| Abstract Scope |
Hydroxyapatite (HAP) is a structurally versatile biomineral with widespread use in biomedical coatings, composites, and dental materials. Its functional properties depend strongly on surface chemistry and local ion environments, which are influenced by morphology and crystallographic orientation. Here, we use multinuclear solid-state NMR—including ¹H, ¹⁹F, and ⁴³Ca MAS and 3QMAS—to investigate HAP nanoparticles synthesized with controlled shapes: nanorods, nanosheets, and nanowires. ⁴³Ca MAS and 3QMAS reveal site-specific isotropic chemical shifts and quadrupolar parameters for the Ca(I) and Ca(II) sites, showing distinct differences across morphologies. ¹H–⁴³Ca TRAPDOR confirms spatial proximity between protons and calcium, enabling assignment of surface-associated hydroxyls. Fluoride uptake behavior, monitored by ¹⁹F and ¹H NMR, varies with particle shape and is linked to defect hydroxyl populations. This study provides atomic-level insights into the structure–function relationship at bio-nano interfaces, with implications for the design of bioactive materials and targeted surface modifications. |