VATA: A Poly(vinyl alcohol)- and Tannic Acid-Based Nontoxic Underwater Adhesive

Borax - and tannic acid-based post-3D-printing treatment to tune the mechanical properties of scaffolds

Digital light processing (DLP) methods are constrained by the narrow range of cell-compatible resins, limiting their use in biomedical applications that require varied mechanical and biofunctional properties. Current bioresins based on natural polymers such as methacrylated gelatine or alginate usually lack sufficient stretchability and toughness. In this study, we propose a post-processing strategy to tune the mechanical and functional properties of a DLP printable polyethylene glycol diacrylate (PEGDA)/polyvinyl alcohol (PVA) resin via simple treatment with 5% (w/v) tannic acid (TA) or borax (B). The TA treatment reduced the resin's toughness by ∼17% and compressive modulus by ∼16%, while B treatment increased the toughness by ∼53% and the compressive modulus by ∼44% compared with non-treated hydrogels. TA-treated hydrogels continuously released over 59% of the loaded TA, demonstrating antibacterial and radical scavenging activities. Moreover, TA-treated hydrogels, DLP-printed in a tubular shape, demonstrated the highest durability, remaining intact for ∼32 cycles before failure, which was ∼17 cycles more than that for the non-treated hydrogels. Our in vivo larval model further confirmed the hydrogels' biocompatibility. This study offers a practical approach for post-fabrication tuning of the mechanical and bioactive properties of DLP-printed PEGDA-PVA hydrogels, expanding the utility of existing resins for potential biomedical applications, such as soft tissue engineering.

Mussel-Inspired Molecular Strategies for Fabricating Functional Materials With Underwater Adhesion and Self-Healing Properties

The exceptional underwater adhesion and self-healing capabilities of mussels have fascinated researchers for over two decades. Extensive studies have shown that these remarkable properties arise from a series of reversible and dynamic molecular interactions involving mussel foot proteins. Inspired by these molecular interaction strategies, numerous functional materials exhibiting strong underwater adhesion and self-healing performance have been successfully developed. This review systematically explores the nanomechanical mechanisms of mussel-inspired molecular interactions, mainly revealed by direct force measurement techniques such as surface forces apparatus and atomic force microscopy. The development of functional materials, including coacervates, coatings, and hydrogels, with underwater adhesion and self-healing properties, is then summarized. Furthermore, the macroscopic material performances are correlated with the underlying molecular mechanisms, providing valuable insights for the rational design of next-generation mussel-inspired functional materials with enhanced underwater adhesion and self-healing properties.

Recent advances in tannic acid-based gels: Design, properties, and applications

With the flourishing of mussel-inspired chemistry, the fast-growing development for environmentally friendly materials, and the need for inexpensive and biocompatible analogues to PDA in gel design, TA has led to its gradual emergence as a research focus due to its remarkable biocompatible, renewable, sustainable and particular physicochemical properties. As a natural building block, TA can be used as a substrate or crosslinker, ensuring versatile functional polymeric networks for various applications. In this review, the design of TA-based gels is summarized in detail (i.e., different interactions such as: metal coordination, electrostatic, hydrophobic, host-guest, cation-π and π-π stacking interactions, hydrogen bonding and various reactions including: phenol-amine Michael and Schiff base, phenol-thiol Michael addition, phenol-epoxy ring opening reaction, etc.). Subsequently, TA-based gels with a variety of functionalities, including mechanical, adhesion, conductive, self-healing, UV-shielding, anti-swelling, anti-freezing, shape memory, antioxidant, antibacterial, anti-inflammatory and responsive properties are introduced in detail. Then, a summary of recent developments in the use of TA-based gels is provided, including bioelectronics, biomedicine, energy, packaging, water treatment and other fields. Finally, the difficulties that TA-based gels are currently facing are outlined, and an original yet realistic viewpoint is provided in an effort to spur future development.

