Recent advances in wet adhesives: Adhesion mechanism, design principle and applications

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

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

Solvent volatilization annealing-prepared Janus film with asymmetric bioadhesion and inherent biological functions to expedite oral ulcer healing

Fabrication of layered bioadhesives with asymmetric bioadhesion, on-demand detachment and inherent biological functions remains a great challenge. This work reports a novel and generalizable solvent volatilization-induced annealing (SVA) strategy to prepare a Janus film with an integrated dual layer structure, asymmetric adhesion, on-demand detachment and inherent biological functions. Depositing polyvinyl pyrrolidone/caffeic acid/lipoic acid (PVP/CA/LA) ethanol solutions onto an ethylcellulose (EC) layer and applying SVA strategy can integrate two layers in molecular-level to obtain the dual-layered Janus film. Porous PVP/p(CA-LA) surface pressed onto wet tissues can absorb interfacial water to form tight tissue contact, and their functional groups can form abundant bonds to induce robust bioadhesion. In contrast, dense EC surface limits water absorption and exhibits minimal adhesion of proteins, cells and tissues. Furthermore, the adhered Janus film can be detached by using a glutathione/sodium bicarbonate solution. Additionally, CA and LA provide the film with desired antibacterial, antioxidant, and anti-inflammatory properties. Finally, by providing the antibacterial and anti-inflammatory microenvironment, the Janus film promotes angiogenesis and significantly expedites the healing of the oral ulcers in rats. This work not only introduces a novel approach for preparing multi-layered and asymmetric materials, but also paving the way for developing adhesive materials with inherent biological functions.

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

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

Sound Wave-Activated Self-Powered Adhesive Dressing for Accelerated Wound Healing

Self-powered wound dressings are effective in treating chronic wounds because of their low toxicity and convenience. However, current self-powered dressings rely on the bending movements of the skin or additional large ultrasonic devices. Herein, a flexible adhesive self-powered wound dressing (FASW) that promotes skin regeneration through daily sound wave driving without relying on skin bending or external sound devices is proposed. The FASW dressing consists of a bioadhesive film (BAF), a unidirectional fluorinated conductive film (UFCF), and a liquid metal (LM) interlayer. Benefiting from the cross-linking of chitosan, the dressing exhibits excellent properties, such as biocompatibility, stretchability, tissue adhesion, and recyclability. In vivo experiments show that the FASW dressing reduced inflammation and stimulated hair follicle regeneration. This wound dressing utilizes previously overlooked natural energies for the treatment of chronic wounds, thereby enhancing the therapeutic effect of traditional self-powered dressings on individuals with movement disorders.

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.

Polyelectrolyte complex-based materials for separations: progress, challenges and opportunities

Polyelectrolyte complex (PEC) based materials could provide a sustainable alternative to conventional materials, especially for separation applications. However, reproducible production remains a challenge due to the many parameters influencing the polyelectrolyte complexation process, eventually affecting the properties and performance of the final material. Here, we provide an overview of how different parameters affect polyelectrolyte complexation and discuss promising PEC-based materials for separation applications, i.e., porous membranes, functional and barrier coatings, adhesives, saloplastics, and extraction media. Additionally, we highlight the challenges and opportunities and discuss what is needed to get to the next level. We envision that collaboration between experimentalists and theoreticians can leverage experimental datasets with accurate descriptions of all the parameters for multiscale modelling, machine learning and artificial intelligence approaches that can be used to design PEC materials and predict their properties.

Vegetable Oils for Material Applications - Available Biobased Compounds Seeking Their Utilities

Materials derived from natural sources are demanded for future applications due to the combination of factors such as sustainability increase and legislature requirements. The availability and efficient analysis of vegetable oils (triacylglycerides) open an enormous potential for incorporating these compounds into various products to ensure the ecological footprint decreases and to provide advantageous properties to the eventual products, such as flexibility, toughness, or exceptional hydrophobic character. The double bonds located in many vegetable oils are centers for chemical functionalization, such as epoxidization, hydroxylation, or many nucleophile substitutions using acids or anhydrides. Naturally occurring castor oil comprises a reactive vacant hydroxyl group, which can be modified via numerous chemical approaches. This comprehensive Review provides an overall insight toward multiple materials utilities for functionalized glycerides such as additive manufacturing (3D printing), polyurethane materials (including their chemical recycling), coatings, and adhesives. This work provides a complex list of investigated and studied applications throughout the available literature and describes the chemical principles for each selected application.

A Dual-Layer Hydrogel Barrier Integrating Bio-Adhesive and Anti-Adhesive Properties Prevents Postoperative Abdominal Adhesions

Postoperative abdominal adhesions are a common and painful complication after surgery, leading to high healthcare costs and diminished quality of life. This report presents a novel bilayer hydrogel barrier featuring an inner adhesive layer and an outer antiadhesive layer. The inner adhesive layer hydrogel (PT) is prepared by mixing polyethyleneimine (PEI) and thioctic acid (TA). The outer layer (HP) hydrogel is fabricated by the conjugation reaction of thermoresponsive zwitterionic hyaluronic acid, phenylboronic acid, and epigallocatechin gallate complex and polyvinyl alcohol based on dynamic boronic ester bond. The PEI/TA layer enhances attachment to moist tissue surfaces in vivo, and the anti-adhesive layer HP hydrogel promotes biocompatibility and anti-inflammation while minimizing protein adsorption and improving mechanical stability. The bilayer hydrogel (HPPT) exhibited rapid gelation, robust adhesion in dynamic and moist environments, superior viscoelastic properties and cellular biocompatibility. A mouse-cecum abdominal wall adhesion model is utilized to evaluate efficacy, and the HPPT hydrogel shows local retention, anti-inflammatory effect, and inhibits fibrin deposition while minimizing adhesion formation. These findings highlight the innovative structural and functional properties of the HPPT hydrogel, positioning it as a promising therapeutic barrier in peritoneal surgery aimed at reducing postoperative adhesions and enhancing surgical outcomes.

