Biodegradation and biocompatibility of PLA and PLGA microspheres

High field gradient targeting of magnetic nanoparticle-loaded endothelial cells to the surfaces of steel stents

A cell delivery strategy was investigated that was hypothesized to enable magnetic targeting of endothelial cells to the steel surfaces of intraarterial stents because of the following mechanisms: (i) preloading cells with biodegradable polymeric superparamagnetic nanoparticles (MNPs), thereby rendering the cells magnetically responsive; and (ii) the induction of both magnetic field gradients around the wires of a steel stent and magnetic moments within MNPs because of a uniform external magnetic field, thereby targeting MNP-laden cells to the stent wires. In vitro studies demonstrated that MNP-loaded bovine aortic endothelial cells (BAECs) could be magnetically targeted to steel stent wires. In vivo MNP-loaded BAECs transduced with adenoviruses expressing luciferase (Luc) were targeted to stents deployed in rat carotid arteries in the presence of a uniform magnetic field with significantly greater Luc expression, detected by in vivo optical imaging, than nonmagnetic controls.

Direct plasmid DNA encapsulation within PLGA nanospheres by single oil-in-water emulsion method

Plasmid DNA was encapsulated within poly(d,l-lactic-co-glycolic acid) (PLGA) nanospheres by using polyethylene glycol (PEG) assisted solubilization technique of plasmid DNA in organic solvents. Plasmid DNA was solubilized in an organic solvent mixture composed of 80% methylene chloride and 20% DMSO by producing PEG/DNA nano-complexes having an average diameter less than 100 nm. DNA could be solubilized in the organic solvent mixture to a greater extent with increasing the weight ratio of PEG/DNA. PLGA nanospheres encapsulating DNA were successfully prepared by the single O/W emulsion method. They exhibited greater loading efficiency and better structural integrity, compared to those prepared by the W/O/W double emulsion method. Plasmid DNA could be successfully delivered to macrophage cells to express an exogenous gene. This new formulation enabled high loading of intact plasmid DNA within PLGA nanospheres useful for DNA vaccines.

PLGA microspheres with high drug loading and high encapsulation efficiency prepared by a novel solvent evaporation technique

PLGA microspheres with high drug loading and high encapsulation efficiency were fabricated by a novel solvent evaporation process-in-situ S/O/W process. Insulin was dissolved in DMSO and dispersed into DCM to form fine particles due to an anti-solvent effect. The in-situ formed suspension was then added into an aqueous phase and emulsified. Microspheres were formed following the evaporation of organic solvents. The experimental results showed that the modified S/O/W process could encapsulate more than 90%(w/w) insulin in the microspheres with a drug loading of over 15% and the initial burst was much less than microspheres made by a W1/O/W2 process. Compared with a traditional water-in-oil-in-water (W1/O/W2) process, the in-situ S/O/W process does not require high solubility of the encapsulated drug in water and, because no special pre-treatment is needed to reduce the particle size of the drug, it is superior to an ordinary S/O/W process. The in-situ S/O/W process is particularly applicable to encapsulate peptides and low molecular weight proteins.

Biodegradable, polymeric nanoparticle delivery systems for cancer therapy

Nanotechnology has the potential to impact the treatment of cancer significantly. This review will explore how this potential is beginning to be realized through the design of polymeric nanoparticle delivery systems. Current research is focused on developing biocompatible nanoparticles capable of targeting specific cancer markers and delivering imaging and therapeutic agents for the detection and treatment of cancer, resulting in a number of preclinical and clinical applications. More sophisticated nanoparticle designs are now in development, including particles able to release multiple drugs for enhanced treatment efficacy and targeted, multifunctional particles capable of combining imaging and drug release.

Expansion of human bone marrow stromal cells on poly-(dl-lactide-co-glycolide) (PDLLGA) hollow fibres designed for use in skeletal tissue engineering

Strategies to expand human bone marrow stromal cells (HBMSC) for bone tissue engineering are a key to revolutionising the processes involved in three-dimensional skeletal tissue reconstruction. To facilitate this process we believe the use of biodegradable porous poly(DL-lactide-co-glycolide) (PDL LGA) hollow fibres as a scaffold used in combination with HBMSC to initiate natural bone repair and regeneration offers a potential solution. In this study, the biocompatibility of 75:25 PDL LGA fibres with HBMSC and the capacity of a PDL LGA fibre-associated HBMSC-monolayer to establish an osteogenic phenotype in vivo was examined. A high proportion of HBMSC survived when expanded on PDL LGA fibres for 6 days, with only 10% of the propidium iodide (pI)-labelled population represented in the sub-G1 DNA peak on analysis by flow cytometry. Tracking carboxy-fluorescein diacetate, succinimidyl ester (CFSE)-labelled HBMSC by flow cytometry indicated that HBMSC attachment to the P(DL)LGA fibres does not interfere with their rate of proliferation. Furthermore, in response to osteogenic stimuli, HBMSC expanded on PDL LGA fibres can differentiate, as expected, along the osteogenic lineage with associated alkaline phosphatase activity. Following implantation into SCID mice, osteogenic-conditioned PDL LGA fibre-HBMSC graft resulted in type I collagen deposition and associated bone mineralisation and osteoid formation, as evidenced by immunohistochemistry and histology. These studies provide evidence that porous PDL LGA hollow fibre-HBMSC graft is an innovative biomaterial that offers new approaches to mesenchymal cell expansion, which could be utilised as a scaffold for skeletal tissue generation.

