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PubMed2001

POE-PEG-POE triblock copolymeric microspheres containing protein. II. Polymer erosion and protein release mechanism.

The first paper of this series presented the fabrication and characterization of POE-PEG-POE triblock copolymeric microspheres containing protein. In this paper, we focus on the polymer erosion and the mechanism of protein release. Fourteen-week in vitro behaviors of POE-PEG-POE microspheres loaded with bovine serum albumin (BSA) have been monitored. SEM micrographs reveal that after 14-week incubation in PBS buffer, pH 7.4, 37 degrees C, the polymeric particles remain spherical despite mass loss of almost 90%. On the other hand, molecular weight undergoes a high initial loss of 38% and 44% during the first 2-week incubation for POE-PEG(5%)-POE and POE-PEG(10%)-POE, respectively. Then, it keeps relatively unchanged over 12 weeks. However, POE-PEG(20%)-POE copolymer provides a better compatibility between the POE and PEG blocks. Hydrolysis is homogeneous through the polymer backbone. Thus, its molecular weight remains relatively constant and mass loss shows quite sustained over the 14-week in vitro release. The similar phenomena are observed in the polydispersity index of the degrading copolymers. SDS-PAGE of the encapsulated BSA within the POE-PEG(5%)-POE microspheres displays that the structural integrity of BSA is intact for at least 8 weeks due to a mild environment provided by the copolymer. In addition, XPS and FTIR are utilized to investigate protein behaviors in the degrading microspheres. Protein release from the POE-PEG-POE microspheres shows a biphasic pattern, characterized by an initial stage followed by a non-detectable release. The non-release phase is dominated by either slow polymer degradation or dense microsphere matrix structures. The microsphere formulation is optimized and a sustained protein release over 2 weeks is achieved by using POE-PEG(20%)-POE at a high protein loading.

Animals↗
PubMed2001

Fabrication, characterization and in vitro release of paclitaxel (Taxol) loaded poly (lactic-co-glycolic acid) microspheres prepared by spray drying technique with lipid/cholesterol emulsifiers.

Spray dry technique was applied to produce paclitaxel loaded microspheres of biodegradable poly (lactic-co-glycolic acid) (PLGA) as an alternative delivery system. Various emulsifiers such as L-alpha-dipalmitoyl-phosphatidylcholine (DPPC), cholesterol, polyvinyl alcohol (PVA), gelatin were incorporated in order to achieve high encapsulating efficiency of paclitaxel in the microspheres and desired properties for a sustained release. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) showed that the surface of the microspheres with high ratio of lipid was spherical and smooth. Those made with other emulsifiers had rougher surface with pores. Incorporation of lipid, cholesterol or gelatin can significantly increase the drug content in the microspheres. The differential scanning calorimetry (DSC) result indicated that the paclitaxel trapped in the microspheres existed in an amorphous or disordered-crystalline status in the polymer matrix. The zeta potential of the microspheres was negative in general and was strongly influenced by the type of the emulsifiers used in fabrication. The system formulated with cholesterol was most stable. The release profiles of various formulations with PVA, gelatin as well as low ratio of DPPC showed almost zero-order release kinetics in the first 3 weeks after an initial burst less than 5% in the first day. The release rate then gradually decreased. The microspheres fabricated with high ratio of DPPC exhibited large initial burst. When cholesterol was combined together with DPPC as an emulsifier, the release became faster.

Antineoplastic Agents, Phytogenic↗
PubMed2003

Poly-D,L-lactide-co-poly(ethylene glycol) microspheres as potential vaccine delivery systems.

Adjuvants aimed at increasing the immunogenicity of recombinant antigens remain a focus in vaccine development. Worldwide, there is currently considerable care for the development of biodegradable microspheres as controlled release of vaccines, since the major disadvantage of several currently available vaccines is the need for repeated administration. Microspheres prepared from the biodegradable and biocompatible polymers, the polylactide (PLA) or polylactide-co-glycolide (PLGA), have been shown to be effective adjuvants for a number of antigens. This review mainly focuses on polylactide-co-poly(ethylene glycol) (PELA) microspheres adjuvant as vaccine delivery systems by summarizing our and other research groups' investigation on properties of the microspheres formulation encapsulating several kinds of antigens. The results indicate that compared with the commonly used PLA and PLGA, PELA showed several potentials in vaccine delivery systems, which may be due to the block copolymer have its capability to provide a biomaterial having a broad range of amphiphilic structure. PELA microspheres can control the rate of release of entrapped antigens and therefore, offer potential for the development of single-dose vaccines. The PELA microspheres have shown great potential as a next generation adjuvant to replace or complement existing aluminum salts for vaccine potential. The review mainly aims to promote the investigation of PELA microspheres adjuvant for antigens for worldwide researcher.

