Bioinspired Soft Robots Based on the Moisture-Responsive Graphene Oxide

Abstract

Graphene oxide (GO), which has many oxygen functional groups, is a promising candidate for use in moisture-responsive sensors and actuators due to the strong water-GO interaction and the ultrafast transport of water molecules within the stacked GO sheets. In the last 5 years, moisture-responsive actuators based on GO have shown distinct advantages over other stimuli-responsive materials and devices. Particularly, inspired by nature organisms, various moisture-enabled soft robots have been successfully developed via rational assembly of the GO-based actuators. Herein, the milestones in the development of moisture-responsive soft robots based on GO are summarized. In addition, the working mechanisms, design principles, current achievement, and prospects are also comprehensively reviewed. In particular, the GO-based soft robots are at the forefront of the advancement of automatable smart devices.

Keywords: actuators; bionics; graphene oxide; moisture responsiveness; soft robots; water molecules.

Figure 1

Interaction between GO and water molecules. a) Photograph of the GO solutions. Reproduced under the terms of the CC‐BY Creative Commons Attribution 4.0 International License.^{[ 51 ]} Copyright 2015, The Authors, Published by Springer Nature. b) Photograph and cross‐sectional SEM image of the GO paper. Reproduced with permission.^{[ 52 ]} Copyright 2012, American Association for the Advancement of Science. c) The binding energy between a water molecule and graphene as well as GO. d) Schematic view for water transportation path within a GO nanosheet. e) Water permeation through the GO paper. f) X‐ray diffraction patterns, g) Raman spectra, and h) lateral friction force of the GO paper under different RH. c–h) Reproduced with permission.^{[ 41 ]} Copyright 2019, Wiley‐VCH.

Figure 2

Design principles and working mechanisms of the GO‐based actuators. Scheme of the bio‐model, typical scheme, and experimental results of moisture‐responsive GO‐based actuators based on a) material gradient, b) structure gradient, and c) moisture gradient. a, left image) For the pine cone image: Reproduced under the terms of the CC‐BY Creative Commons Attribution 4.0 International License.^{[ 66 ]} Copyright 2018, The Authors, Published by Elsevier. a, middle and right images) Reproduced with permission.^{[ 62 ]} Copyright 2015, Wiley‐VCH. b, left image) For the Bauhinia pods image: Reproduced with permission.^{[ 99 ]} Copyright 2011, American Association for the Advancement of Science. b, middle and right images) Reproduced with permission.^{[ 41 ]} Copyright 2019, Wiley‐VCH. c, left image) For the root hygrotaxis image: Reproduced with permission.^{[ 77 ]} Copyright 2019, The Botanical Society of Japan and Springer Japan KK, part of Springer Nature. c, middle and right images) Reproduced with permission.^{[ 78 ]} Copyright 2016, Wiley‐VCH. The excellent actuation performance: d) the curvature change and e) response time among the GO‐based actuators reported within the last 5 years.

Figure 3

Bioinspired soft robots. a) Gripping. Reproduced under the terms of the CC‐BY Creative Commons Attribution 4.0 International License.^{[ 80 ]} Copyright 2019, The Authors, Published by Springer Nature. b) Curling. Reproduced with permission.^{[ 62 ]} Copyright 2015, Wiley‐VCH. c) Rolling. Reproduced with permission.^{[ 41 ]} Copyright 2019, Wiley‐VCH. d) Bending. For the spider image: Reproduced under the terms of the CC‐BY Creative Commons Attribution 4.0 International License.^{[ 100 ]} Copyright 2019, The Authors, Published by Springer Nature. For the scheme and the bending image: Reproduced with permission.^{[ 81 ]} Copyright 2017, Optical Society of America. e) Crawling. For the scorpion image: Reproduced with permission.^{[ 101 ]} Copyright 2019, Elsevier. For the scheme and the scorpion robot image: Reproduced with permission.^{[ 74 ]} Copyright 2019, American Chemical Society. f) Twisting. Reproduced with permission.^{[ 41 ]} Copyright 2019, Wiley‐VCH. g) Self‐healing. For the gecko image: Reproduced with permission.^{[ 102 ]} Copyright 2014, Wiley‐VCH. For the GO self‐healing tail images: Reproduced with permission.^{[ 37 ]} Copyright 2019, Wiley‐VCH.