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Oh S.-T.,Intelligent Textile System Research Center | Oh S.-T.,Research Institute for Agriculture and Life science | Oh S.-T.,University of Suwon | Kim W.-R.,Intelligent Textile System Research Center | And 9 more authors.
Fibers and Polymers | Year: 2011

Polyurethane (PU) foam was combined with protein drug-loaded pH-sensitive alginate-bentonite hydrogel for wound dressings. Alginate is a linear copolymer composed of 1-4-linked β-D-mannuronic acid (M) and its c-5-epimer α-Lguluronic acid (G). The amount of (M) and (G) and their sequential distribution are varied depending on the alginate source. Soluble sodium alginate can become a hydrogel when cross-linked with divalent cations and has widespread applications in the food, drink, pharmaceutical and bioengineering industries. Recently, it has been also proposed as a biomaterial for drug delivery systems. Bentonites are the natural inorganic polymers consisting of a large proportion of expandable clay minerals with a three-layer structure such as montmorillonite, beidellite, nontronite, etc. They are important adjutants and supports for medical products, and they have many useful physicochemical, mechanical, and biological properties such as absence of toxicity, indifference to other raw materials, sorption, swelling, and complex formation properties. Alginate-bentonite hydrogels were prepared at concentration ratios of 10/0, 7/3, 5/5, 3/7. PU foams were prepared using hydrophilic polyols. We investigated the controlled release of a protein drug from PU foam combined with alginate-bentonite hydrogel at different pH values of 4.2, 5.2, 7.2, 8.2. The mechanical properties and cytotoxicity tests of this foam were also studied. © 2011 The Korean Fiber Society and Springer Netherlands. Source


Song W.,Korea Environment Institute KEI | Kim E.,Korea Environment Institute KEI | Lee D.,Seoul National University | Lee D.,Research Institute for Agriculture and Life science | And 2 more authors.
Ecological Modelling | Year: 2013

Species distribution modeling is one of the most effective habitat analysis methods for wildlife conservation. We evaluated the sensitivity of species distribution modeling to different grain sizes and extent sizes from 30m to 4950m using maximum entropy (MaxEnt) modeling. The grain size represents a unit for analysis, whereas the extent size defines the scope of the analysis in a way that reflects the environmental data for the area in which the species of interest occurs. We compared the resulting suitability indexes and habitat areas based on two approaches. The first approach increases the extent size for a fixed grain size. The second approach increases the grain size and the extent size by equal amounts. The suitability index based on the first approach (R2=0.34) was greater than the suitability index based on the second approach (R2=0.89). The first approach was fitted to a logarithmic function with a critical point at approximately 0.5km, converging to about 0.76. In contrast, the second approach showed a linear decrease to values less than 0.5. The distribution of habitat area found with the second method (R2=0.87) was broader than that found with the first method (R2=0.63). The relationship between the extent size and the landscape index of the first method can be displayed as a power-law graph with a critical point of 0.5km. The method of expanding extent size has greater accuracy, although the time that it requires for data processing is long. The results of this study suggest that the maximum grain size should be approximately 1.5km. If the grain size is greater than 1.5km, the accuracy of the habitat suitability index decreases below 0.6, and the predicted habitat suitability increases dramatically. © 2012 Elsevier B.V. Source


Ha J.-W.,Seoul National University | Kim H.-J.,Seoul National University | Kim H.-J.,Research Institute for Agriculture and Life science
Agricultural Engineering International: CIGR Journal | Year: 2015

A front-end loader for agricultural purposes is the most commonly used implement for agri-tractors in Korea. As it is operated to raise, lower and carry various objects in a farming field, it bringsa large amount of stress to a tractor, causing vibrations and often leading to a mechanical breakdown. These high stresses are observed at the starting and ending points of operation, that is, the points at which the highest acceleration and deceleration occur. To reduce the sudden change of the speed, soft-start & end operation were tested with an electrohydraulic directional valve, which has a built-in ramp time spool control function. This valve was controlled by SAE-J1939 associated messages via CAN bus. This shock-absorbing system contains three electronic control unit(ECUs): a loader ECU for receiving and transmitting loader position data, a joystick ECU to convert a lever position that is constantly being changed by an operator into CAN messages, and a valve ECU to regenerate all messages into the J1939 standard to be understood by the electrohydraulic directional valve. By sensing the loader position and speed, the ramp activation point wasdetermined. As expected, applying ramp time control to the front-end loader control system proved to be effective for reducing the shock level, in contrast to that of the conventional control using a hydraulic manual valve. © 2015, Int. Comm. of Agricultural and Biosystems Engineering. All rights reserved. Source


Lim J.S.,Seoul National University | Ki C.S.,Amore Pacific | Kim J.W.,Seoul National University | Lee K.G.,Korea Advanced Institute of Science and Technology | And 4 more authors.
Biopolymers | Year: 2012

In this study we investigated the blend electrospinning of poly(Ïμ-caprolactone) (PCL) and silk fibroin (SF) to improve the biodegradability and biocompatibility of PCL-based nanofibrous scaffolds. Optimal conditions to fabricate PCL/SF (50/50) blend nanofiber were established for electrospinning using formic acid as a cosolvent and three-dimensional (3D) PCL/SF blend nanofibrous scaffolds were prepared by a modified electrospinning process using methanol coagulation bath. The physical properties of 2D PCL/SF blend nanofiber mats and 3D highly porous blend nanofibrous scaffolds were measured and compared. To evaluate cytocompatibility of the 3D blend scaffolds as compared to 3D PCL nanofibrous scaffold, normal human dermal fibroblasts were cultured. It is concluded that biodegradability and cytocompatibility could be improved for the 3D highly porous PCL/SF (50/50) blend nanofibrous scaffold prepared by blending PCL with SF in electrospinning. In addition to the blending of PCL and SF, the 3D structure and high porosity of electrospun nanofiber assemblies may also be important factors for enhancing the performance of scaffolds. © 2012 Wiley Periodicals, Inc. Source


Lee J.,Seoul National University | Ryu J.,Seoul National University | Youn H.J.,Seoul National University | Youn H.J.,Research Institute for Agriculture and Life science
Cellulose | Year: 2012

A conductive paper was made of cellulose fibers with a multilayer of polyethyleneimine (PEI) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and the factors to increase the conductivity of the paper were investigated. The adsorption amount and the structure of PEI and PEDOT:PSS multilayer was changed by controlling salt concentration and the number of layers, and inter-contact degree of fibers was controlled by calendering. The adsorption behavior of the polyelectrolytes onto cellulose was evaluated using a quartz crystal microbalance with dissipation monitoring, and the adsorption amount was quantitatively analyzed through Kjeldahl nitrogen analysis and an Inductively Coupled Plasma Optical Emission Spectrometer. The conductivity of the resultant paper was in the range of 10 -5-10 -4 S/cm without loss of paper strength. The conductivity of the paper increased when the multilayer was formed at low salt concentration and the conductive paper was calendered. It appeared that electron transfer by increased contact between PEDOT:PSS improved the conductivity of the paper. © 2012 Springer Science+Business Media B.V. Source

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