Young-Keun Jeong

In-situ synthesis of reactive hydroxyapatite nano-crystals for a novel approach of surface grafting polymerization

A novel approach to surface modification of hydroxyapatite (HAp) nano-crystals was described based on in-situ synthesis of surface thiol-functionalized HAp (HAp-SH) and subsequent grafting polymerization of ethylene glycol methacrylate phosphate (EGMP). Energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) analyses showed that thiol groups were introduced on HAp surfaces by adding 3-mercaptopropionic acid during hydrothermal synthesis of HAp nano-crystals. The radical chain transfer to surface thiol groups generated the sulfur-centered radicals on HAp nano-surfaces, which initiated the surface grafting polymerization of EGMP. Fourier transform infrared (FT-IR) spectroscopy and powder X-ray diffraction (XRD) analyses confirmed the grafting reaction on HAp surfaces. Zeta potentials of control HAp, thiol-functionalized HAp (HAp-SH), and PolyEGMP-grafted HAp in phosphate buffered saline (PBS) solutions (pH 7.4) were negative and decreased with increasing the amount of grafted PolyEGMP. TEM measurements and time-dependent phase monitoring suggested that the colloidal stability of PolyEGMP-grafted HAp over synthesized HAp nano-crystals in water dramatically increased without inter-crystal aggregation.

Atomic Layer Deposition of Ta-doped TiO2 Electrodes for Dye-Sensitized Solar Cells

Ta-doped TiO 2 inverse opals were obtained by selective etching of a silica template after atomic layer deposition (ALD) of Ta-doped TiO 2 films and were applied as an electrode for dye-sensitized solar cells (DSSCs). Ta content in the Ta-doped TiO 2 film was controlled by the Ta/(Ta+Ti) unitcycle ratios in the Ta―TiO 2 supercycle of ALD. Also, excellent step coverage of nearly 100% in the inverse opal structure was confirmed by field-emission scanning electron microscopy (FE-SEM). Maximum photo-conversion efficiency of 1.56% was achieved with the Ta (3.4 atom %)-doped TiO 2 inverse opal electrode due to increased photocurrent density. However, further Ta doping (> 4.9 atom %) decreased the J sc and photoconversion efficiency.

Mathematical modelling on the controlled-release of indomethacin-encapsulated poly(lactic acid-co-ethylene oxide) nanospheres

The in vitro release behaviour of indomethacin (IMC, 1-[p-chlorobenzoyl]-2-methyl-5-methoxy-3-indoleacetic acid) encapsulated in poly(lactic acid-co-ethylene oxide) (PLA-PEO) nanospheres is investi ...

Characteristic evaluation of Al2O3/CNTs hybrid materials for micro-electrical discharge machining

The characteristic evaluation of aluminum oxide (Al2O3)/carbon nanotubes (CNTs) hybrid composites for micro-electrical discharge machining (EDM) was described. Alumina matrix composites reinforced with CNTs were fabricated by a catalytic chemical vapor deposition method. Al2O3 composites with different CNT concentrations were synthesized. The electrical characteristic of Al2O3/CNTs composites was examined. These composites were machined by the EDM process according to the various EDM parameters, and the characteristics of machining were analyzed using field emission scanning electron microscope (FESEM). The electrical conductivity has a increasing tendency as the CNTs content is increased and has a critical point at 5% Al2O3 (volume fraction). In the machining accuracy, many tangles of CNT in Al2O3/CNTs composites cause violent spark. Thus, it causes the poor dimensional accuracy and circularity. The results show that conductivity of the materials and homogeneous distribution of CNTs in the matrix are important factors for micro-EDM of Al2O3/CNTs hybrid composites.

Apicidin, the histone deacetylase inhibitor, suppresses Th1 polarization of murine bone marrow-derived dendritic cells.

Apicidin is a fungal metabolite shown to exhibit anti-proliferative, anti-invasive, and anti-inflammatory properties by the inhibition of histone deacetylase (HDAC). However, the effects of apicidin on the maturation and immunostimulatory function of dendritic cells (DCs) remain unknown. In this study, we investigated whether apicidin modulates surface molecule expression, cytokine production, endocytosis capacity, and underlying signaling pathways in murine bone marrow-derived DCs. We observed that apicidin significantly attenuated surface molecule expression in LPS-stimulated DCs, suppressed production of interleukin (IL)-12 and proinflammatory cytokines (IL-6 and TNF-α) by DCs, and reduced IFN-γ production by T cells. The apicidin-treated DCs were found to be highly efficient in antigen capture via mannose receptor-mediated endocytosis. Apicidin also inhibited LPS-induced MAPK activation and NF-κB nuclear translocation in DCs. Moreover, the apicidin-treated DCs were incapable of inducing Th1 responses and normal cell-mediated immune responses. These novel findings not only provide new insights into the immunopharmacological role of apicidin in terms of its effects on DCs, but also broaden current perspectives of the immunopharmacological functions of apicidin, and have implications for the development of therapeutic adjuvants for the treatment of DC-related acute and chronic diseases.

