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.

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Magnetic continuum millirobots have presented outstanding potential in ultrahigh-precision engineering including minimally invasive surgery, due to their flexible mechanical structures and dexterous manipulation. Traditional continuum millirobots exhibit limited cargo-loading capacity, which restricts their application. Herein, we propose a novel design scheme of a magnetically actuated untethered hollow continuum millirobot. The millirobot is composed of silicone as the mainframe structure and two tiny magnets for actuation. To improve the loading capacity, partial silicone is removed to create a flexible cavity, which enables cargo delivery and potential in vivo sampling functions under wireless magnetic actuation. Theoretical analysis and experimental testing are conducted to reveal the effectiveness of the proposed design. The soft structure brings a new strategy to achieve multimodal motion including rolling, tumbling, and swinging. Moreover, the magnet part can generate a powerful magnetic force output for dexterous manipulation. These functionalities lay a foundation for playing a greater role in next-generation biomedical applications.