Multimodal Locomotion Control of Needle-Like Microrobots Assembled by Ferromagnetic Nanoparticles

Microrobots have great potential for multiple applications, such as targeted drug delivery and micromanipulation. Several kinds of microrobots assembled by nanoparticles have been proposed by researchers. However, they are difficult to adapt for complex environments, for example, traversing porous materials or climbing over obstacles. Many such environments require multimodal motion control. In this article, we proposed a needle-like microrobot assembled by ferromagnetic nanoparticles, which enables three types of locomotion, defined as axial motion, lateral motion, and rolling motion. The influence of velocities by input frequencies and the lengths of the microrobots are investigated theoretically and experimentally. Moreover, visual feedback path-following control methods are designed for each motion type, and experimentally verified. The needle-like microrobots enable traversing the nonwoven layer of a clinical mask and a seaweed silk barrier by axial motion, which showed a separation and a reaggregation during the traversing process. The needle-like microrobots with rolling motion are capable of climbing over obstacles, which expands its motion scene from 2-D to 3-D. They can overcome even higher obstacles by assembling themselves to form the longer needle-like microrobots. We further expect that with the proposed multimodal motion control of nanoparticle microrobots, they may achieve complex tasks at the microscale.