Improving the delivery capacity of microparticle systems using blends of poly(DL-lactide co-glycolide) and poly(ethylene glycol)

Impact of PEG Content on Doxorubicin Release from PLGA-co-PEG Nanoparticles

Nanoparticles (NPs) have become attractive vehicles for drug delivery in cancer therapy due to their ability to accumulate in tumours and mitigate side effects. This study focuses on the production of doxorubicin (DOX)-loaded NPs comprising Poly (lactic-co-glycolic acid)-Polyethylene glycol with varying PEG proportions and the examination of their impact on drug release kinetics. DOX-loaded NPs, composed of PLGA-co-PEG with PEG contents of 0%, 5%, 10%, and 15%, were synthesized by the solvent evaporation technique, exhibited spherical morphology, and had sizes ranging from 420 nm to 690 nm. In vitro drug release studies revealed biphasic profiles, with higher PEG contents leading to faster and more extensive drug release. The Baker-Lonsdale model demonstrated the best fit to the drug release data, indicating that the release process is diffusion-controlled. The diffusion coefficients for DOX determined ranged from 6.3 × 10-18 to 7.55 × 10-17 cm2s-1 and exhibited an upward trend with increasing PEG content in the polymer. In vitro cytotoxicity tests with CHO cells showed that unloaded NPs are non-toxic, while DOX-loaded PLGA-PEG 15% NPs induced a greater decrease in cellular viability compared to their PLGA counterparts. A mathematical relationship between the diffusion coefficient and PEG percentage was derived, providing a practical tool for optimizing DOX release profiles.

Critical attributes of formulation and of elaboration process of PLGA-protein microparticles

Low drug loading, burst effect during release and drug inactivation account for the main drawbacks of protein microencapsulation in poly(d,l-lactic-co-glycolic) acid (PLGA) matrix by the water-in oil-in water (W/O/W) solvent evaporation method. Thus, the current study was set to invest the critical attributes of formulation and of elaboration process which determine protein loading into microparticles as well as its further release, using albumin as protein model. NaCl concentration in the external aqueous phase, poly(vinyl alcohol) (PVA) concentration and mostly viscosity of both the internal aqueous phase and the organic phase were critical attributes for improving drug loading, with polymer molecular weight and hydrophobicity likewise directly related to albumin loading. In such a way, when using 0.5% PVA as internal aqueous phase the highest albumin loading was achieved. Optimized microparticles exhibited a sustained in vitro release of albumin over 130 days. The influence of the microencapsulation process on albumin stability and biological activity was evaluated by carrying out cell proliferation assays on PC12 cells with albumin released from microparticles. Such assay demonstrated that the microencapsulation procedure optimized in this study did not affect the biological stability of the microencapsulated protein.

Release behaviour of carbamazepine-loaded poly(ε-caprolactone)/poly(ethylene oxide) microspheres

Poly(ε-caprolactone) (PCL), a biodegradable and biocompatible aliphatic polyester has a great potential as a drug carrying material in controlled drug delivery/release systems. The most simple and economical way to tailor the release profile of active substances from biodegradable polymer matrix is by the addition of the second polymeric component in the polymer matrix, i.e. by blending. This study describes the preparation and characterization of a carbamazepine-loaded microspheres by the use of PCL blended with poly(ethylene oxide) as a drug carrying material. By the use of two-component hydrophilic/hydrophobic polymer blend as a microspheres' matrix material, release profile of the drug can be modified and dictated. The microspheres prepared by classical oil-in-water emulsion solvent evaporation technique were characterized with respect to particle size and morphology, polymer matrix composition, encapsulation efficiency, physical state of the drug and in vitro release behaviour. It was presented that the release profile can be modified by the presence and the amount of hydrophilic component in the starting formulation of microspheres.

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.

