Principles of encapsulating hydrophobic drugs in PLA/PLGA microparticles

The necessity for the coating of perfluorodecalin-filled poly(lactide-co-glycolide) microcapsules in the presence of physiological cholate concentrations: Tetronic-908 as an exemplary polymeric surfactant

Recently, we demonstrated that biodegradable poly(lactide-co-glycolide) (PLGA) micro- and nanocapsules with a liquid content of perfluorodecalin are principally useful for the development of artificial oxygen carriers. In order to solve a decisive and well-known problem with PLGA microcapsules, i.e. the spontaneous agglomeration of the capsules after depletion of the emulsifying agent (i.e. cholate), coating with the ABA block copolymer, Tetronic-908 was studied. After Tetronic-908 treatment at concentrations that were harmless to cultured cells, the clustering of the microcapsules was prevented, the adsorption of opsonins was decreased and the attachment to cells was inhibited, but the oxygen transport capacity of PLGA microcapsules was even increased. The present data clearly show that perfluorodecalin-filled PLGA microcapsules must be coated before decreasing the emulsifying agent cholate to physiological concentrations, in order to develop a solution that has the capabilities to function as a potential artificial oxygen carrier suspension.

Polímeros sintéticos biodegradáveis: matérias-primas e métodos de produção de micropartículas para uso em drug delivery e liberação controlada

Micropartículas produzidas a partir de polímeros sintéticos têm sido amplamente utilizadas na área farmacêutica para encapsulação de princípios ativos. Essas micropartículas apresentam as vantagens de proteção do princípio ativo, mucoadesão e gastrorresistência, melhor biodisponibilidade e maior adesão do paciente ao tratamento. Além disso, utiliza menores quantidade de princípio ativo para obtenção do efeito terapêutico proporcionando diminuição dos efeitos adversos locais, sistêmicos e menor toxidade. Os polímeros sintéticos empregados na produção das micropartículas são classificados biodegradáveis ou não biodegradáveis, sendo os biodegradáveis mais utilizados por não necessitam ser removidos cirurgicamente após o término de sua ação. A produção das micropartículas poliméricas sintéticas para encapsulação tanto de ativos hidrofílicos quanto hidrofóbicos pode ser emulsificação por extração e/ou evaporação do solvente; coacervação; métodos mecânicos e estão revisados neste artigo evidenciando as vantagens, desvantagens e viabilidade de cada metodologia. A escolha da metodologia e do polímero sintético a serem empregados na produção desse sistema dependem da aplicação terapêutica requerida, bem como a simplicidade, reprodutibilidade e factibilidade do aumento de escala da produção.

Biomaterials to Enhance Stem Cell Function in the Heart

Transplantation of stem cells into the heart can improve cardiac function after myocardial infarction and in chronic heart failure, but the extent of benefit and of reproducibility of this approach are insufficient. Survival of transplanted cells into myocardium is poor, and new strategies are needed to enhance stem cell differentiation and survival in vivo. In this review, we describe how biomaterials can enhance stem cell function in the heart. Biomaterials can mimic or include naturally occurring extracellular matrix and also instruct stem cell function in different ways. Biomaterials can promote angiogenesis, enhance engraftment and differentiation of stem cells, and accelerate electromechanical integration of transplanted stem cells. Biomaterials can also be used to deliver proteins, genes, or small RNAs together with stem cells. Furthermore, recent evidence indicates that the biophysical environment of stem cells is crucial for their proliferation and differentiation, as well as their electromechanical integration. Many approaches in regenerative medicine will likely ultimately require integration of molecularly designed biomaterials and stem cell biology to develop stable tissue regeneration.

