Bone bonding in sintered hydroxyapatite combined with a new synthesized agent, TAK-778

We studied the stimulatory effects of TAK-778, a new synthetic 3-benzothiepin derivative that promotes osteoblast differentiation, in bone bonding to sintered hydroxyapatite implants in rabbit tibiae. Smooth-surfaced rectangular plates (15 x 10 x 2 mm) made of sintered hydroxyapatite were implanted into the proximal metaphyses of bilateral rabbit tibiae, with TAK-778-containing sustained-release microcapsules packed into the medullary cavity in one limb and untreated microcapsules packed in the contralateral limb to serve as a paired control. At 4, 8, and 16 weeks after implantation, bone bonding at the bone-implant interfaces was evaluated by a detaching test and undecalcified histological examination. The tensile failure load increased from 4 to 16 weeks for both groups; however, the tensile failure load of the TAK-778-treated group was significantly greater than that of the control group at each interval after implantation. Histologically, the TAK-778-treated specimens showed greater active new bone formation mainly in the medullary cavity and more extensive bonding between the implant and bone than the untreated specimens. The results of this study suggest that adding osteoinductive TAK-778 to hydroxyapatite implants may significantly accelerate bone apposition to the implants and improve the bonding process at the interface. This would help to establish an earlier and stronger bonding of orthopedic ceramic implants between the surrounding bone tissue.