Characterization and morphological analysis of a cholecystokinin derivative peptide-loaded poly(lactide-co-glycolide) microspheres prepared by a water-in-oil-in-water emulsion solvent evaporation method

Influence of Polyvinyl Alcohol (PVA) on PVA-Poly-N-hydroxyethyl-aspartamide (PVA-PHEA) Microcrystalline Solid Dispersion Films

This study was conducted to formulate buccal films consisting of polyvinyl alcohol (PVA) and poly-N-hydroxyethyl-aspartamide (PHEA), to improve the dissolution of the drug through the oral mucosa. Ibuprofen sodium salt was used as a model drug, and the buccal film was expected to enhance its dissolution rate. Two different concentrations of PVA (5% w/v and 7.5% w/v) were used. Solvent casting was used to prepare films, where a solution consisting of drug and polymer was cast and allowed to dry. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) were used to investigate the properties of films. In vitro dissolution studies were also conducted to investigate drug release. SEM studies showed that films containing a higher concentration of PVA had larger particles in microrange. FTIR studies confirmed the presence of the drug in films and indicated that ibuprofen sodium did not react with polymers. DSC studies confirmed the crystalline form of ibuprofen sodium when incorporated within films. In vitro dissolution studies found that the dissolution percentage of ibuprofen sodium alone was increased when incorporated within the film from 59 to 74%. This study led to the development of solid microcrystalline dispersion as a buccal film with a faster dissolution rate than the drug alone overcoming problem of poor solubility.

Poly(lactic-co-glycolic acid) devices: Production and applications for sustained protein delivery

Injectable or implantable poly(lactic-co-glycolic acid) (PLGA) devices for the sustained delivery of proteins have been widely studied and utilized to overcome the necessity of repeated administrations for therapeutic proteins due to poor pharmacokinetic profiles of macromolecular therapies. These devices can come in the form of microparticles, implants, or patches depending on the disease state and route of administration. Furthermore, the release rate can be tuned from weeks to months by controlling the polymer composition, geometry of the device, or introducing additives during device fabrication. Slow-release devices have become a very powerful tool for modern medicine. Production of these devices has initially focused on emulsion-based methods, relying on phase separation to encapsulate proteins within polymeric microparticles. Process parameters and the effect of additives have been thoroughly researched to ensure protein stability during device manufacturing and to control the release profile. Continuous fluidic production methods have also been utilized to create protein-laden PLGA devices through spray drying and electrospray production. Thermal processing of PLGA with solid proteins is an emerging production method that allows for continuous, high-throughput manufacturing of PLGA/protein devices. Overall, polymeric materials for protein delivery remain an emerging field of research for the creation of single administration treatments for a wide variety of disease. This review describes, in detail, methods to make PLGA devices, comparing traditional emulsion-based methods to emerging methods to fabricate protein-laden devices. This article is categorized under: Biology-Inspired Nanomaterials > Protein and Virus-Based Structures Implantable Materials and Surgical Technologies > Nanomaterials and Implants Biology-Inspired Nanomaterials > Peptide-Based Structures.

Biodegradable Viral Nanoparticle/Polymer Implants Prepared via Melt-Processing

Viral nanoparticles have been utilized as a platform for vaccine development and are a versatile system for the display of antigenic epitopes for a variety of disease states. However, the induction of a clinically relevant immune response often requires multiple injections over an extended period of time, limiting patient compliance. Polymeric systems to deliver proteinaceous materials have been extensively researched to provide sustained release, which would limit administration to a single dose. Melt-processing is an emerging manufacturing method that has been utilized to create polymeric materials laden with proteins as an alternative to typical solvent-based production methods. Melt-processing is advantageous because it is continuous, solvent-free, and 100% of the therapeutic protein is encapsulated. In this study, we utilized melt-encapsulation to fabricate viral nanoparticle laden polymeric materials that effectively deliver intact particles and generate carrier specific antibodies in vivo. The effects of initial processing and postprocessing on particle integrity and aggregation were studied to develop processing windows for scale-up and the creation of more complex materials. The dispersion of particles within the PLGA matrix was studied, and the effect of additives and loading level on the release profile was determined. Overall, melt-encapsulation was found to be an effective method to produce composite materials that can deliver viral nanoparticles over an extended period and elicit an immune response comparable to typical administration schedules.

