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

An overview of the production methods for core-shell microspheres for parenteral controlled drug delivery

Core-shell microspheres hold great promise as a drug delivery system because they offer several benefits over monolithic microspheres in terms of release kinetics, for instance a reduced initial burst release, the possibility of delayed (pulsatile) release, and the possibility of dual-drug release. Also, the encapsulation efficiency can significantly be improved. Various methods have proven to be successful in producing these core-shell microspheres, both the conventional bulk emulsion solvent evaporation method and methods in which the microspheres are produced drop by drop. The latter have become increasingly popular because they provide improved control over the particle characteristics. This review assesses various production methods for core-shell microspheres and summarizes the characteristics of formulations prepared by the different methods, with a focus on their release kinetics.

Double-Walled Poly-(D,L-lactide-co-glycolide) (PLGA) and Poly(L-lactide) (PLLA) Nanoparticles for the Sustained Release of Doxorubicin

Double-walled nanoparticles (DWNPs), containing doxorubicin as a model drug, were produced using poly-(D,L-lactide-co-glycolide) (PLGA) and poly(L-lactide) (PLLA) by the solvent evaporation technique. Double-walled microparticles containing doxorubicin were also produced to make possible the examination of the inner morphology and drug distribution using optical and fluorescence microscopy. The produced microparticles present a double-walled structure with doxorubicin solubilized in the PLGA-rich phase. The DWNPs produced present very low initial burst values and a sustained DOX release for at least 90 days with release rates decreasing with the increase in the PLLA amount. Zero-order release kinetics were obtained after day 15. The results support that the PLLA layer acts as a rate control barrier and that the diffusion of doxorubicin from the drug-loaded inner PLGA core can be retarded by an increase in the thickness of the unloaded outer layer. The unloaded double-walled nanoparticles produced were used in in vitro tests with CHO cells and demonstrate that they are nontoxic, while the double-walled nanoparticles loaded with doxorubicin caused a great cellular viability and decreased when tested in vitro.

Minocycline Loaded Hybrid Composites Nanoparticles for Mesenchymal Stem Cells Differentiation into Osteogenesis

Bone transplants are used to treat fractures and increase new tissue development in bone tissue engineering. Grafting of massive implantations showing slow curing rate and results in cell death for poor vascularization. The potentials of biocomposite scaffolds to mimic extracellular matrix (ECM) and including new biomaterials could produce a better substitute for new bone tissue formation. A purpose of this study is to analyze polycaprolactone/silk fibroin/hyaluronic acid/minocycline hydrochloride (PCL/SF/HA/MH) nanoparticles initiate human mesenchymal stem cells (MSCs) proliferation and differentiation into osteogenesis. Electrospraying technique was used to develop PCL, PCL/SF, PCL/SF/HA and PCL/SF/HA/MH hybrid biocomposite nanoparticles and characterization was analyzed by field emission scanning electron microscope (FESEM), contact angle and Fourier transform infrared spectroscopy (FT-IR). The obtained results proved that the particle diameter and water contact angle obtained around 0.54 ± 0.12 to 3.2 ± 0.18 µm and 43.93 ± 10.8° to 133.1 ± 12.4° respectively. The cell proliferation and cell-nanoparticle interactions analyzed using (3-(4,5-dimethyl thiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt) MTS assay (Promega, Madison, WI, USA), FESEM for cell morphology and 5-Chloromethylfluorescein diacetate (CMFDA) dye for imaging live cells. Osteogenic differentiation was proved by expression of osteocalcin, alkaline phosphatase activity (ALP) and mineralization was confirmed by using alizarin red (ARS). The quantity of cells was considerably increased in PCL/SF/HA/MH nanoparticles when compare to all other biocomposite nanoparticles and the cell interaction was observed more on PCL/SF/HA/MH nanoparticles. The electrosprayed PCL/SF/HA/MH biocomposite nanoparticle significantly initiated increased cell proliferation, osteogenic differentiation and mineralization, which provide huge potential for bone tissue engineering.

Sustained release of bupivacaine for post-surgical pain relief using core–shell microspheres

Core–shell PLGA/PLLA polymer microspheres sustained 2 weeks in vivo bupivacaine release, providing extended postoperative analgesia without infection or joint damage.

