Femtosecond Laser Regulated Ultrafast Growth of Mushroom-Like Architecture for Oil Repellency and Manipulation

Bioinspired Hierarchical T Structures for Tunable Wettability and Droplet Manipulation by Facile and Scalable Nanoimprinting

Developing surfaces that effectively repel low-surface-tension liquids with tunable adhesive properties remains a pivotal challenge. Micronano hierarchical re-entrant structures emerge as a promising solution, offering a robust structural defense against liquid penetration, minimizing area fraction, and creating narrow gaps that generate substantial upward Laplace pressure. However, the absence of an efficient, scalable, and tunable construction method has impeded their widespread applications. Here, drawing inspiration from springtail epidermal structures, octopus suckers, and rose petals, we present a scalable manufacturing strategy for artificial micronano hierarchical T-shaped structures. This strategy employs double-transfer UV-curing nanoimprint lithography to form nanostructures on microstructured surfaces, offering high structural tunability. This approach enables precise control over topography, feature size, and arrangement of nano- and microscale sections, resulting in superamphiphobic surfaces that exhibit high contact angles (>150°) and tunable adhesive forces for low-surface-energy liquids. These surfaces can be applied to droplet-based microreactors, programmable droplet-transfer systems, and self-cleaning surfaces suitable for various liquids, particularly those with low surface tension. Remarkably, we have also succeeded in fabricating the hierarchical structures on flexible and transparent substrates. We demonstrate the advantages of this strategy in the fabrication of hierarchical micronanostructures, opening up a wide range of potential applications.

Fabrication of Flexible and Re-entrant Liquid-Superrepellent Surface Using Proximity and PNIPAM-Assisted Soft Lithography

The nature-inspired flexible and re-entrant liquid-superrepellent surface has attracted significant attention due to its excellent superomniphobic performance against low-surface-tension liquids. Although conventional photolithography and molding methods offer the advantage of large-area manufacturing, they often involve multiple double-sided alignment and exposure steps, resulting in complex procedures with long processing cycles. In this study, we proposed a straightforward single-exposure ultraviolet proximity lithography method for re-entrant liquid-superrepellent surface fabrication using a photomask with a coaxial circular aperture and ring. A theoretical calculation model for the three-dimensional light intensity distribution in proximity lithography was developed for the prediction of feature sizes for both singly and doubly re-entrant microstructures. Soft lithography techniques, which rely on surface modification and the modulation of the transfer material's flexibility, efficiently optimized the fabrication of flexible re-entrant molds and patterns. By incorporating nanoclay-modified poly(N-isopropylacrylamide) (PNIPAM) into the molding process, we fabricated a three-layer hierarchical structure featuring micrometer-scale wrinkles, re-entrant microstructures, and nanoscale fluorinated silica particles, significantly enhancing the surface's robustness and pressure resistance. The resulting large-area flexible and re-entrant liquid-superrepellent surface demonstrated excellent superomniphobic self-cleaning performance and satisfactory optical transparency, as evidenced by reflection and transmission experiments, showcasing its potential applications in self-cleaning, membrane distillation, and digital microfluidics.

Alcohol-gating femtosecond laser-induced micro/nano-structured membranes with reversible switching wettability and breathability

A reversible liquid gating membrane with the ability to regulate gas/liquid transport is critical for many fields, such as biological applications, multiphase separation, and sewerage treatment. Numerous membranes can respond to external stimuli and dynamically control gas/liquid fluid transport; however, simultaneously achieving regulated gas/liquid transport membranes through simple manufacturing remains a challenge. In this work, we investigated an alcohol-regulation gating membrane via femtosecond laser one-step processing, allowing in situ dynamically controllable gas/liquid transfer. More specifically, the porous membrane, processed by laser, exhibits excellent superhydrophobicity (WCA ∼ 153.4°) and breathability (water-vapor evaporation rates ∼118.3 mg (cm2 h)-1), enabling gas to penetrate but not water. In contrast, it allows the passage of water while preventing the permeation of gas subsequent to the introduction of alcohol. Furthermore, the porous membrane still possesses superbly consistent performance after being placed in air for 90 days or over 100 dropping-drying ethanol cycles test, indicating outstanding durability and reversibility. Significantly, the porous membrane has broad potential applications in medical dressings, providing a new strategy to fabricate next-generation bandages.

