Multifunctional liquid microrobots based on paramagnetic microdroplets

The liquid robot, an advanced form of the soft robot, can freely transform between different morphologies. From the perspective of materials science, difficulty fabricating liquid functional materials hinders the development of liquid robots. Here, we report a paramagnetic-fluid-constructed liquid microrobot (1–1,000 μm) based on paramagnetic microdroplets. The paramagnetism not only allows the scaling down of the liquid robot to microscales but also renders the microrobots reversible between paramagnetic-ferromagnetic transition upon magnetic field application. Furthermore, the paramagnetism equips these microrobots with on-board imaging and sensing abilities. The combined T1-T2 imaging modes cross-validated the real-time motion of the microrobots. The deformation degrees of these microrobots, which vary based on the structure of their surroundings, is measured by an ultra-low-field atomic magnetometer. The fabrication and characterization of these multifunctional paramagnetic liquid microrobots will lay the basis for their in vivo biomedical applications.