Long-Term Assessment of the In Vitro Corrosion Resistance of Biomimetic ACP Coatings Electrodeposited from an Acetate Bath

Abstract

Calcium phosphate coatings are able to improve the osseointegration process due to their chemical composition, which is similar to that of bone tissues. In this work, to increase the long-term corrosion resistance and to improve the osseointegration process of commercially pure titanium Grade 4 (CpTi G4), biomimetic amorphous calcium phosphate (ACP) coatings were electrodeposited for the first time from an acetate bath with a pH level of 7.0 and a Ca:P ratio of 1.67. ACP coatings were obtained on CpTi G4 substrate subjected to sandblasting and autoclaving using electrochemically assisted deposition at a potential of −3 V relative to the open circuit potential for 30 min at room temperature. SEM, EDS, 2D roughness profiles, amplitude-sensitive eddy current method, and Kelvin scanning probe were used for the surface characterization of the biomaterial under study. In vitro corrosion resistance tests were conducted for 21 days in artificial saliva using open circuit potential, polarization curves, and electrochemical impedance spectroscopy measurements. The passive-transpassive behavior was revealed for the obtained ACP coatings. The long-term corrosion resistance test showed a deterioration of the protective properties for CpTi G4 uncoated and coated with ACP with immersion time. The mechanism and kinetics of the pitting corrosion on the CpTi G4|TiO2|ACP coating system are discussed in detail.