A Soft Porous Starfish-Like Millirobot With Omnidirectional Locomotion for Drug Delivery

Soft magnetic millirobots that can operate in confined, heterogeneous environments are promising for biomedical applications such as targeted drug delivery. However, combining robust locomotion, environmental adaptability, and payload integration within a single compact body remains challenging. This letter presents a soft (elastic modulus 692 kPa), lightweight (70 mg), and porous starfish-like millirobot (PSM-Bot) inspired by the radial morphology of starfish and the interconnected porosity of sponges. The PSM-Bot uses five soft arms and a porous magnetic composite to enable omnidirectional steering and intrinsic drug loading. Under external magnetic actuation, the robot generates asymmetric deformation and achieves multimodal locomotion, including crawling (5 mm/s) and rolling (14 mm/s). A mechanics model is developed to explain torque-driven deformation and the mode transition between crawling and rolling. Experiments demonstrate omnidirectional locomotion across diverse terrains, including depressions, serpentine channels, liquid regions, rough surfaces, and slopes. Finally, a stomach-model demonstration verifies targeted navigation and on-site release of a loaded drug surrogate at a designated location. This work provides a new way for multifunctional magnetic soft millirobots with multimodal locomotion capability and integrated biomedical functionality.