Nitinol Modified by Calcium Phosphate Coatings Prepared by Sol-Gel and Electrodeposition Methods

Titanium and its alloys, such as Nitinol, are preferred materials for load-bearings implants and the properties of the implant surface are important variable in implant design. In this work, surface of Nitinol was modified by calcium phosphate (CaP) coatings using the electrochemically assisted deposition and sol-gel method. Chronoamperometry was used for in situ study of initial step of electrodeposition process of an acid CaP (brushite film) that occurs via 3D progressive nucleation and growth mechanism. Electrodeposited film was converted to hydroxyapatite coating (HA) by acid-base reaction. The Nitinol surface was characterized using field emission scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). CaP coatings deposited on the Nitinol surface by electrochemically assisted process were more macroscopically homogenous with good internal cohesion and lower residual stresses in the coating and provide better adhesion to the implant surface in comparison to the sol-gel deposited CaP coatings.