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

Fabrication, characterization and optimization of berberine-loaded PLA nanoparticles using coaxial electrospray for sustained drug release

BACKGROUND

Berberine (BBR) broadly found in medicinal plants has a major application in pharmacological therapy as an anticancer drug. Clinical applications of this promising natural drug are limited due to its poor water solubility and low bioavailability.

OBJECTIVE

In this study, for the first time, we synthesized core-shell BBR-loaded PLA nanoparticles (NPBs) by using coaxial electrospray (CES) to solve the poor bioavailability of BBR.

METHODS

Three-factor (feeding rate, polymeric solution concentration and applied voltage), three-level, Box-Behnken design was used for optimization of the size and particle size distribution of the prepared NPBs.

RESULTS

Based on the results of response surface methodology, the NPBs with the mean size of 265 nm and particle size distribution of 43 nm were synthesized. A TEM image was used to well illustrate the core-shell structure of the NPBs. Encapsulation efficiency and BBR loading capacity for the optimized NPBs were determined at about 81% and 7.5%, respectively. Release of NPBs was examined at pH 7.4 and 5.8. NPBs had a slower release profile than free BBR in both pH values, and the rate of BBR release was more and faster in acidic pH than in physiological one. Effects of the NPBs on the drug release were confirmed by data fitting with six kinetic models. NPBs showed an increased cytotoxic efficacy against HCT116 cells (IC₅₀ = 56 μM), while NIH3T3 cells, non-neoplastic fibroblast cells, (IC₅₀ > 150 μM) were less affected by NPBs. Flow cytometry demonstrated that the cellular uptake of NPBs were higher than BBR at different concentrations.

CONCLUSIONS

A new approach was developed in this study to prepare NPBs using the CES process for improving the efficiency and controlled BBR release. It is concluded that nano-scaled NPBs prepared by CES can improve toxicity and chemotherapeutic properties of BBR against cancerous cells. We believe that these NPBs can exhibit further potential in cancer drug delivery systems. Graphical abstract.

Repurposing rosiglitazone, a PPAR-γ agonist and oral antidiabetic, as an inhaled formulation, for the treatment of PAH

Peroxisome-proliferator-activated-receptor-gamma (PPAR-γ) is implicated, in some capacity, in the pathogenesis of pulmonary arterial hypertension (PAH). Rosiglitazone, an oral antidiabetic and PPAR-γ agonist, has the potential to dilate pulmonary arteries and to attenuate arterial remodeling in PAH. Here, we sought to test the hypothesis that rosiglitazone can be repurposed as inhaled formulation for the treatment of PAH. We have tested this conjecture by preparing and optimizing poly(lactic-co-glycolic) acid (PLGA) based particles of rosiglitazone, assessing the drug particles for pulmonary absorption, investigating the efficacy of the plain versus particulate drug formulation in improving the respiratory hemodynamics in PAH animals, and finally studying the effect of the drug in regulating the molecular markers associated with PAH pathogenesis. The optimized particles were slightly porous and spherical, and released 87.9% ± 6.7% of the drug in 24 h. The elimination half-life of the drug formulated in PLGA particles was 2.5-fold greater than that of the plain drug administered via the same route at the same dose. The optimized formulation, given via the pulmonary route, produced pulmonary selective vasodilation in PAH animals, but oral rosiglitazone had no effect in pulmonary hemodynamics. Rosiglitazone ameliorates the pathogenesis of PAH by balancing the molecular regulators involved in the vasoconstriction and vasodilation of human pulmonary arterial smooth muscle cells. All in all, data generated using intact animal and cellular models point to the conclusion that PLGA particles of an antidiabetic drug can be used for the treatment of a different disease, PAH.

Antimicrobial Properties of Microparticles Based on Carmellose Cross-Linked by Cu(2+) Ions

Carmellose (CMC) is frequently used due to its high biocompatibility, biodegradability, and low immunogenicity for development of site-specific or controlled release drug delivery systems. In this experimental work, CMC dispersions in two different concentrations (1% and 2%) cross-linked by copper (II) ions (0.5, 1, 1.5, or 2.0 M CuCl₂) were used to prepare microspheres with antimicrobial activity against Escherichia coli and Candida albicans, both frequently occurring pathogens which cause vaginal infections. The microparticles were prepared by an ionotropic gelation technique which offers the unique possibility to entrap divalent copper ions in a CMC structure and thus ensure their antibacterial activity. Prepared CMC microspheres exhibited sufficient sphericity. Both equivalent diameter and copper content were influenced by CMC concentration, and the molarity of copper (II) solution affected only the copper content results. Selected samples exhibited stable but pH-responsive behaviour in environments which corresponded with natural (pH 4.5) and inflamed (pH 6.0) vaginal conditions. All the tested samples exhibited proven substantial antimicrobial activity against both Gram-negative bacteria Escherichia coli and yeast Candida albicans. Unexpectedly, a crucial parameter for microsphere antimicrobial activity was not found in the copper content but in the swelling capacity of the microparticles and in the degree of CMC surface shrinking.

