Optimization of preparative conditions for polylactide (PLA) microspheres containing ovalbumin

Preparation and evaluation of sustained release formulation of PLGA using a new injection system based on ink-jet injection technology

We developed a method for the preparation of PLGA particles exhibiting long-term sustained-release of entrapped drugs. The fine droplet drying (FDD) technology using a new injection system based on ink-jet injection technology was adapted as the preparation method. PLGA microspheres containing TRITC-dextran, acetaminophen, and albumin as model drugs were prepared by the FDD technology. The resultant microspheres were uniform in size, with average particle sizes ranging from 16.3 to 33.0 μm and SPAN factors ranging from 0.49 to 0.77. The encapsulation efficiency of drugs showed high values ranging from 75 to 99 wt% of the total amount of water-soluble drug contained in the particles. In an investigation of the optimal operation conditions of the FDD technology, the dew point temperature of the dryer air stream was found to be an important factor for controlling the initial burst of the prepared particles. The TRITC-dextran-containing PLGA microspheres were confirmed to exhibit long-term sustained release for about 90 days, and the mechanism was found to be PLGA degradation rate-limiting. Based on these results, we concluded that long-term sustained-released PLGA particles can be prepared by using FDD technology under a suitable drying condition for controlling the initial burst.

Improvement of the antibacterial activity of daptomycin-loaded polymeric microparticles by Eudragit RL 100: an assessment by isothermal microcalorimetry

The aim of the present study was to develop novel daptomycin-loaded acrylic microparticles with improved release profiles and antibacterial activity against two clinically relevant methicillin-susceptible and methicillin-resistant Staphylococcus aureus strains (MSSA and MRSA, respectively). Daptomycin was encapsulated into poly(methyl methacrylate) (PMMA) and PMMA-Eudragit RL 100 (EUD) microparticles by a double emulsion-solvent evaporation method. For comparison purposes similar formulations were prepared with vancomycin. Particle morphology, size distribution, encapsulation efficiency, surface charge, physicochemical properties, in vitro release and biocompatibility were assessed. Particles exhibited a micrometer size and a spherical morphology. The addition of EUD to the formulation caused a shift in the surface charge of the particles from negative zeta potential values (100% PMMA formulations) to strongly positive. It also improved daptomycin encapsulation efficiency and release, whereas vancomycin encapsulation and release were strongly hindered. Plain and antibiotic-loaded particles presented comparable biocompatibility profiles. The antibacterial activity of the particles was assessed by isothermal microcalorimetry against both MSSA and MRSA. Daptomycin-loaded PMMA-EUD particles presented the highest antibacterial activity against both strains. The addition of 30% EUD to the daptomycin-loaded PMMA particles caused a 40- and 20-fold decrease in the minimum inhibitory (MIC) and bactericidal concentration (MBC) values, respectively, when compared to the 100% PMMA formulations. On the other hand, vancomycin-loaded microparticles presented the highest antibacterial activity in PMMA particles. Unlike conventional methods, isothermal microcalorimetry proved to be a real-time, sensitive and accurate method for assessment of antibacterial activity of antibiotic-loaded polymeric microparticles. Finally, the addition of EUD to formulations proved to be a powerful strategy to improve daptomycin encapsulation efficiency and release, and consequently improving the microparticles activity against two relevant S. aureus strains.

Prospects of pharmaceuticals and biopharmaceuticals loaded microparticles prepared by double emulsion technique for controlled delivery

Several methods and techniques are potentially useful for the preparation of microparticles in the field of controlled drug delivery. The type and the size of the microparticles, the entrapment, release characteristics and stability of drug in microparticles in the formulations are dependent on the method used. One of the most common methods of preparing microparticles is the single emulsion technique. Poorly soluble, lipophilic drugs are successfully retained within the microparticles prepared by this method. However, the encapsulation of highly water soluble compounds including protein and peptides presents formidable challenges to the researchers. The successful encapsulation of such compounds requires high drug loading in the microparticles, prevention of protein and peptide degradation by the encapsulation method involved and predictable release, both rate and extent, of the drug compound from the microparticles. The above mentioned problems can be overcome by using the double emulsion technique, alternatively called as multiple emulsion technique. Aiming to achieve this various techniques have been examined to prepare stable formulations utilizing w/o/w, s/o/w, w/o/o, and s/o/o type double emulsion methods. This article reviews the current state of the art in double emulsion based technologies for the preparation of microparticles including the investigation of various classes of substances that are pharmaceutically and biopharmaceutically active.

