Publications by authors named "Gun Hee Lee"

26 Publications

  • Page 1 of 1

From Diagnosis to Treatment: Recent Advances in Patient-Friendly Biosensors and Implantable Devices.

ACS Nano 2021 Feb 3;15(2):1960-2004. Epub 2021 Feb 3.

Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea.

Patient-friendly medical diagnostics and treatments have been receiving a great deal of interest due to their rapid and cost-effective health care applications with minimized risk of infection, which has the potential to replace conventional hospital-based medical procedures. In particular, the integration of recently developed materials into health care devices allows the rapid development of point-of-care (POC) sensing platforms and implantable devices with special functionalities. In this review, the recent advances in biosensors for patient-friendly diagnosis and implantable devices for patient-friendly treatment are discussed. Comprehensive analysis of portable and wearable biosensing platforms for patient-friendly health monitoring and disease diagnosis is provided, including topics such as materials selection, device structure and integration, and biomarker detection strategies. Moreover, specific challenges related to each biological fluid for wearable biosensor-based POC applications are presented. Also, advances in implantable devices, including recent materials development and wireless communication strategies, are discussed. Furthermore, various patient-friendly surgical and treatment approaches are reviewed, such as minimally invasive insertion and mounting, electrical and optical modulations, and post-operation health monitoring. Finally, the challenges and future perspectives toward the development of the patient-friendly diagnosis and treatment are provided.
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http://dx.doi.org/10.1021/acsnano.0c06688DOI Listing
February 2021

Patterns of Integrative Korean Medicine Practice for Anxiety Disorders: A Survey among Korean Medicine Doctors (KMDs) in Korea.

Evid Based Complement Alternat Med 2020 5;2020:3140764. Epub 2020 Oct 5.

Department of Neuropsychiatry, College of Korean Medicine, Dong-Guk University, 32, Dongguk-ro, Ilsandong-gu, Goyang-si, Gyeonggi-do 10326, Republic of Korea.

Anxiety disorder is known as the most common disease among psychiatric disorders. However, many studies have not been conducted in the Korean medicine area. This study explores the current state of anxiety disorder treatments of Korean medicine through a survey research. The survey for Korean medicine doctors (KMDs) on Korean medicine (KM) diagnosis and treatments for anxiety disorder was conducted online from December 21, 2016, to December 29, 2016. The results were divided into two groups, KMDs and Korean medicine neuropsychiatric specialists (KMNPS), and comparatively analyzed. Self-evaluation and counseling were the most common in both diagnostic methods and evaluation of treatment effects, and KMNPS tended to make extensive use of objective indicators. There was no difference in the rate of psychiatric medication use among the patients between KMD and KMNPS. The main reason for patients wanting KM treatment was the tapering cessation of psychiatric medications. The most common treatments were acupuncture, herbal medicine, and moxibustion, in addition to dry cupping in KMD and psychotherapy in KMNPS. The most important factor for treatment was herbal medicine treatment, followed by rapport formation in KMD and patient's temperament in KMNPS. Opinions on various items were presented as treatment barriers, and KMNPS tended to think more importantly about the patient's family problems. For the items to be additionally trained in the future, KMD chose the diagnostic tools and KMNPS chose psychotherapies. This study is the first study to analyze the clinical patterns for anxiety disorder in KMDs. KMD and KMNPS showed similar patterns in the perception, diagnosis, and treatment of anxiety disorders, but KMNPS tended to use objective indicators and psychotherapy more actively. Further clinical studies for the development of clinical guidelines should be additionally required.
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http://dx.doi.org/10.1155/2020/3140764DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7556402PMC
October 2020

PGAP6, a GPI-specific phospholipase A2, has narrow substrate specificity against GPI-anchored proteins.

J Biol Chem 2020 10 18;295(42):14501-14509. Epub 2020 Aug 18.

Research Institute for Microbial Diseases, Osaka University, Osaka, Japan

PGAP6, also known as TMEM8A, is a phospholipase A2 with specificity to glycosylphosphatidylinositol (GPI) and expressed on the surface of various cells. CRIPTO, a GPI-anchored co-receptor for a morphogenic factor Nodal, is a sensitive substrate of PGAP6. PGAP6-mediated shedding of CRIPTO plays a critical role in an early stage of embryogenesis. In contrast, CRYPTIC, a close family member of CRIPTO, is resistant to PGAP6. In this report, chimeras between CRIPTO and CRYPTIC and truncate mutants of PGAP6 were used to demonstrate that the Cripto-1/FRL1/Cryptic domain of CRIPTO is recognized by an N-terminal domain of PGAP6 for processing. We also report that among 56 human GPI-anchored proteins tested, only glypican 3, prostasin, SPACA4, and contactin-1, in addition to CRIPTO, are sensitive to PGAP6, indicating that PGAP6 has a narrow specificity toward various GPI-anchored proteins.
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http://dx.doi.org/10.1074/jbc.RA120.014643DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7573272PMC
October 2020

Deep-Learning-Based Deconvolution of Mechanical Stimuli with TiCT MXene Electromagnetic Shield Architecture Dual-Mode Wireless Signal Variation Mechanism.

