Xi Tingfei

The underlying biological mechanisms of biocompatibility differences between bare and TiN-coated NiTi alloys.

TiN coating has been demonstrated to improve the biocompatibility of bare NiTi alloys; however, essential biocompatibility differences between NiTi alloys before and after TiN coating are not known so far. In this study, to explore the underlying biological mechanisms of biocompatibility differences between them, the changes of bare and TiN-coated NiTi alloys in surface chemical composition, morphology, hydrophilicity, Ni ions release, cytotoxicity, apoptosis, and gene expression profiles were compared using energy-dispersive spectroscopy, scanning electron microscopy, contact angle, surface energy, Ni ions release analysis, the methylthiazoltetrazolium (MTT) method, flow cytometry and microarray methods, respectively. Pathways binding to networks and real-time polymerase chain reaction (PCR) were employed to analyze and validate the microarray data, respectively. It was found that, compared with the bare NiTi alloys, TiN coating significantly decreased Ni ions content on the surfaces of the NiTi alloys and reduced the release of Ni ions from the alloys, attenuated the inhibition of Ni ions to the expression of genes associated with anti-inflammatory, and also suppressed the promotion of Ni ions to the expression of apoptosis-related genes. Moreover, TiN coating distinctly improved the hydrophilicity and uniformity of the surfaces of the NiTi alloys, and contributed to the expression of genes participating in cell adhesion and other physiological activities. These results indicate that the TiN-coated NiTi alloys will help overcome the shortcomings of NiTi alloys used in clinical application currently, and can be expected to be a replacement of biomaterials for a medical device field.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF LAVES PHASE STRENGTHENING NiAl BASE COMPOSITE FABRICATED BY RAPID SOLIDIFICATION

The Laves phase strengthening NiAl base composite was fabricated by conventionally casting and rapid solidification,and their microstructnre and mechanical properties were investigated together.The results exhibit that the Laves phase in the conventional cast alloy is relative coarse and distributes along the NiAl phase boundary.Moreover,small stick like Laves phase precipitates in the NiAl phase.Due to the segregation of Ni and Al in Laves phase,it still keeps the C14 crystal structure.The rapid solidification refines the NiAl and Laves phase greatly and promotes the formation of NiAl/Laves phase eutectic structure,which surrounds the NiAl phase and forms the cell like structure. However,the rapid solidification can not handicap the precipitation of needle-like Laves phase in the NiAl phase.But,the rapid solidification restrains the formation of α Cr phase.The compression tests show that the cell-like Laves phase strengthening NiAl base composite has better mechanical properties at ambient and elevated temperature,compared with the conventional cast alloy.The improvement of mechanical properties should be attributed to the cell-like Laves phase and the nanocrystallization of the cell-like Laves phase during high-temperature deformation.