Mi Kyeong Jang

Preparation of a Hydrophobized Chitosan Oligosaccharide for Application as an Efficient Gene Carrier

To prepare chitosan-based polymeric amphiphiles that can form nanosized core-shell structures (nanoparticles) in aqueous milieu, chitosan oligosaccharides (COSs) were modified chemically with hydrophobic cholesterol groups. The physicochemical properties of the hydrophobized COSs (COSCs) were investigated by using dynamic light scattering and fluorescence spectroscopy. The feasibility of applying the COSCs to biomedical applications was investigated by introducing them into a gene delivery system. The COSCs formed nanosized self-aggregates in aqueous environments. Furthermore, the physicochemical properties of the COSC nanoparticles were closely related to the molecular weights of the COSs and the number of hydrophobic groups per COS chain. The critical raggregation concentration values decreased upon increasing the hydrophobicity of the COSCs. The COSCs efficiently rcondensed plasmid DNA into nanosized ion-complexes, in contrast to the effect of the unmodified COSs. An investigation of gene condensation, performed using a gel retardation assay, revealed that COS6(Mn= 6,040 Da) containing 5% of cholesteryl chloroformate (COS6C5) formed a stable DNA complex at a COS6C5/DNA weight ratio of 2. In contrast, COS6, the unmodified COS, failed to form a stable COS/DNA complex even at an elevated weight ratio of 8. Furthermore, the COS6C5/DNA complex enhanced thein vitro transfection efficiency on Human embryonic kidney 293 cells by over 100 and 3 times those of COS6 and poly(L-lysine), respectively. Therefore, hydrophobized chitosan oligosaccharide can be considered as an efficient gene carrier for gene delivery systems.

All-trans Retinoic Acid-Associated Low Molecular Weight Water-Soluble Chitosan Nanoparticles Based on Ion Complex

The purpose of this study is to develop novel nanoparticles based on polyion complex formation between low molecular weight water-soluble chitosan (LMWSC) and all-trans retinoic acid (atRA). LMWSC nanoparticles encapsulating atRA based on polyion complex were prepared by mixing of atRA into LMWSC aqueous solution using ultrasonication. In FTIR spectra, the carbonyl group of atRA at 1690 cm−1 disappeared or decreased when ion complexes were formed between LMWSC and atRA. In1H NMR spectra, specific peaks of atRA disappeared when atRA-encapsulated LMWSC (RAC) nanoparticles were reconstituted into D2O while specific peaks both of atRA and LMWSC appeared in D2O/DMSO (1/3, v/v) mixture. XRD patterns also showed that the crystal peaks of atRA were disappeared by encapsulation into LMWSC nanoparticles. LMWSC nanoparticles encapsulating atRA have spherical shapes with particle size below 200 nm. The mechanism of encapsulation of atRA into LMWSC nanoparticles was thought to be an ion complex formation between LMWSC and atRA. LMWSC nanoparticles showed high atRA loading efficiency over 90% (w/w). AtRA was continuously released from nanoparticles over 10 days. Inin vitro cell cytotoxicity test, free atRA showed higher cytotoxic effect against CT 26 colon carcinoma cell line on 1 day. However, RAC nanoparticles showed similar cytotoxicity against CT 26 cells on 2 day. These results suggest the potential for the introduction of LMWSC nanoparticles into various biomedical fields such as drug delivery.

Methotrexate-Incorporated Polymeric Micelles Composed of Methoxy Poly(ethylene glycol) Grafted Chitosan

In this study, methotrexate (MTX)-encapsulated polymeric micelles using methoxy poly(ethylene glycol) (MPEG)-grafted chitosan (ChitoPEG) copolymer were prepared. The MTX-incorporated polymeric micelles of ChitoPEG copolymer has a particle size of around 50-100 nm. In 1H nuclear magnetic resonance (NMR) study, the specific peaks of MTX disappeared in heavy water (D2O) and only the specific peak of MPEG was observed, while all of the peaks were confirmed in dimethyl sulfoxide (DMSO). These results indicated that MTX was complexed with chitosan and then formed an ion complex inner-core of the polymeric micelle in an aqueous environment. The drug contents of the polymeric micelle were around 4∼12% and the loading efficiency of MTX in the polymeric micelles was higher than 60% (w/w) for all of the formulations. The cytotoxicity of MTX and MTX-incorporated polymeric micelle against CT26 tumor cells was not significantly changed.

Synthesis and Characterization of Thermosensitive Nanoparticles Based on PNIPAAm Core and Chitosan Shell Structure

Noble thermosensitive nanoparticles, based on a PNIPAAm-co-AA core and a chitosan shell structure, were designed and synthesized for the controlled release of the loaded drug. PNIPAAm nanoparticles containing a carboxylic group on their surface were synthesized using emulsion polymerization. The carboxylic groups were conjugated with the amino group of a low molecular weight, water soluble chitosan. The particle size of the synthesized nanoparticles was decreased from 380 to 25 nm as the temperature of the dispersed medium was increased. Chitosan-conjugated nanoparticles with 2∼5 wt% MBA, a crosslinking monomer, induced a stable aqueous dispersion at a concentration of 1 mg/1 mL. The chitosan-conjugated nanoparticles showed thermosensitive behaviors such as LCST and size shrinkage that were affected by the PNIPAAm core and induced some particle aggregation around LCST, which was not shown in the NIPAAm-co-AA nanoparticles. These chitosan-conjugated nanoparticles are also expected to be more biocompatible than the PNIPAAm core itself through the chitosan shell structures.

