Moisture-Responsive Wrinkling Surfaces with Tunable Dynamics

Unconstrained dynamic gel swelling generates transient surface deformations

Polymer gels are comprised of a three-dimensional, cross-linked network that can typically withstand the mechanical deformation associated with both swelling and de-swelling. Thus, gels can be designed with smart behaviors that require both stress generation and dissipation, making them well-suited to many applications including membrane technology, water capture devices, and drug delivery systems. In contrast to the fully swelled equilibrium state, limited research characterizes the unsteady-state swelling regime prior to equilibrium. It is in this regime where unique surface deformations can occur. Here we show how internal network constraints and external diffusive pressure can be leveraged to manipulate swelling kinetics and surface deformations in poly(ethylene glycol) gels during unconstrained, three-dimensional swelling. We find that increasing cross-linker molecular weight and swelling in ethanol, as opposed to water, are both effective routes to increase the time it takes to reach equilibrium but do so through different mechanisms. Networks with fewer internal constraints, manipulated via cross-linker chain-length, imbibe more solvent over a longer time. In contrast, swelling in ethanol reduces the amount of solvent imbibed by the network while increasing the time to reach equilibrium. Measurements of surface patterns during swelling establishes that an immediate, fast relaxation at the surface occurs during the first five minutes of swelling. However, the density and persistence of these features varies with solvent quality. These results establish a framework for how soft materials undergo dynamic deformation. Engineering transient surface properties while mitigating unwanted instabilities opens the door for emerging technologies such as smart anti-fouling and sensors.

Interfacial Wrinkling Structures Based on a Double Cross-Linking Strategy Enable a Dual-Mode Optical Information Encryption

Surface wrinkling structures based on a bilayer system are widely employed in storing and encrypting specific optical information. However, constructing a stable wrinkling structure with high-level security remains an extensive challenge due to the delamination issue between the skin layer and the substrate. Herein, a double cross-linking strategy is introduced between a hydrogel layer doped with fluorescent molecules and polydimethylsiloxane to establish a stable interfacial wrinkling structure with dual-mode functionality, in which the light reflection of the wrinkles and fluorescence intensity of fluorescent molecules can be simultaneously regulated by the modulus ratio between the two layers. The spontaneous wrinkling structures with a physically unclonable function can enhance the photoluminescence emission intensity of the wrinkling area under ultraviolet radiation. Meanwhile, the skin layer constructed of acrylamide and acrylic acid copolymer protects the interfacial wrinkling patterns from the loss of a detailed structure for authentication due to external damage. The stable interfacial wrinkling structures with fluorescence can find potential applications in the fields of information storage and encryption.

Biomimetic Photonic Elastomer Exhibiting Stress/Moisture Reconfigurable Wrinkle-Lattice for Reversible Deformation Information Storage

Photonic elastomers, capable of converting imperceptible deformations into visible colors, show significant potential in smart materials. However, instantaneous deformation is arduous to record accurately due to the disappearance of optical information after deformation recovery. Herein, inspired by the folding structures of iridocytes in cephalopods, a stress- and moisture-triggered wrinkling and erasure effect is proposed to be introduced in the construction of a photonic elastomer. Implemented in a dual-network polymer framework with modulatable locking, it allows for reversible deformation storage. The photonic elastomer comprises a surface one-dimensional photonic crystal (1DPC) and a poly(dimethylsiloxane) (PDMS) substrate. The deformed 1DPC lattice transforms into a wrinkled state due to a substrate deformation mismatch, preserving strain-induced structural color information through interchain hydrogen bonding and crystalline shape-locking in dual-network polymers. Reading the color provides multidimensional information about the instantaneous deformation degree and distribution. Moreover, the moisture-induced shape-memory feature of the 1DPC can be triggered with a minute amount of water, like fingertip perspiration or humidity change (35% to 80%), to restore the original color. This stress/moisture-responsive photonic elastomer, with its dynamically reconfigurable wrinkle-lattice, holds great promise for applications in mechanical sensing, inkless writing, and anticounterfeiting, significantly enhancing the versatility of photonic materials.

Fabrication of Self-Wrinkling Polymer Films with Tunable Patterns through an Interfacial-Fuming-Induced Surface Instability Process

Inspired by the superglue fuming method for fingerprint collection, this study developed a novel interfacial-fuming-induced surface instability process to generate wrinkled patterns on polymeric substrates. High-electronegativity groups are introduced on the substrate surface to initiate the polymerization of monomer vapors, such as ethyl cyanoacrylate, which results in the formation of a stiff poly(ethyl cyanoacrylate) capping layer. Moreover, interfacial polymerization resulted in the covalent bonding of the substrate, which led to the volumetric shrinkage of the composite and the accumulation of compressive strain. This process ultimately resulted in the development and stabilization of wrinkled surface morphologies. The authors systematically examined parameters such as the modulus of the epoxy substrate, prestrain, the flow rate of fuming, and operating temperature. The aforementioned technique can be easily applied to architectures with complex outer morphologies and inner surfaces, thereby enabling the construction of surface patterns under ambient conditions without vacuum limitations or precise process control. This study is the first to combine fuming-induced interfacial polymerization with surface instability to create robust wrinkles. The proposed method enables the fabrication of intricate microwrinkled patterns and has considerable potential for use in various practical applications, including microfluidics, optical components, bioinspired adhesive devices, and interfacial engineering.

Tunable evaporation-induced surface morphologies on chitosan film for light management

The surface morphologies of polymer films have been used to improve the performance or enable new applications of films, such as controllable adhesion, shape morphing and light management. However, complicated and destructive methods were applied to produce surface morphologies on chitosan (CS) film. To overcome this challenge, we report an evaporation-induced self-assembly to form the tunable morphologies on the surface of short-chain chitosan film by varying the evaporation rates that influence the aggregation behavior of polymer chains between order and disorder. It enables the simple, tunable and scalable fabrication of surface morphologies on CS film (CS solution concentration: 2 wt%, drying from room temperature (RT) to 80 °C) that provides controllable haze (3-74 %) and high transmittance (>85 %) for the production of hazy and transparent window coatings. This simple approach to producing tunable surface morphologies could inspire the synthesis of multifunctional polymer films with different surface structures, whose applications can be extended to cell culture interfaces, flexible bioelectronic and optoelectronic devices.

