<i>In situ</i> analyses for ion storage materials

Yang, Junghoon,Muhammad, Shoaib,Jo, Mi Ru,Kim, Hyunchul,Song, Kyeongse,Agyeman, Daniel Adjei,Kim, Yong-Il,Yoon, Won-Sub,Kang, Yong-Mook The Royal Society of Chemistry 2016 Chemical Society reviews Vol.45 No.20

<P>Development of high performance electrode materials for energy storage is one of the most important issues for our future society. However, a lack of clear analytical views limits critical understanding of electrode materials. This review covers useful analytical work using X-ray diffraction, X-ray absorption spectroscopy, microscopy and neutron diffraction for ion storage systems. The in situ observation facilitates comprehending real-time ion storage behaviour while the ion storage system is operating, which help us to understand detailed physical and chemical properties. We will discuss how the tools have been used to reveal detailed reaction mechanisms and underlying properties of electrode materials.</P>

Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

Ferrari, Andrea C.,Bonaccorso, Francesco,Fal'ko, Vladimir,Novoselov, Konstantin S.,Roche, Stephan,Bøggild, Peter,Borini, Stefano,Koppens, Frank H. L.,Palermo, Vincenzo,Pugno, Nicola,Garrido, Jos&eacut The Royal Society of Chemistry 2015 Nanoscale Vol.7 No.11

<P>We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.</P>

Devices and materials for high-performance mobile liquid crystal displays

Lee, Seung Hee,Bhattacharyya, Surjya Sarathi,Jin, Heui Seok,Jeong, Kwang-Un The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.24

<P>Mobile liquid crystal displays (LCDs), often playing a role in hand-held computers, have become indispensable electronic tools to human beings in modern society. Innovative technological developments in the devices and materials have paved a successful road toward the development of mobile LCDs. Herein, after reviewing the trends and performance requirements of mobile LCDs, organic–inorganic materials as the key components of high performance mobile LCDs are addressed. Additionally, the developing trends in mobile LCDs are discussed with respect to these materials.</P> <P>Graphic Abstract</P><P>Innovative liquid crystal devices and key materials for mobile TFT-LCDs, affecting mankind's lifestyle, have been reviewed. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm30635b'> </P>

Calligraphic ink enabling washable conductive textile electrodes for supercapacitors

Van Lam, Do,Jo, Kyungmin,Kim, Chang-Hyun,Won, Sejeong,Hwangbo, Yun,Kim, Jae-Hyun,Lee, Hak-Joo,Lee, Seung-Mo The Royal Society of Chemistry 2016 Journal of Materials Chemistry A Vol.4 No.11

<P>The appeal of wearable devices for future electronics has stimulated scientists to unearth novel materials to meet the technological demands of modern society. However, the washability issue still remains a significant challenge. We showed that calligraphic ink, used as a writing tool in East Asian areas for thousands of years, could present a route to translate washable and wearable electrodes into a reality. We prepared washable electrodes by simply coating textiles with the ink. It was observed that the electrical and mechanical performance of the fabricated electrodes remained nearly unchanged even after 10 vigorous laundering cycles using a regular washing machine. In addition, supercapacitors made with those electrodes exhibited excellent cycling stability and high energy/power density. These results establish that everyday calligraphic ink is a simple yet powerful resource for fashioning normal textiles into washable and wearable electrodes for supercapacitors.</P>

Evaluation of cytotoxicity, biophysics and biomechanics of cells treated with functionalized hybrid nanomaterials

Subbiah, Ramesh,Ramasundaram, Subramaniyan,Du, Ping,Hyojin, Kim,Sung, Dongkyung,Park, Kwideok,Lee, Nae-Eung,Yun, Kyusik,Choi, Kyoung Jin Royal Society 2013 Journal of the Royal Society, Interface Vol.10 No.88

