Monolithic Polymer Nanoridges with Programmable Wetting Transitions

Designer Micro-/Nanocrumpled MXene Multilayer Coatings Accelerate Osteogenesis and Regulate Macrophage Polarization

Effective tissue regeneration and immune responses are essential for the success of biomaterial implantation. Although the interaction between synthetic materials and biological systems is well-recognized, the role of surface topographical cues in regulating the local osteoimmune microenvironment─specifically, their impact on host tissue and immune cells, and their dynamic interactions─remains underexplored. This study addresses this gap by investigating the impact of surface topography on osteogenesis and immunomodulation. We fabricated MXene/hydroxyapatite (HAP)-coated surfaces with controlled 2.5D nano-, submicro-, and microscale topographical patterns using our custom bottom-up patterning method. These engineered surfaces were employed to assess the behavior of osteoblast precursor cells and macrophage polarization. Our results demonstrate that MXene/HAP-coated surfaces with microscale crumpled topography significantly influence osteogenic activity and macrophage polarization: these surfaces notably enhanced osteoblast precursor cell spreading, proliferation, and differentiation and facilitated a shift in macrophages toward an anti-inflammatory, prohealing M2 phenotype. The observed cell responses indicate that the physical cues from the crumpled topographies, combined with the chemical cues from the MXene/HAP coatings, synergistically create a favorable osteoimmune microenvironment. This study presents the first evidence of employing MXene/HAP-multilayer coated surfaces with finely crumpled topography to concurrently facilitate osteogenesis and immunomodulation for improved implant-to-tissue integration. The tunable topographic patterns of these coatings coupled with a facile and scalable fabrication process make them widely applicable for various biomedical purposes. Our results highlight the potential of these multilayer coatings with controlled topography to improve the in vivo performance and fate of implants by modulating the host response at the material interface.

Curvature Adjustable Liquid Transport on Anisotropic Microstructured Elastic Film

Directional liquid transport is expected via adjusting chemical components, surface morphology, and external stimuli and is critical for practical applications. Although many studies have been conducted, there are still challenges to achieving real-time transformation of liquid transport direction on the material surface. Herein, we demonstrate a strategy to achieve curvature responsive anisotropic wetting on the elastic film with V-shaped prism microarray (VPM) microstructure, which can be used to control the direction of liquid transport. The results reveal that the curvature change of an elastic film can adjust the arrangement of V-shaped prisms on the elastic film. Correspondingly, the liquid wetting trend will change and even the moving direction reverses with varying arrangements of the V-shaped prisms on the elastic film. Meanwhile, surface hydrophobicity of the VPM elastic film also affects the liquid wetting trend and even shows the opposite transport direction of the liquid, which is up to the water wetting state on the VPM elastic film. Based on these results, the VPM elastic film can serve as a valve to control the liquid transport direction and is promising in the application of liquid directional harvest, chemical reaction, microfluidic, etc.

Growth-Induced Wrinkles and Dotlike Patterns of a Swollen Fluoroalkylated Thin Film by the Reaction of Surface-Attached Polymethylhydrosiloxane

The design of hydrophobic surfaces requires a material which has a low solid surface tension and a simple fabrication process for anchoring and controlling the surface morphology. A generic method for the spontaneous formation of robust instability patterns is proposed through the hydrosilylation of a fluoroalkene bearing dangling chains, R_f = C₆F₁₃(CH₂)₃-, with a soft polymethylhydrosiloxane (PMHS) spin-coated gel polymer (0.8 μm thick) using Karstedt catalyst. These patterns were easily formed by an irreversible swelling reaction due to the attachment of a layer to various substrates. The buckling instability was created by two different approaches for a gel layer bound to a rigid silicon wafer substrate (A) and to a soft nonswelling silicone elastomer foundation (B). The observations of grafted R_f-PMHS films in the swollen state by microscopy revealed two distinct permanent patterns on various substrates: dotlike of wavelength λ = 0.4-0.7 μm (A) or wrinkle of wavelength λ = 4-7 μm (B). The elastic moduli ratios of film/substrate were determined using PeakForce quantitative nanomechanical mapping. The characteristic wavelengths (λ) of the patterns for systems A and B were quantitatively estimated in relation to the thickness of the top layer. A diversity of wrinkle morphologies can be achieved by grafting different side chains on pristine PMHS films. The water contact angle (WCA) hysteresis of fluorinated chain (R_f) was enhanced upon roughening the surfaces, giving highly hydrophobic surface properties for water with static/hysteresis WCAs of 136°/74° in the resulting wrinkle (B) and 119°/41° in the dotlike of lower roughness (A). The hydrophobic properties of grafted films on A with various mixtures of hexyl/fluoroalkyl chains were characterized by static CA: WCA 104-119°, ethylene glycol CA 80-96°, and n-hexadecane CA 17-61°. A very low surface energy of 15 mN/m for R_f-PMHS was found on the smoother dotlike pattern.