Viscoelasticity‐Controlled Relaxation in Wrinkling Surface for Multistage Time‐Resolved Optical Information Encryption

As counterfeit techniques continue to evolve, ensuring the security of conventional "static" encryption methods becomes increasingly challenging. Here, the viscoelasticity-controlled relaxation is introduced for the first time in a bilayer wrinkling system by regulating the density of hydrogen bond networks in polymer to construct a "dynamic" encryption material. The wrinkling surface can manipulate light during the dynamic relaxation process, exhibiting three stages with frosted glass, structural color, and mirror reflection. By regulating the viscoelasticity of skin layer through UV irradiation, the wavelength and the relaxation rate of the wrinkles can be controlled. As a result, dynamic wrinkling anti-counterfeiting patterns and time-resolved multistage information encryption are achieved. Crucially, the encryption material is developed as an anti-counterfeiting label for packing boxes in daily applications, allowing the encrypted information to be activated manually and identified by naked eyes, surpassing the existing time-resolved encryption materials in utilization potential. Besides, the dynamic hydrogen bond networks are extended to various dynamic interaction networks, demonstrating the versatility of the dynamic encryption strategy. This work not only provides an additional dimension for dynamic information encryption in daily practical use, but also offers theoretical guidance for the development of advanced optical anti-counterfeiting and smart display materials in the future.

Hierarchical Wrinkles with Piezopotential Enhanced Surface Tribopolarity for High-Performance Self-Powered Pressure Sensor

Achieving both high sensitivity and wide detecting range is significant for the applications of triboelectric nanogenerator-based self-powered pressure sensors (TPSs). However, most of the previous designs with high sensitivity usually struggle in a narrow pressure detection range (<30 kPa) while expanding the detection range normally sacrifices the sensitivity. To overcome this well-known obstacle, herein, piezopotential enhanced triboelectric effect realized by a rationally designed PDMS/ZnO NWs hierarchical wrinkle structure was exploited to develop a TPS (PETPS) with both high sensitivity and wide detecting range. In this PETPS design, the piezopotential derived from the deformation of ZnO NWs enhances its tribo-charge transferring ability; meanwhile, the hierarchical structure helps to establish a dynamically self-adjustable contact area. Benefiting from these advantages, the PETPS simultaneously achieves high sensitivity (0.26 nC cm-2 kPa-1 from 1 to 25 kPa, and 0.02 nC cm-2 kPa-1 from 25 to 476 kPa), fast response (46 ms), wide sensing range (1 to 476 kPa), and good stability (over 4000 cycles). In addition, the output charge density that is independent of the speed rate of driven force was adopted as the sensing signal of PETPS to replace the commonly used peak voltage/current values, enabling it more adaptive to accurately detect pressure variation in real applications.

Functional PDMS Elastomers: Bulk Composites, Surface Engineering, and Precision Fabrication

Polydimethylsiloxane (PDMS)-the simplest and most common silicone compound-exemplifies the central characteristics of its class and has attracted tremendous research attention. The development of PDMS-based materials is a vivid reflection of the modern industry. In recent years, PDMS has stood out as the material of choice for various emerging technologies. The rapid improvement in bulk modification strategies and multifunctional surfaces has enabled a whole new generation of PDMS-based materials and devices, facilitating, and even transforming enormous applications, including flexible electronics, superwetting surfaces, soft actuators, wearable and implantable sensors, biomedicals, and autonomous robotics. This paper reviews the latest advances in the field of PDMS-based functional materials, with a focus on the added functionality and their use as programmable materials for smart devices. Recent breakthroughs regarding instant crosslinking and additive manufacturing are featured, and exciting opportunities for future research are highlighted. This review provides a quick entrance to this rapidly evolving field and will help guide the rational design of next-generation soft materials and devices.

Interactive deformable electroluminescent devices enabled by an adaptable hydrogel system with optical/photothermal/mechanical tunability

Deformable electroluminescent devices (DELDs) with mechanical adaptability are promising for new applications in smart soft electronics. However, current DELDs still present some limitations, including having stimuli-insensitive electroluminescence (EL), untunable mechanical properties, and a lack of versatile stimuli response properties. Herein, a facile approach for fabricating in situ interactive and multi-stimuli responsive DELDs with optical/photothermal/mechanical tunability was proposed. A polyvinyl alcohol (PVA)/polydopamine (PDA)/graphene oxide (GO) adaptable hydrogel exhibiting optical/photothermal/mechanical tunability was used as the top ionic conductor (TIC). The TIC can transform from a viscoelastic state to an elastic state via a special freezing-salting out-rehydration (FSR) process. Meanwhile, it endows the DELDs with a photothermal response and thickness-dependent light shielding properties, allowing them to dynamically demonstrate "on" or "off" or "gradually change" EL response to various mechanical/photothermal stimuli. Thereafter, the DELDs with a viscoelastic TIC can be utilized as pressure-responsive EL devices and laser-engravable EL devices. The DELDs with an elastic TIC can withstand both linear and out-of-plane deformation, enabling the designs of various interactive EL devices/sensors to monitor linear sliders, human finger bending, and pneumatically controllable bulging. This work offers new opportunities for developing next-generation EL-responsive devices with widespread application based on adaptable hydrogel systems.

Transfer-Printing Hydrogel-Based Platform for Moisture-Driven Dynamic Display and Optical Anti-Counterfeiting

Humidity-responsive materials offer a promising approach to achieving tunable metasurface systems due to their fast and reversible swelling responses to moisture, which enables many important applications, such as real-time humidity sensing, optical switches, dynamic displays, and optical information encryption. However, the humidity-responsive structural coloration generally cannot provide a high spatial resolution and requires a complex patterning process. Here, we present a scalable moisture-driven color-changing Fabry-Pérot (FP)-like cavity composed of a polyvinyl alcohol layer sandwiched between an upper gold nanoparticles assembly and a bottom gold mirror. Through nanoparticle contact printing, we pixelated these cavities with sub-micrometer sizes without crosstalk and achieved an ultrahigh display resolution of ∼400 nm. Meanwhile, these nanoparticle-based FP (NBFP) cavities exhibit more vibrant colors than those of conventional film-based ones due to broadband absorption of the disordered nanoparticle assembly. Moreover, the NBFP cavities exhibit a rapid response (<300 ms), benefiting from the membrane pores formed in the gaps between the adjacent nanoparticles. Finally, we demonstrated the applications of the NBFP cavities in optical anti-counterfeiting and dynamic multi-color printing. These results suggest that our approach will help to realize a colorful, fast, and ultrahigh-resolution dynamic display device in optical security and colorimetric sensing.

