Takayuki Narushima

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

The effects of niobium ions released from 60CaO-30P(2)O(5)-(10-x)Na(2)O-xNb(2)O(5) (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 Nb(2)O(5) was significantly higher than that on the Nb(2)O(5)-free glass, although proliferation was not enhanced on all glasses containing Nb(2)O(5). 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 enhance differentiation and mineralization of osteogenic cells rather than their initial adhesion or proliferation.

Fabrication of low-cost beta-type Ti-Mn alloys for biomedical applications by metal injection molding process and their mechanical properties.

Titanium and its alloys are suitable for biomedical applications owing to their good mechanical properties and biocompatibility. Beta-type Ti-Mn alloys (8-17 mass% Mn) were fabricated by metal injection molding (MIM) as a potential low cost material for use in biomedical applications. The microstructures and mechanical properties of the alloys were evaluated. For up to 13 mass% Mn, the tensile strength (1162-938MPa) and hardness (308-294HV) of the MIM fabricated alloys are comparable to those of Ti-Mn alloys fabricated by cold crucible levitation melting. Ti-9Mn exhibits the best balance of ultimate tensile strength (1046MPa) and elongation (4.7%) among the tested alloys, and has a Youngs modulus of 89GPa. The observed low elongation of the alloys is attributed to the combined effects of high oxygen content, with the presence of interconnected pores and titanium carbides, the formation of which is due to carbon pickup during the debinding process. The elongation and tensile strength of the alloys decrease with increasing Mn content. The Ti-Mn alloys show good compressive properties, with Ti-17Mn showing a compressive 0.2% proof stress of 1034MPa, and a compressive strain of 50%.

Microstructures, mechanical properties and cytotoxicity of low cost beta Ti-Mn alloys for biomedical applications.

UNLABELLED The microstructures, mechanical properties and biocompatibility of low cost β-type Ti-(6-18)Mn alloys were investigated after solution treatment. Ti-9 Mn exhibits the best combination of tensile strength and elongation among the fabricated alloys, and its performance is comparable to or superior to those of Ti-6Al-4V ELI (Ti-64 ELI) in terms of every parameter evaluated. A hardness of 338 HV, a Youngs modulus of 94 GPa, a 0.2% proof stress of 1023 MPa, an ultimate tensile strength of 1048 MPa and elongation of 19% were obtained for Ti-9 Mn. Furthermore, the cell viability and metallic ion release ratios are comparable to those of commercially pure titanium, making this alloy promising for biomedical applications. The Youngs modulus is also lower than that of Ti-64 ELI (110 GPa), which can possibly reduce the stress shielding effect in implanted patients. STATEMENT OF SIGNIFICANCE This study evaluates mechanical and biological performance of low cost solution treated β-type Ti-(6, 9, 13 and 18 mass%)Mn alloys. It includes alloys containing a Mn content range higher than most previously published works (which is around or lower than 8 mass%). Furthermore, the effects of the ω phase and the β phase stability of the alloys over some mechanical properties and microstructures are discussed. Ion release behavior under simulated body fluids and cell viability are also evaluated. For the case of the Ti-9 Mn, a mechanical and biological performance that is comparable to or superior than that of the widely used Ti-6Al-4V ELI and commercially pure Ti was observed.

Synthesis and characterization of Ag-containing calcium phosphates with various Ca/P ratios

Ag-containing calcium phosphate (CaP) powders were synthesized by a precipitation method using aqueous solutions of calcium nitrate, silver nitrate, and ammonium phosphate. The powders were sintered at temperatures ranging from 1173 to 1473 K. The charged atomic ratios of (Ca+Ag)/P and Ag/(Ca+Ag) in solution were varied from 1.33 to 1.67 and from 0 to 0.30, respectively. The Ag content in the as-precipitated CaP powders increased with the charged Ag/(Ca+Ag) atomic ratio in solution and was lower than the charged Ag/(Ca+Ag) value. The as-precipitated CaP powders consisted of hydroxyapatite (HA) as the main phase. Ag nanoparticles were observed on the as-precipitated HA particles under all conditions of Ag addition. After the sintering, HA, β-TCP (tricalcium phosphate), α-TCP, and β-CPP (calcium pyrophosphate) were mainly detected as CaPs on the basis of the Ca/P atomic ratio of the as-precipitated powders. The addition of Ag stabilized the β-TCP phase, and the distribution of Ag in β-TCP was homogeneous. A metallic Ag phase coexisted with HA. The solubility of Ag in HA was estimated to be 0.0019-0.0061 (Ag/(Ca+Ag)) atomic ratio, which was lower than that in β-TCP (higher than 0.0536) and higher than that of β-CPP (below the detection limit of analyses).

Electrical conductivity and ionic transference number of Sr and Baβ-aluminas

Abstract Ba and Srβ-alumina ionic conductors were synthesized by solid state sintering at 2033 to 2073 K and their electrical conductivities were measured by a.c. impedance spectroscopy. The electrical conductivities at 1673 K were 2.05×10−2 and 4.6×10−3 S m−1 for Sr and Baβ-aluminas, respectively. An oxygen concentration cell and d.c. polarization methods were applied to measure the ionic transference numbers. The values obtained by the two methods were almost in agreement at more than 1400 and 1673 K for Srβ-alumina and Baβ-alumina, respectively. Srβ-alumina could have slightly greater ionic transference numbers than Baβ-alumina.

