Effect of organic self-assembled monolayers on the deposition and adhesion of hydroxyapatite coatings on titanium

Organic self-assembled monolayers with nitrogen-containing surface functionalities (amine or alkylammonium) were deposited on acid-etched titanium substrates. These were then coated with apatite deposited from 150 % simulated body fluid at 37 degrees C and pH = 7.6 for 2, 4, and 6 days (after a 2-day "nucleation" step in contact with bioactive glass in 100 % simulated body fluid). Scanning electron microscopy showed that precipitates were numerous on amine- and alkylammonium-modified titanium surfaces after nucleation for 2 days. X-ray diffraction at grazing incidence detected crystalline hydroxyapatite on the modified and unmodified substrates after growth for 2 days. Tape peel tests followed by surface chemical analysis showed that the adhesion of the hydroxyapatite coating to the substrates was improved by amine and by alkylammonium modification of the etched titanium surfaces.