ACS Nano 2020 09 27;14(9):11962-11972. Epub 2020 Aug 27.

Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea.

Passive component-based soft resonators have been spotlighted in the field of wearable and implantable devices due to their remote operation capability and tunable properties. As the output signal of the resonator-based wireless communication device is given in the form of a vector (, a spectrum of reflection coefficient), multiple information can, in principle, be stored and interpreted. Herein, we introduce a device that can deconvolute mechanical stimuli from a single wireless signal using dual-mode operation, specifically enabled by the use of TiCT MXene. MXene's strong electromagnetic shielding effect enables the resonator to simultaneously measure pressure and strain without overlapping its output signal, unlike other conductive counterparts that are deficient in shielding ability. Furthermore, convolutional neural-network-based deep learning was implemented to predict the pressure and strain values from unforeseen output wireless signals. Our MXene-integrated wireless device can also be utilized as an on-skin mechanical stimuli sensor for rehabilitation monitoring after orthopedic surgery. The dual-mode signal variation mechanism enabled by integration of MXene allows wireless communication systems to efficiently handle various information simultaneously, through which multistimuli sensing capability can be imparted into passive component-based wearable and implantable electrical devices.
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http://dx.doi.org/10.1021/acsnano.0c05105DOI Listing
September 2020

Sulfated syndecan 1 is critical to preventing cellular senescence by modulating fibroblast growth factor receptor endocytosis.

FASEB J 2020 08 12;34(8):10316-10328. Epub 2020 Jun 12.

Department of Molecular Medicine, Inha University College of Medicine, Incheon, Korea.

Cellular senescence can be triggered by various intrinsic and extrinsic stimuli. We previously reported that silencing of 3'-phosphoadenosine 5'-phosphosulfate synthetase 2 (PAPSS2) induces cellular senescence through augmented fibroblast growth factor receptor 1 (FGFR1) signaling. However, the exact molecular mechanism connecting heparan sulfation and cellular senescence remains unclear. Here, we investigated the potential involvement of heparan sulfate proteoglycans (HSPGs) in augmented FGFR1 signaling and cellular senescence. Depletion of several types of HSPGs revealed that cells depleted of syndecan 1 (SDC1) exhibited typical senescence phenotypes, and those depleted of PAPSS2-, SDC1-, or heparan sulfate 2-O sulfotransferase 1 (HS2ST1) showed decreased FGFR1 internalization along with hyperresponsiveness to and prolonged activation of fibroblast growth factor 2 (FGF2)-stimulated FGFR1- v-akt murine thymoma viral oncogene homolog (AKT) signaling. Clathrin- and caveolin-mediated FGFR1 endocytosis contributed to cellular senescence through the FGFR1-AKT-p53-p21 signaling pathway. Dynasore treatment triggered senescence phenotypes, augmented FGFR1-AKT-p53-p21 signaling, and decreased SDC1 expression. Finally, the replicatively and prematurely senescent cells were characterized by decreases of SDC1 expression and FGFR1 internalization, and an increase in FGFR1-AKT-p53-p21 signaling. Together, our results demonstrate that properly sulfated SDC1 plays a critical role in preventing cellular senescence through the regulation of FGFR1 endocytosis.
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http://dx.doi.org/10.1096/fj.201902714RDOI Listing
August 2020

Comparative study on biodegradation and biocompatibility of multichannel calcium phosphate based bone substitutes.

Mater Sci Eng C Mater Biol Appl 2020 May 28;110:110694. Epub 2020 Jan 28.

