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A new type of quasi-distributed sensor system is implemented using an active mode locking (AML) laser cavity with multiple partially reflecting segments. The mode locking frequency of the AML laser is linearly proportional to the overall lasing cavity length. To implement multiple resonators having multiple reflection points installed in a sensing fiber, two types of partial reflectors (PRs) are implemented for an in-line configuration, one with fiber Bragg grating and the other with a fiber Fabry&ndash, Perot interferometer. Since the laser has oscillated only when the modulation frequencies for the mode locking frequency match with the corresponding resonator lengths, it is possible to read the multiple partially reflecting segments along the sensing fiber. The difference between two corresponding mode locking frequencies is changing proportionally with the segment length variation between two PRs upon strain application. The segment length change caused by the applied strain can be successfully measured with a linear sensitivity between mode locking frequency and displacement, linearity over 0.99, and spatial position resolution below meter order.

Tissues are often damaged by physical trauma, infection or tumors. A slight injury heals naturally through the normal healing process, while severe injury causes serious health implications. Therefore, many efforts have been devoted to treat and repair various tissue defects. Recently, tissue engineering approaches have attracted a rapidly growing interest in biomedical fields to promote and enhance healing and regeneration of large-scale tissue defects. On the other hand, with the recent advances in nanoscience and nanotechnology, various nanomaterials have been suggested as novel biomaterials. Graphene, a two-dimensional atomic layer of graphite, and its derivatives have recently been found to possess promoting effects on various types of cells. In addition, their unique properties, such as outstanding mechanical and biological properties, allow them to be a promising option for hard tissue regeneration. Herein, we summarized recent research advances in graphene-based nanocomposites for hard tissue regeneration, and highlighted their promising potentials in biomedical and tissue engineering.

A disposable glucose biosensor has been fabricated on the surface of a cost-effective pencil graphite electrode (PGE) by an electrochemical method, using glucose oxidase (GOx) and reduced graphene oxide (rGO). Electrochemical pre-treatment of the PGE enables the adsorption of the rGO–GOx biocomposite. The biocomposites of GOx and rGO were simply prepared by the electrochemical potential cycling method. Efficient immobilization of rGO–GOx is confirmed by field emission scanning electron microscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry measurements. The rGO nanosheets enhance direct electron transfer (DET) between GOx and the electrode surface. Determination of glucose indirectly by O2 reduction was achieved, which showed high sensitivity, selectivity, reproducibility and stability without a redox mediator. The sensor exhibits a linear current response for a wide range of glucose concentrations between 1.0 × 10−5 and 1.0 × 10−3 M (R = 0.998), and a dynamic range up to 10.0 × 10−3 M with a detection limit of 5.8 μM. The rGO–GOx biosensor showed an excellent anti-interference ability against electroactive species and proved to be useful for the determination of glucose in human serum samples.

Osteoprogenitor cells, known as preosteoblasts, that arise from mesenchymal stem cells in the bone marrow are types of cells that work in the growth or repair of bones. These cells possess the prominent potential to differentiate toward the osteogenic lineage, and therefore offer promising opportunities for bone tissue engineering and regenerative therapy. However, to fully exploit the application of osteoprogenitor cells in bone regeneration, it is critical to develop biochemical, physical or pharmaceutical factors that can precisely control their osteogenic differentiation. In this study, we hypothesized that reduced graphene oxide (rGO) and hydroxyapatite (HAp) composites could synergistically enhance the osteogenic differentiation of preosteoblasts. Without interference with the proliferation of MC3T3-E1 preosteoblasts, rGO/HAp composites synergistically enhanced the osteogenic differentiation of the preosteoblasts, which had been confirmed by determining alkaline phosphatase activity and mineralization of calcium and phosphate as early and late stage markers of osteogenic differentiation. This osteogenic activity mediated by rGO/HAp composites was further accelerated under osteogenic culture conditions. It is suggested that rGO/HAp hybrid composites can serve as biocompatible, transferable, and implantable scaffolds for bone regeneration because these graphene-based composite materials have the potential to promote spontaneous osteogenesis in the absence of any osteogenic factors.

Currently, applications of graphene and its derivatives have been reported in many fields. In particular, graphene oxide (GO) has been studied for biomedical applications, such as cell imaging, biosensors and drug delivery systems, because of its good biocompatibility and excellent physicochemical properties. Recently, much research has been conducted to control cell behavior, including attachment, proliferation and differentiation by using GO. On the other hand, the effects of GO on myogenic differentiation have not been explored. In the present study, the influence of GO on myogenic differentiation was investigated. This study assessed the cytotoxicity of GO and evaluated the myogenic differentiation of C2C12 murine myoblasts in growth media containing 10 μg/mL of GO. The physicochemical properties of GO were characterized by using atomic force microscopy (AFM) and Raman spectroscopy. The cytotoxicity was evaluated by using a WST-8 assay. An analysis of myogenic differentiation was performed by using immunofluorescence staining for the myosin heavy chain (MHC; myogenic differentiation marker) and was determined by calculating the amount of multinucleate myotube formation, the fusion index and the maturation index. GO did not exhibit cytotoxicity at low concentrations and effectively stimulated the myogenic differentiation of C2C12 murine myoblasts. Therefore, GO has potential skeletal tissue engineering applications.

