A Bioinspired Mineral Hydrogel as a Self-Healable, Mechanically Adaptable Ionic Skin for Highly Sensitive Pressure Sensing

Combined treatment strategy of hydrogel dressing and physiotherapy for rapid wound healing

Wound care for open wounds is essential for reducing pain, protecting open wounds, speeding up the healing process and avoiding scar formation. Among the various three-dimensional (3D) carrier biomaterials such as films, sponges, and hydrogels, hydrogels are chemically and physically most similar to the natural extracellular matrix (ECM). Meanwhile, hydrogels are also common 3D carriers that can be efficiently loaded with drugs or cells. In addition, it forms a protective barrier on the wound surface to prevent secondary external infections and has the effect of directing skin cell expansion, tissue infiltration, and wound closure. However, the role of functional drugs in wound healing also faces a number of issues such as resistance, dosage, activity, and stability; therefore, a richer array of therapies is needed for wound repair and other areas of development. Physiotherapy, also known as nonpharmacological therapy, is a commonly used clinical treatment. Recently, more and more physiotherapy have been used for wound repair due to their high efficiency and low irritation. In recent reports, many researchers have tended to use hydrogel dressings in combination with physiotherapy, and this combination therapy is beneficial because it can both protect the wound microenvironment and accelerates wound healing. Therefore, this paper reviews the combined use of hydrogel dressings and physiotherapy in wound healing. We present the characteristics of hydrogel and physiotherapy and focus on the progress and problems of these two combined therapies in recent years.

Multilayer iontronic sensors with controlled charge gradients for high-performance, self-powered tactile sensing

Piezoionic sensors have emerged as a promising class of self-powered tactile sensors, utilizing ion transport within soft materials to convert mechanical stimuli into electrical signals. These sensors offer flexibility, biocompatibility, and the ability to detect both static and dynamic forces, making them highly suitable for wearable electronics, robotic skins, and human-machine interfaces. However, conventional piezoionic sensors suffer from low output signals and slow response times due to inefficient ion transport and charge separation. To address these limitations, we propose a multilayered piezoionic sensor incorporating positively and negatively charged surface layers to create a controlled charge gradient. This design enhances ion mobility and reduces binding energy between ion pairs, and accelerates charge redistribution, leading to significantly improved sensing performance. The proposed sensor achieves an enhanced output current of 1.2 μA and a rapid response time of 19 ms, demonstrating superior sensing performances compared to single-layer designs. Additionally, the sensor effectively detects both static and dynamic forces, including vibration stimuli for surface texture detection, and enables air flow mapping by distinguishing both direction and intensity. By overcoming the fundamental limitations of existing piezoionic sensors, our multilayer approach establishes a new paradigm for high-performance, self-powered tactile sensing, paving the way for next-generation soft electronics and smart sensor systems.

Inorganic Hydrogels can be Flexible and Highly Extensible

Inorganic hydrogels have great potential in many applications as sustainable materials, but lack flexibility due to rigid network structures. Here, a novel strategy is proposed-an inorganic polymer hydrogel, prepared by crosslinking long-chain polyphosphate (LPP) with M2+ ions (Ca2+, Mn2+, Mg2+, Ni2+), which effectively address the rigidity and fragility issues commonly associated with traditional inorganic gels. With the most stable hydration shell among those ions, Ni2+ tends to interact indirectly with LPP through hydrogen bonds rather than coordination bonds. The unique Ni2+-phosphate interaction endows the Ni-LPP hydrogels with ultrahigh elongation at break (≈15 000×). Further experiments reveal that the Ni2+-phosphate motif can be applied to other hydrogels as an extension enhancement factor. The highly extensible, good conductive (1.06 ± 0.08 S m-1), self-healing (within 30 s and without stimulation), arbitrarily shapeable, and nonflammable Ni-LPP inorganic hydrogel indicates a bright future in flexible electronics, environmental remediation, and beyond.

Flexible iontronic sensing

The emerging flexible iontronic sensing (FITS) technology has introduced a novel modality for tactile perception, mimicking the topological structure of human skin while providing a viable strategy for seamless integration with biological systems. With research progress, FITS has evolved from focusing on performance optimization and structural enhancement to a new phase of integration and intelligence, positioning it as a promising candidate for next-generation wearable devices. Therefore, a review from the perspective of technological development trends is essential to fully understand the current state and future potential of FITS devices. In this review, we examine the latest advancements in FITS. We begin by examining the sensing mechanisms of FITS, summarizing research progress in material selection, structural design, and the fabrication of active and electrode layers, while also analysing the challenges and bottlenecks faced by different segments in this field. Next, integrated systems based on FITS devices are reviewed, highlighting their applications in human-machine interaction, healthcare, and environmental monitoring. Additionally, the integration of artificial intelligence into FITS is explored, focusing on optimizing front-end device design and improving the processing and utilization of back-end data. Finally, building on existing research, future challenges for FITS devices are identified and potential solutions are proposed.

Bioinspired learning and memory in ionogels through fast response and slow relaxation dynamics of ions

Mimicking biological systems' sensing, learning, and memory capabilities in synthetic soft materials remains challenging. While significant progress has been made in sensory functions in ionogels, their learning and memory capabilities still lag behind biological systems. Here, we introduce cation-π interactions and a self-adaptable ionic-double-layer interface in bilayer ionogels to control ion transport. Fast ion response enables sensing and learning, while slow ion relaxation supports long-term memory. The ionogels achieve bioinspired functions, including sensitization, habituation, classical conditioning, and multimodal memory, with low energy consumption (0.06 pJ per spike). Additionally, the ionogels exhibit mechanical adaptability, such as stretchability, self-healing, and reconfigurability, making them ideal for soft robotics. Notably, the ionogels enable a robotic arm to mimic the selective capture behavior of a Venus flytrap. This work bridges the gap between biological intelligence and artificial systems, offering promising applications in bioinspired, energy-efficient sensing, learning, and memory.

Reusable Liquid Metal-Based Hierarchical Hydrogels with Multifunctional Sensing Capability for Electrophysiology Electrode Substitution

Electrophysiological electrode patches are often used to collect surface electrophysiological signals to monitor and evaluate human health. However, commercial Ag/AgCl gels are very susceptible to electrode-skin interface interference during rehabilitation exercises and cannot achieve a stable collection of electrophysiological signals. In order to solve this challenge, this paper designed a liquid metal-based hierarchical hydrogel, which has a series of great performances, including adhesion to various substrates, efficient self-healing ability, excellent stretchability, and conductivity. Due to the hydrogel's unique rheological and adhesive properties, a conformal electrode/skin interface was generated, thus enabling stable electrophysiological signal acquisition during exercise. In addition, the strain sensor assembled based on the conductive hydrogel can sensitively monitor human limb movements in real time and can even be used for remote intelligent gesture recognition. Therefore, this work provides scientific guidance for developing a next generation of intelligent hydrogels with personal health surveillance, rehabilitation training monitoring, and wearable human-machine interaction.

Molecular Chain Interpenetration-Enabled High Interfacial Compatibility of Ionic and Electronic Conductors for Stretchable Ionic Devices

Ionic devices find applications such as flexible electronics and biomedicines and function by exploiting hybrid circuits of mobile ions and electrons. However, the poor interfacial compatibility of hard electronic conductors with soft ionic conductors in ionic devices leads to low deformability, sensitivity, electromechanical responses, and stability. Herein, an interpenetrating interface between silicone-modified polyurethane/carbon nanotube electronic conductors and ionoelastomers in an ionic device using in situ polymerization is fabricated. A robust interpenetrating electronic/ionic conductor interface is realized through molecular chain entanglement and molecular forces (such as ion-dipole interactions and H-bonds), effectively enhancing the bonding strength and contact area between the components and resulting in an excellent flexibility, stability, and device performance. The electroadhesive prepared based on this strategy exhibits a superrobust shear strength of 317 kPa under a reduced voltage input of -4 V, and the diode and the transistor can undergo arbitrary deformation while maintaining the semiconductor device characteristics, including rectification and switching. In addition, electromechanical transducers exhibit sensitive electrical responses to various deformation signals. This solution to the interfacial compatibility problems of electronic and ionic conductors holds promise for the development of multifunctional ionic devices.

