Advancing high-performance tailored dual-crosslinking network organo-hydrogel flexible device for wireless wearable sensing

Real-time quantification of microfluidic hydrogel crosslinking via gas-phase electrophoresis

This study presents a novel approach for the controlled synthesis and real-time characterization of crosslinked hyaluronic acid (HA) hydrogels utilizing a microfluidic platform coupled with hyphenated electrospray-differential mobility analysis (ES-DMA). By precisely controlling key synthesis parameters within the microfluidic environment, including pH, temperature, reaction time, and the molar ratio of HA to crosslinker (1,4-butanediol diglycidyl ether, BDDE), we successfully synthesized HA hydrogels with tailored size and properties. The integrated ES-DMA system provides rapid, in-line analysis of hydrogel particle size and distribution, enabling real-time monitoring and optimization of the synthesis process. Furthermore, small-angle x-ray scattering (SAXS) was employed to complement ES-DMA analysis, providing valuable insights into the internal structure and extent of crosslinking within the synthesized hydrogels. The evolution of the number-based particle size distribution revealed a strong correlation with the synthesis conditions, demonstrating the high degree of controllability achieved by this integrated approach. This novel methodology offers a promising platform for the high-throughput synthesis of uniform and well-defined hydrogel nanoparticles with enhanced traceability, paving the way for advancements in various applications including drug delivery, tissue engineering, and biomaterials.

Nanoarchitectonics of a Skin-Like Polymeric Hydrogel with High Anti-Swelling and Self-Adhesion Performance for Underwater Communication

Hydrogels are flexible materials characterized by a 3D network structure, which possess high water content and adjustable physicochemical properties. They have found widespread applications in tissue engineering, electronic skin, drug delivery, flexible sensors, and photothermal therapy. However, hydrogel networks often exhibit swelling behavior in aqueous environments, which can result in structural degradation and a loss of gel performance. In this study, polyacrylic acid is utilized as the primary network structure with the incorporation of the natural polymer chitosan. Furthermore, a conductive hydrogel exhibiting good mechanical strength similar to human skin and excellent anti-swelling properties is developed by integrating phytic acid into the hydrogel network. The as-prepared hydrogels exhibited maximum swelling in pure water, achieving an equilibrium swelling rate of 15%. Additionally, a dopamine-grafted polyacrylic acid binder is synthesized through a coupling reaction to enhance the adhesion of the hydrogels to various substrates. The hydrogels demonstrated strong adhesion properties with different substrates. Whether in the air or underwater, the hydrogel sensor effectively monitors human movement behaviors. Furthermore, by utilizing the sensing signals to send Morse code, the hydrogel sensor can facilitate underwater communication. This type of hydrogel sensor is anticipated to play a significant role in wearable sensing applications and underwater communication.

Flexible Pressure, Humidity, and Temperature Sensors for Human Health Monitoring

The rapid advancements in artificial intelligence, micro-nano manufacturing, and flexible electronics technology have unleashed unprecedented innovation and opportunities for applying flexible sensors in healthcare, wearable devices, and human-computer interaction. The human body's tactile perception involves physical parameters such as pressure, temperature, and humidity, all of which play an essential role in maintaining human health. Inspired by the sensory function of human skin, many bionic sensors have been developed to simulate human skin's perception to various stimuli and are widely applied in health monitoring. Given the urgent requirements for sensing performance and integration of flexible sensors in the field of wearable devices and health monitoring, here is a timely overview of recent advances in pressure, humidity, temperature, and multi-functional sensors for human health monitoring. It covers the fundamental components of flexible sensors and categorizes them based on different response mechanisms, including resistive, capacitive, voltage, and other types. Specifically, the application of these flexible tactile sensors in the area of human health monitoring is highlighted. Based on this, an extended overview of recent advances in dual/triple-mode flexible sensors integrating pressure, humidity, and temperature tactile sensing is presented. Finally, the challenges and opportunities of flexible sensors are discussed.