Achieving Extreme Pressure Resistance to Liquids on a Super-Omniphobic Surface with Armored Reentrants

Static repellency and pressure resistance to liquids are essential for high-performance super-omniphobic surfaces. However, these two merits appear mutually exclusive in conventional designs because of their conflicting structural demands: Static liquid repellency necessitates minimal solid-liquid contact, which in turn inevitably undercuts the surface's ability to resist liquid invasion exerted by the elevated pressure. Here, inspired by the Springtail, these two merits can be simultaneously realized by structuring surfaces at two size scales, with a micrometric reentrant structure providing static liquid repellency and a nanometric reentrant structure providing pressure resistance, which dexterously avoids the dilemma of their structural conflicts. The nanometric reentrants are densely packed on the micrometric ones, serving as "armor" that prevents liquids invasion by generating multilevel energy barriers, thus naming the surface as the armored reentrants (AR) surface. The AR surface could repel liquids with very low surface tensions, such as silicone oil (21 mN m-1), and simultaneously resist great pressure from the liquids, exemplified by enduring the impact of low-surface-tension liquids under a high weber number (>400), the highest-pressure resistance ever reported. With its scalable fabrication and enhanced performance, our design could extend the application scope of liquid-repellent surfaces toward ultimate industrial settings.

Design of highly robust super-liquid-repellent surfaces that can resist high-velocity impact of low-surface-tension liquids

Super-liquid-repellent surfaces capable of preventing wetting with various liquids have tremendous application. However, high liquid repellency relies on surface texturing to minimize the solid-liquid interfacial contact, which generally results in impaired interface robustness and pressure resistance. Consequently, the surface tends to undergo a Cassie-Baxter to Wenzel wetting transition and loses liquid repellency under high-velocity liquid impact, especially for low-surface-tension liquids. Here, surface design through combining the nanoscale effect and doubly reentrant structure is demonstrated to solve the above challenge. By utilizing a facile colloidal lithography process, robust liquid repellent surfaces featuring nanoscale doubly reentrant (NDR) structures are constructed. The nanoscale features ensure sufficient triple contact line density at a low solid-liquid contact fraction to enhance the capillary force for liquid suspension. In conjunction with the doubly reentrant topography that maximizes the upward component of capillary force, such NDR surfaces enable an extremely robust solid-liquid-gas composite interface. As a result, the prepared NDR surface maintain excellent repellency upon high-velocity impact of various liquids, including ethylene glycol drops with a Weber number (We) above 306 and ethanol drops with a We of 57. The above findings can help the development of super-liquid-repellent surfaces applicable to harsh conditions of high-velocity liquid impact or high hydrostatic pressure.

Patterned Manipulated Surface Based on Femtosecond Laser with Adjustable Wetting Speed and Directional Fluid Delivery

Recently, due to the crucial roles of multifunctional liquid manipulation surfaces in biomedical transportation, microfluidics, and chemical engineering, the demand for controllable and functional aspects of directed liquid transportation has increased significantly. However, designing an intelligent manipulation surface that is easy to manufacture and fully functional remains an immense challenge. To address this challenge, a smart surface that can regulate the rate of liquid transport within a patterned channel by temperature is reported. A synergistically controlled approach of poly(N-isopropylacrylamide) and micropillar shape-memory polymers (SMPs) was used to modulate the wetting rate of liquids on surfaces. By femtosecond laser direct writing, temperature-responsive composite surfaces are embedded in the microstructure of shape-memory polymers (SMPs) in a patterned manner, resulting in the preparation of novel programmable liquid manipulation surfaces incorporating boundaries possessing asymmetric wettability. Since the smart surface is based on SMP, the superhydrophobic part in the superhydrophobic/controllable wettability patterning platform is also programmed for droplet directional transport, which takes advantage of the difference in wettability between the rewritable indentation track and the periphery to allow droplets to flow into the temperature-controlled velocity track, enriching the functionality of the surface. In addition, based on its excellent controllability and patterning, the surface has been shown to be used in microfluidic circuit chips with self-cleaning properties, which provides new ideas for circuit timing control. This study provides promising prospects for the effective development of multifunctional liquid steering surfaces, lab-on-a-chip, and microfluidic devices.

Self-Growing Organic Materials

The growth of living systems is ubiquitous. Living organisms can continually update their sizes, shapes, and properties to meet various environmental challenges. Such a capability is also demonstrated by emerging self-growing materials that can incorporate externally provided compounds to grow as living organisms. In this Minireview, we summarize these materials in terms of six aspects. First, we discuss their essential characteristics, then describe the strategies for enabling crosslinked organic materials to self-grow from nutrient solutions containing polymerizable compounds. The developed examples are grouped into five categories based on their molecular mechanisms. We then explain the mechanism of mass transport within polymer networks during growth, which is critical for controlling the shape and morphology of the grown products. Afterwards, simulation models built to explain the interesting phenomena observed in self-growing materials are discussed. The development of self-growing materials is accompanied by various applications, including tuning bulk properties, creating textured surfaces, growth-induced self-healing, 4D printing, self-growing implants, actuation, self-growing structural coloration, and others. These examples are then summed up. Finally, we discuss the opportunities brought by self-growing materials and their facing challenges.

