Intrinsically Self-Driven Humidity Actuators Based on Silk Nanofibers Exfoliated Using a Deep Eutectic Solvent

Abstract

Exploring high-performance flexible actuators derived from natural resources is crucial for the development of green and environmentally friendly smart devices. In this study, we exfoliated natural silk using a green deep eutectic solvent (DES) to obtain silk nanofibers with average diameters and lengths in the ranges of 30–40 and 2–5 μm, respectively. After the DES treatment, the internal secondary conformation of silk changed; the concentration of β-sheets increased; and the random coil structure was destroyed. Furthermore, a silk nanofibrous membrane was fabricated via suction filtration-induced self-assembly. The fabricated actuators demonstrated an outstanding response speed of 25 s–1 within a relative humidity range of 0–70%, accompanied by a maximum response value of 70%. They exhibited exceptional durability, with a bending capability of 1.1 cm–1, and could be folded up to 20 times. By leveraging these properties, we successfully developed a unique robot capable of directional crawling and weightlifting through moisture-driven mechanisms. Notably, this innovative robot exhibited an extraordinary lifting capacity, which exceeded ten times its own weight. This paper presents a green and environmentally friendly next-generation method for manufacturing natural biobased humidity-responsive actuators.