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Biomedical subjects

Kunihito Koumoto

Publications and source records attributed to Kunihito Koumoto.

16 recordsLinked to original sources
PubMed2006

Epitaxial film growth and superconducting behavior of sodium-cobalt oxyhydrate, NaxCoO2.yH2O (x approximately 0.3, y approximately 1.3).

We have developed a unique multistep film growth technique, combining reactive solid-phase epitaxy (R-SPE) with an intercalation process, to fabricate epitaxial films of superconducting sodium-cobalt oxyhydrate, Na(0.3)CoO2.1.3H2O. An epitaxial film of Na(0.8)CoO2 grown on an alpha-Al2O3(0001) substrate by R-SPE was subjected to oxidation and hydration treatment, leading to the formation of a Na(0.3)CoO2.1.3H2O epitaxial film. The film exhibited metallic electrical resistivity with a superconducting transition at 4 K, similar to that of bulk single crystals. The present technique is suitable and probably the only method for the epitaxial growth of superconducting Na(0.3)CoO2.1.3H2O.

Journal Article↗
PubMed2006

Micropatterning of copper on a poly(ethylene terephthalate) substrate modified with a self-assembled monolayer.

We have developed a technique for the site-selective electroless deposition of Cu on poly(ethylene terephthalate) (PET) substrate modified with an organic self-assembled monolayer (SAM). The PET substrate was first modified with a silica-like layer by being dip-coated in an acetone solution of 3-aminopropyltrimethoxysilane and treated with UV light. The PET substrate was further modified with thiol groups using a 3-mercaptopropyltrimethoxysilane-SAM and then irradiated by UV light through a photomask to prepare thiol-group regions and OH-group regions. Cu was then deposited on only the thiol-group regions of the substrate by electroless deposition in a neutral solution with no catalysts by using dimethylamineborane as a reducing reagent. This site-selective deposition process can control the deposition conditions by an organic thin film fabricated on a surface-modified PET substrate, and thus can be applied to other low heat-resistant substrates.

Journal Article↗
PubMed2006

Patterning of ZrO2 precursor through a gas-generated self-assembly route.

We designed a gas-generated self-assembly route for patterning of ZrO2 precursor films from an aqueous peroxozirconium solution. Molecular oxygen generated during the decomposition of zirconium complex selectively aggregated on the hydrophobic surface of self-assembled monolayers, which was photo-modified to be a template. This gas layer prevented the solution from attaching to the substrate, so as the deposition of zirconia precursor occurred almost entirely on the hydrophilic sites. In comparison, only isolated islands of deposits were observed on hydrophobic sites, which may be attributed to contamination or adsorption of colloids during the preparation of samples. The resolution of pattern was well improved by using such a gas-generated process. In addition, this approach can be also extended to prepare other micropatterns.

Adsorption↗
PubMed2006

Preparation and characterization of polypeptide-stabilized gold nanoparticles.

Helical polypeptides have a highly rigid conformation. In order to control self-assembling structure in nanoscale, the rigidity of the stabilizing molecules, which is working as scaffolds, is highly important. Furthermore, the molecular lengths of polypeptides can be readily controlled by using their unique polymerization methods. In this study, we have used helical polypeptides as the stabilizing reagent of metal nanoparticles. As for rigid helical polypeptides, poly(gamma-benzyl-L-glutamate) (PBLG) was selected, and was synthesized by N-carboxylic acid anhydride (NCA) polymerization. Preparation of helical polypeptide-stabilized gold nanoparticles using a two-phase reduction process from the corresponding metal salts with NaBH4 is therefore introduced. PBLG itself did not have good stabilizing ability for metal nanoparticles and a terminal attaching ligand was indispensable for nanoparticle stabilization and, for this purpose, lipoic acid was selected. It is estimated that lipoic acid functionalized polypeptide molecules were attached perpendicularly to the particle surface by lipoic acid group. The size and structure, as well as assembling will be discussed in this manuscript.

Drug Stability↗
PubMed2006

Exfoliation of layers in NaxCoO2.

We proposed and developed an exfoliation process for layer-structured NaxCoO2 to prepare CoO nanosheets. Na+ ion exchange by acid treatment was utilized to expand the spacing between the two CoO2 layers in NaxCoO2. Ethylamine was then effectively utilized for the exfoliation of cobalt oxide sheets having nanometer-order thickness and high aspect ratio. CoO nanosheets were observed by TEM micrographs and electron diffraction patterns after drying. Further efforts are needed for the application of exfoliated sheets to an integration process to fabricate self-assembled nanomaterials such as desired layer structures composed of two (or more) kinds of nanosheets.