Fabrication of hybrid composites based on biomineralization of phosphorylated poly(ethylene glycol) hydrogels

A novel route to organic-inorganic composites was described based on biomineralization of poly(ethylene glycol) (PEG)-based hydrogels. The 3-dimensional hydrogels were synthesized by radical crosslinking polymerization of poly(ethylene glycol fumarate) (PEGF) in the presence of ethylene glycol methacrylate phosphate (EGMP) as an apatite-nuclating monomer, acrylamide (AAm) as a compositionmodulating comonomer, and potassium persulfate (PPS) as a radical initiator. We used the urea-mediated solution precipitation technique for biomineralization of hydrogels. The apatite grown on the surface and interior of the hydrogel was similar to biological apatites in the composition and crystalline structure. Powder x-ray diffraction (XRD) showed that the calcium phosphate crystalline platelets on hydrogels are preferentially aligned along the crystallographic c-axis direction. Inductively-coupled plasma mass spectroscopy (ICP-MS) analysis showed that the Ca/P molar ratio of apatites grown on the hydrogel template was found to be 1.60, which is identical to that of natural bones. In vitro cell experiments showed that the cell adhesion/proliferation on the mineralized hydrogel was more pronounced than on the pure polymer hydrogel.

Microstructure and properties of alumina-silicon carbide nanocomposites fabricated by pressureless sintering and post hot-isostatic pressing

Abstract Al 2 O 3 /5%SiC nanocomposites were fabricated by pressureless sintering using MgO as a sintering aid and then post hot-isostatic pressed (HIP), which can subsequently break through the disadvantage of hot-pressing process. The MgO additive was able to promote the densification of the composites, but could not induce the grain growth of Al 2 O 3 matrix due to the grain growth inhibition by nano-sized SiC particles. After HIP treatment, Al 2 O 3 /SiC nanocomposites achieved full densification and homogeneous distribution of nano-sized SiC particles. Moreover, the fracture morphology of HIP treated specimens was identical with that of the hot-pressed Al 2 O 3 /SiC nanocomposites showing complete transgranular fracture. Consequently, high fracture strength of 1 GPa was achieved for the Al 2 O 3 /5%SiC nanocomposites by pressureless sintering and post HIP process.

Dielectrophoretic assembly of semiconducting single-walled carbon nanotube transistor

Abstract A novel burning technique for making a semiconducting single-walled carbon nanotubes (SWNTs) transistor assembled by the dielectrophoretic force was suggested. The fabrication process consisted of two steps. First, to align and attach a bundle of SWNTs between the source and drain, the alternating (AC) voltage was applied to the electrodes. When a bundle of SWNTs was connected between two electrodes, some of metallic nanotubes and semi-conducing nanotubes existed together. The second step is to burn the metallic SWNTS by applying the voltage between two electrodes. With increasing the voltage, more current flowed through the metallic SWNTs, thus, the metallic SWNTs burnt earlier than the semiconducting one. This technique enables to obtain only semi-conducting SWNTs connection in the transistor. Through the I-V characteristic graph, the moment of metallic SWNTs burning and the characteristic of semi-conducing nanotubes were verified.

Laser micromachining of CNT/Fe/Al2O3 nanocomposites

Abstract CNT/Fe/Al 2 O 3 mixed powders were synthesized from Fe/Al 2 O 3 nanopowders using thermal CVD for the homogeneous dispersion of carbon nanotubes CNTs. CNTs consisted of MWNT, and the diameter was approximately 20-30 nm. After sintering, CNTs were homogenously located throughout Al 2 O 3 grain boundary and were buckled. A femto-second laser installed with special optical systems was used for micromachining of the nanocomposites. The relationship between material ablation rate and energy fluence was theoretically investigated and compared with experimental results from cross-sectional SEM analysis. The nanocomposites which have higher content of CNT show a fairly good machining result due to its higher thermal conductivity and smaller grain size as well as lower light transmittance.

Fabrication and sensing property for conducting polymer nanowire-based biosensor for detection of immunoglobulin G

Conducting polymers are excellent sensing materials in the design of bioanalytical sensors because of their electronic conductivity, low energy optical transitions, biocompatibility, and room temperature operation. Among them, Polypyrrole (Ppy) is one of the most extensively used conducting polymers because of a number of properties such as redox activity, rapid electron transfer, and ability to link a variety of biomolecules to pyrrole groups by chemical treatment. In this study, Ppy nanowires were synthesized by an electrospinning method. The nanowires were prepared from a solution mixture of Ppy and poly(ethylene oxide). The method of detection in such a device is based on the selective binding of antigen onto an antibody that is covalently attached to the nanowires. Thus, anti-IgG was immobilized on Ppy nanowires using an EDC {[N-(3-dimethyl aminopropyl)-N2-ethylcarbodiimide hydrochloride]}-NHS(N-hydrosuccinimide) modified technique. Fluorescence images of BSA–FITC (fluorescein isothiocyanate labeling of bovine serum albumin) conjugation demonstrated that antibody was functionalized on the Ppy nanowires without non-specific binding and facilitated selective detection of antigen. Current–voltage (I–V) characterization was used to monitor the change in the conductivity of nanowires while the specific binding interaction occurred. These results of electrical properties enable Ppy nanowire-based biosensors to detect biomolecules in real-time.