Formation of Bone-like Nanocrystalline Apatite Using Self-Assembled Liquid Crystals

A two-step process using liquid crystalline phases combined with controlled postcrystallization for the preparation of bone-like apatite has been developed. First, amorphous calcium phosphate (ACP) spherules with a diameter of 10.8 ± 1.4 nm and specific surface area (SSA) in the range of 150–170 m 2 /g were synthesized within a reverse hexagonal liquid crystalline (LC) phase. Second, the ACP spherules were dispersed and aged in Milli-Q water, where they crystallized into poorly crystalline apatite (PCA). The addition of heparin during aging was explored, which was shown to retard the ACP – PCA conversion. The particle formation within the LC phase was monitored using synchrotron small-angle X-ray scattering, and the formed materials were characterized by X-ray diffraction, conventional and high-resolution transmission electron microscopy, nitrogen adsorption, thermogravimetry with infrared-coupled analysis, and Raman spectroscopy. The PCA formed using the LC–aging route presented bone-resembling features, such as Ca 2+ and OH – deficiency, CO 3 2- substitution, poor crystallinity, and ultrahigh SSA of 356 m 2 /g. The resulting particles were compared to hydroxyapatite synthesized via a conventional water-based precipitation method. The LC–aging route exhibited excellent controllability over the CaP crystallization, which enabled facile tailoring of the resulting material properties for different types of application.