Jong Soo Kim

Dankook University, Eidō, North Chungcheong, South Korea

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Publications (100)322.44 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The effects of heteroatom substitution from a silicon atom to a germanium atom in donor-acceptor type low band gap copolymers, poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl] (PSiBTBT) and poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]germole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl] (PGeBTBT), are studied. The optoelectronic and charge transport properties of these polymers are investigated with a particular focus on their use for organic photovoltaic (OPV) devices in blends with phenyl-C70-butyric acid methyl ester (PC70BM). It is found that the longer C-Ge bond length, in comparison to C-Si, modifies the molecular conformation and leads to a more planar chain conformation in PGeBTBT than PSiBTBT. This increase in molecular planarity leads to enhanced crystallinity and an increased preference for a face-on backbone orientation, thus leading to higher charge carrier mobility in the diode configuration. These results provide important insight into the impact of the heavy atom substitution on the molecular packing and device performance of polymers based on the poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole) (PCPDTBT) backbone.
    Advanced Energy Materials 07/2014; · 14.39 Impact Factor
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    ABSTRACT: Somatic cells are reprogrammed to induced pluripotent stem cells (iPSCs) by overexpression of a combination of defined transcription factors. We generated iPSCs from mouse embryonic fibroblasts (with Oct4-GFP reporter) by transfection of pCX-OSK-2A (Oct4, Sox2, and Klf4) and pCX-cMyc vectors. We could generate partially reprogrammed cells (XiPS-7), which maintained over 20 passages in a partially reprogrammed state; the cells were expressed Nanog but Oct4-GFP negative. When the cells were transferred to serum-free medium (with serum replacement and bFGF), the XiPS-7 cells converted to Oct4-GFP-positive iPSCs (XiPS-7c, fully reprogrammed cells) with ESC-like properties. During the conversion of XiPS-7 to XiPS-7c, we found several clusters of slowly reprogrammed genes, which were activated at later stages of reprogramming. Our results suggest that partial reprogrammed cells can be induced to full reprogramming status by serum-free medium, in which stem cell maintenance- and gamete generation-related genes were upregulated. These long-term expandable partially reprogrammed cells can be used to verify the mechanism of reprogramming.
    Stem cells and development. 06/2014;
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    ABSTRACT: Differentiated somatic cells can be reprogrammed into pluripotent stem cells by transduction of exogenous reprogramming factors. After induced pluripotent stem (iPS) cells are established, exogenous genes are silenced. In the pluripotent state, retroviral genes integrated in the host genome are kept inactive through epigenetic transcriptional regulation. In the present study, we tried to determine whether exogenous genes remain silenced or are reactivated upon loss of pluripotency or on differentiation by using an in vitro system. We induced differentiation of iPS cells into neural stem cells (NSCs) in vitro; the NSCs appeared morphologically indistinguishable from brain-derived NSCs and stained positive for the NSC markers Nestin and Sox2. These iPS cell-derived NSCs (iPS-NSCs) were also capable of differentiating into all three neural subtypes. Interestingly, iPS-NSCs spontaneously formed aggregates on long-term culture and showed reactivation of the Oct4-GFP marker, which was followed by the formation of ES cell-like colonies. The spontaneously reverted GFP-positive (iPS-NSC-GFP+) cells expressed high levels of pluripotency markers (Oct4 and Nanog) and formed germline chimeras, indicating that iPS-NSC-GFP+ cells had the same pluripotency as the original iPS cells. The reactivation of silenced exogenous genes was tightly correlated with the downregulation of DNA methyltransferases (Dnmts) during differentiation of iPS cells. This phenomenon was not observed in doxycycline-inducible iPS cells, where the reactivation of exogenous genes could be induced only by doxycycline treatment. These results indicate that pluripotency can be regained through reactivation of exogenous genes, which is associated with dynamic change of Dnmt levels during differentiation of iPS cells. Stem Cells 2014
    Stem Cells 06/2014; · 7.70 Impact Factor
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    ABSTRACT: The umbilical cord blood (UCB) cells have been reported to secret therapeutic signals, including a series of neurotrophic factors. This suggests the cell source provides suitable therapeutic environments for nerve regeneration that ultimately finds a possible cell therapy for nerves. In this study, we test a collagen hydrogel provides human UCB cells a proper 3D microenvironment that stimulates the release of various neurotrophic factors. When compared to 2D culture, the 3D hydrogel culture significantly enhanced the expression of a series of neutrophic factors, including neurotrophin-4, nerve growth factor, brain-derived neurotrophic factor, and ciliary neurotrophic factor as verified by the gene and protein analysis. To verify the effects of neurotrophic factors secretion, we allowed an indirect interaction of the UCB-environment with human neuronal precursor cells (hNPCs). Results showed significantly enhanced neurite outgrowth and neuronal differentiation of hNPCs. Collectively, our findings demonstrate that the collagen-based 3D hydrogel provides excellent microenvironment for UBC cells to release neurotrophic factors that will be ultimately useful for the neural repair and regeneration purposes.