Animals↗
PubMed1999

Evaluation of mitoxantrone-loaded albumin microspheres following intraperitoneal administration to rats.

Mitoxantrone has demonstrated therapeutic efficacy in the regional treatment of intraperitoneal malignancies. However, severe local toxicity was dose limiting. Consequently, a new injectable sustained delivery formulation of mitoxantrone has been developed: the drug was incorporated (8.2 w/w%) in highly hydrophilic albumin microspheres. In vitro drug release profile was modified by matrix crosslinking extent. The extractable amount of residual crosslinking agent (glutaraldehyde) in the microspheres was lower than 6 ppm. Mitoxantrone concentration in peritoneal fluid and plasma was determined up to 72 h after intraperitoneal administration of 30, 60 and 120 mg mitoxantrone per m2 body surface area as solution and in the form of a dispersion containing mitoxantrone-loaded microspheres to rats. Data analysis revealed sustained release of mitoxantrone from microspheres into peritoneal fluid in all dosage groups. The initial high drug levels in peritoneal fluid and plasma observed after application of mitoxantrone in the solution form were prevented by administration of the drug incorporated in microspheres. However, tumoricidal drug levels in peritoneal fluid were maintained over a comparable time span. In addition, preliminary toxicity data suggest a superior local tolerability of mitoxantrone-loaded microspheres. The dose of intraperitoneally administered mitoxantrone might be increased from 30 to 60 mg per m2 body surface area using the slow release formulation. In conclusion, the described microsphere drug delivery system for mitoxantrone might overcome dose-limiting drug toxicity.

Albumins↗
PubMed1999

Encapsulation of rotavirus into poly(lactide-co-glycolide) microspheres.

Two small-scale double emulsion techniques for incorporation of formaldehyde-inactivated rotavirus particles (FRRV) into poly(lactide-co-glycolide) (PLG) microspheres were developed and optimised. The effects of high-speed homogenisation versus vortex mixing on the double emulsion stability, microsphere size, entrapment efficiency and in vitro release of FRRV in the second emulsification step were studied. A stable double emulsion was verified only when using vortex mixing in this step. Slow removal of the organic phase allowed measurement of the size of the emulsion droplets and subsequent prediction of the size of the resulting microspheres. Microspheres in the size range of 1-10 microm were prepared using both techniques. The homogenisation technique was sensitive to changes in the operating time, the emulsification energy and the volume of the outer aqueous phase, while the vortex technique was more robust. Rotavirus was released in vitro in a triphasic manner with both techniques. The more robust vortex technique was selected for preparation of PLG microspheres containing rotavirus for in vivo studies. After immunisation of mice with a single intramuscular injection, the PLG-FRRV microspheres elicited an IgG antibody response in serum detected by ELISA equally high as that elicited with FRRV alone. These results indicate that the antigenicity of FFRV was retained after incorporation into PLG microspheres using the vortex technique.

Animals↗
PubMed1999

Degradation and protein release properties of microspheres prepared from biodegradable poly(lactide-co-glycolide) and ABA triblock copolymers: influence of buffer media on polymer erosion and bovine serum albumin release.

