Biomimetic calcium phosphate coatings on nitric-acid-treated titanium surfaces

This study describes biomimetic calcium phosphate (Ca-P) coatings formation under simulated physiological conditions on Ti surfaces that go through nitric acid treatment (NT). In the present study, nitric acid treatment was used to treat Ti specimens so that Ti specimens could have the ability to induce Ca-P formation. After careful selection of the NT parameters, Ca-P coatings success fully formed on the nitric-acid-treated Ti surfaces in a supersaturated calcium phosphate solution (SCPS) and in the simulated body fluid (SBF). Before NT, the Ti specimen should go through mixed acid etching to increase its surface roughness because rough surfaces lead to good adherence between coatings and substrates. Amorphous Ca-P coatings were formed on the Ti surfaces by immersing the NT Ti specimens in SBF, while octacalcium phosphate (OCP) coatings were formed in the SCPS after 3 days of immersion. The study firstly proved that nitric acid treatment is not only just for surface passivation but also is another bioactive treatment as an alternative to the alkaline treatment and two-step method. The experimental results also confirmed that the conventional nitric acid treatment of a titanium surface does not increase the titanium oxide on the Ti surfaces. However, extending the nitric acid treatment time and enhancing the nitric acid treatment temperature help to increase Ti surface ability of Ca-P induction in simulated physiological environments. Ti specimens that had 600 min of NT at 60 °C had the best Ca-P induction ability under biomimetic conditions.