Multifunctional polyimide-based femtosecond laser micro/nanostructured films with triple Janus properties

Flexible multifunctional composite films in which opposing surfaces have two or more distinct physical properties are highly applicable for wearable electronic devices, electrical power systems and biomedical engineering. However, fabrication of such "Janus" films can be time consuming, complex or economically not feasible. In this work, Janus polyimide (PI) films were prepared by femtosecond laser direct writing technology, which generated a honeycomb porous structure (HPS) on one side and a lawn-like structure (LLS) on the other. Deposition of silver nanowires (AGNWs) by drop coating on the LLS side (AGNWs@LLS) resulted in a film in which each face possessed highly distinct triple properties. The HPS side was superhydrophobic with a water contact angle (WCA) of ∼153.3° and electrically non-conductive, while the AGNWs@LLS side was superhydrophilic (WCA ∼7.8°) and highly conductive (∼3.8 Ω). Moreover, the AGNWs@LLS face showed ultra-low thermal radiation performance, almost reaching saturation. On a heating table at ∼100 °C, the temperature of the AGNWs@LLS side remained at ∼44.5 °C, while the HPS side exhibited a temperature of ∼93.9 °C. This "triple Janus film" and lasing techniques developed might be useful for designing new materials for the integration and miniaturization of multifunctional electronic equipment.

Bio-inspired switchable soft adhesion for the boost of adhesive surfaces and robotics applications: A brief review

In nature, millions of creatures, such as geckos, tree frogs, octopuses, etc., have evolved fantastic switchable adhesion capabilities to climb swiftly on vertical even inverted surfaces or hunt for prey easily, adapting to harsh and unpredictable environments. Notably, these fascinating adhesive behaviors depend on interfacial forces (friction, van der Waals force, capillary force, vacuum suction, etc.), which primarily originate from the interactions between the soft micro/nanostructures evolved in the natural creatures and objects. Over the past few decades, these biological switchable adhesives have inspired scientists to explore and engineer desirable artificial adhesives. In this review, we summarized the state-of-the-art research on the ultra-fast adhesive motion of three types of biological organisms (gecko, tree frog, and octopus). Firstly, the basic adhesion principles in the three representative organisms, including micro/nanostructures, interfacial forces, and fundamental adhesion models, are reviewed. Then, we discussed the adhesion mechanisms of the prominent organisms from the perspective of soft contacts between micro/nanostructures and the substrates. Later, the mechanics-guided design principles of artificial adhesive surfaces, as well as the smart adhesion strategies, are summarized. The applications of these bio-inspired switchable adhesives are demonstrated, including wearable electronic devices, soft grippers, and climbing robots. The challenges and opportunities in this fast-growing field are also discussed.

Flexible Tri-switchable Wettability Surface for Versatile Droplet Manipulations

Smart surfaces with tunable wettability are promising due to their abilities to create diversified functionalities that the fixed surfaces cannot provide. However, limited by imprecise adjustment of structural geometry and almost conventional switching modes of wettability, it is still challenging to achieve the reversible switching between multiple wetting states. Herein, a novel tri-switchable wettability surface with an in situ switching ability is used for the manipulation of a given droplet, which consists of a stretchable substrate and a micron column array. The femtosecond laser direct writing technique is utilized to generate distinct wettability of the two components. Taking the advantage of good tensile properties, the surface morphology is adjusted in a rapid, reversible way to obtain diverse wetting performances from the lotus-like effect to rice-leaf-like anisotropy and then to the rose-petal-like effect. Based on the triplex wetting transition on the same surface, we further developed a multifunctional device to realize a range of in situ manipulations, including the surface self-cleaning, the directional transport of droplets, and the capture, the vertical transport, and release of droplets. This work paves the way for expanding the field of smart surfaces with tunable wettability beyond conventional dual-property wetting behavior and exhibits versatile manipulations of droplets for microfluidic applications.

Robust Underwater Air Layer Retention and Restoration on Salvinia-Inspired Self-Grown Heterogeneous Architectures

Salvinia's long-term underwater air layer retention ability has inspired researchers to develop artificial microstructures. However, Salvinia has an exquisite combination of a complicated hollow structure and heterogeneous chemical properties, which makes artificial reproduction beyond the capabilities of traditional fabrication techniques. In addition, under extremely low underpressure conditions, the mechanism of retention and restoration of the underwater air layer of Salvinia remains unclear. Herein, by combining the shape memory polymer "top-constrained self-branching (TCSB)" and hydrophilic SiO₂ microspheres trapping, four-branch hollow microstructures with heterogeneous chemical properties are fabricated. By applying underpressure, the crucial role of hydrophilic apexes is unveiled in air layer restoration. Through the calculation of the surface energy, the underlying mechanism is well interpreted. This study holds great promise for developing Salvinia-inspired artificial structures and reveals the underlying mechanism of the robust air retention and recovery capability of Salvinia leaves in extreme environments.

Robust and durable liquid-repellent surfaces

This review provides a comprehensive summary of characterization, design, fabrication, and application of robust and durable liquid-repellent surfaces.