Physicochemical and microstructural properties of porous Zn-doped hydroxyapatite ceramics: cell behavior on their surfaces

Porous hydroxyapatite (HAp) ceramics with macropores of more than 200 μm were fabricated via our new method comprising chemical synthesis and heat treatment. In this study, four types of porous Zn-doped HAp ceramics were produced by adding 0.1, 0.5, 1.0 and 5.0 g of zinc acetate dehydrate to 50 g of a HAp nanoparticle slurry during chemical synthesis and then calcining the mixtures at 1200 °C. Three samples fabricated by adding 0.5, 1.0 and 5.0 g of zinc acetate dehydrate showed a ZnO phase as a byproduct. In contrast, the sample fabricated by adding 0.1 g of zinc acetate dehydrate did not show it. As the additive amounts of Zn ions increased, lattice parameters a and c of the HAp phase increased. By inserting Zn ions into OH channels within HAp lattices, the hydroxyl groups within them decreased, and consequently, the lattice parameter c increased by forming linear O—Zn—O units within them. On the other hand, the lattice parameter a increased because the HAp lattices were disordered owing to the insertion of Zn ions. Moreover, upon examining the cell behavior of our samples, the cells adhered well to and spread widely on the sample without the ZnO phase, similar to porous undoped HAp ceramics 48 h after cell culture. Namely, Zn ions that were themselves inserted into the HAp lattice did not significantly influence cell adhesion. In contrast, the number of adhering cells on the samples with the ZnO phase decreased compared to that without it.