Overcoming the translational barriers of tissue adhesives

Charge balance transition enabled Janus hydrogel for robust wet-tissue adhesion and anti-postoperative adhesion

Janus hydrogels have recently emerged as promising bioadhesives for efficient wet-tissue adhesion and anti-postoperative adhesion. However, existing Janus hydrogel adhesives normally need varied chemical designs of different layers to achieve asymmetric adhesive/anti-adhesive properties on either side. Here, we present a new strategy to construct an adhesive/anti-adhesive Janus hydrogel tissue patch accomplished by switching the charge-balance of the hydrogel layers with similar compositions (anionic carboxyl polymer and cationic ε-polylysine, EPL). The bottom layer (AL) is formed under acidic condition (pH 2.85), featuring abundant -COOH and -NH3 + residues, which provide rapid & robust adhesion to diverse wet tissues (up to 100.4 kPa) with high bursting pressure (362.5 mmHg), while the top layer (MLT) is formed under neutral condition, achieving a balanced charge between -COOH/-NH2 and -COO-/-NH3 + groups, which mimic the overall electroneutral structure of zwitterionic materials for efficient anti-postoperative tissue adhesion (up to 6 weeks). Further in vivo studies validated that the integrated AL/MLT hydrogel patch is biodegradable (within 10 weeks), exhibits broad-spectrum antibacterial activity (up to 99.8 %), and outperforms the commercial fibrin gel in sutureless wound sealing, rat gastric tissue repair, and anti-postoperative adhesion. This strategy may open a new avenue to develop adhesive/anti-adhesive Janus bioadhesives for efficient non-invasive internal tissue sealing and promoted wound healing.

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.

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.

Gelatin-DOPA-knob/fibrinogen hydrogel inspired by fibrin polymerization and mussel adhesion for rapid and robust hemostatic sealing

Tissue adhesives have attracted significant interest in the field of hemostasis. However, challenges including weak tissue adhesion, inadequate biocompatibility, and instability limit their clinical applications. Here, we have developed a gelatin-DOPA-knob/fibrinogen hydrogel inspired by the fibrin polymerization and mussel adhesion, resulting in a biocompatible bioadhesive with outstanding adhesion performance and great storage stability. This strategy involves modifying gelatin with knob peptides and catechol groups inducing crosslinking with fibrinogen to form a hydrogel via knob-hole interactions, and enhancing interfacial adhesion performance by interacting with the blood-covered tissue through catechol groups and knob peptides. This hydrogel exhibits rapid gelation, enhanced mechanical strength and adhesion properties, compared to the commonly used fibrin glue in surgery. The hydrogel significantly reduces the time required to hemostasis and the amount of blood loss in severe hemorrhage models. It ensures superior hemostatic efficacy, excellent biocompatibility, and long-term storage stability, which holds significant promise in medical settings.

A Multifunctional Double-Network Hydrogel Based on Bullfrog Skin Collagen: High-Value Utilization of Aquaculture By-Products

Bullfrog skin, as a by-product of bullfrog processing, is an ideal source of high-quality collagen due to its high protein content and low-fat characteristics. However, its comprehensive utilization is relatively low, and the discarded skins cause resource waste and environmental pollution. In this study, a citric acid extraction process for frog skin collagen was established through single-factor optimization. A multifunctional double-network hydrogel was developed by combining the prepared high-purity type I collagen with oxidized hyaluronic acid (OHA). Due to the network structure design of Schiff base bonds and Zn2+ coordination bonds, the mechanical strength of the hydrogel based on collagen and OHA compositing Zn2+ (Gel-CO@Zn) enhanced significantly. It was found that the Gel-CO@Zn hydrogel had strong tissue adhesion (16.58 kPa shear strength), rapid self-healing (<6 h), and low hemolysis (<5%). Furthermore, the Gel-CO@Zn hydrogel could reduce the survival rate of Staphylococcus aureus and Escherichia coli to 1.06% and 6.73%, respectively, showing good antibacterial properties. Through the treatment of Gel-CO@Zn, the clotting time was shortened from 433 s to 160 s and greatly reduced the blood loss (>60%) in the liver injury model of male Kunming mice. This research not only presents a novel approach for the high-value utilization of aquaculture by-products but also establishes a new paradigm for developing cost-effective, multifunctional biomedical materials, demonstrating the transformation of waste into high-value resources.

Nanocomposite Reinforced Powder With Fast Self-gelling and Robust Wet Adhesive Performances for Acute Hemostasis and Wound Repair

Severe trauma and uncontrolled hemorrhage present significant challenges in achieving hemostasis. Considering the limitations of current hemostatic materials, such as inadequate wet tissue adhesion, prolonged hemostasis time, and insufficient antimicrobial properties, a robust adhesive double cross-linked nano-composite hydrogel powder is developed, consisted of polyacrylic acid (PAA), ɛ-Poly-L-lysine (PLL) and layered double hydroxides (Mg-Al LDH, hereinafter referred to as LDH). The obtained PLL-PAA/LDH composite hydrogel powder exhibited rapid gelation, strong mechanical properties, and superior wet adhesion. Additionally, it offered excellent biocompatibility and antimicrobial properties. In various injury models involving rats and rabbits, the hemostatic performance of the adhesive PLL-PAA/LDH hydrogel powder surpassed that of commercially available n-butyl-2-cyanoacrylate (NBCA) from 3 m. Notably, the introduction of LDH enhanced the interfacial toughness of the gel system and significantly improved its adhesive properties, demonstrating remarkable hemostatic efficacy across different injury models. Furthermore, in models of rat skin incisions and full-thickness infected skin wounds, the composite hydrogel powder exhibited superior seamless suturing and repair effects compared to commercial products. Overall, this study aims to elucidate the biomedical potential of PLL-PAA/LDH composite hydrogel powder for applications in hemostatic sealing, seamless suture prevention of acute bleeding, and wound healing.

Sustainable Protein to Generate High-Strength and Durable All-Underwater Adhesive via Physical Condensation Boosting Chemical Cross-linking

Designing high-performance protein adhesives for hard tissue applications remains challenging. Here, we present a physical condensation boosting chemical cross-linking strategy to produce a high-performance all-underwater adhesive composed of corn-derived zein, genipin, and poly(l-lysine). Physical condensation between anionic zein colloids and cationic poly(l-lysine) generates a soft adhesive. Dehydration of the ionic moieties enables powdery genipin to be pre-encapsulated into the dried bulk of the physical condensate. After experiencing reversible hydration, the genipin-encapsulated adhesive can be injected and bonded to various surfaces under the waterline. Crucially, the condensed adhesive creates confined microenvironments for genipin-bridged slow chemical cross-linking, achieving sequential adhesion and curing, and in situ self-reinforcement. The protein adhesive exhibits an adhesion strength of 2.0 MPa on bovine bone and excellent friction resistance (μ ∼ 0.15). Moreover, the adhesive shows long-term stability in various complex aqueous environments. These properties coupled with excellent biocompatibility, sustainability, and scalable production indicate significant potential in bone adhesion and device coatings.

