Fluorescent double network ionogels with fast self-healability and high resilience for reliable human motion detection

Liquid-free ionic conductive elastomers with high mechanical properties and ionic conductivity for multifunctional sensors and triboelectric nanogenerators

Liquid-free ionic conductive elastomers (ICEs) are ideal materials for constructing flexible electronic devices by avoiding the limitations of liquid components. However, developing all-solid-state ionic conductors with high mechanical strength, high ionic conductivity, excellent healing, and recyclability remains a great challenge. Herein, a series of liquid-free polyurethane-based ICEs with a double dynamic crosslinked structure are reported. As a result of interactions between multiple dynamic bonds (multi-level hydrogen bonds, disulfide bonds, and dynamic D-A bonds) and lithium-oxygen bonds, the optimal ICE exhibited a high mechanical strength (1.18 MPa), excellent ionic conductivity (0.14 mS cm-1), desirable healing capacity (healing efficiency >95%), and recyclability. A multi-functional wearable sensor based on the novel ICE enabled real-time and rapid detection of various human activities and enabled recognizing writing signals and encrypted information transmission. A triboelectric nanogenerator based on the novel ICE exhibited an excellent open-circuit voltage of 464 V, a short-circuit current of 16 μA, a transferred charge of 50 nC, and a power density of 720 mW m-2, enabling powering of small-scale electronic products. This study provides a feasible strategy for designing flexible sensor products and healing, self-powered devices, with promising prospects for application in soft ionic electronics.

Highly Stretchable Double Network Ionogels for Monitoring Physiological Signals and Detecting Sign Language

At the heart of the non-implantable electronic revolution lies ionogels, which are remarkably conductive, thermally stable, and even antimicrobial materials. Yet, their potential has been hindered by poor mechanical properties. Herein, a double network (DN) ionogel crafted from 1-Ethyl-3-methylimidazolium chloride ([Emim]Cl), acrylamide (AM), and polyvinyl alcohol (PVA) was constructed. Tensile strength, fracture elongation, and conductivity can be adjusted across a wide range, enabling researchers to fabricate the material to meet specific needs. With adjustable mechanical properties, such as tensile strength (0.06-5.30 MPa) and fracture elongation (363-1373%), this ionogel possesses both robustness and flexibility. This ionogel exhibits a bi-modal response to temperature and strain, making it an ideal candidate for strain sensor applications. It also functions as a flexible strain sensor that can detect physiological signals in real time, opening doors to personalized health monitoring and disease management. Moreover, these gels' ability to decode the intricate movements of sign language paves the way for improved communication accessibility for the deaf and hard-of-hearing community. This DN ionogel lays the foundation for a future in which e-skins and wearable sensors will seamlessly integrate into our lives, revolutionizing healthcare, human-machine interaction, and beyond.

Multifunctional chitosan-based lanthanide luminescent hydrogel with stretchability, adhesion, self-healing, color tunability and antibacterial ability

Lanthanide luminescent hydrogels have broad application prospects in various fields. However, most of lanthanide hydrogels possess relatively simple functions, which is not conducive to practical applications. Therefore, it is becoming increasingly urgent to develop multifunctional hydrogels. Herein, a multifunctional chitosan-based lanthanide luminescent hydrogel with ultra-stretchability, multi-adhesion, excellent self-healing, emission color tunability, and good antibacterial ability was prepared by a simple one-step free radical polymerization. In this work, our designed lanthanide complexes [Ln(4-VDPA)3] contain three reaction sites, which can be copolymerized with N-[tris(hydroxymethyl) methyl] acrylamide (THMA), acrylamide (AM), and diacryloyl poly(ethylene glycol) (DPEG) to form the first chemical crosslinking network, while hydroxypropyltrimethyl ammonium chloride chitosan (HACC) interacts with the hydroxyl and amino groups derived from the chemical crosslinking network through hydrogen bonds to form the second physical crosslinking network. The structure of the double network as well as the dynamic hydrogen bond and lanthanide coordination endow the hydrogel with excellent stretchability, adhesion and self-healing properties. Moreover, the introduction of lanthanide complexes and chitosan makes the hydrogel exhibit outstanding luminescence and antibacterial performances. This research not only realizes the simple synthesis of multifunctional luminescent hydrogels, but also provides a new idea for the fabrication of biomass-based hydrogels as intelligent and sustainable materials.

