Advanced Materials Research Vols. 47-50

Abstract: It has been found that the composites of carbon nanotubes (CNTs) and epoxy resin could greatly enhance damping ability while the stiffness is kept high. In this paper, carbon nanotube enhanced epoxy resin is fabricated. A testing apparatus for obtaining composite dynamic properties is set up. In particular, the loss factors are measured. Experimental results show that CNT additive can provide the composite with several times higher damping as compared with pure epoxy. A finite element model is built to simulate the composite damping. CNT diameter and segment length are investigated using the developed model. Results show that composite damping is insensitive to CNT segment length while the effect of CNT diameter on composite damping is significant.

Abstract: New biomimetic carbonate-hydroxyapatite nanocrystals (CHA) have been designed and synthesized in order to obtain a remineralization of the altered enamel surfaces. Synthesized CHA mimic for composition, structure, nano dimension and morphology bone apatite crystals and their chemical-physical properties resemble closely those exhibited by enamel natural apatite. CHA can chemically bound themselves on the surface of natural enamel apatite thanks to their tailored biomimetic characteristics. The remineralization effect induced by CHA represents a real new deposition of carbonate-hydroxyapatite into the eroded enamel surface scratches forming a persistent biomimetic mineral coating, which covers and safeguards the enamel structure. The experimental results point out the possibility to use materials alternative to fluoride compounds which is commonly utilized to contrast the mechanical abrasions and acid attacks. The apatitic synthetic coating is less crystalline than enamel natural apatite, but consists of a new biomimetic apatitic mineral deposition which progressively fills the surface scratches. Therefore the application of biomimetic CHA may be considered an innovative approach to contrast the acid and bacteria attacks.

Abstract: H2 production over dye-sensitized Pt/TiO2 nanoparticles with mesostructures under visible light was investigated by using methanol as electron donors. Three types of Ru(II) bipyridyl complexes, which can be attached to Pt/m-TiO2 with different linkage modes, show different photosensitization. The dye tightly linked with m-TiO2 has better durability but the lowest H2 evolution efficiency, whereas the loosely attached dyes possess higher H2 evolution efficiency and preferable durability. It seems that the dynamic equilibrium between the linkage of ground state dye with TiO2 and the divorce of oxidization state dye from the surfaces plays a crucial role in the photochemical behavior during photocatalyst sensitization process. The binuclear Ru(II) shows a better photosensitization in comparison with mono- nuclear Ru(II) dyes due to its large conjugation system and “antenna effect”, which, in turn, improve the visible light harvesting and electron transfer between the dye and TiO2.

Abstract: TiNi/Al-12%Si alloy is a kind of prospective material used as special energy absorbers for eliminating undesirable noise and mechanical vibration. The investigation on the mechanical properties of this composite alloy is of great importance. In this study, the surface deformation of TiNi/Al-12%Si composite alloy under external loading was measured experimentally by means of DSCM method. Some deformation characteristics of TiNi/AlSi composite alloy under the effect of the tensile load and the interaction between TiNi and AlSi are discussed. In addition, the elastic modulus and the poisson ' s ratio of this alloy were measured as well. The results agrees well with the theory predicts.

Abstract: Polypropylene (PP)/ polyethylene terephthalate (PET) composite fibres modified by PP-g-AA as a compatilizer were prepared by melt extrusion in a twin screw extruder. The crystallization and melting behavior of PP fibre and PP/PET composite fibres were investigated with differential scanning calorimeter (DSC)[1]. The results indicate that addition of PET acts as nucleating agent on the PP/PET composite fibres and increases the crystallization temperature of PP. [2,3]The crystallization peak temperature (Tp) increased first and decreased afterwards with the increase of PET, indicating that small amount of PET would promote the crystallization of PP, but excessive would reduce the crystallinity.

Abstract: In this study, the PDMS (polydimethyl siloxane) membranes with different mechanical strength were prepared and applied for the culture of osteoblastic cells. The osteoblastic phenotypes were then analyzed, including attachment, proliferation and differentiation. Meanwhile, the hydrophilicity of membranes was also adjusted by using plasma treatment. From the preliminarily results, the osteoblastic cells would prefer to attach to the PDMS substrate with higher hardness, which also resulted in a higher cell density in cell proliferation for longer culture times. The above tendency would be only significant on the hydrophilic surface, which revealed that the cell would not well recognize the surface properties on the hydrophobic surface. The results also indicated the osteoblastic differentiation would be affected by the mechanical strength of substrate surfaces. To investigate the mechanism of the mechanical effects on cell behaviors, the protein deposition was analyzed on surfaces with different hardness. The outcome suggested that the protein composition on these surfaces would be changed due to the difference in the mechanical properties.

Abstract: As a natural protein, wool keratin was used to improve the cell affinity of poly(L-lactic acid) (PLLA). Small keratin particles were prepared from keratin solution by the spray-drying process. Keratin particles were blended with PLLA/1,4 dioxane solution and paraffin micro-spheres which were used as progens. After the mixture was molded and dried, the paraffin micro-spheres were removed by cyclohexane. PLLA/keratin scaffolds with controlled pore size and well interconnectivity were fabricated. Keratin releasing rate was detected by Fourier transform infrared (FTIR) after the scaffold was immersed into PBS up to 4 weeks. The surface chemical structure was examined by X-ray photoelectron spectroscope (XPS). The results suggested that the keratin could be held into the scaffold which was expected to improve the interactions between osteoblasts and the polymeric scaffolds.

Abstract: Poly-L-Lactide (PLLA) composites were prepared with nano silver particles with the weight ratios of nano silver particles to PLLA (Ag/PLLA) at 0.5%, 2.5%, 5%, 7.5% and 10% (w/w). In vitro cytotoxicity tests were conducted firstly to evaluate the cytotoxicity of the composites. The results indicated that PLLA, 0.5%, 2.5% and 5% Ag/PLLA composites were nontoxic to cells, while 7.5% and 10% Ag/PLLA composites were significantly toxic to cells. Cell proliferation experiments and antibacterial tests were also performed. 5% Ag/PLLA was found the best for cell proliferation with obvious antibacterial property. Thus, Ag/PLLA can be used as nontoxic scaffolds for tissue engineering with antibacterial property.

Abstract: In order to produce nano-structured carbon steel, a 0.45%C steel was quenched and warm-compressed on a Gleeble 3500 Machine. The microstructural evolution during the process was studied by using an optical microscope and a transmission electron microscopy. The starting microstructure was lath martensite with a small amount of flake martensite. A lot of high-angle boundaries between martensite laths were induced after 50% reduction compression at 350°C. The microstructure of the specimen compressed at 600-650°C was nano-carbides + equiaxed ultrafine ferrite grains. The mechanism for grain refinement is incomplete dynamic recrystallization.