Ionic Liquid-Reinforced Multifunctional Hydrogel for the Treatment of Enterocutaneous Fistula

Enterocutaneous fistulas (ECFs) profoundly impact patients' quality of life, contributing to high morbidity rates and increased mortality due to ineffective treatment options. To address this challenge, ECFGel, a multifunctional, tissue adhesive injectable hydrogel, designed to occlude, sterilize, and promote healing of ECF tracts, is developed. ECFGel is formulated using gelatin and oxidized dextran (O-Dex) as base components, which form chemical crosslinks within the hydrogel and with surrounding biological tissues, ensuring tissue adhesiveness. A choline and geranate-based ionic liquid (IL) is incorporated to provide dual functionality, potent antimicrobial activity, and mechanical enhancement. By optimizing IL concentration, ECFGel achieves rapid gelation, enhanced mechanical strength, and improved elastic recoverability. Additionally, iohexol (IOH) is added for radiopacity, enabling real-time imaging and further strengthening the hydrogel's mechanical properties. ECFGel demonstrates antiswelling properties, biodegradability, and effective tract occlusion in porcine soft tissues. It shows strong antimicrobial activity against highly resistant, patient-derived pathogens isolated from clinical ECF cases. In a porcine perianal fistula model, ECFGel enables rapid occlusion and complete healing, promoting tissue maturation, reducing bacterial load, and increasing markers of cell proliferation and vascularization compared to untreated controls. These promising results highlight ECFGel's potential as a new therapeutic option for treating infected ECFs.

Design and characterization of metallic microfasteners for mechanical adhesion to soft tissues

Suturing by hand remains the gold standard for the manufacturing of bioprosthetic heart valves (BHVs), which is a time- and skill-intensive process for attaching tissue valve grafts to stents. Suturing becomes even more challenging for the assembly of small devices, such as pediatric BHVs. Here, we report the development of sutureless mechanical adhesion to tissue (MANTIS), a microstructured tissue fastening technology that mediates rapid attachment of rigid materials to compliant biological tissues. Following characterization of BHV tissue wall thickness, we designed 4 distinct MANTIS microfastener geometries that were fabricated in stainless steel foils via a photochemical machining process. Bioinspired microfastener designs mimicked flexure of the praying mantis claw to provide enhanced tissue entrapment upon insertion via controlled buckling. Tissue adhesion testing was performed on individual microfasteners and microfastener arrays, with all 4 MANTIS designs outperforming controls across normal, 0° shear, and 180° peel loading orientations. Overall, MANTIS shows promise as a sutureless adhesive technology for integrating mechanically disparate materials such as tissues and medical device surfaces. STATEMENT OF SIGNIFICANCE: Attaching rigid materials to soft biological tissues is a challenging problem. Current options such as sutures, staples, and chemical adhesives often fail to simultaneously achieve strong, permanent coupling in a rapidly deployable and compact form factor. Here, we designed and characterized a family of microfastener designs which can quickly puncture and interlock with connective tissue fibers to form strong adhesion that can resist multi-directional loads. This approach is reminiscent of VELCRO® and its hook-and-loop principle of operation, though our work also incorporates a "controllable deformation" functionality inspired by the praying mantis claw. We anticipate MANTIS will provide a valuable new solution for a wide range of applications that require reliable and strong attachment of device surfaces to biological tissues.

A Bio-Adaptive Janus-Adhesive Dressing with Dynamic Lubrication Overlayer for Prevention of Postoperative Infection and Adhesion

Wound postoperative infection and adhesion are prevalent clinical conditions resulting from surgical trauma. However, integrating intraoperative repair and postoperative management into a dressing suitable for wounds with unpredictable surface shapes and surroundings remains a formidable challenge. Here, we attempt to introduce a dynamic antifouling surface as wound protective covering and report an in situ formation of slippery-adhesive Janus gel (SAJG) by assembling hydrogel (N-hydrosuccinimide ester-activated powders) and elastomer (Silicon oil-infused polydimethylsiloxane). First powders can rapidly absorb interfacial water to gel and bond to tissue based on network entanglement, forming a tough adhesive hydrogel. Then precured organosilicon is applied to hydrogel and bonded together, forming a slippery elastomer. Due to the molecular polarity difference between hydrogel and elastomer, SAJG exhibits anisotropic surface behavior as evidenced by liquid repellency (hydrophilic vs. hydrophobic), and adhesion performance (bioadhesion vs. antiadhesion). Further, in vivo models are constructed and results demonstrated that the SAJG can effectively prevent bacterial infection to promote wound healing and avoid postoperative adhesion. Predictably, the morphologically adaptive SAJG with slippery and adhesive properties will have tremendous potential in addressing complex wound infections and postoperative complications.

One-Pot Synthesis of Antibacterial and Antioxidant Self-Healing Bioadhesives Using Ugi Four-Component Reactions

Bioadhesive materials are extensively utilized as alternatives to surgical sutures and wound dressings. Despite significant advancements in their synthesis, current bioadhesives suffer from inadequate mechanical stability, suboptimal wet tissue adhesion, and a lack of inherent antibacterial and antioxidant properties, while requiring multistep synthesis processes, complicating their production for biomedical applications. To address these limitations, we developed a new bioadhesive, named UgiGel, synthesized through a one-pot Ugi four-component reaction (Ugi-4CR). Our strategy utilized gelatin as the backbone, 4-formylphenylboronic acid (4-FPBA) as an aldehyde source for improved adhesion and antibacterial activity, gallic acid (GA) as a carboxylic acid source for improved antioxidant activity and wound healing, and cyclohexyl isocyanide (CyIso) to induce pseudopeptide structures. The internal crosslinking between GA and 4-FPBA via dynamic boronate ester bond formation, triggered by slight pH changes (7.4-7.8) and temperature elevation (25°C-40°C), resulted in the formation of viscoelastic and self-healing hydrogels with water as the only byproduct without the need for initiator/light activation. UgiGel showed higher adhesion to porcine skin tissue (139.8 ± 8.7 kPa) as compared to commercially available bioadhesives, Evicel (26.3 ± 2.6 kPa) and Coseal (19.3 ± 9.9 kPa). It also demonstrated effective antibacterial properties against both Gram-negative and Gram-positive bacteria, as well as antioxidant activity. Additionally, the in vitro studies using NIH-3T3 cells confirmed the biocompatibility of the UgiGel over 7 days of culture. Moreover, in vivo biocompatibility and biodegradation of UgiGel were confirmed via subcutaneous implantation in rats for up to 28 days. Our results demonstrated that UgiGel outperformed commercially available bioadhesives in terms of adhesion, self-healing, and antibacterial activity, without compromising biocompatibility or physical properties, representing a promising multifunctional bioadhesive for wound sealing and repair.

