Comparative structural refinement of nanocrystalline hydroxyapatite

[Display omitted] •A comparative structural refinement of nanocrystalline HA was performed.•Rietveld refinement confirmed the dependence of structural properties on preparation method.•The smallest anisotropic crystallite sizes were recorded in the 7h MS specimen.•TEM images corroborated the single-crystal feature of the 7h MS specimen.•MS HA holds great promise as an effective medical strategy for treating bone cavities. An attempt was made to make a comparative structural refinement of nanocrystalline HA between the mechano-synthesis (MS), ultrasonic-assisted precipitation (UP), biogenic-based process (BP), and commercial grade (CG). Rietveld refinement of XRD patterns illustrated the main characteristic peaks of hexagonal HA. The anisotropic crystallite sizes were observed, where the smallest crystallite sizes of D〈001〉 (24.5 ± 3.1 nm) and D〈100〉 (17.7 ± 1.1 nm) were recorded in the 7h MS specimen. On the contrary, the highest D〈001〉/D〈100〉 ratio of 7.68 was achieved for the UP HA, showing HA crystals preferentially grew in the c-axis direction. The narrow particle size distribution of the 7h MS specimen, with an average diameter of 9 ± 2 nm, was smaller than the crystallite size estimated from the refined XRD pattern, indicating the single-crystal feature. Overall, MS HA holds great promise as an effective medical strategy for treating bone cavities.