HYDROXYAPATITE ALUMINA COMPOSITES AND BONE-BONDING

Hydroxyapatite-alumina (HA/Al2O3) composites, with HA contents of 15, 25, 30 and 70, and pure HA as well as pure Al2O3, were densified at 12 75 degrees C at a top pressure of 200 MPa for 2 h, using glass-encapsu lated hot isostatic pressing. From the sintered ceramics, cylinders 2. 8 x 6 mm(2) were prepared by ultrasonic machining and implanted into t he femoral cortical bones of 12 New Zealand White rabbits for 3 months . After killing the animals, the femur was dissected out and cut into three sections, each containing one cylinder. The specimens were mount ed in a push-out device and force was applied along the long axis of t he cylinder. The maximum force required to loosen the implant was reco rded and the fracture surface of the bone implant was studied by scann ing electron microscopy (SEM). The results indicate the important role of HA in new bone apposition to the implants, reflected by increasing bonding strength with increasing HA content in the composites. Howeve r, the relationship between HA content and the bonding strength was no t linear. The composite with 70% HA and the pure HA ceramic had the sa me level of bonding strength and similar fracture interfaces in SEM, w hich supports the high bonding strength detected (about 15 MPa). Fract ures occurred both in the bone and in the implant, indicating the stre ss transfer ability of the contact zone. This study presents qualitati vely and quantitatively HA-dependent characteristics in bone-bonding. The mechanical strength of the composites was measured by a three-poin t bending test. The bending strength of the materials decreases with i ncreasing HA content.