Chitosan/gelatin microspheres prepared by modified emulsification and ionotropic gelation

Chitosan microspheres were prepared by an emulsion-phase separation technique without the use of chemical cross-linking agents; alternatively, ionotropic gelation was employed in a w/o emulsion. The possibility of three kinds of anions (tripolyphosphate, citrate and sulphate) to interact with chitosan was investigated by turbidimetric titration. The results indicate that there are electrostatic interactions between the above anions and chitosan in a certain region of solution pH (1.0-7.5 for sulphate/chitosan, 4.5-7.5 for citrate/chitosan and 1.9-7.5 for tripolyphosphate/chitosan), that is related to the natural characteristics of the anions. Out of the pH region where anions interact with chitosan, no microspheres were formed. However, even in the pH region where anions can interact with chitosan, only irregular microparticles were obtained in the case of the conventional emulsification and ionotropic gelation method, while spherical microspheres with diameters in the range of tens of microns were obtained when a modified process was employed. The key point of the modified process is the introduction of gelatin and allowing the ionic cross-linking process of chitosan/gelatin w/o emulsions to take place under coagulation conditions at a low temperature. The surface of sodium sulphate cross-linked chitosan/gelatin and sodium citrate cross-linked chitosan/gelatin microspheres was very smooth, but large gaps were observed on the surface of tripolyphosphate/chitosan microspheres. The increase of stirring speed led to a decrease in diameter and a narrowing in size distribution.     

Evaluation of diltiazem hydrochloride-loaded mucoadhesive microspheres prepared by emulsification-internal gelation technique

The problems of frequent administration and variable low bioavailability (40-60%) after oral administration of conventional dosage forms of diltiazem can be attenuated by designing it in the form of mucoadhesive microspheres which would prolong the residence time at the absorption site to facilitate intimate contact with the absorption surface and thereby improve and enhance the bioavailability. Diltiazem-loaded mucoadhesive microspheres were successfully prepared by emulsification-internal gelation technique with a maximum incorporation efficiency of 93.29 +/- 0.26%. The scanning electron microscopic study indicated that the microspheres were spherical in shape and the drug remained dispersed in the polymer matrix at amorphous state, which was further confirmed by x-ray diffraction analysis. The in vitro wash-off test indicated that the microspheres had good mucoadhesive properties. The wash-off was faster at simulated intestinal fluid (phosphate buffer, pH 7.4) than that at simulated gastric fluid (0.1 M HCl, pH 1.2). The in vitro drug release mechanism was non-fickian type controlled by swelling and relaxation of polymer. There was no significant change in drug content and cumulative drug release of drug-loaded microspheres stored at different storage condition after 8 weeks of study.     

Insulin encapsulation in reinforced alginate microspheres prepared by internal gelation.

Insulin-loaded alginate microspheres prepared by emulsification/internal gelation were reinforced by blending with polyanionic additive polymers and/or chitosan-coating in order to increase the protection of insulin at simulated gastric pH and obtain a sustained release at simulated intestinal pH. Polyanionic additive polymers blended with alginate were cellulose acetate phtalate (CAP), Eudragit L100 (EL100), sodium carboxymethylcellulose (CMC), polyphosphate (PP), dextran sulfate (DS) and cellulose sulfate (CS). Chitosan-coating was applied by using a one-stage procedure. The influence of additive polymers and chitosan-coating on the size distribution of microspheres, encapsulation efficiency and release profile of insulin in simulated gastrointestinal pH conditions was studied. The mean diameter of blended microspheres ranged from 65 to 106 microm and encapsulation efficiency of insulin varied from 14 to 100%, reaching a maximum value when CS and DS were incorporated in the alginate matrix. Insulin release, at pH 1.2, was almost prevented by the incorporation of PP, DS and CS. When uncoated microspheres were transferred to pH 6.8, a fast dissolution occurred, independently of the additive polymer blended with alginate, and insulin was completely released. Increasing the additive polymer concentration in the alginate matrix and/or chitosan-coating the blended alginate microspheres did not promote a sustained release of insulin from microspheres at pH 6.8.     

