Ternary design of alloying Zn-0.45Mn with Li to enhance mechanical strength for application in orthopaedics

• The ternary design of alloying Zn-0.45Mn with Li significantly enhances the mechanical strength of the Zn-0.45Mn alloy. • Li improves mechanical properties through dual mechanisms: (1) grain refinement strengthening and secondary phase precipitation strengthening, and (2) strengthening and toughening via Li(Mn,Zn) 4 phase formation following grain coarsening. • The Zn-0.45Mn-0.5Li alloy effectively inhibits fatty infiltration and promotes bone formation, demonstrating its potential application for orthopaedics. Biodegradable Zn alloys have emerged as promising materials in orthopaedics, and optimising their mechanical strength for enhanced clinical applicability remains an active research area. In this study, we developed a ternary Zn-0.45Mn-xLi alloy system (x = 0.05, 0.15, 0.3, and 0.5 wt%) to address these challenges. The optimised Zn-0.45Mn-0.5Li alloy was implanted into the femur of a rat. Material characterisation was performed using scanning electron microscopy, X-ray diffraction, transmission electron microscopy, electrochemical tests, and tensile testing. The corrosion behaviour was explored using electrochemical tests, and the osteogenic effect was evaluated using micro-computed tomography, histology, and immunohistochemistry. The possible underlying mechanisms were explored using alkaline phosphatase staining, Oil Red O staining, immunofluorescence, and transcriptome sequencing. The results showed that Li significantly enhanced the mechanical properties through dual mechanisms: (1) grain refinement strengthening and secondary phase precipitation strengthening, and (2) strengthening and toughening via Li(Mn,Zn) 4 phase formation following grain coarsening. The Zn-0.45Mn-0.5Li alloy strongly inhibited fatty infiltration and promoted bone synthesis through activating the P38/MAPK pathway to drive differentiation fate of stem cells. The ternary design of alloying Zn-0.45Mn with Li can enhance mechanical strength and promote bone formation, showing potential for being used as bone implant material.