Plant-inspired adhesive and tough hydrogel based on Ag-Lignin nanoparticles-triggered dynamic redox catechol chemistry

A novel multi-functional PVA- alginate hydrogel with dynamic bond crosslinking for infected wound repair

The development of multifunctional antibacterial hydrogel dressings with enhanced mechanical properties and biological activity is essential for advancing wound healing strategies. In this study, we report the design and synthesis of a novel multifunctional hydrogel (PVA-Alg/FP), developed by integrating Fe3+, protocatechualdehyde (PA), polyvinyl alcohol (PVA), and sodium alginate (Alg). The hydrogel was crosslinked via multiple dynamic bonds and hydrogen bonds, avoiding the use of toxic crosslinking agents and eliminating the need for additional modification or purification steps. This approach enables the straightforward and efficient preparation of the hydrogel. The resulting hydrogel exhibits outstanding mechanical properties, with a tensile strength of 88.2 kPa. More importantly, compared with conventional PVA-Alg hydrogels crosslinked by glutaraldehyde or epichlorohydrin, our PVA-Alg/FP hydrogel demonstrates a diverse range of functional characteristics, including a high self-healing efficiency of 87.4 % within 10 min, as well as plasticity, ductility, adhesion, Deferoxamine mesylate (DFO)-responsive removal, and near-infrared (NIR) photothermal properties. Additionally, it demonstrates outstanding biocompatibility and a broad spectrum of biological activities, including antioxidant, anti-inflammatory, and antibacterial effects, as well as promoting cell migration. Furthermore, the hydrogel accelerates full-thickness skin wound healing in a Staphylococcus aureus(S.aureus)-infected rat model, providing compelling evidence of its potential as a therapeutic material for infection-induced wounds.

Facile fabrication of antibacterial membranes with human-friendly aloin for water purification

Currently, chemicals or nanoparticles are widely used for modifying membranes to improve their antifouling properties. However, the chemicals released, particularly during long-term water or wastewater filtration, are highly toxic to the environment and humans. Herein, an herb-inspired, green antibacterial membrane with exceptional sustainable antifouling properties was developed using aloin. The resultant membranes exhibited excellent bacterial inactivating efficiency because of the electrostatic interactions between the amine groups on the membrane and the bacterial cells, which contributed to cell deformation. The aloin molecules also significantly increased reactive oxygen species levels, causing oxidative damage to bacterial cells. Moreover, the functional decorative layer, which exhibited remarkable resistance to bacterial adhesion because of the abundant hydroxyl, carbonyl, and amino groups in aloin, endowed the as-prepared membranes with strong polarity, reducing bacterial adhesion and biofilm formation. When applied in a membrane bioreactor, the aloin-modified membranes demonstrated a > 27.0 % lower fouling rate than commercial microfiltration membranes. Overall, the successful fabrication strategy and material features described offer a green alternative for membrane development and provide new avenues for the design of healthcare materials such as wound dressings.

Hydrogel adhesives for tissue recovery

Hydrogel adhesives (HAs) are promising and rewarding tools for improving tissue therapy management. Such HAs had excellent properties and potential applications in biological tissues, such as suture replacement, long-term administration, and hemostatic sealing. In this review, the common designs and the latest progress of HAs based on various methodologies are systematically concluded. Thereafter, how to deal with interfacial water to form a robust wet adhesion and how to balance the adhesion and non-adhesion are underlined. This review also provides a brief description of gelation strategies and raw materials. Finally, the potentials of wound healing, hemostatic sealing, controlled drug delivery, and the current applications in dermal, dental, ocular, cardiac, stomach, and bone tissues are discussed. The comprehensive insight in this review will inspire more novel and practical HAs in the future.

Aminated Lignin/Cellulose-Based Hydrogel with High Adhesion for Wearable Sensors

Hydrogels play a significant role in the flexibility, stretchability, and conductivity of wearable sensors. However, it is still a challenge to achieve multifunctional hydrogel sensors with excellent mechanical strength, outstanding self-adhesion, and high stimulus responsiveness for meeting various demands of practical applications. Here, this work presents a one-pot method to prepare a conductive hydrogel with multifunction by introducing aminated lignosulfonate (A-LS) and aminated cellulose nanocrystals (A-CNC) into the hydrogel matrix. Benefiting from the synergistic effect of dynamic reversible noncovalent bond network with the introduction of nanoparticles in the system, the resultant hydrogel showed excellent mechanical properties. In addition, the prepared hydrogels exhibited remarkable adhesion strength (pig skin: 24 kPa) with sustainable adhesion, which still maintained an adhesion strength above 18 kPa after 20 cycles of adhesion/separation. The resultant hydrogel sensor showed a wide operating range (0-200%), high sensitivity (GF = 0.71 at 0-100% strain; GF = 3.15 at 100-200% strain), and fast response time (320 ms). The high-value utilization of renewable forest biomass resources is conducive to the sustainable development of green chemistry.

Mussel-inspired robust and waterproof soybean protein adhesives enhanced with phenolated lignosulfonate for wood bonding

Plant protein-based adhesives are favored for their cost-effectiveness and environmental friendliness. However, the low reactivity of plant protein and inherent water sensitivity of its adhesive significantly limits their scalability and broader application. Drawing inspiration from mussels, we developed a robust and waterproof bio-based adhesive reinforcing soybean protein (SP) with lignosulfonate. Specifically, the lignosulfonate was modified with phenol and epoxidated to synthesize phenolated lignin epoxy resin (PLEP), which was then added into SP matrix. The resulting adhesive demonstrated excellent bonding performance, with a dry shear strength of 3.59 MPa and a wet shear strength of 2.07 MPa. Finite Element Method (FEM) simulation confirmed a decreased stress concentration due to energy dissipation for the SP/PLEP. Furthermore, the adhesive exhibited an 81.22 % residual rate after water immersion. The adhesion strength was enhanced due to the π-π/cation-π interactions, hydrogen bonds, metal coordination of calcium ions, and covalent bonds formed by amino groups in proteins. Molecular dynamics (MD) analysis verified the enhancement of intermolecular interaction after phenolic modification. Life cycle assessment (LCA) revealed that the environmental impact of SP/PLEP adhesive was lower than that of urea-formaldehyde resin. This study presents a soybean-based adhesive inspired by mussel, offering a straightforward strategy for developing biomimetic adhesives.

AgNPs@Tea Polyphenol-Poly(acrylic acid) Hydrogel Dressing with Synergistic Antibacterial Action and Low Cytotoxicity

Bacterial infections pose a severe threat to human health, and excessive antibiotic use induces bacterial resistance. Although silver-containing nanoparticles exhibit excellent antimicrobial activity without inducing bacterial resistance, their significant cytotoxicity toward mammalian cells remains problematic. This study developed a AgNPs@tea polyphenol-poly(acrylic acid) (AgNPs@TPP-PAA) hydrogel wound dressing. Both silver nanoparticles (AgNPs) and reduced-state TPP demonstrated antibacterial properties. By leveraging the synergistic antibacterial effect between AgNPs and reduced-state TPP, the AgNPs@TPP-PAA hydrogel achieved equivalent antibacterial efficacy to AgNPs. This synergistic mechanism enables the AgNP concentration to be maintained at a low level with minimal cytotoxicity. In contrast to the TPP in the prepared AgNPs@TPP composite existed in an oxidized state, we demonstrated that photogenerated electrons from AgNPs combined with H+ ions dissociated from PAA could effectively reduce the oxidized TPP on the nanoparticle surfaces, thereby restoring their antimicrobial activity. This redox dynamic mechanism provides theoretical support for sustaining antibacterial performance while ensuring biosafety. Antimicrobial studies have shown that AgNPs@TPP-PAA hydrogel dressing has a 100% bactericidal efficiency against Escherichia coli and Staphylococcus aureus at 7.81 μg/mL silver. In AgNPs, it takes 15 μg/mL silver to achieve the same antibacterial effect. The cytotoxicity studies showed that the proliferation rate of L929 cells reached 76.32% for the AgNPs@TPP-PAA hydrogel, which contains 7.81 μg/mL silver. The synergistic antibacterial effect of TPP and silver reduces the silver content required for antibacterial activity, thus reducing the cytotoxicity of the materials.

