Seok Hee Kang

Enhanced Osteogenesis by Reduced Graphene Oxide/Hydroxyapatite Nanocomposites

Recently, graphene-based nanomaterials, in the form of two dimensional substrates or three dimensional foams, have attracted considerable attention as bioactive scaffolds to promote the differentiation of various stem cells towards specific lineages. On the other hand, the potential advantages of using graphene-based hybrid composites directly as factors inducing cellular differentiation as well as tissue regeneration are unclear. This study examined whether nanocomposites of reduced graphene oxide (rGO) and hydroxyapatite (HAp) (rGO/HAp NCs) could enhance the osteogenesis of MC3T3-E1 preosteoblasts and promote new bone formation. When combined with HAp, rGO synergistically promoted the spontaneous osteodifferentiation of MC3T3-E1 cells without hindering their proliferation. This enhanced osteogenesis was corroborated from determination of alkaline phosphatase activity as early stage markers of osteodifferentiation and mineralization of calcium and phosphate as late stage markers. Immunoblot analysis showed that rGO/HAp NCs increase the expression levels of osteopontin and osteocalcin significantly. Furthermore, rGO/HAp grafts were found to significantly enhance new bone formation in full-thickness calvarial defects without inflammatory responses. These results suggest that rGO/HAp NCs can be exploited to craft a range of strategies for the development of novel dental and orthopedic bone grafts to accelerate bone regeneration because these graphene-based composite materials have potentials to stimulate osteogenesis.

Enhanced Neural Cell Adhesion and Neurite Outgrowth on Graphene-Based Biomimetic Substrates

Neural cell adhesion and neurite outgrowth were examined on graphene-based biomimetic substrates. The biocompatibility of carbon nanomaterials such as graphene and carbon nanotubes (CNTs), that is, single-walled and multiwalled CNTs, against pheochromocytoma-derived PC-12 neural cells was also evaluated by quantifying metabolic activity (with WST-8 assay), intracellular oxidative stress (with ROS assay), and membrane integrity (with LDH assay). Graphene films were grown by using chemical vapor deposition and were then coated onto glass coverslips by using the scooping method. Graphene sheets were patterned on SiO2/Si substrates by using photolithography and were then covered with serum for a neural cell culture. Both types of CNTs induced significant dose-dependent decreases in the viability of PC-12 cells, whereas graphene exerted adverse effects on the neural cells just at over 62.5 ppm. This result implies that graphene and CNTs, even though they were the same carbon-based nanomaterials, show differential influences on neural cells. Furthermore, graphene-coated or graphene-patterned substrates were shown to substantially enhance the adhesion and neurite outgrowth of PC-12 cells. These results suggest that graphene-based substrates as biomimetic cues have good biocompatibility as well as a unique surface property that can enhance the neural cells, which would open up enormous opportunities in neural regeneration and nanomedicine.

Graphene oxide-coated guided bone regeneration membranes with enhanced osteogenesis: Spectroscopic analysis and animal study

ABSTRACT Guided bone regeneration (GBR) is a technique where a barrier membrane is placed over the bone defect to prevent cell growth from the connective tissue and epithelium. Titanium (Ti) has excellent mechanical properties and is one of the most frequently used materials in implant dentistry. This study examined how graphene oxide (GO)-coated Ti (GO-Ti) membranes can enhance the osteogenesis of MC3T3-E1 preosteoblasts and promote new bone formation for potential applications to GBR. The physicochemical properties of GO-Ti membranes were characterized by atomic force microscopy, Raman spectroscopy, X-ray diffraction, and contact angle measurements. The cellular behaviors of MC3T3-E1 preosteoblasts on GO-Ti membranes were examined by cell counting kit-8 and alkaline phosphatase (ALP) activity assays. The effects of GO-Ti membranes on bone regeneration were evaluated by implanting them into rat calvarial defects. GO was coated uniformly on Ti substrates, which allowed a decrease in surface roughness and contact. GO-Ti membranes stimulated significantly ALP activity without interfering with their proliferation. Furthermore, GO-Ti membranes enhanced new bone formation significantly in full-thickness calvarial defects without inflammatory responses. Therefore, this suggests that GO-Ti membranes can be applied effectively to GBR because these graphene-coated Ti membranes have potent effects on stimulating osteogenic differentiation and exhibit superior bioactivity.