Advances in Electrically Conductive Hydrogels: Performance and Applications

Electrically conductive hydrogels are highly hydrated 3D networks consisting of a hydrophilic polymer skeleton and electrically conductive materials. Conductive hydrogels have excellent mechanical and electrical properties and have further extensive application prospects in biomedical treatment and other fields. Whereas numerous electrically conductive hydrogels have been fabricated, a set of general principles, that can rationally guide the synthesis of conductive hydrogels using different substances and fabrication methods for various application scenarios, remain a central demand of electrically conductive hydrogels. This paper systematically summarizes the processing, performances, and applications of conductive hydrogels, and discusses the challenges and opportunities in this field. In view of the shortcomings of conductive hydrogels in high electrical conductivity, matchable mechanical properties, as well as integrated devices and machines, it is proposed to synergistically design and process conductive hydrogels with applications in complex surroundings. It is believed that this will present a fresh perspective for the research and development of conductive hydrogels, and further expand the application of conductive hydrogels.

Boosting Sensitivity of Cellulose Pressure Sensor via Hierarchically Porous Structure

Pressure sensors are essential for a wide range of applications, including health monitoring, industrial diagnostics, etc. However, achieving both high sensitivity and mechanical ability to withstand high pressure in a single material remains a significant challenge. This study introduces a high-performance cellulose hydrogel inspired by the biomimetic layered porous structure of human skin. The hydrogel features a novel design composed of a soft layer with large macropores and a hard layer with small micropores, each of which contribute uniquely to its pressure-sensing capabilities. The macropores in the soft part facilitate significant deformation and charge accumulation, providing exceptional sensitivity to low pressures. In contrast, the microporous structure in the hard part enhances pressure range, ensuring support under high pressures and preventing structural failure. The performance of hydrogel is further optimized through ion introduction, which improves its conductivity, and as well the sensitivity. The sensor demonstrated a high sensitivity of 1622 kPa-1, a detection range up to 160 kPa, excellent conductivity of 4.01 S m-1, rapid response time of 33 ms, and a low detection limit of 1.6 Pa, outperforming most existing cellulose-based sensors. This innovative hierarchically porous architecture not only enhances the pressure-sensing performance but also offers a simple and effective approach for utilizing natural polymers in sensing technologies. The cellulose hydrogel demonstrates significant potential in both health monitoring and industrial applications, providing a sensitive, durable, and versatile solution for pressure sensing.

Soft Materials and Devices Enabling Sensorimotor Functions in Soft Robots

Sensorimotor functions, the seamless integration of sensing, decision-making, and actuation, are fundamental for robots to interact with their environments. Inspired by biological systems, the incorporation of soft materials and devices into robotics holds significant promise for enhancing these functions. However, current robotics systems often lack the autonomy and intelligence observed in nature due to limited sensorimotor integration, particularly in flexible sensing and actuation. As the field progresses toward soft, flexible, and stretchable materials, developing such materials and devices becomes increasingly critical for advanced robotics. Despite rapid advancements individually in soft materials and flexible devices, their combined applications to enable sensorimotor capabilities in robots are emerging. This review addresses this emerging field by providing a comprehensive overview of soft materials and devices that enable sensorimotor functions in robots. We delve into the latest development in soft sensing technologies, actuation mechanism, structural designs, and fabrication techniques. Additionally, we explore strategies for sensorimotor control, the integration of artificial intelligence (AI), and practical application across various domains such as healthcare, augmented and virtual reality, and exploration. By drawing parallels with biological systems, this review aims to guide future research and development in soft robots, ultimately enhancing the autonomy and adaptability of robots in unstructured environments.

Thermoelectric Conversion Eutectogels for Highly Sensitive Self-Powered Sensors and Machine Learning-Assisted Temperature Identification

Endowing flexible sensors with self-powering capabilities is of significant importance. However, the thermoelectric conversion gels reported so far suffer from the limitations of insufficient flexibility, signal distortion under repetitive deformation, and insufficient comprehensive performance, which seriously hinder their wide application. In this work, we designed and prepared eutectogels by an ionic liquid and a polymerizable deep eutectic solvent (PDES), which exhibit good mechanical properties, adhesion, and excellent thermoelectric conversion and thermoelectric response performance. The Seebeck coefficient (Si) can reach 30.38 mV K-1 at a temperature difference of 10 K. To amplify the self-powered performance of individual gel units, we assembled them into arrays and further prepared temperature sensors. The combination of the K-means clustering algorithm of machine learning can filter out the noise of traditional thermoelectric sensors and improve the consistency of signals, thereby enabling the prediction of absolute temperature under the conditions of 10 or 20 K temperature difference. This study also demonstrates potential application of these eutectogels in thermoelectric self-powered sensing.

Bioinspired Structural Color Hydrogel Skin from Nonclose-Packed Colloidal Crystal Arrays for Epidermal Sensing

Developing multifunctional structural color hydrogel skin without sacrificing the unique periodic structure of photonic crystals is still a challenge due to the photonic bandgap limitation. Taking advantage of the synergistic effect of electrostatic repulsion and electronic conductivity, an intelligent structural color hydrogel skin with electrical and photonic sensing capabilities has been developed by doping MXene (Ti3C2Tx) nanosheets and adhesive functional groups (nucleobases) into colloidal particle solutions. The introduction of MXene nanosheets could improve both the stability and electrical conductivity of the colloidal particle solutions, resulting in a conductive hydrogel with bright structural colors. With the help of functional groups of nucleobases, the resulting structural color hydrogel was also endowed with high biocompatibility and strong adhesion to different substrates, including the wet surfaces of tissues. It was demonstrated that the structural color hydrogel can not only realize visual sensing of tiny limb movements but also provide stable electrical sensing signals. The intelligent structural color hydrogel can be integrated into a capacitor device as a hydrogel electronic skin to simulate the sensory function of human skin. The results showed that such hydrogel skin can simulate the touch of human skin and perceive tiny movements on the body surface with both electrical and photonic signals. These features of the multifunctional structural color hydrogels make them potentially excellent value in bioinspired hydrogel skin electronics.

Hydrogel-Coated Polydimethylsiloxane with Reversible Transparency for Advanced Optical Switching

Functional soft materials that swell in water often exhibit surface wrinkling, similar to the ridges formed on human skin after prolonged immersion, typically leading to reduced optical transmittance. Surprisingly, there is a scarcity of materials that are transparent underwater yet opaque in air, despite their vast potential in applications such as smart windows, periscopes, and information encryption. Herein, we report a hydrogel-based system comprising a polyacrylamide layer on polydimethylsiloxane (PDMS), demonstrating a reversible transition between opacity in air and high transparency in water or wet conditions. Upon water-induced swelling, the transmittance of the hydrogel layer markedly increases from 7.8% in air to 77.1% with excellent repeatability. This behavior enables applications such as optical encryption and decryption and water writing. Micro- and nanostructural analysis reveals that the optical switching arises from the reduction in local surface roughness upon hydrogel swelling. Furthermore, when employed as a smart window, the hydrogel layer effectively reduces solar power transmission by 36%, achieving a temperature reduction of 5.09 °C under direct sunlight while retaining heat in the absence of sunlight. These findings highlight the hydrogel layer on PDMS as a versatile platform for water-responsive smart devices, offering exciting opportunities in optical encryption, interactive writing systems, and energy-efficient window technologies.