Tissue-Adhesive, Antibacterial, and Antioxidant Hydrogel Sealant for Sealing Colorectal Anastomotic Leakage and Preventing Postoperative Adhesion

Surgical treatment of colorectal diseases typically involves excising the diseased portion of the bowel and anastomosing the remaining sections to reestablish continuity. Surgical suturing has limitations in preventing anastomotic leakage and postoperative adhesion. To address these challenges, a tissue-adhesive, antibacterial, and antioxidant hydrogel is designed to cover and seal colorectal anastomotic wounds. The hydrogel is formed in situ by simply mixing oxidized hyaluronic acid, adipic acid dihydrazide-modified hyaluronic acid, ε-poly-l-lysine, and tannic acid. The hydrogel exhibits a rapid gelation rate and self-healing ability. Compared with commercial fibrin glue, the hydrogel has superior tissue-adhesive strength and wound sealing performance. The hydrogel displays potent reactive oxygen species scavenging ability and antibacterial activity against both Gram-positive and Gram-negative bacteria. The hydrogel also exhibits good biodegradation and biocompatibility. In a cecum-abdominal wall adhesion model in rats, the hydrogel attaches firmly to the injured tissues and serves as a physical barrier to prevent adhesion formation. In anastomotic leakage models after colon resection in rats and rabbits, the hydrogel effectively seals the anastomotic leakage, prevents postoperative adhesion, and promotes anastomotic healing. Thus, this multifunctional hydrogel has strong clinical potential for preventing anastomotic leakage and adhesion formation after colorectal surgery.

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.

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.

Effects of phenolic hydroxyl group structures of Alaska pollock gelatin-based adhesives on soft tissue adhesion and biocompatibility

Marine mussels adhere to various types of substrates in aqueous/wet environments, and their adhesion is controlled by the catechol structure of the phenolic hydroxyl groups. Tissue adhesives with a catechol structure have been designed based on this biomimetic adhesion mechanism. However, the effects of the chemical structure of the phenolic hydroxyl groups on tissue adhesion and biocompatibility have not yet been systematically investigated. In this study, various phenolic hydroxyl group-modified Alaska pollock gelatins (nHy-ApGltns (n = 0, 1, 2, 3)) were synthesized and their function as tissue adhesives with a poly(ethylene glycol)-based 4-armed crosslinker (4S-PEG) was evaluated. The nHy-ApGltn adhesives showed increases in bulk strength and decreases in swelling compared to the original-ApGltn (Org-ApGltn) adhesive. The tensile stress and Young's modulus of the nHy-ApGltn adhesives increased with the introduction of nHy groups. The burst strength of the nHy-ApGltn adhesives had a maximum value at each content; however, a high content of nHy in the nHy-ApGltn adhesives had a negative effect on the burst strength. The burst strength of the porcine aorta with all the nHy-ApGltn adhesives was higher than that with human blood pressure. From histological observations after burst strength measurements, the 2Hy- and 3Hy-ApGltn adhesives showed stable interfacial adhesion compared to the Org-, 0Hy-, and 1Hy-ApGltn adhesives. The nHy-ApGltn (n = 0, 3) adhesives implanted subcutaneously in rats completely degraded within 64 days without severe inflammation or foreign body reactions. Therefore, nHy-ApGltn adhesives with low nHy content have excellent tissue adhesion and biocompatibility in wet environments and have the potential for use in 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.

A self-hygroscopic, rapidly self-gelling polysaccharide-based sponge with robust wet adhesion for non-compressible hemorrhage control and infected wounds healing

Uncontrollable non-compressible hemorrhage and traumatic infection have been major causes of mortality and disability in both civilian and military populations. A dressing designed for point-of-care control of non-compressible hemorrhage and prevention of traumatic infections represents an urgent medical need. Here, a novel self-gelling sponge OHN@ε-pL is developed, integrating N-succinimidyl ester oxidized hyaluronic acid (OHN) and ε-poly-L-lysine (ε-pL). Upon application to the wound site, the sponge can rapidly absorb interfacial fluids and undergo a phase transition from sponge to gel. The transformed gel facilitates robust tissue adhesion and achieves synergistic hemostasis by enriching coagulation factors within the sponge phase and providing a barrier effect in the gel phase. The in vitro and in vivo studies revealed that the optimized OHN@ε-pL3 sponge possesses self-gelling capability, tissue adhesion, enhanced coagulation ability, and exhibits excellent biocompatibility and antibacterial efficacy. In hemostasis, OHN@ε-pL3 sponges exhibited reduced blood loss and decreased hemostatic time compared to commercial hemostatic agents, as demonstrated in rat liver, femoral vein, and tail truncation bleeding models. Furthermore, the OHN@ε-pL3 sponge exhibited superior performance in accelerating wound closure and healing of S. aureus-infected wounds. Collectively, OHN@ε-pL sponges represent a promising candidate for medical dressings, specifically for managing uncontrollable non-compressible hemorrhage and traumatic infections.

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.

Designing hydrogel for application in spinal surgery

Spinal diseases and injuries are prevalent in clinical settings and impose a substantial burden on healthcare systems. Current treatments for spinal diseases are predominantly limited to surgical interventions, drug injections, and conservative treatments. Generally, these treatment modalities have limited or no long-term benefits. Hydrogel-based treatments have emerged as potentially powerful paradigms for improving therapeutic outcomes and the quality of life of patients. Hydrogels can be injected into target sites, including the epidural, intraspinal, and nucleus pulposus spaces, in a minimally invasive manner and fill defects to provide mechanical support. Hydrogels can be designed for the localized and controlled delivery of pharmacological agents to enhance therapeutic effects and reduce adverse reactions. Hydrogels can act as structural supports for transplanted cells to improve cell survival, proliferation, and differentiation, as well as integration into adjacent host tissues. In this review, we summarize recent advances in the design of hydrogels for the treatment of spinal diseases and injuries commonly found in clinical settings, including intervertebral disc degeneration, spinal cord injury, and dural membrane injury. We introduce the design considerations for different hydrogel systems, including precursor polymers and crosslinking mechanisms. Herein, we discuss the therapeutic outcomes of these hydrogels in terms of providing mechanical support, delivering cells/bioactive agents, regulating local inflammation, and promoting tissue regeneration and functional recovery.

