Papers by Author: Masato Ueda

Abstract: Coral reefs face significant damage from factors such as climate change, pollution, and careless tourism. Although vertebrates and corals differ in substance, their skeletal formation mechanisms are very similar. Titanium (Ti) and its alloys are widely utilised as biomedical materials for orthopaedic and dental implants due to their excellent mechanical properties, biocompatibility, and corrosion resistance. Various surface modifications have been developed to enhance cell adhesion and bone formation. This study aimed to investigate polyp adhesion and skeletal formation on Ti nonwoven materials after chemical surface modifications. Polyps were isolated by increasing the salinity of artificial seawater (viesalt, MARINETECH) in which coral fragments were immersed. Ti nonwoven fabric was anodised. The polyp adhered to the substrate on Day1 and expanded along the fibres over a period of about Day15. The moderate roughness and the oxide film formed on the surface improved the wettability of the substrate.

Abstract: Anatase-type TiO₂ films synthesised on quartz glass demonstrated cell adhesion control when illuminated from the backside with a 150 W Xe lamp emitting white light. The UV component was fully absorbed by the TiO₂ film, preventing cell exposure to it. By selectively applying localised light, non-contact control of cell adhesion areas was achieved. If non-toxic films responsive to conventional LED panels could be used, this would enable precise and easy control of cell adhesion areas. The purpose of this study was to synthesise inorganic semiconductor films with a narrower bandgap than TiO₂, responding to visible light from LED, and to investigate their photo-responsive properties. α-Fe₂O₃ films were deposited on borosilicate glass or ITO-coated quartz glass using RF sputtering with the corresponding metallic targets under an Ar or Ar/O₂ mixed atmosphere. XRD analysis showed sharp diffraction peaks, confirming the successful synthesis of the films. The absorption edges of the oxides shifted to longer wavelengths compared to that of TiO₂, corresponding to their bandgap differences. When a tablet device (HUAWEI MediaPad M3 Lite 10wp) displaying a white image was used as a light source, the oxide films showed a noticeable photocurrent. In the photocurrent profile during the on/off cycle of the light, a phenomenon of current flowing in the reverse direction when the light was turned off was observed. Moreover, this current reversal was more pronounced when the grains were fine. This suggests that the grain boundaries acted like a capacitor and induced polarisation behaviour.

Abstract: Titanium and its alloys are the 5th most common metallic materials used world wide but the markets volume of titanium materials, is difficult to expand due to associated production costs, and the decrease of those costs are critical in order to expand their markets. A possible option is the alloy design, i.e. using low price alloying element, such as iron, chromium, manganese and oxygen, and the selection of other raw materials, i.e. grade of sponge titanium. In beta titanium alloy, Ti-Mo system alloy using ferro-molybdeum was developed by USA company or Ti-Cr-Fe-Al beta alloy were also developed by Japan company. In this paper, those developed alloys were explained. Furthermore, substitution of Ti-10V-2Fe-3Al near beta alloy, presenters are studying about Ti-Mn-Fe-Al alloy.

Abstract: In order to reduce the cost of β-type Ti alloys, the use of Fe as an alloying element has been studied. However, Fe is known to have a very high diffusion coefficient in β-Ti of about 2.6×10^-12 m²/s at 1200 K, and its behavior during heat treatment is expected to be difficult to control. By contrast, Mo, which is also a β-stabilizing element, has a diffusion coefficient of only about 2.5×10^-14 m²/s at 1200 K, i.e., roughly 100 times smaller than that of Fe^{1), 2)}. In this study, the effect of the partial substitution of Fe with Mo on the aging behavior of β-Ti alloys was investigated using X-ray diffraction, electric resistivity, and Vickers hardness measurements. Ti-Mo-Fe alloys were solution-treated by holding at 1173 K for 3.6 ks and then quenching in ice water. In the X-ray diffraction patterns for the resulting samples, only peaks associated with the β phase were identified. It was found that the electrical resistivity and Vickers hardness decreased with increasing Mo content. As the Mo-to-Fe ratio increased, the decrease in electrical resistivity and the increase in Vickers hardness occurred later during the isothermal aging process. This was due to a delay in isothermal ω-phase precipitation.

