Materials Science Forum Vols. 475-479

Abstract: A new species of single-cell magnetotactic bacteria, the NMV-1 bacteria, has been found by us. Each NMV-1 bacterium synthesizes itself a chain of magnetic nanoparticles inside its body. When an external magnetic field is applied, long bacteria chains come into being in the direction of the field in the water. More than 30 µm long chains of live bacteria have been observed. Length of bacteria chains is field dependant: the higher the magnetic field is, the longer the bacteria chains are. The bacteria chains orientation is controllable and the chains can be stably trapped. The mechanism of the assembly of long bacteria chains is also discussed. The results show that, while an external magnetic field is applied, the NMV-1 bacteria have strong enough interactions between each other to assemble long bacteria chains. After positioning the bacteria chain, cellular membranes of the bacteria were removed by cell lysis, leaving long chains of magnetic nanoparticles on a substrate. These magnetic nanochains can be potentially used as building blocks for magnetic nanostructures.

Abstract: Cell adhesion to biomaterials and cell proliferation are affected, among others, by the chemical composition and surface microtopography of the biomaterial. These are, in turn, influenced by sterilisation processes. The aim of this study was to evaluate the sensitivity of osteoblasts and fibroblasts to TiN surfaces deprived of an oxide film or with an enhanced oxide film due to sterilisation in plasma or in an autoclave, respectively. Type TiN+T2N+aTi(N) nitrided surface layers were produced under glow discharge conditions and sterilized in plasma Sterrad 100 and in a steam autoclave. The results provide evidence that nitrided surface layers improved wearand corrosion resistance of the titanium alloy and that these features were not influenced by sterilisation procedures that resulted in various oxide films. In vitro study of human fibroblast and osteoblast-like cells cultured on TiN surfaces modified by sterilisation processes showed that cells respond to the presence of an enhanced oxide film by aggregating, exhibiting lower viability and increased apoptosis, while to a surface deprived of oxides, by regular spreading and high viability. It can be concluded that differences in surface composition and topography of the nitrided surface layers due to various types of sterilisation elicit specific cell responses, and plasma sterilisation seems to be optimal for bone implants with this surface layer.

Abstract: Synoviocyte is one of the cells in direct contact with the wear particles and the role of synoviocytes in the prosthesis loosening remains to be further understood. The purpose of the present study is to investigate whether particulate biomaterials cause synoviocyte dead or simply activate these cells. The activation of synoviocyte in response to particulate biomaterial exposure will be indicated with its phagocytotic ability. As to the effects of particulate biomaterials to apoptosis will be tested on rabbit synoviocytes, HIG-82 cells. The results demonstrate that the addition of cobalt particles would lead the HIG-82 cells to apoptosis and apoptosis accompanying caspase3 cleavage, which means that apoptosis of the HIG-82 cells resulted from the addition of cobalt particles might went through caspase-dependent pathway. On the other hand, exposing to nonmetal particles such as TiO2 and SiO2, particles did not provoke apoptosis of the HIG-82 cells. TiO2 particles activated the cells and were phagocytosed by the HIG-82 synoviocytes, no significant biological effects were found while the HIG-82 cells exposed to SiO2 particles.

Abstract: The hydroxyapatite (HA) particle with different morphologies were prepared by adding a certain additive into Ca(H2PO4)2·H2O and controlling the bathing and sintering temperature, and the pure needle-like HA sol were obtained when the bathing temperature was 70°C. The experimental results show that the degree of crystallization of HA increase and the particles tend to accumulate with increasing of the drying and sintering temperatures. The particles of HA were spheroid, which diameters were of less than 100nm when they were sintered at the temperature of 700°C. The effect of nano-hydroxyapatite on remineralization of early enamel caries were studied too. The hardness of dismineralized enamel was increased when dismineralized enamel was remineralized by nano-hydroxyapatite. The SEM analysis shows that the interspace of enamel surface were decreased and the many mineral salts were sedimentated, which indicated that the nano-hydroxyapatie could promote remineralization for the dismineralized enamel.

Abstract: Ti/bioglass composite coatings on titanium alloy were prepared by a subsonic thermal spraying technology. Mixtures of titanium and bioglass powders with different proportions were used as feedstock. The effect of soaking of bioglass on the bond strength of between coatings and substrate was discussed. The bond strength and residual stress were investigated. The morphology was observed using scanning electron microscopy (SEM). The results showed that TiO2, CaTi4(PO4)6, CaTiO3, NaTi2(PO4)3 formed during thermal spraying process and the residual stress in the coatings was in compressive state. After the coatings were heat-treated, soaking of bioglass made some particles achieve metallurgical bond. Furthermore, new bioglass was formed and the compressive stress was increased. The phenomenon of bioglass healing up the cracks in the heat-treated coatings was observed through SEM, which reduced the porosity of the interface layer resulting in the significant increase of the bond strength.

Abstract: Fundamental researches on complex hydrides are recently of great importance to develop practical hydrogen storage materials with higher gravimetric hydrogen densities than those of conventional materials. First, in this paper, we clarify the correlation between B-H atomistic vibrations in [BH4]－-anion and melting temperatures of MBH4 (M = Li, Na, and K) as indexes of hydrogen desorption temperatures. This investigation implies that partial cation substitutions using smaller sized- and/or higher valenced-cations with higher electronegativities might provide higher energy modes of Raman spectra, and then, lower hydrogen desorption temperatures. Next, as an example, LiNH2 and its partial cation substitution materials are examined. At the start of the reaction, the hydrogen desorption temperature for LiNH2 with partial cation substitution drastically decreased, with the increase in Mg concentration, to around 370K for the sample with x = 30.

Abstract: Metal-complex hydrides Li3AlH6 and V-doped Li3AlH6 nanoparticles were synthesized by solid reactions of LiH and LiAlH4 in the absence and in the presence of VCl3, respectively. X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Brunauer- Emmett-Teller sorption, thermogravimetry and differential thermal analysis have been used to investigate the phase composition, microstructure and surface properties. Not only the nanocrystalline Li3AlH6, but also the coexisting catalyst with “valence-transfer” state can influence the dehydrogenation kinetics. The extension of the catalytic mechanism is attractive for reversible hydrogen storage of the alanate system.

Abstract: Some minerals were considered to store hydrogen on the basis of their porous crystal structure. Besides of crystal graphite and zeolite, some natural clay minerals such as palygorskite-sepiolite minerals with nano-scale channels and polar surface can also store hydrogen. The hydrogen storage mechanism of porous minerals was discussed. The experimental results showed a potential application of palygorskite-sepiolite minerals as the media of hydrogen storage.

Abstract: Mg, Ni and Cu nanoparticles were prepared by hydrogen plasma-metal reaction method. Nanostructured Mg2Ni and Mg2Ni0.75Cu0.25 compound were successfully obtained using the metal nanoparticles. The synthesis mechanism, the structure and lattice parameter difference, and the hydrogen absorption behaviors of the two compounds were discussed.

Abstract: The effects of Ca addition on the microstructure and mechanical properties of AZ91 magnesium alloy have been investigated. The main changes in microstructure caused by Ca addition were the grain refinement in the as-cast alloys and the formation of new Al2Ca phase along the grain boundaries. The tensile strength and elongation of the AZ91 magnesium alloy were improved by small addition of Ca due to grain refinement and replacement of Mg17Al12 phase with new Al2Ca compound. However, when above 0.7wt.% Ca was added, mechanical properties of AZ91 magnesium alloy were decreased.