Bioinspired Materials for Controlling Mineral Adhesion: From Innovation Design to Diverse Applications

The advancement of controllable mineral adhesion materials has significantly impacted various sectors, including industrial production, energy utilization, biomedicine, construction engineering, food safety, and environmental management. Natural biological materials exhibit distinctive and controllable adhesion properties that inspire the design of artificial systems for controlling mineral adhesion. In recent decades, researchers have sought to create bioinspired materials that effectively regulate mineral adhesion, significantly accelerating the development of functional materials across various emerging fields. Herein, we review recent advances in bioinspired materials for controlling mineral adhesion, including bioinspired mineralized materials and bioinspired antiscaling materials. First, a systematic overview of biological materials that exhibit controllable mineral adhesion in nature is provided. Then, the mechanism of mineral adhesion and the latest adhesion characterization between minerals and material surfaces are introduced. Later, the latest advances in bioinspired materials designed for controlling mineral adhesion are presented, ranging from the molecular level to micro/nanostructures, including bioinspired mineralized materials and bioinspired antiscaling materials. Additionally, recent applications of these bioinspired materials in emerging fields are discussed, such as industrial production, energy utilization, biomedicine, construction engineering, and environmental management, highlighting their roles in promoting or inhibiting aspects. Finally, we summarize the ongoing challenges and offer a perspective on the future of this charming field.

Two dimensional MoS2 accelerates mechanically controlled polymerization and remodeling of hydrogel

Self-remodeling material can change their physical properties based on mechanical environment. Recently, mechanically controlled polymerization using mechanoredox catalyst enabled composite materials to undergo a permanent structural change, thereby enhancing their mechanical strength. However, a significant delay in material's response was observed due to the sluggish activation of the bulk catalyst for polymerization. Herein, we report a fast, mechanically controlled radical polymerization of water soluble monomers using 2D MoS2 as the mechanoredox catalyst, studied under various mechanical stimuli, including ultrasound, ball milling and low frequency vibrations. Our strategy enables complete polymerization within several minutes of work. This accelerated process can be utilized to create composite hydrogels with the ability to alter their mechanical and electrical properties in response to mechanical stimuli. This strategy has potential for applications in smart materials such as hydrogel sensors, artificial muscles, and implantable biomaterials.

Stretchable Polymer Hydrogels Based Flexible Triboelectric Nanogenerators for Self-Powered Bioelectronics

The rapid development of flexible electronics has led to unprecedented social and economic improvements. But conventional power devices cannot adapt to the advances of flexible electronics. Triboelectric nanogenerators (TENGs) have been used as robust power sources to transform ambient mechanical energy into electricity, thus meeting the power requirements of flexible electronics. Hydrogels are widely used for soft bioelectronics owing to the decent stretchability and biocompatibility. This Review presents the recent progress in the use of hydrogels for TENGs and self-powered hydrogel bioelectronics, including hydrogel synthesis, hydrogel TENGs fabrication, and their applications in wearable electricity generation, self-powered active sensing, and therapeutics. Hydrogel-enabled TENGs are emerging as a novel form of soft bioelectronics. We provided a critical analysis of hydrogel TENGs and insights into future opportunities and directions of this rapidly evolving field. These advancements will push the boundaries of hydrogel bioelectronics and contribute to the development of personalized healthcare solutions.

Intrinsically Stretchable Motion Sensor Enabled by 3D Graphene Foam Integrated Hydrogel

Stretchable hydrogel devices are highly desirable for their capacity to seamlessly integrate significant stretchability, high conductivity, and exceptional biocompatibility. Nonetheless, the substantial disparity in stiffness between soft hydrogels and commonly rigid electrode materials often leads to pronounced performance fluctuations or even complete failure of sensor circuits in practical applications. Here, the study introduces an intrinsically stretchable graphene-hydrogel strain sensor (GHSS) fabricated by integrating a hydrogel and a 3D graphene foam with very closely matched elastic moduli. The GHSS demonstrates a strain detection limit of 0.02%, a rapid response time of 64 ms, and long-term stability, enabling the detection of human joint movements, physiological signals, touch pad input, and exercise monitoring.

Highly Self-Adhesive and Biodegradable Silk Bioelectronics for All-In-One Imperceptible Long-Term Electrophysiological Biosignals Monitoring

Skin-like bioelectronics offer a transformative technological frontier, catering to continuous and real-time yet highly imperceptible and socially discreet digital healthcare. The key technological breakthrough enabling these innovations stems from advancements in novel material synthesis, with unparalleled possibilities such as conformability, miniature footprint, and elasticity. However, existing solutions still lack desirable properties like self-adhesivity, breathability, biodegradability, transparency, and fail to offer a streamlined and scalable fabrication process. By addressing these challenges, inkjet-patterned protein-based skin-like silk bioelectronics (Silk-BioE) are presented, that integrate all the desirable material features that have been individually present in existing devices but never combined into a single embodiment. The all-in-one solution possesses excellent self-adhesiveness (300 N m-1) without synthetic adhesives, high breathability (1263 g h-1 m-2) as well as swift biodegradability in soil within a mere 2 days. In addition, with an elastic modulus of ≈5 kPa and a stretchability surpassing 600%, the soft electronics seamlessly replicate the mechanics of epidermis and form a conformal skin/electrode interface even on hairy regions of the body under severe perspiration. Therefore, coupled with a flexible readout circuitry, Silk-BioE can non-invasively monitor biosignals (i.e., ECG, EEG, EOG) in real-time for up to 12 h with benchmarking results against Ag/AgCl electrodes.

Autonomous Self-Healing Magnetoelectric I-Skin from Self-Bonded Deep Eutectic Polymer

Next-generation ionic skin (i-skin) should be self-healing and self-powered, promoting its development toward lightweight, miniaturization, compact, and portable designs. Previously reported self-powered i-skin mostly either lack the ability to self-repair damaged parts or only have self-healing capabilities some components, falling short of achieving complete device self-healability. In this work, a self-bonding strategy is presented to obtain an all-polymerizable deep eutectic solvent (PDES) magnetoelectric i-skin (MIS) that simultaneously achieves self-powering and full-device autonomous self-healability. The three-layered MIS can easily restore mechanical and electrochemical performance at the full-device level without requiring any external stimulus. The developed MIS can be easily configured into various 3D architectures with highly compatible magnetic and conductive components, offering promising potential for the advancement of embodied energy technologies. The present work provides a versatile and user-friendly platform for producing a wide range of intrinsic self-healing multi-layered devices made from soft materials, with potential applications extending beyond human-machine interfaces and artificial intelligence.

Wearable Biodevices Based on Two-Dimensional Materials: From Flexible Sensors to Smart Integrated Systems

The proliferation of wearable biodevices has boosted the development of soft, innovative, and multifunctional materials for human health monitoring. The integration of wearable sensors with intelligent systems is an overwhelming tendency, providing powerful tools for remote health monitoring and personal health management. Among many candidates, two-dimensional (2D) materials stand out due to several exotic mechanical, electrical, optical, and chemical properties that can be efficiently integrated into atomic-thin films. While previous reviews on 2D materials for biodevices primarily focus on conventional configurations and materials like graphene, the rapid development of new 2D materials with exotic properties has opened up novel applications, particularly in smart interaction and integrated functionalities. This review aims to consolidate recent progress, highlight the unique advantages of 2D materials, and guide future research by discussing existing challenges and opportunities in applying 2D materials for smart wearable biodevices. We begin with an in-depth analysis of the advantages, sensing mechanisms, and potential applications of 2D materials in wearable biodevice fabrication. Following this, we systematically discuss state-of-the-art biodevices based on 2D materials for monitoring various physiological signals within the human body. Special attention is given to showcasing the integration of multi-functionality in 2D smart devices, mainly including self-power supply, integrated diagnosis/treatment, and human-machine interaction. Finally, the review concludes with a concise summary of existing challenges and prospective solutions concerning the utilization of 2D materials for advanced biodevices.

