Tough adhesives for diverse wet surfaces

Immunomodulatory bioadhesive technologies

Bioadhesives have found significant use in medicine and engineering, particularly for wound care, tissue engineering, and surgical applications. Compared to traditional wound closure methods such as sutures and staples, bioadhesives offer advantages, including reduced tissue damage, enhanced healing, and ease of implementation. Recent progress highlights the synergy of bioadhesives and immunoengineering strategies, leading to immunomodulatory bioadhesives capable of modulating immune responses at local sites where bioadhesives are applied. They foster favorable therapeutic outcomes such as reduced inflammation in wounds and implants or enhanced local immune responses to improve cancer therapy efficacy. The dual functionalities of bioadhesion and immunomodulation benefit wound management, tissue regeneration, implantable medical devices, and post-surgical cancer management. This review delves into the interplay between bioadhesion and immunomodulation, highlighting the mechanobiological coupling involved. Key areas of focus include the modulation of immune responses through chemical and physical strategies, as well as the application of these bioadhesives in wound healing and cancer treatment. Discussed are remaining challenges such as achieving long-term stability and effectiveness, necessitating further research to fully harness the clinical potential of immunomodulatory bioadhesives.

Adaptive microgel films with enhancing cohesion, adhesion, and wettability for robust and reversible bonding in cultural relic restoration

Hydrogel adhesives hold significant promise for applications in flexible intelligent systems and biomedical engineering. However, reconciling high toughness with strong, durable, and repeatable interfacial adhesion remains a daunting challenge. Herein, a new strategy was proposed involving the utilization of physically crosslinked microgels to fabricate a high-toughness adhesive microgel film, optimizing cohesion, adhesion, and wettability to significantly enhance interfacial adhesion performance. The microgels were synthesized using polyzwitterions and acrylic acid through inverse emulsion method, leveraging on their intrinsic ability to readily form abundant non-covalent interactions. The resultant microgel-based adhesive film, formed through physical crosslinking and chain entanglement mechanisms, exhibited a tensile strength of 0.34 MPa, an exceptional elongation at break of 1107.79 %, and a toughness of 2842.17 kJ/m3. Furthermore, this adhesive film demonstrated a remarkable adhesive strength of 1740.9 kPa, with its adhesion performance retaining stable and effective even under extreme environmental conditions, including elevated temperatures and complete submersion in aqueous environments. In contrast to conventional hydrogel adhesives, this microgel system achieves superior mechanical robustness, interfacial adhesion, and environmental resistance, highlighting their promising potential candidate for applications in cultural heritage conservation.

Innovative approaches in bioadhesive design: A comprehensive review of crosslinking methods and mechanical performance

In biomedical applications, bioadhesives have become a game-changer, offering novel approaches to tissue engineering, surgical adhesion, and wound healing. This comprehensive review paper provides a thorough analysis of bioadhesives and their categorization according to application site and crosslinking process, bonding efficacy, and mechanical characteristics. The use of bioadhesives to stop bleeding and seal leaks is also covered in the review. The article delves into the various crosslinking techniques used in bioadhesives, including chemical, physical, and hybrid approaches. It emphasizes on how these mechanisms control the adhesive's elasticity, durability, and structural integrity. In addition, the review looks at the mechanical strength of bioadhesives, taking important characteristics like shear strength, toughness, elasticity, and tensile strength into account. It is highlighted how important bioadhesives are to the life sciences because they drive innovation and interdisciplinary cooperation, address present healthcare issues, and create new avenues for therapeutic development. The paper also explores some vital characteristics of bioadhesives that, when strategically combined with one another, improve their efficacy and usefulness in a variety of surgical and medical applications. The analysis concludes by examining nature-inspired adhesives, including those based on geckos, mussels, and tannic acid, and their unique bonding mechanisms and potential for use in advanced biomedical applications.

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.

Chitooligosaccharide endowed tunable adhesion to self-gelling powders for rapid hemostasis and sutureless skin wound closure

Self-gelling powders have recently emerged as promising tissue adhesives for bleeding wound care. However, to simultaneously achieve strong tissue adhesion and on-demand removal without debridement remains a significant challenge. Here, we developed an ultrafast self-gelling powder compositing of acrylic acid/2-aminoethyl methacrylate copolymers (AMA) and chitooligosaccharide (COS). Upon absorbing water/blood from wet tissue surfaces, AMA-COS powders could quickly transform into an integral hydrogel that firmly adhered to tissues (adhesion strength up to 37.74 kPa) based on strong electrostatic interactions, achieving tight wound sealing. Following exposure to COS solutions, the hydrogel exhibited a significant reduction in adhesion strength (3.28 kPa), allowing for easy removal of the adhesive from tissue surfaces. Moreover, the AMA-COS powders could enable effective hemostasis (within 20 seconds) of acute tail, liver, and stomach bleeding on rats. In vivo studies further validated that the AMA-COS powder-based adhesive could enable rapid & robust adhesion and on-demand removal for sutureless skin incision closure and tissue healing, outperforming surgical sutures and commercial cyanoacrylate glue. These features make AMA-COS powder adhesive to be a promising hemostatic sealant for rapid bleeding control and non-invasive wound closure & tissue repair. STATEMENT OF SIGNIFICANCE: Self-gelling powders have recently emerged as promising tissue adhesives for bleeding wound care. However, achieving reliable tissue adhesion while enabling on-demand removal without debridement remains a significant challenge. This work developed a new type of ultrafast self-gelling powder (AMA-COS) with tunable tissue adhesion on varying complexation with chitooligosaccharide (COS) for rapid hemostasis and sutureless skin wound closure. The AMA-COS powders can quickly gel and firmly adhere to tissue surfaces upon water/blood absorption, forming tight wound sealing, while it is able to easily detach from tissue merely by exposure to additional COS solutions. We believe the AMA-COS powder could be a high-efficiency multi-functional fault-tolerant bioadhesive for rapid bleeding control and non-invasive wound closure and tissue repair.

Self-Adhesive and Stretchable Conducting Polymer Blends

Self-adhesive and stretchable conducting polymer blends can have important applications in many areas, particularly wearable electronics and bioelectronics. For example, they can be used as conformal dry electrodes to continuously detect epidermal biopotential signals for the long-term. Although the blends of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), water-borne polyurethane (WPU), and d-sorbitol (SOR) can exhibit high mechanical stretchability and good self-adhesiveness to skin, the mechanism for their self-adhesiveness is not clear because none of the components is self-adhesive individually. Here, the mechanism for the self-adhesiveness is revealed by investigating the structure and properties of related binary and trinary blends. The self-adhesiveness of the blends of PEDOT:PSS, WPU, and SOR is related to the plasticization of PSS- (or PSSH) by SOR, the interaction of PSS- (or PSSH) and SOR with the substrate, and the facilitation of the energy dissipation by the flexible WPU. Moreover, we demonstrated novel self-adhesive blends consisting of PEDOT:PSS, SOR, and PSSH that are used to substitute WPU. Although PSSH is not an elastomer, it can be plasticized by SOR and can thus facilitate the energy dispersion like WPU through the blends. These blends can have high mechanical stretchability and high self-adhesion to various substrates as well.

