A Simple Method to Functionalize the Surface of Plasma Electrolytic Oxidation Produced TiO2 Coatings for Growing Hydroxyapatite

• TiO2 coatings with porous surfaces were produced by plasma electrolytic oxidation.
• Simple pre-immersion in K2HPO4 could functionalize the surfaces of the TiO2.
• Such pre-immersion enhanced substantially the growth of hydroxyapatite in SBF.
• Growth mechanisms of hydroxyapatite via the pre-immersion have been proposed.
• MTT assay shows great osteoblast-like cell activity on the obtained hydroxyapatite.

Conventionally, hydrothermal treatment was often used to modify the TiO2 surface prior to the growth of hydroxyapatite (HA) that is one of the most important implant biomaterials. In this work, a simple pre-immersion of the obtained TiO2 in a weak base, instead of the conventionally high pressure-temperature hydrothermal pre-treatment, was conducted prior to the growth of HA. Firstly, anatase TiO2 coatings with porous surfaces were produced by plasma electrolytic oxidation with optimized processing parameters. X-ray diffraction patterns and field-emission microscopy reveal that the anatase TiO2 films with porous surfaces were produced by plasma electrolytic oxidation. Subsequently, the films were pre-immersed in 0.1–2 M K2HPO4 solutions for only 10 min. Fourier transform infrared spectroscopy shows that the OH functional groups were generated after such pre-immersion, which could enhance significantly the growth of a single phase of HA in simulated body fluid (SBF). Growth mechanisms of HA via the pre-immersion treatment and soaking in SBF have been proposed. Moreover, the proliferation rate and attachment of the MG-63 osteoblast cells were greatly enhanced on the obtained HA compared to that without the immersion pre-treatment from the MTT assay and morphology analyses. This simple immersion pre-treatment evidently provides an easy route for the growth of HA and has great potential for biomedical applications.

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