The aim of the present study was to investigate the influence of the chemical insertion of poly(ethylene oxide), PEO, into a poly(lactide-co-glycolide), PLG, backbone on the mechanisms of in vitro degradation and erosion of the polymer. For this purpose microspheres prepared by a modified W/O/W double emulsion technique using ABA triblock copolymers, consisting of PLG A-blocks attached to central PEO B-blocks were compared with microspheres prepared from PLG. Due to their molecular architecture the ABA triblock copolymers differed in their erosion and degradation behavior from PLG. Degradation occurred faster in the ABA polymers by cleavage of ester bonds inside the polymer backbone. Even erosion was shown to start immediately after incubation in different buffer media. By varying pH and ionic strength of the buffer it was found that both mass loss and molecular weight decay were accelerated in alkaline and acidic pH in the case of the ABA triblock copolymers. Although the pH of the medium had a moderate influence on the degradation of PLG, the molecular weight decay was not accompanied by a mass loss during the observation time. In a second set of experiments we prepared bovine serum albumin, BSA, loaded microspheres from both polymers. The release of BSA from ABA microspheres under in vitro conditions parallels the faster swelling and erosion rates. This could be confirmed by electron paramagnetic resonance, EPR, measurements with spin labeled albumin where an influx of buffer medium into the ABA microspheres was already observed within a few minutes. In contrast, PLG microspheres revealed a burst release without any erosion. The current study shows that the environmental conditions affected the degradation and erosion of the pure polymer microspheres in the same way as the release of the model protein. This leads to the conclusion that the more favorable degradation profile of the ABA triblock copolymers was responsible for the improvement of the release profile.

Animals↗
PubMed2001

Degradable dextran microspheres for the controlled release of liposomes.

A novel delivery concept based on the encapsulation of liposomes in biodegradable dextran microspheres was developed. The microspheres were prepared using a two-phase system, consisting of water/poly(ethylene glycol), and water/methacrylated dextran. Liposomes were encapsulated almost quantitatively and in their intact form, and were released with full preservation of their integrity. The effects of microsphere water content, degree of methacrylate substitution, and type of dextran derivative used on the release rate were investigated. The release of the liposomes from the dextran microspheres was fully controlled by the degradation rate of the spheres. This resulted, after a lag time, in a pulsed release of the liposomes from relatively rapidly degrading microspheres. On the other hand, slower degrading microspheres resulted in sustained release of liposomes over 100 days. The degradation rate of the dextran microspheres, in turn, depended on the water content, the degree of methacrylate substitution, and type of hydrolytically sensitive spacer present in the cross-links.

Dextrans↗
PubMed2001

Long-term delivery of all-trans-retinoic acid using biodegradable PLLA/PEG-PLLA blended microspheres.

All-trans-retinoic acid (atRA) has been proved to be effective against several malignancies in human clinical trials. However, in many patients who were treated with atRA, the cancer relapsed after a brief remission. One reason for such relapse is that atRA is metabolized by specific P450s that are induced in the liver during prolonged atRA treatments. In order to overcome such a drawback of atRA, we prepared biodegradable microspheres to provide continuous release of atRA for a long period of time. These biodegradable microspheres were prepared by poly(L-lactide) (PLLA) and polyethylene glycol (PEG)-PLLA diblock copolymers (PLE) in various blending ratios to control the release rate of atRA. As the PLE content in microsphere was increased, the density of the hydrophilic PEG block of PLE on microsphere surfaces increased and the microspheres were dispersed well in PBS without any surfactants. Various release patterns of atRA were obtained according to PLE and atRA contents in the microspheres. Especially, the pseudo-zero-order release profiles were observed for 5 weeks when the contents of PLE and atRA in the microspheres were above 4 wt.%.

Excipients↗
PubMed2001

Gelatin microspheres crosslinked with D,L-glyceraldehyde as a potential drug delivery system: preparation, characterisation, in vitro and in vivo studies.

To overcome the restriction in using crosslinked gelatin in the pharmaceutical field, D,L-glyceraldehyde (GAL), a non-toxic crosslinking agent, was proposed. Gelatin microspheres crosslinked with different concentrations of GAL (0.5, 1 or 2%, w/v) and for different time periods (1 or 24 h) were prepared. The effect of the preparation variables was evaluated analysing the extent of crosslinking, the morphological aspect, the particle size and the swelling behaviour. To evaluate the pharmaceutical properties, an antihypertensive drug, clonidine hydrochloride, was chosen as drug model and loaded into the microspheres. Either the increase of the crosslinker concentration or of the crosslinking time period decreased both the swelling and the in vitro drug release processes of the microspheres. After the subcutaneous injection, the loaded microspheres crosslinked with the lowest GAL concentration (0.5%, w/v) or for the shortest time period (1 h) showed a reduction of systolic blood pressure (SBP) similar to that recorded with a clonidine hydrochloride solution having the same drug concentration. Instead, the microspheres crosslinked for 24 h with concentrations of GAL higher than 0.5% (w/v) produced a more gradual and sustained SBP reduction and the antihypertensive effect was maintained until 52-72 h. The biocompatibility studies showed that the microspheres crosslinked with GAL are well tolerated in vivo. These results suggest the potential application of gelatin microspheres crosslinked with GAL as a suitable drug delivery system for the subcutaneous administration.

