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. 2020 Oct 14;11:5166. doi: 10.1038/s41467-020-18801-1

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© The Author(s) 2020

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 4 — a, b Snapshots to show the crawling motions of the slender hydrogel sheets with alignment of NSs along (a) or perpendicular (b) to the long axis under the scanning of a light beam. A cut-off filter is applied to filter out the strong green light for better visualization of the hydrogel under light irradiation. Green and blue arrows indicate the light scanning direction and motion direction, respectively. Gel dimensions, 10 mm × 5 mm × 1 mm; power intensity, 3.5 W cm⁻²; scanning speed, 1.7 mm s⁻¹. c Time-variant displacements of the head and the tail of the slender gel sheets under cyclic scanning of a light beam. d, e Variations of the friction coefficient of the PNIPAAm hydrogel and the NS/AuNP-containing PNIPAAm hydrogel against a PVC substrate as a function of test time at 20 and 40 °C (d) or under cyclic irradiation of a green-light beam at 20 °C (e). f, g Simulation results to show the kinematics of the forward (f) and retrograde (g) crawling motions of the monodomain hydrogel on the basis of photo-directed localized isochoric deformation and dynamic friction modulation. The red and blue arrows indicate the anchoring spot and motion direction of the gel. The color scale indicates the normalized temperature.