Biodegradable poly(terephthalate-co-phosphate)s: synthesis, characterization and drug-release properties

To develop biodegradable polymers with favorable physicochemical and biological properties, we have synthesized a series of poly(terephthalate-co-phosphate)s using a two-step poly-condensation. The diol 1,4-bis(2-hydroxyethyl) terephthalate was first reacted with ethylphosphorodichloridate (EOP), and then chain-extended with terephthaloyl chloride (TC). Incorporation of phosphate into the poly(ethylene terephthalate) backbone rendered the co-polymers soluble in chloroform and biodegradable, lowered the Tg, decreased the crystallinity and increased the hydrophilicity. With an EOP/TC molar feed ratio of 80: 20, the polymer exhibited good film-forming property, yielding at 86.6 +/- 1.6% elongation with an elastic modulus of 13.76 +/- 2.66 MPa. This polymer showed a favorable toxicity profile in vitro and good tissue biocompatibility in the muscular tissue of mice. In vitro the polymer lost 21% of mass in 21 days, but only 20% for up to 4 months in vivo. It showed no deterioration of properties after sterilization by gamma-irradiation at 2.5 Mrad on solid CO2. Release of FITC-BSA from the microspheres was diffusion-controlled and exceeded 80% completion in two days. Release of the hydrophobic cyclosporine-A from microspheres was however much more sustained and near zero-ordered, discharging 60% in 70 days. A limited structure-property relationship has been established for this co-polymer series. The co-polymers became more hydrolytically labile as the phosphate component (EOP) was increased and the side chains were switched from the ethoxy to the methoxy structure. Converting the methoxy group to a sodium salt further increased the degradation rate significantly. The chain rigidity as reflected in the Tg values of the co-polymers decreased according to the following diol structure in the backbone: ethylene glycol > 2-methylpropylene diol > 2,2-dimethylpropylene diol. The wide range of physicochemical properties obtainable from this co-polymer series should help the design of degradable biomaterials for specific biomedical applications.

Hydroxyapatite/polylactide biphasic combination scaffold loaded with dexamethasone for bone regeneration

This study presents a novel design of a ceramic/polymer biphasic combination scaffold that mimics natural bone structures and is used as a bone graft substitute. To mimic the natural bone structures, the outside cortical-like shells were composed of porous hydroxyapatite (HA) with a hollow interior using a polymeric template-coating technique; the inner trabecular-like core consisted of porous poly(D,L-lactic acid) (PLA) that was loaded with dexamethasone (DEX) and was directly produced using a particle leaching/gas forming technique to create the inner diameter of the HA scaffold. It was observed that the HA and PLA parts of the fabricated HA/PLA biphasic scaffold contained open and interconnected pore structures, and the boundary between both parts was tightly connected without any gaps. It was found that the structure of the combination scaffold was analogous to that of natural bone based on micro-computed tomography analysis. Additionally, the dense, uniform apatite layer was formed on the surface of the HA/PLA biphasic scaffold through a biomimetic process, and DEX was successfully released from the PLA of the biphasic scaffold over a 1-month period. This release caused human embryonic palatal mesenchyme cells to proliferate, differentiate, produce ECM, and form tissue in vitro. Therefore, it was concluded that this functionally graded scaffold is similar to natural bone and represents a potential bone-substitute material.

Control of drug loading efficiency and drug release behavior in preparation of hydrophilic-drug-containing monodisperse PLGA microspheres

We prepared monodisperse poly(lactide-co-glycolide) (PLGA) microspheres containing blue dextran (BLD)--a hydrophilic drug--by membrane emulsification technique. The effects of electrolyte addition to the w(2) phase and significance of the droplet size ratio between primary (w(1)/o) and secondary (w(1)/o/w(2)) emulsions during the preparation of these microspheres was examined. The droplet size ratio was evaluated from the effect of stirring rate of the homogenizer when preparing the primary emulsion. The drug loading efficiency of BLD in these microspheres increased with stirring rate. It increased to approximately 90% when 2.0% NaCl was added to the w(2) phase. Drug release from these microspheres was slower than that when they were prepared without electrolyte addition. Despite the very high efficiency drug release was gradual because BLD was distributed at the microspheres core. Relatively monodisperse hydrophilic-drug-containing PLGA microspheres with controlled drug loading efficiency and drug release behavior were prepared.

The mechanism of surface-indented protein-loaded PLGA microparticle formation: the effects of salt (NaCl) on the solidification process

The purpose of this study was to evaluate ovalbumin (OVA) leakage pathways and to explore the mechanism of the surface-indented microparticle formation in the preparation of OVA-loaded microparticles. OVA-loaded poly (D,L-lactic-co-glycolic acid) (PLGA) microparticles were prepared by a water-in oil-in water (w/o/w) solvent evaporation method associated with varied NaCl (NaCl) concentrations and adjusted with urea at 1240mOsm kg(-1) in the external aqueous phase. To evaluate dichloromethane (DCM)-related OVA leakage, three stirring rates, 600, 800, 1000rpm at 25 degrees C were carried out during the solvent evaporation stage. Both DCM and OVA levels in the external phase medium and total dispersion were sampled and measured. The time course of particle characteristics was evaluated by microscopy or SEM photography. The surface adsorptive capacities of the prepared microparticles were measured by using bovine serum albumin conjugated with fluorescein isothiocyanate (FITC-BSA). The findings were that the DCM-related OVA leakage accounted for approximately 34%, of the total leakage. By combining NaCl in the external phase, a faster solidifying crust-like structure was formed as a barrier to remarkably reduce OVA loss and improve OVA content from 40.1 to 72.8 microg mg(-1). The yield and OVA content for formulations containing NaCl were much improved by the ionic effect, in addition to the osmotic effect. The total entrapment efficiency was also highly increased from 43 to 72%. The formations of the crust-like surface structure of the microparticle were affected by entrapped drugs, salt content in the external phase and aqueous volume in the inner phase. A scheme was proposed to interpret the formation mechanism of the surface-indented microparticles. In comparison to the surface-smooth microparticles, the surface adsorptive capacities of the surface-indented microparticles were highly improved from 26.6 to 87.0%, determined by the adsorption of FITC-BSA.