Department of Regenerative Medicine, College of Medicine, Soonchunhyang University, Cheonan, South Korea; Institute of Tissue Regeneration, College of Medicine, Soonchunhyang University, Cheonan, South Korea. Electronic address:

The objective of this study was to fabricate multichannel biphasic calcium phosphate (BCP) and β-tricalcium phosphate (TCP) bone substitutes and compare their long-term biodegradation and bone regeneration potentials. Multi-channel BCP and TCP scaffolds were fabricated by multi-pass extrusion process. Both scaffolds were cylindrical with a diameter of 1-mm, a length of 1-mm, and seven interconnected channels. Morphology, chemical composition, phase, porosity, compressive strength, ion release behavior, and in-vitro biocompatibility of both scaffolds were studied. In-vivo biodegradation and bone regeneration efficacies of BCP and TCP were also evaluated using a rabbit model for 1 week, 1 month, and 6 months. BCP exhibited superior compressive strength compared to TCP scaffold. TCP showed higher release of both calcium ions and phosphorous ions than BCP in SBF solution. Both scaffolds showed excellent in-vitro biocompatibility and upregulated the expression of osteogenic markers of MC3T3-E1 cells. In-vivo studies revealed that both cylindrical TCP and BCP scaffolds were osteoconductive and supported new bone formation. Micro-CT data showed that the bone-regeneration efficacy of TCP was higher at one month and at six months after implantation. Histological examination confirmed that TCP degraded faster and had better bone regeneration than BCP after 6 months.
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http://dx.doi.org/10.1016/j.msec.2020.110694DOI Listing
May 2020

Boron Nitride as a Passivation Capping Layer for AlGaN/GaN High Electron Mobility Transistors.

J Nanosci Nanotechnol 2020 Jul;20(7):4450-4453

Nano-Photonics Convergence Technology Group, Korea Institute of Industrial Technology, Gwangju 61012, South Korea.

We report on the electrical characteristics of AlGaN/GaN high-electron mobility transistors (HEMTs) with hexagonal boron nitride (h-BN) as a passivation capping layer. The HEMTs with h-BN layers showed an increase in current drainage and 103-times reduction in the gate-leakage current compared with those of conventional unpassivated HEMTs. Moreover, the extrinsic transconductance and the pulse responses were improved due to the reduced charge-trapping effect at the surface of HEMTs. From our observations, the h-BN can be used as a passivation capping layer for high-power electronic devices.
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http://dx.doi.org/10.1166/jnn.2020.17587DOI Listing
July 2020

Parallel Signal Processing of a Wireless Pressure-Sensing Platform Combined with Machine-Learning-Based Cognition, Inspired by the Human Somatosensory System.

Adv Mater 2020 Feb 16;32(8):e1906269. Epub 2019 Dec 16.

Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea.

Inspired by the human somatosensory system, pressure applied to multiple pressure sensors is received in parallel and combined into a representative signal pattern, which is subsequently processed using machine learning. The pressure signals are combined using a wireless system, where each sensor is assigned a specific resonant frequency on the reflection coefficient (S ) spectrum, and the applied pressure changes the magnitude of the S pole with minimal frequency shift. This allows the differentiation and identification of the pressure applied to each sensor. The pressure sensor consists of polypyrrole-coated microstructured poly(dimethylsiloxane) placed on top of electrodes, operating as a capacitive sensor. The high dielectric constant of polypyrrole enables relatively high pressure-sensing performance. The coils are vertically stacked to enable the reader to receive the signals from all of the sensors simultaneously at a single location, analogous to the junction between neighboring primary neurons to a secondary neuron. Here, the stacking order is important to minimize the interference between the coils. Furthermore, convolutional neural network (CNN)-based machine learning is utilized to predict the applied pressure of each sensor from unforeseen S spectra. With increasing training, the prediction accuracy improves (with mean squared error of 0.12), analogous to humans' cognitive learning ability.
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http://dx.doi.org/10.1002/adma.201906269DOI Listing
February 2020

Nonpolar Organic Dispersion of 2D TiCT MXene Flakes Simultaneous Interfacial Chemical Grafting and Phase Transfer Method.

ACS Nano 2019 Dec 22;13(12):13818-13828. Epub 2019 Nov 22.

KU-KIST Graduate School of Converging Science and Technology , Korea University , Seoul 02841 , Republic of Korea.

Herein, we demonstrate a simple and versatile way for preparing stable TiCT MXene dispersions in nonpolar organic solvents through a simultaneous interfacial chemical grafting reaction and phase transfer method. Alkylphosphonic acid ligands were chemically grafted on the hydroxyl terminal groups of TiCT flakes at the liquid-liquid interface between water and water-immiscible organic medium to form a covalent Ti-O-P bond interfacial nucleophilic addition and sequential condensation reaction at room temperature; the surface-functionalized TiCT flakes concurrently migrated from the aqueous phase to the organic phase. Unlike conventional surface chemical modification methods that require many complex and tedious steps, this is a simple and easy process for fabricating a TiCT organic dispersion in various organic solvents, from highly polar to nonpolar. The nonpolar TiCT dispersion in chloroform also exhibits strong oxidation resistance and stable long-term storage. This approach provides an opportunity for preparing MXene nanocomposites with nonpolar polymeric matrices that are soluble in organic media for future applications such as stretchable electrode.
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http://dx.doi.org/10.1021/acsnano.9b04088DOI Listing
December 2019

Boron nitride nanotubes as a heat sinking and stress-relaxation layer for high performance light-emitting diodes.

