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We propose a scaled-up reactor for the synthesis of hydroxyapatite nanoparticles (nHAp) applicable for lecithin-modified precipitation. A novel 3D-printed BOX reactor allowed, confirmed by computational fluid dynamics analyses, maintaining or improving the hydrodynamic conditions corresponding to the conditions within single-channel millireactors described in our previous work. As confirmed by X-ray diffraction analysis, we obtained hydroxyapatites. Fourier-transform infrared spectroscopy showed the same characteristic functional groups in powders from single-channel millireactors and BOX reactors. Scanning transmission electron microscopy showed that regardless of lecithin modification, the hydroxyapatite powders from the BOX reactor have particles of the same size as those from the single-channel millireactors; the particle size does not exceed 30 nm. Moreover, nanoparticle tracking analysis and dynamic light scattering show that regardless of the selected reactor and the presence of surface modification, particles tend to agglomerate, which we confirmed in zeta potential measurements. The nHAp’ chemical and physical properties and the lecithin-modified nHAp obtained in the BOX reactor do not depend significantly on the reactants’ flow rate, so it is possible to obtain particles with a precipitate suspension productivity of up to 150 g/h. The presented method of hydroxyapatite wet precipitation scale-up is a step toward stable and efficient production of a restorative material for medical and dental applications.

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Control of the morphology and size of particles in processes like crystallization and precipitation remains challenging. We present the simple process of precipitation and controlled hydroxyapatite nanoparticles remodeling into the plate and rod-like morphologies. The precipitation/remodeling process assumes that the temperature and pH change of the remodeling step affect the properties of the resulting particles. The morphology and size of the nanoparticles were determined with scanning electron microscopy images. The functional groups were determined using Fourier Transform Infrared Spectroscopy, while the phase composition and crystallite size in x-ray diffraction experiments. Zeta potential measurements confirmed that particle morphology affects their stability in the aqueous suspensions. The results demonstrated the production of hydroxyapatite nanoparticles as aggregates of crystallites, in which particle morphology depends on remodeling temperature while their size on the remodeling time. Further, the process with lecithin added to modify particles' surfaces to enhance their biocompatibility maintains controllability over hydroxyapatite nanoparticles' morphologies.