Highly Flexible and Broad-Range Mechanically Tunable All-Wood Hydrogels with Nanoscale Channels via the Hofmeister Effect for Human Motion Monitoring

Mechanically robust, flexible, conductive, and anti-freezing hydrogels reinforced by cellulose of wood skeleton

Hydrogels are soft and wet materials, but their applications are always limited by insufficient mechanical strength and toughness, and they are prone to freezing at low temperatures. In this study, we introduced an eco-friendly approach to developing wood-based hydrogels reinforced by the naturally aligned wood skeleton (WS) through the Hofmeister effect. The resulting wood-based composite hydrogels exhibited a high tensile strength of 20 MPa and a strain of 35 % in the longitudinal direction. This impressive mechanical performance was primarily due to densely packed hydrogen bonding, physical entanglements, and van der Waals forces between the cellulose of WS, polyacrylamide (PAM), and poly(vinyl alcohol) (PVA) chains during polymerization. Notably, the polymerization was induced using wood carbon dots as initiators, imparting additional fluorescence features to the hydrogels. Afterward, by incorporating a metal salt (sodium chloride), the developed wood-based hydrogels maintained high conductivity (3.0 S/m) and mechanical properties even under low-temperature conditions (-20 °C). Moreover, the conductive hydrogels exhibited multifunctional sensing capabilities, including strain, temperature, and ultraviolet (UV) irradiation detection, making them highly suitable for applications in human motion monitoring and healthcare, particularly under harsh environmental conditions.

From the synthesis of wearable polymer sensors to their potential for reuse and ultimate fate

The objective of this perspective is to review the high-interest field of wearable polymer-based sensors-from synthesis to use and detection mechanisms-with a focus on their transient nature, potential for reuse, and ultimate fate. While many bulk polymers have long been mass-produced, the materials needed to create polymer-based sensors-often with unique properties (e.g., being electronically conductive)-are still highly active areas of research. Polymer-based materials and composites, when investigated as wearable sensors, have a wide range of applications with most falling under the umbrellas of biochemical and environmental sensing (i.e., chemical reactivity-based detection) or physical sensing (e.g., piezoresistive response). Since the long-term viability of these sensors is a function of not just their initial syntheses but also their ability to be durable, recyclable, or otherwise renewable, a discussion of both the technical and societal aspects of the reuse and ultimate fate of these materials will be covered. This discussion will focus on topics such as environmental impact, sterilization, and other methods for ensuring continued biocompatibility, as well as methods for the transformation, reclamation, or re-implementation of the sensor devices-a major issue the polymer community is facing.

Self-adhesive, freezing-tolerant conductive organohydrogels with variable transparency and rapid repairing for multi-functional sensor

Organohydrogels have garnered considerable attention in the field of flexible sensors, largely because of their flexibility, durability, and multifunctionality. However, conventional organohydrogels demonstrate inadequate conductivity, necessitate substantial preparation time and energy, are challenging to repair following damage, exhibit immutable transparency, and are inherently unstable in extreme environments, which significantly restricts their practical application. Herein, a conventional synergetic self-catalytic system based on catechol molecules and metal ions was innovated for the rapid fabrication of conductive polyacrylic acid (PAA) organohydrogels in H2O/ethylene glycol (EG)/LiCl solvent. The dual self-catalytic system comprises ferric ions (Fe3+) and cellulose nanofibers (CNF) coated with tannic acid (TA@CNF), which form stable redox pairs to activate ammonium persulfate (APS), thereby initiating the polymerization of monomers rapidly and effectively. Compared with other gel prepared by catechol metal ion autocatalysis system, the organohydrogel prepared by us has unique advantages, including: (1) Modifying the pH value of the TA-coated CNF enables a change in the transparency of the organogel and enhances its mechanical properties. (2) The color of the organohydrogel can be modified by adjusting the equilibrium of the redox system by APS. (3) The organohydrogel has the ability to rapid repairing (50 s). Moreover, the organohydrogel exhibits considerable tensile strength, satisfactory self-adhesion (44.2 ± 4.3 kPa), excellent conductivity (1.79 ± 0.035 S/m) and extreme environmental applicability (-60 °C to 45 °C). The organohydrogel displays excellent conductivity, sensitive response to tensile deformation, changeable color, rapid repairing and excellent mechanical properties. Thus, it can be applied to human movement monitoring, information encryption and intelligent control.

