Research ArticleMATERIALS SCIENCE

Dual-gradient enabled ultrafast biomimetic snapping of hydrogel materials

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Science Advances  19 Apr 2019:
Vol. 5, no. 4, eaav7174
DOI: 10.1126/sciadv.aav7174
  • Fig. 1 Illustrative scheme of the snapping deformation.

    (A) Snapping of the Venus flytrap. (B) Inverse snapping of a dual-gradient hydrogel sheet. (C) A carton showing the cross section of a dual-gradient hydrogel.

  • Fig. 2 Inverse snapping of dual-gradient rGO/PDMAEMA hydrogel sheets.

    (A and B) Schematic illustration (A) and cross-sectional SEM image (B) of the dual-gradient structure of rGO/PDMAEMA hydrogel sheets. (C) Shape transformation of the sheets in response to temperature variation. (D and E) Inverse snapping of the sheets with strip patterns to form chiral structures with controlled handedness. Scale bars, 1 cm (C and D).

  • Fig. 3 Programmable inverse snapping enabled by energy prestored within dual-gradient composite hydrogel sheets.

    (A) Schematic illustration of inverse snapping of composite hydrogel sheets when moved from TH to TL. (B) Maximum bending angles of initial curling of hydrogel sheets at different TH (black curve) and corresponding inverse snapping of the sheets in 20°C water (red curve). The gel sheets initially curved toward the HD side when they were stimulated in water with different TH for 10 min. When the curved sheets prestored with energy were subsequently immersed in 20°C water, the sheets snapped inversely depending on the TH for pretreatment. (C) Kinetics of snapping at 20°C for sheets initially treated at different TH. For comparison, the onset time of snapping for all cases was set to the same value. (D) Maximum output energy and lifting weight at 20°C by the same hydrogel sheet after energy storage at different TH. Optical images in the insets show the lifting of 0.06- and 0.065-g iron wires by the snapping of the same hydrogel sheet. The gel was pretreated at 60°C and then immersed in 20°C water to trigger snapping deformation. (E) Height of lifting 0.04-g object at 20°C by hydrogel treated at different TH as a function of lifting time. Scale bars, 1 cm.

  • Fig. 4 Transformation of a dual-gradient composite hydrogel sheet into complex shapes by programming energy prestorage.

    (A) Inverse snapping of a composite hydrogel sheet in 20°C water after NIR irradiation regionally of the sheet in air. (B) Programmable folding of a composite hydrogel sheet into a cube in 20°C water after NIR irradiation of the highlighted regions in air. Scale bars, 1 cm.

  • Fig. 5 General criterion for inverse snapping of hydrogel sheets.

    (A) Production diagram of various hydrogel sheets: composite hydrogel sheets under different initial TH, bilayer PNIPAM hydrogel sheets with different dual gradients, and bilayer hydrogel sheets with different single gradients. The regimes (I) and (II) correspond to the condition of aH/aL > ki-H/ki-L (snapping) and aH/aL < ki-H/ki-L (no snapping), respectively. (B and C) Deformation of different bilayer hydrogel sheets under the stimuli of 20° and 40°C: double gradients (B) and single gradient (C). Scale bars, 1 cm.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/4/eaav7174/DC1

    Section S1. Theoretical derivation of inverse snapping

    Section S2. Energy transformation during the inverse snapping

    Section S3. Characterization of dual-gradient rGO/PAMAEMA hydrogel sheet

    Fig. S1. Schematic illustration of the fabrication process of the GO/PDMAEMA hydrogel sheet.

    Fig. S2. Characterization of dual-gradient rGO/PAMAEMA hydrogel sheet.

    Fig. S3. Temperature-dependent swelling ratio and deforming kinetics.

    Fig. S4. Shape transformations of hydrogel sheets with different patterns and initial shapes.

    Fig. S5. Dependence of inverse snapping on TH.

    Fig. S6. Demonstration of the multiresponsive feature.

    Fig. S7. NIR irradiation–triggered shape transformation.