Factors affecting the loading efficiency of water-soluble drugs in PLGA microspheres

Poly(lactide-co-glycolide), PLGA, microspheres containing blue dextran as a hydrophilic model drug were prepared by a solvent evaporation method from w/o/w emulsions using a micro homogenizer. Effects of surfactant concentration in oil phase, stirring time period and stirring rate in the preparation procedure of primary emulsion (w/o) upon drug-loading efficiency were evaluated. Stirring rate during preparation of primary emulsion and surfactant concentration in oil phase affected drug-loading efficiency and the particle size of primary emulsion. Microspheres having the higher drug-loading efficiency were obtained when size differences between the primary emulsions and the secondary ones were large. That is, when the diameter of the primary emulsion is much smaller than that of the secondary emulsion, PLGA microspheres with high-loading efficiency of blue dextran were obtained.

Incorporation of water-soluble drugs in PLGA microspheres

Poly(lactide-co-glycolide) (PLGA) microspheres containing blue dextran, as a model of water-soluble drugs, were prepared from w(1)/o/w(2) emulsions by using a microhomogenizer and a solvent evaporation method. Effects of preparation conditions, such as, concentration of poly(vinyl alcohol) (PVA) in w(2) phase, viscosity of inner soluble water phase, volume ratio of oil phase to w(1) phase in primary emulsion, PLGA concentration in oil phase, and molecular weight or composition of PLGA, upon the properties of PLGA microspheres containing water-soluble drugs were examined. Concentration of poly(vinyl alcohol) (PVA), the dispersant dissolved in w(2) phase of secondary emulsion did not show any effects on the final particle size. On the other hand, volume ratio of oil phase to water one in primary emulsion affected the final particle size, which seemed to be related to the local PLGA concentration in w(1)/o emulsions. That is, the particle size increased as the volume ratio of w(1) phase against oil phase, w(1)/o (v/v), increased. The loading efficiency, however, was not affected by the volume ratio of w(1)/o (v/v), but affected by blue dextran concentration in w(1) phase. Higher loading efficiency was observed in PLGA microspheres prepared from w(1) phase containing lower concentration of blue dextran. Blue dextran solution (inner water phase) with the lower viscosity may result in the lower leakage ratio of blue dextran during the preparation procedure. Increases in concentration and molecular weight of PLGA made particle size larger.

Biodegradable PLGA Particles for Improved Systemic and Mucosal Treatment of Type I Allergy

Although allergen immunotherapy is basically a story of success, it still needs improvement. The goal of this study was to optimize parenteral and oral allergen formulations through using the biocompatible polymer of lactic and glycolic acid (PLGA). Subcutaneous application of birch pollen allergen Bet v 1 encapsulated in nanoparticles biased the immune response toward Th1 in allergic mice and did not elicit granuloma formation in mice and in human volunteers. When oral immunotherapy of mice was tried with birch pollen-filled PLGA microparticles, mucosal targeting was indispensable for achieving any immune response, and targeting of M-cells was necessary for modulating an ongoing allergic response toward Th1. The authors suggest that biocompatible PLGA nano- or microparticles can be useful tools for upgrading therapy of type I allergy.

Immunization by particle bombardment of antigen-loaded poly-(DL-lactide-co-glycolide) microspheres in mice

In the present study, we investigated whether poly-(DL-lactide-co-glycolide) (50:50) microspheres (PLG MS) containing a model antigen, ovalbumin (OVA), were delivered into mouse skin and the immune responses induced using a microparticulate bombardment system, Helios gene gun system, which can painlessly deliver the powdered drug through the stratum corneum to the epidermal-dermal interface using a high velocity supersonic flow of helium gas to accelerate the particles. The introduction of OVA-loaded PLG MS shows helium pressure-dependence, so that improved introduction can be achieved by a higher helium pressure used, thereby inducing sufficient anti-OVA IgG level. Moreover, in order to determine the type of immune system induced using particle bombardment, we investigated helper T-cell response characterized by the cytokine production in the isolated splenocytes 6 weeks after immunization and consequent production of the anti-OVA IgG subclasses in the serum in mice. As a result, IL-4 production in splenocytes and anti-OVA IgG1 level were preferentially elicited by particle bombardment with OVA-loaded PLG MS compared with IFN-gamma and anti-OVA IgG2a level. It seemed likely that particle bombardment using this system led to a Th-2 type immune response, i.e. a humoral immune response. In conclusion, this microparticulate bombardment system is a promising immunization method, expected to become an alternative to needle injection used to administer a broad range of vaccines for the treatment of various diseases.

