye, was not observed for the microspheres containing the TNF-alpha. The rate of release of the protein from the microspheres was determined in vivo by analysing the residual level of TNF-alpha remaining in the particles following intraperitoneal administration of the microspheres to mice. The release of the protein from the microspheres in vivo was significantly faster than predicted from the results of the in vitro studies. The absence of an initial burst release of TNF-alpha from the multiphase microspheres was reflected in a significant reduction in the plasma level of TNF-alpha when compared to the matrix-type microspheres and a solution of the protein. The controlled release property of the multiphase microspheres is expected to overcome the adverse reactions due to dose dumping that occurs following the local administration of TNF-alpha.     

In vitro and in vivo release properties of brilliant blue and tumour necrosis factor-alpha (TNF-alpha) from poly(D,L-lactic-co-glycolic acid) multiphase microspheres

The dissolution properties of two model compounds, brilliant blue and tumour necrosis factor (TNF-alpha), from poly(D,L-lactic-co-glycolic acid) (PLGA) multiphase microspheres were investigated. In addition, the in vivo release of TNF-alpha from the microspheres, in mice, was studied. The microspheres were prepared by an anhydrous multiple emulsion solvent evaporation method. Multiphase microspheres containing brilliant blue exhibited a three phase release profile in vitro, and displayed a significantly lower level of dye released during the initial phase compared to conventional matrix-type microspheres. Slow release of the dye was observed during the second phase, which was followed by a disintegration of the polymer wall during the third phase of the release process. In vitro dissolution profiles of TNF-alpha were calculated by compensation for the simultaneous degradation of the protein in the dissolution medium. The initial burst release of TNF-alpha was significantly reduced with the multiphase microspheres. The three phase release profile, as seen with the dye, was not observed for the microspheres containing the TNF-alpha. The rate of release of the protein from the microspheres was determined in vivo by analysing the residual level of TNF-alpha remaining in the particles following intraperitoneal administration of the microspheres to mice. The release of the protein from the microspheres in vivo was significantly faster than predicted from the results of the in vitro studies. The absence of an initial burst release of TNF-alpha from the multiphase microspheres was reflected in a significant reduction in the plasma level of TNF-alpha when compared to the matrix-type microspheres and a solution of the protein. The controlled release property of the multiphase microspheres is expected to overcome the adverse reactions due to dose dumping that occurs following the local administration of TNF-alpha.     

Protein loaded biodegradable microspheres based on PLGA-protein bioconjugates.

Biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA) was chemically conjugated to lysozyme, a model protein drug, by coupling a terminal carboxylic acid in PLGA with primary amine groups present in lysozyme. The conjugation was carried out in dimethylsulphoxide (DMSO) by using carbodiimide as a coupling agent. The PLGA-lysozyme conjugate, dissolved in a co-solvent system of DMSO and methylene chloride, was directly formulated into microspheres by an oil-in-water (O/W) single emulsion solvent evaporation technique. Morphological characteristics of the resultant microspheres, loading efficiencies, and protein release behaviours with protein instability problems were investigated in comparison with those of the microspheres prepared by water-in-oil-water (W/O/W) double emulsion and O/W single emulsion techniques which employed PLGA with unconjugated lysozyme for the formulation.     

Chitosan/cellulose acetate microspheres preparation and ranitidine release in vitro

New microspheres containing hydrophilic core and hydrophobic coating as a controlled-release system with no toxic reagents were proposed. Water in oil in water (W/O/W) emulsion and solvent evaporation methods were used to make chitosan/ cellulose acetate (CCA) microspheres sized 200 - 400 microm. Ranitidine hydrochloride, as a model drug, was investigated for its release properties in vitro. The loading efficiency and release rate of ranitidine were affected by chitosan concentration and molecular weight. Higher loadings were obtained at lower concentrations in the interval of 1% to 2%. With chitosan at a 2% concentration microspheres could be obtained with more spherical appearance, smaller size, and higher ranitidine loading efficiency microspheres than at other concentrations. Among the different molecular weight chitosan (47, 145, 308, 499, and 1130 KD) microspheres, the high molecular weight chitosan (1130 KD) microspheres had relatively high loading efficiency (10%). Molecular weight and concentration of chitosan as well as the size of microspheres affected the release of ranitidine. Microspheres smaller than 280 microm released the drug faster than did the bigger by about 10%. The optimal condition for the preparation of the microspheres was chitosan concentration 2%, molecular weight 1130 KD. The ranitidine release from the microspheres was 30% during 48 h in phosphate-buffer saline medium.     

