Yoshiaki Morisada

Synthesis of positively charged calcium hydroxyapatite nano-crystals and their adsorption behavior of proteins.

Positively charged Hap nano-crystals were prepared by using beta-alanine and clarified the adsorption affinity of these surface amide functionalized Hap nano-crystals to proteins. Colloidal surface amide functionalized Hap nano-crystals were prepared by wet method in the presence of various amounts of beta-alanine by changing molar ratio of beta-alanine/Ca (beta/Ca ratio) in the solution. The rod-like nano-crystals were lengthened with addition of beta-alanine though their width did not vary; carboxyl groups of beta-alanine are strongly coordinated to Ca2+ ions exposed on ac and/or bc faces to inhibit particle growth to a- and/or b-axis directions and enhance the particle growth along to the c-axis. No difference can be recognized on the crystal structure among the synthesized Hap nano-crystals by XRD measurements. However, the large difference was recognized by TG-DTA and FTIR measurements. Those measurements revealed that beta-alanine is incorporated on the Hap nano-crystal surface up to the beta/Ca ratio of 1.0, though they are absent in the nano-crystals synthesized at beta/Ca ratio > or = 2.0. The zeta potential (zp) of beta-alanine-Hap nano-crystals prepared at beta/Ca = 0.4 and 1.0 of those incorporating beta-alanine exhibited positive charge at pH < or = 5.9. The saturated amounts of adsorbed BSA for the positively charged beta-alanine-Hap nano-crystals were increased 2.3-2.4-fold by their electrostatic attraction force between positively charged beta-alanine-Hap nano-crystals and negatively charged BSA molecules. We were able to control the adsorption affinity of Hap nano-crystal by changing their surface charge.

Effects of Modification of Calcium Hydroxyapatites by Trivalent Metal Ions on the Protein Adsorption Behavior

The effects of modification of calcium hydroxyapatites (Hap; Ca10(PO4)6(OH)2) by trivalent metal ions (Al(III), La(III), and Fe(III)) on protein adsorption behavior were examined using bovine serum albumin (BSA; isoelectric point (iep) = 4.7 and molecular mass (M(s)) = 67,200 Da). The Al(III)-, La(III)-, and Fe(III)-substituted Hap particles were prepared by the coprecipitation method with different atomic ratios, metal/(Ca + metal), abbreviated as X(metal). The particles precipitated at X(metal) = 0 (original-Hap) were rod-like and 10 x 36 nm2 in size. The short, rod-like original-Hap particles were elongated upon adding metal ions up to X(metal) = 0.10, and the extent of the particle growth was in the order of La(III) < Al(III) << Fe(III). The crystallinity of the materials was slightly lowered by increasing X(metal) for all systems. The adsorption isotherms of BSA onto the Al(III)-, La(III)-, and Fe(III)-substituted Hap particles showed the Langmuirian type. The saturated amounts of adsorbed BSA (n(s)(BSA)) values were strongly dependent on X(metal) in each system. The n(s)(BSA) values for the Fe(III)-substituted Hap system were increased with an increase in X(Fe) (X(metal) value of Hap particles substituted with Fe(III)); the n(s)(BSA) value obtained at X(Fe) = 0.10 was 2.7-fold more than that for the original-Hap particle, though those for the La(III) system were decreased to ca. 1/5. On the other hand, the n(s)(BSA) values for the Al(III) system were decreased with substitution of small amounts of Al(III), showing a minimum point at X(Al) = 0.01, but they were increased again at X(Al) over 0.03. Since the concentrations of hetero metal ions dissolved from the particles exhibited extremely low values, the possibility of binder effects of trivalent cations dissolved from the particle surface for adsorbing BSA to trivalent-ion-substituted Hap particles was excluded. The increase of n(s)(BSA) by an increase in X(Fe) was explained by elongation of mean particle length along with the production of surface hydroxo ions, such as Fe(OH)2+ or Fe(OH)2+, to induce the hydrogen bond between the Fe(III)-substituted Hap surface and BSA molecules, though the number of original C sites established by Ca(II) atoms was reduced. In the case of La(III)-substituted Hap particles, the number of original C sites established by Ca(II) atoms was reduced by La(III) substitution but the mean particle length remained almost constant. Furthermore, surface hydroxo La(III) groups were absent. Therefore, the reduction of n(s)(BSA) was explained by both the unaltered mean particle length and their low surface hydrophilicity. The change of n(s)(BSA) values by X(Al) resembled that of the mean particle length. These results implied that both the mean particle length and surface hydrophilicity of Al(III)-, La(III)-, and Fe(III)-substituted Hap particles are determining factors of the adsorption amounts of BSA.

