Reconstructed Hierarchically Structured Keratin Fibers with Shape‐Memory Features Based on Reversible Secondary‐Structure Transformation

Biocompatible and biodegradable shape-memory polymers have gained popularity as smart materials, offering a wide range of applications and environmental benefits. Herein, the possibility of fabricating regenerated water-triggered shape-memory keratin fibers from wool and cellulose in a more effective and environmentally friendly manner is investigated. The regenerated keratin fibers exhibit comparable shape-memory performance to other hydration-responsive materials, with a shape-fixity ratio of 94.8 ± 2.15% and a shape-recovery rate of 81.4 ± 3.84%. Owing to their well-preserved secondary structure and cross-linking network, keratin fibers exhibit outstanding water-stability and wet stretchability, with a maximum tensile strain of 362 ± 15.9%. In this system, the reconfiguration of the protein secondary structure between α-helix and β-sheet is investigated as the fundamental actuation mechanism in response to hydration. This responsiveness is studied under force loading and unloading along the fiber axis. Hydrogen bonds act as the "switches" clicked by water molecules to trigger the shape-memory effect, while disulfide bonds and cellulose nanocrystals play the role of "net-points" to maintain the permanent shape of the material. Water-triggered shape-memory keratin fibers are manipulable and exhibit potential in the fabrication of textile actuators, which may be applied in smart apparel and programmable biomedical devices.