Preparation of microspheres by the solvent evaporation technique

Localization of bovine serum albumin in double-walled microspheres

Phase separation of binary blends of various combinations of poly (L-lactide) (PLA), and poly (D,L-lactide-co-glycolide) (PLGA), was investigated using differential scanning calorimetry (DSC). Based on this phase separation phenomenon, double-walled microspheres were fabricated. A model agent, bovine serum albumin (BSA) labeled with fluorescein isothiocyanate (FITC-BSA) was localized in each layer. Scanning electron microscopy (SEM) and fluorescence microscopy (FM) were used to assess the formation of double-walled microspheres and the localization of the drug, respectively. When a 1:1 polymer ratio was used, the FITC-BSA was localized in the outer layer. When the relative ratio of PLGA to PLA was increased to 3:1 using the same overall polymer concentration, the FITC-BSA was localized in the inner core. Release studies were carried out to evaluate the advantage of double-walled microspheres compared to single walled microspheres. Microspheres made with FITC-BSA localized in the inner core exhibited a significantly lower initial release rate compared to microspheres where the drug was located in the outer layer, or compared to microspheres made from PLA only. Hence microspheres with a double-walled morphology have the potential for therapeutic use where a high burst might be detrimental.

A potential approach for decreasing the burst effect of protein from PLGA microspheres

A central issue in controlled delivery of therapeutics from biodegradable microspheres is the immediate burst of drug release upon injection. This burst is often observed with microsphere systems made by the double emulsion (w/o/w) technique, and may be prevented by improving the drug distribution throughout the polymer matrix. To this end, protein and polymer (poly-lactide-co-glycolide or PLGA) were dissolved within the same solvent system, and micron-sized microspheres were created from this solution by spontaneous emulsification. Improved protein loading was achieved by ion-pairing the protein with charged surfactants to increase solubility in the single-phase solvent system. Both in vitro and in vivo results showed a much diminished burst: compared to microspheres made by double emulsion, it was reduced over 10-fold.

In situ pore formation in a polymer matrix by differential polymer degradation

A new approach for the in situ formation of porosity in a matrix based on differential polymer degradation has been studied. This approach exploits the differences in polymer properties such as molecular weight, hydrophilicity (hydrophobicity), and degradation to induce preferential degradation of one phase in a biphasic polymer system. Biphasic polymer systems polymers derived from alpha-hydroxy acids and poly(anhydrides), which vary in their erosion characteristics (surface vs. bulk) and hydrophobicities were studied. In addition to examining the generality of the approach, potential advantages of such systems in the context of tissue engineering and drug delivery are briefly discussed.

Evaluation of PLGA microspheres as delivery system for antitumor agent-camptothecin

Camptothecin (CPT) and its analogues are a new class of anticancer agents that have been identified over the past several years. Camptothecin exists in two forms depending on the pH: An active lactone form at pH below 5 and an inactive carboxylate form at basic or physiological neutral pH. Poly(lactide-co-glycolide) (PLGA) microspheres have been considered good delivery vehicles for CPT because of acidic microenvironment formed through PLGA degradation. The objective of this study is to investigate antitumor activity of CPT after it is encapsulated in PLGA microspheres. In this study, PLGA microspheres containing various CPT loadings were prepared and characterized. Cytotoxicity of these microspheres to B16 melanoma cells was then evaluated, and uptake of microspheres by B16 cells was also studied. Analysis of drug stability revealed that CPT is released from the microspheres in its active lactone form over the entire release duration. It was also found that there was no interaction between CPT and PLGA matrix within microspheres through Differential Scanning Calorimetry (DSC) and Fourien Transform Infrared Spectroscopy (FT-IR) and hign performance liquid chromatography (HPLC) studies. Cytotoxicity assay showed that CPT encapsulated in PLGA microspheres still retained its antitumor potency. Uptake study revealed quick uptake of the microspheres by B16 cells, which was desirable. It was concluded that PLGA microspheres were suitable delivery vehicles to stabilize and deliver CPT for the treatment of cancer.