Recent progress in self-healable energy harvesting and storage devices - a future direction for reliable and safe electronics

Electronic devices with multiple features bring in comfort to the way we live. However, repeated use causes physical as well as chemical degradation reducing their lifetime. The self-healing ability is the most crucial property of natural systems for survival in unexpected situations and variable environments. However, this self-repair property is not possessed by the conventional electronic devices designed today. To expand their lifetime and make them reliable by restoring their mechanical, functional, and electrical properties, self-healing materials are a great go-to option to create robust devices. In this review the intriguing self-healing polymers and fascinating mechanism of self-healable energy harvesting devices such as triboelectric nanogenerators (TENG) and storage devices like supercapacitors and batteries from the aspect of electrodes and electrolytes in the past five years are reviewed. The current challenges, strategies, and perspectives for a smart and sustainable future are also discussed.

Carboxymethyl cellulose-based hydrogel with high-density crack microstructures inspired from the multi-tentacles of octopus for ultrasensitive flexible sensing microsystem

Constructing high-density contact-separation sites on conductive materials highly determines the sensitivity of flexible resistance-type sensors relying on the crack microstructures. Herein, inspired from the multiple-tentacle structures on octopus, we demonstrated a sort of novel carbonized ZIF-8@loofah (CZL) as conductive material to develop ultrasensitivity flexible sensor, in which the carbonized ZIF-8 nanoparticles (~100 nm) served as tentacles. Originating from the formation of high-density contact-separation sites, the fabricated CZL-based strain sensor delivered ultrahigh sensitivity of GFmax = 15,901, short response time of 22 ms and excellent durability over 10,000 cycles. These features enable the sensor with efficient monitoring capacity for complex human activities, such as pulse rate and phonation. Moreover, when CZL was assembled into triboelectric nanogenerator (TENG), CZL-based TENG can effectively convert the irregular biomechanical energy into electric energy, providing sustainable power supply for the continuous operation of the sensing micro-system. Our findings established a novel platform to develop high-performance self-powered sensing systems of physiological parameter of human inspired from the nature.

Environment Endurable, Self-Healing, Super-Adhesive, and Mechanically Strong Ionogels for Reliable Sensing

Ionogels possess high conductivity, stretchability, and adhesion, making them promising as flexible sensors. However, it remains challenging to fabricate an ionogel which integrates excellent environment endurance, superior mechanical strength, high self-healing efficiency, and super adhesion. Herein, a supramolecular ionic liquid is synthesized using calcium chloride and 1-butyl-3-methylimidazolium chloride. An advanced ionogel based on this supramolecular ionic liquid is conveniently constructed by a one-pot method with acrylamide and acrylic acid as monomers. The supramolecular cross-linking network, formed by affluent coordination interactions, hydrogen bonds, and electrostatic interactions, provides the ionogel with ideal mechanical strength (tensile strength up to 1.7 MPa), high self-healing efficiency (up to 149%), super adhesion (up to 358 kPa on aluminum), excellent solvent tolerance (less than 10% weight increase, high mechanical and sensing performance retention after being soaked in organic solvents), and low-temperature endurance (breaking elongation can reach 87% at -30 °C). The supramolecular ionogels can function as multi-mode sensors, capable of monitoring strain and different amplitudes of human movements in real-time. Moreover, the sensing performance of ionogels remains unaffected even after being self-healed or exposure to organic solvents. It is expected that this study could offer valuable design ideas to construct advanced gel materials applicable in complicated environment.

