Hisao Kinoshita

Heterogeneous nucleation of hydroxyapatite on protein: structural effect of silk sericin

Acidic proteins play an important role during mineral formation in biological systems, but the mechanism of mineral formation is far from understood. In this paper, we report on the relationship between the structure of a protein and hydroxyapatite deposition under biomimetic conditions. Sericin, a type of silk protein, was adopted as a suitable protein for studying structural effect on hydroxyapatite deposition, since it forms a hydroxyapatite layer on its surface in a metastable calcium phosphate solution, and its structure has been reported. Sericin effectively induced hydroxyapatite nucleation when it has high molecular weight and a β sheet structure. This indicates that the specific structure of a protein can effectively induce heterogeneous nucleation of hydroxyapatite in a biomimetic solution, i.e. a metastable calcium phosphate solution. This finding is useful in understanding biomineralization, as well as for the design of organic polymers that can effectively induce hydroxyapatite nucleation.

Mechanical properties and damage behavior of non-magnetic high manganese austenitic steels

Abstract Fe–Cr–Mn steels have been considered as materials of structural components for fusion reactor because of their low induced-radio-activity compared with SUS316 stainless steels. It has been expected to develop a non-magnetic steel with a high stability of the austenitic phase and a strong resistance to irradiation environments. For these objectives, a series of the Fe–Cr–Mn steels have been examined by tensile tests and simulation irradiation by electrons. The main alloying compositions of the steels developed are; C:0.02–0.2 wt%, Mn: 15 wt%, Cr: 15–16 wt%, N: 0.2 wt%. These steels were heat-treated at 1323 K for 1 h. The structure of the steels after the heat-treatment was austenite single phase. The yield stress of the steels was 350–450 MPa and the elongation were 55–60%. When the steels of high C and N was electron-irradiated at below 673 K, no voids were nucleated and only small dislocation loops were formed with high density. The austenite phase was also stable during irradiation below 673 K. Thus, newly developed high manganese steels have excellent mechanical proprieties and high irradiation resistance at relatively low temperature.

Effect of Ni and Cr concentration on grain boundary segregation in FeCrNi alloys

Abstract FeCrNi austenitic alloys were irradiated to investigate the dependence of radiation induced grain boundary segregation on the initial composition of alloying elements. Electron irradiations were performed at grain boundary by using HVEM with 00 keV accelerating voltage. The irradiation temperature was 723 K and the dose was up to 7 dpa. Measurements of grain boundary composition were made using 200 keV TEM with EDS analysis device. Typical grain boundary segregation, such as Ni enrichment and Cr depletion, was recognized in all specimens. The amounts of segregation varied with the contents of alloying elements. For constant bulk Cr (15 wt% Cr) concentration and for increasing bulk Ni concentration, from 15 to 40 wt%, the highest amount of Ni segregation was observed in the range of 25 to 30 wt% Ni specimens, and Cr concentration at grain boundaries was of almost the same level. For constant bulk Ni (20 wt% NO content and for increasing bulk Cr content, from 15 to 35 wt%, the amount of Cr segregation at grain boundaries increased with greater Cr bulk content and the amount of Ni segregation was almost the same over the range of 15 to 35 wt% Cr. These tendencies of segregation which depend on the alloying composition were consistent with the computer simulation results of the grain boundary segregation.

Biodegradation of Porous Alpha-Tricalcium Phosphate Coated with Silk Sericin

Porous a-tricalcium phosphate (a-TCP) ceramics are attractive as a novel bioresorbable material for bone repair, since they can be easily fabricated through conventional sintering of b-TCP at high temperature. However, the solubility of a-TCP is too high to keep its body until the bone defect is repaired completely. Coating of the a-TCP porous body with organic polymer is a way to reduce the degradation rate. In the present study, biodegradation of a-TCP porous body coated with silk sericin was evaluated in vivo. Bone repair at the defect made in rabbit tibia was nearly completed after 4 weeks. Higher density of cortical bone was estimated for a-TCP coated with sericin than for mere a-TCP. The a-TCP porous body coated with sericin is expected as a material that show less degradation than mere a-TCP, and may result in suitable bone repair.

