Enhanced in vitro bioactivity of porous NiTi–HA composites with interconnected pore characteristics prepared by spark plasma sintering

Abstract

Porous NiTi possesses suitable mechanical characteristics for orthopaedic implants. However, its poor bioactivity is a major challenge in the clinical application. Composite structures of porous NiTi and hydroxyapatite (HA) can be used to promote the bone ingrowth and integration of the implant with the surrounding tissue. But the differences in physical and mechanical properties of these composites are the main problem during sintering. Hence, we report a rapid fabrication of porous NiTi–HA composites using spark plasma sintering (SPS) with space holder method. Effect of HA on pore characteristics, mechanical properties and in vitro bioactivity (corrosion behaviors, ion release and apatite formation ability) of the porous NiTi–HA was investigated. Results showed that interconnected pore characteristics and 29%–37% porosity could be achieved by adding HA from 3 to 10wt.%. Compression test revealed that porous NiTi–HA possessed not only low elastic modulus of 5.6–8.1GPa (close to that of human bone) but also high compressive strength. Furthermore, the addition of HA could improve the bioactivity of porous NiTi significantly. The bioactivity mechanism and a relationship of HA concentration in the NiTi matrix are also discussed. The combination of interconnected pore characteristics, low elastic modulus, high strength and good bioactivity might make this material a candidate for hard tissue implants.