Nature-inspired surface modification strategies for implantable devices

Medical and implantable devices are essential instruments in contemporary healthcare, improving patient quality of life and meeting diverse clinical requirements. However, ongoing problems such as bacterial colonization, biofilm development, foreign body responses, and insufficient device-tissue adhesion hinder the long-term effectiveness and stability of these devices. Traditional methods to alleviate these issues frequently prove inadequate, necessitating the investigation of nature-inspired alternatives. Biomimetic surfaces, inspired by the chemical and physical principles found in biological systems, present potential opportunities to address these challenges. Recent breakthroughs in manufacturing techniques, including lithography, vapor deposition, self-assembly, and three-dimensional printing, now permit precise control of surface properties at the micro- and nanoscale. Biomimetic coatings can diminish inflammation, prevent bacterial adherence, and enhance stable tissue integration by replicating the antifouling, antibacterial, and adhesive properties observed in creatures such as geckos, mussels, and biological membranes. This review emphasizes the cutting-edge advancements in biomimetic surfaces for medical and implantable devices, outlining their design methodologies, functional results, and prospective clinical applications. Biomimetic coatings, by integrating biological inspiration with advanced surface engineering, have the potential to revolutionize implantable medical devices, providing safer, more lasting, and more effective interfaces for prolonged patient benefit.

Dual Functionalized Absorbable Hairy Cellulose-Based Fabric for Efficient Hemostasis and Antibacterial Property

Uncontrolled hemorrhage and subsequent infection at the injury sites are major causes of trauma-related mortality. Herein, we present a novel approach to creating a multifunctional biodegradable textile fabric with hemostatic and antibacterial properties, synthesized through chemical modification, including etherification, oxidation (aldehyde), and amination via a Schiff-based reaction between octadecyl ammonium and oxidized cellulose, followed by calcium ion cross-linking. The fabric demonstrated significant antibacterial efficay against both gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria, validated through assays such as colony counting, minimum inhibitory concentration (MIC), scanning electron microscopy, and fluorescent staining using Acridine Orange and Propidium Iodide. In vitro assessments demonstrated superior performance compared to commercial alternatives in red blood cell attachment (90%), blood clotting index (6%), platelet adhesion, and clotting time (20s) (P-value < 0.001). In vivo studies using a Wistar rat liver injury model confirmed the fabric's effectiveness, reducing bleeding time (3.1 and 6.2-fold) and blood loss (1.2 and 5.48-fold) compared to available commercial hemostatic agents. Pathological, hematological, and biochemical analyses demonstrated the biocompatibility and biodegradability of our developed material with no evidence of systemic toxicity, significant localized inflammatory reactions in the liver, renal, or skin tissues, or vascular thrombosis stimulation.

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.

Strong and tough adhesive hydrogel based on polyacrylate/carboxylated cellulose nanofibers/Zr4+ for high-sensitivity motion monitoring and controlled transdermal drug delivery

Monitoring athletes' movement is crucial for health management and personalized care. Targeted, controlled drug delivery can also enhance treatment effectiveness for chronic pain from issues like muscle strain or joint inflammation. Therefore, multifunctional materials are needed to integrate monitoring, diagnosis, intervention, and treatment within a single system. In this study, a multifunctional double-network hydrogel was developed, featuring poly [2-carboxyethyl acrylate-co-N-(2-hydroxyethyl) acrylamide] as the primary network, carboxylated cellulose nanofibers as the secondary network, and zirconium ions as a physical cross-linking agent. Coordination bonds between zirconium ions and functional groups in the hydrogel imparted excellent mechanical characteristics: a tensile ratio of up to 1150 %, a maximum tensile strength of 0.32 MPa, and a toughness of 1.64 ± 0.26 MJ/m3. The hydrogel also demonstrated outstanding sensing abilities, including a high sensitivity (gauge factor = 1.241), a low detection limit (0.1 %), and fast response time (63 ms), enabling reliable, continuous, high-fidelity monitoring of human motion. Similarly, the hydrogel facilitates targeted, controlled transdermal drug delivery without causing skin irritation or cytotoxicity, making it highly biocompatible. This multifunctional hydrogel offers a promising approach for motion monitoring and targeted drug delivery, advancing chronic pain management for better health recovery.

PEG-based polyurethane bioadhesive for wet and adaptable adhesion to circumcision wounds

Effective wound management is critical in post-operative recovery, particularly in sensitive areas such as circumcision. The aim of this study was to design and assess the efficacy of a novel two-component polyurethane (PU) bioadhesive, designated as PU1000S, for its application in advanced wound care within the context of clinical circumcision procedures. The glue-type bioadhesive was fine-tuned to conformally adhere to the moist tissue surfaces. It rapidly absorbed interfacial water and cured within 160 s, ensuring remarkable surface adaptability to wet tissue surfaces. The PU1000S demonstrated superior lap-shear strength, peaking at 55.12 ± 6.88 kPa, along with exceptional durability. These attributes underscored its strong wet adhesion and remarkable resilience at the interface with moist tissues. Owing to its mechanical adaptability to wet skin tissue, the adhesive layer of PU1000S maintained stability under complex loading associated with twisting, folding and significant volumetric deformation, resulting in minimal debonding. In addition, PU1000S was found to significantly accelerate wound healing by promoting re-epithelialization and collagen deposition, confirming its excellent bioadaptability for initial closure and subsequent tissue repair and regeneration following circumcision. The comprehensive results position PU1000S as a promising candidate for advanced wound care in circumcision, offering superior performance in terms of wet adhesion, durability and bioadaptability. Its application could potentially enhance clinical outcomes and elevate patient satisfaction.

Wet adhesives for hard tissues

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

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.