Nanoscale 2017 Nov;9(42):16223-16231

Applied Quantum Composites Research Center, Korea Institute of Science and Technology, Jeonbuk 55324, Republic of Korea.

High-density threading dislocations, the presence of biaxial compressive strain, and heat generation are the major limitations obstructing the performance and reliability of light emitting diodes (LEDs). Herein, we demonstrate a facile epitaxial lateral overgrowth (ELOG) method by incorporating boron nitride nanotubes (BNNTs) on a sapphire substrate by spray coating to resolve the above issues. Atomic force microscopy, X-ray diffraction, micro-Raman, and photoluminescence measurements confirmed the growth of a high quality GaN epilayer on the BNNT-coated sapphire substrate with reduced threading dislocations and compressive strain owing to the ELOG process. GaN LEDs fabricated using this approach showed a significant enhancement in the internal quantum efficiency and electroluminescence intensity compared to conventional LEDs grown on sapphire. Moreover, reduced efficiency droop and surface temperature at high injection currents were achieved due to the excellent thermal stability and conductivity of BNNTs. Based on our findings we infer that the BNNTs would be a promising material for high power devices vulnerable to self-heating problems.
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http://dx.doi.org/10.1039/c7nr04508eDOI Listing
November 2017

A hybrid composite system of biphasic calcium phosphate granules loaded with hyaluronic acid-gelatin hydrogel for bone regeneration.

J Biomater Appl 2017 Oct 24;32(4):433-445. Epub 2017 Sep 24.

1 Department of Regenerative Medicine, College of Medicine, Soonchunhyang University, Chungnam, Cheonan City, Republic of Korea.

An ideal bone substitute should be made of biocompatible materials that mimic the structure, characteristics, and functions of natural bone. Many researchers have worked on the fabrication of different bone scaffold systems including ceramic-polymer hybrid system. In the present study, we incorporated hyaluronic acid-gelatin hydrogel to micro-channeled biphasic calcium phosphate granules as a carrier to improve cell attachment and proliferation through highly interconnected porous structure. This hybrid system is composed of ceramic biphasic calcium phosphate granules measuring 1 mm in diameter with seven holes and hyaluronic acid-gelatin hydrogel. This combination of biphasic calcium phosphate and hyaluronic acid-gelatin retained suitable characteristics for bone regeneration. The resulting scaffold had a porosity of 56% with a suitable pore sizes. The mechanical strength of biphasic calcium phosphate granule increased after loading hyaluronic acid-gelatin from 4.26 ± 0.43 to 6.57 ± 0.25 MPa, which is highly recommended for cancellous bone substitution. Swelling and degradation rates decreased in the hybrid scaffold compared to hydrogel due to the presence of granules in hybrid scaffold. In vitro cytocompatibility studies were observed by preosteoblasts (MC3T3-E1) cell line and the result revealed that biphasic calcium phosphate/hyaluronic acid-gelatin significantly increased cell growth and proliferation compared to biphasic calcium phosphate granules. Analysis of micro-computed tomography data and stained tissue sections from the implanted samples showed that the hybrid scaffold had good osseointegration and better bone formation in the scaffold one and two months postimplantation. Histological section confirmed the formation of dense collagenous tissue and new bone in biphasic calcium phosphate/hyaluronic acid-gelatin scaffolds at two months. Our study demonstrated that such hybrid biphasic calcium phosphate/hyaluronic acid-gelatin scaffold is a promising system for bone regeneration.
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http://dx.doi.org/10.1177/0885328217730680DOI Listing
October 2017

Apathy in people with epilepsy and its clinical significance: A case-control study.

Seizure 2017 Oct 8;51:80-86. Epub 2017 Aug 8.

Department of Neurology, School of Medicine, Kyungpook National University, Daegu, Republic of Korea. Electronic address:

Purpose: Apathy as a state of decreased motivation has not been highlighted in people with epilepsy (PWE). We investigated its clinical significance in PWE.

Methods: We invited adult PWE who had been administered antiepileptic drugs (AEDs) for at least 1year and compared them with age- and gender-matched healthy controls. Eligible participants completed several questionnaires including the Apathy Evaluation Scale-Self (AES-S), the Korean version of the Neurological Disorders Depression Inventory for Epilepsy (K-NDDI-E), the Generalized Anxiety Disorder-7 (GAD-7), the Epworth Sleepiness Scale (ESS), and the Insomnia Severity Index (ISI), and the Quality of Life in Epilepsy-10 (QOLIE-10). We investigated the degree of interictal apathy in PWE compared with controls and identified its predictors. We also measured the impact of apathy on patients' QOL.

