Preparation and Characterization of Chitosan-Based Nanoparticles

Ultrafine biocompatible chitosan nanoparticles encapsulating multi-coloured quantum dots for bioapplications

Owing to their excellent optical properties, luminescent semi-conductor quantum dots (QDs) have proven themselves to be an attractive choice in biological labeling. However, there exists the concern of cytotoxicity in using these heavy metal-based nanoparticles as molecular probes. In order to improve their general biocompatibility, CdSe/ZnS QDS are encapsulated in the natural biopolymer chitosan, forming monodisperse chitosan nanoparticles in the range of 60 nm in 1 single step. This straight forward method also allows for the synthesis of chitosan nanoparticles encapsulating multi-coloured QDs. In vitro 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity tests on primary myoblast cells suggest that the cytotoxicity of the QDs is greatly reduced after chitosan encapsulation. At the same time, fluorescence confocal microscopy studies also prove that nanoparticles are small enough to be internalized into the myoblast cells. Our results show the ease of synthesizing biocompatible, nanometer-sized chitosan nanoparticles encapsulating QDs and their promise in biological applications such as ultra-sensitive bio-detection and labeling of biomolecules.

Direct Amidation of Poly(γ-glutamic acid) with Benzylamine In Dimethyl Sulfoxide

Partially benzylamidated, amphipathic poly(gamma-glutamic acid) (BzPGA) was synthesized from poly(gamma-glutamic acid) (PGA) and benzylamine by direct amidation in dimethyl sulfoxide (DMSO). Benzylamine and PGA were heated in DMSO for 1 to 26 h at temperatures between 110 and 130 degrees C, producing derivatives of various degrees of benzylamidation as a function of the reaction time and temperature. Neither any carboxyl-activating agent nor catalyst is needed for the reaction to proceed. After purification by dialysis, the product was identified by 1H and 13C 1D and 2D NMR in DMSO-d(6). BzPGA prepared by the new direct amidation method was identical to that obtained with a conventional carbodiimide-mediated reaction in water. The one-pot amidation procedure described in the present article can probably be applied to the synthesis of amides from other amines and carboxylic acids.

Synthesis of a novel glycoconjugated chitosan and preparation of its derived nanoparticles for targeting HepG2 cells

In the study, a novel chitosan (CS) derivative conjugated with multiple galactose residues in an antennary fashion (Gal-m-CS) was synthesized. A galactosylated CS (Gal-CS) was also prepared by directly coupling lactobionic acid on CS. Using an iontropic gelation method, CS and the synthesized Gal-CS and Gal-m-CS were used to prepare nanoparticles (CS, Gal-CS, and Gal-m-CS NPs) for targeting hepatoma cells. TEM examinations showed that the morphology of all three types of NPs was spherical in shape. No aggregation or precipitation of NPs in an aqueous environment was observed during storage for all studied groups, as a result of the electrostatic repulsion between the positively charged NPs. Little fluorescence was observed in HepG2 cells after incubation with the FITC-labeled CS NPs. The intensity of fluorescence observed in HepG2 cells incubated with the Gal-m-CS NPs was stronger than that incubated with the Gal-CS NPs. These results indicated that the prepared Gal-m-CS NPs had the highest specific interaction with HepG2 cells among all studied groups, via the ligand-receptor-mediated recognition.

pH- and thermosensitive polyaniline colloidal particles prepared by enzymatic polymerization

Polyaniline colloids were prepared by enzymatic polymerization using chitosan and poly(N-isopropylacrylamide) as steric stabilizers. The resulting nanoparticles undergo flocculation by changing the pH or temperature of the aqueous dispersions. The environmentally responsive behavior of these colloids contrasts with that of polyaniline colloids synthesized using poly(vinyl alcohol) as the steric stabilizer. The colloid size was a function of the steric stabilizers and ranged from approximately 50 nm for polyaniline particles prepared in the presence of chitosan and partially hydrolyzed poly(vinyl alcohol) up to 350 nm for the particles synthesized using poly(N-isopropylacrylamide). UV-visible and Fourier transform infrared spectroscopic studies indicate that polyaniline colloids are spectroscopically similar to those obtained by traditional dispersion polymerization of aniline by chemical oxidation. These polyaniline colloids have potential applications in thermochromic windows and smart fluids.