Protein encapsulation in and release from monodisperse double-wall polymer microspheres

Biodegradable polymer double-wall microspheres (DWMS) are promising vehicles for macromolecular therapeutics such as proteins and peptides. Using precision particle fabrication (PPF) technology, uniform DWMS with outer diameter approximately 55 μm were fabricated comprising poly(lactide-co-glycolide) cores encapsulating bovine serum albumin (BSA) and approximately 10 μm thick, drug-free, poly(lactic acid) (PLA) shells of varying PLA molecular weight. Also, monolithic single-wall microspheres (SWMS) were fabricated to mimic the BSA-loaded core. The use of relatively fast-extracting ethyl acetate and slowly extracting dichloromethane as shell- and core-phase solvents, respectively, was found to produce DWMS with well-defined core-shell structure, high BSA encapsulation efficiency, and the desired localization of protein in the particle core. Initial protein distribution, particle erosion, and in vitro protein release from DWMS and SWMS were examined. The presence of a BSA-free shell in DWMS decreased the protein release rate and extended the duration of release from approximately 50 days to 70-80 days, demonstrating the capacity of such DWMS to provide enhanced control of protein delivery rates.

Mechanism of drug release from double-walled PDLLA(PLGA) microspheres

The drug release and degradation behavior of two double-walled microsphere formulations consisting of a doxorubicin-loaded poly(d,l-lactic-co-glycolic acid) (PLGA) core (∼46 kDa) surrounded by a poly(d,l-lactic acid) (PDLLA) shell layer (∼55 and 116 kDa) were examined. It was postulated that different molecular weights of the shell layer could modulate the erosion of the outer coating and limit the occurrence of water penetration into the inner drug-loaded core on various time scales, and therefore control the drug release from the microspheres. For both microsphere formulations, the drug release profiles were observed to be similar. The degradation of the microspheres was monitored for a period of about nine weeks and analyzed using scanning electron microscopy, laser scanning confocal microscopy, and gel permeation chromatography. Interestingly, both microsphere formulations exhibited occurrence of bulk erosion of PDLLA on a similar time scale despite different PDLLA molecular weights forming the shell layer. The shell layer of the double-walled microspheres served as an effective diffusion barrier during the initial lag phase period and controlled the release rate of the hydrophilic drug independent of the molecular weight of the shell layer.

Monodisperse double-walled microspheres loaded with chitosan-p53 nanoparticles and doxorubicin for combined gene therapy and chemotherapy

We have designed and evaluated a dual anticancer delivery system to provide combined gene therapy and chemotherapy. Double-walled microspheres consisting of a poly(d,l-lactic-co-glycolic acid) (PLGA) core surrounded by a poly(lactic acid) (PLA) shell were fabricated via the precision particle fabrication (PPF) technique. We make use of the advantages of double-walled microspheres to deliver chitosan-DNA nanoparticles containing the gene encoding the p53 tumor suppressor protein (chi-p53) and/or doxorubicin (Dox), loaded in the shell and core phases, respectively. Different molecular weights of PLA were used to form the shell layer for each formulation. The microspheres were monodisperse with a mean diameter of 65 to 75 μm and uniform shell thickness of 8 to 17 μm. Blank and Dox-loaded microspheres typically exhibited a smooth surface with relatively few small pores, while chi-microspheres containing p53 nanoparticles, with and without Dox, presented rough and porous surfaces. The encapsulation efficiency of Dox was significantly higher when it was encapsulated alone compared to co-encapsulation with chi-p53 nanoparticles. The encapsulation efficiency of chi-p53 nanoparticles, on the other hand, was not affected by the presence of Dox. As desired, chi-p53 nanoparticles were released first, followed by simultaneous release of chi-p53 nanoparticles and Dox at a near zero-order rate. Thus, we have demonstrated that the PPF method is capable of producing double-walled microspheres and encapsulating dual agents for combined modality treatment, such as gene therapy and chemotherapy.

