Morphosynthesis of Zn-Substituted Stoichiometric and Carbonate Hydroxyapatite Nanoparticles and Their Cytotoxicity in Fibroblasts

Hydroxyapatite (Ca₁₀(PO₄)₃(OH)₂) (HAp) is crystallographically and chemically similar to the human hard tissues and has been widely researched. The naturally formed HAp has some impurities of some ions, which provides the biocompatibility as well as the nanosized morphologies in the tissues. In this study, the morphosynthesis of zinc-substituted stoichiometric and carbonate hydroxyapatite (Zn:HAp and Zn:CAp) nanoparticles was investigated from the reagents of CaCl₂, ZnCl₂, and K₂HPO₄. The initial (Ca + Zn)/P ratios of 1.67 and 2.00 were adjusted by the initial ZnCl₂ amount at the Zn/(Ca + Zn) concentration of 0.0-10 mol%. The crystalline sizes of the nanoparticles decreased with increasing the Zn ion amount, suggesting that the Zn substitution significantly suppressed the crystal growth. TEM images of the nanoparticles indicated that all the crystalline sizes are less than 100 nm and the needle-like shapes were significantly changed to spherical shapes with increasing the Zn ion substitution to resultantly exhibit the higher surface areas as well as the nanoparticle aggregation states. Furthermore, all the nanoparticle films electrically plated on a silicone substrate give no cytotoxicity, and the Zn:CAp nanoparticle films significantly provided the bioactive properties for fibroblast ingrowth, suggesting the effect of Zn and carbonate ions on the cytocompatibility.