Carboplatin-loaded PLGA microspheres for intracerebral injection: formulation and characterization

The purpose of this study is to prepare and characterize injectable carboplatinloaded poly(D,L-lactic-co-glycolic) acid copolymer (PLGA) microspheres for the intracerebral treatment of malignant glioma. The microspheres were prepared by an acetone/mineral oil emulsion and solvent evaporation method. Preparation variables were optimized and the following processing conditions resulted in the highest drug loading and best yields of the microspheres compared with those prepared with the other variables: the PLGA concentration was 8%(w/w) in the internal phase; the emulsifier (Span 80) concentration was 8%(w/w) in the external phase; the ratio of the internal phase: the external phase was 1:8; the stirring speed was 1500 rpm; the emulsion time was 15 min; the solvent evaporation time was 3.75 hr. Microspheres so prepared were analysed for size distribution, drug loading, in vitro release and morphological characteristics. The drug release in phosphate buffer solution started with a 10- day slow release period, followed by a fast near zero order release period from 12 to 22 days. The carboplatin release in brain homogenate was slower than in phosphate buffer solution. The morphological changes of the microspheres during the in vitro degradation correlated with the drug relase profile. In conclusion, the carboplatin-loaded PLGA microspheres were specifically prepared to meet the specification as an injectable and biodegradable brain implant.     

Carboplatin-loaded PLGA microspheres for intracerebral injection: formulation and characterization.

The purpose of this study is to prepare and characterize injectable carboplatin-loaded poly(D,L,-lactic-co-glycolic) acid copolymer (PLGA) microspheres for the intracerebral treatment of malignant glioma. The microspheres were prepared by an acetone/mineral oil emulsion and solvent evaporation method. Preparation variables were optimized and the following processing conditions resulted in the highest drug loading and best yields of the microspheres compared with those prepared with the other variables: the PLGA concentration was 8% (w/w) in the internal phase; the emulsifier (Span 80) concentration was 8% (w/w) in the external phase; the ratio of the internal phase: the external phase was 1:8; the stirring speed was 1500 rpm; the emulsion time was 15 min; the solvent evaporation time was 3.75 hr. Microspheres so prepared were analysed for size distribution, drug loading, in vitro release and morphological characteristics. The drug release in phosphate buffer solution started with a 10-day slow release period, followed by a fast near zero order release period from 12 to 22 days. The carboplatin release in brain homogenate was slower than in phosphate buffer solution. The morphological changes of the microspheres during the in vitro degradation correlated with the drug relase profile. In conclusion, the carboplatin-loaded PLGA microspheres were specifically prepared to meet the specification as an injectable and biodegradable brain implant.     

Preparation and in vivo evaluation of thienorphine-loaded PLGA microspheres

Thienorphine-loaded microspheres composed of poly(D,L-lactide-co-glycolide) were prepared by an O/W emulsion solvent evaporation method. HPLC was used to determine the drug loading and drug release, while a LC-MS-MS system was employed to analyze the plasma drug concentration. Results indicated that the PLGA particles obtained were spherical and of appropriate size. The formulation was stable during the test period. In vitro drug release from the microspheres was sustained for about 28 days mostly by the diffusion mechanism. The plasma drug concentration-time profiles were relatively smooth for about 28 days after subcutaneous injection of the drug-loaded microspheres to rats, compared with that for drug suspension. In vitro and in vivo correlation was established.     

盐酸倍他洛尔蒙脱石微球的制备及其体外释放性能的研究

目的制备可满足缓释要求的镶嵌蒙脱石的离子交换缓释微球。方法采用S/O1/O2/O3复乳-溶剂挥发法制备微球,考察处方因素包括复乳相体积比例、药物质量浓度、膜材用量和乳化剂质量分数对微球制备的影响。以微球体外释放为考察指标,优化微球处方。结果研究所得到的微球最佳处方为大豆油∶药物=6∶1,药物∶膜材=1∶5,乳化剂质量分数为0.5%²%。除乳化剂外,其他因素对微球体外释放均有较大影响。所制备微球的体外释放可以达到10h,基本无突释现象。进行形态观察发现,微球较为圆整,粒径比较均匀。结论采用优化处方以复乳-溶剂挥发法所制备盐酸倍他洛尔蒙脱石微球体外具有缓释性能。     

Effects of solvent selection and fabrication method on the characteristics of biodegradable poly(lactide-co-glycolide) microspheres containing ovalbumin

To demonstrate the effect of formulation conditions on the controlled release of protein from poly(lactide-co-glycolide) (PLGA) microspheres for use as a parenteral drug carrier, ovalbumin (OVA) microspheres were prepared using the W/O/W multiple emulsion solvent evaporation and extraction method. Methylene chloride or ethyl acetate was applied as an organic phase and poly(vinyl alcohol) as a secondary emulsion stabilizer. Low loading efficiencies of less than 20% were observed and the in vitro release of OVA showed a burst effect in all batches of different microspheres, followed by a gradual release over the next 6 weeks. Formulation processes affected the size and morphology, drug content, and the controlled release of OVA from PLGA microspheres.     

