Bioinspired Superhydrophobic Fibrous Materials

Solid/Liquid/Gas Three-Phase Interface Enzymatic Reaction-Based Lactate Biosensor with Simultaneously High Sensitivity and Wide Linear Range

Electrochemical lactate biosensors with simultaneously high sensitivity and wide linear detection range are desirable for health monitoring. Nevertheless, the low oxygen level in biological fluids compromises oxidase enzymatic kinetics, which consequently results in a narrow linear detection range and/or low sensitivity. In this study, we addressed this issue by fabricating a solid/liquid/gas three-phase enzyme electrode with sufficiently high oxygen levels in the local reaction zone and much enhanced oxidase enzymatic kinetics. The three-phase enzyme electrode was fabricated by successively immobilizing H2O2 electrocatalyst and lactate oxidase (LOx) on a superhydrophobic porous carbon substrate. Owing to the much-enhanced oxidase enzymatic kinetics, the linear detection upper limit of the three-phase lactate biosensor was increased up to 40 mM, about 57-fold higher than that of the conventional two-phase system (0.7 mM), while a sensitivity as high as 22.28 μA mM-1 cm-2 was maintained. Moreover, a sweat lactate sensing device was fabricated based on the three-phase enzyme electrode and utilized for lactate detection in undiluted sweat during exercise. This three-phase enzyme electrode with both high sensitivity and wide linear range provides a new approach for the development of high-performance lactate sensing systems.

Study on Intelligent Bionic Superhydrophobic Material and its Oil-Water Separation Mechanism

Marine oil spills and improper disposal of daily oil usage have posed significant threat to ecological environments and human health due to rapid industrial development. In this study, an environmentally friendly, simple process and high-performance Fe3O4@SiO2@Polymethyl methacrylate (PMMA)-based smart bionic superhydrophobic oil-absorbing material was developed for effectively collecting and removing oil pollutants from water. By studying the effects of Fe3O4 particle size, polydimethylsiloxane (PDMS) concentration, and heating time on the superhydrophobicity of the materials, the directional regulation of superhydrophobicity and oil-water separation performance of Fe3O4@SiO2@PMMA@PDMS materials was realized. The results showed that the material exhibited optimal performance when the Fe3O4 particle size combination was 20/500 nm/1 μm, the mass ratio of PDMS to Fe3O4@SiO2@PMMA was 7 : 1, and it was heated at 350°C for 1 minute. The coating achieved an apparent contact angle (APCA) of 158.7° and a rolling angle as low as 4.9°. This coating not only remained superhydrophobic after a 21 m abrasion test and 288 h immersion in acid, alkali, salt, and high-temperature solutions, but also efficiently separated oil-water mixtures and water-in-oil emulsions, and the separation efficiency for oil-water mixtures of trichloromethane, dichloromethane and bromomethane was over 99.78 %, and that for water-in-oil emulsions was over 98.34 %. Furthermore, the superhydrophobic magnetic polyurethane (SFPU) sponge prepared using Fe3O4@SiO2@PMMA not only exhibited excellent oil-absorbing capacity (11-28 g/g), but also realized precise oil absorption at multiple sites by magnetic conduction. In the actual oily wastewater test, the oil-water separation efficiency of the sponge reached 90.58 % and the oil absorption capacity reached 17.03 g/g. This efficient oil-water separation performance as well as oil adsorption capacity comes from the fact that the nonpolar molecules (e. g., -CH3) generated by the hydrolysis of PDMS can produce van der Waals adsorption with oil substances, while the excellent micro-nanostructure of the coating surface greatly increases the contact area between oil droplets and the coating, which can make them adsorb or pass through quickly. This multifunctional coating and sponge had immense application potential in fields like offshore oil spill treatment, organic pollution control in water bodies.

Flexible wearable piezoresistive physical sensors with photothermal conversion and self-cleaning functions for human motion monitoring

Flexible wearable sensors can mimic the sensing ability of the skin and transform deformation stimuli into monitorable electrical signals, making them favorable in the fields of personalized healthcare, human motion monitoring, and remote monitoring systems. Here, an innovative piezoresistive physical sensor based on fluorine-free superhydrophobic dodecyltrimethoxysilane/polypyrrole/carbon nanotube (DTMS/PPy/CNT) cotton fabrics (DPC-CFs) was assembled via an environmentally safe and simple dip-coating method. The flexible wearable sensor exhibits self-cleaning capability (high water contact angle of 158.3°), good electrical conductivity (45.43 S m-1), photo-thermal conversion (surface temperature up to 94.8 °C), rapid response/recovery time (60 ms/50 ms), and excellent stability (>2400 cycles), and was successfully applied to dynamic monitoring of a series of human activities such as wrist pulse, voice recognition, and finger bending. Furthermore, the development of the superhydrophobic piezoresistive physical sensor derived from biodegradable cotton fabrics means an important step forward in the evolution of wearable sensors, which not only provide better coverage of three-dimensional irregular surfaces to capture mechanical stimulation signals but also demonstrate better comfort, flexibility and versatility. It is foreseen that such sensors, which are fabricated by utilizing abundant renewable and biodegradable green raw materials, have a broad application prospect in the next generation of biomedical systems, fitness, and human-computer interactive devices.