    Biochemical and Biophysical Research Communications 04/2014; · 2.28 Impact Factor
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    ABSTRACT: Pluripotent stem cells can be derived from preimplantation and postimplantation mouse embryos. Embryonic stem cells (ESCs) derived from blastocysts are in a "naive" pluripotent state and meet all of the criteria for pluripotency, including the ability to generate live pups through tetraploid complementation. Epiblast stem cells (EpiSCs) derived from postimplantation epiblasts are in a "primed" pluripotent state. ESCs and EpiSCs show different phenotypes and gene expression patterns, and EpiSCs are thought to be less pluripotent than ESCs. In this study, we addressed whether EpiSCs can be differentiated into specialized cell types in vitro. To do this, we first derived EpiSCs from E5.5-6.5 mouse embryos containing the Oct4-GFP transgene. We found that EpiSCs expressed pluripotency markers and differentiated into all three germ layers in intro and in vivo. Interestingly, EpiSCs also efficiently differentiated into a homogenous population of neural stem cells (NSCs) in vitro. The EpiSC-derived NSCs (EpiSC-NSCs) expressed NSC markers (Nestin, Sox2, and Musashi), self-renewed for more than 20 passages, and differentiated into neuronal and glial neural cell subtypes in vitro. We then transplanted the EpiSC-NSCs into the neonatal mouse brains, and found that they were able to survive and differentiate into robust neurons and glial cells in the mouse brains, demonstrating that primed pluripotent EpiSCs efficiently form functional NSCs. We compared the global gene expression patterns of NSCs differentiated from EpiSC-NSCs, ESCs, and brain tissue and found that the expression patterns of most genes, including pluripotency and NSC specificity, were similarly clustered, but that the developmental process-related genes were distantly clustered. Moreover, the global gene expression pattern of brain-derived NSCs was more similar to that of ESC-derived NSCs than that of EpiSC-derived NSCs. Taken together, these results indicate that although NSCs, regardless of their origins, display very similar in vitro and in vivo differentiation properties, their global gene expression profiles may differ, depending on the pluripotency state, i.e., naive or primed.
    Stem Cell Research 01/2014; 12(2):506-516. · 4.47 Impact Factor
  • Organic Electronics 01/2014; · 3.84 Impact Factor
  • Source
    Sang Heon Han, Daejun Chang, Jong Soo Kim
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    ABSTRACT: The dispersion characteristics of hydrogen leaking through a small hole from a high-pressure source were investigated experimentally to develop guidelines for determining safety distances for hydrogen stations. Tests were carried out for leaking holes with diameters of 0.5, 0.7 and 1.0 mm and for release pressures of 100, 200, 300 and 400 bar. For these realistic hydrogen leaking conditions, the Froude numbers are so large that the buoyancy effect, manifested by the hydrogen jets bending upward, can be expected to be negligible. Flow visualization was performed using an Nd-YAG laser to confirm that the buoyancy effect was negligible. By letting a thin laser sheet penetrate the center line of a hydrogen jet conveying Al2O3 particles, the particles were illuminated and the hydrogen jet was visualized. The hydrogen concentration was measured by sampling hydrogen at five points along the jet centerline, based on the large Froude number. The measured data were always lower than the isentropic prediction.
