Myung-Seok Choi

Three-dimensional gastric cancer cell culture using nanofiber scaffold for chemosensitivity test.

A three-dimensional (3D) culture of cancer cells has long been advocated as a better model of the malignant phenotype that is most closely related to tumorigenicity in vivo. To investigate the sensitivity of cancer cells to anticancer drugs, nanofiber scaffolds composed of PHBV and collagen peptide were fabricated by electrospinning. A 3D culture of cancer cells was successfully achieved by the use of nanofiber scaffolds. From the result of a chemosensitivity test, it was found that higher concentrations of anticancer drugs were required to achieve a comparable cytotoxic effect in 3D culture due to their structural architecture. These data demonstrate that the electrospun nanofiber scaffolds can provide a 3D model particularly appropriate for investigating mechanisms involved in cancer cell sensitivity to anticancer drugs.

Photophysical properties of composite film of dendron-appended porphyrin and fullerene[60]

Dendron-appended porphyrin (den-por) and C60 (den-C60) were synthesized for the application of photovoltaic materials. The composite films of den-por and den-C60 were subjected to absorption and photoluminescence spectroscopic measurements. We determined that solid-state film, spin-coated with a blend of den-por and den-C60 at weight ratio 1:0.5, showed an efficient photoluminescence quenching via donor-to-acceptor electron transfer.

Size-controlled assemblies of porphyrin-modified pullulan photosensitizers

Pullulan conjugates (i.e. PFP1, PFP4) formed via DCC/DMAP coupling of porphyrin derivatives possessing one (P1) or four (P4) carboxylic acid moieties with folate-appended pullulans (PF) were prepared for application as photosensitizers (PS) for photodynamic therapy. To maximize the desired PS characteristics, the assembly size of PS should be less than 200 nm in water medium. In a PBS buffer solution, PFP4 forms smaller assemblies (~100 nm) than PFP1 (~320 nm) due to its enhanced intramolecular hydrophilicity.

Fabrication and Characterization of Erbium-Doped Fluoropolymer Patterns via UV-Nanoimprint Lithography for Use in Planar Optical Amplifiers

The Er-doped precursor solutions were first prepared using 2,2,3,3,4,4,5,5-octafluoropentyl acrylate as a fluoromonomer, 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol diacrylate as a cross-linking agent, poly(2,2,3,3,4,4,4-heptafluorobutyl acrylate) as a binding polymer, Darocure 4265 as radical photoinitiator and erbium(III) trifluoromethane sulfonate as an erbium source with various weight ratios. The crosslinked, patterned and erbium-doped fluoropolymer films were fabricated by UV-nanoimprint lithography on glass substrates for application as planar optical amplifiers. The fluoropolymer films acting as a host material for the Er ions showed excellent transmission properties—more than 80% over the visible and near-infrared regions—a high thermal decomposition temperature greater than 350°C and the ability to support a high Er concentration—up to 10 wt% based on the polymer matrix. These results were good enough for the films to be used in planar optical amplifier applications.

Enhanced in vitro photocytotoxicity of water-soluble dendritic pheophorbide-a

Photosensitizers can produce highly reactive singlet oxygen with exposure to visible light and are used in photodynamic therapy to treat a variety of tumors. We report on the synthesis of triethylene glycol dendron-conjugated pheophorbide-a5, a novel photosensitizer. The characteristic absorption bands (Soret and Q-bands, λmax = 405 and 670 nm, respectively) of 5 were appeared clearly in aqueous solution, due to the improved water-solubility of the dendron moiety. The value of singlet oxygen quantum yield of 5 (ΦΔ = 0.22) was higher than free pheophorbide-a (ΦΔ = 0.17) as reference in aqueous solution. Compound 5 also exhibited an enhanced in vitro phototoxicity than pheophorbide-a (PhA) in the concentration range of 1.0–5.0 μg/mL: cell viability in cells treated with 5 was reduced by ~20%, indicating a cell death rate of ~80%, while PhA treatment resulted in a cell death rate of only about 10%. These results indicate that 5 will likely be more efficient in PDT applications. Compared with free PhA, compou...