Bioinspired hydrogel for sustained minocycline release: A superior periodontitis solution

Periodontitis treatment remains challenging due to the limitations of clinical medication therapies, including drug cytotoxicity, poor drug retention, immune imbalances, and epithelial barrier damage. Here, inspired by bioisosterism, we develop a dual-network hydrogel-based drug delivery system (M@PP) with materials structurally similar to minocycline (a commonly used medication). The M@PP hydrogel exhibits optimal mechanical strength and bioadhesion, ensuring sufficient drug retention inside periodontal pockets. The sustained release of minocycline, combined with the hydrogel's acidic microenvironment and the antioxidant functional groups, provides M@PP with excellent biocompatibility, potent antibacterial activity (98.1 % against P. gingivalis), and enhanced anti-inflammatory properties. In vivo studies demonstrate that M@PP regulates macrophage polarization, upregulates anti-inflammatory factors, and promotes the expression of epithelial junction-related cytokines. Additionally, M@PP activates pro-osteogenic mediators, with micro-CT analysis revealing increased trabecular bone density, thickness, and bone reconstruction. RNA sequencing further uncovers its therapeutic mechanisms, highlighting bacterial defense, immune modulation and pro-regenerative signaling. These combined benefits create a favorable immune microenvironment, facilitating epithelial barrier restoration and alveolar bone regeneration, achieving superior therapeutic outcomes compared to commercial products. This study presents a promising localized therapeutic strategy for periodontitis and biofilm-associated disorders.

Blood-triggered self-sealing and tissue adhesive hemostatic nanofabric

Current hemostatic fabric often encounters the issue of blood seeping or leaking through the fabric and at the junctions between the fabric and tissue, leading to extra blood loss. Herein, we report a hemostatic nanofabric composed of anionic and cationic nanofibers. Upon contact with wound, the porous nanofabric can absorb the interfacial blood and self-seal to form a compact physical barrier through interfiber bonding, preventing blood from longitudinally penetrating the fabric. This process results in the encapsulation of blood components within the electrostatically crosslinked nanofiber network, creating a robust thrombus that reinforces the physical barrier. Moreover, this nanofabric exhibits strong tissue adhesiveness, inhibiting blood seeping out at the seam of the fabric and tissue. Its hemostatic performance in animal injuries surpasses that of standard cotton gauze and Combat GauzeTM. In the pig femoral artery injury, the blood loss from the nanofabric is only ca. 8% of that from Combat GauzeTM. The nanofabric exhibits excellent biodegradability, hemocompatibility, cytocompatibility, antibacterial activity, and wound healing promotion.

Tunable Wet Adhesion of Sprayable Microgel Glues Driven by a Phase Transition in Polymer Networks

With the emergence of human-computer interaction and related fields, how to realize tunable adhesion on wet and soft materials has become an important issue. In this letter, we propose a strategy for tunable wet adhesion by leveraging the phase transition of polymeric nanoparticles to achieve dynamic, multiscale, and multifactorial synergistic modulation. The strategy is validated by using stimuli-responsive polymer microgel dispersions as sprayable glues, which can switch between swollen and deswollen states through phase transitions, thereby tuning interfacial water molecules. This process dynamically tunes microscopic molecular interactions and the mesoscopic contact area between microgel nanoparticles and the substrate surface, as well as the cohesion within interfacial microgel layers. As a result, adhesion is enhanced in the swollen state, reaching about 373 N m-1, while it is weakened in the deswollen state due to water release. The tunable wet adhesion is reproducible, making the sprayable microgel glues of potential interest for applications (e.g., in hydrogel-based sensors for human motion detection).

PEGNB-Heparin-Liposome composite hydrogels for in situ spraying and ultra-fast adhesion: meeting the challenges of endothelial repair of vascular injury

Carotid atherosclerosis is an essential cause of transient cerebral ischemia, stroke, and other cerebrovascular diseases, and carotid endarterectomy (CEA) is currently the most effective treatment for removing plaque and restoring the vascular lumen. However, the CEA disrupts the integrity and functionality of the endothelium and predisposes it to complications such as restenosis and thrombosis. Hydrogels can closely mimic the natural extracellular matrix, allowing a wide tuning of physical and chemical properties. These properties make hydrogels the most promising candidate materials for the repair of vascular injured intima. In this study, a multifunctional intimal repair hydrogel of poly(ethylene glycol)-norbornene (PEGNB)/ Heparin/ Liposome is proposed with the advantages of ultra-rapid adhesion to the wet tissue of the vascular inner wall, maintenance of adhesion stability under continuous erosion by blood flow. The hydrogel was supplemented with poly(vinyl butyral) (PVB) to reduce its swelling rate, and Rapamycin (RAPA) was encapsulated in this study as the drug into the cationic liposomes. This composite multifunctional (PNHB@Lip(RAPA)) hydrogel has exhibited outstanding anti-coagulation properties, markedly suppressed the proliferation and migration of SMCs, and displayed favourable cytocompatibility and blood compatibility. Concurrently, the capacity of the PNHB@Lip(RAPA) hydrogel to stimulate endovascular regeneration and deter restenosis and thrombus formation was validated through carotid intima damage repair experiments. These findings collectively indicate that the PNHB@Lip(RAPA) hydrogel represents a promising material for intimal injury repair, offering innovative insights into intimal repair methodologies. STATEMENT OF SIGNIFICANCE: Carotid atherosclerosis is a leading cause of transient cerebral ischemia, stroke, and cerebrovascular disorders. Although carotid endarterectomy (CEA) effectively removes plaques, it damages endothelial integrity, increasing the risk of restenosis and thrombosis. To address this, we developed PNHB@Lip(RAPA), a multifunctional intimal repair hydrogel composed of PEGNB, heparin, and rapamycin-encapsulated liposomes. This hydrogel rapidly adheres to wet vascular walls, resists blood flow erosion, and exhibits low swelling. The hydrogel demonstrates superior anticoagulation, inhibits smooth muscle cell proliferation and migration, and shows favourable cytocompatibility. Experimental results confirm its ability to promote endovascular regeneration while preventing restenosis and thrombosis. In summary, PNHB@Lip(RAPA) hydrogel is a promising material for intimal repair, offering innovative solutions to improve CEA postoperative outcomes.

Nonmonotonic Motion of Sliding Droplets on Strained Soft Solids

Soft materials are ubiquitous in technological applications that require deformability, for instance, in flexible, water-repellent coatings. However, the wetting properties of prestrained soft materials are only beginning to be explored. Here we study the sliding dynamics of droplets on prestrained soft silicone gels, both in tension and in compression. Intriguingly, in compression we find a nonmonotonic strain dependence of the sliding speed: mild compressions decelerate the droplets, but stronger compressions lead again to faster droplet motion. Upon further compression, creases nucleate under the droplets until, finally, the entire surface undergoes the creasing instability, causing a "run-and-stop" motion. We quantitatively elucidate the speed modification for moderate prestrains by incremental viscoelasticity, while the acceleration for larger prestrains turns out to be linked to the solid pressure, presumably through a lubrication effect of expelled oligomers.

