Growth and Application of ZnO Nanostructures

Nanostructures are the building blocks of future nanodevices and thus methods for fabricating nanostructures of various materials in various forms are fundamentally important. Among those nanostructures ZnO has received much attention over the past few years due to the wide range of research by many different groups focused on different novel nanostructures with different properties. Although ZnO nanowires have been intensively studied, there are only a few methods that showed promising characteristics for practical applications. Without much effort, it can be grown in many different nanostructure forms, thus allowing various novel devices to be achieved. In this study, we intend to review those methods that enable nanostructure growth to be more controllable and feasible for applications. The methods for fabricating ZnO nanostructures are introduced in the first part. In the second part, the application of those nanostructures are mentioned and explained. Finally, the future realization of nanodevices is discussed.     

Probing Heterogeneous Structure of Aggregates

Naturally occurring aggregates are considered of fractal or fractal-of-fractals interior structure. Recent studies utilizing dye staining and confocal laser scanning microscopy (CLSM) techniques have revealed the extremely complex, interconnected pore networks for floc interior. Detailed structural analysis on the real floc architecture is determined for building up a comprehensive floc model. This work interprets structural characteristics of flocs using multifractal analysis. A direct method by Chhabra and Jensen properly evaluated the singularity strength and singularity spectrum on architectures of two artificial fractal systems. However, direct evaluation of multifractal characteristics of wastewater flocs has limitations, alternatively acquiring analytical results to be misleading. Particularly, the singularity spectrum presents excessively large values in the limit as q → +∞ and exhibits very large error bars in the limit as q → ?∞. This is attributable to the uneven distribution of mass in flocs and insufficient spatial resolutions provided by CLSM techniques. The flaws in applying multifractal analysis on naturally occurring objects are discussed.     

Drying Models and Quality Analysis of Sun-Dried Ciku

Sun drying of ciku (Manilkara zapota) was carried out on different sample sizes to investigate the effects on drying kinetics. It was found that the maximum drying rates of sun-dried ciku decreased with larger product size. Three sunny days are needed to dry the ciku slabs to an average final moisture content of 0.2 g H₂O/g dry mass. The results showed that hardness and chewiness of the dried samples were significantly different (p < 0.05) compared to fresh ciku slabs and commercial dried fruit. The color measurement of dried product showed that L? and b? values significantly decreased (p < 0.05), whereas the a? value increase was not significantly different (p > 0.05) compared to fresh ciku slabs. In addition, sun-dried ciku retained a total polyphenol content (TPC) that was relatively low (p < 0.05) compared to fresh ciku.     

Enhanced Differentiation of Three-Gene-Reprogrammed Induced Pluripotent Stem Cells into Adipocytes via Adenoviral-Mediated PGC-1α Overexpression

Induced pluripotent stem cells formed by the introduction of only three factors, Oct4/Sox2/Klf4 (3-gene iPSCs), may provide a safer option for stem cell-based therapy than iPSCs conventionally introduced with four-gene iPSCs. Peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) plays an important role during brown fat development. However, the potential roles of PGC-1α in regulating mitochondrial biogenesis and the differentiation of iPSCs are still unclear. Here, we investigated the effects of adenovirus-mediated PGC-1α overexpression in 3-gene iPSCs. PGC-1α overexpression resulted in increased mitochondrial mass, reactive oxygen species production, and oxygen consumption. Microarray-based bioinformatics showed that the gene expression pattern of PGC-1α-overexpressing 3-gene iPSCs resembled the expression pattern observed in adipocytes. Furthermore, PGC-1α overexpression enhanced adipogenic differentiation and the expression of several brown fat markers, including uncoupling protein-1, cytochrome C, and nuclear respiratory factor-1, whereas it inhibited the expression of the white fat marker uncoupling protein-2. Furthermore, PGC-1α overexpression significantly suppressed osteogenic differentiation. These data demonstrate that PGC-1α directs the differentiation of 3-gene iPSCs into adipocyte-like cells with features of brown fat cells. This may provide a therapeutic strategy for the treatment of mitochondrial disorders and obesity.     

