Interfacial Structures Associated with Surface Activity in Magnetic Devitrified Glasses for Biomedical Applications

In bioactive magnetic devitrified glasses, the amorphous region with a porous structure is reduced compared to that in relevant glasses due to the formation of crystalline phases, such as magnetite crystals, which deteriorate the bioactive properties that arise from the active surface area. In this study, the local atomic structure associated with surface activity was investigated as an alternative to the reduced amorphous region in bioactive ferrimagnetic devitrified glasses doped with Cu via melt-quenching and ion exchange. Element-specific positron annihilation spectroscopy revealed that the melt-quenching approach effectively introduces Cu ions into the boundaries among magnetite-based crystals, forming void-like open spaces. The interior surfaces of these void-like open spaces within the crystal boundaries act as active areas, as evidenced by the formation of carbonate species through the reaction of Ca with CO2 in the air. The results confirm that Cu ions introduced into the crystal boundaries play an important role not only in imparting antibacterial properties but also in developing locally active surfaces.