The potential-assisted deposition as valuable tool for producing functional apatite coatings on metallic materials

• Nitinol, shape memory alloy, protected with the bioactive HA coatings.
• Potentiostatically deposited brushite film as the precursor for HA formation.
• In situ EIS investigations of HA coated Nitinol under in vitro conditions.
• Poor corrosion resistance of Nitinol covered with HA coatings formed in NaOH.
• Excellent corrosion resistance of Nitinol covered with HA coatings formed in SBF.

Nitinol was coated with hydroxyapatite (HA) by the two-step method that includes electrodeposition of the calcium phosphate (brushite) film, as a precursor for the HA deposition, which is the second reaction step.This work concerns direct comparison of structural and barrier properties of the HA coatings produced by the phase transformation of brushite to HA in (i) an alkaline solution (NaOH) and (ii) a simulated body fluid solution (SBF).Chemical composition and morphology of the surface films were characterized using field emission scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS).The corrosion resistance was determined using in situ method of electrochemical impedance spectroscopy (EIS), under in vitro conditions, in order to optimize the production of bioactive HA coatings on metallic (Nitinol) implants for medical applications.The combination of advantages of the electrodeposition of the HA precursor film on the Nitinol surface and the treatment in an SBF solution, under in vitro conditions, has the potential to provide the HA coatings with the structural and microstructural homogeneity, excellent barrier properties (corrosion resistance) as well as bioactivity.