A flexible multifunctional triboelectric nanogenerator based on bio-inspired nanocellulose/tannic acid@MXene-composited hydrogel for human healthcare

MXene-composited conductive hydrogels have received extensive attention in flexible, portable and self-powered wearable electronics based on triboelectric nanogenerators (TENGs). Yet, the incompatibility of the MXene with hydrogel matrix due to easy oxidation and weak interactions with polymer chains weakens the performance of hydrogels. Herein, inspired by the structure of leaves, tannic acid (TA) with abundant catechol groups was introduced to encapsulate MXene and TEMPO-oxidized cellulose nanofibers (TOCNF) was intercalated to support the MXene nanosheets as leaf vein, forming a stable TOCNF/TA@MXene nano-motif with three-dimensional (3D) network. Benefiting from the addition of TOCNF, TOCNF/TA@MXene exhibited long-term stability (>10 days) in aqueous environment with the presence of oxidant. Therefore, the obtained TOCNF/TA@MXene-composited hydrogel (PCM) exhibited high stretchability (>800 %), reliable fatigue resistance and good adhesiveness, which can be served as electrodes of flexible TENGs. The formed PCM-TENG demonstrated flexibility and versatility, achieving an open-circuit voltage of 106 V, a short-circuit current of ~2 μA and a transfer charge of ~31 nC even in a single-electrode mode. Besides, PCM-TENG showed enduring practicality and responsiveness as a self-powered sensor to detect human biomotions. PCM-TENG also presented desirable photothermal antibacterial capacity and cytocompatibility. All these properties endowed the PCM-TENG with great application potential in human healthcare.

Janus asymmetric galactomannan-based hydrogel with programmable deformation for accelerating wound healing

The development of an asymmetrical engineering dressing that accelerates wound closure is crucial for clinical applications. The hydrogel with a Janus structure that integrates thermo-responsive contraction and adhesive properties was fabricated through a robust cross-linked network of isopropylacrylamide and polyacrylamide, while a functional surface layer was created by cross-linking zwitterionic monomers and hyaluronic acid. The hydrogel exhibited superior tensile stress (80 Kpa), fracture strain (3000 %), tissue adhesiveness (35 Kpa) and high antibacterial activity (with a 99.9 % reduction in bacterial growth). The Janus hydrogel demonstrated significant thermal responsiveness and self-contraction properties, contributing to accelerated wound closure. In vivo experiments showed that the Janus hydrogel facilitated sutureless wound closure and enhanced wound healing through mechanical inward force, significantly improving wound contraction and promoting granulation tissue formation, as well as collagen deposition, resulting in 99 % wound healing efficiency by day 14. These results underscore the novel design of the Janus hydrogel as a multifunctional wound dressing, offering a unique combination of thermo-responsive and adhesive properties, along with excellent antibacterial and healing-promoting effects, making it a promising candidate for clinical wound repair.

Structural modification of oil palm lignin via steam explosion pre-treatment as a potential renewable green substitute in corrosion applications

This research demonstrates the significance of steam explosion pre-treatment on the structural and antioxidant properties of lignin-derived from oil palm fronds (OPF) biomass via organosolv pulping. The isolated lignin was distinguished as steam explosion acid impregnation ethanol organosolv lignin (SEA EOL), and steam explosion water impregnation ethanol organosolv lignin (SEW EOL), subsequently assessed through complementary analyses such as FTIR, NMR (1H, 13C, and 2D-HQSC), GPC, thermal analyses (TGA and DSC), and FRAP (antioxidant activity). SEA EOL appeared to exhibit superior lignin extraction compared to SEW EOL (% yield SEA EOL: 13.66 ± 0.35 % > % yield SEW EOL: 11.54 ± 0.33 %). Apart from that, SEA EOL also exhibited smaller lignin matrixes (Mw SEW EOL: 4693 gmol-1 > Mw SEA EOL: 1838 gmol-1), resulting in a higher phenolic hydroxyl content, S/G ratio, and enhanced antioxidant activity compared to SEW EOL. The preliminary rust conversion study of the artifact was conducted using SEA EOL, revealing that 7 wt% possessed the highest RT% with 95.45 ± 0.13 %. The XRD and surface analysis of the treated rust artifact indicated that the rust had been converted into an amorphous phase.

Photo - electrically responsive dual - network alginate-based composite hydrogels for the controlled release of plant essential nutrients

Hydrogel materials hold great potential in agriculture. In this study, a photo-electric controlled-release double-network hydrogel carrier was fabricated based on polyacrylamide (PAM) and sodium alginate (SA) with the montmorillonite (MMT). This double-network (DN) structure of Fe3+/SA-PAM-MMT (SPMFe3+) gel can efficiently improve stability of the carrier through radical polymerization and ion cross-linking reactions. The physicochemical properties of the composite hydrogels were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis, differential scanning calorimeter, rheometer, electronic universal testing machine and scanning electron microscopy. The SPMFe3+ gel carriers exhibit excellent mechanical properties and photo-electric responsiveness, attributed to their double-network structure and incorporation of MMT. The pore size of the SPM - Fe3+ gel expands under an electric field due to the Coulomb force of carboxyl group on the SA chain. Additionally, the structure of SPMFe3+ was broken under UV-irradiation due to the photochemical reaction of Fe3+-SA. The release of urea is regulated by this photoelectrochemical stimulus - responsive mechanism. Therefore, this work provides a promising approach to prepare dual-responsive controlled-release carriers and demonstrates that SPM-Fe3+-5 % double-network hydrogel has potential applications in controlled-release fertilizers.

Lignocellulose nanofiber-enhanced hydrogel electrolytes with lignin-Al3+ in metal-based neutral deep eutectic solvent for flexible supercapacitors

The mechanical flexibility and high conductivity of hydrogel electrolytes are crucial for their application in supercapacitors. In this study, we developed hydrogel electrolyte based on lignocellulose nanofibers (LCNFs) through nanofibrillation and self-catalytic gelation in a glycerinum/choline chloride/aluminum chloride hexahydrate (Gly/ChCl/AlCl3·6H2O) metal-based neutral deep eutectic solvent (DES) system. The lignin-Al3+ self-catalytic mechanism offered an eco-friendly and sustainable method for synthesizing hydrogel electrolytes, while enhancing their ionic conductivity. The high aspect ratio of LCNFs significantly improved the mechanical strength of the hydrogel electrolyte by facilitating the intertwining of LCNFs with acrylamide molecules. The resulting hydrogel electrolyte demonstrated exceptional mechanical strength (485 kPa), high ionic conductivity (26.1 ms/cm), strong adhesion (225 kPa), and excellent environmental stability (up to -80 °C). A supercapacitor assembled with this hydrogel showed a remarkable specific capacitance (200 F/g) and exhibited high sensitivity in electrical signal applications. This work demonstrates the transformation of wood fiber into functional lignocellulose-based materials, highlighting the high-value utilization of lignocellulose resources for energy storage and other applications.

From waste to wonder: Biomass-derived nanocellulose and lignin-based nanomaterials in biomedical applications

Cellulose and lignin, as the most abundant biomass resources in nature, have been widely utilized in conventional industry. While their high-value potential remained underexplored for decades, recent advancements in nanotechnology and processing techniques have revealed their unique physicochemical properties, biocompatibility, and optical characteristics at the nanoscale, sparking significant interest in biomedical applications. Nanocellulose (NC), characterized by its high surface area, superior mechanical strength, and excellent biocompatibility, holds great promise in drug delivery, wound dressing, and tissue engineering. Similarly, lignin nanoparticles (LNPs) and lignin-based carbon quantum dots (L-CQDs), known for their multi-functionality, low toxicity, and outstanding fluorescence properties, emerge as sustainable alternatives for bio-imaging and bioanalytical detection. This review provides an overview of the hierarchical structure of biomass resources, details the preparation methods of cellulose- and lignin-based nanomaterials, and highlights their advancements in biomedical applications. Furthermore, it addresses the challenges and limitations associated with the clinical applications of these nanomaterials, offering insights and guidance for future research and development.

