MnO2-Based nanosystems for cancer therapy

Cancer is one of the most dangerous diseases worldwide, the treatment of which is still a great problem. The increasing demand of clinical biomedicine and fast development of nanotechnology have quickly promoted the generation of diverse nanosystems for various cancer therapies. As one kind of redox active transition-metal dioxide nanomaterials, manganese dioxide (MnO₂) and its nanocomposites have emerged as a novel class of nanomaterials that show superior advantages and unprecedented performances in cancer therapy due to their large surface area, good absorption and degradation ability, strong fluorescence quenching ability, high oxidation and catalytic activity, etc. According to different morphologies of MnO₂, MnO₂ can be divided into MnO₂ nanosheets, MnO₂ quantum dots (QDs), MnO₂ nanocrystals, MnO₂ nanowires, etc. In this review, the synthesis of MnO₂, especially MnO₂ nanosheets, is first introduced, followed by an introduction of the classification of MnO₂ nanomaterials. Then, recent cancer therapeutic applications of MnO₂ and its nanocomposites are comprehensively overviewed, which are categorized into three parts: chemotherapy, phototherapy and synergistic therapy. In addition, treatment of other diseases based on MnO₂ and its nanocomposites is also discussed. Finally, some crucial unresolved problems, probable challenges and future perspectives about the rational design and construction of MnO₂-based nanosystems for further biomedical applications are also discussed.