The effect of the microstructure of β-tricalcium phosphate on the metabolism of subsequently formed bone tissue

The response of bone cells to a newly developed porous β-tricalcium phosphate composed of rod-shaped particles (RSβ-TCP), β-TCP composed of conventional non-rod-shaped particles (Cβ-TCP), and hydroxyapatite (HA) was analyzed using in vivo implantation and in vitro osteoclastogenesis systems. Implantation of the materials into the rabbit femur showed that RSβ-TCP and Cβ-TCP were bioresorbable, but HA was not. Up to 12 weeks after the implantation, bioresorption of RSβ-TCP and Cβ-TCP accompanied by the formation of new bone occurred satisfactorily. At 24 weeks post-implantation, most of the RSβ-TCP had been absorbed, and active osteogenesis was preserved in the region. However, in the specimens implanted with Cβ-TCP, the amount of not only the implanted Cβ-TCP but also the newly formed bone tissue decreased, and bone marrow dominated the region. The implanted HA was unbioresorbable throughout the experimental period. When osteoclasts were generated on RSβ-TCP, Cβ-TCP, or HA disks, apparent resorption lacunae were formed on the RSβ-TCP and Cβ-TCP, but not HA disks. Quantitation of the calcium concentration in the culture media showed an earlier and more constant release of calcium from RSβ-TCP than Cβ-TCP. These results showed that the microstructure of β-TCP affects the activity of bone cells and subsequent bone replacement.