Aqueous Preparation and Evaluation of Albumin‐Chitosan Microspheres Containing Indomethacin

Controlled‐release egg albumin‐chitosan microspheres containing indomethacin as a model drug were successfully prepared by coacervation method. The proposed method can offer a simple method for microsphere preparation in an aqueous system with the elimination of the use of organic solvents that are usually needed in conventional techniques of microencapsulation. The interaction between negatively charged egg albumin molecules in phosphate buffer, pH 7.2, or sodium hydroxide solution and positively charged chitosan molecules dissolved in diluted acetic acid to form an insoluble precipitate was the principle for the formation of the microspheres. The effects of many process variables, such as amount of formaldehyde as a cross‐linking agent, stirring time, final pH of encapsulation medium, initial drug loading, and albumin concentration or albumin‐to‐chitosan weight ratio, on the properties of the prepared microspheres were investigated. Incorporation efficiencies of the microspheres to the drug were high in most cases and ranged between 63.3 ± 3.6% and 92.39 ± 3.2%, while particle sizes were 435.2 ± 12.6 up to 693.9 ± 34.6 µm for the different tested batches. On the other hand, the values of angles of repose and compressibility indices were in the range of 23.5 ± 0.4 to 32.0 ± 0.7 degrees and 11.1 ± 0.7% to 23.6 ± 0.7% respectively, which indicate overall good free flowing nature of the microspheres of all batches. The maximum required amount of the cross‐linking agent was determined to avoid excessive unnecessary chemicals. It was also noticed that excessive time of stirring and excessive initial drug loading are not recommended as it may lead to microspheres of low properties. The pH of the encapsulation media (pH 3.77 up to pH 4.91) significantly affected the properties of the microspheres. As the pH of the encapsulation media was increased, the incorporation efficiency, particle size, and flowability decreased, along with increase of drug release rate, which could be related to incomplete cross linking of the microspheres matrix. It was also observed that high concentration of albumin solution and accordingly the increase of albumin‐to‐chitosan weight ratio were accompanied with increases in incorporation efficiency and particle size with improved microsphere flowability and slow indomethacin release. Thus, the proposed microspheres showed the ability to control the release of indomethacin, and their properties were highly affected by many process variables that could be controlled to obtain an optimized system.     

Release profiles of theophylline from microspheres consisting of dextran derivatives and cellulose acetate butyrate: effect of polyion complex formation

The objective of this study was to evaluate the utility of mixtures among oppositely charged dextran derivatives as constituents of a controlled release microsphere. Carboxymethyldextran (CMD) and dextran sulfate (DS) were used as polyanions, and [2-(diethylamino) ethyl] dextran (EA) and [2-hydroxypropyltrimethylammonium] dextran (CDC) as polycations. The microspheres consisting of hydrophilic and hydrophobic polymers were prepared by emulsion-solvent evaporation method. The mixtures, CMD/EA, CMD/CDC, DS/EA, and DS/CDC, were used as hydrophilic polymers, because they can interact with each other to form polyion complexes for the improvement of sustained-release performances. Cellulose acetate butyrate and theophylline were used as a model hydrophobic polymer and a model drug, respectively. The yield of microspheres was excellent (more than 95%). According to observation, by scanning election microscopy (SEM) microspheres were spherical with a rough surface. The in vitro drug release from microspheres was examined in the JP XIV first fluid, pH 1.2, and second fluid, pH 6.8, at 37°C, and 100 rpm. In the DS/CDC system, drug release was depressed by formation of a polyion complex and not affected by pH of dissolution medium. The release rate was modulated by the ratio of hydrophilic and hydrophobic matrix. This particulate system, in which the polyion complex matrix is strengthened by a hydrophobic polymer, is a promising formulation for drug delivery.     

Effect of Drug Properties on Physical and Release Characteristics of Eudragit Microspheres Prepared by Spherical Crystallization Technique

Ten compounds having different solubilities and molecular weights were evaluated for incorporation into Eudragit microspheres using the spherical crystallization technique, and the effects of drug-related factors on the properties of Eudragit microspheres were investigated. The entrapment of the active compound within the microspheres was highly dependent on the acidic or basic characteristics of the drug. Structural changes were also observed on the microsphere surface prepared at different pH values. Microspheres prepared with slightly and very slightly soluble drugs such as salicylic acid, naproxen, piroxicam, indomethacin, and methylpred-nisolone indicated controlled-release properties. Generally, drug release from microspheres followed the Fickian diffusion model.     

