Materials Science Forum Vols. 610-613

Abstract: We have developed a new surface treatment, Mgbright, which produces a luster on AZ31 magnesium alloy surfaces. The treatment consists of a chemical process and a coating process, and the primary characteristics are that of developing a luster on AZ31 magnesium alloy and imparting a high resistance to corrosion. When Mgbright was applied, the value of surface roughness, Ra, required for developing luster was 1.5 µm. As the target Ra value of press-formed articles was set to less than 1.5 µm, mass-production press-forming was tested by means of the 100,000 times square-cup drawing method, and the target was achieved. We applied the Mgbright treatment techniques and the square-cup drawing test, and produced a laptop computer chassis.

Abstract: Sulfur hexafluoride (SF6) is widely used by the magnesium industry as a component of cover gas mixtures, which reacts with the melt and forms a protective film on the melt surface. In this study the dew points of the air that acts as carrier gas for SF6 was varied from 203K to 273K, and the effect of the SF6 cover gas humidity and concentration on the efficient protection of molten AZ91D magnesium alloy was investigated in temperatures ranging from 903K to 973K. Gas chromatography (GC) combined with ion chromatography (IC) were used to identify the chemical constituents of the by-products present in the protective atmosphere, while. X-ray photoelectron spectroscopy (XPS) and Auger electron Spectroscopy (AES) were used in the characterization of the protective films formed on the melt. The results indicate that the quantity of SF6 to protect molten Mg from burning decreased with decrease in the humidity of the cover gas XPS showed that the films formed in all atmospheres with different dew points were composed of MgO, MgF2 and MgSO4. However, in cover gases with higher dew point, the amount of MgO of the film tended to increase, due to the dissociation of MgSO4 of the film into H2 and SO4-2 in the presence of moisture, which lead to the destruction of the protective film and oxidization of the melt.

Abstract: The nanocomposite of nano-hydroxyapatite/bacterial cellulose (nHA/BC) obtained by depositing in simulated body fluid (SBF), incorporating their excellent mechanical and biological properties, is expected to have potential applications in bone tissue engineering. However, the biological response evaluation of biomaterials is required to provide useful information to improve their design and application. In this article, the in vitro cytotoxicity of composites nHA/BC as well as its degradation residues was studied. Scanning electron microscopy (SEM) was used to observe the morphology of original materials and their degradation residues. The degree of degradation was evalued by measuring the concentration of reducing sugar (glucose) by ultraviolet spectrophotometer. Bone-forming osteoblasts (OB) and infinite culture cell line L929 fibroblasts were used to measure the cytotocixity of materials with MTT assay. Both kinds of cells in infusion proliferate greatly in a normal form and their relative growth rate (RGR) exceeds by 75%, which shows the cytotoxicity of materials is graded as 0~1, according to the national standard. Nevertheless, bone-forming OB cells, as a kind of target cells, are more susceptive on the cytotoxicity than infinite culture fibroblast cells L929. The results suggest the nanocomposite of nHA/BC without cytotoxicity is greatly promising as a kind of scaffold materials for bone tissue engineering and tissue functional cells are more suited to evaluate the cytotoxicity of biomedical materials.

Abstract: For an application as biomedical materials of high performance with a good biocompatibility, the Ti-O film on Si (110) wafer substrate has been synthesize by means of unbalance reactive magnetron sputtering method and modified by phosphorus ion implantation and succeeding vacuum annealing. X-ray diffraction (XRD) results indicated that such prepared Ti-O film had a rutile structure. X-ray photoelectron spectroscopy (XPS) analysis demonstrates the effect of P ion doping. The contact angle test and sheet resistance results showed that titanium oxide film and phosphorus-doped titanium oxide film became more hydrophilic and higher conductance after annealing. The morphology and roughness of the surface have been investigated using SEM. Antithrombotic property of the titanium oxide thin film was examined by platelet adhesion tests. The results showed that the undoped Ti-O films and the P implant and annealing at 900 °C Ti-O film had good blood compatibility.

Abstract: Silicon microelectrode arrays (Si MEAs) have great potential in recording of neural activity; the biocompatibility of silicon nitride has gained much attention as a part of Si MEAs. In this study, we used alternating polycations, polyethyleneimine (PEI), and polyanions, gelatin, to fabricate multilayer films built up by LbL deposition on silicon nitride wafers. Then the samples surfaces were characterized by contact angle system and atomic force microscopy (AFM). The amount of proteins adsorbed on silicon nitride and modified silicon nitride were measured by a modified Coomassie brilliant blue (CBB) protein assay. Cell culture results showed that the modified silicon nitride could increase the adhesion ability of the hippocampal neurons.