Designing multilayered particulate systems for tunable drug release profiles

Triple-layered microparticles comprising poly(D,L-lactide-co-glycolide, 50:50) (PLGA), poly(L-lactide) (PLLA) and poly(ethylene-co-vinyl acetate, 40 wt.% vinyl acetate) (EVA) were fabricated using a one-step solvent evaporation technique, with ibuprofen drug localized in the EVA core. The aim of this study was to investigate the drug release profiles of these triple-layered microparticles in comparison to double-layered (PLLA/EVA and PLGA/EVA) (shell/core) and single-layered EVA microparticles. Double- and triple-layered microparticles were shown to eliminate burst release otherwise observed for single-layered microparticles. For triple-layered microparticles, the migration of acidic PGA oligomers from the PLGA shell accelerated the degradation of the PLLA mid-layer and subsequently enhanced drug release in comparison to double-layered PLLA/EVA microparticles. Further studies showed that drug release rates can be altered by changing the layer thicknesses of the triple-layered microparticles, and through specific tailoring of layer thicknesses, a zero-order release can be achieved. This study therefore provides important mechanistic insights into how the distinctive structural attributes of triple-layered microparticles can be tuned to control the drug release profiles.

Revolutionizing drug delivery through biodegradable multilayered particles

Modern drug discovery technologies are discovering more and more potent therapeutic agents with narrow therapeutic windows, thus necessitating the improvement of current particulate drug delivery systems. Conventional single-layered polymeric particles have limited control over drug release profiles, including burst release, the inability to provide zero-order, pulsatile, time-delayed release and controlled release of multiple drugs. In an attempt to better control drug release kinetics, the development of multilayered microparticles has been introduced. In this review, we give an overview of the fabrication and characterization techniques of multilayered polymeric microparticles. We also focus on the one-step solvent evaporation technique, and the key process parameters in this technique that affect the formation of microparticle configurations. In addition, the benefits and challenges of multilayered microparticulate system for drug delivery were discussed. This review intends to portray how distinctive structural attributes and degradation behaviors of multilayered microparticles can be exploited to fine-tune drug release profiles and kinetics.

In vitro degradation and drug-release properties of water-soluble chitosan cross-linked oxidized sodium alginate core-shell microgels

Hydrogels based on sodium alginate (SA) have already been widely used in biomedical applications using Ca(2+) as a cross-linker; however, these hydrogels tend to disintegrate in electrolyte solutions. To solve this problem, we present a kind of oxidized sodium alginate (OSA) microgel using water-soluble chitosan (WSC) as a cross-linker. This microgel was successfully prepared via an emulsion cross-linking technique at room temperature. The microgel was cross-linked by the formation of both Schiff base bonds and inter-polyelectrolyte complexes, which can efficiently eliminate the disintegration of the microgel in electrolyte solutions. Morphological properties of the resulting microgels were determined by transmission electron microscopy (TEM), hydrodynamic diameters of the microgels were characterized by dynamic light scattering (DLS). The objective of this work was to achieve the colon-specific delivery of an anti-ulcerative colitis drug. 5-Aminosalicylic acid (5-ASA) was chosen as a model drug and the in vitro drug-release profile was established in buffer solutions with 0.1 M HCl/NaCl (pH 1.2) and 0.1 M phosphate-buffered saline (PBS, pH 7.4) at 37°C. The microgel was incubated in 0.1 M PBS (pH 7.4) at 37°C to determine its degradation behavior. Cell cytotoxicity (tested by MTT assay) showed that this microgel had no significant cytotoxicity. These results indicated that this microgel prepared by introducing WSC into OSA may have potential applications in oral controlled drug-delivery systems. Therefore, the OSA/WSC microgel may be a useful carrier for the colon-specific delivery of anti-inflammatory drugs including 5-ASA and the enhanced therapeutic effect of ulcerative colitis.

