Reversible magnetic soft actuators made of thermoplastic polyurethane and yttrium iron garnet†

Imparting magnetic properties to elastomeric polymers opens up possibilities to generate intelligent materials that may mimic complex biological systems, allowing reversible deformations under a magnetic stimulus. Remotely triggered soft actuators made of thermoplastic polyurethane (TPU) and yttrium iron garnet, Y₃Fe₅O₁₂ (YIG), were prepared through micro melt compounding, a solvent-free and environmentally friendly scalable technique. The magnetic composites (mTPU) present a good interface between particles and the matrix while maintaining the elastomeric behaviour characteristic of TPU. Using a permanent magnet, the magnetomechanical behaviour of mTPU, with two different shapes and thicknesses, led to reversible bending at room temperature with a fast response time. Initial displacements at 100 Oe for a 500 μm thick tape and 85 Oe for a 150 μm thick tape are recorded. Thinner tapes enable more freedom in movement and have higher sensitivity to external magnetic fields, needing lower magnetic forces (around 38 times lower) for bending than the thicker tapes, that in turn allow for a more precise control. A switch actuator, composed of an mTPU/Au bi-layer, was developed to quickly open or close an electrical circuit upon exposure to a magnetic field.