Correlation between heparin release and polymerization degree of organically modified silica xerogels from 3-methacryloxypropylpolysilsesquioxane

This work aimed to investigate the use of an organically modified porous silica matrix (poly(methacryloxypropyl)-poly(silsesquioxane); P-MA-PS) as a release system for heparin. The matrices were obtained from methacryloxypropyltrimethoxysilane (MAS) via the sol-gel process under acidic conditions following photochemical polymerization and cross-linking of the organic matrix. Modulation of the polymerization degree of the organic matrix in the range 0-71% allowed adjusting the release kinetics of heparin according to therapeutic needs. It was demonstrated that higher drug loads and a decreasing polymerization degree resulted in a faster release profile of heparin, which followed a square root of time kinetic according to the Higuchi model. The hydrolytic degradation of hybrid xerogel was found to follow a zero-order kinetic whereas the heparin concentration did not show an influence on the degradation rate of the matrix. Since the released heparin retained its biological activity, the P-MA-PS matrices are of clinically interest, e.g. as coating on drug eluting coronary stents.

Effect of various formulation parameters on the properties of polymeric nanoparticles prepared by multiple emulsion method

This work evaluates and interprets underlying mechanisms behind various aspects related to preparation and physical characteristics of polymeric nanoparticles (NP). These were prepared from different biodegradable polymers according to a water-in-oil-in-water emulsion solvent evaporation method. Polymers used were poly(lactic-co-glycolic) acid (PLGA), poly (lactic acid) (PLA), (PLA-PEG-PLA) triblock and (PLA-PEG-PLA)n multi-block co-polymers. A model DNA, as an example of a hydrophilic drug, was encapsulated in the internal aqueous phase. The primary emulsion was prepared using a high shear turbine mixer. The secondary emulsion was prepared by high-pressure homogenization. Surface morphology and internal structure were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Influence of process variables on the physical properties of NP has been studied. Release of DNA was evaluated. In addition, changes occurring to NP porosity and surface area during degradation were followed. Nanoparticle size was ranging between 200-700 nm, according to the preparation conditions. Homogenizing pressure, concentration of the emulsifying agent used, polymer concentration and type and the concentration of a cryoprotectant had variable effects on NP size, surface area and porosity. Batches of NP where no emulsifying agent was added were obtained successfully. The release rate of the DNA from NP was mainly dependent on porosity, which varied significantly among used polymers. The preparation technique was efficient in encapsulating the model DNA and will be used for plasmid encapsulation in a future work.

BMP-7 loaded microspheres as a new delivery system for the cultivation of human chondrocytes in a collagen type-I gel

In recent years, interest in chondrocyte cultures for transplantation has gained increasing attention. We investigated the use of PGLA microspheres as a new delivery system for BMP-7 and the effects on human chondrocytes cultivated in a 3D collagen gel culture. In an in vitro study, human chondrocytes obtained from osteoarthritic knee joints were released, transferred into a collagen type-I gel, and cultivated up to 14 days. In the treatment group PGLA microspheres loaded with human recombinant BMP-7 protein were added to the matrix. After the cultivation period, histological and immunohistochemical investigations were performed. In addition, the aggrecan core protein and type-II collagen mRNA concentrations were measured by real-time PCR. Histological staining for proteoglycan and collagen type-II protein and quantification via digital image processing revealed a significantly higher content in the samples cultivated with BMP-7 loaded microspheres in comparison to the control samples. Moreover, the collagen gel scaffold was partially remodeled by the chondrocytes and replaced by newly synthesized extracellular matrix. Cellular proliferation as well as apoptosis were low. In conclusion, we consider the PGLA microsphere system to be a functional device for the delivery of growth factors during the cultivation of articular chondrocytes leading to an increased content of type-II collagen and proteoglycan in the extracellular matrix.

Synthetic biodegradable microparticles for articular cartilage tissue engineering

Articular cartilage tissue engineering procedures require the transplantation of chondrocytes that have been expanded in vitro. The expansion is carried out for a considerable time and can lead to a modulation of cell phenotype. However, microcarrier cultures have been shown to allow cell expansion while maintaining the phenotype. Here, we have used the biodegradable polyester poly(lactide-co-glycolide) (PLGA) in the form of microspheres and irregular shaped microparticles with a diameter between 47 and 210 microm. Surface modification of particles was carried out by ammonia plasma treatment and subsequent adsorption of collagen. Alternatively, particles were modified by partial hydrolysis and subsequent immobilization of an amine-terminated dendrimer. Each surface modification step was characterized by X-ray photoelectron spectroscopy. The effectiveness of the surface modification procedures was demonstrated by in vitro cell culture experiments using sheep articular cartilage chondrocytes. A significant influence of both the particle shape and the surface chemistry on the proliferation rate was observed while the phenotype was maintained independent of the surface chemistry or particle shape. Chondrocytes cultured on PLGA microspheres were further assessed for cartilage tissue formation in collagen type I gels in nude mice. The tissue that were formed showed the appearance of a hyaline-like cartilage and the presence of the microspheres substantially reduced the degree of collagen gel contraction over 1-2 months.