Poly(D,L-lactide-co-glycolide) encapsulated poly(vinyl alcohol) hydrogel as a drug delivery system

PURPOSE

The efficiency of encapsulation of water-soluble drugs in biodegradable polymer is often low and occasionally these microcapsules are associated with high burst effect. The primary objective of this study is to develop a novel microencapsulation technique with high efficiency of encapsulation and low burst effect.

METHOD

Pentamidine was used as a model drug in this study. Pentamidine/polyvinyl alcohol (PVA) hydrogel was prepared by freeze-thaw technique. Pentamidine loaded hydrogel was later microencapsulated in poly(lactide-co-glycolide) (PLGA) using solvent evaporation technique. The microcapsules were evaluated for the efficiency of encapsulation, particle size. surface morphology, thermal characteristic, and drug release.

RESULT

Scanning Electron Microscope (SEM) studies revealed that the microcapsules were porous. The microcapsules were uniform in size and shape with the median size of the microcapsules ranging between 27 and 94 microm. The samples containing 10% PLGA showed nearly three times increase in drug loading (18-53%) by increasing the hydrogel content from 0-6%. The overall drug release from the microencapsulated hydrogel, containing 3% and 6% PVA, respectively. was significantly lower than the control batches.

CONCLUSION

The use of a crosslinked hydrogel such as PVA can significantly increase the drug loading of highly water-soluble drugs. In addition. incorporation of the PVA hydrogel significantly reduced the burst effect and overall dissolution of pentamidine.

Characterization of ciclosporin A loaded poly (D,L lactide-co-glycolide) microspheres using modulated temperature differential scanning calorimetry

The aim of this study was to investigate the physical structure of poly (D,L lactide-co-glycolide) (PLGA) microspheres loaded with ciclosporin A in terms of the amorphous properties of the individual components and the phase separation characteristics of the binary systems. Microspheres were prepared using a standard oil-in-water emulsion technique. The thermal properties of the PLGA, ciclosporin A and loaded spheres were investigated using modulated temperature differential scanning calorimetry (MTDSC) using a TA Instruments MTDSC 2920, with scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and high-performance liquid chromatography used as supportive techniques. MTDSC indicated a glass transition for ciclosporin A in the reversing heat flow signal at 107 degrees C, supported by temperature cycling studies, while XRD showed clear evidence for diffraction peaks, thereby indicating that the material as received is semi-crystalline. The unloaded PLGA spheres showed a glass transition (Tg) at 43 degrees C, with no reduction in Tg being observed on loading the peptide up to 50%, w/w. Similarly, no evidence for diffraction peaks were seen for the drug-loaded systems, although the glass transition corresponding to the peptide was observed for the loaded microspheres, suggesting that the drug is present as a separate amorphous phase. Similarly, SEM studies showed the appearance of distinct "islands" on the surface of the spheres that are suggested to correspond to the drug phase, with the size of the islands increasing with drug loading. Evidence is therefore presented that ciclosporin A may exist in a range of solid states, with the degree of crystallinity being altered by processing. In addition, there appears to be little or no miscibility between the drug and PLGA using the manufacturing protocol employed here. These findings may have implications for the choice of manufacturing protocol, the release of peptide drugs from PLGA microspheres and the chemical and physical stability of such drugs.

Sustained release of etanidazole from spray dried microspheres prepared by non-halogenated solvents