Microparticles prepared from sulfenamide-based polymers

Polysulfenamides (PSN), with a SN linkage (RSNR2) along the polymer backbone, are a new class of biodegradable and biocompatible polymers. These polymers were unknown prior to 2012 when their synthesis and medicinally relevant properties were reported. The aim of this study was to develop microparticles as a controlled drug delivery system using polysulfenamide as the matrix material. The microparticles were prepared by a water-in-oil-in-water double-emulsion solvent-evaporation method. For producing drug-loaded particles, FITC-dextran was used as a model hydrophilic compound. At the optimal formulation conditions, the external morphology of the PSN microparticles was examined by scanning electron microscopy to show the formation of smooth-surfaced spherical particles with low polydispersity. The microparticles had a net negative surface charge (-23 mV) as analyzed by the zetasizer. The drug encapsulation efficiency of the particles and the drug loading were found to be dependent on the drug molecular weight, amount of FITC-dextran used in fabricating FITC-dextran-loaded microparticles, concentration of PSN and surfactant, and volume of the internal and external water phases. FITC-dextran was found to be distributed throughout the PSN microparticles and was released in an initial burst followed by more continuous release over time. Confocal laser scanning microscopy was used to qualitatively observe the cellular uptake of PSN microparticles and indicated localization of the particles in both the cytoplasm and the nucleus.

Preparation, characterization and in vitro release properties of morphine-loaded PLLA-PEG-PLLA microparticles via solution enhanced dispersion by supercritical fluids

Morphine-loaded poly(L-lactide)-poly(ethylene glycol)-poly(L-lactide) (PLLA-PEG-PLLA) microparticles were prepared using solution enhanced dispersion by supercritical CO2 (SEDS). The effects of process variables on the morphology, particles size, drug loading (DL), encapsulation efficiency and release properties of the microparticles were investigated. All particles showed spherical or ellipsoidal shape with the mean diameter of 2.04-5.73 μm. The highest DL of 17.92 % was obtained when the dosage ratio of morphine to PLLA-PEG-PLLA reached 1:5, and the encapsulation efficiency can be as high as 87.31 % under appropriate conditions. Morphine-loaded PLLA-PEG-PLLA microparticles displayed short-term release with burst release followed by sustained release within days or long-term release lasted for weeks. The degradation test of the particles showed that the degradation rate of PLLA-PEG-PLLA microparticles was faster than that of PLLA microparticles. The results collectively suggest that PLLA-PEG-PLLA can be a promising candidate polymer for the controlled release system.

Oxycellulose beads with drug exhibiting pH-dependent solubility

The aim of this study was to develop novel hydrogel-based beads and characterize their potential to deliver and release a drug exhibiting pH-dependent solubility into distal parts of gastrointestinal (GI) tract. Oxycellulose beads containing diclofenac sodium as a model drug were prepared by the ionotropic external gelation technique using calcium chloride solution as the cross-linking medium. Resulting beads were characterized in terms of particle shape and size, encapsulation efficacy, swelling ability and in vitro drug release. Also, potential drug-polymer interactions were evaluated using Fourier transform infrared spectroscopy. The particle size was found to be 0.92-0.96 mm for inactive (oxycellulose only) and 1.47-1.60 mm for active (oxycellulose-diclofenac sodium) beads, respectively. In all cases, the sphericity factor was between 0.70 and 0.81 with higher values observed for samples containing higher polymer and drug concentrations. The swelling of inactive beads was found to be strongly influenced by the pH and composition (i.e. Na(+) concentration) of the selected media (simulated gastric fluid vs. phosphate buffer pH 6.8). The encapsulation efficiency of the prepared particles ranged from 58% to 65%. Results of dissolution tests showed that the drug loading inside of the particles influenced the rate of its release. In general, prepared particles were able to release the drug within 12-16 h after a lag time of 4 h. Fickian diffusion was found as the predominant drug release mechanism. Thus, this novel particulate system showed a good potential to deliver drugs specifically to the distal parts of the human GI tract.

