A programmable and biomimetic photo- actuator: a composite of a photo- liquefiable azobenzene derivative and commercial plastic film

Many interesting deformations in nature inspire us to develop novel mechanical systems. Here, a helical gripper was inspired by the predation motion of pythons. It grasped an object by twisting around it, which is different from conventional claw-shape grippers. To mimic this helical deformation, a soft photo-actuator was fabricated by compositing one photo-liquefiable azobenzene derivative and low-density polyethylene (LDPE) film by a specific route. The actuator was programmed to complete a reversible spiralization and despiralization motion. Upon photoirradiation, the azobenzene derivative transformed directly from crystal to isotropic liquid at room temperature, and the microcosmic volume changes were elegantly transferred into the fabricated bilayer films to bring about a large macroscopic deformation. The photoinduced spiral ribbons show controllable handedness and pitch, in correlation with the light intensity and the pre-treatment method. It is the flexibility of the soft actuator and the strength of the helical deformation that make it possible to simulate the helical motion of pythons' predation. The actuator can grasp a variety of objects with different sizes and shapes showing its reliability. The bilayer actuators are easily fabricated, manipulative and recyclable, promising their applications as high-performance photomechanical devices.