Nanochitin-Fortified Polyphenol Complexes for Dry and Wet Adhesion

Synthetic adhesives commonly used in shipbuilding, plumbing, and various industrial and household applications pose environmental and health concerns due to chemical leaching and other issues. In this work, we present a sustainable alternative using chitin nanofibers (ChNF) to enhance the networking and surface binding of biomolecules. We investigate aqueous-based formulations composed of tannic acid (TA), poly(vinyl alcohol) (PVA), and chitin nanofibers, which form robust adhesive complexes. These are driven by multiple interactions involving phenolic and hydroxyl groups, which are present at high densities and contribute to exceptional adhesion upon drying. Unlike most two-component structural adhesives, the ChNF-based adhesives introduced here do not rely on organic solvents and demonstrate versatility across surfaces with contrasting topologies and surface energies, including stainless steel, polypropylene, wood, and others. With an ultimate shear strength reaching up to 20 MPa, these adhesives rival commercially available structural adhesives commonly used for bonding metals, wood, and glass. The addition of chitin nanofibers enhances adhesion by up to 400%, depending on the PVA-to-TA ratio. Furthermore, these adhesives exhibit long-term structural integrity under wet conditions, showing no signs of swelling or degradation. To elucidate the mechanisms underlying adhesion in both wet and dry states, we conducted comprehensive analyses, including morphological, mechanical, rheological, spectroscopic, thermal, and surface characterizations. The findings highlight the potential of ChNF-based adhesives as a viable and sustainable alternative for diverse industrial applications.

Mechanically robust, mouldable, dynamically crosslinked hydrogel flap with multiple functionalities for accelerated deep skin wound healing

Deep cutaneous wounds, which are difficult to heal and specifically occur on dynamic body surfaces, remain a substantial healthcare challenge in clinical practice because of multiple underlying factors, including excessive reactive oxygen species, potential bacterial infection, and extensive degradation of the extracellular matrix (ECM) which further leads to the progressive deterioration of the wound microenvironment. Any available individual wound therapy, such as antibiotic-loaded cotton gauze, cannot address all these issues. Engineering an advanced multifunctional wound dressing is the current need to promote the overall healing process of such wounds. Here, we report a multifunctional hydrogel flap primarily composed of biodegradable polymers gelatin (G) and poly-methyl vinyl ether-alt-maleic acid (MA) as the base material. The hydrogel physically incorporates tannic acid (TA) and vancomycin (V), for added functionality. The resulting hydrogel flap, gelatin- poly-methyl vinyl ether-alt-maleic acid-tannic acid-vancomycin (G-MA-TA-V/E-N), is formed through a chemical crosslinking process using EDC (E) and NHS (N). Thus, the hydrogel flap reveals multiple ideal properties that support its ease of application, including stretchability, porous microstructure (honey-comb structure), mouldability, and adhesiveness to multiple surfaces, including wet biological surfaces. The in vitro studies demonstrated strong antioxidant, antibacterial, and absorption properties essential for accelerated wound-healing applications. In vivo studies further reveal accelerated wound contraction and enhanced healing kinetics, promoting re-epithelialization, angiogenesis, and formation of apocrine glands. These findings underscore the efficacy and cost-effectiveness of fabricated hydrogel flaps as viable therapeutic options for treating deep skin wounds and make it worthwhile to integrate them with medical devices for tissue adhesion.

Coacervate-Derived Assembly of Poly(ethylene glycol) Nanoparticles for Combinational Tumor Therapy

Coacervates have garnered significant attention as potential drug carriers. However, the instability resulting from their intrinsic membrane-free nature restricts the application of coacervates in drug delivery. Herein, the engineering of poly(ethylene glycol) nanoparticles (PEG NPs) is reported using coacervates composed of PEG and polyphenols as the templates, where PEG is subsequently cross-linked based on different chemistries (e.g., thiol-disulfide exchange, click chemistry, and Schiff base reaction). The reported assembly strategy avoids the template removal process and the resultant PEG NPs exhibit excellent stability in the physiological environment compared to coacervates. The presence of polyphenols in PEG NPs enables the loading of various cargos including metal ions (i.e., Ru, Gd, Mn, Fe) and drug molecules (i.e., doxorubicin), which demonstrates their promise in magnetic resonance imaging and combinational tumor therapy. This work provides a promising strategy to promote the development of coacervate-derived NPs as a drug delivery system for biomedical applications.