Atomistic dynamical observation of grain boundary structural changes under electron irradiation

We investigated the structural changes in two grain boundaries with different grain boundary nature during electron irradiation using an atomic-resolution high-voltage electron microscope. It was found that the morphology of one type of grain boundary changed due to boundary movement during the irradiation, whereas another type of grain boundary did not show such structural change. On the other hand, solute segregation was induced in the vicinity of both grain boundaries. It was found that differences between the two grain boundaries, particularly the difference between grain boundary interfacial planes prior to irradiation, caused the different grain boundary migration behavior.

Apatite Deposition on Silk Sericin in a Solution Mimicking Extracellular Fluid: Effects of Fabrication Process of Sericin Film

An apatite-organic polymer hybrid is expected as a novel materia l for medical application, because it shows high biological affinity and high flexibility. In order to fabricate this type of hybrid, a biomimetic process was proposed, in which a bone-like apatite layer c n be coated onto organic substrates by using a simulated body fluid (SBF) at ambient conditions . P tential of induction of heterogeneous nucleation of apatite on substrate materials is an im portant parameter to achieve a successful coating of apatite. Recently, it was reported that se ricin, a protein existing on the surface of raw silk fiber, showed apatite-forming ability in 1.5SBF which has 1.5 times the ion concentrations of SBF. In the present study, the structural effect of sericin on its apatite-forming ability was investigated in 1.5SBF. Apatite was deposited on sericin with high molecular weight and β-sheet structure in 1.5SBF after 7 days. Introduction Hydroxyapatite is a kind of calcium phosphate that has high biological affinity to bone. Sintered hydroxyapatite is now widely used as bone substitute. However, the applic ation of hydroxyapatite is restricted because it does not have enough mechanical properties to bea r a large load. Therefore, a hydroxyapatite-organic polymer hybrid is expected as a novel materi al fo medical application, because it shows high biological affinity and high flexibility. Hydr oxyapatite coating on organic polymers is an attractive way to develop such hybrid materials. Kokubo and his colleagues previously proposed a biomimetic process to deposit a hydroxyapatite layer on vari ous substrates, such as organic polymers. In this process, a bone-like apatite layer can be coat d onto organic polymer substrates by either using a simulated body fluid (SBF) with ion concentrations ne arly equal to those of human blood plasma, or using a more concentrated fluid under mild conditions [1]. Potential of induction of heterogeneous nucleation of apatite on the substrate materials is an impor tant parameter to achieve a successful coating of apatite layer. Apatite crys tals can spontaneously grow in the simulated body fluid (SBF), since SBF is supersaturated with respect t o hydroxyapatite. We recently reported that sericin, a protein existing on the surface of raw si lk fiber, is able to induce apatite deposition in 1.5SBF, which has 1.5 times the ion concentrations of SBF [2]. This me an that sericin has a suitable composition and/or structure for inducing apatite nucleat ion in body environment. In this study, we have investigated the effective structure of sericin needed t o posit apatite crystals in 1.5SBF. Some sericin films were prepared from a solution containing s ericin extracted under various Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 403-406 doi:10.4028/www.scientific.net/KEM.254-256.403

Formation of Al-Based Intermetallic Compound under Ion Implantation at Lower Temperature

The formation process of intermetallic compound under Ni+ion implantation into pure Al was studied at lower temperature below room temperature. Ion implantation was carried out using 250KeV ion accelerator. Cascade damage was introduced Ni+ions implantation at 223K without new phase nucleation. However, when Ni+ions were implanted at room temperature, the grown larger plate-like phases were observed during implantation up to 1x1017 Ni+/cm2. Ni concentration in Al matrix and newly formed phase were 0.3-0.5 and 8.5-13.3at%,respectively. It was identified that the formed phases were close to the ordered orthorhombic structure of Al3Ni type. It was also confirmed from observation with high resolution HVEM that these phases grew with continuous ion implantation. Thus it was clarified that cascades act as preferential nucleation site for intermetallic compound, and the phases nucleated at cascades coalesce in the growth process of each phase during continuous implantation through ion irradiation enhanced diffusion.