Design of Hydrogel Electrolytes Using Strong Bacterial Cellulose with Weak Ionic Interactions

Hydrogel electrolytes with both high ionic conductivity and sufficient mechanical strength are in great demand but remain a long-standing challenge. Here, we report a simple method to fabricate highly conductive and strong hydrogels (IBVA) by leveraging a layered cellulose network with weak ionic interactions. Specifically, bacterial cellulose (BC) membranes with high crystallinity and mechanical strength are employed as the strong skeletons of the hydrogel matrix. Simultaneously, formate anions with a salting-in effect are introduced to tune the aggregation states of polymer chains, endowing the hydrogel with weak hydrogen bonding, and finally forming a "hard-soft-hard" interlocking hierarchical structure. This strategy enables the hydrogel to achieve an ultrahigh ionic conductivity of 105 ± 5 mS cm-1, alongside satisfying mechanical strength (0.78 MPa), outperforming most reported hydrogel electrolytes. Furthermore, the IBVA hydrogel was successfully demonstrated as an electrolyte for supercapacitors, exhibiting the favorable flexibility, broad temperature adaptability, interfacial stability, and stable electrochemical performance. Our proposed method establishes a framework for engineering high-performance hydrogel electrolytes tailored for flexible electronics.

A spider silk-inspired, transparent, anti-freezing ionic conductive hydrogel as a flexible sensor device

As soft material ionic conductors, ionically conductive hydrogels are of great significance for the development of flexible electronics. However, it is still a great challenge to effectively design functional hydrogel structures to address various practical application scenarios (such as low temperature environments) and expand their application range (such as transparent display devices). In this paper, an anti-bacterial and ionically conductive TEMPO-oxidized cellulose nanofiber/polyvinyl alcohol/quaternary ammonium chitosan/Al3+ (CPQA-EH) hydrogel (conductivity of 7.50 ms cm-1) with high transparency (93.7%) is constructed by a simple method of solution mixing and immersion. An organic solvent is used to induce in situ phase separation and multiple interactions between molecular chains to promote crystallization. The hydrogel network structure is regulated step by step, and nanofibrils are induced in situ to form a nano-fishnet structure. The CPQA-EH ionically conductive hydrogel with a nanofibrous network exhibits excellent tensile strength (1341.86 kPa) and toughness (6992.53 kJ m-3). Meanwhile, it shows low-temperature sensing ability even at -80 °C (freezing point of -122.08 °C). The flexible sensor based on the CPQA-EH conductive hydrogel can sensitively recognize external stimuli (strain/pressure). It shows stable detection of the movement of human joints and vocalization, and the hydrogel with high transparency can also be used as a display device to recognize writing signals.

Anionic polyelectrolyte-regulated cellulose nanocrystal-based hydrogels for controllable drug release

The application of inorganic salt-regulated Hofmeister effects in cellulose nanocrystals (CNC)-based hydrogels is hindered by limitations, including poor biocompatibility and difficulties in achieving precise drug release. In this study, we show that the anionic polyelectrolyte regulated Hofmeister effect promotes the aggregation and crystallization of CNC and polyvinyl alcohol (PVA) chains. This structural transformation significantly enhances the controllability of drug release in CNC-based hydrogels. The incorporation of anionic polyelectrolytes into CNC-based hydrogels creates a semi-interpenetrating polymer network (semi-IPN), significantly enhancing their mechanical properties and improving in vitro drug release controllability. Our hydrogel exhibits significant flexibility in controlling both drug release duration and capacity, with adjustable release times ranging from 16 to 52 h and tunable drug release capacities between 10.13 mg/g and 19.21 mg/g. Furthermore, antibacterial and cytotoxicity assays confirm its favorable biocompatibility and moderate antibacterial properties. Overall, our research findings emphasize that the preparation of cellulose-based hydrogels using polyelectrolytes has certain flexible regulatory functions in drug release.

A highly stretchable, self-healing, self-adhesive polyacrylic acid/chitosan multifunctional composite hydrogel for flexible strain sensors

Conductive hydrogels have emerged as excellent candidates for the design and construction of flexible wearable sensors and have attracted great attention in the field of wearable sensors. However, there are still serious challenges to integrating high stretchability, self-healing, self-adhesion, excellent sensing properties, and good biocompatibility into hydrogel wearable devices through easy and green strategies. In this paper, multifunctional conductive hydrogels (PCGB) with good biocompatibility, high tensile (1694 % strain), self-adhesive, and self-healing properties were fabricated by incorporating boric acid (BA) and glucose (Glu) simultaneously into polyacrylic acid (PAA) and chitosan (CS) polymer networks using a simple one-pot polymerization method. Furthermore, the hydrogel strain sensor constructed from the PCGB assembly had great sensing property including high sensitivity (GF = 5.7), durability and stability (5000 cycles). The hydrogel strain sensor was applied to the detection of human motion, which exhibited accurate detection behavior for both large-scale motions and small activities. A strategy to design and fabricate multifunctional conductive hydrogels integrating high stretchability, self-healing, self-adhesion and good biocompatibility was provided, and the multifunctional conductive hydrogels broadened the application of hydrogel-based wearable sensor.

