Antibacterial Dual Network Hydrogels for Sensing and Human Health Monitoring

High toughness, high stability and low hysteresis PVA /HPMC/PA/SBMA/ZnCl2 conductive hydrogels for wearable flexible electronics for multifunctional sensors and supercapacitors

PVA-based conductive hydrogels have enormous potential for applications in wearable flexible electronic devices, but their low ionic conductivity and mechanical strength hinder their practical utility. To address this challenge, we propose a PVA-based incorporating metal salt and zwitterion. We use PA(phytic acid) and HPMC (hydroxypropyl methylcellulose) - compatible properties to prepare PSBMA1-PMAZ1.5 interpenetrating conductive hydrogel with good electrical signal responsiveness, repeatability, compression resistance, and low hysteresis (≤11.68 %). The hydrogel-based flexible strain sensor has a wide detection range, high sensitivity (GF = 1.1 at 0 - 600 %), stable electrical signal response to variations in temperature and humidity, and human movement detection capabilities. The detection range of hydrogel - based supercapacitors is 25 °C - 40 °C, which indicates that the device assembled with activated carbon as the electrode has good capacitance characteristics, and the multifunctional characteristics of PSBMA1-PMAZ1.5 hydrogels are poised to serve as a demonstration for a new generation of flexible electronic products.

Recent advances in tannic acid-based gels: Design, properties, and applications

With the flourishing of mussel-inspired chemistry, the fast-growing development for environmentally friendly materials, and the need for inexpensive and biocompatible analogues to PDA in gel design, TA has led to its gradual emergence as a research focus due to its remarkable biocompatible, renewable, sustainable and particular physicochemical properties. As a natural building block, TA can be used as a substrate or crosslinker, ensuring versatile functional polymeric networks for various applications. In this review, the design of TA-based gels is summarized in detail (i.e., different interactions such as: metal coordination, electrostatic, hydrophobic, host-guest, cation-π and π-π stacking interactions, hydrogen bonding and various reactions including: phenol-amine Michael and Schiff base, phenol-thiol Michael addition, phenol-epoxy ring opening reaction, etc.). Subsequently, TA-based gels with a variety of functionalities, including mechanical, adhesion, conductive, self-healing, UV-shielding, anti-swelling, anti-freezing, shape memory, antioxidant, antibacterial, anti-inflammatory and responsive properties are introduced in detail. Then, a summary of recent developments in the use of TA-based gels is provided, including bioelectronics, biomedicine, energy, packaging, water treatment and other fields. Finally, the difficulties that TA-based gels are currently facing are outlined, and an original yet realistic viewpoint is provided in an effort to spur future development.

Optical-Electronic Skin Based on Tea Polyphenol for Dual Signal Wearable Sensing

The rapid development of smart electronic skin has led researchers to design a variety of flexible and stretchable devices that can be used to monitor physiological and environmental signals. In this work, we successfully demonstrate a color-adjustable and conductive wearable optical-electronic skin (OE-skin) based on photonic crystal hydrogel that is capable of delivering both optical and electrical signal responses synchronously. The OE-skin is fabricated by incorporating a structural colored layer, composed of periodically aligned magnetic nanoparticles, into a polyacrylamide hydrogel matrix that contains tea polyphenols and borax. The dynamic boronate ester bonds formed between borax and the catechol groups of tea polyphenols are able to enhance the mechanical properties of the OE-skin, while also conferring excellent electrical conductivity, high sensitivity, and a rapid electrical response. Additionally, the tea polyphenols, which are natural active compounds derived from tea, possess diverse bioactive properties, thereby endowing the OE-skin with excellent antibacterial and biocompatibility characteristics. In addition, the developed electronic skin successfully demonstrates its capability in synergistic electronic and optical sensing during human motion monitoring, indicating broad application prospects in the field of smart wearable sensors.

Initiatorless polymerization of mechanically robust hydrogels reinforced by cellulose of wood skeleton as multifunctional sensors

Wood-based hydrogel with a unique anisotropic structure is an attractive soft-and-wet material. However, it remains a challenge to simultaneously achieve robust, multi-functional, and multi-response integrations through a sustainable and green approach. Herein, a bioinspired, additive-free method is reported to fabricate composite hydrogels reinforced by naturally high-strength wood skeleton without using any chemical initiators and crosslinking agents. Specifically, polymers (Polyacrylamide/Polyacrylic acid) are grafted from the surfaces of the aligned cellulose of wood skeleton, forming wood-based hydrogels under UV irradiation. Afterward, Fe3+-mediated physical crosslinking is employed further to construct chemically crosslinked poly(acrylamide-co-acrylic acid) networks. Therefore, the resulting initiatorless wood-based hydrogel with a dual-crosslinked network structure exhibits an ultra-high tensile strength of 42 MPa along the longitudinal direction, representing one of the strongest hydrogels ever reported. Furthermore, the wood-based hydrogels with inherent conductive properties appealing versatile sensations on strain, temperature, and light, which could serve as human-motion monitors (detection), thermo-electrochemical sensors, underwater wearable sensors, and smart-home systems. This work offers a green and promising strategy to fabricate robust, anisotropic, flexible, and ionically conductive wood-based hydrogels for multifunctional sensors with excellent performance in complex environments.

Nanoporous Bisphenol A-Based Polymeric Network Featuring Spontaneous Microphase-Separation Enables Transparent Multifunctional Hydrogels

Multifunctional hydrogels have garnered significant interest but remain challenging due to the complex preparation process and high cost of raw materials. Herein, bisphenol A diglycidyl ether (BADGE) and poly(ethylene glycol) diglycidyl ether (PEGDGE) were reacted with 3-amino-1-propanol via a catalyst-free amine-epoxy "click" chemistry, followed by the addition of hydrophilic 1,3-propane sultone (1,3-PS) to a higher water content, and then cross-linked with hexamethylene diisocyanate (HDI) in one-pot to provide a polymer network, i.e., PBAxPEGyPU-PS. The two-step cross-linking method enables greater precision in controlling the cross-linking density and preparation process. The in situ microphase-separated porous PBA50PEG50PU-PS demonstrates nanosized pores of approximately 100 nm and uniform distribution due to the thermodynamic incompatibility, enabling superior mechanical properties and high transparency of 87.9%. Upon a water absorption and water loss cycle, a higher transparency of 89.7% was obtained with a lower nanosized pore of approximately 50 nm due to the solvent-induced self-assembly of its amphiphilic structure. Furthermore, the bilayer hydrogel composed of WPBA90PEG10PU-PS and WPBA50PEG50PU-PS was designed for a "Janus" soft actuator based on the difference between the two sides in swelling ability upon water absorption, which has been applied in underwater grasping and humidity-responsive switch. To maintain the inherent soft elasticity and conductivity of the hydrogel, glycerol (Gly) and sodium ion (Na+) were introduced into the mixture. It shows that WPBA50PEG50PU-PS/Gly67 maintains environmental stability with more than 80% weight at 20 °C for 72 h and shows additional frost resistance at -20 °C, and the dual cross-linking network of WPBA50PEG50PU-PS/Gly67/Na10 exhibits the best comprehensive properties of high tensile strength and good conductivity. Meanwhile, 1,3-PS provides a quaternary ammonium salt and sulfobetaine, endowing the multicomponent WPBA50PEG50PU-PS/Gly67/Na10 with additional antibacterial and sensing capabilities. This work provides a versatile approach for preparing transparent multifunctional hydrogels and highlights their potential in various applications.