Robust 3D-Printable, Injectable, and Adhesive Hydrogels with Stepwise-Triggered Dual Reversible/Irreversible Covalent Linkages for Wound Healing

The development of 3D-printable and injectable biocompatible hydrogels with robust mechanical and adhesive properties useful for biomedical applications remains a great challenge. Herein, stepwise-triggered dual reversible/irreversible covalent linkages are engineered between two functionalized polymers, glycidyl methacrylate-modified polyvinyl alcohol (PVA-GMA) and oxidized sodium alginate tailed with 3-aminophenylboronic acid (OSA-PBA), allowing the availability of PVA-GMA/OSA-PBA (PGOP) hydrogels with versatile properties and functions. The PGOP hydrogels have excellent injectability, processability, mechanical strength (39.5 ± 2.3 kPa), self-healing, elasticity and toughness (80% compressive strain at 84.5 kPa stress), bioadhesion (34.2 ± 2.7 kPa adhesive strength to fresh pig skin, vs 7.3-15.38 kPa for commercial fibrin glue adhesives), degradability, antibacterial property, and biocompatibility (265% cell survival with fibroblasts co-culture for 5 d). With these merits, PGOP pregel and hydrogels can be applied as 3D-printing glue and construct materials to produce diverse 3D hierarchical architectures with high shape fidelity, good mechanical properties, and active materials-laden capacity. The mouse liver hemorrhage model and the full-thickness skin defect model demonstrate that PGOP hydrogels have excellent hemostatic ability and accelerated wound healing capacity. Therefore, this work provides 3D-printable and injectable glue and hydrogel adhesives with favorable mechanical strength useful for various biomedical applications such as tissue engineering and wound healing.

Multi-crosslinking nanoclay/oxidized cellulose hydrogel bandage with robust mechanical strength, antibacterial and adhesive properties for emergency hemostasis

Emergency bleeding presents significant challenges such as high blood flow and rapid hemorrhaging. However, many existing hemostatic bandages face limitations, including the uncontrolled release of hemostatic agents, insufficient mechanical strength, poor adhesion, and complex manufacturing processes. To address these limitations, we developed a multifunctional hydrogel bandage for emergency hemostasis using a one-pot synthesis method. The hydrogel was composed of kaolin, N-hydroxysuccinimide-grafted oxidized microcrystalline cellulose (OMCC-NHS), and polyacrylic acid (PAA). Featuring a multi-crosslinked network, it exhibited favorable elasticity (∼942 %), tensile strength (∼220 kPa), fatigue resistance, and robust tissue adhesion (∼55 kPa)-3.9 times stronger than commercial wound-closure strips, and it maintained adhesion even underwater. In addition to its mechanical properties, the hydrogel also exhibited satisfactory antibacterial activity, cytocompatibility, and histocompatibility. In vivo evaluations revealed an impressive hemostatic performance in rat models of liver bleeding, femoral artery bleeding, and tail amputation. Specifically, in the liver bleeding model, the hydrogel reduced blood loss to only 0.1 g, which is just 32 % of the blood loss seen with medical gauze. Notably, in New Zealand rabbit models with cardiac punctures and liver injuries, the hydrogel achieved rapid hemostasis and stopped the bleeding within seconds. The effective hemostatic ability of this hydrogel is primarily due to its ability to facilitate multistep hemostasis, which includes sealing the wound, rapidly absorbing blood, promoting RBC and platelets adhesion, and activating the intrinsic coagulation cascade. Therefore, this study provides a promising approach for developing gel-based hemostatic bandages, specifically tailored for emergency compressible bleeding scenarios.

Ionogel Adhesives: From Structural Design to Emerging Applications

Adhesives are indispensable in both daily household applications and advanced industrial settings, where they must deliver exceptional bonding performance. Ionogel adhesives, which feature a supporting polymer network infused with ionic liquid (IL), have emerged as promising candidates due to their unique structural and functional properties. The presence of ionic species within ionogels promotes non-covalent interactions-such as ionic bonds, ion-dipole interactions, and hydrogen bonding-that enhance both cohesion within the material and adhesion to various substrates. These characteristics make ionogels ideal for applications that require robust adhesive performance, especially in demanding environments. Despite the growing interest in ionogel adhesives, a comprehensive review of the latest advancements in this area is lacking. This paper aims to fill this gap by categorizing ionogel adhesives based on their composition and discussing strategies to enhance their adhesive properties. Additionally, novel ionogel adhesives designed for specific applications are highlighted. Finally, the current state of research is summarized, and offers insights into the challenges and future opportunities for the development of ionogel adhesives.

In Vitro Evaluation of a Semi-Autologous Fibrin Sealant for Surgical Applications

Surgical success relies on precise tissue approximation using sutures, clips, or staples. Fibrin sealant provides a user-friendly alternative, saving time and maintaining tissue integrity. Yet, its cost and potential bioburden risk are notable drawbacks. To address these concerns, a semi-autologous fibrin sealant is produced from human cryoprecipitate and compared it to a commercial fibrin sealant. The microstructure of the semi-autologous sealant closely resembles the commercial one. Initially, the commercial sealant has superior bonding strength, however, over time, both demonstrate strong adhesive properties. Moreover, when the two sealants contain equivalent fibrinogen concentrations, they show similar bonding strength and rheological properties, including thixotropic behavior, which is essential for their application as bioadhesives. Notably, it is discovered that the mechanical properties of the adhesive are mainly governed by the fibrinogen concentration, with minimal impact of other blood components. This understanding paves the way for the development of an efficient method to boost fibrinogen in blood without extensive separation. This study indicates semi-autologous fibrin glue matches commercial sealant in adhesive properties. This may offer several advantages, such as reduced bioburden, costs, improved immunomodulation, and reduced hypersensitivity and virus transmission risks. These findings hold promising prospects for enhancing the wound healing process in various medical conditions.

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.

Enabling Targeted Drug Delivery for Treatment of Ulcerative Colitis with Mucosal-Adhesive Photoreactive Hydrogel

Ulcerative colitis (UC) is a chronic inflammatory bowel disease. UC treatments are limited by significant adverse effects associated with non-specific drug delivery, such as systematic inhibition of the host immune system. Endoscopic delivery of a synthetic hydrogel material with biocompatible gelation that can efficiently cover irregular tissue surfaces provides an effective approach for targeted drug delivery at the gastrointestinal (GI) tract. An ideal integration of synthetic material with intestinal epithelium entails an integrated and preferable chemically bonded interface between the hydrogel and mucosal surface. In this study, a photo-triggered coupling reaction is leveraged as the crosslinking platform to develop a mucosal-adhesive hydrogel, which is compatible with endoscope-directed drug delivery for UC treatment. The results demonstrated superior spatiotemporal specificity and drug pharmacokinetics with this delivery system in vivo. Delivery of different drugs with the hydrogel leads to greatly enhanced therapeutic efficacy and significantly reduced systemic drug exposure with rat colitis models. The study presents a strategy for targeted and persistent drug delivery for UC treatment.