Milling solid proteins to enhance activity after melt-encapsulation

Polymeric systems for the immobilization and delivery of proteins have been extensively used for therapeutic and catalytic applications. While most devices have been created via solution based methods, hot melt extrusion (HME) has emerged as an alternative due to the high encapsulation efficiencies and solvent-free nature of the process. HME requires high temperatures and mechanical stresses that can result in protein aggregation and denaturation, but additives and chemical modifications have been explored to mitigate these effects. This study explores the use of solid-state ball milling to decrease protein particle size before encapsulation within poly(lactic-co-glycolic acid) (PLGA) via HME. The impact of milling on particle dispersion, retained enzymatic activity, secondary structure stability, and release was explored for lysozyme, glucose oxidase, and the virus-like particle derived from Qβ to fully understand the impact of milling on protein systems with different sizes and complexities. The results of this study describe the utility of milling to further increase the stability of protein/polymer systems prepared via HME.

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.

Solubility of drugs in aqueous polymeric solution: effect of ovalbumin on microencapsulation process

Microencapsulation of water-soluble drugs using coacervation-phase separation method is very challenging, as these drugs partitioned into the aqueous polymeric solution, resulting in poor drug entrapment. For evaluating the effect of ovalbumin on the microencapsulation of drugs with different solubility, pseudoephedrine HCl, verapamil HCl, propranolol HCl, paracetamol, and curcuminoid were used. In addition, drug mixtures comprising of paracetamol and pseudoephedrine HCl were also studied. The morphology, encapsulation efficiency, particle size, and in vitro release profile were investigated. The results showed that the solubility of the drug determined the ratio of ovalbumin to be used for successful microencapsulation. The optimum ratios of drug, ovalbumin, and gelatin for water-soluble (pseudoephedrine HCl, verapamil HCl, and propranolol HCl), sparingly water-soluble (paracetamol), and water-insoluble (curcuminoid) drugs were found to be 1:1:2, 2:3:5, and 1:3:4. As for the drug mixture, the optimum ratio of drug, ovalbumin, and gelatin was 2:3:5. Encapsulated particles prepared at the optimum ratios showed high yield, drug loading, entrapment efficiency, and sustained release profiles. The solubility of drug affected the particle size of the encapsulated particle. Highly soluble drugs resulted in smaller particle size. In conclusion, addition of ovalbumin circumvented the partitioning effect, leading to the successful microencapsulation of water-soluble drugs.

Effect of surfactant HLB and different formulation variables on the properties of poly-D,L-lactide microspheres of naltrexone prepared by double emulsion technique

The aim of this work was to investigate the role of HLB of emulsifier as well as volume of the internal aqueous phase (W(1)) and presence of salt in the external aqueous phase (W(2)) on the morphology, size and encapsulation efficiency of poly(D,L-lactide) microspheres containing naltrexone HCl. PLA microparticles containing naltrexone HCl, an effective opiate antagonist, were prepared by a water-in-oil-in-water emulsification-solvent evaporation procedure. One of the five different emulsifiers: span 80, span 20, tween 85, tween 80 and tween 20, with HLB values from 4-17 were added to W(1). Presence of emulsifier in W(1) resulted in smaller particles with a more dense and uniform internal structure. Incorporation of span 80 (HLB 4.3, suitable for W/O emulsions) yield the highest encapsulation efficiency. Increasing the HLB value to 8 or 11 (span 20 or tween 85) decreased the efficiency of naltrexone HCl-loading. HLB values higher than 15 (tween 80 or tween 20) increased encapsulation efficiency unexpectedly, which could be attributed to migration of these emulsifiers to the O/W(2) interface and modifying the surface properties of microparticles. Increasing the internal water phase volume from 0.2-1.8 ml resulted in larger particle size with poor encapsulation efficiency. Addition of 10% w/w NaCl to the W(2) changed the surface morphology of microspheres from a porous form to a smooth surface. It was shown that, by selecting the appropriate HLB value of emulsifier in W(1), addition of salt to W(2) and controlling the volume of W(1), one can control the encapsulation efficiency, size and morphology of microspheres.

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.