Recent Development of Fibrous Hydrogels: Properties, Applications and Perspectives

Fibrous hydrogels (FGs), characterized by a 3D network structure made from prefabricated fibers, fibrils and polymeric materials, have emerged as significant materials in numerous fields. However, the challenge of balancing mechanical properties and functions hinders their further development. This article reviews the main advantages of FGs, including enhanced mechanical properties, high conductivity, high antimicrobial and anti-inflammatory properties, stimulus responsiveness, and an extracellular matrix (ECM)-like structure. It also discusses the influence of assembly methods, such as fiber cross-linking, interfacial treatments of fibers with hydrogel matrices, and supramolecular assembly, on the diverse functionalities of FGs. Furthermore, the mechanisms for improving the performance of the above five aspects are discussed, such as creating ion carrier channels for conductivity, in situ gelation of drugs to enhance antibacterial and anti-inflammatory properties, and entanglement and hydrophobic interactions between fibers, resulting in ECM-like structured FGs. In addition, this review addresses the application of FGs in sensors, dressings, and tissue scaffolds based on the synergistic effects of optimizing the performance. Finally, challenges and future applications of FGs are discussed, providing a theoretical foundation and new insights for the design and application of cutting-edge FGs.

Skin-Friendly Large Matrix Iontronic Sensing Meta-Fabric for Spasticity Visualization and Rehabilitation Training via Piezo-Ionic Dynamics

Rehabilitation training is believed to be an effectual strategy that can reduce the risk of dysfunction caused by spasticity. However, achieving visualization rehabilitation training for patients remains clinically challenging. Herein, we propose visual rehabilitation training system including iontronic meta-fabrics with skin-friendly and large matrix features, as well as high-resolution image modules for distribution of human muscle tension. Attributed to the dynamic connection and dissociation of the meta-fabric, the fabric exhibits outstanding tactile sensing properties, such as wide tactile sensing range (0 ~ 300 kPa) and high-resolution tactile perception (50 Pa or 0.058%). Meanwhile, thanks to the differential capillary effect, the meta-fabric exhibits a "hitting three birds with one stone" property (dryness wearing experience, long working time and cooling sensing). Based on this, the fabrics can be integrated with garments and advanced data analysis systems to manufacture a series of large matrix structure (40 × 40, 1600 sensing units) training devices. Significantly, the tunability of piezo-ionic dynamics of the meta-fabric and the programmability of high-resolution imaging modules allow this visualization training strategy extendable to various common disease monitoring. Therefore, we believe that our study overcomes the constraint of standard spasticity rehabilitation training devices in terms of visual display and paves the way for future smart healthcare.

Sustainable Silk Fibroin Ionic Touch Screens for Flexible Biodegradable Electronics with Integrated AI and IoT Functionality

The increasing prevalence of electronic devices has led to a significant rise in electronic waste (e-waste), necessitating the development of sustainable materials for flexible electronics. In this study, silk fibroin ionic touch screen (SFITS) is introduced, a new platform integrating natural silk fibroin (SF) with ionic conductors to create highly elastic, environmentally stable, and multifunctional touch interfaces. Through a humidity-induced crystallization strategy, the molecular structure of SF is precisely controlled to achieve a balanced combination of mechanical strength, electrical conductivity, and biodegradability. The assembly and operational reliability of SFITS are demonstrated under various environmental conditions, along with their reusability through green recycling methods. Additionally, the intelligent design and application of SFITS are explored by incorporating Internet of Things (IoT) and artificial intelligence (AI) technologies. This integration enables real-time touch sensing, handwriting recognition, and advanced human-computer interactions. The versatility of SFITS is further exemplified through applications in remote control systems, molecular model generation, and virtual reality interfaces. The findings highlight the potential of sustainable ionic conductors in next-generation flexible electronics, offering a path toward greener and more intelligent device designs.

Cation-π Interactions Based Conductive Hydrogels with Slide-Ring Structure Toward Super Long-Time in-air/Underwater Linear Sensing and Communication

Conductive hydrogels (CHs) are attracted more attention in the flexible wearable sensors field, however, how to stably apply CHs underwater is still a big challenge. In order to achieve the usage of CHs in aquatic environments, the integrated properties such as water retention ability, resistance to swelling, toughness, adhesiveness, linear GF sensing, and long-term usage are necessary to consider, but rarely reported in the previous reports. This paper proposes CHs prepared using cationic and aromatic monomers along with polyrotaxanes-based crosslinkers. Due to the intermolecular cation-π interactions and topological slide-ring-based polyrotaxanes, the CHs exhibit good mechanical performance, adhesive nature, and anti-swelling properties. The presence of slide-ring-based topological architecture effectively mitigates stress concentration. Additionally, the encapsulation of PA allows CHs to maintain functionality even after 240 days of direct placement at room temperature. Notably, the designed CHs exhibit linear sensitivity in detecting land/underwater human motions, and serve as Morse code signal transmitters for information transmission. Thus, the designed CHs may have broad applications in the underwater wearable sensors field.

Development of green synthesised AgNPs decorated on MWCNT modified guar gum-based self-healing hydrogel for strain sensors

Flexible conductive hydrogel strain sensors are gaining popularity due to their exceptional stretchability, sensitivity, and potential for wearable devices. However, their widespread use is hindered by significant issues, such as poor electrical conductivity and weak response time. To address these challenges, new hydrogels based on guar gum, borax, and glycerol have been fabricated via a green synthesis technique. These hydrogels were reinforced with functionalised multiwalled carbon nanotubes (f-MWCNTs) and silver nanoparticle decorated multiwalled carbon nanotubes (AgNP-MWCNTs). The resulting conductive hydrogels exhibited a self-healing capability of 83.2% and effective strain sensing with a gauge factor of 6.58. The incorporation of AgNP-MWCNTs significantly improved the electrical conductivity up to 3.05 ± 0.02 S m- 1, thanks to the tunnelling effect between f-MWCNTs and the synergic interaction of AgNP-MWCNTs. Moreover, the hydrogel sensors displayed excellent durability, enduring 3000 cycles of tensile loading and unloading at 50% strain. This innovative use of green design principles offers a straightforward, cost-effective, and environmentally friendly process for producing high-performance soft materials. These materials hold significant promise for various practical applications, including artificial skins, flexible electronics, and healthcare monitoring, highlighting the high relevance and impact of this research.

A universal framework for determining the effect of operating parameters on piezoionic voltage generation

The piezoionic effect, the generation of a transient voltage in a polymer matrix infused with ion embedded solvent upon the application of a mechanical stimulus, has demonstrated potential applications in ionic sensing, actuation, interfaces, and energy harvesting. Considerable progress has been made to increase voltage output based on optimizing the morphology and composition of materials. However, regardless of the materials used, in order to design and operate piezoionic devices efficiently, the effect of operating parameters, for example, the strength, speed, and location of the mechanical stimulus, as well as the collection of the piezoionic signal using electrodes are of equal importance. Yet, there has not been any systematic exploration of such operating parameters, leading to the present ad hoc approaches to the design, operation, and performance evaluation of piezoionic systems. In this work, we systematically show the effect of operating parameters on piezoionic voltage generation and provide a universal framework to describe new observations. To elucidate the relationship between the piezoionic response and the underlying mechanism, we propose a novel spatial-temporal strategy for characterizing the piezoionic effect. To ensure generality, newfound insights are modeled and cross-validated over a wide range of experimental data. New observations and new theoretical attributions resulting from this work provide the first systematic method towards optimizing the structure, geometry, and test of piezoionic devices.