Etanidazole, a kind of radiosensitizer, was encapsulated in the spray-dried microspheres using biodegradable polymer PLGA 65:35 as the carrier for controlled release applications. Two non-halogenated solvents, e.g., ethyl acetate (EA) and ethanol, were tested to modify the properties of microspheres prepared by the commonly used solvent dichloromethane (DCM) alone. Their effects on the release behavior, morphology, particle size, and encapsulation efficiency of etanidazole-loaded microspheres were determined, and results were compared with DCM. The particle formation process via spray drying technique was also analyzed in order to understand the results obtained. It was found that larger percentage of EA (in the solvent mixture consisting of DCM and EA) in the fabrication of PLGA 65:35 microspheres decreases the initial burst, release rate and prolongs the release duration of etanidazole. In contrast to the spherical and porous microspheres prepared by DCM, the microspheres prepared by the solvent EA are all nonporous with a doughnut like surface structure due to its comparatively rapid phase transition (phase inversion) but slow solvent evaporation rate (longer time required to solidify). Increasing the polymer concentration (e.g., 4%, w/v) can bring about much more spherical microspheres by spray drying. Although ethanol, as a co-solvent, can dissolve a higher amount of etanidazole and lead to a higher drug encapsulation efficiency, the addition of ethanol in the DCM solvent can significantly increase the initial burst and the release rate of the microspheres due to the inhomogeneous drug distribution and structure of microspheres caused by phase separation. This study shows that ethyl acetate is an excellent low-toxic solvent that can be used in the spray drying technique for decreasing the initial burst, prolonging the release duration of a highly water-soluble drug like etanidazole. The use of EA provides a promising way to develop a sustained release system for etanidazole and other highly water-soluble drugs.

Biocompatible stabilizers in the preparation of PLGA nanoparticles: a factorial design study

Poly(lactic-co-glycolic-acid) nanoparticles are often produced using the w/o/w emulsification solvent evaporation method. In most cases poly(vinyl alcohol) (PVA) is used as stabilizer of the emulsion. The goal of this study was to compare a series of polymers to PVA in a 2(2) full factorial design study. The influence of the concentration of PVA and the polymers tested on particle size and zeta potential value was evaluated before and after freeze-drying of the prepared particles. Nanoparticles were obtained with most polymers when they were used in combination with PVA. Leaving PVA out of the formulation, however, increased the size of the particles over 1 microm. Two exceptions are poloxamer and carbopol, which can be considered as valuable alternatives to PVA. Zeta potential values were usually slightly negative, the most extreme zeta potential values were measured when poloxamer and carbopol were employed. The use of gelatin type A made it possible to achieve positive values. The original 2(2) full factorial design study was further expanded to a central composite design for poloxamer and carbopol, in order to fit the measured data to a quadratic model and to calculate response surfaces.

Characterization of biodegradable drug delivery vehicles with the adhesive properties of leukocytes

The site-specific expression of selectins (E- and P-selectin) on endothelial cells of blood vessels during inflammation provides an opportunity for the targeted delivery of anti-inflammatory drugs to inflammatory sites. Previous work in our laboratory has shown that artificial capsules with the adhesive properties of leukocytes can be made by attaching leukocyte adhesive ligands to polystyrene microspheres. In this work, we have adapted this technology to create a targeted delivery system using biodegradable, poly lactic-co-glycolic-acid (PLGA) microspheres. Biotinylated-Sialyl Lewis(x) (sLe(x)), a carbohydrate that serves as a ligand to selectins, was attached to the surface of avidin-linked PLGA microspheres. These carbohydrate-coated microspheres mimic the adhesive behavior of leukocytes on selectins in flow chambers, displaying slow rolling under flow. The rolling velocities displayed by sLe(x)-coated microspheres were similar to those displayed by leukocytes rolling on P- or E-selectin coated surfaces, and these rolling velocities, which relate to the residence time of the capsules, can be tuned by changing the density of carbohydrate residues on microsphere surfaces. We have also demonstrated that these microspheres will release model drugs on a time scale of several days. Therefore, we have made a targeted drug delivery vehicle that mimics the adhesive properties of leukocytes and is biodegradable.

Release mechanisms from gentamicin loaded poly(lactic-co-glycolic acid) (PLGA) microparticles

To provide local gentamicin delivery for 1 week based on a biodegradable system, poly(lactic-co-glycolic acid) (PLGA) microparticles were developed utilizing a 50/50 blend of Resomer RG 502H, an uncapped variety of 13.5 kD, and Resomer RG 503, an endcapped polymer of 36.2 kD. The liberation mechanism was investigated by analysis of morphological changes and thermal analysis focusing on the polymer glass transition temperature (T(g)) and the mechanical properties. The release of gentamicin was related to a structural breakdown of the particles reaching a critical molecular weight. A T(g) of < 37 degrees C in the hydrated state was not indicative of collapse and agglomeration of the particles because the mechanical strength of the polymer structures in the rubbery state may still render sufficient support. As the gap between incubation temperature and T(g) widened, the mechanical stability of the PLGA microparticles decreased and became decisive. Particles prepared with RG 502H show a lower ability to bear mechanical stress than RG 503 and 50/50 RG 502H/RG 503 microparticles.

