Biocompatibility of the micro-patterned NiTi surface produced by femtosecond laser

Biocompatibility of the micro-patterned NiTi surface produced by femtosecond laser (FSL) was studied in this work. The surface characteristics of the laser treated NiTi alloys were investigated by scanning electron microscopy (SEM), atom force microscopy (AFM), X-ray diffractometry (XRD) and X-ray photoelectron spectrum (XPS). The biocompatibility was evaluated by in vitro cell culture test. The results showed that, grooves, ripples, which covered by nanoparticles were formed on the sample surfaces, and the Ni/Ti ratio on the alloy surface increased with increasing laser energy. The crystal structure was not changed by laser treatment. However, the cell culture test proved that the micro-patterns induced by FSL were beneficial to improve the biocompatibility of NiTi alloys: the growth of osteoblasts oriented along the grooves, a large amount of synapses and filopodias were formed due to the ripples, holes and nanoparticles on the alloy surface, and the proliferation rate and alkaline phosphatase (ALP) content of cells were increased after FSL treatment. However, due to the toxicity of Ni ions on cell growth, the NiTi alloy surface should not be treated by laser fluence of more than 3.82 J/cm2 to obtain the ideal biocompatibility.

► We fabricated different micro-patterns (grooves, ripples, holes and nanoparticles) on NiTi alloy surfaces to improve the biocompatibility. ► The new method of femtosecond laser (FSL) machining technique was used to obtain the novel micro-patterns, and the authors explored the mechanism of the FSL machining process. ► We the surface characteristics of NiTi surfaces before and after the FSL treatment, and evaluated the influence of FSL treatment on biocompatibility of NiTi alloys.