Three-dimensional graphene oxide-coated polyurethane foams beneficial to myogenesis

Abstract The development of three dimensional (3D) scaffolds for promoting and stimulating cell growth is one of the greatest concerns in biomedical and tissue engineering. In the present study, novel biomimetic 3D scaffolds composed of polyurethane (PU) foam and graphene oxide (GO) nanosheets were designed, and their potential as 3D scaffolds for skeletal tissue regeneration was explored. The GO-coated PU foams (GO-PU foams) were characterized by scanning electron microscopy and Raman spectroscopy. It was revealed that the 3D GO-PU foams consisted of an interconnected foam-like network structure with an approximate 300 μm pore size, and the GO was uniformly distributed in the PU foams. On the other hand, the myogenic stimulatory effects of GO on skeletal myoblasts were also investigated. Moreover, the cellular behaviors of the skeletal myoblasts within the 3D GO-PU foams were evaluated by immunofluorescence analysis. Our findings showed that GO can significantly promote spontaneous myogenic differentiation without any myogenic factors, and the 3D GO-PU foams can provide a suitable 3D microenvironment for cell growth. Furthermore, the 3D GO-PU foams stimulated spontaneous myogenic differentiation via the myogenic stimulatory effects of GO. Therefore, this study suggests that the 3D GO-PU foams are beneficial to myogenesis, and can be used as biomimetic 3D scaffolds for skeletal tissue engineering.

Preparation of ZnO Nanorod/Graphene/ZnO Nanorod Epitaxial Double Heterostructure for Piezoelectrical Nanogenerator by Using Preheating Hydrothermal.

Well-aligned ZnO nanostructures have been intensively studied over the last decade for remarkable physical properties and enormous applications. Here, we describe a one-step fabrication technique to synthesis freestanding ZnO nanorod/graphene/ZnO nanorod double heterostructure. The preparation of the double heterostructure is performed by using thermal chemical vapor deposition (CVD) and preheating hydrothermal technique. In addition, the morphological properties were characterized by using the scanning electron microscopy (SEM). The utility of freestanding double heterostructure is demonstrated by fabricating the piezoelectric nanogenerator. The electrical output is improved up to 200% compared to that of a single heterostructure owing to the coupling effect of the piezoelectricity between the arrays of ZnO nanorods on the top and bottom of graphene. This unique double heterostructure have a tremendous potential for applications of electrical and optoelectrical devices where the high number density and specific surface area of nanorod are needed, such as pressure sensor, immuno-biosensor and dye-sensitized solar cells.

Recent Progress in Flexible/Wearable Electronics

Flexible devices have been developed from their rigid, heavy origins to become bendable, stretchable and portable. Such a paper displays, e-skin, textile electronics are emerging research areas and became a mainstream of overall industry. Thin film transistors, diodes and sensors built on plastic sheets, textile and other uncon- ventional substrates have a potential applications in wearable displays, biomedical devices and electronic system. In this review, we describe current trends in technologies for flexible/wearable electronics.

용매증발기반 자기조립을 이용한 단일벽 탄소나노튜브 정렬 및 트랜지스터 응용

Controlling the stick and slip motions of the contact lines in a confined geometry comprised of a spherical lens with a flat substrate is useful for manufacturing polymer ring patterns. We used a sphere on a flat geometry, by which we could control the interfaces of the solution, vapor and substrate. By this method, hundreds of concentric ring-pattern formations of a linear conjugated polymer, poly [2-methoxy-5-(2-thylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), were generated with excellent regularity over large areas after complete solvent evaporation. Subsequently, the MEH-PPV ring patterns played a role as a directed template to organize highly regular concentric rings of single-walled carbon nanotubes(SWCNTs); when a droplet of the SWCNT suspension in water was casted onto the prepared substrate, hydrophobic polymer patterns confined the water dispersed SWCNTs in between the hydrophilicized SiO2/Si substrate. As the solvent evaporated, SWCNT-rings were formed in between MEH-PPV rings with controlled density. Finally, we used a lift-off process to produce SWCNT patterns by the removal of a sacrificial polymer template with organic solvent. We also fabricated a field effect transistor using self-assembled SWCNT networks on a SiO2/Si substrate.