A review on biowaste-derived hydroxyapatite composites: materials, synthesis and 3D printing fabrication methods

This review critically evaluates recent advancements in the valorization of biowaste for the synthesis of hydroxyapatite (HA), a biocompatible calcium phosphate widely employed in dental, orthopaedic, and bone-regeneration applications. Emphasis is placed on the influence of key synthesis routes on the resulting structural and physicochemical characteristics of HA, including chemical precipitation, hydrothermal processing, mechanochemical methods, and calcination. Comparative analysis highlights the distinct advantages of naturally derived HA over fully synthetic counterparts, particularly its trace ion composition and structural similarity to human bone. The integration of additive manufacturing technologies such as stereolithography (SLA), selective laser sintering (SLS), fused deposition modeling (FDM), direct ink writing (DIW), binder jetting (BJ) and digital light processing (DLP) enables precise fabrication of patient-specific HA scaffolds with tailored porosity and mechanical properties. Reported mechanical performances of 3D printed HA structures range from compressive strengths of 1.6–170 MPa, porosities level of 25–96 %, and elastic moduli of 10 MPa-10 GPa, reflecting variability across additive manufacturing modalities. Additionally, debinding and sintering processes, and the use of sintering aids are also assessed for their role in optimizing densification, phase stability, and bioactivity. Overall, the valorization of biowaste into HA through environmentally sustainable synthesis combined with advanced manufacturing presents a promising pathway for reducing waste streams, decreasing reliance on synthetic precursors, and enabling scalable, cost-effective production of next generation biomaterials for regenerative medicine. © 2025 The Authors.