Bioinspired Anisotropic Slippery Cilia for Stiffness-Controllable Bubble Transport

Recent Advances in Superhydrophobic Materials Development for Maritime Applications

Underwater superhydrophobic surfaces stand as a promising frontier in materials science, holding immense potential for applications in underwater infrastructure, vehicles, pipelines, robots, and sensors. Despite this potential, widespread commercial adoption of these surfaces faces limitations, primarily rooted in challenges related to material durability and the stability of the air plastron during prolonged submersion. Factors such as pressure, flow, and temperature further complicate the operational viability of underwater superhydrophobic technology. This comprehensive review navigates the evolving landscape of underwater superhydrophobic technology, providing a deep dive into the introduction, advancements, and innovations in design, fabrication, and testing techniques. Recent breakthroughs in nanotechnology, magnetic-responsive coatings, additive manufacturing, and machine learning are highlighted, showcasing the diverse avenues of progress. Notable research endeavors concentrate on enhancing the longevity of plastrons, the fundamental element governing superhydrophobic behavior. The review explores the multifaceted applications of superhydrophobic coatings in the underwater environment, encompassing areas such as drag reduction, anti-biofouling, and corrosion resistance. A critical examination of commercial offerings in the superhydrophobic coating landscape offers a current perspective on available solutions. In conclusion, the review provides valuable insights and forward-looking recommendations to propel the field of underwater superhydrophobicity toward new dimensions of innovation and practical utility.

Underwater Bubble Manipulation on Surfaces with Patterned Regions with Infused Lubricants

The flexible manipulation of underwater gas bubbles on solid substrates has attracted considerable research interest from scientists in the fields of water electrolysis, bubble microreactions, drug delivery, and heat transfer. Inspired by the oxygen-binding mechanisms of aquatic organisms, scientists have designed a series of interfacial materials for use in collecting gases, detecting and grading bubbles, and conducting microbubble reactions. Aerophilic surfaces are commonly used in underwater bubble manipulation platforms due to their excellent gas-trapping properties. However, during bubble transport, some of the bubbles are retained in the rough structure of the aerophilic surface and cause gas loss, which in the long run reduces the gas transport function. In addition, the aerophilic surface is prone to failure in high-humidity and high-pressure underwater environments. The lubricant-infused surface features an oil layer that remains stable on a rough substrate and is immiscible with water. Additionally, the bubbles are transported over the oil layer without causing losses other than those dissolved in water. These attributes make it more favorable than the aerophilic surface. Inspired by the unique properties of Nepenthes and cactus spines, we developed a patterned slippery surface [patterned lubricant-infused surface (PLIS)] through laser etching and ammonia etching that facilitates the coexistence of superaerophobic and aerophilic surfaces. The PLIS executes bubble capture utilizing a difference in wettability measuring 78°, transports bubbles through Laplace force and buoyancy, and regulates bubble release by restricting the contact area on the PLIS. The PLIS can be prepared rapidly and affordably in just about an hour, and its potential for large-scale production is high. Following tests for shear, acid and alkali resistance, and corrosion resistance, the PLIS exhibited impressive weathering resistance and appears to have potential for application in some extreme environments.

Bioinspired Fluoride-Free Magnetic Microcilia Arrays for Anti-Icing and Multidimensional Droplet Manipulation

The accumulation of ice on surfaces will bring safety issues to various human activities. Researchers have been actively developing superhydrophobic surfaces (SHS) as good anti-icing materials. However, some limitations, such as high cost, complexity of preparation, and lack of sufficient durability in extreme environments, restrict their practical applications. Inspired by bronchial mucosa cilia structure and the superhydrophobic lotus leaf structure, we generated ordered magnetic microcilia arrays (MMA) surfaces within 1 min by a fast and controllable microhole assisted magnetic-induced microcilia self-growth method. Fluoride-free superhydrophobic MMA (SMMA) was prepared by impregnating MMA into hexadecyltrimethoxysilane (HDTMS) modified SiO2 solution. SMMA exhibits excellent static anti-icing performance, which can significantly delay the freezing of static droplets in supercooled environments. The SMMA surface still maintains excellent dynamic anti-icing performance at -30 °C after 100 times of supercooled droplet impact. Furthermore, SMMA shows anti-icing performance for up to 2 months at low temperatures (-18 °C). Due to the sensitive magnetic response and excellent bending properties of the cilia, the MMA and SMMA surfaces also demonstrate outstanding multifunctional droplet manipulation under a magnetic field. The MMA surface has the ability to vertically capture and release droplets. The SMMA can achieve horizontal transport of droplets, mixing and microchemical detection, antigravity droplet transport in an 8° inclined array, and even complex objects can be easily transported. More importantly, the SMMA surface exhibits outstanding mechanical durability and chemical stability. It provides insights into the preparation of integrated anti-icing and droplet manipulation surfaces by using a simple green and low-cost method.

