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Seoul, South Korea

Lee E.-J.,Dankook University | Kim H.-E.,Seoul National UniversitySeoul
Materials Science and Engineering C | Year: 2016

Therapeutic agents such as growth factors have been widely applied to promote bone regeneration with implantable biomaterials. In this study, a hybrid of chitosan-xerogel membrane was combined with bone morphogenetic protein-2 (BMP-2) for enhancing bone regeneration. The characteristics of the hybrid membrane as a carrier of BMP-2 were compared with that of the pure chitosan membrane, and the effect of combining the hybrid membrane with BMP-2 on its bone healing ability was evaluated using in vitro and in vivo animal tests. The amount of BMP-2 adsorbed on the pure chitosan membrane was less than that on the hybrid membrane and, therefore, the cellular behaviors of the pure chitosan membrane were only slightly improved by the protein treatment. In contrast, the hybrid membrane showed excellent affinity toward BMP-2, and the adsorption of BMP-2 elicited a dramatic improvement in the cellular responses of the hybrid membrane. Moreover, the in vivo study demonstrated that bone regeneration was significantly enhanced when using the hybrid membrane with BMP-2 as compared to the hybrid membrane without BMP-2. These results suggest that the hybrid membrane is very efficient in carrying BMP-2 and accelerates the bone healing process through the successful delivery of BMP-2 and its osteoconductive composition. © 2015 Elsevier B.V. Source


Hahm T.S.,Seoul National UniversitySeoul
Plasma Science and Technology | Year: 2015

Bulk ion heating rate from nonlinear Landau damping of high mode number Toroidal Alfvén Eigenmodes (TAEs) is calculated in the frame work of weak turbulence theory. The heating rate is lower than the nonlinear spectral transfer rate to more stable modes, but relatively insensitive to the details of linear damping mechanisms. Source


Cho S.M.,Seoul National UniversitySeoul | Chung D.S.,Seoul National UniversitySeoul
Talanta | Year: 2016

Headspace (HS) extraction can be carried out easily and aptly via single drop microextraction coupled with capillary electrophoresis (CE). However, one drawback is the difficulty of keeping the single drop stably at the capillary tip. To solve this problem, we have recently demonstrated HS in-tube microextraction (ITME) of acidic compounds such as chlrophenols in an acidic sample using a basic run buffer plug in the separation capillary for CE as an acceptor phase. In this report, an organic acceptor plug in a capillary was used to extract neutral organic volatile pollutants such as BTEX (benzene, toluene, ethylbenzene, and m-xylene). After extraction, the analytes enriched in the organic acceptor plug were analyzed with micellar electrokinetic chromatography (MEKC). The enrichment factors for BTEX in a standard solution were up to 350 under an optimal condition of 25 °C for 20 min. As an application, BTEX spiked into bottled water were analyzed with HS-ITME-MEKC, and the enrichment factors for BTEX were up to 320. The limits of detections were 1-4 ppb, which are at least 200 times lower than the US Environmental Protection Agency guidelines for drinking water, except benzene. The entire procedure of HS-ITME-MEKC was carried out automatically using a commercial CE instrument. © 2015 Elsevier B.V. Source


Chuah W.H.,Seoul National UniversitySeoul | Zhang W.L.,Inha University | Choi H.J.,Inha University | Seo Y.,Seoul National UniversitySeoul
Macromolecules | Year: 2015

The sedimentation stability of a carbonyl iron (CI)-based magnetorheological (MR) fluid was improved by wrapping CI particles with a polystyrene (PS) foam layer. The PS layer on the CI particles was synthesized via conventional dispersion polymerization and was subsequently foamed using a supercritical carbon dioxide fluid to produce core-shell structured particles. The density of particles decreased after the PS-layer wrapping and subsequent PS-layer foaming. The surface morphology was observed by scanning electron microscope (SEM) and the specific surface areas were determined by Brunauer-Emmett-Teller (BET) adsorption measurements. Both modifications (PS-layer wrapping and foaming) increased the surface roughness of the particles, yet preserved particle's spherical shape. The effect of the volume expansion after modification on the magnetorheological properties was investigated by using a vibrating sample magnetometer (VSM) and a rotational rheometer. All suspensions tested presented similar MR behaviors with the only difference in their yield stress strengths. Finally, the sedimentation properties of the synthesized particles was examined using a Turbiscan apparatus. MR fluids containing the newly developed CI particles wrapped with the foamed PS layer exhibited remarkably improved stability against sedimentation due to the reduced mismatch in density between the particles and the carrier medium. © 2015 American Chemical Society. Source


Choi K.,Seoul National UniversitySeoul | Jo J.H.,Seoul National UniversitySeoul
Journal of Sedimentary Research | Year: 2015

Morphodynamics of intertidal channels were monitored in order to understand their implication on the architecture of inclined heterolithic stratification (IHS) in the open-coast Yeochari macro tidal flat on southern Ganghwa Island in Gyeonggi Bay, west coast of Korea. The tidal flat is divisible into narrow salt marshes in the upper intertidal zone, a concave-up upper to middle intertidal zone with small tidal creeks, and a channelized lower intertidal zone. Channels in the lower intertidal zone are 200-600 m wide and 1-2.5 m deep at bankful stage. They are sinuous in planform and have well-defined point bars and cutbanks. IHS is exposed along the cutbanks. High-precision leveling of the tidal channel bank unveiled that a point bar in the lower intertidal zone migrated about 400 m in 39 months. Channel migration is pronounced during the summer rainy season, when the point bar migrated as fast as 40 m per month, which led to rapid sediment accumulation of as much as 40 cm per month. In contrast, channel migration rate during winter is notably reduced, down to less than 1 m per month. Point-bar geometry alternates between a concave-up profile in summertime and a convex-up profile during the remainder of the year. Enhanced ebb currents during the rainy season, due to increased runoff discharge caused by heavy precipitation, accelerated point-bar migration. Remarkable rill erosion induced by heavy precipitation especially during low tide led to the rapid accumulation of sediment at the lower part of the point bar and the channel base, creating concave-up point-bar geometry. During the remainder of the year, the point bar retains a convex-up profile by continued sedimentation with insignificant rill erosion. Wave activity, particularly during winter, seems to facilitate deposition in the upper part of the point bar by providing more sediment into the channel. The present study illuminates the fact that the stratigraphic architecture of IHS of intertidal origin is controlled largely by monsoonal weather and to a lesser degree by tidal process even in a macrotidal environment. Careful examination of IHS geometry may hint at the depositional setting in terms of tidal frame (intertidal versus subtidal) and climate regime (monsoonal versus non-monsoonal). Copyright © 2015, SEPM (Society for Sedimentary Geology). Source

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