An Adhesive Hydrogel with "Load-Sharing" Effect as Tissue Bandages for Drug and Cell Delivery

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.

A self-gelling hemostatic powder boosting radiotherapy-elicited NK cell immunity to combat postoperative hepatocellular carcinoma relapse

Liver resection represents a main curative treatment for patients with early-stage hepatocellular carcinoma (HCC), but there is a rather high incidence of postoperative HCC relapse, which severely shortens long-term survival time. Currently, no standard adjuvant strategies are available for preventing HCC relapse in clinical practice. Impaired natural killer (NK) cell anti-tumor immunity has been disclosed as a crucial root of HCC relapse, indicating that reinstating NK cell anti-tumor immunity may show promise to curb HCC relapse. Coincidently, mounting evidence shows that radiotherapy (RT) can trigger NK cell anti-tumor immunity, though its mechanisms have never been completely elucidated. Herein, we uncover that RT can induce immunogenic cell death and activate cGAS-STING pathway in HCC cells to elicit NK cell anti-tumor immunity. However, RT is also revealed to enhance autophagy and CD73 expression in HCC cells, as well as neutrophil extracellular traps (NETs) formation, which largely limits RT-induced activation of NK cell anti-tumor immunity. Therefore, a cocktail of autophagy inhibitor 3-methyladenine, CD73 inhibitor ARL 67156 trisodium and NETs lyase DNase I may sensitize RT to reinvigorate NK cell anti-tumor immunity and thus prevent HCC relapse postresection. To minimize therapy-related side effects, a nanocomposite powder encapsulating such a triple-drug cocktail is developed. This powder can rapidly form adhesive hydrogel in situ after applied to surgical margin, consequently fulfilling liver-localized sustained drug delivery. Importantly, it can sensitize RT to reinstate NK cell anti-tumor immunity to combat postoperative HCC relapse in Heap1-6-HCC murine model. Besides, this powder can also generate rapid hemostasis in rat and porcine models. Altogether, this work provides an innovative strategy to thwart postoperative HCC relapse and bleeding.

Injectable and implantable hydrogels for localized delivery of drugs and nanomaterials for cancer chemotherapy: A review

Multiple chemotherapeutic strategies have been developed to tackle the complexity of cancer. Still, the outcome of chemotherapeutic regimens remains impaired by the drugs' weak solubility, unspecific biodistribution and poor tumor accumulation after systemic administration. Such constraints triggered the development of nanomaterials to encapsulate and deliver anticancer drugs. In fact, the loading of drugs into nanoparticles can overcome most of the solubility concerns. However, the ability of systemically administered drug-loaded nanomaterials to reach the tumor site has been vastly overestimated, limiting their clinical translation. The drugs' and drug-loaded nanomaterials' systemic administration issues have propelled the development of hydrogels capable of performing their direct/local delivery into the tumor site. The use of these macroscale systems to mediate a tumor-confined delivery of the drugs/drugs-loaded nanomaterials grants an improved therapeutic efficacy and, simultaneously, a reduction of the side effects. The manufacture of these hydrogels requires the careful selection and tailoring of specific polymers/materials as well as the choice of appropriate physical and/or chemical crosslinking interactions. Depending on their administration route and assembling process, these matrices can be classified as injectable in situ forming hydrogels, injectable shear-thinning/self-healing hydrogels, and implantable hydrogels, each type bringing a plethora of advantages for the intended biomedical application. This review provides the reader with an insight into the application of injectable and implantable hydrogels for performing the tumor-confined delivery of drugs and drug-loaded nanomaterials.

Cationic Carbon Dot Reinforced Highly Tensile, Tough, Dehydration Resistant Polyelectrolyte Hydrogels with Fluorescence for Flexible Sensing and Information Anti-Counterfeiting

With the rapid development of wearable devices, there is an increasing demand for multifunctional conductive soft materials. Nanocomposite hydrogels containing carbon nanofillers such as carbon dots (CDs) composite gels emerge as promising candidates. However, traditional CDs nanocomposite hydrogels face limitations in terms of mechanical strength, stability and elasticity. To overcome these critical challenges, in this work, a cationic carbon dots (CCDs)-reinforced polyelectrolyte hydrogel engineered through synergistic electrostatic assembly and salting-out strategies is developed. The polyacrylic acid/sodium hyaluronate/cationic carbon point glycerol-water binary solvent fluorescent organohydrogel (PAH-CG) is fabricated. The resulting organohydrogel PAH-CG successfully overcame the plasticizing effect of glycerol, resulting in a significant enhancement of mechanical properties, with a 149-fold increase in Young's modulus compared to the control hydrogel. Specifically, the PAH-CG hydrogel exhibited high tensile strain (1200%-2734%), tensile strength (234 kPa), and modulus (275 kPa), alongside excellent elasticity, fluorescence, and dehydration resistance. The improvement in mechanical properties leads to excellent performance in flexible sensor applications. Concurrently, glycerol incorporation not only amplifies fluorescence intensity but also improves dehydration resistance and moisture absorption. Applications for encrypted transmission of information and anti-counterfeiting have been developed based on these properties, making PAH-CG hydrogels a promising platform for advanced smart devices.

Acid-Triggered Charge-Switchable Antibacterial Hydrogel for Accelerated Healing of Gastric Mucosal Wounds

Infection with Helicobacter pylori (H. pylori) is a primary etiological factor for chronic gastritis, peptic ulcers, and gastric cancer. The limited specificity of antibiotics against H. pylori, combined with the risk of severe adverse events from endoscopic submucosal dissection (ESD), presents a major global health challenge in treating gastric mucosal injuries. To address this issue, we developed a targeted antibacterial hydrogel based on a charge-reversal amphiphilic molecule, designed for the harsh gastric acid environment and capable of immediate and strong adhesion. The hydrogel is composed of acryl aspartate (AASP) and cysteine-grafted carboxymethyl chitosan (CMCS-NAC) as the base matrix, integrated with gastric acid-responsive charge-reversal antibacterial molecules (C16N-DCA). Simulated studies show that C16N-DCA undergoes charge reversal under acidic conditions (pH 3), enabling targeted H. pylori eradication mediated by gastric acid, with 98% efficacy and sustained antibacterial activity for up to 36 h. In vitro and in vivo experiments in rodent and porcine models confirmed its safety and efficacy in acidic gastric conditions. This hydrogel offers strong tissue protection and effectively modulates the gastric wound microenvironment, facilitating wound healing and presenting an easily adoptable solution for gastric wound management.

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.

Self-Crosslinking AuNPs Composite Hydrogel Bolus for Radiophotothermal Therapy

Radiophotothermal therapy is a promising treatment for superficial tumors. Traditional radiotherapy requires tissue boluses on the patient's skin to increase therapeutic effectiveness due to the dose-buildup effect of high-energy radiation. However, combining radiotherapy with photothermal therapy leads to uncertainties as the low-penetration near-infrared light dose is reduced after penetrating the bolus. To enhance precision and effectiveness, this study introduces a novel bolus made of AuNPs@poly(AM-THMA-DMAEMA) composite hydrogel. This hydrogel is prepared through a one-pot method involving the reduction of trihydrate chloroauric acid (HAuCl4·3H2O) and copolymerization of acrylamide (AM) and N-[Tris(hydroxymethyl)methyl]acrylamide (THMA) in a redox system with dimethylaminoethyl methacrylate (DMAEMA) and potassium persulfate (KPS). The gold nanoparticles (AuNPs) improve the mechanical strength (tensile strength of 320.84 kPa, elongation at break of 830%) and antibacterial properties (>99% against Staphylococcus aureus). The local surface plasmon resonance (LSPR) effect of AuNPs enables the hydrogel to absorb near-infrared light for precise monitoring of the infrared radiation dose. The hydrogel's biocompatibility is enhanced by the absence of additional crosslinking agents, and its excellent surface adhesion strength is due to numerous hydrogen bonds and electrostatic interactions. This study offers new possibilities for nanoparticle composite hydrogels as tissue boluses, achieving high precision and efficiency in radiophotothermal therapy.