Mechanical response of surface wettability of Janus porous membrane and its application in oil-water separation

Smart surfaces with switchable wettability are widely studied for environmental application. Although a large number of stimulation routes provide broad prospects for the development of smart surfaces, achieving high sensitivity, fast response and recovery, simple operation, security and good stability is still challenging. Herein, a Janus membrane via electrospinning, chemical bath deposition and heat treatment is constructed. By using the hydrophilic ZIF-L nanosheet to functionalize the hydrophobic thermoplastic polyurethane (TPU) substrate, a smart surface utilizes the ZIF-L crack induced by strain in the hydrophilic layer to control surface wettability is obtained. In the range of 0%-100% strain, the wettability of the smart surface presents an obvious change with stretching, and water contact angle of the surface shows a monotonic increase with a maximum tuning range from 47° to 114°. Due to local fusion of the TPU microfibers and good binding between the ZIF-L layer and the TPU substrate after heat treatment, the prepared Janus membrane exhibits consistent and symmetrical hydrophilic-hydrophobic-hydrophilic transition curves in 50 stretching-releasing cycles. Thanks to the porous and asymmetric architecture, the membrane shows good oil-water separation performance, and the separation flux increases with the increase of strain, while the separation efficiency is always higher than 98%. Because of the excellent structural stability, the robust membrane with 100% strain maintains its oil-water separation property for 50 stretching-releasing cycles. This study provides a new perspective for the development of smart material with stimuli responsive surface for oily wastewater purification.

3D Multiscale Micro-/Nanofolds by Femtosecond Laser Intermittent Ablation and Constrained Heating on a Shape Memory Polymer

Spontaneous wrinkling of films with a thickness gradient offers a new opportunity for constructing various 3D hierarchical surface morphologies. Unfortunately, accurately and facilely controlling the gradient film thickness to yield multiscale and 3D hierarchical micro-/nanostructures is still difficult. Here, a rapid, facile, and highly controllable fabricating strategy for realizing 3D multiscale hierarchical micro-/nanofolds on a shape memory polymer (SMP) surface is reported. First, the nanoparticle film with gradient thickness is rapidly (100 ms to 4 s) and facilely obtained by laser intermittent ablation on the SMP, termed as laser ablation-induced gradient thickness film. Following one-time constrained heating, the 3D micropillars grow out of the substrate based on the "self-growing effect," and the nanoparticle gradient film on its top shrinks into multiscale micro-/nanofolds simultaneously. Significantly, the evolution process and the underlying mechanism of the 3D micro-/nanofolds are systematically investigated. Fundamental basis enables us to accurately regulate the gradient thickness of nanoparticle films and feature size of folds by varying laser scanning times and scanning path. Finally, desirable patterns on micro-/nanofolds can be readily realized by programmable laser cleaning technology, and the tunable adhesion of the water droplet on the multiscale structured surface is demonstrated, which is promising for microdroplet manipulation.