Sodium fusidate-poly(D,L-lactide-co-glycolide) microspheres: Preparation, characterisation andin vivoevaluation of their effectiveness in the treatment of chronic osteomyelitis

PURPOSE

The aim of this study was to prepare poly(D,L-lactide-co-glycolide) (PLGA) microspheres containing sodium fusidate (SF) using a double emulsion solvent evaporation method with varying polymer:drug ratios (1:1, 2.5:1, 5:1) and to evaluate its efficiency for the local treatment of chronic osteomyelitis.

METHODS

The particle size and distribution, morphological characteristics, thermal behaviour, drug content, encapsulation efficiency and in vitro release assessments of the formulations had been carried out. Sterilized SF-PLGA microspheres were implanted in the proximal tibia of rats with methicillin-resistant Staphylococcus aureus (MRSA) osteomyelitis. After 3 weeks of treatment, bone samples were analysed with a microbiological assay.

RESULTS

PLGA microspheres between the size ranges of 2.16-4.12 microm were obtained. Production yield of all formulations was found to be higher than 79% and encapsulation efficiencies of 19.8-34.3% were obtained. DSC thermogram showed that the SF was in an amorphous state in the microspheres and the glass transition temperature (T(g)) of PLGA was not influenced by the preparation procedure. In vitro drug release studies had indicated that these microspheres had significant burst release and their drug release rates were decreased upon increasing the polymer:drug ratio (p < 0.05). Based on the in vivo data, rats implanted with SF-PLGA microspheres and empty microspheres showed 1987 +/- 1196 and 55526 +/- 49086 colony forming unit of MRSA in 1 g bone samples (CFU/g), respectively (p < 0.01).

CONCLUSION

The in vitro and in vivo studies had shown that the implanted SF loaded microspheres were found to be effective for the treatment of chronic osteomyelitis in an animal experimental model. Hence, these microspheres may be potentially useful in the clinical setting.

Effect of Chitosan Salts and Molecular Weight on a Nanoparticulate Carrier for Therapeutic Protein

The objective of this study was to investigate the potential of chitosan salts as a carrier in the preparation of protein-loaded nanoparticles. Glutamic and aspartic acids were used to prepare chitosan salts of 35, 100, and 800 KDa. Nanoparticles of chitosan base, chitosan glutamate, and chitosan aspartate were produced by ionotropic gelation with sodium tripolyphosphate (TPP). Bovine serum albumin (BSA) was applied as a model protein at loading concentrations ranging from 0.2 to 2 mg/mL. The size of the nanoparticles, as measured by photon correlation spectroscopy, was in the range of 195 to 3450 nm, depending on type and molecular weight of chitosan. Nanoparticles prepared with higher molecular weight chitosan showed larger sizes. The encapsulation was controlled by the competition of BSA in forming ionic cross-linking with chitosan and by the entrapment of BSA during the gelation process. Higher BSA encapsulation efficiency (EE) was obtained for nanoparticles prepared with chitosan salts compared to those prepared with the base. The higher EE was a result of a higher degree of ionization, causing more active sites to interact with BSA. In addition, a higher and faster release of BSA from the nanoparticles into pH 7.4 buffer medium was observed for nanoparticles of the chitosan salts than was observed for nanoparticles of the chitosan base. The higher and faster release was attributed to higher EE and lower entrapment of BSA within the matrix of the nanoparticle during the gelation process. The influence of molecular weight on the property of nanoparticles exhibited different effects. The difference was a result of different organic acids used to prepare nanoparticles leading to the difference in polymer conformation and viscosity of organic acid solution. Therefore, this study showed that the characteristics of chitosan nanoparticles loaded with a protein drug could be readily modulated by changing the salt form or the molecular weight of the chitosan carrier.