Plant Polyphenol-Based Injectable Hydrogels: Advances and Biomedical Applications

Plant polyphenol-based hydrogels, known for their biocompatibility and adhesive properties, have emerged as promising materials in biomedical applications. These hydrogels leverage the catechol group's ability to form stable bonds in moist environments, similar to mussel adhesive proteins. This review provides a comprehensive overview of their synthesis, adhesion mechanisms, and applications, particularly in wound healing, tissue regeneration, and drug delivery. However, challenges related to in vivo stability and long-term biocompatibility remain critical barriers to clinical translation. Future research should focus on enhancing the bioactivity, biocompatibility, and scalability of these hydrogels, while addressing concerns related to toxicity, immune responses, and large-scale manufacturing. Advances in artificial intelligence-assisted screening and 3D/4D bioprinting are expected to accelerate their development and clinical translation. Furthermore, the integration of biomimetic designs and responsive functionalities, such as pH or temperature sensitivity, holds promise for further improving their therapeutic efficacy. In conclusion, the development of multifunctional plant polyphenol-based hydrogels represents a promising frontier in advancing personalized medicine and minimally invasive treatments.

Microencapsulation of sacha inchi oil using tannic acid, yeast cells and xanthan gum as wall materials

This study investigated the encapsulation of sacha inchi oil using complex coacervation of recovered yeast cells and xanthan gum via double emulsion. Turbidimetric analysis revealed interactions between yeast cells (YC) and tannic acid (TA), which increased turbidity to a 1:3 YC:XG ratio suggesting that TA could be a promising crosslinking agent for enhancing coacervation. Optimal encapsulation efficiency was achieved at a core-to-wall ratio of 1:1 in a core solution concentration of 1 % relative to the total polymer concentration. Under these conditions, the microparticles exhibited an average particle size of 72.44 ± 1.83 μm, with low water activity and water solubility. Morphological analysis suggests that the microcapsules showed a heterogeneous structure formed by different layers of wall material, potentially making them suitable for use in food matrices. The use of TA to form TA-YC:XG microcapsules improved the oxidative stability (39.84 ± 0.43 meqO2/kg of peroxide value after six simulated months) of the microcapsules and slowed down oil release (approximately 20 % in simulated gastric fluid) during the in vitro digestion test. These finds highlight the potential of microencapsulation using recovered yeast cells as a strategy to enhance encapsulation efficiency and protect against oxidation and digestion challenges. This approach opens new possibilities for the use of sacha inchi oil as a food ingredient.

An Autonomously Liquefied Hydrogel Adhesive for Programmable Bioelectronic Interface

Hydrogel adhesives have many important applications in the fields of drug delivery, regenerative medicine, and bioelectronics. The detachment of hydrogel adhesives under the benign conditions is vital to the definitive surgical repair and implanted devices. Although stimuli-mediated detachment of hydrogel adhesives has been achieved, it is still a grand challenge to develop a transient adhesive with programmable adhesion and autonomous detachment from the substrate, especially the hairy skins. Here, we report a transient hydrogel adhesive driven by antagonistic enzyme reaction networks for programmable bioelectronic interface. The transient hydrogel shows tunable mechanical properties, adjustable adhesive strength, and autonomous sol-gel-sol transition with a programmable lifetime. Moreover, the transient hydrogel adhesive enables conformable and stable adhesion to various materials. In particular, the bioelectrode coated by the transient hydrogel adhesive allows to record stable and high-quality electromyogram, electrocardiogram, and electroencephalogram signals directly on the hairy skins without hair shaving. Notably, the autonomous liquefication of the hydrogel adhesives enables the easy removal of bioelectrode from hairy skins after usage without any noticeable damages to the hairy skins and electrode. This work paves a new avenue in the innovative development of hydrogel adhesives for the conformable and detachable bioelectronic interface.

Scalable Preparation of Polyzwitterionic Hydrogels Based on Hydration Shielding-Accelerated Redox Self-Catalytic Polymerization (HS-A-RP)

Traditional synthesis methods for polyzwitterionic hydrogels involve harsh conditions, such as thermal or UV irradiation, prolonged durations, and high monomer concentrations. Herein, we address these challenges at the meantime by proposing a novel chemical method, called hydration-shielding accelerated self-catalytic polymerization (HS-A-RP), facilitating the preparation of polyzwitterionic hydrogels. The discovery is that polyvinyl alcohol (PVA) chains can generate hydration shielding around hydrated zwitterionic monomers, promoting their effective aggregation and rapid crosslinking polymerization under the assistance of silver ions (Ag+)-potassium persulfate (S2O8 2-) redox catalyst. The HS-A-RP method performs under mild condition (-5 °C to 37 °C) without extra energy, overcomes the critical monomer polymerization concentration limitation (wt%: 0.3%), and completes within an ultrashort polymerization time (<60 s). The prepared polyzwitterionic hydrogels possesses a denser network and superior mechanical properties compared to those prepared by traditional thermal/UV methods, exhibiting good antiswelling behavior, excellent lubrication performance, and significant antibacterial and anti-fouling properties. These significant advances endow HS-A-RP with attractive application potentials in manufacturing functional hydrogel coatings for biomedical device, in situ encapsulation of thermally sensitive materials, and excellent sand fixation abilities. Moreover, HS-A-RP method is suitable for scalable manufacture and decorative coating of polyzwitterionic hydrogels on diverse substrates in extreme environmental conditions.

Fast fabrication of stimuli-responsive MXene-based hydrogels for high-performance actuators with simultaneous actuation and self-sensing capability

Poly(N-isopropylacrylamide) (PNIPAM) composite hydrogels have recently emerged as promising candidates for soft hydrogel actuators. However, developing a facile and fast method to obtain multifunctional PNIPAM hydrogel actuators with simulating biological versatility remains a major challenge. Herein, we developed a fast-redox initiation system to prepare PNIPAM/sodium carboxymethyl cellulose (CMC)/T3C2Tx MXene nanocomposite hydrogel with multidirectional actuating behaviors and improved mechanical properties. The rapid thermoresponsive behavior of the PNIPAM/CMC/MXene layer bestows its corresponding bilayer actuator with an extraordinary actuation speed of 9.36°/s in hot water. Owing to the high photothermal conversion of MXenes, this PNIPAM/CMC/MXene hydrogel displays a range of remote-controlled actuations upon NIR light irradiation, including bending, rolling, displacement, and simulations of the sea eel's hunting behaviors in a water environment. More importantly, based on the excellent electrical properties of MXene, the PNIPAM/CMC/MXene-based hydrogel actuators have accomplished a self-sensing function by integrating the surface temperature-bending angle-the relative resistance changes during the NIR light-driven actuation process. The photothermal actuator's integrated actuation and sensing capabilities have facilitated the feedback of the contact and movement dynamics of the bioinspired artificial tongue. The straightforward preparation and multifunctional design of MXene-based hydrogel may facilitate the development of soft smart actuators.

Construction of environmentally stable self-adhesive conductive cellulose hydrogel for electronic skin sensor via autocatalytic fast polymerization strategy at room temperature

Bio-based conductive hydrogels are catching a widespread attention in the field of flexible sensors and human-machine interface interaction. Here, an enhanced autocatalytic system constructed from dopamine-encapsulated cellulose nanofibers (DA@CNF) and Cu2+ in a glycerol-water binary solvent achieved fast auto-polymerization of hydrogels within 60 s. X-ray photoelectron spectra (XPS), UV-vis spectrum (UV), Cyclic Voltammetry (CV) and electron paramagnetic resonance (EPR) were used to characterize the autocatalytic system. The hydrogel obtained has excellent mechanical properties (strain >900 %, compressive strength >800 kPa, toughness >700 kJ/m3), reproducible adhesive properties (>10 times), excellent high and low temperature (-20-60 °C) adaptability and stability. And the excellent electrical conductivity endows the hydrogel with high strain sensitivity (GF = 5.15) over a wide strain range (400 %). The excellent overall performance ensures the stability and accuracy of the hydrogel as a flexible electronic skin for signal detection during human-computer interface interaction. This work contributes a new research strategy for the rational design and green development of biomass-based conductive hydrogel sensors.

