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Hong S.,Korea University | Hong S.,KoreaUniversity | Song S.-J.,Korea University | Song S.-J.,KoreaUniversity | And 8 more authors.
Journal of Bioscience and Bioengineering | Year: 2013

The fabrication of patterned microstructures within three-dimensional (3D) matrices is a challenging subject in tissue engineering and regenerative medicine. A 3D, free-moving bioprinting system was developed and hydrogels were patterned by varying the process parameters of z-axis moving velocity and ejection velocity. The patterning of hydrogel based microfibers in a 3D matrigel was achieved with dimensions of 4.5mm length and widths from 79 to 200μm. Hyaluronan-based hydrogels mixed with fibroblasts (L929), mouse endothelial cells (MS1), or human mesenchymal stem cells (hMSCs) were patterned using a 3D moving axis bioprinter and cell behavior was monitored in culture for up to 16 days. L929 and MS1 cells and hMSCs in patterned hydrogel revealed cell-cell interactions and a morphological dependency on cell types. HMSCs formed spheres through cell aggregation, while L929 cells increased in cellular mass without cell aggregation and MS1 dispersed into the matrix instead of aggregating. The aggregation of hMSCs was attenuated by treatment with Rho kinase (ROCK) inhibitor and cadherin antibody. This reflected the close relationship between cell aggregation and migration with RhoA and cell-cell adhesion molecules. Angiogenic-specific gene expression profiles showed that expression of CD105 decreased to 22% in the ROCK inhibitor group compared to control group. These results showed that cell-based patterns in a 3D matrix are highly dependent on both cell aggregation and migration over time. © 2013 The Society for Biotechnology, Japan.

Kim D.-J.,Korea University | Kim D.-J.,University of Cambridge | Kim D.-J.,KoreaUniversity | Kim H.,Korea University | And 6 more authors.
Clinical Neurology and Neurosurgery | Year: 2016

Objective Shunt failure is common in hydrocephalic patients. The cerebrospinal fluid (CSF) infusion test enables the assessment of CSF absorption capacity, which is represented by the resistance to CSF outflow (ROUT) However, shunt failure may not only affect the CSF absorption capacity but also the intracranial compliance or compensatory properties. Spectral analysis of the ICP signal obtained during the infusion test may enable the comprehensive assessment of the overall deterioration caused by shunt failure. Material and methods A total of 121 hydrocephalic shunted patients underwent the infusion test with continuous intracranial pressure (ICP) and arterial blood pressure (ABP) recording. The maximum amplitudes of three major frequency bandwidths (0.2-2.6, 2.6-4.0 and 4.0-15 Hz, respectively) were calculated from the ICP. Statistical analyses were conducted to identify factors significantly associated with shunt failure, to construct an index (i.e., the shunt response parameter, SRP) for detecting shunt failure, and to define thresholds for ROUT and SRP. Results The ROUT threshold for detecting shunt failure was 7.59 mmHg/ml/min, and this threshold showed an accuracy of 82.64%. All spectral parameters were found to be significantly associated with shunt patency (p < 0.05). The SRP exhibited significantly better accuracy than ROUT in detecting shunt failure (91.74%). Conclusion The hydrodynamic assessment of shunted patients enhanced by spectral analysis during the infusion test detected shunt failure with high accuracy. Although further validation is needed, the SRP exhibited promising results. © 2016 Elsevier B.V. All rights reserved.

Kim S.-G.,KoreaUniversity | Choi Y.H.,KoreaUniversity | Yang D.G.,KoreaUniversity | Kim Y.-G.,KoreaUniversity | Lee H.,KoreaUniversity
IEEE Transactions on Applied Superconductivity | Year: 2016

This paper reports the charge-discharge and thermal-electrical characteristics of GdBCO single-pancake coils employing various types of grease, such as N-grease (N coil), Si-based grease (Si coil), and vacuum grease (V coil), as an insulation material to ameliorate the charging-discharging delay observed in no-insulation (NI) coils. The charge-discharge test results confirmed that the use of grease as an insulation material can effectively reduce leakage current because the turn-to-turn grease layers serve as an effective insulation material. In sudden discharge tests, the time constant values of coils wound with N-grease, Si-based grease, and vacuum grease were drastically lower than those of the NI coil. In the over-current test at 1.5 $I-{c}$, the maximum voltages of N and Si coils were 3.8 times lower than that of the V coil, indicating that the thermal and electrical stabilities of N and Si coils were considerably enhanced. Moreover, the heat dissipating test results indicated that the peak temperature of the Si coil was lower than those of other coils because the Si-based grease acted as the most effective heat dissipater in the event of local hot spot generation in the coil. In conclusion, among the various types of grease tested in this study, Si-based grease may be the most effective turn-to-turn insulator for the development of highly stable second-generation (2G) HTS magnets with ameliorated charging-discharging delay of NI coil. © 2002-2011 IEEE.

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