An electronic fuel injection system of automobiles have been commercialized at the end of 1960’s, they have been adopted as environmental measures for many automobiles and motorcycles. In recent years, metal injection molding (MIM) has been adopted as a process for manufacturing a solenoid valve which is a component of electronic fuel injector, and has been commercialized using PB permalloy. However, Ni that is an element of PB permalloy is expensive material, there was a problem that it is difficult to produce the product at low cost. As a solution to this problem, we can use Fe-Cr alloys, although there are few studies on Fe-Cr alloys by MIM process. In addition, when this materials are used in an alternating magnetic field, there is a problem that core loss increases in high frequency range.

In this study, we made MIM specimens using Fe-Cr-Si alloy powders containing Si in addition to Cr and investigated the influence of Cr and Si contents on the magnetic properties. These results revealed that high performance soft magnetic material can be obtained by setting the Si content 3% and reducing the Cr content.

The synergy of high strength and ductility is crucial for industrial applications. Grain refinement strengthening is a well-known method for strength improvement. However, it leads to poor ductility due to plastic strain instability in the early stage of deformation. Recently developed novel heterogeneous microstructure designed materials called “Harmonic Structure” (HS) can overcome this strength-ductility trade-off. HS designed materials consist of grain size gradient wherein fine grains (‘Shell’) form a connected network surrounding coarse grains (‘Core’). The HS materials exhibit an outstanding combination of strength and ductility that is associated with high strain hardening due to suppressing local deformation. However, the conventional mechanical milling (MM) process for fabricating HS designed materials is time-consuming. Therefore, in the present study, a novel Bi-modal Milling (BiM) process is proposed to achieve HS designed materials more efficiently in a shorter time. The HS design has been applied to SUS316L powder via conventional MM and novel BiM process. Both the HS compacts exhibited approximately similar mechanical properties. Therefore, the proposed BiM technique is more appropriate for the industrial production of HS designed materials.

The hydroxyapatite (HAp) formation ability after soaking in a simulated body fluid, MC3T3-E1 cell differentiation and related surface potentials of rutile-type TiO₂ surfaces formed on Ti are controlled by varying the Ti heat treatment conditions in a N₂ atmosphere containing a trace amount of O₂. The zeta potentials of the samples heated at 873 and 973 K for 1 h are large negative and positive values, respectively. Scanning transmission electron microscopy, electron energy loss spectroscopy, and calculations of defect formation energies reveal that nitrogen atoms incorporated into TiO₂ during surface formation produce the charged defects (NO)_O⁻¹ and (N₂)_O⁺² for the scales formed in 1 h at 873 and 973 K, respectively. HAp formation and MC3T3-E1 cell differentiation is more pronounced on charged nitrogen-doped TiO₂ surfaces compared to on an untreated, neutral Ti surface. An adhesive protein such as Fn adsorbs equally on charged and untreated Ti surfaces in culture medium. However, the adsorption of Ca and P was only detected on charged nitrogen-doped TiO₂ surfaces. The enhanced adsorption of inorganic ions and Fn is probably responsible for promoting initial stage of osteoblast differentiation. The present findings lead to physical models of surface charge distributions that elucidate the relationship between nitrogen-related defects, charged surfaces and cell differentiation mechanisms.

When bioinert materials with fine pores were immersed in simulated body fluid with higher pH in comparison with conventional SBF and subsequently temperature of this SBF was raised, fine particles of calcium phosphate, which we named ‘apatite nuclei’, were precipitated on the surface and in the pores of the substrate. Thus-treated substrate showed high hydroxyapatite formation ability in SBF and will be utilized for bioactive functional materials in orthopedic or dental fields. In our present studies, SUS316L steel, CoCr-based alloy and polyetheretherketone, which cannot bond to living bone spontaneously in living body nevertheless they are attractive artificial bones from a viewpoint of mechanical properties, showed high hydroxyapatite formation ability by applying the above surface modification process. By utilizing hydroxyapatite formation ability of apatite nuclei, in addition, hydroxyapatite capsules could be synthesized.

