Development of biodegradable Mg-Zn-Zr-based temporary implant materials through multidirectional forging and laser shock peening

Biodegradable magnesium alloys have been a fascinating but challenging research arena, as development of such alloys for clinical applications can be a game changer in orthopedics, while controlling the degradation rate of magnesium alloys in physiological conditions is an area of concern. In quest of solution to the existing issue, this study involves development of biodegradable Mg-4Zn-0.6Zr alloy subjected to multidirectional forging (MDF) for bulk property improvement and laser shock peening for surface property improvement. The MDF process was carried out for 5 passes and resulted in significant grain refinement of the alloy from 180 ± 12 μm to 16 ± 5 μm after 5 MDF passes as observed through Scanning Electron Microscope (SEM), Laser Shock Peening (LSP) induced further grain refinement in nano scale as evident through Transmission Electron Microscope (TEM). After 5 MDF passes, the average microhardness of the alloy increased to 101.8 HV due to grain refinement and strain, further rising to 112.6 HV post-LSP from additional grain refinement and dislocations, while tensile tests showed a 141% improvement in Ultimate Tensile Strength (UTS) after 3 MDF passes compared to the homogenized state. The results of the electrochemical corrosion tests indicated that both MDF and LSP resulted in the least corrosion rate, about a factor of one order of magnitude reduction in comparison to the homogenized sample. The key results including mechanical properties, corrosion behaviour in Hanks Balanced Salt Solution and cytotoxicity evaluation employing MG-63 osteoblast-like cells suggest that the considered Mg-4Zn-0.6Zr alloy could be a worthy candidate to be further explored as a bioimplant material.