Bio-Inspired Highly Stretchable and Ultrafast Autonomous Self-Healing Supramolecular Hydrogel for Multifunctional Durable Self-Powered Wearable Devices

As skin bioelectronics advances, hydrogel wearable devices have broadened perspectives in environment sensing and health monitoring. However, their application is severely hampered by poor mechanical and self-healing properties, environmental sensitivity, and limited sensory functions. Herein, inspired by the hierarchical structure and unique cross-linking mechanism of hagfish slime, a self-powered supramolecular hydrogel is hereby reported, featuring high stretchability (>2800% strain), ultrafast autonomous self-healing capabilities (electrical healing time: 0.3 s), high self-adhesiveness (adhesion strength: 6.92 kPa), injectability, ease of shaping, antimicrobial properties, and biocompatibility. It is observed that by embedding with the highly hygroscopic salt LiCl in supramolecular hydrogel, the hydrogel not only showed excellent electrical conductivity but also presented favorable anti-freezing and water retention properties in extremely cold environments and natural settings. Given these attributes, the hydrogel served as a multifunctional durable self-powered wearable device with high sensitivity (gauge factor: 3.68), fast response time (160 ms), low detection limit, and frequency sensitivity. Moreover, the multifunctional applicability of this supramolecular hydrogel is further demonstrated in long-term cold environments sensing, remote medical communication, and underwater communication. Overall, these findings pave the way for the sustainable development of hydrogel-based wearable devices that are self-powered, durable, and offer high performance, environmental adaptability, and multi-sensory capabilities.

Alphabet Handwriting Recognition: From Wood-Framed Hydrogel Arrays Design to Machine Learning Decoding

Handwriting recognition is a highly integrated system, demanding hardware to collect handwriting signals and software to deal with input data. Nonetheless, the design of such a system from scratch with sustainable materials and an easily accessible computing network presents significant challenges. In pursuit of this goal, a flexible, and electrically conductive wood-derived hydrogel array is developed as a handwriting input panel, enabling recognizing alphabet handwriting assisted by machine learning technique. For this, lignin extraction-refill, polypyrrole coating, and polyacrylic acid filling, endowing flexibility, and electrical conduction to wood are sequentially implemented. Subsequently, these woods are manufactured into a 5 × 5 array, creating a matrix of signals upon handwriting. Efficient handwritten recognition is then achieved through appropriate manual feature extraction and algorithms with low complexity within a computing network, as demonstrated in this work, the strategic choice of expertise-based feature engineering and simplified algorithms effectively boost the overall model performance on handwriting recognition. With potential adaptability, further applications in customized wearable devices and hands-on healthcare appliances are envisioned.

Wood Cell Wall Nanoengineering toward Anisotropic, Strong, and Flexible Cellulosic Hydrogel Sensors

Achieving highly ionic conductive hydrogels from natural wood remains challenging owing to their insufficient surface area and low number of active sites on the cell wall. This study proposes a viable strategy to design a strong and anisotropic wood-based hydrogel through cell wall nanoengineering. By manipulating the microstructure of the wood cell wall, a flexible cellulosic hydrogel is achieved through Schiff base bonding via the polyacrylamide and cellulose molecular chains. This results in excellent flexibility and mechanical properties of the wood hydrogel with tensile strengths of 22.3 and 6.1 MPa in the longitudinal and transverse directions, respectively. Moreover, confining aqueous salt electrolytes within the porous structure gives anisotropic ionic conductivities (19.5 and 6.02 S/m in the longitudinal and transverse directions, respectively). The wood-based hydrogel sensor has a favorable sensitivity and a stable working performance at a low temperature of -25 °C in monitoring human motions, thereby demonstrating great potential applications in wearable sensor devices.