A Heterojunction Piezoelectric Antimicrobial Asymmetric Hydrogel for Dynamic Wound Healing and Monitoring

Dynamic wound care presents significant challenges for conventional dressings due to the complex environment and high-frequency motion associated with such injuries. In this study, a multifunctional photo-crosslinked piezoelectric hydrogel (OAPS) is developed, incorporating heterojunction Se-doped KH570 modified BaTiO3 nanoparticles (Se-BT570 NPs) as a core component, and designed to address antimicrobial and monitoring needs in wound care, particularly at sites with high-frequency movement. The OAPS hydrogel effectively utilizes the inherent high-frequency motion in dynamic wounds, enhancing antimicrobial efficacy and enabling real-time monitoring of wound and human health statuses. This is achieved through the synergistic effects of piezoelectric properties and nano-heterostructures that enable self-driven charge transfer. Such integration allows for dual applications in both diagnosis and treatment. Experimental results demonstrated that the OAPS hydrogel exhibits excellent mechanical strength and adhesive properties, effectively adapting to high-frequency motion. Additionally, the hydrogel can be activated by dynamic wound environments to perform antimicrobial and wound monitoring functions, significantly accelerating the healing of dynamic wounds, with an efficacy rate of 99.75%. This study highlights the potential of piezoelectric nanomaterials in dynamic wound healing, offering a promising strategy for managing complex, dynamic wound care.

Multi-targeted nanogel drug delivery system alleviates neuroinflammation and promotes spinal cord injury repair

Spinal cord injury (SCI) is significantly hampered by an inflammatory microenvironment, prompting continued efforts in drug development to address inflammation. Research shows that quercetin (Que) exhibits excellent performance in reducing inflammation and neuroprotection. However, its application is limited by poor solubility, notable side effects, and the unique pathophysiology of the spinal cord. In this study, we introduce a novel multifunctional liposome hydrogel drug delivery system (QLipTC@HDM), obtained by incorporating liposomes with blood-spinal cord barrier penetration and injury site targeting properties (LipTC) into a dual-network viscous hydrogel (HDM). Our results demonstrate that encapsulating Que in LipTC (QLipTC) enhances solubility, minimizes toxic side effects, facilitates lesion targeting, and aids in crossing the blood-spinal cord barrier. Moreover, encapsulation in HDM significantly prolongs the retention of QLipTC at the injury site after local administration. Crucially, our findings reveal that QLipTC@HDM induces M2 phenotype transformation in glial cells and in mice with SCI, thereby mitigating inflammation. This intervention additionally preserves the integrity of the blood-spinal cord barrier, optimizes the spinal cord microenvironment, reduces glial scarring, promotes axonal regeneration, and enhances motor function recovery in SCI mice. In summary, our investigations highlight the potential of this disease-specific drug delivery system as a promising therapeutic approach for the treatment and management of SCI.

The mussel-inspired GelMA/dopamine/hyaluronic acid composite hydrogel dressing for wet surface adhesion

Tissue adhesives have attracted wide attention as alternatives to sutures. Further developments in adhesives with excellent adhesion and biocompatibility for wet tissue surfaces are still required. This study provides a new solution for the development of bioadhesives for use on tissue surfaces under wet conditions. In this study, a novel adhesive composite hydrogel (GDHA) consisting of methacrylated gelatin (GelMA), hyaluronic acid (HA) and dopamine (DA) is developed by Schiff base reaction and photo-crosslinking. A series of experiments including material characterization, mechanical tests, biocompatibility test and experiments in mice have been done to evaluate the proposed dressing. The results show that GDHA composite hydrogel dressing retains the photo-crosslinking properties of GelMA, which makes it easier to be prepared. In addition, the dressing overcomes the easy oxidation disadvantages of existing mussel-inspired adhesives by grafting DA onto HA, which makes it adhere more stable, especially for wet surfaces. Besides, the GDHA hydrogel exhibits excellent biocompatibility and it could promote wound healing by reducing inflammatory cells and accelerating collagen deposition in a full-layer skin wound mode of mice. These results suggest that the GDHA hydrogel with stable adhesion and great biocompatibility is an alternative for wet surface, presenting potential clinical applications.

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.

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.

Preventing postsurgical colorectal cancer relapse: A hemostatic hydrogel loaded with METTL3 inhibitor for CAR-NK cell therapy

Colorectal cancer (CRC) recurrence post-surgery remains a major challenge. While Chimeric Antigen Receptor (CAR)-engineered natural killer (NK) cells hold immense therapeutic potential, their intratumoral infiltration ability remains limited, hampering efficacy. Building upon prior research suggesting that chemokines like C-X-C motif chemokine ligand 9 (CXCL9) and C-X-C motif chemokine ligand 10 (CXCL10) recruit CAR-NK cells, we hypothesized that tumor cell m6A methylation, regulated by Methyltransferase-like 3 (METTL3), influences chemokine secretion. This study aims to elucidate the underlying mechanisms and improve METTL3 inhibition efficiency. We designed an adhesive hemostasis hydrogel loaded with STM2457, a METTL3 inhibitor, aimed at sustained release in the acidic tumor microenvironment. In vitro, the hydrogel promoted CAR-NK cell recruitment and tumor killing via sustained METTL3 inhibition. The hydrogel's Schiff base bonds further enabled intestinal adhesion and hemostasis in an incomplete tumor resection model of CRC. Combining the hydrogel with CAR-NK cell therapy significantly reduced CRC recurrence in vivo. Overall, our study reveals the crucial role of METTL3 in CRC recurrence and proposes a promising, multimodal strategy using STM2457-loaded hydrogel and CAR-NK cells for enhanced therapeutic efficacy.

Bioadhesive supramolecular polymer/hyaluronic acid hydrogel with sustained release of zinc ions and dexamethasone for diabetic wound healing

Diabetic patients often struggle with wound healing and are at higher risk of infections, necessitating the development of a stretchable, adhesive hydrogel dressing with antibacterial and angiogenesis-promoting properties. In this study, we synthesized a series of adhesive, antibacterial and anti-inflammatory hydrogels using free radical polymerization with materials including methacrylated hyaluronic acid (HAMA), N-[tris(hydroxymethyl)methyl]acrylamide (THMA), and 3-(bis(pyridin-2-ylmethyl)amino)propyl methacrylate (DPAMA). By leveraging the strong affinity of zinc(II)-dipicolylamine coordination complexes for the phosphorylated groups in dexamethasone sodium phosphate (DMSP), Zn2+ and DMSP were successfully incorporated into the hydrogel. The results demonstrated that the hydrogels possessed excellent adhesiveness and mechanical properties, enabling them to adhere closely to the skin while remaining easily removable without causing trauma. Antibacterial tests demonstrated significant inhibitory effects against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), attributed to the slow release of Zn2+, which effectively suppressed bacterial growth. Additionally, the slow release of DMSP provided strong anti-inflammatory effects. The DHTDZ2 hydrogel, containing 1.5 mg/mL Zn2+ and 4 mg/mL DMSP, significantly accelerated the healing of full-thickness skin wounds. In vitro angiogenesis, immunofluorescence, and immuno-histochemical results further confirmed that the DHTDZ2 hydrogel promoted angiogenesis and reduced the expression of pro-inflammatory factors. In summary, the hydrogel is an effective wound healing dressing that can reduce wound infections and inflammation.