Viscoelastic and flow behaviour of β-lactoglobulin/lactoferrin coacervates: Influence of temperature and ionic strength

Heteroprotein complex coacervation has potential for a wide range of applications. However, the sensitivity of coacervates to slight changes in physico-chemical conditions may constitute a technological barrier for their development and deserves to be better understood. In this study, the rheological properties of β-lactoglobulin/lactoferrin (βLG/LF) heteroprotein complex coacervates were investigated with respect to narrow changes of temperature (5-40 °C) and ionic strength (0 to 10 mM added NaCl). The apparent viscosity of βLG/LF coacervates prepared at 20 °C showed a high sensitivity to temperature, decreasing progressively at elevated temperatures. Frequency sweep experiments demonstrated that coacervates behave as a viscoelastic liquid throughout the investigated frequency range at T>10°C. Time-temperature superposition principle revealed that the interaction involved in the coacervation process were temperature-independent. The calculated activation energy was approximately 85 kJ/mol. The addition of NaCl (up to 10mM) prior to coacervation, resulted in an increase of the viscosity but did not show a clear trend in the evolution of viscoelastic moduli. These new insights allow a better understanding of the interactions involved in concentrated protein coacervates enabling better control over their potential uses.

A Self-Adhesive Flexible and Stretchable Compliant Surface Sensor for Real-Time Monitoring of Starch-Based Food Processing

Flexible sensors have attracted great attention because of their important applications in many areas. It is important to monitor the surface of starch-based food during food processing because it can provide key information related to the appearance, texture level, and chewiness of the food. However, there is no report on real-time monitoring of the surface of steamed bread in the literature. Here, we report a self-adhesive and stretchable compliant sensor that can be mounted to the surface of starch-based food and provides real-time signals for the steaming process. The sensors consisting of biocompatible poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), poly(vinyl alcohol) (PVA), tannic acid (TA), and glycerol can be fabricated by solution processing. Because it is stretchable and self-adhesive to the dough surface, it is compliant with the expansion or contraction of the dough during food processing. Its resistance varies with the shape and volume of the dough and thus can be monitored in a real-time manner. This is the first report of a surface sensor that can monitor the steaming process of starch-based food.

Bioinspired Design of an Underwater Adhesive Based on Tea Polyphenol-Modified Silk Fibroin

Adhesives have garnered significant interest recently due to their application in the field of biomedical applications. Nonetheless, developing adhesives that exhibit robust underwater adhesion and possess antimicrobial properties continues to pose a significant challenge. In this study, motivated by the adhesive mechanism observed in mussels in aquatic environments, dopamine (DA) was added to modify the silk fibroin (SF) solution. Subsequently, tea polyphenol (TP) was incorporated to form a sticky mixture, resulting in a biomimetic adhesive (TP-DA/SF). TP-DA/SF demonstrated rapid, robust, and indiscriminate adhesion to a wide array of substrates and even biological tissues (39 kPa). TP-DA/SF exhibits the ability to replicate the mussel adhesion mechanism of mussels underwater thanks to its biomimetic design. This characteristic provides the material with robust adhesion (40 kPa), notable reusability (at least 10 times), and long-lasting stability, especially in aquatic settings. It is worth noting that TP-DA/SF also demonstrated high adhesion in various water environments, even in solutions with a pH of 7.4 and buffered saline (PBS), which is one of the most widely used buffers in biochemistry research, offering salt-balancing and adjustable pH buffering capabilities. Meanwhile, TP-DA/SF exhibits excellent antibacterial and antioxidant properties due to its tea polyphenol content. After 15 days of wound closure in SD rats, the healing rate in the experimental group reached 93.4%, compared to 83.9% in the control group. Thus, the TP-DA/SF adhesive holds promising potential for biomedical applications, including sutureless wound closure and tissue adhesion.

