Nanoarchitectonics for Electrospun Membranes with Asymmetric Wettability

Sandwiched Copper Foam with Symmetrical Wettability for Direction-Independent Fog Collection

The Janus membrane demonstrates its advantages in timely drainage and directional water transport properties for efficient fog water collection, which helps alleviate global water shortages. However, the direction-dependent collection and inefficient directional water transport properties limit its widespread application. Herein, a single-layered sandwich-structured copper foam that features a superhydrophilic inner layer and double-deck external hydrophobic layers is prepared by a simple method. This innovative architecture demonstrates direction-independent fog harvesting capabilities through the synergistic integration of symmetric wettability gradients and robust structural integrity. Such sandwiched copper foam shows its superiority in rapid directional water transport and timely drainage properties which can quickly regenerate the fresh outer hydrophobic surface as well as the direction-independent unidirectional water transport properties. The rapid directional water transport property combined with the timely drainage of the sandwiched copper foam benefits the continuous better performance of fog collection compared to that of conventional Janus membranes. Clearly, the development of such sandwiched copper foam with a direction-independent unidirectional water transport property enables the effective and durable collection of fog droplets in environments with dynamically changeable winds. Overall, this work provides a new idea for the fabrication of advanced materials for direction-independent fog collection.

Recent Advances in Asymmetric Wettability Dressings for Wound Exudate Management

The management of wound exudate is of vital importance for wound healing. Exudate accumulation around wound prolongs inflammation and hinders healing. Although traditional dressings can absorb wound exudate, they are unable to drain exudate in time, often resulting in a poor feature with wound healing. In recent years, the appearance of asymmetric wettability dressings has shown great potential in exudate management. Here, we summarize the latest progress of 3 kinds of asymmetric wettability wound dressings in exudate management, including Janus structure, sandwich structure, and gradient structure. The most common Janus structural dressing among asymmetric wettability dressings is highlighted from 2 aspects: single-layer modified Janus structure and double-layer Janus structure. The challenges faced by asymmetric wettability wound dressings are discussed, and the developing trends of smart wound dressings in this field are prospected.

Recent advances in regulation methods for selective separation and precise control of two-dimensional (2D) lamellar membranes

Selective separation and precise control of the structure and surface characterization for two-dimensional (2D) membranes is the key technology that needs to be revealed for further development of the material in practical application. Current researches focus on the cross-linking and modification of single nanosheet to improve and manipulate the performance of 2D lamellar membranes. In this paper, the selectivity principles such as size exclusion, charge properties, and surface chemical affinity in the separation process of 2D membranes were comprehensively and systematically reviewed, as well as the preparation of hybrid membranes combining the advantages of various raw materials. We also analyzed the practical application of the separation principles in relevant researches and discussed the development directions of 2D membranes. These inductions have certain summary and guiding significance for the selective regulation and goal-oriented design of 2D membranes.

A Double-Layer Polyurethane Electrospun Membrane with Directional Sweat Transport Ability for Use as a Soft Strain Sensor

Wearable electronics for long-term monitoring of physiological signals should be capable of removing sweat generated during daily motion, which significantly impacts signal stability, human comfort, and safety of the electronics. In this study, we developed a double-layer polyurethane (PU) membrane with sweat-directional transport ability that can be applied for monitoring strain signals. The PU membrane was composed of a hydrophilic, conductive layer and a relatively hydrophobic layer. The double-layer PU composite membrane exhibited varied pore size and opposite hydrophilicity on its two sides, enabling the spontaneous pumping of sweat from the hydrophobic side to the hydrophilic side, i.e., the directional transport of sweat. The membrane can be used as a strain sensor to monitor motion strain over a broad working range of 0% to 250% with high sensitivity (GF = 4.11). The sensor can also detect simple human movements even under sweating conditions. We believe that the strategy demonstrated here will provide new insights into the design of next-generation strain sensors.

Directional Moisture-Wicking Triboelectric Materials Enabled by Laplace Pressure Differences

Wearable sensors are experiencing vibrant growth in the fields of health monitoring systems and human motion detection, with comfort becoming a significant research direction for wearable sensing devices. However, the weak moisture-wicking capability of sensor materials leads to liquid retention, severely restricting the comfort of the wearable sensors. This study employs a pattern-guided alignment strategy to construct microhill arrays, endowing triboelectric materials with directional moisture-wicking capability. Within 2.25 s, triboelectric materials can quickly and directionally remove the droplets, driven by the Laplace pressure differences and the wettability gradient. The directional moisture-wicking triboelectric materials exhibit excellent pressure sensing performance, enabling rapid response/recovery (29.1/37.0 ms), thereby achieving real-time online monitoring of human respiration and movement states. This work addresses the long-standing challenge of insufficient moisture-wicking driving force in flexible electronic sensing materials, holding significant implications for enhancing the comfort and application potential of electronic skin and wearable electronic devices.

