Microrobots have the potential to dramatically change many aspects of medicine by navigating bodily fluids to perform targeted diagnosis and therapy. Researchers have proposed numerous microrobotic swimming methods, with the vast majority utilizing magnetic fields to wirelessly power and control the microrobot. In this paper, we theoretically and experimentally compare the two most promising methods of microrobot swimming-using magnetic fields to rotate helical propellers that mimic bacterial

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... agella, and pulling with magnetic field gradients-considering the practical limitations in the generation of magnetic fields. We find that swimming with a helical propeller generally becomes more desirable as size decreases, and will likely be the best choice for in vivo applications.