Acrylate-based transdermal therapeutic system of nitrendipine

The objective of the present research investigation was to fabricate an acrylate-based transdermal therapeutic system (TTS) of nitrendipine, which could deliver drug at maximum input rate so as to deliver drug in minimum patch size. Transdermal patches were fabricated using synthesized acrylate pressure-sensitive adhesives (PSAs): PSA1, PSA2, and commercially available PSA3 and PSA4 using d-limonene as permeation enhancer. Effect of concentration of d-limonene on permeation kinetics of nitrendipine in PSAs was studied. Fabricated TTS in mentioned PSAs were evaluated for in-vitro release and permeation kinetics through guinea-pig skin. Cumulative release of drug in PSA1, PSA2, PSA3, and PSA4 was observed to be 45%, 40%, 25%, and 25%, respectively, upto 24 hr. Flux of drug through guinea-pig skin calculated at 48 hr in PSA1, PSA2, PSA3, and PSA4, with and without d-limonene, was observed to be 0.346 ± 0.10, 0.435 ± 0.17, 0.410 ± 0.17, and 0.162 ± 0.06, and 0.625 ± 0.19, 1.161 ± 0.46, 0.506 ± 0.17, and 0.520 ± 0.18 (µg/cm²/hr), respectively. The TTS in PSA2 showed comparatively high flux and could deliver drug at high input rate through transdermal route. PSA2 was found to have good rate-controlling property and could be successfully employed in transdermal delivery of nitrendipine.     

Use of proteins to minimize the physical aging of EUDRAGIT sustained release films

The objective of this study was to investigate the influence of two proteins, albumin and type B gelatin, on the physical aging of EUDRAGIT® RS 30 D and RL 30 D coated theophylline pellets. The physicomechanical properties of sprayed films, thermal properties of cast films, influence of proteins on the zeta potential and particle size of the dispersion, and the release of proteins from cast films under simulated dissolution conditions were investigated. The release rate of theophylline decreased significantly over time from pellets coated with an acrylic dispersion containing 10% albumin when there was no acidification of the acrylic dispersion; however, when pellets were coated with an acidified EUDRAGIT®/albumin dispersion, the theophylline release rate was stable for dosage forms stored in the absence of humidity. The drug release rate was faster for pellets coated with acrylic dispersions containing 10% gelatin compared to the albumin-containing formulations. When sprayed films were stored at 40°C/75% RH, the water vapor permeability decreased significantly for both EUDRAGIT® films and those containing EUDRAGIT® and albumin; however, there was no significant change in this parameter when 10% gelatin was present. Albumin was released from the acrylic films when the pH of the dissolution media was below the isoelectric point of the protein while no quantitative release of gelatin was observed in pH 1.2 or 7.4 media. The effect of gelatin to prevent the decrease in drug release rate was due to stabilization in water vapor permeability of the film. Acidification of the polymeric dispersion resulted in electrostatic repulsive forces between albumin and the acrylic polymer, which stabilized the drug release rate when the dosage forms were stored in aluminum induction sealed containers at both 40°C/75% RH and 25°C/60% RH.     

Physicochemical properties of amphotericin B liposomes prepared by reverse-phase evaporation method

The physicochemical properties of phosphatidylcholine-cholesterol liposomes containing amphotericin B and prepared by reverse-phase evaporation method were studied. Uniformly dispersed liposomal suspensions were obtained by employing 3:1 ratio (by volume) of diethyl ether to normal saline, 5 min sonication time at 7°C, and evaporation of diethyl ether at 25°C. Microscopic examination showed that the prepared liposomes were spheroids with unilamellar, oligolamellar, or multilamellar structure. The liposomes containing amphotericin B 2.0 mol% of total lipid led to the highest percentage of drug entrapment. Liposomes with maximum entrapment efficiency were obtained from using 250 µmol of total lipid. The liposomal amphotericin B possessing the highest drug entrapment efficiency (approximately 95%) with particle size range of 1307-1451 nm was the one composed of 1:1 molar ratio of phosphatidylcholine to cholesterol.     