PLGA nanoparticles improve the oral bioavailability of curcumin in rats: characterizations and mechanisms

The overall goal of this paper was to develop poly(lactic-co-glycolic acid) nanoparticles (PLGA-NPs) of curcumin (CUR), named CUR-PLGA-NPs, and to study the effect and mechanisms enhancing the oral bioavailability of CUR. CUR-PLGA-NPs were prepared according to a solid-in-oil-in-water (s/o/w) solvent evaporation method and exhibited a smooth and spherical shape with diameters of about 200 nm. Characterization of CUR-PLGA-NPs showed CUR was successfully encapsulated on the PLGA polymer. The entrapment efficiency and loading rate of CUR were 91.96 and 5.75%, respectively. CUR-PLGA-NPs showed about 640-fold in water solubility relative to that of n-CUR. A sustained CUR release to a total of approximately 77% was discovered from CUR-PLGA-NPs in artificial intestinal juice, but only about 48% in artificial gastric juice. After oral administration of CUR-PLGA-NPs, the relative bioavailability was 5.6-fold and had a longer half-life compared with that of native curcumin. The results showed that the effect in improving oral bioavailability of CUR may be associated with improved water solubility, higher release rate in the intestinal juice, enhanced absorption by improved permeability, inhibition of P-glycoprotein (P-gp)-mediated efflux, and increased residence time in the intestinal cavity. Thus, encapsulating hydrophobic drugs on PLGA polymer is a promising method for sustained and controlled drug delivery with improved bioavailability of Biopharmaceutics Classification System (BCS) class IV, such as CUR.

Mechanisms of burst release from pH-responsive polymeric microparticles

OBJECTIVES

Microencapsulation of drugs into preformed polymers is commonly achieved through solvent evaporation techniques or spray drying. We compared these encapsulation methods in terms of controlled drug release properties of prepared microparticles and investigated the underlying mechanisms responsible for the 'burst release' effect.

METHODS

Using two different pH-responsive polymers with a dissolution threshold of pH 6 (Eudragit L100 and AQOAT AS-MG), hydrocortisone, a model hydrophobic drug, was incorporated into microparticles below and above its solubility within the polymer matrix.

KEY FINDINGS

Although, spray drying was an attractive approach due to rapid particle production and relatively low solvent waste, the oil-in-oil microencapsulation method was superior in terms of controlled drug release properties from the microparticles. Slow solvent evaporation during the oil-in-oil emulsification process allowed adequate time for drug and polymer redistribution in the microparticles and reduced uncontrolled drug burst release. Electron microscopy showed that this slower manufacturing procedure generated nonporous particles whereas thermal analysis and X-ray diffractometry showed that drug loading above the solubility limit of the drug in the polymer generated excess crystalline drug on the surface of the particles. Raman spectral mapping illustrated that drug was homogeneously distributed as a solid solution in the particles when loaded below saturation in the polymer with consequently minimal burst release.

CONCLUSIONS

Both the manufacturing method (which influenced particle porosity and density) and drug:polymer compatibility and loading (which affected drug form and distribution) were responsible for burst release seen from our particles.

Effect of bases with different solubility on the release behavior of risperidone loaded PLGA microspheres

Poly (D, L-lactide-co-glycolide) (PLGA) microspheres are attractive delivery vehicles due to their excellent sustained release capabilities. One major problem with PLGA microspheres is that the hydrophobic properties of PLGA generally cause a lag period in the process of drug release, leading to fluctuation of drug concentration in the blood and various resulting adverse reactions. Herein, Mg(OH)₂, an inorganic base, and arginine, an organic base, were separately co-encapsulated into risperidone-loaded PLGA microspheres at varying concentration using the solvent evaporation method to improve release profiles from the microspheres. High encapsulation efficiencies were obtained in all formulations. The surface of base-free microspheres was smooth, whereas a few pores formed in base co-encapsulated microspheres. After 7-days degradation, many inter-connecting pores were formed in the interior of the microspheres containing 10 mg Mg(OH)₂. The final pH in the microspheres with Mg(OH)₂ was higher than in those with arginine after 28-days degradation. The initial release of risperidone from microspheres containing Mg(OH)₂ was higher than from those containing arginine, and the latter release exhibited a more uniform pattern. Microspheres with 5mg and 10mg arginine exhibited zero-order release kinetics. However, both bases eliminated the lag phase of release. These results indicate that the incorporation of bases has potential in addressing the problem of the lag period in drug release from PLGA microspheres, and improving release behavior toward an ideal model.

