Nano-Metamaterial: A State-of-the-Art Material for Magnetic Resonance Imaging.

Metamaterials are artificially designed materials with multilevel-ordered microarchitectures, which exhibit extraordinary properties not occurring in nature, and their applications have been widely exploited in various research fields. However, the progress of metamaterials for biomedical applications is relatively slow, largely due to the limitations in the size tailoring. When reducing the maximum size of metamaterials to nanometer scale, their multilevel-ordered microarchitectures are expected to obtain superior functions beyond conventional nanomaterials with single-level microarchitectures, which will be a prospective candidate for the next-generation diagnostic and/or therapeutic agents. Here, a forward-looking discussion on the superiority of nano-metamaterials for magnetic resonance imaging (MRI) according to the imaging principles, which is attributed to the unique periodic arrangement of internal multilevel structural units in nano-metamaterials, is presented. Moreover, recent advances in the development of nano-metamaterials for high-performance MRI are introduced. Finally, the challenges and future perspectives of nano-metamaterials as promising MRI contrast agents for biomedical applications are briefly commented.