Preparation and characterization of chitosan microspheres containing doxifluridine

Chitosan microspheres containing 5-fluorouracil (5-FU), tegafur (FT), and doxifluridine (DFUR) were prepared by the dry-in-oil method using silicone oil with no surfactant as a dispersion medium. For DFUR-containing chitosan microspheres (DFUR-M), reacetylation with acetic anhydride or coating using chitosan and glutaraldehyde was performed. DFUR-M, reacetylated DFUR-M, and chitosan-coated DFUR-M were investigated on in vitro drug release, and the former two microspheres were examined for in vivo degradation after subcutaneous (s.c.) implantation in mice, and in vivo plasma concentration-time profiles after s.c. implantation in rats. The present method gave fairly large microspheres purely composed of chitosan and drug because of no use of surfactant, which showed the mean particle diameters of 300-900 µm and the drug contents of 4-22% (w/w). Encapsulation efficiency of DFUR was higher than that of 5-FU and FT. DFUR-M and reacetylated DFUR-M exhibited spherical shape except chitosan-coated DFUR-M. DFUR-M showed high initial rapid release, which was suppressed to some extent by reacetylation or chitosan coating. DFUR-M and reacetylated DFUR-M subcutaneously implanted were gradually degraded, and approximately half or a little more of the microspheres disappeared from the implanted site at 3 weeks postimplantation. DFUR-M and reacetylated DFUR-M implanted subcutaneously gave similar plasma concentration-time profiles of DFUR, which did not indicate prolonged release in vivo. DFUR-containing chitosan microspheres with fairly large size and good drug content could be obtained by the present preparation but remained to be improved for drug release properties.     

纳米羟基磷灰石/聚氨酯载药微球的制备及性能

通过乳液聚合法制备了负载阿莫西林的纳米羟基磷灰石/聚氨酯(n-HA/PU)载药微球,通过正交设计实验对其制备工艺进行了优化,采用红外光谱、热重分析、扫描电镜等分析了微球的结构和性能,对其体外药物缓释过程进行探讨。研究结果表明,复合微球粒径大小与固含量、聚乙烯吡咯烷酮(PVP)含量、搅拌速度等有关,所制备的微球平均粒径为0.8~1.2mm;载药微球的优化制备工艺条件为:原料配比-NCO∶-OH=2∶1,预聚时间180min,预聚温度80℃,nHA含量3%,固含量7%,搅拌速度600r/min,PVP用量3%,所制备微球的载药量为6.58%,包封率为86.86%。体外缓释结果表明,载药微球的释药行为符合Higuchi动力学,半衰期(t1/2)为22.29h,具有良好的药物缓释作用。     

Microencapsulation of a hydrophilic drug into a hydrophobic matrix using a salting-out procedure. II. Effects of adsorbents on microsphere properties

Wax microspheres of the hydrophilic drug guaifenesin were prepared by the congealable disperse-phase method using a salting-out procedure. In order to improve the particle properties of the microspheres, adsorbents (colloidal silica, magnesium stearate, and talc) were used during preparation. The effects of adsorbents on microsphere properties such as the angle of repose (AR), compressibility index (CI), geometric mean diameter (GMD), loading efficiency (LE), and in vitro drug release (DR) were determined. The AR, CI, and GMD of the microspheres were significantly reduced in the presence of the adsorbents. Increase in the concentrations of colloidal silica and magnesium stearate led to lower LE and faster DR, while talc showed no effect, which could be due to the particle diameter and specific surface area of the adsorbents. The microspheres prepared with colloidal silica were chosen to be compressed into tablets since they were smaller, more uniform, and had better flow properties than those made with magnesium stearate and talc. The in vitro drug release profile of the microsphere tablets was compared with that of commercially available Mucinex®, sustained release guaifenesin matrix tablets. Similar release profiles were observed between the two tablets. Scanning electronic microscopy (SEM) studies of the broken tablets revealed that the deformation of the microspheres caused by compression was minimal.     

