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The effects of Ti, Al and V concentrations and the extraction conditions on the cell viabilities of murine fibroblast L929 cells, murine osteoblast-like MC3T3-E1 cells and fibroblast V79 cells taken from the lungs of Chinese hamsters were investigated by the cell culture method using metallic particles. The particles were sterilized under a U.V. lamp for 14.4 ks (4 h) and suspended independently in Eagle's minimum essential medium (Eagle's medium) for the L929 cell seeding and α modified Eagle's medium (α medium) for the MC3T3-E1 cell seeding containing 10 vol% fetal bovine serum and 7.5% NaHCO 3 These mediums were kept for 172.8 ks (48 h) in an incubator under a 95%air-5%CO 2 atmosphere (defined as medium extraction). Medium without metallic particles was also kept inside the incubator under similar conditions and was used as the control for all the cell cultures. These mediums were filtered with a 0.2 μm filter. 1.0×10 4 to 5.0 × 10 4 L929 cells/mL, 5 × 10 4 MC3T3-E1 cells/mL and 10 2 V79 cells/dish were seeded in both the control and in the medium extract using the metallic particles. For the titanium particle extraction, the maximum Ti concentrations in the Eagle's medium and α medium were 0.2 and 0.3 mass ppm, respectively. Hence the L929 and MC3T3-E 1 cells proliferated in the same ratio as those of the control. Also, the colony formation ratio (number of colonies in the medium extract with metallic particles/average number of colonies in the control) of V79 cells was unity. For the Al particle extraction with ultrapure water for 172.8 ks (48 h), gel formation of aluminum hydroxide was observed. However, the relative growth ratio (the number of cells in medium extract with metallic particles/average number of cells in control) of the L929 cells was unity when the Eagle's medium was prepared after filtering with a 0.2 μm membrane filter. On the contrary, the relative growth ratios of the L929 cells for both Eagle's MEM extract without fetal bovine serum and the Eagle's medium extract were zero. For the aluminum particle extraction, the relative growth ratios of the L929 and MC3T3-E1 cells sharply decreased as the Al concentration in the medium increased to approximately 0.2 to 0.5 mass ppm. This aluminum effect on L929 cell viability tended to be stronger in the Eagle's medium containing a small quantity of V ions (≤0.03 ppm). The effects of Al concentration on the colony formation ratio of the V79 cells showed the same tendency as those of the relative growth ratios of the L929 and MC3T3-E1 cells. The relative growth ratio of the L929 cells sharply decreased when V concentration in the Eagle's medium increased to 0.2 mass ppm and became zero at approximately 0.5-mass ppm. The effects of V concentration on the colony formation ratio of the V79 cells were also similar to the relative growth ratio of the L929 cells. The relative growth ratio of the MC3T3-E 1 cells decreased from 0.002 mass ppm of V concentration and approached zero at approximately 0.2 mass ppm.

The effects of Ti and Al oxide films on the relative growth ratio of murine fibroblast L929 and the colony formation ratio of fibroblast V79 cells derived from the lung of a Chinese hamster were investigated. Titanium and aluminum particles were oxidized inside an oven at 453 K (180°C) for 7.2 ks. These particles were suspended in Eagle's medium and kept for 173 ks (48 h) inside an incubator under a 95%air-5%CO 2 atmosphere. Eagle's medium without metallic particles was also kept inside the incubator under similar conditions for the control. The mediums were filtered with a 0.2 μm membrane filter to remove metallic particles (Eagle's medium extract). 3.0 × 10 4 L929 cells/dish and 10 2 V79 cells/dish were seeded in both the control and in the Eagle's medium extracts. In the case of oxidized Al particle extraction, the relative growth ratio of L929 cells was 0.8± 0.07 after 346 ks (4 d) of incubation. A relatively strong oxide film formed on the surfaces of the Al particles, hence the relative growth ratio of the L929 cells markedly increased. Al and Ti plates were polished to a mirror-like finish using diamond paste and alcohol, well proliferated colonies of V79 cells were observed on the mirror-like finished Ti plate (Ra=4.8±0.2 nm), whereas no colonies existed on the mirror-like finished Al plate (Ra=38.5 ±8.4 nm). However, the colonies appeared when the Al plates were acid-treated with a solution of NaHCO 3 and C 2 H 4 O 2 (Ra=43.4±10.1 nm) after mirror-like finishing, and also when roughening with #240 water-proof emery paper (Ra=1548±169 nm). The colony formation ratio of the V79 cells was found to depend on the surface roughness (Ra) and strength of the Al oxide film.