Clarification of material flow and defect formation during friction stir welding

Abstract The defect formation mechanism during friction stir welding (FSW) was investigated by the three-dimensional visualisation of material flow around a tool. The three-dimensional flow patterns under various FSW conditions were obtained using two pairs of X-ray transmission real time imaging systems. The flow patterns revealed that the tilt of horizontal material flow around the tool and the stagnation of material flow on the advancing side (AS) of the tool were significantly correlated to the formation of defects. The material flow velocity during FSW was directly calculated based on the results of three-dimensional visualisation. The material flow velocity on the AS obviously decreased under the condition where defects were formed.

Effects of Heat Treatment of Calcium Hydroxyapatite Particles on the Protein Adsorption Behavior

The effects of heat treatment of calcium hydroxyapatite (Hap) on the protein adsorption behavior were examined using typical proteins of bovine serum albumin (BSA: isoelectric point (iep) = 4.7, molecular mass (Ms) = 67,200 Da, acidic protein), myoglobin (MGB: iep = 7.0, Ms = 17,800 Da, neutral protein), and lysozyme (LSZ: iep = 11.1, Ms = 14,600 Da, basic protein). The TEM, XRD, and gas adsorption measurements ascertained that all of the Hap particles examined were highly crystallized and nonporous. The Hap single phase was continued up to the heat treatment temperature of 600 degrees C. However, after treatment above 800 degrees C in air, the beta-Ca3(PO4)2 (beta-TCP) phase slightly appeared. TG and ICP-AES measurements suggested that all of the Hap particles are Ca2+-deficient. Also, it was indicated from FTIR and XPS measurements that a partially dehydrated oxyhydroxyapatite (pd-OHap) was formed after treatment at high temperature. The saturated amounts of adsorbed BSA (nsBSA) did not vary on the Hap particles after heat treatment at 200 and 400 degrees C. However, nsBSA values were increased by raising the heat treatment temperature above 600 degrees C. The adsorption coverage of BSA was increased up to ca. 1.4. This adsorption coverage of BSA (thetaBSA) over unity suggests that the BSA molecules densely adsorbed and a part of BSA molecules adsorbed as end-on type on the Hap particle surface or BSA molecules became contracted. Similar adsorption behavior was observed on the LSZ system, but the adsorption coverage of LSZ (thetaLSZ) values are much less than thetaBSA. On the other hand, no effect of the heat treatment of Hap particles was observed on the adsorption of MGB. The increases of nsBSA and nsLSZ were explained by the increase of calcium and phosphate ions in the solutions dissolved from beta-TCP formed after heat treatment of Hap, especially treated at high temperature. The dissolved Ca2+ and PO(4)3 - ions may act as binders between proteins and Hap surfaces; the adsorption of Ca2+ ions on the Hap surface offers an adsorption site for BSA owing to its positive charge. In the case of adsorption of positively charged LSZ molecules, PO43- ions act as a binder in an opposite way. Since the MGB molecules are neutral, no binding effect of either ion was observed.

Three-Dimensional Visualization of Material Flow During Friction Stir Welding of Steel and Aluminum

Material flow is a key phenomenon to obtain sound joints by friction stir welding (FSW), and it is highly dependent of the welded material. It is well known that the optimal FSW condition depends on the welded material. However, the material flow during FSW has not been totally clarified in spite of many researches. Especially, the material flow of steel during FSW is still unclear. It seems difficult to understand the material flow by the traditional method such as the tracer method or observation of the microstructure in the stir zone. Therefore, in this study, the material flow of steel was three dimensionally visualized by x-ray radiography using two pairs of x-ray transmission real-time imaging systems, and was then compared with the material flow of aluminum. The result revealed the effect of the welded material on the material flow during FSW.