Biodegradable insulin-loaded PLGA microspheres fabricated by three different emulsification techniques: investigation for cartilage tissue engineering

Growth, differentiation and migration factors facilitate the engineering of tissues but need to be administered with defined gradients over a prolonged period of time. In this study insulin as a growth factor for cartilage tissue engineering and a biodegradable PLGA delivery device were used. The aim was to investigate comparatively three different microencapsulation techniques, solid-in-oil-in-water (s/o/w), water-in-oil-in-water (w/o/w) and oil-in-oil-in-water (o/o/w), for the fabrication of insulin-loaded PLGA microspheres with regard to protein loading efficiency, release and degradation kinetics, biological activity of the released protein and phagocytosis of the microspheres. Insulin-loaded PLGA microspheres prepared by all three emulsification techniques had smooth and spherical surfaces with a negative zeta potential. The preparation technique did not affect particle degradation nor induce phagocytosis by human leukocytes. The delivery of structurally intact and biologically active insulin from the microspheres was shown using circular dichroism spectroscopy and a MCF7 cell-based proliferation assay. However, the insulin loading efficiency (w/o/w about 80%, s/o/w 60%, and o/o/w 25%) and the insulin release kinetics were influenced by the microencapsulation technique. The results demonstrate that the w/o/w microspheres are most appropriate, providing a high encapsulation efficiency and low initial burst release, and thus these were finally used for cartilage tissue engineering. Insulin released from w/o/w PLGA microspheres stimulated the formation of cartilage considerably in chondrocyte high density pellet cultures, as determined by increased secretion of proteoglycans and collagen type II. Our results should encourage further studies applying protein-loaded PLGA microspheres in combination with cell transplants or cell-free in situ tissue engineering implants to regenerate cartilage.

Surface characterisation of bioadhesive PLGA/chitosan microparticles produced by supercritical fluid technology

PURPOSE

Novel biodegradable and mucoadhesive PLGA/chitosan microparticles with the potential for use as a controlled release gastroretentive system were manufactured using supercritical CO(2) (scCO(2)) by the Particle Gas Saturated System (PGSS) technique (also called CriticalMix(TM)).

METHODS

Microparticles were produced from PLGA with the addition of mPEG and chitosan in the absence of organic solvents, surfactants and crosslinkers using the PGSS technique. Microparticle formulations were morphologically characterized by scanning electron microscope; particle size distribution was measured using laser diffraction. Microparticle surface was analyzed using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) to evaluate the presence of chitosan on the surface. Mucoadhesiveness of the microparticles was evaluated in vitro using a mucin assay employing two different kinds of mucin (Mucin type III and I-S) with different degrees of sialic acid contents, 0.5-1.5% and 9-17%, respectively.

RESULTS

The two analytical surface techniques (XPS and ToF-SIMS) demonstrated the presence of the chitosan on the surface of the particles (<100 μm), dependent on the polymer composition of the microparticles. The interaction between the mucin solutions and the PLGA/chitosan microparticles increased significantly with an increasing concentration of mucin and chitosan.

CONCLUSIONS

The strong interaction of mucin with the chitosan present on the surface of the particles suggests a potential use of the mucoadhesive carriers for gastroretentive and oral controlled drug release.

Highly loaded, sustained-release microparticles of curcumin for chemoprevention

Curcumin, a dietary polyphenol, has preventive and therapeutic potential against several diseases. Because of the chronic nature of many of these diseases, sustained-release dosage forms of curcumin could be of significant clinical value. However, extreme lipophilicity and instability of curcumin are significant challenges in its formulation development. The objectives of this study were to fabricate an injectable microparticle formulation that can sustain curcumin release over a 1-month period and to determine its chemopreventive activity in a mouse model. Microparticles were fabricated using poly(D, L-lactide-co-glycolide) polymer. Conventional emulsion solvent evaporation method of preparing microparticles resulted in crystallization of curcumin outside of microparticles and poor entrapment (∼1%, w/w loading). Rapid solvent removal using vacuum dramatically increased drug entrapment (∼38%, w/w loading; 76% encapsulation efficiency). Microparticles sustained curcumin release over 4 weeks in vitro, and drug release rate could be modulated by varying the polymer molecular weight and/or composition. A single subcutaneous dose of microparticles sustained curcumin liver concentration for nearly a month in mice. Hepatic glutathione-s-transferase and cyclooxygenase-2 activities, biomarkers for chemoprevention, were altered following treatment with curcumin microparticles. The results of these studies suggest that sustained-release microparticles of curcumin could be a novel and effective approach for cancer chemoprevention.

