Improved osteoblast response to UV-irradiated PMMA/TiO2 nanocomposites with controllable wettability.

Osteoblast response was evaluated with polymethylmethacrylate (PMMA)/titanium dioxide (TiO2) nanocomposite thin films that exhibit the controllable wettability with ultraviolet (UV) treatment. In this study, three samples of PMMA/TiO2 were fabricated with three different compositional volume ratios (i.e., 25/75, 50/50, and 75/25) followed by UV treatment for 0, 4, and 8 h. All samples showed the increased hydrophilicity after UV irradiation. The films fabricated with the greater amount of TiO2 and treated with the longer UV irradiation time increased the hydrophilicity more. The partial elimination of PMMA on the surface after UV irradiation created a durable hydrophilic surface by (1) exposing higher amount of TiO2 on the surface, (2) increasing the hydroxyl groups on the TiO2 surface, and (3) producing a mesoporous structure that helps to hold the water molecules on the surface longer. The partial elimination of PMMA on the surface was confirmed by Fourier transform infrared spectroscopy. Surface profiler and atomic force microscopy demonstrated the increased surface roughness after UV irradiation. Both scanning electron microscopy and energy-dispersive X-ray spectroscopy demonstrated that particles containing calcium and phosphate elements appeared on the 8 h UV-treated surface of PMMA/TiO2 25/75 samples after 4 days soaking in Dulbecco's Modified Eagle Medium. UV treatment showed the osteoblast adhesion improved on all the surfaces. While all UV-treated hydrophilic samples demonstrated the improvement of osteoblast cell adhesion, the PMMA/TiO2 25/75 sample after 8 h UV irradiation (n = 5, P value = 0.000) represented the best cellular response as compared to other samples. UV-treated PMMA/TiO2 nanocomposite thin films with controllable surface properties represent a high potential for the biomaterials used in both orthopedic and dental applications.

Role of the Interface between Ag and ZnO in the Electric Conductivity of Ag Nanoparticle-Embedded ZnO.

The addition of Ag nanoparticles (Ag NPs) with an average size of 30 nm into ZnO increases the electric conductivity up to 1000 times. While a similar increase in the conductivity is observed in a mixture of Ag nanoparticles and Al-doped ZnO (AZO) films, a physical mechanism underlying the change in electric conductivity is not the same for Ag NP-added ZnO and Ag NP-added AZO. In Ag NP-added ZnO, an ohmic junction is formed at the ZnO-Ag interface, and electrons are accumulated in ZnO near the ZnO-Ag interface until electron-rich islands are connected. However, in Ag NP-added AZO, electrons in Ag NPs move to the AZO matrix via thermionic emission and travel through the AZO matrix. This change in electron transport at ZnO-Ag and AZO-Ag interfaces is due to the fact that the work function of ZnO (4.62 eV) is larger than those of Ag (4.24 eV) and AZO (4.15 eV). An increase in Ag NP content in the ZnO matrix leads to the overlap of the electron accumulation regions and forms a percolation path for the electron transport without deteriorating the electron mobility. Hence, the electron concentration increases to 2.4 × 1020/cm3 in the 1.4 vol % Ag NP-added ZnO film. In addition, Ag NPs have a negligible effect on the transmittance, and the best Haacke figure of merit (ΦH) values are 2.86 and 5.18 for ZnO:Ag NP and AZO:Ag NP, respectively.

Novel Carrier Doping Mechanism for Transparent Conductor: Electron Donation from Embedded Ag Nanoparticles to the Oxide Matrix.

A trade-off between the carrier concentration and carrier mobility is an inherent problem of traditional transparent conducting oxide (TCO) films. In this study, we demonstrate that the electron concentration of TCO films can be increased without deteriorating the carrier mobility by embedding Ag nanoparticles (NPs) into Al-doped ZnO (AZO) films. An increment of Ag NP content up to 0.7 vol % in the AZO causes the electron concentration rising to 4 × 1020 cm-3. A dependence of the conductivity on temperature suggests that the energy barrier for the electron donation from Ag NPs at room temperature is similar to the Schottky barrier height at the Ag-AZO interface. In spite of an increase in the electron concentration, embedded Ag NPs do not compromise the carrier mobility at room temperature. This is evidence showing that this electron donation mechanism by Ag NPs is different from impurity doping, which produces both electrons and ionized scattering centers. Instead, an increase in the Fermi energy level of the AZO matrix partially neutralizes Al impurities, and the carrier mobility of Ag NP embedded AZO film is slightly increased. The optical transmittance of mixture films with resistivity less than 1 × 10-3 Ω·cm still maintains above 85% in visible wavelengths. This opens a new paradigm to the design of alternative TCO composite materials which circumvent an inherent problem of the impurity doping.

An accurate electrocardiographic algorithm for differentiation of tremor-induced pseudo-ventricular tachycardia and true ventricular tachycardia.

Tremor-induced electrocardiographic artifacts could be misdiagnosed as ventricular tachycardia (VT). However, there has been no electrocardiographic algorithm effectively differentiating pseudo-VT. In this study, we used 3 electrocardiographic "signs": "Sinus" sign, "Spike" sign, and "Notch" sign, and created an electrocardiographic algorithm. The algorithm was prospectively tested in 98 electrocardiographs (37 tremor-induced pseudo-VT and 61 true VT) Thirty-six out of 37 (97.3%) tremor-induced pseudo-VTs could be accurately diagnosed. In conclusion, this is the first study to systemically analyze the tremor-induced pseudo-VT. Our new electrocardiographic algorithm provides a useful tool for a rapid and accurate diagnosis.

Heteroepitaxial Cu2O thin film solar cell on metallic substrates.

Heteroepitaxial, single-crystal-like Cu2O films on inexpensive, flexible, metallic substrates can potentially be used as absorber layers for fabrication of low-cost, high-performance, non-toxic, earth-abundant solar cells. Here, we report epitaxial growth of Cu2O films on low cost, flexible, textured metallic substrates. Cu2O films were deposited on the metallic templates via pulsed laser deposition under various processing conditions to study the influence of processing parameters on the structural and electronic properties of the films. It is found that pure, epitaxial Cu2O phase without any trace of CuO phase is only formed in a limited deposition window of P(O2) - temperature. The (00l) single-oriented, highly textured, Cu2O films deposited under optimum P(O2) - temperature conditions exhibit excellent electronic properties with carrier mobility in the range of 40-60 cm(2) V(-1) s(-1) and carrier concentration over 10(16) cm(-3). The power conversion efficiency of 1.65% is demonstrated from a proof-of-concept Cu2O solar cell based on epitaxial Cu2O film prepared on the textured metal substrate.

Hierarchical graphene/metal grid structures for stable, flexible transparent conductors.

We report an experimental study on the fabrication and characterization of hierarchical graphene/metal grid structures for transparent conductors. The hierarchical structure allows for uniform and local current conductivity due to the graphene and exhibits low sheet resistance because the microscale silver grid serves as a conductive backbone. Our samples demonstrate 94% diffusive transmission with a sheet resistance of 0.6 Ω/sq and a direct current to optical conductivity ratio σdc/σop of 8900. The sheet resistance of the hierarchical structure may be improved by over 3 orders of magnitude and with little decrease in transmission compared with graphene. Furthermore, the graphene protects the silver grid from thermal oxidation and better maintains the sheet resistance of the structure at elevated temperature. The graphene also strengthens the adhesion of the metal grid with the substrate such that the structure is more resilient under repeated bending.