Multi-functional P(3HB) microsphere/45S5 Bioglass-based composite scaffolds for bone tissue engineering

Novel multi-functional P(3HB) microsphere/45S5 Bioglass-based composite scaffolds exhibiting potential for drug delivery were developed for bone tissue engineering. 45S5 Bioglass-based glass-ceramic scaffolds of high interconnected porosity produced using the foam-replication technique were coated with biodegradable microspheres (size<2 microm) made from poly(3-hydroxybutyrate), P(3HB), produced using Bacillus cereus SPV. A solid-in-oil-in-water emulsion solvent extraction/evaporation technique was used to produce these P(3HB) microspheres. A simple slurry-dipping method, using a 1 wt.% suspension of P(3HB) microspheres in water, dispersed by an ultrasonic bath, was used to coat the scaffold, producing a uniform microsphere coating throughout the three-dimensional scaffold structure. Compressive strength tests confirmed that the microsphere coating slightly enhanced the scaffold mechanical strength. It was also confirmed that the microsphere coating did not inhibit the bioactivity of the scaffold when immersed in simulated body fluid (SBF) for up to 4 weeks. The hydroxyapatite (HA) growth rate on P(3HB) microsphere-coated 45S5 Bioglass composite scaffolds was very similar to that on the uncoated control sample, qualitatively indicating similar bioactivity. However, the surface topography of the HA surface layer was affected as shown by results obtained from white light interferometry. The roughness of the surface was much higher for the P(3HB) microsphere-coated scaffolds than for the uncoated samples, after 7 days in SBF. This feature would facilitate cell attachment and proliferation. Finally, gentamycin was successfully encapsulated into the P(3HB) microspheres to demonstrate the drug delivery capability of the scaffolds. Gentamycin release kinetics was determined using liquid chromatography-mass spectrometry. The release of the drug from the coated composite scaffolds was slow and controlled when compared to the observed fast and relatively uncontrolled drug release from the bone scaffold (without microsphere coating). Thus, this unique multifunctional bioactive composite scaffold has the potential to enhance cell attachment and to provide controlled delivery of relevant drugs for bone tissue engineering.

Preparation, characterization, and in vivo evaluation of insulin-loaded PLA-PEG microspheres for controlled parenteral drug delivery

AIM

The aim of this study was to prepare insulin-loaded poly(lactic acid)-polyethylene glycol microspheres that could control insulin release at least for 1 week and evaluate their in vivo performance in a streptozotocin-induced diabetic rat model.

METHODS

The microspheres were prepared using a water-in-oil-in-water double emulsion solvent evaporation technique. Different formulation variables influencing the yield, particle size, entrapment efficiency, and in vitro release profiles were investigated. The pharmacokinetic study of optimized formulation was performed with single dose in comparison with multiple dose of Humulin 30/70 as a reference product in streptozotocin-induced diabetic rats.

RESULTS

The optimized formulation of insulin microspheres was nonporous, smooth-surfaced, and spherical in structure under scanning electron microscope with a mean particle size of 3.07 microm and entrapment efficiency of 42.74% of the theoretical amount incorporated. The in vitro insulin release profiles was characterized by a bimodal behavior with an initial burst release because of the insulin adsorbed on the microsphere surface, followed by slower and continuous release corresponding to the insulin entrapped in polymer matrix.

CONCLUSIONS

The optimized formulation and reference were comparable in the extent of absorption. Consequently, these microspheres can be proposed as new controlled parenteral delivery system.

In vivoandin vitrocharacteristics for insulin-loaded PLA microparticles prepared by w/o/w solvent evaporation method with electrolytes in the continuous phase

Insulin-loaded poly(lactide) (PLA) microparticles were successfully prepared by 6% w/v PLA in the organic phase, 10% w/v PVP and varied types of 5%w/v electrolytes in the continuous phase, by using a water-in-oil-in-water emulsion/ solvent extraction technique. Addition of electrolytes such as NaCl, CaCl2 into the external phase significantly improved insulin entrapment efficiency compared to the case of no additives. NaCl was the most effective for obtaining high entrapment efficiency, with microparticle yield 81.2%, trapping efficiencies 49%, insulin-loading level 5.5% w/w and mean particle size 14.8 microm. The distribution (%) of insulin on the PLA microparticles surface, outer layer and core were 8, 37 and 43%, respectively. The cumulative release of insulin had an upper limit of approximately 24% of the insulin load at 24 days. A steady release rate was 0.5 microg insulin/mg microparticles/day of insulin release maintained for 24 days. Total protein-leaking amount was reduced after addition of electrolytes in the continuous aqueous phase. Rabbit glucose levels were evaluated after subcutaneous 20 mg insulin-loaded PLA microparticles or PLA blank microparticles. Study results show that the insulin-loaded PLA microparticles significantly reduced the glucose level than PLA blank microparticles. The insulin-loaded PLA microparticles, physicochemical characterization data and the animal result obtained in this study may be relevant in optimizing the PLA microparticle formulation incorporation and delivery insulin carriers.

