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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 phase with a selective solvent. Namely, the trench-pit structures were formed in the PS-112K/PMMA-133K blend, while for the PS-112K/PMMA-534K blend, pit morphologies were observed. This facile approach offers a new way of simultaneously processing two or more nonvolatile components via controlled evaporation to produce new kinds of structures with hierarchical order in a simple, robust, and one-step manner. [ABSTRACT FROM AUTHOR]

A drop of semicrystalline polymer, poly(ethylene oxide) (PEO), solution was placed in a restricted geometry consisting of a sphere on a flat substrate (i.e., sphere-on-flat geometry). Upon solvent evaporation from the sphere-on-flat geometry, microscopic concentric rings of PEO with appropriate high molecular weight were produced via controlled, repetitive pinning (“stick”) and depinning (“slip”) cycles of the contact line. The evaporation-induced concentric rings of PEO exhibited a fibrillar-like surface morphology. Subsequent isothermal crystallization of rings at 40 and 58 °C led to the formation of multilayer of flat-on lamellae (i.e., spiral morphology). In between adjacent spirals, depletion zones were developed during crystallization, as revealed by AFM measurements. The present highly ordered, concentric PEO rings may serve as a platform to study cell adhesion and motility, neuron guidance, cell mechanotransduction, and other biological processes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The surface-induced structure formation of polymer-dispersed liquid crystals (PDLCs) on a chemically patterned substrate was studied for the first time. The patterns on the substrate were successfully transferred to the PDLC film, resulting in alternating LC-rich and polymer-rich phases. This simple approach offers a new means of organizing micrometer-sized LC domains into well-ordered structures in a polymer matrix of PDLCs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background: In the field of biomedical engineering, many studies have focused on the possible applications of graphene and related nanomaterials due to their potential for use as scaffolds, coating materials and delivery carriers. On the other hand, electrospun nanofiber matrices composed of diverse biocompatible polymers have attracted tremendous attention for tissue engineering and regenerative medicine. However, their combination is intriguing and still challenging. Results: In the present study, we fabricated nanofiber matrices composed of M13 bacteriophage with RGD peptide displayed on its surface (RGD-M13 phage) and poly(lactic-co-glycolic acid, PLGA) and characterized their physicochemical properties. In addition, the effect of graphene oxide (GO) on the cellular behaviors of C2C12 myoblasts, which were cultured on PLGA decorated with RGD-M13 phage (RGD/PLGA) nanofiber matrices, was investigated. Our results revealed that the RGD/PLGA nanofiber matrices have suitable physicochemical properties as a tissue engineering scaffold and the growth of C2C12 myoblasts were significantly enhanced on the matrices. Moreover, the myogenic differentiation of C2C12 myoblasts was substantially stimulated when they were cultured on the RGD/PLGA matrices in the presence of GO. Conclusion: In conclusion, these findings propose that the combination of RGD/PLGA nanofiber matrices and GO can be used as a promising strategy for skeletal tissue engineering and regeneration. [ABSTRACT FROM AUTHOR]

Background: Electrospinning is a simple and effective method for fabricating micro- and nanofiber matrices. Electrospun fibre matrices have numerous advantages for use as tissue engineering scaffolds, such as high surface area-to-volume ratio, mass production capability and structural similarity to the natural extracellular matrix (ECM). Therefore, electrospun matrices, which are composed of biocompatible polymers and various biomaterials, have been developed as biomimetic scaffolds for the tissue engineering applications. In particular, graphene oxide (GO) has recently been considered as a novel biomaterial for skeletal muscle regeneration because it can promote the growth and differentiation of myoblasts. Therefore, the aim of the present study was to fabricate the hybrid fibre matrices that stimulate myoblasts differentiation for skeletal muscle regeneration. Results: Hybrid fibre matrices composed of poly(lactic-co-glycolic acid, PLGA) and collagen (Col) impregnated with GO (GO-PLGA-Col) were successfully fabricated using an electrospinning process. Our results indicated that the GO-PLGA-Col hybrid matrices were comprised of randomly-oriented continuous fibres with a three-dimensional non-woven porous structure. Compositional analysis showed that GO was dispersed uniformly throughout the GO-PLGA-Col matrices. In addition, the hydrophilicity of the fabricated matrices was significantly increased by blending with a small amount of Col and GO. The attachment and proliferation of the C2C12 skeletal myoblasts were significantly enhanced on the GO-PLGA-Col hybrid matrices. Furthermore, the GO-PLGA-Col matrices stimulated the myogenic differentiation of C2C12 skeletal myoblasts, which was enhanced further under the culture conditions of the differentiation media. Conclusions: Taking our findings into consideration, it is suggested that the GO-PLGA-Col hybrid fibre matrices can be exploited as potential biomimetic scaffolds for skeletal tissue engineering and regeneration because these GO-impregnated hybrid matrices have potent effects on the induction of spontaneous myogenesis and exhibit superior bioactivity and biocompatibility. [ABSTRACT FROM AUTHOR]