Effect of the emulsion stability on the morphology and porosity of semicrystalline poly l-lactide microparticles prepared by w/o/w double emulsion-evaporation

PLGA/PLA-Based Long-Acting Injectable Depot Microspheres in Clinical Use: Production and Characterization Overview for Protein/Peptide Delivery

Over the past few decades, long acting injectable (LAI) depots of polylactide-co-glycolide (PLGA) or polylactic acid (PLA) based microspheres have been developed for controlled drug delivery to reduce dosing frequency and to improve the therapeutic effects. Biopharmaceuticals such as proteins and peptides are encapsulated in the microspheres to increase their bioavailability and provide a long release period (days or months) with constant drug plasma concentration. The biodegradable and biocompatible properties of PLGA/PLA polymers, including but not limited to molecular weight, end group, lactide to glycolide ratio, and minor manufacturing changes, could greatly affect the quality attributes of microsphere formulations such as release profile, size, encapsulation efficiency, and bioactivity of biopharmaceuticals. Besides, the encapsulated proteins/peptides are susceptible to harsh processing conditions associated with microsphere fabrication methods, including exposure to organic solvent, shear stress, and temperature fluctuations. The protein/peptide containing LAI microspheres in clinical use is typically prepared by double emulsion, coacervation, and spray drying techniques. The purpose of this review is to provide an overview of the formulation attributes and conventional manufacturing techniques of LAI microspheres that are currently in clinical use for protein/peptides. Furthermore, the physicochemical characteristics of the microsphere formulations are deliberated.

In-vitro and in-vivo evaluation of polymeric microsphere formulation for colon targeted delivery of 5-fluorouracil using biocompatible natural gum katira

The aim was to develop oral site-specific rate-controlled anticancer drug delivery to pacify systemic side-effects and offer effective and safe therapy for colon cancer with compressed dose and duration of treatment. The double emulsion solvent evaporation method was employed. To check functionality, DAPI-staining and in-vivo anticancer study of Ehrlich Ascites Carcinoma bearing mice was tested. Histopathology of liver and kidney and Cell morphology of EAC cell was also performed. Formulated and optimized polymeric microsphere of 5-FU showed excellent physicochemical features. In-vitro, DAPI results pointed drug-treated groups displayed the prominent feature of apoptosis. The percentage of apoptotic of entrapped drug played in a dose-dependent manner. Significant decreases in EAC liquid tumors and increased life span of treated mice were observed. Rate of variation of cell morphology was more in 5-FU loaded microsphere than 5-FU injection. Hematological and biochemical parameter's and Histopathology of liver and kidney resulted that due to control released formulation have slow release rate, that gives less trace on liver and kidney function. Finally, we foresee that polymeric microsphere of 5-FU applying natural gum katira could be an assuring micro-carrier for active colon targeting delivery tool with augmented chemotherapeutic efficacy and lowering side effect against colon cancer.

Poly-lactide-co-glycolide nanoparticles containing voriconazole for pulmonary delivery: in vitro and in vivo study

Poly-lactide-co-glycolide nanoparticles (207-605 nm) containing voriconazole (VNPs) were developed using a multiple-emulsification technique and were also made porous during preparation in presence of an effervescent mixture for improved pulmonary delivery. Pulmonary deposition of the particles was studied using a customized inhalation chamber. VNPs had a maximum of 30% (w/w) drug loading and a zeta potential (ZP) value around -20 mV. In the initial 2 hours, 20% of the drug was released from VNPs, followed by sustained release for 15 days. Porous particles had a lower mass median aerodynamic diameter (MMAD) than nonporous particles. Porous particles produced the highest initial drug deposition (~120 μg/g of tissue). The drug was detectable in lungs until 7 days and 5 days after administration, for porous and nonporous particles, respectively. VNPs with improved drug loading were successfully delivered to murine lungs. Porous nanoparticles with lower MMADs showed better pulmonary deposition and sustained presence in lungs.

FROM THE CLINICAL EDITOR

In this paper, voriconazole-containing porous nanoparticles were studied for inhalational delivery to lung infections in a murine model, demonstrating prolonged half-life and improved pulmonary deposition.

Influence of PEG in PEG-PLGA microspheres on particle properties and protein release

The aim of the present study was to compare different commercial available types of Poly(d,l-lactide-co-glycolide) (PLGA), multiblock copolymers of PLGA and polyethylene gylcol (PEG) as well as blends of PLGA and PEG regarding the preparation of microparticles and the release behavior of encapsulated protein. Microspheres were prepared by the solvent evaporation technique using the same conditions for each formulation. The encapsulation rate of bovine serum albumin (BSA) was unaffected by the different polymer types, and the mean was 79±4%. Microspheres composed of blends of PLGA and PEG showed a porous structure, a higher specific surface area, an inhomogenous distribution of protein and a higher release rate of BSA than microspheres consisting of PLGA, whereas the release profiles were the same. The specific surface area of microparticle formulations composed of diblock copolymers was the highest with 8.57±0.07m(2)/g emphasized by a highly porous, sponge-like structure. The triblock copolymer formulation revealed nearly spherical particles with a slightly uneven surface. Although the triblock copolymer consists of 10% PEG, the specific surface area was the lowest of all formulations. The rapid hydration due to PEG leads to a swollen matrix, which released the protein in a slow and continuous way.