Preparation, characterization, and in vitro evaluation of physostigmine-loaded poly(ortho ester) and poly(ortho ester)/poly(D,L-lactide-co-glycolide) blend microspheres fabricated by spray drying

The physostigmine-loaded poly(ortho ester) (POE), poly(dl-lactide-co-glycolide) (PLGA) and POE/PLGA blend microspheres were fabricated by a spray drying technique. The in vitro degradation of, and physostigmine release from, the microspheres were investigated. SEM analysis showed that the POE and POE/PLGA blend particles were spherical. They were better dispersed when compared to the pure PLGA microspheres. Two glass transition temperature ( Tg ) values of the POE/PLGA blend microspheres were observed due to the phase separation of POE and PLGA in the blend system. XPS analysis proved that POE dominated the surfaces of POE/PLGA blend microspheres, indicating that the blend microspheres were coated with POE. The encapsulation efficiencies of all the microspheres were more than 95%. The incorporation of physostigmine reduced the Tg value of microspheres. The Tg value of the degrading microspheres increased with the release of physostigmine. For instance, POE blank microspheres and physostigmine-loaded POE microspheres had a Tg value of 67 degrees C and 48 degrees C, respectively. After 19 days in vitro incubation, Tg of the degrading POE microspheres increased to 55 degrees C. Weight loss studies showed that the degradation of the blend microspheres was accelerated with the presence of PLGA because its degradation products catalyzed the degradation of both POE and PLGA. The release rate of physostigmine increased with increase of PLGA content in the blend microspheres. The initial burst release of physostigmine was effectively suppressed by introducing POE to the blend microspheres. However, there was an optimized weight ratio of POE to PLGA (85:15 in weight), below which a high initial burst was induced. The POE/PLGA blend microspheres may make a good drug delivery system.

Quantitative determination of the antitumor alkyl ether phospholipid edelfosine by reversed-phase liquid chromatography–electrospray mass spectrometry: application to cell uptake studies and characterization of drug delivery systems

Edelfosine is a synthetic alkyl ether phospholipid that represents a promising class of antitumor agents. However, analytical methods to measure these type compounds are scarce. The lack of a reliable methodology to quantify edelfosine is a major problem in ongoing and scheduled preclinical and clinical trials with this drug. We evaluated the applicability of high-performance liquid chromatography-mass spectrometry to determine edelfosine in biological samples and polymeric delivery systems. Sample pre-treatment involved polymer precipitation or cell lysis with methanol. HPLC separation was performed on an Alltima RPC(18) narrow-bore column and edelfosine quantification was done by electrospray ionization mass spectrometry (ESI-MS) using positive ion mode and selected ion monitoring. Assays were linear in the tested range of 0.3-10 microg/ml. The limit of quantification was 0.3 ng/sample in both matrices, namely biological samples and polymeric delivery systems. The interassay precision ranging from 0.79 to 1.49%, with relative errors of -6.7 and 12.8%. Mean extraction recovery was 95.6%. HPLC-ESI-MS is a reliable system for edelfosine analysis and quantification in samples from different sources, combining advantages of full automation (rapidity, ease of use, no need of extensive extraction procedures) with high analytical performance and throughput.

Influence of Manufacturing Parameters on Development of Contraceptive Steroid Loaded Injectable Microspheres

The main objective of this work was to develop a system consisting of polymeric microspheres loaded with steroid drugs. The drugs were encapsulated using biodegradable poly(lactide-co-glycolide) (PLG) and poly(epsilon-caprolactone) (PCL) by double emulsion solvent evaporation method. The lipophilic drugs, levonorgestrel and ethinylestradiol were made soluble by adding ethanol/water mixture. The effects of parameters like polymer concentration and stabilizer concentration were studied on the size, size distribution, surface properties and loading efficiencies of microspheres. The formulated microspheres were smooth, spherical and uniform in shape and size. Fourier transformed infrared spectroscopy and differential scanning calorimetry studies seemed to confirm the absence of chemical interaction between the drugs and the polymers, while the drugs were dispersed in the polymer. The increase in polymer concentrations increased the size as well as the loading efficiency of microspheres. Data obtained in this study demonstrated that the PLG/PCL microspheres may be a suitable polymeric carrier for long acting injectable drug delivery.