An oxidative metal ions-free lignin-catalyzed multifunctional hydrogel bioelectronics for codable eye communication

To meet the stringent requirements of wearable and flexible electronics for functionality and comfort, it is urgent to develop green conductive, self-adhesive, and stretchable functional hydrogels. The chelates of transition metal ions and lignosulfonate sodium (LS) can impart multi-functionality to the hydrogel and significantly improve the hydrogel's gelation speed. However, the presence of metal ions may weaken the adhesiveness of hydrogels by shielding the functional adhesive groups. Here, an oxidative metal ions-free lignin-catalyzed multifunctional polyacrylic acid (PAA) hydrogel is proposed. LS itself can undergo a redox reaction with the initiator to generate many free radicals, thereby catalyzing the rapid polymerization of polymer monomers at room temperature and subsequent gelation. Furthermore, LS can easily improve the hydrogels' softness (compressive modulus: ∼7 kPa) and stretchability (maximum ∼2700 %). Interestingly, LS can simultaneously promote the hydrogel's conductivity, adhesion, and UV blocking. Notably, the hydrogel integrating these advantageous features is suitable as non-invasive electronics in the human epidermis. We explored its ability to act as adhesive bioelectrodes to collect electrooculographic signals in patients with physical and language impairments. Bioelectrodes can recognize the patient's eye movements. The displayed electrical signal can be output in 6 languages after being encoded. This provides a valuable case for LS-doped functional hydrogels in the medical field.

A Flexible Organomagnetic Single-Layer Composite Film with Built-In Multistimuli Responsivity

Materials possessing multiple properties and functionalities, that can be controlled or modulated by external stimuli, are a central focus of current research in materials sciences due to their potential to significantly enhance various future technological applications. Herein, we report a significant advancement in this field through the development of a smart, multifunctional organomagnetic composite material. By utilizing a thin layer of polydimethylsiloxane (PDMS) and polypyrrole (PPy) precursors, doped with nickel nanoparticles (NiNPs), we have created an innovative organomagnetic, PDMS/PPy/NiNPs (PPN), single-layer composite film that displays multistimuli responsivity. The study presents the first demonstration of a multifunctional flexible, three-component film structure integrating the structural and flexible PDMS component, together with a conductive polymer component and metal-based nanoparticles into a single-layer design, which displays enhanced and unprecedented responsivity properties against multiple different stimuli. Unlike typical stacked multilayered structures, that exhibit one or two functionalities at most, this novel configuration exhibits multiple functionalities, including magnetoresistance, mechanical stress response, piezoresistivity, and temperature change sensitivity. The as-prepared film demonstrates notable magnetoresistance responsivity, with a relative electrical resistance, ΔR/R0, changing under a weak magnetic field and under ambient conditions. The significance of our study lies in the film's versatility, stability, and sensitivity, especially within the physiological temperature range, making it highly relevant for future biomedical applications. Furthemore, the film's sensitivity to mechanical deformation reveals an impressive piezoresistance behavior. Unlike existing multilayer architectures of higher complexity, our single-layer thin film offers a simpler, more flexible, and reliable solution with a broad range of stimuli-sensing capabilities. The significance of this novel multiresponsive composite material is underscored by the growing demand for advanced materials in biomedical devices, magnetic switches, sensors, electronic skin, transistors, and organic spintronic devices. These promising organomagnetic self-standing layers provide a robust platform for future technological innovations.

A harsh environmental resistant and long-term stable ionic conductive hydrogel by one-step preparation for wireless health activity and physiological state detection

Benefiting from the good electromechanical performance, ionic conductive hydrogel can easily convert the deformation into electrical signals, showing great potential in wearable electronic devices. However, due to the high water content, icing and water evaporation problems seriously limit their development. Although additives can ease these disadvantages, the accompanying performance degradation and complex preparation processes couldn't meet application needs. In this work, a convenient method was provided to prepare ionic conductive hydrogels with sensitive electromechanical performance, harsh environmental tolerance, and long-term stability without additives. Based on the hydratability between metal ions and water molecules resulting in spatial condensation of the hydrogel framework, the hydrogel exhibits good flexibility and ionic conductivity (70.3 mS/cm). Furthermore, the metal salt can bind with water molecules to reduce the vapor pressure, thus endowing the hydrogel with good freezing resistance (-40 °C) and long-term stability over a wide temperature range (-20 °C-50 °C). Based on these unique advantages, the hydrogel shows good sensitivity. Even in a harsh environment, it still maintained excellent stability (-20 °C-50 °C, GF = 2.2, R2 > 0.99). Assembled with a Wi-Fi device, the hydrogel sensor demonstrates good health activity and physiological state detection performance, demonstrating great potential for wearable medical devices.

Advancements and Applications of Micro and Nanostructured Capacitive Sensors: A Review

Capacitors are essential components in modern electrical systems, functioning primarily to store electrical charges and regulate current flow. Capacitive sensors, developed in the 20th century, have become crucial in various applications, including touchscreens and smart devices, due to their ability to detect both metallic and non-metallic objects with high sensitivity and low energy consumption. The advancement of microelectromechanical systems (MEMS) and nanotechnology has significantly enhanced the capabilities of capacitive sensors, leading to unprecedented sensitivity, dynamic range, and cost-effectiveness. These sensors are integral to modern devices, enabling precise measurements of proximity, pressure, strain, and other parameters. This review provides a comprehensive overview of the development, fabrication, and integration of micro and nanostructured capacitive sensors. In terms of an electric field, the working and detection principles are discussed with analytical equations and our numerical results. The focus extends to novel fabrication methods using advanced materials to enhance sensitivities for various parameters, such as proximity, force, pressure, strain, temperature, humidity, and liquid sensing. Their applications are demonstrated in wearable devices, human-machine interfaces, biomedical sensing, health monitoring, robotics control, industrial monitoring, and molecular detection. By consolidating existing research, this review offers insights into the advancements and future directions of capacitive sensor technology.

Air-Writing Recognition Enabled by a Flexible Dual-Network Hydrogel-Based Sensor and Machine Learning

Accurate air-writing recognition is pivotal for advancing state-of-the-art text recognizers, encryption tools, and biometric technologies. However, most existing air-writing recognition systems rely on image-based sensors to track hand and finger motion trajectories. Additionally, users' writing is often guided by delimiters and imaginary axes which restrict natural writing movements. Consequently, recognition accuracy falls short of optimal levels, hindering performance and usability for practical applications. Herein, we have developed an approach utilizing a one-dimensional convolutional neural network (1D-CNN) algorithm coupled with an ionic conductive flexible strain sensor based on a sodium chloride/sodium alginate/polyacrylamide (NaCl/SA/PAM) dual-network hydrogel for intelligent and accurate air-writing recognition. Taking advantage of the excellent characteristics of the hydrogel sensor, such as high stretchability, good tensile strength, high conductivity, strong adhesion, and high strain sensitivity, alongside the enhanced analytical ability of the 1D-CNN machine learning (ML) algorithm, we achieved a recognition accuracy of ∼96.3% for in-air handwritten characters of the English alphabets. Furthermore, comparative analysis against state-of-the-art methods, such as the widely used residual neural network (ResNet) algorithm, demonstrates the competitive performance of our integrated air-writing recognition system. The developed air-writing recognition system shows significant potential in advancing innovative systems for air-writing recognition and paving the way for exciting developments in human-machine interface (HMI) applications.

Myelin Sheath-Inspired Hydrogel Electrode for Artificial Skin and Physiological Monitoring

Significant advancements in hydrogel-based epidermal electrodes have been made in recent years. However, inherent limitations, such as adaptability, adhesion, and conductivity, have presented challenges, thereby limiting the sensitivity, signal-to-noise ratio (SNR), and stability of the physiological-electrode interface. In this study, we propose the concept of myelin sheath-inspired hydrogel epidermal electronics by incorporating numerous interpenetrating core-sheath-structured conductive nanofibers within a physically cross-linked polyelectrolyte network. Poly(3,4-ethylenedioxythiophene)-coated sulfonated cellulose nanofibers (PEDOT:SCNFs) are synthesized through a simple solvent-catalyzed sulfonation process, followed by oxidative self-polymerization and ionic liquid (IL) shielding steps, achieving a low electrochemical impedance of 42 Ω. The physical associations within the composite hydrogel network include complexation, electrostatic forces, hydrogen bonding, π-π stacking, hydrophobic interaction, and weak entanglements. These properties confer the hydrogel with high stretchability (770%), superconformability, self-adhesion (28 kPa on pigskin), and self-healing capabilities. By simulating the saltatory propagation effect of the nodes of Ranvier in the nervous system, the biomimetic hydrogel establishes high-fidelity epidermal electronic interfaces, offering benefits such as low interfacial contact impedance, significantly increased SNR (30 dB), as well as large-scale sensor array integration. The advanced biomimetic hydrogel holds tremendous potential for applications in electronic skin (e-skin), human-machine interfaces (HMIs), and healthcare assessment devices.

