Bioactive NiTi shape memory alloy used as bone bonding implants

The aim of this study is to convert the bio-inert NiTi surface into a bioactive one and to evaluate its biocompatibility and bone integration in vivo. To make a bioactive layer on the surface of NiTi, the alloy was immersed in HNO3 and in NaOH aqueous solution in turn, and then soaked in simulated body fluid (SBF) for 48 h. Ca- and P-rich layer was observed using environmental scanning electron microscope (ESEM) and energy-dispersion X-ray Spectroscopy (EDS). Furthermore, X-ray diffraction (XRD) spectrum confirmed that this layer is hydroxyapatite (HA). The coated and uncoated cylindrical implants were bilaterally implanted into the femurs of rabbits. At 6 and 13 weeks after implantation, the interfaces between the bone and the implant were evaluated by undecalcified histological examination under light and fluorescent microscope as well as ESEM. The results show that osteoblasts actively proliferated on the HA coating at 6 weeks after implantation. After 13 weeks, a large amount of new bone directly in contact with the host bone was observed. The interface is intact. In contrary, the uncoated implant–bone interface has gaps and fibrous layer was observed.