Advanced Materials Research Vols. 26-28

Abstract: In many biomedical devices such as catheters and diagnostic sensors, blood compatibility is required. The best way to control this property is to prevent or drastically reduce the adsorption of proteins. Poly(ethylene glycol) terminated amine at both terminals, NH2-PEG-NH2, is immobilized on a commercially pure titanium, a 316L austenitic stainless steel, and a cobalt-chromium-molybdenum alloy with immersion or electrodeposition. Chemical bonding states at the interface and orientation of PEG molecules were characterized using X-ray photoelectron spectroscopy, glow discharge optical emission spectroscopy, and Fourie-transformed infrared spectrometer with a reflection absorption spectrometer. As a result, NH2-PEG-NH2 was immobilized onto metal surface as a U-shape mainly with stable NHO bonding in electrodeposition. In the case of electrodepostion, the concentration of active surface hydroxyl groups on surface oxide film played an important role in the immobilization.

Abstract: The microstructure and mechanical properties of compacts produced from hot-pressing the Co-29Cr-6Mo alloy powder, fabricated by gas atomization, were investigated in this study. The average diameter of the alloy powder is 41 μm. Electron probe micro analysis revealed that the concentration scattering of chromium and molybdenum is relatively small between the powders. The compact hot-pressed at 1273 K in Ar with an applied pressure of 80 MPa possesses the relative density of 97% and the fine grain (2.7 μm). The ultimate tensile strength of the compact is 1240 MPa, which is comparable to that of the forged Co-29Cr-6Mo alloy.

Abstract: Phase stability of cation co-doped zirconia ceramics is examined. As the result, in contrast to the result in small amount of single cation doped zirconia, phase stability of co-doped zirconia ceramics can not be simply explained from ionic radius and valency of dopant or from the change in axis ratio. We focus on oxygen vacancy concentration and binding energy between oxygen vacancy and doped cation. By estimating phase stability from these factors, it is found that concentration of oxygen vacancy and the binding energy between the dopant and the oxygen vacancy are important factors for understanding the phase stability of zirconia ceramics.

Abstract: Effect of the sigma (σ) phase in Co-29Cr-6Mo alloy on corrosion and mechanical behavior has been investigated. The area fraction of the σ phase varies depending on the aging time at 1023 K. The area fraction of the sigma phase increases with increasing aging time and reaches 0.6 % after aging at 1023 K for 21.6 ks. Inductively coupled plasma atomic emission spectrometer (ICP-AES) analysis revealed the quantity of released Co ion shows almost the same values regardless of different area fraction of the σ phase. In addition, plastic elongation and 0.2% proof strength exhibit almost the same values, although the alloys have different area fraction of the σ phase. These results suggest that a small amount of the σ phase (<0.6%) hardly affect the corrosion and mechanical properties in the Co-29Cr-6Mo alloy.

Abstract: The effect of second phase particles on tetragonal to monoclinic (t-m) phase transformation of zirconia is examined, which causes the degradation of zirconia in vivo. Silica is selected as the second phase particles and dispersed 0.1 to 10mol% into 3mol% yttria stabilized tetragonal zirconia polycrystal (3Y-TZP). As the result, phase transformation is promoted in all the samples examined in comparison with 3Y-TZP. Non-dispersed specimen exhibits better phase stability than that in silica doped one. Since the thermal expansion coefficient is smaller in order of silica and zirconia, the residual stresses induced during cooling from the sintering temperature must be the dominant factor to determine the phase stability in these materials.

Abstract: We started investigation of new Ti-based bulk metallic glass (BMG) alloys with higher glass forming ability (GFA) for dental implants for medical market. These Ti-based BMG alloys do not contain Ni, Al and Be elements which are well known to be harmful for human body. In particular, cylindrical rod specimens of newly designed Ti-based BMG alloys with produced by copper mold casting exhibit compressive strength of above 1800 MPa. Ti-based BMG alloys also have high corrosion resistance that is passivated at the lower passive current densities of approximately 10-2Am-2 in 1 mass% lactic acid, 10-2~10-3Am-2 in PBS (-) at 310K which are lower than those of pure Titanium and Ti-6Al-4V alloy. These BMG alloys have high potentials to be applied as biomaterials in various forms, such as melt spun ribbons and cylindrical rods.

