Effects of organic modifiers and temperature on the synthesis of biomimetic carbonated hydroxyapatite

Carbonated hydroxyapatite (CHA) was synthesized through a precipitation method using different organic modifiers namely citric acid, acetic acid, glutamic acid and gallic acid. These organic modifiers were used in order to control the nucleation of the synthesis process and crystallinity of the particles. Field Emission Scanning Electron Microscopy (FESEM) and Transmission Emission Microscopy (TEM) data showed that among the samples, CHA produced in the presence of citric acid was the smallest with rod shape (19-25 nm) whereas, in the presence of gallic acid CHA particles became largest with flake shape (127-143 nm). Citric acid controlled nucleation by inhibiting crystal growth along a axis whereas, glutamic acid influenced nucleation through inhibition along c axis both resulting in rod shaped particles. Acetic acid also hindered crystal growth, however, to a lesser extent and the particles were flake shaped. CHA particles synthesized with gallic acid connected with each other due to pi-pi stacking interaction producing the largest particles. The synthesized particles were poorly crystallized with crystallinity ranging from 18.5% to 30%. Fourier Transform Infrared Spectroscopy (FTIR) results confirmed that all the samples were carbonated hydroxyapatite and from Energy Dispersive X-Ray (EDX) it was confirmed that the Ca/P ratio of the samples was around 1.7 indicating non-stoichiometric CHA. It was also found that with the increase in temperature, both the particle size and crystallinity increased.