Oxygen vacancy modulation in two-dimensional metal oxides for biomedical applications

Two-dimensional metal oxides (2D MOs), as a typical representative of 2D inorganic materials, exhibit unique physicochemical properties and have received much attention in the field of nanomedical research. However, the complex physiological environment in living organisms stimulates further research into the functionality of 2D MOs to improve their ability to assemble therapeutic, diagnostic, and regenerative devices in organisms. One promising strategy, oxygen vacancy (OV, plural: OVs) engineering, can modulate the band structure and the number of active sites of 2D MOs, giving them additional functions in biological applications. Recently, researchers have developed various types of 2D MOs containing OVs via different synthetic routes, which have been extensively studied in biomedicine. Amorphization is also an effective method to introduce OVs in 2D MOs, but currently they have not been used in biological applications. This review summarizes generation, preparation, and characterization techniques of OVs in 2D MOs, as well as the role and application of OVs-rich 2D MOs in biomedical fields. Moreover, the prospects and challenges for the development of OVs-rich 2D MOs, especially amorphous 2D MOs, are discussed to facilitate the further development of these materials for biomedical applications.