Catechol-based chemistry for hypoglycemia-responsive delivery of zinc-glucagon via hydrogel-based microneedle patch technology

Hypoglycemia is a serious and potentially life-threatening condition for people with insulin-dependent diabetes. To provide a safeguard against hypoglycemia, we introduce a "smart" microneedle (MN) patch that senses glucose levels and delivers a blood glucose-raising agent (Zinc-Glucagon (Z-GCN)) in response to hypoglycemia. Herein, we describe the use of catechol and boronic acid chemistry to design a self-crosslinkable hydrogel-based MN that stimulates the release of Z-GCN during hypoglycemia. In this design, the catechol groups bind to Z-GCN through metal-ligand complexation. At hyperglycemia, boronic acids react with glucose to generate cyclic boronate esters. As the glucose concentration decreases, the boronic acid groups dissociate and are favored over Z-GCN in binding with catechol, which promotes the release of Z-GCN. We fully characterize the fabricated MN in vitro. Moreover, we further evaluate the MN and demonstrate the in vivo glucose-responsive delivery of Z-GCN from the patch. We also show its effectiveness in preventing hypoglycemia for up to 6 h in type 1 diabetic male rats against two consecutive insulin overdose challenges. Since many proteins/peptides have a high binding affinity to metal ions, the introduced mechanism driven by the competitive binding of catechol-metal ions has great implications in drug delivery applications of various protein/peptide-based therapeutics.

4D printing biological stimuli-responsive hydrogels for tissue engineering and localized drug delivery applications - part 1

INTRODUCTION

The advent of 3D printing has revolutionized biomedical engineering, yet limitations in creating dynamic human tissues remain. The emergence of 4D printing, which introduces time as a fourth dimension, offers new possibilities by enabling the production of adaptable, stimuli-responsive structures. A thorough literature search was performed across various databases, including Google Scholar, PubMed, Scopus, and Web of Science, to identify pertinent studies published up to 2025. The search parameters were confined to articles published in English that concentrated on peer-reviewed clinical studies.

AREAS COVERED

This review explores the transition from 3D to 4D printing and focuses on stimuli-responsive materials, particularly hydrogels, which react to environmental changes. The literature search examined recent studies on the interaction of these materials with biological stimuli, emphasizing their application in tissue engineering and drug delivery applications.

EXPERT OPINION

4D printing, combined with smart materials, holds immense promise for advancing biomedical treatments, including customized therapies and regenerative medicine. However, technological challenges must be addressed to realize its full potential.

Bioactive silver nanoparticles derived from Carica papaya floral extract and its dual-functioning biomedical application

Replacing synthetic phytochemicals with natural plant extracts for metal nanoparticle synthesis enable cost-effective, large-scale production with reduced environmental and health risks while enhancing biomedical efficacy. This study presents the green synthesis of silver nanoparticles (AgNPs) using a flavonol-enriched extract from male papaya flowers (KQE), an underutilized agricultural waste. Using 20% (v/v) KQE, highly stable, spherical KQ-AgNPs (12.3 ± 3.0 nm) were synthesized via in-situ generation of free radicals, such as ortho-quinones, which reduced Ag+ ions. KQ-AgNPs exhibit superior antibacterial activity against both gram-positive and gram-negative bacteria compared to chemically synthesized AgNPs (AgNPs-Chem) and KQE alone. In vitro anticancer assays reveal enhanced cytotoxicity against breast carcinoma cells (MCF-7) with an IC50 of 21.25 ± 1.14 µg/mL, significantly lower than AgNPs-Chem (33.05 ± 3.13 µg/mL), while maintaining high biocompatibility with normal cells (HEK-293) with a greater IC50 of 169.96 ± 2.3 µg/mL. This study highlights the dual therapeutic potential of KQ-AgNPs, emphasizing their enhanced antibacterial and anticancer efficacy while exemplifying an innovative waste-to-wealth approach.

Solvent-free processing of lignin into robust room temperature phosphorescent materials

Producing room temperature phosphorescent (RTP) materials from biomass resources using a solvent free method is essential but hard to achieve. Here, we discovered that lignin dissolved well in the liquid monomer, 2-hydroxyethyl acrylate (HEA), due to extensive hydrogen bonding and non-bonding interactions between lignin and HEA. Motivated by this discovery, we developed a solvent free system consisting of HEA and urethane dimethacrylate (UDMA) for converting lignin into RTP materials. With this design, lignin generated radicals upon UV irradiation, which initiated the polymerization of HEA (as monomer) and UDMA (as crosslinker). The as-obtained polymer network rigidifies lignin and activates the humidity/water-resistant RTP of lignin with a lifetime of 202.9 ms. Moreover, the afterglow color was successfully tuned to red after loading with RhB via energy transfer (TS-FRET). Using these properties, the as-developed material was used as photocured multiple-emission RTP inks, luminescent coatings and a smart anti-counterfeiting logo for a medicine bottle.

Antibacterial and Osteogenesis Promotion of Bionic Extracellular Matrix Implant Coating Based on Gallic Acid Self-Assembly

Oral health problems, particularly tooth defects, can significantly affect people's quality of life and overall well-being. The development of titanium (Ti) dental implants has largely replaced natural tooth roots to prevent periodontal and gastrointestinal diseases. However, challenges such as postoperative bacterial infections and poor osseointegration continue to hinder progress in dental implant technology. To tackle these issues, we used hydroxypropyl trimethylammonium chloride chitosan (HACC) and gallic acid-modified gelatin (GAG) to create extracellular matrix (ECM) coatings on titanium using layer-by-layer self-assembly. GAG showed better water solubility at room temperature, being over 99.0 times more soluble than regular gelatin. In vivo and in vitro analyses of the ECM coatings revealed their antibacterial properties and their ability to promote osteogenic differentiation, resulting in over 31.5 times more calcareous deposits than Ti. This strategy shows potential for improving oral health and reducing the complications associated with dental implants in clinical settings.

Intrinsically Adhesive and Conductive Hydrogel Bridging the Bioelectronic-Tissue Interface for Biopotentials Recording

Achieving high-quality biopotential signal recordings requires soft and stable interfaces between soft tissues and bioelectronic devices. Traditional bioelectronics, typically rigid and dependent on medical tape or sutures, lead to mechanical mismatches and inflammatory responses. Existing conducting polymer-based bioelectronics offer tissue-like softness but lack intrinsic adhesion, limiting their effectiveness in creating stable, conductive interfaces. Here, we present an intrinsically adhesive and conductive hydrogel with a tissue-like modulus and strong adhesion to various substrates. Adhesive catechol groups are incorporated into the conductive poly(3,4-ethylenedioxythiophene) (PEDOT) hydrogel matrix, which reduces the PEDOT size and improves dispersity to form a percolating network with excellent electrical conductivity and strain insensitivity. This hydrogel effectively bridges the bioelectronics-tissue interface, ensuring pristine signal recordings with minimal interference from bodily movements. This capability is demonstrated through comprehensive in vivo experiments, including electromyography and electrocardiography recordings on both static and dynamic human skin and electrocorticography on moving rats. This hydrogel represents a significant advancement for bioelectronic interfaces, facilitating more accurate and less intrusive medical diagnostics.

Bioinspired hierarchical porous tough adhesive to promote sealing of high-pressure bleeding

Timely and stable sealing of uncontrolled high-pressure hemorrhage in emergency situations outside surgical units remains a major clinical challenge, contributing to the high mortality rate associated with trauma. The currently widely used hemostatic bioadhesives are ineffective for hemorrhage from major arteries and the heart due to the absence of biologically compatible flexible structures capable of simultaneously ensuring conformal tough adhesion and biomechanical support. Here, inspired by the principle of chromatin assembly, we present a tissue-conformable tough matrix for robust sealing of severe bleeding. This hierarchical matrix is fabricated through a phase separation process, which involves the in-situ formation of nanoporous aggregates within a microporous double-network (DN) matrix. The dispersed aggregates disrupt the rigid physical crosslinking of the original DN matrix and function as a dissipative component, enabling the aggregate-based DN (aggDN) matrix to efficiently dissipate energy during stress and achieve improved conformal attachment to soft tissues. Subsequently, pre-activated bridging polymers facilitate rapid interfacial bonding between the matrix and tissue surfaces. They synergistically withstand considerable hydraulic pressure of approximately 700 mmHg and demonstrate exceptional tissue adhesion and sealing in rat cardiac and canine aortic hemorrhages, outperforming the commercially available bioadhesives. Our findings present a promising biomimetic strategy for engineering biomechanically compatible and tough adhesive hydrogels, facilitating prompt and effective treatment of hemorrhagic wounds.