Solutions for Lipophilic Drugs: A Biodegradable Polymer Acting as Solvent, Matrix, and Carrier to Solve Drug Delivery Issues

The purpose of this study was to investigate the polyester hexylsubstituted poly(lactide) (hexPLA) as a possible solvent for lipophilic substances and excipient for pharmaceutical formulations. HexPLA is a biodegradable and semi-solid polymer, which allows the incorporation of active substances by simple mixing and local or systemic application to the patient through injection. The solvent behavior of hexPLA was investigated by adding the lipophilic dye Sudan III to the polymer matrix and optical monitoring of the dissolution process over time by microscopy. As a drug, the antipsychotic compound Haloperidol was analyzed for its solubility in hexPLA of different molecular weights by preparing saturated solutions, and measuring the amount of incorporated drug with UV spectroscopy. The influence of the rate of solubilized to suspended drug on the burst release behavior of Haloperidol from hexPLA-formulations was investigated in release tests. It is demonstrated that hexPLA dissolves both lipophilic substances, Sudan III and Haloperidol. In the molecular weight range between 2,000 g/mol and 10,000 g/mol, a lower molecular weight hexPLA resulted in a higher incorporation capacity for Haloperidol. By changing from a suspension formulation of Haloperidol to a solution formulation, the initial burst release established for classical PLA and PLGA systems could be minimized. HexPLA is shown to be a potent solvent and excipient for lipophilic drugs, allowing the initial burst of drug release to be modified and controlled.

Intracellular release of 17-β estradiol from cationic polyamidoamine dendrimer surface-modified poly (lactic-co-glycolic acid) microparticles improves osteogenic differentiation of human mesenchymal stromal cells

Human bone marrow mesenchymal stromal cells (MSCs) are considered a potential cell source for MSC-based bone regeneration, but improvements in the proliferation and differentiation capacity of MSCs are necessary for practical applications. Estrogen effectively improves MSC capabilities and has strong potential as a regulator of MSCs. The aim of this study was to develop a delivery system that provides intracellular release of estrogen and test its ability to improve osteogenic differentiation of MSCs. Biodegradable poly (lactic-co-glycolic acid) (PLGA) microparticles were developed that entrap 17-β estradiol (E2) and provide intracellular release of E2. The results show that we can prepare PLGA particles with efficient loading of E2 and maintain release of E2 up to 7 days. Surface modifying E2-loaded PLGA particles with cationic polyamidoamine dendrimers enabled increased uptake by human MSCs. Human MSC uptake of the E2-loaded PLGA particles significantly upregulates osteogenic differentiation markers of alkaline phosphatase and osteocalcin. In conclusion, cationic-modified PLGA particles can serve as a tool for intracellular delivery of estrogen to effectively execute estrogen regulation of MSCs. This approach has the potential to improve the osteogenic capabilities of MSCs and to develop appropriate environments of implantation for MSC-based bone tissue engineering.

Materials for pharmaceutical dosage forms: molecular pharmaceutics and controlled release drug delivery aspects

Controlled release delivery is available for many routes of administration and offers many advantages (as microparticles and nanoparticles) over immediate release delivery. These advantages include reduced dosing frequency, better therapeutic control, fewer side effects, and, consequently, these dosage forms are well accepted by patients. Advances in polymer material science, particle engineering design, manufacture, and nanotechnology have led the way to the introduction of several marketed controlled release products and several more are in pre-clinical and clinical development.

Formulation and in vitro characterization of Eudragit® L100 and Eudragit® L100-PLGA nanoparticles containing diclofenac sodium

The aim of this study was to formulate and characterize Eudragit® L100 and Eudragit® L100-poly(lactic-co-glycolic acid) (PLGA) nanoparticles containing diclofenac sodium. Diclofenac generates severe adverse effects with risks of toxicity. Thus, nanoparticles were prepared to reduce these drawbacks in the present study. These nanoparticles were evaluated for surface morphology, particle size and size distribution, percentage drug entrapment, and in vitro drug release in pH 6.8. The prepared nanoparticles were almost spherical in shape, as determined by atomic force microscopy. The nanoparticles with varied size (241-274 nm) and 25.8-62% of entrapment efficiency were obtained. The nanoparticles formulations produced the release profiles with an initial burst effect in which diclofenac sodium release ranged between 38% and 47% within 4 h. The extent of drug release from Eudragit® L100 nanoparticles was up to 92% at 12 h. However, Eudragit®/PLGA nanoparticles showed an initial burst release followed by a slower sustained release. The cumulative release at 72 h was 56%, 69%, and 81% for Eudragit®/PLGA (20:80), Eudragit®/PLGA (30:70) and Eudragit®/PLGA (50:50) nanoparticles, respectively. The release profiles and encapsulation efficiencies depended on the amount of Eudragit in the blend. These data demonstrated the efficacy of these nanoparticles in sustaining the diclofenac sodium release profile.