Morphological Diagram of Dynamic-Interfacial-Release-Induced Surface Instability

In this study, a morphological diagram was constructed for quantitatively predicting various modes of surface instabilities caused by the dynamic interfacial release of strain in initially flat bilayer composites comprising an elastomer and a capping layer. Theory, experiment, and simulation were combined to produce the diagram, which enables systematic generation of the following instability patterns: wrinkle, fold, period-double, delamination, and coexisting patterns. The pattern that forms is most strongly affected by three experimental parameters: the elastic modulus of the elastomer, the elastic modulus of the capping layer, and the thickness of the capping layer. The morphological diagram offers understanding of the formation of complex patterns and development of their applications. Critically, the wrinkle alignment can be well controlled by changing the direction of the interfacial release to enable the creation of centimeter-sized and highly ordered lamellar wrinkled patterns with a single orientation on a soft elastomer without the need for costly high-vacuum instruments or complex fabrication processes. The method and diagram have great potential for broad use in many practical applications ranging from flexible electronic devices to smart windows.

Wrinkled Interfaces: Taking Advantage of Anisotropic Wrinkling to Periodically Pattern Polymer Surfaces

Periodically patterned surfaces can cause special surface properties and are employed as functional building blocks in many devices, yet remaining challenges in fabrication. Advancements in fabricating structured polymer surfaces for obtaining periodic patterns are accomplished by adopting "top-down" strategies based on self-assembly or physico-chemical growth of atoms, molecules, or particles or "bottom-up" strategies ranging from traditional micromolding (embossing) or micro/nanoimprinting to novel laser-induced periodic surface structure, soft lithography, or direct laser interference patterning among others. Thus, technological advances directly promote higher resolution capabilities. Contrasted with the above techniques requiring highly sophisticated tools, surface instabilities taking advantage of the intrinsic properties of polymers induce surface wrinkling in order to fabricate periodically oriented wrinkled patterns. Such abundant and elaborate patterns are obtained as a result of self-organizing processes that are rather difficult if not impossible to fabricate through conventional patterning techniques. Focusing on oriented wrinkles, this review thoroughly describes the formation mechanisms and fabrication approaches for oriented wrinkles, as well as their fine-tuning in the wavelength, amplitude, and orientation control. Finally, the major applications in which oriented wrinkled interfaces are already in use or may be prospective in the near future are overviewed.

Novel Green Reversible Humidity-Responsive Hemiaminal Dynamic Covalent Network for Smart Window

Recently, smart windows have attracted widespread attention on account of their unique features, yet traditional smart windows still rely on external energy support to accomplish dynamic reversible switching, which not only confines usage but also causes waste of energy. For this purpose, we have prepared hemiaminal dynamic covalent network (HDCN) film with outstanding flexibility and strength by a simple and low-cost method, in which the modulus is 206.28 MPa and the elongation at break is 39.02%. Additionally, the transition from a transparent to an opaque state is achieved when the film is stimulated by humidity, and the dynamic transformation of the film to different phases of transparency is obtained when the film is exposed to different relative humidities (60-99%). Most importantly, HDCN film fulfills the modern green requirements and enables complete dissolution in a certain mildly acidic solution, avoiding environmental pollution when the material is discarded due to loss of function. The dynamic tunability of HDCN film demonstrates great advantages and potential in smart windows and anticounterfeiting.

Adaptive 2D and Pseudo-2D Systems: Molecular, Polymeric, and Colloidal Building Blocks for Tailored Complexity

Two-dimensional and pseudo-2D systems come in various forms. Membranes separating protocells from the environment were necessary for life to occur. Later, compartmentalization allowed for the development of more complex cellular structures. Nowadays, 2D materials (e.g., graphene, molybdenum disulfide) are revolutionizing the smart materials industry. Surface engineering allows for novel functionalities, as only a limited number of bulk materials have the desired surface properties. This is realized via physical treatment (e.g., plasma treatment, rubbing), chemical modifications, thin film deposition (using both chemical and physical methods), doping and formulation of composites, or coating. However, artificial systems are usually static. Nature creates dynamic and responsive structures, which facilitates the formation of complex systems. The challenge of nanotechnology, physical chemistry, and materials science is to develop artificial adaptive systems. Dynamic 2D and pseudo-2D designs are needed for future developments of life-like materials and networked chemical systems in which the sequences of the stimuli would control the consecutive stages of the given process. This is crucial to achieving versatility, improved performance, energy efficiency, and sustainability. Here, we review the advancements in studies on adaptive, responsive, dynamic, and out-of-equilibrium 2D and pseudo-2D systems composed of molecules, polymers, and nano/microparticles.

Smart Polymer Surfaces with Complex Wrinkled Patterns: Reversible, Non-Planar, Gradient, and Hierarchical Structures

This review summarizes the relevant developments in preparing wrinkled structures with variable characteristics. These include the formation of smart interfaces with reversible wrinkle formation, the construction of wrinkles in non-planar supports, or, more interestingly, the development of complex hierarchically structured wrinkled patterns. Smart wrinkled surfaces obtained using light-responsive, pH-responsive, temperature-responsive, and electromagnetic-responsive polymers are thoroughly described. These systems control the formation of wrinkles in particular surface positions and the reversible construction of planar-wrinkled surfaces. This know-how of non-planar substrates has been recently extended to other structures, thus forming wrinkled patterns on solid, hollow spheres, cylinders, and cylindrical tubes. Finally, this bibliographic analysis also presents some illustrative examples of the potential of wrinkle formation to create more complex patterns, including gradient structures and hierarchically multiscale-ordered wrinkles. The orientation and the wrinkle characteristics (amplitude and period) can also be modulated according to the requested application.

Review on Mechanoresponsive Smart Windows: Structures and Driving Modes

The growing awareness about the global energy crisis and extreme weather from global warming drives the development of smart windows market. Compared to conventional electrochromic, photochromic, or thermochromic smart windows, mechanoresponsive smart windows present advantages of simple construction, low cost, and excellent stability. In this review, we summarize recent developments in mechanoresponsive smart windows with a focus on the structures and properties. We outline the categories and discuss the advantages and disadvantages. Especially, we also summarize six unconventional driving modes to generate mechanical strain, including pneumatic, optical, thermal, electric, magnetic, and humidity modes. Lastly, we provide practical recommendations in prospects for future development. This review aims to provide a useful reference for the design of novel mechanoresponsive smart windows and accelerate their practical applications.