Wet adhesives for hard tissues

The development of wet adhesives capable of bonding in aqueous environments, particularly for hard tissues such as bone, tooth, and cartilage, remains a significant challenge in material chemistry and biomedical research. Currently available hard tissue adhesives in clinical practice lack well-defined wet adhesion properties. Nature offers valuable inspiration through the adhesive mechanisms of marine organisms, advancing the design of bioinspired wet adhesives. Beyond biomimetic approaches, alternative strategies have emerged for the design of wet adhesives. This review systematically summarizes the current design strategies for wet adhesives, focusing on their applications to hard tissues. Then, the unique chemical, physical, mechanical, and biological requirements for wet adhesives applied to hard tissues are also discussed. The importance of understanding natural adhesion mechanisms and the need for high-performance materials that can meet the complex demands of hard tissue adhesion in a complex and delicate physiological microenvironment are highlighted. Finally, this review clarifies the future research directions that can further facilitate the clinical application of wet adhesives for hard tissues. STATEMENT OF SIGNIFICANCE: The significance of this review lies in its comprehensive analysis of wet adhesives for hard tissues, a field that has been largely overlooked despite its critical importance in biomedical applications. The insights gained from studying natural adhesives and the translation of these mechanisms into synthetic materials have the potential to revolutionize medical procedures involving hard tissue repair and regeneration. This review meticulously addresses the distinct challenges and specific requirements of hard tissue adhesives, providing an exhaustive roadmap for researchers striving to develop wet adhesives that can endure the demanding physiological conditions inside the human body. In doing so, it aims to facilitate the transition from laboratory findings to practical clinical applications.

Adhesive and Conductive Hydrogels for the Treatment of Myocardial Infarction

Myocardial infarction (MI) is a leading cause of mortality among cardiovascular diseases. Following MI, the damaged myocardium is progressively being replaced by fibrous scar tissue, which exhibits poor electrical conductivity, ultimately resulting in arrhythmias and adverse cardiac remodeling. Due to their extracellular matrix-like structure and excellent biocompatibility, hydrogels are emerging as a focal point in cardiac tissue engineering. However, traditional hydrogels lack the necessary conductivity to restore electrical signal transmission in the infarcted regions. Imparting conductivity to hydrogels while also enhancing their adhesive properties enables them to adhere closely to myocardial tissue, establish stable electrical connections, and facilitate synchronized contraction and myocardial tissue repair within the infarcted area. This paper reviews the strategies for constructing conductive and adhesive hydrogels, focusing on their application in MI repair. Furthermore, the challenges and future directions in developing adhesive and conductive hydrogels for MI repair are discussed.

NaOH/urea aqueous solution facilitates spectroscopic quantitation of lignin in corn stalk

A facile spectrometric determination of lignin in corn straw was constructed through dissolving the lignin-carbohydrate complex in aqueous solution at room temperature, where NaOH/urea was induced to prepare a transparent aqueous solution of carbohydrate-linked lignin for quantification at 298 nm without any interference from the carbohydrate.

Robust-adhesion and high-mechanical strength hydrogel for efficient wet tissue adhesion

Bioadhesive hydrogels show great promise in wound closure due to their minimally invasive nature and ease of use. However, they typically exhibit poor wet adhesion and mechanical properties on wet tissues. Herein, a ready-to-use bioadhesive hydrogel (denoted as PAA-NHS/C-CS) with rapidly robust adhesion and high mechanical strength is developed via a simple one-pot UV crosslinking polymerization of acrylic acid (AA), catechol-functionalized chitosan (C-CS), and acrylic acid N-hydroxysuccinimide ester (AA-NHS ester). Benefitting from the hydrogen bonds and electrostatic attractions formed between PAA-NHS and C-CS, the as-prepared hydrogel exhibits high tensile strength (∼630 kPa), fracture strain (∼1950%), and toughness (∼4250 kJ m-3) in the fully swollen state. Besides, the noncovalent interactions and covalent crosslinking formed between the dual adhesive moieties (the NHS ester and catechol groups) and the tissue surface endow the hydrogel with high shear strength (∼160 kPa), interfacial toughness (∼630 J m-2), and burst pressure (∼447 mmHg) on wet porcine skin. By integrating the high mechanical properties, rapid robust adhesion, and operational convenience, the as-prepared PAA-NHS/C-CS hydrogel shows great promise in wound closure.

Green Manufacture of Hydrated Polymers Coatings with On-Demand Mechanics and Lubricity Based on Novel Biobased Polymerizable Deep Eutectic Solvents

The aging population necessitates a critical need for medical devices, where polymers-based surface lubrication coating is essential for optimal functionality. In fact, lubrication and mechanical requirements vary depending on the service environment of different medical devices. Until now, key mean is still blank for general preparation of hydrophilic polymers-based lubrication coatings with on-demand mechanics and lubricity. This study introduces a novel hydrophilic lubrication coating with tunable mechanical properties and lubricity, derived from eco-friendly polymerizable deep eutectic solvents (PDESs) containing betaine, hydroxyethyl acrylate, glycerol, and tannic acid. Unlike traditional high molecular weight polymers, this approach leverages small-molecule, high-biobased PDESs, thereby simplifying the synthesis process. The resulting coating demonstrates exceptional adhesion to a range of medical device materials─including glass, stainless steel, polyvinyl chloride, and polyurethane─thanks to the high content of hydroxyl groups and pyrogallol motifs from tannic acid. It also enables the precise tuning of mechanical strength, modulus, adhesion, hydrophilicity, and lubrication properties by varying the amounts of glycerol and tannic acid. Furthermore, the coating undergoes a hydration-induced transition from high-strength, high-friction to low-strength, low-friction states, maintaining repeatable performance. Additionally, the synergistic effects of betaine and tannic acid in the PDES contribute to its notable antimicrobial properties. In summary, these PDESs demonstrate significant potential for enhancing lubrication in a range of biomedical devices.

Metal-phenolic network biointerface-mediated cell regulation for bone tissue regeneration

Bone tissue regeneration presents a significant challenge in clinical treatment due to inadequate coordination between implant materials and reparative cells at the biomaterial-bone interfaces. This gap underscores the necessity of enhancing interaction modulation between cells and biomaterials, which is a crucial focus in bone tissue engineering. Metal-polyphenolic networks (MPN) are novel inorganic-organic hybrid complexes that are formed through coordination interactions between phenolic ligands and metal ions. These networks provide a multifunctional platform for biomedical applications, with the potential for tailored design and modifications. Despite advances in understanding MPN and their role in bone tissue regeneration, a comprehensive overview of the related mechanisms is lacking. Here, we address this gap by focusing on MPN biointerface-mediated cellular regulatory mechanisms during bone regeneration. We begin by reviewing the natural healing processes of bone defects, followed by a detailed examination of MPN, including their constituents and distinctive characteristics. We then explore the regulatory influence of MPN biointerfaces on key cellular activities during bone regeneration. Additionally, we illustrate their primary applications in addressing inflammatory bone loss, regenerating critical-size bone defects, and enhancing implant-bone integration. In conclusion, this review elucidates how MPN-based interfaces facilitate effective bone tissue regeneration, advancing our understanding of material interface-mediated cellular control and the broader field of tissue engineering.