In this paper, we examined a novel molecularly imprinted polymer (MIP) patterned matrix, consisting of methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) as functional and cross-linking monomers, respectively, for detection of trace atrazine in an aqueous solution. A solvent assisted soft lithography and UV-initiated polymerization were used to develop striped poly(MAA-EGDMA) patterns. In comparison to a planar MIP film (Δ f p-MIP = −158 Hz), the striped patterns showed faster sensing response (Δ f s-MIP = −269 Hz) for the 30 min detection period due to the relatively increased binding sites generated from the MIP stripes. Furthermore, the sensitivity of the MIP sensor was found to be −9.98 Hz (μM) −1 via gravimetric quartz crystal microbalance (QCM) measurements and the selectivity of the MIP stripes was evaluated through sensing characteristics of other herbicides. Thus, a control of binding sites via this lithographic technique could contribute to the development of efficient MIP sensing platforms.

The interfacial friction of graphene transferred on a SiO2 grating was investigated using a lateral force microscope with various sliding directions. Quantification of the frictional force of graphene, using adhesion force and friction loop measured from both sloped and flat surfaces, revealed that graphene has a low surface energy and repetitive friction switching from 0.066 to 0.087, which indicates an extremely low shear strength of the contact junction, along with a peculiar periodicity of 60°, which is consistent with the lattice periodicity of graphene. The observed periodicity was attributed to the atomistic incommensurability at the interface, with minimal lattice deformation under interfacial sliding conditions.

We present broadband antireflective microstructures (AMSs) for high-performance imaging systems in mid- and far-infrared wavelength ranges. Diffraction efficiencies of AMSs on ZnS substrates were calculated using a rigorous coupled wave analysis method. The results show the effect of height, period, and shape of AMSs on the reflection characteristics. We also discuss the optimum geometry of AMSs by considering fabrication tolerances.

Hierarchically arranged stripes of photoswitchable liquid crystal polymers (LCPs) containing azobenzene moieties were conveniently crafted via a flow-enabled self-assembly (FESA). Interestingly, by subjecting a drop of LCP solution to dry in a restricted geometry comprising two nearly parallel plates with a stationary upper plate and a movable lower plate that programmably traveled in a "stop-and-move" manner during the FESA process, photoswitchable LCP stripes were yielded, displaying two modes of deposition, namely, periodic primary stripes of large dimensions and regularly spaced secondary stripes of small dimensions situated between adjacent primary stripes (i.e., forming hierarchical LCP stripes). Notably, these hierarchical azobenzene moieties-containing stripes demonstrated sequential photoinduced reversible phase transition (i.e., photoswitching) due to the thickness difference between primary and secondary stripes. A UV light-induced expansion effect was observed on the LCP stripes. Clearly, such rapid creation of hierarchical stripes by FESA represents a robust means of organizing polymers, nanoparticles, colloids, DNA, etc. into complex yet ordered patterns over a large area in a simple and controllable manner for potential use in surface relief grating, photoactuators, photoswitchable devices, antifake labels, etc.

Tissues are often damaged by physical trauma, infection or tumors. A slight injury heals naturally through the normal healing process, while severe injury causes serious health implications. Therefore, many efforts have been devoted to treat and repair various tissue defects. Recently, tissue engineering approaches have attracted a rapidly growing interest in biomedical fields to promote and enhance healing and regeneration of large-scale tissue defects. On the other hand, with the recent advances in nanoscience and nanotechnology, various nanomaterials have been suggested as novel biomaterials. Graphene, a two-dimensional atomic layer of graphite, and its derivatives have recently been found to possess promoting effects on various types of cells. In addition, their unique properties, such as outstanding mechanical and biological properties, allow them to be a promising option for hard tissue regeneration. Herein, we summarized recent research advances in graphene-based nanocomposites for hard tissue regeneration, and highlighted their promising potentials in biomedical and tissue engineering.

Graphene is a two-dimensional atomic layer of graphite, where carbon atoms are assembled in a honeycombed lattice structure. Recently, graphene family nanomaterials, including pristine graphene, graphene oxide and reduced graphene oxide, have increasingly attracted a great deal of interest from researchers in a variety of science, engineering and industrial fields because of their unique structural and functional features. In particular, extensive studies have been actively conducted in the biomedical and related fields, including multidisciplinary and emerging areas, as their stimulating effects on cell behaviors have been becoming an increasing concern. Herein, we are attempting to summarize some of recent findings in the fields of tissue regeneration concerning the graphene family nanomaterial-functionalized biomimetic scaffolds, and to provide the promising perspectives for the possible applications of graphene family nanomaterial.

Bioinspired nanogenerators based on vertically aligned phage nanopillars are inceptively demonstrated. Vertically aligned phage nanopillars enable not only a high piezoelectric response but also a tuneable piezoelectricity. Piezoelectricity is also modulated by tuning of the protein's dipoles in each phage. The sufficient electrical power from phage nanopillars thus holds promise for the development of self-powered implantable and wearable electronics.