Particle manipulation under X-force fields

Particle manipulation is a central technique that enhances numerous scientific and medical applications by exploiting micro- and nanoscale control within fluidic environments. In this review, we systematically explore the multifaceted domain of particle manipulation under the influence of various X-force fields, integral to lab-on-a-chip technologies. We dissect the fundamental mechanisms of hydrodynamic, gravitational, optical, magnetic, electrical, and acoustic forces and detail their individual and synergistic applications. In particular, our discourse extends to advanced multi-modal manipulation strategies that harness the combined power of these forces, revealing their enhanced efficiency and precision in complex assays and diagnostic frameworks. The integration of cutting-edge technologies such as artificial intelligence and autonomous systems further enhances the capabilities of these microfluidic platforms, leading to transformative innovations in personalized medicine and point-of-care diagnostics. This review not only highlights current technological advances, but also forecasts the trajectory of future developments, emphasizing the escalating precision and scalability essential for advancing lab-on-a-chip applications.

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

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

Boosting mechanical durability under high humidity by bioinspired multisite polymer for high-efficiency flexible perovskite solar cells

Flexible perovskite solar cells (FPSCs) with high stability in moist air are required for their practical applications. However, the poor mechanical stability under high humidity air remains a critical challenge for flexible perovskite devices. Herein, inspired by the exceptional wet adhesion of mussels via dopamine groups, we propose a multidentate-cross-linking strategy, which combine multibranched structure and adequate dopamine anchor sites in three-dimensional hyperbranched polymer to directly chelate perovskite materials in multiple directions, therefore construct a vertical scaffold across the bulk of perovskite films from the bottom to the top interfaces, intimately bind to the perovskite grains and substrates with a strong adhesion ability, and enhance mechanical durability under high humidity. Consequently, the modified rigid PSCs achieve superior PCE up to 25.92%, while flexible PSCs exhibit a PCE of 24.43% and maintain 94.1% of initial PCE after 10,000 bending cycles with a bending radius of 3 mm under exposed to 65% humidity.

Advances in adhesion of microneedles for bioengineering

Microneedles have provided promising platforms in various fields thanks to their safety, painlessness, minimal invasiveness and ease of operation. The excellent adhesion of microneedles is the key characteristic to achieve long-term and comfortable treatment. However, a complex environment, such as the roughness of skin, various bodily fluids in vivo, and the movement of the body, presents great challenges to the adhesion characteristics of microneedles. This review mainly reports the remarkable adhesion properties of microneedles based on interlocking by shape effects, chemical bonds, and suction forces. Firstly, the main mechanisms of adhesion and various types of microneedles are introduced, with an emphasis on the progress in adhesive microneedles. Combined with the preparation and application of microneedles, the challenges and future trends of adhesive microneedles are discussed.

Dual Temperature- and pH-Responsive Layered Hydrogels Synthesized via Halogen Bond-Based Solid Phase Radical Polymerization

Stimuli-responsive shape-changing layered hydrogels were, for the first time, prepared via solid-phase polymerization, where halogen bond-based solid-phase radical polymerization was utilized. Monomer cocrystals were assembled to form predetermined layered structures before polymerization, and all layers are polymerized at one time. AB bilayer and ABA and ABC trilayer hydrogel sheets that consisted of temperature- and pH-responsive layers were prepared. The obtained layered sheets were responsive to temperature and pH in dual manners at relatively wide ranges of temperature (5-65 °C) and pH (2.0-11.0). The bilayer sheets exhibited bending upon stimuli. The bending angle was tunable, and the bending direction (negative and positive directions) was also switchable in response to temperature and pH. The trilayer sheets exhibited switchable concave, trapezoid, and convex shape changes with modulated angles, which were unprecedented shape changes. Because of the ease of operation and wide monomer scope (using radical polymerization and halogen bonding), the present method offers a facile and versatile approach to fabricate stimuli-responsive shape-changing hydrogel materials.

Multifunctional Conductive Hydrogel for Sensing Underwater Applications and Wearable Electroencephalogram Recording

Flexible electronics have been rapidly advancing and have garnered significant interest in monitoring physiological activities and health conditions. However, flexible electronics are prone to detachment in humid environments, so developing human-friendly flexible electronic devices that can effectively monitor human movement under various aquatic conditions and function as flexible electrodes remains a significant challenge. Here, we report a strongly adherent, self-healing, and swelling-resistant conductive hydrogel formed by combining the dual synergistic effects of hydrogen bonding and dipole-dipole interactions. The hydrogel has a commendable linear operating range (∼200% strain, GF = 1.44), stability of electrical signals for 200 cycles, excellent conductivity (2.18 S m-1), self-healing properties (∼30 min), and durable underwater adhesion stability. The conductive hydrogel can be developed into a flexible electronic sensor for detecting motion signals, such as joint flexion and swallowing, as well as for real-time underwater communication using Morse code. Additionally, the integration of this polymer with a low contact impedance facilitates real-time, high-fidelity detection of electroencephalogram (EEG) signals, serving as a flexible electrode. It is believed that our hydrogel will have good prospects in future wearable electronics.

Water has different effects on adhesive strength during placement versus loading of spider silk attachment discs

Spiders use piriform silk attachment discs to adhere threads during web construction and to secure safety lines. Water could degrade attachment disc adhesion by either interfering with placement of the discs or later reducing adhesion during loading. We tested the effect of water on the adhesion of attachment discs for the spider Latrodectus hesperus, which spins webs in mostly dry environments. We compared adhesion for discs spun on wet versus dry glass that were subsequently loaded in either wet or dry conditions. Attachment discs placed on wet glass showed similar adhesion to discs placed on dry glass. However, water significantly decreased both peak force of adhesion and work of adhesion when loading occurred under wet conditions, regardless of initial placement conditions. Furthermore, failure mode shifted from rupture of draglines in dry loading conditions to adhesive failure of discs in wet loading conditions. Our results show the importance of considering both the conditions in which biological structures are produced and those in which the structures perform as potentially independent factors for performance. Our results also suggest that adhesion in wet conditions can challenge some spiders, potentially leading to specialization of attachment discs for riparian or aquatic species.