Fabrication of a Janus Copper Mesh by SiO2 Spraying for Unidirectional Water Transportation and Oil/Water Separation

Massive discharge of oily wastewater and frequent occurrence of offshore oil spills have posed an enormous threat to the socioeconomic and ecological environments. Janus membranes with asymmetric wettability properties have great potential for oil/water separation applications and have attracted widespread attention. However, existing Janus membranes still suffer from complex and costly manufacturing processes, low permeability, and poor recyclability. Herein, a novel and facile strategy was proposed to fabricate a Janus copper mesh with opposite wettability for unidirectional water transport and efficient oil/water separation. The hydrophilic side of the Janus copper mesh was prepared by coating it with Cu(OH)2 nanoneedles via a chemical oxidation method. The hydrophobic side was fabricated by coating it with hydrophobic SiO2 nanoparticles via a facile spraying method. The as-prepared Janus copper mesh showed asymmetric surface wettability, which can achieve unidirectional water transport and efficient oil/water separation with excellent recyclability, exhibiting great application potential for droplet manipulation and wastewater purification.

Functional electrospun nanofibers: fabrication, properties, and applications in wound-healing process

Electrostatic spinning as a technique for producing nanoscale fibers has recently attracted increasing attention due to its simplicity, versatility, and loadability. Nanofibers prepared by electrostatic spinning have been widely studied, especially in biomedical applications, because of their high specific surface area, high porosity, easy size control, and easy surface functionalization. Wound healing is a highly complex and dynamic process that is a crucial step in the body's healing process to recover from tissue injury or other forms of damage. Single-component nanofibers are more or less limited in terms of structural properties and do not fully satisfy various needs of the materials. This review aims to provide an in-depth analysis of the literature on the use of electrostatically spun nanofibers to promote wound healing, to overview the infinite possibilities for researchers to tap into their biomedical applications through functional composite modification of nanofibers for advanced and multifunctional materials, and to propose directions and perspectives for future research.

Control the hydrophilic layer thickness of Janus membranes by manipulating membrane wetting in membrane distillation

Janus membranes with asymmetric wettability have attracted wide attentions for their robust anti-oil-wetting/fouling abilities in membrane distillation (MD). Compared to traditional surface modification approaches, in this study, we provided a new approach which manipulated surfactant-induced wetting to fabricate Janus membrane with a controllable thickness of the hydrophilic layer. The membranes with 10, 20, and 40 μm of wetted layers were obtained by stopping the wetting induced by 40 mg L^-1 Triton X-100 (J = 25 L m^-2 h^-1) at about 15, 40, and 120 s, respectively. Then, the wetted layers were coated using polydopamine (PDA) to fabricate the Janus membranes. The resulting Janus membranes showed no significant change in porosities or pore size distributions compared with the virgin PVDF membrane. These Janus membranes exhibited low in-air water contact angles (< 50°), high underwater oil contact angles (> 145°), and low adhesion with oil droplets. Therefore, they all showed excellent oil-water separation performance with ∼100% rejection and stable flux. The Janus membranes showed no significant decline in flux, but a trade-off existed between the hydrophilic layer thicknesses and the vapor flux. Utilizing membranes with tunable hydrophilic layer thickness, we elucidated the underlying mechanism of such trade-off in mass transfer. Furthermore, the successful modification of membranes with different coatings and in-situ immobilization of silver nanoparticles indicated that this facile modification method is universal and can be further expanded for multifunctional membrane fabrication.

Biocompatible curcumin coupled nanofibrous membrane for pathogens sterilization and isolation

Airborne transmission of pathogens is the most probable cause for the spread of respiratory diseases, which can be intercepted by personal protective equipment such as masks. In this study, an efficient antiviral personal protective filter was fabricated by coupling the biocompatible curcumin (CCM) with nanofibrous polytetrafluoroethylene (PTFE) membrane. The CCM extracted from plants was first dissolved in acidified ethanol at a certain pH and temperature to optimize its loading concentration, antiviral activation, and binding forces on the polyethylene terephthalate (PET) support to form a pre-filtration layer at the front section of the filter. Ultrathin PTFE membrane was then fabricated on the antibacterial-antiviral PET support (A-A PET) by controllable heating lamination. This functional layer of the filter exhibits good gas permeance (3423.6 m³/(m²·h·kPa)) and ultrafine particles rejection rate (>98.79%). Moreover, the obtained A-A filter exhibit a high antibacterial rate against a variety of bacteria (E. coli, B. subtilis, A. niger, and Penicillium were 99.84%, 99.02%, 93.60%, 95.23%, respectively). Forthwith virucidal (SARS-CoV-2) efficiency of the A-A filter can reach 99.90% for 5 min. The filter shows good stability after 10 heating cycles, demonstrating its reusability.