Lectin-conjugated PLGA nanoparticles loaded with thymopentin: Ex vivo bioadhesion and in vivo biodistribution

The conjugation of lectins onto PLGA nanoparticles has been demonstrated to effectively improve the intestinal absorption of thymopentin. In this study, thymopentin-loaded nanoparticles made from fluorescein isothiocyanate labeled PLGA were modified with wheat germ agglutinin (WGA). The specific bioadhesion of nanoparticles on rat intestinal mucosa was studied ex vivo. An important increase of interaction between WGA-conjugated nanoparticles and the intestinal segments was observed compared with that of the unconjugated one (p<0.05). Fluorescence photomicrographs confirmed the bioadhesion of WGA-conjugated nanoparticles on intestinal villous epithelium as well as Peyer's patches. Biodistribution of nanoparticles was evaluated using tissues obtained from rats, to which nanoparticles were orally administered. The highest amount of WGA-conjugated nanoparticles was detected in small intestine, suggesting an increase of intestinal bioadhesion and endocytosis. The systemic uptake was as high as 6.48-13.4% of dose at 1 day and 7.32-15.26% at 7 days, which representing an increase of almost 1.4-3.1 fold across the intestine compared to <4.9% of the unconjugated one. The enhanced uptake was related to the increasing of WGA density on nanoparticles. These results further revealed the promising potential of lectin-conjugated nanoparticles on the improvement of intestinal bioadhesion and absorption for oral drug delivery.

The application of microbubbles for targeted drug delivery

Interest in microbubbles as vehicles for drug delivery has grown in recent years, due in part to characteristics that make them well suited for this role and in part to the need the for localized delivery of drugs in a number of applications. Microbubbles are inherently small, allowing transvascular passage, they can be functionalized for targeted adhesion, and can be acoustically driven, which facilitates ultrasound detection, production of bioeffects and controlled release of the cargo. This article provides an overview of related microbubble biofluid mechanics and reviews recent developments in the application of microbubbles for targeted drug delivery. Additionally, related advances in non-bubble microparticles for drug delivery are briefly described in the context of targeted adhesion.

Doxorubicin-loaded PLGA nanoparticles by nanoprecipitation: preparation, characterization and in vitro evaluation

AIMS

The lack of specificity of chemotherapeutic agents to cancer tissue commonly leads to dose-limiting side effects and poor therapeutic results. Drug delivery systems promise to improve the deficiencies of chemotherapeutic treatment by modifying the biodistribution and pharmacokinetics of the drug in vivo. Here, we report the preparation, characterization and in vitro evaluation of a carrier for the chemotherapeutic drug doxorubicin based on acid-capped poly(lactic-co-glycolic acid) nanoparticles.

METHODS

Doxorubicin-loaded nanoparticles were prepared by nanoprecipitation with bovine serum albumin as the stabilizer. Nanoparticles were characterized and their interaction with MDA-MB-231 breast cancer cells was examined with confocal microscopy and a toxicological assay.

RESULTS

Spherical particles with an average diameter of 230 nm, a zeta-potential of -45 mV and a maximum drug loading of 5 wt% were prepared. Doxorubicin was found to be quickly released at endolysosomal pH of 4.0 but was released at a slower rate at pH 7.4. Nanoparticles were found to deliver the drug into cells quickly and in higher quantity than when presented in solution and were found to result in a therapeutic efficacy comparable to the free drug.

DISCUSSION

Nanoprecipitation was found to be a promising method for the preparation of nanoparticles with relatively high doxorubicin loading. The pH-dependent release behavior is discussed to possibly be a result of accelerated degradation of the polymer and decreasing ionic interaction between the drug and the polymer at acidic pH. Additional studies are needed to determine why increased nuclear localization of the drug when delivered in the form of nanoparticles did not result in increased therapeutic efficacy in vitro.

CONCLUSION

Nanoparticles formulated by nanoprecipitation of acid-ended poly(lactic-co-glycolic acid) were found to be able to control the release of doxorubicin in a pH-dependent manner and to effectively deliver high payloads of the drug in an active form to MDA-MB-231 breast cancer cells.

Nanoparticles of hydrophobically modified dextrans as potential drug carrier systems

Nanoparticles combining a hydrophobically modified dextran core and a polysaccharide surface coverage were elaborated. Their suitability for applications like drug delivery was evaluated. The selected polysaccharide, dextran, was chemically modified by the covalent attachment of hydrocarbon groups (aliphatic or aromatic) via the formation of ether links. According to the extent of modification, either water-soluble or water-insoluble dextran derivatives were obtained. The latter exhibited solubility in organic solvents like tetrahydrofuran or dichloromethane saturated with water. Water-soluble dextran derivatives were used as polymeric surfactants for the control of nanoparticles surface characteristics. Nanoparticles were prepared either by o/w emulsion or solvent-diffusion methods. The size and surface properties of dextran nanoparticles were correlated to processing conditions. The stability of colloidal suspensions was examined as a function of ionic strength and related to the particle surface characteristics. The redispersability of freeze-dried suspensions without the addition of cryoprotectant was demonstrated. Finally, the degradability of modified dextrans was compared to that of starting dextran, after enzymatic hydrolysis in the presence of dextranase.

