Preparation of biodegradable microspheres and microcapsules: 2. Polyactides and related polyesters

Drug loaded poly[Lac(Glc-Leu)] microparticles: formulation and release characteristics

Valdecoxib has been entrapped in sub-5 microm particles of poly[Lac(Glc-Leu)] copolymer using a oil-in-water (o/w) emulsification-solvent evaporation technique. To achieve monodispersed sized particles, a microfluidizer was used as ultrasonication device. Formulation parameters such as effect of polymer load, ultrasonication time, stabilizer concentration and stirring rate have a profound effect on particle size, and polydispersity. By adjustment of these parameters, microparticles ranging from about 0.8 to more than 4 microm have been prepared.

Synthesis, Characterization, Biodegradation, and Drug Delivery Application of Biodegradable Lactic/Glycolic Acid Polymers: Part III. Drug Delivery Application

Lactic/glycolic acid polymers (PLGA) are widely used for drug delivery systems. The microsphere formulation is the most interesting dosage form of the PLGA-based controlled release devices. In this study, the previously reported PLGA were used to prepare drug-containing microspheres. Progesterone was used as a model drug. The progesterone microspheres were prepared from PLGA having varied compositions and varied molecular weight. The microscopic characterization shows that the microspheres are spherical, nonaggregated particles. The progesterone-containing PLGA microspheres possess a Gaussian size distribution, having average size from 70-134 microm. A solvent extraction method was employed to prepare the microspheres. The microencapsulation method used in this study has high drug encapsulation efficiency. The progesterone release from the PLGA microspheres and the factors affecting the drug release were studied. The release of progesterone from the PLGA microspheres is affected by the properties of the polymer used. The drug release is more rapid from the microspheres prepared using the PLGA having higher fraction of glycolic acid moiety. The drug release from the microspheres composed of higher molecular weight PLGA is faster. The drug content in microspheres also has an effect on the drug release. Higher progesterone content in microspheres yields a quicker initial burst release of the drug.

The robustness and flexibility of an emulsion solvent evaporation method to prepare pH-responsive microparticles

A microparticle preparation method based on an emulsion of ethanol in liquid paraffin stabilised using sorbitan sesquioleate which produces enteric microparticles of excellent morphology, size and pH-sensitive drug release was assessed for its robustness to changes in formulation and processing parameters. Prednisolone and methacrylic acid and methyl methacrylate copolymer (Eudragit S) were the drug and polymer of choice. Emulsion solvent evaporation procedures are notoriously sensitive to changes in methodology and so emulsion stirring speed, drug loading, polymer concentration and surfactant (emulsifier) concentration were varied; microparticle size, encapsulation efficiency, yield and in vitro dissolution behaviour were assessed. The yield and encapsulation efficiency remained high under all stirring speeds, drug loadings and polymer concentrations. This suggests that the process is flexible and efficiency can be maintained. Surfactant concentration was an important parameter; above an optimum concentration resulted in poorly formed particles. All processing parameters affected particle size but this did not alter the acid resistance of the microparticles. At high pH values the smaller microparticles had the most rapid drug release. In conclusion, the microparticle preparation method was resistant to many changes in processing, although surfactant concentration was critical. Manipulation of particle size can be used to modify the drug release profiles without adversely affecting the gastro-resistant properties of these pH-responsive microparticles.

Poly(ethylene glycol)-modified proteins: implications for poly(lactide-co-glycolide)-based microsphere delivery

The reduced injection frequency and more nearly constant serum concentrations afforded by sustained release devices have been exploited for the chronic delivery of several therapeutic peptides via poly(lactide-co-glycolide) (PLG) microspheres. The clinical success of these formulations has motivated the exploration of similar depot systems for chronic protein delivery; however, this application has not been fully realized in practice. Problems with the delivery of unmodified proteins in PLG depot systems include high initial "burst" release and irreversible adsorption of protein to the biodegradable polymer. Further, protein activity may be lost due to the damaging effects of protein-interface and protein-surface interactions that occur during both microsphere formation and release. Several techniques are discussed in this review that may improve the performance of PLG depot delivery systems for proteins. One promising approach is the covalent attachment of poly(ethylene glycol) (PEG) to the protein prior to encapsulation in the PLG microspheres. The combination of the extended circulation time of PEGylated proteins and the shielding and potential stabilizing effects of the attached PEG may lead to improved release kinetics from PLG microsphere system and more complete release of the active conjugate.