Wearable Sensors, Data Processing, and Artificial Intelligence in Pregnancy Monitoring: A Review

Pregnancy monitoring is always essential for pregnant women and fetuses. According to the report of WHO (World Health Organization), there were an estimated 287,000 maternal deaths worldwide in 2020. Regular hospital check-ups, although well established, are a burden for pregnant women because of frequent travelling or hospitalization. Therefore, home-based, long-term, non-invasive health monitoring is one of the hot research areas. In recent years, with the development of wearable sensors and related data-processing technologies, pregnancy monitoring has become increasingly convenient. This article presents a review on recent research in wearable sensors, physiological data processing, and artificial intelligence (AI) for pregnancy monitoring. The wearable sensors mainly focus on physiological signals such as electrocardiogram (ECG), uterine contraction (UC), fetal movement (FM), and multimodal pregnancy-monitoring systems. The data processing involves data transmission, pre-processing, and application of threshold-based and AI-based algorithms. AI proves to be a powerful tool in early detection, smart diagnosis, and lifelong well-being in pregnancy monitoring. In this review, some improvements are proposed for future health monitoring of pregnant women. The rollout of smart wearables and the introduction of AI have shown remarkable potential in pregnancy monitoring despite some challenges in accuracy, data privacy, and user compliance.

From lab to wearables: Innovations in multifunctional hydrogel chemistry for next-generation bioelectronic devices

Functional hydrogels have emerged as foundational materials in diagnostics, therapy, and wearable devices, owing to their high stretchability, flexibility, sensing, and outstanding biocompatibility. Their significance stems from their resemblance to biological tissue and their exceptional versatility in electrical, mechanical, and biofunctional engineering, positioning themselves as a bridge between living organisms and electronic systems, paving the way for the development of highly compatible, efficient, and stable interfaces. These multifaceted capability revolutionizes the essence of hydrogel-based wearable devices, distinguishing them from conventional biomedical devices in real-world practical applications. In this comprehensive review, we first discuss the fundamental chemistry of hydrogels, elucidating their distinct properties and functionalities. Subsequently, we examine the applications of these bioelectronics within the human body, unveiling their transformative potential in diagnostics, therapy, and human-machine interfaces (HMI) in real wearable bioelectronics. This exploration serves as a scientific compass for researchers navigating the interdisciplinary landscape of chemistry, materials science, and bioelectronics.

Highly Transparent, Mechanically Robust, and Conductive Eutectogel Based on Oligoethylene Glycol and Deep Eutectic Solvent for Reliable Human Motions Sensing

Recently, eutectogels have emerged as ideal candidates for flexible wearable strain sensors. However, the development of eutectogels with robust mechanical strength, high stretchability, excellent transparency, and desirable conductivity remains a challenge. Herein, a covalently cross-linked eutectogel was prepared by exploiting the high solubility of oligoethylene glycol in a polymerizable deep eutectic solvent (DES) form of acrylic acid (AA) and choline chloride (ChCl). The resulting eutectogel exhibited high transparency (90%), robust mechanical strength (up to 1.5 MPa), high stretchability (up to 962%), and desirable ionic conductivity (up to 1.22 mS cm-1). The resistive strain sensor fabricated from the eutectogel exhibits desirable linear sensitivity (GF: 1.66), wide response range (1-200%), and reliable stability (over 1000 cycles), enabling accurate monitoring of human motions (fingers, wrists, and footsteps). We believe that our DES-based eutectogel has great potential for applications in wearable strain sensors with high sensitivity and reliability.

A wearable conductive hydrogel with triple network reinforcement inspired by bio-fibrous scaffolds for real-time quantitatively sensing compression force exerted on fruit surface

INTRODUCTION

Mechanical stresses incurred during post-harvest fruit storage and transportation profoundly impact decay and losses. Currently, the monitoring of mechanical forces is primarily focused on vibrational forces experienced by containers and vehicles and impact forces affecting containers. However, the detection of compressive forces both among interior fruit and between fruit and packaging surfaces remains deficient. Hence, conformable materials capable of sensing compressive stresses are necessary.

OBJECTIVES

In the present study, a triple-network-reinforced PSA/LiCl/CCN@AgNP conductive hydrogel was synthesized for compression force detection on fruit surfaces based on changes in intrinsic impedance under mechanical loading.

METHODS

The conductive hydrogel was characterized in terms of its adhesion, mechanics, frost resistance, water retention, conductivity, mechanical force-sensing properties, and feasibility for monitoring mechanical forces. Then, a portable complex impedance recorder was developed to interface with the conductive hydrogel and its mechanical force sensing ability was evaluated.

RESULTS

Beyond its inherent conductivity, the hydrogel exhibited notable pressure sensitivity within the strain range of 1 % to 80 %. The conductive hydrogel also demonstrated a commendable adhesion property, favorable tensile property (580 % elongation at break), substantial compressive strength and durability, and a long-term water retention capability. After exposure to -20 °C for 96 h, the hydrogel maintained its mechanical strength, affirming its anti-freezing property. In addition, a portable complex impedance recorder with sustained signal measurement stability was developed to quantitatively acquire the hydrogel resistance changes in response to compression forces. Finally, the effectiveness of the conductive hydrogel for sensing compression force on the surface of apple fruits was validated.

CONCLUSION

The conductive hydrogel holds promise for applications in smart packaging, wherein it can detect crucial mechanical stress on fruit, convert it into electrical signals, and further transmit these signals to the cloud, thereby enabling the real-time sensing of mechanical forces experienced by fruits and enhancing post-harvest fruit loss management.

Research on the osteogenic properties of 3D-printed porous titanium alloy scaffolds loaded with Gelma/PAAM-ZOL composite hydrogels

Although titanium alloy is the most widely used endoplant material in orthopedics, the material is bioinert and good bone integration is difficult to achieve. Zoledronic acid (ZOL) has been shown to locally inhibit osteoclast formation and prevent osteoporosis, but excessive concentrations of ZOL exert an inhibitory effect on osteoblasts; therefore, stable and controlled local release of ZOL may reshape bone balance and promote bone regeneration. To promote the adhesion of osteoblasts to many polar groups, researchers have applied gelatine methacryloyl (Gelma) combined with polyacrylamide hydrogel (PAAM), which significantly increased the hydrogen bonding force between the samples and improved the stability of the coating and drug release. A series of experiments demonstrated that the Gelma/PAAM-ZOL bioactive coating on the surface of the titanium alloy was successfully prepared. The coating can induce osteoclast apoptosis, promote osteoblast proliferation and differentiation, achieve dual regulation of bone regeneration, successfully disrupt the balance of bone remodelling and promote bone tissue regeneration. Additionally, the coating improves the metal biological inertness on the surface of titanium alloys and improves the bone integration of the scaffold, offering a new strategy for bone tissue engineering to promote bone technology.

Bibliometric analysis of artificial intelligence in healthcare research: Trends and future directions

Objective

The presence of artificial intelligence (AI) in healthcare is a powerful and game-changing force that is completely transforming the industry as a whole. Using sophisticated algorithms and data analytics, AI has unparalleled prospects for improving patient care, streamlining operational efficiency, and fostering innovation across the healthcare ecosystem. This study conducts a comprehensive bibliometric analysis of research on AI in healthcare, utilising the SCOPUS database as the primary data source.

Methods

Preliminary findings from 2013 identified 153 publications on AI and healthcare. Between 2019 and 2023, the number of publications increased exponentially, indicating significant growth and development in the field. The analysis employs various bibliometric indicators to assess research production performance, science mapping techniques, and thematic mapping analysis.