Sprayable Ionic Tattoo Exploiting Biocompatible and Recyclable Organogel for AI-Assisted Multisignal Sensing

In the field of human-computer interaction (HCI), gel-based ionic tattoos have emerged as a notable innovation owing to their human-like softness and elasticity. These ionic tattoos are highly valued for their biocompatibility, stability, and user-experience comfortability. This research has focused on combining the environmentally stable and biocompatible green solvent with dynamically degradable and reusable polymer networks to develop a propylene glycol-based supramolecular organogel (PGOG). It demonstrates an impressive elongation of 10 400% at break. The photocured PGOG can be recycled on-demand in water and formulated into a portable spray solution, which can be sprayed on the back of the hand just like a sunscreen spray, providing a seamless and comfortable fit that closely matches the skin's contours. Additionally, an integrated ionic circuit is designed with the capability of sensing temperature, humidity, and strain signals with the assistance of AI, demonstrating its potential application in intelligent artificial skin.

Lithium Bond-Mediated Molecular Cascade Hydrogel for Injury-Free and Repositionable Adhesive Bioelectronic Interfaces

Flexible bioelectronic interfaces with adhesive properties are essential for advancing modern medicine and human-machine interactions. However, achieving both stable adhesion and non-damaging detachment remains a significant challenge. In this study, a lithium bond-mediated molecular cascade hydrogel (LMCH) for bioelectronic interfaces is designed, which facilitates robust adhesion at the tissue level and permits atraumatic detachment for repositioning as required. By integrating the adhesive properties of the molecular cascade structure with the elastic characteristics of the hydrogel interface, the LMCH interface not only achieved a high adhesion strength (197 J m-2) on the skin, but also significantly extended the cracking cycles on the tissue surface during the peeling process from 4 to 380, marking an enhancement of nearly two orders of magnitude. Furthermore, with Young's modulus similar to that of human tissue (25 kPa), exceptional stretchability (1080%), and high ionic conductivity (7.14 S m-1), the LMCH interface demonstrates outstanding tissue compatibility, biocompatibility, and stable detection capabilities for electrocardiogram (ECG) and electromyogram (EMG) signals. This study presents new insights and potential for advancing bioelectronics and implantable interface technologies.

Hydrogel-Impregnated Robust Interlocking Nano Connector (HiRINC) for Noninvasive Anti-Migration of Esophageal Stent

Migration of implanted self-expandable metallic stent (SEMS) in the malignant or benign esophageal stricture is a common complication but not yet resolved. Herein, this research develops a hydrogel-impregnated robust interlocking nano connector (HiRINC) to ensure adhesion and reduce the mechanical mismatch between SEMSs and esophageal tissues. Featuring a network-like porous layer, HiRINC significantly enhances adhesion and energy dissipation during esophageal peristalsis by utilizing mechanical interlocking and increasing hydrogen bonding sites, thereby securing SEMS to tissues. The anti-swelling property of HiRINC prevents excessive hydrogel expansion, avoiding esophageal blockage. Ex vivo and in vivo adhesion tests confirm that the HiRINC outperforms flat surfaces without RINC structures and effectively prevents stent migration. HiRINC-coated SEMS maintains its position and luminal patency, minimizing stent-induced tissue hyperplasia and inflammatory responses in rat and porcine esophageal models during the 4-week follow-up. This novel HiRINC-SEMS can ensure anti-migration and prolonged stent patency in the rat and porcine esophagus and seems to be expanded to other nonvascular luminal organs and various implantable metallic devices.

Hydrogel tissue adhesive: Adhesion strategy and application

Hydrogel tissue adhesives have emerged as a promising alternative to conventional wound closure methods such as sutures and staples due to their operational simplicity demonstrated biocompatibility and capacity for multifunctional integration. However, complex and variable tissue microenvironments and dynamic adhesion surfaces still challenge the actual adhesion performance of adhesives, especially natural polymer-based adhesives. In addition, to expand the application of adhesives in biomedical fields, there is an urgent need to further improve tissue adhesion performance through composition design, adhesion mechanism research and bioeffect development. This review focuses on the adhesive properties of adhesives and their applications in biomedical fields. Adhesion-cohesion equilibria, forms of adhesion failure, methods for improving cohesion and various interfacial adhesion mechanisms are presented. Moreover, practical biomedical applications of tissue adhesives are reviewed, focusing on skin, heart, stomach, liver, and cornea. Finally, this review looks ahead to a new generation of multi-functional, strong adhesion tissue adhesives, in the hope of providing inspiration to those working in the field.

Light-Driven PAA Adhesive: A Green Bonding Platform Integrating High-Performance, Environmental Resilience, and Closed-Loop Recyclability

The increasing demand for environmentally benign materials has driven significant interest in water-based adhesives due to their low toxicity and ecological advantages. However, conventional formulations face persistent challenges including limited bonding strength, complex manufacturing processes, and compromised storage stability. To address these limitations, a polyacrylic acid-based aqueous adhesive (PAA) is developed through a novel visible-light catalytic platform. This approach ensures a mild catalytic cycle, thereby promoting sustained stability. The strategic integration of hydrogen bonding, electrostatic interactions, and mechanical interlocking enhances interfacial adhesion. Notably, the adhesive demonstrates an adhesion strength of up to 20.86 MPa on wood and 12.91 MPa on bamboo substrates. Its composition confers stability across diverse environmental conditions, including extreme temperature variations (-196 °C-200 °C), prolonged storage (> 270 days), and resistance to mechanical stress and solvent exposure. Furthermore, PAA exhibits full recyclability through a water-mediated dissociation and recovery process. This study represents a pioneering application of novel visible-light catalysis in adhesive synthesis, advancing the development of sustainable high-performance bonding systems.

Shape-adaptive, deformable and adhesive hydrogels enable stable closure of long incision wounds

Effective closure of long incision wounds is crucial in clinical practice but remains challenging for existing bioadhesives due to the deformations of the long incisions. Herein, we propose a concept of shape-adaptive adhesion and achieve it by designing a class of shape-adaptive, deformable adhesive hydrogels (DAHs) for long incision wound closure. The design strategy is facile yet universally applicable, which involves aldehyde polysaccharides as adhesive primers and microgel-type gelators as building blocks. We demonstrate that the microgel-type gelators are responsible for the integration of a deformable matrix in situ, and aldehyde polysaccharides enhance the adhesive performance of the matrix at cost of a little deformability. Optimization of the flexibility of DAH network is effective in balancing the adhesive and deformable properties, thus developing DAHs featured with the adaptability to irregular shapes, robust adhesive properties, and appropriate deformability. As a result, DAHs achieve shape-adaptive adhesion by effectively bonding the long incision and deforming with it without failure. In vivo results clearly show that DAHs stably close the 4 cm-long incision wounds on the backs and the more dynamic incisions on the napes of rats. The shape-adaptive adhesion achieved by DAHs may provide an alternative way for long incision wound treatment. STATEMENT OF SIGNIFICANCE: Bioadhesive is emerging as an effective tool in clinical wound treatment. However, the closure of severe long incision wounds by currently available bioadhesives is still challenging. In this work, we proposed a concept of shape-adaptive adhesion and accordingly developed a bioadhesive building strategy for long incision wound closure. The strategy is universally applicable, which involves aldehyde polysaccharide as an adhesive primer and microgel-type gelators as building blocks. The results showed that the strategy is effective in developing bioadhesives (DAHs) that simultaneously possess shape-adaptive properties, robust adhesive properties and appropriate deformability, thus overcoming the limitations of most existing bioadhesives. With these features, DAHs successfully achieved shape-adaptive adhesion and stable closure of long incision wounds, providing an effective way for wound treatment.

