Advances and prospects of RAFT polymerization-derived nanomaterials in MRI-assisted biomedical applications

Magnetic resonance imaging (MRI) is recognized as the most powerful clinical imaging modality due to its ability to produce detailed three-dimensional anatomical images and high spatial resolution in a non-invasive manner without the use of harmful radioactive nuclides or ionizing radiation. Conventional small molecule contrast agents (CAs) for MRI, such as paramagnetic transition metal ion chelates or iron oxide nanoparticles, are limited by lower relaxivity, shorter blood circulation time and their potential toxic effects. Functional polymers capable of being detected by MRI have therefore become attractive, offering the unique advantage of pre-design due to their chemical flexibility, structural diversity, and tailoring of properties. Reversible addition-fragmentation chain-transfer (RAFT) polymerization is a powerful tool that not only enables the precise formation of macromolecular building blocks with complex structures and functions, but also provides a direct method for preparation of polymeric nanoparticles with multiple morphologies suitable for biomedical applications. In addition, when combining RAFT polymers with inorganic/metallic complex nanocomposites, the polymer provides the ability to encapsulate therapeutic molecules, thereby combining diagnostic and therapeutic functions in what is known as a theranostic nanomedicine. In this review, we highlight recent advances in the development of multifunctional polymers as MRI CAs designed and prepared by RAFT polymerization and their performance in diagnosis and treatment of disease. In addition, the review will address the challenges and future opportunities for RAFT-mediated MRI-based theranostics in guiding the treatment of diseases including malignant tumors.