A rapid and robust organ repair polyacrylamide/alginate adhesive hydrogel mediated via interfacial adhesion-trigger molecules

Adhesive hydrogels have been widely explored as tissue adhesives for wound sealing and repair. However, developing adhesive hydrogels with simple preparation techniques and strong adhesion to internal organs in a short time remains a challenge. In this study, we developed a strategy for robust and rapid tissue adhesion of internal organ sealing and repair by an interfacial adhesion-molecule triggered hydrogel system. In this system, polyphenol molecules act as adhesion-trigger reagents to achieve fast and strong adhesion of polyacrylamide/alginate hydrogels on the surface of wound tissue by rapidly forming abundant hydrogen bonds at the interface. The adhesion energy is significantly enhanced by 45 times under the mediation of polyphenol adhesion-trigger molecules, resulting in a robust (> 600 J m-2) tissue adhesion in just 30 s. This interfacial adhesion system demonstrates good biocompatibility, strong sealing performance on multiple organs (porcine heart, lung, stomach, and intestine), and excellent repair properties in gastric perforation wounds of rabbits in vivo. Moreover, immunocytochemical and transcriptomic analyses reveal that this interfacial adhesion system significantly promotes vascular regeneration and inhibits inflammatory responses during wound repairing. The proposed hydrogel provides a facile strategy for rapid and robust tissue adhesion, and shows potential applications in organ sealing and repair.

Copper-MOF and tannic acid-empowered composite cryogel as a skin substitute for accelerated deep wound healing

The effective management of deep skin wounds remains a significant healthcare challenge that often deteriorates with bacterial infection, oxidative stress, tissue necrosis, and excessive production of wound exudate. Current medical approaches, including traditional wound dressing materials, cannot effectively address these issues. There is a great need to engineer advanced and multifunctional wound dressings to address this multifaceted problem effectively. Herein, a rationally designed composite cryogel composed of a Copper Metal-Organic Framework (Cu-MOF), tannic acid (TA), polyvinyl alcohol (PVA), and zein protein has been developed by freeze-thaw technique. Cryogels display a remarkable swelling capacity attributed to their interconnected microporous morphology. Moreover, dynamic mechanical behaviour with the characteristics of potent antimicrobial, antioxidant, and biodegradation makes it a desirable wound dressing material. It was further confirmed that the material is highly biocompatible and can release TA and copper ions in a controlled manner. In-vivo skin irritation in a rat model demonstrated that composite cryogel did not provoke any irritation/inflammation when applied to the skin of a healthy recipient. In a deep wound model, the composite cryogel significantly accelerates the wound healing rate. These findings highlight the multifunctional nature of composite cryogels and their promising potential for clinical applications as advanced wound dressings.

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

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

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.

Polyphenol-Enabled 2D Nanopatch for Enhanced Nasal Mucoadhesion and Immune Activation

The advancement of effective nasal mucoadhesive delivery faces challenges due to rapid mucociliary clearance (MCC). Conventional studies have employed mucoadhesive materials, mainly forming spherical nanoparticles, but these offer limited adhesion to the nasal mucosa. This study hypothesizes that a 2D nanoscale structure utilizing adhesive polyphenols can provide a superior strategy for countering MCC, aligning with the planar mucosal layers. We explore the use of tannic acid (TA), a polyphenolic molecule known for its adhesive properties and ability to form complexes with biomolecules. Our study introduces an unprecedented 2D nanopatch, assembled through the interaction of TA with green fluorescent protein (GFP), and cell-penetrating peptide (CPP). This 2D nanopatch demonstrates robust adhesion to nasal mucosa and significantly enhances immunoglobulin A secretions, suggesting its potential for enhancing nasal vaccine delivery. The promise of a polyphenol-enabled adhesive 2D nanopatch signifies a pivotal shift from conventional spherical nanoparticles, opening new pathways for delivery strategies through respiratory mucoadhesion.