Multi-characteristic tannic acid-reinforced polyacrylamide/sodium carboxymethyl cellulose ionic hydrogel strain sensor for human-machine interaction

Big data and cloud computing are propelling research in human-computer interface within academia. However, the potential of wearable human-machine interaction (HMI) devices utilizing multiperformance ionic hydrogels remains largely unexplored. Here, we present a motion recognition-based HMI system that enhances movement training. We engineered dual-network PAM/CMC/TA (PCT) hydrogels by reinforcing polyacrylamide (PAM) and sodium carboxymethyl cellulose (CMC) polymers with tannic acid (TA). These hydrogels possess exceptional transparency, adhesion, and remodelling features. By combining an elastic PAM backbone with tunable amounts of CMC and TA, the PCT hydrogels achieve optimal electromechanical performance. As strain sensors, they demonstrate higher sensitivity (GF = 4.03), low detection limit (0.5 %), and good linearity (0.997). Furthermore, we developed a highly accurate (97.85 %) motion recognition system using machine learning and hydrogel-based wearable sensors. This system enables contactless real-time training monitoring and wireless control of trolley operations. Our research underscores the effectiveness of PCT hydrogels for real-time HMI, thus advancing next-generation HMI systems.

Super tough and high adhesive eutectic ionogels enabled by high-density hydrogen bond network

Ionogels have attracted tremendous interest for flexible electronics due to their excellent deformability, conductivity, and environmental stability. However, most ionogels suffer from low strength and poor toughness, which limit their practical applications. This article presents a strategy for fabricating ionogels with high toughness by constructing high-density hydrogen bonds within their microstructure. The ionogels exhibit a maximum fracture strength of 11.44 MPa, and can sustain a fracture strain of 506%. They also demonstrate a fracture energy of 27.29 MJ m-3 and offer a wide range of mechanical property adjustments (fracture stress from 0.3 to 11.44 MPa, fracture strain from 506% to 1050%). Strain sensors assembled with ionogels demonstrate exceptional sensing performance and enable motion detection of human joints. This study provides a new approach for achieving strong and tough ionogel design used for high-performance flexible electronic applications.

Rapid Radiation Synthesis of a Flexible, Self-Healing, and Adhesive Ionogel with Environmental Tolerance for Multifunctional Strain Sensors

Ionogels are increasingly used in flexible strain sensors, but it is still challenging to incorporate multifunctional properties such as flexibility, self-healing, adhesion, temperature resistance, and electrical conductivity. Herein, a facile and rapid one-step photoinitiated polymerization strategy is employed to prepare multifunctional ionogels by filling a hydrophobic and conductive ionic liquid into a flexible, hydrophobic fluoropolymer matrix. Thanks to the presence of abundant noncovalent interactions (hydrogen-bonding and ion-dipole interactions), the ionogels exhibit high transparency, excellent mechanical properties, self-healing ability, and adhesion. Moreover, rich C-F bonds in the fluoropolymer matrix can eliminate the interference of water molecules, resulting in excellent environmental tolerance such as high and low temperature resistance, waterproofness, and anticorrosion. Furthermore, the ionogel-based wearable strain sensor can sensitively detect and differentiate human movements and subtle muscle movements and serve as a Morse code signal transmitter for information transmission. The presented work provides an effective method to develop versatile flexible conductive ionogels for wearable devices and ionotronics.

Highly Tough, Stretchable, and Recyclable Ionogels with Crosslink-Enhanced Emission Characteristics for Anti-Counterfeiting and Motion Detection

Traditional luminescent ionogels often suffer from poor mechanical properties and a lack of recyclability and regeneration, which limits their further application and sustainable development. Herein, a luminescent ionogel with strong mechanical properties and good recyclability has been designed and fabricated by introducing dynamic coordination bonds via in situ one-step crosslinking of acrylic acid in ionic liquid of 1-ethyl-3-methylimidazolium diethylphosphate by zinc dimethacrylate. Due to the special crosslinking of dynamic coordination bonds along with the hydrogen bond interaction, the as-prepared ionogel displays excellent stretchability and toughness, good self-adhesiveness, fast self-healability, and recyclability. Interestingly, the obtained ionogels exhibit tunable photoluminescence caused by the crosslink-enhanced emission (CEE) effect from the coordination bonds. Importantly, ionogels can be applied in information storage, information encryption, anti-counterfeiting due to their simple and in situ preparation method, and their special fluorescence performances. Moreover, an ionogel-based wearable sensor has rapid response time and a high gauge factor of 3.22 within a wide strain range from 1 to 700%, which can monitor various human movements accurately from subtle to large-scale motions. This paper offers a promising way to fabricate sustainable functional ionic liquid-based composites with CEE characteristics via an in situ one-step polymerization method.