Multifunctional Adhesive Hydrogels: From Design to Biomedical Applications

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

Octopus-Inspired Adhesives with Switchable Attachment to Challenging Underwater Surfaces

Adhesives that excel in wet or underwater environments are critical for applications ranging from healthcare and underwater robotics to infrastructure repair. However, achieving strong attachment and controlled release on difficult substrates, such as those that are curved, rough, or located in diverse fluid environments, remains a major challenge. Here, an octopus-inspired adhesive with strong attachment and rapid release in challenging underwater environments is presented. Inspired by the octopus's infundibulum structure, a compliant, curved stalk, and an active deformable membrane for multi-surface adhesion are utilized. The stalk's curved shape enhances conformal contact on large-scale curvatures and increases contact stress for adaptability to small-scale roughness. These synergistic mechanisms improve contact across multiple length scales, resulting in switching ratios of over 1000 within ≈30 ms with consistent attachment strength of over 60 kPa on diverse surfaces and conditions. These adhesives are demonstrated through the robust attachment and precise manipulation of rough underwater objects.

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.

A Janus hydrogel that enables wet tissue adhesion and resists abdominal adhesions

Hydrogels have indeed achieved significant advancements, yet their clinical translation has been hampered by their inherent limitations in wet adhesion properties. Furthermore, the design of adhesive hydrogels that can resist postoperative adhesions remains an intricate challenge. In this study, we introduce a Janus hydrogel (JGP) that offers a novel approach to address these challenges. The JGP hydrogel has two asymmetrical sides, consisting of an adhesion layer (AL) and an anti-adhesion layer (AAL). Specifically, the AL incorporates three key components: N-[tris(hydroxymethyl)methyl]acrylamide (THMA), acrylic acid (AAc), and the acrylic acid N-hydroxysuccinimide ester (AAc-NHS). By drying the AL, it has a rapid water absorption capability. The abundance of hydroxyl and carboxyl groups in the AL enables the formation of robust hydrogen bonds with tissues, thereby achieving superior adhesive properties. Additionally, the synergistic effect of THMA's tridentate hydrogen bonding and the covalent bonding formed by AAc-NHS with tissue ensures long-lasting wet adhesion. To realize the anti-adhesion function, one side of the AL was immersed in a solution of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA), which undergoes crosslinking to form the AAL. A comprehensive series of tests have confirmed that the JGP hydrogel exhibits exceptional mechanical properties, efficient and enduring adhesion, excellent biocompatibility, and degradability. Moreover, it possesses remarkable hemostatic properties and robust anti-abdominal adhesion characteristics.

Mechanical Regulation of Polymer Gels

The mechanical properties of polymer gels devote to emerging devices and machines in fields such as biomedical engineering, flexible bioelectronics, biomimetic actuators, and energy harvesters. Coupling network architectures and interactions has been explored to regulate supportive mechanical characteristics of polymer gels; however, systematic reviews correlating mechanics to interaction forces at the molecular and structural levels remain absent in the field. This review highlights the molecular engineering and structural engineering of polymer gel mechanics and a comprehensive mechanistic understanding of mechanical regulation. Molecular engineering alters molecular architecture and manipulates functional groups/moieties at the molecular level, introducing various interactions and permanent or reversible dynamic bonds as the dissipative energy. Molecular engineering usually uses monomers, cross-linkers, chains, and other additives. Structural engineering utilizes casting methods, solvent phase regulation, mechanochemistry, macromolecule chemical reactions, and biomanufacturing technology to construct and tailor the topological network structures, or heterogeneous modulus compositions. We envision that the perfect combination of molecular and structural engineering may provide a fresh view to extend exciting new perspectives of this burgeoning field. This review also summarizes recent representative applications of polymer gels with excellent mechanical properties. Conclusions and perspectives are also provided from five aspects of concise summary, mechanical mechanism, biofabrication methods, upgraded applications, and synergistic methodology.

Cu2O-SnO2-PDA heterozygous nanozyme doped hydrogel mediated conglutinant microenvironment regulation for wound healing therapy

Bacterial infection significantly hinders the wound healing process. Overuse of antibiotics has led to the rise of drug resistance in bacteria, making the development of smart medical dressings that promote wound healing without antibiotics, a critical need. In this study, Cu₂O-SnO₂-PDA (PCS) nanoenzymes with Fenton-like activity and high photothermal conversion efficiency were developed. These nanoenzymes were then incorporated into a hydrogel through cross-linking of acrylamide (AM) and N-[Tris-(hydroxymethyl)methyl] acrylamide (THMA), forming a tough, highly-adhesive, and self-healing composite hydrogel (AT/PCS) with antimicrobial properties. The AT/PCS hydrogel exhibits excellent mechanical strength and adhesion, facilitating increased oxygen levels and strong adherence to the wound site. Moreover, it effectively regulates the wound microenvironment by combining synergistic chemodynamic therapy (CDT) and photothermal therapy (PTT) for antibacterial treatment. The AT/PCS hydrogel enhances collagen deposition and expedites wound healing in a rat model, largely due to its potent antibacterial properties.

pH-responsive bioadhesive with robust and stable wet adhesion for gastric ulcer healing

Development of bioadhesives that can be facilely delivered by endoscope and exhibit instant and robust adhesion with gastric tissues to promote gastric ulcer healing remains challenging. In this study, an advanced bioadhesive is prepared through free radical polymerization of ionized N-acryloyl phenylalanine (iAPA) and N-[tris (hydroxymethyl) methyl] acrylamide (THMA). The precursory polymer solution exhibits low viscosity with the capability for endoscope delivery, and the hydrophilic-hydrophobic transition of iAPA upon exposure to gastric acid can trigger gelation through phenyl groups assisted multiple hydrogen bonds formation and repel water molecules on tissue surface to establish favorable environment for interfacial interactions between THMA and functional groups on tissues. The in-situ formed hydrogel features excellent stability in acid environment (14 days) and exhibits firm wet adhesion to gastric tissue (33.4 kPa), which can efficiently protect the wound from the stimulation of gastric acid and pepsin. In vivo studies reveal that the bioadhesive can accelerate the healing of ulcers by inhibiting inflammation and promoting capillary formation in the acetic acid-induced gastric ulcer model in rats. Our work may provide an effective solution for the treatment of gastric ulcers clinically.

Evaluation of composition effects on the tissue-adhesive, mechanical and physical properties of physically crosslinked hydrogels based on chitosan and pullulan for wound healing applications

Tissue adhesion of hydrogels plays an important role in wound healing, which can improve the efficiency of wound treatment, stop bleeding, facilitate tissue growth and wound closure. However, most non-covalent crosslinked hydrogels have weak tissue adhesion and rheological properties. Furthermore, it remains a challenge to synthesize a fully physically crosslinked hydrogel with good rheological properties without compromising its tissue adhesion strength. In this paper, a physically crosslinked hydrogel was developed from a mixture of chitosan and pullulan in different polymer volume ratios using aqueous NaOH. Fourier transform infrared spectroscopy, scanning electron microscopy, thermal analysis, rheological and lap shear tests were used to evaluate the influence of polymer volume ratios on the rheological, and tissue adhesive properties of the hydrogels. It was found that the hydrogels possessed high tissue adhesive strength ranging from 18.0 ± 0.90 to 49.0 ± 2.45 kPa and good storage moduli up to 5.157 ± 1.062 kPa. Gentamicin was incorporated into this polymer matrix and the release profile was investigated. The ratio of chitosan and pullulan to obtain hydrogels with optimum viscoelastic and tissue adhesive properties was identified to be CS/PUL 2:1. These results indicated that the synthesized hydrogels can be potential materials for biomedical applications such as medical adhesives and wound dressings.