Nanostructured materials for applications in drug delivery and tissue engineering

Research in the areas of drug delivery and tissue engineering has witnessed tremendous progress in recent years due to their unlimited potential to improve human health. Meanwhile, the development of nanotechnology provides opportunities to characterize, manipulate and organize matter systematically at the nanometer scale. Biomaterials with nano-scale organizations have been used as controlled release reservoirs for drug delivery and artificial matrices for tissue engineering. Drug-delivery systems can be synthesized with controlled composition, shape, size and morphology. Their surface properties can be manipulated to increase solubility, immunocompatibility and cellular uptake. The limitations of current drug delivery systems include suboptimal bioavailability, limited effective targeting and potential cytotoxicity. Promising and versatile nano-scale drug-delivery systems include nanoparticles, nanocapsules, nanotubes, nanogels and dendrimers. They can be used to deliver both small-molecule drugs and various classes of biomacromolecules, such as peptides, proteins, plasmid DNA and synthetic oligodeoxynucleotides. Whereas traditional tissue-engineering scaffolds were based on hydrolytically degradable macroporous materials, current approaches emphasize the control over cell behaviors and tissue formation by nano-scale topography that closely mimics the natural extracellular matrix (ECM). The understanding that the natural ECM is a multifunctional nanocomposite motivated researchers to develop nanofibrous scaffolds through electrospinning or self-assembly. Nanocomposites containing nanocrystals have been shown to elicit active bone growth. Drug delivery and tissue engineering are closely related fields. In fact, tissue engineering can be viewed as a special case of drug delivery where the goal is to accomplish controlled delivery of mammalian cells. Controlled release of therapeutic factors in turn will enhance the efficacy of tissue engineering. From a materials point of view, both the drug-delivery vehicles and tissue-engineering scaffolds need to be biocompatible and biodegradable. The biological functions of encapsulated drugs and cells can be dramatically enhanced by designing biomaterials with controlled organizations at the nanometer scale. This review summarizes the most recent development in utilizing nanostructured materials for applications in drug delivery and tissue engineering.

Novel chitosan-derived nanomaterials and their micelle-forming properties

Six novel N-alkyl-N-dimethyl and N-alkyl-N-trimethyl chitosan derivatives were chemically synthesized and characterized using FT-IR, 1H NMR, 13C NMR, differential scanning calorimetry (DSC), and X-ray diffraction spectrometry (XRD). The alkyl groups included octyl (C8H17-), decanyl (C10H21-), and lauryl (C12H25-). These chitosan derivatives were also evaluated for their micelle-forming properties using dynamic light scattering (DLS) and transmission electron microscopy (TEM) techniques. All six chitosan derivatives were capable of forming polymeric micelles in water with an average particle diameter ranging from 36 to 218 nm. Both N-octyl-N-dimethyl and N-octyl-N-trimethyl chitosan derivatives formed nanomicelles under the experimental conditions, with an average particle diameter of 36.0 and 52.5, respectively. Both the length of alkyl group and the N-trimethylation degree of the chitosan derivatives altered the size of their polymeric micelles. To further understand the effect of N-alkyl substitution degree of chitosan derivatives on size of their micelles, additional five N-octyl-N-trimethyl chitosan derivatives with N-alkyl substitution degree ranging from 8 to 58% were prepared and their micelle sizes were determined. The results showed that the diameter of the nanomicelles was proportional to the degree of N-octyl substitution. These data suggest that novel N-alkyl-N-dimethyl and N-alkyl-N-trimethyl chitosan derivatives may form nanomicelles. Additional research is required to further investigate the potential value-added utilization of these chitosan derivatives in controlled release and targeted delivery of hydrophobic bioactive food factors.

Synthesis and Study of Cross-Linked Chitosan-N-Poly(ethylene glycol) Nanoparticles

The present investigation describes the synthesis and characterization of novel biodegradable nanoparticles based on chitosan. Poly(ethylene glycol) dicarboxylic acid was used for intramolecular cross-linking of the chitosan linear chains. The condensation reaction of carboxylic groups and pendant amino groups of chitosan was performed by using water-soluble carbodiimide. The prepared nanosystems were stable in aqueous media. The structure of the products was determined by nuclear magnetic resonance (NMR) spectroscopy, and the particle size was identified by dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. It was found that biodegradable cross-linked chitosan nanoparticles experienced considerable swelling because of the length and flexibility of the cross-linking agent. The aqueous solutions or dispersions of nanoparticles were stable and clear or mildly opalescent systems depending on the ratio of cross-linking and molecular weight of chitosan, findings consistent with values of transmittance above 75%. Particle size measured by TEM varied in the range of 4-24 nm. In the swollen state, the average size of the individual particles measured by DLS was in the range of 50-120 nm depending on the molecular weight of chitosan and the ratio of cross-linking.

Stable and pH-sensitive nanogels prepared by self-assembly of chitosan and ovalbumin

Two natural macromolecules, chitosan and ovalbumin, were used to produce nanogels by a new, green, and convenient method. Chitosan and ovalbumin solutions were mixed; the pH of the resulting solution was adjusted; and the solution was successively stirred and heated. After that, ovalbumin gelled forming nanospheres. The chitosan chains are supposed to be partly trapped in the nanogel core upon heating because of the electrostatic attractions between chitosan and ovalbumin, while the rest of the chitosan chains should form the shell of the nanogels. The nanogels did not change the size distribution after long-time storage and did not dissociate in the pH range of 2-10.5. The dispersibility, size, and hydrophobicity/hydrophilicity of the nanogels are pH-dependent. The nanogels are good candidates for cosmetic and pharmaceutical applications.