Patterned, morphing composites via maskless photo-click lithography

Morphing materials, also known as smart materials are attracting increasing attention as sensors, actuators and in soft robotic applications. In this work bilayered morphing composites were created by exploiting the thiol-ene photoclick reaction via maskless digital light processing (DLP). This technique allows for gradients and patterns of near infrared (nIR)-triggered materials to be efficiently crosslinked to substrates, with suitable interfacial adhesion to realise complex morphing. Photo-thermally responsive composites are produced by DLP patterning of reduced graphene oxide-filled chitosan-methacrylamide (rGO-chitosan-MA) on thiolated polydimethylsiloxane substrates via thiol-ene photoclick reaction. Morphing composites with parallel striped patterns and box-like hinges were printed via DLP to realise self-rolling and self-folding behaviours. Bilayered structures, with gradient rGO-chitosan-MA thicknesses (2-8 μm), were produced by controlling the light intensity from the DLP device. These gradient bilayered structures enable photothermal-triggered gradient bending and morphing exemplified here by a "walking worm" and a kirigami-inspired "opening flower". Thermo-mechanical calculations were performed to estimate bending angles, and finite element analysis applied to simulate self-folding and bending. The difference between simulation and measurements is in the range 0.4-7.6%, giving confidence to the assumptions and simplifications applied in design.