A Near-Infrared Photothermal-Responsive Underwater Adhesive with Tough Adhesion and Antibacterial Properties

Developing tunable underwater adhesives that possess tough adhesion in service and easy detachment when required remains challenging. Herein, a strategy is proposed to design a near infrared (NIR) photothermal-responsive underwater adhesive by incorporating MXene (Ti3C2Tx)-based nanoparticles within isocyanate-modified polydimethylsiloxane (PDMS) polymer chains. The developed adhesive exhibits long-term and tough adhesion with an underwater adhesion strength reaching 5.478 MPa. Such strong adhesion is mainly attributed to the covalent bonds and hydrogen bonds at the adhesive-substrate interface. By making use of the photothermal-response of MXene-based nanoparticles and the thermal response of PDMS-based chains, the adhesive possesses photothermal-responsive performance, exhibiting sharply diminished adhesion under NIR irradiation. Such NIR-triggered tunable adhesion allows for easy and active detachment of the adhesive when needed. Moreover, the underwater adhesive exhibits photothermal antibacterial property, making it highly desirable for underwater applications. This work enhances the understanding of photothermal-responsive underwater adhesion, enabling the design of tunable underwater adhesives for biomedical and engineering applications.

Recent Advances in Poly(vinyl alcohol)-Based Hydrogels

Poly(vinyl alcohol) (PVA) is a versatile synthetic polymer, used for the design of hydrogels, porous membranes and films. Its solubility in water, film- and hydrogel-forming capabilities, non-toxicity, crystallinity and excellent mechanical properties, chemical inertness and stability towards biological fluids, superior oxygen and gas barrier properties, good printability and availability (relatively low production cost) are the main aspects that make PVA suitable for a variety of applications, from biomedical and pharmaceutical uses to sensing devices, packaging materials or wastewater treatment. However, pure PVA materials present low stability in water, limited flexibility and poor biocompatibility and biodegradability, which restrict its use alone in various applications. PVA mixed with other synthetic polymers or biomolecules (polysaccharides, proteins, peptides, amino acids etc.), as well as with inorganic/organic compounds, generates a wide variety of materials in which PVA's shortcomings are considerably improved, and new functionalities are obtained. Also, PVA's chemical transformation brings new features and opens the door for new and unexpected uses. The present review is focused on recent advances in PVA-based hydrogels.

Natural Underwater Bioadhesive Offering Cohesion Modulation via Hydrogen Bond Disruptor: A Highly Injectable and in Vivo Stable Remedy for Gastric Ulcer Resolution

Injectable bioadhesives are attractive for managing gastric ulcers through minimally invasive procedures. However, the formidable challenge is to develop bioadhesives that exhibit high injectability, rapidly adhere to lesion tissues with fast gelation, provide reliable protection in the harsh gastric environment, and simultaneously ensure stringent standards of biocompatibility. Here, a natural bioadhesive with tunable cohesion is developed based on the facile and controllable gelation between silk fibroin and tannic acid. By incorporating a hydrogen bond disruptor (urea or guanidine hydrochloride), the inherent network within the bioadhesive is disturbed, inducing a transition to a fluidic state for smooth injection (injection force <5 N). Upon injection, the fluidic bioadhesive thoroughly wets tissues, while the rapid diffusion of the disruptor triggers instantaneous in situ gelation. This orchestrated process fosters the formed bioadhesive with durable wet tissue affinity and mechanical properties that harmonize with gastric tissues, thereby bestowing long-lasting protection for ulcer healing, as evidenced through in vitro and in vivo verification. Moreover, it can be conveniently stored (≥3 m) postdehydration. This work presents a promising strategy for designing highly injectable bioadhesives utilizing natural feedstocks, avoiding any safety risks associated with synthetic materials or nonphysiological gelation conditions, and offering the potential for minimally invasive application.

Tuning the underwater adhesiveness of antibacterial polysaccharides complex coacervates

HYPOTHESIS

Adjusting the water content and mechanical properties of polyelectrolyte coacervates for optimal underwater adhesion requires simultaneous control of the macromolecular design and the type and concentration of the salt used. Using synthetic or bio-inspired polymers to make coacervates often involves complicated chemistries and large variations in salt concentration. The underwater adhesiveness of simple, bio-sourced coacervates can be tuned with relatively small variations in salt concentration. Bio-sourced polymers can also impart beneficial biological activities to the final material.

EXPERIMENTS

We made complex coacervates from charged chitosan (CHI) and hyaluronic acid (HA) with NaCl as the salt. Their water content and viscoelastic properties were investigated to identify the formulation with optimal underwater adhesion in physiological conditions. The coacervates were also studied in antibacterial and cytotoxicity experiments.

