Changing bioperformance of TiO2 amorphous nanotubes as an effect of inducing crystallinity

Controlled-diameter TiO2 nanotubes were obtained by electrochemical anodizing of two different substrates (Ti and Ti6Al7Nb) in an aqueous electrolyte. As-formed TiO2 nanotubes are amorphous and by subjecting to thermal treatments, the structure becomes crystalline. An optimal thermal treatment with a specific anatase/rutile ratio was chosen, determined from X-ray diffraction (XRD). The electrochemical behaviour of annealed and as-formed samples was followed with Tafel plots and Electrochemical impedance spectroscopy (EIS), while surface analysis involved scanning electron microscopy (SEM) and contact angle measurements (CA). Annealed samples have a more hydrophilic character than as-formed as well as a better stability in bioliquids. Such behaviour of annealed samples is connected with a better biocompatibility expressed in terms of cell morphology and gene expression of bone specific markers obtained from Reverse Transcription Polymerase Chain Reaction (RT-PCR).

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► TiO2 nanotubes are obtained on Ti and on Ti6Al7Nb, furthermore optimal thermal treatments are chosen.
► Annealed TiO2 nanotubes are more stable regarding corrosion.
► RT-PCR data present a two fold increase of osteocalcin expression in MG-63 cells grown on annealed TiO2 nanotubes.
► All these data suggest that annealed TiO2 nanotubes may represent a promising material for orthopaedic cellular therapy.