InactiveVibrio choleraewhole-cell vaccine-loaded biodegradable microparticles:in vitrorelease and oral vaccination

An approach is proposed using Vibrio cholerae (VC)-loaded microparticles as oral vaccine delivery systems for improved vaccine bioavailability and increased therapeutic efficacy. The VC-loaded microparticles were prepared with 50:50 poly(DL-lactide-co-glycolide) (PLG), 75:25 poly(DL-lactide-co-glycolide) and poly(lactide acid) (PLA)/PEG blend copolymers by the solvent evaporation method. VC was successfully entrapped in three types of microparticles with loading efficiencies and loading levels as follows: 50:50 PLG systems: 97.8% and 55.4 +/- 6.9 micro g/mg; 75:25 PLG systems: 89.2% and 46.5 +/- 4.4 micro g/mg; PLA/PEG-blended systems: 82.6% and 53.7 +/- 5.8 micro g/mg. The different distributions of VC in the core region and on the surface were as follows: 50:50 PLG systems 25.7 +/- 1.9 and 6.2 +/- 0.9 micro g/mg; 75:25 PLG systems: 25.8 +/- 2.2 and 3.6 +/- 0.4 micro g/mg; PLA/PEG-blended systems: 32.4 +/- 2.1 and 5.2 +/- 1.0 micro g/mg, respectively. In vitro active release of VC was affected mainly by matrix type and VC-loaded location in microparticles. The therapeutic immunogenic potential of VC loaded with 50:50 PLG, 75:25 PLG and PLA/PEG-blended microparticles was evaluated in adult mice by oral immunization. Significantly higher antibody responses and serum immunoglobin Ig G, IgA and IgM responses were obtained when sera from both VC-loaded 75:25 PLG and PLA/PEG-blended microparticles immunized mice were titrated against VC. The most immunogenicity in evoking serum IgG, IgA and IgM responses was immunized by VC-loaded PLA/PEG-blended microparticles, and with VC challenge in mice, the survival rate (91.7%).

Synthesis and Characterization of Biodegradable Networks Providing Saturated-Solution Prolonged Delivery

Numerous peptide drugs require continuous and local delivery to obtain optimum therapeutic effect. Herein, we describe the incorporation of a model peptide drug, vitamin B12, as well as goserelin acetate, in biodegradable elastomer cylinders through photo-cross-linking. The elastomer was prepared from acrylated star-poly(epsilon-caprolactone-co-D,L-lactide). Release was manipulated through the incorporation of poly(ethylene glycol) diacrylate (PEGD) into the network at concentrations up to 30% (w/w). The PEGD in the network caused rapid swelling that remained constant throughout the release period. The degree of swelling was low, ranging from 10 to 45% (w/w), and increasing as the PEGD content increased. Release proceeded with a minimal initial burst, and extended periods of nearly constant release, ranging from approximately 5 to 70% mass fraction released, were obtained. The release rate was independent of particle size and increased as the cylinder diameter decreased, as the amount of PEGD increased, as the molecular weight of PEGD increased, and as the agent loading increased. Moreover, goserelin acetate, which has a comparable diffusivity but greater aqueous solubility, was released at a greater rate than vitamin B12. This release behavior is explained as a balance between agent dissolution in the swollen polymer matrix and diffusion through the polymer matrix bulk.

Precipitation casting of polycaprolactone for applications in tissue engineering and drug delivery

Microporous materials have been produced by gradual precipitation from solutions of poly(epsilon-caprolactone) (PCL) in acetone induced by solvent extraction across a semi-permeable PCL membrane which is formed in situ at the polymer solution/non-solvent interface. Microparticulates of hydroxyapatite and inulin polysaccharide, respectively, were incorporated in precipitation cast PCL matrices to illustrate potential applications in hard tissue repair and macromolecular drug release. Microporous PCL and HA filled PCL materials were found to provide a favourable surface for attachment and growth of primary human osteoblasts in cell culture. The in vitro degradation characteristics of microporous PCL and inulin/PCL materials in PBS at 37 degrees C were monitored over 45 months. Microporous PCL demonstrated zero weight loss, minor changes in molecular weight characteristics and a fairly constant indentation resistance of around 1 MN/m2. Inulin-loaded PCL materials exhibited a total weight loss of approximately 17% after 12 months in PBS. The indentation resistance decreased by 50% from an initial value of 28 MN/m2 in the first 2 months and then remained stable. Precipitation cast materials based on PCL are expected to be useful for formulating long-term, controlled release devices for bioactive molecules such as growth factors and hormones and extended-residence supports for cell growth and tissue development.

