Light-Actuated Anisotropic Microactuators from CNT/Hydrogel Nanocomposites

The functionality of hydrogel actuators can be enhanced by speeding up response times and converting their isotropic swelling and contraction into more complex deformations. We present a composite microactuator which combines poly(N-isopropylacrylamide) (PNIPAM), a widely used temperature-responsive polymer, with carbon nanotubes (CNTs) to achieve these goals. The anisotropy of vertically aligned CNT forests transforms the isotropic (de)swelling of PNIPAM into anisotropic motion. The high optical absorption and anisotropic heat conductivity of carbon nanotubes allows us to use low power light illumination for both local and global PNIPAM actuation, with sub-second response times. We demonstrate a wide variety of CNT skeleton microstructures to show a range of actuation behaviours, including fast reversible movement, swimming, active switching from low to high light absorption states, auxetic lattice shape changes, and good cycling stability.