Bone bonding strength of sputtered hydroxyapatite films subjected to a low temperature hydrothermal treatment

Hydroxyapatite (HA) was coated onto titanium substrates using radio frequency sputtering, and the coated HA films were crystallized in an autoclave at 110 degrees C using a low temperature hydrothermal method. The crystallite size, the Ca/P ratio, and the surface of the films were observed using XRD, EDS, and SEM, respectively. An immersion test was carried out in physiological saline solution, and the film-to-substrate adhesion strength was measured using a pull-out test. From the XRD patterns, a sputtered film subjected to the hydrothermal treatment had crystallized after 24 h, and the crystallite size increased from 38.0+/-8.7 to 81.4+/-19.1 nm. In immersion tests, an as-sputtered film completely dissolved after 1 d, whereas a sputtered film subjected to the hydrothermal treatment survived to 18.7+/-5.8% of the initial film thickness after four weeks. In pull-out tests, the adhesion strength of the sputtered film to the substrate increased from 1.9+/-0.2 to 5.3+/-1.6 MPa after the hydrothermal treatment. A sputtered film subjected to the hydrothermal treatment and a plasma-sprayed coating on titanium columns were implanted in the diaphysis of the femora of six adult dogs, and a pull-out test was carried out after two, four, and 12 weeks. The sputtered film showed higher bone bonding strength than the plasma-sprayed coating at any period.