Abstract: The nano-indentation response, the film-substrate adhesion behaviors and the friction and wear properties of the DLC/SiC (diamond-like carbon/silicon carbon) double layer thin films (SiC films as interlayer) deposited on nanocrystalline titanium substrate using magnetron sputtering technique at room temperature were investigated. The results show that the DLC films exhibited a low nano-hardness (7.4 GPa) and Young's modulus (62.2 GPa) but a high hardness-to-modulus ratio (0.119). The films-substrate system displayed a good interface adhesion and a good friction/wear properties with the friction coefficient of about 0.1, the special wear rate in the magnitude order of 10−6 mm3 m−1 N−1 together with little film cracking and interface delaminating even at considerably high contact load, when sliding against Si3N4 (silicon nitride) ball using ball-on-disc wear tester under Kokubo simulation body fluid (SBF) at room temperature. The high wear-resistance is in accordance with the high ductility of the films, the good modulus match in the films-substrate system, and the high hardness-to-modulus ratio of the films. The nano-indentation response, the film-substrate adhesion behaviors and the tribological properties are in accordance and can be ascribed to the high activity of the nanocrystalline Ti substrate

Abstract: Skin wounds, burns and scars represent a major burden upon world healthcare costs. The successful creation in vitro of skin substitutes has been the focus of a concentrated research activity for the last 30 or more years, culminating in some success for its translation into the clinical setting. In this paper, a novel artificial skin of bacterial cellulose has been biosynthesized by Acetobacter xylinum and modified by chitosan. BC is thought as an optimal substrate material of artificial skin. It is thought to be an interesting material for using as a substratum of artificial skin because it could provide moist environment to a wound resulting in a better wound healing. But BC has no antimicrobial activity to reduce the probability of wound infection. To achieve antimicrobial activity of BC, it was modified by chitosan due to its antibiotic activity. The structure and components were characterized by FTIR and ESEM. The results indicated the nano-composites of BC and chitosan are promising and potential for wound dressings.

Abstract: Based on (3-methacryloxypropyl)-Polyhedral oligomeric silsesquioxane (MP-POSS) (MP), vinyl-POSS (VP), (3-glycidoxypropyl)-POSS (GP) and modified with 5, 10, 15, 20 and 25 wt-% titanium tetrabutoxide (TTB), three hybrid nanofilms (f-MPT, f-VPT and f-GPT) were prepared using hydrolytic condensation and crosslinking. The transparency of the films was measured at the ranges of ultraviolet A (UV-A) (320-400 nm) spectrum which can cause a much greater risk of skin changes. The average transparency (AT) values of three films were about 65-78% (320-350 nm) and 85-89% (350-400 nm), which implies that these films indeed can provide a physical barrier for blocking the UV-A absorbed into the skin, indicating functionality of the POSS/TiO2 materials as the sun protection factor (SPF) ingredients in a sunscreen. The AT values of three films were in the order of f-MPT>f-GPT>f-VPT due to complete-cage structures of building blocks (POSS) and the size of organic branches covalently bonded to the silica network in the molecular structures. This indicates that VPT powder might be significantly better to selected for the SPF. The TTB addition results in the hybrid structure containing TiO2 which causes a decrease in the AA radiation from sunlight. Lower transparency of the films containing 25 wt-% TTB fractions is ascribed to more amounts of TTB in the modified films.

Abstract: Calcium phosphate cement (CPC) is a self-hardening material for bone repairing. ZnO whisker is a new type reinforced materials lately, which is acerose single crystal fiber. In this study, ZnO whisker was added into the CPC with different ratios, and each specimen kept at 37 oC in 100% humidity for 24 hrs. The phase and microstructure of the calcium phosphate pastes were investigated using X-ray diffraction and scanning electron microscopy, respectively. It has been found that ZnO whisker could supply nucleating center, TTCP and DCPA could be much easier to form HA around the ZnO whisker. The adding amount of ZnO whisker is a key factor that determines the mechanical properties.

Abstract: Recently, biological system has revealed astonishing complex photonic structures. Freshwater pearls shows striking optical effects, such as reflection and interference, which closely related to its nanometer-scale multiplayer structure. In this paper, we tried to fabricate idea biological two-dimensional (2D) photonic crystals by growing freshwater pearls induced by Rare Earth Elements (REE) Cerium at a concentration of 1.2 mg•L-1. Comparing with the reference pearls cultured in nature freshwater, the superficial microstructure of REE pearls and their glossiness have taken large changes. The nacre of the REE pearls is structured 2D periodic photonic crystals layered structure, and each layer is composed by regular aragonite sheets, while the nature pearls has a mesa structure made of the spindly blocks, which were investigated by means of scanning electron microscopy (SEM). The glossiness of the pearls corresponds with the microstructure, the REE pearls possessing idea photonic crystals have higher glossiness than that of the nature pearls, which attribute to the strong interference effect of light on the photonic structure of REE pearls. It also provides an opportunity to grow perfect photonic crystals by culturing water pearls.