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Jin, Young Ju,Kang, Sunah,Park, Pona,Choi, Dongkil,Kim, Dae Woo,Jung, Dongwook,Koh, Jaemoon,Jeon, Joohee,Lee, Myoungjin,Ham, Jiyeon,Seo, Ji-Hun,Jin, Hong-Ryul,Lee, Yan American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.22
<P>Expanded polytetrafluoroethylene (ePTFE), also known as Gore-Tex, is widely used as an implantable biomaterial in biomedical applications because of its favorable mechanical properties and biochemical inertness. However, infection and inflammation are two major complications with ePTFE implantations, because pathogenic bacteria can inhabit the microsized pores, without clearance by host immune cells, and the limited biocompatibility can induce foreign body reactions. To minimize these complications, we covalently grafted a biomembrane-mimic polymer, poly(2-methacryloyloxylethyl phosphorylcholine) (PMPC), by partial defluorination followed by UV-induced polymerization with cross-linkers on the ePTFE surface. PMPC grafting greatly reduced serum protein adsorption as well as fibroblast adhesion on the ePTFE surface. Moreover, the PMPC-grafted ePTFE surface exhibited a dramatic inhibition of the adhesion and growth of Staphylococcus aureus, a typical pathogenic bacterium in ePTFE implants, in the porous network. On the basis of an analysis of immune cells and inflammation-related factors, i.e., transforming growth factor-beta (TGF-beta) and myeloperoxidase (MPO), we confirmed that inflammation was efficiently alleviated in tissues around PMPC-grafted ePTFE plates implanted in the backs of rats. Covalent PMPC may be an effective strategy for promoting anti-inflammatory and antibacterial functions in ePTFE implants and to reduce side effects in biomedical applications of ePTFE.</P>
Enhancing Ductile-mode Cutting of Calcium Fluoride Single Crystals with Solidified Coating
Yan Jin Lee,Jing Yi Chong,Akshay Chaudhari,Hao Wang 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.7 No.6
Positive improvements have been observed during machining brittle materials under high hydrostatic pressure, but the techniques to achieve such desirable effects often utilize complex and expensive equipment or tools. This work presents a cost-efficient method to achieve ductile-mode machining of brittle materials at higher uncut chip thicknesses, by the application of a solidified coating on workpiece surface before a machining process. Orthogonal microcutting experiments were conducted on calcium fluoride single crystals oriented with the (111) plane and an increase in critical uncut chip thickness was observed with the solidified coating. The primary cause has been resolved to be mechanical-related and results in a stabilized microcutting process. Transmission electron microscopy provided evidence of slip deformation occurring in the machined subsurface regions and a layer thickness of subsurface damages reduced by ~ 45% under the influence of the solidified coating. In addition, erratic fluctuations in direction of the resultant machining force were subdued with the applied coating, which is proved to be caused by the compressive stresses induced from the sandwiching of the CaF2 material between the tool and the solidified coating. The proposed technique successfully reduces the cost and pollution in the fabrication process of optical components from the use of coolant in an ultraprecision machining process to the time consumed by eliminating the subsurface damage with abrasive slurries in post-machining polishing.
Lee, Jungwoon,Xia, Yan,Son, Mi‐,Young,Jin, Guanghai,Seol, Binna,Kim, Min‐,Jeong,Son, Myung Jin,Do, Misol,Lee, Minho,Kim, Dongsup,Lee, Kyeong,Cho, Yee Sook WILEY‐VCH Verlag 2012 Angewandte Chemie Vol.124 No.50
<P><B>Pluripotenz‐Booster</B>: RSC133, ein neues synthetisches Derivat von Indolacrylsäure/Indolpropionsäure, zeigt zweifache Aktivität, indem es Histondeacetylase und DNA‐Methyltransferase inhibiert. Außerdem verbessert es wirksam die Reprogrammierung von menschlichen somatischen Zellen in einen pluripotenten Zustand und unterstützt Wachstum und Erhaltung von humanen pluripotenten Stammzellen (hPSCs).</P>
Evaluation of the Oral Acute Toxicity of Black Ginseng in Rats
Lee, Mi-Ra,Oh, Chang-Jin,Li, Zheng,Li, Jing-Jie,Wang, Chun-Yan,Wang, Zhen,Gu, Li-Juan,Lee, Sang-Hwa,Lee, Jae-Il,Lim, Beong-Ou,Sung, Chang-Keun The Korean Society of Ginseng 2011 Journal of Ginseng Research Vol.35 No.1
We studied the acute oral toxicity of black ginseng (BG) produced by heat process in rats. Single acute BG extract doses of 0, 5, 10, and 15 g/kg dissolved in saline were administered by oral gavage and the animals were kept under observation for 14 days. The single administration of BG extract up to 15 g/kg did not produce mortality, behavioral change or abnormal clinical signs in the rats. These results indicated that the oral $LD_{50}$ of the BG extract in the rats is higher than 15 g/kg. Compared to the control group, no treatment-related biologically significant effects of BG extract were noted in the measurements of the body weight or food intake. At the end of the period, the biochemical parameters and hematological parameters were analyzed in the plasma and blood. A histopathological examination of the liver and kidney was also conducted. Only the blood nitrogen urea and potassium levels in the biochemical indices showed significant differences at 10 and 15 g/kg doses of BG extract compared to the control group. These changes were not considered to be due to the toxicity. None of the other clinical chemistry parameters were affected. Therefore, these results indicate that the BG by heat processing is virtually nontoxic.
Sustainability of Methods for Augmented Ultra-Precision Machining
Yan Jin Lee,Hao Wang 한국정밀공학회 2024 International Journal of Precision Engineering and Vol.11 No.2
Optical-grade surfaces can be manufactured on metals and ceramics through precise control of diamond cutting tools in ultra-precision machining and traditional optimization of machining parameters. However, researchers have sought out innovative techniques that further improve precision manufacturing efficiency by reducing cutting forces, improving machined surface quality, and lowering tool wear. Many augmentations have been categorized as sustainable solutions simply based on the observation of reduced cutting forces, but an in-depth perspective of the actual energy savings is rarely provided. Thus, this review provides systematic evaluations of the actual energy consumed to implement these augmentations in comparison to the effective energy savings, which would justify the appropriate categorization of green technology. These augmentations include workpiece, tool, and process modifications that would serve as examples for future research to adopt this uncommon perspective of identifying the true significance of the reported results toward sustainable manufacturing. The article also proposes a three-tiered discussion for future research and development in this field, with the final objective of identifying optimal sustainable manufacturing methods with a well-supported theoretical foundation.