Kirigami-Inspired Highly Stretchable, Conductive, and Hierarchical Ti3C2Tx MXene Films for Efficient Electromagnetic Interference Shielding and Pressure Sensing

Although Ti₃C₂T_x MXene sheets are highly conductive, it is still a challenge to design highly stretchable MXene electrodes for flexible electronic devices. Inspired by the high stretchability of kirigami patterns, we demonstrate a bottom-up methodology to design highly stretchable and conductive polydimethylsiloxane (PDMS)/Ti₃C₂T_x MXene films for electromagnetic interference (EMI) shielding and pressure sensing applications by constructing wrinkled MXene patterns on a flexible PDMS substrate to create a hierarchical surface with primary and secondary surface wrinkles. The self-controlled microcracks created in the valley domains of the hierarchical film via a nonuniform deformation during prestretching/releasing cycles endow the hierarchical PDMS/MXene film with a high stretchability (100%), strain-invariant conductivity in a strain range of 0%-100%, and stable conductivities over an 1000-cycle fatigue measurement. The stretchable film exhibits a highly stable EMI shielding performance of ≈30 dB at a tensile strain of 50%, and its EMI shielding efficiency increases further to 103 dB by constructing a two-film structure. Furthermore, a highly stretchable and sensitive iontronic sensor array with integrated MXene-based electrodes and circuits is fabricated by a stencil printing process, exhibiting high sensitivity (66.3 nF kPa^-1), excellent dynamic cycle stability over 1000 cycles under different frequencies, and sensitive pressure monitoring capability under a tensile strain of 50%.

An Acoustic Meta-Skin Insulator

Acoustic metamaterials with artificial microstructures are attractive to realize intriguing functions, including efficient waveguiding, which requires large impedance mismatches to realize total side reflection with negligible transmission and absorption. While large impedance mismatch can be readily realized in an air environment, acoustic waveguiding in an underwater environment remains elusive due to insufficient impedance mismatch of state-of-the-art metamaterials. Here, a superhydrophobic acoustic metasurface of microstructured poly(vinylidene fluoride) membrane, referred to as a "meta-skin" insulator, which is able to confine acoustic waves in an all-angle and wide spectrum range due to tremendous impedance mismatch at stable air/water interfaces, viz., the Cassie-Baxter state is demonstrated. By utilizing the meta-skin insulator with broadband and high throughput, orbital-angular-momentum multiplexing at a high spectral efficiency and binary coding along large-angle bending channels for bit-error-free acoustic data transmission in an underwater environment are demonstrated. Very different from optical and/or electrical cable communications, acoustic waves can be simply and effectively coupled into remote meta-skin acoustic fibers from free space, which is technologically significant for long-haul and anti-interference communication. This work can enlighten many fluidic applications based on efficient waveguiding, such as in vivo ultrasound medical treatment and imaging.

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 L_c), 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.

Ultrathin Film Composite Membranes Fabricated by Novel In Situ Free Interfacial Polymerization for Desalination

Ultrathin polyamide nanofilms are desirable as the separation layers for the highly permeable thin-film composite (TFC) membranes, and recently, their lowest thickness limits have attracted a lot of attention from researchers. Due to the interference of the underlying substrate, preparing a defect-free, ultrathin polyamide nanofilm directly on top of a membrane substrate remains a great challenge. Herein, we report a novel fabrication technique of TFC membranes, named in situ free interfacial polymerization (IFIP), where the IP reaction occurs at the uniform, free oil-water interface dozens of microns above the substrate, and then the resulting nanofilm spontaneously assembles into the TFC structure without extra manual transfer. This IFIP method not only overcomes the limitations of conventional IP, succeeding in preparing ultrathin-nanofilm composite membranes for nanofiltration and reverse osmosis application, but also enables scale membrane manufacturing that is not feasible via previously reported free-standing IP. Based on the IFIP method, the thickness of the polyamide nanofilm was successfully reduced to ca. 3-4 nm, which we believe is close to the ultrathin limit of the polyamide nanofilm for separation application. Meanwhile, the structure-performance relationship revealed that the strategy of increasing TFC membrane permeance by reducing polyamide layer thickness also had a limit. Besides, the IP mechanisms in regard to the formation of surface morphology and film growth were explored by combining experimental and molecular simulation methods. Overall, this work is expected to push forward the fundamental study and practical application of the ultrathin-film composite membrane.