Microencapsulation by solvent extraction/evaporation: reviewing the state of the art of microsphere preparation process technology

The therapeutic benefit of microencapsulated drugs and vaccines brought forth the need to prepare such particles in larger quantities and in sufficient quality suitable for clinical trials and commercialisation. Very commonly, microencapsulation processes are based on the principle of so-called "solvent extraction/evaporation". While initial lab-scale experiments are frequently performed in simple beaker/stirrer setups, clinical trials and market introduction require more sophisticated technologies, allowing for economic, robust, well-controllable and aseptic production of microspheres. To this aim, various technologies have been examined for microsphere preparation, among them are static mixing, extrusion through needles, membranes and microfabricated microchannel devices, dripping using electrostatic forces and ultrasonic jet excitation. This article reviews the current state of the art in solvent extraction/evaporation-based microencapsulation technologies. Its focus is on process-related aspects, as described in the scientific and patent literature. Our findings will be outlined according to the four major substeps of microsphere preparation by solvent extraction/evaporation, namely, (i) incorporation of the bioactive compound, (ii) formation of the microdroplets, (iii) solvent removal and (iv) harvesting and drying the particles. Both, well-established and more advanced technologies will be reviewed.

Fabrication of porous hollow silica nanoparticles and their applications in drug release control

Preparation and characterization of porous hollow silica nanoparticles (PHSN) for controlled release applications were investigated. Through orthogonally designed experiments, the optimal synthesis conditions for the preparation of PHSN were obtained and the produced PHSN were characterized by BET, SEM, TEM and IR. Scanning and transmission electron microscopy images revealed their hollow shell-core structure and also demonstrated that the size and shape of PHSN are determined by the templating CaCO3 nanoparticles. The produced PHSN were applied as a carrier to study the controlled release behaviors of Brilliant Blue F (BB), which was used as a model drug. Being loaded into the inner core and on the surfaces of the nanoparticles, BB was released slowly into a bulk solution for about 1140 min as compared to only 10 min for the normal SiO2 nanoparticles, thus exhibited a typical sustained release pattern without any burst effect. In addition, higher BET of the carriers, lower pH value and lower temperature prolonged BB release from PHSN, while stirring speed showed little influence on the release behavior. It showed that PHSN have a promising future in controlled drug delivery applications.

Controlled release of anti-cocaine catalytic antibody from biodegradable polymer microspheres

Recent reports have shown that anti-cocaine catalytic monoclonal antibody 15A10 reduces the toxic effect of cocaine by increasing its breakdown to systemically inert products ecgonine methylester and benzoic acid. This study reports the microencapsulation of antibody 15A10 using biodegradable poly (lactic-glycolic) acid (PLGA) by double emulsion technique. Formulation parameters such as protein loading, polymer molecular weight and the presence of zinc carbonate were studied for their effects on in-vitro release of antibody from microspheres. The initial burst release was decreased by the reduction of the protein (as % of total ingredients) in the formulation. Although changing the polymer molecular weight did not cause a reduction in initial burst release, it was effective in improving the release rate. The inclusion of zinc carbonate in microsphere preparation resulted in increase in initial burst release. An in-vivo study in mice revealed the presence of antibody in blood up to ten days following subcutaneous injections. These data demonstrate a potential for a sustained-release formulation of monoclonal antibody 15A10 for treatment of cocaine addiction.

Biodegradable micelles/polymersomes from fumaric/sebacic acids and poly(ethylene glycol)

Linear unsaturated oligo-anhydrides containing terminal acylchloride groups have been synthesized by polycondensation of fumaric or sebacic acid with either fumaryl chloride or sebacoyl chloride. Reaction of these oligo-anhydrides with poly(ethylene glycol) produce di- and tri-block copolymers. The oligo-anhydrides and block copolymers have been characterized by gel permeation chromatography (GPC), NMR and FT-IR spectroscopies. The tri-block copolymers composed of two PEG end blocks and an oligo-anhydride center block have been used in encapsulation of calcein (encapsulation efficiency up to 40%). Encapsulation and release profile of calcein (as a model hydrophilic drug) from the di-block copolymers (micelles) and tri-block copolymer vesicles (polymersomes) as well as their in-vitro hydrolytic degradation (pH=7.4 degrees C, 37 degrees C) are reported.

Toxic characteristics of methoxy poly(ethylene glycol)/poly(epsilon-caprolactone) nanospheres; in vitro and in vivo studies in the normal mice

Amphiphilic diblock polymeric nanospheres composed of methoxy poly(ethylene glycol) (MePEG) and poly(epsilon-caprolactone)(PCL) was prepared for application as a novel drug carrier. We could obtain the MePEG/PCL nanospheres that exhibited an average diameter of less than 200 nm with narrow size distribution and a relatively high drug-loading efficiency of about 41.98% and 20.8% for indomethacin and paclitaxel, respectively. To estimate the toxicity of nanospheres, we investigated cytotoxicity using the normal human fibroblast, the median lethal dose (LD(50)) and various organ toxicities using male ICR mice. The indomethacin-loaded nanosphere showed higher cell viability than indomethacin in the cytotoxicity test using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. The LD(50) of MePEG/PCL nanospheres determined by Litchfield-Wilcoxon method was 1.47 g/kg. After the mice were intraperitoneally injected with MePEG/PCL nanospheres as a half-dose level of LD(50) for 7 days, no significant histopathologic changes were observed in MePEG/PCL nanospheres-treated mice compared with normal mice in the light and electron microscopic observations of various organs such as heart, lung, liver and kidney. It was suggested that MePEG/PCL nanospheres might be useful candidate as a novel injectable drug carrier for hydrophobic drugs such as indomethacin and paclitaxel.