Nature-inspired adhesive systems

Many organisms in nature thrive in intricate habitats through their unique bio-adhesive surfaces, facilitating tasks such as capturing prey and reproduction. It's important to note that the remarkable adhesion properties found in these natural biological surfaces primarily arise from their distinct micro- and nanostructures and/or chemical compositions. To create artificial surfaces with superior adhesion capabilities, researchers delve deeper into the underlying mechanisms of these captivating adhesion phenomena to draw inspiration. This article provides a systematic overview of various biological surfaces with different adhesion mechanisms, focusing on surface micro- and nanostructures and/or chemistry, offering design principles for their artificial counterparts. Here, the basic interactions and adhesion models of natural biological surfaces are introduced first. This will be followed by an exploration of research advancements in natural and artificial adhesive surfaces including both dry adhesive surfaces and wet/underwater adhesive surfaces, along with relevant adhesion characterization techniques. Special attention is paid to stimulus-responsive smart artificial adhesive surfaces with tunable adhesive properties. The goal is to spotlight recent advancements, identify common themes, and explore fundamental distinctions to pinpoint the present challenges and prospects in this field.

Overview of Dynamic Bond Based Hydrogels for Reversible Adhesion Processes

Polymeric hydrogels are soft materials with a three-dimensional (3D) hydrophilic network capable of retaining and absorbing large amounts of water or biological fluids. Due to their customizable properties, these materials are extensively studied for developing matrices for 3D cell culture scaffolds, drug delivery systems, and tissue engineering. However, conventional hydrogels still exhibit many drawbacks; thus, significant efforts have been directed towards developing dynamic hydrogels that draw inspiration from organisms' natural self-repair abilities after injury. The self-healing properties of these hydrogels are closely associated with their ability to form, break, and heal dynamic bonds in response to various stimuli. The primary objective of this review is to provide a comprehensive overview of dynamic hydrogels by examining the types of chemical bonds associated with them and the biopolymers utilized, and to elucidate the chemical nature of dynamic bonds that enable the modulation of hydrogels' properties. While dynamic bonds ensure the self-healing behavior of hydrogels, they do not inherently confer adhesive properties. Therefore, we also highlight emerging approaches that enable dynamic hydrogels to acquire adhesive properties.

Hydrogel-tissue adhesion by particle bridging: sensitivity to interfacial wetting and tissue composition

Solid particles placed at the interface between hydrogels and biological tissues can create an adhesive joint through the adsorption of macromolecules onto their surfaces. Here, we investigated how this adhesion by particle bridging depends on the wetting of tissue surfaces and on the heterogeneities in tissue composition. Ex vivo peeling experiments were performed using poly(ethylene glycol) films coated with aggregates of silica nanoparticles deposited on the internal tissues of porcine liver. We show that the adhesion produced by particle bridging is altered by the presence of fluid wetting the tissue-hydrogel interface. For both uncoated and coated films, a transition from lubricated to adhesive contact was observed when all the interfacial fluid was drained. The presence of a silica nanoparticle coating shifted the transition towards more hydrated conditions and significantly enhanced adhesion in the adhesive regime. After 5 min of contact, the adhesion energy achieved on liver parenchyma with the coated films (7.7 ± 1.9 J m-2) was more than twice that of the uncoated films (3.2 ± 0.3 J m-2) or with a surgical cyanoacrylate glue (2.9 ± 1.9 J m-2). Microscopic observations during and after peeling revealed different detachment processes through either particle detachment or cohesive fracture in the tissue. These mechanisms could be directly related to the microanatomy of the liver parenchyma. The effects of both interfacial wetting and tissue composition on adhesion may provide guidelines to tailor the design of tissue adhesives using particle bridging.

Functional hydrogels for hepatocellular carcinoma: therapy, imaging, and in vitro model

Hepatocellular carcinoma (HCC) is among the most common malignancies worldwide and is characterized by high rates of morbidity and mortality, posing a serious threat to human health. Interventional embolization therapy is the main treatment against middle- and late-stage liver cancer, but its efficacy is limited by the performance of embolism, hence the new embolic materials have provided hope to the inoperable patients. Especially, hydrogel materials with high embolization strength, appropriate viscosity, reliable security and multifunctionality are widely used as embolic materials, and can improve the efficacy of interventional therapy. In this review, we have described the status of research on hydrogels and challenges in the field of HCC therapy. First, various preparation methods of hydrogels through different cross-linking methods are introduced, then the functions of hydrogels related to HCC are summarized, including different HCC therapies, various imaging techniques, in vitro 3D models, and the shortcomings and prospects of the proposed applications are discussed in relation to HCC. We hope that this review is informative for readers interested in multifunctional hydrogels and will help researchers develop more novel embolic materials for interventional therapy of HCC.

A low-swelling hydrogel as a multirole sealant for efficient dural defect sealing and prevention of postoperative adhesion

Dural defects and subsequent complications, including cerebrospinal fluid (CSF) leakage, are common in both spine surgery and neurosurgery, and existing clinical treatments are still unsatisfactory. In this study, a tissue-adhesive and low-swelling hydrogel sealant comprising gelatin and o-phthalaldehyde (OPA)-terminated 4-armed poly(ethylene glycol) (4aPEG-OPA) is developed via the OPA/amine condensation reaction. The hydrogel shows an adhesive strength of 79.9 ± 12.0 kPa on porcine casing and a burst pressure of 208.0 ± 38.0 cmH2O. The hydrogel exhibits a low swelling ratio at physiological conditions, avoiding nerve compression in the limited spinal and intracranial spaces. In rat and rabbit models of lumbar and cerebral dural defects, the 4aPEG-OPA/gelatin hydrogel achieves excellent performance in dural defect sealing and preventing CSF leakage. Moreover, local inflammation, epidural fibrosis and postoperative adhesion in the defect areas are markedly reduced. Thus, these findings establish the strong potential of the hydrogel sealant for the effective watertight closure of dural defects.

Emerging approaches for the development of artificial islets

The islet of Langerhans, functioning as a "mini organ", plays a vital role in regulating endocrine activities due to its intricate structure. Dysfunction in these islets is closely associated with the development of diabetes mellitus (DM). To offer valuable insights for DM research and treatment, various approaches have been proposed to create artificial islets or islet organoids with high similarity to natural islets, under the collaborative effort of biologists, clinical physicians, and biomedical engineers. This review investigates the design and fabrication of artificial islets considering both biological and tissue engineering aspects. It begins by examining the natural structures and functions of native islets and proceeds to analyze the protocols for generating islets from stem cells. The review also outlines various techniques used in crafting artificial islets, with a specific focus on hydrogel-based ones. Additionally, it provides a concise overview of the materials and devices employed in the clinical applications of artificial islets. Throughout, the primary goal is to develop artificial islets, thereby bridging the realms of developmental biology, clinical medicine, and tissue engineering.