Comparative study on sustained release of human growth hormone from semi-crystalline poly(L-lactic acid) and amorphous poly(D,L-lactic-co-glycolic acid) microspheres: morphological effect on protein release

Recombinant human growth hormone (rhGH) was encapsulated by a double emulsion solvent evaporation method within two biodegradable microspheres having different polymer compositions. Semi-crystalline poly(L-lactic acid) (PLA) and amorphous poly(D,L-lactic-co-glycolic acid) (PLGA) were used for the encapsulation of hGH. Protein release profiles from the two microspheres were comparatively evaluated with respect to their morphological difference. Both of the microspheres similarly exhibited rugged surface and porous internal structures, but their inner pore wall morphologies were quite different. The slowly degrading PLA microspheres had many nano-scale reticulated pores on the wall, while the relatively fast degrading PLGA microspheres had a non-porous and smooth wall structure. From the PLA microspheres, hGH was released out in a sustained manner with an initial approximately 20% burst, followed by constant release, and almost 100% complete release after a 1-month period. In contrast, the PLGA microspheres showed a similar burst level of approximately 20%, followed by much slower release, but incomplete release of approximately 50% after the same period. The different hGH release profiles between PLA and PLGA microspheres were attributed to different morphological characters of the pore wall structure. The inter-connected nano-porous structure of PLA microspheres was likely to be formed due to the preferable crystallization of PLA during the solvent evaporation process.

Measuring the heterogeneity of protein loading in PLG microspheres using flow cytometry

Poly (DL-lactide co-glycolide) (PLG) microspheres with mean sizes up to 1 microm containing Fluorescein Isothiocyanate labelled Bovine Serum Albumin (FITC-BSA) were prepared by the water-in oil-in water (w/o/w) emulsion solvent evaporation technique. Protein loading and loading efficiency determined by the BCA total protein assay increased with microsphere size as measured by laser diffractometry. Protein loaded microspheres were analysed using flow cytometry (FC) to provide fast and reproducible measurements of the size and protein loading of individual microspheres within a sample thereby quantifying in detail the batch heterogeneity. The FC analysis demonstrated that as the size of individual microspheres within a batch increased, so the protein loading tended to increase. For example, the protein loading of microspheres increased from 2.7 to 8.9 wt.% as the size of microspheres increased from 0.42 to 1.45 microm, respectively. Measurements taken during a subsequent protein release experiment indicated that smaller microspheres within a sample released their protein more quickly than larger sizes. Flow cytometry has been shown to provide detailed information, at the level of individual microspheres, about the heterogeneity in size and protein loading of a microsphere sample and could thus lead to improvement of the release characteristics of microsphere-based delivery systems for biopharmaceuticals.

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.

Evaluation of novel particles as pulmonary delivery systems for insulin in rats

The purpose of the study was to evaluate the influence of calcium phosphate (CAP) and polyethylene glycol (PEG) particles on the systemic delivery of insulin administered by the pulmonary route. Two methods of pulmonary delivery were employed: intratracheal instillation and spray instillation. Insulin-CAP-PEG particles in suspension (1.2 U/kg, 110-140 micro L) were administered to the lungs of fasted rats by intratracheal instillation (INCAPEG) or spray instillation (SINCAPEG). Control treatments consisted of insulin solution (1.2 U/kg) by intratracheal instillation, spray instillation, and subcutaneous administration (SC). Plasma concentrations of insulin and glucose were determined by chemiluminescence and colorimetric methods, respectively. Data were analyzed by compartmental and non-compartmental methods, and pharmacokinetic (PK) and pharmacodynamic (PD) parameters of insulin disposition were determined. PK analysis suggested that insulin administered in particles had a longer half-life, a longer mean residence time, and a smaller rate of elimination than insulin in solution. In addition, insulin bioavailability after SINCAPEG was 1.8-fold that of insulin solution administered SC. PD analysis showed that smaller areas under the effect curve and, conversely, larger areas above the effect curve were obtained after INCAPEG in comparison to insulin solution. The magnitude of this effect was increased after SINCAPEG. The presence of CAP-PEG particles appears to positively influence the disposition of insulin administered to the lungs of Sprague-Dawley rats. Spray instillation appears to be a more efficient method of delivering insulin to the lungs of rats than intratracheal instillation.