Designing bioactive delivery systems for tissue regeneration

The direct infusion of macromolecules into defect sites generally does not impart adequate physiological responses. Without the protection of delivery systems, inductive molecules may likely redistribute away from their desired locale and are vulnerable to degradation. In order to achieve efficacy, large doses supplied at interval time periods are necessary, often at great expense and ensuing detrimental side effects. The selection of a delivery system plays an important role in the rate of re-growth and functionality of regenerating tissue: not only do the release kinetics of inductive molecules and their consequent bioactivities need to be considered, but also how the delivery system interacts and integrates with its surrounding host environment. In the current review, we describe the means of release of macromolecules from hydrogels, polymeric microspheres, and porous scaffolds along with the selection and utilization of bioactive delivery systems in a variety of tissue-engineering strategies.

Lung perfusion imaging with monosized biodegradable microspheres

After intravenous injection, particles larger than red blood cells will be trapped in the first capillary bed that they encounter. This is the principle of lung perfusion imaging in nuclear medicine, where macroaggregated albumin (MAA) is radiolabeled with (99m)Tc, infused into a patient's arm vein, and then imaged with gamma scintigraphy. Our aim was to evaluate if monosized microspheres could replace (99m)Tc-MAA. Biodegradable poly(L-lactide) microspheres containing chelating bis(picolylamine) end groups were prepared by a flow focusing method on a microfluidic glass chip and were of highly homogeneous size (9.0 +/- 0.4 microm). The microspheres were radiolabeled with [(99m)Tc(H(2)O)(3)(CO)(3)](+) and then evaluated in mice for lung perfusion imaging. Fifteen minutes after injection, 79.6 +/- 3.8% of the injected activity was trapped in the lungs of mice. Monosized biodegradable radioactive microspheres are, thus, appropriate lung perfusion imaging agents. Other sizes of these highly uniform microspheres have the potential to improve diagnostic and therapeutic approaches in diverse areas of medicine.

Polymeric Microspheres for Medical Applications

Synthetic polymeric microspheres find application in a wide range of medical applications. Among other applications, microspheres are being used as bulking agents, embolic- or drug-delivery particles. The exact composition of the spheres varies with the application and therefore a large array of materials has been used to produce microspheres. In this review, the relation between microsphere synthesis and application is discussed for a number of microspheres that are used for different treatment strategies.

Microencapsulation of rosmarinic acid using polycaprolactone and various surfactants

Rosmarinic acid (RA) has a number of interesting biological activities, e.g. anti-viral, anti-bacterial, anti-inflammatory and antioxidant. The antioxidant activity of RA is stronger than that of vitamin E. Despite its strong antioxidant activity, it was limited to use in cosmetics because of the low water solubility, discolouration and chemical instability. The purpose of this study was to prepare RA-loaded polycaprolactone (PCL) microspheres using emulsion solvent evaporation method and characterize them with different surfactants used in the formation process. Finally, long-term stability of RA was evaluated in the cosmetic formulation. As a result, PCL microspheres were found to be spherical in shape, with zwitterionic surfactant-PCL particles being the smallest size distribution and highest entrapment efficiency of RA. Emulsions containing RA-loaded PCL microspheres showed a better long-term stability of the RA compared with those containing only RA. These results suggest that RA may be stably and efficiently encapsulated into polycaprolactone microspheres.

