• Proceedings of the Korean Society of Applied Pharmacology
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• 1994.04a
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• pp.129-130
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• 1994

The science of toxicology is the understanding of the mechanisms by which exogenous agents produce deleterious effects in biological systems. The actions of chemicals such as drugs are ultimately exerted at the cellular and gene levels. Over the past decade. several in vitro alternative methods such as cultured cells for assessing the toxicity of various xenobiotics have been proposed to reduce the use of animals. In this workshop three advanced methods will be presented. These methods are novel important models for toxicologic studies. Dr. Tabuchis group has establishcd two immortalized gastric surface mucosa cell lines from the pminary cultore of gastric fundic mucosal cells of adult transgenic mice harboring a temperature sensitive simian virus 40 large T-anugen gene. As the immortalized cell lines of various tissues possess unique characteristics to maintain their normal functions for several months, these cell lines are extremely useful for not only toxicity testing but also pharmacological screening in new drug development. Professor Funatsu have studied the formation of spherical multicelluar aggregates of adult rat hepatocytes(spheroid) having tissue like structure. The sphcroid shown thre is a prototype module of an artificial liver support system. Thus, the urea synthesis activity of the artificial liver was maintained at least to days in 100％ rat blood plasma. Dr. Takezawa and his coworkers have developed a novel culture system of multicellular spheroids considered 〃organoids〃 by utilizing a thermo-responsive polymer as a substratum of anchorage dependent cells. His final goal is to reconstitute the organoids of various normal organs, e.g., liver, skin etc. and also abnormal deseased organs such as tumor.

• The Korean Journal of Rheology
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• v.8 no.1
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• pp.58-68
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• 1996

고분자 가공에서 가장널리 사용되고 있는 사출공정은 비등온의 싸이클 공정이므로 사출조건에 따라 성형품은 다양한 형태의 열이력과 변형이력을 받게 되고 그 결과 최종성형 품의 기계적 물성이 현저히 달라지게 된다. 그러므로 우수한 물성을 갖는 성형품을 얻기위 해서는 열이력과 변형이력에 연관되어 나타나는 미세구조의 변화와 잔류응력을 최소화할수 있는 최적 성형조건의 선정이 대단히 중요하게 된다. 본 연구에서는 수치모사실험을 기초로 설정한 성형조건의 범위에서 다양한 사출성형실험을 수행하여 얻은 시편을 대상으로 미세구 조의 변화와 잔류응력에 미치는 성형조건의 영향을 조사함으로써 최적성형조건을 선정하기 위한 방안을 찾고자 하였다. 편광현미경을 사용하여 관찰한 결정성 고분자수지 시편의 내부 구조는 전형적인 skin-core 구조를 보일뿐만아니라 충전속도, 사출온도, 금형온도, 및 gate로 부터의 위치 변화에 따라 미세구조가 현저히 변함을 알수 있었으며 광탄성법과 layer removal method를 이용하여 조사한 무정형 고분지수 시편의 잔류응력은 금형온도와 사출압 에 가장 영향을 많이 받으며 두께 방향으로 parabola한 분포를 가짐을 알수 있었다. 이상의 결과로부터 사출조건의 변화에 따라 잔류응력과 내부구조가 현저히 변하게 되며 이는 성형 품의 물성에 직접적인 영향을 미치고 있음을 알수 있었다.

• Structural Engineering and Mechanics
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• v.68 no.3
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• pp.325-334
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• 2018

The Nonlinear dynamic response of a sandwich plate subjected to the low velocity impact is theoretically and experimentally investigated. The Hertz law between the impactor and the plate is taken into account. Using the Extended High Order Sandwich Panel Theory (EHSAPT) and the Ritz energy method, the governing equations are derived. The skins follow the Third order shear deformation theory (TSDT) that has hitherto not reported in conventional EHSAPT. Besides, the three dimensional elasticity is used for the core. The nonlinear Von Karman relations for strains of skins and the core are adopted. Time domain solution of such equations is extracted by means of the well-known fourth-order Runge-Kutta method. The effects of core-to-skin thickness ratio, initial velocity of the impactor, the impactor mass and position of the impactor are studied in detail. It is found that these parameters play significant role in the impact force and dynamic response of the sandwich plate. Finally, some low velocity impact tests have been carried out by Drop Hammer Testing Machine. The results are compared with experimental data acquired by impact testing on sandwich plates as well as the results of finite element simulation.