Biodegradable block copolymers

Recently, block copolymers have got tremendous impetus on the ongoing research in the area of drug delivery technology, due to their capability to provide a biomaterial having a broad range of amphiphilic characteristics, as well as targeting the drugs to specific site. This article is an attempt to review applications of block copolymers in surface modification, drug targeting, nano and microparticles, hydrogels, micelles etc. The physicochemical properties of block copolymers and various synthetic routes for block copolymers are also discussed.

Novel microparticulate system made of poly(methylidene malonate 2.1.2)

Formulation of PMM 2.1.2 microparticles entrapping ovalbumin as a model protein was achieved by using a double emulsion solvent evaporation method. Parameters such as the nature of the solvent, polymer concentration and polymer molecular weight were investigated. Preparation process led to the formation of spherical and smooth particles with a mean diameter of 5 microm, and an encapsulation efficiency and protein loading level of up to 16 and 2.9% w/w, respectively. After an initial burst of approximately 10%, the protein was released at a rate of less than 1% per day. This slow release kinetics of encapsulated ovalbumin in phosphate buffer indicates that most of the protein was encapsulated within the polymer matrix. Degradation of PMM 2.1.2 microparticles in the presence of esterases indicated that side chain hydrolysis of the polymer was the rate-determining step in bioerosion; cleavage of the ester side chain, which was further hydrolyzed to glycolic acid and ethanol, led to an acrylic acid and subsequent solubilization of the polymer. However, slow polymer backbone solubilization after degradation was observed.

Indomethacin-loaded methoxy poly(ethylene glycol)/ poly(epsilon-caprolactone) diblock copolymeric nanosphere: pharmacokinetic characteristics of indomethacin in the normal Sprague-Dawley rats

We prepared the drug-loaded polymeric nanospheres composed of the methoxy poly(ethylene glycol) (MePEG) and poly(epsilon-caprolactone) (PCL) that showed a narrow size distribution and average diameter of less than 200 nm. We could obtain the nanosphere having a relatively high drug-loading efficiency of about 42% when the feed weight ratio of indomethacin (IMC) to polymer was 1:1. To investigate the IMC pharmacokinetics in the IMC-loaded MePEG/PCL nanosphere (DMEP70) using the rats as animal model, we analyzed the IMC concentration in plasma with HPLC after i.v. bolus administered at a dose of 10 mg/kg in free IMC (control) and IMC-loaded MePEG/PCL nanosphere (DMEP70) groups via tail vein. Pharmacokinetics parameters (mean +/- s.d.) such as the mean residence time (MRT, h), the steady-state volume of distribution (Vdss, l), the terminal half-time (t 1/2, h) and the plasma clearance (CL, l/h) of IMC in each groups (control vs. DMEP70) were determined; MRT (16.97 +/- 4.83 vs. 28.69 +/- 11.28, p < 0.01); Vdss (14.26 +/- 4.86 vs. 20.37 +/- 12.04, p < 0.05); t 1/2 (15.12 +/- 4.77 vs. 23.1 +/- 8.24, p < 0.01); CL (0.84 +/- 0.27 vs. 0.71 +/- 0.41). From these results, we could concluded that MEP70 has a significant potential for sustained release and the enhancement of circulation time of loaded drug by prolonging terminal half-life, increasing MRT and Vdss of IMC. Therefore, The MePEG/PCL block copolymeric nanosphere system is being considered as promising biodegradable and biocompatible drug carrier vehicles for parentral use and may be useful as sustained release injectable delivery systems for hydrophobic drugs.

Taxol-loaded block copolymer nanospheres composed of methoxy poly(ethylene glycol) and poly(epsilon-caprolactone) as novel anticancer drug carriers

We prepared the methoxy poly(ethylene glycol) (MePEG)/poly(epsilon-caprolactone) (PCL) amphiphilic block copolymeric nanospheres containing taxol which has promising anticancer activity. MePEG/PCL block copolymeric nanospheres (MEP50) showed a narrow size distribution and an average diameter of less than 100 nm. When the initial weight ratio of taxol to polymer was 0.5:1.0, we could obtain the nanospheres having a relatively high drug-loading of more than about 20%. The size of the MePEG/PCL nanospheres also increased according to the taxol loading. However, the nanospheres did not exhibit a significant change in the size distribution and also showed a size of less than 100 nm for even that with drug-loading content (DLC) of about 20%. From the 1H NMR analysis, we identified that the MePEG/PCL nanospheres prepared by dialysis procedure have core-shell structure consisting of the hydrophilic outer shell of MePEG and the hydrophobic inner core of PCL. We confirmed the low toxicity of MePEG/PCL nanospheres (MEP70) in the acute toxicity study using male ICR mice. In addition, considering the extremely lipophilic characteristics of taxol, this MePEG/PCL, nanosphere system with high taxol loading content and suspended properties in water could be useful for the delivery of taxol.

