Synthesis of hydroxyapatite on titanium coated with organic self-assembled monolayers

The work focuses the formation of hydroxyapatite (HA) layers from simulated body fluids (SBF) onto titanium coated with NH₂-, SH-, and SO₃H-SAMs, respectively, at room temperature and 37 °C as well as pH values of SBF of 7.4, 8, and 8.4. At an upside up arrangement of the samples in the SBF, the formation of sufficient thick HA layers with a pillow like structure onto all SAMs were observed, which is believed to be caused by combined homogeneous and heterogeneous precipitation of HA from the SBF. These layers do not show sufficient adhesive strength. An upside down arrangement of the samples result in the formation of up to 5–10 μm thick flat HA layers with a much higher adhesive strength, which is believed to be due to formation of HA from the SBF only by heterogeneous precipitation. Also HA layers were obtained onto all studied SAMs, SH-SAM appears to favour the formation of HA resulting in a layer with a thickness of about 10 μm and an almost stoichiometric Ca/P-ratio of the layer of 1.72. All other layers exhibit much lower ratios.