Microstructure and properties of TiO2 nanotube coatings on bone plate surface fabrication by anodic oxidation

TiO2 nanotube coatings with different structures were prepared on bone plate surface by anodic oxidation at different voltages or time and in an ethylene glycol solution containing 0.3 wt% ammonium fluoride (NH4F) and 2 vol% deionized water. Subsequently, the morphology, elemental composition, crystalline structure, surface roughness, microhardness, contact angle, adhesion force, corrosion resistance and wear resistance of the as-prepared coatings were characterized. At the optimized oxidation voltage of 60 V in microstructural, biocompatibility and properties of coatings considerations, the prolonged oxidation within a certain range led to increasing nanotube thickness and inner diameter, which further improved the properties of TiO2 nanotube coating samples. Specifically, surface roughness and adhesion force of the coatings increased progressively, the maximum adhesion force was (12.10 ± 0.50) N, while their contact angle and microhardness decreased gradually. Moreover, the coatings also exhibited the enhanced corrosion resistance in simulated body fluid (SBF), with the corrosion potential or the corrosion current increased by 56.91% or decreased by 79.45% to the largest extent. During dry friction, both friction coefficient and wear groove depth declined, corresponding reduction rates up to 22.52% and 49.01% evidenced the improved wear resistance. Besides, the major wear mechanism of the coating was a combination of abrasive and adhesive wear. Accordingly, the voltage of oxidation at 60 V and the oxidation time of 6 h were determined as the optimum processing parameters for preparing TiO2 nanotube coating on the bone plate surface, and the nanotube inner diameter and coating thickness were (118 ± 3.5) nm and (34 ± 2.8) μm, respectively. The novelties of the present study are: A uniform and neat TiO2 nanotube coatings were fabricated using the anodic oxidation method. The effects of oxidation voltage and oxidation time on the microstructure of TiO2 nanotube array were further examined, and the relationship between oxidation parameters and coating morphology was concluded. On that basis, the changes in the structural parameters of TiO2 nanotube coatings under other oxidation parameters can be inferred. The morphology, elemental composition, crystalline structure, surface roughness, microhardness, contact angle, adhesion force, corrosion resistance and wear resistance of TiO2 nanotube coatings were systematically studied, and the relationship between roughness and hydrophilicity of the coatings was discussed. The wear process of anodized TiO2 nanotube coatings under dry friction conditions was explained according to the friction coefficient curves, and the wear mechanism of the coating was clarified based on the wear morphology and the energy spectrum analysis of the coatings. The optimum oxidation voltage and oxidation time for preparing of TiO2 nanotube coating on the bone plate surface by anodization were determined as 60 V and 6 h, respectively, when the electrolyte was an ethylene glycol solution containing 0.3 wt% NH4F and 2 vol% deionized water.