Results

The study reveals insights into research hotspots, thematic focus, and emerging trends in AI and healthcare research. Based on an extensive examination of the Scopus database provides a brief overview and suggests potential avenues for further investigation.

Conclusion

This article provides valuable contributions to understanding the current landscape of AI in healthcare, offering insights for future research directions and informing strategic decision making in the field.

Engineering Tough Supramolecular Hydrogels with Structured Micropillars for Tunable Wetting and Adhesion Properties

Soft-lithography is widely used to fabricate microstructured surfaces on plastics and elastomers for designable physical properties such as wetting and adhesions. However, it remains a big challenge to construct high-aspect-ratio microstructures on the surface of hydrogels due to the difficulty in demolding from the gel with low strength and stiffness. Demonstrated here is the engineering of tough hydrogels by soft-lithography to form well-defined micropillars. The mechanical properties of poly(acrylamide-co-methacrylic acid) hydrogels with dense hydrogen-bond associations severely depend on temperature, with Young's modulus increasing from 8.1 MPa at 15 °C to 821.8 MPa at -30 °C, enabling easy demolding at low temperatures. Arrays of micropillars are maintained on the surface of the gel, and can be used at room temperature when the gel restores soft and stretchable. The hydrogel also exhibits good shape-memory property, favoring tailoring the morphology with a switchable tilt angle of micropillars. Consequently, the hydrogel shows tunable wetting and adhesion properties, as manifested by varying contact angles and adhesion strengths. These surface properties can also be tuned by geometry and arrangement of micropillars. This facile strategy by harnessing tunable viscoelasticity of supramolecular hydrogels should be applicable to other soft materials, and broaden their applications in biomedical and engineering fields.

High-Performance Organic-Inorganic Hybrid Conductive Hydrogels for Stretchable Elastic All-Hydrogel Supercapacitors and Flexible Self-Powered Integrated Systems

Conductive polymer hydrogels exhibit unique electrical, electrochemical, and mechanical properties, making them highly competitive electrode materials for stretchable high-capacity energy storage devices for cutting-edge wearable electronics. However, it remains extremely challenging to simultaneously achieve large mechanical stretchability, high electrical conductivity, and excellent electrochemical properties in conductive polymer hydrogels because introducing soft insulating networks for improving stretchability inevitably deteriorates the connectivity of rigid conductive domain and decreases the conductivity and electrochemical activity. This work proposes a distinct confinement self-assembly and multiple crosslinking strategy to develop a new type of organic-inorganic hybrid conductive hydrogels with biphase interpenetrating cross-linked networks. The hydrogels simultaneously exhibit high conductivity (2000 S m-1), large stretchability (200%), and high electrochemical activity, outperforming existing conductive hydrogels. The inherent mechanisms for the unparalleled comprehensive performances are thoroughly investigated. Elastic all-hydrogel supercapacitors are prepared based on the hydrogels, showing high specific capacitance (212.5 mF cm-2), excellent energy density (18.89 µWh cm-2), and large deformability. Moreover, flexible self-powered luminescent integrated systems are constructed based on the supercapacitors, which can spontaneously shine anytime and anywhere without extra power. This work provides new insights and feasible avenues for developing high-performance stretchable electrode materials and energy storage devices for wearable electronics.

Exploring the Potentials of Chitin and Chitosan-Based Bioinks for 3D-Printing of Flexible Electronics: The Future of Sustainable Bioelectronics

Chitin and chitosan-based bioink for 3D-printed flexible electronics have tremendous potential for innovation in healthcare, agriculture, the environment, and industry. This biomaterial is suitable for 3D printing because it is highly stretchable, super-flexible, affordable, ultrathin, and lightweight. Owing to its ease of use, on-demand manufacturing, accurate and regulated deposition, and versatility with flexible and soft functional materials, 3D printing has revolutionized free-form construction and end-user customization. This study examined the potential of employing chitin and chitosan-based bioinks to build 3D-printed flexible electronic devices and optimize bioink formulation, printing parameters, and postprocessing processes to improve mechanical and electrical properties. The exploration of 3D-printed chitin and chitosan-based flexible bioelectronics will open new avenues for new flexible materials for numerous industrial applications.

Gels/Hydrogels in Different Devices/Instruments-A Review

Owing to their physical and chemical properties and stimuli-responsive nature, gels and hydrogels play vital roles in diverse application fields. The three-dimensional polymeric network structure of hydrogels is considered an alternative to many materials, such as conductors, ordinary films, constituent components of machines and robots, etc. The most recent applications of gels are in different devices like sensors, actuators, flexible screens, touch panels, flexible storage, solar cells, batteries, and electronic skin. This review article addresses the devices where gels are used, the progress of research, the working mechanisms of hydrogels in those devices, and future prospects. Preparation methods are also important for obtaining a suitable hydrogel. This review discusses different methods of hydrogel preparation from the respective raw materials. Moreover, the mechanism by which gels act as a part of electronic devices is described.

Highly conductive, rapid self-healing, and anti-freezing poly(3,4-ethylenedioxythiophene)/lignosulfonate-cationic guar gum ionogels for multifunctional sensors

Soft ionic conductors exhibit immense potential for applications in soft ionotronics, including ionic skin, human-machine interface, and soft luminescent device. Nevertheless, the majority of ionogel-based soft ionic conductors are plagued by issues such as freezing, evaporation, liquid leakage, and inadequate self-healing capabilities, thereby constraining their usability in complex environments. In this study, we present a novel strategy for fabricating conductive ionogels through the proportionally mixing cationic guar gum (CGG), water, 1-butyl-3-methylimidazolium chloride (BmimCl)/glycerol eutectic-based ionic liquid, and poly(3,4-ethylenedioxythiophene)/lignosulfonate (PEDOT/LS). The resultant benefits from strong hydrogen bonding and electrostatic interactions among its constituents, endowing it with an ultrafast self-healing capability (merely 30 s) while sustaining high electrical conductivity (~16.5 mS cm-1). Moreover, it demonstrates exceptional water retention (62 % over 10 days), wide temperature tolerance (-20 to 60 °C), and injectability. A wearable sensor fabricated from this ionogel displayed remarkable sensitivity (gauge factor = 17.75) and a rapid response to variations in strain, pressure, and temperature, coupled with both long-term stability and wide working temperature range. These attributes underscore its potential for applications in healthcare devices and flexible electronics.

On the dual crosslinking for functionality enhancement of poly (acrylamide-co-acrylic acid)/chitosan-aluminum (III) ions and its characterization and sensory hydrogel fibers

In this report, we present a dual crosslinking hydrogel fiber made from polyamine saccharides chitosan (CS), synthesized through UV polymerization. This process utilizes Irgacure 2959 and N,N'-Methylenebisacrylamide (MBAA) as initiators, followed by immersion in an aluminum chloride (AlCl3) solution. The resulting hydrogel incorporates a dual crosslinking mechanism, quantitatively studied via Nuclear Magnetic Resonance (NMR) spectroscopy. This mechanism involves chemical crosslinking through radical graft polymerization of acrylamide and acrylic acid onto CS in the presence of MBAA, and physical crosslinking through hydrogen bonding interactions between P(AAm-co-AA) and a metal coordination bond. The mechanical properties of the hydrogel fiber enable it to withstand stresses up to 656 kPa and strains exceeding 300 %. Additionally, the hydrogel fiber exhibits conductivity at 1.96 Scm-1. Serving as a multifunctional material, it acts as a strain sensor and finds utility in optics. Remarkably, it demonstrates the capability to detect human motions such as finger bending and minor deformations like vibrations of the vocal cords. Furthermore, its ability to guide dynamic light makes it promising for optical applications. Consequently, this multifunctional hydrogel fiber emerges as a highly promising candidate for diverse applications in fields such as bioengineering and electronics.