Human mesenchymal stem cells (hMSCs) have great potential as cell sources for bone tissue engineering and regeneration, but the control and induction of their specific differentiation into bone cells remain challenging. Graphene-based nanomaterials are considered attractive candidates for biomedical applications such as scaffolds in tissue engineering, substrates for SC differentiation and components of implantable devices, due to their biocompatible and bioactive properties. Despite the potential biomedical applications of graphene and its derivatives, only limited information is available regarding their osteogenic activity. This study concentrates upon the effects of reduced graphene oxide (rGO)-coated hydroxyapatite (HAp) composites on osteogenic differentiation of hMSCs. The average particle sizes of HAp and rGO were 1270 ± 476 nm and 438 ± 180 nm, respectively. When coated on HAp particulates, rGO synergistically enhanced spontaneous osteogenic differentiation of hMSCs, without hampering their proliferation. This result was confirmed by determining alkaline phosphatase activity and mineralization of calcium and phosphate as early and late stage markers of osteogenic differentiation. It is suggested that rGO-coated HAp composites can be effectively utilized as dental and orthopedic bone fillers since these graphene-based particulate materials have potent effects on stimulating the spontaneous differentiation of MSCs and show superior bioactivity and osteoinductive potential.

Extracellular matrices (ECMs) are network structures that play an essential role in regulating cellular growth and differentiation. In this study, novel nanofibrous matrices were fabricated by electrospinning M13 bacteriophage and poly(lactic-co-glycolic acid) (PLGA) and were shown to be structurally and functionally similar to natural ECMs. A genetically-engineered M13 bacteriophage was constructed to display Arg-Gly-Asp (RGD) peptides on its surface. The physicochemical properties of RGD peptide-displaying M13 bacteriophage (RGD-M13 phage)/PLGA nanofibers were characterized by using scanning electron microscopy and Fourier-transform infrared spectroscopy. We used immunofluorescence staining to confirm that M13 bacteriophages were homogenously distributed in RGD-M13 phage/PLGA matrices. Furthermore, RGD-M13 phage/PLGA nanofibrous matrices, having excellent biocompatibility, can enhance the behaviors of vascular smooth muscle cells. This result suggests that RGD-M13 phage/PLGA nanofibrous matrices have potentials to serve as tissue engineering scaffolds.

In recent years, graphene and its derivatives have attracted much interest in various fields, including biomedical applications. In particular, increasing attention has been paid to the effects of reduced graphene oxide (rGO) on cellular behaviors. On the other hand, dicalcium phosphate (DCP) has been widely used in dental and pharmaceutical fields. In this study, DCP composites coated with rGO (DCP-rGO composites) were prepared at various concentration ratios (DCP to rGO concentration ratios of 5:2.5, 5:5, and 5:10 μg/mL, respectively), and their physicochemical properties were characterized. In addition, the effects of DCP-rGO hybrid composites on MC3T3-E1 preosteoblasts were investigated. It was found that the DCP-rGO composites had an irregular granule-like structure with a diameter in the range order of the micrometer, and were found to be partially covered and interconnected with a network of rGO. The zeta potential analysis showed that although both DCP microparticles and rGO sheets had negative surface charge, the DCP-rGO composites could be successfully formed by the unique structural properties of rGO. In addition, it was demonstrated that the DCP-rGO composites significantly increased alkaline phosphatase activity and extracellular calcium deposition, indicating that the DCP-rGO hybrid composites can accelerate the osteogenic differentiation by the synergistic effects of rGO and DCP. Therefore, in conclusion, it is suggested that the DCP-rGO hybrid composites can be potent factors in accelerating the bone tissue regeneration.

Shape-memory polymers (SMPs) are an intriguing class of smart materials possessing reversible shape change and recovery capabilities. Effective routes to shape-memory porous films (SMPFs) are few and limited in scope owing to the difficulty in manipulating the shape change of pores by conventional methods. Herein we report an unconventional strategy for crafting light-driven SMPFs by judiciously constructing highly ordered porous films via a facile "breath figure" approach, followed by sequential vapor crosslinking and nondestructive directional light manipulation. Micropores can thus be transformed into other shapes including rectangle, rhombus and size-reduced micropores at room temperature. The transformed micropores can be reverted to their original shapes by either thermal annealing or UV irradiation. As such, this strategy expands the rich diversity of SMPs accessible.

A zero-power, low-cost ultraviolet (UV)-C colorimetric sensor is demonstrated using a gallium oxide and reduced graphene oxide (rGO) hybrid via photoelectrochemical reactions. A wide bandgap semiconductor (WBS) such as gallium oxide with an energy bandgap of 4.9 eV generates electron-hole pairs (EHPs) when exposed under a mercury lamp emitting 254 nm. While the conventional UVC sensors employing WBS convert the generated EHPs into an electrical signal via a solid-state junction device (SSD), our newly proposed UVC sensory system works by converting EHPs into an electrochemical reaction. The electrochemical reaction causes the degradation of a cationic thiazine redox dye, methylene blue (MB) and thereby spontaneously changes its color. As more rGO was hybridized with the gallium oxide, MB degradation was effectively expedited. Thus, the level of MB degradation under UVC can be evaluated as a UVC indicator. Unlike conventional SSD-based UVC sensors, our responsive colorimetric sensor can be applied where needed inexpensively and zero power.