Multifunctional films based on tannic acid-coated cellulose nanocrystals and zinc-coating reinforced sodium carboxymethyl cellulose/polyvinyl alcohol for food active packaging

Multifunctional packaging materials made from biomass resources are key to achieving packaging storage and environmental friendliness. The aim of this study is to prepare high-performance cellulose-based packaging films to improve the high-value utilization of cellulose resources. In this paper, the blended films of sodium carboxymethyl cellulose (CMC) and poly(vinyl alcohol) (PVA) were used as the substrate and doped with tannic acid (TA)-coated cellulose nanocrystals (CNC@TA). Then, zinc ions (Zn2+) were decorated on the film surface by adsorption self-assembly. The modified films (Z-CPC@T5 films) were prepared with excellent mechanical properties (tensile strength and elongation at break of 73.85 MPa and 19.68 %, respectively). Meanwhile, the presence of CNC@TA provided the films with UV and oxidation resistance. In addition, the zinc coating formed on the film surface conferred water resistance, hydrophobicity, and structural stability (water contact angle up to 97.09°). The modified films also showed excellent antimicrobial and water-vapor barrier properties. The modified films preserved cherries for at least 16 days with a quality retention of 87.20 %. In addition, cytotoxicity tests confirmed the non-toxic properties of the modified films. Overall, this strategic fusion of internal and external dual crosslinking expanded the application potential of active packaging materials.

Stable, recyclable, hybrid ionic-electronic conductive hydrogels with non-covalent networks enhanced by bagasse cellulose nanofibrils for wearable sensors

Conductive hydrogels are utilized in flexible sensors due to their high-water content, excellent elasticity, and shape controllability. However, the sharp increase in resistance of this material under enormous strain leads to instability in the sensing process. This study presents a straightforward method for creating a stable, recyclable, hybrid ionic-electronic conductive (HIEC) hydrogel via a simple one-pot strategy using polyvinyl alcohol (PVA), bagasse cellulose nanofibrils (CNF), and graphene(G) with sodium dodecylbenzene sulfonate (SDBS). The SDBS/G hemimicelles are formed through hydrophobic and π-π stacking interactions between SDBS and G, enhancing the dispersibility of G. Then SDBS/G hemimicelles were integrated into a non-covalent cross-linking network from CNF and PVA, which ensures recyclability and stability. The CNF-PVA-Graphene (CPG) hydrogel exhibited high and stable sensing sensitivity (average gauge factor up to 1.99), high conductivity (0.36 S/m), low graphene concentration (0.16 wt%), low detection limit (1 %), and fast response time (0.17 s). The sensor can detect large (wrist and knee) and small (pulse and laryngeal prominence) body movements. After recycling, the hydrogel sensors maintained high conductivity sensitivity (average gauge factor up to 1.01) and good tensile properties (360 % strain). This study introduces a new approach of hybrid conductive biomass-based hydrogel sensors for precisely monitoring human movements.

Thermoelectric Gel Enabling Self-Powered Facial Perception for Expression Recognition and Health Monitoring

By analyzing facial features to perform expression recognition and health monitoring, facial perception plays a pivotal role in noninvasive, real-time disease diagnosis and prevention. Current perception routes are limited by structural complexity and the necessity of a power supply, making timely and accurate monitoring difficult. Herein, a self-powered poly(vinyl alcohol)-gellan gum-glycerol thermogalvanic gel patch enabling facial perception is developed for monitoring emotions and atypical pathological states. Due to the high thermopower of 1.89 mV/K as well as excellent stretchability of 680%, the on-face-conformed thermoelectric gel can operate upon facial thermoelectric variation resulting from different interfacial contact statuses between the gel and face induced by facial muscle activities. With the aid of machine learning, the patch array delivers accurate perception of facial activities of 11 muscles in real time, achieving active expression recognition and health monitoring with the accuracy of 98 and 96%, respectively. This work provides a promising strategy of actively monitoring multisite physiological activities, advancing the development of intelligent wearable bioelectronics for physical or mental monitoring.

Advances in polysaccharide-based conductive hydrogel for flexible electronics

Polysaccharides, being the most abundant natural polymers, play a pivotal role in the development of hydrogel materials. Polysaccharide-based conductive hydrogels have found extensive applications in flexible electronics due to their excellent conductivity and biocompatibility. This review highlights recent advancements in this area, starting with an overview of polysaccharide materials such as chitosan, cellulose, starch, cyclodextrin, alginate, hyaluronic acid, and agarose. It then explores different classifications of conductive hydrogels: ionic conductive, electronic conductive, and ionic-electronic composite types. The review also covers key characteristics of these hydrogels, including mechanical properties, self-healing, adhesion, structural color, antibacterial, responsiveness, biocompatibility and anti-swelling. Representative applications, such as flexible sensors, triboelectric nanogenerators, supercapacitors, and flexible electronic wound dressings, are summarized. Finally, the review addresses current challenges and provides guidance for future research, aiming to advance the field of polysaccharide-based conductive hydrogels in flexible electronics.

Bioactive Deep Eutectic Solvent-Involved Sprayable Versatile Hydrogel for Monkeypox Virus Lesions Treatment

To address the issues of infectious virus, bacterial secondary infections, skin pigmentation, and scarring caused by monkeypox virus (MPXV), a sprayable hydrogel with versatile functions was developed with comprehensive properties. Based on current research, the bioactive deep eutectic solvent (DES) of rosmarinic acid-proanthocyanidin-glycol (RPG) was designed and synthesized as active agent, and molecular docking was applied to discover its binding to MPXV proteins through H-bonds and van der Waals interactions, and the docking results show the binding energies between RA, PC, Gly and MPXV proteins are -58.7188, -50.2311, and -18.4755 kcal/mol, respectively. Additionally, poly(vinyl alcohol) (PVA), borate, and xylitol (Xyl) were integrated with RPG to prepare the PB-RPG-Xyl hydrogel, which was characterized by popular ways. The pH-responsive properties of the hydrogel accelerated the release of RPG under acidic conditions, resulting in an increased cumulative release percentage of 84.83% at pH 5.5 at 210 min. Besides that, it was proved to have the expected sprayability, self-healing, adhesion, and shape-adaptability. The results of molecular dynamic simulation were meaningful to understanding its formation and self-healing mechanisms. Furthermore, the hydrogel shows ideal degradability, removability, and biocompatibility. Lastly, its multiple functions were systematically explored, including UV-blocking, blood clotting, cooling, antioxidant, antibacterial, and virus inhibition properties. The developed sprayable PB-RPG-Xyl hydrogel represents the first promising dressing based on natural bioactive DES for MPXV lesions management, which not only expands the application of green solvents in health care but also provides a convenient and effective treatment process for MPXV infection in the face of difficult skin lesions and complex treatment needs.

Advances in agar-based composites: A comprehensive review

This review article explores the developments and applications in agar-based composites (ABCs), emphasizing various constituents such as metals, clay/ceramic, graphene, and polymers across diversified fields like wastewater treatment, drug delivery, food packaging, the energy sector, biomedical engineering, bioplastics, agriculture, and cosmetics. The focus is on agar as a sustainable and versatile biodegradable polysaccharide, highlighting research that has advanced the technology of ABCs. A bibliometric analysis is conducted using the Web of Science database, covering publications from January 2020 to March 2024, processed through VOSviewer Software Version 1.6.2. This analysis assesses evolving trends and scopes in the literature, visualizing co-words and themes that underscore the growing importance and potential of ABCs in various applications. This review paper contributes by showcasing the existing state-of-the-art knowledge and motivating further development in this promising field.

Dynamic Double-Networked Hydrogels by Hybridizing PVA and Herbal Polysaccharides: Improved Mechanical Properties and Selective Antibacterial Activity

Chinese herbal medicine has offered an enormous source for developing novel bio-soft materials. In this research, the natural polysaccharide isolated from the Chinese herbal medicine Dendrobium was employed as the secondary building block to fabricate a "hybrid" hydrogel with synthetic poly (vinyl alcohol) (PVA) polymers. Thanks to the presence of mannose units that contain cis-diol motifs on the chain of the Dendrobium polysaccharides, efficient crosslinking with the borax is allowed and reversible covalent borate ester bonds are formed. Eventually, highly dynamic and double-networked hydrogels were successfully prepared by the integration of Dendrobium polysaccharides and PVA. Interestingly, the introduction of polysaccharides has given rise to more robust and dynamic hydrogel networks, leading to enhanced thermal stability, mechanical strength, and tensile capacity (>1000%) as well as the rapid self-healing ability (<5 s) of the "hybrid" hydrogels compared with the PVA/borax single networked hydrogel. Moreover, the polysaccharides/PVA double network hydrogel showed selective antibacterial activity towards S. aureus. The reported polysaccharides/PVA double networked hydrogel would provide a scaffold to hybridize bioactive natural polysaccharides and synthetic polymers for developing robust but dynamic multiple networked hydrogels that are tailorable for biomedical applications.