In vitro degradation and release profiles for poly-dl-lactide-poly(ethylene glycol) microspheres containing human serum albumin

Poly-dl-lactide-poly(ethylene glycol) (PELA) block copolymers containing same the content (10%) of polyethylene glycol (PEG) were synthesized with five different molecular weight of PEG by ring-opening polymerization. PELA microspheres containing human serum albumin (HSA) were elaborated by solvent extraction method based on the formation of double w/o/w emulsion. In vitro matrix degradation and protein release of these microspheres were performed in phosphate-buffered saline (PBS) (154 mM, pH 7.43). The degradation profiles were characterized by measuring the loss of microspheres mass, the decrease of polymer intrinsic viscosity, the decrease of pH value of degradation medium, the reduction of polymer number-average molecular weight (M(n)) and the change of molecular weight polydispersity (M(w)/M(n)). The release profiles were investigated from the measurement of protein presented in the release medium at various intervals. It showed that the matrix degradation and protein release profiles were highly polymer-dependent. The extent of burst release in the initial protein release increased with the decrease of molecular weight of PELA copolymer. It is suggested that these matrix polymers may be optimized as carriers in protein (antigen) delivery system for different purposes.

Biodegradable poly(D,L-lactic acid)-poly(ethylene glycol)-monomethyl ether diblock copolymers: structures and surface properties relevant to their use as biomaterials

To obtain biodegradable polymers with variable surface properties for tissue culture applications, poly(ethylene glycol) blocks were attached to poly(lactic acid) blocks in a variety of combinations. The resulting poly(D,L-lactic acid)-poly(ethylene glycol)-monomethyl ether (Me.PEG-PLA) diblock copolymers were subject to comprehensive investigations concerning their bulk microstructure and surface properties to evaluate their suitability for drug delivery applications as well as for the manufacture of scaffolds in tissue engineering. Results obtained from 1H-NMR, gel permeation chromatography, wide angle X-ray diffraction and modulated differential scanning calorimetry revealed that the polymer bulk microstructure contains poly(ethylene glycol)-monomethyl ether (Me.PEG) domains segregated from poly(D,L-lactic acid) (PLA) domains varying with the composition of the diblock copolymers. Analysis of the surface of polymer films with atomic force microscopy and X-ray photoelectron spectroscopy indicated that there is a variable amount of Me.PEG chains present on the polymer surface, depending on the polymer composition. It could be shown that the presence of Me.PEG chains in the polymer surface had a suppressive effect on the adsorption of two model peptides (salmon calcitonin and human atrial natriuretic peptide). The possibility to modify polymer bulk microstructure as well as surface properties by variation of the copolymer composition is a prerequisite for their efficient use in the fields of drug delivery and tissue engineering.

Development of microspheres for neurological disorders: from basics to clinical applications

Drug delivery to the central nervous system remains a challenging area of investigation for both basic and clinical neuroscientists. Numerous drugs are generally excluded from blood to brain transfer due to the negligible permeability of the brain capillary endothelial wall, which makes up the blood brain barrier in vivo. For several years, we have explored the potential applications of the microencapsulation of therapeutic agents to provide local controlled drug release in the central nervous system. Due to their size, these microparticles can be easily implanted by stereotaxy in discreet, precise and functional areas of the brain without damaging the surrounding tissue. This type of implantation avoids the inconvenient insertion of large implants by open surgery and can be repeated if necessary. We have established the compatibility of poly(lactide-co-glycolide) microspheres with brain tissues. Presently, the most developed applications concern Neurology and Neuro-oncology, with local delivery of neurotrophic factors and antimitotic drugs into neurodegenerative lesions and brain tumours, respectively. The drugs that had been encapsulated by our group included nerve growth factor (NGF), 5-fluorouracil (5-FU), idoxuridine and BCNU. Preclinical studies have been performed with each drug. Studies with NGF are reported as an example. A phase I/II clinical trial has been carried out in patients with newly diagnosed glioblastomas to assess the potentialities of 5-FU-loaded microspheres when intracranially implanted.

Why does PEG 400 co-encapsulation improve NGF stability and release from PLGA biodegradable microspheres?

PURPOSE

The aim of this work was to understand the mechanism by which co-encapsulated PEG 400 improved the stability of NGF and allowed a continuous release from PLGA 37.5/25 microspheres.

METHODS

Microparticles were prepared according to the double emulsion method. PEG 400 was added with NGF in the internal aqueous phase (PEG/PLGA ratio 1/1 and 1.8/1). Its effect was investigated through interfacial tension studies. Protein stability was assessed by ELISA.