Abstract: The element of zirconium (Zr) belongs to the same group 4 as Ti in the periodic table. Therefore it possesses similar chemical properties. The Ti-Zr binary system forms a continuous solid solution for both high temperature β phase with the body centered cubic (BCC) structure and low temperature α phase with the hexagonal close-packed (HCP) structure throughout the entire range of composition. As is well known, on the other hand, the element of iron (Fe) is not only inevitable but also effective element in Ti.By incorporating Fe at the stage of alloy design, off-grade sponge titanium can be employed. Both elements seem to be effective in strengthening the titanium alloys. The purpose of this work was to prepare Ti-Zr-Fe alloys and then mechanical property and heat treatment behaviours were investigated as a fundamental research. Ti-x mass% Zr-1mass% Fe alloys (x=0, 5, 10) were melted in a laboratory-scale arc furnace under a high purity argon atmosphere from the sponge Ti, the sponge Zr and the Fe wire. The resulting ingots were hot forged and rolled at approximately 1120 K to obtain plates of approximately 2 mm in thickness. Well-mixed and homogeneous samples could be obtained, oxygen contaminations were less than 0.09 %. Solid solution of Zr into Ti was confirmed by the XRD peak shift in α phase. Vickers hardness and proof stress increased with Zr content. No remarkable changes could be observed in the microstructures after the solution treatment at 1173 K. However, Young’s modulus increased at x=10 by the treatment.

Abstract: Estimated 30 percent or more of coral reefs are now in danger of extinction by coastal construction increases and global temperatures rise. Several restoration techniques such as fragmentation, forming, Biorock have been developed in the past few years. In vertebrates such as mammals, osteoblast is known to form the bones composed of hydroxyapatite. Therefore, bone substitutional devices are generally surface modified to improve the adhesion of osteoblasts on the surfaces. Titanium dioxide film is often employed as the surface material for hard tissue substitutes made of titanium and its alloys. In hard corals, on the other hand, the soft tissue covered on the skeletons made of calcium carbonate has osteoblasts as well. The purpose of this work was to investigate the potential of titanium (Ti) and titanium dioxide (TiO₂) as scaffolds for proliferating coral reefs by analysing the several interfacial reactions. The rods of pure Ti were anodised in aqueous phosphoric acid at a constant voltage of 80 V. The surfaces were confirmed to be anatase type TiO₂. The coral fragments were kept in contact with the rods in a lab-scale aquarium with artificial seawater for several days. The colony of polyps vigorously expanded on the surfaces. Fragments of coral were placed on pure Ti, TiO₂ coated pure Ti in Petri dishes and were reared in artificial seawater. Fine spherical precipitates of calcium carbonate with aragonite structure, which is the same inorganic substance as corals, were observed radially and regularly on the surfaces of TiO₂. In addition, the adherence of planula larva to the sputtered TiO₂ film was observed by using a QCM (Quartz Crystal Microbalance) method. The approach and adhesion of planula larva to the surface could be detected by monitoring the resonance frequency and resistance. The surfaces might have a great potential in coral reef regenerations.

Abstract: Titanium and its alloys possess high specific strength, excellent corrosion resistance and good biocompatibility [1] [2]. Since oxygen is an unavoidable impurity in such materials, it has been adopted as an alloying element in the development of low-cost titanium alloys. Therefore, it is important to investigate the role of oxygen in these alloys, especially in β-type alloys. In the present study, the effects of oxygen on the electrical resistivity, Vickers hardness and heat treatment behavior of a Ti-20mass%V alloy which is the lowest concentration for which the fully retained β phase is obtained were assessed. The electrical resistivity and Vickers hardness of solution-treated and quenched specimens increased with increasing oxygen content, due to the dissolution of oxygen into the β phase and solid solution hardening, respectively. Upon isothermal aging at 673 K, the addition of O accelerated a-phase precipitation. The addition of O was found to suppress the appearance of the athermal ω phase in the solution-treated and quenched state.