Macromolecule Release from Monodisperse PLG Microspheres: Control of Release Rates and Investigation of Release Mechanism

Novel macromolecular therapeutics such as peptides, proteins, and DNA are advancing rapidly toward the clinic. Because of typically low oral bioavailability, macromolecule delivery requires invasive methods such as frequently repeated injections. Parenteral depots including biodegradable polymer microspheres offer the possibility of reduced dosing frequency but are limited by the inability to adequately control delivery rates. To control release and investigate release mechanisms, we have encapsulated model macromolecules in monodisperse poly(D,L-lactide-co-glycolide) (PLG) microspheres using a double-emulsion method in combination with the precision particle fabrication technique. We encapsulated fluorescein-dextran (F-Dex) and sulforhodamine B-labeled bovine serum albumin (R-BSA) into PLG microspheres of three different sizes: 31, 44, and 80 microm and 34, 47, and 85 microm diameter for F-Dex and R-BSA, respectively. The in vitro release profiles of both compounds showed negligible initial burst. During degradation and release, the microspheres hollowed and swelled at critical time points dependant upon microsphere size. The rate of these events increased with microsphere size resulting in the largest microspheres exhibiting the fastest overall release rate. Monodisperse microspheres may represent a new delivery system for therapeutic proteins and DNA and provide enhanced control of delivery rates using simple injectable depot formulations.

Nanoparticles of poly(lactide)-tocopheryl polyethylene glycol succinate (PLA-TPGS) copolymers for protein drug delivery

Nanoparticles (NPs) of poly(lactide)-tocopheryl polyethylene glycol succinate (PLA-TPGS) copolymers with various PLA:TPGS component ratios were prepared by the double emulsion technique for protein drug formulation with bovine serum albumin (BSA) as a model protein. Influence of the PLA:TPGS component ratio and the BSA loading level on the drug encapsulation efficiency (EE) and in vitro drug release behavior was investigated. The PLA-TPGS NPs achieved 16.7% protein drug loading and 75.6% EE, which exhibited a biphasic pattern of controlled protein release with higher initial burst for those NPs of more TPGS content. Furthermore, the released proteins retained good structural integrity for at least 35 days at 37 degrees C as indicated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and circular dichroism (CD) spectroscopy. Compared with other biodegradable polymeric NPs such as poly(D,L-lactide-co-glycolide) (PLGA) NPs, PLA-TPGS NPs could provide the encapsulated proteins a milder environment. Confocal laser scanning microscopy (CLSM) observation demonstrated the intracellular uptake of the PLA-TPGS NPs by NIH-3T3 fibroblast cells and Caco-2 cancer cells. This research suggests that PLA-TPGS NPs could be of great potential for clinical formulation of proteins and peptides.

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.

Microspheres for Drug Delivery

With advances in biotechnology, genomics, and combinatorial chemistry, a wide variety of new, more potent and specific therapeutics are being created. Because of common problems such as low solubility, high potency, and/or poor stability of many of these new drugs, the means of drug delivery can impact efficacy and potential for commercialization as much as the nature of the drug itself. Thus, there is a corresponding need for safer and more effective methods and devices for drug delivery. Indeed, drug delivery systems—designed to provide a therapeutic agent in the needed amount, at the right time, to the proper location in the body, in a manner that optimizes efficacy, increases compliance and minimizes side effects—were responsible for $47 billion in sales in 2002, and the drug delivery market is expected to grow to $67 billion by 2006.

Current advances in sustained-release systems for parenteral drug delivery

Major progresses in the development of parenteral sustained-release systems have been made in recent years as evidenced by the regulatory approval and market launch of several new products. Both the availability of novel carrier materials and the advances in method of fabrication have contributed to these commercial successes. With the formulation challenges associated with biologics, new delivery systems have also been evolved specifically to address the unmet needs in the parenteral sustained release of proteins. In this review paper, different new carriers systems and preparation methods are discussed with special focus on their applications to biologicals.

Microspheres Made of Poly(ɛ-caprolactone)-Based Amphiphilic Copolymers: Potential in Sustained Delivery of Proteins