A new class of bioactive and biodegradable soybean-based bone fillers

The reconstruction of large bone defects in periodontal, maxillofacial, and orthopedic surgery relies on the implantation of biomaterials able to support the growth of new tissue. None of the materials currently available is able to combine all the properties required, which are (i) easy handling, (ii) biodegradation, (iii) low immunogenicity, and more importantly, (iv) induction of tissue regeneration. A new class of biodegradable biomaterials has been obtained by simple thermosetting of defatted soybean curd. The final material can be processed into films, porous scaffolds, and granules for different surgical needs. When incubated in physiological solutions the material shows water uptake of 80%, elongation at break of 0.9 mm/mm, and 25% (w/w) degradation in 7 days. Soybean-based biomaterial granules are shown to reduce the activity of the monocytes/macrophages and of the osteoclasts and to induce osteoblast differentiation in vitro, thus demonstrating a bone regeneration potential suitable for many clinical applications.

The Stabilizer Influence on Morphological Characteristics of Poly-(DL-Lactide-Co-Glycolide) Nanospheres

Copolymer poly(D,L-lactide-co-glycolide) is used for obtaining the systems for controlled delivery of medicaments. Its specific characteristics make it suitable for various researches where its synthesis is performed in different ways. Using the system for controlled delivery of medicaments, an equal concentration of the medicament is achieved in the body throughout an extended period of time and it has advantages over the conventional methods. In this paper we present a new solvent/non-solvent chemical method for obtaining DLPLG nanospheres. In the experiment various stabilizers were used in order to examine their influence on morphological characteristics of DLPLG particles. The samples were characterized by Infrared Spectroscopy (IR), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM) and Stereological analysis.

Stabilizer-induced viscosity alteration biases nanoparticle sizing via dynamic light scattering

The size dependent features of colloids at the nanometer scale have been issues of increasingly intensive research. In order to be able to correctly relate characteristics to certain size-populations, accurate and reliable particle sizing by dynamic light scattering (DLS) is a main prerequisite. So far, the complexity of the systems due to the presence of surfactants, proteins, and so forth in the nanoparticle suspensions has not been accounted for. In this work, practically relevant quantities of the frequently used PEO-PPO triblock copolymer surfactant Pluronic F-68 were studied for their effect on the size determination of nanoparticles by DLS. Induced changes in the tenside-content of the nanosphere suspension were monitored using a photometric assay and were correlated to the respective variances in mean particle size. These measurements showed that alterations in the range from 0.005 to 2% of Pluronic content are associated with shifts in diameter of 200 nm-particles by as much as 65 nm. The considerable changes that were found have been attributed to the surfactant-concentration-dependent fluctuations in the viscosity of the nanoparticle suspension, which affect the dimensions of colloids calculated according to the Stokes-Einstein relation.

Update on neuropharmacological treatments for alcoholism: scientific basis and clinical findings

The past decade has seen an expansion of research and knowledge on pharmacotherapy for the treatment of alcohol dependence. The Food and Drug Administration (FDA)-approved medications naltrexone and acamprosate have shown mixed results in clinical trials. Oral naltrexone and naltrexone depot formulations have generally demonstrated efficacy at treating alcohol dependence, but their treatment effect size is small, and more research is needed to compare the effects of different doses on drinking outcome. Acamprosate has demonstrated efficacy for treating alcohol dependence in European trials, but with a small effect size. In U.S. trials, acamprosate has not proved to be efficacious. Research continues to explore which types of alcohol-dependent individual would benefit the most from treatment with naltrexone or acamprosate. The combination of the two medications demonstrated efficacy for treating alcohol dependence in one European study but not in a multi-site U.S. study. Another FDA-approved medication, disulfiram, is an aversive agent that does not diminish craving for alcohol. Disulfiram is most effective when given to those who are highly compliant or who are receiving their medication under supervision. Of the non-approved medications, topiramate is among the most promising, with a medium effect size in clinical trials. Another promising medication, baclofen, has shown efficacy in small trials. Serotonergic agents such as selective serotonin reuptake inhibitors and the serotonin-3 receptor antagonist, ondansetron, appear to be efficacious only among certain genetic subtypes of alcoholic. As neuroscientific research progresses, other promising medications, as well as medication combinations, for treating alcohol dependence continue to be explored.