Hydrophobic TPU/CNTs-ILs Ionogel as a Reliable Multimode and Flexible Wearable Sensor for Motion Monitoring, Information Transfer, and Underwater Sensing

Ionogel-based sensors have gained widespread attention in recent years due to their excellent flexibility, biocompatibility, and multifunctionality. However, the adaptation of ionogel-based sensors in extreme environments (such as humid, acidic, alkaline, and salt environments) has rarely been studied. Here, thermoplastic polyurethane/carbon nanotubes-ionic liquids (TPU/CNTs-ILs) ionogels with a complementary sandpaper morphology on the surface were prepared by a solution-casting method with a simple sandpaper as the template, and the hydrophobic flexible TPU/CNTs-ILs ionogel-based sensor was obtained by modification using nanoparticles modified with cetyltrimethoxysilane. The hydrophobicity improves the environmental resistance of the sensor. The ionogel-based sensor exhibits multimode sensing performance and can accurately detect response signals from strain (0-150%), pressure (0.1-1 kPa), and temperature (30-100 °C) stimuli. Most importantly, the hydrophobic TPU/CNTs-ILs ionogel-based sensors can be used not only as wearable strain sensors to monitor human motion signals but also for information transfer, writing recognition systems, and underwater activity monitoring. Thus, the hydrophobic TPU/CNTs-ILs ionogel-based sensor offers a new strategy for wearable electronics, especially for applications in extreme environments.

Modeling of Shear Flows over Superhydrophobic Surfaces: From Newtonian to Non-Newtonian Fluids

The design and use of superhydrophobic surfaces have gained special attentions due to their superior performances and advantages in many flow systems, e.g., in achieving specific goals including drag reduction and flow/droplet handling and manipulation. In this work, we conduct a brief review of shear flows over superhydrophobic surfaces, covering the classic and recent studies/trends for both Newtonian and non-Newtonian fluids. The aim is to mainly review the relevant mathematical and numerical modeling approaches developed during the past 20 years. Considering the wide ranges of applications of superhydrophobic surfaces in Newtonian fluid flows, we attempt to show how the developed studies for the Newtonian shear flows over superhydrophobic surfaces have been evolved, through highlighting the major breakthroughs. Despite the fact that, in many practical applications, flows over superhydrophobic surfaces may show complex non-Newtonian rheology, interactions between the non-Newtonian rheology and superhydrophobicity have not yet been well understood. Therefore, in this Review, we also highlight emerging recent studies addressing the shear flows of shear-thinning and yield stress fluids in superhydrophobic channels. We focus on reviewing the models developed to handle the intricate interaction between the formed liquid/air interface on superhydrophobic surfaces and the overlying flow. Such an intricate interaction will be more complex when the overlying flow shows nonlinear non-Newtonian rheology. We conclude that, although our understanding on the Newtonian shear flows over superhydrophobic surfaces has been well expanded via analyzing various aspects of such flows, the non-Newtonian counterpart is in its early stages. This could be associated with either the early applications mainly concerning Newtonian fluids or new complexities added to an already complex problem by the nonlinear non-Newtonian rheology. Finally, we discuss the possible directions for development of models that can address complex non-Newtonian shear flows over superhydrophobic surfaces.

Advances in the Research of Photo, Electrical, and Magnetic Responsive Smart Superhydrophobic Materials: Synthesis and Potential Applications

With the rapid advancement of technology, the wettability of conventional superhydrophobic materials no longer suffice to meet the demands of practical applications. Intelligent responsive superhydrophobic materials have emerged as a highly sought-after material in various fields. The exceptional superhydrophobicity, reversible wetting, and intelligently controllable characteristics of these materials have led to extensive applications across industries, including industry, agriculture, defense, and medicine. Therefore, the development of intelligent superhydrophobic materials with superior performance, economic practicality, enhanced sensitivity, and controllability assumes utmost importance in advancing technology worldwide. This article provides a summary of the wettability principles of superhydrophobic surfaces and the mechanisms behind intelligent responsive superhydrophobicity. Furthermore, it reviews and analyzes the recent research progress on light, electric, and magnetic responsive superhydrophobic materials, encompassing aspects such as material synthesis, modification, performance, and responses under diverse external stimuli. The article also explores the challenges associated with different types of responsive superhydrophobic materials and the unique application prospects of light, electric, and magnetic responsive superhydrophobic materials. Additionally, it outlines the future directions for the development of intelligent responsive superhydrophobic materials.

Guarding skin under PPE: Mechanistic insights and technological innovations

In the presence of diseases transmitted through respiratory droplets and direct contact, healthcare workers (HCWs) necessitate the use of personal protective equipment (PPE). For optimal safety, PPE should securely conform to the skin during extended wear. However, conventional PPE often lacks adequate air permeability and hygroscopicity, trapping heat and moisture emitted by the body within the enclosure. Such a hot and humid internal environment can induce skin damage, such as erythema, rash, pruritus, and itching among others, leading to microbial growth on the skin surface, the production of inflammatory mediators at the wound site and an increased risk of infection. This review strives to comprehensively elucidate the fundamental mechanisms triggering adverse skin reactions and their resultant manifestations. Furthermore, we explore recent advancements aimed at inhibiting these mechanisms to effectively mitigate the occurrence of skin lesions.