Octacalcium phosphate (OCP; Ca₈(HPO₄)₂(PO₄)₄·5H₂O) is a precursor of hydroxyapatite (HA; Ca₁₀(PO₄)₆(OH)₂). OCP is allowed to convert into HA (Ca-deficient HA) through a hydrolysis reaction in vivo and in vitro, because OCP and HA are metastable and stable phase under the physiological condition, respectively. Dissolution-reprecipitation reaction and ion diffusion-crystallization in hydrated layer are considered the mechanisms of the hydrolysis reaction. We have reported that chemical environment regulated by the hydrolysis of OCP stimulates osteoblastic and osteoclastic differentiation resulting in showing higher osteoconductivity and biodegradability of this material in various animal bone defect models. Based on these results, the possibility applying OCP as a bone substitute has been examined. Adsorption of serum proteins also controls the activities of the cells on the surface of biomaterials. Previous in vivo and in vitro studies indicate that accumulation of serum proteins onto OCP surface is involved in the bone formation by osteoblasts. However, it is still unclear about how surrounding chemical environment regulated by the OCP affects the behavior of serum protein adsorption onto OCP crystals. In this review article, the bioactivities of OCP related with its physiochemical properties including the protein adsorption will be explained.

Biomineralization is biosynthetic process to form the biominerals such as bones, teeth, and seashells, that has been focused because it enables the fabrication of accurately controlled inorganic crystal and addition of functionality based on the hybrid structure between organic and inorganic matters. In the previous studies, mechanisms of nucleation and crystal growth of inorganic matter have discussed from investigation utilizing many kinds of organic template (protein, peptide, and synthetic macromolecule). Moreover, development of organic/inorganic fusion materials inspired by biomineralization has been demonstrated potentiality as biomaterials for medical application. In this review, we discuss the effects of two- and three-dimensional ordered templates utilizing self-assembly of biomacromolecules such as peptide and nucleopeptide on the nucleation and growth mechanism of inorganic crystals formed by mineralization.

Tuning the morphology and the structure is one of effective method for improving physical and chemical properties of materials. This study introduces sensing properties dependency on morphology and structure of SnO₂. Since a morphology-controlled SnO₂ nanosheet in an aqueous solution possessed large surface of (101) crystal facet, the SnO₂ nanosheet exhibited superior response and recovery times in addition to a high alkene gas selectivity as compared to a SnO₂ nanoparticle, which has large surface of the most stable (110) crystal facet. Furthermore, a structure-controlled bridge-type of SnO₂ nanosheet thin film exhibited an improved gas sensor signal response for the large size of gas molecules. Thus, the improvement of the sensing properties of SnO₂ was realized with tuning of morphology and structure through the precise control of crystal growth in the aqueous solution.

An inorganic-organic composite consisting of biorebsorbable β-tricalcium phosphate (β-TCP) and a biodegradable polymer is one of the most important materials for artificial bone with good shapability. In the present work, in order to activate bone-forming cells immediately after being implanted in a living body, a function for releasing therapeutic ions was incorporated to the composite. A small amount (8 vol%) of 46.1SiO₂·24.4Na₂O/MgO·26.9CaO·2.6P₂O₅ (mol%) glass particles was embedded successfully in the composite. When the glass particles containing Na₂O were included in the composite, the molecular weight of the polymer as the matrix phase was severely reduced and its hydrolysis in Tris-HCl buffer solution was drastically accelerated. On the other hand, when the glass particles containing MgO were included, therapeutic ions such as Ca²⁺, Mg²⁺, and silicate ions were continuously released with almost no change in the pH of the buffer solution. The release amount of silicate ions was well controlled, to avoid excessive dissolution, compared to those of Ca²⁺ and Mg²⁺ ions. The glass is one of the great promising candidates as a source in the composite for releasing therapeutic ions that enhance bone formation.