Micro-porous TiO_2 coatings co-doped with Zn^(2+) and Ag nanoparticles were fabricated on Ti by microarc oxidation(MAO) for 0.5, 1.5, 2 and 4 min, respectively. The evolutions of morphology and phase component of the coating as a function of processing time were investigated. The microstructure of the 2 min treated coating was further observed by transmission electron microscopy to explore the coating formation mechanism. The amounts of Ag and Zn released from the 2 min treated coating were measured and the antibacterial properties of the coatings against Staphylococcus aureus(S. aureus) were also investigated. The obtained results showed that with prolonged MAO time, the contents of Ag and Zn on the coating surfaces increased. All the coatings were micro-porous with pore diameters of 1–4 μm; however,some pores were blocked by deposits on the 4 min treated coating. The 2 min treated coating was composed of amorphous TiO_2, anatase, rutile, ZnO, Zn_2TiO_4 and homogenously distributed Ag nanoparticles.After immersion, Zn^(2+), Ag+, Ti^(2+) and Ca^(2+) were released from the coating and with the immersion time prolonged, the accumulated concentrations of these ions increased. After immersion for 36 weeks, the accumulated Zn^(2+) and Ag+concentrations were 6.88 and 0.684 ppm, respectively, which are higher than the minimal inhibitory concentration but much lower than the cytotoxic concentration. Compared with polished Ti control, the coatings co-doped with Zn^(2+) and Ag nanoparticles significantly inhibited the adhesions of S. aureus and reduced the amounts of planktonic bacteria in culture medium, indicating that the Zn and Ag co-doped TiO_2 could be a bio-adaptable coating for long-lasting anti-microbial performance.
SrTiO_3 nanotube films with good adhesion strengths to Ti substrates were fabricated by using a hybrid approach with a modified anodization and a hydrothermal treatment(HT). The effect of Sr^(2+) concentration in HT solutions on the morphologies and phase components of the nanotubes were investigated,the SrTiO_3 nanotubes formation mechanism was explored, and the adhesion strengths, hydrophilicity and apatite-forming ability of the SrTiO_3 nanotubes were also evaluated. The results demonstrated that with increasing the incorporation of Sr^(2+) into the nanotubes, no obvious changes of the lengths and outer diameters of the nanotubes were observed, but the wall thickness and the crystallinity of SrTiO_3 in the nanotubes increased. The accumulation of Sr at the inner tube wall indicated that the reaction of Sr^(2+) with TiO_2 mainly occurred in the vicinity of internal surfaces of the closely arranged nanotubes. The formation of the SrTiO_3 nanotubes could be attributed to an in situ dissolution–recrystallization process.The Sr TiO_3 nanotubes exhibited good hydrophilicity and bioactivity, and the induced apatite preferred to nucleate on the nanotubes with higher crystallinity and Sr content, indicating a good bio-adaptability of the SrTiO_3 nanotubes for orthopedic application.
Materials that undergo a reversible change of crystal structure through martensitic transformation(MT)possess unusual functionalities including shape memory, superelasticity, and low/negative thermal expansion. These properties have many advanced applications, such as actuators, sensors, and energy conversion, but are limited typically in a narrow temperature range of tens of Kelvin. Here we report that, by creating a nano-scale concentration modulation via phase separation, the MT can be rendered continuous by an in-situ elastic confinement mechanism. Through a model titanium alloy, we demonstrate that the elastically confined continuous MT has unprecedented properties, such as superelasticity from below 4.2 K to 500 K, fully tunable and stable thermal expansion, from positive, through zero, to negative, from below 4.2 K to 573 K, and high strength-to-modulus ratio across a wide temperature range.The elastic tuning on the MT, together with a significant extension of the crystal stability limit, provides new opportunities to explore advanced materials.