Control of encapsulation efficiency in polymeric microparticle system of tolmetin

Ethylcellulose microparticles containing tolmetin sodium, an anti-inflammatory drug, were prepared by a solvent diffusion method based on the formation of multiple W/O(1)/O(2)-emulsion. The drug used was TOL, which is water-soluble and n-hexane was used as the non-solvent. Important parameters in the evaluation of a microencapsulation technique are actual drug loading, the encapsulation efficiency, the yield, solvent systems, dispersed phase to continuous phase ratio (DP/CP ratio), composition of continuous phase, drug distribution in microparticles and stability of primary emulsion. A small volume of internal aqueous phase and volume of organic solvent were favorable to achieve high drug encapsulation efficiencies. Since drug release during the initial stages depends mostly on the diffusion escape of the drug, major approaches to prevent the initial burst have focused on efficient encapsulation of the drug within the microparticles. For this reason, control of efficiency and the extent of initial burst are based on common formulation parameters. Most parameters affect encapsulation efficiency and initial burst by modifying solidification rate of dispersed phase. In order to prevent many unfavorable events such as pore formation, drug loss, and drug migration that occur while the dispersed phase is in the semi-solid state, it is important to understand and optimize these variables.

Pickering-type water-in-oil-in-water multiple emulsions toward multihollow nanocomposite microspheres

Multihollow hydroxyapatite (HAp)/poly(L-lactic acid) (PLLA) nanocomposite microspheres were readily fabricated by solvent evaporation from a "Pickering-type" water-in-(dichloromethane solution of PLLA)-in-water multiple emulsion stabilized with HAp nanoparticles. The multiple emulsion was stabilized with the aid of PLLA molecules used as a wettability modifier for HAp nanoparticles, although HAp nanoparticles did not work solely as particulate emulsifiers for Pickering-type emulsions consisting of pure dichloromethane and water. The interaction between PLLA and HAp nanoparticles at the oil-water interfaces plays a crucial role toward the preparation of stable multiple emulsion and multihollow microspheres.

Investigation on processing variables for the preparation of fluconazole-loaded ethyl cellulose microspheres by modified multiple emulsion technique

Fluconazole-loaded ethyl cellulose microspheres were prepared by alginate facilitated (water-in-oil)-in-water emulsion technology and the effects of various processing variables on the properties of microspheres were investigated. Scanning electron microscopy revealed spherical nature and smooth surface morphology of the microspheres except those prepared at higher concentration of emulsifiers and higher stirring speeds. The size of microspheres varied between 228 and 592 mum, and as high as 80% drug entrapment efficiency was obtained depending upon the processing variables. When compared up to 2 h, the drug release in pH 1.2 HCl solution was slower than in pH 7.4 phosphate buffer saline solution. However, this trend was reversed at high shear conditions. The microspheres provided extended drug release in alkaline dissolution medium and the drug release was found to be controlled by Fickian-diffusion mechanism. However, the mechanism shifted to anomalous diffusion at high shear rates and emulsifier concentrations. The aging of microspheres did not influence the drug release kinetics. However, the physical interaction between drug and excipients affected the drug dissolution behaviors. X-ray diffractometry (X-RD) and differential scanning calorimetry (DSC) analysis revealed amorphous nature of drug in the microspheres. Fourier transform infrared (FTIR) spectroscopy indicated stable character of fluconazole in the microspheres. The stability testing data also supported the stable nature of fluconazole in the microspheres. The fluconazole extracted from 80% drug-loaded formulation showed good in vitro antifungal activity against Candida albicans. Thus, proper control of the processing variables involved in this modified multiple emulsion technology could allow effective incorporation of slightly water soluble drugs into ethyl cellulose microspheres without affecting drug stability.

Poly (epsilon-caprolactone) microparticles containing Levobunolol HCl prepared by a multiple emulsion (W/O/W) solvent evaporation technique: effects of some formulation parameters on microparticle characteristics

The aim of this study was to prepare poly (epsilon-caprolactone) (PCL) microparticles of Levobunolol HC1 (L-HC1) for use as an anti-glaucomatous drug to the eye. The double emulsion (W/O/W) solvent evaporation technique was used for encapsulating L-HC1 as a hydrophilic drug. The study examined the impact of different factors including the pH and volume of the external aqueous phase, the concentration of polyvinylalcohol (PVA) and Pluronic F68 (PF68) used as stabilizers and drug/polymer ratios on the characteristics of the microparticles. Scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were used to identify the physical state of the drug and polymer. The zeta potential of the particles was also identified. Entrapment efficiency was found to be highest with a 0.5% PVA concentration and 100 mL volume of external aqueous phase at pH 12. The high efficiency was due to a reduction in the degree of drug ionization. The microparticles were spherical and appropriately sized for ophthalmic application. Drug release from the microparticles appears to consist of two components, with an initial rapid release followed by a slower stage. Drug release was slower when the microparticle was incorporated into the thermally reversible gel (Pluronic F127) in comparison to drug release from the free drug incorporated into the gel and drug release from the free microparticle.

