Photothermally Reconfigurable Shape Memory Magnetic Cilia

Functional artificial cilia usually require maintaining an applied stimulus or are programmed to perform one-way processes that cannot be reset. Reconfigurable artificial cilia are desirable, whose shape can be set, locked, unlocked, and reconfigured. Magnetic iron microparticles were dispersed in a thermoplastic polyurethane shape memory polymer matrix and formed into artificial, magnetic cilia that respond simultaneously to magnetic fields and light. Temporary shapes obtained through combined magnetic actuation and photothermal heating can be locked by switching off the light and magnetic field. Subsequently turning on the light without the magnetic field drives recovery of the permanent shape of the magnetic cilia. The permanent shape can also be programmed after preparing the cilia by applying mechanical constraints and annealing at high temperature. Spatially controlled actuation of magnetic cilia is demonstrated by applying a mask for pattern transfer into the array of magnetic cilia. Development of a theoretical model aids understanding the behavior of reconfigurable magnetic cilia and provides guidelines for their design and optimization.