Preparation and Characterization of Nanoparticles Using Poly(N-isopropylacrylamide)- Poly(ε-caprolactone) and Poly(ethylene glycol)-Poly(ε-caprolactone) Block Copolymers with Thermosensitive Function

Thermosensitive nanoparticles were prepared via the self-assembly of two different poly(ε-caprolactone)-based block copolymers of poly(N-isopropylacrylamide)-b-poly(ε-caprolactone) (PNPCL) and poly(ethylene glycol)-b-poly(ε-caprolactone) (PEGCL). The self-aggregation and thermosensitive behaviors of the mixed nanoparticles were investigated using1H-NMR, turbidimetry, differential scanning microcalorimetry (micro-DSC), dynamic light scattering (DLS), and fluorescence spectroscopy. The copolymer mixtures (mixed nanoparticles, M1-M5, with different PNPCL content) formed nano-sized self-aggregates in an aqueous environment via the intra- and/ or intermolecular association of hydrophobic PCL chains. The microscopic investigation of the mixed nanoparticles showed that the critical aggregation concentration (cac), the partition equilibrium constants (Kv) of pyrene, and the aggregation number of PCL chains per one hydrophobic microdomain varied in accordance with the compositions of the mixed nanoparticles. Furthermore, the PNPCL harboring mixed nanoparticles evidenced phase transition behavior, originated by coil to the globule transition of PNiPAAm block upon heating, thereby resulting in the turbidity change, endothermic heat exchange, and particle size reduction upon heating. The drug release tests showed that the formation of the thermosensitive hydrogel layer enhanced the sustained drug release patterns by functioning as an additional diffusion barrier.

Transesterification and compatibilization in the blends of bisphenol-A polycarbonate and poly(trimethylene terephthalate)

Melt blending of Bisphenol A polycarbonate(PC) and poly(trimethylene terephthalate)(PTT) was carried out over the entire composition range. The mixing time was varied up to 90 min. The resulting samples were analyzed by FT-IR, DSC, XRD, DMTA,1H NMR, and SEM. The process of transesterification between the two polymers and their resulting compatibilization were observed. The behaviors of the PTT-rich and PC-rich blends were different and an equilibrium was found to exist. Peculiar behavior, which was different from that of the PTT-rich and PC-rich blends, was exhibited by the 50/50(PTT/PC) blend.

All-trans Retinoic Acid Release from Surfactant-free Nanoparticles of Poly(DL-lactide-co-glycolide)

In this study, we prepared all-trans retinoic acid (ATRA)-encapsulated, surfactant-free, PLGA nanoparticles. The nanoparticles were formed by nanoprecipitation process, after which the solvent was removed by solvent evaporation or dialysis method. When a nanoparticle was prepared by the nanoprecipitation - solvent evaporation method, the nanoparticles were bigger than the nanoparticles of the nanoprecipitation - dialysis method, despite the higher although loading efficiency. Nanoparticles from the nanoprecipitation - dialysis method were smaller than 200 nm in diameter, while the loading efficiency was not significantly changed. Especially, nanoparticles prepared from DMAc, 1,4-dioxane, and DMF had a diameter of less than 100 nm. In the transmission electron microscopy (TEM) observations, all of the nanoparticles showed spherical shapes. The loading efficiency of ATRA was higher than 90 % (w/w) at all formulations with exception of THF. The drug content was increased with increasing drugfeeding amount while the loading efficiency was decreased. In the drug release study, an initial burst was observed for 2∼6 days according to the variations of the formulation, after which the drug was continuously released over one month. Nanoparticles from the nanoprecipitation - dialysis method showed faster drug release than those from the nanoprecipitation — solvent evaporation method. The decreased drug release kinetics was observed at lower drug contents. In the tumor cell cytotoxicity test, ATRA-encapsulated, surfactant-free, PLGA nanoparticles exhibited similar cytotoxicity with that of ATRA itself.

Enhanced gene delivery system using disulfide-linked chitosan immobilized with polyamidoamine

AbstractWe developed a polyamidoamine (PAMAM) conjugated disulfide-linked chitosan (dsCS-PAM) for nonviral gene delivery. At weight ratio of 128, dsCS and dsCS-PAM showed positive zeta potential of around 9.5 mV and 14.5 mV, respectively, demonstrating their ability to form complexes with plasmid DNA (pDNA) for cell transfection. CS-PAM and dsCS-PAM formed complexes with pDNA in a reducing environment containing 5 mM DLdithiothreitol (DTT) at weight ratio 32 and 16, respectively. PAMAM conjugated chitosan derivatives, dsCS-PAM and CS-PAM, showed higher in vitro transfection efficiency than unconjugated derivatives dsCS and CS. Approximately 80% of A549 and 293 cells were viable in the presence of up to 100 μg/mL of dsCS-PAM. The results of this study demonstrate that dsCS-PAM has the potential to be a safe gene delivery carrier.

Enhance of Tumor Targeting by Receptor-Mediated Endocytosis Using Low Molecular Water-Soluble Chitosan Nanoparticles Loaded with Anticancer Agent

In this study, we prepared using low molecular weight water-soluble chitosan nanoparticle loaded paclitaxel (LMWSC-NPT) and investigated the potential as a drug carrier which is able to accumulate in the tumor site. In the experiment of receptor-mediated endocytosis, LMWSC-NPT was treated with sodium azid (NaN3) as an inhibitor of endocytosis process. As results, the antitumor activity of LMWSC-NPT treated with sodium azid didn’t show but LMWSC-NPT was shown the high antitumor activity. Therefore, LMWSC-NPs modified with hydrophobic group will be useful anticancer agent carrier via receptor-mediated endocytosis.