Upcycling Cotton Textile Waste into 4D Printed Humidity-Responsive Smart Structures

Textile waste has emerged as a significant global challenge. In response, increasing attention is being directed toward the recycling of textile waste, especially cellulose, as a sustainable strategy to mitigate the environmental impact of industrial waste. However, current recycling methods offer limited application scenarios and often suffer from low efficiency. Herein, we developed a humidity-responsive actuator entirely derived from waste cotton fabrics. A composite ink was formulated by decolorizing, dissolving, nanofabricating, and mixing the waste cotton fabrics, and a humidity-responsive actuator was fabricated using direct ink writing technology. The actuator exhibits reversible and significant bending behavior under humidity stimulation, achieving a bending curvature of approximately 1.4 cm–1 with a rapid response. We demonstrated that the humidity-responsive actuator can mimic natural motions such as butterfly wing spreading, flower blooming, gripping device, and crawling robot. More importantly, based on this actuator, we simulated intelligent, sweat-responsive wearable devices that autonomously deform during physical activity to enhance sweat evaporation and air convection, thereby supporting personalized heat and moisture regulation. This work highlights the potential of waste cotton fabrics for efficient recycling and intelligent applications. It offers a scalable, and cost-effective strategy for 4D printing of humidity-responsive actuators, paving the way for developing environmentally friendly smart devices.