Materials Science Forum Vols. 610-613

Abstract: A kind of metastable β type Ti-30Nb-13Zr-0.5Fe (wt.%) alloy for biomedical application was newly designed and developed. In order to exam the phase transformation during aging and its effects on the mechanical properties, the alloy was β solubilized and aged at 350°C-550°C for 4 hours. The microstructures were observed by OM and TEM, and the phase structures were identified by XRD. The tensile tests were performed with various aged microstructures. The results show that a lot of ω phase precipitates during aging at 350°C, leading to the increase of strength and elastic modulus and drastic decrease of plasticity. Aging at 450°C, dot α phase uniformly precipitates from metastable β phase. The good combination of high strength 、high plasticity and low elastic modulus was obtained under this aging condition. With increasing aging temperature and aging time α precipitations coarsen and precipitation free zones (PFZ) along prior β grain boundaries form, which are the main reasons to lower the strength and plasticity.

Abstract: Magnesium alloys have attracted scientists’ attention as potential implant materials, due to their excellent biocompatibility and good mechanical compatibility. Potentiodynamic electrochemical technique was applied to investigate the corrosion behavior of magnesium alloy AX53 (Mg-4.76Al-3.17Ca) in Hank's solutions, 0.9 wt% NaCl+0.7 g/L NaHCO3 solutions and 0.9 wt% NaCl solutions at room temperature. Corrosion morphologies of the alloys were observed by means of scanning electron microscope, and the chemical compositions were examined through x-ray diffraction. The results demonstrated that free corrosion potential (Ecorr) of AX53 in 0.9 wt % NaCl solution rose rapidly at initial stage, and then stabilized, whereas Ecorr of this alloy increased continuously in the other two solutions. Corrosion rates in Hank’s solutions were lower than in the other solutions. Intergranular corrosion occurred in these solutions.

Abstract: Nickel Titanium alloy has been used widely in clinical iatrology for years because of its unique shape memory capability, proper elasticity and considerable biocompatibility. But as an implanted material, its possible release of Ni ions which might cause toxic effect and its improvable biocompatibility draw attentions of researchers. In this study, chitosan/heparin multilayer is coated on NiTi shape memory alloy by electrostatic self-assemble method. Field emission scanning electron microscopy (FE-SEM), contact angle test is used to show its surface character; hemolysis test, dynamic clotting time experiment and platelet binding test are utilized to investigate the blood compatibility of the materials. The results reveal that the hydrophilic character of the coated one is better than the substrate, and blood compatibility of NiTi is improved by coating treatment.

Abstract: The reciprocating corrosion wear behavior of a nickel-free austenitic stainless steel 13Cr24Mn0.44N flat against a Si3N4 ceramic counter ball was investigated in two kinds of aqueous such as artificial body solution and distilled water by using the ball-on-flat configuration with 300 μm amplitude at various normal loads. The worn surfaces of the new stainless steel were observed by scanning electron microscopy (SEM). Elements valence in wear scars were also detected by X-ray photoelectron spectroscopy (XPS). The influences of the load and aqueous media on the friction coefficient and wear resistance of the new stainless steel were analyzed. It is clear that the friction coefficient decreased in both aqueous with the load increasing. The lubricative surface film formed on the wear scars in the artificial body solution could reduce the friction coefficient, and result in a lower wear loss in the artificial body solution than that in the distilled water, which demonstrates a negative interactive effect between wear and corrosion.

Abstract: In this study, biocompatible polymer poly(ethylene oxide) (PEO), gelation (denatured collagen) and nanometer silver colloid was added to the electrospinnning solution of alginate sodium to get anti-bacterial nanofiber mats. The morphology and mechanical properties of the electrospun mats have been investigated. Smooth fibers with diameters around 300 nm were obtained from 4.0 % solutions of varied alginate/PEO/gelation proportion. The anti-water property of the electrospun mats has been improved by crosslink with glutaraldehyde acetone solution and aqueous calcium chloride and ethanol.