Photo-induced stress relaxation in reconfigurable disulfide-crosslinked supramolecular films visualized by dynamic wrinkling

Stress relaxation in reconfigurable supramolecular polymer networks is strongly related to intermolecular behavior. However, the relationship between molecular motion and macroscopic mechanics is usually vague, and the visualization of internal stress reflecting precise regulation of molecules remains challenging. Here, we present a strategy for visualizing photo-driven stress relaxation induced by infinitesimal perturbations in the intermolecular exchange reaction via reprogrammable wrinkle patterns. The supramolecular films exhibit visible changes in microscopic wrinkle topography through ultraviolet (UV)-induced dynamic disulfide exchange reaction. In accordance with the trans-scale theoretical models, which quantitatively evaluate the chemical-dependent mechanical stresses in the supramolecular network, the unexposed disordered wrinkles evolved into highly oriented patterns and underwent subsequent mutations after thermal treatment. The stress-sensitive wrinkle macro-patterns can be repetitively written/erased through network topology rearrangement using different stimuli. This strategy provides an approach for visualizing and understanding the molecular behavior from dynamic chemistry to mechanical changes, and directly programming wrinkle patterns with regulated structures.

Strong and tough self-wrinkling polyelectrolyte hydrogels constructed via a diffusion-complexation strategy

Self-wrinkling hydrogels enable various engineering and biomedical applications. The major challenge is to couple the self-wrinkling technologies and enhancement strategies, so as to get rid of the poor mechanical properties of existing self-wrinkling gels. Herein we present a facile diffusion-complexation strategy for constructing strong and ultratough self-wrinkling polyelectrolyte hydrogels with programmable wrinkled structures and customizable 3D configurations. Driven by the diffusion of low-molecular-weight chitosan polycations into the polyanion hydrogels, the high-modulus polyelectrolyte complexation shells can form directly on the hydrogel surface. Meanwhile, the polyanion hydrogels deswell/shrink due to the low osmotic pressure, which applies an isotropous surface compressive stress for inducing the formation of polygonal wrinkled structures. When the diffusion-complexation reaction occurs on a pre-stretched hydrogel sheet, the long-range ordered wrinkled structures can form during the springback/recovery of the hydrogel matrix. Moreover, through controlling the regions of diffusion-complexation reaction on the pre-stretched hydrogels, they can be spontaneously transformed into various 3D configurations with ordered wrinkled structures. Notably, because of the introduction of plenty of electrostatic binding (i.e., sacrificial bonds), the as-prepared self-wrinkling gels possess outstanding mechanical properties, far superior to the reported ones. This diffusion-complexation strategy paves the way for the on-demand design of high-performance self-wrinkling hydrogels.

Light-Induced Surface Wrinkling on Azo-Based Composite Films

Here we report a simple micro/nano patterning strategy based on light-induced surface wrinkling. Namely, we fabricated a film/substrate system composed of polydimethylsiloxane (PDMS) as a soft substrate and non-photosensitive polymer polystyrene (PS) mixed with azo-polymer (polydisperse orange 3, PDO3) as a stiff film. Taking advantage of the photo-thermal effect and photo-softening effect of PDO3, we fabricated various microstructured wrinkling morphologies by a simple light illumination. We investigated the influence of two exposure modes (i.e., static selective exposure and dynamic moving exposure), the illumination conditions, the composition of the blended film, and the film thickness on the resulting wrinkling patterns. It is highly expected that this azo-based photosensitive wrinkling system will be extended to functional systems for the realization of light-induced surface micro/nanopatterning.

Dynamic Surface Wrinkles for In Situ Light-Driven Dynamic Gratings

Dynamic diffraction gratings (DDGs) are considered as one of the most promising technologies for application in smart optical devices because of their in situ dynamic regulation of light propagation on demand; however, it is still a challenge to fabricate dynamic periodic micro/nanostructures due to limited materials and processes. Here, a facile and feasible strategy to construct a near-infrared (NIR) radiation-driven DDG is developed based on a double-sided surface pattern, which is fabricated by dynamic wrinkles and/or soft-imprinted static wrinkles. Poly(dimethylsiloxane) (PDMS) containing carbon nanotubes (CNTs) serves as the substrate, and wrinkles are formed on both sides. The resulting double-sided wrinkle pattern can be used as a DDG to generate various adjustable two-dimensional (2D) diffraction patterns driven by NIR light. Furthermore, with various combinations of wrinkles, we demonstrated a single-sided responsive DDG and a double-sided responsive DDG to realize the evolution of diffraction patterns from 2D to one-dimensional (1D) and 2D to zero-dimensional (0D), respectively. The results provide an alternative for DDGs that will have wide applications in smart display, sensing, and imaging systems.

Dynamic multifunctional devices enabled by ultrathin metal nanocoatings with optical/photothermal and morphological versatility

Smart devices characterized by micro-/nanotopographies, such as cracks, wrinkles, folds, etc., have been fabricated for widespread application. Here, with the combination of multiscale hierarchical architecture, ultrathin metal nanocoatings with high optical/photothermal tunability and morphological versatility, and surface/interface engineering, a set of multifunctional devices with multistimuli responsiveness was fabricated. These devices can adapt to external stimuli with reversible and instantaneous responses in optical signals, which include strain-regulated light-scattering properties, photothermal-responsive wrinkled surface coupled with moisture-responsive structural color, and mechanically controllable light-shielding properties. The structural designs that rationally overlay micro-/nanostructured ultrathin nanocoatings with other elements are the key to realize this advanced system, which provides avenues for designing versatile, tunable, and adaptable multifunctional devices.

Inspired by the intriguing adaptivity of natural life, such as squids and flowers, we propose a series of dynamic and responsive multifunctional devices based on multiscale structural design, which contain metal nanocoating layers overlaid with other micro-/nanoscale soft or rigid layers. Since the optical/photothermal properties of a metal nanocoating are thickness dependent, metal nanocoatings with different thicknesses were chosen to integrate with other structural design elements to achieve dynamic multistimuli responses. The resultant devices demonstrate 1) strain-regulated cracked and/or wrinkled topography with tunable light-scattering properties, 2) moisture/photothermal-responsive structural color coupled with wrinkled surface, and 3) mechanically controllable light-shielding properties attributed to the strain-dependent crack width of the nanocoating. These devices can adapt external stimuli, such as mechanical strain, moisture, light, and/or heat, into corresponding changes of optical signals, such as transparency, reflectance, and/or coloration. Therefore, these devices can be applied as multistimuli-responsive encryption devices, smart windows, moisture/photothermal-responsive dynamic optics, and smartphone app–assisted pressure-mapping sensors. All the devices exhibit high reversibility and rapid responsiveness. Thus, this hybrid system containing ultrathin metal nanocoatings holds a unique design flexibility and adaptivity and is promising for developing next-generation multifunctional devices with widespread application.