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

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

Bio-inspired anti-swelling amyloid-fiber lysozyme adhesive for rapid wound closure and hemostasis

Instant adhesion to wet biological surfaces and reduced swelling of tissue adhesives are crucial for rapid wound closure and hemostasis. However, previous strategies to reduce swelling were always accompanied by a decrease in the tissue bonding strength of the adhesive. Moreover, the irreducibility of the covalent bonds in currently reported adhesives results in the adhesives losing their tissue adhesive ability. To tackle the challenge, a superior anti-swelling coacervate adhesive possessing fast self-healing properties through physical interactions (electrostatic interactions, hydrogen bonding) and chemical crosslinking (Schiff base reaction) was obtained with aldehyde-modified γ-PGA (γ-PGA-CHO), a natural lysozyme (LZM) and an amyloid fiber reduced lysozyme (RLZM). The instant shear adhesion strength and burst pressure tolerance of the adhesive on wet pig intestine reached 50.8 kPa (2.6 times that of CA glue) and 142.5 mmHg (5.9 times that of CA glue), and it maintained an adhesion strength of 37.4 kPa after exposure to the physical environment for 12 h and the swelling rate was only 34.0% underwater. The in vitro and in vivo experiments provided the coacervate adhesive with potential applicability for emergency rescue and wound care scenarios.

Supramolecular adhesives inspired from adhesive proteins and nucleic acids: molecular design, properties, and applications

Bioinspired supramolecular adhesives have been recently emerging as novel functional materials, which have shown a wide range of applications in wearable sensors and tissue engineering such as tissue adhesives and wound dressings. In this review, we summarize and discuss two main types of biologically inspired supramolecular adhesives from adhesive proteins and nucleic acids. The widely studied catechol-based adhesives, that originated from adhesive proteins of marine organisms such as mussels, and recently emerging nucleobase-containing supramolecular adhesives are both introduced and discussed. Both bioinspired adhesives from nucleic acids and adhesive proteins involve multiple supramolecular interactions such as hydrogen bonding, hydrophobic interactions, π-π stacking, and so on. Several major types of these bioinspired adhesives are summarized, respectively, including polymer-based, hydrogel-based, and other types of adhesives. The novel molecular design and adhesion properties are focused on and highlighted for each type of bioinspired adhesive. In addition, the potential applications of these bioinspired supramolecular adhesives in different realms including tissue engineering and biomedical devices are discussed. This review concludes with issues and challenges in the area of the bioinspired adhesives, hopefully promoting further developments and broader applications of novel supramolecular adhesives.

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.

A Self-Gelling Powder Based on Polyacrylic Acid/Polyethyleneimine/Polyethylene Glycol for High-Performance Hemostasis and Antibacterial Activity

Powder-based hemostatic materials have offered unprecedented opportunities for the effective sealing and repair of irregularly shaped wounds and high-pressure, noncompressible arterial bleeding wounds caused by surgeries, traffic accidents, and wartime injuries. However, inadequate adhesion to bleeding wounds and poor hemostasis in biological tissues remains challenging. Herein, we report a self-gelling hemostatic powder based on polyacrylic acid/polyethyleneimine/polyethylene glycol (named PPG) for rapid hemostasis and effective antibacterial ability. When deposited on bleeding wounds, PPG powder can absorb interfacial liquid and rapidly swell into a physically cross-linked hydrogel in situ within 2 s to form a pressure-resistant physical barrier. Furthermore, the in vivo and in vitro results indicate that, as an effective sealant, the PPG powder possesses ease of use, excellent hemocompatibility, strong antibacterial abilities, and superior blood clotting abilities. The effective hemostatic sealing capability of the PPG powder is demonstrated in a variety of injury models in rats and rabbits. All of these factors show that, with its superior wound treatment abilities, PPG powder is a profound biomaterial for surgical applications.

Design Strategy, On-Demand Control, and Biomedical Engineering Applications of Wet Adhesion

The adhesion of tissues to external devices is fundamental to numerous critical applications in biomedical engineering, including tissue and organ repair, bioelectronic interfaces, adhesive robotics, wearable electronics, biomedical sensing and actuation, as well as medical monitoring, treatment, and healthcare. A key challenge in this context is that tissues are typically situated in aqueous and dynamic environments, which poses a bottleneck to further advancements in these fields. Wet adhesion technology (WAT) presents an effective solution to this issue. In this review, we summarize the three major design strategies and control methods of wet adhesion, comprehensively and systematically introducing the latest applications and advancements of WAT in the field of biomedical engineering. First, single adhesion mechanism under the frameworks of the three design strategies is systematically introduced. Second, control methods for adhesion are comprehensively summarized, including spatiotemporal control, detachment control, and reversible adhesion control. Third, a systematic summary and discussion of the latest applications of WAT in biomedical engineering research and education were presented, with a particular focus on innovative applications such as tissue-electronic interface devices, ingestible devices, end-effector components, in vivo medical microrobots, and medical instruments and equipment. Finally, opportunities and challenges encountered in the design and development of wet adhesives with advanced adhesive performance and application prospects are discussed.

Powdered Medical Adhesive with Long Lasting Adhesion in Water Environment

Medical adhesives have been used under surgical conditions. However, it is always a big challenge to maintain long-term adhesion in a water environment. Besides, it usually takes a long time to complete the adhesion, and the operation might be complicated. In this study, tannic acid and gelatin solution under acidic conditions were mixed, flocculated, lyophilized, and crushed; thus, a powdered medical adhesive (POWDER) was prepared with long-lasting adhesion in a water environment, convenience, and low price. Tannic acid bound gelatin and maintained adhesive force primarily through hydrogen bonding and reacted with amino sulfhydryl and other amino acid residues after oxidation into aldehyde, exhibiting excellent underwater adhesion. Oxidized dextran (ODex) powder rich in an aldehyde group was introduced to provide covalent binding in the adhesive. In vitro and in vivo studies showed that POWDER could quickly adhere to various tissues in the water environment. In vitro skin adhesion experiments demonstrated that it could achieve effective adhesion in a water environment for up to 60 days. Its blood compatibility, low cytotoxicity, and biodegradability were also verified. The POWDER developed in this study is of great significance for patients who need rapid wound treatments.

