Soft millirobots have evolved into various therapeutic applications in the medical field, including for vascular dredging, cell transportation, and drug delivery, owing to adaptability to their surroundings. However, most soft millirobots cannot quickly enter, retrieve, and maintain operations in their original locations after removing the external actuation field. This study introduces a soft magnetic millirobot for targeted medicine delivery that can be transported into the body through a catheter and anchored to the tissues. The millirobot has a bilayer adhesive body with a mussel-inspired hydrogel layer and an octopus-inspired magnetic structural layer. It completes entry and retrieval with the assistance of a medical catheter based on the difference between the adhesion of the hydrogel layer in air and water. The millirobot can operate in multiple modes of motion under external magnetic fields and underwater tissue adhesion after self-unfolding with the structural layer. The adaptability and recyclability of the millirobots are demonstrated using a stomach model. Combined with ultrasound (US) imaging, operational feasibility within organisms is shown in isolated small intestines. In addition, a highly efficient targeted drug delivery is confirmed using a fluorescence imaging system. Therefore, the proposed soft magnetic millirobots have significant potential for medical applications.
Keywords: bio-inspired bilayer adhesive surfaces; magnetic materials; soft millirobot; targeted drug delivery.
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