Carangiform-Like Magnetic Milliswimmer With Negative Buoyancy for Agile 3D Navigation in Confined Fluid Environments

Miniature soft robots designed with magnetoelastic materials have the potential for noninvasive navigation in narrow spaces and innovative clinical therapies. However, the complex environment inside the body imposes stringent requirements on the motility and environmental adaptability of robots. Inspired by carangiform fish morphology and kinematics, a 3D free-swimming magnetic milliswimmer with enhanced controllability, maneuverability, and environmental adaptability is developed. This milliswimmer is negatively buoyant like most fishes and employs magnetic torque to actuate its body. It mimics fish muscle contractions and generates a carangiform-like body curvature distribution that results in comparable swimming behavior and performance. Compared with previous designs, it achieves over six times the equivalent motion performance and enables gravity-resisting free-swimming, with fish-like maneuverability (a minimum turning radius of just 0.05 body length and a maximum turning rate of up to 4737 deg s⁻¹). Its ability to transport and release cargo precisely while navigating three-dimensionally in an ex vivo porcine urinary system is demonstrated. The designed bionic magnetic soft robot is expected to advance biomedical applications of magnetoelastic materials, particularly in urinary and other clinical treatments.