Recently, there have been tremendous efforts to develop the biofunctional scaffolds by incorporating various biochemical factors. In the present study, we fabricated poly(lactic-co-glycolic acid) (PLGA) nanofiber sheets decorated with graphene oxide (GO) and RGD peptide. The decoration of GO and RGD peptide was readily achieved by using RGD peptide-displaying M13 bacteriophage (RGD-M13 phage) and electrospinning. Furthermore, the aligned GO-decorated PLGA/RGD peptide (GO-PLGA/RGD) ternary nanofiber sheets were prepared by magnetic field-assisted electrospinning, and their potentials as bifunctional scaffolds for facilitating myogenesis were explored. We characterized the physicochemical and mechanical properties of the sheets by scanning electron microscopy, Raman spectroscopy, contact angle measurement, and tensile test. In addition, the C2C12 skeletal myoblasts were cultured on the aligned GO-PLGA/RGD nanofiber sheets, and their cellular behaviors, including initial attachment, proliferation and myogenic differentiation, were evaluated. Our results revealed that the GO-PLGA/RGD nanofiber sheets had suitable physicochemical and mechanical properties for supporting cell growth, and could significantly promote the spontaneous myogenic differentiation of C2C12 skeletal myoblasts. Moreover, it was revealed that the myogenic differentiation was further accelerated on the aligned GO-PLGA/RGD nanofiber sheets due to the synergistic effects of RGD peptide, GO and aligned nanofiber structure. Therefore, , it is suggested that the aligned GO-PLGA/RGD ternary nanofiber sheets are one of the most promising approaches for facilitating myogenesis and promoting skeletal tissue regeneration.

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.

Cylindrical silk fiber (SF) was coated with Graphene oxide (GO) for capacitive humidity sensor applications. Negatively charged GO in the solution was attracted to the positively charged SF surface via electrostatic force without any help from adhesive intermediates. The magnitude of the positively charged SF surface was controlled through the static electricity charges created on the SF surface. The GO coating ability on the SF improved as the SF’s positive charge increased. The GO-coated SFs at various conditions were characterized using an optical microscope, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy, and LCR meter. Unlike the intact SF, the GO-coated SF showed clear response-recovery behavior and well-behaved repeatability when it was exposed to 20% relative humidity (RH) and 90% RH alternatively in a capacitive mode. This approach allows humidity sensors to take advantage of GO’s excellent sensing properties and SF’s flexibility, expediting the production of flexible, low power consumption devices at relatively low costs.

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.

In this study, vanadium pentoxide (V2O5) nanowires (NWs) with a diameter of 100–200 nm and a length of up to several micrometers as cathode for lithium ion batteries are synthesize using an electrospinning method. The reduced graphene oxide (rGO) and V2O5 NWs (GVO) composites are form by wet mixing the electrospun V2O5 NWs and rGO. Surface morphologies, microstructure and elemental mapping, and chemical bonding states of the composites are characterize. The initial and 60 cycles discharge capacities of GVO composite composed of 1 wt% rGO show up to 225 mAh g−1 and 125 mAh g−1, even higher than pure V2O5 NWs, when the lithium ion battery cycled between 2.0 and 4.0 V with a rate of 0.2 C, because of highly conductive rGO. The GVO composite could be promising as a high performance cathode for lithium ion batteries.

The zero (0-D) and one-dimensional (1-D) carbon nanomaterials have gained attention among researchers because they exhibit a larger surface area to volume ratio, and a smaller size. Furthermore, carbon is ubiquitously present in all living organisms. However, toxicity is a major concern while utilizing carbon nanomaterials for biomedical applications such as drug delivery, biosensing, and tissue regeneration. In the present review, we have summarized some of the recent findings of cellular and animal level toxicity studies of 0-D (carbon quantum dot, graphene quantum dot, nanodiamond, and carbon black) and 1-D (single-walled and multi-walled carbon nanotubes) carbon nanomaterials. The in vitro toxicity of carbon nanomaterials was exemplified in normal and cancer cell lines including fibroblasts, osteoblasts, macrophages, epithelial and endothelial cells of different sources. Similarly, the in vivo studies were illustrated in several animal species such as rats, mice, zebrafish, planktons and, guinea pigs, at various concentrations, route of administrations and exposure of nanoparticles. In addition, we have described the unique properties and commercial usage, as well as the similarities and differences among the nanoparticles. The aim of the current review is not only to signify the importance of studying the toxicity of 0-D and 1-D carbon nanomaterials, but also to emphasize the perspectives, future challenges and possible directions in the field.

