Hot-Exturded Zn-Cu-Zr Alloys For Biodegradable Implants Application

Zn has been regarded as the most promising biodegradable metal due to its moderate degradation rate.However,the poor mechanical properties of pure Zn can hardly meet the clinical requirements for biomedical implant applications,and its non-uniform corrosion mode may cause premature mechanical failure of implants.Moreover,the excessive release of Zn²⁺by the degradation of Zn-Based medical implant will cause cytotoxicity.Herein,we designed and fabricated a series of hot-extruded Zn-Cu-Zr alloys to improve the mechanical properties,inhibit uneven corrosion of Zn.The microstructure,mechanical properties,degradation behavior and biocompatibility of the alloys were studied.Also,the underlying correlation between the microstructure and properties are discussed.The hot-extruded Zn-Cu-Zr alloys were composed of refined Zn matrix grains,Cu Zn₅phase and Zn₂₂Zr phase.The second phase particles were uniformly distributed in the Zn matrix.During the hot extrusion process,dramatic deformation regions were formed nearby the second phase particles,which promoted the dynamic recrystallization of the Zn matrix,and refined the matrix grains.The hot-extruded Zn-Cu-Zr alloys exhibited higher strength and ductility than pure Zn.This is mainly attributed to the obstruction effect of the refined matrix phase grains and the dispersed second phase grains on the movement of dislocations.The degradation behavior of hot-extruded Zn-Cu-Zr alloys in hank's solution showed that the addition of Zr element improved the thermodynamic stability of alloys.Thus the corrosion tendency was also declined.Besides,the non-uniform degradation mode of hot-extruded Zn is mainly caused by the loose corrosion product layer formed on the surface.The refined matrix grains of Zn-Cu-Zr alloys promoted the deposition of a more uniform,and denser corrosion product layer,and thus inhibited the non-uniform corrosion,such a uniform degradation mode reduced the risk of premature failure of the mechanical properties of the implant during service.The results of osteoblast culture experiments in vitro showed that hot-extruded Zn-Cu-Zr alloys showed good cytotoxicity to the osteoblast.Moreover,the alloys enhanced the activity and promote the proliferation of osteoblasts.This is mainly due to suppressed Zn²⁺release.In summary,it can be concluded that alloying and thermomechanical processing can improve the mechanical properties and degradation behavior of the Zn-based alloys via regulating the microstructure.Moreover such modification method can also improve the cell compatibility.This work provides a reference for the development and research of new biodegradable metals.