Infant friendly adhesive film containing glucose for neonatal hypoglycemia

Neonatal hypoglycemia is a common disease in newborns, which can precipitate energy shortage and follow by irreversible brain and neurological injury. Herein, we present a novel approach for treating neonatal hypoglycemia involving an adhesive polyvinylpyrrolidone/gallic acid (PVP/GA) film loading glucose. The PVP/GA film with loose cross-linking can be obtained by mixing their ethanol solution and drying complex. When depositing this soft film onto wet tissue, it can absorb interfacial water to form a hydrogel with a rough surface, which facilitates tight contact between the hydrogel and tissue. Meanwhile, the functional groups in the hydrogels and tissues establish both covalent and non-covalent bonds, leading to robust bioadhesion. Moreover, the adhered PVP/GA hydrogel can be detached without damaging tissue as needed. Furthermore, the PVP/GA films exhibit excellent antibacterial properties and biocompatibility. Notably, these films effectively load glucose and deliver it to the sublingual tissue of newborn rabbits, showcasing a compelling therapeutic effect against neonatal hypoglycemia. The strengths of the PVP/GA film encompass excellent wet adhesion in the wet and highly dynamic environment of the oral cavity, on-demand detachment, antibacterial efficacy, biocompatibility, and straightforward preparation. Consequently, this innovative film holds promise for diverse biomedical applications, including but not limited to wearable devices, sealants, and drug delivery systems.

Multihydrogen Bond Modulated Polyzwitterionic Removable Adhesive Hydrogel with Antibacterial and Hemostatic Function for Wound Healing

Wound management is a major challenge worldwide, placing a huge financial burden on the government of every nation. Wound dressings that can protect wounds, accelerate healing, prevent infection, and avoid secondary damage continue to be a major focus of research in the health care and clinical communities. Herein, a novel zwitterionic polymer (LST) hydrogel incorporated with [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (SBMA), mussel-inspired N-[tris(hydroxymethyl)methyl] acrylamide (THMA), and lithium magnesium salt was prepared for functional wound dressings. The incorporation of the THMA monomer containing three hydroxyl groups gives the hydrogel suitable adhesion properties (∼6.0 KPa). This allows the LST zwitterionic hydrogels to bind well to the skin, which not only protects the wound and ensures its therapeutic efficacy but also allows for painless removal and reduced patient pain. Zwitterionic sulfobetaine units of SBMA provide antimicrobial and mechanical properties. The chemical structure and microscopic morphology of LST zwitterionic hydrogels were systematically studied, along with their swelling ratio, adhesion, and mechanical properties. The results showed that the LST zwitterionic hydrogels had a uniform and compact porous structure with the highest swelling and mechanical strain of 1607% and 1068.74%, respectively. The antibacterial rate of LST zwitterionic hydrogels was as high as 99.49%, and the hemostatic effect was about 1.5 times that of the commercial gelatin hemostatic sponges group. In further studies, a full-thickness mouse skin model was selected to evaluate the wound healing performance. Wounds covered by LST zwitterionic hydrogels had a complete epithelial reformation and new connective tissue, and its vascular regenerative capacity was increased to about 2.4 times that of the commercial group, and the wound could completely heal within 12-13 days. This study provides significant advances in the design and construction of multifunctional zwitterionic hydrogel adhesives and wound dressings.

Ultrasound imaging guided targeted sonodynamic therapy enhanced by magnetophoretically controlled magnetic microbubbles

Sonodynamic therapy (SDT) utilizes ultrasonic excitation of a sensitizer to generate reactive oxygen species (ROS) to destroy tumor. Two dimensional (2D) black phosphorus (BP) is an emerging sonosensitizer that can promote ROS production to be used in SDT but it alone lacks active targeting effect and showed low therapy efficiency. In this study, a stable dispersion of integrated micro-nanoplatform consisting of BP nanosheets loaded and Fe3O4 nanoparticles (NPs) connected microbubbles was introduced for ultrasound imaging guided and magnetic field directed precision SDT of breast cancer. The targeted ultrasound imaging at 18 MHz and efficient SDT effects at 1 MHz were demonstrated both in-vitro and in-vivo on the breast cancer. The magnetic microbubbles targeted deliver BP nanosheets to the tumor site under magnetic navigation and increased the uptake of BP nanosheets by inducing cavitation effect for increased cell membrane permeability via ultrasound targeted microbubble destruction (UTMD). The mechanism of SDT by magnetic black phosphorus microbubbles was proposed to be originated from the ROS triggered mitochondria mediated apoptosis by up-regulating the pro-apoptotic proteins while down-regulating the anti-apoptotic proteins. In conclusion, the ultrasound theranostic was realized via the magnetic black phosphorus microbubbles, which could realize targeting and catalytic sonodynamic therapy.

Swim bladder-derived biomaterials: structures, compositions, properties, modifications, and biomedical applications

Animal-derived biomaterials have been extensively employed in clinical practice owing to their compositional and structural similarities with those of human tissues and organs, exhibiting good mechanical properties and biocompatibility, and extensive sources. However, there is an associated risk of infection with pathogenic microorganisms after the implantation of tissues from pigs, cattle, and other mammals in humans. Therefore, researchers have begun to explore the development of non-mammalian regenerative biomaterials. Among these is the swim bladder, a fish-derived biomaterial that is rapidly used in various fields of biomedicine because of its high collagen, elastin, and polysaccharide content. However, relevant reviews on the biomedical applications of swim bladders as effective biomaterials are lacking. Therefore, based on our previous research and in-depth understanding of this field, this review describes the structures and compositions, properties, and modifications of the swim bladder, with their direct (including soft tissue repair, dural repair, cardiovascular repair, and edible and pharmaceutical fish maw) and indirect applications (including extracted collagen peptides with smaller molecular weights, and collagen or gelatin with higher molecular weights used for hydrogels, and biological adhesives or glues) in the field of biomedicine in recent years. This review provides insights into the use of swim bladders as source of biomaterial; hence, it can aid biomedicine scholars by providing directions for advancements in this field.

Dual-Modified Hyaluronic Acid for Tunable Double Cross-Linked Hydrogel Adhesives

Conventional techniques for the closure of wounds, such as sutures and staples, have significant drawbacks that can negatively impact wound healing. Tissue adhesives have emerged as promising alternatives, but poor adhesion, low mechanical properties, and toxicity have hindered their widespread clinical adoption. In this work, a dual modified, aldehyde and methacrylate hyaluronic acid (HA) biopolymer (HA-MA-CHO) has been synthesized through a simplified route for use as a double cross-linked network (DCN) hydrogel (HA-MA-CHO-DCN) adhesive for the effective closure and sealing of wounds. HA-MA-CHO-DCN cross-links in two stages: initial cross-linking of the aldehyde functionality (CHO) of HA-MA-CHO using a disulfide-containing cross-linker, 3,3'-dithiobis (propionic hydrazide) (DTPH), leading to the formation of a self-healing injectable gel, followed by further cross-linking via ultraviolet (UV) initiated polymerization of the methacrylate (MA) functionality. This hydrogel adhesive shows a stable swelling behavior and remarkable versatility as the storage modulus (G') has shown to be highly tunable (103-105 Pa) for application to many different wound environments. The new HA-MA-CHO-DCN hydrogel showed excellent adhesive properties by surpassing the burst pressure and lap-shear strength for the widely used bovine serum albumin-glutaraldehyde (BSAG) glue while maintaining excellent cell viability.