Abstract: Microstructure and texture of Ti-Nb-Si based alloys, prepared by water quenching from β-phase field, cold rolling and recrystallization heat treatment followed by water quenching, were investigated in terms of optical microstructure and analysis of X-ray pole figure result. Optical microstructure observation and X-ray diffraction analysis revealed that the microstructure of as-quenched sample appeared to mixture appearance consisting of mostly bcc-structured β phase and small amount of orthorhombic-structured α″ phase. After cold rolling elongated structure parallel to the rolling direction was observed, and equiaxed structure with the average grain size of about 20~30μm was developed for the sample after recrystallization heat treatment. In as-cold rolled sample we have found well-developed α-fiber texture components which are frequently observed in bcc-structured metals and alloys. In recrystallized sample, rotated cube texture component was weakly detected. The variation of elastic modulus values was interpreted in terms of changes in texture components depending on thermomechanical processing.

Abstract: Most structural optimization methods are based on mathematical algorithms that require substantial gradient information. The selection of the starting values is also important to ensure that the algorithm converges to the global optimum. This paper describes a new structural configuration optimization method based on the harmony search (HS) meta-heuristic algorithm. The HS algorithm does not require initial values and uses a random search instead of a gradient search, so derivative information is unnecessary. A benchmark truss example is presented to demonstrate the effectiveness and robustness of the proposed approach compared to other optimization methods. Results reveal that the proposed approach is capable of solving configuration optimization problems, and may yield better solutions than those obtained using earlier methods.

Abstract: In this work, triethyl phosphate (TEP) was used to bioactivating titanium. Titanium plates grafted with TEP were immersed in a two times concentrated simulated body fluid (2SBF) to investigate deposition of hydoxyapatite (HA) on the surface. A phosphate buffer solution (PBS) with bovine serum albumin (BSA) was used to evaluate adsorption of protein on the grafted titanium surface. The morphology, component and structure of samples were examined by scanning electronic microscopy, attenuated total reflection Fourier transform infrared spectroscopy and X-ray diffraction respectively. The concentration change of BSA in adsorption test was examined with the ultraviolet-visible absorption spectra (UV). The analyses showed that TEP grafted onto the titanium surface. In 2SBF, calcium and phosphate ions deposited spontaneously onto the grafted titanium surface and formed a HA coating with a network-like microporous structure after being immersed for 3 days. The coating consisted of HA particles with 180-265nm in thickness and 72-85nm in width. The diameter of the micropores was about 200nm. The HA coating appeared better uniformity than that on the modified titanium using phosphoric acid. BSA rapidly adsorbed onto the grafted titanium surface at first half an hour and then the adsorption quantity almost kept constant. These results indicate that TEP grafting is an effective approach to modify bioactivity of titanium.

Abstract: A silicon-containing apatite layer was prepared on a metallic titanium substrate coated with a silica layer. The silica layer on a titanium substrate was derived from water glass through heat-treatment at 300 °C for 2 hr and subsequent acid-treatment using 0.1 N-HCl at 50 °C for 2 hr. The silica layer was homogeneously coated with nano-sized vaterite powders (~ 0.5 μm in diameter). The vaterite coating was achieved by utilizing the interaction of surface potentials between the positively charged vaterite and the negatively charged silica layer. After soaking the sample in simulated body fluid at 37 °C for 3 days, hydroxyapatite (HA) formed on the surface of the silica-coated titanium. The HA layer was found to include a trace amount of releasable silicon, which may enhance the osteoblast proliferation.