    Fig. S8. aH, aL, ki-H, and ki-L for different hydrogel sheets.

    Fig. S9. AFM characterization of GO.

    Movie S1. Inverse snapping of hydrogel sheet submerged from 60°C into 20°C water.

    Movie S2. Inverse snapping of patterned hydrogel sheet.

    Movie S3. Jumping and somersaulting motion.

    Movie S4. Inverse snapping of hydrogel sheet submerged from 40°C into 20°C water.

    Movie S5. Lifting processes of hydrogel actuator after energy storage at 60°C.

    Movie S6. Lifting processes of hydrogel actuator after energy storage at 50°C.

    Movie S7. Inverse snapping of hydrogel sheet submerged from 5 M NaCl into 20°C water.

    Movie S8. Inverse snapping of hydrogel sheet submerged from 60°C into 0°C water.

    Movie S9. Inverse snapping of hydrogel sheet submerged from 60°C into 35°C water.

    Movie S10. Inverse snapping of hydrogel sheet submerged from 5 M NaCl into 0.1 M NaCl.

    Movie S11. Local energy storage upon NIR irradiation.

    Movie S12. Local energy release to induce triangle shape deformation.

    Movie S13. Inverse snapping of dual-gradient bilayer PNIPAM hydrogel sheet.

    Movie S14. Inverse snapping of single-gradient bilayer PNIPAM hydrogel sheet.

  • Supplementary Materials

    The PDF file includes:

    • Section S1. Theoretical derivation of inverse snapping
    • Section S2. Energy transformation during the inverse snapping
    • Section S3. Characterization of dual-gradient rGO/PAMAEMA hydrogel sheet
    • Fig. S1. Schematic illustration of the fabrication process of the GO/PDMAEMA hydrogel sheet.
    • Fig. S2. Characterization of dual-gradient rGO/PAMAEMA hydrogel sheet.
    • Fig. S3. Temperature-dependent swelling ratio and deforming kinetics.
    • Fig. S4. Shape transformations of hydrogel sheets with different patterns and initial shapes.
    • Fig. S5. Dependence of inverse snapping on TH.
    • Fig. S6. Demonstration of the multiresponsive feature.
    • Fig. S7. NIR irradiation–triggered shape transformation.
    • Fig. S8. aH, aL, ki-H, and ki-L for different hydrogel sheets.
    • Fig. S9. AFM characterization of GO.
    • Legends for movies S1 to S14

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    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.avi format). Inverse snapping of hydrogel sheet submerged from 60°C into 20°C water.
    • Movie S2 (.avi format). Inverse snapping of patterned hydrogel sheet.
    • Movie S3 (.avi format). Jumping and somersaulting motion.
    • Movie S4 (.avi format). Inverse snapping of hydrogel sheet submerged from 40°C into 20°C water.
    • Movie S5 (.avi format). Lifting processes of hydrogel actuator after energy storage at 60°C.
    • Movie S6 (.avi format). Lifting processes of hydrogel actuator after energy storage at 50°C.
    • Movie S7 (.avi format). Inverse snapping of hydrogel sheet submerged from 5 M NaCl into 20°C water.
    • Movie S8 (.avi format). Inverse snapping of hydrogel sheet submerged from 60°C into 0°C water.
    • Movie S9 (.avi format). Inverse snapping of hydrogel sheet submerged from 60°C into 35°C water.
    • Movie S10 (.avi format). Inverse snapping of hydrogel sheet submerged from 5 M NaCl into 0.1 M NaCl.
    • Movie S11 (.avi format). Local energy storage upon NIR irradiation.
    • Movie S12 (.avi format). Local energy release to induce triangle shape deformation.
    • Movie S13 (.avi format). Inverse snapping of dual-gradient bilayer PNIPAM hydrogel sheet.
    • Movie S14 (.avi format). Inverse snapping of single-gradient bilayer PNIPAM hydrogel sheet.

    Files in this Data Supplement:

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