3D Printing of Tough Hydrogel Scaffolds with Functional Surface Structures for Tissue Regeneration

Hydrogel scaffolds have numerous potential applications in the tissue engineering field. However, tough hydrogel scaffolds implanted in vivo are seldom reported because it is difficult to balance biocompatibility and high mechanical properties. Inspired by Chinese ramen, we propose a universal fabricating method (printing-P, training-T, cross-linking-C, PTC & PCT) for tough hydrogel scaffolds to fill this gap. First, 3D printing fabricates a hydrogel scaffold with desired structures (P). Then, the scaffold could have extraordinarily high mechanical properties and functional surface structure by cycle mechanical training with salting-out assistance (T). Finally, the training results are fixed by photo-cross-linking processing (C). The tough gelatin hydrogel scaffolds exhibit excellent tensile strength of 6.66 MPa (622-fold untreated) and have excellent biocompatibility. Furthermore, this scaffold possesses functional surface structures from nanometer to micron to millimeter, which can efficiently induce directional cell growth. Interestingly, this strategy can produce bionic human tissue with mechanical properties of 10 kPa-10 MPa by changing the type of salt, and many hydrogels, such as gelatin and silk, could be improved with PTC or PCT strategies. Animal experiments show that this scaffold can effectively promote the new generation of muscle fibers, blood vessels, and nerves within 4 weeks, prompting the rapid regeneration of large-volume muscle loss injuries.

"Bottom-up" and "top-down" strategies toward strong cellulose-based materials

Cellulose, as the most abundant natural polymer on Earth, has long captured researchers' attention due to its high strength and modulus. Nevertheless, transferring its exceptional mechanical properties to macroscopic 2D and 3D materials poses numerous challenges. This review provides an overview of the research progress in the development of strong cellulose-based materials using both the "bottom-up" and "top-down" approaches. In the "bottom-up" strategy, various forms of regenerated cellulose-based materials and nanocellulose-based high-strength materials assembled by different methods are discussed. Under the "top-down" approach, the focus is on the development of reinforced cellulose-based materials derived from wood, bamboo, rattan and straw. Furthermore, a brief overview of the potential applications fordifferent types of strong cellulose-based materials is given, followed by a concise discussion on future directions.

Muscle-Inspired Formable Wood-Based Phase Change Materials

Phase change materials (PCMs) are crucial for sustainable thermal management in energy-efficient construction and cold chain logistics, as they can store and release renewable thermal energy. However, traditional PCMs suffer from leakage and a loss of formability above their phase change temperatures, limiting their shape stability and versatility. Inspired by the muscle structure, formable PCMs with a hierarchical structure and solvent-responsive supramolecular networks based on polyvinyl alcohol (PVA)/wood composites are developed. The material, in its hydrated state, demonstrates low stiffness and pliability due to the weak hydrogen bonding between aligned wood fibers and PVA molecules. Through treatment of poly(ethylene glycol) (PEG) into the PVA/wood PEG gel (PEG/PVA/W) with strengthened hydrogen bonds, the resulting wood-based PCMs in the hard and melting states elevate the tensile stress from 10.14 to 80.86 MPa and the stiffness from 420 MPa to 4.8 GPa, making it 530 times stiffer than the PEG/PVA counterpart. Capable of morphing in response to solvent changes, these formable PCMs enable intricate designs for thermal management. Furthermore, supported by a comprehensive life cycle assessment, these shape-adaptable, recyclable, and biodegradable PCMs with lower environmental footprint present a sustainable alternative to conventional plastics and thermal management materials.

Engineering Tough and Elastic Polyvinyl Alcohol-Based Hydrogel with Antimicrobial Properties

Hydrogels have been extensively used for tissue engineering applications due to their versatility in structure and physical properties, which can mimic native tissues. Although significant progress has been made towards designing hydrogels for soft tissue repair, engineering hydrogels that resemble load-bearing tissues is still considered a great challenge due to their specific mechano-physical demands. Here, we report microporous, tough, yet highly compressible poly(vinyl alcohol) (PVA)-based hydrogels for potential applications in repairing or replacing different load-bearing tissues. The synergy of freeze-thawing and the Hofmeister effect, which controlled the spatial arrangement and aggregation of polymer chains, facilitated the formation of micro-structured frameworks with tunable porosity. While the maximum mechanical strength, toughness, and stretchability of the engineered hydrogel were ~390 kPa, ~388 kJ/m3, and ~170%, respectively, the Young's modulus based on compression testing was found to be in the range of ~0.02 - 0.30 MPa, highlighting the all-in-one mechanically enriched nature of the hydrogel system. Furthermore, the minimal swelling and degradation rate of the engineered hydrogel met the specific requirements of load-bearing tissues. Finally, excellent antibacterial resistance as well as in vitro biocompatibility of the hydrogel demonstrated its potential for the replacement of load-bearing tissues.

