Programmable Polymer Actuators Perform Continuous Helical Motions Driven by Moisture

Powerful soft actuators that can perform programmable actuations are highly desired for the development of soft robotics. Herein, we report a moisture-driven polymer actuator, PPA, which is a composite of poly­(3,4-ethylenedioxythiophene)/polyvinyl alcohol/copolymer of acrylic acid and 2-acrylanmido-2-methylpropanesulfonic acid. PPA can not only generate powerful actuation with a contractile stress up to 13 MPa, but can also perform programmable helical motions. PPA films with internal stress along the radial directions were prepared by a simple solution-casting method. Driven by moisture, rectangular strips cut from the same PPA film but with different cutting angles (the oblique angle between the long axis of the PPA strip and the radial axis of the PPA film) can perform direct bending and left-handed or right-handed helical motions, demonstrating the generation of chirality from asymmetric internal stress. By modulating the distribution of internal stress in PPA strips, their moving direction and speed are readily prescribed. The powerful and programmable PPA strips can be used to make soft devices, such as moisture-responsive switches and transporters. Our strategy of generating and utilizing internal stress in responsive polymers represents a promising platform for fabricating smart soft actuators.