In Vivo Inspired Conditions to Synthesize Biomimetic Hydroxyapatite

We present a simple one-pot crystallization method, inspired by biological conditions, for the synthesis of hydroxyapatite (Ca-5(PO4)(3)OH) nanocrystals. The reaction proceeds via NH3 vapor diffusion into a CaCl2-NaH2PO4 mixed solution that is free of any organic additives. The advantage of relying on acidic calcium-phosphate precursors here is, first, that the reaction can be performed at room temperature within a short time and without direct pH control and, second, that it does not produce any secondary phases or byproduct. Furthermore, the addition of NaHCO3 to the salt solution or the introduction of (NH4)(2)CO3 instead of NH3 lead, respectively, to the precipitation of B- or A-type carbonate-apatite phases according to the FT-IR data. Multinuclear solid state NMR studies and especially (CCP)-C-13 experiments allow an in-depth characterization showing the presence of A/B substitutions in carbonated samples as well and indicate a close similarity to deproteinated bovine compact bone. A precipitation mechanism accounting for the precipitation of mainly A- or B-type carbonated apatite under the respective experimental conditions is proposed.