Preparation and Characterization of Poly(D,L-Lactic-Co-Glycolic Acid) Microspheres Containing Flurbiprofen Sodium

This study aimed to prepare biodegradable microspheres containing flurbiprofen sodium, a nonsteroidal anti-inflammatory drug (NSAID), as the drug delivery system to the periodontal pocket. Microspheres were prepared from biodegradable copolymers of poly (D,L-lactic-co-glycolic acid) (PLGA) using solvent evaporation method. The effects of the different copolymers and amounts of polyvinyl alcohol (PVA) as a dispersing agent on characteristics of the microspheres were evaluated. Although there was no correlation between microsphere size and amount of PVA, an optimum PVA concentration was essential to achieve narrower size distributions of microspheres. As the concentration of PVA increased, the drug loading of the microspheres increased. The effect of PVA on drug loading was found to be statistically significant for those microspheres prepared from PLGA 50:50 (p < 0.05). Regarding copolymer composition, PLGA 85:15 provided higher drug loading into the microspheres than PLGA 50:50 (p < 0.05). The recoveries of microspheres (60-80%) were affected neither by different PVA concentrations nor by copolymer compositions (p > 0.05). According to the first-order release rate constants of the microspheres, the microspheres of PLGA 50:50 released the drug at the highest rate consistently, with the highest hydrophilicity of this copolymer.

In Vitro Performance of Carbamazepine Loaded to Various Molecular Weights of Poly (D, L-Lactide-Co-Glycolide)

The purpose of this study was to develop and assess the in vitro characteristics of carbamazepine-loaded microspheres. A solvent evaporation method was used to incorporate carbamazepine (CBZ) into poly (D,L-lactide-co-glycolide) (PLGA) with different molecular weights. The optimum conditions for CBZ-PLGA microspheres preparation were considered and the in vitro release of CBZ of PLGA microspheres were followed up to 24 hr in USP dissolution medium. The effect of using different ratios of PLGA microspheres, prepared with different molecular weights, for optimizing CBZ release also was investigated. CBZ encapsulation efficiency was 68 to 82% for all prepared formulations. Thermograms of CBZ-PLGA microspheres suggest that CBZ was totally entrapped with the PLGA polymer. The presence of Pluronic F-68 has improved the encapsulation of CBZ, resulted in better and smoother microspheres surfaces and enhanced its release pattern. CBZ release profiles were biphasic patterns; after an initial burst, a constant CBZ release rate was observed up to 24 hr. The release from these PLGA-based spherical matrices was consistent with the diffusion mechanism. CBZ dissolution T(50%) was significantly affected (> 3-fold) by increasing the lactide percent from 33.3 to 66.6% from different microspheres mixtures. The present study provides evidence that the encapsulation of CBZ to PLGA microspheres, either as a single polymer or mixture of two, was a successful attempt to control the release of CBZ.

Preparation of hydrogel hollow particles for cell encapsulation by a method of polyester core degradation

Implantation of encapsulated cells in particles of less than 1 mm (micro-encapsulation) has been proposed as a cell synthesized bio-molecule delivery system. Encapsulation provides immuno-isolation, protecting foreign cells from host immune system while nutrients, oxygen and therapeutic products can diffuse freely across capsule walls. A new method is described for the synthesis of a new family of hollow microparticles for cell encapsulation. Unlike other micro-encapsulation methods, encapsulation in those devices will take place after capsule synthesis, by micro-injection. The microcapsules were prepared by a three-steps original procedure: first, synthesis of a core particle, followed by coating with a layer of epichlorohydrin cross-linked amylo-pectin gel and, finally, selective degradation of the core particle to create the cavity. Initial experiments make use of amylo-pectin cross-linked with trimetaphosphate as core particle material. However, selective degradation was difficult to achieve. In further essays, polyesters were used successfully for the preparation of core particles. Optimizations were carried out and the permeability and morphology of the hollow particles were investigated. The preliminary results show that the new method has the potential to become a standard procedure to obtain hydrogel hollow particles. Moreover, the permeability study seems to be in accordance with specifications for immuno-isolation.

PLGA microspheres for the delivery of a novel subunit TB vaccine

Biodegradable poly(dl-lactide-co-glycolide) microspheres were prepared using a modified double emulsion solvent evaporation method for the delivery of the subunit tuberculosis vaccine (Ag85B-ESAT-6), a fusion protein of the immunodominant antigens 6-kDa early secretory antigenic target (ESAT-6) and antigen 85B (Ag85B). Addition of the cationic lipid dimethyl dioctadecylammonium bromide (DDA) and the immunostimulatory trehalose 6,6'-dibehenate (TDB), either separately or in combination, was investigated for the effect on particle size and distribution, antigen entrapment efficiency, in vitro release profiles and in vivo performance. Optimised formulation parameters yielded microspheres within the desired sub-10 microm range (1.50 +/- 0.13 microm), whilst exhibiting a high antigen entrapment efficiency (95 +/- 1.2%) and prolonged release profiles. Although the microsphere formulations induced a cell-mediated immune response and raised specific antibodies after immunisation, this was inferior to the levels achieved with liposomes composed of the same adjuvants (DDA-TDB), demonstrating that liposomes are more effective vaccine delivery systems compared with microspheres.