FINDINGS

As predicted by linear rheology, the CHI-HA coacervates at 0.1 and 0.2 M NaCl had the highest pull-off adhesion strengths of 44.4 and 40.3 kPa in their respective supernatants. In-situ physical hardening of the 0.2 M coacervate upon a salt switch in 0.1 M NaCl resulted in a pull-off adhesion strength of 62.9 kPa. This material maintained its adhesive properties in physiological conditions. Finally, the optimal adhesive was found to be non-cytotoxic and inherently antimicrobial through a chitosan release-killing mechanism.

A grape seed protein-tannic acid powder to transform various non-adhesive hydrogels into adhesive gels

Realizing adhesion between wet materials remains challenging because of the interfacial water. Current strategies depend on complicated surface modifications, resulting in limited functions. Herein, a facile strategy based on the powder of grape seed protein and tannic acid (GSP-TA) was reported to endow various non-adhesive hydrogels adhesion without chemical modifications for both hydrogels and adherents. The GSP-TA powder has the capability to absorb interfacial water, form an adhesive layer on the hydrogel surface, diffusion into the underneath hydrogel matrix, and establish the initial adhesion within 5 s. By forming multiple non-covalent interactions between powders and substrates, the GSP-TA powder served as an efficient surface treating agent, enabling robust adhesion to solid substrates (wood, cardboard, glass, iron, and rubber) and wet tissues (pigskin, muscle, liver and heart). The adhesive strength for wood, cardboard, glass, iron, and rubber was 145.92 ± 5.93, 123.93 ± 15.98, 66.24 ± 7.67, 98.22 ± 4.13, and 80.83 ± 7.48 kPa, respectively. Because of reversible interactions, the adhesion was also repeatable. Due to the merits of grape seed protein and plant polyphenol, it could be completely degraded within 11 days. Bearing several merits, this strategy has promising applications in wound patches, tissue repair, and sensors.

Wetting-enhanced adhesion of photo-polymerized supramolecular adhesives for both smooth and rough surfaces

Efficient interactions between an adhesive and a substrate surface at the molecular level are the basis for the formation of robust adhesion, which substantially relies on interfacial wetting. However, strong adhesives usually improve cohesion but compromise interfacial properties. Herein, we have reported a kind of robust supramolecular adhesive based on the outstanding mobility and interfacial wettability of adhesive precursors. In situ fast photopolymerization endows supramolecular adhesives with more outstanding adhesion for both smooth and rough surfaces in air and underwater in contrast to their counterparts from thermal polymerization. In addition to their low viscosity and high monomer concentration, supramolecular adhesive precursors without any organic solvents possess well-defined hydrogen bonding interactions. These superior properties consistently contribute to the wetting of the substrate and the formation of adhesive polymers with high molecular weights. This work highlights that enhancing interfacial wetting between an adhesive and a substrate is a promising route to achieving robust adhesion.

Natural Polymer-Polyphenol Bioadhesive Coacervate with Stable Wet Adhesion, Antibacterial Activity, and On-Demand Detachment

Medical adhesives are emerging as an important clinical tool as adjuvants for sutures and staples in wound closure and healing and in the achievement of hemostasis. However, clinical adhesives combining cytocompatibility, as well as strong and stable adhesion in physiological conditions, are still in demand. Herein, a mussel-inspired strategy is explored to produce adhesive coacervates using tannic acid (TA) and methacrylate pullulan (PUL-MA). TA|PUL-MA coacervates mainly comprise van der Waals forces and hydrophobic interactions. The methacrylic groups in the PUL backbone increase the number of interactions in the adhesives matrix, resulting in enhanced cohesion and adhesion strength (72.7 Jm-2), compared to the non-methacrylated coacervate. The adhesive properties are kept in physiologic-mimetic solutions (72.8 Jm-2) for 72 h. The photopolymerization of TA|PUL-MA enables the on-demand detachment of the adhesive. The poor cytocompatibility associated with the use of phenolic groups is here circumvented by mixing reactive oxygen species-degrading enzyme in the adhesive coacervate. This addition does not hamper the adhesive character of the materials, nor their anti-microbial or hemostatic properties. This affordable and straightforward methodology, together with the tailorable adhesivity even in wet environments, high cytocompatibility, and anti-bacterial activity, enables foresee TA|PUL-MA as a promising ready-to-use bioadhesive for biomedical applications.