Results: The mean overall AES-S score in PWE was similar to that of controls. However, the score was significantly higher in patients with uncontrolled epilepsy than controls (p<0.01). Among subscale scores of the AES-S, the mean behavioral score was significantly higher in PWE than controls (p<0.01). Education level, employment, household income, disease duration, AED-related factors, seizure control, and scores of the K-NDDI-E, GAD-7, ESS, and ISI were associated with the overall AES-S score by univariate analyses. However, major predictors were the K-NDDI-E (β=0.476, p<0.001) and duration of AED intake (β=0.151, p<0.01). The degree of apathy was significantly higher in patients receiving AEDs for 20 years or more than those receiving AEDs for 1-9 years (p<0.01). The overall AES-S score was inversely correlated with the overall QOLIE-10 score (p<0.001).

Conclusion: Duration of AED intake in PWE seems to be a critical factor for apathy regardless of comorbid depression.
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http://dx.doi.org/10.1016/j.seizure.2017.08.003DOI Listing
October 2017

Incorporation of BMP-2 loaded collagen conjugated BCP granules in calcium phosphate cement based injectable bone substitutes for improved bone regeneration.

Mater Sci Eng C Mater Biol Appl 2017 Aug 1;77:713-724. Epub 2017 Apr 1.

Department of Regenerative Medicine, College of Medicine, Soonchunhyang University, 366-1 Ssangyong dong, Cheonan 330-090, South Korea; Institute of Tissue Regeneration, College of Medicine, Soonchunhyang University, 366-1 Ssangyong dong, Cheonan 330-090, South Korea. Electronic address:

The objective of the present study was to incorporate surface modified porous multichannel BCP granule into CPC to enhance its in vivo biodegradation and bone tissue growth. The multichannel BCP granule (15wt%) was first coated with collagen subsequent to BMP-2 loading (ccMCG-B). It was then embedded into CPC to form CPC-ccMCG-B system. The newly developed CPC-ccMCG-B system was then examined for SEM, EDX, XRD, setting time, compressive strength, injectability, pH change, BMP-2 release, in vitro as well as in vivo studies and further compared with CPC. Optimized CPC (0.45mL/g) was found based on setting time and compressive strength studies. In vivo studies exhibited improved new bone formation and better degradation of CPC after 2 and 4weeks of implantation as compared to CPC as resulted from effective BMP-2 signaling. Our results suggest that CPC-ccMCG-B system might be used as a promising injectable bone substitutes in clinical applications.
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http://dx.doi.org/10.1016/j.msec.2017.03.296DOI Listing
August 2017

Comparative Bone Regeneration Potential Studies of Collagen, Heparin, and Polydopamine-Coated Multichannelled BCP Granules.

ASAIO J 2018 Jan/Feb;64(1):115-121

From the Department of Regenerative Medicine, College of Medicine and Institute of Tissue Regeneration, Soonchunhyang University, Cheonan, South Korea.

The current study is a comparative assessment of the bone regeneration potentiality of bone substitutes composed of bioactive polymer-coated biphasic calcium phosphate (BCP) granules. The bone substitutes were primarily composed of multichanneled BCP granules, which were coated separately with biochemical polymer coatings, namely collagen, heparin, or polydopamine (PD), using chemical methods. The morphologic features and chemical structure of the granules and surface coatings were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. The biological characterizations in terms of cellular interaction with the bone substitutes in vitro (MTT assay and proliferation) and in vivo (bone regeneration efficacy) were performed and compared with uncoated BCP granules. It was found that PD-coated BCP granules were superior to the others with respect to promoting more rapid healing. Therefore, PD multichannel BCP granule system can be used as a promising injectable bone substitute for clinical applications.
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http://dx.doi.org/10.1097/MAT.0000000000000582DOI Listing
July 2018

A GPI processing phospholipase A2, PGAP6, modulates Nodal signaling in embryos by shedding CRIPTO.

J Cell Biol 2016 Dec 23;215(5):705-718. Epub 2016 Nov 23.