Biodegradable magnesium scaffolds: Part II: peri-implant bone remodeling

In this study, histomorphometrical parameters of the peri-implant bone remodeling around degrading open-porous scaffolds made of magnesium alloy AZ91D were investigated and compared with the peri-implant bone remodeling around an autologous bone transplant in the contralateral side in a rabbit model after 3 and 6 months. Osteoblast activity was displayed by collagen I (alpha 2) mRNA in situ hybridization. Major scaffold degradation was completed within 3 months after implantation showing no osteolysis around the scaffolds, both after 3 and 6 months. Enhanced formation of unmineralized extracellular matrix and an enhanced mineral apposition rate adjacent to the degrading magnesium scaffolds were accompanied by an increased osteoclastic bone surface, which resulted in higher bone mass and a tendency to a more mature trabecular bone structure around the magnesium scaffolds compared to the control. These results show that even fast-degrading magnesium scaffolds induce extended peri-implant bone remodeling with a good biocompatibility. In summary, this study shows that degrading magnesium scaffolds promote both bone formation and resorption in a rabbit model and are therefore very promising candidates for the development of novel implants in musculoskeletal surgery.

Biodegradable magnesium scaffolds: Part 1: appropriate inflammatory response

Current tissue engineering strategies focus on the replacement of pathologically altered tissues by the transplantation of cells in combination with supportive biocompatible scaffolds. Scaffolds for tissue engineering strategies in musculoskeletal research require an appropriate mechanical stability. In recent studies, considerable attention has thus been given to magnesium alloys as biodegradable implants. The aim of this study was to characterize the biocompatibility of magnesium scaffolds by the inflammatory host response. Open porous scaffolds made of the magnesium alloy AZ91D were implanted into the distal femur condyle of rabbits and were compared to autologous bone, which was transplanted into the contralateral condyle in a 3 and 6 months follow-up group. After 3 months, magnesium scaffolds were already largely degraded and most of the original magnesium alloy has disappeared. Concomitantly, a fibrous capsule enclosed the operation site. Histological analysis revealed that the magnesium scaffolds caused no significant harm to their neighboring tissues. This study shows that even fast degrading magnesium scaffolds show a good biocompatibility and react in vivo with an appropriate inflammatory host response. Magnesium alloy based implants are therefore a very promising approach in the development of mechanically suitable and open porous scaffolds for the replacement of subchondral bone in cartilage tissue engineering.

Nanosystems for simultaneous imaging and drug delivery to T cells

The T-cell response defines the pathogenesis of many common chronic disease states, including diabetes, rheumatoid arthritis, and transplant rejection. Therefore, a diagnostic strategy that visualizes this response can potentially lead to early therapeutic intervention, avoiding catastrophic organ failure or prolonged sickness. In addition, the means to deliver a drug dose to those cells in situ with the same specificity used to image those cells would provide for a powerful therapeutic alternative for many disease states involving T cells. In this report, we review emerging nanosystems that can be used for simultaneous tracking and drug delivery to those cells. Because of their versatility, these systems--which combine specific receptor targeting with an imaging agent and drug delivery--are suited to both basic science and applications, from developing therapeutic strategies for autoimmune and alloimmune diseases, to noninvasive tracking of pathogenic T-cell migration.

PLA Nano- and Microparticles for Drug Delivery: An Overview of the Methods of Preparation

The controlled release of medicaments remains the most convenient way of drug delivery. Therefore, a wide variety of reports can be found in the open literature dealing with drug delivery systems. In particular, the use of nano- and microparticles devices has received special attention during the past two decades. PLA and its copolymers with GA and/or PEG appear as the preferred substrates to fabricate these devices. The methods of fabrication of these particles will be reviewed in this article, describing in detail the experimental variables associated with each one with regard to the influence of them on the performance of the particles as drug carriers. An analysis of the relationship between the method of preparation and the kind of drug to encapsulate is also included. Furthermore, certain issues involved in the addition of other monomeric substrates than lactic acid to the particles formulation as well as novel devices, other than nano- and microparticles, will be discussed in the present work considering the published literature available.

5-Fluorouracil plasma levels and biodegradation of subcutaneously injected drug-loaded microspheres prepared by spray-drying poly(d,l-lactide) and poly(d,l-lactide-co-glycolide) polymers

Microspheres (MS) of 5-fluorouracil-loaded poly(D,L-lactide) (PLA), poly(D,L-lactide-co-glycolide) 75/25 (PLGA 75/25) and poly(D,L-lactide-co-glycolide) 50/50 (PLGA 50/50) prepared by the spray-drying technique were subcutaneously injected in the back of Wistar rats in order to evaluate the 5-fluorouracil (5-FU) release and the biodegradation characteristics. Determination of plasma 5-FU concentration by HPLC with analysis of data using a non-compartmental model showed drug in plasma between 9 and 14 days after administration of drug-loaded PLGA 50/50 or PLA and PLGA 75/25 microspheres, respectively, with a maximum drug concentration of 2.4+/-0.2microg/mL at 24h (5-FU-loaded PLGA 50/50 MS), 2.5+/-0.1microg/mL at 48h (5-FU-loaded PLGA 75/25 MS), and 2.3+/-0.1microg/mL at 24h (5-FU-loaded PLA MS). Pharmacokinetically, a significant increase of AUC (up to 50 times) and MRT (up to 196 times) of 5-FU with regard to the administration of the drug in solution was observed. Scanning electron microscopy and histological studies indicated that a small fibrous capsule was observed around the microspheres in the site of injection. One month after the injection of PLGA 50/50 MS and 2 months after the injection of PLGA 75/25 and PLA MS, masses of polymers, instead of single microspheres, were observed. Close to them, macrophagic cells were present, and blood vessels were observed in the connective tissue. Total absence of fibrous capsule and injected microspheres was observed after 2 (for PLGA 50/50 MS) or 3 (PLGA 75/25 and PLA MS) months.

