Effect of citric acid on the nucleation of hydroxyapatite in a simulated body fluid.

The role of citric acid in a simulated body fluid (SBF) was examined with the main focus on its induction ability of hydroxyapatite (HAp) nucleation on a bioinert collagen membrane. Collagen membranes were soaked in the SBF with citric acid concentrations in the range of 0-4 mM; then, carbonate-containing HAp crystals grew within a limited range, i.e., 0.3-2 mM. The results were explained in terms of chemical interaction among calcium ion, citric acid and collagen membrane, especially strong chelation ability of citric acid with the calcium ion.