Apatite Formation on Silk Fiber in a Solution Mimicking Body Fluid

Apatite-organic polymer hybrid is expected as a novel mater ial for bone repair. A biomimetic process has focused attention on fabricating such hybrids, w here bone-like apatite is deposited on an organic polymer surface in solutions mimicking physiolog ica conditions. In this process, organic polymer substrates can be coated with bone-like apati te layer by soaking in a simulated body fluid (SBF) with ion concentrations nearly equal to t hose of human extracellular fluid or more concentrated fluids at ambient conditions. To achieve a suc cessful fabrication on such a hybrid, organic substrates should have effective site for nuclea tion of bone-like apatite on their surfaces. In this study, we examined apatite-forming ability of silk fiber in 1.5SBF which has ion concentrations 1.5 times those of SBF. Apatite formation was observed on raw silk fiber and accelerated by a prior treatment with CaCl 2 solution. It is concluded that sericin has a potential on induction of apatite nucleation in the solutions mimicking body environment. Introduction Natural bone is an organic-inorganic hybrid containing about 70 mass% of hydroxyapatite and 30 mass% of collagen. This hybrid structure provides specific mechani cal properties, such as high fracture toughness and high flexibility, and allows bones to bear under stress. Therefore, fabrication of apatite-organic polymer hybrid is one of attractive methods to design a novel bone substitute, since such a hybrid material has both bone-bonding ability, i.e. bioac tivity, and mechanical properties analogous to natural bone. In order to fabricate this type of hybrid, Kokubo and his colleagues proposed a biomimetic process, in which bone-like apatit e layer can be coated onto organic substrates by using a simulated body fluid (SBF) with ion c oncentrations nearly equal to those of human extracellular fluid or more concentrated fluids at ambient conditions [1]. To obtain a successful fabrication through biomimetic process, organic substrates should have effective sites for nucleation of bone-like apatite on their surfaces in the solutions. We previously found that polyamide films which are modified with carboxyl groups and calci um chloride (CaCl 2) show apatite-forming ability in 1.5SBF which has ion concentrations 1.5 ti mes those of SBF [2]. This indicates that apatite can be deposited on a certain type of poly amide after exposure to body environment, when the polyamide has carboxyl groups in its structure as w ll as calcium ion. In the present study, to investigate apatite-forming ability of natur al polyamide, that is polypeptide, we examined apatite formation on silk fiber in 1.5SBF. Enhancement of apa tite formation was also Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 31-34 doi:10.4028/www.scientific.net/KEM.240-242.31

Damage behavior in an electron/helium dual-beam irradiated Fe–Cr–Mn(W,V) alloy

Abstract Results of dual-beam irradiations with electrons and helium ions indicated that the formation of secondary defects (dislocation loops, dislocation networks, voids) was enhanced in an irradiated Fe–Cr–Mn(W,V) alloy, and in particular, voids formed preferentially on dislocation lines at elevated temperature and that the segregation of Cr, Mn to sinks was suppressed. The reason was that helium strongly interacts with vacancies, which in turn decreases the diffusivity of vacancies and increases the density of sinks in matrix.

Effect of Helium and Aging Treatment on Radiation Damage Behavior in Low Activation Fe-Cr-Mn (W, V) Alloy

The effects of helium and aging treatment on radiation damage behavior in low activation Fe-Cr-Mn ( W, V) alloy were investigated by electron and helium ion dual-beam irradiation in a high voltage electron microscope. Specimens were aged at 673 K, 823 K and 923 K for 1000, 3000 and 10000 hours. Electron and He ion dual-beam irradiations were performed at 627 K to 10 dpa. M23C6 type carbides were precipitated in the aged specimens, and the amount of the precipitates was increased with increasing aging temperature and aging time. He bubbles were formed during dual-beam irradiation in all of the specimens. The cavity swelling under dual-beam irradiations was increased with increasing the aging temperature and aging time. It was suggested that cavity swelling is closely related to the concentration of solutes such as Cr and C in the matrix, namely cavity growth rate becomes higher with decreasing of the solutes in solution.