RESULTS

A novel application of PEG in protein stabilization during encapsulation was evidenced by adsorption kinetics studies. PEG 400 limited the penetration of NGF in the interfacial film of the primary emulsion. Consequently, it stabilized the NGF by reducing the contact with the organic phase. In addition, it avoided the NGF release profile to level off by limiting the irreversible NGF anchorage in the polymer layers. On the other hand, the amount of active NGF released in the early stages was increased. During microparticle preparation, NaCl could be added in the external aqueous phase to modify the structure of microparticles. This allowed to reduce the initial release rate without affecting the protein stability always encountered in the absence of PEG.

CONCLUSIONS

PEG 400 appeared of major interest to achieve a continuous delivery of NGF over seven weeks from biodegradable microparticles prepared by the double emulsion technique.

Diphtheria and tetanus toxoid microencapsulation into conventional and end-group alkylated PLA/PLGAs

The feasibility of biodegradable polyester microspheres (MS) for single injection vaccines will greatly depend on the toxoid stability within the MS exposed to in vivo conditions. This study examined the effects of polymer type and co-encapsulated additives on diphtheria (Dtxd) and tetanus (Ttxd) toxoid entrapment and stability. The co-encapsulated stabilizers influenced significantly the entrapment of Dtxd and Ttxd in PLA/PLGA MS. Typically, 5% BSA or trehalose decreased the amount of Dtxd entrapped in spray-dried MS, whereas BSA increased the entrapment in coacervated MS. Further, the entrapment of Dtxd decreased as a function of polymer hydrophobicity in spray-dried MS. Without additives, approx. 64, 43 and 16% entrapment efficiency of ELISA-reactive antigen was obtained for 14-17 kDa PLGA 50:50, PLGA 75:25 and PLA, respectively. The novel end-group stearylated 1-PLAs were only processed by coacervation. Satisfactory entrapment of 30-60% Dtxd was obtained. Here, albumin was a prerequisite for toxoid encapsulation, as BSA-free formulations produced strong toxoid precipitation. Furthermore, protein burst release increased with the more hydrophobic polymers, with Dtxd, Ttxd and the co-encapsulated BSA following a similar pattern and magnitude. This investigation also revealed that the method of protein extraction from the microspheres (O/W-partition or polymer hydrolysis) as well as the analytical methods (HPLC or ELISA) strongly influenced the determined amount of encapsulated toxoid and BSA. In conclusion, the study revealed the complexity of antigen microencapsulation when using different preparation and analytical techniques, as well as different types of materials.

Optimization of preparative conditions for poly-DL-lactide- polyethylene glycol microspheres with entrapped Vibrio cholera antigens

Poly-dl-lactide-polyethylene glycol (PELA) with different contents of polyethylene glycol(PEG) were synthesized and the PEG content was estimated according to the integral height of hydrogen shown in 1H-NMR. PELA microspheres containing V. cholera antigen, outer membrane protein (OMP) were prepared by a water-in-oil-in-water (W/O/W) based on solvent evaporation procedure. Antigen microspheres with smooth surface, suitable size for oral administration (0.5-5 microm), high loading efficiency (about 60%) and low level of residual solvent (lower than 20ppm) were obtained. Microspheres prepared from PELA with PEG content of about 10% achieved the highest loading efficiency among PELA copolymers and poly-dl-lactide (PLA) homopolymer, which suggested that microspheres size, morphology and the precipitation rate of polymer showed considerable relations with OMP loading efficiency. The regulation of the solvent components of the oil phase contributes to a stable emulsion W/O, and it is concluded that the stable emulsion W/O plays a significant role in improving the protein loading efficiency of obtained microspheres. The addition of stabilizer, such as gelatin and polyvinyl alcohol, into the internal water phase before emulsification produced no significant difference in OMP entrapment and microspheres size. A higher OMP loading efficiency was achieved by adding NaCl or adjusting the pH at the iso-electric point of OMP in the external water phase. It was indicated in vitro that PELA microspheres with smaller size showed larger extent of initial release and higher release rate, whereas microspheres with the diameter of 2.17 microm showed no apparent burst effect.

Preparation and characterization of biodegradable nanospheres composed of methoxy poly(ethylene glycol) and DL-lactide block copolymer as novel drug carriers

We synthesized amphiphilic diblock copolymer based on methoxy poly(ethylene glycol) (MePEG) and dl-lactide with different molar composition in bulk without catalyst. Using the resulting amphiphilic diblock copolymers, we prepared drug-loaded polymeric nanospheres by micelle formation through solution behavior of amphiphilic copolymer in selective solvents. The structure of MePEG/dl-lactide diblock copolymers was identified by IR, WAXD, GPC, 1H-NMR. The size of nanosphere measured by dynamic light scattering showed a narrow monodisperse size distribution and average diameter less than 200 nm. From the surface chemical composition of nanosphere by ESCA, the presence of MePEG chains on the nanosphere layers was confirmed. The critical micelle concentration of ML50 sample investigated by fluorescence spectroscopy was 1.44x10-7 mol/l which is lower than common low molecular weight surfactants. In addition, we could obtain nanospheres having a relatively high drug-loading of about 33.0% when the feed weight ratio of indomethacin to polymer was 1:1. In vitro release experiments of the indomethacin-loaded MePEG/dl-lactide nanospheres exhibited sustained release behavior without any burst effects. The results of cytotoxicity tests showed that the MePEG/dl-lactide nanospheres didn't induce any relevant cell damage.

