Research ArticleAPPLIED SCIENCES AND ENGINEERING

Spider dragline silk as torsional actuator driven by humidity

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Science Advances  01 Mar 2019:
Vol. 5, no. 3, eaau9183
DOI: 10.1126/sciadv.aau9183
  • Fig. 1 Schematic diagram of the apparatus for measuring the torsional actuation of silks or other fibers driven by the RH.

  • 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.

  • Fig. 3 Torsional actuation of spider dragline silks with increasing the RH from 40 to 100%.

    (A) Torsional actuation of N. pilipes spider dragline silk (121 mm in length, 3.1 ± 0.1 μm in diameter). (B) Rotation speed (blue line) and angular acceleration (red line) of the torsional actuation of N. pilipes spider dragline silk. (C) Torsional actuation of A. versicolor spider dragline silk (87.9 mm in length, 6.7 ± 0.1 μm in diameter). (D) The rotation speed (blue line) and angular acceleration (red line) of A. versicolor spider dragline silk. Inset shows the SEM images of representative silks.

  • Fig. 4 Torsional actuation of dragline silks to RH cyclically changing from ~40 to ~100%.

    (A) N. pilipes dragline silk (98 mm in length, 3.1 ± 0.1 μm in diameter). (B) A. versicolor dragline silk (87.9 mm in length, 6.7 ± 0.1 μm in diameter). (C) N. edulis dragline silk (82 mm in length, 2.8 ± 0.1 μm in diameter). The horizontal dashed lines indicate the RH thresholds for the triggering of twist. The vertical dashed lines indicate the start and end of the induced twist. Note that the rotation direction of clockwise direction observed from top to bottom paddle is consistent for all silk samples.

  • Fig. 5 Mechanisms for humidity-induced torsion in dragline silks on a molecular level.

    (A) Representative angle displacement curve for MaSp2, showing consistent and negative angles traveling down the strands, which corresponds to clockwise twist. Inset shows molecular model of MaSp2. (B) Representative angle displacement curve for MaSp1, showing alternating positive and negative angles. Inset shows molecular model of MaSp1. (C) Hydrogen bond density scaled by the number of those residues present in the MaSp2 sequence. Proline shows the lowest hydrogen bond density compared to other residues. (D) Hydrogen bonds (shown in blue) within a 3-Å radius around (i) glutamine (Gln), (ii) glycine (Gly), and (iii) proline (Pro). (E) Hydrogen bond density scaled by end-to-end molecular length within a 3-Å radius around amino acids Glu, Gly, Ser, Tyr, and all amino acids in sequences MaSp1 and MaSp2. (F) Hydrogen bonds shown in blue in (i) MaSp1 and (ii) MaSp2 molecules. (G) Secondary structure content in MaSp1 and MaSp2. (H) The location of proline residues (with proline rings shown in red) in MaSp2 depicts a striated, linear ring orientation. Zoomed panel shows dotted guiding lines representative of linear proline ring orientation. Error bars in (C), (E), and (G) show SD over 1 ns.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/3/eaau9183/DC1

    Fig. S1. SEM images of the N. pilipes spider dragline silk before and after testing.

    Fig. S2. Twist of the N. pilipes spider dragline silk with increasing RH from 40 to 100%.

    Fig. S3. Twist of the N. pilipes spider dragline silk to RH cyclically changing from ~40 to ~100%.

    Fig. S4. Raman spectrum of the N. pilipes spider dragline silk.

    Fig. S5. Raman spectrum of the virgin dragline silk of N. edulis spider.

    Fig. S6. Raman spectrum of the virgin dragline silk of A. versicolor spider.

    Fig. S7. Flow chart for the molecular dynamics simulation and the determination of molecular twist.

    Fig. S8. Approach to estimating molecular twist.

    Fig. S9. Angle displacement between residue 0 and residue 1 to 70 for MaSp2 protein.

    Fig. S10. Angle displacement between residue 0 and residue 1 to 70 for MaSp1 protein.

    Table S1. Raman band assignment for the N. pilipes, N. edulis, and A. versicolor dragline silks.

    Note S1. Supplementary method for the spider silk harvesting.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. SEM images of the N. pilipes spider dragline silk before and after testing.
    • Fig. S2. Twist of the N. pilipes spider dragline silk with increasing RH from 40 to 100%.
    • Fig. S3. Twist of the N. pilipes spider dragline silk to RH cyclically changing from ~40 to ~100%.
    • Fig. S4. Raman spectrum of the N. pilipes spider dragline silk.
    • Fig. S5. Raman spectrum of the virgin dragline silk of N. edulis spider.
    • Fig. S6. Raman spectrum of the virgin dragline silk of A. versicolor spider.
    • Fig. S7. Flow chart for the molecular dynamics simulation and the determination of molecular twist.
    • Fig. S8. Approach to estimating molecular twist.
    • Fig. S9. Angle displacement between residue 0 and residue 1 to 70 for MaSp2 protein.
    • Fig. S10. Angle displacement between residue 0 and residue 1 to 70 for MaSp1 protein.
    • Table S1. Raman band assignment for the N. pilipes, N. edulis, and A. versicolor dragline silks.
    • Note S1. Supplementary method for the spider silk harvesting.

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