Dynamically Adaptive Bubbling for Upgrading Oxygen Evolution Reaction Using Lamellar Fern-Like Alloy Aerogel Self-Standing Electrodes

Adopting renewable electricity to produce "green" hydrogen has been a critical challenge because at a high current density the mass transfer capability of most catalytic electrodes deteriorates significantly. Herein, a unique lamellar fern-like alloy aerogel (LFA) electrode, showing a unique dynamically adaptive bubbling capability and can effectively avoid stress concentration caused by bubble aggregation is reported. The LFA electrode is intrinsically highly catalytic-active and shows a highly porous, resilient, hierarchically ordered, and well-percolated conductive network. It not only shows superior gas evacuation capability but also exhibits significantly improved stability at high current densities, showing the record lowest oxygen evolution reaction (OER) overpotential of 244 mV at 1000 mA cm-2 and stably over 6000 h. With the merits of mechanical robustness, excellent electron transport, and efficient bubble evacuation, LFA can be self-standing catalytic electrode and gas diffusion layers in anion-exchange-membrane water electrolysis (AEMWE), which can achieve 3000 mA cm-2 at a low voltage of 1.88 V and can sustain stable electrolysis at 2000 mA cm-2 for over 1300 h. This strategy can be extended to various gas evolution reactions as a general design rule for multiphase catalysis applications.

Ultrahigh Efficient Collection of Underwater Bubbles by High Adsorption and Transport, Coalescence, and Collection Integrating a Conical Arrayed Surface

The capture and utilization of underwater fuel bubbles such as methane can alleviate the greenhouse effect, solve the global energy crisis, and possibly improve the endurance of underwater equipment. However, previous research routinely failed to achieve the integrated process of continuous adsorption, transportation, and collection of bubbles limited by the trade-off between the bubble adhesion and transport efficiency dependent on interfacial pinning, tremendously hindering the direct capture and utilization of underwater fuel bubbles. To break through this bottleneck, a magnetic-guided conical arrayed surface (CAS) associated with a laser etching technique is fabricated conveniently to realize superhydrophobicity. The bubbles on laser-etched CAS have higher adhesiveness and low-pinning transport compared with those on the nonlaser-etched surface. Intriguingly, the gas film adsorbed within the CAS seems to be a gas channel, which accelerates the bubble coalescence and fast spreading to eventually realize the integration of transport, coalescence, and collection. The dynamic behaviors of bubble adsorption, transportation, and coalescence on CAS are probed to reveal the mechanism of the gas film-generating process within conical arrays. Furthermore, a novel underwater bubble-collecting device with multiangled CAS is proposed to achieve multidirectional capture, highly efficient transportation, and collection of rising bubbles. The results advance our understanding of dynamic behaviors of bubbles at solid-liquid interfaces and facilitate design and manufacturing of an apparatus for bubble collection.

Bubble Engineering on Micro-/Nanostructured Electrodes for Water Splitting

Bubble behaviors play crucial roles in mass transfer and energy efficiency in gas evolution reactions. Combining multiscale structures and surface chemical compositions, micro-/nanostructured electrodes have drawn increasing attention. With the aim to identify the exciting opportunities and rationalize the electrode designs, in this review, we present our current comprehension of bubble engineering on micro-/nanostructured electrodes, focusing on water splitting. We first provide a brief introduction of gas wettability on micro-/nanostructured electrodes. Then we discuss the advantages of micro-/nanostructured electrodes for mass transfer (detailing the lowered overpotential, promoted supply of electrolyte, and faster bubble growth kinetics), localized electric field intensity, and electrode stability. Following that, we outline strategies for promoting bubble detachment and directional transportation. Finally, we offer our perspectives on this emerging field for future research directions.

Nanoparticles with transformable physicochemical properties for overcoming biological barriers

In recent years, tremendous progress has been made in the development of nanomedicines for advanced therapeutics, yet their unsatisfactory targeting ability hinders the further application of nanomedicines. Nanomaterials undergo a series of processes, from intravenous injection to precise delivery at target sites. Each process faces different or even contradictory requirements for nanoparticles to pass through biological barriers. To overcome biological barriers, researchers have been developing nanomedicines with transformable physicochemical properties in recent years. Physicochemical transformability enables nanomedicines to responsively switch their physicochemical properties, including size, shape, surface charge, etc., thus enabling them to cross a series of biological barriers and achieve maximum delivery efficiency. In this review, we summarize recent developments in nanomedicines with transformable physicochemical properties. First, the biological dilemmas faced by nanomedicines are analyzed. Furthermore, the design and synthesis of nanomaterials with transformable physicochemical properties in terms of size, charge, and shape are summarized. Other switchable physicochemical parameters such as mobility, roughness and mechanical properties, which have been sought after most recently, are also discussed. Finally, the prospects and challenges for nanomedicines with transformable physicochemical properties are highlighted.

Fluid manipulation via multifunctional lubricant infused slippery surfaces: principle, design and applications

Water-repellent interfaces with high performance have emerged as an indispensable platform for developing advanced materials and devices. Inspired by the pitcher plant, slippery liquid-infused porous surfaces (SLIPSs) with reliable hydrophobicity have proven to possess great potential for various applications in droplet and bubble manipulation, droplet energy harvesting, condensation, fog collection, anti-icing, and anti-biofouling due to their excellent properties such as persistent surface hydrophobicity, molecular smoothness, and fluidity. This review aims to introduce the development history of interaction between SLIPSs and fluids as well as the design principles, preparation methods, and various applications of some of the more typical SLIPSs. The fluid manipulation strategies of the slippery surfaces have been proposed including the wettability pattern, oriented micro-structure, and geometric gradient. At last, the application prospects of SLIPSs in various fields and the challenges in the design and fabrication of slippery surfaces are analyzed. We envision that this review can provide an overview of the fluid manipulating processes on slippery surfaces for researchers in both academic and industrial fields.