Influence of irradiation sterilization on poly(lactide-co-glycolide) microspheres containing anti-inflammatory drugs

Gamma-irradiation is finding increasing use in the sterilization of pharmaceutical products. However, irradiation might also affect the performance of drug delivery systems. In this study, the influence of gamma-irradiation on the physicochemical properties of two commonly used non-steroidal anti-inflammatory drugs (NSAIDs) [naproxen sodium (NS) and diclofenac sodium (DS)] was investigated. The drugs were incorporated in poly(lactide-co-glycolide) (PLGA, 50:50; molecular weight 34000 or 88000 Da) microspheres. The biodegradable microspheres were irradiated at doses of 5, 15, 25 kGy using a 60Co source. Drug loading of irradiated and non-irradiated microspheres with both 34000 and 88000 Da polymers were essentially the same. A significant difference was noticed in the particle sizes of the irradiated as compared to the non-irradiated formulations. Notably, in release studies, the amount of active substance released from PLGA microspheres showed an increase with increasing irradiation dose. In DSC, the glass transition temperatures (Tg) of microspheres exhibited a slow increase with irradiation dose.

Preparation of Silica Particles Encapsulating Retinol Using O/W/O Multiple Emulsions

Retinol, a cosmetic ingredient, was entrapped within inorganic microspheres obtained from sol-gel reaction of TEOS in o/w/o multiple emulsions as microreactors. In o/w/o multiple emulsions, the retinol was emulsified as an internal oil phase in a aqueous solution of 3.0 wt% Tween 20 prior to emulsification into an external oil phase. The multiple emulsions appeared to be stable enough in the presence of HPC polymer in the external oil phase. In sol-gel reaction, the hydrolysis and condensation rate of TEOS were greatly dependent upon the catalyst and the molar ratio of H(2)O to TEOS (R(W)). In this study, sphere-like microspheres entrapping retinol were best formed with the addition of NH(4)OH as a catalyst when the concentration of TEOS was at the R(W) value of 4. Microspheres obtained under these conditions were 15-40 &mgr;m with very dense surfaces containing a few globules 1.17-2.35 &mgr;m. Also, they showed the slower release of retinol into the external ethanol phase and higher loading and encapsulation efficiency. Copyright 2001 Academic Press.

Targeting drug delivery to radiation-induced neoantigens in tumor microvasculature

Radiation can be used to guide drugs to specific sites such as neoplasms or aberrant blood vessels. When blood vessels are treated with ionizing radiation, they respond by expressing a number of cell adhesion molecules and receptors that participate in homeostasis. Examples of radiation-induced molecules in blood vessels include ICAM-1, E-selectin, P-selectin and the beta(3) integrin. We have observed that the endothelium and blood components respond to oxidative stress in a similar, if not identical manner in all tumor models. Although we have identified several other radiation-induced molecules within tumor blood vessels, the beta(3) target for drug delivery achieves the greatest site-specific peptide binding within irradiated tumor blood vessels. We have focused on peptides and antibodies that bind to integrin beta(3). beta(3)-binding proteins have been conjugated to fluorochromes and radionuclides to study the site specificity and microscopic distribution. We have found immunofluorescent and immunohistochemical staining of beta(3) within the lumen of blood vessels immediately following irradiation. To determine whether it is feasible to guide drug delivery to irradiated tumors, we studied ligands to alpha(2b)beta(3) (fibrinogen). Peptides within fibrinogen that bind to alpha(2b)beta(3) includes the dodecapeptide, HHLGGAKQAGDV and the RGD peptide. We utilized 131I conjugation to these ligands to study the biodistribution in tumor bearing mice. Our clinical trial consists of the RGD peptidomimetic, biapcitide, labeled with 99mTc. This study shows that it is feasible to guide drugs to human neoplasms by use of radiation-guided peptides. These studies have shown that peptides that bind to these integrins bind to tumors following exposure to ionizing radiation.