Glycol chitosan as a stabilizer for protein encapsulated into poly(lactide-co-glycolide) microparticle

Glycol chitosan (GC), a chitosan derivative conjugated with ethylene glycol, is soluble in water at a neutral/acidic pH and is viscous. This GC was incorporated into poly(lactide-co-glycolide) (PLGA) microparticles (prepared by the multi-emulsion W(1)/O/W(2) (water-in-oil-in-water) method) to stabilize lysozyme (Lys) used as a model protein. Herein, GC's viscous property helped to improve Lys encapsulation efficacy and reduce Lys denaturaton at the water/organic solvent interface. When the GC concentration in the W(1) phase increased, the formation of non-covalent Lys aggregates decreased. This may be because the aqueous microdroplets surrounded by the firm viscous interface protect Lys from the degrading environment formed by the water/organic solvent interface. In an in vitro Lys release test, 40mg incorporation of GC led to continuous Lys release of up to 78wt.% for 1 month and presented bioactivity of more than 95% for Lys released from microparticles. In addition, there was negligible immune response in the tissue treated with the GC-incorporated PLGA microparticles, whereas there was a moderate foreign body reaction in the muscle layer and many configurations of neutrophils in the tissue treated with the PLGA microparticles without GC. It is expected that GC facilitates a decrease in immune responses exacerbated as a consequence of PLGA degradation.

Protein complexed with chondroitin sulfate in poly(lactide-co-glycolide) microspheres

Chondroitin sulfate (CsA) is an acidic mucopolysaccharide, which is able to form ionic complexes with positively charged proteins. In this study, a protein-CsA complex was constructed to nano-sized particles. Zeta potential measurements revealed that a CsA-to-protein fraction of greater than 0.1 results in a neutralization of the positive charge on lysozyme (Lys). Based on this preliminary study, we have prepared poly(lactide-co-glycolide) (PLGA) microspheres harboring Lys/CsA complexes via the multi-emulsion method. Protein stability in the PLGA microspheres was preserved during both microsphere preparation and protein release. The profiles of Lys release from the PLGA microspheres evidenced nearly zero-order kinetics, depending on the quantity of CsA. An in vivo fluorescent image of experimental mouse tissue showed that the PLGA microspheres with the Lys/CsA complex had released the entirety of their Lys without no residual amount after 23 days, but microspheres without the complex harbored a great deal of residual Lys, which is attributable to its degradation by acidic PLGA degradates. The tissue reaction evidenced by the PLGA microspheres stabilized with CsA showed minimal foreign body reaction and little configuration of immune cells including neutrophils and macrophages, but the reactions of the PLGA microspheres without CsA were characterized by a relatively elevated inflammation. These results show that CsA is a viable candidate for long-acting micro-particular protein delivery.

Preparation, characterization, cytotoxicity and transfection efficiency of poly(DL-lactide-co-glycolide) and poly(DL-lactic acid) cationic nanoparticles for controlled delivery of plasmid DNA

The objective of this study was to investigate the effect of formulation parameters (i.e. polymer molecular weight and homogenization speed) on various physicochemical and biological properties of cationic nanoparticles. Cationic nanoparticles were prepared using different molecular weights of poly(DL-lactide-co-glycolide) (PLGA) and poly(DL-lactic acid) (PLA) by double emulsion solvent evaporation at two different homogenization speeds, and were characterized in terms of size, surface charge, morphology, loading efficiency, plasmid release, plasmid integrity, cytotoxicity, and transfection efficiency. Cationic surfactant, cetyltrimethylammonium bromide (CTAB), was used to provide positive charge on the surface of nanoparticles. Reporter plasmid gWIZ Beta-gal was loaded on the surface of nanoparticles by incubation. Use of higher homogenization speed and lower molecular weight polymer led to a decrease in mean particle size, increase in zeta potential, increase in plasmid loading efficiency, and a decrease in burst release. The nanoparticles displayed good morphology as evident from scanning electron micrographs. In vitro cytotoxicity study by MTT assay showed a low toxicity. Structural integrity of the pDNA released from nanoparticles was maintained. Transfecting human embryonic kidney (HEK293) cells with nanoparticles prepared from low molecular weight PLGA and PLA resulted in an increased expression of beta-galactosidase as compared to those prepared from high molecular weight polymer. Our results demonstrate that the PLGA and PLA cationic nanoparticles can be used to achieve prolonged release of pDNA, and the plasmid release rate and transfection efficiency are dependent on the formulation variables.