Microspheres of amphiphilic multi-block poly(ester-ether)s (PEE)s and poly(ester-ether-amide)s (PEEA)s based on poly(epsilon-caprolactone) (PCL) were investigated as delivery systems for proteins. The interest was mainly focused on the effect of their molecular structure and composition on the overall properties of the microspheres, encapsulating bovine serum albumin (BSA) as a model protein. PEEs and PEEAs were prepared using a alpha,omega-dihydroxy-terminated PCL macromer (Mn= 2.0 kDa) as a hydrophobic component. Hydrophilic oxyethylene sequences were generated using poly(ethylene oxide)s (PEO)s of different molecular mass (Mn= 300-600 Da) in the case of PEEs, or 4,7,10-trioxa-1,13-tridecanediamine (Trioxy) and PEO150 (Mn= 150 Da) in the case of PEEAs. The copolymers showed a decrease of Tm and crystallinity values as compared with PCL. Within each class of copolymers, the bulk hydrophilicity increased with increasing the number of oxyethylene groups in the chain repeat unit. PEEAs were more hydrophilic than PEEs with a similar number of oxyethylene groups. Discrete spherical particles were prepared by both PEEs and PEEAs and their BSA encapsulation efficiency related to copolymer properties. Interestingly, the insertion of short hydrophilic segments is enough to significantly affect protein distribution inside microspheres and its release profiles, as compared to PCL microspheres. Different degradation rates and mechanisms were observed for copolymer microspheres, mainly depending on the distribution of oxyethylene units along the chain. The results highlight that a fine control over the structural parameters of amphiphilic PCL-based multi-block copolymers is a key factor for their application in the field of protein delivery.

Microparticle formation and its mechanism in single and double emulsion solvent evaporation

The emulsification is the first step of the emulsification solvent evaporation method and has been extensively investigated. On the contrary the second step, the solvent transport out from the emulsion droplets that determine the particle morphology and with great influence on the microparticles encapsulation and release behavior has been scarcely studied. This study investigates the mechanism of the solvent elimination from the emulsion droplets and its influence on the particle morphology, encapsulation and release behavior. Usually, the solvent is highly volatile that makes the solvent elimination process very fast thus difficult to observe. In order to observe in detail the microparticle formation, the initial emulsion was monitored by optical microscope under controlled solvent evaporation conditions. The results from the optical microscopic observations corroborated with laser diffractometry analysis showed that in single emulsion formulations, spherical microparticles are formed by accelerated solvent elimination due to the combined effects of high solvent volatility and polymer precipitation. The solvent expulsion accompanied by important shrinkage generates on the microparticle surface a thin layer of nanoparticles attested by scanning electron microscopy and laser diffractometry. During the intense solvent elimination, the encapsulated substance is drained, affecting the loading efficiency. Furthermore, it will concentrate towards the microparticle surface contributing to the initial burst release. In double emulsion formulations, microparticles with different morphologies are generated due to the presence of the aqueous-phase microdroplets inside the emulsion droplet. During the solvent elimination, these microdroplets generally coalesce under the pressure of the precipitating polymer. Depending mainly on the polymer concentration and emulsification energies, the final microparticles will be a mixture of honeycomb, capsule or plain structure. During the shrinkage due to the incompressibility of the inner microdroplets, the precipitating polymer wall around them may break forming holes through which the encapsulated substance is partly expulsed. Through these holes, the encapsulated substance is further partitioning with the external aqueous phase during solvent evaporation and contributes to the initial burst release during the application.

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.

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.

Preparation and Characterization of Temperature-Sensitive Poly(N-isopropylacrylamide)-b-poly(d,l-lactide) Microspheres for Protein Delivery

Temperature-sensitive diblock copolymers, poly(N-isopropylacrylamide)-b-poly(D,L-lactide) (PNIPAAm-b-PLA) with different PNIPAAm contents were synthesized and utilized to fabricate microspheres containing bovine serum albumin (BSA, as a model protein) by a water-in-oil-in-water double emulsion solvent evaporation process. XPS analysis showed that PNIPAAm was a dominant component of the microspheres surface. BSA was well entrapped within the microspheres, and more than 90% encapsulation efficiency was achieved. The in vitro degradation behavior of microspheres was investigated using SEM, NMR, FTIR, and GPC. It was found that the microspheres were erodible, and polymer degradation occurred in the PLA block. Degradation of PLA was completed after 5 months incubation in PBS (pH 7.4) at 37 degrees C. A PVA concentration of 0.2% (w/v) in the internal aqueous phase yielded the microspheres with an interconnected porous structure, resulting in fast matrix erosion and sustained BSA release. However, 0.05% PVA produced the microspheres with a multivesicular internal structure wrapped with a dense skin layer, resulting in lower erosion rate and a biphasic release pattern of BSA that was characterized with an initial burst followed by a nonrelease phase. The microspheres made from PNIPAAm-b-PLA with a higher portion of PNIPAAm provided faster BSA release. In addition, BSA release from the microspheres responded to the external temperature changes. BSA release was slower at 37 degrees C (above the LCST) than at a temperature below the LCST. The microspheres fabricated with PNIPAAm-b-PLA having a 1:5 molar ratio of PNIPAAm to PLA and 0.2% (w/v) PVA in the internal aqueous phase provided a sustained release of BSA over 3 weeks in PBS (pH 7.4) at 37 degrees C.