    International Journal of Hydrogen Energy 01/2014; · 3.55 Impact Factor
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    ABSTRACT: Understanding the vertical phase separation of donor and acceptor compounds in organic photovoltaics is requisite for the control of charge transport behavior and the achievement of efficient charge collection. Here, the vertically phase-separated morphologies of poly(3-hexylthiophene):[6,6]phenyl-C61-butyric acid methyl ester (P3HT:PCBM) blend films are examined with transmission electron microtomography, dynamic secondary ion mass spectroscopy, and X-ray photoelectron spectroscopy. The 3D morphologies of the processed films are analyzed and how the solvent additive causes vertical segregation is determined. The photocurrent–voltage characteristics of the vertically segregated blend films are strongly dependent on the 3D morphological organization of the donor and acceptor compounds in the photoactive layer. This dependence is correlated with asymmetric carrier transport at the buried interface and the air surface in the vertically segregated blend films.
    Advanced Energy Materials 01/2014; 4(2). · 14.39 Impact Factor
  • Jong Soo Kim, Sung Il Park, Ki Young Shin
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    ABSTRACT: This paper focuses on a quantity flexibility contract through which two or more heterogeneous suppliers periodically deliver a single type of product to a buyer as promised in the contract. The buyer starts each period by informing each supplier of the order size for the period and the reservation quantity for all future periods within a planning horizon. The order size for the current period is finalized according to the amount previously reserved, although this amount can be increased or decreased by a predetermined percentage of the reservation amount. In this paper, a linear programming model including several key features of a quantity flexibility contract is developed from the buyer's perspective. A rolling-horizon implementation strategy is suggested for efficient implementation of the contract. Computational experiments demonstrate that the proposed method can be used to determine a cost effective solution for the buyer in a reasonable amount of time.
    Computers & Operations Research 01/2014; 41:98-108. · 1.91 Impact Factor
  • Sung Il Park, Jong Soo Kim
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    ABSTRACT: It is common practice in many industries to use a replenishment contract with a mechanism of capacity reservation. In this paper, we focus on a multi-period capacity reservation contract practiced between a buyer, who buys a single type of product and sells it to end-customers, and two or more heterogeneous suppliers, who produce and replenish the product as agreed upon contractually. In this paper, a mathematical model including several key features of a real contract is developed for a single supplier situation from the buyer’s perspective. It is then extended to a multiple supplier model for a system in which there are several heterogeneous suppliers with different capacities and prices. A rolling-horizon implementation strategy is suggested for the efficient application of the models. Extensive computational experiments demonstrate that the model and strategy can produce cost effective contractual terms for the buyer within a few seconds.
    Applied Mathematical Modelling 01/2014; 38(s 5–6):1866–1880. · 2.16 Impact Factor
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    ABSTRACT: The umbilical cord blood (UCB) cells have been reported to secret therapeutic signals, including a series of neurotrophic factors. This suggests the cell source provides suitable therapeutic environments for nerve regeneration that ultimately finds a possible cell therapy for nerves. In this study, we test a collagen hydrogel provides human UCB cells a proper 3D microenvironment that stimulates the release of various neurotrophic factors. When compared to 2D culture, the 3D hydrogel culture significantly enhanced the expression of a series of neutrophic factors, including neurotrophin-4, nerve growth factor, brain-derived neurotrophic factor, and ciliary neurotrophic factor as verified by the gene and protein analysis. To verify the effects of neurotrophic factors secretion, we allowed an indirect interaction of the UCB-environment with human neuronal precursor cells (hNPCs). Results showed significantly enhanced neurite outgrowth and neuronal differentiation of hNPCs. Collectively, our findings demonstrate that the collagen-based 3D hydrogel provides excellent microenvironment for UBC cells to release neurotrophic factors that will be ultimately useful for the neural repair and regeneration purposes.
