Fig. 4: Tunable mechanical properties and shape-memory effect of regenerated keratin.

a Schematic of the α-keratin in reduced state and directional rearrangement of α-helices induced by stretching. b Cyclic loading of reduced keratin to 50% strain. c Stress-strain curves of reduced and oxidized keratin until fracture. Scale bars, 2 mm. d Schematic of the α-keratin in oxidized state and uncoiling of helices upon stretch. e Cyclic loading of oxidized keratin to 50% strain. f Change of secondary structure percentage under 50% strain quantified from Raman deconvolution of amide I band. A more significant decrease of α-helix can be observed within oxidized sample, indicating the uncoiling of helices into metastable β-sheets. Data are presented as mean ± s.d. (n = 3 independently prepared keratin film samples). g Schematic of the shape memory effect triggered by hydration signal. h Demonstration of shape memory effect with a badge model and a tensegrity structure. Scale bars, 3 cm. Source data are provided as a Source Data file.