Hydroxypropyl cellulose-based photonic actuators coupling structural color and programmable deformation

Hydroxypropyl cellulose (HPC), a widely available and sustainable cellulose derivative, can self-assemble into cholesteric structures, exhibiting dynamic structural color tunable by concentration or mechanical stress. However, preserving this dynamic optical response in the solid state remains challenging. Here, we report free-standing, humidity-responsive photonic actuators that integrate structural color change and deformation by co-assembling methacrylate functionalized HPC with acrylamide through covalently double cross-linked networks. This approach anchors the cholesteric structures within polymeric networks, enabling reversible structural color responses to humidity. Furthermore, the mechanical modulus and moisture absorption capacity of the resulting films can be tuned through controlled UV irradiation duration. Patterned HPC films with regions of varied modulus and moisture absorption capacity were fabricated using predesigned photomasks, exhibit reversible deformations (including bending, twisting, mimicking the blooming of flowers, and walking motion) coupled with visible structural color changes in response to humidity changes. These multifunctional HPC-based actuators are promising for applications in sustainable photonic robotics, biomimetic devices, and intelligent sensing applications.