• Macromolecular Research
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• v.15 no.4
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• pp.370-378
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• 2007

Mechanical stimulation is known to activate several cellular signal transduction pathways, leading to the induction of signaling molecules and extracellular matrix (ECM) proteins, thereby modulating cellular activities, such as proliferation and survival. In this study, primary human dermal fibroblasts (HDFs) were seeded onto chitosan-based scaffolds, and then cultured for 3 weeks in a bioreactor under a cyclic strain of 1 Hz frequency. Compared to control samples cultured under static conditions, the application of a cyclic strain stimulated the proliferation of HDFs in I week, and by week 3 the thickness of the cell/scaffold composites increased 1.56 fold. Moreover, immunohistochemical staining of the culture media obtained from the cell/scaffold samples subjected to the cyclic strain, revealed increases in the expression and secretion of ECM proteins, such as fibronectin and collagen. These results suggest that the preconditioning of cell/scaffold composites with a cyclic strain may enhance the proliferation of HDFs, and even facilitate integration of the engineered artificial dermal tissue into the host graft site.

• YAKHAK HOEJI
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• v.51 no.5
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• pp.343-349
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• 2007

To investigate the effect of ethanol extract of Saxifraga stolonifera MEERBURGH on skin care, we measured anti-oxidant and anti-aging activity. S. stolonifera ethanol extract itself had anti-oxidant activity in a dose-dependent manner in DPPH radical scavenging. Silica dose-dependently increased the intracellular ROS generation in RAW 264.7 cells. S. stolonifera ethanol extract inhibited silica-induced intracellular superoxide anion generation, $H_2O_2$ and hydroperoxide generation in RAW 264.7 cells. S. stolonifera ethanol extract significantly inhibited both hyaluronidase and elastase activity, also significantly inhibited MMP-1(collagenase) activity as well. In NIH 3T3 fibroblast cells, S. stolonifera ethanol extract significantly increased collagen-like polymer synthesis, which suggesting the S. stolonifera ethanol extract might be used as hydration and anti-wrinkle agents. From the above results, it is suggested that the main ingredients of S. stolonifera ethanol extract play an important role in anti-oxidant and anti-aging activity.

• Proceedings of the Membrane Society of Korea Conference
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• 1994.04a
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• pp.55-56
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• 1994

There has been many attempts to improve the membrane performance using pervaporation processes[l-3]. They are 1) blending polymer with the high flux and one with high selectivity, 2) an incorporation of functional groups interacting with permeants into a membrane through copolymerization or modification, 3) composite membrane or asymmetric membrane structure with a thin skin layer which acts as a selective layer. Among them, a polymeric membrane containing ion complex group receives an extensive attention recently because ionic complex is known to activate the water transport through ion-dipole interaction. It is especially advantageous in the separation of organic-water system. We applied the ideas of the activation of water transport through ion-dipole. We have reported on the in-sire complex membrane to separate water from aqueous aceiic acid and pyridme solution[4-5] based on the simple acid-base theory. Water transport was enhanced through in-situ complex between pyridine moiety in the membrane and the incoming acetic acid in the feed. In this case, catalytic transport mechanism was proposed. In the present study we used pyridine solution as a feed and the sulfonic acid group in the membrane.