Surfactant dependent morphology of polymeric capsules of perfluorooctyl bromide: influence of polymer adsorption at the dichloromethane-water interface

In a strategy to develop more stable ultrasound contrast agents (UCAs), we have designed a process to obtain nano/microcapsules with a single core of liquid perfluorocarbon within a biodegradable polymeric shell of homogeneous thickness. During the optimization of perfluorooctyl bromide (PFOB) encapsulation by solvent emulsion-evaporation, a marked influence of surfactants has been observed. While sodium cholate leads to spherical capsules of homogeneous thickness, sodium taurocholate induces to the formation of "acorn"-particles with one hemisphere of PFOB and another one of PLGA, and polyvinyl alcohol is responsible for the coexistence of both morphologies. Whereas the theoretical model proposed by Torza and Mason [J. Colloid Interface Sci. 33 (1970) 67] fails to predict the observed morphologies, microscopic observations of the evaporation and interfacial tension measurements provide an insight into the mechanism of formation of these structures. Most probably, there is a competition between PLGA and the surfactant stabilizing the emulsion at the dichloromethane-water interface. If PLGA is able to adsorb at the interface, the core-shell morphology is obtained, otherwise the acorn morphology is preferentially formed. When the surfactant rearrangement at the interface is long (>30 min), a coexistence of morphologies can be obtained.

Coating of indomethacin-loaded embolic microspheres for a successful embolization therapy

Indomethacin-loaded dietheylaminoethyl trisacryl microspheres (DEAE-MS), originally designed for therapeutic embolization, were encapsulated using two methods: coacervation and solvent evaporation/extraction. This encapsulation was achieved using a biocompatible polymer, the PLGA 50 : 50, and aimed to control the release of the anti-inflammatory non-steroidal drug (AINSD) in the occluded vessel. PLGA degradation study showed that it had an erosion half-life of approximately 35 days. Scanning electron microscopy (SEM) photographs showed that microcapsules (MC) prepared by coacervation had a wrinkled surface while those prepared using solvent-removal process showed non-porous, smooth surface, those of originally DEAE-MS showed a macro-porous, rough surface. The mean diameters were 61 microm for naked DEAE-MS vs. 71 microm and 65 microm for MC prepared by coacervation and solvent evaporation/extraction method, respectively. In vitro release study of indomethacin adsorbed onto MS indicated that drug release from MC was controlled by a diffusion process. Indomethacin diffusivity from MC was much lower than its free diffusivity from MS (mean 14.5 and 10.5 times lower for formulations prepared by coacervation and solvent evaporation/extraction method, respectively). This indicates that efficient indomethacin concentrations could be maintained over much longer time-periods in the embolized region, which is assumed to be beneficial in inhibiting normally occurring inflammatory reaction and the subsequent revascularization; responsible for treatment failure when definitive occlusion is required.

In vivo fate and therapeutic efficacy of PF‐4/CTF microspheres in an orthotopic human glioblastoma model

The correlation between glioma grade and angiogenesis suggests that antiangiogenic therapies are potentially therapeutically effective for these tumors. However, to achieve tumor suppression, antiangiogenic therapies need to be administered daily using high systemic quantities. We designed a biodegradable polymeric device that overcomes those barriers by providing sustained local delivery of a C-terminal fragment of platelet factor 4 (PF-4/CTF), an antiangiogenic agent. Fluorescent-labeled microspheres composed of poly lactic-coglycolic acid (PLGA) were loaded with rhodamine-labeled PF-4/CTF and formulated to release their contents over time. Fluorescent labeling enabled the correlation between the in vitro to the in vivo kinetic and release studies. PF-4/CTF microspheres were injected into established intracranial human glioma tumors in nude mice. Noninvasive magnetic resonance imaging (MRI) was used to assess the therapeutic response. Tumor size, microvessel density, proliferation, and apoptosis rate were measured by histological analysis. Intracranially, the microspheres were located throughout the tumor bed and continuously released PF-4/CTF during the entire experimental period. MRI and histological studies showed that a single injection of microspheres containing PF-4/CTF caused a 65.2% and 72% reduction in tumor volume, respectively, with a significant decrease in angiogenesis and an increase in apoptosis. Our data demonstrate that polymeric microspheres are an effective therapeutic approach for delivering antiangiogenic agents that result in the inhibition of glioma tumor growth.