Tailoring viscoelastic and mechanical properties of the foamed blends of EVA and various ethylene‐styrene interpolymers

Foamed materials (EVA/ESI) have been prepared from blends of ethylene‐vinyl acetate copolymer (EVA) and ethylene‐styrene interpolymers (ESI) in the presence of various amounts of dicumyl peroxide (DCP). Four ESIs of different compositions were employed in this study; their styrene contents ranged from 30 to 73 wt% and their T_g ranged from −2 to 33°C. It has been found that microcellular morphology, degree of crosslinking and expansion ratio were strongly affected by the DCP concentration and the type of ESI employed. A minimum degree of crosslinking was required for making good foams and the same degree of crosslinking could be achieved by employing a smaller amount of DCP for an EVA/ESI blend having a higher styrene content. In contrast to other EVA blends, such as EVA/LDPE, these EVA/ESI blends exhibited no existence of any optimum DCP concentration, and the α glass transition temperatures of the foams varied with the ESI type, covering a wide span from 0°C to 37°C. Therefore, it was possible to tailor the T_g of an EVA/ESI blend by choosing an appropriate type of ESI. Furthermore, by correctly tailoring the T_g, the EVA/ESI foam could be made into a rubbery material with a custom‐designed damping factor. Tensile strength and modulus of the EVA/ESI foams increased generally with an increase in the styrene content, with the exception that ESIs with very low styrene content will confer on the blend a high modulus at small strain and a large elongation at break.     

Non‐isothermal crystallization of poly(ethylene oxide)/silver nanoplate composites

The non‐isothermal crystallization of poly(ethylene oxide) (PEO)/silver nanoplate composites was studied using differential scanning calorimetry. The non‐isothermal crystallization was analyzed by combining the Avrami and Ozawa equations. It was found that the Avrami exponent for neat PEO ranges from 2.51 to 2.53, whereas it ranges from 2.54 to 3.16 for its composites, indicating that the spherical crystal morphology does not change with the addition of nanoplates. However, the rate determination of crystal growth transfers from diffusion to nucleation. The crystallization half‐time showed an increase with the addition of silver nanoplates in PEO, indicating that the overall crystallization rate of PEO decreases with the addition of nanoplates. However, the nucleation activity is larger than unity in the composites and the value increases with an increase in the nanoplate content. This behavior implies that the nanoplates act as anti‐nucleating agents to hinder nucleation. Copyright © 2011 Society of Chemical Industry     

Isothermal crystallization of polyethylene oxide/silver nanoplate composites

This research was accomplished to investigate the kinetics of isothermal crystallization of polyethylene oxide (PEO)/silver nanoplate composites. It was obtained that the spherulites increased in size and numbers with time for the composites with various particle loadings. Additionally, the spherulite growth rate of composites decreased with an increase in the crystallization temperature and increased with the addition of nanoplates. The spherulite growth rate was further analyzed by the theory developed by Lauritzen and Hoffman. The product of the lateral surface free energy (σ) and the end surface free energy (σ_e) decreased with an increase in the content of nanoplates. We proposed the possible crystallization mechanisms of these PEO/nanoplate composites according to the change of σ and σ_e with the presence of nanoplates. A controlled experiment showed a minor change in PEO crystallization with the presence of a surfactant C₁₆TAB. This implied that the unique size and shape of nanoplates plays a key role on hindering the primary nucleation of PEO and increasing the spherulite growth rate. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Shaping conjugated hollow fibers using a four‐segmented arc spinneret