Effect of gap on FSW joint formation and development of friction powder processing

Abstract A gap between two materials is a critical problem for friction stir welding (FSW). It is generated by a mismatch at the interface between two materials and causes defects and porosities due to the lack of material in the joint. In this study, friction powder processing (FPP) is proposed to solve this problem. Metal powder is first added to the gap between and then the FSW is performed. The effect of the gap width on the joint properties was first investigated, and the FPP feasibility was then assessed by adding pure Al powder to the gap between A1050-H24 plates. In addition, the mechanical properties and microstructures were investigated when adding a dissimilar powder, such as Cu powder, to the gap between Al plates. When using pure Al powder, the formation of defects is prevented. When using pure Cu powder, Al2Cu precipitates were formed in the stir zone, and consequently, the hardness significantly increased.

Improvement of toughness and strength of thick structural steel weld by friction stir welding conditions

Abstract Structural steel plates with tensile strength of 490 MPa and 6 mm in thickness were successfully joined with microstructural control by single sided one-pass butt friction stir welding (FSW). The microstructure in the stir zone (SZ) could be changed to bainite, bainite with proeutectoid ferrite, and fine equiaxed ferrite based on the welding temperature. The bainite increased the hardness and tensile strength, and the ferrite gave the joint similar mechanical properties similar to the base metal. The welding temperature was controlled between below Ac1 and above Ac3 by the rotating rate of the tool and tool materials; i.e. Ir–Re alloy and sintered c-BN with W–Re.

Design of Joint Properties by Friction Powder Processing

Friction powder processing (FPP) has been developed based on the principle of friction stir welding (FSW) or friction stir processing (FSP). The FPP is a method to design the properties of the processed area by performing FSP after powder with a controlled composition is placed in the gap between two plates. The FPP experiments were performed using a tool with the shoulder diameter of 15mm and the probe diameter of 6mm. The tool traveled at 100mm/min and rotated at 1500rpm. A1050 aluminum was used as the plate. Pure Al powder (89μm average grain diameter) and pure Cu powder (106μm average grain diameter) were used as the additives. When using pure Al powder, the pure Al powder left in the base metal after the first pass is sufficiently stirred by performing the second pass and then a good joint without defects is obtained. However, more than three passes are not effective for improving the strength of the welded area. When using pure Cu powder, nanoscale Al2Cu precipitates are uniformly formed in the stir zone, and accordingly, the hardness is significantly increased.

Effect of friction stir processing on microstructure of laser clad cobalt-based alloy

Abstract (The microstructural refinement of cobalt-based alloy (Stellite No. 6) by laser cladding and friction stir processing (FSP) was studied. A nanometer-sized microstructure consisting of fine carbide (particle size: 100–200 nm) and a grain (grain size: 150–250 nm) was successfully fabricated by the FSP on the laser clad cobalt-based alloy. The nanostructured cobalt-based alloy (Stellite No. 6) had an extremely high hardness of about 750 HV.

Three-dimensional visualization of material flow during friction stir welding for steel and aluminum by two pairs of X-ray transmission systems

Material flow is a key phenomenon to obtain sound joints by FSW, and it is affected by the welded material. However, the material flow during FSW has not been totally clarified. It seems to be difficult to understand the material flow by the tracer method or observation of the microstructure in the stir zone. Therefore, in this study, the material flows of steel and aluminum were three-dimensionally visualized by X-ray radiography using a tiny spherical tungsten tracer. The movement of the tracer during the friction stir welding was observed by two pairs of x-ray transmission real-time imaging systems. The three-dimensional material flow is also obtained by observing locus of the tracer. The result revealed the effect of the welded material on the material flow.