Addition of Citric Acid to Hydroxyapatite Slurry for Stable Dispersion of Nanoparticles

抄録

Due to its excellent biocompatibility, hydroxyapatite is used as an implant material. Synthesis of highly dispersed hydroxyapatite nanoparticles is demanded because the properties of sintered hydroxyapatite scaffolds depend on the dispersibility of nanoparticles as raw material. We examined the effect of citric acid addition in hydroxyapatite slurry synthesized from Ca(NO₃)₂, NH₄H₂PO₄ and tris-hydroxymethyl aminomethane (tris), while the citric acid is conventionally added in the solution from the beginning of apatite synthesis. Tris was used as base to precipitate hydroxyapatite, and immediately afterwards, citric acid was added to adjust the pH of the hydroxyapatite slurries. Citric acid was also selected as the dispersant and stabilizer for the hydroxyapatite slurries. The addition of citric acid to the slurry conferred a negative charge to the hydroxyapatite surface, which increased the absolute value of zeta potential of the particles. The zeta potential of particles in a pH 8.6 slurry was -24.6 mV, which prevented their agglomeration and sedimentation. Thus, the adsorption of citric acid effectively dispersed the hydroxyapatite particles. The hydrodynamic diameter of the particles decreased as the pH of the slurry decreased by the addition of citric acid.