An investigation into the effects of residual water on the glass transition temperature of polylactide microspheres using modulated temperature DSC

The objective of the study was to ascertain residual water levels in polylactide and polylactide-co-glycolide microspheres prepared using the solvent evaporation technique and to investigate the effects of that water on the glass transitional behaviour of the microspheres. Microspheres were prepared from polylactic acid (PLA) and polylactide-co-glycolide (PLGA) 50:50 and 75:25 using a standard solvent evaporation technique. The glass transition was measured as a function of drying conditions using modulated temperature DSC. The microspheres were found to contain very low levels of dichloromethane, while residual water levels of up to circa 3% w/w were noted after freeze or oven drying, these levels being higher for microspheres containing higher glycolic acid levels. The residual water was found to lower the T(g) following the Gordon-Taylor relationship. The data indicate that the microparticles may retain significant water levels following standard preparation and drying protocols and that this drying may markedly lower the T(g) of the spheres.

Effect of chloroquine on phagolysosomal fusion in cultured guinea pig alveolar macrophages: implications in drug delivery

The aim of this study was to evaluate the effects of chloroquine on phagolysosomal fusion (PLF) in cultured guinea pig alveolar macrophages (AMs). This technique may be of significance for antitubercular drugs, because.the survival of Mycobacterium tuberculosis is linked to evasion of PLF. Guinea pig AMs were obtained from anesthetized animals after exsanguination. The AMs were cultured at a density of 1 x 10(6) cell/mL in 24-well plates after attachment to 13-mm coverslips. Culture conditions were at 37 degrees C, with 95% air/5% CO2 in Roswell Park Memorial Institute (RPMI) 1640 medium with 10% heat-inactivated fetal bovine serum. Rhodamine-dextran (70 kd) was incubated with the cells at 0.25 mg/mL for 24 hours to label the lysosomes. Chloroquine treatment where indicated was performed at 10-20 microg/mL for 1 hour. Fluorescent BioParticles were then added, and PLF was monitored by formation of an orange-yellow fluorescence on fusion of green fluorescent BioParticles with rhodamine-labeled lysosomes. PLF endpoints were measured by scoring for the percentage of orange-yellow cells in the field of view. Image analysis to measure the intensity of the orange-yellow color was performed by obtaining a, b values for 5 x 5 pixel areas using the PhotoAdobe program 4.0.1. The results indicated that the rate of PLF was enhanced by chloroquine. Thus, chloroquine may be used to potentiate the effects of rifampicin. This may be confirmed by studies involving similar dual fluorophore labeling techniques of fluorescein-labeled formulation in macrophages infected with M.tuberculosis. Preliminary studies with the rhodamine-labeled formulation confirmed cellular uptake and persistence for up to 7 days in culture.

Hydrophobic ion pair formation between leuprolide and sodium oleate for sustained release from biodegradable polymeric microspheres

Leuprolide acetate, an analogue of luteinizing hormone-releasing hormone (LH-RH), was hydrophobically ion paired with a long chain fatty acid, sodium oleate, in an aqueous solution. Solution behaviors of the complex formed between leuprolide and sodium oleate were investigated in terms of aqueous solubility, turbidity, particle size, and zeta potential as a function of molar ratio between the two species. It was found that with increasing the stoichiometric molar amounts of sodium oleate to leuprolide approached up to 2.5-3, the solution became gradually turbid with increasing particle sizes, indicating leuprolide precipitation as a result of hydrophobic ion pairing. On the other hand, beyond that critical molar ratio range, the solution turned into clear with much reduced particle size, indicative of micelle formation. The hydrophobically modified leuprolide-oleate complex was lyophilized and directly encapsulated within biodegradable poly(D, L-lactic-co-glycolic acid) (PLGA) microspheres via a single oil-in-water (O/W) emulsion method. Microsphere morphology, leuprolide release behavior, and polymer mass erosion profiles were examined in comparison to the PLGA microspheres prepared with free leuprolide.

