Hidemi Ukai

Early bone formation around calcium‐ion‐implanted titanium inserted into rat tibia

Rat tibia tissue into which calcium ion (Ca2+)-implanted titanium was surgically placed was histologically analyzed to investigate the performance of the Ca(2+)-implanted titanium as a biomaterial. Calcium ions were implanted into only one side of titanium plates at 10(17) ions/cm2 and the Ca(2+)-treated titanium was surgically implanted into rat tibia for 2, 8, and 18 days. Tetracycline and calcein were used as hard-tissue labels. After excision of the tibia, the tissues were fixed, stained, embedded in polymethyl methacrylate, and sliced. The specimens were observed using a fluorescence microscope. A larger amount of new bone was formed on the Ca(2+)-treated side than on the untreated side, even at 2 days after surgery. In addition, part of the bone made contact with the Ca2(+)-treated surface. On the other hand, bone formation on the untreated side was delayed and the bone did not make contact with the surface. Mature bone with bone marrow formed in 8 days. Neither macrophage nor inflammatory cell infiltration was observed. The results indicated that Ca(2+)-implanted titanium is superior to titanium alone for bone conduction.

AMOUNT OF HYDROXYL RADICAL ON CALCIUM-ION-IMPLANTED TITANIUM AND POINT OF ZERO CHARGE OF CONSTITUENT OXIDE OF THE SURFACE-MODIFIED LAYER

To compare the surface properties of calcium-ion (Ca2+)-implanted titanium with those of titanium and to investigate the mechanism of bone conductivity of Ca2+-implanted titanium, amounts of hydroxyl radical of Ca2+-implanted titanium and titanium were estimated. Also, the point of zero charge (p.z.c.) of oxide constituting surface oxides of Ca2+-implanted titanium and titanium was determined. Results showed that the amount of active hydroxyl radical on Ca2+-implanted titanium was found to be significantly larger than that on titanium, indicating that the number of electric-charging sites of Ca2+-implanted titanium in electrolyte is more than that of titanium. The p.z.c. values of rutile (TiO2), anatase (TiO2), and perovskite (CaTiO3), were estimated to be 4.6, 5.9, and 8.1, respectively. Thus, Ca2+-implanted titanium surface is charged more positively in bioliquid than titanium, accelerating the adsorption of phosphate ions.

Extremely corrosion-resistant bulk amorphous alloys

The addition of chromium, tantalum and molybdenum was the best combination of small additions in enhancing the corrosion resistance of amorphous Ni-16P-4B alloys in concentrated hydrochloric acid. Preparation of rod-shaped amorphous alloys with small contents of these three corrosion-resistant elements were attempted by copper-mold casting. Ni-5Cr-5Ta-3Mo-16P-4B alloy of 1 mm diameter is identified as a single amorphous phase alloy and spontaneously passive in 6 and 12 M HCl, similarly to melt-spun amorphous counterpart, although high resolution TEM observation reveals the presence of nanocrystalline precipitates of about 2 nm in diameter. Ni-5Cr-5Ta-5Mo-16P-4B alloy is also amorphous by X-ray diffraction but contains nanocrystallites of about 5 nm in diameter, the anodic current in 6 M HCl being more than one order of magnitude higher than that of the melt-spun amorphous counterpart. All other copper-mold cast Ni-Cr-Ta-Mo-16P-4B alloys are composed of crystalline precipitates in the amorphous matrix. Sheath-rolling consolidation of gas-atomized amorphous alloy powders to form the amorphous alloy sheet of about 2 mm was attempted for the Ni-10Cr-5Nb-16P-4B alloy which has a particularly wide temperature interval of the supercooled liquid of 64K. The sheath-rolled alloy specimen are identified as an amorphous single phase by X-ray diffraction and high resolution transmission microscopy. However, because of inclusions of very minor crystalline powders in the major amorphous alloy powders before consolidation, crystalline powder inclusions in the consolidated amorphous matrix was preferentially dissolved by an immersion test in 6 M HCl. In a waste incinerator, the sheath-rolled Ni- 10Cr-5Nb-16P-4B alloy showed no detectable weight loss at 393 and 433K for 20 days, maintaining metallic luster.