Osteoinduction with HA/TCP Ceramics of Different Composition and Porous Structure in Rabbits

To determine the effect of material factors on Ca-P biomaterial-induced osteogenesis, six kinds of biphasic calcium phosphate (BCP) ceramics with different HA to TCP ratio (HA/TCP 2-8, 7-3) and different porous structure (micro-, macro- and micro/macro- porous structures) were implanted intramuscularly in rabbits. Different tissue response was detected histologically and microradiographically after the ceramic samples were implanted in the dorsal muscles of rabbits for 3 and 6 months. Obvious bone formation was found in two kinds of ceramics with the same micro/macro- porous structure at both 3 and 6 months. In contrast, no bone formation or host tissue invasion was detected in two other kinds of ceramics with only microporous structure, even after 6 months implantation. Some bone formation was found occasionally in two kinds of ceramics with only macro-porous structure at 6 months. Bone tissue was usually formed in direct contact with the pore surface and was only located in non-dissolved porous regions. Osteocyte lacunae were seen and no pathological calcifications were observed. These results indicate that micro- and macro-porous structure play an important role in the osteoinduction with Ca-P ceramics. Furthermore, the results showed that the osteoinductive capacity of BCP ceramics was influenced by the different dissolution rate through changing HA/TCP ratio.