Programmable Lamellar Eutectic Zn-2Al-Mg Biodegradable Implants Manufactured by Laser Powder Bed Fusion for Synergistic Strength-Ductility and Osteogenesis.

Abstract

Zn emerges considerable potential for bone repair as a biodegradable implant due to its biodegradability, good biocompatibility, and biofunctions. Nevertheless, the clinical applications of Zn encounter a profound bottleneck arising from insufficient mechanical properties and relatively slow degradation. In this work, novel Zn-2Al-Mg eutectic implants are developed by laser powder bed fusion (LPBF), aiming to overcome the mechanical dilemma meanwhile endowing remarkable osteogenesis. During LPBF, Mg-doping effectively lowers the eutectic point by altering Zn/Al ratio, promoting eutectic nucleation. Further, lamellar eutectic in Zn-2Al-Mg alloys is programmable by manipulating Mg-doping and non-equilibrium rapid solidification of LPBF. Consequently, Zn-2Al-0.3Mg eutectic exhibits a remarkably enhanced strength (155.1 MPa) and ductility (10.6%). This synergistic mechanical reinforcement is motivated by initial dislocation-mediated plastic deformation due to heterogeneous eutectic interface and incremental strain-hardening capacity owing to extra grain boundary slips. Also, Mg-doping accelerates the degradation of Zn-2Al-Mg implants, thereby promoting biocompatibility and antibacterial activity. Furthermore, in vivo bone repair surgery on rabbit radiuses demonstrates that as-printed Zn-2Al-Mg implants possess satisfying osteogenesis and osseointegration, evidenced by abundant formation and ingrowth of new bone tissues. Overall, this study not only develops a promising candidate for biodegradable alloys but also sheds light on designing and manufacturing state-of-the-art biomedical implants.