Engineering biodegradable polyester particles with specific drug targeting and drug release properties

Poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) microspheres and nanoparticles remain the focus of intensive research effort directed to the controlled release and in vivo localization of drugs. In recent years engineering approaches have been devised to create novel micro- and nano-particles which provide greater control over the drug release profile and present opportunities for drug targeting at the tissue and cellular levels. This has been possible with better understanding and manipulation of the fabrication and degradation processes, particularly emulsion-solvent extraction, and conjugation of polyesters with ligands or other polymers before or after particle formation. As a result, particle surface and internal porosity have been designed to meet criteria-facilitating passive targeting (e.g., for pulmonary delivery), modification of the drug release profile (e.g., attenuation of the burst release) and active targeting via ligand binding to specific cell receptors. It is now possible to envisage adventurous applications for polyester microparticles beyond their inherent role as biodegradable, controlled drug delivery vehicles. These may include drug delivery vehicles for the treatment of cerebral disease and tumor targeting, and co-delivery of drugs in a pulsatile and/or time-delayed fashion.

Development and evaluation of novel biodegradable microspheres based on poly(d,l-lactide-co-glycolide) and poly(ε-caprolactone) for controlled delivery of doxycycline in the treatment of human periodontal pocket: In vitro and in vivo studies

This study reports on the development of novel biodegradable microspheres prepared by water-in-oil-water (W/O/W) double emulsion technique using the blends of poly(d,l-lactide-co-glycolide) (PLGA) and poly(epsilon-caprolactone) (PCL) in different ratios for the controlled delivery of doxycycline (DXY). Doxycycline encapsulation of up to 24% was achieved within the polymeric microspheres. Blend placebo microspheres, drug-loaded microspheres and pristine DXY were analyzed by Fourier transform infrared spectroscopy (FT-IR), which indicated no interaction between drug and polymers. Differential scanning calorimetry (DSC) on drug-loaded microspheres confirmed the polymorphism of DXY and indicated a molecular level dispersion of DXY in the microspheres. Scanning electron microscopy (SEM) confirmed the spherical nature and smooth surfaces of the microspheres produced. Mean particle size of the microspheres as measured by dynamic laser light scattering method ranged between 90 and 200 mum. In vitro release studies performed in 7.4 pH media indicated the release of DXY from 7 to 11 days, depending upon the blend ratio of the matrix. Up to 11 days, DXY concentrations in the gingival crevicular fluid were higher than the minimum inhibitory concentration of DXY against most of the periodontal pathogens. One of the developed formulations was subjected to in vivo efficacy studies in thirty sites of human periodontal pockets. Significant results were obtained with respect to both microbiological and clinical parameters up to 3 months even as compared to commercial DXY gel. Statistical analyses of the release data and in vivo results were performed using the analysis of variance (ANOVA) method.

Flurbiprofen loaded biodegradable nanoparticles for ophtalmic administration

Poly(lactic/glycolic) acid nanoparticles incorporating flurbiprofen (FB) were prepared by the solvent displacement technique using poloxamer 188 as a stabilizer to improve the availability of the drug for the prevention of the inflammation caused by ocular surgery. A 2(3) + star design was applied to investigate the influence of several factors such as the pH of the aqueous phase, the initial concentration of the stabilizer, and the drug used to prepare the nanoparticles (NPs) on the physicochemical properties (particle size analysis, zeta potential, and drug loading efficiency) of the colloidal system. The best formulations were those prepared at pH 3.5 with a concentration of 1.5 mg/mL of FB and 10 or 20 mg/mL of poloxamer 188. These formulations showed an appropriate average size for ophthalmic administration (232.8 and 277.6 nm, respectively) and a good yield of entrapment efficiency (94.60% and 93.55%, respectively). The release behavior of FB from the developed NPs was complete and exhibited a biphasic pattern. Formulations did not show toxicity on ocular tissues. In vivo anti-inflammatory efficacy was assessed in the rabbit eye after topical instillation of sodium arachidonate (SA). A higher decrease of the SA-induced inflammation was obtained for the NP formulations.