Degradable polymer bone adhesives

Highly comminuted fractures and bone defects pose a significant challenge for orthopedic surgery. Current surgical procedures commonly rely on metal implants (such as bone plates, nails and pins) for fracture internal and external fixations, but they are likely to result in problems, such as stress shielding and poor bone healing. Bone adhesive represents an attractive alternative for the treatment of fracture. The ideal bone adhesive should satisfy several performance requirements, including high adhesion strength for bone tissues, rapid in-situ curing in a physiological environment, good biocompatibility with no toxicity, degradability, and good stability in vivo. Among these requirements, degradability is a crucial characteristic of bone adhesives. This property enables the material to be easily removed without the need for surgery at a later stage, ensuring the regeneration of bone tissue without any hindrance. The degradation rate of bone adhesive varies depending on the application scenarios and tissues, ranging from weeks to years. Many bone adhesives are unable to guarantee degradability while achieving other necessary performances. Therefore, this article provides a detailed overview of the strategies to fabricate biodegradable polymer bone adhesives that can maintain high bulk and adhesion strength, biocompatibility and other properties. Finally, the current challenges in the clinical translation of bone adhesives and their future development directions are discussed.

An active shrinkage and antioxidative hydrogel with biomimetic mechanics functions modulates inflammation and fibrosis to promote skin regeneration

Achieving scar-free skin regeneration in clinical settings presents significant challenges. Key issues such as the imbalance in macrophage phenotype transition, delayed re-epithelialization, and excessive proliferation and differentiation of fibroblasts hinder wound healing and lead to fibrotic repair. To these, we developed an active shrinkage and antioxidative hydrogel with biomimetic mechanical functions (P&G@LMs) to reshape the healing microenvironment and effectively promote skin regeneration. The hydrogel's immediate hemostatic effect initiated sequential remodeling, the active shrinkage property sealed and contracted the wound at body temperature, and the antioxidative function eliminated ROS, promoting re-epithelialization. The spatiotemporal release of LMs (ACEI) during the inflammation phase regulated macrophage polarization towards the anti-inflammatory M2 phenotype, promoting progression to the proliferation phase. However, the profibrotic niche of macrophages induced a highly contractile α-SMA positive state in myofibroblasts, whereas the sustained LMs release could regulate this niche to control fibrosis and promote the correct biomechanical orientation of collagen. Notably, the biomimetic mechanics of the hydrogel mimicked the contraction characteristics of myofibroblasts, and the skin-like elastic modulus could accommodate the skin dynamic changes and restore the mechanical integrity of wound defect, partially substituting myofibroblasts' mechanical role in tissue repair. This study presents an innovative strategy for skin regeneration.

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.

Smart design in biopolymer-based hemostatic sponges: From hemostasis to multiple functions

Uncontrolled hemorrhage remains the leading cause of death in clinical and emergency care, posing a major threat to human life. To achieve effective bleeding control, many hemostatic materials have emerged. Among them, nature-derived biopolymers occupy an important position due to the excellent inherent biocompatibility, biodegradability and bioactivity. Additionally, sponges have been widely used in clinical and daily life because of their rapid blood absorption. Therefore, we provide the overview focusing on the latest advances and smart designs of biopolymer-based hemostatic sponge. Starting from the component, the applications of polysaccharide and polypeptide in hemostasis are systematically introduced, and the unique bioactivities such as antibacterial, antioxidant and immunomodulation are also concerned. From the perspective of sponge structure, different preparation processes can obtain unique physical properties and structures, which will affect the material properties such as hemostasis, antibacterial and tissue repair. Notably, as development frontier, the multi-functions of hemostatic materials is summarized, mainly including enhanced coagulation, antibacterial, avoiding tumor recurrence, promoting tissue repair, and hemorrhage monitoring. Finally, the challenges facing the development of biopolymer-based hemostatic sponges are emphasized, and future directions for in vivo biosafety, emerging materials, multiple application scenarios and translational research are proposed.

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.

Adhesive and antibacterial guar gum-based nanocomposite hydrogel for remodeling wound healing microenvironment

Hydrogels are promising wound dressings due to their extracellular matrix-like properties and tunable structure-function characteristics. Besides the physical isolation effect, hydrogel dressings are highly expected to possess tissue-adhesive performance and antibacterial capacity, which are beneficial for their clinical translations. Herein, a guar gum (GG)-based nanocomposite hydrogel was fabricated by mixing methacrylated GG (GGMA), acrylic acid, acrylated 3-aminophenylboronic acid, mangiferin (MF)-loaded cetyltrimethyl ammonium chloride (CTAC) micelles (MF@CTAC) and radical initiator. This hydrogel exhibited stable and tunable mechanical property as well as excellent biocompatibility. Borate crosslinking and physical interactions of the hydrogel produced a certain degree of self-healing ability, good tissue adhesive and hemostatic capacity. MF endowed the hydrogel with good antioxidant ability and excellent synergistic antibacterial ability with CATC. In vivo experiments indicated that the hydrogel significantly accelerated wound healing with a narrower wound edge, thicker granulation tissue, maturer epidermis and dermis tissue, higher collagen deposition level, milder inflammatory response, and enhanced angiogenesis. The hydrogel without adding antibiotics and other exogenous active ingredients showed great application potential as a versatile wound dressing material.

Pullulan dialdehyde cross-linked dual-action adhesive with high adhesion to lung tissue and the capability of pH-responsive drug release

To address the main challenges for thoracoscopic lung cancer surgery, including persistent pulmonary air leaks and cancer recurrence, this study developed an in-situ adhesive that can effectively adhere to the lung and release the anticancer drug in response to pH. The adhesive was formulated using hydrophobically modified cold-water fish skin gelatin (hm-CFG) and cross-linking agent pullulan dialdehyde (PDA), in which succinic dihydrazide-modified doxorubicin (SDH-DOX) can be incorporated. Utilizing PDA could improve both cohesion and interfacial adhesion, while also offering drug-loading sites through the aldehyde groups that were not involved in cross-linking. The optimal adhesive formulation was 9C10-CFG/PDA (30 w/v% 9 mol% decanal modified CFG/20 w/v% PDA). The 9C10-CFG/PDA adhesive exhibited suitable cohesive strength, good mechanical flexibility (tensile strain over 170 %), and strong interface adhesion. The burst strength of 9C10-CFG/PDA adhesive (131.5 ± 22.2 mm Hg) was almost 6-fold higher than that of commercial fibrin sealant. In a rat pneumothorax model, 9C10-CFG/PDA adhesive displayed favorable wound-sealing properties, as evidenced by CT imaging and restored rat behavior. When combined with the anticancer drug, SDH-DOX@Adhesive could release the drug in response to pH more gradually than DOX@Adhesive. This dual-action adhesive is anticipated to mitigate post-surgical occurrences of lung air leaks and cancer recurrence.