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

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

Improvement of a bovine serum albumin microencapsulation process by screening design

The first objective of this study was to prepare microspheres containing a model protein by double emulsion-solvent evaporation/extraction method. This method was modified to consider the fragile nature of proteins. These modifications related to the reduction of polymer loss, of agitation duration and of contact time between protein and solvent. The polymer used was poly(epsilon-caprolactone) and the model protein was bovine serum albumin. The control of the microsphere properties constituted a second objective of this project. A screening design methodology was used to evaluate the effects of the process and formulation variables on microsphere properties. Twelve operating factors were retained, and the particle properties considered were the mean size, the encapsulation efficiency, and the surface state. The statistical analysis of the results allowed determining the most influent factors. Considering the whole results, it appeared that the polymer concentration, the osmotic pressure equilibrium and the volume of the inner, outer and organic phases were the most important parameters. Following this screening study, it was possible to produce particles of small size with high entrapment efficiency (near to 80%) and smooth surface. A good batch to batch reproductibility was obtained.

Drug–polymer microparticles produced by supercritical assisted atomization

The supercritical assisted atomization (SAA) was proposed as a new technique to produce composite microparticles for drug controlled release. Ampicillin trihydrate and chitosan were selected as model drug and carrier, respectively, and 1% v/v acetic acid aqueous solution was used as solvent. The effect of the polymer/drug ratio on particle morphology and drug release rate was evaluated. SEM analysis indicated that non-coalescing spherical microparticles formed by chitosan/ampicillin were produced by SAA. All coprecipitates produced have a sharp particle distribution, with diameters ranging between about 0.1 and 6 microm. SAA composite microparticles were characterized by X-ray, DSC, EDX and UV-vis analysis. A solid solution of the chitosan and ampicillin was produced and a stabilizing effect of the polymer on the drug has resulted that protects ampicillin from thermal degradation. A prolonged release from SAA coprecipitates with respect to raw drug and physical mixtures of chitosan and ampicillin was obtained; moreover, the polymer/drug ratio has revealed to be a controlling parameter for drug release. Drug release mechanisms characteristic of swelling-controlled systems were observed, with ampicillin release depending on both relaxation and diffusive mechanisms. An empirical binomial equation was used to describe experimental data, showing a fair good agreement with ampicillin release data if both the relaxational and the diffusional parameters are function of the polymer/drug ratio.

Phase structure and enzymatic degradation of poly(L-lactide)/atactic poly(3-hydroxybutyrate) blends: an atomic force microscopy study

Phase structures and enzymatic degradation of poly(l-lactide) (PLLA)/atactic poly(3-hydroxybutyrate) (ata-PHB) blends with different compositions were characterized by using atomic force microscopy (AFM). Differential scanning calorimetry (DSC) thermograms of PLLA/ata-PHB blends with different compositions showed two glass transition temperatures, indicating that the PLLA/ata-PHB blends are immiscible in the melt. Surface morphologies of the thin films for PLLA/ata-PHB blends were determined by AFM. Phase separated morphology was recognized from the AFM topography and phase images. The domain size of the components was dependent on the blend ratio. Enzymatic degradation of the PLLA/ata-PHB blends was performed by using both PHB depolymerase and proteinase K. Either PLLA or ata-PHB domains were eroded depending on the kinds of enzyme. Surface morphologies after enzymatic degradation have revealed the phase structure along the depth direction. Enzymatic adsorption of PHB depolymerase was examined on the surface of PLLA/ata-PHB blends. The enzyme molecules were found on both domains of the binary blends. The larger number of enzyme molecules was found on the PLLA domains relative to those on the ata-PHB domains, suggesting the higher affinity of the enzyme against PLLA domain.

Preparation of uniform biodegradable microparticles using laser ablation

In an attempt to prepare uniformly sized biodegradable microparticles for controllable drug eluting and targeting characteristics, a novel technique by employing ultrashort pulse (USP) laser has been developed. This method involves pumping a drug-polymer solution through a small orifice creating a liquid stream. A USP laser constantly fires at the stream to cut it into discrete droplets and consequently solid particles can be obtained with monodisperse size distribution. Through mathematical modeling, volumetric flow rate, orifice size, laser spot size, and laser frequency were found as sole factors determining the size profile of the resulting microparticles. By choosing appropriate set of variables, monosized biodegradable microparticles with wide range of particle size may be prepared.