A comprehensive review on preparation and functional application of the wood aerogel with natural cellulose framework

As the traditional aerogel has defects such as poor mechanical properties, complicated preparation process, high energy consumption and non-renewable, wood aerogel as a new generation of aerogel shows unique advantages. With a natural cellulose framework, wood aerogel is a novel nano-porous material exhibiting exceptional properties such as light weight, high porosity, large specific surface area, and low thermal conductivity. Furthermore, its adaptability to further functionalization enables versatile applications across diverse fields. Driven by the imperative for sustainable development, wood aerogel as a renewable and eco-friendly material, has garnered significant attention from researchers. This review introduces preparation methods of wood aerogel based on the top-down strategy and analyzes the factors influencing their key properties intending to obtain wood aerogels with desirable properties. Avenues for realizing its functionality are also explored, and research progress across various domains are surveyed, including oil-water separation, conductivity and energy storage, as well as photothermal conversion. Finally, potential challenges associated with wood aerogel exploitation and utilization are addressed, alongside discussions on future prospects and research directions. The results emphasize the broad research value and future prospects of wood aerogels, which are poised to drive high-value utilization of wood and foster the development of green multifunctional aerogels.

Degradable and Recyclable Hydrogels for Sustainable Bioelectronics

Hydrogel bioelectronics has been widely used in wearable sensors, electronic skin, human-machine interfaces, and implantable tissue-electrode interfaces, providing great convenience for human health, safety, and education. The generation of electronic waste from bioelectronic devices jeopardizes human health and the natural environment. The development of degradable and recyclable hydrogels is recognized as a paradigm for realizing the next generation of environmentally friendly and sustainable bioelectronics. This review first summarizes the wide range of applications for bioelectronics, including wearable and implantable devices. Then, the employment of natural and synthetic polymers in hydrogel bioelectronics is discussed in terms of degradability and recyclability. Finally, this work provides constructive thoughts and perspectives on the current challenges toward hydrogel bioelectronics, providing valuable insights and guidance for the future evolution of sustainable hydrogel bioelectronics.

A Wood-Derived Periosteum for Spatiotemporal Drug Release: Boosting Bone Repair through Anisotropic Structure and Multiple Functions

Existing artificial periostea face many challenges, including difficult-to-replicate anisotropy in mechanics and structure, poor tissue adhesion, and neglected synergistic angiogenesis and osteogenesis. Here, inspired by natural wood (NW), a wood-derived elastic artificial periosteum is developed to mimic the structure and functions of natural periosteum, which combines an elastic wood (EW) skeleton, a polydopamine (PDA) binder layer, and layer-by-layer (LBL) biofunctional layers. Specifically, EW derived from NW is utilized as the anisotropic skeleton of artificial periosteum to guide cell directional behaviors, moreover, it also shows a similar elastic modulus and flexibility to natural periosteum. To further enhance its synergistic angiogenesis and osteogenesis, surface LBL biofunctional layers are designed to serve as spatiotemporal release platforms to achieve sequential and long-term release of pamidronate disodium (PDS) and deferoxamine (DFO), which are pre-encapsulated in chitosan (CS) and hyaluronic acid (HA) solutions, respectively. Furthermore, the combined effect of PDA coating and LBL biofunctional layers enables the periosteum to tightly adhere to damaged bone tissue. More importantly, this novel artificial periosteum can boost angiogenesis and bone formation in vitro and in vivo. This study opens up a new path for biomimetic design of artificial periosteum, and provides a feasible clinical strategy for bone repair.

β-Lactoglobulin-based aerogels: Facile preparation and sustainable removal of organic contaminants from water

Economically and efficiently removing organic pollutants from water is still a challenge in wastewater treatment. Utilizing environmentally friendly and readily available protein-based natural polymers to develop aerogels with effective removal performance and sustainable regeneration capability is a promising strategy for adsorbent design. Here, a robust and cost-effective method using inexpensive β-lactoglobulin (BLG) as raw material was proposed to fabricate BLG-based aerogels. Firstly, photocurable BLG-based polymers were synthesized by grafting glycidyl methacrylate. Then, a cross-linking reaction, including photo-crosslinking and salting-out treatment, was applied to prepared BLG-based hydrogels. Finally, the BLG-based aerogels with high porosity and ultralight weight were obtained after freeze-drying. The outcomes revealed that the biocompatible BLG-based aerogels exhibited effective removal performance for a variety of organic pollutants under perfectly quiescent conditions, and could be regenerated and reused many times via a simple and rapid process of acid washing and centrifugation. Overall, this work not only demonstrates that BLG-based aerogels are promising adsorbents for water purification but also provides a potential way for the sustainable utilization of BLG.