A 3D bioprinted adhesive tissue engineering scaffold to repair ischemic heart injury

Adhesive tissue engineering scaffold (ATES) devices can be secured on tissues by relying on their intrinsic adhesive properties, hence, avoiding the complications such as host tissue/scaffold damage that are associated with conventional scaffold fixation methods like suturing or bioglue. This study introduces a new generation of three-dimensional (3D) bioprinted ATES systems for use as cardiac patches to regenerate the adult human heart. Tyramine-modified methacrylated hyaluronic acid (HAMA-tyr), gelatin methacrylate (GelMA), and gelatin were used to create the hybrid bioink formulation with self-adhesive properties. ATESs were bioprinted and further modified to improve the adhesion properties. In-depth characterization of printing fidelity, pore size, mechanical properties, swelling behavior, as well as biocompatibility was used to create ATESs with optimal biological function. Following in vitro testing, the ATESs were tested in a mouse model of myocardial infarction to study the scaffold adhesive strength in biological milieu. The method developed in this study can be used to manufacture off-the-shelf ATESs with complex cellular and extracellular architecture, with robust potential for clinical translation into a variety of personalized tissue engineering and regenerative medicine applications.

Naturally Inspired Tree-Ring Structured Dressing Provides Sustained Wound Tightening and Accelerates Closure

Mechanically regulated wound dressings require a rational combination of contraction and adhesion functions as well as balancing exudate-induced swelling issues. However, many of the reported dressings face the dilemma of impaired function and impeded wound self-contraction due to fluid-absorbing swelling. In this study, inspired by the tree ring, a core-ring structured hydrogel dressing capable of mechanical modulation is designed, and prepare it using a simple two-step photopolymerization process. The core covers the center of the wound, contracts spontaneously at body temperature to generate a contractile force of 3.4 kPa, and resists swelling. Meanwhile, the ring adheres to the normal epidermis around the wound and transfers the contraction stress to the wound edge. The integration of a functionally independent core and ring ultimately achieves effective wound traction and avoids dressing swelling. In murine and porcine skin wound-healing models, this hydrogel with a closely connected core and ring promotes healing by accelerating epidermal closure (50% closure in mouse skin on day 2, 85% closure in pig skin on day 8), collagen deposition, vascular maturation, and extracellular matrix remodeling. These results can guide further research on mechanical force modulation in wound healing, with the potential for clinical translation.

A supramolecular hydrogel leveraging hierarchical multi-strength hydrogen-bonds hinged strategy achieving a striking adhesive-mechanical balance

To obtain high-performance tissue-adhesive hydrogel embodying excellent mechanical integrity, a supramolecular hydrogel patch is fabricated through in situ copolymerization of a liquid-liquid phase separation precursor composed of self-complementary 2-2-ureido-4-pyrimidone-based monomer and acrylic acid coupled with subsequent corporation of bioactive epigallocatechin gallate. Remarkably, the prepared supramolecular hydrogel leverages hierarchical multi-strength hydrogen-bonds hinged strategy assisted by alkyl-based hydrophobic pockets, broadening the distribution of binding strength of physical junctions, striking a canonical balance between superb mechanical performance and robust adhesive capacity. Ultimately, the fabricated supramolecular hydrogel patch stands out as a high stretchability (1500 %), an excellent tensile strength (2.6 MPa), a superhigh toughness (12.6 MJ m-3), an instant and robust tissue adhesion strength (263.2 kPa for porcine skin), the considerable endurance under cyclic loading and reversible adhesion, a superior burst pressure tolerance (108 kPa) to those of commercially-available tissue sealants, and outstanding anti-swelling behavior. The resultant supramolecular hydrogel patch demonstrates the rapid hemorrhage control within 60 s in liver injury and efficient wound closure and healing effects with alleviated inflammation and reduced scarring in full-thickness skin incision, confirming its medical translation as a promising self-rescue tissue-adhesive patch for hemorrhage prevention and sutureless wound closure.

Activation of muscle amine functional groups using eutectic mixture to enhance tissue adhesiveness of injectable, conductive and therapeutic granular hydrogel for diabetic ulcer regeneration

Herein, Polydopamine-modified microgels and microgels incorporated with superficial epoxy groups were synthesized and applied as precursors for the fabrication of four granular hydrogels. To enhance the tissue adhesiveness, a ternary deep eutectic solvent was synthesized to activate the muscle amine functional groups facilitating the formation of robust NC bonds at ambient conditions. At a certain shear rate of 10 s-1, hydrogel DMG displayed a viscosity of 9×103 Pa/s, representing the highest complex viscosity among the tested hydrogels primarily driven by quinone groups in PDA which enhanced reversible interactions, thereby increasing particle cohesion. Moreover, the intersection point escalating from about 4×103 to approximately 9×104 as the concentration of DMG increased from 0 % (for MG) to 70% (7D3MG) by weight. There was a decrease in adhesion strength from 0.45 ± 0.08 N in MG to 0.39 ± 0.16 N, 0.35± 0.18 N, and 0.33 ± 0.15 N for 3D7MG, 7D3MG, and DMG respectively, suggesting that MG was capable of forming numerous covalent bonds, thereby enhancing its adhesion to the substrate. The type of eutectic mixture affected the electrical conductivity and a very important point was the changes in resistance value with time. For MG catalyzed by [DES]AZG, the resistance increased only by 1.3 % (from 3.37 to 3.81 kΩ) at day 3 and 37.09 % (from 3.37 to 4.62 kΩ) at day 5. The 3D7MG hydrogel exhibited superior therapeutic efficacy toward diabetic wound regeneration. The proliferation index value for 3D7MG-[DES]AZG and 3D7MG-[DES]AG were calculated 42.3 % and 58.6 %, respectively, while the control group exhibited a lower value of 37.8 %.

A Pressure-Sensitive, Repositionable Bioadhesive for Instant, Atraumatic Surgical Application on Internal Organs

Pressure-sensitive adhesives are widely utilized due to their instant and reversible adhesion to various dry substrates. Though offering intuitive and robust attachment of medical devices on skin, currently available clinical pressure-sensitive adhesives do not attach to internal organs, mainly due to the presence of interfacial water on the tissue surface that acts as a barrier to adhesion. In this work, a pressure-sensitive, repositionable bioadhesive (PSB) that adheres to internal organs by synergistically combining the characteristic viscoelastic properties of pressure-sensitive adhesives and the interfacial behavior of hydrogel bioadhesives, is introduced. Composed of a viscoelastic copolymer, the PSB absorbs interfacial water to enable instant adhesion on wet internal organs, such as the heart and lungs, and removal after use without causing any tissue damage. The PSB's capabilities in diverse on-demand surgical and analytical scenarios including tissue stabilization of soft organs and the integration of bioelectronic devices in rat and porcine models, are demonstrated.

