The motion of artificial molecular machines has been amplified into the shape transformation of polymer materials that have been compared to muscles, where mechanically active molecules work together to produce a contraction. In spite of this progress, harnessing cooperative molecular motion remains a challenge in this field. Here, we show how the light-induced action of artificial molecular switches modifies not only the shape but also, simultaneously, the stiffness of soft materials. The heterogeneous design of these materials features inclusions of free liquid crystal in a liquid crystal polymer network. When the magnitude of the intrinsic interfacial tension is modified by the action of the switches, photo-stiffening is observed, in analogy with the mechanical response of activated muscle fibers, and in contrast to melting mechanisms reported so far. Mechanoadaptive materials that are capable of active tuning of rigidity will likely contribute to a bottom-up approach towards human-friendly and soft robotics.

Developing shape-shifting materials requires combining the flexibility needed by shape-shifting properties, with the toughness that is demanded to maintain their mechanical performance. Typically, in liquid crystal networks, the amplitude of the shape transformation can be hindered by large cross-linking densities. Here, we argue that a promising strategy to address this limitation consists in integrating liquid crystal networks into an anisotropic and porous material that acts as an orienting scaffold. This strategy shows similarities with the principles of stimuli-responsive deformation in plants, where inflexible elements with specific orientations are integrated into a stimuli-responsive matrix. By aligning liquid crystals in a porous polypropylene orienting scaffold, we demonstrate liquid crystal networks that respond to humidity with a shape change, yet they display high elastic modulus and toughness. Various chiral shapes can be generated in single and double layers of these films, and the complexity of their actuation modes is enhanced, including twisting, curling or winding. We anticipate that these hybrid composites and the strategy they embody can find application to other stimuli-responsive anisotropic soft materials.

We highlight four different concepts that can be used as a design principe to establish self-organization using chemical reactions as a driving force to sustain gradients: reaction–diffusion, reaction–convection, Marangoni flow and diffusiophoresis.