Animals↗
PubMed2001

Bioavailability of cyclosporin A dispersed in sodium lauryl sulfate-dextrin based solid microspheres.

The purpose of this work was to develop a solid dispersion system containing cyclosporin A (CsA) in order to improve the bioavailability of poorly water-soluble CsA. Solid dispersion systems that are spherical in shape (CsA-microspheres) were prepared with varying ratios of CsA/sodium lauryl sulfate/dextrin using a spray-drying technique. The effects of sodium lauryl sulfate (SLS) and dextrin on the dissolution of CsA dispersed in SLS-dextrin based solid microspheres were investigated. The bioavailability of CsA-microspheres was compared with CsA powder alone and commercial Sandimmun in dogs. SLS significantly enhanced the dissolution of CsA from microspheres, while dextrin did not affect this. The CsA-microspheres at the CsA/SLS/dextrin ratio of 1/3/1, which gave the highest dissolution rate of CsA among the formula treated, was selected as an optimal formula for oral delivery. This formula gave significantly higher blood levels, area under the drug concentration-time curve (AUC) and maximum blood concentration of drug (Cmax) of CsA in dogs compared with the CsA powder alone. The AUC, Cmax and time to reach maximum blood concentration (Tmax) of CsA with CsA-microspheres was not significantly different from those after oral administration of Sandimmun, suggesting the similar bioavailability to Sandimmun in dogs. Our study demonstrates that the CsA-microspheres prepared with SLS and dextrin, with improved bioavailability of CsA, would be useful to deliver a poorly water-soluble CsA and could be applicable to other poorly water-soluble drugs.

Animals↗
PubMed2002

Adsorption of an ionizable drug onto microspheres: experimental and modeling studies.

The purpose of this work was to study the in vitro equilibria and the adsorption kinetics of an ionizable drug, indomethacin, onto commercially available cationic polymeric microspheres: DEAE Trisacryl LS and QA Trisacryl LS. Isotherms were fitted to theoretical equations allowing accurate predictions of drug loading at different salt concentrations. Isotherm measurements were quickly obtained by simple column breakthrough experiments. The nature of the ion exchange group of the microspheres was observed to be preponderant for adsorption, as the tertiary amine derivative exhibited 53% more capacity than its quaternary amine counterpart. The maximum equilibrium uptake capacity in a 5 mM Tris-HCl buffer at pH 7.4 is 303 mmol/ml of particle volume, for DEAE microspheres. Transport properties of indomethacin into the tertiary amine microspheres were obtained in agitated contactor. Microbeads loading was completed in a 1-6 min range and was found to be controlled by pore diffusion mechanism. Equilibrium uptake data was fitted to the Langmuir and the mass action law models. Adsorption kinetics were fitted to a pore diffusion model. Good correlation was obtained between the theoretical models and the experimental data. The methodology outlined in this work provided a simple approach of estimating adsorption behavior of drugs onto ion-exchange macroporous microspheres. Although significant indomethacin loading was obtained onto the DEAE microspheres, the rapid rate of diffusion is not compatible with sustained release properties sought for this type of microspheres.

Adsorption↗
PubMed2002

Formulation factors in preparing BTM-chitosan microspheres by spray drying method.

Chitosan (CTS) microspheres were prepared by a spray drying method using type-A gelatin and ethylene oxide-propylene oxide block copolymer as modifiers. Surface morphological characteristics and surface charges of prepared microspheres were investigated by using scanning electron microscopy (SEM) and microelectrophoresis. The particle shape, size and surface morphology of microspheres were significantly affected by the concentration of gelatin. Betamethasone disodium phosphate (BTM)-loaded microspheres demonstrated good drug stability (less 1% hydrolysis product), high entrapped efficiency (95%) and positive surface charge (37.5 mV). The in vitro drug release from the microspheres was related to gelatin content. Microspheres containing gelatin/CTS 0.4 approximately 0.6(w/w) had a prolong release pattern for 12 h. These formulation factors were correlated to particulate characteristics for optimizing BTM microspheres in pulmonary delivery.