Surface enzyme-polymerization endows Janus hydrogel tough adhesion and regenerative repair in penetrating orocutaneous fistulas

Penetrating orocutaneous or oropharyngeal fistulas (POFs), severe complications following unsuccessful oral or oropharyngeal reconstruction, remain complex clinical challenges due to lack of supportive tissue, contamination with saliva and chewed food, and dynamic oral environment. Here, we present a Janus hydrogel adhesive (JHA) with asymmetric functions on opposite sides fabricated via a facile surface enzyme-initiated polymerization (SEIP) approach, which self-entraps surface water and blood within an in-situ formed hydrogel layer (RL) to effectively bridge biological tissues with a supporting hydrogel (SL), achieving superior wet-adhesion and seamless wound plugging. The tough SL hydrogel interlocked with RL dissipates energy to withstand external mechanical stimuli from continuous oral motions like chewing and swallowing, thus reducing stress-induced damage. In male New Zealand rabbit POF models, the JHA demonstrates strong adhesion and fluid-tight sealing, and maintained firm sealing for over 3 days without any decreased signs under a normal diet. After 12 days, both extraoral cutaneous and mucosal wounds achieved complete closure, with mechanical strengths comparable to normal tissues. Similar therapeutic efficacy was also confirmed in male beagle dog POF models. Thus, the proposed JHA hydrogel shows great potential for deep wound sealing and providing mechanical support to assist healing in penetrating fistulas and other injuries.

Dynamic silicone hydrogel gauze coatings with dual anti-blood adhesion mechanism for rapid hemostasis and minimal secondary damage

Hemostatic materials that can rapidly control bleeding without causing secondary damage or sharp pain upon removal are receiving increasing demands in acute trauma treatments and first-aid supplies. Here, we report the development of a dynamic silicone hydrogel coating on medical gauze to enable rapid hemostasis and synergistic anti-blood adhesion properties. The silicone hydrogel can spontaneously form oriented cross-linked structures on fibrous medical gauze through a solution-processing method to achieve macroscopic superhydrophobicity with microscopic surface slipperiness, resulting in excellent anti-blood adhesion with the on-wound peeling force at ~0 millinewton. The development of dynamic silicone hydrogel coating on medical gauze enables a unique integration of advanced features including instant bleeding control, excellent anti-blood adhesion, and excellent air permeability. The proposed strategy is also suitable for scalable production, making it promising in the applications of trauma management.

Self-Reinforcing Ionogel Bioadhesive Interface for Robust Integration and Monitoring of Bioelectronic Devices with Hard Tissues

Integrating bioelectronic devices with hard tissues, such as bones and teeth, is essential for advancing diagnostic and therapeutic technologies. However, stable and durable adhesion in dynamic, moist environments remains challenging. Traditional bioadhesives often fail to maintain strong bonds, especially when interfacing with metal electrodes and hard tissues. This study introduces a self-reinforcing ionogel bioadhesive interface (IGBI) combining silk fibroin and calcium ions, designed to provide robust and conductive integration of bioelectronic devices with hard tissues. The IGBI exhibits strong adhesion (up to 186 J m-2) and undergoes mechanical self-reinforcement through a structural transition in silk fibroin under physiological conditions. In vivo experiments demonstrate the IGBI's effectiveness in repairing bone defects and reimplanting teeth, with the added capability of wireless, real-time monitoring of bone healing. This approach allows for continuous tracking of tissue regeneration without a second invasive surgery for device removal. The IGBI represents a significant advancement in bioelectronic integration, offering a durable and versatile solution for challenging environments. Such unique self-reinforcing properties make the IGBI a promising material for biomedical applications where traditional adhesives are insufficient.

Breaking the boundaries of wound closure: A novel polyurethane tissue adhesive with enhanced healing properties

Over the past few decades, there have been advancements in the development of high-performance tissue adhesives as alternatives to traditional sutures and staples for rapid and effective wound closure post-surgery. While tissue adhesives offer advantages such as ease of use, short application time, and minimal tissue damage, they also face challenges related to biocompatibility, biodegradability, and adhesive strength. In this study, L-lysine diisocyanate (LDI) and trimethylolpropane (TMP) were utilized as the primary raw materials to produce a prepolymer terminated with NCO, resulting in the development of a new biocompatible polyurethane tissue adhesive (TMP-LDI). Additionally, SiO2 nanoparticles were incorporated into the prepolymer, significantly enhancing the adhesive strength of the TMP-LDI tissue adhesive through the "nanobridging effect," achieving a strength of 170.4 kPa. Furthermore, the SiO2/TMP-LDI tissue adhesive exhibited satisfactory temperature change during curing and degradation performance. In vitro and in vivo studies demonstrated that SiO2/TMP-LDI exhibited good biocompatibility, efficient hemostasis, antimicrobial properties, and the ability to promote wound healing. This research presents a novel approach for the development of tissue adhesives with superior adhesive performance.

Mechanical and Dimensional Stability of Gelatin-Based Hydrogels Through 3D Printing-Facilitated Confined Space Assembly

Hydrogels have emerged as promising biomaterials for tissue regeneration; yet, their inherent swelling can cause deformation and reduced mechanical properties, posing challenges for practical applications in biomedical engineering. Traditional methods to reduce hydrogel swelling often involve complex synthesis procedures with limited flexibility. Inspired by nature's efficient designs, we present here the approach to improve hydrogel performance using 3D printing-assisted microstructure engineering. By utilizing polymerization-induced phase separation of hydrogel from copolymerization of gelatin methacrylate and hydroxyethyl methacrylate (poly(GelMA-co-HEMA)) in the confined space during vat photopolymerization (VPP) 3D printing, we replicate the cuttlebone-like microstructure of hydrogels with enhanced mechanical properties and swelling resistance. We demonstrate here a 4-fold increase in elastic modulus compared to bulk polymerization of poly(GelMA-co-HEMA), together with improved mechanical and dimensional stability. This method offers promising opportunities for practical biomedical and tissue engineering applications, overcoming previous limitations in the design and performance.

