Modification of pore-wall in direct ink writing wollastonite scaffolds favorable for tuning biodegradation and mechanical stability and enhancing osteogenic capability

Surface chemistry and mechanical stability determine the osteogenic capability of bone implants. The development of high-strength bioactive scaffolds for in-situ repair of large bone defects is challenging because of the lack of satisfying biomaterials. In this study, highly bioactive Ca-silicate (CSi) bioceramic scaffolds were fabricated by additive manufacturing and then modified for pore-wall reinforcement. Pure CSi scaffolds were fabricated using a direct ink writing technique, and the pore-wall was modified with 0%, 6%, or 10% Mg-doped CSi slurry (CSi, CSi-Mg6, or CSi-Mg10) through electrostatic interaction. Modified CSi@CSi-Mg6 and CSi@CSi-Mg10 scaffolds with over 60% porosity demonstrated an appreciable compressive strength beyond 20 MPa, which was 2-fold higher than that of pure CSi scaffolds. CSi-Mg6 and CSi-Mg10 coating layers were specifically favorable for retarding bio-dissolution and mechanical decay of scaffolds in vitro. In-vivo investigation of critical-size femoral bone defects repair revealed that CSi@CSi-Mg6 and CSi@CSi-Mg10 scaffolds displayed limited biodegradation, accelerated new bone ingrowth (4-12 weeks), and elicited a suitable mechanical response. In contrast, CSi scaffolds exhibited fast biodegradation and retarded new bone regeneration after 8 weeks. Thus, tailoring of the chemical composition of pore-wall struts of CSi scaffolds is beneficial for enhancing the biomechanical properties and bone repair efficacy.