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.