Customized surface adhesive and wettability properties of conformal electronic devices

Conformal and body-adaptive electronics have revolutionized the way we interact with technology, ushering in a new era of wearable devices that can seamlessly integrate with our daily lives. However, the inherent mismatch between artificially synthesized materials and biological tissues (caused by irregular skin fold, skin hair, sweat, and skin grease) needs to be addressed, which can be realized using body-adaptive electronics by rational design of their surface adhesive and wettability properties. Over the past few decades, various approaches have been developed to enhance the conformability and adaptability of bioelectronics by (i) increasing flexibility and reducing device thickness, (ii) improving the adhesion and wettability between bioelectronics and biological interfaces, and (iii) refining the integration process with biological systems. Successful development of a conformal and body-adaptive electronic device requires comprehensive consideration of all three aspects. This review starts with the design strategies of conformal electronics with different surface adhesive and wettability properties. A series of conformal and body-adaptive electronics used in the human body under both dry and wet conditions are systematically discussed. Finally, the current challenges and critical perspectives are summarized, focusing on promising directions such as telemedicine, mobile health, point-of-care diagnostics, and human-machine interface applications.

Serotonin-functionalized starch-based hemostatic sponges enhance platelet activation in the management of non-compressible hemorrhage

Massive hemorrhage poses a serious threat to human health and even life. Access to rapid and potent hemostatic materials is crucial for lowering mortality rates. Starch-based materials exhibit good biocompatibility and are extensively utilized in hemostatic. However, existing starch-based hemostatic products suffer from limited hemostatic efficacy. Serotonin, an indoleamine naturally occurring in the human body, is recognized for its potent platelet-activating properties. Therefore, this study focused on enhancing the procoagulant activity of starch by incorporating serotonin into the starch backbone via esterification and amidation reactions, yielding a novel serotonin-loaded starch-based hemostatic sponge (SLS sponge). The SLS sponges featured exceptional porosity (≥80 %) and water absorption capacity (≥2000 %), which rapidly initiated the coagulation cascade reaction, promoted the adhesion and aggregation of red blood cells and platelets, and intensified platelet activation. This multifaceted approach synergistically enhanced hemostasis via both active and passive coagulation mechanisms. Notably, the SLS sponges adhered firmly to the wound surfaces without pressure. Compared with gelatin sponges, the SLS sponges significantly reduced blood loss by approximately 40.5 % and shortened the time to achieve hemostasis by approximately 28.9 %. These findings indicate that the newly developed SLS sponges are a promising active hemostatic material, particularly effective in managing non-compressible hemorrhages.

Bioinspired Asymmetric-Adhesion Janus Hydrogel Patch Regulating by Zwitterionic Polymers for Wet Tissues Adhesion and Postoperative Adhesion Prevention

Asymmetrically adhesive hydrogel patch with robust wet tissue adhesion simultaneously anti-postoperative adhesion is essential for clinical applications in internal soft-tissue repair and postoperative anti-adhesion. Herein, inspired by the lubricative role of serosa and the underwater adhesion mechanism of mussels, an asymmetrically adhesive hydrogel Janus patch is developed with adhesion layer (AL) and anti-adhesion layer (anti-AL) through an in situ step-by-step polymerization process in the mold. The AL exhibits excellent adhesion to internal soft-tissues. In contrast, the anti-AL demonstrated ultralow fouling property against protein and fibroblasts, which hinders the early and advanced stages of development of the adhesion. Moreover, the Janus patch simultaneously promotes tissue regeneration via ROS clearance capability of catechol moieties in the AL. Results from in vivo experiments with rabbits and rats demonstrate that the AL strongly adheres to traumatized tissue, while the anti-AL surface demonstrate efficacy in preventing of post-abdominal surgery adhesions in contrast to clinical patches. Considering the advantages in terms of therapeutic efficacy and off the shelf, the Janus patch developed in this work presents a promise for preventing postoperative adhesions and promoting regeneration of internal tissue defects.

An Environmentally Stable, Biocompatible, and Multilayered Wound Dressing Film with Reversible and Strong Adhesion

Reversible adhesives for wound care improve patient experiences by permitting reuse and minimizing further tissue injury. Existing reversible bandages are vulnerable to water and can undergo unwanted deformation during removal and readdressing procedures. Here, a biocompatible, multilayered, reversible wound dressing film that conforms to skin and is waterproof is designed. The inner layer is capable of instant adhesion to various substrates upon activation of the dynamic boronic ester bonds by water; intermediate hydrogel layer and outer silicone backing layer can enhance the dressing's elasticity and load distribution for adhesion, and the silicone outer layer protects the dressing from exposure to water. The adhesive layer is found to be biocompatible with mouse skin. Skin injuries on the mouse skin heal more rapidly with the film compared to no dressing controls. Evaluations of the film on skin of freshly euthanized minipigs corroborate the findings in the mouse model. The film remains attached to skins without delamination despite subjecting to various degrees of deformation. Exposure to water softens the film to allow removal from the skin without pulling any hair off. The multilayered design considers soft mechanics in each layer and will offer new insights to improve wound dressing performance and patient comfort.