Lignin nanoparticle/MXene-based conductive hydrogel with mechanical robustness and strain-sensitivity property via rapid self-gelation process towards flexible sensor

Conductive hydrogels have been showcased with substantial potential for soft wearable devices. However, the tedious preparation process and poor trade-off among overall properties, i.e., mechanical and sensing performance, severely limits flexibility of electronics' applications. Herein, we have developed a rapid self-gelation system for achieving high-performance conductive hydrogel within several minutes at ambient condition. The rapid gelation mechanism is attributed to the hydroxyl radical species generated with the help of lignin nanoparticle-Mn+1 (Ag+, Ca2+, Mg2+, Al3+ and Fe3+) based on reversible redox reaction and MXene activization effect. By adjusting the material components, the cross-linked polymer network can be highly strengthened by multiple physical interactions and nano-reinforcement, strongly supporting the mechanical performance. Comparatively, Fe3+-based conductive hydrogel displays integrated merits of mechanical robustness, high stretchability and good electrical conductivity. Meanwhile, due to excellent mechanical and electrical performance, such hydrogel-based sensor possesses good sensing performance, i.e., high sensitivity (maximum GF: 1.08), cyclic reliability and wide work window (0-860 %), displaying promising application in strain-induced detection. Our sensors also produce stable and reliable signal output for signature/vocal recognition. Apparently, the strategy developed herein sets up an innovative concept for highly-efficient green fabricating advanced hydrogel materials for emerging wearable electronics.

Strong, tough, antibacterial, antioxidant, biodegradable multi-functional intelligent hydrogel film for real-time detection and maintenance of salmon freshness

In this study, we prepared a new multi-functional intelligent hydrogel preservation film using soy hull nanocellulose (SHNC), polyvinyl alcohol (PVA), chitosan (CS), and anthocyanin (Anth) as raw materials. The physicochemicals of the hydrogel preservation film, and its role in monitoring the freshness and freshness of salmon was evaluated. The results showed that the monomers were crosslinked by hydrogen, ester bonds, and electrostatic interactions in the hydrogel film, and there were three-dimensional pores in the hydrogel film. Meanwhile, SHNC/PVA/CS/Anth-3 exhibited excellent mechanical properties (elongation: 345.26 %; tensile strength: 26.84 MPa; compressive strength: 139.27 MPa) and excellent biodegradation performance. Additionally, the hydrogel film displayed excellent antioxidant and antibacterial properties (90.59 %). The preservation experiment showed that, at 4 °C, the hydrogel film could not only inhibit the growth and reproduction of bacteria on the surface of salmon meat, but it could also detect the freshness of salmon meat in real time, Meanwhile, the film could extend the shelf life of salmon meat from 6 d to 14 d. This study provides a new perspective for constructing a multi-functional intelligent hydrogel preservation film.

Novel functional hydrogels based on lignin‑silver nanoparticles with adhesion, antimicrobial, antioxidant and anti-freezing properties for wound dressings and pressure strain sensors

As wound dressings and wearable electronics advance, it is critical to develop an efficacious strategy for integrating a variety of powerful functions into hydrogels. In this work, sodium lignosulfonate‑silver nanoparticles and the functional [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide structure (SBMA) are introduced into the multifunctional lignin-based hydrogel system. The sodium lignosulfonate‑silver nanoparticles, by catalyzing multiple redox reactions, facilitate the swift curing of hydrogels at room temperature. This process is advantageous for the structural refinement of hydrogel polymer segments and the integration of multiple functionalities. The synergistic effect of functional structure and nanoparticles bestows the hydrogel with superior adhesion, mechanical properties, antimicrobial properties and antioxidant properties. The introduction of a functional structure not only deferments the release of sodium lignosulfonate‑silver nanoparticles, but also imparts satisfactory conductivity and anti-freezing properties to the hydrogels. In applications related to wound dressings and pressure strain sensors, hydrogels demonstrate excellent potential. They effectively facilitate wound healing and enable the monitoring of limb movement. This work introduces a simple and effective approach to prepare lignin-based functional hydrogels, exhibiting significant potential for wound dressings and pressure strain sensors applications.

Tough Polyurethane Hydrogels with a Multiple Hydrogen-Bond Interlocked Bicontinuous Phase Structure Prepared by In Situ Water-Induced Microphase Separation

Hydrogels with mechanical performances similar to load-bearing tissues are in demand for in vivo applications. In this work, inspired by the self-assembly behavior of amphiphilic polymers, polyurethane-based tough hydrogels with a multiple hydrogen-bond interlocked bicontinuous phase structure through in situ water-induced microphase separation strategy are developed, in which poly(ethylene glycol)-based polyurethane (PEG-PU, hydrophilic) and poly(ε-caprolactone)-based polyurethane (PCL-PU, hydrophobic) are blended to form dry films followed by water swelling. A multiple hydrogen bonding factor, imidazolidinyl urea, is introduced into the synthesis of the two polyurethanes, and the formation of multiple hydrogen bonds between PEG-PU and PCL-PU can promote homogeneous microphase separation for the construction of bicontinuous phase structures in the hydrogel network, by which the hydrogel features break strength of 12.9 MPa, fracture energy of 2435 J m-2, and toughness of 48.2 MJ m-3. As a biomedical patch, the outstanding mechanical performances can withstand abdominal pressure to prevent hernia formation in the abdominal wall defect model. Compared to the commercial PP mesh, hydrogel can prevent tissue/organ adhesion to reduce inflammatory responses and promote angiogenesis, thereby accelerating the repair of abdominal wall defects. This work may provide useful inspiration for researchers to design different gel materials through solvent-induced microphase separation.

Multi-crosslinked strong, tough and anti-freezing organohydrogels for flexible sensors

Hydrogels are promising sensing materials for various smart and biocompatible applications; nevertheless, it is still challenging to enhance their mechanical property and stability in wide temperature windows and under extreme conditions (such as dry and swelling states). Herein, we report a strong, tough, anti-freezing and anti-dehydration organohydrogel achieved by designing a dual-network structure with multi-crosslinking interactions. The interpenetrated poly (vinyl alcohol) (PVA) chains and poly[N,N-dimethyl(methylacrylethyl)ammonium propane sulfonate] (PDMAPS)/polyacrylamide (PAM) block copolymer chains provided abundant hydrogen bonds and cation-anion dipole interactions; besides, dimethyl sulfoxide and CaCl2 were added to further improve the mechanical properties as well as facilitate the conductivity and anti-freezing property of the organohydrogel. By systematically optimizing the multi-interactions among these components, the organohydrogel achieved high tensile strength (2.7 MPa), high stretchability (630%), and considerable ionic conductivity (2.4 mS cm-1 at RT). More importantly, it achieved remarkable stability in a wide temperature range of -40 to 80 °C. Moreover, organohydrogel sensors in resistive and triboelectric nanogenerator (TENG) modes were demonstrated for strain/temperature sensing and non-contact distance/material sensing, respectively, suggesting their great potentials in flexible electronics in the future.

Lignin alkali regulated interfacial polymerization towards ultra-selective and highly permeable nanofiltration membrane

Thin-film composite polyamide (TFC PA) membranes hold promise for energy-efficient liquid separation, but achieving high permeance and precise separation membrane via a facile approach that is compatible with present manufacturing line remains a great challenge. Herein, we demonstrate the use of lignin alkali (LA) derived from waste of paper pulp as an aqueous phase additive to regulate interfacial polymerization (IP) process for achieving high performance nanofiltration (NF) membrane. Various characterizations and molecular dynamics simulations revealed that LA can promote the diffusion and partition of aqueous phase monomer piperazine (PIP) molecules into organic phase and their uniform dispersion on substrate, accelerating the IP reaction and promoting greater interfacial instabilities, thus endowing formation of TFC NF membrane with an ultrathin, highly cross-linked, and crumpled PA layer. The optimal membrane exhibited a remarkable water permeance of 26.0 L m-2 h-1 bar-1 and Cl-/SO42- selectivity of 191.0, which is superior to the state-of-the-art PA NF membranes. This study provides a cost-effective scalable strategy for fabricating ultra-selective and highly permeable NF membrane for precise ion-ion separation and small organic compounds removal.