• Textile Coloration and Finishing
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• v.25 no.2
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• pp.118-125
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• 2013

Poly(vinyl alcohol) (PVA)/titanium dioxide ($TiO_2$) composite nanofibers were produced at different $TiO_2$ concentrations (0.5, 1 and 1.5 wt.%) using the electrospinning method. The parameters of electrospinning including polymer contents, voltage and tip-to-collector distance (TCD) were optimized for fabrication process. The study showed that 7.5 wt.% PVA, 15 kV applied voltage and 15 cm TCD are the best condition to obtain uniform PVA/$TiO_2$ nanofibers. $TiO_2$ nanoparticles give significant effect in fiber morphology. $TiO_2$ content increases the diameter of the fibers and roughen the fiber surfaces. The PVA/$TiO_2$ nanofibers were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD).

• Macromolecular Research
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• v.17 no.7
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• pp.533-537
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• 2009

This paper introduces a modified electro spinning system for biomedical wound-healing applications. The conventional electrospinning process requires a grounded electrode on which highly charged electro spun ultrafine fibers are deposited. Biomedical wound-healing membranes, however, require a very low charge and a low level of remnant solvent on the electrospun membrane, which the conventional process cannot provide. An electrohydrodynamic process complemented with field-controllable electrodes (an auxiliary electrode and guiding electrodes) and an air blowing system was used to produce a membrane, with a considerably reduced charge and low remnant solvent concentration compared to one fabricated using the conventional method. The membrane had a small average pore size (102 nm) and high porosity (85.1%) for prevention of bacterial contamination. In vivo tests on rats showed that these directly electro spun fibrous membranes produced using the modified electro spinning process supported the good healing of skin bums.

• YAKHAK HOEJI
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• v.42 no.4
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• pp.353-358
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• 1998

The MeOH extract of the bark of Paeonia moutan showed potent inhibitory effect on the mushroom tyrosinase activity in vitro. The activity-guided fractionation of t he MeOH extract resulted in the isolation of three active compounds. The chemical structures of these compounds were elucidated by chemical and spectroscopic evidence as catechin, 1,2,3,6-tetra-O-galloyl-${\beta}$-D-glucose and 1,2,3,4,6-penta-0-galloyl-${\beta}$-D-glucose, respectively. Among them, the inhibitory activity by 1,2,3,6-tetra-galloyl-${\beta}$-D-glucose on mushroom tyrosinase was more potent $(IC_{50}=3.5\;{\mu}M)$ than that of kojic acid $(IC_{50}=8.7\;{\mu}M)$ ,but catechin enhanced the mushroom tyrosinase activity 50% in the concentration of 34.5M.

• Journal of Life Science
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• v.28 no.3
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• pp.331-338
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• 2018

Melanin is a polymer substance that plays an important role in the determination of hair growth and skin color in vivo. However, melanin, which is over-produced by reactive oxygen species, is known to cause stains, freckles, and hypercholesterolemia, which are associated with aging. Previous studies have shown that polyphosphate, one of the components of Rhynchosia Nulubilis, inhibits skin aging induced by ultraviolet rays. The aim of this study is to investigate the direct effect of Rhynchosia Nulubilis ethanolic extract (RNEE) on melanin synthesis. In this study, RNEE showed no antioxidative effects on scavenging activity of DPPH radical in addition to reducing power. The cytotoxicity of RNEE was increased in a dose-dependent manner in an MTT assay. In addition, RNEE increased tyrosinase activity and melanin synthesis in DOPA-oxidation experiments. RNEE did not promote the conversion L-DOPA into melanin in live cells, but melanin production was promoted in the RNEE-treated group after H2O2 pretreatment compared to the control group in which melanin production was reduced by treatment with H2O2. In addition, RNEE increased the expression level of tyrosinase related protein-2 (TRP-2) and increased the expression level of tyrosinase related protein-1 (TRP-1) at a concentration of $16{\mu}g/ml$. In particular, it was found that RNEE increased the expression level of SOD-3, by which superoxide anion is converted to hydrogen peroxide, higher than the control and ${\alpha}$-MSH used as a positive control at a concentration of more than $16{\mu}g/ml$. The results suggest that RNEE can induce melanogenesis related to black hair.