Synthesis of calcium phosphate nanoparticles in a droplets-based microfluidic device

Calcium phosphates (CaP) biomaterials are one of the commonly used synthetic bone graft alternatives, due to their chemical resemblance to the mineral bone component. Nanoparticles of CaP and especially hydroxyapatite (HAp) ,which represents one of the most thermodynamically stable calcium phosphate materials, were synthesized using a custom-designed 3D-printed microfluidic device, enabling the continuous-flow synthesis with precise control over size and uniformity. HAp were synthesized using calcium chloride and disodium phosphate with a starting molar ratio (Ca/P) of 1.67. By optimizing the CaCk concentrations, particle sizes were effectively reduced, achieving uniform and dispersible nanoparticles with sizes as small as 41.5 nm for a concentration of 0.01 M. Characterization included FT-IR analysis, confirming the presence of phosphate and carbonate groups, SEM imaging revealing spherical morphologies, and X-ray diffraction highlighting good crystallinity. DLS and Zeta potential measurements demonstrated homogeneous size distribution. The synthesized nanoparticles demonstrated effective fluoride adsorption, with an adsorption capacity of 63 mg/g, and efficiency of 83%. Adsorption isotherms fitted the Langmuir model, and thermodynamic study indicated a slightly endothermic and non-spontaneous process.