Simultaneous enhancement of anti-corrosion, biocompatibility, and antimicrobial activities by hierarchically-structured brushite/Ag3PO4- coated Mg-based scaffolds

Development of bone graft substitutes with appropriate integration of mechanical, biodegradable, and biofunctional properties, which promote bone formation while simultaneously preventing implant-associated infections, remains a great challenge. Herein we designed and synthesized a brushite/Ag3PO4-coated Mg-Nd-Zn-Zr scaffolds through chemical solution deposition of a composite coating onto the fluorinated Mg-based scaffolds generated with template replication method. The coated Mg-based open-porous scaffolds exhibit hierarchically-structured surface with cube-shaped Ag3PO4 nanoparticles uniformly distributed on top of microsized brushite grains. Immersion test reveals that the initial degradation rate of the coated scaffolds could be reduced by similar to 81% compared to the original scaffolds. The mean corrosion rate in 4 weeks falls into 0.10-0.15 mm/year to meet clinical requirements. The compatibility and ALP activity of cells grown in the extracts from the coated Mg-based scaffolds were increased compared with Ti control and original scaffolds, mainly due to the favorable microenvironment generated by Mg biodegradation. Besides, the coated Mg-based scaffold demonstrated potent antimicrobial activity via the synergistic actions of alkaline degradation products of Mg and the Ag species in the coating, achieving > 99.5% antibacterial rate against both gram-positive and gram-negative bacteria with relatively low silver content. Taken together, this study presents a new candidate of brushite/Ag3PO4-coated Mg-based scaffold with appropriate degradation characteristics, cytocompatibility, and antimicrobial activities for bone tissue engineering applications.