Coated Materials, Biocompatible↗
PubMed2005

Self-assembly patterning of silica colloidal crystals.

We developed a self-assembly process of silica particles to fabricate desired patterns of colloidal crystals having high feature edge acuity and high regularity. A micropattern of colloidal methanol prepared on a self-assembled monolayer in hexane was used as a mold for particle patterning, and slow dissolution of methanol into hexane caused shrinkage of molds to form micropatterns of close-packed SiO2 particle assemblies. This result is a step toward the realization ofnano/micro periodic structures for next-generation photonic devices by a self-assembly process.

Journal Article↗
PubMed2005

The formation mechanism of a textured ceramic of thermoelectric [Ca2CoO3](0.62)[CoO2] on beta-Co(OH)2 templates through in situ topotactic conversion.

We investigated the formation mechanism of thermoelectric [Ca(2)CoO(3)](0.62)[CoO(2)] (CCO) on beta-Co(OH)(2) templates with maintained orientations by identifying the intermediate phases and specifying the relationship between their crystallographic orientations. We mixed beta-Co(OH)(2) templates with the complementary reactant CaCO(3) and prepared a compact by tape casting, with the developed (001) plane of the templates aligned along the casting plane. High-temperature XRD of the compact revealed that beta-Co(OH)(2) decomposed into Co(3)O(4) by 873 K, and Co(3)O(4) reacted with CaO to form CCO by 1193 K via the formation of the newly detected intermediate phase beta-Na(x)()CoO(2)-type Ca(x)()CoO(2) at 913-973 K. Pole figure measurements and SEM and TEM observations revealed that the relationship between the crystallographic planes was (001) beta-Co(OH)(2)//{111} Co(3)O(4)//(001) Ca(x)()CoO(2)//(001) CCO. The crystal structures of the four materials possess the common CoO(2) layer (or similar), which is composed of edge-sharing CoO(6) octahedra, parallel to the planes. The cross-sectional HRTEM analysis of an incompletely reacted specimen showed transient lattice images from Ca(x)()CoO(2) into CCO, in which every other CoO(2) layer of Ca(x)()CoO(2) was preserved. Thus, it was demonstrated that a textured CCO ceramic is produced through a series of in situ topotactic conversion reactions with a preserved CoO(2) layer of its template.

Journal Article↗
PubMed2004

Acid-base properties and zeta potentials of self-assembled monolayers obtained via in situ transformations.

Siloxane-anchored, self-assembled monolayers (SAMs) on single crystal Si were prepared with a variety of surface functional groups using a single commercially available surfactant (1-bromo-11-(trichlorosilyl)undecane) followed by in situ transformations. Polar (thioacetate and thiol), nonpolar (methyl), acidic (sulfonic and carboxylic), basic (various amines), and ionic (alkylammonium) surface functionalities were prepared. For primary amine and sulfonate surfaces, the degree of surface charge as a function of pH was determined ex situ using X-ray photoelectron spectroscopy (XPS). Sulfonate SAMs exhibited much higher effective pKa (approximately 2) than dilute sulfonic acid (-5 to -6), and amine SAMs exhibited much lower pKa (approximately 3) than dilute organic amines (approximately 10). This is attributed to the stabilization of nonionized groups by adjacent ionized groups in the SAM. Zeta potentials of these SAMs as a function of pH were consistent with the XPS results and indicated that ionizable SAM surfaces can generate surface potentials much higher than those of nonionic SAMs (thioacetate, methyl) and typical oxide surfaces.

Journal Article↗
PubMed2004

Self-assembly patterning of colloidal crystals constructed from opal structure or NaCl structure.

We developed a novel self-assembly process to fabricate an orderly array of particle wires constructed from a close-packed colloidal crystal without preparation of patterned templates. A substrate was immersed vertically into a SiO2 colloidal solution, and the liquid surface moved downward upon evaporation of solution. Particles formed a mono-/multiparticle layer, which was cut by the periodic drop-off of solution. The orderly array of particle wires was successfully fabricated, showing the suitability of the self-assembly process for the fabrication of nano-/microstructures constructed from nano-/microparticles or blocks. The mechanism of the assembly process and control of thickness, width, and interval of particle wires were further discussed. Moreover, an array of particle wires constructed not from close-packed face-centered cubic (or hexagonal close packed) structure but from two kinds of particles was realized to fabricate an array of particle wires with NaCl structure by this self-assembly process.

Journal Article↗
PubMed2004

Micropatterning of lanthanum-based oxide thin film on self-assembled monolayers.

