The slow resorption with replacement by bone of a hydrothermally synthesized pure calcium-deficient hydroxyapatite.

A newly developed calcium-deficient hydroxyapatite composed of rod-shaped particles synthesized by the hydrothermal method (HHA) and stoichiometric hydroxyapatite (SHA) synthesized by the sintering method was used for in vivo implantation and in vitro culture systems to compare these biological responses. In the rabbit femur, implanted HHA was slowly resorbed and about 80% of the implant remained 24 weeks after implantation; however, up to 72 weeks after implantation, most of the implanted HHA was resorbed. The implanted SHA was unresorbed throughout the experimental period, but degradation by the invasion of newly formed bone was seen at 72 weeks after implantation. Bone histomorphometry showed that the volume of newly formed bone and the number of osteoclasts in the implanted region were significantly higher in HHA than in SHA 24 weeks after implantation. In vitro culture of C2C12 cells with the induction of osteoblastic phenotypes using recombinant bone morphogenetic protein-2 showed similar cell density and the induction of alkaline phosphatase activity between the cells on HHA and SHA discs. In vitro osteoclastogenesis of HHA and SHA discs using bone marrow macrophages and recombinant receptor activator of nuclear factor-kappaB ligand showed higher TRAP activity of osteoclasts cultured on HHA discs. These results showed that slow biodegradability did not always correlate to final replaceability in bone tissue, and suggested that the activity of osteoclasts correlated to the bone-forming activity of osteoblasts.

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

The response of bone cells to a newly developed porous beta-tricalcium phosphate composed of rod-shaped particles (RSbeta-TCP), beta-TCP composed of conventional non-rod-shaped particles (Cbeta-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 RSbeta-TCP and Cbeta-TCP were bioresorbable, but HA was not. Up to 12 weeks after the implantation, bioresorption of RSbeta-TCP and Cbeta-TCP accompanied by the formation of new bone occurred satisfactorily. At 24 weeks post-implantation, most of the RSbeta-TCP had been absorbed, and active osteogenesis was preserved in the region. However, in the specimens implanted with Cbeta-TCP, the amount of not only the implanted Cbeta-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 RSbeta-TCP, Cbeta-TCP, or HA disks, apparent resorption lacunae were formed on the RSbeta-TCP and Cbeta-TCP, but not HA disks. Quantitation of the calcium concentration in the culture media showed an earlier and more constant release of calcium from RSbeta-TCP than Cbeta-TCP. These results showed that the microstructure of beta-TCP affects the activity of bone cells and subsequent bone replacement.

Osteoblast proliferation behavior and bone formation on and in CO3apatite-collagen sponges with a porous hydroxyapatite frame.

To develop a new biodegradable scaffold biomaterial reinforced with a frame, synthesized CO3apatite (CO3Ap) was mixed with a neutralized collagen gel. Then, 0 and 70% (w/w) CO3Ap-collagen mixtures (70% CO3Ap weight/mixture weight) were lyophilized into sponges in a HAp frame ring with 0.5-mm pores. SEM observation of CO3Ap-collagen sponges showed favorable pores for cells invasion. Mouse osteoblast MC3T3-E1 cells were cultured in alphaMEM with 10% FCS for 1, 10 and 20 days. Matrix substances on the pure collagen sponge samples increased with the culture period such that the sponge surface was almost covered. A sectional view of hematoxylin-eosin staining confirmed that osteoblast cells had well invaded the CO3Ap-collagen sponge. When these sponge-frame complexes were implanted beneath the periosteum cranii of rats, newly created bone was observed to grow toward the inner core of the complex from the surface of the periosteum cranii. Based on these results, reinforced CO3Ap-collagen sponges are expected to be used as hard tissue scaffold biomaterials for therapeutic purposes.