Papers by Author: Kenzo Asaoka

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Authors: Masayuki Kon, Razia Sultana, Emi Fujihara, Kenzo Asaoka, Tetsuo Ichikawa
Abstract: Film-coating on the surface of titanium was investigated by hydrothermal treatments with a maximal pressure of 6.3 MPa (280°C) in CaO solution and water to improve bioactivity and biocompatibility. As a result, calcium titanate (CaTiO3) film was formed on the titanium surface. The surface-coated titanium was immersed in a simulated body fluid (SBF) to estimate its bioactivity. Apatite precipitation was observed on all hydrothermal-treated titanium surfaces after immersion in SBF for 4 weeks. In particular, the apatite precipitation of titanium treated with 6.3 MPa in CaO solution was clearer and larger in amount than those of all other hydrothermal-treated specimens. The results suggest that surface modification of titanium with high-pressure hydrothermal treatments can be expected to improve bioactivity and biocompatibility.
Authors: Kenzo Asaoka, Kunimitsu Maejima
Abstract: Thermal desorption spectroscopy (TDS) was applied to measure the hydrogen in titanium (Ti). Because fracture by hydrogen embrittlement for medical/dental devices of Ti and Ti alloys was reported, dependence of surface oxidation film on hydrogen absorption and desorption behaviors of cp-Ti was carried out. To form the surface oxide film (rutile), the Ti wire samples were annealed in an ambient air at 800oC for 2 hours. Half of the specimens were immersed in a mixed solution of NaF and H3PO4 (APF). The part of the specimens were removed the surface films by abrasion after the heat and the immersion in the APF solution. TDS analysis was applied to detect released ions/molecules during heating from room temperature to 1200oC in a high vacuum vessel for the TiH2 powders, the Ti samples with and without the above treatments. High ion intensity was detected for hydrogen (m/z = 2), and ion intensities of the other ions/molecules were almost the background level in measurements. The concentration of hydrogen in the samples related with heat and chemical process was determined quantitatively, and was not significantly increased by the annealing and the immersion in APF solution if the sample had the tough surface film. However, the sample, which had been removed the surface films before the immersion in APF, showed typical chemical degradation after the immersion in APF for 7 days, that is, high ion intensities of hydrogen, fluoride, water and hydroxyl ions were detected. It was concluded that the control of the surface oxide film on the medical/dental Ti devices is important in determining its longevity.
Authors: Kenichi Hamada, Fumiaki Kawano, Kenzo Asaoka
Abstract: NiTi shape memory alloy fiber-embedded denture-base-resin matrix smart composites were developed as a new denture base material for a “smart denture”, whose shape could be recovered simply by heating after fracture. Three types of fiber surface treatment were applied for the composites and their properties were evaluated by the fiber-pull-out test and bending test, and shape change after repair was examined. A high interface debonding strength increased the fracture strain but did not affect bending strength, and a low interface sliding strength minimized shape change after repair. These results indicate that the fiber-matrix interface with a strong bonding but easy sliding after debonding could improve the preciseness of “smart repair”.
Authors: Luciana M. Hirakata, Masayuki Kon, Tetsuya Yuasa, Youji Miyamoto, Kenzo Asaoka
Authors: Kenichi Hamada, Fumiaki Kawano, Kenzo Asaoka
Authors: Emi Fujihara, Masayuki Kon, Kenzo Asaoka
Abstract: The purpose of this study was to determine if a strontium (Sr)-containing mixing liquid could be used as an exchanging agent for calcium phosphate cement crystallized with Sr-replacing hydroxyapatite (Sr-HAP). Alpha-tricalcium phosphate (α-TCP) powder was mixed with Srcontaining and phosphorous (P)-containing solutions, that is, SrCl2 or SrCl2+CaCl2 solution and NaH2PO4 or Na2HPO4 solution. After storage in the incubator for 7 days, the α-TCP crystals in all set cements were confirmed to have been transformed to HAP crystals by the mixing liquids. The XRD patterns of the set cements implied that the Sr-HAP could be precipitated by using Srcontaining solutions as the mixing liquid because of the chemical shift of a peak (002) in XRD of the HAP crystal. The solubility (shaking immersion in physiological saline) of set cements containing Sr was markedly higher than that of set cement not containing Sr. These results revealed that the Sr-containing solutions used as mixing liquids for α-TCP cement acted as precipitating agents for Sr-HAP. Sr-HAP-precipitating cement could be useful because of its pharmacological activity with high solubility.
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