Adhesive, Biocompatible, Antibacterial, and Degradable Collagen-Based Conductive Hydrogel as Strain Sensor for Human Motion Monitoring

The conductive hydrogels (CHs) are promising for developing flexible energy storage devices, flexible sensors, and electronic skin due to the unique features of excellent flexibility and high conductivity. However, poor biocompatibility and antibacterial properties seriously limit their application in the biomedical field. Collagen, one of the main components of the extracellular Matrix (ECM), is the ideal matrix for constructing hydrogels due to good biocompatibility with human tissue. Here, dopamine-polypyrrole-collagen (DA-PPY-COL) hydrogel was constructed by dopamine-mediated pyrrole in situ polymerization in a collagen matrix. As a strain sensor, it can be affixed to different parts of the human body to monitor large-scale motion movements and fine micro-expressions in real time. The performance was attributed to its good self-adhesion, flexibility, and electrical conductivity. Biological experiments have shown that it has good antimicrobial properties, biocompatibility, and degradability, allowing the hydrogel to safely monitor human motor behavior. This work not only offers a material preparation strategy for constructing biomimetic electronic skin and wearable sensors but also demonstrates the great potential prospect for implantable degradable medical device applications.

Photothermal enhanced antibacterial chitosan-based polydopamine composite hydrogel for hemostasis and burn wound repairing

Bleeding and bacterial infection are common problems associated with wound treatment, while effective blood clotting and vessel regeneration promotion are the primary considerations to design the wound dressing materials. This research presents a chitosan-based hydrogel with grafted quaternary ammonium and polyphosphate (QCSP hydrogel) as the antibacterial hemostatic dressing to achieve burn wound treatment. The tissue adhesion of the hydrogel sealed the blood flow and the polyphosphate grafted to the chitosan promoted the activation of coagulation factor V to enhance the hemostasis. At the same time, the grafted quaternary ammonium enhanced the antibacterial ability of the biodegradable hydrogel wound dressing. In addition, the polydopamine as a photothermal agent was composited into the hydrogel to enhance the antibacterial and reactive oxygen scavenging performance. The in vivo hemostasis experiment proved the polyphosphate enhanced the coagulation property. Moreover, this photothermal property of the composite hydrogel enhanced the burn wound repairing rate combined with the NIR stimulus. As a result, this hydrogel could have potential application in clinic as dressing material for hemostasis and infection prone would repairing.

A soft electronic skin simulating the multi-scale human touch for the detection of fruit freshness

Realizing biomimicry for human tactile perception is a meaningful challenge. In this work, a soft matter system with multi-scale energy dissipation structure is designed to realize flexible sensing and detection by biomimetic human touch. At the molecular scale, the supramolecular interactions are introduced into the hydrogel system, including the hydrophobic interaction and the ion attraction between macromolecular segments. At the micron scale, a system of "button" permeable macromolecules is constructed to absorb external forces and store energy through the sliding of macromolecules inside the "button". By adjusting the molecular scale and micron scale structure, the obtained hydrogels demonstrate excellent mechanical properties, electrical conductivity and response sensitivity. This novel hydrogel withstands 200 compression cycles without creep deformation and outputs a stable response signal in terms of compression cycles with the signal volatility of around 1 %. Based on its good durability, this hydrogel, which simulates human multi-scale tactility, has outstanding application potential in detecting fruit damage that is difficult to observe. Notably, the construction of this multi-scale energy dissipation structure is universal for increasing the mechanical property of ACG hydrogels. The high-strength hydrogels adjusted by this strategy is significantly toughened, and the mechanical properties increased by 38 %. This work is of guiding significance for the preparation of high-performance hydrogels.

High-strength polyvinyl alcohol/gelatin/LiCl dual-network conductive hydrogel for multifunctional sensors and supercapacitors

The synthesis of conductive hydrogels with high mechanical strength, toughness, optimal fracture growth rate and the capability to detect diverse human body movements poses a significant challenge in the realm of flexible electronics. In this study, a one-pot technique utilized effectively to fabricate conductive materials by doping LiCl into a mixture of polyvinyl alcohol (PVA) and gelatin. The PVA/gelatin/LiCl0.3(PGL) conductive hydrogel demonstrates exceptional robustness, flexibility, and resistance to deformation, enabling the monitoring of various physiological signals such as temperature and humidity. Additionally, the PGL demonstrates exceptional elongation properties (up to 1111.32 %), high lifting capacity (up to 25 kg), resistance to deformation, and sustained stability of peak signals even after 300 cycles at 50 % strain. The hydrogel electrolyte exhibits a conductivity of 2.114 S/m at 25 °C and a specific capacitance of up to 48.75 F/g, along with favorable mechanical and electrochemical characteristics. These findings suggest that the PVA/gelatin/LiCl0.3 hydrogel supercapacitor (PGLSC) conductive hydrogel shows significant potential for integration into flexible electronics and wearable technology devices.

Nanocomposite Hydrogel for Real-Time Wound Status Monitoring and Comprehensive Treatment

Current skin sensors or wound dressings fall short in addressing the complexities and challenges encountered in real-world scenarios, lacking adequate capability to facilitate wound repair. The advancement of methodologies enabling early diagnosis, real-time monitoring, and active regulation of drug delivery for timely comprehensive treatment holds paramount significance for complex chronic wounds. In this study, a nanocomposite hydrogel is devised for real-time monitoring of wound condition and comprehensive treatment. Tannins and siRNA containing matrix metalloproteinase-9 gene siRNA interference are self-assembled to construct a degradable nanogel and modified with bovine serum albumin. The nanogel and pH indicator are encapsulated within a dual-crosslinking hydrogel synthesized with norbornene dianhydride-modified paramylon. The hydrogel exhibited excellent shape adaptability due to borate bonding, and the click polymerization reaction led to rapid in situ curing of the hydrogel. The system not only monitors pH, temperature, wound exudate alterations, and peristalsis during wound healing but also exhibits hemostatic, antimicrobial, anti-inflammatory, and antioxidant properties, modulates macrophage polarization, and facilitates vascular tissue regeneration. This therapeutic approach, which integrates the monitoring of pathological parameters with comprehensive treatment, is anticipated to address the clinical issues and challenges associated with chronic diabetic wounds and infected wounds, offering broad prospects for application.

Conductive hydrogels: intelligent dressings for monitoring and healing chronic wounds

Conductive hydrogels (CHs) represent a burgeoning class of intelligent wound dressings, providing innovative strategies for chronic wound repair and monitoring. Notably, CHs excel in promoting cell migration and proliferation, exhibit powerful antibacterial and anti-inflammatory properties, and enhance collagen deposition and angiogenesis. These capabilities, combined with real-time monitoring functions, play a pivotal role in accelerating collagen synthesis, angiogenesis and continuous wound surveillance. This review delves into the preparation, mechanisms and applications of CHs in wound management, highlighting their diverse and significant advantages. It emphasizes the effectiveness of CHs in treating various chronic wounds, such as diabetic ulcers, infected wounds, temperature-related injuries and athletic joint wounds. Additionally, it explores the diverse applications of multifunctional intelligent CHs in advanced wound care technologies, encompassing self-powered dressings, electrically-triggered drug delivery, comprehensive diagnostics and therapeutics and scar-free healing. Furthermore, the review highlights the challenges to their broader implementation, explores the future of intelligent wound dressings and discusses the transformative role of CHs in chronic wound management, particularly in the context of the anticipated integration of artificial intelligence (AI). Additionally, this review underscores the challenges hindering the widespread adoption of CHs, delves into the prospects of intelligent wound dressings and elucidates the transformative impact of CHs in managing chronic wounds, especially with the forthcoming integration of AI. This integration promises to facilitate predictive analytics and tailor personalized treatment plans, thereby further refining the healing process and elevating patient satisfaction. Addressing these challenges and harnessing emerging technologies, we postulate, will establish CHs as a cornerstone in revolutionizing chronic wound care, significantly improving patient outcomes.

