In vitro bioactivity and osteoblast response on chemically modified biomedical porous NiTi synthesized by capsule-free hot isostatic pressing

Porous biomedical NiTi with an average porosity of 56% and a general pore size of 50–800 μm was synthesized by capsule-free hot isostatic pressing (CF-HIP) with NH4HCO3 as a space holder. In order to enhance the surface bioactivity, the porous alloy was subjected to H2O2 to form a TiO2 coating followed by a NaOH treatment. Scanning electron microscopy (SEM), thin film X-ray diffraction (TF-XRD), and X-ray photoelectron spectroscopy (XPS) revealed that a porous sodium titanate (Na2TiO3) film formed on the surface of the porous NiTi due to the chemical reaction between NaOH and pre-formed TiO2 at the interface between the NaOH solution and porous NiTi. An apatite layer was formed on the film after immersion in simulated body fluids (SBF) at 37 °C while no apatite could be found on the surface of the untreated porous NiTi. Formation of the apatite layer indicates that the chemically treated porous NiTi possesses excellent bioactivity and this bodes well for applications in bone implants. In our preliminary cell culture tests, osteoblast cells were found to attach and proliferate better on the chemically treated samples compared to the untreated alloys.