Versatile Solid-State Medical Superglue Precursors of α-Lipoic Acid

α-Lipoic acid (αLA) is an attractive building block for medical adhesives. However, due to poor water solubility of αLA and high hydrophobicity of poly(αLA), elevated temperatures, organic solvents, or complex preparations are typically required to obtain and deliver αLA-based adhesives to biological tissue. Here, we report αLA-based powder and low-viscosity liquid superglues that polymerize and bond rapidly upon contact with wet tissue. A monomeric mixture of αLA, sodium lipoate, and an activated ester of lipoic acid was used to formulate the versatile adhesives. Stress-strain measurements of the wet adhesives confirmed the high flexibility of the adhesive. Moreover, a small molecule regenerative drug was successfully incorporated into and released from the adhesive without altering the physical and adhesive properties. In vitro and in vivo studies of the developed adhesives confirmed their cell and tissue compatibility, biodegradability, and potential for sustained drug delivery. Moreover, due to the inherent ionic nature of the adhesives, they demonstrated high electric conductivity and sensitivity to deformation, allowing for the development of a tissue-adherent strain sensor.

Stretchable all-gel organic electrochemical transistors

Stretchable organic electrochemical transistors (OECTs) are promising for flexible electronics. However, the balance between stretchability and electrical properties is a great challenge for OECTs. Here, high-performance stretchable all-gel OECTs based on semiconducting polymer gel active layers and poly(ionic liquid) ionogel electrolytes are developed. The all-gel network structures effectively promote ion penetration/transport and endows the OECTs with high stretchability. The resulting OECTs exhibit an excellent combination of ultra-high transconductance of 86.4 mS, on/off ratio of 1.2 × 105, stretchability up to 50%, and high stretching stability up to 10000 cycles under 30% strain. We demonstrate that the all-gel OECTs can be used as stretchable pressure-sensitive electronic skins with a low detection limit for tactile perception of robotic hands. In addition, the all-gel OECTs can be applied as stretchable artificial synapses for neuromorphic simulation and highly sensitive stretchable gas sensors for simulating olfactory perception process and monitoring food quality. This work provides a general all-gel strategy toward high-performance flexible electronics.

Mucus-Inspired Supramolecular Adhesives: Exploring the Synergy between Dynamic Networks and Functional Liquids

The exceptional physicochemical and mechanical properties of mucus have inspired the development of dynamic mucus-based materials for a wide range of applications. Mucus's combination of noncovalent interactions and rich liquid phases confer a range of properties. This perspective explores the synergy between dynamic networks and functional liquids in mucus-inspired supramolecular adhesives. It delves into the biological principles underlying mucus's dynamic regulation and adhesive properties, the fundamentals of supramolecular adhesive design, and the transformative potential of these materials in biomedical applications. Finally, this perspective proposes potential directions for the molecular engineering of mucus-inspired supramolecular materials, emphasizing the need for interdisciplinary approaches to harness their full potential for biomedical and sustainable applications.

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.

Covalently reactive microparticles imbibe blood to form fortified clots for rapid hemostasis and prevention of rebleeding

Owing to the inherently gradual nature of coagulation, the body fails in covalently crosslinking to stabilize clots rapidly, even with the aid of topical hemostats, thus inducing hemostatic failure and potential rebleeding. Although recently developed adhesives confer sealing bleeding sites independently of coagulation, interfacial blood hampers their adhesion and practical applications. Here, we report a covalently reactive hemostat based on blood-imbibing and -crosslinking microparticles. Once contacting blood, the microparticles automatically mix with blood via imbibition and covalently crosslink with blood proteins and the tissue matrix before natural coagulation operates, rapidly forming a fortified clot with enhanced mechanical strength and tissue adhesion. In contrast to commercial hemostats, the microparticles achieve rapid hemostasis (within 30 seconds) and less blood loss (approximately 35 mg and 1 g in the rat and coagulopathic pig models, respectively), while effectively preventing blood-pressure-elevation-induced rebleeding in a rabbit model. This work advances the development and clinical translation of hemostats for rapid hemostasis and rebleeding prevention.

Improving Complex Coacervate Tissue Adhesive Performance Using Bridging Polymer Chains

Complex coacervates have emerged as promising tissue adhesives due to their excellent wet adhesion and tunable properties. However, maintaining stable adhesion on soft, dynamic tissues remains challenging. In this study, the use of a bridging polymer was investigated to enhance the adhesive properties of a complex coacervate adhesive (CCA) composed of poly(allylamine hydrochloride) (pAH) and polysulfopropyl methacrylate (pSPMA). The CCA undergoes solidification as a result of a change in salt concentration, forming a robust adhesive under physiological conditions. Pretreatment with pAH, but not pSPMA, significantly improved adhesion energy on both model hydrogels and biological tissues by forming a polymer-rich bridging layer at the interface. The beneficial effect was driven by accumulation of pAH in superficial layers of both the CCA and the substrates. This enabled the CCA to withstand higher deformation before adhesive failure. These findings underscore the potential of bridging polymers to improve CCAs and other tissue adhesives for biomedical applications.

Medical adhesives for soft tissue wound repair with good biocompatibility, flexibility, and high adhesive strength

Compared with traditional soft tissue wound closure methods such as sutures and staplers, bioadhesives have significant advantages in terms of tissue compatibility, ease of use, and wound adaptability, making them a hot topic among current wound repair materials. This study aimed to select polyurethane materials with good biocompatibility and high mechanical strength, optimize the prepolymer formula, develop new curing agents, and obtain a new dual-component polyurethane bioadhesive. Furthermore, key research will be conducted on its mechanical properties and tissue adhesion performance. The results show that through the optimization of prepolymer formulations and the development of novel curing agents, a dual-component polyurethane bioadhesive with good biocompatibility, flexibility, and high adhesive strength was obtained. This adhesive can quickly and effectively bond common soft tissue (skin, muscle) traumatic wounds, with an adhesive strength of up to 72 kPa. This adhesive matches well with the mechanical properties of soft tissues and safely and tightly adheres to the surface of soft tissues. Additionally, this dual-component polyurethane adhesive holds promise for repairing other soft tissues, such as the lungs and intestines, with broad application prospects.

