Asymmetric actuators via lignin-cellulose nanofibrous composite films with programmable wet-light dual-responsiveness

Multi-stimuli-responsive actuators attract significant interest due to their flexibility and adaptability to complex environments. However, achieving controllable response directionality and complex programmable deformation remains challenging. In this study, a humidity- and UV-visible light-responsive base film was developed using cellulose nanofibrils (CNF)/polyvinyl alcohol (PVA) functionalized with 4-hydroxyazobenzene (Azo). An asymmetric multi-stimuli-responsive composite film was fabricated via sequential coating of a polyimide (PI)/lignin oligomer (LIG) blend solution onto this substrate, exhibiting excellent dual humidity-light responsive deformation. The PI/LIG coating demonstrated excellent compatibility with the substrate, endowing the composite with excellent photothermally driven deformation and enhanced thermal stability. Under near-infrared (NIR) irradiation (100 mW/cm², 60 s), the irradiated surface reached a maximum temperature of 64.07 °C. The actuator exhibited a moisture response sensitivity of 0.206 cm^-1/%RH^-1, along with excellent reversibility and remarkable responsiveness to sunlight, LED light, and NIR light. The distinct interfacial composition and response gradients enabled controllable deformation directions under moisture and light stimuli. Furthermore, stimulus-driven 2D-to-3D structural transformations, including grasping, lifting, and hinge-like motions, were achieved through diverse patterning strategies. This work provides a rapid and scalable approach for developing programmable patterned actuators with sophisticated deformation capabilities based on sustainable carbohydrate-derived materials.