Tensile tests of interface between bone and plasma-sprayed HA coating-titanium implant.

Tensile strength testing of the interface between bone and a plasma-sprayed hydroxyapatite (HA) coating-Ti-6Al-4V (implant I) and an HA coating-Ti (implant II) was performed. The bone-implant interface and tensile failure mode were evaluated by light microscopy (LM), SEM-energy dispersive X-ray analysis, and backscattered electron imaging. The crystallinity of the HA coating of implant I and implant II was 62 and 40%, respectively. Eleven semidisk implants of each type were inserted in the left tibia of 22 rabbits in each period. After 2, 4, 8, and 16 weeks, the tensile strength of the bone-implant I was 0.86, 1.32, 1.10, and 0.92 MPa, respectively; the value of the bone-implant II was 0.66, 0.92, 0.84, and 1.12 MPa, respectively. No significant difference was found in tensile strength between implant I and implant II, and between the data of different periods. LM and SEM revealed that the two types of coatings behave the same in bone. Failure after the tensile test mainly occurred at the bony tissue at 2 and 4 weeks, inside the HA coating layer at 8 weeks, and at the HA coating-metal substrate interface at 16 weeks. Degradation and delamination of the HA coating continued with time, resulting in the interfacial tensile strength not increasing with time. Thus, we concluded that differences between the two implants, mainly the difference in crystallinity of the HA coating (62 vs. 40%), have no significant influence on bone bonding ability, bone bonding strength, tensile failure mode, and degradation of the coating.