A natural polyphenolic nanoparticle--knotted hydrogel scavenger for osteoarthritis therapy

Exploring highly efficient and cost-effective biomaterials for osteoarthritis (OA) treatment remains challenging, as current therapeutic strategies are difficult to eradicate the excessive reactive oxygen species (ROS) and nitric oxide (NO) at damaged sites. Tea polyphenol (TP) nanoparticles (NPs), a nature-inspired antioxidant in combination with 2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO), a NO scavenger, could provide maximized positive therapeutic effects on OA by eradicating both ROS and NO. Notably, this combination not only improves the half-life of the TP monomer and the drug loading efficiency of carboxy-PTIO but also prevents nitrite from being harmful to tissue. Moreover, the protonation ability of carboxy-PTIO allows smart acid-responsive release in response to environmental pH, which provides conditioned treatment strategies for OA. In in vitro experiments, TP/PTIO NPs downregulated proinflammatory cytokine release via synergistic removal of ROS and NO and suppression of ROS/NF-κB and iNOS/NO/Caspase-3 signaling. For in vivo experiments, NPs were cross-linked with 4-arm-PEG-SH to form an injectable hydrogel system. The release of TP and carboxy-PTIO from the system efficiently prevents cartilage inflammation and damage via similar signaling pathways. Overall, the proposed system provides an efficient approach for OA therapy.

Multifunctional Adhesive Hydrogels: From Design to Biomedical Applications

Adhesive hydrogels characterized by structural properties similar to the extracellular matrix, excellent biocompatibility, controlled degradation, and tunable mechanical properties have demonstrated significant potential in biomedical applications, including tissue engineering, biosensors, and drug delivery systems. These hydrogels exhibit remarkable adhesion to target substrates and can be rationally engineered to meet specific requirements. In recent decades, adhesive hydrogels have experienced significant advancements driven by the introduction of numerous multifunctional design strategies. This review initially summarizes the chemical bond-based design strategies for tissue adhesion, encompassing static covalent bonds, dynamic covalent bonds, and non-covalent interactions. Subsequently, the multiple functionalities imparted by these diverse design strategies, including highly stretchable and tough performances, responsiveness to microenvironments, anti-freezing/heating properties, conductivity, antibacterial activity, and hemostatic properties are discussed. In addition, recent advances in the biomedical applications of adhesive hydrogels, focusing on tissue repair, drug delivery, medical devices, and wearable sensors are reviewed. Finally, the current challenges are highlighted and future trends in this rapidly evolving field are discussed.

Trojan Horse Bioheterojunction Empowers Adhesive Hydrogel with Robust Antibacterial Activity and Sensing Capacity for Infected Cutaneous Regeneration

Strategic integration of adhesive hydrogels with phototherapy-based antibacterial properties has been extensively leveraged in infected tissue repair. Nevertheless, the interference of bacterial heat shock proteins and antioxidant defense systems attenuates the bactericidal potency of phototherapy. To address this imposing predicament, a Trojan horse bioheterojunction (Th-bioHJ) incorporating liquid metal and copper sulfide is devised to confer an adhesive hydrogel with multimodal and comprehensive antibacterial properties for remedying infectious wounds. Th-bioHJ generates phototherapeutic effects and interrupts the electron transport chain with the Trojan horse strategy, achieving rapid and robust sterilization. Additionally, Th-bioHJ promotes cell migration and angiogenesis. In vivo studies elucidate the remarkable efficacy of Th-bioHJ hydrogel in rapidly eradicating bacteria, promoting angiogenesis and boosting infectious cutaneous regeneration. Meanwhile, the Th-bioHJ hydrogel demonstrates exceptional biointerface adhesion and sensing capabilities for real-time motion monitoring. This study provides groundbreaking insights into the innovative application of an adhesive hydrogel in the management of infected wounds.

Poly(thioctic acid) Hydrogels Integrated with Self-Healing, Bioadhesion, Antioxidation, and Antibiosis for Infected Wound Treatment

Bacterial infections pose significant challenges in wound healing and are a serious threat to human health. Hydrogels have emerged as an ideal wound dressing due to their three-dimensional network, which facilitates exudate absorption and maintains a moist environment conducive to healing. Herein, we developed integrated hydrogels composed of poly(thioctic acid) (PTA), polydopamine (PDA), and curcumin (Cur). The formation of covalent and hydrogen bonds among PTA, PDA, and Cur endowed the hydrogels with excellent self-healing and bioadhesion properties. These hydrogels were utilized as dressings for healing Staphylococcus aureus-infected wounds. The PDA-PTA-Cur 16 hydrogel showed the best overall performance in stability, bioadhesion, antioxidant activity, and antibacterial effectiveness. The in vivo results revealed that the PDA-PTA-Cur 16 hydrogel accelerated infected wound healing by inhibiting bacterial growth, alleviating inflammation, promoting collagen deposition, and inducing angiogenesis. This multifunctional hydrogel not only enhances wound healing but also presents a promising strategy for combating bacterial infections in clinical settings.

Room temperature phosphorescent wood hydrogel

Room temperature phosphorescent (RTP) hydrogels exhibit great potential but show poor mechanical performance (Tensile strengthen <1 MPa) and non-tunable RTP performance, hindering their practical applications. Here, we develop wood hydrogel (W-hydrogel) by the in situ polymerization of acrylamide in the presence of delignified wood. As a result of the molecular interactions between the components of delignified wood and polyacrylamide, the W-hydrogel exhibit a tensile strengthen of 38.4 MPa and green RTP emission with a lifetime of 32.5 ms. Moreover, the tensile strength and RTP lifetime are increased to 153.8 MPa and 69.7 ms, upon treating W-hydrogel with ethanol. Significantly, the mechanical and RTP performance of W-hydrogel is switched by alternating "ethanol and water" treatments. Additionally, W-hydrogel is used as energy donor in order to produce red afterglow emission using RhB via an energy transfer process. Taking advantage of these properties, W-hydrogel is processed into multiple hydrogel-based luminescent materials.

A natural carboxylated sisal fiber/chitosan/kaolin porous sponge for rapid and effective hemostasis

To improve chitosan hemostasis, carboxylated sisal fiber and kaolin were introduced to obtain carboxylated sisal fiber/chitosan/kaolin (SF/CS/K) composite sponges (the weight ratio of 3: 3:4, 4:4:2, 5:5:0) by freeze-drying method. The results showed that the ionic cross-linking of the carboxylated sisal fiber with chitosan and kaolin-loading endowed the composite sponges with not only oriented groove porous structure, high mechanical strength, porosity, water absorption and compress recovery, but also suitable biodegradation, good cytocompatibility, hemocompatibility, protein adsorption, antibacterial activity. Especially, compared with commercial gelatin hemostatic sponges, the composite sponge of SF/CS/K displayed better coagulation ability and hemostatic effect, and animal experiments further demonstrated that the bleeding amount and hemostatic time of SF/CS/K were greatly reduced in rat hemostatic models of tail amputation, femoral vein trauma and liver injury, owing to the synergistic hemostatic effect of chitosan, kaolin and sisal fiber, as well as the groove porous structure, which endowed them with strong adhesion for red blood cells. Conclusively, SF/CS/K2 composite sponge had the best hemostatic effect because of the most appropriate component ratio, which is a novel promising natural hemostatic sponge for effective and rapid hemostasis in deep massive bleeding sites.

Multi-functional Gleditsia sinensis galactomannan-based hydrogel with highly stretchable, adhesive, and antibacterial properties as wound dressing for accelerating wound healing

Design and development of a multifunctional wound dressing with self-healing, adhesive, and antibacterial properties to attain optimal wound closure efficiency are highly desirable in clinical applications. Nevertheless, conventional hydrogels face significant barriers in their mechanical strength, adhesive performance, and antibacterial properties. Herein, a tough hydrogel based on aldehyde-grafted galactomannan was synthesized through radical copolymerization and Schiff base reaction, incorporating hyaluronic acid, acrylamide, and the zwitterionic monomer to create a multi-crosslinked structure. The multiple crosslink structure pattern consisting of multiple hydrogen bonding, ionic interactions, reversible Schiff bases bonds, and molecular chain entanglement endowed this hydrogel with multiple functionalities, including high tensile strength (25 kPa), tensile strain (2200 %), toughness (391.59 kJ/m3), and Young's modulus (9.77 kPa). The presence of catechol groups and zwitterionic groups endow hydrogels with outstanding adhesion strength (42.21 kPa), which satisfied the adhesive demand for the ample motion of specific areas. The zwitterionic monomer provided long-lasting antibacterial properties and promoted migration and growth of negatively charged cells, capable of establishing efficient antibacterial barriers and serving as wound dressing. The in vivo and vitro experiments manifested that the optimized hydrogel demonstrated an inconspicuous inflammatory response, facilitating rapid healing of full-thickness skin wound in rat models. Therefore, this work provides a promising strategy and an ideal candidate for wound healing dressings in treating infected skin wounds.