Deformation-Resistant Underwater Adhesion in a Wide Salinity Range

Conventional adhesives experience reduced adhesion when exposed to aqueous environments. The development of underwater adhesives capable of forming strong and durable bonds across various wet substrates is crucial in biomedical and engineering domains. Nonetheless, limited emphasis placed on retaining high adhesion strengths in different saline environments, addressing challenges such as elevated osmotic pressure and spontaneous dimensional alterations. Herein, a series of ionogel-based underwater adhesives are developed using a copolymerization approach that incorporates "dynamic complementary cross-linking" networks. Synergistic engineering of building blocks, cross-linking networks, pendant groups and counterions within ionogels ensures their adhesion and cohesion in brine spanning a wide salinity range. A high adhesion strength of ≈3.6 MPa is attained in freshwater. Gratifyingly, steady adhesion strengths exceeding 3.3 MPa are retained in hypersaline solutions with salinity ranging from 50 to 200 g kg-1, delivering one of the best-performing underwater adhesives suitable for diverse saline solutions. A combination of outstanding durability, reliability, deformation resistance, salt tolerance, and self-healing properties showcases the "self-contained" underwater adhesion. This study shines light on the facile fabrication of catechol-free ionogel-based adhesives, not merely boosting adhesion strengths in freshwater, but also broadening their applicability across various saline environments.

Endocytosis-Inspired Zwitterionic Gel Tape for High-Efficient and Sustainable Underoil Adhesion

Marine oil exploration is important yet greatly increases the risk of oil leakage, which will result in severe environment pollution and economic losses. It is an urgent need to develop effective underoil adhesives. However, realizing underoil adhesion is even harder than those underwater, due to the stubborn attachment of a highly viscous oil layer on target surface. Here, inspired by endocytosis, a tough gel tape composed of zwitterionic polymer network and zwitterionic surfactants is developed. The amphiphilic surfactants can form micelle to capture the oil droplets and transport them from the interface to gel via electrostatic attraction of polymer backbone, mimicking the endocytosis and achieving robust underoil adhesion. Benefiting from the oil-resistance of polymer backbone, the gel further realizes a combination of i) long-term adhesion with high durability, ii) repeated adhesion in oil, and iii) renewable adhesion efficiency after exhausted use. The tape exhibits an ultra-high adhesive toughness of 2446.86 J m-2 to stainless steel in silicone oil after 30 days' oil-exposure; such value of adhesive toughness surpasses many of those achieved in underwater adhesion and is greater than underoil adhesion performance of commercial tape. The strategy illustrated here will motivate the design of sustainable and efficient adhesives for wet environments.

A bio-inspired Janus hydrogel patch facilitates oral ulcer repair by combining prolonged wet adhesion and lubrication

Oral ulcers, the most common type of mucosal lesion, are both highly prevalent and prone to recurrence. In the persistently moist environment of the oral cavity, current therapeutic patches face challenges such as short adhesion time, disruption by food particles and bacteria, and oral movements. To address these challenges, we develop a Janus patch, named ANSB, inspired by the multi-layered and asymmetric structure of natural mucosa, featuring a long-lasting adhesive layer and a lubricating layer. By eliminating the salivary barrier and leveraging covalent crosslinking between tissue surface amine groups and N-hydroxysuccinimide ester (NHS), the adhesive layer-composed of gelatin and acrylic acid-achieves rapid (≤ 30 s), strong (≥ 45 kPa), and durable (≥ 8 h) adhesion to wet buccal tissues. Furthermore, the efficient lubricating effect (COF = 0.02 ± 0.003) provided by zwitterions renders the lubricating layer of ANSB highly similar to natural mucosal tissue, effectively preventing bacterial invasion, secondary damage, and unintended adhesion. Additionally, the strong interlayer bonding and complementary mechanical properties are confirmed, resulting in a unified performance characterized by rapid wet adhesion, hydration lubrication, and enhanced mechanical strength. Importantly, ANSB treatment demonstrates a long-term protective barrier and superior therapeutic effects in rat oral ulcers, inhibiting pseudomembrane formation and accelerating tissue regeneration without causing secondary damage. Consequently, this distinctive Janus patch, characterized by prolonged adhesion, efficient lubrication, and simple preparation, holds significant potential for clinical oral ulcer treatment. STATEMENT OF SIGNIFICANCE: Oral ulcers, with healing impeded by secondary injury and bacterial invasion due to the absence of protective barriers, are highly prevalent and recurrent. However, sustaining therapeutic materials and physical barriers in the highly dynamic and moist oral environment poses a considerable challenge. In this study, a Janus patch (ANSB) that integrated a soft wet adhesive layer and a tough lubricating layer was developed to reconstruct a new protective barrier thus preventing external stimuli such as secondary damage and bacterial infiltration. This innovative patch with high therapeutic potential for oral ulcers may offer a new way for ulcer treatment based on barrier protection.

Nanoscale Strategies for Enhancing the Performance of Adhesive Dry Electrodes for the Skin

High-quality electrophysiological monitoring requires electrodes to maintain a compliant and stable skin contact. This necessitates low impedance, good skin compliance, and strong adhesion to ensure continuous and stable contact under dynamic conditions. In this context, adhesive epidermal dry electrodes are advancing rapidly, which is promising for long-term applications in clinical diagnosis, wearable health monitoring, and human-machine interfaces. However, challenges persist, as conventional technologies usually fall short of meeting the high standards required for electrophysiological electrodes. This Perspective discusses four key aspects for high-performance epidermal electrodes from an adhesive perspective: initial adhesion, water resistance, dynamic stability, and removal simplicity. We review recent nanoscale strategies addressing these issues, providing a comprehensive guideline to enhance the application performance of epidermal dry electrodes. Additionally, we explore key nanoscale strategies and their associated functions, future technology roadmaps, and prospects for dry adhesive epidermal electrodes.