<P>Hybrids consisting of carboxylated, single-walled carbon nanotube (c-SWNT)–silver nanoparticles (AgNPs)-DNA–poly vinyl alcohol (PVA) are synthesized via sequential functionalization to mimic the theragnostic (therapy and diagnosis) system. Carboxylation of SWNT has minimized the metal impurities with plenty of –COOH groups to produce hybrid (c-SWNT-AgNPs). The hybrid is further wrapped with DNA (hybrid-DNA) and encapsulated with PVA as hybrid composite (HC). Materials were tested against human alveolar epithelial cells (A549), mouse fibroblasts cells (NIH3T3) and human bone marrow stromal cells (HS-5). The composition-sensitive physico-chemical interactions, biophysics and biomechanics of materials-treated cells are evaluated. The cell viability was improved for HC, hybrid-PVA and c-SWNT when compared with SWNT and hybrid. SWNT and hybrid showed cell viability less than 60% at high dose (40 µg ml<SUP>−1</SUP>) and hybrid-PVA and HC retained 80% or more cell viability. The treatment of hybrid nanomaterials considerably changed cell morphology and intercellular interaction with respect to the composition of materials. Peculiarly, PVA-coated hybrid was found to minimize the growth of invadopodia of A549 cells, which is responsible for the proliferation of cancer cells. Surface roughness of cells increased after treatment with hybrid, where cytoplasmic regions specifically showed higher roughness. Nanoindentation results suggest that changes in biomechanics occurred owing to possible internalization of the hybrid. The changes in force spectra of treated cells indicated a possible greater interaction between the cells and hybrid with distinct stiffness and demonstrated the surface adherence and internalization of hybrid on or inside the cells.</P>

Variation in wall shear stress in channel networks of zebrafish models

Choi, Woorak,Kim, Hye Mi,Park, Sungho,Yeom, Eunseop,Doh, Junsang,Lee, Sang Joon Royal Society 2017 Journal of the Royal Society, Interface Vol.14 No.127

<P>Physiological functions of vascular endothelial cells (ECs) vary depending on wall shear stress (WSS) magnitude, and the functional change affects the pathologies of various cardiovascular systems. Several in vitro and in vivo models have been used to investigate the functions of ECs under different WSS conditions. However, these models have technical limitations in precisely mimicking the physiological environments of ECs and monitoring temporal variations of ECs in detail. Although zebrafish (Danio rerio) has several strategies to overcome these technical limitations, zebrafish cannot be used as a perfect animal model because applying various WSS conditions on blood vessels of zebrafish is difficult. This study proposes a new zebrafish model in which various WSS can be applied to the caudal vein. The WSS magnitude is controlled by blocking some parts of blood-vessel networks. The accuracy and reproducibility of the proposed method are validated using an equivalent circuit model of blood vessels in zebrafish. The proposed method is applied to lipopolysaccharide (LPS)-stimulated zebrafish as a typical application. The proposed zebrafish model can be used as an in vivo animal model to investigate the relationship between WSS and EC physiology or WSS-induced cardiovascular diseases.</P>

Enhanced signal-to-noise ratios in frog hearing can be achieved through amplitude death

Royal Society 2013 Journal of the Royal Society, Interface Vol.10 No.87

<P>In the ear, hair cells transform mechanical stimuli into neuronal signals with great sensitivity, relying on certain active processes. Individual hair cell bundles of non-mammals such as frogs and turtles are known to show spontaneous oscillation. However, hair bundles <I>in vivo</I> must be quiet in the absence of stimuli, otherwise the signal is drowned in intrinsic noise. Thus, a certain mechanism is required in order to suppress intrinsic noise. Here, through a model study of elastically coupled hair bundles of bullfrog sacculi, we show that a low stimulus threshold and a high signal-to-noise ratio (SNR) can be achieved through the amplitude death phenomenon (the cessation of spontaneous oscillations by coupling). This phenomenon occurs only when the coupled hair bundles have inhomogeneous distribution, which is likely to be the case in biological systems. We show that the SNR has non-monotonic dependence on the mass of the overlying membrane, and find out that the SNR has maximum value in the region of amplitude death. The low threshold of stimulus through amplitude death may account for the experimentally observed high sensitivity of frog sacculi in detecting vibration. The hair bundles' amplitude death mechanism provides a smart engineering design for low-noise amplification.</P>

Improvement of the aerodynamic performance by wing flexibility and elytra–hind wing interaction of a beetle during forward flight

Le, Tuyen Quang,Truong, Tien Van,Park, Soo Hyung,Quang Truong, Tri,Ko, Jin Hwan,Park, Hoon Cheol,Byun, Doyoung Royal Society 2013 Journal of the Royal Society, Interface Vol.10 No.85