    Biochemical and Biophysical Research Communications 01/2014; · 2.28 Impact Factor
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    ABSTRACT: We report a detailed characterization of the thin film morphology of all-polymer blend devices by applying a combined analysis of physical, chemical, optical, and charge transport properties. This is exemplified by considering a model system comprising poly(3-hexylthiophene) (P3HT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT). We show that the interactions between the two conjugated polymer components can be controlled by pre-forming the P3HT into highly ordered nanowire structures prior to blending with F8BT, and by varying the molecular weight of the F8BT. As a result, it is possible to produce films containing highly ordered P3HT with hole mobilities enhanced by three orders of magnitude over the pristine blends. Raman spectroscopy under resonant excitation conditions is used to probe the molecular order of both P3HT and F8BT phases within the blend films and these morphological studies are complemented by measurements of photocurrent generation. The resultant increase in photocurrent is associated with the enhanced charge carrier mobilities. The complementary analytical method demonstrated here is applicable to a wide range of polymer blend systems for all applications where the relationships between morphology and device performance are of interest.
    The Journal of Chemical Physics 08/2013; 139(6):064901. · 3.12 Impact Factor
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    Molecules and Cells 04/2013; · 2.21 Impact Factor
  • Source
    Sang Heon Han, Daejun Chang, Jong Soo Kim
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    ABSTRACT: A hydrogen supplying system for hydrogen fuel cell cars is anticipated to utilize highly pressurized hydrogen gas at pressures up to 700 bar. In this highly pressurized environment, large amount of hydrogen can be leaked from a relatively small hole caused by material and mechanical defects. A leaked hydrogen jet can reach very far in distance and the size of the leak plays an important role in determining the safety of hydrogen recharge facilities. This study numerically investigated the concentration distribution and the mass flux of hydrogen leaked from a highly pressurized source through a hole whose size is less than 1.0 mm. Numerical analysis was performed in axisymmetric coordinates on the assumption that the hydrogen jet has a huge Froude number and that buoyancy forces can be negligible. The predicted hydrogen concentration along the centerline of a hydrogen jet was compared with experimental data for verification of the numerical analysis and it satisfied the hyperbolic decay characteristics and matched the experiment well. The mass fluxes for the various hole lengths of this study were found to be 5%–20% less than those predicted using an isentropic flow assumption.
    International Journal of Hydrogen Energy 03/2013; 38(8):3503–3512. · 3.55 Impact Factor
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    ABSTRACT: Embryonic stem cells (ESCs) have the capacity to undergo directed differentiation into contracting cardiomyocytes. Therefore, functional cardiomyocytes derived from human embryonic stem cells (hESC-CMs) are potential candidates for cellular cardiomyoplasty to regenerate the myocardium after infarction. However, the directed differentiation of hESCs induces not only contracting cardiomyocytes but also other cell types. Thus, a risk of teratoma formation and oncologic transformation exists following the transplantation of hESC-CMs containing other cell lineages. In addition, the transplantation of hESC-CMs into the infarcted myocardium limits therapeutic efficacy due to low viability and poor engraftment. In this study, we established an efficient preparation method to obtain pure contracting cardiomyocytes from hESCs. We also developed a delivery system to achieve enhanced viability and a functional connection with the host myocardium after transplantation in a myocardial infarction model. A serum-free medium was used to obtain pure contracting cardiomyocytes from other cell lineages after the cardiac differentiation of hESCs. Aggregates of purified hESC-CMs were formed, and then the expression of cardiomyocyte-specific markers and the viability of the aggregated CMs were examined in hypoxic conditions. In addition, we determined whether the viability of the hESC-CMs and their ability to engraft with the host myocardium could be enhanced by transplanting them as aggregates in a myocardial infarction model. The therapeutic efficacy of the cardiomyocytes was examined by immunohistochemical analyses as well as physiological analyses of left-ventricular function. We found that the transplantation of contracting hESC-CM aggregates improved their survival and function in infarcted rat hearts in comparison to the transplantation of dissociated cells. Our method using hESC-CMs can be considered an effective strategy for clinical applications without critical barriers.
    Biomaterials 03/2013; · 8.31 Impact Factor
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    ABSTRACT: The performances of organic photovoltaic cells were improved by matching the energy levels of three photon-harvesting layers with distinct light absorption spectra. Pentacene, phthalocyanine, and C70, which have shallow, intermediate, and deep energy levels, respectively, were introduced as photon harvesting layers to form a cascade structure and secure appropriate band offsets at all interfaces. This architecture yielded higher values of the open-circuit voltage and short-circuit current density than a standard bilayer structure based on pentacene and C70. A device prepared with metal-free phthalocyanine performed better than a device with Cu phthalocyanine because the energy levels were more appropriately tuned.
