Bokyung Kong
KAIST
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Featured researches published by Bokyung Kong.
Bioconjugate Chemistry | 2011
Gwang Sig Yu; Yun Mi Bae; Hye Choi; Bokyung Kong; Insung S. Choi; Joon Sig Choi
In this study, we introduced histidine residues into l-arginine grafted PAMAM G4 dendrimers to enhance proton buffering capacity and evaluated the physicochemical characteristics and transfection efficacies in vitro. The results showed that the synthesized PAMAM G4 derivatives effectively delivered pDNA inside cells and the transfection level improved considerably as the number of histidine residues increased. Grafting histidine residues into the established polymer vector PAMAM G4-arginine improved their proton buffering capacity. The cytotoxicity of PAMAM G4 derivatives was tested and it was confirmed that they displayed relatively lower cytotoxicity compared to PEI25KD in various cell lines. Also, confocal microscopy results revealed that PAMAM G4 derivatives effectively delivered pDNA into cells, particularly into the nucleus. These PAMAM dendrimer derivatives conjugated with histidines and arginines may provide a promising polymeric gene carrier system.
Biomaterials | 2009
Bokyung Kong; Joon Sig Choi; Saewha Jeon; Insung S. Choi
This paper describes the formation of poly(N-isopropylacrylamide) (PNIPAAm) and poly[(N-isopropylacrylamide)-r-((3-(methacryloylamino)propyl)-dimethyl(3-sulfopropyl)ammonium hydroxide)] (P(NIPAAm-r-MPDSAH)) films on a glass surface via surface-initiated, atom transfer radical polymerization as a cell-culture platform. The films of PNIPAAm with various thicknesses and of P(NIPAAm-r-MPDSAH) with various ratios of NIPAAm and MPDSAH are formed to investigate the behaviors of cell adhesion and detachment. In the case of the PNIPAAm-grafted glass surfaces, the optimal film thickness, achieving the effective control of both cell adhesion and detachment, is estimated to be 11-13 nm for NIH 3T3 fibroblast cells. The adhesion and detachment behaviors of NIH 3T3 fibroblast cells are further tuned by incorporating the hydrophilic and non-biofouling MPDSAH moiety into the PNIPAAm system. The cell adhesion and detachment are controlled best, when the ratio of NIPAAm and MPDSAH is 75:1 (NIPAAm:MPDSAH).
Biomaterials | 2010
Woo Kyung Cho; Bokyung Kong; Hyung Ju Park; Jinkyu Kim; Won Chegal; Joon Sig Choi; Insung S. Choi
In this work, we compared the long-term stability and integrity of cell patterns on newly reported, zwitterionic poly((3-(methacryloylamino)propyl)dimethyl(3-sulfopropyl)ammonium hydroxide) (poly(MPDSAH)) films with those on widely used, poly(poly(ethylene glycol) methyl ether methacrylate) (poly(PEGMEMA)) ones. The micropatterns of both polymers were formed on a silicon oxide surface by a combination of micropattern generation of a photoresist, vapor deposition of a silane-based polymerization initiator, and surface-initiated, atom transfer radical polymerization (SI-ATRP) of each monomer, MPDSAH or PEGMEMA. The successful formation of the silane initiator SAMs, and poly(MPDSAH) and poly(PEGMEMA) micropatterns was confirmed by X-ray photoelectron spectroscopy (XPS) and imaging ellipsometry. Onto each substrate patterned with poly(MPDSAH) or poly(PEGMEMA), NIH 3T3 fibroblast cells were seeded, and the cell micropatterns were generated by the selective adhesion of cells on the cell-adhesive region of the patterned surfaces. The cell pattern formed on the poly(MPDSAH)-patterned surface was observed to have a superior ability of finely maintaining its original, line-shaped structure up to for 20 days, when compared with the cell pattern formed on the poly(PEGMEMA)-patterned surface. In order to verify the relationship between the integrity of the cell micropatterns and the stability of the underlying non-biofouling polymer layers, we also investigated the long-term stability of the polymer films themselves, immersed in the cell culture media, for one month, in the aid of ellipsometry, contact goniometry, and XPS.
Langmuir | 2010
Daewha Hong; Woo Kyung Cho; Bokyung Kong; Insung S. Choi
In this work, we developed a controlled oxidation reaction of vinyl-terminated self-assembled monolayers (SAMs) to carboxylic acid-terminated ones to generate radially inward wettability gradient surfaces. The hydrophobicity was introduced on a silicon wafer by SAMs of 10-undecenyltrichlorosilane, and after the initial drop in oxidation, followed by the dilution-by-dropping method, radial-wettability gradient surfaces having hydrophilic centers and hydrophobic exteriors were generated. This direct drop reaction on the SAMs did not require an elastomeric stamp to be fabricated, which allowed for facile tuning of the gradients in terms of sizes and shapes. The fabricated wettability gradient surfaces possessed a water-collecting capability toward the hydrophilic center, which was inactive on previous linear wettability gradient surfaces.
Synthetic Communications | 2012
Kuk Ro Yoon; Suk-Pyo Hong; Bokyung Kong; Insung S. Choi
Abstract The aliphatic polyesters are normally synthesized by ester interchange reactions or direct esterification of hydroxyacids or diacid/diol combinations. Biotransformation, utilizing the enzymes as catalysts, was accepted as an alternative route for the synthesis of aliphatic polyesters and offers various advantages compared with the conventional, metal-catalyzed polymerization reactions. Previous studies indicated that lipase-catalyzed polycondensation reactions between diols and diacids occurred preferentially at primary hydroxyl groups of diols, when diols contained both primary and secondary hydroxyl groups. In this work, we investigated lipase-catalyzed polycondensation of diacids and secondary hydroxyl group–containing diols, and successfully synthesized polyesters by polycondensation with secondary hydroxyl groups as well as primary hydroxyl groups. Various diols, glycerol, 1,2-propanediol, 1,3-butanediol, 2,3-butanediol, and 2,4-pentanediol were tested for the polycondensation. The polymerization was achieved by heating a mixture of lipase B, sebacic acid, and the diols in anhydrous toluene at 100 °C for 72 h. The resulting polymers were characterized by 1H and 13C NMR spectroscopy, Fourier transform–infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography. GRAPHICAL ABSTRACT
Langmuir | 2007
Woo Kyung Cho; Bokyung Kong; Insung S. Choi
Macromolecular Chemistry and Physics | 2005
Dong Jin Kim; Sung Min Kang; Bokyung Kong; Wan-Joong Kim; Hyun-jong Paik; Hyeon Choi; Insung S. Choi
Angewandte Chemie | 2009
Sung Ho Yang; Kyung-Bok Lee; Bokyung Kong; Jin-Hyun Kim; Hak-Sung Kim; Insung S. Choi
Langmuir | 2007
Bokyung Kong; Jungkyu K. Lee; Insung S. Choi
Advanced Functional Materials | 2008
Young Shik Chi; Hye Ryung Byon; Bong-Soo Lee; Bokyung Kong; Hee Cheul Choi; Insung S. Choi