Macromolecular radical networks for organic soft magnets

Abstract

Recent advances in magnetic materials have enabled new functions and capabilities in small-scale robotic devices for minimally invasive surgery and therapy. Although most magnetic soft robots comprise magnetic particles and films embedded in soft polymer matrices, the metallic particles often present safety hazards due to the corrosion and leaching of cytotoxic species. Here, we develop metal-free, lightweight, and intrinsically magnetic polymers based on stable organic free radicals. By directly incorporating nitroxide radical groups into a crosslinked polymer network, we fabricate 3D organic magnets that are soft, compressible, and biocompatible and do not leach out. Leveraging the paramagnetic and viscoelastic properties of the gels, we demonstrate the bending, rolling, and pulling actuation of the soft magnetic gels, as well as imaging and actuation in a magnetic resonance imaging system. These intrinsically magnetic polymers open new opportunities for the design of fully organic magnetoactive materials and actuators for future biocompatible soft robotic applications. © 2023 Elsevier Inc.