Tuning the specific surface area of pure monophasic hydroxyapatite nanoparticles synthesized by sol-gel method using a capillary-based microfluidic process

The surfactant-free sol-gel synthesis of hydroxyapatite nanoparticles was adapted for in-flow production using a capillary-based microfluidic device. Different parameters have been investigated, including the capillary arrangements (core-shell and side-by-side), the capillary diameter, and the flow rate of the precursor solutions. The nanoparticles synthesized were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and specific surface area measurement according to the Brunauer-Emmett-Teller (BET) theory. The results were compared with those of hydroxyapatite nanoparticles obtained by the conventional batch sol-gel synthesis method. The morphology of the nanoparticles changed due to the use of different capillary arrangements and thus exhibited a higher specific surface area than the batch process. The highest specific surface area was observed when using a side-by-side arrangement using a capillary with an internal diameter of 100 μm and a flow rate of 100 μL/min reaching an increase of the specific surface area by two-fold (61 m 2 /g) as compared to the conventional batch sol-gel method (29 m 2 /g) without affecting any of their other properties including cell viability. • No surfactant was used to synthesize hydroxyapatite nanoparticles. • The specific surface area was higher by microfluidics as compared to the batch mode (29 m 2 /g). • The side-by-side capillary arrangement led to the more promising results (61 m 2 /g).