Surface imprinting is an effective and simple method to fabricate and retain imprinted templates and recognizable nanocavities after template extraction. The imprinted effects can be controlled depending on the surface morphological changes. In general, a planar film has a limited area compared to a structured film with relatively higher surface-to-volume (S/V) ratio (A/A0), leading to the conventional sensing response upon the functionality of monomers in a fixed chemical composition. To increase the limited sensing properties and develop simple fabrication of porous arrays on a large area, we herein demonstrate the 2,4-dichlorophenoxyacetic acid (2,4-D, herbicide)-imprinted porous thin film lithographically patterned using photopolymerization and silica colloidal array as a master mold, derived by a unidirectional rubbing method. The resonant frequency changes with respect to the adsorption of 2,4-D molecules on a template-extracted porous poly(MAA-co-EGDMA) (MIP) film in a 10&minus, 1 mM aqueous solution of 2,4-D for 1 h, and when compared to the planar MIP film, the higher sensing response (&Delta, f = &minus, 283 &plusmn, 7 Hz &asymp, 1543 &plusmn, 38 ng/cm2) appears on the porous MIP film due to the specific recognition toward the more accessible templated cavities of the structured porous array, indicating an imprinting effect (If) value of 3.5. In addition, a higher selectivity for 2,4-D was also displayed on the porous MIP film compared to other herbicides. From these results, it was revealed that these improved sensing properties can be determined from the effects of various parameters (template functionality, film structuring, hydroxyl groups of silica colloids, etc.).

Hierarchical nanostructures have received much attention in recent years for their enhanced fundamental properties and potential applications in manifold areas. Herein, we report a simple and robust strategy for the fabrication of hierarchically nanostructured arrays of network-loaded ZnO nanorods (NRs) for use in UV photodetectors based on comprehensively optimized experimental conditions using the Taguchi approach. Specifically, the critical roles of the morphological and structural characteristics of ZnO NRs on the UV sensing properties are systematically evaluated. Results show that the specific deposition conditions of the secondary colloidal ZnO NRs onto the surface of the vertically grown ZnO NRs contribute to the formation of tightly organized networks over large areas, which act as favorable energy junction barriers, and thus play a significant role in enhancing the performance of the UV photodetector. Under optimal conditions, the sensitivity of the prepared UV sensors was improved to 8000, which has not been reported yet in the field of ZnO-based UV sensors with vertical networked nanostructures. Our comprehensive studies to optimize sensitivity, responsivity, and response/recovery times suggest a highly viable route for practical applications in photodetectors using this facile implementation of ZnO NRs.

Recently, the portable and wearable electronic devices, operated in the power range of microwatt to miliwatt, become available thank to the nanotechnology development and become an essential element for a comfortable life. Our recent research interest mainly focuses on the fabrication of piezoelectric nanogenerators based on smart nanomaterials such as zinc oxide novel nanostructure, M13 bacteriophage. In this talk, we present a simple strategy for fabricating the freestanding ZnO nanorods/graphene/ZnO nanorods double sided heterostructures. The characterization of the double sided heterostructures by using SEM, and Raman scattering spectroscopy reveals the key process and working mechanism of a formation of the heterostructure. The mechanism is discussed in detail in term of the decomposed seed layer and the vacancy defect of graphene. The approach consists of a facile one-step fabrication process and could achieve ZnO coverage with a higher number density than that of the epitaxial single heterostructure. The resulting improvement in the number density of nanorods has a direct beneficial effect on the double side heterostructured nanogenerator performance. The total output voltage and current density are improved up to~2 times compared to those of a single heterostructure due to the coupling of the piezoelectric effects from both upward and downward grown nanorods. The facile one-step fabrication process suggests that double sided heterostructures would improve the performance of electrical and optoelectrical device, such as touch pad, pressure sensor, biosensor and dye-sensitized solar cells. Further, ioinspired nanogenerators based on vertically aligned phage nanopillars are inceptively demonstrated. Vertically aligned phage nanopillars enable not only a high piezoelectric response but also a tuneable piezoelectricity. Piezoelectricity is also modulated by tuning of the protein's dipoles in each phage. The sufficient electrical power from phage nanopillars thus holds promise for the development of self-powered implantable and wearable electronics.

Photolithography is a unique process that can effectively manufacture micro/nano-sized patterns on various substrates. On the other hand, the meniscus-dragging deposition (MDD) process can produce a uniform surface of the substrate. Graphene oxide (GO) is the oxidized form of graphene that has high hydrophilicity and protein absorption. It is widely used in biomedical fields such as drug delivery, regenerative medicine, and tissue engineering. Herein, we fabricated uniform GO micropatterns via MDD and photolithography. The physicochemical properties of the GO micropatterns were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), and Raman spectroscopy. Furthermore, cell migration on the GO micropatterns was investigated, and the difference in cell migration on triangle and square GO micropatterns was examined for their effects on cell migration. Our results demonstrated that the GO micropatterns with a desired shape can be finely fabricated via MDD and photolithography. Moreover, it was revealed that the shape of GO micropatterns plays a crucial role in cell migration distance, speed, and directionality. Therefore, our findings suggest that the GO micropatterns can serve as a promising biofunctional platform and cell-guiding substrate for applications to bioelectric devices, cell-on-a-chip, and tissue engineering scaffolds.