Tannic acid based multifunctional hydrogels with mechanical stability for wound healing

Conventional wound dressings have poor tissue adhesion and mechanical stability, restricting their applications in dynamic motion environments. Tannic acid (TA) was ideal candidates for current dressing materials due to their well-known antioxidant and anti-inflammatory properties. However, the inevitable polymerization problem of TA limited the one-step synthesis of dressings. Herein, we reported a simple one-pot method to prepare double-network hydrogels containing N-acryloyl glycinamide (NAGA), N-hydroxyethyl acrylamide (HEAA) and TA. The resulting NHT hydrogel exhibited excellent tensile properties, fatigue resistance, and notch insensitivity to ensure mechanical stability under large deformation and stress in vitro. The NHT hydrogel also demonstrated room-temperature self-healing, broad adhesion to various substrates, synergistic swelling ability. In addition, catechol and benzene rings from TA helped shield against UV radiation and acted as free radical scavengers to relieve oxidative stress in wound damage. As a result, full-layer wounds in mice treated with NHT patches showed a higher healing rate, in which epithelialization was completed within 14 days. The integrated function enables hydrogel to maintain mechanical stability in dynamic motion environments with high strain and defects, with great potential for future clinical translation.

Polyphenol-Mediated Adhesive and Anti-Inflammatory Double-Network Hydrogels for Repairing Postoperative Intervertebral Disc Defects

Hydrogels have garnered tremendous attention for their applications in the repair of intervertebral disk (IVD) degeneration and postoperative IVD defects. However, it is still challenging to develop a hydrogel fulfilling the requirements for high mechanical properties, adhesive capability, biocompatibility, antibacterial properties, and anti-inflammatory performance. Herein, we report a multifunctional double-network (DN) hydrogel composed of physically cross-linked carboxymethyl chitosan (CMCS) and tannic acid (TA) networks as well as chemically cross-linked acrylamide (AM) networks, which integrates the properties of high strength, adhesion, biocompatibility, antimicrobial activity, and anti-inflammation for the repair of postoperative IVD defects. The treatment with CMCS/TA/PAM DN hydrogels can significantly decrease the levels of inflammatory cytokines and degeneration-related factors and upregulated collagen type II alpha 1. In addition, the hydrogels can effectively seal the annulus fibrosus defect, prevent nucleus pulposus degeneration, retain IVD height, and restore the biomechanical properties of the disc to some extent. This polyphenol-mediated DN hydrogel is promising for sealing IVD defects and preventing herniation after lumbar discectomy.

Construction of Iron-Scavenging Hydrogel via Thiol-Ene Click Chemistry for Antibiotic-Free Treatment of Bacterial Wound Infection

Bacteria, especially drug-resistant strains, can quickly cause wound infections, leading to delayed healing and fatal risk in clinics. With the growing need for alternative antibacterial approaches that rely less on antibiotics or eliminate their use altogether, a novel antibacterial hydrogel named Ovtgel is developed. Ovtgel is formulated by chemically crosslinking thiol-modified ovotransferrin (Ovt), a member of the transferrin family found in egg white, with olefin-modified agarose through thiol-ene click chemistry. Ovt is designed to sequester ferric ions essential for bacterial survival and protect wound tissues from damages caused by the reactive oxygen species (ROS) generated in Fenton reactions. Experimental data have shown that Ovtgel significantly enhances wound healing by inhibiting bacterial growth and shielding tissues from ROS-induced harms. Unlike traditional antibiotics, Ovtgel targets essential trace elements required for bacterial survival in the host environment, preventing the development of drug resistance in pathogenic bacteria. Ovtgel exhibits excellent biocompatibility due to the homology of Ovt to mammalian transferrin. This hydrogel has the potential to serve as an effective antibiotic-free solution for combating bacterial infections.

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.

Triboelectric Nanogenerator Made with Stretchable, Antibacterial Hydrogel Electrodes for Biomechanical Sensing

Triboelectric nanogenerators (TENGs) have attracted widespread attention as a promising candidate for energy harvesting due to their flexibility and high power density. To meet diverse application scenarios, a highly stretchable (349%), conductive (1.87 S m-1), and antibacterial electrode composed of carbon quantum dots/LiCl/agar-polyacrylamide (CQDs/LiCl/agar-PAAm) dual-network (DN) hydrogel is developed for wearable TENGs. Notably, the concentration of agar alters the pore spacing and pore size of the DN hydrogel, thereby impacting the network cross-linking density and the migration of conductive ions (Li+ and Cl-). This variation further affects the mechanical strength and conductivity of the hydrogel electrode, thus modulating the mechanical stability and electrical output performance of the TENGs. With the optimal agar content, the tensile strength and conductivity of the hydrogel electrode increase by 211 and 719%, respectively. This enhancement ensures the stable output of TENGs during continuous operation (6000 cycles), with open-circuit voltage, short-circuit current, and transferred charge increasing by 200, 530, and 155%, respectively. Additionally, doping with CQDs enables the hydrogel electrode to effectively inhibit the Gram-negative bacterium Escherichia coli. Finally, the TENGs are utilized as a self-power smart ring for efficient and concise information transmission via Morse code. Consequently, this study introduces a creative approach for designing and implementing multifunctional, flexible wearable devices.

Multifunctional, High-Strength Electronic Skin Based on the Natural Sheepskin Fiber Network for Multifaceted Human Health Monitoring and Management

Inspired by the animal skin fiber network, we developed an electronic skin (e-skin) utilizing natural sheepskin as the primary substrate. This innovative design addresses the limitations of conventional e-skins, including inadequate mechanical strength, overly complex artificial network construction, and limited health monitoring capabilities. This e-skin successfully retains the structure and properties of natural sheepskin while exhibiting exceptional mechanical strength (with a breaking strength of 4.01 MPa) and high elongation (with an elongation at a break of 304.8%). Moreover, it possesses various desirable attributes such as electrical conductivity, antibacterial properties, biocompatibility, and environmental stability. In addition, this e-skin has the advantage of diverse data collection (joint movement, bioelectricity, foot health detection, and speech disorder communication systems). Therefore, this e-skin breaks the traditional construction strategy and single-mode application and is expected to become an ideal material for building smart sensor devices.

Bridging papermaking and hydrogel production: Nanoparticle-loaded cellulosic hollow fibers with pitted walls as skeleton materials for multifunctional electromagnetic hydrogels

Electromagnetic hydrogels have attracted significant attention due to their vast potential in soft robotics, biomedical engineering, and energy harvesting. To facilitate future commercialization via large-scale industrial processes, we present a facile concept that utilizes the specialized knowledge of papermaking to fabricate hydrogels with multifunctional electromagnetic properties. The principles of papermaking wet end chemistry, which involves the handling of interactions among cellulosic fibers, fines, polymeric additives, and other components in aqueous systems, serves as a key foundation for this concept. Notably, based on these principles, the versatile use of chemical additives in combination with cellulosic materials enables the tailored design of various products. Our methodology exploits the unique hierarchically pitted and hollow tube-like structures of papermaking grade cellulosic fibers with discernible pits, enabling the incorporation of magnetite nanoparticles through lumen loading. By combining microscale softwood-derived cellulosic fibers with additives, we achieve dynamic covalent interactions that transform the cellulosic fiber slurry into an impressive hydrogel. The cellulosic fibers act as a skeleton, providing structural support within the hydrogel framework and facilitating the dispersion of nanoparticles. In accordance with our concept, the typical hydrogel exhibits combined attributes, including electrical conductivity, self-healing properties, pH responsiveness, and dynamic rheologic behavior. Our approach not only yields hydrogels with interesting properties but also aligns with the forefront of advanced cellulosic material applications. These materials hold the promise in remote strain sensing devices, electromagnetic navigation systems, contactless toys, and flexible electronic devices. The concept and findings of the current work may shed light on materials innovation based on traditional pulp and paper processes. Furthermore, the facile processes involved in hydrogel formation can serve as valuable tools for chemistry and materials education, providing easy demonstrations of principles for university students at different levels.

