Developing a mechanochemical surface pretreatment to increase the adhesion strength of hydroxyapatite electrophoretic coating on the NiTi alloy as a bone implant

In this work, the pretreatments of sandblasting for 5, 15, 20, and 30 s followed by acid-etching were conducted to improve the adhesion strength amid the NiTi substrate and an electrophoretic coating of hydroxyapatite as a bone implant. The composition, microstructure, and surface topography of materials govern their properties. Therefore, characterizations of prepared specimens were performed using X-ray diffraction as well as quantitative phase analysis, differential scanning calorimetry, optical microscopy, scanning electron microscopy, atomic force microscopy and a roughness measuring device. The micro-scale mechanical properties were evaluated using a nanoindentation test. The electrochemical measurements were done using a multipurpose electrochemical test rig. The results display that the sandblasting for 20 s followed by acid-etching results in the suitable average roughness of Ra = 1.543 ± 0.053 μm and the adhesion strength is improved by 50% compared to sandblasted state. Also, the mentioned mechanochemical pretreatment make it more effective during electrochemical reactions and improve corrosion protection efficiency by 57.61%. Therefore, this surface pretreatment can be considered as a proper approach before the electrophoretic coating of hydroxyapatite on the NiTi substrate to increase the adhesion strength and diminish the stress shielding effect after implantation as a bone implant. [Display omitted] •Sandblasting followed by acid-etching are applied on NiTi before HA electrophoretic coating.•Stress-induced B19' is dominant phenomenon during sandblasting of NiTi.•The surface roughness saturation appears at 0.6 MPa for sandblasting time of 15 s.•Acid-etching moderates roughness of sandblasted NiTi with uniform superficial TiO.•This pretreatment enhances adhesion strength and diminishes stress shielding effect.