Multimodal Locomotion of Magnetic Droplet Robots Using Orthogonal Pairs of Coils

Recently, several fluidlike, shape-adaptable magnetic microrobots have been developed to overcome the drawbacks posed by the rigid structure of traditional magnetic microrobots. However, most of their control systems rely on permanent magnet-based systems, which are unfeasible for large-scale environments, such as in vivo applications. Herein, an electromagnetic system comprising orthogonal pairs of coils is used to generate global magnetic fields, that is, magnetic fields that are applied equally to large volumes, for the multimodal locomotion of ferrofluidic robots composed of magnetic micro-/nanoparticles. Three main magnetic field configurations, with their respective locomotion mechanisms, are explored: uniform rotating fields for droplet fission-fusion motions and locomotion; magnetic trapping point-based locomotion for single- and collective-droplet manipulation; and field-free region-based dragging locomotion and selective droplet control. The effectiveness of the proposed multimodal locomotion mechanisms and potential applications are experimentally demonstrated in minichannels through selective mixing, targeted delivery, and optimized magnetic heating applications. These locomotion mechanisms using global fields enable the use of fluidlike magnetic microrobots in large-volume applications.