Nature-Inspired Wet Drug Delivery Platforms

Nature has created various organisms with unique chemical components and multi-scale structures (e.g., foot proteins, toe pads, suckers, setose gill lamellae) to achieve wet adhesion functions to adapt to their complex living environments. These organisms can provide inspirations for designing wet adhesives with mediated drug release behaviors in target locations of biological surfaces. They exhibit conformal and enhanced wet adhesion, addressing the bottleneck of weaker tissue interface adhesion in the presence of body fluids. Herein, it is focused on the research progress of different wet adhesion and bioinspired fabrications, including adhesive protein-based adhesion and inspired adhesives (e.g., mussel adhesion); capillarity and Stefan adhesion and inspired adhesive surfaces (e.g., tree frog adhesion); suction-based adhesion and inspired suckers (e.g., octopus' adhesion); interlocking and friction-based adhesion and potential inspirations (e.g., mayfly larva and teleost adhesion). Other secreted protein-induced wet adhesion is also reviewed and various suckers for other organisms and their inspirations. Notably, one representative application scenario of these bioinspired wet adhesives is highlighted, where they function as efficient drug delivery platforms on target tissues and/or organs with requirements of both controllable wet adhesion and optimized drug release. Finally, the challenges of these bioinspired wet drug delivery platforms in the future is presented.

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.

Adhesion Evolution: Designing Smart Polymeric Adhesive Systems with On-Demand Reversible Switchability

Smart polymeric switchable adhesives represent a rapidly emerging class of advanced materials, exhibiting the ability to undergo on-demand transitioning between "On" and "Off" adhesion states. By selectively tuning external stimuli triggers (including temperature, light, electricity, magnetism, and chemical agents), we can engineer these materials to undergo reversible changes in their bonding capabilities. The strategic design selection of stimuli is a pivotal factor in the design of switchable adhesive systems. This review outlines recent advancements in the field of smart switchable polymeric adhesives over the past decade with a focus on the selection of stimulus triggers. These systems are further categorized into one of four adhesion switching mechanisms upon initiation by a specific stimuli-trigger: (i) interfacial adhesion, (ii) stiffness, (iii) contact area, or (iv) suction-based switching. Evaluation of adhesion switching performance across systems is primarily made based on three key metrics: (i) maximum adhesion strength, (ii) switch ratio, and (iii) switch time. Different stimuli and mechanisms offer distinct advantages and limitations, influencing the performance characteristics and applicability of these materials across domains such as detachable biomedical devices, robotic grippers, and climbing robots. This review thus offers a perspective on the present advancements and challenges in this emerging field, along with insights into future directions.

Exploring Stimuli-Responsive Natural Processes for the Fabrication of High-Performance Materials

Climate change and environmental pollution have underscored the urgency for more sustainable alternatives in synthetic polymer production. Nature's repertoire of biopolymers with excellent multifaceted properties alongside biodegradability could inspire next-generation innovative green polymer fabrication routes. Stimuli-induced processing, driven by changes in environmental factors, such as pH, ionic strength, and mechanical forces, plays a crucial role in natural polymeric self-assembly process. This perspective aims to close the gap in understanding biopolymer formation by highlighting the essential role of stimuli triggers in facilitating the bottom-up fabrication, allowing for the formation of intricate hierarchical structures. In particular, this perspective will delve into the stimuli-responsive processing of high-performance biopolymers produced by mussels, caddisflies, velvet worms, sharks, whelks, and squids, which are known for their robust mechanical properties, durability, and wet adhesion capabilities. Finally, we provide an overview of current advancements and challenges in understanding stimuli-induced natural formation pathways and their translation to biomimetic materials.

Development of smart adhesive using lanthanide-doped phosphor and carboxymethyl cellulose-reinforced gum Arabic

Smart polymer glue with photoluminescence and water-repellent properties was developed. The luminescent adhesive continues emitting light for up to 120 min after turning the excitation source off. Nanoparticles of lanthanide strontium aluminum oxide (LSAO) (8-13 nm) were consistently immobilized into carboxymethyl cellulose-reinforced gum Arabic (CMC/GA) adhesive. Using various concentrations of LSAO, the generated adhesives showed emission intensity at 519 nm and an excitation band at 365 nm. Depending on LSAO content, both of afterglow and fluorescence emission were monitored. Photochromism was detected as the transparent adhesive film changes color to green under ultraviolet irradiation. A greenish-yellow lightening in a darkened place was also observed. The nanocomposite resistance to scratches and hydrophobicity were found to enhance as the LSAO content was increased in the carboxymethyl cellulose-reinforced gum Arabic matrix. The LSAO@CMC/GA nanocomposite showed high durability and photostability. The present strategy proved the viability of a potential mass production toward photoluminescent adhesives for various smart applications, such as smart packaging, anti-counterfeiting printing, smart windows, and safety signs.

Novel Functional Dressing Materials for Intraoral Wound Care

Intraoral wounds represent a particularly challenging category of mucosal and hard tissue injuries, characterized by the unique structures, complex environment, and distinctive healing processes within the oral cavity. They have a common occurrence yet frequently inflict significant inconvenience and pain on patients, causing a serious decline in the quality of life. A variety of novel functional dressings specifically designed for the moist and dynamic oral environment have been developed and realized accelerated and improved wound healing. Thoroughly analyzing and summarizing these materials is of paramount importance in enhancing the understanding and proficiently managing intraoral wounds. In this review, the particular processes and unique characteristics of intraoral wound healing are firstly described. Up-to-date knowledge of various forms, properties, and applications of existing products are then intensively discussed, which are categorized into animal products, plant extracts, natural polymers, and synthetic products. To conclude, this review presents a comprehensive framework of currently available functional intraoral wound dressings, with an aim to provoke inspiration of future studies to design more convenient and versatile materials.