Sprayable Zwitterionic Antibacterial Hydrogel With High Mechanical Resilience and Robust Adhesion for Joint Wound Treatment

Wound healing in movable parts, including the joints and neck, remains a critical challenge due to frequent motions and poor flexibility of dressings, which may lead to mismatching of mechanical properties and poor fitting between dressings and wounds; thus, increasing the risk of bacterial infection. This study proposes a sprayable zwitterionic antibacterial hydrogel with outstanding flexibility and desirable adhesion. This hydrogel precursor is fabricated by combining zwitterionic sulfobetaine methacrylate (SBMA) with poly(sulfobetaine methacrylate-co-dopamine methacrylamide)-modified silver nanoparticles (PSBDA@AgNPs) through robust electrostatic interactions. About 150 s of exposure to UV light, the SBMA monomer polymerizes to form PSB chains entangled with PSBDA@AgNPs, transformed into a stable and adhesion PSB-PSB@Ag hydrogel at the wound site. The resulting hydrogel has adhesive strength (15-38 kPa), large tensile strain (>400%), suitable shape adaptation, and excellent mechanical resilience. Moreover, the hydrogel displays pH-responsive behavior; the acidic microenvironment at the infected wound sites prompts the hydrogel to rapidly release AgNPs and kill bacteria. Further, the healing effect of the hydrogel is demonstrated on the rat neck skin wound, showing improved wound closing rate due to reduced inflammation and enhanced angiogenesis. Overall, the sprayable zwitterionic antibacterial hydrogel has significant potential to promote joint skin wound healing.

Stimuli-Responsive Hydrogel Adhesives for Wound Closure and Tissue Regeneration

Sutures and staplers, as gold standards for clinical wound closure, usually cause secondary tissue injury and require professional technicians and equipment. The noninvasive hydrogel adhesives are used in various biomedical applications, such as wound closure, tissue sealing, and tissue regeneration, due to their remarkable properties. Recently-developed hydrogel adhesives, especially stimuli-responsive hydrogels, have shown great potential owing to their advantages in regulating their performance and functions according to the wound situations or external conditions, thus allowing the wounds to heal gradually. However, comprehensive summary on stimuli-responsive hydrogels as tissue adhesives is rarely reported to date. This review focuses on the advances in the design of various stimuli-responsive hydrogel adhesives over the past decade, including the systems responsive to pH, temperature, photo, and enzymes. Their potential biomedical applications, such as skin closure, cardiovascular and liver hemostasis, and gastrointestinal sealing, are emphasized. Meanwhile, the challenges and future development of stimuli-responsive hydrogel adhesives are discussed. This review aims to provide meaningful insights for the further design of next-generation of hydrogel adhesives for wound closure and tissue regeneration.

Hydrogel Crosslinked with Nanoparticles for Prevention of Surgical Hemorrhage and Recurrence of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is acknowledged as an immunosuppressive neoplasm, whereby the inactive microenvironment facilitates immune tolerance and evasion of HCC. Post-surgical resected liver cancer exhibits a proclivity for relapse, rendering prevention of recurrence challenging as it may transpire at any point subsequent to surgery. Among the various anti-recurrence interventions, the primary clinical approach involving the administration of regimens atezolizumab and bevacizumab (A+T) is deemed the most efficacious in reversing the tumor microenvironment, albeit still lacking in complete satisfaction. Therefore, the objective is to utilize a recently developed block copolymer as a protective carrier for two specific monoclonal antibody drugs. Subsequently, a modified hemostatic hydrogel will be synthesized for application during hepatic surgery. The immunotherapy impact of this approach is significantly prolonged and intensified due to the combined hemostasis properties and controlled release of the constituents within the synthesized nanocomposite hydrogel. Furthermore, these nanocomposite hydrogels exhibit remarkable efficacy in preventing postoperative wound bleeding and substantially enhancing the safety of liver cancer resection. This research on the anti-recurrence hydrogel system presents a novel therapeutic approach for addressing local recurrence of liver cancer, potentially offering a substantial contribution to the field of surgical treatment for liver cancer in the future.

Injectable, Adhesive Albumin Nanoparticle-Incorporated Hydrogel for Sustained Localized Drug Delivery and Efficient Tumor Treatment

Injectable hydrogels are receiving increasing attention as local depots for sustained anticancer drug delivery. However, most current hydrogel-based carriers lack tissue-adhesive ability, a property that is important for the immobilization of drug-loaded systems at tumor sites to increase local drug concentration. In this study, we developed a paclitaxel (PTX)-loaded injectable hydrogel with firm tissue adhesion for localized tumor therapy. PTX-loaded bovine serum albumin (BSA) nanoparticles (PTX@BN) were prepared, and the drug-loaded hydrogel was then fabricated by cross-linking PTX@BN with o-phthalaldehyde (OPA)-terminated 4-armed poly(ethylene glycol) (4aPEG-OPA) via a condensation reaction between OPA and the amines in BSA. The hydrogel showed firm adhesion to various organs and tumor tissues ex vivo due to the condensation reaction of unreacted OPA groups and amines in the tissues. The PTX-loaded nanocomposite hydrogels sustained PTX release over 30 days following the Korsmeyer-Peppas model and exhibited notable inhibition activities against mouse C26 colon and 4T1 breast cancer cells in vitro. Following peritumoral injection into mice with C26 or 4T1 tumors, the PTX@BN-loaded hydrogel significantly enhanced the antitumor efficacy and prolonged animal survival time compared to free PTX solutions with low systemic toxicity. Therefore, the adhesive, PTX-loaded nanocomposite hydrogels have the potential for efficient localized tumor therapy.

2D nanomaterial-based 3D network hydrogels for anti-infection therapy

Two-dimensional nanomaterials (2D NMs) refer to nanomaterials that possess a planar topography with a thickness of one or several atomic layers. Due to their large specific surface areas, atomic thickness, rough edges, and electron confinement in two dimensions, they have emerged as promising antimicrobial agents over antibiotics in combating bacterial infections. However, 2D NMs encounter issues such as low bio-safety, easy aggregation, and limited tissue penetration efficiency. To address these concerns, hydrogels with three-dimensional (3D) networks have been developed to encapsulate 2D NMs, aiming to enhance their biocompatibility, biodegradability, and ability to regulate and remodel the tissue microenvironment at the infected site. This review systematically summarizes the current studies on 2D NM-based antibacterial hydrogels with 3D network structures (named 2N3Hs). Firstly, we introduce the emerging types of 2N3Hs and describe their antibacterial actions. Subsequently, we discuss the applications of 2N3Hs in three biomedical fields, including wound dressing, cancer treatment, and bone regeneration. Finally, we conclude the review with current challenges and future developments for 2N3Hs, highlighting their potential as a promising choice for next-generation biomedical devices, particularly in the field of tissue engineering and regenerative medicine. This review aims to provide a comprehensive and panoramic overview of anti-infective 2N3Hs for various biomedical applications.