Simultaneous Realization of Superoleophobicity and Strong Substrate Adhesion in Water via a Unique Segment Orientation Mechanism

The underwater superoleophobicity of a coating is often caused by its preferential water affinity, which, however, normally weakens the substrate adhesion property. In this work, a new strategy is reported for achieving strong underwater adhesion between a well-designed amphiphilic polyurethane coating and a diverse range of substrates while also rendering the coating surface's superoleophobicity. When the coating, which is a mixture of an amphiphilic polyurethane and a water miscible solvent, is immersed in water, the hydrophobic segments aggregate to orientate and pile along the surface of substrates via a segment orientation mechanism triggered by solvent exchange with water penetration to exert strong adhesion. At the same time, the hydrophilic segments will physically crosslink to form a hydrogel coating, endowing the substrate with underwater superoleophobicity. This work provides a facile, versatile, and scalable approach for the future design of superoleophobic coatings in a water environment.

Light-driven dynamic surface wrinkles for adaptive visible camouflage

Camouflage is widespread in nature, engineering, and the military. Dynamic surface wrinkles enable a material the on-demand control of the reflected optical signal and may provide an alternative to achieve adaptive camouflage. Here, we demonstrate a feasible strategy for adaptive visible camouflage based on light-driven dynamic surface wrinkles using a bilayer system comprising an anthracene-containing copolymer (PAN) and pigment-containing poly (dimethylsiloxane) (pigment-PDMS). In this system, the photothermal effect-induced thermal expansion of pigment-PDMS could eliminate the wrinkles. The multiwavelength light-driven dynamic surface wrinkles could tune the scattering of light and the visibility of the PAN film interference color. Consequently, the color captured by the observer could switch between the exposure state that is distinguished from the background and the camouflage state that is similar to the surroundings. The bilayer wrinkling system toward adaptive visible camouflage is simple to configure, easy to operate, versatile, and exhibits in situ dynamic characteristics without any external sensors and extra stimuli.

Biomimetic and bioinspired surface topographies as a green strategy for combating biofouling: a review

Biofouling refers to the adverse attachment and colonization of fouling organisms, including macromolecules, bacteria, and sessile invertebrates, on the surfaces of materials submerged in aquatic environments. Almost all structures working in watery surroundings, from marine infrastructures to healthcare facilities, are affected by this sticky problem, resulting in massive direct and indirect economic loss and enormous cost every year in protective maintenance and remedial cleaning. Traditional approaches to preventing marine biofouling primarily rely on the application of biocide-contained paints, which certainly impose adverse effects on the ocean environment and marine ecology. Biomimicry offers an efficient shortcut to developing environmentally friendly antifouling techniques and has yielded encouraging and promising results. The antifouling strategies learned from nature can be broadly classified into two categories according to the nature of the cues applied for biofouling control. One is the chemical antifouling techniques, which are dedicated to extracting the effective antifoulant compounds from marine organisms and synthesizing chemicals mimicking natural antifoulants. In contrast, the physical biomimetic (BM) antifouling practices focus on the emulation and optimization of the physical cues such as micro and nanoscale surface topographies learned from naturally occurring surfaces for better antifouling efficacy. In this review, a synopsis of the techniques for manufacturing the BM and bioinspired (BI) antifouling surface topographies is introduced, followed by the bioassay to assess the antifouling performance of the structured surfaces. Then, the BM and BI surface topographies that were reported to possess enhanced antifouling competence are introduced, followed by a summary of theoretical modeling. The whole paper is concluded by summarizing the studies' deficiencies so far and outlooking the research directions in the future.

Nature-inspired robust hydrochromic film for dual anticounterfeiting

Nature-inspired materials have been actively developed for anticounterfeiting applications. Among a variety of stimuli-responsive anticounterfeiting strategies, hydrochromic materials exhibit reversible color change in response to moisture or water and have the advantage of being easy to authenticate. However, the security level of current hydrochromic anticounterfeiting materials is not sufficient for practical applications since they only exhibit a single anticounterfeiting function, where the information switches between visible and invisible. To improve the security level and efficiency of hydrochromic anticounterfeiting materials, here we developed a robust dual hydrochromic material via the self-assembly of polyurethane (PU)-polyelectrolytes colloids with which the desired information can not only switch between visible and invisible but also transform from one pattern to another within 3 s without the need of any external instruments. The bio-inspiration, material design and demonstrated hydrochromic properties might have profound implications for using colloidal complexes to make advanced anticounterfeiting materials.

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Micro-structures are formed by self-assembly of polyurethane-polyelectrolyte colloids

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Information changes from one pattern to another within 3 s when exposed to water

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The hydrochromic films are mechanically robust in both dry and wet state

Light-Induced Programmable 2D Ordered Patterns Based on a Hyperbranched Poly(ether amine) (hPEA)-Functionalized Graphene Film

Dynamic complex surface topography with ordered and tunable morphologies, which can provide on-demand control of surface properties to realize smart surfaces, is gaining much attention yet remains challenging in terms of fabrication. Here, a facile, robust, and controllable method is demonstrated to fabricate programmable two-dimensional (2D) ordered patterns with multiresponsive 2D ultrathin materials, comprised of anthracene-capped hyperbranched poly(ether amine) (hPEA-AN)-functionalized graphene (hPEA-AN@G). By combining the stimuli-responsiveness and UV sensitivity of hPEA-AN and excellent out-of-plane deformation and NIR-to-thermal conversion of graphene, the process of "writing/uploading" initial information is conducted through the initial exposure to 365 nm UV light to generate the 2D ordered pattern first; second, inducing swelling strain via moisture to create the hierarchical topographic pattern (orderly oriented pattern) is the process of "modification and erasable rewriting"; third, alternating NIR or 254 nm UV light blanket exposure are the two ways of erasing the information. Consequently, taking advantage of the multiresponsive dynamic wrinkling/ordered patterning, we can program globally 2D ordered surface patterns with diverse morphologies on demand and manipulate the resulted surface properties as desired.