Injectable sustained release microparticles of curcumin: a new concept for cancer chemoprevention

Poor oral bioavailability limits the use of curcumin and other dietary polyphenols in the prevention and treatment of cancer. Minimally invasive strategies that can provide effective and sustained tissue concentrations of these agents will be highly valuable tools in the fight against cancer. The objective of this study was to investigate the use of an injectable sustained release microparticle formulation of curcumin as a novel approach to breast cancer chemoprevention. A biodegradable and biocompatible polymer, poly(d,l-lactide-co-glycolide), was used to fabricate curcumin microparticles. When injected s.c. in mice, a single dose of microparticles sustained curcumin levels in the blood and other tissues for nearly a month. Curcumin levels in the lungs and brain, frequent sites of breast cancer metastases, were 10- to 30-fold higher than that in the blood. Further, curcumin microparticles showed marked anticancer efficacy in nude mice bearing MDA-MB-231 xenografts compared with other controls. Repeated systemic injections of curcumin were not effective in inhibiting tumor growth. Treatment with curcumin microparticles resulted in diminished vascular endothelial growth factor expression and poorly developed tumor microvessels, indicating a significant effect on tumor angiogenesis. These results suggest that sustained delivery of chemopreventives such as curcumin using polymeric microparticles is a promising new approach to cancer chemoprevention and therapy.

Antibiotic-releasing porous polymethylmethacrylate constructs for osseous space maintenance and infection control

The use of a strategy involving space maintenance as the initial step of a two-stage regenerative medicine approach toward reconstructing significant bony or composite tissue defects in the craniofacial area, preserves the void volume of bony defects and could promote soft tissue healing prior to the subsequent definitive repair. One of the complications with a biomaterial-based space maintenance approach is local infection, which requires early, effective eradication, ideally through local antibiotic delivery. The purpose of this study is to develop a dual function implant material for maintaining osseous space and releasing an antibiotic to eliminate local infection in bony defects. Colistin, a polymyxin antibiotic, was chosen specifically to address infections with Acinetobacter species, the most common pathogen associated with combat-related traumatic craniofacial injuries. Porous polymethylmethacrylate (PMMA) constructs incorporating poly(lactic-co-glycolic acid) (PLGA) microspheres were fabricated by mixing a clinically used bone cement formulation of PMMA powder and methylmethacrylate liquid with a carboxymethylcellulose (CMC) hydrogel (40 or 50 wt%) to impart porosity and PLGA microspheres (10 or 15 wt%) loaded with colistin to control drug release. The PMMA/CMC/PLGA construct featured mild setting temperature, controllable surface/bulk porosity by incorporation of the CMC hydrogel, reasonably strong compressive properties, and continuous drug release over a period of 5 weeks with total drug release of 68.1-88.3%, depending on the weight percentage of CMC and PLGA incorporation. The concentration of released colistin was well above its reported minimum inhibitory concentration against susceptible species for 5 weeks. This study provides information on the composition parameters that enable viable porosity characteristics/drug release kinetics of the PMMA/CMC/PLGA construct for the initial space maintenance as part of a two-stage regenerative medicine approach.

Understanding the quality of protein loaded PLGA nanoparticles variability by Plackett-Burman design

The aim of this investigation was to screen and understand the product variability due to important factors affecting the characteristics CyA-PLGA nanoparticles prepared by O/W emulsification-solvent evaporation method. Independent variables studied were cyclosporine A (CyA) (X(1)), PLGA (X(2)), and emulsifier concentration namely SLS (X(3)), stirring rate (X(4)), type of organic solvent employed (chloroform or dichloromethane, X(5)) and organic to aqueous phase ratio (X(6)). The nanoparticles properties considered were encapsulation efficiency (Y(1)), mean particle size (Y(2)), zeta potential (Y(3)), burst effect (Y(4)) and dissolution efficiency (Y(5)). The statistical analysis of the results allowed determining the most influent factors. The nanoparticles were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray powder diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The factors combination showed variability of entrapment efficiency (Y(1)), mean particle size (Y(2)) and zeta potential (Y(3)) from 10.17% to 93.01%, 41.60 to 372.80 nm and 29.60 to 34.90 mV, respectively. Initially, nanoparticles showed burst effect followed by sustained release during the 7-day in vitro release study period. The dissolution efficiency (Y(5)) varied from 52.67% to 84.11%. The nanoparticles revealed Higuchi release pattern and release occurred by coupling of diffusion and erosion. In conclusion, this study revealed the potential of QbD in understanding the effect of formulation and process variables on the characteristics on CyA-PLGA nanoparticles.