Alternative sequential combinations of electrocoagulation with electrooxidation and peroxi-coagulation for effective treatment of adhesive production industry wastewater

Adhesive production industry wastewater can be characterized by high chemical oxygen demand (COD) sourced from high refractory organic contaminants and high total suspended solids (TSS) concentration. Biodegradability of the wastewater is low and wastewater quality is unstable. Various treatment processes have limited applicability in such characterized wastewater. In this study, the treatment performance of electrochemical processes was investigated. Because it is not possible to meet the discharge standards by application of only one process for high refractory organic content, sequential electrochemical processes were studied in this work. In the first step of the sequential process, electrocoagulation (EC) using Al electrodes by which better performance was achieved was applied. In the second step, electrooxidation (EO) and peroxi-coagulation (PC) processes were applied to the EC effluent. In EO, Ti/MMO was selected as the most effective anode whereas in PC, Fe was used as the anode, and graphite was used as the cathode. Box-Behnken Design was applied to optimize the operating conditions of EO and PC processes and to obtain mathematical model equations. In the EC process, 77% COD, 78.5% TSS, and 85% UV254 removal efficiency were obtained under the optimum conditions (pH 7.2, reaction time 35 min, and current density 0.5 mA/cm2). With the EO and PC processes applied to the effluent of EC, 68.5% COD, 77% TSS, and 83% UV254 removal and 77.5% COD, 87% TSS, and 86.5% UV254 removal were obtained, respectively. The specific energy consumption of EC-EO and EC-PC processes was 16.08 kWh/kg COD and 15.06 kWh/kg COD, respectively. Considering the treatment targets and process operating costs, it was concluded that both sequential electrochemical systems could be promising alternative systems for the treatment of adhesive production industry wastewater.

Biocompatible polymer-based micro/nanorobots for theranostic translational applications

Recently, micro/nanorobots (MNRs) with self-propulsion have emerged as a promising smart platform for diagnostic, therapeutic and theranostic applications. Especially, polymer-based MNRs have attracted huge attention due to their inherent biocompatibility and versatility, making them actively explored for various medical applications. As the translation of MNRs from laboratory to clinical settings is imperative, the use of appropriate polymers for MNRs is a key strategy, which can prompt the advancement of MNRs to the next phase. In this review, we describe the multifunctional versatile polymers in MNRs, and their biodegradability, motion control, cargo loading and release, adhesion, and other characteristics. After that, we review the theranostic applications of polymer-based MNRs to bioimaging, biosensing, drug delivery, and tissue engineering. Furthermore, we address the challenges that must be overcome to facilitate the translational development of polymeric MNRs with future perspectives. This review would provide valuable insights into the state-of-the-art technologies associated with polymeric MNRs and contribute to their progression for further clinical development.

Mechanochemistry: Fundamental Principles and Applications

Mechanochemistry is an emerging research field at the interface of physics, mechanics, materials science, and chemistry. Complementary to traditional activation methods in chemistry, such as heat, electricity, and light, mechanochemistry focuses on the activation of chemical reactions by directly or indirectly applying mechanical forces. It has evolved as a powerful tool for controlling chemical reactions in solid state systems, sensing and responding to stresses in polymer materials, regulating interfacial adhesions, and stimulating biological processes. By combining theoretical approaches, simulations and experimental techniques, researchers have gained intricate insights into the mechanisms underlying mechanochemistry. In this review, the physical chemistry principles underpinning mechanochemistry are elucidated and a comprehensive overview of recent significant achievements in the discovery of mechanically responsive chemical processes is provided, with a particular emphasis on their applications in materials science. Additionally, The perspectives and insights into potential future directions for this exciting research field are offered.

Mussel Foot Protein-Inspired Adhesive Tapes with Tunable Underwater Adhesion

Instant and strong adhesion to underwater adherends is a big challenge due to the continuous interference of water. Mussel foot protein-bioinspired catechol-based adhesives have garnered great interest in addressing this issue. Herein, a novel self-made catecholic compound with a long aliphatic chain was utilized to prepare thin (∼0.07 mm) and optically transparent (>80%) wet/underwater adhesive tapes by UV-initiated polymerization. Its adhesion activity was water-triggered, fast (<1 min), and strong (adhesion strength to porcine skin: ∼1.99 MPa; interfacial toughness: ∼610 J/m2, burst pressure: ∼1950 mmHg). The effect of the catechol/phenol group and positively charged moiety on the wet/underwater adhesion to abiotic/biotic substrates was investigated. On the wet/underwater adherends, the tape with catechol groups presented much higher interfacial toughness, adhesion strength, and burst pressure than the analogous tape with phenol groups. The tape with both the catechol group and cationic polyelectrolyte chitosan had a more impressive improvement in its adhesion to wet/underwater biological tissues than to abiotic substrates. Therefore, catechol and a positive moiety in the tape would synergistically enhance its wet/underwater adhesion to various substrates, especially to biological tissues. The instant, strong, and noncytotoxic tape may provide applications in underwater adhesion for sealing and wound closure.

A dry double-sided tape post-treated with tannic acid for long-term adhesion in a wet environment

Medical adhesives have been used for wound closure with many advantages over sutures, but the wet environment in the human body poses a big challenge for its application. The currently used dry double-sided tape (DST) can remove the water barrier by water absorption, but its over-swelling makes it difficult to achieve long-term adhesion. In this study, a dry double-sided tape post-treated with tannic acid (DST-TA) was developed. A double network adhesive composed of polyacrylic acid and gelatin was first prepared by free radical photocrosslinking, and was post-treated in acidic (pH = 2) tannic acid solution. Tannic acid was immobilized in the DST through the catecholyl group, which could form hydrogen bonds with the DST, or react with the amino group on the gelatin by oxidizing to quinone. In vivo and in vitro studies demonstrated that DST-TA had significantly higher swelling resistance and tensile strength than DST. The introduced catecholyl group could reduce over-swelling of the DST, and improve short-term and long-term adhesion in a wet environment. We also demonstrated that the DST-TA had good hemocompatibility, biodegradability, and no cytotoxicity, offering a potential option for long-term medical adhesive in a wet environment.