Microencapsulation of hemoglobin in chitosan-coated alginate microspheres prepared by emulsification/internal gelation

Chitosan-coated alginate microspheres prepared by emulsification/internal gelation were chosen as carriers for a model protein, hemoglobin (Hb), owing to nontoxicity of the polymers and mild conditions of the method. The influence of process variables related to the emulsification step and microsphere recovering and formulation variables, such as alginate gelation and chitosan coating, on the size distribution and encapsulation efficiency was studied. The effect of microsphere coating as well its drying procedure on the Hb release profile was also evaluated. Chitosan coating was applied by either a continuous microencapsulation procedure or a 2-stage coating process. Microspheres with a mean diameter of less than 30 microm and an encapsulation efficiency above 90% were obtained. Calcium alginate cross-linking was optimized by using an acid/CaCO(3) molar ratio of 2.5, and microsphere-recovery with acetate buffer led to higher encapsulation efficiency. Hb release in gastric fluid was minimal for air-dried microspheres. Coating effect revealed a total release of 27% for 2-stage coated wet microspheres, while other formulations showed an Hb release above 50%. Lyophilized microspheres behaved similar to wet microspheres, although a higher total protein release was obtained with 2-stage coating. At pH 6.8, uncoated microspheres dissolved in less than 1 hour; however, Hb release from air-dried microspheres was incomplete. Chitosan coating decreased the release rate of Hb, but an incomplete release was obtained. The 2-stage coated microspheres showed no burst effect, whereas the 1-stage coated microspheres permitted a higher protein release.     

Chitosan-reinforced alginate microspheres obtained through the emulsification/internal gelation technique.

Alginate microspheres prepared by emulsification/internal gelation were chosen as carriers for a model protein, hemoglobin (Hb). Reinforced chitosan-coated microspheres were obtained by an uninterrupted method, in order to simplify the coating process, minimize protein losses during production and to avoid Hb escape under acidic conditions. Microspheres recovery was evaluated as well as its morphology by determination of Hb encapsulation efficiency and microscopic observation, respectively. The formation of chitosan membrane made of it interaction with alginate was assessed by DSC (differential scanning calorimetry) and FT-IR (Fourier-transform infrared spectrometry) studies. Spherical uncoated microspheres with a mean diameter of 20 microm and encapsulation efficiency above 89% were obtained. Coated microspheres provided similar encapsulation efficiency but a higher mean diameter was obtained due to microspheres clumping during the coating step. Protein loss occurred mainly during emulsification rather than recovery. FT-IR and DSC together indicated electrostatic interactions between alginate carboxylate and chitosan ammonium groups as the main forces for complex formation. Hb release from microspheres showed a pH-dependent profile and was affected by chitosan coating. Under simulated gastric conditions, a total Hb burst release from uncoated microspheres was decreased with one-stage and two-stage chitosan coatings (68% and 28%, respectively). At pH 6.8, the Hb release from coated microspheres was fast but incomplete. These results suggest an optimization of the coating method to protect Hb under acidic conditions and to permit a complete but sustained release of Hb.     

Shape optimization and characterization of polysaccharide beads prepared by ionotropic gelation

The shape of drug loaded polysaccharide beads produced by ionotropic gelation has been optimized, with the aim of producing spherical beads suitable for further technological operations, such as coating. The optimization was performed on a model system sodium alginate/theophylline by inclusion of various fillers. Incorporation of excipients markedly influenced the morphological characteristics of the beads. The undesired irregular shape of beads caused by incorporation of the drug could only be improved by incorporating a combination of polycarbophil (PK) and polyvinylpyrrolidone (PVP). The spherical shape of these beads was stabilized mechanically by numerous air bubbles trapped inside the beads, which prevented the collapse of the beads during drying. The optimized method was shown to be applicable to a target system of pectin and an anti-inflammatory drug, LK-423.     