Preparation and characterization of injectable microspheres of contraceptive hormones

Present study describes the development of a new formulation of levonorgestrel and ethinylestradiol based on double emulsion-solvent evaporation technique using poly(epsilon-caprolactone) (PCL) as biodegradable polymer. The effect of polymer concentration on microspheres and entrapment of drug into microspheres were studied. PCL was selected because of its hydrophobicity and advantages over other biodegradable polymers. Characterization of biodegradable polymer used for controlled drug delivery is essential to ensure reproducibility of in vitro and in vivo performances. The selected characterisation techniques established for PCL microspheres include its loading and entrapment efficiencies, DSC to analyse thermal behaviour, SEM to observe surface morphology, drug content of microspheres and in vitro release of drugs from microspheres. The SEM reports showed that microspheres were with smooth surface and DSC thermograms revealed no interaction between drug and polymer. The entrapment was found to be 58 and 47% for 1:10 and 1:5 batches and in vitro release studies showed that about 69.7% of LNG and 66.7% of EE from 1:10 batch and about 80% of LNG and 75.5% of EE from 1:5 batch for 150 days.

Optimization of topical cidofovir penetration using microparticles

Cidofovir is a new class of antiviral agent with potent in vitro and in vivo activity against a broad spectrum of herpes viruses. The aim of this work was to obtain a prolonged therapeutic effect of cidofovir in the basal epidermis after its topical application. For this purpose, poly(lactide-co-glycolide) (PLGA) microparticles were prepared by solvent evaporation and spray-drying methods. Microparticles prepared by spray-drying showed a encapsulation efficiency of 80%. Conversely, for all the microspheres prepared by the W/O/W solvent evaporation method the encapsulation efficiency was low. Also, microparticles prepared by spray-drying showed a higher burst release. Skin penetration and distribution experiments were carried out with cidofovir-loaded microparticles prepared by spray-drying, since these carriers presented the best characteristics in terms of size and encapsulation efficiency. A cidofovir solution in 0.2% PVA served for comparison. Penetration experiments were carried out in Franz type diffusion cells with an available diffusion area of 1.76 cm(2), using porcine skin. The results obtained showed that the amount of cidofovir penetrated, over a 24 h time period, was higher with the drug solution than with microparticles. Cidofovir distribution in porcine skin, after topical application of microparticles and drug solution for 24 h, was determined by horizontal slicing of the skin. The profiles obtained for the two formulations showed that the quantity of cidofovir retained in the skin decreased with the depth. Besides the amount of cidofovir found in the basal epidermis (120-150 microm) was much higher with microparticles than with the control solution. These data showed that cidofovir-loaded microparticles could improve cidofovir topical therapy since these vehicles increased drug retention in the basal epidermis and decreased its penetration through the skin.

Production and characterization of biodegradable Povidone-iodine microsphere as a intramammary disinfectant

Microspheres composed of biocompatible, biodegradable poly DL-lactide-co-glycolide (DL-PLGA) and Povidone-iodine were evaluated as an intramammary disinfectant delivery system in vitro prior to infusion into mammary glands. Microsphere was prepared by solvent evaporation method and particle size, morphology and in vitro release kinetics were examined. The microspheres were ranged in size from 25 microm to 155 microm (mean diameter = 65.7 microm). Povidone-iodine was dispersed on the surface of microsphere and microsphere was spherical in shape with a smooth surface. The yield of microsphere was 57.3% and the encapsulation efficiency was 69.6%. In in vitro release study, a burst effect (50.9%) was observed during the first two days and a sustained release then continued for the next 28 days. Results of the present study demonstrated that microsphere have the potential for new intramammary disinfectant formulations that can provide increased efficacy of therapy against mastitis pathogens.

Formulation and in vitro-in vivo evaluation of piribedil solid lipid micro- and nanoparticles

Modification of the dissolution rate and, thus, the enhancement of the bioavailability of a dopaminergic drug, piribedil, which has a low aqueous solubility and short elimination half-life have been the aim in this study. Preparations of micron and submicron particles using solid lipid carriers have been performed for this purpose. For the avoidance of solvent residues resulting from the preparation technique, cold and hot homogenization methods have been used to prepare solid lipid particles. After obtaining an appropriate particle size, piribedil loading and preparation yield by the use of those two methods, various formulations have been prepared with different lipid, drug and surfactant materials. The factors mentioned were found to affect properties of the particles, and the release rate was found to be the fastest in acidic medium. Suspensions of pure piribedil and a formulation, selected according to the results obtained from in vitro dissolution and particle size experiments, were compared using tremor tests in mice. The same suspensions were applied perorally to rabbits and bioavailability of the solid lipid particle was found to be higher than the pure piribedil. After an in vitro-in vivo evaluation of piribedil solid lipid particles developed for Parkinson's disease therapy, it has been determined that release rate could be controlled and piribedil bioavailability could be improved.

