Microstructures and bond strengths of plasma-sprayed hydroxyapatite coatings on porous titanium substrates

Hydroxyapatite (HA) coating was carried out by plasma spraying on bulk Ti substrates and porous Ti substrates having a Young’s modulus similar to that of human bone. The microstructures and bond strengths of HA coatings were investigated in this study. The HA coatings with thickness of 200–250 μ m were free from cracks at interfaces between the coating and Ti substrates. XRD analysis revealed that the HA powder used for plasma spraying had a highly crystallized apatite structure, while the HA coating contained several phases other than HA. The bond strength between the HA coating and the Ti substrates evaluated by standard bonding test (ASTM C633-01) were strongly affected by the failure behavior of the HA coating. A mechanism to explain the failure is discussed in terms of surface roughness of the plasma-sprayed HA coatings on the bulk and porous Ti substrates.     

Novel method for site-controlled surface nanodot fabrication by ion beam synthesis

By using a Ga FIB system to spatially control the implantation of Ga into SiO(2) followed by vacuum annealing, we have fabricated self-assembled surface Ga nanodots with a high degree of control of nucleation location. The morphology of the Ga nanodots is closely related to Ga dose, showing a critical dose needed for nucleation that results in Ga nanodot formation just below the surface, while at higher doses Ga nanodots form on the surface as metallic Ga droplets. Possible applications include defining nucleation sites for subsequent growth, use as Ga source for GaN or GaAs quantum dots, or as catalyst for nanowire growth.     

Deformation of metastable betaTi-15Mo-5Zr alloy single crystals

Deformation modes have been investigated in metastable beta Ti-15Mo-5Zr alloy single crystals using both transmission electron microscopy techniques and multisurface trace analysis. {332} twinning and 〈111〉 crystallographic slip were observed to occur at an initial stage of deformation depending on deformation axis. {332} twinning occurs in a crystal whose tensile axis lies around 〈111〉, while 〈111〉 slip appears in a crystal having the tensile axis in the neighborhood of 〈001〉 to 〈011〉. The twinning system which possesses the maximum resolved shear stress is always operative in both tensile and compressive deformations. Single crystals of this alloy exhibit an asymmetry of the active slip plane and of the yield stress in a manner similar to other bcc metals and dilute alloys.     

Coordination and Bond Character of Silicon and Aluminum Ions in Amorphous Thin Films in the System SiO2-Al2O3

The coordination and bond character of the cations in amorphous SiO₂-Al₂O₃ films prepared by rf sputtering were examined by studying chemical shifts in the SiK and AlK X-ray emission spectra. The coordination number of Si ions in these films was always 4, regardless of composition, whereas the average coordination number of Al ions changed from 4 to 5, depending onAl₂O₃ content. TheSi-O-Al bond type seemed to appear as Al₂O₃ was introduced into amorphous SiO₂ films or vice versa.     

Voltage holding study of 1 MeV accelerator for ITER neutral beam injector

Voltage holding test on MeV accelerator indicated that sustainable voltage was a half of that of ideal quasi-Rogowski electrode. It was suggested that the emission of the clumps is enhanced by a local electric field concentration, which leads to discharge initiation at lower voltage. To reduce the electric field concentration in the MeV accelerator, gaps between the grid supports were expanded and curvature radii at the support corners were increased. After the modifications, the accelerator succeeded in sustaining -1 MV in vacuum without beam acceleration. However, the beam energy was still limited at a level of 900 keV with a beam current density of 150 A∕m(2) (346 mA) where the 3 × 5 apertures were used. Measurement of the beam profile revealed that deflection of the H(-) ions was large and a part of the H(-) ions was intercepted at the acceleration grid. This causes high heat load on the grids and the breakdowns during beam acceleration. To suppress the direct interception, new grid system was designed with proper aperture displacement based on a 3D beam trajectory analysis. As the result, the beam deflection was compensated and the voltage holding during the beam acceleration was improved. Beam parameter of the MeV accelerator was increased to 980 keV, 185 A∕m(2) (427 mA), which is close to the requirement of ITER accelerator (1 MeV, 200 A∕m(2)).     

Wear resistance of surface-modified TiNbSn alloy

Journal of Materials Science - The wear resistance of TiNbSn alloy surfaces treated by plasma nitriding, TiN sputtering, and anodic oxidation was investigated with the goal of suppressing the...     

GFP expression by intracellular gene delivery of GFP-coding fragments using nanocrystal quantum dots

Gene therapy is an attractive approach to supplement a deficient gene function. Although there has been some success with specific gene delivery using various methods including viral vectors and liposomes, most of these methods have a limited efficiency or also carry a risk for oncogenesis. We herein report that quantum dots (QDs) conjugated with nuclear localizing signal peptides (NLSP) successfully introduced gene-fragments with promoter elements, which promoted the expression of the enhanced green fluorescent protein (eGFP) gene in mammalian cells. The expression of eGFP protein was observed when the QD/gene-construct was added to the culture media. The gene-expression efficiency varied depending on multiple factors around QDs, such as (1) the reading direction of the gene-fragments, (2) the quantity of gene-fragments attached on the surface of the QD-constructs, (3) the surface electronic charges varied according to the structure of the QD/gene-constructs, and (4) the particle size of QD/gene complex varied according to the structure and amounts of gene-fragments. Using this QD/gene-construct system, eGFP protein could be detected 28 days after the gene-introduction whereas the fluorescence of QDs had disappeared. This system therefore provides another method for the intracellular delivery of gene-fragments without using either viral vectors or specific liposomes.     

Photo-induced properties of anodic oxide films on Ti6Al4V

Photocatalytic activity and wettability of the anodic oxide layer on Ti6Al4V prepared by anodization in a sulfuric acid electrolyte are explored. The oxide is composed mainly of TiO₂ with V₂O₅, VO₂ and Al₂O₃. The crystal structure of the TiO₂ varies from anatase to rutile with the sulfuric acid concentration in the electrolyte. Anatase exhibits better photocatalytic activity compared with rutile, which is different from those on Ti and Ti-Nb-Sn alloy. Contact angles of the oxides decrease with ultraviolet light illumination, and hydrophilicity is observed in the rutile oxide. Both photocatalytic activity and hydrophilicity are inferior to the corresponding Ti and Ti-Nb-Sn alloy, which is explained by the presence of Al₂O₃ in the anodic oxide.