    Chemical Physics Letters 02/2013; 557:88–91. · 2.15 Impact Factor
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    ABSTRACT: Modulation of electronic structures and surface properties of transparent carbon nanotube films is a challenging issue for their application in optoelectronic devices. Here, we report, for the first time, that graphene oxide (GO) nanosheets play the role of a p-doping agent and surface energy modifier of single-walled carbon nanotube (SWCNT)-based transparent conducting electrodes (TCEs). The deposition of highly oxidized, small-sized (i.e., diameter of less than 500 nm) GO nanosheets onto a SWCNT network film reduces the sheet resistance of the pristine film to 60% of its original value by p-doping. The modified TCEs exhibit an outstanding optoelectronic feature of high conductivity with high transparency. Moreover, the wettability of the electrode surface was also noticeably increased, which is advantageous for the solution-based processing of organic electronics. Furthermore, the organic photovoltaic (OPV) cells with the GO-doped SWCNT anodes on flexible substrates were successfully demonstrated. In stark contrast to a power conversion efficiency of 0.44% for pristine SWCNT anodes, GO-doped SWCNT anodes show a drastically enhanced power conversion efficiency of 2.7%.
    Nanoscale 11/2012; · 6.73 Impact Factor
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    ABSTRACT: We study the molecular order and morphology in poly(3-hexylthiophene) (P3HT), poly(3-hexylselenophene) (P3HS) thin films and their blends with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). We find that substitution of the sulphur atoms in the thiophene rings of P3HT by heavy selenium atoms increases the tendency of the molecules to form better ordered phase; interestingly, their overall fraction of ordered phase is however much lower than P3HT-based films. The higher tendency of P3HS molecules to order (aggregate) is consistent with more planar chain conformation simulated. The lower fraction of ordered phase (or the higher fraction of disordered phase) in P3HS-based films is clearly identified by in-plane skeleton Raman modes under resonant excitation conditions; i.e. a smaller ratio of the C=C modes associated with the ordered (~1422 cm-1) and disordered (~1446 cm-1) phases (I1422 cm-1/I1446 cm-1 = 1.4 for P3HS and 0.6 for P3HS:PCBM), compared with P3HT-based films (I1449 cm-1/I1470 cm-1 = 2.5 for P3HT and 1.0 for P3HT:PCBM) and a larger Raman dispersion of the C=C mode: P3HS (17 cm-1) vs P3HT (6 cm-1) and P3HS:PCBM (36 cm-1) vs P3HT:PCBM films (23 cm-1). The higher fraction of disordered phase in P3HS prevents the formation of micron-sized PCBM aggregates in blend films during thermal annealing. Importantly, this lower fraction, but better quality of ordered phase in P3HS molecules strongly influences P3HS:PCBM photovoltaic performance, producing smaller short circuit current (Jsc) in pristine devices, but much larger increase in Jsc after annealing compared to P3HT:PCBM devices. Our results clarify the effects of heavy atom substitution in low band gap polymers and their impact on blend morphology and device performance. Furthermore, our study clearly demonstrates Resonant Raman spectroscopy as a simple, but powerful structural probe which provides important information about "fraction/ quantity of ordered phase" of molecules, not easily accessible using traditional X-ray based techniques.
    ACS Nano 10/2012; · 12.03 Impact Factor
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    ABSTRACT: MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression at post-transcriptional levels through mRNA degradation or translation inhibition. Little is known regarding miRNA participation in regulating hematopoietic, or more specifically erythroid differentiation. This study was aimed at identifying erythroid lineage-specific miRNAs expressed during in vitro erythropoiesis using human embryonic stem cells (hESCs) and human umbilical cord blood (CB) CD34+ cells. CD34+ hematopoietic cells were produced from hESCs in vitro and subsequently induced to differentiate into erythroid cells by culture in sequence on OP9 feeder cells and then with mesenchymal stromal cells (MSC) in the presence of cytokines. Expression profiles of erythroid lineage-specific miRNAs were analyzed by quantitative PCR during in vitro differentiation. Expression levels of miR-142-3p, miR-142-5p, miR-146a and miR-451 were dynamically changed during differentiation of hESCs to CD34+ hematopoietic cells, and in subsequent differentiation of the CD34+ cells into the erythroid lineage. This suggests that these four miRNAs might be involved in regulating erythropoiesis.