Shape optimization and characterization of polysaccharide beads prepared by ionotropic gelation

The shape of drug loaded polysaccharide beads produced by ionotropic gelation has been optimized, with the aim of producing spherical beads suitable for further technological operations, such as coating. The optimization was performed on a model system sodium alginate/theophylline by inclusion of various fillers. Incorporation of excipients markedly influenced the morphological characteristics of the beads. The undesired irregular shape of beads caused by incorporation of the drug could only be improved by incorporating a combination of polycarbophil (PK) and polyvinylpyrrolidone (PVP). The spherical shape of these beads was stabilized mechanically by numerous air bubbles trapped inside the beads, which prevented the collapse of the beads during drying. The optimized method was shown to be applicable to a target system of pectin and an anti-inflammatory drug, LK-423.     

Production of alginate microspheres by internal gelation using an emulsification method

Alginate is a natural polysaccharide found in brown algae. Alginates are widely used in the food and pharmaceutical industries and have been employed as a matrix for the entrapment of drugs, macromolecules and biological cells. Alginate microspheres can be produced by the external or internal gelation method using calcium salts. The addition of calcium chloride solution in the final phase of production of microspheres by external gelation method using an emulsification technique causes the disruption of the equilibrium of the system being stirred, resulting in a significant degree of clumping of microspheres. Therefore, in this study, production of alginate microspheres by the internal gelation method using a modified emulsification technique was explored. The influence of calcium salt, added in varying amounts and at different stages, on the morphology of the microspheres was investigated. The effects of other hardening agents and different drying methods were also studied.     

Alginate microspheres prepared by internal gelation: development and effect on insulin stability

Recombinant human insulin was encapsulated within alginate microspheres by the emulsification/internal gelation technique with the objective of preserving protein stability during encapsulation procedure. The influence of process and formulation parameters was evaluated on the morphology and encapsulation efficiency of insulin. The in vitro release of insulin from microspheres was studied under simulated gastrointestinal conditions and the in vivo activity of protein after processing was assessed by subcutaneous administration of extracted insulin from microspheres to streptozotocin-induced diabetic rats. Microspheres mean diameter, ranging from 21 to 287 microm, decreased with the internal phase ratio, emulsifier concentration, mixer rotational speed and increased with alginate concentration. Insulin encapsulation efficiency, near 75%, was not affected by emulsifier concentration, mixer rotational speed and zinc/insulin hexamer molar ratio but decreased either by increasing internal phase ratio and calcium/alginate mass ratio or by decreasing acid/calcium molar ratio and alginate concentration. A high insulin release, above 75%, was obtained at pH 1.2 and under simulated intestinal pH a complete dissolution of microspheres occurred. Extracted insulin from microspheres decreased hyperglycemia of diabetic rats proving to be bioactive and showing that encapsulation in alginate microspheres using the emulsification/internal gelation is an appropriate method for protein encapsulation.     

Formation of alginate microspheres produced using emulsification technique

This study investigated the formative process of alginate microspheres produced using an emulsification technique. The alginate microspheres were produced by cross-linking alginate globules dispersed in a continuous organic phase using various calcium salts: calcium chloride, calcium acetate, calcium lactate and calcium gluconate. The size, shape, drug content and Ca2+ content of the microspheres were evaluated. The tack, viscosity and pH of the calcium salt solution and percentage of Ca2+ partitioned into the organic phase were determined. Microscopic examination of the test emulsion at various stages of the emulsification process was also carried out. The propensity of cross-linking reaction was found to be dependent on successful collision between alginate and calcium salt globules. Examination of the characteristics of microspheres indicated that the formed microsphere was a resultant product of alginate globule clustering. The growth propensity of microspheres was promoted by the higher rate and extent of cross-linkage which was governed by the pH, tack and/or Ca2+ content of the cross-linking solution, as well as the dissociation constant and diffusivity of the calcium salt. Overall, the amount of free Ca2+ cross-linked with alginate in the formed microspheres was in the following order: calcium acetate > calcium chloride + calcium acetate > calcium chloride + calcium gluconate; calcium chloride + calcium lactate > calcium chloride. In microencapsulation by emulsification, the mean size of the microspheres produced can be modified by varying the tack, pH and Ca2+ content of the cross-linking solution and through the use of a combination of calcium salts. The shape of the microspheres produced was, nonetheless, unaffected by the physicochemical properties of the cross-linking solution.     