New titanium alloys containing zirconium, tin, niobium, tantalum and palladium are being developed by our group. Using metallic particles we investigated effects of Zr, Sn, Nb, Ta and Pd concentrations in Eagle's medium and a medium, added as alloying elements for the new Ti alloy, on the colony formation ratio of fibroblast V79 cells taken from the lungs of Chinese hamsters, and on the relative growth ratios of murine fibroblast L929 and murine osteoblast-like MC3T3-E 1 cells. Moreover, we investigated the effects of chromium and molybdenum concentrations on the colony formation ratio of V79 cells and on the relative growth ratios of L929 and MC3T3-E1 cells. The effects of Co, Ni, Fe and Si concentrations on the relative growth ratios of L929 and MC3T3-E cells were examined. Various sterilized metallic particles were extracted after incubation for 86.4 ks (I d) to 432 ks (5 d) under a 95%air-5%CO 2 atmosphere at 310 K (37°C). The maximum concentrations of Zr, Sn, Nb, Ta and Cr released into Eagle's medium and α medium after 0.2 μm membrane filtering were 2.1, 4.1, 0.5, 0.07 and 0.14 mass ppm, respectively. Therefore, the colony formation of the V79 cells and the relative growth ratios of L929 and MC3T3-E1 cells were nearly unity. For palladium particle extraction, the colony formation of V79 cells and the relative growth ratio of L929 cells gradually decreased from a concentration of approximately 2 mass ppm or higher and reached nearly zero at greater than 20 mass ppm. Influences of Mo, Fe, Ni and Co concentrations on the MC3T3-E1 cell viabilities were more pronounced at lower concentrations than with the L929 and V79 cells. In the case of Mo particle extraction, the relative growth ratio of MC3T3-E cells decreased from the concentration of about 10 mass ppm. For iron, nickel and cobalt particle extractions, the MC3T3-E1 cell viabilities decreased from concentrations of about 2, 1 and I mass ppm or higher, respectively, and the relative growth ratio of MC3T3-E1 cells decreased to zero at concentrations greater than 20 mass ppm. In the case of Si particle extraction, the relative growth ratio of the L929 cells was nearly unity at the high concentrations of 65 mass ppm and over. However, the relative growth ratio of MC3T3-E1 cells decreased from I mass ppm and was nearly zero at concentrations greater than 50 mass ppm.

Ti-15 mass%Zr-4%Nb-4%Ta-0.2%Pd-0.2%0-0.05%N and Ti-15%Sn-4%Nb-2%Ta-0.2%Pd-0.2%O alloys without V and Al elements for surgical implantation were cast by vacuum arc-melting in response to recent concerns about the long term safety of Ti-6%Al-4%V extra low interstitial alloy (ASTM standard for surgical implantation). After the alloys were forged in their and α + β regions, specimens 30 mm in diameter and 13 mm in height were arc-melted in an argon gas atmosphere with a titanium casting machine for dental use using a tungsten electrode. The molten alloys were cast into a graphite mold by centrifugal force. The cast microstructures of the Ti-Zr and Ti-Sn alloys consisted of α' martensitic structure. To examine of the centrifugal alloys properties for dental application, the corrosion resistance and mechanical properties of the alloys were investigated by the anodic polarization in 5 mass% HCl and 1 mass% lactic acid solutions, the measurements of micro-Vickers hardness and the tensile test at room temperature. The anodic polarization properties of the Ti-Zr and Ti-Sn alloys cast in a 1% lactic acid solution are almost the same as those of Ti-Zr and Ti-Sn alloys annealed at 973 K for 7.2 ks after α+β forging. A rapid increase in current density resulted from low potential in a 5% HCl solution in comparison with the annealed Ti-Zr and Ti-Sn alloys. The passive films on the Ti-15%Zr-4%Nb-2%Ta-0.2%Pd and the Ti-15%Sn-4%Nb-2%Ta-0.2%Pd alloys in a 1% lactic acid solution consisted of TiO 2 , ZrO 2 , SnO 2 , Nb 2 O 5 , Ta 2 O 5 and PdO or Pd as demonstrated by X-ray photoelectron spectroscopy (XPS). Micro-Vickers hardness does not change from the surface to the centeral part in castings. The strength of the cast Ti-Zr and Ti-Sn alloys was higher than those of the annealed Ti-Zr and Ti-Sn alloys. However, the ductility of the cast alloys was lower than the annealing ones.