Tannic acid crosslinked chitosan/gelatin/SiO2 biopolymer film with superhydrophobic, antioxidant and UV resistance properties for prematuring fruit packaging

The environmental pollution caused by plastic films urgently requires the development of non-toxic, biodegradable, and renewable biopolymer films. However, the poor waterproof and UV resistance properties of biopolymer films have limited their application in fruit packaging. In this work, a novel tannic acid cross-linked chitosan/gelatin film with hydrophobic silica coating (CGTS) was prepared. Relying on the adhesion of tannic acid and gelatin to silica, the coating endows CGTS film with excellent superhydrophobic properties. Especially, the contact angle reaches a maximum value 152.6°. Meanwhile, tannic acid enhanced the mechanical strength (about 36.1 %) through the forming of hydrogen bonding and the network structure. The prepared CGTS films showed almost zero transmittance to ultraviolet light and exhibited excellent radical scavenging ability (∼76.5 %, DPPH). Hence, CGTS film is suitable as a novel multifunctional packaging material for the agriculture to protect premature fruits, or the food industry used in environments exposed to ultraviolet radiation and rainwater.

A comprehensive exploration of hydrogel applications in multi-stage skin wound healing

Hydrogels, as an emerging biomaterial, have found extensive use in the healing of wounds due to their distinctive physicochemical structure and functional properties. Moreover, hydrogels can be made to match a range of therapeutic requirements for materials used in wound healing through specific functional modifications. This review provides a step-by-step explanation of the processes involved in cutaneous wound healing, including hemostasis, inflammation, proliferation, and reconstitution, along with an investigation of the factors that impact these processes. Furthermore, a thorough analysis is conducted on the various stages of the wound healing process at which functional hydrogels are implemented, including hemostasis, anti-infection measures, encouraging regeneration, scar reduction, and wound monitoring. Next, the latest progress of multifunctional hydrogels for wound healing and the methods to achieve these functions are discussed in depth and categorized for elucidation. Finally, perspectives and challenges associated with the clinical applications of multifunctional hydrogels are discussed.

Highly elastic, fatigue-resistant, antibacterial, conductive, and nanocellulose-enhanced hydrogels with selenium nanoparticles loading as strain sensors

The fabrication of highly elastic, fatigue-resistant and conductive hydrogels with antibacterial properties is highly desirable in the field of wearable devices. However, it remains challenging to simultaneously realize the above properties within one hydrogel without compromising excellent sensing ability. Herein, we fabricated a highly elastic, fatigue-resistant, conductive, antibacterial and cellulose nanocrystal (CNC) enhanced hydrogel as a sensitive strain sensor by the synergistic effect of biosynthesized selenium nanoparticles (BioSeNPs), MXene and nanocellulose. The structure and potential mechanism to generate biologically synthesized SeNPs (BioSeNPs) were systematically investigated, and the role of protease A (PrA) in enhancing the adsorption between proteins and SeNPs was demonstrated. Additionally, owing to the incorporation of BioSeNPs, CNC and MXene, the synthesized hydrogels showed high elasticity, excellent fatigue resistance and antibacterial properties. More importantly, the sensitivity of hydrogels determined by the gauge factor was as high as 6.24 when a high strain was applied (400-700 %). This study provides a new horizon to synthesize high-performance antibacterial and conductive hydrogels for soft electronics applications.

Self-healing, antioxidant, and antibacterial Bletilla striata polysaccharide-tannic acid dual dynamic crosslinked hydrogels for tissue adhesion and rapid hemostasis

Biomaterials capable of achieving effective sealing and hemostasis at moist wounds are in high demand in the clinical management of acute hemorrhage. Bletilla striata polysaccharide (BSP), a natural polysaccharide renowned for its hemostatic properties, holds promising applications in biomedical fields. In this study, a dual-dynamic-bonds crosslinked hydrogel was synthesized via a facile one-pot method utilizing poly(vinyl alcohol) (PVA)-borax as a matrix system, followed by the incorporation of BSP and tannic acid (TA). Chemical borate ester bonds formed around borax, coupled with multiple physical hydrogen bonds between BSP and other components, enhanced the mechanical properties and rapid self-healing capabilities. The catechol moieties in TA endowed the hydrogel with excellent adhesive strength of 30.2 kPa on the surface of wet tissues and facilitated easy removal without residue. Benefiting from the synergistic effect of TA and the preservation of the intrinsic properties of BSP, the hydrogel exhibited outstanding biocompatibility, antibacterial, and antioxidant properties. Moreover, it effectively halted acute bleeding within 31.3 s, resulting in blood loss of 15.6 % of that of the untreated group. As a superior hemostatic adhesive, the hydrogel in this study is poised to offer a novel solution for addressing future acute hemorrhage, wound healing, and other biomedical applications.

Amphibious Multifunctional Hydrogel Flexible Haptic Sensor with Self-Compensation Mechanism

In recent years, hydrogel-based wearable flexible electronic devices have attracted much attention. However, hydrogel-based sensors are affected by structural fatigue, material aging, and water absorption and swelling, making stability and accuracy a major challenge. In this study, we present a DN-SPEZ dual-network hydrogel prepared using polyvinyl alcohol (PVA), sodium alginate (SA), ethylene glycol (EG), and ZnSO4 and propose a self-calibration compensation strategy. The strategy utilizes a metal salt solution to adjust the carrier concentration of the hydrogel to mitigate the resistance drift phenomenon to improve the stability and accuracy of hydrogel sensors in amphibious scenarios, such as land and water. The ExpGrow model was used to characterize the trend of the ∆R/R0 dynamic response curves of the hydrogels in the stress tests, and the average deviation of the fitted curves ϵ¯ was calculated to quantify the stability differences of different groups. The results showed that the stability of the uncompensated group was much lower than that of the compensated group utilizing LiCl, NaCl, KCl, MgCl2, and AlCl3 solutions (ϵ¯ in the uncompensated group in air was 276.158, 1.888, 2.971, 30.586, and 13.561 times higher than that of the compensated group in LiCl, NaCl, KCl, MgCl2, and AlCl3, respectively; ϵ¯ in the uncompensated group in seawater was 10.287 times, 1.008 times, 1.161 times, 4.986 times, 1.281 times, respectively, higher than that of the compensated group in LiCl, NaCl, KCl, MgCl2 and AlCl3). In addition, for the ranking of the compensation effect of different compensation solutions, the concentration of the compensation solution and the ionic radius and charge of the cation were found to be important factors in determining the compensation effect. Detection of events in amphibious environments such as swallowing, robotic arm grasping, Morse code, and finger-wrist bending was also performed in this study. This work provides a viable method for stability and accuracy enhancement of dual-network hydrogel sensors with strain and pressure sensing capabilities and offers solutions for sensor applications in both airborne and underwater amphibious environments.

