Synopsis
Previously we have shown that honeycomb-shaped hydroxyapatite ceramics (HC-HAP) of different tunnel sizes control the formation bone and cartilage when implanted into rat skin with bone morpho-genetic protein (BMP). The HC-HAP of larger tunnel size (300-400µm) induced bone directly, while the smaller size (90-110µm) induced endochondral ossification. Concerning this interesting tendency of bone-cartilage biphasic phenomena that was observed in hydroxyapatite ceramics, we wanted to know whether the same phenomena occur in β-tri-calcium phosphate (β-TCP) ceramics. We prepared honey-comb-shaped β-TCP ceramics (HC-β-TCP) of disk type with three-different tunnel sizes, 300, 75 and 50µm, having tunnel numbers of 37, 568 and 907 per ceramic, respectively within a cross-section of 3.1µm disk diameter. When implanted into rats subcutaneously with BMP-2, HC-β-TCP of three different tunnel diameters all induced active bone tissue formation, with the highest ALP value in HC-β-TCP with tunnel diameter of 75µm. Interestingly, an appreciable amount of cartilage formation was observed only in the early stage of implantation of the HC-β-TCP with a tunnel size of 50µn;m, but not with ones of 75µm, and as expected, of 300µm. The results were essentially similar to ones obtained using hydroxyapatite with tunnel sizes of 90-110µm, in which clear endochondral processes were observed. We hypothesized that the slightly different tendency may be attributed mainly to the chemical properties of the two ceramics: hydroxyapatite is non-biodegradable, while β-TCP is a biodegradable ceramic.
Key words: HC-β-TCP, artificial ECM, geometry, hydroxyapatite, chondrogenesis, osteogenesis