Anti-Inflammatory Agents↗
PubMed2003

The effect of the drug/polymer ratio on the properties of the verapamil HCl loaded microspheres.

In this study, the microspheres containing verapamil hydrochloride (VRP) were prepared with Eudragit RS 100 by solvent evaporation method. In the solvent evaporation method one of the parameters which affect to the formation and properties of the microspheres is the variations of drug/polymer ratios. The aim of our study is to examine the effects of this parameter on the VRP loaded microspheres. To achieve this purpose, only drug/polymer ratio was altered while the other formulation parameters were kept constant and percentage yield value, incorporation efficiency, particle size and distribution of the microspheres were analyzed and micrographs of the microspheres were taken to determine the effects of the increase in the polymer amount of formulations. All the dispersed phase viscosities were evaluated by comparing them with the variations in particle size and distribution of the microspheres. In vitro dissolution tests were done by using dissolution media with three different pH in sequence as half-change method with flow through cell and the effect of the variation in polymer ratio on drug dissolution was evaluated according to dissolution test results. As a result of our study, it is thought that the variation in drug/polymer ratios might have an influence on the physical characteristics of the microspheres and the increasing amount of polymer might be result in decreased drug dissolve.

Chemistry, Pharmaceutical↗
PubMed1999

The characterization and release kinetics evaluation of baclofen microspheres designed for intrathecal injection.

Baclofen, a water soluble drug advocated for the treatment of spinal spasticity, was microencapsulated, using the oil/water emulsion extraction process in an attempt to identify the appropriate experimental conditions capable of producing microspheres releasing baclofen over 2-4 weeks. Individual microspheres ranging in size from 15 to 30 microns were formed exhibiting smooth surfaces at low drug payload (12.8% w/w), irregular and rough surface at high drug content (33.9% w/w). The microencapsulation yield remained practically unchanged (85-90%) up to theoretical payloads of 37.5% w/w, and decreased markedly to 70% when the initial theoretical payload was 50% w/w. The in vitro release profile of baclofen from the poly(D,L-lactide-co-glycolide) microspheres was biphasic only for the high drug payload microspheres with a rapid release of 70% within 48 h, followed by a slower release rate over at least 25 days. In contrast, the microspheres containing low baclofen contents (12.8% w/w) exhibited a gradual and progressive release rate over the course of the experiment. The baclofen release data did not fit either the general equation which describes the diffusional release of dispersed tiny drug particles from spherical micromatrices, or to the kinetic equations which describe the release of dissolved drug from monolithic microspherical devices. It appears that the release of baclofen from the present microspheres is not governed by a unique mechanism. This should be attributed either to the presence of some uncoated drug particles or to the large size of the embedded drug particles compared with the relatively small size of the spherical micromatices, or to some polymeric erosion occurring after several days incubation in the release medium.

Baclofen↗
PubMed1999

Protein encapsulation in biodegradable amphiphilic microspheres.

MPOE-PLA microspheres containing bovine serum albumin (BSA) were prepared by the double emulsion method with high encapsulation efficiency ( approximately 93%). Confocal scanning microscopic analysis using MPOE-PLA labelled with 1-pyrenemethanol showed the MPOE coating of the microsphere surface. This coating improves the performance of the release system compared with PLA microspheres; the hydrophilic chains reduce the BSA adsorption onto the microspheres and increase the amount of BSA released in the supernatant. Microsphere analysis using atomic force microscopy showed that the presence of the MPOE chains also leads to surface roughness. Studies of the diffusion of 1% rhodamine aqueous solution into the microspheres by means of confocal microscopy showed a fast diffusion of water through the matrices containing high molecular weight MPOE chains (?10 000 g mol-1) and could explain the fast release of BSA from these microspheres.

Adsorption↗
PubMed1999

Poly(acrylic acid) microspheres containing beta-cyclodextrin: loading and in vitro release of two dyes.