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.

The fabrication of mechanically durable and stretchable superhydrophobic PDMS/SiO2 composite film

Stretchable superhydrophobic film was fabricated by casting silicone rubber polydimethylsiloxane (PDMS) on a SiO₂ nanoparticle-decorated template and subsequent stripping. PDMS endowed the resulting surface with excellent flexibility and stretchability. The use of nanoparticles contributed to the sustained roughening of the surface, even under large strain, offering mechanically durable superhydrophobicity. The resulting composite film could maintain its superhydrophobicity (water contact angle ≈ 161° and sliding angle close to 0°) under a large stretching strain of up to 100% and could withstand 500 stretching–releasing cycles without losing its superhydrophobic properties. Furthermore, the obtained film was resistant to long term exposure to different pH solutions and ultraviolet light irradiation, as well as to manual destruction, sandpaper abrasion, and weight pressing.

Stretchable superhydrophobic film was fabricated by casting silicone rubber polydimethylsiloxane (PDMS) on a SiO₂ nanoparticle-decorated template and subsequent stripping.

Wetting state transition of a liquid gallium drop at the nanoscale

Wetting state transition regulated by surface roughness has increasing importance for its wide applications.

Carboxylated wood-based sponges with underoil superhydrophilicity for deep dehydration of crude oil

Carboxylated wood-based sponges with underoil superhydrophilicity are elegantly developed via a top-down strategy from natural woods and demonstrated outstanding performances in the deep dehydration of water cut crude oil.

Crack growth-driven wettability transition on carbon black/polybutadiene nanocomposite coatings via stretching

Ordered topography patterns with a mechanical response are usually designed to achieve wettability switching by geometric parameter changes through mechanical stimuli. However, their fabrication often needs expensive and complicated micro/nano-fabrication processing (e.g. photolithography and ion etching). In this study, a nano-carbon black (CB)/polybutadiene (PB) coating with a Wenzel superhydrophobic state was prepared on a rubber substrate by a facile method combining solution mixing and spraying coating. By stretching the composite coating, the generated cracks divided the continuous coating into new micro-nano mastoids, resulting in the formation of new hierarchical roughness for Cassie superhydrophobicity. The Wenzel-to-Cassie transition behavior was dependent on the CB loading in the coating. During stretching, the cracks propagated more rapidly in the coating with higher CB loading and induced the desired hierarchical structure to consequently enable the Wenzel-to-Cassie transition earlier at a lower stretching strain. The stretched coating presented good anti-wetting (a sliding angle of 5°) and low water adhesion. After releasing, the coating returned to its original Wenzel state by structure recovery. Thus, the switchable wettability of the coating can be adopted for no-loss water droplet transfer by controlling the droplet adhesion through cyclic stretching-releasing, and exhibits good potential for microfluidic and biomedical applications.

Designing Hierarchical Nanostructures from Conformable and Deformable Thin Materials

This Perspective focuses on the design of hierarchical structures in deformable thin materials by patterning mechanical instabilities. Fabrication of three-dimensional (3D) structures with multiple length scales-starting at the nanoscale-can result in on-demand surface functionalities from the modification of the mechanical, chemical, and optical properties of materials. Conventional top-down lithography, however, cannot achieve 3D patterns over large areas (>cm²). In contrast, a bottom-up approach based on controlling strain in layered nanomaterials conformally coated on polymeric substrates can produce multiscale structures in parallel. In-plane and out-of-plane structural hierarchies formed by conformal buckling show unique structure-function relationships. Programmable hierarchical surfaces offer prospects to tune global- and local-level characteristics of nanomaterials that will positively impact applications in nanomechanics, nanoelectronics, and nanophotonics.