Synthesis, characterization, and in vitro degradation of a biodegradable photo-cross-linked film from liquid poly(epsilon-caprolactone-co-lactide-co-glycolide) diacrylate

There has been little study on the effect of composition or molecular weight on the biodegradation rate of photo-cross-linked biodegradable aliphatic polyesters though such information is important for tissue engineering scaffolds. We have synthesized a new series of photopolymerizable linear poly(epsilon-caprolactone-co-lactide-co-glycolide) diacrylates with different molecular weights (Mn = 1800, 4800, and 9300 Da) and compositions (20%, 40%, and 60% epsilon-CL) and studied their biodegradation rates. The resultant oligomers were amorphous and appeared as viscous liquids at room temperature. Liquid-to-solid polymerization was carried out by UV irradiation in the presence of a photoinitiator. The photocuring yield was high (greater than 95%), and the photo-cross-linked polymers were amorphous and rubbery. Mechanical measurements showed that the polymers can be stretchable or rigid; the high molecular weight/low epsilon-CL network has a strain of 176% and a modulus of 1.66 MPa while the low molecular weight/high epsilon-CL network has a strain of 21% and a modulus of 12.3 MPa. In a 10 week in vitro biodegradation study, the polymers exhibited a two-stage degradation behavior. In the first stage, the polymer weight and strain remained almost constant, but a linear decrease in the Young's modulus (E) and ultimate stress (sigma) were observed. Lower oligomer molecular weight or epsilon-CL content correlated with a faster decrease in Young's modulus. In the second stage, which began when the Young's modulus dropped below 1 MPa, there was rapid weight loss and strain increase. The lower the epsilon-CL content, the earlier the second stage happened. Low molecular weight and high epsilon-CL content correlated with a longer modulus half-life (time for the modulus to degrade to 50% of its initial value). The degradation results suggest principles that may be helpful in predicting the biodegradation behavior of similar polymeric cross-linked networks. Films formed from these new polymers have excellent biocompatibility with smooth muscle cells.

Modified Paclitaxel-loaded Nanoparticles for Inhibition of Hyperplasia in a Rabbit Arterial Balloon Injury Model

PURPOSE

This study tested the possibility of localized intravascular infusion of positive charged paclitaxel-loaded nanoparticles (NPs) to better prevent neointimal formation in a rabbit carotid artery injury model.

MATERIALS AND METHODS

NPs were prepared by oil-water emulsion/solvent evaporation technique using biodegradable poly (lactide-co-glycolide) (PLGA). A cationic surfactant, didodecyldimethylammonium bromide (DMAB), was absorbed on the NP surface by electrostatic attraction between positive and negative charges. NPs were characterized in such aspects as size, surface morphology, surface charges as well as in vitro drug release profile. Balloon injured rabbit carotid arteries were treated with single infusion of paclitaxel-loaded NP suspension and observed for 28 days. The inhibitory effects of NPs on neointima formation were evaluated as end-point.

RESULTS

NPs showed spherical shape with a diameter ranging from 200 to 500 nm. Negatively charged PLGA NPs shifted to positive after the DMAB modification. The in vitro drug release profile showed a biphasic release pattern. Morphometric analyses on the retrieved artery samples revealed that the inhibitory effect of intima proliferation was dose-dependent. At a concentration of 30 mg ml(-1), NP infusion completely inhibited intima proliferation in a rabbit vascular injury model.

CONCLUSIONS

Paclitaxel-loaded NPs with DMAB modification were proven an effective means of inhibiting proliferative response to vascular injury in a rabbit model.

Characterization of particles fabricated with poly(D, L-lactic-co-glycolic acid) and an ornithine-histidine peptide as carriers of oligodeoxynucleotide for delivery into primary dendritic cells

We report the formulation of particles to deliver oligodeoxynucleotides (ODN) into primary murine dendritic cells (DCs), the most potent antigen-presenting cells (APCs) known, using poly(D,L-lactic-co-glycolic acid) (PLGA) and a small cationic peptide. PLGA polymer and the ODN were fabricated into nano-sized spherical particles with the aid of O10H6 (O = ornithine, H = histidine). We have previously determined that O10H6 condenses DNA and is less toxic to DCs than a similar lysine-based peptide. The colloidal particles are stabilized by negative surface potentials. The peptide and the ODN can be detected in the fabricated particles with reflectance infrared spectroscopy. Significant ODN uptake can be observed in DCs exposed to the particles. Confocal imaging studies reveal that ODN can be internalized and escape from lysosomes in DCs. Taken together, these data suggest that combining PLGA and O10H6 is a feasible method to generate ODN-containing nano-sized particles for applications in DCs.

Enzymatic photochemical sensing using luciferase-immobilized polymer nanoparticles covered with artificial cell membrane

We prepared phospholipid polymer nanoparticles immobilized with luciferase, and the nanoparticles were applied as photochemical sensing nanoparticles. An amphiphilic water-soluble polymer having a phosphorylcholine group was used as an emulsifier and a surface modifier to prepare the nanoparticles. The polymer was composed of three kinds of monomer units, that is, 2-methacryloyloxyethyl phosphorylcholine (MPC) as a hydrophilic and bioinert unit, n-butyl methacrylate as a hydrophobic unit and p-nitrophenyl ester having methacrylate as an enzyme-immobilizing unit. The p-nitrophenyl ester groups to immobilize the proteins were located on the surface of the nanoparticles. Luciferase was immobilized by the reaction between the p-nitrophenyl ester groups and the amino group. The enzymatic reaction on the nanoparticles was followed using a microdialysis system with an optical fiber having a 800 microm diameter in the probe. The nanoparticles conjugated with luciferase reacted with ATP, luciferin and oxygen. It is concluded that the nanoparticles are a promising tool for a photochemical sensing microdiagnostic system.

