Fabrication, Nanomechanical Properties and In Vitro Evaluation of (Ti, O)/Ti Composite Coating on NiTi Shape Memory Alloy

In this investigation, to improve the long-term biocompatibility, bioactivity and mechanical properties of NiTi shape memory alloy (SMA), a sufficiently thick (Ti, O)/Ti composite coating (about 1.2 micron in thickness) was fabricated on NiTi SMA substrate using the plasma immersion ion implantation and deposition (PIIID) technique. Cross-sectional morphology of the composite coating was observed using scanning electron microscopy (SEM) and its thickness was evaluated by energy dispersive X-ray spectroscopy (EDX). X-ray diffraction (XRD) results showed that there were no diffraction peaks corresponding to TiO2 for the (Ti, O)/Ti composite coating, indicating that the (Ti, O) layer existed in the amorphous or nano-sized or poorly crystalline state in the composite coating. Nanohardness and elastic modulus of the composite coating were determined via nanoindentation tests. Pin-on-disc wear test results showed improved wear resistance of (Ti, O)/Ti coated NiTi SMA. For in vitro biological assessment of the composite coating, SaOS-2 osteoblast-like cells were cultured on coated and uncoated NiTi SMA samples. SaOS-2 cells seeded on (Ti, O)/Ti coated samples spread and adhered better than on uncoated samples.