NGF release from poly(D,L-lactide-co-glycolide) microspheres. Effect of some formulation parameters on encapsulated NGF stability

Poly(d,l-lactide-co-glycolide) (PLGA 37.5/25 and 25/50) biodegradable microparticles, which allow the locally delivery of a precise amount of a drug by stereotactic injection in the brain, were prepared by a W/O/W emulsion solvent evaporation/extraction method which had been previously optimized. The aim of this work was to study the influence of two formulation parameters (the presence of NaCl in the dispersing phase and the type of PLGA) on the NGF release profiles and NGF stability during microencapsulation. A honey-comb-like structure characterized the internal morphology of the microspheres. The initial burst was attributed to the rapid penetration of the release medium inside the matrix through a network of pores and to the desorption of weakly adsorbed protein from the surface of the internal cavities. The non-release fraction of the encapsulated protein observed after twelve weeks of incubation was accounted for firstly by the adsorption of the released protein on the degrading microparticles and secondly by the entanglement of the encapsulated protein in the polymer chains. The use of sodium chloride in the dispersing phase of the double emulsion markedly reduced the burst effect by making the microparticle morphology more compact. Unfortunately, it induced in parallel a pronounced NGF denaturation. Finally, it appeared that microparticles made from a hydrophilic uncapped PLGA 37.5/25 in the absence of salt, allowed the release of intact NGF at least during the first 24 h as determined by both ELISA and a PC12 cell-based bioassay.

Influence of the preparation methods on the drug release behaviour of loperamide-loaded nanoparticles

Polylactide (PLA) or poly(lactide-coglycolide) (PLGA) nanoparticles containing loperamide (LPM) were prepared by an incorporation or adsorption method with the objective of developing nanoparticles with a rapid drug release. The use of polymers such as PLA with lower molecular weights and the addition of sorbitan fatty acid esters (SFAE) for the incorporation led to an almost complete entrapment of LPM in nanoparticles. Preparation of PLA nanoparticles by adsorption was performed by addition of LPM methanol solution before, during and after evaporation of dichloromethane from the system. The adsorption of LPM onto the nanoparticles with low molecular weight PLA (m.w. 2000) showed an isotherm with a good correlation to the Langmuir equation. A high amount of LPM can be entrapped or adsorbed in nanoparticles only with low molecular weights of PLA or PLGA. In the incorporation method, the addition of SFAEs increased drug entrapment. However, in the adsorption method they had no effect on nanoparticle drug adsorption. The drug-release profiles from both nanoparticles, prepared by the adsorption and incorporation methods, were biphasic with an initial rapid release and a second slower release phase, although their initial extents of release were different. The release rates were almost the same for both the adsorption and incorporation method without SFAEs. The addition of SFAEs to the adsorption system increased the extent of drug release from nanoparticles. In conclusion, a rapid loperamide release from nanoparticles can be achieved by use of PLA or PLGA with low molecular weights and in the adsorption method by the addition of SFAEs.

Methoxy poly(ethylene glycol) and epsilon-caprolactone amphiphilic block copolymeric micelle containing indomethacin. II. Micelle formation and drug release behaviours

Amphiphilic diblock copolymer composed of methoxy poly(ethylene glycol) and epsilon-caprolactone (epsilon-CL) was prepared by polymerization of epsilon-CL initiated with MePEG. MePEG/epsilon-CL block copolymeric micelles containing indomethacin (IMC) were prepared by a dialysis method and evaluated as a novel drug carrier. The size of micelle formed was less than 200 nm, and the size distribution of the micelle showed a narrow and monodisperse unimodal pattern. Also, the micelles formed by a dialysis method exhibited spherical structures. The indomethacin content in nanospheres was about 42.2%, for those prepared using copolymer, having molecular weight of about 12,000 and polymer/IMC weight ratio of 1/1. A release rate of indomethacin from nanospheres was slow, and thus the release continued over 15 days. As the molecular weights of the copolymer and the amount of drug entrapped increased, the release rate decreased. These results indicated that the drug-loaded nanospheres could be useful as a novel drug carrier in injectable delivery systems for hydrophobic drugs.

Preparation of microspheres by the solvent evaporation technique

The microencapsulation process in which the removal of the hydrophobic polymer solvent is achieved by evaporation has been widely reported in recent years for the preparation of microspheres and microcapsules based on biodegradable polymers and copolymers of hydroxy acids. The properties of biodegradable microspheres of poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) have been extensively investigated. The encapsulation of highly water soluble compounds including proteins and peptides presents formidable challenges to the researcher. The successful encapsulation of such entities requires high drug loading in the microspheres, prevention of protein degradation by the encapsulation method, and predictable release of the drug compound from the microspheres. To achieve these goals, multiple emulsion techniques and other innovative modifications have been made to the conventional solvent evaporation process.