Surfactive water-soluble copolymers for the preparation of controlled surface nanoparticles by double emulsion/solvent evaporation

We have already shown that polylactide (PLA) nanoparticles covered with a hydrophilic polymeric layer can be prepared by simple emulsion/solvent evaporation by using amphiphilic copolymers as surfactants during the procedure. The external layer is then constituted by the hydrophilic part of the macromolecular surfactant. This kind of nanospheres is useful for the encapsulation of lipohilic molecules. The use of amphiphilic copolymers as surfactants in the preparation of PLA nanospheres with controlled surface properties, was then applied to the double emulsion/solvent evaporation procedure. The aim was to allow the encapsulation of water-soluble bioactive molecules in PLA particles with controlled surface properties. In this paper, we describe the results obtained with three different water-soluble monomethoxypolyethylene oxide (MPEO)-b-PLA diblock copolymers used as surfactants in the preparation of nanoparticles by double emulsion/solvent evaporation. After organic solvent evaporation, the obtained nanospheres were proved to be really covered by a MPEO layer whose characteristics were determined. It was firstly shown that the MPEO-covered particles did not flocculate at 25 degrees C, even in 4 M NaCl while suspensions of bare nanospheres were destabilized for a NaCl concentration as low as 0.04 M. On the other hand, the suspensions of MPEO-covered nanoparticles in 0.3 M Na2SO4 were found to be very sensitive to temperature as they flocculated at a temperature lying between 45 and 55 degrees C depending on the MPEO-b-PLA composition. This property was attributed to the fact that MPEO is a polymer with a low critical solution temperature. The concentration of MPEO at the nanoparticle surface was then calculated for the three kinds of particles, from the initial flocculation temperature, and was found to be comparable to the value determined directly.

Influences of excipients on in vitro release and in vivo performance of tetanus toxoid loaded polymer particles

Protein instability during microencapsulation has been one of the major hurdles of biodegradable polymer particles-based vaccine delivery systems. In the present work, effect of serum albumin, sucrose and sodium bicarbonate on surface morphology, entrapment efficiency, in vitro release and in vivo performance tetanus toxoid (TT) loaded PLA particles were investigated. Use of serum albumin as well as high concentration of protein antigen ( approximately 60mg/ml) helped in protecting the immunoreactivity of the antigen during primary emulsification step of particle formulation. Incorporation of sucrose in the internal aqueous phase led to the reduction in encapsulation efficiency of TT from 43.8+/-4.3% to 27.3+/-3.6% in PLA particles and resulted with formation of particles having irregular surface characteristics. Addition of sodium bicarbonate along with sucrose during primary emulsion led to slight improvement in encapsulation efficiency of TT (34.3+/-3.2%) but affected the in vivo performance in terms of serum anti-TT antibody titers from single point immunization. Restoration of osmotic balance by adding equivalent amount of sucrose in external aqueous phase helped in preventing multiple emulsion instability and subsequently improved the encapsulation efficiency of TT to 63.1+/-4.2%. Maximum entrapment efficiency of TT up to 69.2+/-5.1% was achieved when serum albumin, sucrose and sodium bicarbonate were used in internal aqueous phase and sucrose was used in the external aqueous phase. Polymer particles entrapping tetanus toxoid along with optimal stabilizers showed burst release of immunoreactive antigen (>40% in early period) and elicited high and sustained anti-TT antibody titers from single point intramuscular immunization. Anti-TT antibody titers were further enhanced upon immunization of admixture of PLA particles and alum. Choice and use of stabilizers during particle formulation thus need careful considerations not only to protect the immunoreactivity of the antigen, but also to produce stable, uniform particles for optimal in vivo performances.

PLGA microcapsules with novel dimpled surfaces for pulmonary delivery of DNA

We describe the fabrication of DNA-loaded poly(lactic-co-glycolic acid) (PLGA) microcapsules with novel surface morphologies that will be of use in pulmonary delivery. Our approach was to examine surface morphology and DNA encapsulation efficiency as a function of primary emulsion stability; using two surfactant series based on hydrophile-lipophile balance and hydrophobe molecular weight. Hydrophilic non-ionic surfactants yielded the most stable water-in-dichloromethane emulsions (HLB values >8). These surfactants normally favor convex (o/w) interfacial curvatures and therefore this atypical behavior suggested a relatively high surfactant solvation in the dichloromethane 'oil' phase. This was consistent with the large fall in the glass transition temperature for microspheres prepared with Tween 20, which therefore efficiently penetrated the PLGA matrix and acted as a plasiticizer. Blends of Pluronic triblock copolymers performed poorly as water-in-dichloromethane emulsifiers, and were therefore used to generate hollow microspheres ('microcapsules') with low densities (0.24 g/cm(3)). Although the Pluronic-stabilized emulsions resulted in lower DNA loading (15-28%), microspheres (approximately 8 microm) with novel dimpled surfaces were fabricated. The depth and definition of the dimples was greatest for triblock copolymers with high MW hydrophobe blocks. By cascade impaction, the geometric mean weight diameter of the microcapsules was 3.43 microm, suggesting that they will be of interest as biodegradable pulmonary delivery vehicles.