Poly(ethylene carbonate) microspheres: manufacturing process and internal structure characterization

The granulocyte-macrophage colony stimulating factor (GM-CSF), a water-soluble cytokine, was encapsulated in poly(ethylene carbonate) microspheres (MS) by a double emulsion w(1)/o/w(2) solvent evaporation method. Poly(ethylene carbonate) is a new polymer of high molecular weight (MW) and forms polymer matrices that are exclusively surface bioerodible. In the frame of this study, the influence of the polymer molecular weight and the polymer concentration in the organic phase on the physico-chemical characteristics of the microspheres were investigated. Ninety percent of the microspheres had a diameter ranging between 4 and 136 microm, with a mean value of 30 microm. The encapsulation ratios ranged from 2.22 to 2.51% (w/w) depending on the molecular weight of the polymer corresponding to an encapsulation efficiency of 70 to 100%, respectively. Independent of the polymer molecular weight used, the in vitro drug release was very low, ranging from 5.61 to less than 1% of the total encapsulated GM-CSF amount. Scanning electron microscopy (SEM) analysis showed microparticles with spherical shapes and smooth surfaces containing a few small globules. The inner structure of the microspheres appeared to consist of a polymeric matrix surrounding numerous globules. These globules have different sizes, shape and distribution in the polymeric matrix, depending on the concentration of the polymer solution and on the polymer molecular weight. In addition, it was demonstrated that the GM-CSF lowered the interfacial tension between the GM-CSF aqueous solution and the methylene chloride organic phase. The active critical concentration was as low as 0.008 mg/ml. It was therefore suggested that this particular behavior contributed to the stabilization of the primary emulsion during the formation of the microspheres, leading to rather high encapsulation efficiency.

In vitro and in vivo evaluation of a somatostatin analogue released from PLGA microspheres

The purpose of this study was to design poly(lactide-co-glycolide) (PLGA) microspheres for the continuous delivery of the somatostatin analogue, vapreotide, over 2-4 weeks. The microspheres were produced by spray-drying and the desired characteristics, i.e. high encapsulation efficiency and controlled release over 2-4 weeks, achieved through optimizing the type of polymer, processing solvent, and co-encapsulated additive. The in vitro release was tested in fetal bovine serum preserved with 0.02% of thiomersal. Furthermore, formulations were injected intramuscularly into rats to obtain pharmacokinetic profiles. Encapsulation efficiency was between 34 and 91%, depending on the particular formulation. The initial peptide release (within 6 h) was lowest, i.e. <20%, when acetic acid was used as processing solvent and highest, i.e. 57%, with dichloromethane. The various co-encapsulated additives generally lowered the encapsulation efficiency by 15-30%. The best formulation in terms of low burst and effective drug serum levels (>1 ng/ml) over 21-28 days in rats was the one made with end-group uncapped PLGA 50:50, the solvent acetic acid and the additive polyethyleneglycol. In conclusion, the optimization of formulation parameters allowed us to produce vapreotide-loaded PLGA microspheres of suitable characteristics for therapeutic use.