Abstract: Ti alloys are attractive materials for such applications, they are expensive due to the costly alloying elements such as Nb or Mo. The present authors have adopted Mn as a low-cost alloying element, and melted Ti-7, 7.5 and 8 mass%Mn-1.5 and 3mass%Al alloys using a laboratory-scale arc furnace. All specimens prepared from bottom ingots were heat treated at 1223 K for 3.6 ks and quenched in ice water. In the 7 and 7.5Mn-Al alloys, the β phase and orthorhombic martensite were identified using X-ray diffraction. In the 8Mn-Al alloys, only the β phase was identified. In the 7, 7.5, and 8Mn-Al alloys, the electrical resistivity at room and liquid nitrogen temperature increased with increasing Al content due to dissolution of Al into the β phase, whereas the Vickers hardness decreased with increasing Al content due to decreasing formation of athermal omega by the addition of Al. Heat treatment at 673 K for 60 s almost completely returned deformed Ti-7 and 7.5Mn-3Al specimens to their original shapes, and heat treatment at 773 K for 60 s almost returned deformed Ti-8Mn-Al specimens to their original shapes.

Abstract: Several techniques have been employed to attach/detach cells to/from a substrate. Cells cultured on a substrate are generally detached from the substrate into a sheet by the destruction of protein between the cells and the substrate using enzymes such as trypsin. However, the enzymes also damage the adhesion molecules among the cells. TiO₂ is an n-type semiconductor with an energy band gap of 3.0-3.2 eV, which displays a photocatalytic activity under ultraviolet (UV) light. The purpose of this work was to fabricate photo-responsive cell culture vessel using TiO₂ film and to investigate adhesion behaviour of cells on it. TiO₂ films were prepared on SiO₂ plates by a sol-gel method using titanium tetraisopropoxide. Primary osteoblasts were seeded on the vessels and then incubated at 37 °C. During the incubation, UV irradiation was performed continuously from back-side of the vessels. Basically the number of cells monotonically increased with incubation periods under darkness. Previous light irradiation promoted the cell adhesion on the surface. The formation of Ti-OH groups on the TiO₂ seems to be facilitated by the UV irradiation. In contrast, the cells decreased under continuous light irradiation. The cells were not exposed to UV in the vessels since it was completely absorbed by the TiO₂ layer. It might be due to generated photocurrent or hydroxyl radicals on the TiO₂ surface. These results imply that the adhesion/proliferation/detachment behaviours of cells can be controlled by the photocatalytic reaction of TiO₂ and the irradiation patterns.

Abstract: Titanium is considered to be a ubiquitous element since it has the 9th-highest Clarke number of all elements. Iron and manganese can also be used as beta stabilizers for Ti alloys, and can be considered to be ubiquitous because of their 4th- and 11th-highest Clarke numbers, respectively. However, investigations into the behavior of Ti-Mn-Fe alloys during heat treatment have shown that in some alloys, the isothermal omega phase is precipitated. Because this phase can lead to brittleness, it is very important to prevent it from forming. It is well known that aluminum can suppress the precipitation of the isothermal omega phase. Thus, in the present study, we investigated the effect of Al content on the phase constitution and heat-treatment behavior of Ti-8.5mass%Mn-1mass%Fe-0 to 4.5mass%Al alloys using electrical resistivity, Vickers hardness, and X-ray diffraction measurements. In all solution-treated and quenched alloys, only the beta phase was identified, thus confirming the suppression of omega-phase precipitation. The resistivity was found to increase monotonically with Al content, while the Vickers hardness decreased up to 3 mass% Al and then remained constant.