Fig. 2. SEM images of the fibers and the responses to environmental humidity stimulus.

(A) B. mori silk (7.7 ± 0.3 μm in diameter). (B) Human hair (68.7 ± 2.5 μm in diameter). (C) Kevlar fiber (10.7 ± 0.2 μm in diameter). (D) Torsional responses of the representative fibers to environmental humidity: B. mori silk fiber (65.1 mm in length), human hair (69.5 mm in length), and Kevlar fiber (86.9 mm in length). A negligible twist driven by humidity can be seen in these fibers.