Oral immunogenicity of the inactivated Vibrio cholerae whole-cell vaccine encapsulated in biodegradable microparticles

Vibrio cholerae (VC)-loaded microparticles as an oral vaccine delivery system were prepared with 6% w/v poly(DL-lactide-co-glycolide)(PLG) in the oil phase as well as 10% w/v PVP and 5% w/v NaCl in the aqueous phase, by an water-in-oil-in-water emulsion/solvent extraction technique. VC was successfully entrapped in the microparticles with trapping efficiencies up to 97.8% and a loading level of 55.4+/-6.9 microg/mg. The microparticle delivery system with a particle size of 3.8 microm had different distribution of VC content in the core region (25.7+/-1.9 microg/mg) and surface (6.2+/-0.9 microg/mg). The immunogenic potential of VC-loaded microparticles in comparison with PLG microparticles or VC solution was evaluated in adult mice by oral immunization, in which mice received one dose of 20 mg VC-loaded microparticles or 20 mg VC-loaded microparticles physical mixed with amphotericin B. The control group received 20 mg PLG microparticle or VC solution. Serum samples were collected from all tested mice on the day of immunization and at 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 weeks postimmunization. Sera were examined for vibriocidal antibodies by microtitration and Vibrio-specific serum IgG and IgM antibodies were assessed by the ELISA method. IgG and IgM antibodies to intact VC were detected in sera from all animals immunized with VC. The response was specific and of high magnitude. Significantly higher antibody responses were obtained when sera from both VC-loaded microparticles and VC-loaded microparticles physical mixed with amphotericin B immunized mice were titrated against VC. The immunogenicity of VC-loaded microparticles mixed with amphotericin B in evoking serum IgG and IgM responses was higher than that of VC-loaded microparticles only. These results demonstrate that VC-loaded microparticles physical mixed with amphotericin B and VC-loaded microparticles orally administered evoke Vibrio-specific serum IgG and IgM responses as well as vibriocidal antibody activity in mice. The VC incorporation, physicochemical characterization data, and the animal results obtained in this study may be relevant in optimizing the vaccine incorporation and delivery properties of these potential vaccine targeting carriers.

Enhanced immunogenicity of a hepatitis B virus peptide vaccine using oligosaccharide ester derivative microparticles

Controlled release microspheres can overcome many of the disadvantages of multiple vaccine delivery such as rate of uptake and cost of administration. Proteins and peptides are difficult to administer using conventional polymers owing to protein degradation, premature release and stability. Here we report the successful development of room temperature stable, controlled release formulations using oligosaccharide ester derivatives (OEDs) of trehalose and a synthetic peptide analogue of hepatitis B surface antigen. Employing a range of different OED preparations, we have optimised the immunogenicity of the peptide formulation such that mice injected with a single preparation of microspheres consisting of trehalose octaacetate (TR101; Group G) produce high titre anti-hepatitis B (anti-HBs) surface antigen antibodies. The kinetics of the immune response could be manipulated with different peptide/OED formulations and correlated with the OED composition of the microspheres. Our data demonstrate the considerable potential of OED microspheres as novel delivery systems for vaccines. The ability to induce strong immune responses, without the requirement for multiple doses or cold-chain storage, could radically improve vaccination programmes in developing countries.

Biodegradable microspheres containing group B Streptococcus vaccine: immune response in mice

OBJECTIVE

This study seeks to show the feasibility of producing a group B Streptococcus (GBS) vaccine, which is capable of producing both a local IgA immune response at the mucosal surface where GBS is colonized and a humoral IgG response, which is capable of transplacental passive immunization.

