Defect-engineered biphasic calcium phosphate scaffolds from Nile tilapia bone: Calcination-controlled phase evolution and structure–bioactivity coupling

Porous biphasic calcium phosphate (BCP) scaffolds were fabricated from Nile tilapia bone waste via microwave-assisted processing. The extracted powders were subsequently calcined at 500–1000 °C to tailor precursor characteristics, phase evolution, and defect chemistry. Increasing calcination temperature promoted particle coarsening and carbonate removal. Below 700 °C, single-phase hydroxyapatite (HAp) was retained. At ≥ 700 °C, HAp/β-tricalcium phosphate (β-TCP) compositions emerged, with β-TCP content increasing from 7.6 % to 16.9 %. Scaffolds fabricated via polyurethane sponge replication and sintered at 1250 °C exhibited highly interconnected porous architectures with porosities ranging from 77.5 % to 89 %. Carbonate-rich precursors promoted shrinkage, microcracking, and finer pore fractions, whereas higher-temperature calcined powders yielded crack-free scaffolds with improved structural stability. Sintering further increased β-TCP content (15–24.4 %) and promoted dehydroxylation, as confirmed by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), indicating the formation of OH − vacancies. In vitro evaluation revealed that scaffolds calcined at 500 °C exhibited the highest direct cell proliferation due to a favorable micropore fraction, while those calcined at 1000 °C demonstrated superior bioactivity attributed to the greatest OH − vacancy concentration (ΔOH − = 10.77 %). These findings establish calcination temperature as a critical processing parameter governing phase evolution, defect chemistry, and biological performance in sustainable biowaste-derived BCP scaffolds.