This study discusses a light‐weight bicomponent hollow fiber that is formed from a low‐density material on the inside, such as polypropylene (PP), and a regularly dyeable material outside, such as polyterephthalate (PET) or nylon. Finite elements and the Optimesh‐3D remeshing approach are adopted to identify the main controlling factors of spinning the sheath‐core hollow fiber without the consideration of winding actions are performed, based on a four‐segmented arc spinneret design. The results indicate that the deflection of melt streams under the spinneret is a major factor that controls the gluing of the gap between arc segments. A greater mismatch between the viscosities of the sheath and the core causes a greater deflection and increases the likelihood of gluing events. Beyond deflection, die swelling under the spinneret is another issue of concern in the processing of bicomponent hollow fibers. Finally, the simulation results are compared with experimental data, and the most appropriate conditions for forming a PET/PP hollow fiber were obtained. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Destabilizing effects of fructose-1,6-bisphosphate on membrane bilayers

Fructose-1,6-bisphosphate (FBP) is a high-energy glycolytic intermediate that decreases the effects of ischemia; it has been used successfully in organ perfusion and preservation. How the cells utilize external FBP to increase energy production and the mechanism by which the molecule crosses the membrane bilayer are unclear. This study examined the effects of FBP on membrane bilayer permeability, membrane fluidity, phospholipid packing, and membrane potential to determine how FBP crosses the membrane bilayer. Large unilamellar vesicles composed of egg phosphatidylcholine (Egg PC) were made and incubated with 50 mM FBP spiked with ¹⁴C-FBP at 30°C. Uptake of FBP was significant (P<0.05) and dependent on the lipid concentration, suggesting that FBP affects membrane, bilayer permeability. With added calcium (10 mM), FBP uptake by lipid vesicles decreased significantly (P<0.05). Addition of either 5 or 50 mM FBP led to a significant increase (P<0.05) in Egg PC carboxyfluorescein leakage. We hypothesized that the membrane-permeabilizing effects of FBP may be due to a destabilization of the membrane bilayer. Small unilamellar vesicles composed of dipalmitoyl pC (DPPC) were made containing either diphenyl-1,3,5-hexatriene (DPH) or trimethylammmonia-DPH (TMA-DPH) and the effects of FBP on the fluorescence anisotropy (FA) of the fluorescent labels examined. FBP caused a significant decrease in the FA of DPH in the liquid crystalline state of DPPC (P<0.05), had no effect on FA of TMA-DPH in the liquid crystalline state of DPPC, but increased the FA of TMA-DPH in the gel state of DPPC. From phase transition measurements with DPPC/DPH or TMA-DPH, we calculated the slope of the phase transition as an indicator of the cooperativity of the DPPC molecules. FBP significantly decreased the slope, suggesting a decrease in fatty acyl chain interaction (P<0.05). The addition of 50 mM FBP caused a significant decrease (P<0.05) in the liquid crystalline/gel state fluorescence ratio of merocyanine 540, indicating increased head-group packing. To determine what effects these changes would have on cellular membranes, we labeled human endothelial cells with the membrane potential probe 3,3′-dipropylthiacarbocyanine iodide (DiSC₃) and then added FBP. FBP caused a significant, dose-dependent decrease in DiSC₃ fluorescence, indicating membrane depolarization. We suggest that FBP destabilizes membrane bilayers by decreasing fatty acyl chain interaction, leading to significant increases in membrane permeability that allow FBP to diffuse into the cell where it can be used as a glycolytic intermediate.     

Surface,Biocompatible and Hemocompatible Properties of Meta‐Amorphous Titanium Oxide Film

This study involved modification of the surface of Ti by micro‐arc oxidation (MAO). A rough and porous oxide film with good wettability was formed on the Ti surface. This MAO‐treated film exhibited a meta‐amorphous structure comprising crystalline anatase and rutile TiO₂ as well as amorphous phases. In addition, the incorporation of Ca and P in the MAO‐treated film was induced by micro‐arc discharge. The biological responses of the MAO‐treated surfaces were evaluated by observing the adhesion of MG63 osteoblast‐like cells and platelets. The MAO‐treated Ti had a considerably better biocompatibility and blood compatibility than untreated Ti.