We studied the direct micropatterning of a lanthanum-based thin film on a template of self-assembled monolayers in an aqueous solution at 80 degrees C. The template composed of silanol and octadecyl areas was prepared by UV-modified octadecyltrichlorosilane SAMs through a photomask. The amorphous La(2)O(CO(3))(2) x H(2)O thin films were selectively deposited in the silanol regions. Crystallized La(2)O(3) was obtained after heating at 800 degrees C in air.

Journal Article↗
PubMed2004

Fabrication of self-assembled monolayers (SAMs) and inorganic micropattern on flexible polymer substrate.

By grafting (aminopropyl)triethoxysilane (APTES) as the buffer layer on poly(ethylene terephthalate) (PET) surface, the SAMs ofoctadecyltrichlorosilane (OTS), phenyltrichlorosilane (PTCS), vinyltrichlorosilane (VTCS), andp-tolyltrichlorosilane (TTCS) were fabricated on the flexible polymer substrate. The properties of SAMs were accurately controlled by adjusting the immersing time of substrates in the solutions and the concentration of the solutions. The SAMs acted as templates, and TiO2 micropattern was successfully deposited on OTS, TTCS, and PTCS SAMs.

Journal Article↗
PubMed2004

Light-excited superhydrophilicity of amorphous TiO2 thin films deposited in an aqueous peroxotitanate solution.

We report on the photoinduced superhydrophilicity of the surface of amorphous TiO2. Amorphous TiO2 thin films were prepared on self-assembled monolayers by the peroxotitanate-complex deposition (PCD) and liquid-phase deposition (LPD) methods. The surface morphology and topography were characterized in detail. The contact angles were 34 degrees and 66 degrees for the as-deposited thin films through the PCD and LPD methods, respectively, which slowly increased to about 70 degrees and 73 degrees after being stored in air. After irradiation by UV light, the contact angle vanished and the surface exhibited superhydrophilicity. The superhydrophilicity and hydrophobicity could be switched by alternatively exposing the surface to UV light and drying in an atmosphere filled with organic gases. Although the oxidation of the contamination on the surface has effects on the increase in hydrophilicity, the X-ray photoelectron spectroscopy results suggested that the superhydrophilicity was also related to the transformation of the Ti-OH groups to groups that have dangling bonds. This paper indicates that an amorphous TiO2 thin film does not need to be heated to obtain superhydrophilicity; such a self-cleaning surface can be achieved at room temperature by our newly developed environmentally friendly method.

Journal Article↗
PubMed2004

The effect of surface charge on hydroxyapatite nucleation.

Both the charged surfaces and condition of supersaturated solutions are thought to be the important factors that greatly affect the nucleation of hydroxyapatite (HAp) onto the substrates. In the present study self-assembled monolayers (SAM) terminated with amino (NH2-SAM) and hydroxyl (OH-SAM) headgroups were employed to generate the positively and negatively charged surfaces, respectively. The soaking experiments for HAp nucleation were carried out in the supersaturated solutions (1.5 SBF) with Ca2+ and PO4(3-) ions concentrations 1.5 times higher than in simulated body fluid (SBF). The stability of solutions deeply depends on pH values if other factors (temperature, ionic series and their concentration, etc.) are fixed. Consequently, the opposite micropatterns of HAp films were observed on the UV-patterned SAM with NH2 and OH terminals in a stable solution (1.5 SBF, pH=7.2) where no particles formed and in an unstable solution (1.5 SBF, pH=7.6) where homogeneous nucleation occurred. The preferential nucleation of HAp was found on negative surface (OH-SAM) in a stable supersaturated solution, while selective deposition of HAp was formed on positive surface (NH2-SAM) in the unstable solution. Considering the latter results, it is conceivable that the electrostatic adhesion of microparticles formed in the solution dominated the formation of HAp in the unstable solution.

Adsorption↗
PubMed2004

High-resolution transmission electron microscopy study of Ca(3)Co(4)O(9).

The crystal structure of Ca(3)Co(4)O(9) was investigated using high-resolution transmission electron microscopy (HRTEM) and the image-simulation method. The c(*) was 10.8A and the b parameters were 4.56A for the Ca(2)CoO(3) block and 2.82A for the CoO(2) sheet. The [110] zone axis HRTEM images confirmed that Ca(3)Co(4)O(9) has a modulated layered structure with modulation. For the first time, the atomic positions of the Ca and Co atoms in the Ca(2)CoO(3) block were identified, corresponding to three rows of dark spots in the [110] direction. The observed HRTEM images for Ca(2)CoO(3) agreed well with the calculated images based on the structural model obtained by the Rietveld refinement method.

Calcium↗