Neurons are electrically excitable cells that transmit and process information in the nervous system. Recently, the differentiation of human neural stem cells to neurons has been shown to be enhanced on graphene substrates, and differentiated neurons have been shown to be able to still carry electrical signals when stimulated by graphene electrodes. Graphene films grown by using chemical vapor deposition were transferred onto glass coverslips by using the scooping method and were then coated with fetal bovine serum for a neuronal cell culture. The graphene substrates as biomimetic cues have been shown to enhance the neurite outgrowth of PC-12 cells. Our findings suggest that graphene has a unique surface property that can promote neuronal cells, which should open tremendous opportunities in neuroscience, neural engineering and regenerative medicine.

This study concentrates upon investigating differential cellular responses to carbon nanoparticles (CNPs) such as pristine graphene flakes, single-walled carbon nanotubes (SWCNTs) and multiwalled CNTs (MWCNTs), in human dermal fibroblasts (HDFs) vs. the L-929 fibroblast cell line. Characterizing the surface morphology of each CNP by using scanning electron microscopy, we determined their cytotoxicity profiles by quantifying the mitochondrial activity. Graphene was found to have an irregular flake-like shape with various lengths within the ranges of 50 ∼ 1500 nm. The estimated sizes of the SWCNTs and the MWCNTs were about 400 nm and 1000 nm in diameter, respectively and several µm in length. All the CNPs tested here exerted adverse effects on the viability of HDFs even at 15.6 ppm, through intracellular uptake whereas except MWCNTs, they did not show any cytotoxicity against L-929 cells at 250 ppm. This result suggests that CNPs can have a differential influence on normal fibroblasts vs. immortalized ones.

A multi-performance MWCNT-reinforced chitosan nanocomposite was fabricated by two methods: a freeze-drying process associated with the sublimation and compression (SAC) method; and the casting-evaporation (CE) method. We obtained ordered and multilayered structures with limited porosity, and well-dispersed MWCNT structures of the chitosan nanocomposite, especially with the SAC method. In the case of the nanocomposite films prepared by the CE method, the mechanical strength and elongation were significantly increased by up to about 40% compared with the pure chitosan films. On the other hand, the ordered and porous multilayered pure chitosan films prepared by the SAC method showed significantly lower tensile strength and elongation compared to the pure solid chitosan films. However, the relative enhancement of the mechanical properties of multilayered MWCNT/chitosan nanocomposites with porosity was higher, especially in terms of the elongation, which showed a twofold improvement in strain. The relaxed bond, which could be a relatively strong hydrogen bond, between the functional groups in the chitosan chains and the functionalized surface of the MWCNTs might be stretched under stress, thereby improving the ductility of the multilayered nanocomposite films. In addition, the viscoplastic behavior of the films by the CE method could become more active with increasing strain rate. Interestingly, ordered and porous pure chitosan films did not reveal the viscoplastic behavior; it rather presented strain softening and viscoelastic characteristics. However, the interaction between the chitosan chains and the surface-modified MWCNTs could regenerate viscoplasticity of the chitosan films.

Electrospun polyacrylonitrile (PAN) nanofibers were subjected to surface modification by atmospheric pressure (AP) plasma treatment with reactive gases. There was no damage to the surfaces after this plasma treatment, and no significant changes were observed in the morphologies of the nanofibers. The surface energies of O2- and N2-plasma-treated PAN (abbreviated as OPP and NPP, respectively) nanofibers increased by almost 138.7% and 190.6%, respectively, in comparison with that of an untreated nanofiber (256.6 mJ/m2). The binding energies of both OPP and NPP samples increased through the formation of many hydrophilic bonds involving oxygen. The current–voltage (I–V) characteristics of the nanofibers were determined for the different reactive gases, and the plasma-treated nanofibers showed higher protein immobilization compared to the untreated ones. This result indicates that electrospun PAN nanofibers have the potential to be used in protein biosensor systems.

This paper describes the fabrication and design principles for using transparent graphene interconnects in stretchable arrays of microscale inorganic light emitting diodes (LEDs) on rubber substrates. We demonstrate several appealing properties of graphene for this purpose, including its ability to spontaneously conform to significant surface topography, in a manner that yields effective contacts even to deep, recessed device regions. Mechanics modeling reveals the fundamental aspects of this process, as well as the use of the same layers of graphene for interconnects designed to accommodate strains of 100% or more, in a completely reversible fashion. These attributes are compatible with conventional thin film processing and can yield high-performance devices in transparent layouts. Graphene interconnects possess attractive features for both existing and emerging applications of LEDs in information display, biomedical systems, and other environments.

The conversion of graphene oxide (GO) into reduced graphene oxide (rGO) is imperative for the electronic device applications of graphene-based materials. Efficient and cost-effective fabrication of highly uniform GO films and the successive reduction into rGO on a large area is still a cumbersome task through conventional protocols. Improved film casting of GO sheets on a polymeric substrate with quick and green reduction processes has a potential that may establish a path to the practical flexible electronics. Herein, we report a facile deposition process of GO on flexible polymer substrates to create highly uniform thin films over a large area by a flow-enabled self-assembly approach. The self-assembly of GO sheets was successfully performed by dragging the trapped solution of GO in confined geometry, which consisted of an upper stationary blade and a lower moving substrate on a motorized translational stage. The prepared GO thin films could be selectively reduced and facilitated from the simple laser direct writing process for programmable circuit printing with the desired configuration and less sample damage due to the non-contact mode operation without the use of photolithography, toxic chemistry, or high-temperature reduction methods. Furthermore, two different modes of the laser operating system for the reduction of GO films turned out to be valuable for the construction of novel graphene-based high-throughput electrical circuit boards compatible with integrating electronic module chips and flexible humidity sensors.

