Additive manufacturing enabled, micro architected, hierarchically porous nHA/Mg (OH)₂ nano composite scaffolds for bone recovery applications

Scaffold architecture, infill density, and material composition critically influence the mechanical, structural, and biological performance of bone tissue engineering scaffolds. In this study, nano-hydroxyapatite (nHA) reinforced photopolymer scaffolds incorporating magnesium hydroxide (Mg (OH)₂) were fabricated via digital light processing (DLP). Diamond, Gyroid, and Primitive lattice geometries were designed using pure and composite resins with varying infill densities (35%, 40%, and 45%) and nHA contents (2.5%, 5%, and 7.5%). Physicochemical properties were characterized by SEM, FTIR, and XRD, while Micro-CT evaluated porosity and pore interconnectivity. Mechanical behavior was assessed through uniaxial compression testing, bioactivity through simulated body fluid (SBF) immersion, and antibacterial activity using the agar disc diffusion method. Micro-CT confirmed highly interconnected porous networks, with structural parameters strongly influenced by lattice type and infill density. Increasing the infill density from 35% to 45% significantly improved compressive strength across all architectures, confirming the dominant role of relative density in load-bearing performance. Three-way ANOVA showed that scaffold structure, density, and nHA content all had significant effects on compressive strength, with structure and density exerting the strongest influence. Diamond scaffolds exhibited the highest compressive strength, reaching approximately 11–12 MPa at 45% infill. The incorporation of nHA had a non-monotonic effect on mechanical performance, with 5 wt% nHA yielding the highest compressive strength across all scaffold architectures and infill densities (2.63–11.62 MPa), whereas increasing the nHA content to 7.5 wt% reduced the compressive strength to 2.17–8.49 MPa across all scaffold architectures and infill densities. SBF immersion demonstrated apatite formation, confirming bioactivity, while Mg(OH)₂ exhibited concentration dependent antibacterial activity in suspension under the tested conditions. Overall, optimized architecture and composition produced mechanically robust and bioactive scaffolds with potential antibacterial functionality associated with Mg(OH)₂ incorporation suitable for bone regeneration.