Oil core/polymer shell microcapsules by internal phase separation from emulsion droplets. II: controlling the release profile of active molecules

Microcapsules with oil cores and solid polymer shells have been prepared by precipitation of the polymer from the internal phase of an oil-in-water emulsion. The dispersed phase consists of a polymer, a good solvent for the polymer (dichloromethane), and a poor solvent for the polymer (hexadecane). Removal of the good solvent results in phase separation of the polymer within the emulsion droplet, leading to the formation of a polymeric shell surrounding the poor solvent. A UV-active organic molecule is added to the oil phase prior to emulsification. Provided this molecule has some water solubility, the release profile of the molecule from the capsule can be determined. While the microcapsule size was kept approximately constant, the influence of a wide range of factors on the release profile has been studied. These include the type and molecular weight of the shell-forming polymer, the molecular weight of the active ingredient molecule, the shell thickness, the use of copolymers or polymer blends to form the shell, the effect of cross-linking the shell or heating the capsule to temperatures above the T(g) value of the polymer after the shell has been formed, and the effect of changes in the pH of the release solution in the case when a weak polyelectrolyte is used as the shell polymer. The differences in behavior are discussed in terms of the properties of the polymer shell, in particular the thickness, the polymer/release molecule interaction, and the free volume/porosity. Variation of these parameters allows one to control both the final release yield and the rate of release for time periods between a few hours and days.

Improvement of Porosity of a Calcium Phosphate Cement by Incorporation of Biodegradable Polymer Microspheres

In this study a biodegradable polymer microspheres were used to make an alpha-TCP calcium phosphate bone cement macroporous. The biodegradable polymer microspheres were synthesised at the laboratory and a sieve fraction of this microspheres ranging between 100 and 300 microns was incorporated in a calcium phosphate cement, where the powder contained a-Ca3(PO4)2 (a-TCP). The microspheres content of the cement was 10 %. The cement pastes were prepared at liquid-to-powder ratios from 0.32 to 0.40 ml/g. X-ray diffraction and Infra-red spectroscopy was performed to analyse the reaction on powdered samples that were let to set at different times in a Ringer’s solution at body temperature. Mercury porosimetry has been used at the main method for porosity measurements. Scanning electron microscopy (SEM) was performed on fractured samples fro microstructural analysis. The microspheres seemed to retard slightly the cement setting and to reduce progressively the compressive strength after aging in aqueous solutions which were continuously refreshed. SEM pictures and XRD patterns of the samples after 1 and 4 weeks of aging showed that the microspheres were dissolved progressively. Mercury porosimetry measurements assessed at different times of aging showed an improvement in the total porosity and the pore diameter of the set material and confirmed SEM and XRD results.

Enzymatic Degradation of Poly(l-lactide) Film by Proteinase K: Quartz Crystal Microbalance and Atomic Force Microscopy Study

Enzymatic degradation of the poly(L-lactide) (PLLA) amorphous film by proteinase K has been investigated by combination of the complementary techniques of quartz crystal microbalance and atomic force microscopy (AFM). The erosion rate increased with increasing enzyme concentrations and attained to be constant under the condition of [proteinase K] > 100 microg/mL. The amount of the enzyme molecules adsorbed to the film was quantitatively evaluated at various concentrations by AFM, and it revealed that the erosion rate is determined by the amount of adsorbed enzyme. Adsorption of proteinase K was irreversible despite lack of the binding domain, so that the enzyme molecules on the film surface could be observed directly by AFM. Transformation of the enzyme molecule caused by packing in high density on the surface was observed at higher enzyme concentrations. The "footprint" of the individual proteinase K molecule on the PLLA film after enzymatic degradation suggests that the enzyme moves on the surface to hydrolyze the film around it.

Biodegradable polymers for microencapsulation of drugs

Drug delivery has become increasingly important mainly due to the awareness of the difficulties associated with a variety of old and new drugs. Of the many polymeric drug delivery systems, biodegradable polymers have been used widely as drug delivery systems because of their biocompatibility and biodegradability. The majority of biodegradable polymers have been used in the form of microparticles, from which the incorporated drug is released to the environment in a controlled manner. The factors responsible for controlling the drug release rate are physicochemical properties of drugs, degradation rate of polymers, and the morphology and size of microparticles. This review discusses the conventional and recent technologies for microencapsulation of the drugs using biodegradable polymers. In addition, this review presents characteristics and degradation behaviors of biodegradable polymers which are currently used in drug delivery.

Continuous Delivery of Endogenous Inhibitors from Poly(Lactic-Co-Glycolic Acid) Polymeric Microspheres Inhibits Glioma Tumor Growth

Purpose: There is an urgent need for modalities that can localize and prolong the administration of the antitumor agents, particularly antiangiogenic, to achieve long-term tumor inhibition. However, one of the major obstacles is designing a device in which the biological activity of sensitive endogenous inhibitors is retained. We have designed a biodegradable polymeric device, which provides a unique and practical means of localizing and continuously delivering hemopexin (PEX) or platelet factor 4 fragment (PF-4/CTF) at the tumor site while maintaining their biological activity. The potential and efficacy of this system is shown in vitro and in vivo in a human glioma mouse model.