We report the first study of the controlled, evaporative self-organization of a polymer blend from a restricted geometry comprised of a spherical lens upon a Si substrate (i.e., a sphere-on-flat geometry). This geometry facilitated the control over the evaporation rate of solvent, thereby eliminating the temperature gradient and the possible convective instabilities. In this study, a drop of polystyrene (PS) and poly(methyl methacrylate) (PMMA) toluene solution evaporated in the sphere-on-flat geometry. The combination of controlled, consecutive pinning−depinning cycles (i.e., “stick−slip”) of the contact line at the edge of the geometry, spontaneous phase separation of incompatible polymers at the microscopic scale, and a dewetting process in the late stage of phase segregation led to the formation of gradient, hierarchically structured polymer blend rings composed of phase-separated PS and PMMA. The topographic distribution of PS and PMMA phases on the ring surface were revealed after removal of the PS ...

Hundreds of gradient concentric rings of linear conjugated polymer, (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4- phenylenevinyl-ene], i.e., MEH-PPV) with remarkable regularity over large areas were produced by controlled "stick-slip" motions of the contact line in a confined geometry consisting of a sphere on a flat substrate (i.e., sphere-on-flat geometry). Subsequently, MEH-PPV rings were exploited as a template to direct the formation of gradient concentric rings of multiwalled carbon nanotubes (MWNTs) with controlled density. This method is simple, cost effective, and robust, combining two consecutive self-assembly processes, namely, evaporation-induced self-assembly of polymers in a sphere-on-flat geometry, followed by subsequent directed self-assembly of MWNTs on the polymer-templated surfaces.

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.

Recently, there has been considerable effort to develop suitable scaffolds for tissue engineering applications. Cell adhesion is a prerequisite for cells to survive. In nature, the extracellular matrix (ECM) plays this role. Therefore, an ideal scaffold should be structurally similar to the natural ECM and have biocompatibility and biodegradability. In addition, the scaffold should have biofunctionality, which provides the potent ability to enhance the cellular behaviors, such as adhesion, proliferation and differentiation. This study concentrates on fabricating cell-adhesive matrices composed of RGD peptide-displaying M13 bacteriophage (RGD-M13 phage) and poly(lactic-co-glycolic acid, PLGA) nanofibers. Long rod-shaped M13 bacteriophages are non-toxic and can express many desired proteins on their surface. A genetically engineered M13 phage was constructed to display RGD peptides on its surface. PLGA is a biodegradable polymer with excellent biocompatibility and suitable physicochemical property for adhesive matrices. In this study, RGD-M13 phage/PLGA hybrid nanofiber matrices were fabricated by electrospinning. The physicochemical properties of these matrices were characterized by scanning electron microscopy, atomic force microscopy, Raman spectroscopy, and contact angle measurement. In addition, the cellular behaviors, such as the initial attachment, proliferation and differentiation, were analyzed by a CCK-8 assay and immunofluorescence staining to evaluate the potential application of these matrices to tissue engineering scaffolds. The RGD-M13 phage/PLGA nanofiber matrices could enhance the cellular behaviors and promote the differentiation of C2C12 myoblasts. These results suggest that the RGD-M13 phage/PLGA nanofiber matrices are beneficial to myoblast differentiation and can serve as effective tissue engineering scaffolds.

Osteoprogenitor cells play a significant role in the growth or repair of bones, and have great potential as cell sources for regenerative medicine and bone tissue engineering, but control of their specific differentiation into bone cells remains a challenge. Graphene-based nanomaterials are attractive candidates for biomedical applications as substrates for stem cell (SC) differentiation, scaffolds in tissue engineering, and components of implant devices owing to their biocompatible, transferable and implantable properties. This study examined the enhanced osteogenic differentiation of human mesenchymal stem cells (hMSCs) by reduced graphene oxide (rGO) nanoparticles (NPs), and rGO NPs was prepared by reducing graphene oxide (GO) with a hydrazine treatment followed by annealing in argon and hydrogen. The cytotoxicity profile of each particle was examined using a water-soluble tetrazolium-8 (WST-8) assay. At different time-points, a WST-8 assay, alkaline phosphatase (ALP) activity assay and alizarin red S (ARS) staining were used to determine the effects of rGO NPs on proliferation, differentiation and mineralization, respectively. The results suggest that graphene-based materials have potential as a platform for stem cells culture and biomedicalapplications.