Eudragit coating of chitosan-prednisolone conjugate microspheres and in vitro evaluation of coated microspheres

Chitosan-prednisolone conjugate microspheres (Ch-SP-MS) were prepared, and Eudragit coating was applied in order to efficiently deliver the microspheres and drug to the intestinal disease sites. The Eudragit L100-coated microspheres (Ch-SP-MS/EuL100) were examined for particle characteristics and the release of drug and Ch-SP-MS in different pH media at 37°C. Ch-SP-MS were spherical, with a mean size of 4.5 μm and prednisolone content of 3.3% (w/w). Ch-SP-MS/EuL100 were fairly spherical, with a mean size of 22. 5 μm and drug content of 0.32% (w/w). At pH 1.2, the release extent was less than 5% even at 48 h, and Eudragit coating tended to suppress the release. In contrast, at pH 6.8 and 7.4, Ch-SP-MS/EuL100 tended to show somewhat faster drug release than Ch-SP-MS. Ch-SP-MS/EuL100 displayed a release extent of 23 and 27% at pH 6.8 and 7.4, respectively. Ch-SP-MS aggregated at pH 1.2, but almost kept their initial size and shape at pH 6.8 and 7.4. Ch-SP-MS/EuL100 almost maintained their original shape and size at pH 1.2, and gradually released Ch-SP-MS at pH 6.8 and 7.4 due to dissolution of the Eudragit layer. Eudragit coating is suggested to be useful to efficiently deliver Ch-SP-MS to the intestinal disease sites.     

Erosion characteristics of an erodible tablet incorporated in a time-delayed capsule device

A time-delayed oral drug delivery device was investigated in which an erodible tablet (ET), sealing the mouth of an insoluble capsule, controlled the lag-time prior to drug release. The time-delayed capsule (TDC) lag-time may be altered by manipulation of the excipients used in the preparation of the ET. Erosion rates and drug release profiles from TDCs were investigated with four different excipient admixtures with lactose: calcium sulphate dihydrate (CSD), dicalcium phosphate (DCP), hydroxypropylmethyl cellulose (HPMC; Methocel® K100LV grade) and silicified microcrystalline cellulose (SMCC; Prosolv® 90 grade). Additionally, the compressibility of different insoluble coated capsules was tested at different moisture levels to determine their overall integrity and suitability for oral delivery. Erosion rates of CSD, DCP, and SMCC displayed a nonlinear relationship to their concentration, while HPMC indicated rapid first-order erosion followed by zero-order erosion, the onset of which was dependent on the HPMC concentration. Capsule integrity was confirmed to be most suitable for oral delivery when the insoluble ethyl cellulose coat was applied to a hard gelatin capsule using an organic spray coating process. T_50% drug release times varied between 245 (± 33.4) and 393 (± 40.8) minutes for 8% and 20% DCP, respectively, T_50% release times of 91 (± 22.1) and 167 (± 34.6) were observed for 8% and 20% CSD; both formulations showed incidence of premature drug release. The SMCC formulations showed high variability due to lamination effects. The HPMC formulations had T_50% release times of 69 (± 13.9), 213 (± 25.4), and 325 (± 30.3) minutes for 15%, 24%, and 30% HPMC concentrations respectively, with no premature drug release. In conclusion, HPMC showed the highest reproducibility for a range of time-delayed drug release from the assembled capsule formulation. The method of capsule coating was confirmed to be important by investigation of the overall capsule integrity at elevated humidity levels. The erosion characteristics of ETs containing HPMC may be described by gravimetric loss. The novel time-delayed capsule device presented in this study may be assembled to include an erodible tablet with a known concentration of HPMC. A variety of suitable drugs for targeted chronopharmaceutical therapy can beincorporated into such a device, ultimately improving drug efficacy and patient compliance, and reducing harmful side effects.     

Preparation, in Vitro and in Vivo Evaluation of Liposomal/Niosomal Gel Delivery Systems for Clotrimazole

Clotrimazole, which is an imidazole derivative antifungal agent, was widely used for the treatment of mycotic infections of the genitourinary tract. To develop alternative formulation for the vaginal administration of clotrimazole to provide sustained and controlled release of appropriate drug for local vaginal therapy, liposomes/niosomes were evaluated as delivery vehicles. To optimize the preparation of liposomes/niosomes with regard to size and entrapment efficiency, multilamellar liposomes/niosomes containing drug were prepared by lipid hydration method. The prepared liposomes/niosomes were incorporated into 2% carbopol gel, and the systems were evaluated for drug stability in phosphate-buffered saline (pH 7.4) and simulated vaginal fluid at 37 ± 1°C. Further, the vesicle gel system was evaluated by antifungal activity and tolerability on tissue level in rat.     