NSAID Drugs Release from Injectable Microspheres Produced by Supercritical Fluid Emulsion Extraction

Supercritical fluid emulsion extraction is an innovative technology that uses supercritical carbon dioxide (SC‐CO₂) to extract the dispersed oily phase of an emulsion. This technology was used to produce poly‐lactic‐co‐glycolic acid (PLGA) microspheres charged with two common NSAIDs: piroxicam (PX) and diclophenac sodium (DF). Single (O/W) and double (W/O/W) emulsions were tested and a comparative study between the characteristics of the microspheres obtained by SC‐CO₂ extraction and the ones produced by conventional solvent evaporation (SE) is proposed. Varying the droplet dimensions, microspheres with mean diameters (MDs) of 1, 2, and 3 µm were obtained; however, the microspheres produced by SC‐CO₂ gave always a better reproduction of the MD of original droplets because aggregation phenomena often modify the mean size and distribution of the microparticles produced by SE. Moreover, very efficient drug loadings (88% w/w of DF in PLGA using W/O/W emulsion and 97% of PX w/w in PLGA starting from O/W emulsion) were measured in the products obtained by SC‐CO₂, respectively; whereas, the SE produced a drug loading of 30% in the case of double emulsion and of 70% for single emulsion. Solvent residue of 10 ppm was also measured by SC‐CO₂ technology against the 600 ppm of the SE products. The release profiles of the entrapped drugs were also monitored to check the structure of the microspheres produced by this new technology. © 2009 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 1484–1499, 2010     

Preparation,characterization and taste-masking properties of polyvinylacetal diethylaminoacetate microspheres containing trimebutine

The objectives of this study were to produce acid soluble, polyvinylacetal diethylaminoacetate (AEA) microspheres containing trimebutine (as maleate), using a water-in-oil-in-water (w/o/w) emulsion solvent evaporation method, to characterize their in-vitro release properties, and to evaluate the taste-masking potential of this formulation in human volunteers. The pH of the external aqueous phase was the critical factor in achieving a high loading efficiency for trimebutine in the microencapsulation process; nearly 90% (w/w) loading efficiency was obtained at above pH 10. Trimebutine was completely released from AEA microspheres within 10 min in a dissolution test at pH 1.2, simulating conditions in the stomach, whereas at pH 6.8, the pH in the mouth, only small quantities of trimebutine were released in the initial 1-2 min. The results of a gustatory sensation test in healthy volunteers confirmed the taste-masking effects of the AEA microspheres. Finally, an attempt was made to encapsulate the salts of other basic drugs (lidocaine, imipramine, desipramine, amitriptyline, promethazine and chlorpheniramine) into AEA microspheres using the w/o/w emulsion evaporation method. The loading efficiencies were ranked in almost inverse proportion with the solubility of the drugs in the external aqueous phase. This study demonstrated the possibility of masking the taste of salts of basic drugs by microencapsulation with AEA using a w/o/w emulsion solvent evaporation method.     

Microencapsulation of ovalbumin in poly(lactide-co-glycolide) by an oil-in-oil (o/o) solvent evaporation method

Abstract

The objective of this study was to produce biodegradable poly(lactide-co-glycolide) (PLGA; 50/50) microspheres by an oil-in-oil (o/o) solvent evaporation method to prolong the in vitro release of ovalbumin (OVA) as a model protein. The effects, on loading efficiency, microsphere yield, morphology and drug release, of two dispersing agents, aluminum tristearate and Span 80, in mineral oil were examined. PLGA 50/50 microspheres containing OVA powder (sieved through a 53 μm mesh) were prepared using an o/o solvent evaporation method. When aluminum tristearate was employed as a dispersing agent, the loading efficiency and yield of OVA had maximum values of 89 and 72% at 0·15% (w/v) aluminum tristearate, respectively. Morphology studies suggested that the obtained microspheres were spherical, and had a smooth surface. The diameters of the microspheres ranged between 100 and 200 μm. The loading efficiency, or yield, for microspheres decreased significantly above or below 0·15% (w/v) aluminum tristearate, and microspheres wkh irregular shapes were observed. The minimum sedimentation volume ratio (F) was obtained at a dispersity of carbon black particles in ethanol containing 0·15% (w/v) aluminum tristearate by a sedimentation study, and the cloudy supernatant suggested a defiocculated suspension. However, on the contrary, when Span 80 was added into the mineral oil as a dispersing agent, the concentration of Span 80 had little or no effect on the characteristics of the prepared microspheres. Drug loadings (60–70%) were obtained within the Span 80 concentrations employed in the present study (0·05–1·0% (w/v)). The yields were also in the same levels. The microspheres prepared in mineral oil containing Span 80 had an average diameter less than 50 μm in all cases. Sustained-release characteristics were demonstrated for PLGA microspheres prepared in mineral oil containing aluminum tristearate as a dispersing agent, even though a burst release at the initial phase was observed. This initial burst release from PLGA microspheres was reduced to some extent by micronization of the OVA powder using a planetary-type ball mill. However, PLGA microspheres prepared in mineral oil containing Span 80 as a dispersing agent, exhibited a large initial burst release. This burst release seems to be due to the smaller size of microspheres and the OVA powder adhering to the surface of PLGA microspheres (confirmed by scanning electron microscope (SEM) study).     