Harnessing Biomimicry for Controlled Adhesion on Material Surfaces

Nature serves as an abundant wellspring of inspiration for crafting innovative adhesive materials. Extensive research is conducted on various complex forms of biological attachment, such as geckos, tree frogs, octopuses, and mussels. However, significant obstacles still exist in developing adhesive materials that truly replicate the behaviors and functionalities observed in living organisms. Here, an overview of biological organs, structures, and adhesive secretions endowed with adhesion capabilities, delving into the intricate relationship between their morphology and function, and potential for biomimicry are provided. First, the design principles and mechanisms of adhesion behavior and individual organ morphology in nature are summarized from the perspective of structural and size constraints. Subsequently, the value of engineered and bioinspired adhesive materials through selective application cases in practical fields is emphasized. Then, a forward-looking gaze on the conceivable challenges and associated opportunities in harnessing biomimetic strategies and biological materials for advancing adhesive material innovation is highlighted and cast.

DOTAGEL: a hydrogen and amide bonded, gelatin based, tunable, antibacterial, and high strength adhesive synthesized in an unoxidized environment

The development of bioadhesives that concurrently exhibit high adhesion strength, biocompatibility, and tunable properties and involve simple fabrication processes continues to be a significant challenge. In this study, a novel bioadhesive named DOTAGEL is synthesized by crosslinking gelatin (GA), dopamine (DA), and tannic acid (TA) in an unoxidized environment due to the advantage of controlling the degree of protonation in GA and TA, as well as controlling the degree of intermolecular amide and hydrogen bonding in the acidic medium. DOTAGEL (DA + TA + GA) shows superior adhesion strengths of 104.6 ± 46 kPa on dry skin and 35.6 ± 4.5 kPa on wet skin, up to 13 attachment-detachment cycles, retains adhesion strength under water for up to 10 days and is capable of joining two cut parts of internal organs of mice. Moreover, DOTAGEL shows strong antibacterial properties, self-healing, and biocompatibility since it contains TA, a natural and antibacterial cross-linker with abundant hydroxyl groups and the capability of forming non-covalent bonds in an unoxidized environment, and dopamine hydrochloride, a mussel inspired biomaterial containing both the amine and catechol groups for amide bonding and hydrogen bonding with TA and GA. The cross-linking among 20% (w/v) GA, 0.2% (w/v) DA, and 20% (w/v) TA is done by the centrifugation process at room temperature. Two different acids, hydrochloric acid and acetic acid, were used for tuning the pH of the medium, which led to two different samples named DOTAGEL/AA and DOTAGEL/HCL. The degree of cross-linking and mechanical and biochemical properties, like adhesion strength, degradation rate, antibacterial properties, stickiness, etc., are tuned by adjusting the pH of the medium. DOTAGEL/HCL showed 6.5 times faster degradation in 10 days, a faster release rate in the antibacterial study, 2 times adhesion strength in a dry medium, and more stickiness. The novelty lies not only in increased adhesion strength but also in the single-step fabrication process of the adhesive in the acidic medium. This research proposes the formation of a tunable antibacterial adhesive that is capable of working on wet surfaces within the body and that has the potential to become a successful tissue adhesive with a wide range of possibilities in controlled drug delivery at wound sites and other biomedical applications.

Strain-Programmed Adhesive Patch for Accelerated Photodynamic Wound Healing

As an alternative to tissue adhesives, photochemical tissue bonding is investigated for advanced wound healing. However, these techniques suffer from relatively slow wound healing with bleeding and bacterial infections. Here, the versatile attributes of afterglow luminescent particles (ALPs) embedded in dopamine-modified hyaluronic acid (HA-DOPA) patches for accelerated wound healing are presented. ALPs enhance the viscoelastic properties of the patches, and the photoluminescence and afterglow luminescence of ALPs maximize singlet oxygen generation and collagen fibrillogenesis for effective healing in the infected wounds. The patches are optimized to achieve the strong and rapid adhesion in the wound sites. In addition, the swelling and shrinking properties of adhesive patches contribute to a nonlinear behavior in the wound recovery, playing an important role as a strain-programmed patch. The protective patch prevents secondary infection and skin adhesion, and the patch seamlessly detaches during wound healing, enabling efficient residue clearance. In vitro, in vivo, and ex vivo model tests confirm the biocompatibility, antibacterial effect, hemostatic capability, and collagen restructuring for the accelerated wound healing. Taken together, this research collectively demonstrates the feasibility of HA-DOPA/ALP patches as a versatile and promoting solution for advanced accelerated wound healing, particularly in scenarios involving bleeding and bacterial infections.

Mechanically skin-like and water-resistant self-healing bioelastomer for high-tension wound healing

The biomedical application of self-healing materials in wet or (under)water environments is quite challenging because the insulation and dissociation effects of water molecules significantly reduce the reconstruction of material-interface interactions. Rapid closure with uniform tension of high-tension wounds is often difficult, leading to further deterioration and scarring. Herein, a new type of thermosetting water-resistant self-healing bioelastomer (WRSHE) was designed by synergistically incorporating a stable polyglycerol sebacate (PGS) covalent crosslinking network and triple hybrid dynamic networks consisting of reversible disulfide metathesis (SS), and dimethylglyoxime urethane (Dou) and hydrogen bonds. And a resveratrol-loaded WRSHE (Res@WRSHE) was developed by a swelling, absorption, and crosslinked network locking strategy. WRSHEs exhibited skin-like mechanical properties in terms of nonlinear modulus behavior, biomimetic softness, high stretchability, and good elasticity, and they also achieved ultrafast and highly efficient self-healing in various liquid environments. For wound-healing applications of high-tension full-thickness skin defects, the convenient surface assembly by self-healing of WRSHEs provides uniform contraction stress to facilitate tight closure. Moreover, Res@WRSHEs gradually release resveratrol, which helps inflammatory response reduction, promotes blood vessel regeneration, and accelerates wound repair.

Dynamic injectable tissue adhesives with strong adhesion and rapid self-healing for regeneration of large muscle injury

Wounds often necessitate the use of instructive biomaterials to facilitate effective healing. Yet, consistently filling the wound and retaining the material in place presents notable challenges. Here, we develop a new class of injectable tissue adhesives by leveraging the dynamic crosslinking chemistry of Schiff base reactions. These adhesives demonstrate outstanding mechanical properties, especially in regard to stretchability and self-healing capacity, and biodegradability. Furthermore, they also form robust adhesion to biological tissues. Their therapeutic potential was evaluated in a rodent model of volumetric muscle loss (VML). Ultrasound imaging confirmed that the adhesives remained within the wound site, effectively filled the void, and degraded at a rate comparable to the healing process. Histological analysis indicated that the adhesives facilitated muscle fiber and blood vessel formation, and induced anti-inflammatory macrophages. Notably, the injured muscles of mice treated with the adhesives displayed increased weight and higher force generation than the control groups. This approach to adhesive design paves the way for the next generation of medical adhesives in tissue repair.