In vivo study on biocompatibility and bonding strength of Ti/Ti-20 vol.% HA/Ti-40 vol.% HA functionally graded biomaterial with bone tissues in the rabbit

Ti/Ti-20 vol.% HA/Ti-40 vol.% HA functionally graded biomaterial (FGM) was fabricated by a hot-pressing technique. Then the comprehensive biocompatibility and bonding strength of the FGM with bone tissues in the rabbit were systematically investigated by in vivo studies in comparison with those of Ti metal. The microstructure of sintered FGM varied gradually from Ti side to Ti-40 vol.% HA side with a graded distribution of each element. There are some fibrous tissues existing at the interface between Ti implant and newborn bones at 4 weeks in vivo. Contrarily new bone tissues can contact directly with Ti-40 vol.% HA graded layer in the FGM at or after 4 weeks in vivo. At 8 weeks, the bonding interfaces between Ti-40 vol.% HA graded layer in the FGM and new bones cannot already be distinguished and the FGM was osseointegrated fully with bone tissues into one bony body. During all implanting periods, the increasing rate of bonding strength for the FGM is higher than that of pure Ti. At 3 months in vivo, the shear fracture for Ti-40 vol.% HA graded layer in the FGM implants occurred in new bone tissues zones near the interface between the FGM implants and bones tissues. The bonding strength of the FGM implants could even exceed the shear strength of new bone tissues (4.73 MPa). Obviously the FGM has better biocompatibility and osseointegration abilities than Ti metal, especially during the early stage after the implantation, which can be due to the existence of the graded layers mixed by HA and Ti. Therefore, it is a promising biomaterial for hard tissue replacement.