In vivo evaluations of hydroxyapatites with small and large grain sizes

The effect of grain size of hydroxyapatite on its osteoconductivity was newly investigated. The hydroxyapatite discs, which had small (specimen S) and large grain size (specimen L), were prepared through microwave sintering at 1100°C for 6 and 720 min, respectively. The average grain size of specimen S was about 15 times smaller than that of specimen L. The surface energy of specimen S was about 1.6 times higher than that of specimen L under the same surface roughness. For the osteoconductivity test, porous hydroxyapatite granules were prepared using PEG porogen. The osteoconductivity of specimen S was superior to that of specimen L four weeks after implantation in calvarial defects of New Zealand white rabbits. Taken together, it can be concluded that the hydroxyapatite with small grain size had a higher osteoconductivity compared with the hydroxyapatite with large grain size due to its high surface energy.