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Pohang, South Korea

Choi W.-C.,Gachon UniversityGyeonggi do | Picornell M.,North Carolina A&T State University | Hamoush S.,North Carolina A&T State University
Construction and Building Materials | Year: 2016

Surface and subsurface defects, such as the scaling of a concrete surface, corrosion of the reinforcement, carbonation of concrete, cracks in concrete, etc., are often observed in historical structures. In order to assess the performance of the aged concrete in a historical structure, a combination of impact echo and ultrasonic surface wave techniques as well as ground penetrating radar (GPR) are believed to be the most effective approaches to determine not only the overall quality of the concrete in the structural components, but also the extent of any internal deterioration that may be present in the structure. In this study, the field evaluation of the old concrete in a historical reinforced concrete structure (a stadium) has been conducted using destructive and nondestructive methods. The extent of the damage and unseen patterns of concrete deterioration were determined successfully based on the results obtained using GPR and a seismic property analyzer. In addition, the material properties of the old concrete were compared to laboratory test results. © 2016 Published by Elsevier Ltd. Source

Zhong L.,Gachon UniversityGyeonggi do | Yun K.,Gachon UniversityGyeonggi do
International Journal of Nanomedicine | Year: 2015

Nanosized ZnO particles with diameters of 15 nm were prepared with a solution precipitation method at low cost and high yield. The synthesis of the particles was functionalized by the organic solvent dimethylformamide, and the particles were covalently bonded to the surface of graphene oxide. The morphology of the graphene oxide sheets and ZnO particles was confirmed with field emission scanning electron microscopy and biological atomic force microscopy. Fourier transform infrared spectroscopy and X-ray diffraction were used to analyze the physical and chemical properties of the ZnO/graphene oxide composites that differed from those of the individual components. Enhanced electrochemical properties were detected with cyclic voltammetry, with a redox peak of the composites at 0.025 mV. Excellent antibacterial activity of ZnO/graphene oxide composites was observed with a microdilution method in which minimum inhibitory concentrations of 6.25 µg/mL for Escherichia coli and Salmonella typhimurium, 12.5 µg/mL for Bacillus subtilis, and 25 µg/mL for Enterococcus faecalis. After further study of the antibacterial mechanism, we concluded that a vast number of reactive oxygen species formed on the surface of composites, improving antibacterial properties. © 2015, Zhong and Yun. Source

Subbiah R.,Korea Institute of Science and Technology | Subbiah R.,Korean University of Science and Technology | Jeon S.B.,Gachon UniversityGyeonggi do | Jeon S.B.,Korea Research Institute of Standards and Science | And 5 more authors.
International Journal of Nanomedicine | Year: 2015

In order for nanoparticles (NPs) to be applied in the biomedical field, a thorough investigation of their interactions with biological systems is required. Although this is a growing area of research, there is a paucity of comprehensive data in cell-based studies. To address this, we analyzed the physicomechanical responses of human alveolar epithelial cells (A549), mouse fibroblasts (NIH3T3), and human bone marrow stromal cells (HS-5), following their interaction with silver nanoparticles (AgNPs). When compared with kanamycin, AgNPs exhibited moderate antibacterial activity. Cell viability ranged from ≤ 80% at a high AgNPs dose (40 µg/mL) to>95% at a low dose (10 µg/mL). We also used atomic force microscopycoupled force spectroscopy to evaluate the biophysical and biomechanical properties of cells. This revealed that AgNPs treatment increased the surface roughness (P<0.001) and stiffness (P<0.001) of cells. Certain cellular changes are likely due to interaction of the AgNPs with the cell surface. The degree to which cellular morphology was altered directly proportional to the level of AgNP-induced cytotoxicity. Together, these data suggest that atomic force microscopy can be used as a potential tool to develop a biomechanics-based biomarker for the evaluation of NP-dependent cytotoxicity and cytopathology. © 2015 Subbiah et al. Source

Jeong H.R.,Gachon UniversityGyeonggi do | An S.S.A.,Gachon UniversityGyeonggi do
Clinical Interventions in Aging | Year: 2015

Human islet amyloid polypeptide (h-IAPP) is a peptide hormone that is synthesized and cosecreted with insulin from insulin-secreting pancreatic β-cells. Recently, h-IAPP was proposed to be the main component responsible for the cytotoxic pancreatic amyloid deposits in patients with type 2 diabetes mellitus (T2DM). Since the causative factors of IAPP (or amylin) oligomer aggregation are not fully understood, this review will discuss the various forms of h-IAPP aggregation. Not all forms of IAPP aggregates trigger the destruction of β-cell function and loss of β-cell mass; however, toxic oligomers do trigger these events. Once these toxic oligomers form under abnormal metabolic conditions in T2DM, they can lead to cell disruption by inducing cell membrane destabilization. In this review, the various factors that have been shown to induce toxic IAPP oligomer formation will be presented, as well as the potential mechanism of oligomer and fibril formation from pro-IAPPs. Initially, pro-IAPPs undergo enzymatic reactions to produce the IAPP monomers, which can then develop into oligomers and fibrils. By this mechanism, toxic oligomers could be generated by diverse pathway components. Thus, the interconnections between factors that influence amyloid aggregation (eg, absence of PC2 enzyme, deamidation, reduction of disulfide bonds, environmental factors in the cell, genetic mutations, copper metal ions, and heparin) will be presented. Hence, this review will aid in understanding the fundamental causative factors contributing to IAPP oligomer formation and support studies for investigating novel T2DM therapeutic approaches, such as the development of inhibitory agents for preventing oligomerization at the early stages of diabetic pathology. © 2015 Jeong and An. Source

Ramasamy S.,Gachon UniversityGyeonggi do | Bennet D.,Gachon UniversityGyeonggi do | Kim S.,Gachon UniversityGyeonggi do | Kim S.,Graduate Gachon Medical Research Institute
International Journal of Nanomedicine | Year: 2014

This review will present a brief discussion on the recent advancements of bioelectrical impedance cell-based biosensors, especially the electric cell-substrate impedance sensing (ECIS) system for screening of various bioactive molecules. The different technical integrations of various chip types, working principles, measurement systems, and applications for drug targeting of molecules in cells are highlighted in this paper. Screening of bioactive molecules based on electric cell-substrate impedance sensing is a trial-and-error process toward the development of therapeutically active agents for drug discovery and therapeutics. In general, bioactive molecule screening can be used to identify active molecular targets for various diseases and toxicity at the cellular level with nanoscale resolution. In the innovation and screening of new drugs or bioactive molecules, the activeness, the efficacy of the compound, and safety in biological systems are the main concerns on which determination of drug candidates is based. Further, drug discovery and screening of compounds are often performed in cell-based test systems in order to reduce costs and save time. Moreover, this system can provide more relevant results in in vivo studies, as well as high-throughput drug screening for various diseases during the early stages of drug discovery. Recently, MEMS technologies and integration with image detection techniques have been employed successfully. These new technologies and their possible ongoing transformations are addressed. Select reports are outlined, and not all the work that has been performed in the field of drug screening and development is covered. © 2014 Ramasamy et al. Source

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