Gecko toe pads inspired in situ switchable superhydrophobic shape memory adhesive film

Recently, smart adhesive superhydrophobic surfaces have attracted much attention. However, it is still a challenge to obtain a superhydrophobic surface with shape memory adhesive performance. Herein, inspired by the special back-scrolling/unfolding ability of gecko toe pads and corresponding tunable adhesion, we report such a film produced by sticking a layer of superhydrophobic pillar structured polyurethane (s-PU) onto a shape memory polyurethane-cellulose nanofiber (PU-CNF) substrate to mimic the hair-like skin structure and underlying muscle of the gecko toe pads, respectively. Similar to the muscle of the gecko toe pads, the excellent shape memory effect of the PU-CNF substrate can help the obtained film to memorize and repeatedly display different shapes and solid/water contact models. Thus reversible switching between multiple states from the low-adhesive rolling performance to the high-adhesive pinning performance can be realized. Meanwhile, based on its smart wetting performance, not only the traditional in situ capture/release of one microdroplet, but also the step-by-step release of different droplets can be realized on our film. This work reports a new superhydrophobic shape memory adhesive film, which offers a novel strategy for surface adhesion control and meanwhile opens a new road for applications in controlled droplet manipulation.

Dynamic Interpenetrating Polymer Network (IPN) Strategy for Multiresponsive Hierarchical Pattern of Reversible Wrinkle

Dynamic micro-/nanowrinkle patterns with response to multienvironmental stimuli can offer a facile method for on-demand regulation of surface properties, thus allowing for generation of a smart surface. Here a practical yet robust strategy is described to fabricate redox, light and thermal responsive wrinkle by building dynamic double interpenetrating polymer network (IPN) as the top layer for a typical bilayer system. IPNs were constructed through the photochemical reaction of a mixture comprised of light-sensitive anthracene-containing polymer (PAN) and redox-sensitive disulfide-containing diacrylate monomer (DSDA). Thanks to the dynamic covalent reversible C-C bond in PAN and S-S bond in DSDA, the morphology of wrinkled surface not only can be reversibly and precisely (micrometer scale) tailored to all kinds of complicated hierarchical pattern permanently, but also can be controlled temporarily by irradiation of near-infrared light (NIR). A sine wave model is proposed to investigate the dynamics of real-time reversible wrinkle evolution. This general approach based on IPN allows independent multistimuli control over wettability and optical properties on the wrinkled surface, thus, presents a considerable alternative to implement a smart surface.

Random Lasing Engineering in Poly-(9-9dioctylfluorene) Active Waveguides Deposited on Wrinkles Corrugated Surfaces

This paper investigates the correlation between the random lasing properties of organic waveguides made by poly-(9-9dioctylfluorene) (PFO) thin films and the morphology of wrinkled corrugated substrates. The capability to individually control the wrinkle wavelength, shape, and height allows us to separately investigate their role on the sample emission properties. We demonstrate that the main parameter determining the presence of coherent random lasing is the substrate roughness and that, contrary to what could be qualitatively expected, as the roughness increases, coherent random lasing is progressively reduced. Coherent random lasing is observed only for a substrate roughness below 33 nm, while higher roughness leads to amplified spontaneous emission (up to 70 nm) or to the absence of light amplification in the film (above 70 nm). We demonstrate that this result is due to a progressive reduction of the light amplification efficiency in the PFO film, evidencing that coherent random lasing can be obtained only with a right interplay between light amplification and scattering. Besides clarifying the basic aspects of random lasing in organic waveguides, our work opens the way to the realization of organic random lasers with predictable emission properties, thanks to the high control level of the scattering properties of the wrinkled corrugated surfaces.

Mechanics Modeling of Hierarchical Wrinkle Structures from the Sequential Release of Prestrain

Three-dimensional (3D) hierarchical wrinkles can be generated on prestrained thermoplastic substrates by sequential cycles of skin layer growth followed by the release of prestrain. However, no mechanics models have explained the formation of multigenerational nanostructures using this nanofabrication process. This article describes an analytical model that can represent multiscale wrinkles with arbitrary numbers of generations. Structural features including wrinkle wavelengths and amplitudes on the nanoscale that are predicted by minimizing the total deformation energy of the system. The calculated wavelengths in each generation are in good agreement with experiment. Our mathematical approach provides design principles for achieving multigenerational hierarchical structures.