ten observed. The irregular multirings (‘coffee rings’) are formed via repeated pinning and depinning events (i.e., ‘stickslip’ motion) of the contact line. [4–6,10] The evaporation flux varies spatially, with the highest flux observed at the edge of the drop. Therefore, to form spatially periodic patterns at the microscopic scale, the flow field in an evaporating liquid must be delicately harnessed. In this regard, recently, a few attempts have been made to guide the droplet evaporation in a confined geometry [17–20] with [17] or without [18–22] the use of external fields. Patterns of remarkably high fidelity and regularity have been produced. [18–22] However, interfacial interactions between nonvolatile solutes and substrates govern the stability of thin films and have not been explored in these studies. The synergy of controlled self-assemblies of solutes, and their destabilization mediated by the interaction between solutes and substrates during the solvent evaporation, can

A drop of polymer solution was constrained in a sphere-on-flat geometry, resulting in a liquid capillary bridge. As solvent evaporated, intriguing surface patterns of polymer formed, which were strongly dependent on the molecular weight (MW) of polymer. Dotted arrays were formed at low MW; concentric rings were produced at intermediate MW; concentric rings, rings with fingers, and punch-hole-like structures, however, were yielded at high MW. Rings with fingers as well as punch-hole-like structures were manifestations of simultaneous occurrence of the "stick -slip" motion of the contact line and the fingering instabilities of rings. In addition, the curvature of the sphere in the sphere-on-flat geometry was found to affect the pattern formation. A decrease in the curvature of the sphere led to an earlier onset of the formation of punch-hole-like structures when high-MW polymer was employed as the nonvolatile solute.

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.

Because of its excellent charge carrier mobility at the Dirac point, graphene possesses exceptional properties for high-performance devices. Of particular interest is the potential use of graphene nanoribbons or graphene nanomesh for field-effect transistors. Herein, highly aligned DNA nanowire arrays were crafted by flow-assisted self-assembly of a drop of DNA aqueous solution on a flat polymer substrate. Subsequently, they were exploited as "ink" and transfer-printed on chemical vapor deposited (CVD)-grown graphene substrate. The oriented DNA nanowires served as the lithographic resist for selective removal of graphene, forming highly aligned graphene nanoribbons. Intriguingly, these graphene nanoribbons can be readily produced over a large area (i.e., millimeter scale) with a high degree of feature-size controllability and a low level of defects, rendering the fabrication of flexible two terminal devices and field-effect transistors.

The rapid pattern formation of well-ordered block copolymer (BCP) nanostructures is practical for next-generation nanolithography applications. However, there remain critical hurdles to achieve the rapid self-assembly of BCPs with a high Flory-Huggins interaction parameter (χ), owing to their slow kinetics. In this article, we report that a binary solvent vapor annealing methodology can significantly accelerate the self-assembly kinetics of poly(dimethylsiloxane-b-styrene) (PDMS-b-PS) BCPs with a high-χ. In particular, we systemically analyzed the effects of the mixing ratio of a binary solvent composed of a PDMS-selective solvent (heptane) and a PS-selective solvent (toluene), showing an ultrafast self-assembly time (≤1 min) to obtain a well-ordered nanostructure. Moreover, we successfully accomplished extremely fast generation of sub-20 nm dot patterns within an annealing time of 10 s in a 300 nm-wide trench by means of binary solvent annealing. We believe that these results are also applicable to other solvent-based annealing systems of BCPs and that they will contribute to the realization of next-generation ultrafine lithography applications.

During the last decade, much attention has been paid to graphene-based nanomaterials because they are considered as potential candidates for biomedical applications such as scaffolds for tissue engineering and substrates for the differentiation of stem cells. Until now, electrospun matrices composed of various biodegradable copolymers have been extensively developed for tissue engineering and regeneration; however, their use in combination with graphene oxide (GO) is novel and challenging. In this study, nanofiber matrices composed of poly(lactic-co-glycolic acid, PLGA) and M13 phage with RGD peptide displayed on its surface (RGD peptide-M13 phage) were prepared as extracellular matrix (ECM)-mimicking substrates. RGD peptide is a tripeptide (Arg-Gly-Asp) found on ECM proteins that promotes various cellular behaviors. The physicochemical properties of PLGA and RGD peptide-M13 phage (PLGA/RGD peptide) nanofiber matrices were characterized by atomic force microscopy, Fourier-transform infrared spectroscopy and thermogravimetric analysis. In addition, the growth of C2C12 mouse myoblasts on the PLGA/RGD peptide matrices was examined by measuring the metabolic activity. Moreover, the differentiation of C2C12 mouse myoblasts on the matrices when treated with GO was evaluated. The cellular behaviors, including growth and differentiation of C2C12 mouse myoblasts, were substantially enhanced on the PLGA/RGD peptide nanofiber matrices when treated with GO. Overall, these findings suggest that the PLGA/RGD peptide nanofiber matrices can be used in combination with GO as a novel strategy for skeletal tissue regeneration.

A simple route to highly regular concentric ring patterns of an organometallic polymer, poly(ferrocenyldimethylsilane) (PFDMS), is developed simply by allowing a drop containing PFDMS to evaporate in a confined geometry consisting of a sphere on a Si surface. Thermal treatment of PFDMS transforms it, with the retention of concentric ring patterns, into magnetic ceramic rings.