High-tear resistant gels crosslinked by DA@CNC for 3D printing flexible wearable devices

Photocurable gels have broad application prospects in biomedicine, bionics, flexible wearable devices and other fields. However, there are still some problems in the current photocurable gels, such as notch sensitivity, that is, poor tear resistance. In this study, we provided a photocurable gel with excellent tear resistance. The gel prepolymer is mainly composed of hydroxymethylacrylamide (NAM) and cellulose nanocrystals (CNC) modified with dopamine hydrochloride (DA), referred to as DA@CNC. After photocuring, the prepared gels show excellent mechanical properties such as tear resistance, elasticity and toughness. The introduction of DA@CNC not only endows gels with a large amount of energy dissipation through hydrogen bond crosslinking, but also effectively resists crack expansion as a nano-sized reinforcing phase, which greatly improves the tear resistance of the gels. Even at a 40 % gap, the elongation at break of the gel can still reach 1445 %. In addition, the DA can endow the gel with good electrical conductivity and excellent sensitivity (GF = 23.8). Some flexible wearable devices like finger sleeve and wristband can be customized by photocurable 3D printing using the gel with high toughness. This high-performance gel has great application potential in flexible wearable devices.

A novel strategy to construct hydrogels with anti-swelling and water-retention abilities by covalent surface modification

Hydrogels have been widely used in various fields due to their diverse properties and flexible preparation methods. However, limited by the open network structure, hydrogels inevitably lose water in air or absorb water in aqueous solution, resulting in the loss of intrinsic functions, which severely hinders their practical applications. To address this issue, a general strategy was developed by subsequently modifying the surface of hydrogels with branched polyethyleneimine (PEI) and (3-(methacryloxy)propyl)trimethoxysilane (MPS) to covalently construct a dense cross-linked siloxane layer on the hydrogel surface. As a proof of concept, poly(2-(dimethylamino)ethyl methacrylate)/sodium alginate (PDMAEMA/SA) hydrogels were chosen as the model hydrogels to verify the feasibility of this strategy. The hydrogels adsorbed PEI to form amino-rich surfaces through hydrogen bonding, followed by covalently grafting MPS through rapid and catalyst-free mutual chemical reactions between acrylates and amine groups, as well as the hydrolysis of MPS. After modification, robust hydrophobic surfaces were successfully fabricated on the hydrophilic hydrogels. The modified hydrogels exhibited extraordinary anti-swelling and water-retention abilities. As the most typical intrinsic properties of hydrogels, the conductivity and sensing performance were well preserved. The strategy reported here provides a new insight into the construction of hydrogels with anti-swelling and water-retention abilities.

Building synergistic multiple active sites in branch-leaf nanostructured carbon nanofiber derived from MOF/COF hybrid for flexible wearable Zn-air battery

Covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) have attracted growing attention in electrochemical energy storage and conversion systems (e.g., Zn-air batteries, ZABs) owing to their structural tunability, ordered porosity and high specific surface area. In this work, for the first time, the three-dimensional (3D) highly open catalyst (CNFs/CoZn-MOF@COF) possessing hierarchical porous structure and high-density active sites of uniform cobalt (Co) nanoparticles and metal-Nx (M-Nx, M = Co and Zn) is demonstrated, which is fabricated using electrospinning technique in combination with MOF/COF hybridization strategy and direct pyrolysis. Benefiting from the well-designed branch-leaf nanostructures, plentiful and uniform active sites on the MOF/COF-derived carbon frameworks, as well as the synergistic effect of multiple active sites, CNFs/CoZn-MOF@COF catalyst achieves superior electrocatalytic activity and stability towards both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with a small potential gap (ΔE = 0.75 V). In situ Raman spectroscopy and X-ray photoelectron spectroscopy results indicate that the CoOOH intermediates are the main active species during OER/ORR. Significantly, both aqueous and all-solid-state rechargeable ZABs assembled with CNFs/CoZn-MOF@COF as the air cathode show high open-circuit potential, outstanding peak power density, large capacity and long cycle life. More impressively, the obtained all-solid-state ZAB also displays superb mechanical flexibility and device stability under different, showcasing great application deformations potential in portable and wearable electronics. This work provides a new insight into the design and exploitation of bifunctional catalysts from MOF/COF hybrid materials for energy storage and conversion devices.