Universal law of hierarchical dynamics in gels arising from confluence of local physically dynamic bonds

Gels comprised of dynamic bonds are important candidates for the emerging 'intelligent' gels due to their unique characteristics. We report a universal law of hierarchical gel dynamics arising from association-dissociation of physical crosslinks, as discerned from dynamic light scattering (DLS) on diverse sets of complex gels. It is the first experimental evidence of a stretched exponential decay with a universal exponent 1/3 in DLS for all the physical gels, complementing more than five decades of DLS studies on conventional chemical gels. Here we show that diversely different chemistries of dynamic bonds map into the observed unifying law for large-scale collective dynamical properties of physical gels. This discovery allows identification of whether physical or chemical bonds dominate the crosslinks in complex gels, as well as extraction of local energetics of the constituent physical crosslinks by their characteristic relaxation times. It also elicits large-scale functional properties applicable in smart gels.

Development of Bioorthogonally Degradable Tough Hydrogels Using Enamine N-Oxide Based Crosslinkers

Inducibly degradable polymers present new opportunities to integrate tough hydrogels into a wide range of biomaterials. Rapid and inducible degradation enables fast transition in material properties without sacrificing material integrity prior to removal. In pursuit of bioorthogonal chemical modalities that will enable inducible polymer degradation in biologically relevant environments, enamine N-oxide crosslinkers are developed for double network acrylamide-based polymer/alginate hydrogels. Bioorthogonal dissociation initiated by the application of aqueous diboron solution through several delivery mechanisms effectively lead to polymer degradation. Their degradation by aqueous B2(OH)4 solution results in a fracture energy half-life of <10 min. The biocompatibility of the degradable hydrogels and B2(OH)4 reagent is assessed, and the removability of strongly adhered tough hydrogels on mice skin is evaluated. Thermoresponsive PNiPAAm/Alg hydrogels are fabricated and application of the hydrogels as a chemically inducible degradable intraoral wound dressing is demonstrated. It is demonstrated through in vivo maximum tolerated dose studies that diboron solution administered to mice by oral gavage is well tolerated. Successful integration of enamine N-oxides within the tough double network hydrogels as chemically degradable motifs demonstrates the applicability of enamine N-oxides in the realm of polymer chemistry and highlights the importance of chemically induced bioorthogonal dissociation reactions for materials science.

Engineering Adhesive Hydrogels for Hemostasis and Vascular Repair

Adhesive hydrogels with tunable mechanical properties and strong adhesion to wet, dynamic tissues have emerged as promising materials for tissue repair, with potential applications in wound closure, hemorrhage control, and surgical adhesives. This review highlights the key design principles, material classifications, and recent advances in adhesive hydrogels designed for vascular repair. The limitations of existing adhesive hydrogels, including insufficient mechanical durability, suboptimal biocompatibility, and challenges in targeted delivery, are critically evaluated. Furthermore, innovative strategies-such as incorporating self-healing capabilities, developing stimuli-responsive systems, integrating functional nanocomposites, and employing advanced fabrication techniques like 3D bioprinting-are discussed to enhance adhesion, mechanical stability, and vascular tissue regeneration. While significant progress has been made, further research and optimization are necessary to advance these materials toward clinical translation, offering a versatile and minimally invasive alternative to traditional vascular repair techniques.

An Enhanced Long-Term Wet Adhesion Strategy of Spatial Control the Emergence of Dual Covalent Cross-Linking for Sutureless Cornea Transplant

Corneal transplantation regeneration requires bioadhesives to perform long-term and stable adhesion functions in a wet environment. However, many current studies focus on the instantaneous or short-term adhesion persistence of bioadhesives, and ignore the evaluation of their long-term wet adhesion behaviors which is urgent for keratoplasty repair process. In view of this situation, a dual covalent cross-linking hydrogel (ASO) bioadhesive is developed. The ASO bioadhesive comprised acrylated gelatin(G-AA), thiolated gelatin(G-SH), and oxidized dextran (OD). Introduction of thiol chemistry made the emergence of ASO dual covalent cross-linking controllable by UV light irradiation. The analysis of this feature revealed an intriguing phenomenon. The ASO bioadhesive demonstrated spatially specific control over cross-linking behavior by first penetrating the tissue and then initiating cross-linking, thereby significantly enhancing its long-term wet adhesion ability. The ASO bioadhesive can maintain more than 50% adhesion after being immersed in wet environment for one month. Subsequently, ASO bioadhesive demonstrated long-term wet adhesive stability once again on corneal lamellar transplantation model through maintaining strong anchorage of corneal donor to recipient bed and promoting their integration. The unprecedented adhesive mechanism presented in this study provided innovated theoretical basis for designing bioadhesives with superior long-term wet adhesion.

Bioelectronics hydrogels for implantable cardiac and brain disease medical treatment application

Hydrogel-based bioelectronic systems offer significant benefits for point-of-care diagnosis, treatment of cardiac and cerebral disease, surgical procedures, and other medical applications, ushering in a new era of advancements in medical technology. Progress in hydrogel-based bioelectronics has advanced from basic instrument and sensing capabilities to sophisticated multimodal perceptions and feedback systems. Addressing challenges related to immune responses and inflammation regulation after implantation, physiological dynamic mechanism, biological toxicology as well as device size, power consumption, stability, and signal conversion is crucial for the practical implementation of hydrogel-based bioelectronics in medical implants. Therefore, further exploration of hydrogel-based bioelectronics is imperative, and a comprehensive review is necessary to steer the development of these technologies for use in implantable therapies for cardiac and brain/neural conditions. In this review, a concise overview is provided on the fundamental principles underlying ionic electronic and ionic bioelectronic mechanisms. Additionally, a comprehensive examination is conducted on various bioelectronic materials integrated within hydrogels for applications in implantable medical treatments. The analysis encompasses a detailed discussion on the representative structures and physical attributes of hydrogels. This includes an exploration of their intrinsic properties such as mechanical strength, dynamic capabilities, shape-memory features, stability, stretchability, and water retention characteristics. Moreover, the discussion extends to properties related to interactions with tissues or the environment, such as adhesiveness, responsiveness, and degradability. The intricate relationships between the structure and properties of hydrogels are thoroughly examined, along with an elucidation of how these properties influence their applications in implantable medical treatments. The review also delves into the processing techniques and characterization methods employed for hydrogels. Furthermore, recent breakthroughs in the applications of hydrogels are logically explored, covering aspects such as materials, structure, properties, functions, fabrication procedures, and hybridization with other materials. Finally, the review concludes by outlining the future prospects and challenges associated with hydrogels-based bioelectronics systems.