A highly stretchable, adhesive, and antibacterial hydrogel with chitosan and tobramycin as dynamic cross-linkers for treating the infected diabetic wound

Diabetic wounds pose a significant challenge due to their susceptibility to bacterial infection in a high-glucose environment, which impedes the wound healing process. To address this issue, there is a pressing need to develop suitable hydrogels that can promote the regeneration of diabetic wounds in clinical practice. In this study, we designed and fabricated a highly stretchable, adhesive, transparent, and antibacterial hydrogel through a one-pot radical polymerization of N-[Tris (hydroxymethyl) methyl] acrylamide (THMA) and acrylic acid (AA), and with chitosan and the antibiotic tobramycin as the dynamic physical crosslinkers. The copolymer contains a large number of carboxyl and hydroxyl groups, which can form an interpenetrating network structure with chitosan and tobramycin through multiple dynamic non-covalent bonds. This hydrogel exhibited over 1600 % elongation through an energy dissipation mechanism and strong adhesion to various surfaces without any chemical reaction. In vivo, studies conducted on a staphylococcus aureus-infected full-thickness diabetic skin wound model demonstrated that the hydrogel loaded with tobramycin as one of the crosslinkers had a long-lasting antibacterial activity and effectively accelerated wound healing. Therefore, the antibiotic-loaded adhesive hydrogel we proposed holds great promise as a treatment for bacteria-infected diabetic wounds.

Self-Healable Adhesive Hydrogel with a Preserved Underwater Adhesive Ability Based on Histidine-Zinc Coordination and a Bioengineered Hybrid Mussel Protein

Mussels are marine organisms that are capable of constructing an underwater adhesion between their bodies and rigid structures. It is well known that mussels achieve underwater adhesion through the presence of mussel adhesive proteins (MAPs) that contain high levels of 3,4-dihydroxyphenylalanine (DOPA). Although the extraordinary underwater adhesive properties of mussels are attributed to DOPA, its capacity to play a dual role in surface adhesion and internal cohesion is inherently limited. However, mussels employ a combination of chemical moieties, not just DOPA, along with anatomical components, such as plaque and byssus, in underwater adhesion. This also involves junction proteins that connect the plaque and byssus. In this study, a novel hybrid MAP was bioengineered via the fusion of the plaque protein (foot protein type 1) and the histidine-rich domain of the junction protein (foot protein type 4). To achieve direct adhesion underwater, the adhesive should maintain surface adhesion without disintegrating. Notably, the histidine-Zn-coordinated hybrid MAP hydrogel maintained a high surface adhesion ability even after cross-linking because of the preservation of its unoxidized and non-cross-linked DOPA moieties. The formulated adhesive hydrogel system based on the bioengineered hybrid MAP exhibited self-healing properties, owing to the reversible metal coordination bonds. The developed adhesive hydrogel exhibits outstanding levels of bulk adhesion in underwater environments, highlighting its potential as an effective adhesive biomaterial. Therefore, the introduction of histidine-rich domains into MAPs may be applied in various studies to formulate mussel-inspired adhesives with self-healing properties and to fully utilize the adhesive ability of DOPA.

Multifunctional chitosan-based gel sponge with efficient antibacterial, hemostasis and strong adhesion

Developing wound dressings with solid adhesive properties that enable efficient, painless hemostasis and prevent wound infection remain a huge challenge. Herein, the tris(hydroxymethyl) methyl glycine-modified chitosan derivative (CTMG) was prepared and freeze-dried after simply adjusting the concentration of CTMG to obtain the chitosan-based gel sponge with desired multi-hollow structure, special antibacterial and biocompatibility. The adhesion strength on porcine skin was impressive up to 113 KPa, much higher than fibrin glue. It can withstand the pressure that far exceeds blood pressure. CTMG exhibits bacteriostatic abilities as demonstrated in a bacteriostatic assay, and alongside biocompatibility, as shown in cytotoxicity and hemolytic assays. Moreover, CTMG gel sponge showed hemostatic properties in both in vivo and in vitro hemostasis experiments. During an experiment on liver hemorrhage in rats, CTMG gel sponge proved to be more effective in controlling bleeding than other hemostatic sponges available on the market, indicating its promising hemostatic properties. CTMG gel sponge possesses the potential to function as a wound dressing and hemostatic material, making it suitable for various clinical applications.

Bioadhesive Technology Platforms

Bioadhesives have emerged as transformative and versatile tools in healthcare, offering the ability to attach tissues with ease and minimal damage. These materials present numerous opportunities for tissue repair and biomedical device integration, creating a broad landscape of applications that have captivated clinical and scientific interest alike. However, fully unlocking their potential requires multifaceted design strategies involving optimal adhesion, suitable biological interactions, and efficient signal communication. In this Review, we delve into these pivotal aspects of bioadhesive design, highlight the latest advances in their biomedical applications, and identify potential opportunities that lie ahead for bioadhesives as multifunctional technology platforms.

A facile strategy to fabricate a skin-like hydrogel with adhesive and highly stretchable attributes through small molecule triggering toward flexible electronics

Polyacrylamide hydrogel is a promising matrix in biomedical applications due to its biocompatibility, transparency and flexibility. However, its implementation in skin-attachable applications is impeded by its inherent deficiency in surface-adaptive adhesion and inadequate mechanical conformity to skin tissues. Herein, tris, a biocompatible small molecule with a triple hydrogen bonding cluster in its molecule structure, is introduced for the first time into a polyacrylamide hydrogel. This incorporation is achieved via a facile one-pot strategy, resulting in a highly stretchable hydrogel with an impressive strain capacity (2574.75 ± 28.19%), a human dermis tissue-compatible Young's modulus (27.89 ± 2.05 kPa) and an intrinsically universal adhesion capacity (16.66 ± 0.32 N). These superior properties are attributed to the elevated hydrogen bonding density and the plasticizing effect induced by tris, without compromising the hydrogel's excellent transparency (>90% transmittance). Moreover, by incorporating calcium ions into the resulting soft adhesive hydrogel, we demonstrate its utility in skin-like sensors, leading to a substantial enhancement in strain sensitivity and electrical conductivity, in conjunction with the plasticizing influence exerted by tris. This work offers a facile and environmentally friendly solution to fabricate ultra-stretchable adhesive polyacrylamide hydrogel matrixes for dynamic surfaces, even under large deformation, which can broaden their potential applications in integrated bioelectronics.

Platelet Rich Plasma Loaded Multifunctional Hydrogel Accelerates Diabetic Wound Healing via Regulating the Continuously Abnormal Microenvironments

Continuous oxidative stress and cellular dysfunction caused by hyperglycemia are distinguishing features of diabetic wounds. It has been a great challenge to develop a smart dressing that can accelerate diabetic wound healing through regulating abnormal microenvironments. In this study, a platelet rich plasma (PRP) loaded multifunctional hydrogel with reactive oxygen species (ROS) and glucose dual-responsive property is reported. It can be conveniently prepared with PRP, dopamine (DA) grafted alginate (Alg-DA), and 6-aminobenzo[c][1,2]oxaborol-1(3H)-ol (ABO) conjugated hyaluronic acid (HA-ABO) through ionic crosslinks, hydrogen-bond interactions, and boronate ester bonds. The hydrogel possesses injectability, moldability, tissue adhesion, self-healing, low hemolysis, and hemostasis performances. Its excellent antioxidant property can create a low oxidative stress microenvironment for other biological events. Under an oxidative stress and/or hyperglycemia state, the hydrogel can degrade at an accelerated rate to release a variety of cytokines derived from activated blood platelets. The result is a series of positive changes that are favorable for diabetic wound healing, including fast anti-inflammation, activated macrophage polarization toward M2 phenotype, promoted migration and proliferation of fibroblasts, as well as expedited angiogenesis. This work provides an efficient strategy for chronic diabetic wound management and offers an alternative for developing a new-type PRP-based bioactive wound dressing.