Microemulsion and diafiltration approaches: An attempt to maximize the global yield of DNA-loaded nanospheres

The yield of DNA-loaded nanospheres in its widest definition includes encapsulation efficiency and the integrity of the loaded molecules plus the production yield of fabricated nanospheres. The former aspect could be considerably improved by adopting the microemulsion concept to enhance the stability of the primary emulsion during the preparation of nanospheres by the double emulsion solvent-removal method. The droplet size of the mentioned emulsion was monitored by means of photon electron correlation spectroscopy and could serve as an index for emulsion fineness and stability. DNA stability as a function of applied mechanical stress was monitored by horizontal agarose gel electrophoresis. The impact of the primary emulsion on nanosphere porosity was assessed as well. Regarding the second aspect of the global yield of nanospheres, i.e. production yield, a modified diafiltration technique was adopted for the washing and recovery processes in comparison with the traditional and for the conservation of particle size characteristics of the recovered nanospheres.

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.

Some basic parameters of microspheres fabricated from a branched oligoester by a rapid procedure

Microspheres were prepared from a branched copolymer of DL-lactic acid with mannitol containing native albumin and albumin labelled with fluorescein isothiocyanate, using a rapid method of distribution of methylformate as the solvent of the copolymer from the intermediate phase of the multiple w/o/w emulsion. The primary w/o emulsion was prepared by the method of homogenization with a turbine or, alternatively, by the method of dispersion with ultrasound in modified vessels. Different additives in the external aqueous phase, such as polyvinyl alcohol or the gelatin hydrolyzate as emulsifiers were tested. Ammonium sulphate, methylformate or ethyl acetate were used as moderators of solidification of microspheres. The effect of these selected formulation parameters on the size, encapsulation efficiency, yield of microspheres and on the course of the BSA and FITC-BSA release in vitro conditions were examined.

Development of biodegradable poly(propylene fumarate)/poly(lactic-co-glycolic acid) blend microspheres. I. Preparation and characterization

We developed poly(propylene fumarate)/poly(lactic-co-glycolic acid) (PPF/PLGA) blend microspheres and investigated the effects of various processing parameters on the characteristics of these microspheres. The advantage of these blend microspheres is that the carbon-carbon double bonds along the PPF backbone could be used for their immobilization in a PPF scaffold. Microspheres containing the model drug Texas red dextran were fabricated using a double emulsion-solvent extraction technique. The effects of the following six processing parameters on the microsphere characteristics were investigated: PPF/PLGA ratio, polymer viscosity, vortex speed during emulsification, amount of internal aqueous phase, use of poly(vinyl alcohol) (PVA) in the internal aqueous phase, and PVA concentration in the external aqueous phase. Our results showed that the microsphere surface morphology was affected most by the viscosity of the polymer solution. Microspheres fabricated with a kinematic viscosity of 39 centistokes had a smooth, nonporous surface. In most microsphere formulations, the model drug was dispersed uniformly in the polymer matrix. For all fabricated formulations, the average microsphere diameter ranged between 19.0 and 76.9 microm. The external PVA concentration and vortex speed had most effect on the size distribution. Entrapment efficiencies varied from 60 to 98% and were most affected by the amount of internal aqueous phase, vortex speed, and polymer viscosity. Overall, we demonstrated the ability to fabricate PPF/PLGA blend microspheres with similar surface morphology, entrapment efficiency, and size distribution as conventional PLGA microspheres.

Control of encapsulation efficiency and initial burst in polymeric microparticle systems

Initial burst is one of the major challenges in protein-encapsulated microparticle systems. Since protein release during the initial stage depends mostly on the diffusional escape of the protein, major approaches to prevent the initial burst have focused on efficient encapsulation of the protein within the microparticles. For this reason, control of encapsulation efficiency and the extent of initial burst are based on common formulation parameters. The present article provides a literature review of the formulation parameters that are known to influence the two properties in the emulsion-solvent evaporation/extraction method. Physical and chemical properties of encapsulating polymers, solvent systems, polymer-drug interactions, and properties of the continuous phase are some of the influential variables. Most parameters affect encapsulation efficiency and initial burst by modifying solidification rate of the dispersed phase. In order to prevent many unfavorable events such as pore formation, drug loss, and drug migration that occur while the dispersed phase is in the semi-solid state, it is important to understand and optimize these variables.