Experimental Design: Polymeric microspheres made of poly(lactic-co-glycolic acid) (PLGA) were loaded with very low amounts of PEX and PF-4/CTF. The release profiles of these factors from PLGA and their biological activity were confirmed in vitro using proliferation assays done on endothelial and tumor cells. Tumor inhibition using this system was studied in nude mice bearing a human s.c. glioma.

Results: PEX and PF-4/CTF released in vitro from PLGA microspheres were biologically active and significantly inhibited the proliferation of human umbilical vein endothelial cells, bovine capillary endothelial cells, and U87-MG cells. A single local s.c. injection of PLGA microspheres loaded with low amounts of PEX or PF-4/CTF resulted in an 88% and 95% reduction in glioma tumor volume 30 days post-treatment. Immunohistochemical analysis of the treated tumors showed a marked decrease in tumor vessel density compared with untreated tumors.

Conclusion: Our findings show that polymeric microspheres are a very promising approach to locally and efficiently deliver endogenous inhibitors to the tumor site leading to a significant inhibition of the tumor.

Oil core-polymer shell microcapsules prepared by internal phase separation from emulsion droplets. I. Characterization and release rates for microcapsules with polystyrene shells

Microcapsules with an oil core surrounded by a polymeric shell have been prepared by the controlled phase separation of polymer dissolved within the oil droplets of an oil-in-water emulsion. The dispersed oil phase consists of the shell polymer (polystyrene), a good solvent for the polymer (dichloromethane), and a poor solvent for the polymer (typically hexadecane). Removal of the good solvent results in phase separation of the polymer within the oil droplets. If the three interfacial tensions between the core oil, the shell-forming polymer, and the continuous phase are of the required relative magnitudes, a polymer shell forms surrounding the poor solvent. A UV-responsive organic molecule was added to the oil phase, prior to emulsification, to investigate the release of a model active ingredient from the microcapsules. This molecule should be soluble in the organic core but also have some water solubility to provide a driving force for release into the continuous aqueous phase. As the release rate of the active ingredient is a function of the thickness of the polymeric shell, for controlled release applications, it is necessary to control this parameter. For the preparative method described here, the thickness of the shell formed is directly related to the mass of polymer dissolved in the oil phase. The rate of volatile solvent removal influences the porosity of the polymer shell. Rapid evaporation leads to cracks in the shell and a relatively fast release rate of the active ingredient. If a more gentle evaporation method is employed, the porosity of the polymer shell is decreased, resulting in a reduction in release rate. Cross-linking the polymer shell after capsule formation was also found to decrease both the release rate and the yield of the active ingredient. The nature of the oil core also affected the release yield.

Crystal Growth and Solid-State Structure of Poly(lactide) Stereocopolymers

Solid-state structure and melting behavior for random stereocopolymers of L-lactide with meso-lactide (P(L-LA-co-meso-LA)) with different meso-LA compositions of 0, 2, 4, and 10 mol % were investigated under various isothermal crystallization conditions. The crystalline morphology of P(L-LA-co-meso-LA) samples changed from the spherulitic aggregates to hexagonal lamellae stacking with a rise in crystallization temperature. Under each crystallization condition, P(L-LA-co-meso-LA) samples formed alpha-crystal modifications for homopolymer of L-LA. By using the atomic force microscopy and small-angle X-ray scattering, the stacking structure of lamellar crystals was examined for the isothermally crystallized P(L-LA-co-meso-LA) thin films. The lamellar thickness of P(L-LA-co-meso-LA) ranged from 6.2 to 15.5 nm, and the values increased with crystallization temperature. Melting profiles of crystalline regions were examined by the differential scanning calorimetry (DSC) for the P(L-LA-co-meso-LA) samples. Distinct two melting peaks were detected in the DSC thermograms of several samples. Investigations on the time-dependent changes in lamellar structure and melting temperature of the P(L-LA-co-meso-LA) samples under isothermal crystallization conditions provided the evidence that a small amount of D-lactyl units was trapped in the crystalline regions during early stage of crystallization process under the certain crystallization condition. In addition, it was found that the D-lactyl units trapped in crystalline regions were excluded from crystalline lamellae to form the thermally stable crystals without changes in crystal thickness during further isothermal storage at a crystallization temperature. The equilibrium melting temperature (T(m)0) of P(L-LA-co-meso-LA) samples was estimated by using modified Hoffman-Weeks methods, and the obtained values decreased from 215 to 184 degrees C as the meso-LA composition was increased from 0 to 10 mol %. Furthermore, the crystal growth kinetics of the P(L-LA-co-meso-LA) samples was analyzed by using the secondary nucleation theory. Transitions of crystalline regime both from regime III to regime II and from regime II to regime I were detected for each sample. The transition temperature from regime II to regime I of each of the P(L-LA-co-meso-LA) samples was very close to the temperature region revealed the morphological changes in the crystalline aggregates from the spherulitic aggregates to hexagonal lamellae stacking.

