The role of crystalline phase in the dissolution mechanism and mechanical response of bioresorbable MgZnCa bulk metallic glasses and composites

The dissolution behaviour and mechanical properties of bioresorbable Mg-based alloys are strongly governed by their atomic structure: crystalline or amorphous. Amorphous, partially crystalline, and crystalline forms of the biodegradable Mg66Zn30Ca4 alloy were fabricated and their dissolution in phosphate-buffered saline (PBS) and their post-immersion mechanical performance were investigated. Such distinct structures were developed by different cooling rates during solidification. The fully amorphous Mg66Zn30Ca4 alloy exhibited a corrosion resistance comparable to that of commercial Mg-based alloy WE43, while partially crystalline and crystalline counterparts showed accelerated dissolution. Additionally, although as-cast Mg66Zn30Ca4 with different levels of amorphous structure showed a higher compressive strength, all of the Mg66Zn30Ca4 samples lost their strength after immersion, unlike WE43, which remained stable. These materials, therefore, in their current form, do not have the requisite properties for clinical use. The paper demonstrates that structural state plays a critical role in governing dissolution kinetics and mechanical performance in bioresorbable MgZnCa alloys, providing important design considerations for tailoring implant materials. Future prospects for success will need developing an ability to control the volume fraction and spatial distribution of crystalline phases and their morphology.