Lysine-Triggered Polymeric Hydrogels with Self-Adhesion, Stretchability, and Supportive Properties

Hydrogels, recognized for their flexibility and diverse characteristics, are extensively used in medical fields such as wearable sensors and soft robotics. However, many hydrogel sensors derived from biomaterials lack mechanical strength and fatigue resistance, emphasizing the necessity for enhanced formulations. In this work, we utilized acrylamide and polyacrylamide as the primary polymer network, incorporated chemically modified poly(ethylene glycol) (DF-PEG) as a physical crosslinker, and introduced varying amounts of methacrylated lysine (LysMA) to prepare a series of hydrogels. This formulation was labeled as poly(acrylamide)-DF-PEG-LysMA, abbreviated as pADLx, with x denoting the weight/volume percentage of LysMA. We observed that when the hydrogel contained 2.5% w/v LysMA (pADL2.5), compared to hydrogels without LysMA (pADL0), its stress increased by 642 ± 76%, strain increased by 1790 ± 95%, and toughness increased by 2037 ± 320%. Our speculation regarding the enhanced mechanical performance of the pADL2.5 hydrogel revolves around the synergistic effects arising from the co-polymerization of LysMA with acrylamide and the formation of multiple intermolecular hydrogen bonds within the network structures. Moreover, the acid, amine, and amide groups present in the LysMA molecules have proven to be instrumental contributors to the self-adhesion capability of the hydrogel. The validation of the pADL2.5 hydrogel's exceptional mechanical properties through rigorous tensile tests further underscores its suitability for use in strain sensors. The outstanding stretchability, adhesive strength, and fatigue resistance demonstrated by this hydrogel affirm its potential as a key component in the development of robust and reliable strain sensors that fulfill practical requirements.

Mechanically Excellent, Notch-Insensitive, and Highly Conductive Double-Network Hydrogel for Flexible Strain Sensor

A novel double-network conductive hydrogel based on lithium acetate/gelatin/polyacrylamide (PAAM) was synthesized by heating-cooling and subsequent γ-ray radiation-induced polymerization and cross-linking. Owing to the hydrogen bonding interaction between lithium acetate, physical cross-linked gelatin, and chemical cross-linked PAAM, the resultant hydrogel exhibited high tensile strength (1260 kPa), high ionic conductivity (35.2 mS cm-1), notch-insensitivity (tensile strength 415 kPa, elongation at break 872% with transverse notch), and extensive strain monitoring range (0.15-800%) under optimum conditions. The lithium acetate/gelatin/polyacrylamide hydrogel strain sensor attached to the skin can sensitively monitor the subtle movements of the human body. The strain sensor based on the resultant hydrogel with transverse notch can still work for 1200 cycles, due to that the covalent-cross-linked PAAm chain bridges the cracks and stabilizes the deformation, while the physical-cross-linked gelatin was unzipped to make the blunting of notch. The conductive hydrogel with high-sensitivity and high stability is expected to be used as materials for the preparation of flexible strain sensors in the future.

A grape seed protein-tannic acid powder to transform various non-adhesive hydrogels into adhesive gels

Realizing adhesion between wet materials remains challenging because of the interfacial water. Current strategies depend on complicated surface modifications, resulting in limited functions. Herein, a facile strategy based on the powder of grape seed protein and tannic acid (GSP-TA) was reported to endow various non-adhesive hydrogels adhesion without chemical modifications for both hydrogels and adherents. The GSP-TA powder has the capability to absorb interfacial water, form an adhesive layer on the hydrogel surface, diffusion into the underneath hydrogel matrix, and establish the initial adhesion within 5 s. By forming multiple non-covalent interactions between powders and substrates, the GSP-TA powder served as an efficient surface treating agent, enabling robust adhesion to solid substrates (wood, cardboard, glass, iron, and rubber) and wet tissues (pigskin, muscle, liver and heart). The adhesive strength for wood, cardboard, glass, iron, and rubber was 145.92 ± 5.93, 123.93 ± 15.98, 66.24 ± 7.67, 98.22 ± 4.13, and 80.83 ± 7.48 kPa, respectively. Because of reversible interactions, the adhesion was also repeatable. Due to the merits of grape seed protein and plant polyphenol, it could be completely degraded within 11 days. Bearing several merits, this strategy has promising applications in wound patches, tissue repair, and sensors.

Injectable Conductive Hydrogel with Self-Healing, Motion Monitoring, and Bacteria Theranostics for Bioelectronic Wound Dressing

Wounds at joints are difficult to treat and tend to recover more slowly due to the frequent motions. When using traditional hydrogel dressings, they are easy to crack and undergo bacterial infection, difficult to match and monitor the irregular wounds. Integrating multiple functions within a hydrogel dressing to achieve intelligent wound monitoring and healing remains a significant challenge. In this research, a multifunctional hydrogel is developed based on polysaccharide biopolymer, poly(vinyl alcohol), and hydroxylated graphene through dynamic borate ester bonding and supramolecular interaction. The prepared hydrogel not only exhibits rapid self-healing (within 60 s), injectable, conductive and motion monitoring properties, but also realizes in situ bacterial sensing and killing functions. It shows excellent bacterial sensitivity (within 15 min) and killing ability via the changes of electrical signals and photothermal therapy, avoiding the emergence of drug-resistant bacteria. In vivo experiments prove that the hydrogel can promote wound healing effectively. In addition, it displays great electromechanical performance to achieve real-time monitoring and prevent re-tearing of the wound at human joints. The injectable pH-responsive hydrogel with good biocompatibility demonstrates considerable potential as multifunctional bioelectronic dressing for the detection, treatment, management, and healing of infected joint wounds.

MXene/Silk Fibroin Strengthened PVA-Based Eutectogel with Excellent Self-Healing Ability and Environmental Adaptability: Design, Synthesis, and Sensing Application

A superelastic self-healing eutectogel was designed and prepared using poly (vinyl alcohol) (PVA) as the bulk skeleton material, while silk fibroin (SF) and two-dimensional (2D) MXene (Ti3C2TX) as reinforcing fillers. In brief, the eutectogel possesses a high tensile strength of 7.63 MPa, and its elongation at break reached 1115.2%, higher than most reported polymers (<1000%). In addition, the eutectogel-assembled sensor has a high ionic conductivity of 0.61 S/m and a high strain sensitivity of 5.17 kPa-1. Moreover, eutectogel shows excellent self-healing ability and can achieve self-healing quickly within 10 min, while its tensile strength and elongation at break can be restored to 84.7% and 97.4% of the initial levels. Besides, a stable electrical signal can be transmitted after 200 cycles at 30% strain. Finally, the eutectogel can withstand various environmental conditions, such as atmospheric or even vacuum evaporation and low-temperature freezing, while maintaining good mechanical and sensing performances. The assembled flexible sensors based on the eutectogel demonstrate their significant application prospects in wearable devices, especially human physiological monitoring.

Chitin nanocrystals stabilized liquid metal for highly stretchable and anti-freeze hydrogels as flexible strain sensor

Conductive hydrogels show extensive applications in flexible electronics and biomedical areas, but it is a challenge to simultaneously achieve high mechanical properties, satisfied electrical conductivity, good biocompatibility, self-recovery and anti-freezing properties through a simple preparation method. Herein, chitin nanocrystals (ChNCs) were employed to encapsulate liquid metal nanoparticles (LMNPs) to ensure the dispersion stability of LMNPs in a hydrogel system composed of polyacrylamide (PAM) and polyvinyl alcohol (PVA). The synergistic effect of ChNCs-stabilized LMNPs imparts remarkable conductivity to the hydrogel, making it an effective strain sensor for human motion. With 1 % LMNPs, the composite hydrogel stretches up to 2100 %, showing excellent stretchability. Under 10 cycles of 200 % strain, hysteresis loop curves overlap, indicating outstanding fatigue resistance. The hydrogel exhibits remarkable self-recovery, enduring 1400 % deformation without rupture. In addition, its effective antifreeze properties result from immersion in a glycerol-water solvent. Even at -20 °C and 60 °C, the hydrogel maintains stable, reproducible resistance changes at 150 % tensile strain. Therefore, the high-performance conductive hydrogel containing ChNCs stabilized LM has promising applications in flexible wearable sensing devices.

