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

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.