Showing papers by "Takayuki Narushima published in 2012"

Effects of niobium ions released from calcium phosphate invert glasses containing Nb2O5 on osteoblast-like cell functions.

Abstract: The effects of niobium ions released from 60CaO-30P2O5-(10-x)Na2O-xNb2O5 (mol %, x = 0–10) glasses on MC3T3-E1 cell functions were evaluated by culture tests with two systems; cell culture on glass plates, or in culture media containing glass extracts. Alkaline phosphatase (ALP) activity in the cells cultured on the glass plates containing 3 and 5 mol % of Nb2O5 was significantly higher than that on the Nb2O5-free glass, although proliferation was not enhanced on all glasses containing Nb2O5. Cells cultured in the medium containing 3 × 10–7 M niobium ions showed the highest ALP activity in comparison with other Nb-containing media or normal medium, regardless of the presence of osteogenic factors (ascorbic acid, β-glycerophosphate and dexamethasone) in the media. Calcium deposition by the cells cultured in the medium containing 3 × 10–7 M niobium ions was twice as high as those cultured in medium containing no niobium ions. The effects of niobium ions were thought to depend on ion concentration, and to en...

Precipitates in Biomedical Co-28Cr-6Mo-(0–0.41)C Alloys Heat-Treated at 1473 K to 1623 K (1200 °C to 1350 °C)

Abstract: The phase and formation/dissolution of biomedical Co-28Cr-6Mo-xC (x = 0, 0.12, 0.16, 0.24, 0.33, and 0.41, in mass pct) alloys were investigated before and after heat treatment at high temperatures. The heat-treatment temperatures and holding periods were varied from 1473 K to 1623 K (1200 °C to 1350 °C) and from 0 ks to 43.2 ks, respectively. The intermetallic σ phase was observed in the as-cast and heat-treated alloys without added carbon. In the carbon-added alloys, the M23C6-type, π-phase (M2T3X-type carbide with a β-Mn structure), η-phase (M6C-M12C-type), and M7C3-type carbides were observed depending on the carbon content and heat-treatment conditions. A complete precipitate dissolution was achieved in the alloys with a carbon content of 0 to 0.24 mass pct. The holding time required for complete precipitate dissolution in the carbon-added alloys increased with increasing heat-treatment temperature above 1548 K (1275 °C). The formation of π-phase and M7C3-type carbides was observed in the carbon-added alloys during heat treatment at high temperatures of 1548 K to 1623 K (1275 °C to 1350 °C). Two types of π phase with different lattice constants and chemical compositions were confirmed in the alloys with carbon contents of 0.24, 0.33, and 0.41 mass pct after heat treatment at 1573 K to 1623 K (1300 °C to 1350 °C). The M7C3-type carbide observed at high temperatures occurred in a starlike precipitate with a complicated microstructure.

Precipitates in Biomedical Co-Cr-Mo-C-N-Si-Mn Alloys

Abstract: The microstructures of biomedical ASTM F 75/F 799 Co-28Cr-6Mo-0.25C-0.175N-(0 to 1)Si-(0 to 1)Mo alloys (mass pct) were investigated before and after heat treatment, with special attention paid to the effect of nitrogen on the phases and the dissolution of precipitates. The heat treatment temperatures and holding periods employed ranged from 1448 to 1548 K (1175 to 1275 °C) and 0 to 43.2 ks, respectively. A blocky-dense π-phase precipitate and a lamellar cellular colony, which consisted of an M2X type precipitate and a γ phase, were mainly detected in the as-cast alloys with and without added Si, respectively. The addition of nitrogen caused cellular precipitation, while the addition of Si suppressed it and enhanced the formation of the π phase. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analyses suggested that a discontinuous reaction, i.e., γ 1 → γ 2 + M2X, might be a possible formation mechanism for the lamellar cellular colony. Nitrogen was enriched in the M2X type, η-phase, and π-phase precipitates, but was excluded from the M23X6 type precipitate. Complete precipitate dissolution was observed in all of the alloys under varied heat treatment conditions depending on the alloy composition. The addition of nitrogen decreased the time required for complete precipitate dissolution at low heat-treatment temperatures. At high temperatures, i.e., 1548 K (1275 °C), complete precipitate dissolution was delayed by the partial melting that accompanied the formation of the precipitates such as the π phase resulting in the boundary between the complete and incomplete precipitate dissolution regions in having a C-curved shape.

Biomechanical evaluation of amorphous calcium phosphate coated TNTZ implants prepared using a radiofrequency magnetron sputtering system

Abstract: 1Research Unit for Interface Oral Health Science, Graduate School of Dentistry, Tohoku University, Sendai 980-8577, Japan 2Institute for Materials Research, Tohoku University, Sendai 980-8575, Japan 3Division of Advanced Prosthetic Dentistry, Graduate School of Dentistry, Tohoku University, Sendai 980-8577, Japan 4Division of Craniofacial Function Engineering, Graduate School of Dentistry, Tohoku University, Sendai 980-8577, Japan 5Department of Materials Processing, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan

π-Phase and χ-Phase: New Precipitates in Biomedical Co–Cr–Mo Alloys

Abstract: The phases of precipitates in ASTM F 75 and F 799 Co–Cr–Mo alloys are reviewed with a focus on new precipitates of the π- and χ-phases. The π-phase carbide was observed at temperatures of 1,548–1,623 K where partial melting in Co–Cr–Mo–C system alloys occurred. Si was slightly enriched in the π-phase precipitate and nitrogen substituted carbon in the octahedral sites of the π-phase. It is suggested that the formation and stability in the partial melting region and the transformation of the π-phase take part in the final constitution of the precipitates in ASTM F 75 and F 799 alloys. A χ-phase has been detected in the as-cast and heat-treated Co–Cr–Mo alloy with a midlevel carbon content and the addition of Si. The χ-phase precipitate is an intermetallic compound. The conditions under which the χ-phase is formed are limited by the heat-treatment temperature and chemical composition.

Calcium Phosphate-Coated Titanium Alloy Implants Prepared by Radiofrequency Magnetron Sputtering: A Review

Abstract: This review summarized dental implant coated with calcium phosphate films, especially prepared by radiofrequency (RF) magnetron sputtering system. Calcium phosphate films on titanium alloys fabricated by RF magnetron sputtering system have very thin layer (within 500 nm), high bonding strength (over 60 MPa) and excellent biocompatibilities, even though its films created under the condition of room temperature. This method may be providing the effective interface between tissues and some other materials.

Accelerated Bone Formation Around Titanium Dental Implants with Amorphous Calcium Phosphate Coating in Rabbits

Abstract: The aim of this study was to investigate the bone response of titanium dental implant with amorphous calcium phosphate (ACP) coating film fabricated using RF magnetron sputtering in rabbit. Calcium phosphate coating using RF magnetron sputtering acquires high bonding strength and nano-uniformity of films. Moreover, it is reported that ACP was resorbed rapidly in vitro. The ACP-coated and non-coated implants were placed into rabbits. After 1, 2 and 4 weeks of implantation, the implant stability was evaluated by resonance frequency analysis (RFA) and bone formation was also evaluated histomorphometrically. The ACP-coated implants showed higher stability in RFA and improved bone-implant contact ratio in 4 weeks. Titanium dental implant coated with ACP fabricated using RF magnetron sputtering accelerated bone formation compared with that of non-coated implants.