Electrical conductivity of alkaline-earth metal β-aluminas and their application to a CO2 gas sensor

Sr and Baβ-aluminas in a single phase were synthesized in the MO-MgO-Al 2 O 3 (M = Sr and Ba) system by a solid state sintering method. The electrical conductivity was measured at 873 to 1473 K by an AC impedance method. The total electrical conductivities of Srβ-alumina and Baβ-alumina were 1.2 × 10 -2 S m -1 and 6.7 × 10 -4 S m -1 at 1473 K, respectively. A CO 2 gas sensor using the Srβ-alumina was constructed. The sensor could be used at more than 1000 K.

Calorimetric study on hydration of CaO-based oxides

Abstract Hydration behavior of compounds in Ca–(Si, Al or Fe)–O systems, CaO–(FeO or MnO) solid solutions and various kind of slags were investigated using calorimetric and dilatometric techniques in order to clarify the effects of CaO-based oxides on stability of steelmaking slag. Slow hydration rate and large volume expansion were observed in 3CaO·Al 2 O 3 , which was a harmful component for stabilizing slag. Heat of hydration and volume expansion of CaO solid solutions were almost the same as those of pure CaO in lower solute content region than 30-mole%, while the hydration rate decreased as MnO contents increased in higher solute content region. Hydration behavior of converter slag was dominated by free lime contained in the slag. It was suggested that 3CaO·Al 2 O 3 affected hydration behavior of ladle furnace free (LF) slag because Al dissolution was detected after calorimetric measurements and slow expansion rates and higher heat of hydration than that calculated with free lime contents were observed for LF slag.

NKG2D⁺ IFN-γ⁺ CD8⁺ T cells are responsible for palladium allergy.

Nickel, cobalt, and chromium are well known to be causal agents of allergic contact dermatitis. Palladium (Pd) can also cause allergic disease and exposure results from wide use of this metal in dental restorations and jewelry. Metal allergy is categorized as a delayed-type hypersensitivity, and metal-responsive T cell clones have been isolated from allergic patients. However, compared to nickel, little is known about the pathology of allergic disease mediated by Pd, and pathogenic T cells are poorly understood. To identify the pathogenic T cells that are responsible for onset of Pd allergy, we enriched metal-responsive lymphocytes by sequential adoptive transfer of involved lymph node cells. Here we show that sequential adoptive transfer gradually increased the incidence and the intensity of Pd allergy, and CD8+ T cells are responsible for the disease as CD8+ T cell-depleted mice and β2-microglobulin-deficient mice did not develop Pd allergy. In addition, we found that draining lymph node cells skewed toward CD8+ T cells in response to Pd challenge in 8th adoptive transferred recipient mice. The CD8+ T cells expressed NKG2D, a costimulatory molecule involved in the production of IFN-γ. NKG2D ligand was also induced in Pd-injected tissues. Furthermore, both NKG2D ligand-transgenic mice, where NKG2D is downmodulated, and IFN-γ-deficient mice showed impaired Pd allergy. Taken together, these results indicate that IFN-γ-producing NKG2D+ CD8+ T cells are responsible for Pd allergy and suggest that NKG2D is a potential therapeutic target for treatment of metal allergy.

Evaluation of thin amorphous calcium phosphate coatings on titanium dental implants deposited using magnetron sputtering.

Objective:Calcium phosphate is used for dental material because of its biocompatibility and osteoconductivity. Amorphous calcium phosphate (ACP) coatings deposited by magnetron sputtering can control their thickness and absorbability. This study aimed to evaluate and characterize ACP coatings deposited via magnetron sputtering. It was hypothesized that ACP coatings would enhance bone formation and be absorbed rapidly in vivo. Methods:ACP coatings that are 0.5 &mgr;m in thickness were deposited via magnetron sputtering on dental implants. Uncoated implants served as controls. The effect of the ACP coatings in vivo was investigated in New Zealand white rabbit. To evaluate the effect of the ACP coatings on the bone response of the implants, the removal torque, implant stability quotient, and histomorphometric analysis were performed on the implants at 1, 2, and 4 weeks after implantation. Results:Results of the x-ray diffraction analyses confirmed the deposition of ACP coatings. Images from the scanning electron microscopy revealed that the coatings were dense, uniform, and 0.5 &mgr;m in thickness and that they were absorbed completely. Mechanical stability and bone formation in the case of the ACP-coated implants were higher than those of control. Conclusion:These results suggest that implants coated with thin ACP layers improve implant fixation and accelerate bone response.

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

The phase and dissolution behavior of precipitates in biomedical ASTM F75 Co-Cr-Mo-C-Si-Mn alloys were investigated. Alloys of five different compositions, Co-28Cr-6Mo-0.25C-1Si, Co-28Cr-6Mo-0.25C-1Mn, Co-28Cr-6Mo-0.25C-1Si-1Mn, Co-28Cr-6Mo-0.15C-1Si, and Co-28Cr-6Mo-0.35C-1Si, were heat-treated from 1448 to 1548 K. The precipitates observed in the as-cast and heat-treated alloys were carbides (M23C6 type, h-phase, and p-phase) and an intermetallic compound (c-phase). The main precipitates observed after heat treatment at high temperatures such as 1548 K were p-phase and M23C6 type carbide. At these high temperatures, two types of starlike precipitates—dense and stripe-patterned—were observed. The starlike-dense precipitate was the p-phase, and the starlike precipitate with a stripe pattern was identified as the M23C6 type carbide and metallic fcc g-phase. In the alloys heat-treated at 1448 to 1498 K, blocky-dense M23C6 type carbide was primarily observed. c-phase was detected in the Co-28Cr-6Mo-0.15C-1Si alloy under as-cast condition and after heat treatment at 1448–1523 K for a short holding time. The addition of Si seemed to increase the holding time for complete precipitate dissolution because of the effects of Si on the promotion of p-phase formation at high temperatures and the increased carbon activity in the metallic matrix.