Spider-inspired regenerated silk fibroin fiber actuator via microfluidic spinning

Wild spider silks exhibit unique supercontraction and reversible contraction/expansion behavior with changes in humidity. These properties are highly desirable in applications such as mechanical actuators and artificial muscles. However, sources of such natural spider silk are insufficient for industrial and practical applications. Research on regenerated protein actuators is highly significant for the development of robotics in biological applications. Herein, we biomimick the novel humidity actuation of natural spider silks by regenerating the abundantly available silkworm silk fibroin using a microfluidic spinning technology. We successfully engineer the fibril alignment and diameter of the desired microfluidic-spun regenerated silk fibers (MRSFs) by controlling the dehydration and shearing of silk fibroins (SFs). These MRSFs exhibit a unique directional initial contraction property once exposed to humidity or organic solvents, which is caused by a transition of the mesoscopic hierarchical structure of SF molecules between the hydrophilic and hydrophobic domains. Further, the MRSFs can be directionally aligned on hydrophobic substrates, thus realizing the facile programming of the folding shapes and deformation manner. The MRSF actuators show a rapid response to humid conditions, as well as high stability and excellent repeatability. We apply the MRSF actuators to smart cargo carriage and convertible structural coloration, offering broad application prospects for biomedical, biocompatible, and biodegradable robotics.