Regulating degradation in MgZnCa metallic glass: Formation of zinc-rich amorphous layer through internal zinc migration

Advancing biodegradable medical implants, along with an in-depth understanding of their degradation mechanisms, is critical to revolutionizing orthopedic medicine and improving patient outcomes. MgZnCa metallic glass (MG) stands out among degradable metallic materials due to its superior potential for orthopedic applications than traditional crystalline alloys. Despite its advantages, there has been a lack of comprehensive insight into the degradation behavior of MgZnCa MG, particularly under conditions simulating daily activities of patients. In this work, the degradation mechanism of MgZnCa MG is elucidated, highlighting the formation of a distinctive Zn-rich amorphous layer that markedly decelerates the matrix degradation. Detailed analysis reveals that the unique amorphous structure of MgZnCa MG facilitates the selective dissolution of Mg and Ca, resulting in numerous vacancies within the matrix. These vacancies facilitate the inward migration of Zn atoms, culminating in the formation of a dense Zn-rich layer. This cyclical formation and dissolution of the Zn-rich layer serve as a buffer in the degradation pathway, thus ensuring a degradation rate for MgZnCa MG that is significantly slower than that of its crystalline counterparts.