Formation of alginate microspheres produced using emulsification technique

This study investigated the formative process of alginate microspheres produced using an emulsification technique. The alginate microspheres were produced by cross-linking alginate globules dispersed in a continuous organic phase using various calcium salts: calcium chloride, calcium acetate, calcium lactate and calcium gluconate. The size, shape, drug content and Ca²⁺ content of the microspheres were evaluated. The tack, viscosity and pH of the calcium salt solution and percentage of Ca²⁺ partitioned into the organic phase were determined. Microscopic examination of the test emulsion at various stages of the emulsification process was also carried out. The propensity of cross-linking reaction was found to be dependent on successful collision between alginate and calcium salt globules. Examination of the characteristics of microspheres indicated that the formed microsphere was a resultant product of alginate globule clustering. The growth propensity of microspheres was promoted by the higher rate and extent of cross-linkage which was governed by the pH, tack and/or Ca²⁺ content of the cross-linking solution, as well as the dissociation constant and diffusivity of the calcium salt. Overall, the amount of free Ca²⁺ cross-linked with alginate in the formed microspheres was in the following order: calcium acetate > calcium chloride + calcium acetate > calcium chloride + calcium gluconate; calcium chloride + calcium lactate > calcium chloride. In microencapsulation by emulsification, the mean size of the microspheres produced can be modified by varying the tack, pH and Ca²⁺ content of the cross-linking solution and through the use of a combination of calcium salts. The shape of the microspheres produced was, nonetheless, unaffected by the physicochemical properties of the cross-linking solution.     

Release characteristics of pectin microspheres prepared by an emulsification technique

The potential application of pectin as a matrix polymer for making microspheres by an emulsification technique was explored, and the drug release property of these pectinate microspheres containing drug cores of varying aqueous solubilities: sulphanilamide, sulphaguanidine and sulphathiazole, was investigated using different dissolution media. The size and size distribution, specific surface area, drug content and drug release property of the pectinate microspheres were determined. The solubility and solution pH of drugs and their propensity to interact with pectin were characterized. Pectinate microspheres were successfully prepared by external gelation, using a modified emulsification technique. The kinetics of drug release from the microspheres best fitted Higuchi's model. Interestingly, the lowest percentage of drug released was produced by microspheres which were smallest in size and, therefore, largest in specific surface area, and containing sulphanilamide, the most aqueous soluble and the lowest molecular weight drug. Mathematical correlation study indicated that the drug release profile of pectinate microspheres was notably affected by the drug content and the extent of drug-pectin interaction in the microspheres. Generally, a higher percentage of drug was released from the microspheres with a higher drug content and/or lower extent of drug-pectin interaction. The extent of drug-pectin interaction was highest in microspheres containing sulphanilamide, followed by sulphaguanidine and sulphathiazole, opposite to that of drug content.     

Release characteristics of pectin microspheres prepared by an emulsification technique

The potential application of pectin as a matrix polymer for making microspheres by an emulsification technique was explored, and the drug release property of these pectinate microspheres containing drug cores of varying aqueous solubilities: sulphanilamide, sulphaguanidine and sulphathiazole, was investigated using different dissolution media. The size and size distribution, specific surface area, drug content and drug release property of the pectinate microspheres were determined. The solubility and solution pH of drugs and their propensity to interact with pectin were characterized. Pectinate microspheres were successfully prepared by external gelation, using a modified emulsification technique. The kinetics of drug release from the microspheres best fitted Higuchi's model. Interestingly, the lowest percentage of drug released was produced by microspheres which were smallest in size and, therefore, largest in specific surface area, and containing sulphanilamide, the most aqueous soluble and the lowest molecular weight drug. Mathematical correlation study indicated that the drug release profile of pectinate microspheres was notably affected by the drug content and the extent of drug-pectin interaction in the microspheres. Generally, a higher percentage of drug was released from the microspheres with a higher drug content and/or lower extent of drug-pectin interaction. The extent of drug-pectin interaction was highest in microspheres containing sulphanilamide, followed by sulphaguanidine and sulphathiazole, opposite to that of drug content.     

