Zinc-based Biodegradable Materials For Biomedical Applications

In recent years,biodegradable biomedical metallic materials have attracted widely attention in the field of materials science and medicine because of its irreplaceable mechanical properties and biodegradability in vivo.In addition to Mg and Fe,Zn as an essential element of human osteogenesis is expected to become a new generation of biodegradable medical metallic materials due to its appropriate degradation rate in vivo.Besides,the metal silver has good biocompatibility and bactericidal properties,so Zn-Ag alloy is expected to be a new kind of biodegradable biomedical metallic material with suitable degradation rate,excellent mechanical property and bactericidal function.In this paper,Zn-Ag alloys with different Ag content were prepared by casting method using pure cast zinc and silver as raw materials.The microstructures,mechanical properties,in vitro degradation performance together with antibacterial and bactericidal activities of Zn-Ag alloys were carried out and studied.The results of optical microscopy and scanning electron microscopy show that Zn-Ag alloy has a lamellar microstructure when the mass fraction of silver in Zn-Ag alloy is less than 3.5 wt.%,and the higher the silver content is,the finer the grain is.When the silver content exceeds 3.5 wt.%,the microstructure of Zn-Ag alloy changed to dendrites,and the dendrites are obviously refined when the Ag content reaches 4.5 wt.%.The mechanical properties of Zn-Ag alloy were measured by SHT5305 microcomputer control electro-hydraulic servo universal testing machine and HMV-2T microhardness tester.The results showed that the mechanical properties of Zn-Ag alloy increased with the increase of Ag content in the alloys,the compressive yield strength increased from 92.39 MPa?as-cast pure zinc?to251.02 MPa?Zn-4.5Ag?,and the Vickers hardness was increased from 37HV?as-cast pure zinc?to 85HV?Zn-6Ag?.The biodegradability of Zn-Ag alloy in vitro was studied by simulating body fluid immersion method and electrochemical method.The results showed that when the Ag content up to 1.5 wt.%,Zn-Ag alloy reached the maximum corrosion weightlessness.When the content of silver in Zn-Ag alloy increased from 3.5wt.%to 6 wt.%,the corrosion of the matrix phase?Zn solid solution?was serious,while the second phase AgZn₃ in the alloy has good corrosion resistance.In addition,the experimental results show that the corrosion products on the surface of Zn-Ag alloy are mainly Ca?P containing compounds,indicating that Zn-Ag alloy can effectively induce Ca?P deposition to show good biological activity.Dipping method of e.Coli was adopted to test Zn-Ag alloy bacteriostatic bactericidal performance,results show that the Zn-Ag alloy showed good antibacterial and bactericidal performance,and silver content is higher the rate of antibacterial is higher,when the silver content increased to 6 wt.%antibacterial rate can reach 100%.In conclusion,the Zn-Ag alloy made by this paper with excellent mechanical properties?controllable biodegradation properties and antibacterial sterilization function,has the potential to become a new generation of degradable biomedical metal materials.