Bioinspired Flexible Hydrogelation with Programmable Properties for Tactile Sensing

Tactile sensing requires integrated detection platforms with distributed and highly sensitive haptic sensing capabilities along with biocompatibility, aiming to replicate the physiological functions of the human skin and empower industrial robotic and prosthetic wearers to detect tactile information. In this regard, short peptide-based self-assembled hydrogels show promising potential to act as bioinspired supramolecular substrates for developing tactile sensors showing biocompatibility and biodegradability. However, the intrinsic difficulty to modulate the mechanical properties severely restricts their extensive employment. Herein, by controlling the self-assembly of 9-fluorenylmethoxycarbonyl-modifid diphenylalanine (Fmoc-FF) through introduction of polyethylene glycol diacrylate (PEGDA), wider nanoribbons are achieved by untwisting from well-established thinner nanofibers, and the mechanical properties of the supramolecular hydrogels can be enhanced 10-fold, supplying bioinspired supramolecular encapsulating substrate for tactile sensing. Furthermore, by doping with poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and 9-fluorenylmethoxycarbonyl-modifid 3,4-dihydroxy-l-phenylalanine (Fmoc-DOPA), the Fmoc-FF self-assembled hydrogels can be engineered to be conductive and adhesive, providing bioinspired sensing units and adhesive layer for tactile sensing applications. Therefore, the integration of these modules results in peptide hydrogelation-based tactile sensors, showing high sensitivity and sustainable responses with intrinsic biocompatibility and biodegradability. The findings establish the feasibility of developing programmable peptide self-assembly with adjustable features for tactile sensing applications.

Nature-Inspired Molecular-Crowding Enabling Wide-Humidity Range Applicable, Anti-Freezing, and Robust Zwitterionic Hydrogels for On-Skin Electronics

Hydrogels are currently in the limelight for applications in soft electronics but they suffer from the tendency to lose water or freeze when exposed to dry environments or low temperatures. Molecular crowding is a prevalent occurrence in living cells, in which molecular crowding agents modify the hydrogen bonding structure, causing a significant reduction in water activity. Here, a wide-humidity range applicable, anti-freezing, and robust hydrogel is developed through the incorporation of natural amino acid proline (Pro) and conductive MXene into polyvinyl alcohol (PVA) hydrogel networks. Theoretical calculations reveal that Pro can transform "free water" into "locked water" via the molecular-crowding effect, thereby suppressing water evaporation and ice forming. Accordingly, the prepared hydrogel exhibits high water retention capability, with 77% and 55% being preserved after exposure to 20 °C, 28% relative humidity (RH) and 35 °C, 90% RH for 12 h. Meanwhile, Pro lowers the freezing temperature of the hydrogel to 34 °C and enhances its stretchability and strength. Finally, the PVA/Pro/MXene hydrogels are assembled as multifunctional on-skin strain sensors and conductive electrodes to monitor human motions and detect tiny electrophysiological signals. Collectively, this work provides a molecular crowding strategy that will motivate researchers to develop more advanced hydrogels for versatile applications.

Continuous dual-network alginate hydrogel fibers with superior mechanical and electrical performance for flexible multi-functional sensors

Hydrogel fibers play a crucial role in the design and manufacturing of flexible electronic devices. However, continuous production of hydrogel fibers with high strength, toughness, and conductivity remains a significant challenge. In this study, ion-conductive sodium alginate/polyvinyl alcohol composite hydrogel fibers with an interlocked dual network structure were prepared through continuous wet spinning based on the pH-responsive dynamic borate ester bonds. Owing to the interlocked dual network structure, the resulting hydrogel fibers integrated superior performance of strength (4.31 MPa), elongation-at-break (>1500 %), ion conductivity (17.98 S m-1) and response sensitivity to strain (GF = 3.051). Benefiting from the excellent performance, the composite hydrogel fiber could be applied as motion-detecting sensors, including high-frequency, high-speed reciprocating mechanical motion, and human motion. Furthermore, the superior compatibility for human-computer interaction of the hydrogel fiber was also demonstrated, which a manipulator could be controlled to perform different actions, by a smart glove equipped with the hydrogel fiber sensors.

Multiperformance PAM/PVA/CaCO3 Hydrogel for Flexible Sensing and Information Encryption

Currently, the development of hydrogels with excellent mechanical properties (elasticity, fatigue resistance, etc.) and conductive properties can better meet their needs in the field of flexible sensor device applications. Generally, hydrogels with a denser cross-linking density tend to have better mechanical properties, but the improvement in mechanical properties comes at the expense of reduced electrical conductivity. Directly generating CaCO3 in the hydrogel prepolymer can not only increase the cross-linking density of its network but also introduce additional ions to enhance its internal ionic strength, which is beneficial to improving the conductivity of the hydrogel. It is still a big challenge to directly generate CaCO3 in the static prepolymer solution and ensure its uniform dispersion in the hydrogel. Herein, we adopted an improved preparation method to ensure that the directly generated CaCO3 particles can be evenly dispersed in the static prepolymer solution until the polymerization is completed. Finally, a PAM/PVA/CaCO3 hydrogel with supertensile, compressive, toughness, and fatigue resistance properties was prepared. In addition, the presence of free Na+ and Cl- gives the hydrogel excellent conductivity and sensing performance to monitor daily human activities. On the basis of the application of hydrogels in information communication, we have further deepened this application by combining the characteristics of hydrogels themselves. Combined with ASCII code, the hydrogel can also be applied in information exchange and information encryption and decryption, achieving the antitheft function in smart locks. A variety of excellent performance integrated PAM/PVA/CaCO3 hydrogels have broad application prospects for flexible sensors, highlighting great potential in human-computer interaction and intelligent information protection.

From Fluorescence-Transfer-Lightening-Printing-Assisted Conductive Adhesive Nanocomposite Hydrogels toward Wearable Interactive Optical Information-Electronic Strain Sensors

The interactive flexible device, which monitors the human motion in optical and electrical synergistic modes, has attracted growing attention recently. The incorporation of information attribute within the optical signal is deemed advantageous for improving the interactive efficiency. Therefore, the development of wearable optical information-electronic strain sensors holds substantial promise, but integrating and synergizing various functions and realizing strain-mediated information transformation keep challenging. Herein, an amylopectin (AP) modified nanoclay/polyacrylamide-based nanocomposite (NC) hydrogel and an aggregation-induced-emission-active ink are fabricated. Through the fluorescence-transfer printing of the ink onto the hydrogel film in different strains with nested multiple symbolic information, a wearable interactive fluorescent information-electronic strain sensor is developed. In the sensor, the nanoclay plays a synergistic "one-stone-three-birds" role, contributing to "lightening" fluorescence (≈80 times emission intensity enhancement), ionic conductivity, and excellent stretchability (>1000%). The sensor has high biocompatibility, resilience (elastic recovery ratio: 97.8%), and strain sensitivity (gauge factor (GF): 10.9). Additionally, the AP endows the sensor with skin adhesiveness. The sensor can achieve electrical monitoring of human joint movements while displaying interactive fluorescent information transformation. This research poses an efficient strategy to develop multifunctional materials and provides a general platform for achieving next-generation interactive devices with prospective applications in wearable devices, human-machine interfaces, and artificial intelligence.

Permeable Bioelectronics toward Biointegrated Systems

Bioelectronics integrates electronics with biological organs, sustaining the natural functions of the organs. Organs dynamically interact with the external environment, managing internal equilibrium and responding to external stimuli. These interactions are crucial for maintaining homeostasis. Additionally, biological organs possess a soft and stretchable nature; encountering objects with differing properties can disrupt their function. Therefore, when electronic devices come into contact with biological objects, the permeability of these devices, enabling interactions and substance exchanges with the external environment, and the mechanical compliance are crucial for maintaining the inherent functionality of biological organs. This review discusses recent advancements in soft and permeable bioelectronics, emphasizing materials, structures, and a wide range of applications. The review also addresses current challenges and potential solutions, providing insights into the integration of electronics with biological organs.