STUDY DESIGN

Inactivated GBS antigen was microencapsulated in poly (D, L-lactic-co-glycolic acid) (PLG) with a water-in-oil-in-water double emulsion technique. Immunostimulatory synthetic oligodeoxynucleotides containing cytidine-phosphate-guanosine (CpG) motifs were coencapsulated as a potent adjuvant. The ICR strain of mouse was used in these studies. Female mice with normal immune systems were immunized with the PLG microparticles containing GBS type III polysaccharide (GBS PS) vaccine and CpG adjuvant (PLG/GBS/CpG) via the oral, vaginal, or nasal routes or by the intramuscular or intraperitoneal routes. Booster doses were administered 4 weeks after the initial immunization. Vaginal washings and blood samples were obtained 3 weeks after the booster dose and examined for both IgG and secretory IgA (sIgA) GBS antibodies with the use of an enzyme-linked immunoabsorbent assay method.

RESULTS

PLG/GBS/CpG microparticles elicited a significantly higher GBS antibody response when compared with nonencapsulated GBS antigen or PLG-encapsulated GBS PS vaccine without the addition of the CpG adjuvant. IgG and secretory IgA (sIgA) antibodies to GBS antigen were documented in both the vaginal washings and blood samples.

CONCLUSION

Preliminary findings indicate that this novel PLG/GBS/CpG vaccine elicited both IgA and IgG antibody responses to the GBS PS antigen studied. This antibody response may provide both protection against maternal GBS colonization and passive transplacental immunization for the fetus and neonate.

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.

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.

Formulation factors for preparing ocular biodegradable delivery system of 5-fluorouracil microparticles

Microparticles containing 5-fluorouracil (5-FU) were prepared using poly(DL-lactide-co-glycolide) with an oil-in-oil emulsion/solvent extraction technique. Particle characteristics including size distribution, 5-FU loading efficiencies, in vitro release and degradation were investigated. The dispersed phase was composed of PLG dissolved in dichloromethane, and the continuous phase was paraffin oil containing lecithin. 5-FU was successfully entrapped in the microparticles with trapping efficiencies up to 76%, loading level 10% w/v, and particle size 3 microm. Release profiles of 5-FU loaded microparticles were determined to follow a first-order-time relationship. An optimized preparation of 5-FU microparticles was achieved and was capable of controlling the release of 5-FU over 21 days with an in vitro delivery rate of 0.4 microg 5-FU/mg particles/day in the study. Preliminary animal studies indicated that the 5-FU loaded microparticles as an ocular delivery system showed no ocular toxicity and no significant inflammatory response in rabbits for 2 months. The 5-FU loaded microparticles approach, with PLG, might be a potential for the application of long-term delivery of hydrophilic drugs in the eye.

The stability of insulin in biodegradable microparticles based on blends of lactide polymers and polyethylene glycol

Insulin-loaded microparticles were produced from blends of poly(ethylene glycol) (PEG) with poly (L-lactide) (PLA) homopolymer and poly (DL-lactide co-glycolide) copolymers (PLG) using a water-in-oil solvent extraction method. The dispersed phase was composed of PLG/PEG or PLA/PEG dissolved in dichloromethane, and the continuous phase was methanol containing 10% PVP. Characteristics, including particle size distribution, insulin loading capacity and efficiencies, in vitro release, degradation and stability, were investigated. The stability of insulin associated with microparticles prepared using PEG and 50:50 PLG and PLA was analysed by HPSEC and quantified by peak area following incubation in PBS at 37 degrees C for up to 1 month. Insulin was successfully entrapped in the PLG/PEG and PLA/PEG microparticles with trapping efficiencies up to 56 and 48%, loading levels 17.8 and 10.6% w/w, and particle sizes 8 and 3 microm, respectively. The insulin-loaded PLG/PEG and PLA/PEG microparticles were capable of controlling the release of insulin over 28 days with in vitro delivery rates of 0.94 and 0.65 microg insulin/mg particles/day in the first 4 days and a steady release with rate of 0.4 and 0.43 microg insulin/mg particles/day over the following 4 weeks, respectively. Extensive degradation of the PLG/PEG microparticles also occurred over 4 weeks, whereas the use of PLA/PEG blends resulted in a stable microparticle morphology and much reduced fragmentation and aggregation of the associated insulin.