Mechanical Compatibility in Stitch Configuration and Sensor Adhesion for High-Fidelity Pulse Wave Monitoring

Wearable electronics can achieve high-fidelity monitoring of pulse waveforms on the body surface enabling early diagnosis of cardiovascular diseases (CVDs). Textile-based wearable devices offer advantages in terms of high permeability and comfort. However, knitted strain sensors struggle to capture small-range deformation signals due to stress dissipation during friction and slip of yarns within the textiles. They are optimized for mechanical adaptability and adhesive capability. In this work, the stitch configurations of knitted structure are adjusted to optimize the energy dissipation ratio during deformation and waveform fitting performance. These electric-mechanical results enabled the selection of the most suitable knitted structure for the clinical diagnosis. On the other hand, the sensor's adhesion is optimized with respect to electrical-force-strain coupling and energy transfer efficiency at the interface between skin and sensor. The balance between the storage modulus and loss modulus are adjusted via the crosslinking degree of the polyacrylamide (PAAm) hydrogel network. As a result, the optimized knitted sensor enables stable collection of pulse waveforms from the radial and dorsalis pedis arteries. In human patient evaluations, the knitting-based strain sensor can distinguish patients with different potential CVD risks through extracted characteristic indicators.

Hydrogels in cardiac tissue engineering: application and challenges

Cardiovascular disease remains the leading cause of global mortality. Current stem cell therapy and heart transplant therapy have limited long-term stability in cardiac function. Cardiac tissue engineering may be one of the key methods for regenerating damaged myocardial tissue. As an ideal scaffold material, hydrogel has become a viable tissue engineering therapy for the heart. Hydrogel can not only provide mechanical support for infarcted myocardium but also serve as a carrier for various drugs, bioactive factors, and cells to increase myocardial contractility and improve the cell microenvironment in the infarcted area, thereby improving cardiac function. This paper reviews the applications of hydrogels and biomedical mechanisms in cardiac tissue engineering and discusses the challenge of clinical transformation of hydrogel in cardiac tissue engineering, providing new strategies for treating cardiovascular diseases.

On-Demand Removal of Rapid Hemostatic Sponge for Non-Compressible Hemorrhage Through Disrupting Ionic Bonds

Self-expanding hemostatic sponge plays an important role in the control of non-compressible hemorrhage in deep wound. After hemostasis is accomplished, the sponge adheres to the wound via blood clots, posing a considerable challenge in wound debridement. A kind of protocatechualdehyde modified chitosan/sodium alginate composite hemostatic sponge with on-demand removal performance is designed in this study. After absorbing blood, the compression sponge rapidly expands and compresses the damaged blood vessels. The physical compression of the hemostatic sponge and the chemical adhesion of catechol is used to promote rapid hemostasis of the wound. The composite hemostatic sponge demonstrated outstanding hemostasis performance in both mouse liver and rat femoral artery bleeding model. Notably, after complete hemostasis of the rat femoral artery, the composite sponge is rapidly removed from the wound by rinsing it with a suitable concentration of Sodium carbonate (Na2CO3) solution. This composite hemostatic sponge featuring the on-demand removal capability demonstrates outstanding application potential for non-compressible hemorrhage in deep wounds and provides a novel way for constructing removable hemostatic sponges.

Strong but Reversible Super Fatty Acid Adhesives with Adjustable On-Off Temperature

Reversible adhesion is highly desired for intelligent engineering, reassembling devices, and recycling resources. However, many reported reversible adhesives require solvent or pH stimuli to achieve adversity switches, which are very inconvenient for practical applications. So far, thermally responsive adhesives are reported to be very appealing in achieving facile reversible adhesion. However, the fixed on-off switching temperature limits their application in different scenarios. Herein, we report employing fatty acids and polyvinylpyrrolidone to construct supramolecular thermosetting adhesives. The adhesives can switch between solid and liquid states owing to phase transition, resulting in reversible adhesion with a robust strength of ∼4 MPa and a large on-off ratio of ∼40. Upon variation of the chain length of fatty acids, the super fatty acid adhesives can be designed to display reversible adhesion at the desired temperature. This study will open up new inspiration for developing high-performance reversible adhesives for sustainable development.

Multifunctional Silk Fibroin Hydrogels with Strong Adhesion for Tissue Sealing and Wearable Electronic Sensors

Multifunctional hydrogels with excellent adhesion, biodegradability, and conductivity are essential for overcoming the obstacles of postoperative secondary injury, flexible sensing instability, and so on. Herein, we develop a multifunctional silk fibroin (SF) hydrogel modified with poly(acrylic acid). Owing to the stable chemical cross-linking network and the abundant carboxylic acid groups of the SF network, the SF hydrogel exhibits a high tensile strength of 74.34 kPa due to sufficient cohesion and interfacial interactions. Additionally, the tensile strain reaches a maximum of 414.6%, the compressive strength is 0.9 MPa, and the shear adhesive strength for pig skin tissues is as high as 64 kPa. Compared with most hydrogels, our multifunctional SF hydrogel with a low swelling ratio provides excellent adhesion, biodegradation, and conductivity, which shows advantages in terms of invasive tissue sealing. The use of self-adhesive SF hydrogels as conductive hydrogels in flexible sensors also benefits the collection of physiological electricity and human motion signals in the field of wearable and implantable electronic devices.

Recyclable and Self-Healing Polyurethane Vitrimers via Dynamic Bonding with In-Situ Polymerized PHPMA

The development of lightweight, durable, and recyclable polymer materials with self-healing properties remains a significant challenge in materials science, particularly for applications requiring extended service life and sustainability. This study addresses these challenges by introducing a novel thermoplastic polyurethane (PU)-based vitrimer system, synthesized via in situ polymerization using hydroxypropyl methacrylate (HPMA)-hydroxyl precursor and Tin(II) 2-ethylhexanoate (Sn(Oct)2)-catalyst. Unlike conventional vitrimer systems, this approach leverages dynamic bond exchange reactions without the formation of new covalent bonds, ensuring efficient stress relaxation and recyclability. Notably, the PU-PHPMA-73-Sn(Oct)2 composition exhibited superior mechanical properties and maintained its performance after three recycling cycles, highlighting its durability and circular potential. Stress relaxation studies further confirmed the temperature-dependent bond exchange kinetics, with activation energies of 122.8±8.1 kJ/mol and 21.6±2.4 kJ/mol for different compositions, correlating with the hydroxyl content. The vitrimer also demonstrated an 88.5 % self-healing efficiency, showcasing its ability to autonomously repair damage and extend material lifespan. This lightweight, self-healing, thermally stable, and recyclable vitrimer system presents significant advancements over traditional PU-based materials, with promising applications in medical devices, automotive components, adhesives, and advanced coatings, particularly where longevity and sustainability are critical.