Influence of formulation parameters on the characteristics of poly(D, L-lactide-co-glycolide) microspheres containing poly(L-lysine) complexed plasmid DNA

This study describes the influence of polymer type, surfactant type/concentration, and target drug loading on the particle size, plasmid DNA (pDNA) structure, drug loading efficiency, in vitro release, and protection from DNase I degradation of poly(D, L-lactide-co-glycolide) (PLGA) microspheres containing poly(L-lysine) (PLL) complexed pDNA. PLGA microspheres containing pDNA-PLL were prepared using the water-in-oil-in-water (w-o-w) technique with poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) as surfactants in the external aqueous phase. A complex ratio of 1:0.33 (pDNA-PLL, w/w) enhanced the stability of pDNA during microsphere preparation. Higher pDNA-PLL loading efficiency (46.2%) and supercoiled structure (64.9%) of pDNA were obtained from hydrophobic PLGA (M(w) 31000) microspheres compared with hydrophilic PLGA or low-molecular-weight PLGA microspheres. The particle size decreased from 6.6 to 2.2 microm when the concentration of PVA was increased from 1 to 7%. At the same concentration of surfactant, PVA stabilized microspheres showed higher pDNA-PLL loading efficiency (46.2%) than PVP stabilized microspheres (24.1%). Encapsulated pDNA in PLGA microspheres was protected from enzymatic degradation and maintained in the supercoiled form. The pDNA-PLL microspheres showed in vitro release of 95.9 and 84.9% within 38 days from the low-molecular-weight PLGA and hydrophilic PLGA microspheres, respectively, compared to 54.2% release from the hydrophobic, higher-molecular-weight PLGA microspheres. The results suggest loading and release of pDNA-PLL complex can be influenced by surfactant concentration and polymer type.

Changing the pH of the external aqueous phase may modulate protein entrapment and delivery from poly(lactide-co-glycolide) microspheres prepared by a w/o/w solvent evaporation method

The milk model protein, beta lactoglobulin (BLG), was encapsulated into microspheres prepared by a multiple emulsion/solvent evaporation method. The effect of the pH of the outer aqueous phase on protein encapsulation and release as well as on microsphere morphology has been investigated. At all tested pH values, the encapsulation efficiency was shown to decrease with increasing the initial amount of BLG. This was correlated with the reduced stability of the primary emulsion as the initial BLG increased. In addition, reducing the solubility of BLG in the external aqueous phase by decreasing the pH to the isoelectric point of BLG (pI 5.2) resulted in an improved protein encapsulation. Moreover, it was shown that combining pH modification and optimal stability of the first emulsion yielded microspheres with a high encapsulation efficiency. However, release kinetic studies revealed that a significant burst release was observed with microspheres loaded with large amounts of BLG, especially when prepared in a medium at pH 5.2. This burst effect was attributed to morphology changes in the microsphere surface which was characterized by the presence of pores or channels able to accelerate the release of BLG. These pores were assumed to result from the presence of large amounts of protein molecules on the microsphere surface, that aggregate during microsphere formation at pH 5.2. Indeed, single adsorption experiments have shown that BLG had a higher affinity for the particle surface when the pH was close to the pI. Thus, reducing the solubility of a protein in the external aqueous phase allows the product of microspheres with a better encapsulation efficiency, although this benefit is provided by a strong adsorption of the protein on microsphere surface.

Multiple emulsion technology for the design of microspheres containing peptides and oligopeptides

This paper reviews the preparation and characterization of small poly(lactic-co-glycolic acid) microspheres (mean size lower than 10 µm) containing small peptides and prepared by a water-in-oil-in-water emulsion solvent evaporation technique. These microspheres were shown to encapsulate very efficiently a 33 amino acid peptide (V3 BRU) and in vitro release kinetics studies showed that such microspheres could be employed for both oral vaccination and controlled release. The encapsulation of a seven amino acid peptide (pBC 264) led on the contrary to a very low encapsulation efficiency. In order to increase the encapsulation of pBC 264, two strategies were adopted: (i) taking into account the solubility of pBC 264 at different pH, the inner aqueous phase was maintained at a basic pH where the peptide was soluble, while the external aqueous phase was acidic; (ii) ovalbumin was added to stabilize the inner emulsion. These two strategies allowed us to increase significantly the encapsulation rate of pBC 264. Nevertheless, the in vitro release kinetics of the peptide were strongly influenced by the presence of ovalbumin which seems to form pores in the microsphere structure. By contrast, when ovalbumin was replaced by Pluronic(R) F68, microspheres did not have pores, thus the release profile and the extent of the burst were much smaller. When microspheres were stereotactically implanted in the rat brain, in vivo release profiles were in good agreement with the release observed in vitro. In conclusion, these microspheres are well suited for the slow delivery of neuropeptides in the brain, a feature expected to facilitate the study of long term effects of these compounds.