Integrity and zeta potential of fluoridated hydroxyapatite nanothick coatings for biomedical applications

Fluoridated hydroxyapatite (FHA) coatings exhibit great potential for applications on implants which require good bioactivity and high antibacterial activity. This work is a comparative study of chemical stability, adhesive strength and zeta potential of a nanothick (about 200 nm) FHA coating which is densely and uniformly deposited on a titanium substrate electrochemically. The chemical stability of the nanothick coatings was evaluated using a dissolution test in a simulated physiological solution. The dissolution tests indicate that the fluorine-containing calcium phosphate (CaP) coating with an appropriate heat treatment is chemically stable in a physiological environment, even more so than its HA counterpart. The adhesive strength of FHA coatings was evaluated by the critical load obtained from nanoscratching tests. The critical load which caused coating failure in scratching was determined by a method which correlated the scratching morphology with a sudden change in friction coefficient. The adhesive strength of a nanothick FHA coating was 147% larger than that of HA coating with the same thickness level. The fluorine addition does not have a significant effect on the characteristics of the negative zeta potential of apatite coatings. The solid integrity of this nanothick FHA coating makes it an excellent candidate for biomedical applications.