Theoretical and experimental investigations on the size of alginate microspheres prepared by dropping and spraying

In order to produce functional microspheres with different ranges of sizes for various applications, the size of alginate droplets prepared by dropping and spraying was studied. It was shown that the mean diameter could be controlled by liquid flow velocity and applied voltage as operating parameters using a conventional dropping and an electrostatic dropping method, separately. The formation mechanism of alginate droplets could be categorized into two different modes: Dripping mode and jetting mode. By employing an effective force analysis, the diameters in each modes showed to be well agreed with the numerical simulation within 7% deviations. It was testified that the initial amount of surface charges had a high impact on droplet diameter and the liquid flow velocity played a more important role on mean diameter of alginate droplets by electrostatic dropping method in dripping mode than in jetting mode. Then, an empirical equation and a semi-empirical model were used to simulate the diameter of droplets obtained by spraying and spraying with electrostatic field (SEF) method, respectively. The decrease in diameter was more sensitive to the increase of gas flow rate than to the decrease of liquid flow rate, and the results of two models fitted well with experimental values. The simulations showed that SEF yielded a 20% lower on droplet diameter than simple spraying method.     

Theoretical and experimental investigations on the size of alginate microspheres prepared by dropping and spraying

In order to produce functional microspheres with different ranges of sizes for various applications, the size of alginate droplets prepared by dropping and spraying was studied. It was shown that the mean diameter could be controlled by liquid flow velocity and applied voltage as operating parameters using a conventional dropping and an electrostatic dropping method, separately. The formation mechanism of alginate droplets could be categorized into two different modes: Dripping mode and jetting mode. By employing an effective force analysis, the diameters in each modes showed to be well agreed with the numerical simulation within 7% deviations. It was testified that the initial amount of surface charges had a high impact on droplet diameter and the liquid flow velocity played a more important role on mean diameter of alginate droplets by electrostatic dropping method in dripping mode than in jetting mode. Then, an empirical equation and a semi-empirical model were used to simulate the diameter of droplets obtained by spraying and spraying with electrostatic field (SEF) method, respectively. The decrease in diameter was more sensitive to the increase of gas flow rate than to the decrease of liquid flow rate, and the results of two models fitted well with experimental values. The simulations showed that SEF yielded a 20% lower on droplet diameter than simple spraying method.     

Biodegradable bromocryptine mesylate microspheres prepared by a solvent evaporation technique. I: Evaluation of formulation variables on microspheres characteristics for brain delivery

The aim of this study was to formulate biodegradable microspheres containing an anti-parkinsonian agent, bromocryptine mesylate, for brain delivery. The effect of formulation parameters (e.g. polymer, emulsifying agent type and concentration) on the characteristics of the microspheres produced, the efficiency of drug encapsulation, the particle size distribution and in vitro drug release rates from the bromocryptine mesylate microspheres were investigated using a 3(2) factorial design. Bromocryptine mesylate was encapsulated into biodegradable polymers using the following three different polymers; poly(L-lactide), poly(D,L-lactide) and poly(D,L-lactide-co-glycolide). The SEM photomicrographs showed that the morphology of the microspheres greatly depended on the polymer and emulsifying agent. The results indicate that, regardless of the polymer type, increase in emulsifying agent concentration from 0.25-0.75% w/v markedly decreases the particle size of the microspheres. Determination of particle size revealed that the use of 0.75% w/v of emulsifying agent concentration and a polymer solution concentration of 10% w/v resulted in optimum particle size. In order to prepare biodegradable microspheres with high drug content and small particle size, selection of polymer concentration as well as emulsifying agent concentration is critical. Polymer type has a less pronounced effect on the percentage encapsulation efficiency and particle size of microspheres than on the t(50%). The microspheres prepared by all three polymers, at a polymer concentration of 10% w/v and an emulsifying agent concentration of 0.75% w/v with NaCMC:SO (4:1, w/v) mixture was as the optimum formulation.     