Double-Cross-Linked Hydrogel with Long-Lasting Underwater Adhesion: Enhancement of Maxillofacial In Situ and Onlay Bone Retention

Bone retention is a usual clinical problem existing in a lot of maxillofacial surgeries involving bone reconstruction and bone transplantation, which puts forward the requirements for bone adhesives that are stable, durable, biosafe, and biodegradable in wet environment. To relieve the suffering of patients during maxillofacial surgery with one-step operation and satisfying repair, herein, we developed a double-cross-linked A-O hydrogel named by its two components: [(3-Aminopropyl) methacrylamide]-co-{[Tris(hydroxymethyl) methyl] acrylamide} and oxidated methylcellulose. With excellent bone adhesion ability, it can maintain long-lasting stable underwater bone adhesion for over 14 days, holding a maximum adhesion strength of 2.32 MPa. Schiff-base reaction and high-density hydrogen bonds endow the hydrogel with strong cohesion and adhesion performance as well as maneuverable properties such as easy formation and injectability. A-O hydrogel not only presents rarely reported long-lasting underwater adhesion of hard tissue but also owns inherent biocompatibility and biodegradation properties with a porous structure that facilitates the survival of bone graft. Compared to the commercial cyanoacrylate adhesive (3 M Vetbond Tissue Adhesive), the A-O hydrogel is confirmed to be safer, more stable, and more effective in calvarial in situ bone retention model and onlay bone retention model of rat, providing a practical solution for the everyday scenario of clinical bone retention.

Ultrastrong bonding, on-demand debonding, and easy re-bonding of non-sticking materials enabled by reversibly interlocked macromolecular networks-based Janus-like adhesive

Simultaneously gluing hydrophobic and hydrophilic materials is a highly desired but intractable task. Herein, we developed a facile strategy using reversibly interlocked macromolecular networks (ILNs) as an adhesive. As shown by the proof-of-concept assembly of glass/ILNs/fluoropolymer (i.e., a simplified version of a photovoltaic module), the sandwiched ILNs were stratified after hot-pressing owing to temporary decrosslinking enabled by the built-in reversible covalent bonds. The fragmented component networks were enriched near their respective thermodynamically favored substrates to form a Janus-like structure. Strong elaborate interfacial bespoke chemical bonds and mechanical interlocking were thus established accompanied by the reconstruction of ILNs after cooling, which cooperated with the robust cohesion of the core part of the ILNs resulting from topological entanglements and led to a record-high peeling strength of 64.86 N cm-1. Also, the ILN-based Janus-like adhesive possessed reversible recyclability, adhesivity and on-demand de-bondability. The molecular design detailed in this study serves as a guide for developing a high-performance smart adhesive that firmly bonds non-sticking materials. Compared with existing Janus adhesives, our ILNs-based adhesive not only shows extremely useful reversibility but also greatly simplifies the adhesion process with no surface treatment required.

Peptide/glycyrrhizic acid supramolecular polymer: An emerging medical adhesive for dural sealing and repairing

Medical adhesives have emerged as potential materials for sealing, hemostasis and wound repairing in modern clinical surgery. However, most of existing medical adhesives are still far away from the clinical requirements for simultaneously meeting desirable tissue adhesion, safety, biodegradability, anti-swelling property, and convenient operability. Here, we present an entirely new kind of peptide-based underwater adhesives, which are constructed via cross-linked supramolecular copolymerization between cationic short peptides and glycyrrhizic acid (GA) in an aqueous solution. We revealed the unique molecular mechanism of the peptide/GA supramolecular polymers and underlined the importance of arginine residues in the enhancement of the bulk cohesion of the peptide/GA adhesive. We thus concluded a design guideline that the peptide sequence has to be encoded with multiple arginine termini and hydrophobic residues. The resulting adhesives exhibited effective tissue adhesion, robust cohesion, low cell cytotoxicity, acceptable hemocompatibility, inappreciable inflammation response, appropriate biodegradability, and excellent anti-swelling property. More attractively, the dried peptide/GA powder was able to rapidly self-gel into adhesives by absorbing water, suggesting conveniently clinical operability. Animal experiments showed that the peptide/GA supramolecular polymers could be utilized as reliable medical adhesives for dural sealing and repairing.

Hybrid cross-linked sodium carboxymethyl starch/polyacrylamide flexible sensing hydrogels with adhesion, antimicrobial properties and multiple responses

Ionic hydrogels used as ideal and flexible strain sensor materials should have excellent mechanical, adhesive and antimicrobial properties. However, it is challenging to achieve these multifunctional requirements simultaneously. Herein, we designed and prepared a multifunctional ionic hydrogel with a multi-length tentacle bentonite backbone to initiate the free radical polymerization of acrylic acid bentonite (AABT) and acrylamide (AAm). The interactions of covalent cross-linking, hydrogen bonding cross-linking, charge interactions and physical entanglement between hybrid polyacrylamide-AABT (PAAm-AABT), sodium carboxymethyl starch (SCMS) and PAAm form an multi-in-one hybrid supramolecular network hydrogel (CABZ). This CABZ ion-conductive hydrogel is capable of detecting weak deformation with a detection limit of 1 % strain, high tensile properties of 995 %, excellent strength of 254.5 kPa, fast response (≈0.21 s), high sensitivity of 0.86 and high conductivity of 0.37 S/m. In addition, this CABZ ion-conductive hydrogel has impressive adhesion properties with shear adhesion strength up to 50.78 kPa and broad-spectrum antibacterial properties achieved by AABT-loaded ZnO nanoparticles. Through special AABT hybrid cross-linking, the CABZ ion-conductive hydrogel achieves stable mechanical properties, highly sensitive signal response and antimicrobial properties, which will make it a good choice for flexible wearable sensor materials.

Immune homeostasis modulation by hydrogel-guided delivery systems: a tool for accelerated bone regeneration

Immune homeostasis is delicately mediated by the dynamic balance between effector immune cells and regulatory immune cells. Local deviations from immune homeostasis in the microenvironment of bone fractures, caused by an increased ratio of effector to regulatory cues, can lead to excessive inflammatory conditions and hinder bone regeneration. Therefore, achieving effective and localized immunomodulation of bone fractures is crucial for successful bone regeneration. Recent research has focused on developing localized and specific immunomodulatory strategies using local hydrogel-based delivery systems. In this review, we aim to emphasize the significant role of immune homeostasis in bone regeneration, explore local hydrogel-based delivery systems, discuss emerging trends in immunomodulation for enhancing bone regeneration, and address the limitations of current delivery strategies along with the challenges of clinical translation.

Aquatic Diatoms-Inspired Universal Adhesive Coacervates Triggered by Water

Adhesives with strong underwater adhesion performance are urgently needed in diverse areas. However, designing adhesives with long-term stability to diverse materials underwater in a facile way is challenging. Here, inspired by aquatic diatoms, a series of novel biomimetic universal adhesives is reported that shows tunable performance with robust and long-lasting stable underwater adhesion to various substrates, including wet biological tissues. The versatile and robust wet-contact adhesives are pre-polymerized by N-[tris(hydroxymethyl)methyl]acrylamide, n-butyl acrylate, and methylacrylic acid in dimethyl sulfoxide and spontaneously coacervated in water triggered by solvent exchange. The synergistic interaction between hydrogen bonding and hydrophobic interaction allows the hydrogels with instant and strong adhesion to various substrate surfaces. The slowly formed covalent bonds enhance cohesion and adhesion strength in hours. The spatial and timescale-dependent adhesion mechanism endows the adhesives with strong and long-lasting stable underwater adhesion to be coupled with fault-tolerant convenient surgical operations.