Design and in vitro evaluation of gentamicin-Eudragit microspheres intended for intra-ocular administration

The conditions of preparation of gentamicin sulfate microspheres with high drug loading and a particle size less than 5 micro m, using a double-emulsion-solvent evaporation technique, intended for intra-ocular administration are described. The microspheres were prepared from poly methacrylate (Eudragit RS and RL) polymers cross-linked with polyvinyl alcohol. The parameters that improved the incorporation efficiency of gentamicin in the microspheres and controlled the particle size and surface morphology were investigated. Modifying the secondary aqueous phase by partially saturating it with various concentrations of either KCl or gentamicin increased the incorporation efficiency of the drug and affected the mean diameters of the microspheres. However, these characteristics were not altered when the initial drug loading was increased in the formulations. The modified gentamicin microspheres exhibited a smooth surface with an incorporation efficiency rate of 12.59% and a mean diameter of 4.06 micro m. The antimicrobial efficiency of gentamicin released from the modified particles against selected Gram-positive and -negative organisms including Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa confirmed that the entrapped gentamicin seemed to remain unaltered by the encapsulation process.

Mechanistic evaluation of the glucose-induced reduction in initial burst release of octreotide acetate from poly(d,l-lactide-co-glycolide) microspheres

One major obstacle for development of injectable biodegradable microspheres for controlled peptide and protein delivery is the high initial burst of drug release occurring over the first day of incubation. We describe here the significant reduction in initial burst release of a highly water-soluble model peptide, octreotide acetate, from poly(D,L-lactide-co-glycolide) microspheres by the co-encapsulation of a small amount of glucose (e.g., 0.2%w/w), i.e., from 30+/-20% burst - glucose to 8+/-3% + glucose (mean+/-SD, n=4). This reduction is unexpected since hydrophilic additives are known to increase porosity of microspheres, causing an increase in permeability to mass transport and a higher burst. Using the double emulsion-solvent evaporation method of encapsulation, the effect of glucose on initial burst in an acetate buffer pH 4 was found to depend on polymer concentration, discontinuous phase/continuous phase ratio, and glucose content. Extensive characterization studies were performed on two microsphere batches, +/-0.2% glucose, to elucidate the mechanism of this effect. However, no significant difference was observed with respect to specific surface area, porosity, internal and external morphology and drug distribution. Continuous monitoring of the first 24-h release of octreotide acetate from these two batches disclosed that even though their starting release rates were close, the microspheres + glucose exhibited a much lower release rate between 0.2 and 24h compared to those - glucose. The microspheres + glucose showed a denser periphery and a reduced water uptake at the end of 24-h release, indicating decreased permeability. However, this effect at times was offset as glucose content was further increased to 1%, causing an increase in surface area and porosity. In summary, we conclude that the effect of glucose on initial burst are determined by two factors: (1) increased initial burst due to increased osmotic pressure during encapsulation and drug release, and (2) decreased initial burst due to decreased permeability of microspheres.

Improved entrapment efficiency of hydrophilic drug substance during nanoprecipitation of poly(l)lactide nanoparticles

The purpose of this research was to improve the entrapment efficiency of a model hydrophilic drug substance, sodium cromoglycate, loaded inside polylactic acid nanoparticles by a modified nanoprecipitation method. The effect of formulation parameters was studied to improve the entrapment efficiency of the drug substance inside the nanoparticles. Several parameters (changes in the amount of model drug, solvent selection, electrolyte addition, pH alteration) were tested in order to increase the loading of the hydrophilic drug in the hydrophobic nanoparticles. Lowering of the pH was the most efficient way to increase the drug loading; up to approximately 70% of the sodium cromoglycate used in the particle formation process could be loaded inside the particles. The loading efficiency without the pH change was around 10% to 15% at maximum. The crystallinity values and crystal habits of the sodium cromoglycate nanoparticles were studied (x-ray diffraction) before and after the lowering of the pH. The change in pH conditions during the nanoprecipitation process did not affect markedly the crystallinity properties of the drug substance. According to this study, it is possible to improve the entrapment efficiency of hydrophilic sodium cromoglycate inside of the nanoparticles by small changes in the process parameters without alterations in the physical properties of the original drug substance.

Controlled release of the fibronectin central cell binding domain from polymeric microspheres

Non-ionic surfactants have been employed as alternatives to PVA for the emulsification-encapsulation of a conformationally labile protein (FIII9'-10) into PLGA microspheres. FIII9'-10 was encapsulated using a w/o/w double emulsification-evaporation technique and the microspheres fabricated were characterized by SEM and CLSM. The peptide backbone integrity of FIII9'-10 was assayed by SDS-PAGE and the degree of unfolding of FIII9'-10 following emulsification-encapsulation was assessed using a fibroblast cell-attachment assay. The encapsulation efficiency for FIII9'-10 was 25% when using PVA, compared to 50-60% when using Igepal CA-630 or Triton-X100, with values below for the other surfactants. FIII9'-10 released from microspheres promoted cell attachment in a concentration-dependent manner, only Igepal CA-630 and Triton X-100 maintaining near-maximal cell attachment, indicating that the conformation of the relatively unstable FIII9' domain was preserved. All non-ionic surfactants reduced microsphere surface porosity, compared to PVA, and an increasing surface rugosity (leading to minor 'ridges') could be correlated with decreasing surfactant HLB. Low surface porosities did not effect the diffusion of FIII9'-10 from the microspheres' internal pores in a 'burst release', as may have been imagined. In summary, non-ionic surfactants should be considered over PVA for the maintenance of biological activity of conformationally labile proteins during encapsulation.