Transparency Change Mechanochromism Based on a Robust PDMS-Hydrogel Bilayer Structure

Hydrogels and polydimethylsiloxane (PDMS) are complementary to each other, since the hydrophobic PDMS provides a more stable and rigid substrate, while the water-rich hydrogel possesses remarkable hydrophilicity, biocompatibility, and similarity to biological tissues. Herein a transparent and stretchable covalently bonded PDMS-hydrogel bilayer (PHB) structure is prepared via in situ free radical copolymerization of acrylamide and allylamine-exfoliated-ZrP (AA-e-ZrP) on a functionalized PDMS surface. The AA-e-ZrP serves as cross-linking nano-patches in the polymer gel network. The covalently bonded structure is constructed through the addition reaction of vinyl groups of PDMS surface and monomers, obtaining a strong interfacial adhesion between the PDMS and the hydrogel. A mechanical-responsive wrinkle surface, which exhibs transparency change mechanochromism, is created via introducing a cross-linked polyvinyl alcohol film atop the PHB structure. A finite element model is implemented to simulate the wrinkle formation process. The implication of the present finding for the interfacial design of the PHB and PDMS-hydrogel-PVA trilayer (PHPT) structures is discussed.

Regulating surface wrinkles using light

Regulating existing micro and nano wrinkle structures into desired configurations is urgently necessary yet remains challenging, especially modulating wrinkle direction and location on demand. In this work, we propose a novel light-controlled strategy for surface wrinkles, which can dynamically and precisely regulate all basic characteristics of wrinkles, including wavelength, amplitude, direction and location (λ, A, θ and Lc ), and arbitrarily tune wrinkle topographies in two dimensions (2D). By considering the bidirectional Poisson's effect and soft boundary conditions, a modified theoretical model depicting the relation between stress distributions and the basic characteristics was developed to reveal the mechanical mechanism of the regulation strategy. Furthermore, the resulting 2D ordered wrinkles can be used as a dynamic optical grating and a smart template to reversibly regulate the morphology of various functional materials. This study will pave the way for wrinkle regulation and guide fabrication technology for functional wrinkled surfaces.

Harnessing Dynamic Wrinkling Surfaces for Smart Displays

Reversible and switchable wrinkling surfaces in response to various external stimuli have extensive potential applications. In this Letter, we prepared the reversible wrinkling on poly(dimethylsiloxane) (PDMS) surfaces, responsive to the solvents, by ultraviolet-ozone (UVO) treatment with/without mechanical prestrain. Based on the solvent-responsive wrinkling, three types of optical transparency dynamics were achieved easily in a single and simple film-substrate system, including (I) completely reversible transparency with controlled relaxation time and isotropic light scattering; (II) completely reversible transparency with anisotropic light scattering and tunable diffusion degree; and (III) incompletely reversible transparency. The reversibility and stability of wrinkles can be controlled by tailoring the solvent type, UVO exposure time, and mechanical prestrain. The underlying mechanisms for the three wrinkling dynamics have been clearly elucidated. The extremely simple material system and the facile but efficient technique pave a novel way for realizing versatile optical dynamics for smart displays.

Symmetrical Wrinkles in Single-Component Elastomers with Fingerprint-Inspired Robust Isotropic Dry Adhesive Capabilities

Robust and inexpensive dry adhesives have a great potential in multitudinous industrial applications. However, to date, the fabrication of dry adhesives, prepared using high aspect ratio structures in general, requires specific equipment and time-consuming processes, which limit their practicable utilization. Inspired from human fingerprints, in this study, we created durable single-component elastomer surfaces with symmetric and multiple concentric-shaped wrinkled patterns that exhibit isotropic dry adhesion capabilities. The dynamic interfacial release-induced surface wrinkling property of a rigid degradable polymeric capping layer [i.e., poly(l-lactide) (PLLA)] was exploited on a soft elastomer substrate [i.e., polydimethylsiloxane (PDMS)] to spontaneously form wrinkled PLLA/PDMS bilayer composites. After conducting a two-step thermal curing process on the composite and hydrolysis of the PLLA capping layer, a single-component microwrinkled PDMS surface with a large area and symmetric patterns could be generated. The patterns show flexible, durable, and isotropic dry adhesion capabilities that could be controlled by tuning their geometrical parameters (wrinkle wavelengths and amplitudes) and elastic modulus. In particular, the formation of symmetrically wrinkled patterns without using expensive lithography for patterning and costly material precursors is an advantage and could be extended to other industrial applications, such as damage-free transportation, biomimetic climbing robots, and biocompatible medical patches.

Bioinspired Multiscale Wrinkling Patterns on Curved Substrates: An Overview

The surface wrinkling of biological tissues is ubiquitous in nature. Accumulating evidence suggests that the mechanical force plays a significant role in shaping the biological morphologies. Controlled wrinkling has been demonstrated to be able to spontaneously form rich multiscale patterns, on either planar or curved surfaces. The surface wrinkling on planar substrates has been investigated thoroughly during the past decades. However, most wrinkling morphologies in nature are based on the curved biological surfaces and the research of controllable patterning on curved substrates still remains weak. The study of wrinkling on curved substrates is critical for understanding the biological growth, developing three-dimensional (3D) or four-dimensional (4D) fabrication techniques, and creating novel topographic patterns. In this review, fundamental wrinkling mechanics and recent advances in both fabrications and applications of the wrinkling patterns on curved substrates are summarized. The mechanics behind the wrinkles is compared between the planar and the curved cases. Beyond the film thickness, modulus ratio, and mismatch strain, the substrate curvature is one more significant parameter controlling the surface wrinkling. Curved substrates can be both solid and hollow with various 3D geometries across multiple length scales. Up to date, the wrinkling morphologies on solid/hollow core-shell spheres and cylinders have been simulated and selectively produced. Emerging applications of the curved topographic patterns have been found in smart wetting surfaces, cell culture interfaces, healthcare materials, and actuators, which may accelerate the development of artificial organs, stimuli-responsive devices, and micro/nano fabrications with higher dimensions.

