Precipitation of hydroxyapatite nanoparticles in 3D-printed reactors

Abstract

We combine a wet chemical precipitation method and 3D-printing technology in the design of a process for the continuous production of hydroxyapatite nanoparticles (10–30 nm). Our goal was to create a simple technology for the precipitation of hydroxyapatite (HAp) with properties mimicking natural bone. To influence HAp precipitation and to obtain nanosized particles, an additive of nontoxic surfactant lecithin (LE) was applied. HAp-LE particles were produced in two Y-shaped continuous reactors of different lengths, operating at atmospheric pressure and room temperature. The products obtained were characterized in terms of their crystal structure (XRD), chemical composition (FTIR), morphology of nanoparticles (SEM) and particle size distribution (DLS, NTA). A new application of chemical oxygen demand (COD) analysis was proposed to determine the quantity of lecithin in HAp-LE powders. For both reactors, process parameters such as the concentration of lecithin and the aging conditions of the product were investigated. We obtained carbonated HAp with a spherical shape, and found that the aging temperature has the most significant influence on the properties of HAp-LE (crystallinity, crystallite size, and particle size). The influence of lecithin concentration on the particle size is non-monotonic. The obtained HAp-LE exhibits properties similar to those of natural hydroxyapatite.