Biomimetic Design of Hydration-Responsive Silk Fibers and their Role in Actuators and Self-Modulated Textiles

Hydration-induced shape-morphing behavior has been discovered in many natural fiber-based materials, yet this smart behavior in regenerated fibers from biopolymers lacks investigation. Here, hierarchically structured silk fibers are developed with anisotropic long-range molecular organization and water-responsive effects resembling natural spider silk. The regenerated silk fibers exhibit the water-triggered shape-memory effect and a water-driven cyclic response. The reversible hydrogen bonds and transformation in the metastable secondary structure from α-helices/random coils to β-sheets are explored as the mechanisms responsible for the water-responsiveness. The silk fibers obtained possess a tensile strength higher than 104 MPa at a fracture strain of ≈100%, showing noticeable toughness. The water-responsive silk fibers exhibit a shape recovery rate of ∼83% and generate a maximum actuation stress of up to 18 MPa during the water-driven cyclic contraction that outperforms most traditional natural textile fibers. The regenerated silk fibers show potential for use in water-driven actuators, artificial muscle, and smart fabrics based on the integration of suitable mechanical properties and water responsiveness.