Heat Resistant Polymer Matrix Containing Acrylo-Polyhedral Silsesquioxane for Erbium-Doped Waveguide Amplifier Applications

We report on the fabrication of fluorinated polymer film as host material for erbium ions (Er3+) with a goal of achieving sufficient thermal stability, optical clarity and a chemical resistance to withstand typical fabrication processing. Precursor solutions were prepared using 2,2,3,3,4,4,5,5-octafluoropentyl acrylate as a fluoromonomer, tetrahydrofurfuryl acrylate as a solubility enhancer, Ebecryl 220 as a cross-linking agent, acrylo-polyhedral oligomeric silsesquioxane as a heat-resistance improver and Darocur 4265 as a radical photoinitiator with various weight ratios. Fluoropolymer films prepared from the precursor solution had excellent transmission properties (low transmission losses less than 2% over the visible and near-infrared regions) and high thermal decomposition temperatures (greater than 350 °C). Er3+-doped precursor solution was also prepared by adding of erbium(III) trifluoromethane sulfonate as an erbium source. The crosslinked, patterned and Er3+-doped fluoropolymer films were successfully fabricated using the Er3+-doped precursor solution by both micromolding in capillaries and soft-imprint lithography on glass substrates for Er3+-doped waveguide amplifier applications.

Synthesis and Optical Properties of Dendritic Porphyrin-Erbium Complexes

Organic compound with lanthanide complexes have been greatly researched for the advance of optical property and processibility to apply on optical amplifiers. We studied on lanthanide metal-dendritic porphyrin complex in solution state. Peripherally substituted carboxylic groups on G1 and G2 dendritic porphyrins were gradually occurred to form the precipitation with increasing Er3+ions in solution state. With increasing the amount of Er3+ions resulting complexes begin to form loosely cross-linked complexes causing precipitation in THF solution. No optical change of G2-Er complex was observed in the presence of large excess (10eq-100eq) of strong chelating ligand such as EDTA in THF solution, which is indicative that G2-Er is chemically very stable because of so-called dendritic chelating effect.

Fabrication and Characterization of Erbium-Doped Polymer Patterns by Lift-Off Process for Planar Optical Amplifiers

Erbium-doped aqueous polymer solutions were prepared using polyvinylpyrrolidone as a host polymer, potassium persulfate as a thermal cross-linking agent, erbium (III) trifluoromethane sulfonate as an erbium source, ethylene glycol as an antifoaming agent and DISPERBYK-180 as a dispersing agent with various weight ratios. The cross-linked, patterned and Er3+-doped polymer films were fabricated using the solutions by a lift-off process for application to planar optical amplifiers. The polymer films fabricated in this study showed excellent transmission of more than 90% over the visible and NIR regions, a high thermal decomposition temperature of about 380°C and high Er3+ concentration up to 20 wt.% based on a polymer matrix without aggregation, making this material sufficient for planar optical amplifiers.

Preparation and Physical Properties of Erbium-Doped Polymer Patterns by Micromolding in Capillaries for Optical Waveguide Amplifiers

Er3+-doped precursor solutions were first prepared using 2,2,3,3,4,4,5,5-octafluoropentyl acrylate as a fluoromonomer, tetrahydrofurfuryl acrylate as a solubility enhancer, Ebecryl 220 as a cross-linking agent, Darocur 4265 as a radical photoinitiator and erbium(III) trifluoromethane sulfonate as an erbium source with various weight ratios. The crosslinked, patterned and erbium-doped fluoropolymer films were fabricated by micromolding in capillaries on glass substrates for planar optical amplifier applications. The fluoropolymer films acting as host materials for the Er3+ ions had excellent transmission properties (more than 90% over the visible and near-infrared regions), high thermal decomposition temperatures (greater than 300°C) and the ability to support high erbium complex concentrations (up to 10 wt% based on the polymer matrix). These results are sufficient for the films to be used in planar optical amplifier applications.

Fabrication and Optical Properties of Erbium-Doped Polymer Films

The crosslinked, fluorinated, patterned and erbium (Er3+) doped polymer films were fabricated by UV-curing after a simple spin-coating. Er3+-doped solutions containing Irgacure 819 used as a radical-type photoinitiator were prepared using erbium (III) trifluoromethane sulfonate as an erbium source, 2,2,3,3,4,4,5,5-octafluoropentyl acrylate as a fluorinated monomer, trimethylolpropane triacrylate and Ebecyl 810 resin as a crosslinking agent with various weight ratios. The fluorinated polymer films fabricated in this study showed the excellent transmission property more than 80% over visible and NIR region, and high thermal decomposition temperature about 310°C sufficient for optical device applications. From these results, the Er3+-doped polymer films developed in this study could be applied to optical telecommunication devices.