Microspheres for protein delivery prepared from amphiphilic multiblock copolymers. 1. Influence of preparation techniques on particle characteristics and protein delivery

The entrapment of lysozyme in amphiphilic multiblock copolymer microspheres by emulsification and subsequent solvent removal processes was studied. The copolymers are composed of hydrophilic poly(ethylene glycol) (PEG) blocks and hydrophobic poly(butylene terephthalate) (PBT) blocks. Direct solvent extraction from a water-in-oil (w/o) emulsion in ethanol or methanol did not result in the formation of microspheres, due to massive polymer precipitation caused by rapid solvent extraction in these non-solvents. In a second process, microspheres were first prepared by a water-in-oil-in-water (w/o/w) emulsion system with 4% poly(vinyl alcohol) (PVA) as stabilizer in the external phase, followed by extraction of the remaining solvent. As non-solvents ethanol, methanol and mixtures of methanol and water were employed. However, the use of alcohols in the extraction medium resulted in microspheres which gave an incomplete lysozyme release at a non-constant rate. Complete lysozyme release was obtained from microspheres prepared by an emulsification-solvent evaporation method in PBS containing poly(vinyl pyrrolidone) (PVP) or PVA as stabilizer. PVA was most effective in stabilizing the w/o/w emulsion. Perfectly spherical microspheres were produced, with high protein entrapment efficiencies. These microspheres released lysozyme at an almost constant rate for approximately 28 days. The reproducibility of the w/o/w emulsion process was demonstrated by comparing particle characteristics and release profiles of three batches, prepared under similar conditions.

Controlled release of beta-estradiol from PLAGA microparticles: the effect of organic phase solvent on encapsulation and release

To determine the effect of the organic solvent used during microparticle preparation on the in vitro release of beta-estradiol, a number of formulations were evaluated in terms of size, shape and drug delivery performance. Biodegradable microparticles of poly(lactide-co-glycolide) were prepared containing beta-estradiol that utilized dichloromethane, ethyl acetate or a mixture of dichloromethane and methanol as the organic phase solvent during the particle preparation. The drug delivery behavior from the microparticles was studied and comparisons were made of their physical properties for different formulations. The varying solubilities of beta-estradiol and poly(lactide-co-glycolide) in the solvents studied resulted in biodegradable microparticles with very different physical characteristics. Microparticles prepared from solid suspensions of beta-estradiol using dichloromethane as the organic phase solvent were similar in appearance to microparticles prepared without drug. Microparticles prepared from dichloromethane/methanol solutions appeared transparent to translucent depending on the initial amount of drug used in the formulation. Microparticles prepared using ethyl acetate appeared to have the most homogeneous encapsulation of beta-estradiol, appearing as solid white spheres regardless of initial drug content. Studies showed that microparticles prepared from either ethyl acetate or a mixture of dichloromethane and methanol gave a more constant release profile of beta-estradiol than particles prepared using dichloromethane alone. For all formulations, an initial burst of release increased with increasing drug loading, regardless of the organic solvent used.

Encapsulation and release of rhodium(II) citrate and its association complex with hydroxypropyl-beta-cyclodextrin from biodegradable polymer microspheres

Rhodium(II) carboxylates and their derivatives constitute a promising class of second-generation transition metal compounds with anticancer properties. While most transition metal anticancer compounds chelate DNA and cause extensive chromosomal damage, rhodium(II) carboxylates act on the enzyme DNA polymerase alpha and hence cause minimal chromosomal damage. Rhodium(II) citrate, a recent member of the rhodium(II) carboxylate family is highly promising as an antitumor agent. However, due to its high water solubility, a high systemic dose is necessary to achieve efficacy. In this paper, we have explored the complexation of rhodium(II) citrate with hydroxypropyl-beta-cyclodextrin as a means to improve encapsulation and release kinetics from poly(dl-lactic-co-glycolic) acid (PLGA) and poly(anhydride) microspheres. We observed that complexation of rhodium(II) citrate with hydroxypropyl-beta-cyclodextrin significantly increased both the encapsulation efficiency and duration of release in both polymer systems.