    Molecules and Cells 07/2012; 34(2):177-83. · 2.21 Impact Factor
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    ABSTRACT: In this study, the immunological effect of silver nanoparticles on innate immunity was investigated using primary human monocytes. After exposure to silver nanoparticles, production of IL-1β, a critical cytokine involved in induction of innate immunity, significantly increased as particle size decreased. These results suggest that silver nanoparticles may evoke an immunologically active state. The size effect of silver nanoparticles on IL-1β production was also further investigated. 5 nm and 28 nm silver nanoparticles induced inflammasome formation and subsequent caspase-1 activation. Using inhibitors, we found exposure to silver nanoparticles caused leakage of cathepsins from lysosomes and efflux of intracellular K(+). These two events induced superoxide within mitochondrial membranes, leading to inflammasome formation. 5 nm silver nanoparticles produced more hydrogen peroxide and were more cytotoxic than 28 nm silver nanoparticles, suggesting the balance between superoxide and hydrogen peroxide governs cell fate, death or activation. Moreover, these findings also suggest that the immunological significance of silver nanoparticles should be considered with respect to their capacity to synergistically activate immune responses.
    Biomaterials 07/2012; 33(28):6858-67. · 8.31 Impact Factor

Publication Stats

702 Citations
322.44 Total Impact Points

Institutions

  • 2014
    • Dankook University
      • College of Dentistry
      Eidō, North Chungcheong, South Korea
  • 2013–2014
    • Konkuk University
      • Department of Animal Biotechnology
      Sŏul, Seoul, South Korea
  • 2011–2014
    • Imperial College London
      • Centre for Plastic Electronics
      Londinium, England, United Kingdom
  • 2007–2014
    • Pohang University of Science and Technology
      • • Department of Chemical Engineering
      • • School of Environmental Science and Engineering
      Geijitsu, North Gyeongsang, South Korea
  • 2005–2014
    • Hanyang University
      • • Major in Anatomy and Cell Biology
      • • Department of Food and Nutrition
      • • Department of Biomedical Science
      • • Department of Industrial Engineering
      Sŏul, Seoul, South Korea
    • Korea Institute of Science and Technology
      Sŏul, Seoul, South Korea
  • 2011–2013
    • CHA University
      • Department of Biomedical Science
      Sŏul, Seoul, South Korea
  • 2007–2013
    • Hankuk University of Foreign Studies
      Sŏul, Seoul, South Korea
  • 2012
    • Korea Electrotechnology Research Institute-KERI
      • Advanced Medical Device Research Center
      Tsau-liang-hai, Busan, South Korea
  • 2002–2012
    • Ajou University
      • • Department of Gastroenterology
      • • Department of Pediatrics
      Seoul, Seoul, South Korea
  • 2005–2010
    • Sungkyunkwan University
      • • Samsung Medical Center
      • • Department of Neurosurgery
      Seoul, Seoul, South Korea
  • 2009
    • Ulsan University Hospital
      Urusan, Ulsan, South Korea
  • 2008
    • City of Hope National Medical Center
      • Department of Molecular Medicine
      Duarte, CA, United States
  • 2004–2008
    • University of Ulsan
      • • Department of Biological Sciences
      • • Department of Biological Science
      Ulsan, Ulsan, South Korea
    • National Fisheries Research and Development Institution
      Sŏul, Seoul, South Korea
  • 2003–2007
    • Korea University
      • Department of Materials Science and Engineering
      Sŏul, Seoul, South Korea
    • Kyungpook National University
      • College of Agriculture and Life Sciences
      Daikyū, Daegu, South Korea
  • 1999–2000
    • Korea Advanced Institute of Science and Technology
      • Department of Computer Science
      Seoul, Seoul, South Korea