Branched polyesters based on poly[vinyl-3-(dialkylamino)alkylcarbamate-co-vinyl acetate-co-vinyl alcohol]-graft-poly(d,l-lactide-co-glycolide): Effects of polymer structure on cytotoxicity

Branched polyesters of the general structure poly[vinyl-3-(dialkylamino)alkylcarbamate-co-vinyl acetate-co-vinyl alcohol]-graft-poly(d,l-lactide-co-glycolide) have shown potential for nano- and micro-scale drug delivery systems. For further optimization of this polymer class their cytotoxicity needs to be characterized establishing structure-toxicity relationships. Effects of type and degree of amine substitution as well as molecular weight on cytotoxicity were evaluated in L929 mouse fibroblasts using a MTT assay whereas interactions with cell membranes were quantified by LDH release and caspase (3/7)-activation. Finally, direct cell-polymer contact assays were conducted. Ungrafted amine-modified polymer backbone yielded IC(50) values in the range of 0.05-10mg/ml. Generally higher toxicities were observed with an increasing degree of amine substitution. Amine substituents could be ranked as diethylaminopropylamine (DEAPA)<diethylaminoethylamine (DEAEA)<dimethylaminopropylamine (DMAPA) but the degree of amine substitution was more dominant than the type of amine function. Membrane interactions seem to cause necrotic cell reactions in a dose-dependent manner for highly charged amine-poly(vinyl alcohol) (PVA) backbones. To attenuate cytotoxic effects DEAPA-PVA backbones were grafted with biodegradable PLGA side chains at molecular ratios of 1:10 and 1:20. Cytotoxicity of extracts of these polymers was significantly lower compared to ungrafted polymers possibly caused by shielding of polycationic backbone with hydrophobic PLGA side chains. P(33)-20, a polymer containing a sufficiently high degree of amine substitution could serve as a lead candidate for further investigations. In conclusion, structure-toxicity relationships could be established and shielding the polycationic backbone using PLGA side chains seems to be a promising strategy meriting further investigations.

Macrophage-mediated biodegradation of poly(DL-lactide-co-glycolide) in vitro

Biodegradation of poly-DL-lactide-co-glycolide (PLGA) both in vitro and in vivo has been well documented. However, the roles that macrophages and their fused multinucleated giant cells (MNGCs) play in this biodegradation are still unclear. The current study aimed to investigate macrophage-mediated biodegradation of PLGA thin films and of PLGA composites with hydroxyapatite (HA) and tricalcium phosphate (TCP) ceramic powders in vitro using a murine macrophage cell line (RAW 264.7). The interactions were analyzed by using cell viability assays, scanning electron microscopy, and focused ion beam microscopy. The results showed that RAW 264.7 cells effectively attached and proliferated on the PLGA films and PLGA-HA, PLGA-TCP composites. The RAW 264.7 cells were observed to aggregate and fuse to form MNGCs. The cell processes on the membrane, or pseudopodia, penetrated into the PLGA films and evidently eroded the surface. We conclude that macrophages and fused MNGCs actively respond to PLGA films as substratum and degrade the surface of this polymer.

Poly(D,L-lactide-coglycolide) particles containing gentamicin: pharmacokinetics and pharmacodynamics in Brucella melitensis-infected mice

Drug delivery systems containing gentamicin were studied as a treatment against experimental brucellosis in mice. Micro- and nanoparticles prepared by using poly(D,L-lactide-coglycolide) (PLGA) 502H and microparticles made of PLGA 75:25H were successfully delivered to the liver and the spleen, the target organs for Brucella melitensis. Both polymers have the same molecular weight but have different lactic acid/glycolic acid ratios. Microparticles of PLGA 502H and 75:25H released their contents in a sustained manner, in contrast to PLGA 502H nanoparticles, which were degraded almost completely during the first week postadministration. The values of the pharmacokinetic parameters after administration of a single intravenous dose of 1.5 mg/kg of body weight of loaded gentamicin revealed higher areas under the curve (AUCs) for the liver and the spleen and increased mean retention times (MRTs) compared to those for the free drug, indicating the successful uptake by phagocytic cells in both organs and the controlled release of the antibiotic. Both gentamicin-loaded PLGA 502H and 75:25H microparticles presented similar pharmacokinetic parameter values for the liver, but those made of PLGA 75:25 H were more effective in targeting the antibiotic to the spleen (higher AUCs and MRTs). The administration of three doses of 1.5 mg/kg significantly reduced the load associated with the splenic B. melitensis infection. Thus, the formulation made with the 75:25H polymer was more effective than that made with 502H microspheres (1.45-log and 0.45-log reductions, respectively, at 3 weeks posttreatment). Therefore, both, pharmacokinetic and pharmacodynamic parameters showed the suitability of 75:25H microspheres to reduce the infection of experimentally infected mice with B. melitensis.