Microspheres containing poly(acrylic acid) and beta-cyclodextrin or maltose were prepared by a w/o solvent evaporation technique. The dispersed aqueous phase contained poly(acrylic acid) (800 mg) and beta-cyclodextrin or maltose (0, 200 or 800 mg). Food-grade olive oil was the continuous phase. Microsphere particle size was consistently between 15 and 25 microm, and carbohydrate content was in good agreement with that added to the dispersed phase in all cases. Two dyes, phenolphthalein and rhodamine B, having different solubility characteristics and strengths of association with beta-cyclodextrin, were selected for loading and in vitro release studies. Microspheres were loaded by soaking in a saturated propan-2-ol solution of the appropriate dye (6 h). Microsphere dye content ranged between 2.8 and 4.8 mg/g microspheres for phenolphthalein and between 2.2 and 3.7 mg/g for rhodamine B. Release studies were performed in phosphate buffer (pH 7.4; 37 degrees C). No difference in the release profile of either dye was observed between microspheres. The failure of microspheres containing beta-cyclodextrin in particular, to alter the in vitro release kinetics of either dye may be due to a number of factors and include: (i) limited cross-linking giving rise to a the rapid hydration of the polymer matrix; (ii) perturbation of the dye-beta-cyclodextrin complex by oil and/or organic solvent residues; and (iii) conformational changes/steric hindrance of the beta-cyclodextrin cavity (due to its covalent binding with PAA) resulting in a reduction in its ability to form inclusion complexes.

Acrylic Resins↗
PubMed2003

Preparation of bupivacaine-loaded poly(epsilon-caprolactone) microspheres by spray drying: drug release studies and biocompatibility.

Poly(epsilon-caprolactone) microspheres containing bupivacaine were prepared by the spray-drying process. The average size of drug loaded microspheres was less than 3 microm in diameter, and the percentage of entrapment efficiency was 91 +/- 3%. In vitro drug release kinetic in phosphate buffer at 37 degrees C showed a hyperbolic profile, with a burst-effect during the first hour. Subcutaneous injection of bupivacaine-loaded microspheres in the back of rats caused an increase in drug concentration in plasma. Maximum bupivacaine concentration in plasma was 237 +/- 58 ng/ml at 105 h, and drug was detected in plasma for 16 days. The half-life time of the drug was increased by more than 125 times with regard to that of the drug administered in a solution by intraperitoneal injection. After 30 days of injection, a mass formed by microspheres surrounded by a thin fibrous capsule was observed. Small blood vessels and multinucleate foreign body giant cells with macrophagic function around microspheres were detected. After 60 days of injection a subcutaneous mass was also observed, which was formed of more degraded dispersed microspheres in conjunctive tissue, which had a normal structure. Thus, bupivacaine-loaded poly(epsilon-caprolactone) microspheres could be considered as a device to be used in the treatment of severe pain that is not responsive to opioids for example in cancer-related syndromes or in intractable herpetic neuralgia.

Anesthetics, Local↗
PubMed2004

Cytarabine release from comatrices of albumin microspheres in a poly(lactide-co-glycolide) film: in vitro and in vivo studies.

Cytarabine (ara-C) was included in albumin microspheres and these microspheres were immersed in a poly(lactide-co-glycolide) (PLGA) film to constitute a comatrix system to develop a prolonged form of release. Cytarabine-loaded albumin microspheres were synthesized by emulsion, and 25 or 50 mg of drug were included in the disperse phase. Thus, microspheres with 46+/-4 microg drug/mg microspheres and 50+/-5 microg drug/mg microspheres were obtained, which means a percentage of incorporation efficiency of 42+/-4% and 25+/-2%, respectively. These cytarabine-loaded microspheres were used to prepare PLGA-comatrices. Kinetic release studies indicated that total cytarabine release only takes place in the presence of protease, probably due to the fact that glutaraldehyde establishes covalent links with the amine side group of the drug and cross-links it with the protein matrix. A slower kinetic release of the drug was obtained from PLGA-comatrices, although only 80% of the included cytarabine was released on day 7. The comatrices were subcutaneously implanted in the back of rats and in both cases the ara-C administered dose was 36 mg of ara-C per kg of body weight. The drug was detected in plasma 10 days. The mean residence time (MRT) of the drug administered by these comatrices was 87-91 times larger when compared to the value obtained when the drug was administered in solution by intraperitoneal injection. The histological studies show that a degradative process of the comatrices takes place. The comatrices do not damage surrounding tissue; a normal regeneration of the implanted zone was observed.

Animals↗