Magnetically-driven deployable structure inspired by worms

This study investigates the protrusion mechanism of the unsegmented marine worm Phascolosoma stephensoni to inspire new actuation strategies for soft robotics. A magnetically driven, soft fluidic transmission mechanism is developed to deploy a proboscis-like structure, achieving an elongation ratio of up to 2.5 relative to the system’s initial resting length. The design integrates an active fluid-filled trunk with four magnetic bending units (15 mm × 30 mm × 2 mm) and a passive proboscis housed inside during rest. Under external magnetic fields, the units compress the trunk, driving the proboscis deployment through fluid displacement, while hyperelastic passive strips enable its retraction when the magnetic field is switched off. The units were fabricated from DragonSkin-10 silicone with 5 µm NdFeB particles at concentrations ranging from 40 wt% to 70 wt%. Increasing particle content from 40 to 70 wt% yields a magnetization gain of up to ∼200% and marked improvements in bending performance. A trunk analytical model was developed and validated with a 2.4% error to guide the proboscis design. Final performances were evaluated in terms of proboscis displacement (up to 45 mm, i.e. a ratio of up to 2.5 relative to the system’s initial resting length), internal pressure variation (up to 3 kPa), and tip force (up to 1 N). These results demonstrate how optimizing magneto-mechanical properties enables a fully soft, wirelessly actuated fluidic transmission mechanism, paving the way for applications such as targeted delivery in constrained and delicate environments.