High strength, self-activating ability and fast adhesion of polyurethane adhesives based on rosin structure in different environments

Underwater adhesives hold significant relevance in daily life and applications. Despite great efforts, the development of high-performance underwater adhesives through a simple and effective method remains a difficult challenge. Herein, a high adhesion and environmentally stable polyurethane underwater adhesive (DAP-PU) was developed based on rosin with a hydrogenated phenanthrene ring skeleton to design hydrophobic domains, and combined with multi-strength hydrogen bonding interactions to construct "polar hydrophobic domains". DAP-PU exhibits a strong underwater bonding and adhesion performance on various substrates (steel, aluminum, PMMA and glass) in harsh aqueous conditions (1 M NaCl, pH 5 and seawater), with the highest peel and shear strengths on stainless steel substrates reaching 12.88 N cm-1 and 1.7 MPa, respectively. In addition, DAP-PU can be used in various fields such as underwater sand consolidation, underwater sealing and repair.

Regulation of the gelatin helix-to-coil transition through chain confinements at the polymer-protein interface and protein-protein interface

Gelatin is an essential material widely used in biomedical applications due to its characteristic temperature responsivity-helix-to-coil transition. However, the current helix-to-coil transition is limited by its single-step behavior and the difficulty in designing a specific onset temperature. In this study, we investigated the fundamentals of the helix-to-coil transition with a focus on gelatin chain mobility. We observed distinctive kinetics of the helix-to-coil transition, which is resilient and can actuate in multiple steps or with a controllable onset point. This was achieved by confining the gelatin chain with a hydrophilic polymer or gelatin itself. The confinement approach serves two purposes: first, it prevents excessive mobility of the generated coils, maintaining physical resilience after the helix-to-coil transition; second, the interfacial confinement between the polymer and gelatin, referred to as polymer-protein interface confinement, restricts the helix-to-coil transition, resulting in a multistep transition process. Additionally, strong confinement at the interface between gelatins of different origins, that is protein-protein interface confinement, shifts the onset temperature to a higher point. This fundamental comprehension of helix-to-coil transition could contribute to broadening the biomedical application potential of gelatin materials. STATEMENT OF SIGNIFICANCE: Gelatin is essential in biomedical applications due to its characteristic temperature responsivity-helix-to-coil transition. Herein, we fundamentally investigated the distinctive kinetics of the helix-to-coil transition, which is resilient and can actuate in multiple steps or with a controllable onset point. This was achieved by confining the gelatin chain with a hydrophilic polymer or gelatin itself. The gelatin chain confinement prevents excessive mobility of the generated coils, maintaining physical resilience after the helix-to-coil transition. The interfacial confinement between the polymer and gelatin restricts the helix-to-coil transition, resulting in a multistep transition process. Additionally, strong confinement at the interface between gelatins of different origins shifts the onset temperature to a higher point.

Hydrogel Adhesive with Tunable Multifunctionality by the Addition of Weak Bonds Based on Polydopamine for Versatile Wound Healing Applications and Biointerfaces

Developing high-performance adhesives that integrate both strength and flexibility is essential for versatile medical applications; however, achieving both properties simultaneously in a single material remains a challenge. In this study, we introduce polydopamine (PDA) into hydrogel networks to form sacrificial bonds, which consist of multiple types of noncovalent, energy-dissipating interactions under stress, allowing the material to stretch and recover without breaking. This mechanism not only enables synergistic interactions that enhance both strength and extensibility but also allows for rapid and robust adhesion to various tissue interfaces, effectively sealing defects and stopping bleeding in models of tail, liver, and heart injuries. Additionally, the hydrogels demonstrate excellent antibacterial properties, biocompatibility, and in situ macrophage modulation. In both rat and pig injury models, the hydrogel adhesives efficiently close wounds and accelerate healing. These findings underscore the significant potential of these sacrificially bonded hydrogels for surgical applications, including hemostatic sealing, infection prevention, and sutureless wound closure. Additionally, they could also serve as bioelectronics interfacing materials, enabling the recording and stimulation of physiological activities.

Bioadhesives and bioactive hydrogels for wound management

Delayed wound healing remains a major challenge in biomedical research, often leading to complications such as scarring, acute trauma, and chronic diseases. Effective wound management is crucial for enhancing treatment outcomes, preventing complications, and promoting tissue regeneration. In response to this need, a variety of polymeric biomaterials have been developed. A growing focus in the field involves the design of bioadhesives and bioactive materials, which offer promising solutions for wound management. Recent advances in materials engineering have led to the development of polymer biomaterials with excellent biocompatibility, strong adhesion to biological surfaces, and bioactive properties that support rapid wound closure and tissue repair. This review discusses the latest progress in the development and application of bioadhesives and bioactive hydrogels for wound management and tissue regeneration, highlighting potential directions for future biomaterial research.

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.

Superwetting Gels: Wetting Principles, Applications, and Challenges

Along with the in-depth understanding of wetting behaviors in nature, superwetting gels have received a lot of attention in the past decade. The viscoelasticity of gel materials makes wetting characteristics different from those of rigid materials and brings diverse functionality. In this Review, we summarize the current progress in principles of gel wettability from two aspects: wetting on gels and wetting of gels. Distinct from rigid substrates, the viscoelasticity and solid-liquid coexistence of gel materials introduce additional factors, including surface tension and deformation, resulting in various wetting phenomena. Besides, the similarity between gels and tissues broadens its applications in biomedical devices and smart interfacial regulation. We further conclude the current application that utilizes superwetting gels. Finally, we provide our perspective for future research directions.

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.

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.

Electrostatically Enhanced Biomimetic Asymmetric Hydrogel with a Dung Beetle-Inspired Pattern for Internal Trauma Sealing

Herein, a biologically asymmetric adhesion-patterned hydrogel induced by the dung beetle surface was proposed for internal trauma sealing. The electrostatic interaction-enhanced dual networks endowed the hydrogel patch with superior mechanical performance, thus achieving a favorable sealing ability. Poly(acrylic acid) (pAA), chitooligosaccharide (COS), and gelatin were used as the composition of our hydrogel system. Concurrently, the bionic raised structure enabled a significant adhesion drop effect. The surface waviness function, fitted to the curved bumps, showed the design direction of the patterned bumps, which was indicative of subsequent research. Also, the microparticle deposition method could exert a synergistic effect with the patterned surface, which together contributed to the asymmetry of the adhesive hydrogel patch. Following simulation experiments such as in vitro bursting tests, we conducted a rat gastric trauma model to validate the application potential of this bionic asymmetric patterned patch. The asymmetric adhesion hydrogel patch had an excellent sealing effect, antiadhesive properties, and operability and was expected to have a promising application prospect, providing a strategy for the design of subsequent in vivo trauma-sealing biomaterials.