Novel Formulations of Vitamins and Insulin by Nanoengineering of Polyelectrolyte Multilayers around Microcrystals

Microcapsules loaded with vitamin K3 (VK3), biotin, or insulin were prepared by using a novel coating technology based on the layer-by-layer (LbL) deposition of oppositely charged polyelectrolytes onto microcrystal templates. This produced multilayered, polymeric shells of varying thickness around the crystalline cores. Dissolution of the core material (VK3 with ethanol, biotin with basic solution, and insulin with acidic solution), resulted in its release through the shells. Microelectrophoresis was employed to monitor the microcrystal coating process; confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM) were used to verify multilayer coating and the formation of hollow polymer shells following removal of the microcrystal templates. The release rates of both VK3 and insulin decreased as the wall thickness (the number of polyelectrolyte layers deposited onto the microcrystal cores), increased. The release time could be varied by a factor of more than ten, depending on the number of polyelectrolyte layers applied. Following the addition of 70 mass % ethanol, the solubility of VK3 increased by as much as 170-fold, resulting in an increased rate of VK3 release. By selecting appropriate polymer materials for the shells, and by controlling the number of polyelectrolyte layers applied, shells of various thickness, stiffness, aqueous solubility, dispersibility, biocompatibility, and permeability can be constructed.

Quantitative analysis of three-dimensional fluid flow in rotating bioreactors for tissue engineering

Tissue engineering has emerged as a viable alternative to the problem of organ and tissue shortage. Our laboratory has developed matrices for bone tissue engineering based on sintered spherical particles and, using bioreactor technology, has demonstrated the ability to produce highly mineralized matrices in vitro. In this study, porous microcapsule scaffolds were developed for bone tissue engineering in the high aspect ratio vessel rotating bioreactor. The motion of individual microcapsules as well as scaffolds in the bioreactor were studied by numerical simulation and in situ imaging analysis. Results show that spherical microcapsules with density less than the surrounding fluid exhibited two motions: (1) a periodic circular orbit with tangential speed equal to the free fall speed of the particle, and (2) an inward radial migration of the circular orbit toward the center of the bioreactor vessel. Lighter-than-water scaffolds were fabricated by sintering poly(lactic-co-glycolic acid) hollow microcarriers with diameter from 500 to 860 microm into a fixed three-dimensional geometry with approximately 30% pore volume and 180 to 190 microm median pore size. Scaffolds were fabricated with aggregate densities ranging from 0.65 g/mL and 0.99 g/mL by appropriate combinations of hollow and solid microcarriers within the scaffold. Scaffold velocity in the bioreactor for the above range of densities was accurately predicted by numerical simulation and ranged from 100 mm/s to 3 mm/s. Maximum shear stress estimation due to media flow over the exterior of the scaffold ranged from 0.3 N/m(2) to 0.006 N/m(2). Internal perfusion velocity through scaffolds also was calculated and ranged from 13 mm/s to 0.2 mm/s. Estimates of maximum interior shear stress ranged from 0.03 to 0.0007 N/m(2). These analytical methods provide an excellent vehicle for the study of bone tissue synthesis in three-dimensional culture with fluid flow.

Effect of acid–base interaction between silica and fragrant oil in the PCL/PEG microcapsules

In this work, the biodegradable poly(epsilon-caprolactone) (PCL)/poly(ethylene glycol) (PEG) microcapsules were prepared in the presence of SiO(2) and fragrant oil using emulsion solvent evaporation method. And SiO(2) was chemically treated in 30 wt.% hydrochloric acid and sodium hydroxide. The effect of chemical treatment on SiO(2) surfaces was studied in terms of pH, acid-base value, and N(2)/77 K gas adsorption. Image analyzer and scanning electron microscope (SEM) were used to observe the shape and surface change of the prepared microcapsules. And the variation of surface free energy of microcapsules was characterized by contact angles. The results showed that the average diameter, surface free energy, and fragrant oil release rate of microcapsules were increased with increasing the PEG ratio. Also, it was found that in the case of basic treated SiO(2), the fragrant oil adsorption capacity and release rate were decreased due to the decrease of specific surface area or the increase of acid-base interactions between basic SiO(2) and acidic fragrant oil.