Injectable PLGA microsphere/calcium phosphate cements: physical properties and degradation characteristics

Calcium phosphate (CaP) cements show an excellent biocompatibility and often have a high mechanical strength, but in general degrade relatively slow. To increase degradation rates, macropores can be introduced into the cement, e.g., by the inclusion of biodegradable microspheres into the cement. The aim of this research is to develop an injectable PLGA microsphere/CaP cement with sufficient setting/cohesive properties and good mechanical and physical properties. PLGA microspheres were prepared using a water-in-oil-in-water double-emulsion technique. The CaP-cement used was Calcibon, a commercially available hydroxyapatite-based cement. 10:90 and 20:80 dry wt% PLGA microsphere/CaP cylindrical scaffolds were prepared as well as microporous cement (reference material). Injectability, setting time, cohesive properties and porosity were determined. Also, a 12-week degradation study in PBS (37 degree C) was performed. Results showed that injectability decreased with an increase in PLGA microsphere content. Initial and final setting time of the PLGA/CaP samples was higher than the microporous sample. Porosity of the different formulations was 40.8% (microporous), 60.2% (10:90) and 69.3% (20:80). The degradation study showed distinct mass loss and a pH decrease of the surrounding medium starting from week 6 with the 10:90 and 20:80 formulations, indicating PLGA erosion. Compression strength of the PLGA microsphere/CaP samples decreased siginificantly in time, the microporous sample remained constant. After 12 weeks both PLGA/CaP samples showed a structure of spherical micropores and had a compressive strength of 12.2 MPa (10:90) and 4.3 MPa (20:80). Signs of cement degradation were also found with the 20:80 formulation. In conclusion, all physical parameters were well within workable ranges with both 10:90 and 20:80 PLGA microsphere/CaP cements. After 12 weeks the PLGA was totally degraded and a highly porous, but strong scaffold remained.

In vitro cytotoxicity and drug release properties of pH- and temperature-sensitive core-shell hydrogel microspheres

A simple method has been developed to prepare smart P(N,N-diethylacrylamide-co-methacrylic acid) (P(DEA-co-MAA)) microspheres that consist of well-defined temperature-sensitive cores and pH sensitive shells. The microgels have been prepared by surfactant-free emulsion polymerization using water as the solvent. The core-shell hydrogel microspheres have been characterized by Fourier transform infrared (FTIR) spectroscopy, UV spectrometry, dynamic light scattering (DLS) and transmission electron micrograph (TEM). Preliminary characterization of the biocompatibility of hydrogel microspheres has been done by the cytotoxicity assays using the HeLa human breast cancer cell line as probes. The in vitro drug release indicates that drug release rate, encapsulation efficiency (EE) and release kinetics depend upon the pH value and copolymer composition. According to this study, the hydrogel microspheres based on P(DEA-co-MAA) could serve as suitable candidate for drug site-specific carrier in intestine.

A high-throughput microparticle microarray platform for dendritic cell-targeting vaccines

Immunogenomic approaches combined with advances in adjuvant immunology are guiding progress toward rational design of vaccines. Furthermore, drug delivery platforms (e.g., synthetic particles) are demonstrating promise for increasing vaccine efficacy. Currently there are scores of known antigenic epitopes and adjuvants, and numerous synthetic delivery systems accessible for formulation of vaccines for various applications. However, the lack of an efficient means to test immune cell responses to the abundant combinations available represents a significant blockade on the development of new vaccines. In order to overcome this barrier, we report fabrication of a new class of microarray consisting of antigen/adjuvant-loadable poly(D,L lactide-co-glycolide) microparticles (PLGA MPs), identified as a promising carrier for immunotherapeutics, which are co-localized with dendritic cells (DCs), key regulators of the immune system and prime targets for vaccines. The intention is to utilize this high-throughput platform to optimize particle-based vaccines designed to target DCs in vivo for immune system-related disorders, such as autoimmune diseases, cancer and infection. Fabrication of DC/MP arrays leverages the use of standard contact printing miniarraying equipment in conjunction with surface modification to achieve co-localization of particles/cells on isolated islands while providing background non-adhesive surfaces to prevent off-island cell migration. We optimized MP overspotting pin diameter, accounting for alignment error, to allow construction of large, high-fidelity arrays. Reproducible, quantitative delivery of as few as 16+/-2 MPs per spot was demonstrated and two-component MP dosing arrays were constructed, achieving MP delivery which was independent of formulation, with minimal cross-contamination. Furthermore, quantification of spotted, surface-adsorbed MP degradation was demonstrated, potentially useful for optimizing MP release properties. Finally, we demonstrate DC co-localization with PLGA MPs on isolated islands and that DCs do not migrate between islands for up to 24 h. Using this platform, we intend to analyze modulation of DC function by providing multi-parameter combinatorial cues in the form of proteins, peptides and other immuno-modulatory molecules encapsulated in or tethered on MPs. Critically, the miniaturization attained enables high-throughput investigation of rare cell populations by reducing the requirement for cells and reagents by many-fold, facilitating advances in personalized vaccines which target DCs in vivo.