Dynamic wrinkling pattern exhibiting tunable fluorescence for anticounterfeiting applications

A dynamic surface pattern with a topography and fluorescence in response to environmental stimulus can enable information recording, hiding, and reading. Such patterns are therefore widely used in information security and anticounterfeiting. Here, we demonstrate a dynamic dual pattern using a supramolecular network comprising a copolymer containing pyridine (P4VP-nBA-S) and hydroxyl distyrylpyridine (DSP-OH) as the skin layer for bilayer wrinkling systems, in which both the wrinkle morphology and fluorescence color can be simultaneously regulated by visible light-triggered isomerization of DSP-OH, or acids. Acid-induced protonation of pyridines can dynamically regulate the cross-linking of the skin layer through hydrogen bonding, and the fluorescence of DSP-OH. On selective irradiation with 450 nm visible light or acid treatment, the resulting hierarchical patterned surface becomes smooth and wrinkled reversibly, and simultaneously its fluorescence changes dynamically from blue to orange-red. The smart surfaces with dynamic hierarchical wrinkles and fluorescence can find potential application in anticounterfeiting.

Low-Cost, Robust Pressure-Responsive Smart Windows with Dynamic Switchable Transmittance

Mechanically responsive smart windows with adjustable light transmittance have attracted more and more attention due to their great potential in our daily life. However, their fabrication normally requires complicated preparation such as oxygen plasma treatment and high-cost materials (i.e., poly(dimethylsiloxane) (PDMS)), which hinders their practical applications. Herein, a principally different mechanically responsive smart window, i.e., a pressure-responsive smart window, is reported, which is achieved by harnessing the synergistic interactions (i.e., hydrogen bonding and surface roughness compensation) between the two constituent parts, i.e., hydrogel and agar films. The pressure-responsive smart window features the ultrafast response time (37.5 ms) and high transmittance changes (∼50%) with excellent repeatability, which can be stained with different colors and operated on a flexible substrate. Since the pressure-responsive smart window enables the utilization of the low-cost material and does not require the external energy input, it is anticipated that it may have great potential in practical applications.

Hierarchical 3D Patterns with Dynamic Wrinkles Produced by a Photocontrolled Diels-Alder Reaction on the Surface

Three-dimensional (3D) reconfigurable patterns with dynamic morphologies enable the on-demand control of surface properties, such as optical, wetting, and adhesive properties, to achieve smart surfaces. Here, a simple yet general strategy is developed for fabricating 3D patterns with reversible wrinkles on the surface, in which a Diels-Alder (D-A) reaction in the top layer, which consists of a reversible cross-linked polymer network composed of a furan-containing copolymer (PSFB) and bismaleimide (BMI), can be spatially controlled by the photodimerization of BMI. When a photomask is used during irradiation with ultraviolet (UV) light, selective photodimerization of the maleimide leads to the diffusion of maleimide from the unexposed region to the exposed region, resulting in the generation of a diffused relief pattern. By controlling the reversible D-A reaction at different temperatures, orthogonal wrinkles can be sequentially and reversibly generated or erased in both the exposed and unexposed regions on the surface. Theoretical modeling with boundary effects reveals that the orientation of the wrinkle in the exposed region is perpendicular to the boundary, whereas the wrinkle in the unexposed region is parallel to the boundary. This strategy, based on a photocontrolled D-A reaction, provides an important and robust alternative for fabricating 3D patterned surfaces with dynamic topographies.

Highly Efficient and Environmentally Friendly Fabrication of Robust, Programmable, and Biocompatible Anisotropic, All-Cellulose, Wrinkle-Patterned Hydrogels for Cell Alignment

Wrinkled hydrogels from biomass sources are potential structural biomaterials. However, for biorelated applications, engineering scalable, structure-customized, robust, and biocompatible wrinkled hydrogels with highly oriented nanostructures and controllable intervals is still a challenge. A scalable biomass material, namely cellulose, is reported for customizing anisotropic, all-cellulose, wrinkle-patterned hydrogels (AWHs) through an ultrafast, auxiliary force, acid-induced gradient dual-crosslinking strategy. Direct immersion of a prestretched cellulose alkaline gel in acid and relaxation within seconds allow quick buildup of a consecutive through-thickness modulus gradient with acid-penetration-directed dual-crosslinking, confirmed by visual 3D Raman microscopy imaging, which drives the formation of self-wrinkling structures. Moreover, guided by quantitative mechanics simulations, the structure of AWHs is found to exhibit programmable intervals and aligned nanostructures that differ between ridge and valley regions and can be controlled by tuning the prestretching strain and acid treatment time, and these AWHs successfully induce cell alignment. Thus, a new avenue is opened to fabricate polysaccharide-derived, programmable, anisotropic, wrinkled hydrogels for use as biomedical materials via a bottom-up method.

Fast Dual-Stimuli-Responsive Dynamic Surface Wrinkles with High Bistability for Smart Windows and Rewritable Optical Displays

The dynamic dual-stimuli-responsive surface wrinkles on a bilayer film with high bistability are unattainable and attractive for the applications of smart windows and optical displays. Here, we report a new strategy in developing moisture and temperature dual-responsive surface wrinkles on the polyvinyl alcohol/polydimethylsiloxane (PVA/PDMS) bilayer film by rationally designing the modulus changes of the PVA skin layer upon moisture and temperature. By optimizing the thickness of the PVA layer to 4.5 μm, the as-prepared surface wrinkles show long-awaited properties, such as fast response time, excellent reversibility without degradation of optical contrast, and high light transmittance modulation, which greatly outperforms the reported surface wrinkles. Moreover, the surface wrinkles on the bilayer film remain highly bistable without additional energy consumption for more than five months in ambient room conditions both in the opaque and transparent states. These promising dual-stimuli-responsive surface wrinkles on bilayer films hold great promises for various applications triggered by moisture and temperature, such as smart windows and rewritable optical displays.

Controlling silk fibroin conformation for dynamic, responsive, multifunctional, micropatterned surfaces

Protein micro/nanopatterning has long provided sophisticated strategies for a wide range of applications including biointerfaces, tissue engineering, optics/photonics, and bioelectronics. We present here the use of regenerated silk fibroin to explore wrinkle formation by exploiting the structure-function relation of silk. This yields a biopolymer-based reversible, multiresponsive, dynamic wrinkling system based on the protein's responsiveness to external stimuli that allows on-demand tuning of surface morphologies and properties. The polymorphic transitions of silk fibroin enable modulation of the wrinkle patterns and, consequently, the material's physical properties. The interplay between silk protein chains and external stimuli enables control over the protein film's wrinkling dynamics. Thanks to the versatility of regenerated silk fibroin as a technological substrate, a number of demonstrator devices of varying utility are shown ranging from information encoding to modulation of optical transparency and thermal regulation.