A Self-Healing Conductive Elastomer Based on a Polymerizable Deep Eutectic Solvent

Conductive elastomers are extensively used in electronics; however, they are prone to mechanical damage, have shortened service life, and cause environmental pollution and resource waste under the influence of external factors. Therefore, conductive elastomers with rapid self-healing properties are crucial for solving these problems. To that end, a conductive elastomer based on a polymerizable deep eutectic solvent as the matrix is developed in this study. The contents of certain small molecules and conductive particles are adjusted to yield a conductive elastomer with excellent comprehensive performance. The elastomer exhibited noteworthy fracture strength (15.7 MPa), ultrahigh fracture elongation (2400%), excellent light transmittance (95.6%), and remarkable self-healing characteristics, with complete electrical healing achieved within 0.6 s, ≈63% strain, and ≈64% stress recovered within 1 min, and healing efficiency close to 99% realized within 24 h. By leveraging these properties, the elastomer is used to construct a sensor that exhibited a gauge factor of ≈0.574 in the strain range 0-2400% and excellent stability. Moreover, the CCK-8 toxicity test and fluorescence staining experiment have demonstrated that conductive elastomers have excellent cell compatibility and also have excellent potential in the field of biomedicine. In particular, the sensor is effectively applied in human motion detection, health monitoring.

TEMPO bacterial cellulose and MXene nanosheets synergistically promote tough hydrogels for intelligent wearable human-machine interaction

Conductive hydrogels have received increasing attention in the field of wearable electronics, but they also face many challenges such as temperature tolerance, biocompatibility, and stability of mechanical properties. In this paper, a double network hydrogel of MXene/TEMPO bacterial cellulose (TOBC) system is proposed. Through solvent replacement, the hydrogel exhibits wide temperature tolerance (-20-60 °C) and stable mechanical properties. A large number of hydrogen bonds, MXene/TOBC dynamic three-dimensional network system, and micellar interactions endow the hydrogel with excellent mechanical properties (elongation at break ~2800 %, strength at break ~420 kPa) and self-healing ability. The introduction of tannic acid prevents the oxidation of MXene and the loss of electrical properties of the hydrogel. In addition, the sensor can also quickly (74 ms) and sensitive (gauge factor = 15.65) wirelessly monitor human motion, and the biocompatibility can well avoid the stimulation when it comes into contact with the human body. This series of research work reveals the fabrication of MXene-like flexible wearable electronic devices based on self-healing, good cell compatibility, high sensitivity, wide temperature tolerance and durability, which can be used in smart wearable, wireless monitoring, human-machine Interaction and other aspects show great application potential.

Hydrophobically Associated Hydrogel for High Sensitivity and Resolution of an Interdigital Electrode Pressure Sensor

Hydrogel-based flexible strain sensors have been known for their excellent ability to convert different motions of humans into electrical signals, thus enabling real-time monitoring of various human health parameters. In this work, a composite hydrogel with hydrophobic association and hybrid cross-linking was fabricated by using polyacrylamide (PAm), surfactant sodium dodecyl sulfate (SDS), lauryl methacrylate (LMA), and polypyrrole (PPy). The dynamic dissociation-conjugation among LMA, SDS, and PPy could dissipate energy to improve the toughness of hydrogels. The SDS/PPy/LMPAm composite hydrogel with a toughness of 1.44 MJ/m3, tensile fracture stress of 345 kPa, tensile strain of 1021%, and electrical conductivity of 0.57 S/m was obtained. Furthermore, an interdigital electrode flexible pressure sensor was designed to replace the bipolar electrode flexible pressure sensor, which greatly improved the sensitivity and resolution of the pressure sensor. The SDS/PPy/LMPAm composite hydrogel-based interdigital electrode flexible pressure sensor showed extraordinary stability and identified different hand gestures as well as monitored the pulse signal of humans. Moreover, the characteristic systolic and diastolic peaks were clearly observed. The pulse frequency (65 times/min) and the radial artery augmentation index (0.57) were calculated, which are very important in evaluating the arterial vessel wall and function of human arteries.

Conductive and Eco-friendly Biomaterials-based Hydrogels for Noninvasive Epidermal Sensors: A Review

As noninvasive wearable electronic devices, epidermal sensors enable continuous, real-time, and remote monitoring of various human physiological parameters. Conductive biomaterials-based hydrogels as sensor matrix materials have good biocompatibility, biodegradability, and efficient stimulus response capabilities and are widely applied in motion monitoring, healthcare, and human-machine interaction. However, biomass hydrogel-based epidermal sensing devices still need excellent mechanical properties, prolonged stability, multifunctionality, and extensive practicality. Therefore, this paper reviews the common biomass hydrogel materials for epidermal sensing (proteins, polysaccharides, polyphenols, etc.) and the various types of noninvasive sensing devices (strain/pressure sensors, temperature sensors, glucose sensors, electrocardiograms, etc.). Moreover, this review focuses on the strategies of scholars to enhance sensor properties, such as strength, conductivity, stability, adhesion, and self-healing ability. This work will guide the preparation and optimization of high-performance biomaterials-based hydrogel epidermal sensors.

Tannic acid-coated cellulose nanocrystal-reinforced transparent multifunctional hydrogels with UV-filtering for wearable flexible sensors

Ionically conductive hydrogels are an ideal alternative material for applications in wearable flexible sensors to monitor human health. However, producing hydrogels with both high sensitivity and excellent versatility is difficult, and their transparency and UV-blocking properties are significantly limited. Here, with mussel- and gecko-inspired biomimicry, all-biomass-based hydrogels (OGTCGs) with self-adhesive, self-healing, transparent, UV-filtering, frost-resistant, environmentally stable, antibacterial, and biocompatible properties were designed and constructed via a simple one-step approach with a water/glycerol system and borax added without any crosslinker using synergistic dynamic covalent and noncovalent chemistry. The transparency of the OGTCG hydrogel reached 81.06 %, while the added tannic acid-coated cellulose nanocrystal (TA@CNC) induced a UV-blocking effect. The OGTCG hydrogel exhibited a high toughness (218.67 kPa) and modulus (100.32 kPa) reinforced by TA@CNC. The OGTCG hydrogel showed good self-healing abilities with an efficiency of over 90 % after 6 h. In a binary solvent system, the OGTCG hydrogel had environmental stability, as illustrated by density functional theory (DFT), greatly broadening its application range. Moreover, it had an electrical conductivity of 2.3 mS cm-1 and a sensitivity of 3.97. Therefore, with its rapid response and real-time monitoring capabilities, the OGTCG hydrogel shows great potential for applications in monitoring human health.

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.

Biocompatible, Antibacterial, and Stable Deep Eutectic Solvent-Based Ionic Gel Multimodal Sensors for Healthcare Applications

In this study, we investigated a novel approach to fabricate multifunctional ionic gel sensors by using deep eutectic solvents (DESs) as replacements for water. When two distinct DESs were combined, customizable mechanical and conductive properties were created, resulting in improved performance compared with traditional hydrogel-based strain sensors. DES ionic gels possess superior mechanical properties, transparency, biocompatibility, and antimicrobial properties, making them suitable for a wide range of applications such as flexible electronics, soft robotics, and healthcare. We conducted a comprehensive evaluation of the DES ionic gels, evaluating their performance under extreme temperature conditions (-70 to 80 °C), impressive optical transparency (94%), and biocompatibility. Furthermore, a series of tests were conducted to evaluate the antibacterial performance (Escherichia coli) of the DES ionic gels. Their wide strain (1-400%) and temperature (15-50 °C)-sensing ranges demonstrate the versatility and adaptability of DES ionic gels for diverse sensing requirements. The resulting DES ionic gels were successfully applied in human activity and vital sign monitoring, demonstrating their potential for biointegrated sensing devices and healthcare applications. This study offers valuable insights into the development and optimization of hydrogel sensors, particularly for applications that require environmental stability, biocompatibility, and antibacterial performance, thereby paving the way for future advancements in this field.