The corrosion resistances of Ti-15%Zr-4%Nb-4%Ta-0.2%Pd-0.2%O-0.05%N and Ti-15%Sn-4%Nb-2%Ta-0.2%Pd-0.2%O alloys were compared with pure Ti grade 2, Ti-6%Al-4%V ELI (Extra low interstitial), Ti-6%Al-2%Nb-1%Ta and type Ti-15% Mo-5%Zr-3%Al alloys for medical implants by anodic polarization and immersion tests at 310 K in various pseudo saline solutions. The change in current density was small up to passivity zones in 1 mass% lactic acid, PBS (Phosphate-buffered saline solution) (-), calf serum and Eagle's MEM (Minimum essential medium) + bovine serum solutions except 5% HCI. The current density change of Ti-15%Zr-4% Nb-4%Ta-0.2%Pd-0.2%O-0.05%N alloy was lowest among the whole Ti alloys. The current densities in a region higher than 2 V tend to increase in the following relation; Ti-6%Al-4%V ELI > Pure Ti grade 2>Ti-6%Al-2%Nb-1%Ta> Ti-15%Sn-4%Nb-2%Ta-0O.2%Pd-0.2%0 > Ti-15%Zr-4%Nb-4%Ta-0.2%Pd-0.2%O-0.05%N alloy in α+β type alloys. Otherwise the passive current density of the β type Ti-15%Mo-5%Zr-3%Al alloy was higher than that of α + β type alloys. Passive films formed on the Ti-15%Mo-5%Zr-3%Al alloy in the calf serum consisted mainly of Ti 4+ , Zr 4+ , Al 6+ and Mo as demonstrated by X-ray photoelectron spectroscopy (XPS). The rate of Ti ions released from Ti alloys in a deaerated 5% HCl solution decreased with increasing Zr, Nb, Ta, and Pd contents. Especially, the rate of Ti ions released from Ti-15%Zr-4%Nb-(2∼4%)Ta-Pd alloys containing Pd in the range from 0 to 0.2% decreased remarkably compared to 0.2 to 0.5%Pd. The passive films formed on the Ti-Zr-Nb-Ta-Pd and Ti-Sn-Nb-Ta-Pd alloys containing 0.2% Pd in the immersion test consisted mainly of Ti 4+ , Zr 4+ , Sn 4+ , Sn, Nb 5 +, Ta 5+ and Pd. The rate of released Ti increased by the following relation; Ti-15%Sn-4%Nb-2%Ta-0.2%Pd-0.2%nO≥Ti-6°/nAl-2%Nb-1%Ta≥Ti-6%Al-4%V ELI≥Pure Ti grade 2>Ti-15%Zr-4%Nb-4%Ta-0.2%Pd-0.2%O-0.05%N ≥ β type Ti-15%Mo-5%Zr-3%Al alloy.

The corrosion resistance of implant alloys was investigated by anodic polarization measurements in a pseudo physiological solution. Role of alloying elements in passive film formed on implant alloys by the anodic polarization was also examined with X-ray photoelectron spectroscopy (XPS). Passivity zones of SUS316L stainless steel and Co-Cr alloys are narrow, and a rapid increase in the current density is observed from a low potential as compared to Ti alloys. The passive current density of Ti-15%Zr-4%Nb-2%Ta-0.2%Pd alloy (mass%) is very low. Effects of protein and dissolved oxygen with 90%N 2 + 5%CO 2 + 5% O 2 gas bubbling on anodic polarization curves are not detected. The passive film formed on the Ti-6%Al-4% V extra low interstitial alloy consists mainly of TiO2, A1 2 O 3 and small amounts of V oxide. Passive films on the Ti-15%Zr-4%Nb-2%Ta-0.2%Pd and Ti-15% Sn-4%Nb-2%Ta-0.2%Pd alloys consist of TiO 2 , ZrO 2 , SnO 2 , Nb 2 O 5 , Ta 2 O 5 and PdO or Pd. XPS spectra from the Co-Cr alloy and SUS316L stainless steel show peaks of Cr2O3, CoO, Fe oxide, Mo oxide, Ni, Co, Fe, Mo and Cr. As Ni, V and Co are strong cytotoxic elements, it was found that biocompatibility of SUS 316L, Co-Cr, Ti-6%Al-4% V ELI alloys become lesser after a long time use in the living body. The thickness of the passive film on Ti alloys is thinner than that of Co-Cr alloy. Passive film formed on the Ti-15%Zr-4%Nb-2%Ta-0.2%Pd alloy is strong and stable.