Humidity-Driven Soft Actuator Built up Layer-by-Layer and Theoretical Insight into Its Mechanism of Energy Conversion

An improved protocol is proposed for preparation of a humidity-sensitive soft actuator through the layer-by-layer assembling of weight-ratio-variable composites of sodium alginate (SA) and poly(vinyl alcohol) (PVA) into laminated structures. The design induces nonuniform hygroscopicity in the thickness direction and gives rise to strong interfacial interaction between layers, making the actuator have directional motility. A mathematical model reveals that the directional motion is driven by the chemical potential of humidity, and its energy conversion efficiency from humidity to mechanical work reaches 81.2% at 25 °C. By coating with CoCl₂, the composite film of SA@PVA/CoCl₂ can act as a warning sign that provides reminder information to prevent people from slipping or falling by a conspicuous red sign during a high-humidity environment. When the film is involved in a bidirectional switch, it is capable of turning on/off light-emitting diodes by humidity, showing promising potential in control over humidity-dependent devices.

Buckled Structures: Fabrication and Applications in Wearable Electronics

Wearable electronics have attracted a tremendous amount of attention due to their many potential applications, such as personalized health monitoring, motion detection, and smart clothing, where electronic devices must conformably form contacts with curvilinear surfaces and undergo large deformations. Structural design and material selection have been the key factors for the development of wearable electronics in the recent decades. As one of the most widely used geometries, buckling structures endow high stretchability, high mechanical durability, and comfortable contact for human-machine interaction via wearable devices. In addition, buckling structures that are derived from natural biosurfaces have high potential for use in cost-effective and high-grade wearable electronics. This review provides fundamental insights into buckling fabrication and discusses recent advancements for practical applications of buckled electronics, such as interconnects, sensors, transistors, energy storage, and conversion devices. In addition to the incorporation of desired functions, the simple and consecutive manipulation and advanced structural design of the buckled structures are discussed, which are important for advancing the field of wearable electronics. The remaining challenges and future perspectives for buckled electronics are briefly discussed in the final section.

All-Optical Reversible Azo-Based Wrinkling Patterns with High Aspect Ratio and Polarization-Independent Orientation for Light-Responsive Soft Photonics

Azobenzene-containing polymers (azopolymers) can serve as building blocks for an emerging class of soft photonics. Using their photoresponses for the micro/nanofabrication of smart surface is a key but still a challenging step. Here, we report a simple visible-light-illumination strategy to trigger diverse configurations of surface wrinkling on azopolymer-based film/substrate systems, which can be switched between flat and wrinkled states by controlling the intensity of the incident light. Different photoresponsive characteristics of azobenzene are involved in driving the wrinkling/dewrinkling switch. For the first time, we achieve the controlled wrinkling with an unexpected high aspect ratio and surprisingly polarization-independent ordered orientation by exploiting the unique photosoftening effect of azobenzene. Theoretical analysis reveals that an in situ photoinduced reversible soft/hard-contrast boundary determines the wrinkling orientation, which is used to fabricate diverse on-demand hierarchical wrinkles. These photoresponsive systems find broad photonic applications that are not easily accessible to other systems, e.g., optically reversible smart display, information security, and well-regulated optical devices.

Macroscopic Geometry-Dominated Orientation of Symmetric Microwrinkle Patterns

Orientated wrinkle patterns with controlled microarchitectures are highly attractive because of their potential and broad application in technologies ranging from flexible electronic devices to smart windows. Here, we demonstrate a macroscopic, geometry-dominated strategy to fabricate symmetric microwrinkles with precisely controllable pattern dimensions and orientations through a dynamic interfacial release process. The release-induced approach is based on the release of multilayer elastomer composites from polymeric sacrificial layers in solutions combined with crosslinking-induced contraction of the elastomer substrates. Crosslinking-induced contraction provides the driving force for developing and stabilizing surface wrinkle formation, whereas the polymeric sacrificial layer provides a mild and simultaneous release process to form orientated wrinkles through kinetic control of local strain development. The macroscopic shape of the composite controls release kinetics, hence strain history, leading to the generation of photonic reflective surfaces. Moreover, stable wrinkles fabricated from various materials including metals, ceramics, and carbons can be achieved. This versatile, mold-free, and cost-effective platform technology demonstrates how global strain distributions can be harnessed through kinetics to drive local pattern development.

Curvature-Controlled Wrinkling Surfaces for Friction

Topographical patterns endow material surfaces with unique and intriguing physical and chemical properties. Spontaneously formed wrinkling has been harnessed to generate surface topography for various functionalities. Despite promising applications in biomedical devices and robot engineering, the friction behavior of wrinkling on curved surfaces remains unclear. Herein, wrinkled surfaces are induced by sputtering metals on soft polymer microspheres. The wrinkle morphologies and length scales can be controlled precisely by tailoring the microsphere radius (substrate curvature) and film thickness. The wrinkled surfaces exhibit controlled friction property, depending on the wrinkling patterns and length scales. An increase in friction force with increasing surface roughness is generally found for dimple patterns and labyrinth patterns. The dimple patterns show the lowest friction due to strong curvature constraint. The herringbone patterns exhibit apparent friction anisotropy with respect to topographic orientation. These results will guide future design of wrinkled surfaces for friction by harnessing substrate curvature.

Theoretical and Experimental Study of Reversible and Stable Wetting States of a Hierarchically Wrinkled Surface Tuned by Mechanical Strain

The wetting behavior of hierarchically wrinkled surfaces has attracted great interest because of its broad application in flexible electronic, microfluidic chip, and biomedicine. However, theoretical studies concerning the relationship between the apparent contact angle and mechanical strain applied on the soft and flexible surface with a hierarchically wrinkled structure are still limited. We established a theoretical framework to describe and understand how prestrain and applied dynamic strain reversibly tune the wettability of the hierarchically wrinkled surface. More specifically, a direct relationship between the mechanical strain and contact angle was built through reversible tuning of the amplitude and the wavelength of the wrinkled structures caused by mechanical strain, which allowed for more precise adjustment of surface wettability. To verify the accuracy of the theoretical relationship between the contact angle and mechanical strain, a soft surface with a hierarchically wrinkled structure was prepared by combining wrinkled microstructures and strip ones. The results showed that the experimental contact angles were in agreement with the theoretical ones within a limited error range. This will be helpful for further investigation on the wettability of hierarchically wrinkled surfaces.