Preparation of nanohydroxyapatite with diverse morphologies and optimization of its effective aqueous colloidal dispersions for biomedical applications

Hydroxyapatite (HAp) is a bioactive and important material for medical applications. Therefore, search for new possibilities in combining hydroxyapatite with other compounds opens a promising path for creating innovative biomaterials. For this purpose, the preparation of effective aqueous colloidal dispersions based on nanohydroxyapatite (nHAp) of varying degrees of crystallinity and morphology was investigated. Nanohydroxyapatite was prepared by co-precipitation with post-processed freeze-drying, hot-air drying, sintering, and hydrothermal synthesis with tri-sodium citrate. The prepared nanosized powders were analyzed by using X-ray powder diffraction, scanning, and transmission electron microscopy techniques. The influence of post-processing techniques, such as lyophilization, freezing, hot-air drying, and sintering, on the crystallinity and morphology of prepared nanohydroxyapatite suspensions was investigated. Aqueous nanohydroxyapatite colloidal dispersions were prepared using deionized water and tri-sodium citrate solution (0.01% wt.) with an ultrasonic homogenizer. The study demonstrated that the most effective aqueous colloidal dispersion of nHAp (stable for at least 14 days) can only be obtained using a tri-sodium citrate solution together with freeze-drying. When the material shows higher crystallinity and a more clearly rod-like shape, even tri-sodium citrate does not help maintain the stability of the colloids for a long time. These findings are significant for future investigation involving the preparation of new materials based on nHAp, such as hydrogels, membranes, scaffolds, cement, and composites for biomedical applications. They can be applied in theranostics and drug delivery systems.