Effect of Additives on Stability of Etoposide in PLGA Microspheres

The purpose of this article was to determine the shelf life of etoposide in poly(lacticco-glycolic acid) (PLGA) microspheres prepared with and without additives (i.e., tricaprin and isopropyl myristic acid ester [IPM]). The microspheres were prepared by a single-emulsion solvent extraction technique with and without 25% w/w additive. The batches of microspheres were subjected to an accelerated stability study at two elevated temperatures (70°C and 80°C or 80°C and 90°C). Samples were taken at 7, 14, 21, 28, and 35 days for estimation of drug content by high-performance liquid chromatography (HPLC). The drug stability in the microspheres was determined by plotting the log percentage drug remaining versus time to obtain the degradation rate constant k of etoposide at the measured temperature. This degradation rate constant was then used in the Arrhenius equation to obtain the activation energy of etoposide, which was utilized to determine the shelf life of the microspheres at room temperature. The results showed that all three microsphere formulations had good long-term stability at room temperature (6.62-8.86 years at 25°C). The plain microspheres were shown to possess a shelf life of 6.62 years, and the IPM and tricaprin were the most stable with shelf lives of 8.25 and 8.86 years, respectively.     

Investigation on Process Parameters Involved in Polylactide-Co-Glycolide Microspheres Preparation

Indomethacin loaded polylactide-co-glycolide (PLGA) microspheres were prepared by emulsification solvent evaporation. The preparation involves several process parameters that can affect the morphological characteristics, the “in vitro” and “in vivo” dissolution behaviour of microspheres.

The evaluation of three process parameters, emulsification stirring rate, emulsifier concentration and dispersed phase to continuous phase ratio was carried out in order to correlate them to some microsphere properties.

Results show that the variables evaluated affect mainly microspheres drug content and, at less extent, particle size.     

Influence of Stabilization Temperature on the Entrapment of Adriamycin in Albumin Microspheres

Adriamycin associated bovine serum albumin (BSA) microspheres have been prepared by the method involving emulsion and suspension technology. Stabilization of the carrier matrix was achieved by heat treatment at 105, 120, 135 and 150°C.

Following zero to four washings, each of these four batches of microspheres have been evaluated for the amount of associated adriamycin using HPLC. At high stabilization temperatures, migration of adriamycin to the microsphere surface is reduced leading to increased drug entrapment. Results demonstrate that the proportion of entrapped to total drug increases with increase in stabilization temperature of the carrier.     

Effect of heat on characteristics of chitosan film coated on theophylline tablets

The effect of heat on the characteristics of chitosan film coated on theophylline tablets was studied. Chitosan of high viscosity grade with molecular weight in the range of 800,000-1,000,000, 80-85% degree of deacetylation was used as a film former by dissolving in 1% v/v acetic acid solution. The coated tablets had been cured at 40, 60, and 100°C for 6, 12, and 24 hr. The morphology of the film at the edge and surface of coated tablets was investigated using scanning electron microscopy. Film cracking was increased and clearly observed in the coated tablets cured at 100°C for 24 hr. As a result, more water could be absorbed into the tablets, followed by faster disintegration and faster drug release. The evidence of partial conversion of chitosonium acetate to chitin in the ¹³C nuclear magnetic resonance (NMR) spectra of chitosan films cured at 40, 60, and 100°C was observed, but it had no effect on drug release behavior. Theophylline tablets coated with chitosan films gave sustained release behavior in various media, i.e., distilled water, 0.1 N hydrochloric acid, pH 4.5 acetate buffer, and pH 6.8 phosphate buffer. In addition, the film coating temperature at 55-60°C and curing process at 40 and 60°C had no effect on the drug release from theophylline tablets coated with chitosan polymer. Finally, it might be concluded that both the physical and chemical properties of chitosan films were affected by heat.     