W/O/W double emulsion technique using ethyl acetate as organic solvent: effects of its diffusion rate on the characteristics of microparticles

Monomethoxypoly(ethylene glycol)-b-poly(DL-lactide) copolymer (PELA) microparticles loading lysozyme were prepared through a modified W/O/W double emulsion-solvent diffusion method using ethyl acetate (EA) as organic solvent. The modified process was divided into five steps: (1) primary emulsification (W1/O), (2) re-emulsification (W1/O/W2), (3) pre-solidification, (4) solidification and (5) purification. The pre-solidification step was carried out in the modified process to control the diffusion rate of EA from oil phase into outer aqueous phase, in order to prevent the wall polymer from precipitation, which usually occurred when the diffusion rate was too fast. The adequately rapid solidification of microparticle caused by controlled fast diffusion of EA and the use of amphiphilic copolymer PELA as wall material, facilitated a high protein entrapment (always above 94%) and full preservation of bioactivity of entrapped lysozyme. It was found that the volume of the outer aqueous phase in the re-emulsification step and the shear stress in the pre-solidification step had a significant effect on the diffusion rate of EA from the droplets into outer aqueous solution, and thereby on the characteristics of the resultant microparticles. With the volume or the shear stress increasing, the removal rate of EA increased, resulting in rapid solidification of the microparticles. This result led to a lower burst effect and a slower lysozyme release from the microparticles. This study suggests that the modified W/O/W double emulsion-solvent diffusion method with EA as organic solvent is a prospective technique to prepare biodegradable microparticles containing water-soluble sensitive agents.

Poly(D,L-lactide-co-glycolide) microspheres containing 5-fluorouracil: optimization of process parameters

The objective of this research was to optimize the processing parameters for poly(D,L-lactide-co-glycolide) (PLGA) microspheres of 5-fluorouracil (5-FU) and to mathematically relate the process parameters and properties of microspheres. Microspheres were prepared by a water-in-oil-in-water emulsion solvent evaporation technique. A 3(2) factorial design was employed to study the effect of the volume of the internal phase of the primary emulsion and the volume of the external phase of the secondary emulsion on yield, particle size, and encapsulation efficiency of microspheres. An increase in the volume of the internal phase of the primary emulsion resulted in a decrease in yield and encapsulation efficiency and an increase in particle size of microspheres. When the volume of the external phase of the secondary emulsion was increased, a decrease in yield, particle size, and encapsulation efficiency was observed. Microspheres with good batch-to-batch reproducibility could be produced. Scanning electron microscopic study indicated that microspheres existed as aggregates.

Poly(lactide-co-glycolide) microspheres for the controlled release of oligonucleotide/polyethylenimine complexes

In this article, microspheres able to induce the controlled release of oligonucleotide/polyethylenimine complexes are proposed. A model oligonucleotide (the oligothymidilate pdT16) was encapsulated within poly(lactide-co-glycolide) microspheres alone or associated with polyethylenimine (PEI) at different nitrogen/phospate (N/P) ratios. Microspheres were prepared by the multiple emulsion-solvent evaporation technique and characterized for morphology, diameter, encapsulation efficiency, and release kinetics. The introduction of PEI in the internal aqueous phase resulted in the formation of a soluble complex with pdT16 and in a strong increase of the oligonucleotide encapsulation efficiency. PEI affected microsphere morphology inducing the formation of very porous particles yielding to an accelerated release of pdT16. When incubated with HeLa cells, microspheres encapsulating pdT16/PEI complexes allowed both a reduction of the complex toxicity and an improvement of the intracellular penetration of the released oligonucleotide. We conclude that biodegradable microspheres encapsulating oligonucleotides/PEI complexes have a great potential as controlled release system because they allow the sustained release of an oligonucleotide carrier that crosses biological membranes and locates in nucleus.

Auto-catalyzed poly(ortho ester) microspheres: a study of their erosion and drug release mechanism

A study has been carried out to investigate the degradation and protein release mechanisms of BSA-loaded microspheres made with auto-catalyzed poly(ortho esters) (POEs) of varying diol composition and molecular weights. Due to the instability of the POE/dichloromethane primary emulsion, microspheres made using the W/O/W double emulsion solvent extraction/evaporation method showed a multivesicular internal structure. An O/W single emulsion process yielded dense POE microspheres. Using electron scanning microscopy, the microspheres were observed to erode throughout their matrices with increasing internal pore sizes and a steady loss of mass. However, despite a substantial weight loss of almost 80% after an in vitro period of 129 days, the molecular weight of the polymer remained relatively unchanged with loss averaging about 18 and 32% for low- and high-molecular-weight POEs, respectively. Such constancy in molecular weight was similarly reflected in the glass transition temperature of the degrading microspheres. The differences in both the molecular weight loss and polydispersity index changes depended largely on the molecular weight of the polymer. For protein release of POE microspheres, an induction period followed by BSA release for a period of 3 to 10 days was observed. The lag time depended on the hydrophilicity and the molecular weight of the polymer as well as the morphology of the microspheres. Protein release was incomplete, possibly due to the slow degradation of the POE polymers, protein aggregation and protein degradation.

