Hyungbin Son

Enhancement of piezoelectricity via electrostatic effects on a textile platform

We have shown the enhanced piezoelectricity by electrostatic effects on a textile based platform. The electrostatic and piezoelectric effects were hybridized by integrating piezoelectric ZnO nanowires and a charged dielectric film on a wearable textile substrate. The hybrid textile nanogenerator produced an output voltage of 8 V and an output current of 2.5 μA. Using a simple AC–DC converter circuit, we operated the green organic light-emitting diode and a liquid crystal display panel using a 100 dB sonic wave.

Thermal Conversion of Electronic and Electrical Properties of AuCl3-Doped Single-Walled Carbon Nanotubes

By using carbon-free inorganic atomic layer involving heat treatment from 150 to 300 °C, environmentally stable and permanent modulation of the electronic and electrical properties of single-walled carbon nanotubes (SWCNTs) from p-type to ambi-polar and possibly to n-type has been demonstrated. At low heat treatment temperature, a strong p-doping effect from Au(3+) ions to CNTs due to a large difference in reduction potential between them is dominant. However at higher temperature, the gold species are thermally reduced, and thermally induced CNT-Cl finally occurs by the decomposition reaction of AuCl(3). Thus, in the AuCl(3)-doped SWCNTs treated at higher temperature, the p-type doping effect is suppressed and an n-type property from CNT-Cl is thermally induced. Thermal conversion of the majority carrier type of AuCl(3)-doped SWNTs is systematically investigated by combining various optical and electrical tools.

Modulation of the Dirac point voltage of graphene by ion-gel dielectrics and its application to soft electronic devices.

We investigated systematic modulation of the Dirac point voltage of graphene transistors by changing the type of ionic liquid used as a main gate dielectric component. Ion gels were formed from ionic liquids and a non-triblock-copolymer-based binder involving UV irradiation. With a fixed cation (anion), the Dirac point voltage shifted to a higher voltage as the size of anion (cation) increased. Mechanisms for modulation of the Dirac point voltage of graphene transistors by designing ionic liquids were fully understood using molecular dynamics simulations, which excellently matched our experimental results. It was found that the ion sizes and molecular structures play an essential role in the modulation of the Dirac point voltage of the graphene. Through control of the position of their Dirac point voltages on the basis of our findings, complementary metal-oxide-semiconductor (CMOS)-like graphene-based inverters using two different ionic liquids worked perfectly even at a very low source voltage (V(DD) = 1 mV), which was not possible for previous works. These results can be broadly applied in the development of low-power-consumption, flexible/stretchable, CMOS-like graphene-based electronic devices in the future.

Categorizer: a tool to categorize genes into user-defined biological groups based on semantic similarity.

BackgroundCommunalities between large sets of genes obtained from high-throughput experiments are often identified by searching for enrichments of genes with the same Gene Ontology (GO) annotations. The GO analysis tools used for these enrichment analyses assume that GO terms are independent and the semantic distances between all parent–child terms are identical, which is not true in a biological sense. In addition these tools output lists of often redundant or too specific GO terms, which are difficult to interpret in the context of the biological question investigated by the user. Therefore, there is a demand for a robust and reliable method for gene categorization and enrichment analysis.ResultsWe have developed Categorizer, a tool that classifies genes into user-defined groups (categories) and calculates p-values for the enrichment of the categories. Categorizer identifies the biologically best-fit category for each gene by taking advantage of a specialized semantic similarity measure for GO terms. We demonstrate that Categorizer provides improved categorization and enrichment results of genetic modifiers of Huntington’s disease compared to a classical GO Slim-based approach or categorizations using other semantic similarity measures.ConclusionCategorizer enables more accurate categorizations of genes than currently available methods. This new tool will help experimental and computational biologists analyzing genomic and proteomic data according to their specific needs in a more reliable manner.

Comparison Study on Photodynamic Anticancer Activity of Multifunctional Magnetic Particles by Formation of Cations

In this paper, we have synthesized multifunctional magnetic particles (MNPs) using by two different ferrite submicrometer paticles (Fe₃O₄@HP and CoFe₂O₄@HP) with different surface properties. Two different multifunctional particles have the same particle sizes within the error tolerance of 4.5%. The concentration measurement of the hematoporphyrin (HP) molecule indicates that the weight of HP molecules bonded to the surface of the Fe₃O₄ particles is smaller than that of the CoFe₂O₄ particles. Moreover, we have evaluated their biocompatibilities and photodynamic anticancer activities on mammalian cells. The two MNPs have demonstrated that they both have good biocompatibilities without any cytotoxicity and anticancer activities in the concentration range of 0-50 μg/mL. Specifically, photodynamic-killing activities of both MNPs were measured to be 100% for CoFe₂O₄@HP, and were measured to be 37.9 ± 3.5% and 9.2 ± 2.5% for Fe₃O₄@HP in 25 and 50 μg/mL of both MNPs. These results suggest that both MNPs can be safely used to for clinical photodynamic cancer therapy, although the CoFe₂O₄@HP showed a slightly better photo-killing efficacy compared with the Fe₃O₄@HP in prostate cancer.

Measurement of adhesion and bonding strength studies in 3D interconnect structures using atomic force microscopy

The wafer bonding process has become a flexible approach to material and device integration. The bonding strength in 3-dimensional processes is a crucial factor in various interface bonding processes such as silicon to silicon, silicon to metal, and oxide to adhesive intermediates. A method for measurement of bonding strength is proposed utilizing an ‘atomic force microscopy (AFM) applied carbon nanotube (CNT) probe tip’ which requires relatively simple preparation of sample and is able to measure bond strength regardless of film type. The bonding strength of the SiO2-Si surfaces cleaned with SPFM was 0.089 J/m2, while the bonding strength of surfaces cleaned with RCA 1 (NH4OH:H2O:H2O2) was 0.044 J/m2. This work verified the possibility that the new method is capable of accurately measuring bonding strength. It was also confirmed that more effective bonding is possible after cleaning with SPFM.