Research Institute for Microbial Diseases, Osaka University, Suita, Osaka 565-0871, Japan

Glycosylphosphatidylinositol-anchored proteins (GPI-APs) can be shed from the cell membrane by GPI cleavage. In this study, we report a novel GPI-processing enzyme, termed post-glycosylphosphatidylinositol attachment to proteins 6 (PGAP6), which is a GPI-specific phospholipase A2 mainly localized at the cell surface. CRIPTO, a GPI-AP, which plays critical roles in early embryonic development by acting as a Nodal coreceptor, is a highly sensitive substrate of PGAP6, whereas CRYPTIC, a close homologue of CRIPTO, is not sensitive. CRIPTO processed by PGAP6 was released as a lysophosphatidylinositol-bearing form, which is further cleaved by phospholipase D. CRIPTO shed by PGAP6 was active as a coreceptor in Nodal signaling, whereas cell-associated CRIPTO activity was reduced when PGAP6 was expressed. Homozygous Pgap6 knockout mice showed defects in early embryonic development, particularly in the formation of the anterior-posterior axis, which are common features with Cripto knockout embryos. These results suggest PGAP6 plays a critical role in Nodal signaling modulation through CRIPTO shedding.
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http://dx.doi.org/10.1083/jcb.201605121DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5147002PMC
December 2016

The role of graphene formed on silver nanowire transparent conductive electrode in ultra-violet light emitting diodes.

Sci Rep 2016 07 8;6:29464. Epub 2016 Jul 8.

Applied Quantum Composites Research Center, Korea Institute of Science and Technology, Jeonbuk 565-905, South Korea.

This paper reports a highly reliable transparent conductive electrode (TCE) that integrates silver nanowires (AgNWs) and high-quality graphene as a protecting layer. Graphene with minimized defects and large graphene domains has been successfully obtained through a facile two-step growth approach. Ultraviolet light emitting diodes (UV-LEDs) were fabricated with AgNWs or hybrid electrodes where AgNWs were combined with two-step grown graphene (A-2GE) or conventional one-step grown graphene (A-1GE). The device performance and reliability of the UV-LEDs with three different electrodes were compared. The A-2GE offered high figure of merit owing to the excellent UV transmittance and reduced sheet resistance. As a consequence, the UV-LEDs made with A-2GE demonstrated reduced forward voltage, enhanced electroluminescence (EL) intensity, and alleviated efficiency droop. The effects of joule heating and UV light illumination on the electrode stability were also studied. The present findings prove superior performance of the A-2GE under high current injection and continuous operation of UV LED, compared to other electrodes. From our observation, the A-2GE would be a reliable TCE for high power UV-LEDs.
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http://dx.doi.org/10.1038/srep29464DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4937441PMC
July 2016

Carbon-nanotube-assisted nanoepitaxy of Si-doped GaN for improved performance of InGaN/GaN light-emitting diodes.

Nanotechnology 2016 Jul 27;27(27):275602. Epub 2016 May 27.

School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center, Chonbuk National University, Jeonju 54896, Korea.

Using single-walled carbon nanotubes (SWCNTs) as nanomasks on an undoped GaN template, a significant biaxial stress relaxation was achieved in the subsequently-grown Si-doped n-GaN layer. Enhanced near band edge (NBE) emission intensity, similar free carrier concentrations, and the reduced peak width of the asymmetric (102) crystallographic plane all confirmed the suppression of threading dislocations due to the nanoepitaxial growth process. Temperature-dependent photoluminescence (PL) revealed improved internal quantum efficiency (IQE) of InGaN/GaN multi-quantum wells (MQWs) grown on this n-GaN layer. Furthermore, enhanced light output power and a remarkable reduction in efficiency droop were observed for the blue light-emitting diodes (LEDs), especially at higher injection currents. Our results emphasize the strong potential for SWCNTs as nanomasks in the heteroepitaxy of GaN-based devices without the exploitation of complicated lithography or etching processes.
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http://dx.doi.org/10.1088/0957-4484/27/27/275602DOI Listing
July 2016

Dual-Wavelength Light Emission from CdSe/ZnS Quantum Dots on Blue Light-Emitting Diodes.

J Nanosci Nanotechnol 2015 Dec;15(12):10037-40

We fabricated light-emitting device by using CdSe/ZnS quantum dots (QDs) on InGaN/GaN blue light-emitting diodes (LEDs) for converting blue emission into green emission. By adding Au nanoparticles (ANPs) to generate localized surface plasmon mode, the integrated intensity of green emission of LEDs with CdSe/ZnS QDs on ANPs is enhanced by about 55%, without any drawback in electrical characteristics of LEDs. This result is attributed to an increased conversion efficiency by resonance coupling between localized surface plasmons in ANPs and excitons in CdSe/ZnS QDs.
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http://dx.doi.org/10.1166/jnn.2015.10662DOI Listing
December 2015

Efficient stress-relaxation in InGaN/GaN light-emitting diodes using carbon nanotubes.

Nanoscale 2015 Oct;7(37):15099-105

School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center, Chonbuk National University, Jeonju 561-756, Republic of Korea.

