Can multifunctionality of bioresorbable BMGs be tuned by controlling crystallinity?

Ca-Mg-Zn bulk metallic glasses (BMGs) are promising biomaterials for orthopaedic applications because when they get reabsorbed, a retrieval surgery is not needed. In this study, Ca-Mg-Zn metallic glasses with different compositions, Ca_56.02Mg_20.26Zn_23.72 and Zn_50.72Mg_23.44Ca_25.84, were fabricated by induction melting followed by copper mould casting. Their degree of crystallinity was modified by annealing, obtaining exemplar specimens of fully amorphous, partially amorphous (i.e., a BMG composite (BMGC)) and fully crystalline alloys. The microstructure, thermodynamic and corrosion performance of these alloys were evaluated as well as their electrochemical behaviour. The results of polarisation tests demonstrate that the corrosion resistance of the Zn-rich alloy is markedly better than the Ca-rich BMG. Corrosion rates of these Ca-and Zn-rich alloys with different degrees of crystallinity illustrate that the corrosion behaviours of alloys strongly depend on their microstructure, which shows a positive correlation between the corrosion current density and the crystallised volume fraction of the alloy. This study aims to shed light on the impact of the amorphicity-to-crystallinity ratio on the multifunctional properties of BMGs/BMGCs, and to assess how feasible it is to fine-tune those properties by controlling the percentage of crystallinity.