Leakage Proof, Flame-Retardant, and Electromagnetic Shield Wood Morphology Genetic Composite Phase Change Materials for Solar Thermal Energy Harvesting

Phase change materials (PCMs) offer a promising solution to address the challenges posed by intermittency and fluctuations in solar thermal utilization. However, for organic solid-liquid PCMs, issues such as leakage, low thermal conductivity, lack of efficient solar-thermal media, and flammability have constrained their broad applications. Herein, we present an innovative class of versatile composite phase change materials (CPCMs) developed through a facile and environmentally friendly synthesis approach, leveraging the inherent anisotropy and unidirectional porosity of wood aerogel (nanowood) to support polyethylene glycol (PEG). The wood modification process involves the incorporation of phytic acid (PA) and MXene hybrid structure through an evaporation-induced assembly method, which could impart non-leaking PEG filling while concurrently facilitating thermal conduction, light absorption, and flame-retardant. Consequently, the as-prepared wood-based CPCMs showcase enhanced thermal conductivity (0.82 W m-1 K-1, about 4.6 times than PEG) as well as high latent heat of 135.5 kJ kg-1 (91.5% encapsulation) with thermal durability and stability throughout at least 200 heating and cooling cycles, featuring dramatic solar-thermal conversion efficiency up to 98.58%. In addition, with the synergistic effect of phytic acid and MXene, the flame-retardant performance of the CPCMs has been significantly enhanced, showing a self-extinguishing behavior. Moreover, the excellent electromagnetic shielding of 44.45 dB was endowed to the CPCMs, relieving contemporary health hazards associated with electromagnetic waves. Overall, we capitalize on the exquisite wood cell structure with unidirectional transport inherent in the development of multifunctional CPCMs, showcasing the operational principle through a proof-of-concept prototype system.

Antifreezing, Antidrying, and Conductive Hydrogels for Electronic Skin Applications at Ultralow Temperatures

Although conductive hydrogel-based flexible electronic devices have superb flexibility and high conductivities, they tend to malfunction in dry or frigid areas. Herein, an ultralow-temperature tolerant, antidrying, and conductive composite hydrogel is designed for electronic skin applications on the basis of the synergy of double-cross-linked polymer networks, Hofmeister effect, and electrostatic interaction and fabricated by in situ free radical polymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid and acrylic acid in the presence of poly(vinyl alcohol) and conductive MXene sheets, followed by impregnation with LiCl. Thanks to the synergy of LiCl and the charged polar terminal groups of the synthesized polymers, the composite hydrogel can not only bear an ultralow temperature of -80 °C without freezing but also maintain its original mass. Meanwhile, the resultant hydrogel possesses satisfactory self-regeneration ability benefiting from the moisturizing effect of LiCl. The conductive network of MXene sheets greatly improves the ionic conductivity of the hydrogel at low temperatures, exhibiting an ionic conductivity of 1.4 S m-1 at -80 °C. Furthermore, the electronic skin assembled by the multifunctional hydrogel is efficient in monitoring human motions at -80 °C. The antifreezing and antidrying features along with favorable ionic conductivity, high tensile strength, and outstanding flexibility make the composite hydrogel promising for applications in frigid and dry regions.

High-Strength, High-Swelling-Resistant, High-Sensitivity Hydrogel Sensor Prepared with Wood That Retains Lignin

Wood-derived hydrogels possess satisfactory longitudinal strength but lack excellent swelling resistance and dry shrinkage resistance when achieving high anisotropy. In this study, we displayed the preparation of highly dimensional stable wood/polyacrylamide hydrogels (wood/PAM-Al3+). The alkali-treated wood retains lignin as the skeleton of the hydrogel. Second, Al ions were added to the metal coordination with lignin. Finally, by employing free radical polymerization, we construct a conductive electronic network using polyaniline within the wood/PAM-Al3+ matrix to create the flexible sensor. This approach leverages lignin's integrated structure within the middle lamella to provide enhanced swelling resistance and stronger binding strength in the transverse direction. Furthermore, coordination between lignin and Al ions improves the mechanical strength of the wood hydrogel. Polyaniline provides stable linear pressure and temperature responses. The wood/PAM-Al3+ exhibits a transverse swelling ratio of 3.90% while achieving a longitudinal tensile strength of 20.5 MPa. This high-strength and high-stability sensor is capable of monitoring macroscale human behavior. Therefore, this study presents a simple yet innovative strategy for constructing tough hydrogels while also establishing an alternative pathway for exploring lignin networks in new functional materials development.