A hydrogel system for drug loading toward the synergistic application of reductive/heat-sensitive drugs

The preparation of hydrogels as drug carriers via radical-mediated polymerization has significant prospects, but the strong oxidizing ability of radicals and the high temperatures generated by the vigorous reactions limits the loading for reducing/heat-sensitive drugs. Herein, an applicable hydrogel synthesized by radical-mediated polymerization is reported for the loading and synergistic application of specific drugs. First, the desired sol is obtained by polymerizing functional monomers using a radical initiator, and then tannic-acid-assisted specific drug mediates sol-branched phenylboric acid group to form the required functional hydrogel (New-gel). Compared with the conventional single-step radical-mediated drug-loading hydrogel, the New-gel not only has better chemical/physical properties but also efficiently loads and releases drugs and maintains drug activity. Particularly, the New-gel has excellent loading capacity for oxygen, and exhibits significant practical therapeutic effects for diabetic wound repair. Furthermore, owing to its high light transmittance, the New-gel synergistically promotes the antibacterial effect of photosensitive drugs. This gelation strategy for loading drugs has further promising biomedical applications.

Mussel-Inspired Wet-Adhesive Multifunctional Organohydrogel with Extreme Environmental Tolerance for Wearable Strain Sensor

As a flexible artificial material, the conductive hydrogel has broad application prospects in flexible wearable electronics, soft robotics, and biomedical monitoring. However, traditional hydrogels still face many challenges, such as long-term stability, availability in extreme environments, and long-lasting adhesion to the skin surface under sweaty or humid conditions. To circumvent the above issues, one kind of ionic conductive hydrogel was prepared by a simple one-pot method that dissolved chitosan (CS), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), tannic acid (TA), and 2-methoxy-ethyl acrylate (MEA) into dimethyl sulfoxide (DMSO)/H2O solvent. The resulting hydrogel showed excellent tensile properties (1440%), extreme environmental tolerance (-40-60 °C), adhesion (72 KPa at porcine skin), ionic conductivity (0.87 S m-1), and high-efficiency antibacterial property. Furthermore, the produced organohydrogel strain sensor exhibited high strain sensitivity (GF = 4.07), excellent signal sensing capabilities (human joint movement, microexpression, and sound signals), and long-term cyclic stability (400 cycles). Looking beyond, this work provides a simple and promising strategy for using hydrogel sensors in extreme environments for e-skin, health monitoring, and wearable electronic devices.

Electrochemical Wearable Biosensors and Bioelectronic Devices Based on Hydrogels: Mechanical Properties and Electrochemical Behavior

Hydrogel-based wearable electrochemical biosensors (HWEBs) are emerging biomedical devices that have recently received immense interest. The exceptional properties of HWEBs include excellent biocompatibility with hydrophilic nature, high porosity, tailorable permeability, the capability of reliable and accurate detection of disease biomarkers, suitable device-human interface, facile adjustability, and stimuli responsive to the nanofiller materials. Although the biomimetic three-dimensional hydrogels can immobilize bioreceptors, such as enzymes and aptamers, without any loss in their activities. However, most HWEBs suffer from low mechanical strength and electrical conductivity. Many studies have been performed on emerging electroactive nanofillers, including biomacromolecules, carbon-based materials, and inorganic and organic nanomaterials, to tackle these issues. Non-conductive hydrogels and even conductive hydrogels may be modified by nanofillers, as well as redox species. All these modifications have led to the design and development of efficient nanocomposites as electrochemical biosensors. In this review, both conductive-based and non-conductive-based hydrogels derived from natural and synthetic polymers are systematically reviewed. The main synthesis methods and characterization techniques are addressed. The mechanical properties and electrochemical behavior of HWEBs are discussed in detail. Finally, the prospects and potential applications of HWEBs in biosensing, healthcare monitoring, and clinical diagnostics are highlighted.

Simple and Rapid Way to a Multifunctionally Conductive Hydrogel for Wearable Strain Sensors

Conductive hydrogels have gained increasing attention in the field of wearable smart devices. However, it remains a big challenge to develop a multifunctionally conductive hydrogel in a rapid and facile way. Herein, a conductive tannic acid-iron/poly (acrylic acid) hydrogel was synthesized within 30 s at ambient temperature by the tannic acid-iron (TA@Fe3+)-mediated dynamic catalytic system. The TA@Fe3+ dynamic redox autocatalytic pair could efficiently activate the ammonium persulfate to initiate the free-radical polymerization, allowing the gelation to occur easily and rapidly. The resulting hydrogel exhibited enhanced stretchability (3560%), conductivity (33.58 S/m), and strain sensitivity (gauge factor = 2.11). When damaged, it could be self-healed through the dynamic and reversible coordination bonds between the Fe3+ and COO- groups in the hydrogel network. Interestingly, the resulting hydrogel could act as a strain sensor to monitor various human motions including the huge movement of deformations (knuckle, wrist) and subtle motions (smiling, breathing) in real time due to its enhanced self-adhesion, good conductivity, and improved strain sensitivity. Also, the obtained hydrogel exhibited efficient electromagnetic interference (EMI) shielding performance with an EMI shielding effectiveness value of 24.5 dB in the X-band (8.2-12.4 GHz). Additionally, it displayed antibacterial properties, with the help of the activity of TA.

Hydrogel-Based Bioelectronics and Their Applications in Health Monitoring

Flexible bioelectronics exhibit promising potential for health monitoring, owing to their soft and stretchable nature. However, the simultaneous improvement of mechanical properties, biocompatibility, and signal-to-noise ratio of these devices for health monitoring poses a significant challenge. Hydrogels, with their loose three-dimensional network structure that encapsulates massive amounts of water, are a potential solution. Through the incorporation of polymers or conductive fillers into the hydrogel and special preparation methods, hydrogels can achieve a unification of excellent properties such as mechanical properties, self-healing, adhesion, and biocompatibility, making them a hot material for health monitoring bioelectronics. Currently, hydrogel-based bioelectronics can be used to fabricate flexible bioelectronics for motion, bioelectric, and biomolecular acquisition for human health monitoring and further clinical applications. This review focuses on materials, devices, and applications for hydrogel-based bioelectronics. The main material properties and research advances of hydrogels for health monitoring bioelectronics are summarized firstly. Then, we provide a focused discussion on hydrogel-based bioelectronics for health monitoring, which are classified as skin-attachable, implantable, or semi-implantable depending on the depth of penetration and the location of the device. Finally, future challenges and opportunities of hydrogel-based bioelectronics for health monitoring are envisioned.

Extreme-environment-adapted eutectogel mediated by heterostructure for epidermic sensor and underwater communication

In recent years, gel-based ion conductor has been widely considered in wearable electronics because of the favorable flexibility and conductivity. However, it is of vital importance, yet rather challenging to adapt the gel for underwater and dry conditions. Herein, an anti-swelling and anti-drying, intrinsic conductor eutectogel is designed via a one-step radical polymerization of acrylic acid and 2, 2, 2‑trifluoroethyl methacrylate in binary deep eutectic solvents (DESs) medium. On the one hand, the synergistic effects of hydrophilic/hydrophobic heteronetworks can elicit the integrity stability of eutectogel in liquid environment. It is proved that both the mechanical property and conductivity are maintained after immersing in different salt, alkaline and acid solution and organic solvent for one month. On the other hand, the eutectogel inherits well conductivity (93 mS/m), anti-drying and antibacterial properties from DESs. Based on the above features, the resulting eutectogel can be assembled as smart sensor for stable information transmission in air and underwater with fast response time (1 s), high sensitivity (Gauge factor = 1.991) and long-time reproducibility (500 cycles, 70 % strain). Considering the simple preparation and integration of multiple functions, the binary cooperative complementary principle can provide insights into the development of next-generation conductive soft materials.