Effects of carbon nanotubes (CNTs) on the processing and in-vitro degradation of poly(DL-lactide-co-glycolide)/CNT films

Nanocomposite films based on single wall carbon nanotubes (SWNTs) and poly(DL-lactide-co-glycolide) copolymer (50:50 PLGA) were processed and analyzed. The purpose of this study was to investigate the effect of different functionalization systems on the physical stability and morphology of PLGA films. Both covalent and non covalent functionalization of carbon nanotubes were considered in order to control the interactions between PLGA and SWNTs and to understand the role of the filler in the biodegradation properties. Using a solvent casting process, different PLGA/SWNT nanocomposites were prepared and incubated using organic solution under physiological conditions. In-vitro degradation studies were conducted by measurements of weight loss, infrared spectroscopy, glass transition temperature and SEM observations as a function of the incubation time, over a 9-week period. All PLGA films were degraded by hydrolitical degradation. However, a different degradation mechanism was observed in the case of functionalized SWNTs with respect to pristine material. It has been observed that system composition and SWNT functionalization may play a crucial role on the autocatalytic effect of the degradation process. These studies suggest that the degradation kinetics of the films can be engineered by varying carbon nanotube (CNT) content and functionalization. The combination of biodegradable polymers and CNTs opens a new perspective in the self-assembly of nanomaterials and nanodevices.

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

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

Stereological analysis of the poly-(DL-lactide-co-glycolide) submicron sphere prepared by solvent/non-solvent chemical methods and centrifugal processing

Fine particles made of poly(lactide-co-glycolide) (DLPLG) are excellent candidates for controlled release of delivering drugs and genes, because of their degradable nature. The preparation of DLPLG submicron spheres poses serious challenges that are not necessarily present when preparing macroparticles. In the present paper, DLPLG powder is produced with chemical method using solvent/non-solvent systems with subsequent centrifugation of the solution. The samples were characterized by infrared spectroscopy (IR), scanning electron microscopy (SEM) and stereological analysis. By changing the aging time with non-solvent and time and velocity of the centrifugal processing, it is possible to influence on the morphology and uniformity of the copolymer particles. Powder of the series with short aging time with non-solvent and longest time and velocity of the centrifugal processing has smallest particles and highest uniformity, where mean particles sizes were between 150 nm and 230 nm depending on which stereological parameters are considered (D(max), maximal diameters, feret X or feret Y).

Fabrication and characterization of rigid magnetic monodisperse microspheres for protein adsorption

This article describes the fabrication of a rigid magnetic monodisperse bead (M-PGMA-TRI, 4.92 microm) with polyglycidyl methacrylate (PGMA) cross-linked by trimethylolpropane trimethacrylate (TRI). This was realized by adding a proper amount (2%, w/w) of TRI after 3 h of the dispersion-polymerization reaction with the monomer of GMA. The mono-sized microspheres were further processed to introduce magnetic granules by sulfonation and penetration-deposition approaches. The monodisperse bead (M-PGMA) without TRI addition was also fabricated for comparison. The morphology, size and magnetic characteristics of the microspheres were extensively characterized. The M-PGMA-TRI microspheres were nonporous, of smooth surface and superparamagnetic with a saturation magnetization of 13.0 emicro/g. Recycled use of the material for protein adsorption exhibited stability of the magnetic properties of the M-PGMA-TRI, as compared to the significant loss of the saturation magnetization of the M-PGMA. The chemical stability of the M-PGMA-TRI was also confirmed by examining its protein adsorption and magnetic properties after incubation in various solutions such as acidic buffer (pH 2.2) for 24 h. The adsorption capacity of gamma-globulin reached 287.2 mg/g and kept stable in the repeated adsorption/desorption/regeneration cycles. The results indicated that the introduction of 2% TRI was promising for producing rigid magnetic mono-sized microspheres for protein adsorption.

