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Changwon, South Korea

Lee Y.,Gwangju Institute of Science and Technology | Geckeler K.E.,Korea Institute of Materials Science
Advanced Materials | Year: 2010

With the increasing interest in the biological applications of carbon nanotubes, their interactions in the biological interphase and their general cytotoxicity have become major issues. In spite of their salient properties, major hurdles still exist for their use in biological applications, due to their main characteristics, including their hydrophobic surfaces and tendency to aggregate, as well as their unknown interactions in the cellular interphase. In this Research News, these characteristics of carbon nanotubes, a model nanomaterial, are investigated. Thus, the cytotoxicity of carbon nanotubes, the infl uence of functionalization, as well as their interactions with different mammalian cell lines are studied. Moreover, suggestions for the improvement of their biocompatibility and the design of biocompatible carbon nanotube-based systems are provided. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Park S.S.,Ulsan National Institute of Science and Technology | You B.S.,Korea Institute of Materials Science
Scripta Materialia | Year: 2011

The tensile properties of extruded Mg-Sn-Al-Zn alloy at elevated temperature were investigated. Low-temperature superplasticity was found in the alloy, which exhibited tensile elongations of 410-950% at strain rates in the range 1 × 10-3-1 × 10-4 s-1 at 473 K. The superplastic deformation behavior was attributed to the fine-grained microstructure, which contained thermally stable Mg2Sn precipitates. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source

Sung J.H.,Ohio State University | Kim J.H.,Korea Institute of Materials Science | Wagoner R.H.,Ohio State University
International Journal of Plasticity | Year: 2010

An empirical plasticity constitutive form describing the flow stress as a function of strain, strain-rate, and temperature has been developed, fit to data for three dual-phase (DP) steels, and compared with independent experiments outside of the fit domain. Dubbed the "H/V model" (for "Hollomon/Voce"), the function consists of three multiplicative functions describing (a) strain hardening, (b) strain-rate sensitivity, and (c) temperature sensitivity. Neither the multiplicative structure nor the choice of functions (b) or (c) is novel. The strain hardening function, (a), has two novel features: (1) it incorporates a linear combination coefficient, α, that allows representation of Hollomon (power law) behavior (α = 1), Voce (saturation) behavior (α = 0) or any intermediate case (0 < α < 1, and (2) it allows incorporation of the temperature sensitivity of strain hardening rate in a natural way by allowing α to vary with temperature (in the simplest case, linearly). This form therefore allows a natural transition from unbounded strain hardening at low temperatures toward saturation behavior at higher temperatures, consistent with many observations. Hollomon, Voce, H/V models and others selected as representative from the literature were fit for DP590, DP780, and DP980 steels by least-squares using a series of tensile tests up to the uniform strain conducted over a range of temperatures. Jump-rate tests were used to probe strain rate sensitivity. The selected laws were then used with coupled thermo-mechanical finite element (FE) modeling to predict behavior for tests outside the fit range: non-isothermal tensile tests beyond the uniform strain at room temperatures, isothermal tensile tests beyond the uniform strain at several temperatures and hydraulic bulge tests at room temperature. The agreement was best for the H/V model, which captured strain hardening at high strain accurately as well as the variation of strain hardening with temperature. The agreement of FE predictions up to the tensile failure strain illustrates the critical role of deformation-induced heating in high-strength/high ductility alloys, the importance of having a constitutive model that is accurate at large strains, and the implication that damage and void growth are unlikely to be determinant factors in the tensile failure of these alloys. The new constitutive model may have application for a wide range of alloys beyond DP steels, and it may be extended to larger strain rate and temperature ranges using alternate forms of strain rate sensitivity and thermal softening appearing in the literature. © 2010 Elsevier Ltd. All rights reserved. Source

Lee S.-H.,Korea Institute of Materials Science
Journal of the American Ceramic Society | Year: 2011

The densification of an Al3BC3-SiC system during pressureless sintering was investigated. Densification of SiC could be achieved after sintering at 1850°C for 2 h by adding 10 wt% Al3BC 3. The formation of partly crystallized grain boundaries and a core-rim structure within SiC grains indicated that liquid phase sintering was the major densification mechanism. The initial shrinkage at 1430°C was caused by the formation of a liquid silicate phase. Sintering shrinkage accelerated above 1580°C due to the rearrangement of SiC particles. The dissolution-reprecipitation of SiC and the final removal of pores occurred above 1780°C. In contrast to Al2O3 additive which has low efficiency, Al3BC3 strongly promoted the pressureless sintering of SiC. © 2011 The American Ceramic Society. Source

Yun H.S.,Korea Institute of Materials Science
International journal of nanomedicine | Year: 2011

Mesoporous bioactive glasses (MBGs) are very attractive materials for use in bone tissue regeneration because of their extraordinarily high bone-forming bioactivity in vitro. That is, MBGs may induce the rapid formation of hydroxy apatite (HA) in simulated body fluid (SBF), which is a major inorganic component of bone extracellular matrix (ECM) and comes with both good osteoconductivity and high affinity to adsorb proteins. Meanwhile, the high bioactivity of MBGs may lead to an abrupt initial local pH variation during the initial Ca ion-leaching from MBGs at the initial transplant stage, which may induce unexpected negative effects on using them in in vivo application. In this study we suggest a new way of using MBGs in bone tissue regeneration that can improve the strength and make up for the weakness of MBGs. We applied the outstanding bone-forming bioactivity of MBG to coat the main ECM components HA and collagen on the MBG-polycarplolactone (PCL) composite scaffolds for improving their function as bone scaffolds in tissue regeneration. This precoating process can also expect to reduce initial local pH variation of MBGs. The MBG-PCL scaffolds were immersed in the mixed solution of the collagen and SBF at 37°C for 24 hours. The coating of ECM components on the MBG-PCL scaffolds and the effect of ECM coating on in vitro cell behaviors were confirmed. The ECM components were fully coated on MBG-PCL scaffolds after immersing in SBF containing dilute collagen-I solution only for 24 hours due to the high bone-forming bioactivity of MBG. Both cell affinity and osteoconductivity of MBG-PCL scaffolds were dramatically enhanced by this precoating process. The precoating process of ECM components on MBG-PCL scaffold using a high bioactivity of MBG was not only effective in enhancing the functionality of scaffolds but also effective in eliminating the unexpected side effect. The MBG-PCL scaffold-coated ECM components ideally satisfied the required conditions of scaffold in tissue engineering, including 3D well-interconnected pore structures with high porosity, good bioactivity, enhanced cell affinity, biocompatibility, osteoconductivity, and sufficient mechanical properties, and promise excellent potential application in the field of biomaterials. Source

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