Cellulose-based bi-layer hydrogel evaporator with a low evaporation enthalpy for efficient solar desalination

Interfacial evaporation through hydrogel-based evaporators is emerging as a sustainable and cost-effective strategy for drinkable water production. Herein, a specially designed bi-layer hydrogel evaporator was fabricated and used for efficient solar water desalination. With cotton linter as cellulose precursor, it was dispersed in a highly concentrated ZnCl2 (65 %) solution, and cross-linked by epichlorohydrin to prepare cellulose composite hydrogel. After removing inorganic salts by salt-leaching, polyaniline (PANi) with broadband and wide-range light absorption was then integrated into the top surface of hydrogel through in situ polymerization to construct a bi-layer evaporator. As a solar evaporator, the water could be evaporated with a low-energy demand, and the heat from the sunlight could be confined at the interface to achieve efficient water evaporation. Therefore, the hydrogel evaporator demonstrates an optimal water evaporation rate of 3.02 kg m-2 h-1 and photothermal conversion efficiency of 89.09 % under 1 sun (1 kW m-2) irradiation. This work provides new possibilities for efficient solar water purification systems with assured water quality.

Construction methods and biomedical applications of PVA-based hydrogels

Polyvinyl alcohol (PVA) hydrogel is favored by researchers due to its good biocompatibility, high mechanical strength, low friction coefficient, and suitable water content. The widely distributed hydroxyl side chains on the PVA molecule allow the hydrogels to be branched with various functional groups. By improving the synthesis method and changing the hydrogel structure, PVA-based hydrogels can obtain excellent cytocompatibility, flexibility, electrical conductivity, viscoelasticity, and antimicrobial properties, representing a good candidate for articular cartilage restoration, electronic skin, wound dressing, and other fields. This review introduces various preparation methods of PVA-based hydrogels and their wide applications in the biomedical field.

Salting-Out Effect Realizing High-Strength and Dendrite-Inhibiting Cellulose Hydrogel Electrolyte for Durable Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries are limited by poor Zn stripping/plating reversibility. Not only can hydrogel electrolytes address this issue, but also they are suitable for constructing flexible batteries. However, there exists a contradiction between the mechanical strength and the ionic conductivity for hydrogel electrolytes. Herein, high-concentration kosmotropic ions are introduced into the cellulose hydrogel electrolyte to take advantage of the salting-out effect. This can significantly improve both the mechanical strength and ionic conductivity. Additionally, the obtained cellulose hydrogel electrolyte (denoted as Con-CMC) has strong adhesion, a wide electrochemical stability window, and good water retaining ability. The Con-CMC is also found to accelerate the desolvation process, improve Zn deposition kinetics, promote Zn deposition along the (002) plane, and suppress parasitic reactions. Accordingly, the Zn/Zn cell with Con-CMC demonstrates dendrite-free behavior with prolonged lifespan and can endure extremely large areal capacity of 25 mAh cm-2. The Con-CMC also enables a large average Coulombic efficiency of 99.54% over 500 cycles for the Zn/Cu cell. Furthermore, the assembled pouch-type Zn/polyaniline full battery provides great rate capability, superior cyclability (even with limited Zn anode excess), a slow self-discharge rate, and outstanding affordability to external forces. Overall, this work extends our knowledge of the rational design of hydrogel electrolytes.

Nanofiber Composite Reinforced Organohydrogels for Multifunctional and Wearable Electronics

Composite organohydrogels have been widely used in wearable electronics. However, it remains a great challenge to develop mechanically robust and multifunctional composite organohydrogels with good dispersion of nanofillers and strong interfacial interactions. Here, multifunctional nanofiber composite reinforced organohydrogels (NCROs) are prepared. The NCRO with a sandwich-like structure possesses excellent multi-level interfacial bonding. Simultaneously, the synergistic strengthening and toughening mechanism at three different length scales endow the NCRO with outstanding mechanical properties with a tensile strength (up to 7.38 ± 0.24 MPa), fracture strain (up to 941 ± 17%), toughness (up to 31.59 ± 1.53 MJ m-3) and fracture energy (up to 5.41 ± 0.63 kJ m-2). Moreover, the NCRO can be used for high performance electromagnetic interference shielding and strain sensing due to its high conductivity and excellent environmental tolerance such as anti-freezing performance. Remarkably, owing to the organohydrogel stabilized conductive network, the NCRO exhibits superior long-term sensing stability and durability compared to the nanofiber composite itself. This work provides new ideas for the design of high-strength, tough, stretchable, anti-freezing and conductive organohydrogels with potential applications in multifunctional and wearable electronics.

