Preparation and characterization of highly crystalline hydroxyapatite (HAp) from the scales of an anadromous fish (): a comparative study with the freshwater fish scale () derived HAp.

Waste generation from fish processing sectors has become a significant environmental concern. This issue is exacerbated in countries with high aquaculture production and inefficient fish scale (FS) utilization. This study prepared and compared highly crystalline hydroxyapatite (HAp) from the FS of an anadromous fish, (I-HAp), and a freshwater fish, (R-HAp). Acid-alkali treatment followed by high-temperature calcination was employed for HAp synthesis. XRD analysis indicated a monoclinic crystal structure for I-HAp and a hexagonal structure for R-HAp, with both containing β-TCP as a secondary phase. Rietveld refinement quantified β-TCP at 8% for I-HAp and 7.2% for R-HAp. Crystallite size of the samples was estimated by various methods (Scherrer's method, Scherrer equation average method, linear straight-line method, straight line passing the origin method, Monshi-Scherrer method, Halder-Wagner method, Williamson-Hall method, and size-strain plot method), consistently indicating microcrystalline HAp. FESEM and TEM analyses revealed larger particle sizes for I-HAp, confirmed by DLS measurements. Surface elemental analysis by XPS confirmed the presence of Na and Mg as impurities along with the elements of the HAp structure. FTIR and Raman spectroscopy identified expected functional groups, while EDX determined elemental composition. Both HAp samples exhibited bioactivity through apatite layer formation in simulated body fluid. Furthermore, the combined results of the cell viability and hemocompatibility studies indicate the biocompatibility of the prepared samples.