A facile method to facilitate epitaxial lateral overgrowth (ELO) of gallium nitride (GaN) was developed by using single-walled carbon nanotubes (SWCNTs). High-quality GaN was achieved on sapphire by simply coating the SWCNTs as an intermediate layer for stress and defect mitigation. SWCNTs maintained their integrity at high reaction temperature and led to suppression of edge dislocations and biaxial stress relaxation by up to 0.32 GPa in a GaN template layer. InGaN/GaN multi-quantum-well light-emitting diodes (LEDs) on this high-quality GaN template offered enhanced internal quantum efficiency and light output power with reduced efficiency droop. The method developed here has high potential to replace current ELO methods such as patterned sapphire substrates or buffer layers like SiO2 and SiNx.
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http://dx.doi.org/10.1039/c5nr04239aDOI Listing
October 2015

Effect of strain relaxation in InGaN/GaN multi-quantum wells with self-assembled Pt nanoclusters.

J Nanosci Nanotechnol 2014 Nov;14(11):8347-51

We report effect of the strain relaxation in InGaN/GaN multi-quantum well (MQW) structures grown on platinum nanocluster-coated sapphire substrate (PNSS) by metal organic chemical vapor deposition. The photoluminescence (PL) intensity of InGaN/GaN MQWs on PNSS was significantly enhanced compared to that of the InGaN/GaN MQWs on flat sapphire substrate due to the reduction of defect density and residual strain by self-assembled Pt nanoclusters. We confirmed the reduction of strain-induced piezoelectric field by the power dependence of the PL in InGaN/GaN MQWs on PNSS. Cathodoluminescence shows that a large bright area with overall strong peak intensity is attributed to the suppression of In inhomogeneity and strain relaxation in InGaN/GaN MQWs on PNSS. Based on these results, we suggest that the self-assembled Pt nanocluster can be applied to increase the quantum efficiency through improved crystal quality and internal strain relaxation in MQWs.
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http://dx.doi.org/10.1166/jnn.2014.9938DOI Listing
November 2014

Clinical manifestations of patients with CASPR2 antibodies.

J Neuroimmunol 2015 Apr 6;281:17-22. Epub 2015 Mar 6.

Department of Neurology, Laboratory for Neurotherapeutics, Biomedical Research Institute, Seoul National University Hospital, Korea Autoimmune Synaptic and Paraneoplastic Encephalitis Registry (KASPER), Seoul, South Korea. Electronic address:

Contactin-associated protein-like 2 (CASPR2) is one of the target antigens of voltage-gated potassium channels (VGKC) complex antibodies. There has been relatively little information in the literature regarding CASPR2 autoimmunity, especially in Asian population. We investigated the presence of CASPR2 antibodies in patients with presumed autoimmune neurological disorders and described the clinical features, laboratory findings, and responses to immunotherapy. Five patients were identified to be positive for CASPR2 antibodies. The results obtained here suggested that CASPR2 antibodies might be the possible cause of epilepsy even in the absence of typical features of limbic encephalitis and that immunotherapy could provide a favorable outcome.
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http://dx.doi.org/10.1016/j.jneuroim.2015.03.005DOI Listing
April 2015

Direct growth of GaN layer on carbon nanotube-graphene hybrid structure and its application for light emitting diodes.

Sci Rep 2015 Jan 19;5:7747. Epub 2015 Jan 19.

School of Semiconductor and Chemical Engineering &Semiconductor Physics Research Center, Chonbuk National University, Jeonju 561-756, Republic of Korea.

We report the growth of high-quality GaN layer on single-walled carbon nanotubes (SWCNTs) and graphene hybrid structure (CGH) as intermediate layer between GaN and sapphire substrate by metal-organic chemical vapor deposition (MOCVD) and fabrication of light emitting diodes (LEDs) using them. The SWCNTs on graphene act as nucleation seeds, resulting in the formation of kink bonds along SWCNTs with the basal plane of the substrate. In the x-ray diffraction, Raman and photoluminescence spectra, high crystalline quality of GaN layer grown on CGH/sapphire was observed due to the reduced threading dislocation and efficient relaxation of residual compressive strain caused by lateral overgrowth process. When applied to the LED structure, the current-voltage characteristics and electroluminescence (EL) performance exhibit that blue LEDs fabricated on CGH/sapphire well-operate at high injection currents and uniformly emit over the whole emission area. We expect that CGH can be applied for the epitaxial growth of GaN on various substrates such as Si and MgO, which can be a great advantage in electrical and thermal properties of optical devices fabricated on them.
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http://dx.doi.org/10.1038/srep07747DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4297988PMC
January 2015

Enhanced optical output power by the silver localized surface plasmon coupling through side facets of micro-hole patterned InGaN/GaN light-emitting diodes.