Miscibility behavior and formation mechanism of stabilized felodipine-polyvinylpyrrolidone amorphous solid dispersions

In the present study, solid dispersion systems of felodipine (FEL) with polyvinylpyrrolidone (PVP) were developed, in order to enhance solid state stability and release kinetics. The prepared systems were characterized by using Differential Scanning Calorimetry, X-Ray Diffraction, and Scanning Electron Microscopy techniques, while the interactions which take place were identified by using Fourier Transformation-Infrared Spectroscopy. Due to the formation of hydrogen bonds between the carbonyl group of PVP and the amino groups of FEL, transition of FEL from crystalline to amorphous state was achieved. The dispersion of FEL was found to be in nano-scale particle sizes and dependent on the FEL/PVP ratio. This modification leads to partial miscibility of the two components, as it was verified by DSC and optimal glass dispersion of FEL into the polymer matrix since no crystalline structure was detected with XRD. The above deformation has a significant effect on the dissolution enhancement and the release kinetics of FEL, as it causes the pattern to change from linear to logarithmic. An impressive optimization of the dissolution profile is observed corresponding to a rapid release of FEL in the system containing 10% w/w of FEL, releasing 100% in approximately 20 min. The particle size of dispersed FEL into PVP matrix could be classified as the main parameter affecting dissolution optimization. The mechanism of such enhancement consists of the lower energy required for the dissolution due to the amorphous transition and the fine dispersion, which leads to an optimal contact surface of the drug substance with the dissolution media. The prepared systems are stable during storage at 40 ± 1°C and relative humidity of 75 ± 5%. Addition of sodium docusate as surfactant does not affect the release kinetics, but only the initial burst due to its effect on the surface tension and wettability of the systems.     

Carnauba Wax Microspheres Loaded with Valproic Acid: Preparation and Evaluation of Drug Release

Abstract

To minimize unwanted toxic effects of valproic acid (1) by the kinetic control of drug release, gastroresistant carnauba wax microspheres loaded with the antiepileptic agent were prepared. The preparation was based on a technique involving melting and dispersion of drug-containing wax in an aqueous medium. The resulting emulsion after cooling under rapid stirring produced solid, discrete, reproducible free flowing microspheres which converted the liquid drug droplets into solid material. About 94% of the isolated microspheres were of particle size range 200-425 μm. The microspheres were analyzed to determine the drug content in various particle size range and to characterize the in vitro release profile. The average drug content was 26% w/w. The intestinal drug discharge of 1 from the carnauba wax microspheres was studied and compared with the release patterns observed for white beeswax and hexadecanol microspheres previously described. The drug release performance was greatly affected by the material used in the microencapsulation process. In the intestinal environment carnauba wax microspheres exhibited more rapid initial rate of release and about 80% of the entrapped drug was discharged in 120 min while complete release occurred in about 8 h.     

Thermolysis and Photolysis of C60 Diozonides

Ozonation of C₆₀ in o-xylene produced three C₆₀(O₃)₂ diozonides that were separated from one another and from two C₆₀(O₃)₃ triozonides by High Performance Liquid Chromatography (HPLC). Upon thermolysis at 10, 15, and 16.6°C, each of the diozonides dissociated sequentially, first to a C₆₀O(O₃) oxyozonide, then to a C₆₀O₂ diepoxide. The three diepoxides were stable in solution for at least 3 weeks. The mean lifetimes of the three diozonides were 52 ± 5, 62 ± 6, and 17.3 ± 1.8 min, respectively (all at 15°C). The mean lifetimes of the three oxyozonides were 69.7 ± 0.7 and 58 ± 6 min at 16.6°C, respectively and about 240 min at 10°C. Photolysis of the diozonides yielded two dioxidoannulenes with UV-Vis adsorption maxima at 333 and 332 nm, and what appeared to be an epoxide-oxidoannulene with UV-Vis adsorption maximum at 327 nm. These annulenes were observed to form dimers. We have synthesized and characterized six C₆₀O₂ dioxides, at least three and possibly four of which were hitherto unknown. We report the discovery of oxyozonides that form during the dissociation of diozonides.     

Albumin Microspheres: effect of process Variables on size Distribution and in Vitro Release

Abstract

Albumin microspheres used as target drug delivery systems were prepared from egg albumin by polymerization technique using glutaral dehyde as the cross linking agent. The present study was designed to evaluate the effect of process variables on the nicrosphere size distribution and in vitro drug release. Phase volume ratio and speed of agitation exerted greater influence on the microsphere size distribution whereas the albumin concentration and cross linking time effected only the yield and surface characteristics of the microspheres respectively. Lower phase volume ratios resulted in small and uniform microspheres with smooth surfaces in narrow size range. Speed of agitation exhibited an inverse relationship with size. In vitro release pattern of drug from the microspheres showed a biphasic profile and the release rates were prolonged upon increase in the concentration of cross linking agent and cross linking time.