Use of thermodynamic parameters for design of double-walled microsphere fabrication methods

Double-walled microspheres (DWMS), with drug localized to the particle core, present a promising route for control of drug release rates, for example, by varying the degradation rate or erosion mechanism of the polymer used to form the shell or the thickness of the shell. DWMS are often difficult to fabricate, however. Thermodynamic descriptions for polymer-polymer immiscibility, drug distribution between phases and polymer-solution spreading coefficient provide predictions of appropriate solvents and polymer concentrations for efficiently producing well-formed DWMS. As an example, thermodynamic parameters for a polyphosphoester/poly(D,L-lactide-co-glycolide) (PLG) DWMS system, encapsulating piroxicam, have been calculated and the predictions tested experimentally. Appropriate choices of solvents and initial polymer concentrations resulted in DWMS with the desired polyphosphoester shells and piroxicam located selectively in PLG cores.

Small-molecule release from poly(D,L-lactide)/poly(D,L-lactide-co-glycolide) composite microparticles

Addition of biodegradable polymer shells surrounding polymeric, drug-loaded microparticles offers the opportunity to control drug release rates. A novel fabrication method was used to produce microparticles with precise control of particle diameter and the thickness of the polymer shell. The effect of shell thickness on release of a model drug, piroxicam, has been clearly shown for 2- to 15-microm thick shells of poly(D,L-lactide) (PDLL) surrounding a poly(D,L-lactide-co-glycolide) (PLG) core and compared to pure PLG microspheres loaded with piroxicam. Furthermore, the core-shell microparticles are compared to microspheres containing blended polymers in the same mass ratios to demonstrate the importance of the core-shell morphology. Combining PDLL(PLG) microcapsules of different shell thicknesses allows nearly constant release rates to be attained for a period of 6 weeks.

In vitro degradation of polyanhydride/polyester core-shell double-wall microspheres

Double-wall microspheres (DWMS), comprising distinct polymer core and shell phases, are useful and interesting for controlled-release drug delivery. In particular, the presence of a surface-eroding polymer core may be expected to limit water penetration and, therefore, delay degradation of the core phase and drug release. In this study, solid microspheres and DWMS were fabricated using a surface-eroding polymer (poly[1,6-bis(p-carboxyphenoxy)hexane]; PCPH) and a bulk-eroding polymer (poly(D,L-lactide-co-glycolide); PLG). Erosion of the particles was observed by optical and electron microscopy, while polymer degradation was followed by gel permeation chromatography, during incubation in buffer at 37 degrees C. Degradation and erosion were very different depending on which polymer formed the particle shell. Nevertheless, the relatively thin (approximately 5 microm) PCPH shells could not prevent water penetration, and the PLG cores completely eroded by 6 weeks of incubation.

Microspheres for Drug Delivery

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

Delivery systems for small molecule drugs, proteins, and DNA: the neuroscience/biomaterial interface

Manipulation of cellular processes in vivo by the delivery of drugs, proteins or DNA is of paramount importance to neuroscience research. Methods for the presentation of these molecules vary widely, including direct injection (either systemic or stereotactic), osmotic pump-mediated chronic delivery, or even implantation of cells engineered to indefinitely secrete a factor of interest. Biomaterial-based delivery systems represent an alternative to more traditional approaches, with the possibility of increased efficacy. Drug-releasing biomaterials, either as injectable microspheres or as three-dimensional implants, can deliver a molecule of interest (including small molecule drugs, biologically active proteins, or DNA) over a more prolonged period of time than by standard bolus injection, avoiding the need for repeated administration. Furthermore, sustained-release systems can maintain therapeutic concentrations at a target site, thus reducing the chance for toxicity. This review summarizes applications of polymer-based delivery of small molecule drugs, proteins, and DNA specifically relevant to neuroscience research. We detail the fabrication procedures for the polymeric systems and their utility in various experimental models. The biomaterial field offers unique experimental tools with downstream clinical application for the study and treatment of neurologic disease.