Ti-15mass%Zr-4%Nb-4%Ta-0.2%Pd and Ti-15%Sn-4%Nb-2%Ta-0.2%Pd alloys not containing V and At for surgical implantation were cast by plasma electron beam melting. The effect of heat treatment on room temperature strength and corrosion fatigue strength were investigated by aging treatment after solution treatment. The alloys were forged in their α and α + β regions, and then solution-treated at 953∼1173 K for 3.6 ks. Optimized solution treatment conditions are 1038 K -3.6 ks for Ti-Zr alloy and 1098 K -3.6 ks for Ti-Sn alloy containing 15∼20 vol% of primary α phase. After solution treatment under the optimized conditions, aging treatment was carried out at 623∼873 K for 600 s ∼ 108 ks. Optimized aging conditions for Ti-Zr and Ti-Sn alloys were at 673 K for 36 ks and at 723 K for 36 ks, respectively. The room temperature strengths of these solution treated and aged alloys were about 30% higher than the annealed alloys. It is revealed by transmission electron microscopic observation that, fine α phase precipitates in α' martensitic matrix are responsible for the age hardening. The corrosion fatigue test in a physiological saline solution was carried out under the condition of a tension to tension mode with a sine wave at a stress ratio of 0.1, at a frequency of 10 Hz in Eagle's MEM+fetal bovine serum solution using an environment cell with 90%N 2 +5% CO 2 +5%O 2 gas bubbling at 310 K. The fatigue strength at 10 7 cycles in solution-treated and aged Ti-15%Zr-4%Nb-4%Ta-0.2%Pd and Ti-15%Sn-4%Nb-2% Ta-0.2%Pd alloys were about 650 MPa and 800 MPa respectively, which were about 20∼30% higher than those of the annealed alloys.

The effect of Zr, Sn, Nb, Ta, Pd, N and O on the corrosion resistance of titanium alloys for medical implants was investigated by measuring the anodic polarization curves at 310 K in 5 mass% H 2 SO 4 and 5%HCl solutions deaerated by high-purity N 2 gas bubbling. The critical current density for passivation (I c ) and passive current density at 0.6 V versus SCE of the titanium alloys markedly decreased with increasing Zr, Nb, Ta, and Pd contents in the range from 5 to 20, 4 to 8, 2 to 4 and 0 to 0.2%, respectively, although Sn had an adverse effect in the range from 10 to 20 mass%. The effect of N and O on I, was undetected. The log (I c ) value decreased linearly with increasing bond order (B o ) value representing the covalent bond strength between Ti and the alloying elements

Titanium alloys for medical implants were cast using 5∼20 mass%Zr, 10∼20%Sn, 4-∼8%Nb, 2∼4%Ta and 0∼0.2%Pd as alloying elements instead of using harmful Al and V. The alloys were forged in their α and α+β regions and then annealed at 973 K for 7.2 ks. The annealed microstructures of the alloys consisted mainly of the acicular structure containing 10 to 30 volume% elongated β grains. While the room temperature tensile strength of the Ti-(5∼15%)Zr-4%Nb-2%Ta-0.2%Pd alloys increased slightly with increasing Zr content, the strength of the Ti-(10∼20%)Sn-4%Nb-2%Ta-0.2%Pd alloys increased markedly with increasing Sn content. The Ti-15%Sn-4%Nb-2%Ta-0.2%Pd alloy surpassed the Ti-6%Al-4%V extra low interstitial (ELI) alloy for medical implants (ASTM F136-84 Standard) in tensile strength as well as in elongation and reduction of area