3D-Printed Bone Spacers with Dual-Phase Structure: A Comparison of Biogenic and Commercial Hydroxyapatite for Potential Treatment of Bone Defects

Biogenic hydroxyapatite (Bio-HAp) derived from fish scales was synthesized via an alkali heat treatment method and applied to fabricate dual-phase structured bone spacers using extrusion-based 3D printing. The printed spacers were designed with a dense outer shell and a porous inner core to balance mechanical integrity and internal porosity. A comparative evaluation was conducted between Bio-HAp and commercial hydroxyapatite (Co-HAp) bone spacers in terms of physicochemical characteristics, microstructure, mechanical performance, and in vitro cytocompatibility. FE-TEM analysis revealed that Bio-HAp particles exhibited nanoscale dimensions with mixed rod-like and irregular morphologies, while EDS confirmed a Ca/P ratio of 1.67, consistent with stoichiometric HAp. After sintering, Bio-HAp spacers demonstrated higher total porosity (∼51%) compared to Co-HAp spacers (∼44%), while both maintained comparable compressive strength and modulus within the reported range of human bone. XRD analysis confirmed the preservation of the HAp phase after sintering for both materials. In vitro cytotoxicity assessment using a live/dead assay with human chondrocyte progenitor cells (HCPCs) showed high cell viability (>96%) for both Bio-HAp and Co-HAp spacers over 7 days, indicating good cytocompatibility. Overall, the results demonstrate that fish scale-derived Bio-HAp is a viable alternative to Co-HAp for fabricating dual-phase ceramic bone spacers with suitable structural, mechanical, and biological properties for potential bone defect applications.