Physicochemical Characterisation and Calcium Release Behaviour of Fish-Scale-Derived Hydroxyapatite Nanomaterials

Fish scales are a calcium-rich biogenic waste source for hydroxyapatite (HAp), but the influence of processing route on material characteristics and calcium-release behaviour remains insufficiently understood. This study compared fish-scale-derived HAp produced by calcination and wet-chemical processing. Pretreated fish scales were processed by calcination at 1200 °C (cnHAp) or acid-assisted ultrasonic extraction followed by alkaline precipitation (wnHAp). The materials were characterised using Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy–energy-dispersive X-ray spectroscopy and high-resolution transmission electron microscopy. Calcium concentrations were measured by inductively coupled plasma optical emission spectrometry at 0, 24 and 72 h and analysed using two-way mixed-design repeated-measures analysis of variance. Both materials exhibited characteristic HAp functional groups and diffraction features but differed in crystallographic ordering and morphology. cnHAp showed greater crystallographic ordering and a smaller mean particle size (42.41 ± 12.45 nm) than wnHAp (181.09 ± 48.58 nm), with Ca/P atomic ratios of 1.87 and 1.57, respectively. Calcium concentration differed significantly by processing group, time and their interaction (all p < 0.001), with cnHAp consistently showing higher concentrations. Processing route substantially influenced the physicochemical characteristics and temporal calcium-release behaviour of fish-scale-derived HAp.