Preparation and characterization of poly(lactic acid)-poly(ethylene glycol)-poly(lactic acid) (PLA-PEG-PLA) microspheres for controlled release of paclitaxel

Microspheres of a new kind of copolymer, poly(lactic acid)-poly(ethylene glycol)-poly(lactic acid) (PLA-PEG-PLA), are proposed in the present work for clinical administration of an antineoplastic drug paclitaxel with hypothesis that incorporation of a hydrophilic PEG segment within the hydrophobic PLA might facilitate the paclitaxel release. Paclitaxel-loaded PLA-PEG-PLA microspheres of various compositions were prepared by the solvent extraction/evaporation method. Characterization of the microspheres was then followed to examine the particle size and size distribution, the drug encapsulation efficiency, the colloidal stability, the surface chemistry, the surface and internal morphology, the drug physical state and its in vitro release behavior. The effects of polymer types, solvents and drug loading were investigated. It was found that in the microspheres the PEG segment was homogeneously distributed and caused porosity. Significantly faster release from PLA-PEG-PLA microspheres resulted in comparison with the PLGA counterpart. Incorporation of water-soluble solvent acetone in the organic solvent phase further increased the porosity of the PLA-PEG-PLA microspheres and facilitated the drug release. A total of 49.6% sustained release of paclitaxel within 1 month was achieved. Potentially, the presence of PEG on the surface of PLA-PEG-PLA microspheres could improve their biocompatibility. PLA-PEG-PLA microspheres could thus be promising for the clinical administration of highly hydrophobic antineoplastic drugs such as paclitaxel.

Preparation and in vitro evaluation of Eudragit microspheres containing acetazolamide

The aim of this study was to prepare and evaluate Eudragit (RS and RL) microspheres containing acetazolamide. Microspheres were prepared by solvent evaporation method using acetone/liquid paraffin system. The influence of formulation factors (stirring speed, polymer:drug ratio, type of polymer, ratio of the combination of polymers) on particle size, encapsulation efficiency and in vitro release characteristics of the microspheres were investigated. The yields of preparation and the encapsulation efficiencies were high for all formulations the microspheres were obtained. Mean particle size changed by changing the polymer:drug ratio or the stirring speed of the system. Although acetazolamide release rates from Eudragit RS microspheres were very slow and incomplete for all formulations, they were fast from Eudragit RL microspheres. When Eudragit RS was added to Eudragit RL microsphere formulations, release rates slowed down and achieved the release profile suitable for peroral administration.

Effect of Water on the Surface Molecular Mobility of Poly(lactide) Thin Films: An Atomic Force Microscopy Study

Physical properties associated with molecular mobility on the surface of thin films with 300 nm thickness for poly(lactide)s (PLAs) were studied under vacuum conditions as well as under aqueous conditions by using friction force mode atomic force microscopy (AFM). Two types of PLAs were applied for the experimental samples as uncrystallizable PLA (uc-PLA) and crystallizable PLA (c-PLA). The friction force on the surface of thin films was measured as a function of temperature to assess the surface molecular mobility both under vacuum and under aqueous conditions. A lower glass-transition temperature of the uc-PLA surface in water was detected than that under vacuum conditions. In the case of the c-PLA thin film, change in friction force was detected at a lower temperature under aqueous conditions than in vacuo. A morphological change was observed in the c-PLA thin film during heating process from room temperature to 100 degrees C by temperature-controlled AFM. The surface of the c-PLA thin film became rough due to the cold crystallization, and the crystallization of c-PLA molecules in water took place at a lower temperature than in vacuo. These friction force measurements and AFM observations suggest that molecular motion on the surface of the both uc- and c-PLA thin films is enhanced in the presence of water molecules. In addition, in situ AFM observation of the enzymatic degradation process for the c-PLA thin film crystallized at 160 degrees C was carried out in buffer solution containing proteinase K at room temperature. The amorphous region around the hexagonal crystal was eroded within 15 min. It has been suggested that the adsorption of water molecules on the PLA film surface enhances the surface molecular mobility of the glassy amorphous region of PLA and induces the enzymatic hydrolysis by proteinase K.

Annealing and melting behavior of poly(l-lactic acid) single crystals as revealed by in situ atomic force microscopy

In situ annealing and melting of folded-chain single crystals of poly(l-lactic acid) (PLLA) was examined by temperature-controlled atomic force microscopy (AFM). Prominent changes in the crystal appearance during annealing could be followed in real time by the AFM at temperatures above the original crystallization temperature. Thickening of the crystal edges could be occasionally observed, and this indicates that the crystal edges are less perfect than the central, well-ordered regions. At higher annealing temperatures, melting of the unthickened part started. The melting of the unthickened region progressed from the boundaries of the thickened portion normal to the growth face, rather than to the folding surfaces. In addition, it is suggested that melting also initiates at defective or distorted sites in the crystal as revealed by transmission electron microscopy (TEM) and AFM.