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HIGHLIGHTS • An overview of the formation mechanisms, fabrication methods, and applications of bioinspired wrinkling patterns on curved substrates is provided. • The effect of substrate curvature is described in detail to clarify the difference of wrinkling patterns between planar and curved substrates. • Opportunities and challenges of the surface wrinkling in the biofabrication, three-dimensional micro/nano fabrication, and fourdimensional printing are discussed.

Template‐free, highly efficient, and large‐area construction of complex multiscale architectures is still a great challenge for microfabrications. Inspired by the hierarchical micropapillae on the superhydrophobic surface of natural rose petals, here, a facile 3D shrinking method is reported to build a graphene oxide (GO) papillae array. Circular GO speckles with a gradient of thickness are deposited on an inflated latex balloon through the water‐evaporation‐driven assembly of GO nanosheets, which then shrink into hierarchical papillae under compressive stresses upon deflation. The fluoroalkylsilane modified GO papillae array exhibits a combined performance of strong superhydrophobicity (CA > 170°), tunable adhesive force (39.2–129.4 µN), and ultralarge liquid capacity (25 µL). The wetting states (Wenzel, Cassie‐I, and Cassie‐Baxter), the adhesive forces, and the liquid capacities all can be tuned by varying the buckling topography (microwrinkle or microfold), the papillae number (3, 4, 6, or 7), and the array arrangement (triangle, square, or hexagon). For one single papillae, the highest adhesive force and the highest liquid capacity incresed to a record breaking value of 26.5 µN and 4.2 µL, respectively, which are promising for programmable manipulations of microdroplets and relevant for multistep microreactions.

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.

Water-soluble ribbon-like g-C3N4 and various special assemblies were obtained from dicyandiamide using NaCl crystals as a hard template.

Recently, flexible and wearable devices are increasingly in demand and graphene has been widely used due to its exceptional chemical, mechanical and electrical properties. Building complex buckling patterns of graphene is an essential strategy to increase its flexible and stretchable properties. Herein, a facile dimensionally controlled four-dimensional (4D) shrinking method was proposed to generate hierarchical reduced graphene oxide (rGO) buckling patterns on curved substrates mimicking different parts of the uniforms. The reduced graphene oxide ridges (rGORs) generated on the spherical substrate seem isotropic, while those generated on the cylindrical substrate are obviously more hierarchical or oriented, especially when the cylindrical substrate are shrinking via two steps. The oriented rGORs are superhydrophobic and strain sensitive but obviously anisotropic along the axial and circumferential directions. The sensitivity of rGORs along the axial direction is much higher than those along the circumferential direction. In addition, the intrinsic solvent barrier property of graphene enables the crack-free rGORs an excellent chemical protective performance, withstanding DCM immersion for more than 2.5 h. The flexible rGORs-based strain sensors can be used to detect both large and subtle human motions and activities by achieving high sensitivity (maximum gauge factor up to 48), high unidirectional stretchability (300−530%), and ultrahigh areal stretchability (up to 2690%). Excellent durability was also demonstrated for human motion monitoring with resistance to hand rubbing, ultrasonic cleaning, machine washing, and chemical immersion.

Sandwichlike hybrids of reduced graphene oxide (rGO) and hexagonal boron nitride (h-BN) were prepared via heat treatment of the self-assemblies of graphene oxide (GO) and ammonia borane (AB). TG-DSC-QMS analysis indicate a mutually promoted redox reaction between GO and AB; 900 °C is a proper temperature to transfer the hybrids into inorganic sandwiches. XRD, XPS, and Raman spectra reveal the existence of h-BN embedded into the rGO frameworks. High-resolution SEM and TEM indicate the layer-by-layer structure of the hybrids. The content of h-BN can be increased with increase of the mass ratio of AB and the highest heat treatment temperature. The complex permittivity and the microwave absorption are tunable with the variation of the content of h-BN. When the mass ratio of GO/AB is 1:1, the microwave absorption of the hybrid treated at 900 °C is preferable in the range of 6-18 GHz. A minimum reflection loss, -40.5 dB, was observed at 15.3 GHz for the wax composite filled with 25 wt % hybrids at the thickness of 1.6 mm. The qualified frequency bandwidth reaches 5 GHz at this thickness with a low surface density close to 1.68 kg/m. The layer-by-layer structure of the hybrid makes great contributions to the increased approaches and possibilities of electron migrating and hopping, which has both highly efficient dielectric loss and excellent impedance matching for microwave consumption.

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