Opt Express 2014 Jun;22 Suppl 4:A1051-8

Light extraction efficiency of GaN-based light emitting diodes were significantly enhanced using silver nanostructures incorporated in periodic micro-hole patterned multi quantum wells (MQWs). Our results show an enhancement of 60% in the wall-plug efficiency at an injection current of 100 mA when Ag nano-particles were deposited on side facet of MQWs passivated with SiO2. This improvement can be attributed to an increase in the spontaneous emission rate through resonance coupling between localized surface plasmons in Ag nano-particles and the excitons in MQWs.
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http://dx.doi.org/10.1364/OE.22.0A1051DOI Listing
June 2014

Modulation of interferon signaling by hepatitis C virus non-structural 5A protein: implication of genotypic difference in interferon treatment.

FEBS Lett 2010 Sep;584(18):4069-76

National Research Laboratory of Hepatitis C Virus, Ilsong Institute of Life Science, Hallym University, Dongan-gu, Anyang, Republic of Korea.

Interferon (IFN) response rate in hepatitis C virus (HCV) patients has been varied with genotypes. In this study, we investigated the effects of HCV NS5A protein on IFN resistance and compared the genotypic differences of NS5A. We showed that IFN-α-, poly I:C-, and Sendai virus-induced ISRE transcriptional activities were inhibited by both genotype 1b and 2a NS5A protein. We demonstrated that not only genotype 1b but also genotype 2a NS5A exerted the similar extent of IFN-α-induced antiviral activity. We showed that NS5A derived from both genotype 1b and 2a showed no significant differential IFN responses as seen in HCV patients. These data imply that some other host factor may be involved in genotypic differences of IFN antagonism in HCV patients.
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http://dx.doi.org/10.1016/j.febslet.2010.08.032DOI Listing
September 2010

Risperidone dosing pattern and clinical outcome in psychosis: an analysis of 1713 cases.

J Clin Psychiatry 2005 Jul;66(7):887-93

Department of Psychiatry, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea.

Background: In treating patients with psychosis, practicing clinicians use various dosing strategies of antipsychotic medications, including risperidone. To evaluate the outcome of different risperidone dosing strategies in clinical practice, we undertook a large, prospective, naturalistic study in which daily dosage was determined freely by local standards of care.

Method: In a 6-week trial between December 2000 and January 2002, 1713 patients with DSM-IV schizophrenia and related psychoses were treated with risperidone, with the dose, daily changes in dose, and weekly changes in Brief Psychiatric Rating Scale score documented. Cluster analysis was performed to identify homogeneous dosing patterns among the heterogeneous total population.

Results: Of the 6 dosing patterns identified by cluster analysis, a 2-week titration cluster, with a starting dose of 1.8 mg/day titrated to a maximum dose of 4.7 mg/day at day 14, and a 1-week titration cluster, with a starting dose of 2.6 mg/day titrated to a maximum dose of 5.4 mg/day at day 7, showed superior clinical outcomes compared with the other clusters, in which titrations were slower and higher.

Conclusion: Our results indicate that the current consensus regarding risperidone dosing is appropriate for clinical practice, whereas a slower titration schedule does not guarantee a better clinical outcome, thus emphasizing the need for appropriate early titration.
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http://dx.doi.org/10.4088/jcp.v66n0711DOI Listing
July 2005

Synthetic wogonin derivatives suppress lipopolysaccharide-induced nitric oxide production and hydrogen peroxide-induced cytotoxicity.

Arch Pharm Res 2005 Feb;28(2):216-9

Department of Pharmacology, Kangwon National University, Chuncheon 200-701, Korea.

Wogonin (5,7-dihydroxy-8-methoxyflavone) has been reported to exhibit a variety of biological properties including anti-inflammatory and neuroprotective functions. In this study, biological activities of diverse synthetic wogonin derivatives have been evaluated in two experimental cell culture models. Inhibitory activities of wogonin derivatives on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in BV2 microglial cells and on hydrogen peroxide (H2O2)-induced neuronal cell death in SH-SY5Y human neuroblastoma were examined. Wogonin derivatives such as WS2 and WS3 showed more potent suppressive activities on LPS-induced NO production and H2O2-induced cytotoxicity than wogonin itself. In addition, thiol substitution played a minor role in enhancing the activities of the derivatives. These findings may contribute to the development of novel anti-inflammatory and neuroprotective agents derived from wogonin.
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http://dx.doi.org/10.1007/BF02977718DOI Listing
February 2005