Biomimetic hydroxyapatite (HAp) coatings on pure Mg and their physiological corrosion behavior

The deposition of bioactive hydroxyapatite (HAp) coatings on pure magnesium (Mg) surfaces was studied. A modification of the biomimetic deposition method was used, which consisted in the incorporation of a supersaturated calcification solution (SCS). Different preparation parameters were modulated to obtain HAp and/or doped apatite coatings with different characteristics. The influence of the surface pre-treatments and soaking time in SCS on the physicochemical properties and the corrosion performance of the biomimetic HAp coatings were evaluated. Two different pre-treatments were explored to condition the sample's surface for the biomimetic HAp deposition. After the surface pre-treatments, the Mg samples were covered with HAp coatings by soaking in SCS during two immersion periods specifically chosen for this study: 2 h and 6 h, respectively. Scanning electron microscopy, coupled with energy-dispersive X-ray spectroscopy (SEM/EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman Spectroscopy, and Fourier transform infrared (FTIR), were applied for the chemical, morphological, and structural characterization of the resulting biomimetic HAp-coatings. The in vitro corrosion behavior was studied by open circuit potential (OCP) measurements and electrochemical impedance spectroscopy (EIS) during immersion tests in Ringer's physiological solution for up to 14 days. The results showed that HAp coatings were successfully deposited on the pure Mg substrates. Furthermore, the corrosion studies in Ringer's solution showed that HAp coating behavior depends not only on the pre-treatment type but also on the immersion time in SCS. These results open the door to propose different strategies to control-on demand-the corrosion rate of Mg coated with biomimetic HAp. These systems could be a promising alternative for designing and developing new temporary implants for the human body.