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Biomedical subjects

Masayuki Nogami

Publications and source records attributed to Masayuki Nogami.

7 recordsLinked to original sources
PubMed2005

Optical properties and valence change of europium ions in a sol-gel Al2O3-B2O3-SiO2 glass by femtosecond laser pulses.

The Al2O3-B2O3-SiO2 glass containing europium ions was prepared by a sol-gel method. Fluorescence line-narrowing spectra (FLN) indicate two different environments of the Eu 3+ ions. The calculated second crystal-field parameters exhibit the opposite behaviors of the two different environments. The FLN excitation and emission spectra before and after irradiation show that the change of the emission mainly comes from the Eu 3+ ions at site I, revealing that the concentration ratio of the Eu 3+ ions at site I to site II was decreased. The emission spectra confirmed that some Eu 3+ ions were reduced into Eu 2+ ions. The excitation spectra indicate that the Eu 3+ ions at the sites with higher covalence degree can be easily reduced, implying that the Eu 3+ ions are more easily reduced at site I than at site II. The absorption spectra before and after irradiation exhibit that the absorption of Eu 2+ ions increases and that the positive hole centers appear. These results suggest a mechanism of the formation of the Eu 2+ ions by femtosecond laser irradiation.

Journal Article↗
PubMed2005

Enhancement of third-order optical nonlinearities in 3-dimensional films of dielectric shell capped Au composite nanoparticles.

The composite nanoparticles of Au-core capped by CdS shells of different thickness were prepared and assembled into densely packed 3-dimensional films by the layer-by-layer self-assembly (LBL) technique. These films exhibited the 3-dimensional structure of densely packed Au@CdS composite nanoparticles and the shell thickness was tunable by changing the concentration of Cd2+-thiourea complexes. These multilayer films exhibited enhanced third-order optical nonlinear responses and ultrafast response times (several picoseconds). The third-order nonlinear optical susceptibility of the film with the CdS shell thickness of 4.4 nm was estimated to be 1.48 x 10(-9) esu and the value decreases with the increase of the CdS shell thickness. The enhancement of the optical nonlinearity was explained based on the calculation according to the electrostatic approximation by the solution of Laplace's equation under the boundary conditions appropriate to the model of core-shell nanoparticles, and mainly attributed to localized electric field effects in the CdS shell region. Additionally, the nonlinearity was optimized by determination of the values of the dielectric constant and thickness of the different shell.

Journal Article↗
PubMed2005

Macroporous calcium phosphate glass-ceramic prepared by two-step pressing technique and using sucrose as a pore former.

Macroporous calcium phosphate glass-ceramic with an initial glass composition of 60CaO.30P2O5.3TiO2.7Na2O in mol% was successfully prepared by sintering the mixture compact consisting of calcium phosphate glass and sucrose powders, which was formed using a two-step pressing technique. After burning off the sucrose phase, a 3D interconnected macroporous structure was formed in the sintered body, in which the skeleton consisting of the calcium phosphate glass-ceramic (including beta-calcium pyrophosphate and beta-tricalcium phosphate as the crystalline phases) was transformed from the initial glass during the sintering. The macropores with several hundred microns in diameter and the large interconnection size (approximately 100 microm), which result from the controllably large-sized sucrose particles and the hot-pressing at a little higher temperature than the sucrose's melting point, are believed to meet the requirements for cell adhesion and bone tissue regeneration well. Moreover, in vitro dissolution behavior study indicates that the calcium phosphate glass-ceramic is soluble to an acetic acid solution of pH 5-7. These, together with the simplicity and feasibility of the innovative fabrication method itself, show that the formed porous glass-ceramic has a promising potential for application to a scaffold for bone tissue engineering.

Biocompatible Materials↗
PubMed2005

Template guided self-assembling two-dimensional array of Au@SiO2 core-shell nanoparticles for room-temperature single electron transistors.

The composite nanoparticles of a gold core capped by a SiO2 shell with well-controlled thickness have been synthesized and fabricated into two-dimensional array on silicon surface by a simple self-assembly method combined with an AFM nanolithography technique. Current-voltage measurements of the Au@SiO2 composite nanoparticles (shell thickness of 6 nm) show a well-pronounced Coulomb staircase with a period of 300 mV at room temperature, demonstrating single electron transistor behavior. The step width of the Coulomb staircase can be tuned by controlling the thickness of SiO2 shell. The tunable single electron tunneling properties make the 2D array of Au@SiO2 composite nanoparticles an ideal candidate for planar single electron transistor devices.

Colloids↗
PubMed2003

Bioactive calcium phosphate invert glass-ceramic coating on beta-type Ti-29Nb-13Ta-4.6Zr alloy.

A fine, strong coating consisting of a bioactive calcium phosphate invert glass-ceramic can be prepared easily by reaction of the glassy phase with an oxide layer formed on a new beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr, when the metal, on which the mother glass powders with a composition of 60CaO-30P(2)O(5)-7Na(2)O-3TiO(2) in mol% are placed, is heated at 800 degrees C in air. A compositionally gradient layer is developed on the titanium alloy during the heating. Tensile bonding strength of the coating to the metal is significantly higher than those of the coatings to conventional metals such as Ti-6Al-4V alloy or pure titanium. The oxidized layer on Ti-29Nb-13Ta-4.6Zr alloy is relatively thinner than that on Ti-6Al-4V alloy even with heat treatment in air; large tensile stresses are not generated in the layer.

Alloys↗
PubMed2003

Preparation of poly(lactic acid) composites containing calcium carbonate (vaterite).

A new type of ceramic-polymer biomaterial having excellent apatite-forming ability in simulated body fluid was prepared by hot-pressing a mixture of poly(-L-lactic acid) (PLA) and calcium carbonate (vaterite). After PLA dissolved in methylene chloride was mixed with calcium carbonate consisting of vaterite, the mixture was dried completely and subsequently hot-pressed uniaxially under a pressure of 40 MPa at 180 degrees C. When 30 wt% vaterite was introduced, the modulus of elasticity was effectively improved by 3.5-6 GPa, which was about twice higher than the modulus of PLA. The composite showed no brittle fracture behavior and a comparably high bending strength of approximately 50 MPa. The composite containing 30 wt% vaterite formed a 5-15-microm-thick bonelike apatite layer on its surface after soaking in SBF at 37 degrees C even for 1-3d.

Apatites↗