<P>In this work, the aerodynamic performance of beetle wing in free-forward flight was explored by a three-dimensional computational fluid dynamics (CFDs) simulation with measured wing kinematics. It is shown from the CFD results that twist and camber variation, which represent the wing flexibility, are most important when determining the aerodynamic performance. Twisting wing significantly increased the mean lift and camber variation enhanced the mean thrust while the required power was lower than the case when neither was considered. Thus, in a comparison of the power economy among rigid, twisting and flexible models, the flexible model showed the best performance. When the positive effect of wing interaction was added to that of wing flexibility, we found that the elytron created enough lift to support its weight, and the total lift (48.4 mN) generated from the simulation exceeded the gravity force of the beetle (47.5 mN) during forward flight.</P>

Mechanically inferior constituents in spider silk result in mechanically superior fibres by adaptation to harsh hydration conditions: a molecular dynamics study

Kim, Yoonjung,Lee, Myeongsang,Baek, Inchul,Yoon, Taeyoung,Na, Sungsoo Royal Society 2018 Journal of the Royal Society, Interface Vol.15 No.144

<P>Spider silk exhibits mechanical properties such as high strength and toughness that are superior to those of any man- made fibre (Bourzac 2015 Nature 519, S4-S6 (doi:10.1038/519S4a)). This high strength and toughness originates from a combination of the crystalline (exhibiting robust strength) and amorphous (exhibiting superb extensibility) regions present in the silk (Asakura et al. 2015 Macromolecules 48, 2345-2357 (doi:10.1021/acs.macromol.5b00160)). The crystalline regions comprise a mixture of polyalanine and poly-glycine-alanine. Poly-alanine is expected to be stronger than poly-glycine-alanine, because alanine exhibits greater interactions between the strands than glycine (Tokareva et al. 2014 Acta Biomater. 10, 1612-1626 (doi:10.1016/j.actbio.2013.08.020)). We connect this characteristic sequence to the interactions observed upon the hydration of spider silk. Like most proteinaceous materials, spider silks become highly brittle upon dehydration, and thus water collection is crucial to maintaining its toughness (Gosline et al. 1986 Endeavour 10, 37-43 (doi:10.1016/0160-9327(86)90049-9)). We report on the molecular dynamic simulations of spider silk structures with different sequences for the crystalline region of the silk structures, of wild-type (WT), poly-alanine, and poly-glycine-alanine. We reveal that the characteristic sequence of spider silk results in the b-sheets being maintained as the degree of hydration changes and that the high water collection capabilities of WT spider silk sequence prevent the silk from becoming brittle and weak in dry conditions. The characteristic crystalline sequence of spider dragline silk is therefore relevant not for maximizing the interactions between the strands but for adaption to changing hydration conditions to maintain an optimal performance even in harsh conditions.</P>

M-type potassium conductance controls the emergence of neural phase codes: a combined experimental and neuron modelling study

Kwag, Jeehyun,Jang, Hyun Jae,Kim, Mincheol,Lee, Sujeong Royal Society 2014 Journal of the Royal Society, Interface Vol.11 No.99

<P>Rate and phase codes are believed to be important in neural information processing. Hippocampal place cells provide a good example where both coding schemes coexist during spatial information processing. Spike rate increases in the place field, whereas spike phase precesses relative to the ongoing theta oscillation. However, what intrinsic mechanism allows for a single neuron to generate spike output patterns that contain both neural codes is unknown. Using dynamic clamp, we simulate an <I>in vivo</I>-like subthreshold dynamics of place cells to <I>in vitro</I> CA1 pyramidal neurons to establish an <I>in vitro</I> model of spike phase precession. Using this <I>in vitro</I> model, we show that membrane potential oscillation (MPO) dynamics is important in the emergence of spike phase codes: blocking the slowly activating, non-inactivating K<SUP>+</SUP> current (<I>I</I><SUB>M</SUB>), which is known to control subthreshold MPO, disrupts MPO and abolishes spike phase precession. We verify the importance of adaptive <I>I</I><SUB>M</SUB> in the generation of phase codes using both an adaptive integrate-and-fire and a Hodgkin–Huxley (HH) neuron model. Especially, using the HH model, we further show that it is the perisomatically located <I>I</I><SUB>M</SUB> with slow activation kinetics that is crucial for the generation of phase codes. These results suggest an important functional role of <I>I</I><SUB>M</SUB> in single neuron computation, where <I>I</I><SUB>M</SUB> serves as an intrinsic mechanism allowing for dual rate and phase coding in single neurons.</P>