Alendronate PLGA microspheres with high loading efficiency for dental applications

PURPOSE: Alendronate sodium, used systemically as a bone protective agent, proved to also be effective locally in various dental bone applications. Development of alendronate-loaded microspheres with high loading efficiency for such applications would be greatly challenged by the hydrophilicity and low MW of the drug. The aim of this study was to incorporate alendronate sodium, into poly (lactide-co-glycolide) (PLGA) microspheres (MS) with high loading efficiency. METHODS: Three multiple emulsion methods: water-in-oil-in-water (W/O/W), water-in-oil-in-oil (W/O(1)/O(2)) and solid-in-oil-in-oil (S/O(1)/O(2)) were tested. In addition to entrapment efficiency, MS were characterized for surface morphology, particle size, in vitro drug release and in vitro degradation of the polymer matrix. Alendronate microspheres with maximum drug loading and good overall in vitro performance were obtained using the W/O(1)/O(2) emulsion technique. RESULTS: Drug release from the microspheres exhibited a triphasic release pattern over a period of 13 days, the last fast release phase being associated with more rapid degradation of the PLGA matrix. CONCLUSIONS: Biocompatible, biodegradable PLGA microspheres incorporating alendronate sodium with high loading efficiency obtained in this study may offer promise as a delivery system for bisphosphonates in dental and probably other clinical applications.     

Stabilization of protein encapsulated in poly(lactide-co-glycolide) microspheres by novel viscous S/W/O/W method

In stabilizing proteins during microsphere fabrication, the viscous solid-in-water-in-oil-in-water (S/W/O/W) method was compared to the conventional multi-emulsion W/O/W and S/O/W method. Solid proteins lyophilized with cyclodextrin derivatives and polyethylene glycol (PEG) pass through an organic solvent phase and are then embedded in aqueous microdroplets of first emulsion. Proteins were stabilized at the water/organic solvent interface by an internal aqueous phase containing viscous polysaccharides, and then can be safely encapsulated without degradation. In addition, these microspheres showed a long-term protein release followed by nearly zero-order kinetics with minimal initial burst. This means that the viscous S/W/O/W method provides a safe strategy for microsphere fabrication and has promising properties, involving the preservation of protein bioactivity, the inhibition of protein denaturation or agglomeration, and long-term protein release.     

New drug salt formation in biodegradable microspheres

PURPOSE: To investigate the effects of inorganic salts in the external phase of an oil-in-water (O/W) emulsion method during microsphere preparation. METHODS: An O/W emulsion method was used to prepare poly(D,L-lactic acid) microspheres containing quinidine sulfate. Different inorganic salts were used in the external phase during microsphere preparation. Microsphere drug loading was determined by UV and the drug salt anions inside the microspheres were determined by ion chromatography. RESULTS: New drug salts were formed during encapsulation in the microspheres when salts with non-common anions to the drug salt were used. Drug loading increased when NaClO4 or NaSCN were used. The fraction of drug as the new salt in microspheres increased non-linearly with the salt concentration in the external phase, however, the fraction of drug as the new encapsulated salt was linearly related to drug loading. Drug loading decreased and new salt fraction increased with increasing organic solvent volume or with decreasing cosolvent polarity. CONCLUSIONS: Introducing salts containing non-common anions to the drug salt employed in the external phase of O/W emulsion microsphere method leads to new salt formation. The extent of new drug salt formation is affected by salt levels added, cosolvent type and polymer concentration.     

Encapsulation of water-soluble drugs by a modified solvent evaporation method. I. Effect of process and formulation variables on drug entrapment

Pseudoephedrine HCl, a highly water-soluble drug, was entrapped within poly (methyl methacrylate) microspheres by a water/oil/water emulsification-solvent evaporation method. An aqueous drug solution was emulsified into a solution of the polymer in methylene chloride, followed by emulsification of this primary emulsion into an external aqueous phase to form a water/oil/water emulsion. The middle organic phase separated the internal drug-containing aqueous phase from the continuous phase. Microspheres were formed after solvent evaporation and polymer precipitation. The drug content of the microspheres increased with increasing theoretical drug loading, increasing amounts of organic solvent, polymer and polymeric stabilizer, and decreased with increasing stirring time, increasing pH of the continuous phase and increased volume of the internal and external aqueous phase.