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

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

A controlled release system for proteins based on poly(ether ester) block-copolymers: polymer network characterization

The properties of a series of multiblock copolymers, based on hydrophilic poly(ethylene glycol) (PEG) and hydrophobic poly(butylene terephthalate) (PBT) blocks were investigated with respect to their application as a matrix for controlled release of proteins. The degree of swelling, Q, of the copolymers increased with increasing PEG content and with increasing molecular weight of the PEG segment. Within the composition range tested, Q varied from 1.26 for polymers with PEG segments of 600 g/mol and a PBT content of 60 weight.% up to 3.64 for polymers with PEG segments of 4000 g/mol and a PEG/PBT weight ratio of 80:20. Equilibrium stress (compression)-strain measurements were performed in order to estimate mesh sizes. The mesh size of the copolymers ranged from 38 to 93 A, which was experimentally confirmed by diffusion of vitamin B(12) (hydrodynamic diameter d(h)=16.6 A), lysozyme (d(h)=41 A) and bovine serum albumin (d(h)=72 A). The in vitro degradation of PEG/PBT copolymers with a PEG block length of 1000 g/mol and PEG/PBT weight ratios of 70:30, 60:40 and 40:60 was studied. Matrices with increasing PEG contents exhibited a faster weight loss in phosphate-buffered saline (pH 7.4) at 37 degrees C. Over a degradation period of 54 days, M(n) decreased by about 35-45%, while the composition of the matrices, determined by NMR, remained almost constant.

Protein encapsulation within poly(ethylene glycol)-coated nanospheres. II. Controlled release properties

The development of injectable nanoparticulate "stealth" carriers for protein delivery is a major challenge. The aim of this work was to investigate the possibility of achieving the controlled release of a model protein, human serum albumin (HSA), from poly(ethylene glycol) (PEG)-coated biodegradable nanospheres (mean diameter of about 200 nm) prepared from amphiphilic diblock PEG-poly(lactic acid) (PLA) copolymers. HSA was efficiently incorporated into the nanospheres, reaching loadings as high as 9% (w/w). Results of the in vitro release studies showed that it is possible to control the HSA release by choosing the appropriate nanosphere size, loading, and composition. These results also revealed that, following their release, HSA molecules readsorbed onto the nanospheres surfaces when they were not protected by a PEG coating. We were surprised to observe that in spite of the water uptake of the PLA-PEG nanospheres [11-29% (w/w)], the copolymer did not significantly degrade after a 15-day incubation period. Therefore, we concluded that during this time HSA release from PLA-PEG nanospheres followed a diffusion mechanism where bulk erosion and surface desorption were negligible.

The stability and immunogenicity of a protein antigen encapsulated in biodegradable microparticles based on blends of lactide polymers and polyethylene glycol

Protein-loaded microparticles were produced from blends of poly(ethylene glycol) (PEG) with poly(L-lactide) (PLA) homopolymer or poly(DL-lactide co-glycolide) copolymers (PLG) using a water-in oil-in oil method. The stability of ovalbumin (OVA) associated with microparticles prepared using PEG and 50:50 PLG, 75:25 PLG and PLA, respectively, was analysed by SDS-PAGE and quantified by scanning densitometry following incubation in PBS at 37 degrees C for up to 1 month. Fragmentation and aggregation of OVA was detected with all 3 formulations. The extent of both processes correlated with the degradation rate of the lactide polymer used and decreased in the order PLA < 75:25 PLG < 50:50 PLG. Extensive degradation of the PLG/PEG microparticles also occurred over 4 weeks whereas the use of PLA/PEG blends resulted in a stable microparticle morphology and much reduced fragmentation and aggregation of the associated protein. Following a single sub-cutaneous immunisation, high levels of specific serum IgG antibody were elicited by OVA associated with the PLA/PEG particles. Injection of OVA associated with the 75:25 PLG/PEG microparticles resulted in very low levels of specific antibody. A higher response was induced by the 50:50 PLG/PEG formulation but there was very large inter-animal variation in this group. Antibody levels elicited by all 3 formulations were significantly higher than those elicited by a single injection of soluble OVA. Analysis of antigen specific IgG1 and IgG2a antibody subtype levels also revealed the greater efficacy of the PLA/PEG microparticles as an adjuvant system. The use of PLA/PEG microparticles shows improved protein loading and delivery capacity while maintaining a high level of stability of the associated protein. These results indicate a strong correlation between the stability of microencapsulated antigen and the magnitude of the immune response following sub-cutaneous immunisation.

