Designing magnetic nanoparticles for in vivo applications and understanding their fate inside human body

Magnetic nanoparticles are widely used for in vivo applications such as in disease diagnostics-magnetic resonance imaging, treatment-magnetoresponsive therapy, hyperthermia agents and in the delivery of drugs to specific cells, due to the unique physicochemical properties which materials posses at the nanoscale. Despite important therapeutic implications of magnetic nanoparticles, a major challenge for new magnetic materials is to ensure compliance with the nano-safety regulatory framework for in vivo usage. Whilst a large number of in vitro toxicity studies have been accomplished in literature, understanding the exact fate of magnetic nanoparticles inside the human body still remains evasive. In this review, the classification and properties of magnetic nanoparticles which facilitate their in vivo applications are discussed, followed by a description of the latest toxicology advancements in the research of magnetic nanoparticles and detailed discussions on the challenges associated with the safe removal/degradation of magnetic nanoparticles inside the body. We also provide insights on how newly designed magnetic materials can be tested prior to their in vivo use and aim to provide the reader with a comprehensive understanding of the fate of magnetic nanoparticles inside human blood vessels.