Surface design of Mg-Zn alloy temporary orthopaedic implants: Tailoring wettability and biodegradability using laser surface melting

Magnesium-based alloys have attracted significant attention for biomedical applications due to its biodegradability as well as density and elastic modulus which are close to those of human bone. However, the uncontrolled biodegradation and hydrogen evolution are of major concern. In this work, laser surface melting (LSM) has been carried out to tailor initial corrosion rates of Mg-2.2Zn alloy implants. Melt pool dimensions, microstructure and surface topography of the LSM samples were analysed. The wettability and in vitro degradation characteristics of untreated and treated alloy were compared. LSM resulted in much finer cellular microstructural features than as cast alloy and the melted region depths between 65 and 115 mu m. Higher treatment depths helped to extend the corrosion protection time by suppressing the corrosion front movement. Polished LSM samples resulted in overall corrosion rates of 0.5-0.62 mm/year which was about 40%-50% reduction compared to the as-cast alloy. Accelerated biomineralisation of the surface via enhancements in the surface energy due to microstructural refinement as well as microstructural homogeneity and Zn enrichment in alpha-Mg, favoured improvement of the overall corrosion performance of LSM-treated alloy.