Abstract: The graded composite materials were fabricated by direct inkjet printing of nano-electropolar mineral and nano-hydroxyapatite powders for the study of inhibiting function on streptococcus mutans, which is a primary pathogen for human dental caries. The electropolar mineral can be utilized in many fields due to its spontaneous permanent polarity and far infrared emission properties. In this study, the graded distribution of the streptococcus mutans on the surface of graded composite materials was investigated by energy dispersion spectrometry, and the mechanism of which is that the streptococcus mutans was remained in the culture of pH at about 8.5 self-adjustment induced by the electropolar mineral. This culture inhibits growth and acid production of streptococcus mutans. Therefore, this composite materials have inhibitory effects on streptococcus mutans, and can be used as a promising biomaterial for preventing human teeth from caries.

Abstract: Enzymes, immobilized on pH/temperature/ion-responsive carriers, relieve poor contact and could be conveniently recycled as well. Enzymes were immobilized on pH-responsive carriers often by covalent method, which was better than non-covalent method (adsorption). The immobilized enzymes showed slight steric hindrance for enzymatic reaction, but always lose much activity during recycle process. The Km values were often increased significantly via immobilization on temperature/ion responsive carriers, while the immobilized enzymes expressed superior reusability. Both covalent and non-covalent methods were fit for enzymes to be immobilized on temperature-responsive carriers. Non-covalent method (entrapment) was preferential choose for enzymes to be immobilized on ion-responsive carriers. Many drawbacks, such as large activity loss and slow respondence during stimulus occurrence, seriously restrained the effect of the immobilized enzymes. It was supposed to open up special stimuli-responsive materials for enzymes immobilization, and choose proper immobilization methods, correspondingly.

Abstract: Carbonated hydroxyapatite (CHA) and hydroxyapatite (HA) were prepared by the wet chemical method. The contact angle was measured to calculate the surface energy. The biomineralization process in SBF solution of HA and CHA were investigated in vitro. The cell attachment and proliferation behavior of CHA and HA were compared by the cell culture experiments. The results show that the polar component of surface energy of B-type CHA is higher than that of HA. Osteoblastic cells attach and proliferate very well on the surface, which indicates the excellent cell compatibility. The CHA have high bioactivity owing to rapid formation of hydroxyl-carbonate-apatite (HCA) mineralized layer on the biomaterial’s surface in SBF.

Abstract: The aim of this paper is to present a synthesis method of poly(ε-caprolactone) by the ring opening polymerization of ε-caprolactone catalyzed with nontoxic magnesium lactate. The results indicated that Mg(Lac)2 is a catalyst with moderate activity for the polymerization of ε-caprolactone. Effects of the catalyst and reaction temperatures on the microstructure of the ε-caprolactone and L-lactide copolymers were investigated by means of 13C-NMR spectroscopy. An increase in the reaction temperature enhances the role of transesterification and the extent of randomness.

Abstract: Ti-bioglass was sprayed on Ti6Al4V substrate. The crystallization dynamics of Ti-bioglass was analyzed by differential scanning calorimetry(DSC). The structure and morphology of the coatings were studied by SEM, TEM and AFM. The results showed that new phase Ca5(PO4)3F formed at 695.2°C when bioglass crystallized. The formation activation energy was 147.76KJ/mol and the crystallization exponent was less than 3 (n<3). It indicated that the crystallization happened on the surface. When 20 wt% bioglass was mixed with Ti powders, the formation activation energy was 324.6KJ/mol and the crystallization exponent was larger than 3 (n>3), which indicated that an integrated crystallization happened. Micro- or nano-scale R-TiO2, A-TiO2 and Na2Ti6O13 crystals precipitated on the surface of the coating after crystallization treatment. These crystals have a function of self-seal on the cracks on the coatings and form a metallurgical interface between the substrate and the coating.