Multifunctional hydrogel based on polyvinyl alcohol/chitosan/metal polyphenols for facilitating acute and infected wound healing

Bacterial-infected wounds could cause delayed wound healing due to increased inflammation, especially wounds infected by drug-resistant bacteria remain a major clinical problem. However, traditional treatment strategies were gradually losing efficacy, such as the abuse of antibiotics leading to enhanced bacterial resistance. Therefore, there was an urgent need to develop an antibiotic-free multifunctional dressing for bacterially infected wound healing. This study demonstrated the preparation of a multifunctional injectable hydrogel and evaluated its efficacy in treating acute and infected wounds. The hydrogel was prepared by a one-step mixing method, and cross-linked by natural deep eutectic solvent (DES), polyvinyl alcohol (PVA), chitosan (CS), tannic acid (TA), and Cu2+ through non-covalent interactions (hydrogen bonds and metal coordination bonds). PVA/CS/DES/CuTA500 hydrogel has multiple functional properties, including injectability, tissue adhesion, biocompatibility, hemostasis, broad-spectrum antibacterial, anti-inflammatory, and angiogenesis. Most importantly, in the MRSA-infected skin wound model, PVA/CS/DES/CuTA500 hydrogel could ultimately accelerate infected wound healing by killing bacteria, activating M2 polarization, inhibiting inflammation, and promoting angiogenesis. In summary, the PVA/CS/DES/CuTA500 hydrogel showed great potential as a wound dressing for bacterial infected wounds treatment in the clinic.

Tough and highly conductive deep eutectic solvent-based gel electrolyte strengthened by high aspect ratio of hemp lignocellulosic nanofiber

Flexible electronic sensing and energy storage technology impose heightened demands on the mechanical and stable properties of gel electrolyte materials. Lignocellulosic nanofiber (LCNF) present a promising avenue for improving the properties of electrolyte networks and mechanical strength. In this study, LCNF derived from hemp fibers was prepared using lactic acid/choline chloride deep eutectic solvent (DES) through a combination of cooking and colloid mill mechanical treatment to achieve nanocellulose with a high aspect ratio and uniform dimensions. The outcomes demonstrated that LCNF, a width of below 20 nm and a length of over 5 μm, can be effectively produced through the DES cooking pretreatment in conjunction with colloid mill mechanical treatment. Meanwhile, DES lignin possessed a purity of ∼90 % and was obtained as a by-product. Subsequently, the as-prepared LCNF was integrated as a nanofiller into gel electrolyte. Ag-L NPs/LCNF/DES/PAA exhibited dense porous structures and showcased exceptional properties, including a high conductivity exceeding 10 mS/cm and remarkable adhesion strength surpassing 100 KPa. The presence of LCNF allowed Ag-L NPs/LCNF/DES/PAA to achieve strains above 1000 % and compression properties over 1000 KPa. The supercapacitor based on this assembly had a high specific capacitance of 271 F g-1 at 0.5 A g-1), along with an impressive capacity retention rate reaching ∼100 % after 3000 cycles. This investigation offers valuable insights into the utilization of lignocellulosic multi-component approaches in the development of flexible electronic devices.

Preparation of Alkali-Resistant Lignin Nanospheres Loaded with Silver Nanoparticles and Their Applications Toward Antibiosis and Printing

Lignin nanoparticles (LNPs) loaded with silver nanoparticles have exhibited significant application potential in antibacterial and catalytic fields. However, the high solubility of LNPs in silver ammonia solution makes it difficult to achieve the reduction of Ag+ and the adsorption of silver nanoparticles. In this study, a protecting agent, terephthalic aldehyde (TA) is used to block lignin condensation and introduce aldehyde groups onto the lignin molecular backbone during lignin extraction. Furthermore, the TA stabilized lignin (TASL) is cross-linked with bisphenol A diglycidyl ether (BADGE) to enhance its alkali resistance performance and subsequently prepared into alkali-resistance BADGE- TASL hybrid LNPs (BADGE- TASL hy-LNPs) by anti-solvent precipitation and self-assembly. Because the presence of a large number of aldehyde groups in TASL compensates for the loss of phenolic hydroxyl groups caused by crosslinking reactions, a high loading of silver nanoparticles of 54.00% is obtained after redox reaction and adsorption in silver ammonia solution. When the BADGE-TASL hy-LNPs@Ag is used as an antibacterial agent, its inhibition efficiency reached ≈99%. Besides, the BADGE-TASL hy-LNPs@Ag can serve as a printing material for the preparation of conductive printing ink. Therefore, this study provides a strategy for lignin functionalization and application in printed electronics and antimicrobial fields.

Brick-cement system inspired fabrication of Ti3C2 MXene nanosheet reinforced high-performance of chitosan/gelatin/PVA composite films

The increasing need for convenient, fast, and nutritious of prepared foods elevate the development of biodegradable antibacterial packaging materials with excellent performance. Inspired by the brick-cement-like system, the two-dimensional nanomaterial Ti3C2 MXene as nanofillers with optothermal response function was employed to strength the performance of chitosan/gelatin/polyvinyl alcohol composite films (CGPF-Mxs). The results revealed that the high-modulus Ti3C2 MXene material improved the microstructures density of macromolecule polymers by physical interactions, as well as enhancements in mechanical properties, thermal stability, barrier properties, water resistance, and antioxidation performance of the composite films. The composite film with 0.75 % Ti3C2 MXene demonstrated the optimal performance. Additionally, the composite films exhibited efficient photothermal effect, which showed inhibition rate of 98.53 % for Staphylococcus aureus and 82.91 % for Escherichia coli under near-infrared laser. The proposed film revealed a potential application as packaging material for maintaining the quality of cooked meat products.

Asymmetric porous hydrogel encapsulating vulcanized molecular brushes with anti-bacterial adhesion, anti-infection, and pro-healing properties towards infected wound treatment

Inspired by the hierarchical structure of the skin, asymmetric porous hydrogel encapsulating vulcanized molecular brushes (VMB@APH) as multifunctional wound dressing has been integrally constructed. The as-obtained VMB@APH effectively combines the anti-bacterial adhesion, anti-infection, and pro-healing properties, which is of great significance for accelerating the recovery of infected wounds.

An integrally formed Janus supramolecular bio-gel with intelligent adhesion for multifunctional healthcare

Despite the rapid development of Janus adhesive hydrogels, most of them still entail complex fabrication processes and have the inherent flaws, such as fragility and instability, thereby restricting their biomedical applications. In this study, a novel Janus bio-gel with strong mechanical and intelligent adhesion functions is facilely fabricated through a gravity-driven settlement strategy, employing poly-cyclodextrin microspheres (PCDMs). This strategy takes advantage of the sedimentation behavior of PCDMs with various diameters to establish structural disparities on both sides of the Janus bio-gel, thereby resolving multiple predicaments including the tedious synthesis steps and poor bonding of multilayer hydrogels. Owing to the multiple dynamic interactions between polymers and PCDMs, the Janus supramolecular bio-gel demonstrates outstanding mechanical toughness (1.97 MJ/m3) and elongation rate (≈800 %). More attractively, the resulting Janus bio-gel exhibits remarkable adhesiveness (316.4 J/m2 for interfacial toughness) and adhesive differences that are exceed 50 times between the two surfaces. Furthermore, the Janus supramolecular bio-gel also has excellent antibacterial properties, biocompatibility, environmental stability, and multiple monitoring functions, accelerating wound stably healing and monitoring physiologic parameters on the skin. This strategy provides a straightforward and promising approach to directly achieve multifunctional integration for smart health management.