Biodegradable bromocryptine mesylate microspheres prepared by a solvent evaporation technique. I: Evaluation of formulation variables on microspheres characteristics for brain delivery

The aim of this study was to formulate biodegradable microspheres containing an anti-parkinsonian agent, bromocryptine mesylate, for brain delivery. The effect of formulation parameters (e.g. polymer, emulsifying agent type and concentration) on the characteristics of the microspheres produced, the efficiency of drug encapsulation, the particle size distribution and in vitro drug release rates from the bromocryptine mesylate microspheres were investigated using a 3 2 factorial design. Bromocryptine mesylate was encapsulated into biodegradable polymers using the following three different polymers; poly(L-lactide), poly(D,L-lactide) and poly(D,L-lactide-co-glycolide). The SEM photomicrographs showed that the morphology of the microspheres greatly depended on the polymer and emulsifying agent. The results indicate that, regardless of the polymer type, increase in emulsifying agent concentration from 0.25-0.75% w/v markedly decreases the particle size of the microspheres. Determination of particle size revealed that the use of 0.75% w/v of emulsifying agent concentration and a polymer solution concentration of 10% w/v resulted in optimum particle size. In order to prepare biodegradable microspheres with high drug content and small particle size, selection of polymer concentration as well as emulsifying agent concentration is critical. Polymer type has a less pronounced effect on the percentage encapsulation efficiency and particle size of microspheres than on the t 50% . The microspheres prepared by all three polymers, at a polymer concentration of 10% w/v and an emulsifying agent concentration of 0.75% w/v with NaCMC:SO (4:1, w/v) mixture was as the optimum formulation.     

Evaluation of ibuprofen-loaded microspheres prepared from novel copolyesters

The utility of two novel linear random copolyesters to encapsulate and control the release of ibuprofen, via microspheres, was investigated. Various manufacturing parameters, including temperature, disperse phase volume and polymer:ibuprofen ratios were altered during the microsphere production. The effects of these changes on the morphological characteristics of the microspheres, yield, drug loading, encapsulation efficiency and drug release rates were examined. The diameter of the microspheres ranged from 36 to 89 microm and showed both smooth and ridged surfaces. Microsphere diameter was probably determined by the internal phase volume, while surface morphology was controlled by manufacturing temperature. Greater encapsulation efficiency was obtained by increasing the polymer:ibuprofen ratio and by reducing the internal phase volume. For all batches there was an initial burst drug release into phosphate buffer (pH 7.4) over the first 2-4h, which was followed by a much slower release rate over the remaining time period. Drug release rates during both these phases were dependent upon the amount and nature of the polymer in the microspheres, noting that the more hydrophilic polymer provided faster release rates. Ibuprofen solubility appeared to play a dominant role in controlling release, although both encapsulation efficiency and microsphere morphology were also contributing factors.     

Formulation and evaluation of ethyl cellulose microspheres prepared by the multiple emulsion technique

The aim of this study was to formulate and evaluate microencapsulated controlled release preparations of metformin hydrochloride using ethyl cellulose as the retardant material with high entrapment efficiency and extended release. Microspheres were prepared by the double emulsion solvent diffusion method. A mixed solvent system consisting of acetonitrile and dichloromethane in 1:1 ratio and light liquid paraffin were chosen as the primary and secondary oil phases, respectively. Span 80 was used as the surfactant for stabilizing the secondary oil phase. The prepared microspheres were characterized by drug loading, optical microscopy and scanning electron microscopy (SEM). The in vitro release studies were performed in a series of buffer solutions with variable pH. The drug loaded microspheres showed 55-85% of entrapment and the release was extended for up to 12 h. SEM studies revealed that the microspheres were spherical and porous in nature. Data obtained from in vitro release studies were fitted to various kinetic models and high correlation was obtained with the Higuchi model. The drug release was found to be diffusion controlled. Oral administration of the microspheres to the albino mice provided decreased plasma glucose for more than 10 h.     

Drug encapsulation in alginate microspheres by emulsification.

A method based on an emulsification process was developed for the production of calcium alginate microspheres. Isopropyl alcohol and acetone, which are strong dehydrating agents, were used to aid in the hardening and drying of the microspheres. However, the amount of drug encapsulated was very low. This was due to the drug being soluble in the dehydrating solvents. In the absence of the solvents a high percentage of drug was encapsulated, and this was further increased by forming the microspheres by phase inversion. It was also found that a suspension of the drug particles was required for effective microencapsulation. The efficiency of drug encapsulation generally increased with the ratio of drug to encapsulating material. The microspheres produced were free-flowing and most of them were smaller than 150 microns.