POE-PEG-POE triblock copolymeric microspheres containing protein. I. Preparation and characterization

Poly(ortho ester) (POE)-poly (ethylene glycol) (PEG) triblock copolymers (POE-PEG-POE) with different PEG contents were synthesised as carriers for controlled protein delivery. POE-PEG-POE microspheres containing bovine serum albumin (BSA) were prepared using a double-emulsion (water-in-oil-in-water) process. In this first paper of a two-part series, we report the fundamentals of the fabrication and characterization of POE-PEG-POE microspheres. Because the triblock copolymer is more hydrophilic than neat poly(ortho ester), the triblock copolymer yields a more stable first emulsion (water-in-oil) and a greater BSA encapsulation efficiency (90% vs. 30%). No BSA is found on POE-PEG-POE microsphere surfaces measured by X-ray photoelectron spectroscopy, while uniform BSA distributions are observed within the microspheres by confocal microscopy. SEM pictures show that an increase in PEG content results in microspheres with a denser cross-section because of a more stable first emulsion and better affinity between the copolymer and water. POE-PEG(20%)-POE suffers significant swelling during the fabrication process and yields the biggest microspheres. However, the POE-PEG(30%)-POE microspheres are much smaller since the dissolution loss of POE-PEG(30%)-POE in the external water phase may be much higher than that of POE-PEG(20%)-POE. The salt concentration in the external water phase significantly affects the morphology of the resultant microspheres. Microspheres with a dense wall are produced when using pure water as the external water phase. Polymer concentration has less impact on BSA encapsulation efficiency but has a considerable effect on microsphere size and morphology. Increasing the concentration of the polyvinyl alcohol emulsifier does not cause an obvious decrease in microsphere size. However, increased BSA loading results in bigger microspheres.

Development and characterization of lipid microparticles as a drug carrier for somatostatin

Somatostatin, a therapeutic peptide with a high therapeutical potential but a very short biological half-live was encapsulated within microparticles by a modified solvent evaporation method and a melt dispersion method without the use of organic solvent. As the use of synthetic polymer matrix materials often goes along with detrimental effects on incorporated peptides, we investigated the potential of physiological lipids such as glyceryl tripalmitate (Dynasan 116) as an alternative matrix material. The two preparation methods were evaluated with respect to surface topography, particle size distribution, encapsulation efficiency, in-vitro release behavior and modification of the resulting microparticles. Microparticles with a suitable particle size distribution for i.m. or s.c. injection could be prepared with both methods. The encapsulation efficiency of the peptide into glyceryl tripalmitate microparticles was substantially influenced by the preparation method and the physical state of the peptide to be incorporated. The melt dispersion technique and the incorporation of the drug as an aqueous solution gave the best results with actual drug loadings up to 9% and an encapsulation efficiency of approximately 90%. Microparticles prepared by the melt dispersion technique crystallized in the unstable alpha-modification. The peptide was released almost continuously over 10 days with no burst effect, 20-30% of the incorporated somatostatin was not released in the monitored time period.

Preparation and characterization of hCG-loaded polylactide or poly(lactide-co-glycolide) microspheres using a modified water-in-oil-in-water (w/o/w) emulsion solvent evaporation technique

A modified w/o/w emulsion solvent evaporation technique was adopted to prepare human Chorionic Gonadotropin (hCG)-loaded polylactide (PLA) or poly(lactide-co-glycolide) (PLGA) microspheres. The effects of preparative parameters, such as stirring rate, polymer MW and concentration, and the composition of both the inner aqueous phase and oil phase etc., on hCG entrapment efficiency and microsphere characteristics were investigated. It was found that by adding 20% glycerol into the inner aqueous phase and 40% acetone into the oil phase, smooth microspheres approximately 1 microm in diameter could be produced with high hCG entrapment efficiency (>90%). In vitro release test showed a burst release of hCG from PLGA (75:25) microspheres, followed by sustained release of 55% hCG over 2 months. The initial hCG burst from PLGA microspheres increased with the glycerol concentration in the inner aqueous phase, but decreased to a low value (ca. 20%) with the addition of acetone into the oil phase, which could be attributed to the associated changes in surface morphology of the microspheres. In vivo experiments demonstrated that a single shot of hCG-loaded PLGA microspheres could produce a comparable antibody response with the inoculation of free hCG four times.