Erythropoietin loaded microspheres prepared from biodegradable LPLG-PEO-LPLG triblock copolymers: protein stabilization and in-vitro release properties

Biodegradable microspheres containing recombinant human Erythropoietin (EPO) were prepared from ABA triblock copolymers, consisting of hydrophobic poly(l-lactic-co-glycolic acid) A blocks and hydrophilic polyethylenoxide (PEO) B blocks. Different polymer compositions were studied for the microencapsulation of EPO using a modified double-emulsion process (W/O/W). The encapsulation efficiency for EPO, ranging from 72% to 99% was quite acceptable. The formation of high molecular weight EPO aggregates, however, was higher than in poly(d,l-lactide-co-glycolide) (PLG) microparticles. Using different excipients with known protein stabilizing properties, such as Bovine Serum Albumin (BSA), Poly-l-Histidine (PH), Poly-l-Arginine (PA) or a combination of PA with Dextran 40 (D40), the EPO aggregate content was significantly reduced to <5% of the encapsulated EPO. In contrast to PLG, ABA triblockcopolymers containing >7 mol % PEO, allowed a continuous release of EPO from microspheres for up to 2 weeks under in-vitro conditions. The release profile was comparable to FITC-Dextran 40 kDa (FD 40) loaded microspheres in the initial release phase, while EPO release was leveling off at later time points. BSA additionally prolonged the EPO release, while blends of PLG and PEO did not generate continuous EPO release profiles. LPLG-PEO-LPLG triblock-copolymers (35 mol % PEO; 30 kDa) in combination with 5% BSA yielded both an acceptable level of EPO aggregates and a continuous release profile under in-vitro conditions for up to 2 weeks. The formation of EPO aggregates at later time points is probably induced by acidic cleavage products of the biodegradable polymer and requires further optimization of the ABA polymer composition.

The control of protein release from poly(DL-lactide co-glycolide) microparticles by variation of the external aqueous phase surfactant in the water-in oil-in water method

Poly(DL-lactide co-glycolide) microparticles below 5 microm in size and containing ovalbumin (OVA), were prepared using the water-in oil-in water (w/o/w) technique with either polyvinyl alcohol (PVA) or polyvinylpyrrolidone (PVP) as stabilisers in the external aqueous phase. PVP-stabilised microparticles exhibited higher protein loading (8.2%, w/w relative to 4.0% for PVA stabilised microparticles) and increased core loading (encapsulation) of protein (70% vs. 30% for the PVA system). The use of PVP instead of PVA to prepare microparticles also resulted in reduction in the initial burst release of OVA, together with sustained protein release over 28 days and an increase in the protein delivery capacity from 35 to 45 microg/mg particles. The changes in protein loading and delivery characteristics are considered to arise in part from an increase in the viscosity of the droplets of polymer solution, constituting the primary water-in oil emulsion, by diffusion of PVP from the external aqueous phase. Variation of the external aqueous phase surfactant provides a promising approach for improving the loading of therapeutic proteins and vaccine antigens within biodegradable microparticles and for modulating their release pattern.

Oral immunization of rainbow trout with antigen microencapsulated in poly(DL-lactide-co-glycolide) microparticles

The model protein antigen, human gamma globulin (HGG) was microencapsulated in poly(DL-lactide-co-glycolide) microparticles and administered orally to rainbow trout. Oncorhynchus mykiss (Walbaum, 1792). Using a Western blotting technique it was demonstrated that the dynamics of passage through the gut were different for the microencapsulated and soluble antigen. The association of HGG with microparticles increased the retention time of the antigen in the stomach and delayed its entry into the intestinal region. After the delivery of microencapsulated HGG, antigen was detected in gut contents in fragmented form which suggested that some of the antigen was present at the particle surface and therefore susceptible to proteolysis. However, a greater amount of intact antigen was detected in the posterior intestine and in the bloodstream of fish, which were administered with microparticle-associated than soluble antigen, indicating that the antigen was partially protected. Immunization with microencapsulated HGG resulted in the detection of specific antibody in the serum but levels were not significantly greater than after the delivery of soluble antigen. However, specific antibody was detected in the intestinal mucus of fish which were administered with the microencapsulated antigen after boosting with soluble HGG but not in fish which were primed with the soluble antigen.