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

Abstract

Hydroxyapatite (HA) was coated onto titanium substrates using radio frequency sputtering, and the coated HA films were crystallized in an autoclave at 110°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.