Achieving excellent biodegradability and bioactivity in spark plasma sintered porous hydroxyapatite composite scaffolds via modulating nano-MgO addition

Porous hydroxyapatite(HA)-based scaffolds have demonstrated limited clinical effectiveness in bone defect repair, primarily due to the functional mismatch between biodegradation and osteoconduction. Integrating therapeutic metal oxide nanoparticles into bioscaffolds is a widely recognized and effective strategy to address this challenge. In this study, series of nano-MgO/HA composite scaffolds were fabricated by combining a space-holder strategy with spark plasma sintering (SPS) technology under pressure less. The composition, structural characteristics, in vitro long-term biodegradability, bioactivity, biocompatibility and their interactions were systematically investigated. The results revealed that composite scaffolds primarily consisted of HA and MgO phases. Furthermore, due to the inhibitory effect of nano-MgO, the grains within the composite scaffold remain nanocrystalline, with sizes <100 nm. Upon the addition of nano-MgO, the pore characteristics were enhanced, with overall porosity ranging from approximately 49% to 56% and average pore sizes between 246 μm and 318 μm. Biodegradation tests conducted in Tris-HCl buffer solution demonstrated that the degradation rate of composite scaffolds increased to 32.79% in 12 weeks, compared to 4.14% for HA scaffold. Furthermore, in simulated body fluid (SBF), composite scaffolds exhibited a dramatically improved capacity for osteoapatite formation, with the weight gain rate increasing from 1.5% for HA scaffold to 11.46%. Fundamentally, these stem from the preferential dissolution of nano-MgO, which shifts the scaffold's degradation behavior from surface corrosion to pitting corrosion, thereby expanding the solid-liquid interface. Furthermore, the internal acicular nanocrystals within it accelerate the degradation and deposition process while providing additional nucleation sites for osteapatite formation. These findings suggest that when the nano-MgO content was 16.6 wt.%, the scaffolds (10MH) exhibited suitable pore characteristics, excellent biodegradability and bioactivity and good biocompatibility. In summary, hydroxyapatite composite scaffolds adding bioabsorbable nano-MgO represent highly promising biomaterials for bone regeneration.