Biological Tissue-Inspired Ultrasoft, Ultrathin, and Mechanically Enhanced Microfiber Composite Hydrogel for Flexible Bioelectronics

Hydrogels offer tissue-like softness, stretchability, fracture toughness, ionic conductivity, and compatibility with biological tissues, which make them promising candidates for fabricating flexible bioelectronics. A soft hydrogel film offers an ideal interface to directly bridge thin-film electronics with the soft tissues. However, it remains difficult to fabricate a soft hydrogel film with an ultrathin configuration and excellent mechanical strength. Here we report a biological tissue-inspired ultrasoft microfiber composite ultrathin (< 5 μm) hydrogel film, which is currently the thinnest hydrogel film as far as we know. The embedded microfibers endow the composite hydrogel with prominent mechanical strength (tensile stress ~ 6 MPa) and anti-tearing property. Moreover, our microfiber composite hydrogel offers the capability of tunable mechanical properties in a broad range, allowing for matching the modulus of most biological tissues and organs. The incorporation of glycerol and salt ions imparts the microfiber composite hydrogel with high ionic conductivity and prominent anti-dehydration behavior. Such microfiber composite hydrogels are promising for constructing attaching-type flexible bioelectronics to monitor biosignals.

Triple-functional bone adhesive with enhanced internal fixation, bacteriostasis and osteoinductive properties for open fracture repair

At present, effective fixation and anti-infection implant materials represent the mainstay for the treatment of open fractures. However, external fixation can cause nail tract infections and is ineffective for fixing small fracture fragments. Moreover, closed reduction and internal fixation during the early stage of injury can lead to potential bone infection, conducive to bone nonunion and delayed healing. Herein, we designed a bone adhesive with anti-infection, osteogenic and bone adhesion fixation properties to promote reduction and fixation of open fractures and subsequent soft tissue repair. It was prepared by the reaction of gelatin (Gel) and oxidized starch (OS) with vancomycin (VAN)-loaded mesoporous bioactive glass nanoparticles (MBGNs) covalently cross-linked with Schiff bases. Characterization and adhesion experiments were conducted to validate the successful preparation of the Gel-OS/VAN@MBGNs (GOVM-gel) adhesive. Meanwhile, in vitro cell experiments demonstrated its good antibacterial effects with the ability to stimulate bone marrow mesenchymal stem cell (BMSCs) proliferation, upregulate the expression of alkaline phosphatase (ALP) and osteogenic proteins (RunX2 and OPN) and enhance the deposition of calcium nodules. Additionally, we established a rat skull fracture model and a subcutaneous infection model. The histological analysis showed that bone adhesive enhanced osteogenesis, and in vivo experiments demonstrated that the number of inflammatory cells and bacteria was significantly reduced. Overall, the adhesive could promote early reduction of fractures and antibacterial and osteogenic effects, providing the foothold for treatment of this patient population.

Copper(I)-Iodide Clusters as Carriers for Regulating and Visualizing Release of Aroma Molecules

Achieving the controlled release of functional substances is indispensable in many aspects of life. Especially for the aroma molecules, their effective delivery of flavor and fragrance is challenging. Here, selected pyridines, as highly volatile odorants, were individually coordinated with copper(I) iodide (Cu^II) via a straightforward one-pot synthesis method, rapidly forming pure or even crystalline Cu^II cluster-based profragrances at room temperature. The obtained profragrances enabled the stable and high loading of volatile fragrances under ambient conditions and guaranteed their long-lasting release during heating. Furthermore, the intrinsic emission luminescence of these solid-state profragrances decayed along with the aroma release, which can serve as an additional indicator for monitoring the delivery process. This research sets a precedent for using Cu^II clusters as dual-purpose release agents and greatly expands their potential applications.

Recent Advances in Designing Fibrous Biomaterials for the Domain of Biomedical, Clinical, and Environmental Applications

Unique properties and potential applications of nanofibers have emerged as innovative approaches and opportunities in the biomedical, healthcare, environmental, and biosensor fields. Electrospinning and centrifugal spinning strategies have gained considerable attention among all kinds of strategies to produce nanofibers. These techniques produce nanofibers with high porosity and surface area, adequate pore architecture, and diverse chemical compositions. The extraordinary characteristics of nanofibers have unveiled new gates in nanomedicine to establish innovative fiber-based formulations for biomedical use, healthcare, and a wide range of other applications. The present review aims to provide a comprehensive overview of nanofibers and their broad range of applications, including drug delivery, biomedical scaffolds, tissue/bone-tissue engineering, dental applications, and environmental remediation in a single place. The review begins with a brief introduction followed by potential applications of nanofibers. Finally, the future perspectives and current challenges of nanofibers are demonstrated. This review will help researchers to engineer more efficient multifunctional nanofibers with improved characteristics for their effective use in broad areas. We strongly believe this review is a reader's delight and will help in dealing with the fundamental principles and applications of nanofiber-based scaffolds. This review will assist students and a broad range of scientific communities to understand the significance of nanofibers in several domains of nanotechnology, nanomedicine, biotechnology, and environmental remediation, which will set a benchmark for further research.