Behaviour of titanium and titania-based ceramics in vitro and in vivo

Cylinders, 2.8 mm in diameter and 6 mm in length which were produced from hot isostatically pressed titania (TI), titania-hydroxyapatite composite (TI/HA) and hydroxyapatite (HA) as well as commercially pure titanium (c.p. Ti), were implanted in the femurs of New Zealand white rabbits. The animals were killed at 1 and 3 months after implantation to study the development of bonding strength between the bone and the implant using the push-out test. The surface roughness and ion release of these materials in different solutions were also studied. Titania and titanium showed similar push-out strengths at 1 and 3 months after implantation. This indicates that bone has a similar response to titanium and titania due to the similarity of the surface constitute. Titania-hydroxyapatite composite showed a significant increase in bonding strength at 1 and 3 months after implantation compared with titania. A gap, < 2 microns wide, was observed by SEM at the bone-TI interface while the bone-HA interface was fully mineralized. No release of titanium ions from titania (rutile) was detected in the solutions used, including 0.1 M HCl, whilst release of titanium ions from c.p. Ti was measured in 0.02 M lactic acid and 0.1 M HCl. The results suggested that a further oxidation of titanium may improve the stability of c.p. Ti and that titania-based material may be a strong biocompatible ceramic suitable for medical applications.