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.

The preparation and characterization of monomethoxypoly(ethylene glycol)-b-poly-DL-lactide microcapsules containing bovine hemoglobin

Methoxypoly(ethylene glycol)-b-poly-DL-lactide (PELA) microcapsules containing bovine hemoglobin (bHb) were prepared by a W/O/W double emulsion-solvent diffusion process. bHb solution was used as the internal aqueous phase, PELA/organic solvent as the oil phase, and polyvinyl alcohol (PVA) solution as the external aqueous phase. This W/O/W double emulsion was added into a large volume of water (solidification solution) to allow organic solvent to diffuse into water. The optimum preparative condition for PELA microcapsules loaded with bovine hemoglobin was investigated. It was found that homogenization rate, type of organic solvent, and volume of the solidification solution influenced the activity of bovine hemoglobin encapsulated. When the homogenization rate was lower than 9000 rpm and ethyl acetate was used as the organic solvent, there was no significant influence on the activity of hemoglobin. High homogenization rate as 12 000 rpm decreased the P50 and Hill coefficient. Increasing the volume of solidification solution had an effect of improving the activity of microencapsulated hemoglobin. The composition of the PELA had the most important influence on the success of encapsulation. Microcapsules fabricated by PELA with MPEG2k block (molecular weight of MPEG block: 2000) achieved a high entrapment efficiency of 90%, better than PL A homopolymer and PELA with MPEG5k blocks. Hemoglobin microcapsules with native loading oxygen activity (P50 = 26.0 mmHg, Hill coefficient = 2.4), mean size of about 10 microm, and high entrapment efficiency (ca. 93%) were obtained at the optimum condition.

POE/PLGA composite microspheres: formation and in vitro behavior of double walled microspheres

The poly(ortho ester) (POE) and poly(D,L-lactide-co-glycolide) 50:50 (PLGA) composite microspheres were fabricated by a water-in-oil-in-water (w/o/w) double emulsion process. The morphology of the composite microspheres varied depending on POE content. When the POE content was 50, 60 or 70% in weight, the double walled microspheres with a dense core of POE and a porous shell of PLGA were formed. The formation of the double walled POE/PLGA microspheres was analysed. Their in vitro degradation behavior was characterized by scanning electron microscopy, gel permeation chromatography, Fourier-transform infrared microscopy and nuclear magnetic resonance spectroscopy (NMR). It was found that compared to the neat POE or PLGA microspheres, distinct degradation mechanism was achieved in the double walled POE/PLGA microspheres system. The degradation of the POE core was accelerated due to the acidic microenvironment produced by the hydrolysis of the outer PLGA layer. The formation of hollow microspheres became pronounced after the first week in vitro. 1H NMR spectra showed that the POE core was completely degraded after 4 weeks. On the other hand, the outer PLGA layer experienced slightly retarded degradation after the POE core disappeared. PLGA in the double walled microspheres kept more than 32% of its initial molecular weight over a period of 7 weeks.

Oral insulin--a perspective

Diabetes mellitus is generally controlled quite well with the administration of oral medications or by the use of insulin injections. The current practice is the use of one or more doses, intermediate or long acting insulin per day. Oral insulin is a promising yet experimental method providing tight glycemic control for patients with diabetes. A biologically adhesive delivery systems offer important advantage over conventional drug delivery systems. The engineered polymer microspheres made of erodable polymer display strong adhesive interactions with gastrointestinal mucus and cellular lining can traverse both the mucosal epithelium and the follicle associated epithelium covering the lymphoid tissue of Peyer's patches. Alginate, a natural polymer recovered from seaweed is being developed as a nanoparticle for the delivery of insulin without being destroyed in the stomach. Alginate is in fact finding application in biotechnology industry as thickening agent, a gelling agent and a colloid stabilizer. Alginate has in addition, several other properties that have enabled it to be used as a matrix for entrapment and for the delivery of a variety of proteins such as insulin and cells. These properties include: a relatively inert aqueous environment within the matrix; a mild room temperature encapsulation process free of organic solvents; a high gel porosity which allows for high diffusion rates of macromolecules; the ability to control this porosity with simple coating procedures and dissolution and biodegradation of the system under normal physiological conditions.

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

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