An electroadhesive hydrogel interface prolongs porcine gastrointestinal mucosal theranostics

Establishing a robust and intimate mucosal interface that allows medical devices to remain within lumen-confined organs for extended periods has valuable applications, particularly for gastrointestinal theranostics. Here, we report the development of an electroadhesive hydrogel interface for robust and prolonged mucosal retention after electrical activation (e-GLUE). The e-GLUE device is composed of cationic polymers interpenetrated within a tough hydrogel matrix. An e-GLUE electrode design eliminated the need for invasive submucosal placement of ground electrodes for electrical stimulation during endoscopic delivery. With an electrical stimulation treatment of about 1 minute, the cationic polymers diffuse and interact with polyanionic proteins that have a relatively slow cellular turnover rate in the deep mucosal tissue. This mucosal adhesion mechanism increased the adhesion energy of hydrogels on the mucosa by up to 30-fold and enabled in vivo gastric retention of e-GLUE devices in a pig stomach for up to 30 days. The adhesion strength was modulated by polycationic chain length, electrical stimulation time, gel thickness, cross-linking density, voltage amplitude, polycation concentration, and perimeter-to-area ratio of the electrode assembly. In porcine studies, e-GLUE demonstrated rapid mucosal adhesion in the presence of luminal fluid and mucus exposure. In proof-of-concept studies, we demonstrated e-GLUE applications for mucosal hemostasis, sustained local delivery of therapeutics, and intimate biosensing in the gastrointestinal tract, which is an ongoing clinical challenge for commercially available alternatives, such as endoclips and mucoadhesive. The e-GLUE platform could enable theranostic applications across a range of digestive diseases, including recurrent gastrointestinal bleeding and inflammatory bowel disease.

Advanced Dual-Cross-Linking Strategy for Upgrading Formaldehyde-Free Olefin Adhesives

Adhesives are extensively used in industry and construction, with formaldehyde-free options gaining popularity due to their enhanced safety and chemical stability. However, their water resistance remains a significant limitation. In this study, a simple and efficient strategy based on a physicochemical dual cross-linking synergistic network was proposed to develop a new formaldehyde-free adhesive (IBMP-BT). The unique structure, featuring stable chemical cross-linking formed by amidation and a network of multiple hydrogen bonds, enables enhanced water resistance, strength, and toughness of the adhesive. The dry shear strength and toughness of the IBMP-BT adhesive reached 2.03 MPa and 0.600 J, respectively, representing improvements of 89.7% and 255.03% compared to those of the unmodified adhesive. The wet bonding strength of the IBMP-BT adhesive was 1.16 MPa, significantly exceeding the requirements of China's national standards. This innovative network design allows olefin copolymers to replace traditional formaldehyde-based products, leading to the creation of high-performance adhesives.

Melatonin-Loaded Hydrogel Modulates Circadian Rhythms and Alleviates Oxidative Stress and Inflammation to Promote Wound Healing

Circadian rhythm disruption, commonly caused by factors such as jet lag and shift work, is increasingly recognized as a critical factor impairing wound healing. Although melatonin is known to regulate circadian rhythms and has potential in wound repair, its clinical application is limited by low bioavailability. To address these challenges, we developed an alginate-based dual-network hydrogel as a delivery system for melatonin, ensuring its stable and sustained release at the wound site. This approach enhances the efficacy of melatonin in modulating the wound healing process. We investigated the effects of circadian rhythm disruption on the wound microenvironment under the influence of the melatonin-loaded hydrogel with a focus on its biocompatibility, hemostatic properties, and antioxidant response functions. Additionally, we elucidated the mechanisms by which the melatonin-loaded hydrogel system promotes wound healing. Our findings provide insights into the relationship between circadian rhythm disruption and wound healing, offering a promising strategy for the management of chronic wounds associated with circadian rhythm disorders.

Molecular self-assembly strategy tuning a dry crosslinking protein patch for biocompatible and biodegradable haemostatic sealing

Uncontrolled haemorrhage is a leading cause of trauma-related fatalities, highlighting the critical need for rapid and effective haemostasis. Current haemostatic materials encounter limitations such as slow clotting and weak mechanical strength, while most of bioadhesives compromise their adhesion performance to wet tissues for biocompatibility and degradability. In this study, a molecular self-assembly strategy is proposed, developing a biocompatible and biodegradable protein-based patch with excellent adhesion performance. This strategy utilizes fibrinogen modified with hydrophobic groups to induce self-assembly into a hydrogel, which is converted into a dry patch. The protein patch enhances adhesion performance on the wet tissue through a dry cross-linking method and robust intra/inter-molecular interactions. This patch demonstrates excellent haemostatic efficacy in  both porcine oozing wound and porcine severe acute haemorrhage. It maintains biological functionality, and ensures sustained wound sealing while gradually degrading in vivo, making it a promising candidate for clinical tissue sealing applications.

A Wet-Adhesion and Swelling-Resistant Hydrogel for Fast Hemostasis, Accelerated Tissue Injury Healing and Bioelectronics

Hydrogel bioadhesives with adequate wet adhesion and swelling resistance are urgently needed in clinic. However, the presence of blood or body fluid usually weakens the interfacial bonding strength, and even leads to adhesion failure. Herein, profiting from the unique coupling structure of carboxylic and phenyl groups in one component (N-acryloyl phenylalanine) for interfacial drainage and matrix toughening as well as various electrostatic interactions mediated by zwitterions, a novel hydrogel adhesive (PAAS) is developed with superior tissue adhesion properties and matrix swelling resistance in challenging wet conditions (adhesion strength of 85 kPa, interfacial toughness of 450 J m-2, burst pressure of 514 mmHg, and swelling ratio of <4%). The PAAS hydrogel can not only realize fast hemostasis of liver, heart, artery rupture, and sealing of pulmonary air-leakage but also accelerate the recovery of stomach and liver defects in rat, rabbit, and pig models. Moreover, PAAS hydrogel can precisely and durably monitor various physiological activities (pulse, electrocardiogram, and electromyogram) even under humid environments (immersion in water for 3 days), and can be employed for the evaluation of in vivo sealing efficiency for artery rupture. The work provides a promising hydrogel adhesive for clinical hemostasis, tissue injury repair, and bioelectronics.

In Vitro Engineered ECM-incorporated Hydrogels for Osteochondral Tissue Repair: A Cell-Free Approach

Prevalence of osteoarthritis has been increasing in aging populations, which has necessitated the use of advanced biomedical treatments. These involve grafts or delivering drug molecules entrapped in scaffolds. However, such treatments often show suboptimal therapeutic effects due to poor half-life and off-target effects of drug molecules. As a countermeasure, a 3D printable robust hydrogel-based tissue-repair platform is developed containing decellularized extracellular matrix (dECM) from differentiated mammalian cells as the therapeutic cargo. Here, pre-osteoblastic and pre-chondrogenic murine cells are differentiated in vitro, decellularized, and incorporated into methacrylated gelatin (GelMA) solutions to form osteogenic (GelO) and chondrogenic (GelC) hydrogels, respectively. Integrating the bioactive dECM from differentiated cell sources allows GelO and GelC to induce differentiation in human adipose-derived stem cells (hASCs) toward osteogenic and chondrogenic lineages. Further, GelO and GelC can be covalently adhered using a carbodiimide coupling reaction, forming a multi-layered hydrogel with potential application as a bioactive osteochondral plug. The designed multi-layered hydrogel can also induce differentiation of hASCs in vitro. In conclusion, the bioactive dECM carrying 3D printed robust hydrogel offers a promising new drug and cell-free therapeutic strategy for bone and cartilage repair and future osteoarthritis management.