Dynamic Control of Multimodal Motion for Bistable Soft Millirobots in Complex Environments

Soft millirobots are highly promising for biomedical applications due to their reconfigurability and multifunctionality within physiological environments. However, the diverse and narrow biological cavity environments pose significant adaptability challenges for these millirobots. Here, we present a dual-morphology, thin-film millirobot equipped with a magnetic drive head and a functional tail to facilitate multimodal motion and targeted cell delivery. The millirobot can reversibly switch between two distinct morphologies in response to environmental stimuli through the deformation of its hydrogel body. Utilizing these dual morphologies, the millirobot can perform robust multimodal fundamental motions controlled by magnetic fields. We encapsulate fundamental motions with specific programmable magnetic field parameters into motion primitives, allowing easy invocation and adjustment of motion modes on demand. A knowledge graph is established to map terrain features to motion units, enabling the identification of optimal motion modes based on typical terrain characteristics. Experimental results indicate that the millirobot can effectively switch its morphology and movement modes to navigate various terrains, including narrow and curved channels as small as 1 mm, 0.8 mm high stairs with a 15° incline, and even the complex environment of a swine intestinal lumen. Its functional tail can carry immune cells to target and kill cancer cells. This robot can transport drugs and cells while navigating complex terrains through multimodal motion, paving the way for targeted medical tasks in intricate human environments in the future.