Gyrification-Inspired Highly Convoluted Graphene Oxide Patterns for Ultralarge Deforming Actuators

Abstract

Gyrification in the human brain is driven by the compressive stress induced by the tangential expansion of the cortical layer, while similar topographies can also be induced by the tangential shrinkage of the spherical substrate. Herein we introduce a simple three-dimensional (3D) shrinking method to generate the cortex-like patterns using two-dimensional (2D) graphene oxide (GO) as the building blocks. By rotation-dip-coating a GO film on an air-charged latex balloon and then releasing the air slowly, a highly folded hydrophobic GO surface can be induced. Wrinkling-to-folding transition was observed and the folding state can be easily regulated by varying the prestrain of the substrate and the thickness of the GO film. Driven by the residue stresses stored in the system, sheet-to-tube actuating occurs rapidly once the bilayer system is cut into slices. In response to some organic solvents, however, the square bilayer actuator exhibits excellent reversible, bidirectional, large-deformational curling properties on wetting and drying. An ultralarge curvature of 2.75 mm was observed within 18 s from the original negative bending to the final positive bending in response to tetrahydrofuran (THF). In addition to a mechanical hand, a swimming worm, a smart package, a bionic mimosa, and two bionic flowers, a crude oil collector has been designed and demonstrated, aided by the superhydrophobic and superoleophilic modified GO surface and the solvent-responsive bilayer system.

Stretchable and Washable Strain Sensor Based on Cracking Structure for Human Motion Monitoring

“…The buckling mechanism (e.g. wrinkled or wavy structure) 9,15,37,45 has been proven to be an effective strategy for fabricating stretchable devices from non-stretchable materials 36 , as the applied stress can be effectively absorbed by expansion of the buckled structure until fully straightened, and also the adhesion of the ink is improved 46 . Thus, the stretchability performance was dependent on the level of pre-strain 47 and electrically active areas of Ag-DS/CF were observed to remain intact during repeatable stretching up to strains of 75% in the direction of the X-axis for configuration 50.…”

“…Achieving large stretchability (ɛ > 50%) and a high sensitivity (GF > 100) with a wide detection range have been the key factors in the development of strain sensors. This has been proven to be difficult 9,20,22,34,35 because large stretching requires structural integrity, whereas substantial changes in the electrically active area are required in order to achieve high sensitivity 36,37 . However, several studies have shown that this is possible with highly sensitive piezoresistive structures 11,13,16,20,34,38,39 , but these sensors often show high contact resistance further limiting their feasibility to wearable sensing.…”

Bioinspired Multiscale Wrinkling Patterns on Curved Substrates: An Overview

“…Therefore, surface wrinkling of thin stiff shells on hollow soft substrates will be the center of this section. Compared with solid core-shell systems, the expansion and contraction of hollow soft spheres and cylindrical tubes composed of elastic walls can be induced by inflation and deflation, and the contractioninduced compressive stress in the shells can be regulated by varying the pressure difference [54,55,61,157,199]. For hollow core-shell systems with thick walls (≥ 10 mm), directly pumping the air from the cavity is an efficient way to generate homogeneous compression in the shell, and sufficiently large compressive stress is able to trigger surface instability.…”

“…c-f Digital images of the bending and recover process of c a worm-like swimmer, d a smart package, e two bionic flowers, and f a bionic mimosa. All scale bars in the images are 1 cm [55]. Copyright 2017 American Chemical Society https://doi.org/10.1007/s40820-020-00436-y © The authors [185,205].…”

“…Copyright 2015 The American Association for the Advancement of Science. g3,g4 Highly convoluted GO patterns for bionic actuator [55]. Copyright 2017 American Chemical Society bending and stretchability of dielectric elastomer actuator (DEA) [220,[266][267][268].…”