Collective Behaviors of Magnetic Microparticle Swarms: From Dexterous Tentacles to Reconfigurable Carpets.

Microrobot swarms have promising prospects in biomedical applications ranging from targeted cargo delivery to minimally invasive surgery. However, such potential is constrained by the small output force and low efficiency of the current microrobot swarms. To address this challenge, we report a tentacle-like reconfigurable microrobot swarm by programming paramagnetic microparticles into reconfigurable carpets with numerous cilia. This wirelessly controlled microrobot swarm is constructed via a strong gradient magnetic field in combination with a programmable oscillating magnetic field. The gradient magnetic field is supplied by a permanent magnet, which enables fast formation of a microrobot swarm with powerful collective behaviors via cooperative physical structures within the swarm. The oscillating magnetic field is produced by a custom-built electromagnetic coil system, which is adopted as an actuation device for conducting dexterous manipulation via controllable oscillation motion. Using the proposed microrobot swarming strategy, a milligram-level magnetic carpet achieves a millinewton-level output force. By applying different types of magnetic fields, the magnetic carpet accomplishes dexterous manipulation tasks, lesion removal, and controllable drug diffusion with a high-efficiency response in microscale executions. The formation and control mechanisms of the microrobot swarm reported here provide a practical candidate for in vivo biomedical treatment.