Effect of heterogeneous multi-layered gelatin scaffolds on the diffusion characteristics and cellular activities of preosteoblasts

AbstractIn vitro bone tissue development requires mimicking the in vivo bone environment, as well as a suitable combination of cells and scaffold for optimal results. We developed heterogeneous multilayered gelatin scaffolds with diverse compositions of porous structures by using a stacking procedure in which each layer had a different pore size depending on the gelatin concentration used. We then used these gelatin scaffolds to investigate the in vitro effect of varying porous structural compositions on the diffusion characteristics and cellular activity of MC3T3-E1 cells. We have shown that multilayered scaffolds with a larger pore size on the outer layers exhibited enhanced diffusion characteristics such as the diffusion coefficient compared to other scaffolds, including single-layered scaffolds with single pore size and multilayered scaffolds with a smaller pore size on the outer layers. Moreover, multilayered scaffolds with a larger pore size on the outer layers promoted cell adhesion, proliferation, and differentiation of MC3T3-E1 preosteoblast cells by providing a favorable environment for the cells within the tissue-engineered scaffold.

Three-Dimensional Graphene–RGD Peptide Nanoisland Composites That Enhance the Osteogenesis of Human Adipose-Derived Mesenchymal Stem Cells

Graphene derivatives have immense potential in stem cell research. Here, we report a three-dimensional graphene/arginine-glycine-aspartic acid (RGD) peptide nanoisland composite effective in guiding the osteogenesis of human adipose-derived mesenchymal stem cells (ADSCs). Amine-modified silica nanoparticles (SiNPs) were uniformly coated onto an indium tin oxide electrode (ITO), followed by graphene oxide (GO) encapsulation and electrochemical deposition of gold nanoparticles. A RGD–MAP–C peptide, with a triple-branched repeating RGD sequence and a terminal cysteine, was self-assembled onto the gold nanoparticles, generating the final three-dimensional graphene–RGD peptide nanoisland composite. We generated substrates with various gold nanoparticle–RGD peptide cluster densities, and found that the platform with the maximal number of clusters was most suitable for ADSC adhesion and spreading. Remarkably, the same platform was also highly efficient at guiding ADSC osteogenesis compared with other substrates, based on gene expression (alkaline phosphatase (ALP), runt-related transcription factor 2), enzyme activity (ALP), and calcium deposition. ADSCs induced to differentiate into osteoblasts showed higher calcium accumulations after 14–21 days than when grown on typical GO-SiNP complexes, suggesting that the platform can accelerate ADSC osteoblastic differentiation. The results demonstrate that a three-dimensional graphene–RGD peptide nanoisland composite can efficiently derive osteoblasts from mesenchymal stem cells.

Size-dependent effects of graphene oxide on the osteogenesis of human adipose-derived mesenchymal stem cells

Graphene derivatives are known to be suitable for biomedical applications, especially for stem cell-based therapies. Herein, we report the size effects of graphene oxide (GO) on differentiation of human adipose-derived mesenchymal stem cells (hADMSCs), using micro-sized (MGO) and nano-sized graphene oxide (NGO) sheets. The MGO and NGO sheets having lateral sizes of 1-10 μm and 100-300 nm, respectively, are coated on glass substrates by drop casting. The hADMSCs grown on the MGO-coated substrates show enhanced cell spreading and proliferation rate when compared with those of NGO counterpart, regardless of their densities. The GO size-dependency of hADMSCs becomes more prominent when it comes to their differentiation capabilities. After 4 weeks of differentiation under the same culture conditions, the osteogenesis of hADMSCs grown on the MGO-coated substrate is particularly higher than that on the NGO-coated substrate. The difference in osteogenic differentiation of hADMSCs is found to be most dominant after 21-28 days of differentiation according to the calcification level of osteoblasts. These finding signify the importance of graphene size in controlling the osteogenesis of hADMSCs, which may shed new insight into the use of graphene-based materials for stem cell research and therapy.

The Adoption of Building Information Modeling in the Design Organization: An Empirical Study of Architects inKorean Design Firms

Recently, Building Information Modeling (BIM) technology has attracted much attention in the Architecture, Engineering, and Construction (AEC) industry. Despite the growing interest in BIM technology, the benefits of BIM have not yet been fully realized during the course of implementation of BIM because of its low adoption rate among architects. Therefore, it is significant important in successful adoption of BIM in design organizations, understanding of the factors influencing the adoption of BIM. The aim of this study is to empirically examine the individual, organizational, social, and technical factors affecting architects’ adoption of BIM. The 162 architects with experience using BIM tools at three major design firms in South Korea were selected to participate in the face-to-face survey. This study extends the Technology Acceptance Model (TAM) by incorporating constructs such as computer self-efficacy from the individual domain, top management support and technical support from the organizational domain, subjective norm from the social domain and compatibility from the technical domain. The results strongly support the extended TAM in predicting the intention of users to adopt BIM. It also demonstrates the significant effect of computer self-efficacy, top management support, subjective norm, and compatibility on behavioral intention through perceived ease of use and perceived usefulness. This study provides academics and practitioners with the understanding of factors leading to the successful implementation of BIM in design organizations. It also provides insight into the role management plays in the adoption of BIM among architects in the AEC industry.