Uniform double-walled polymer microspheres of controllable shell thickness

A method for fabricating uniform double-walled microspheres with controllable size and shell thickness has been developed. The method, based on previous work to fabricate uniform microspheres, employs multiple concentric nozzles to produce a smooth coaxial jet comprising an annular shell and core material, which is acoustically excited to break up into uniform core-shell droplets. The orientation of the jets, material flow rates, and rate of solvent extraction are controlled to create uniform and well-centered "double-walled" microspheres exhibiting a controllable shell thickness. Double-walled microspheres were fabricated with different arrangements of bulk-eroding poly(D,L-lactide-co-glycolide) (PLG) and surface-eroding poly[(1,6-bis-carboxyphenoxy) hexane] (PCPH). Variation of the fabrication parameters allowed complete encapsulation by the shell phase, including the efficient formation of a PCPH shell encapsulating a PLG core. Utilizing this technology, double-walled microsphere shell thickness can be varied from <2 microm to tens of microns while maintaining complete and well-centered core encapsulation for double-walled microspheres near 50 microm in overall diameter.

Polymer microspheres for controlled drug release

Polymer microspheres can be employed to deliver medication in a rate-controlled and sometimes targeted manner. Medication is released from a microsphere by drug leaching from the polymer or by degradation of the polymer matrix. Since the rate of drug release is controlled by these two factors, it is important to understand the physical and chemical properties of the releasing medium. This review presents the methods used in the preparation of microspheres from monomers or from linear polymers and discusses the physio-chemical properties that affect the formation, structure, and morphology of the spheres. Topics including the effects of molecular weight, blended spheres, crystallinity, drug distribution, porosity, and sphere size are discussed in relation to the characteristics of the release process. Added control over release profiles can be obtained by the employment of core-shell systems and pH-sensitive spheres; the enhancements presented by such systems are discussed through literature examples.

Localization of bovine serum albumin in double-walled microspheres

Phase separation of binary blends of various combinations of poly (L-lactide) (PLA), and poly (D,L-lactide-co-glycolide) (PLGA), was investigated using differential scanning calorimetry (DSC). Based on this phase separation phenomenon, double-walled microspheres were fabricated. A model agent, bovine serum albumin (BSA) labeled with fluorescein isothiocyanate (FITC-BSA) was localized in each layer. Scanning electron microscopy (SEM) and fluorescence microscopy (FM) were used to assess the formation of double-walled microspheres and the localization of the drug, respectively. When a 1:1 polymer ratio was used, the FITC-BSA was localized in the outer layer. When the relative ratio of PLGA to PLA was increased to 3:1 using the same overall polymer concentration, the FITC-BSA was localized in the inner core. Release studies were carried out to evaluate the advantage of double-walled microspheres compared to single walled microspheres. Microspheres made with FITC-BSA localized in the inner core exhibited a significantly lower initial release rate compared to microspheres where the drug was located in the outer layer, or compared to microspheres made from PLA only. Hence microspheres with a double-walled morphology have the potential for therapeutic use where a high burst might be detrimental.

Three-month, zero-order piroxicam release from monodispersed double-walled microspheres of controlled shell thickness

Double-walled microspheres represent an increasingly important class of drug delivery devices that provide enhanced control of drug delivery schedules. Clearly, the overall particle size and shell thickness are important parameters in modulating the drug release rates. Precision particle fabrication technology has been used to fabricate double-walled microspheres of predefined uniform diameters of 40-60 microm exhibiting a poly(D,L-lactide-co-glycolide) (PLG) core and poly(L-lactide) (PL) shell of controllable thickness from approximately 2 to 10 microm. The release of a model small-molecule drug, piroxicam, from uniform microspheres of pure PLG and PL is compared to the release from double-walled microspheres exhibiting different PL shell thicknesses. The presence of the PL shell enveloping a PLG core essentially eliminated the initial "burst" of piroxicam that was observed when the drug was released from pure PLG microspheres. In addition, increasing the PL shell thickness shifted the release profile from a biphasic shape for pure PLG microspheres to zero-order piroxicam release over 3 months for the thickest (approximately 10 microm) PL shell.