Effect of Tannic Acid Concentrations on Temperature-Sensitive Sol-Gel Transition and Stability of Tannic Acid/Pluronic F127 Composite Hydrogels

Recently, interest in polyphenol-containing composite adhesives for various biomedical applications has been growing. Tannic acid (TA) is a polyphenolic compound with advantageous properties, including antioxidant and antimicrobial properties. Additionally, TA contains multiple hydroxyl groups that exhibit biological activity by forming hydrogen bonds with proteins and biomacromolecules. Furthermore, TA-containing polymer composites exhibit excellent tissue adhesion properties. In this study, the gelation behavior and adhesion forces of TA/Pluronic F127 (TA/PluF) composite hydrogels were investigated by varying the TA and PluF concentrations. PluF (above 16 wt%) alone showed temperature-responsive gelation behavior because of the closely packed micelle aggregates. After the addition of a small amount of TA, the TA/PluF hydrogels showed thermosensitive behavior similar to that of PluF hydrogels. However, the TA/PluF hydrogels containing more than 10 wt% TA completely suppressed the thermo-responsive gelation kinetics of PluF, which may have been due to the hydrogen bonds between TA and PluF. In addition, TA/PluF hydrogels with 40 wt% TA showed excellent tissue adhesion properties and bursting pressure in porcine intestinal tissues. These results are expected to aid in understanding the use of mixtures of TA and thermosensitive block copolymers to fabricate adhesive hydrogels for versatile biomedical applications.

Bioinspired Injectable Polyurethane Underwater Adhesive with Fast Bonding and Hemostatic Properties

Underwater adhesives with injectable, organic solvent-free, strong, fast adhesion, and hemostatic properties have become an urgent need in biomedical field. Herein, a novel polyurethane underwater adhesive (PUWA) inspired by mussels is developed utilizing the rapid post-cure reaction of isocyanate esterification without organic solvents. The PUWA is created through the injectable two component curing process of component A (biocompatible polyurethane prepolymer) and component B (dopamine modified lysine derivatives: chain extender-LDA and crosslinker-L3DA). The two-component adhesive cures quickly and firmly underwater, with an impressive bonding strength of 40 kPa on pork skin and excellent burst pressure of 394 mmHg. Moreover, the PUWA exhibits robust adhesion strength in hostile environments with acid, alkali and saline solutions. Combined with excellent biocompatibility and hemostatic performance, the PUWA demonstrates effectively sealing wounds and promoting healing. With the ability to bond diverse substrates rapidly and strongly, the PUWA holds significant potential for application in both biomedical and industrial fields.

Solvent-Exchange Triggered Solidification of Peptide/POM Coacervates for Enhancing the On-Site Underwater Adhesion

Peptide-based biomimetic underwater adhesives are emerging candidates for understanding the adhesion mechanism of natural proteins secreted by sessile organisms. However, there is a grand challenge in the functional recapitulation of the on-site interfacial spreading, adhesion and spontaneous solidification of native proteins in water using peptide adhesives without applied compressing pressure. Here, a solvent-exchange strategy was utilized to exert the underwater injection, on-site spreading, adhesion and sequential solidification of a series of peptide/polyoxometalate coacervates. The coacervates were first prepared in a mixed solution of water and organic solvents by rationally suppressing the non-covalent interactions. After switching to a water environment, the solvent exchange between bulk water and the organic solvent embedded in the matrix of the peptide/polyoxometalate coacervates recovered the hydrophobic effect by increasing the dielectric constant, resulting in a phase transition from soft coacervates to hard solid with enhanced bulk cohesion and thus compelling underwater adhesive performance. The key to this approach is the introduction of suitable organic solvents, which facilitate the control of the intermolecular interactions and the cross-linking density of the peptide/polyoxometalate adhesives in the course of solidification under the water line. The solvent-exchange method displays fascinating universality and compatibility with different peptide segments.

Development of Biocompatible Mussel-Inspired Cellulose-Based Underwater Adhesives

Conventional adhesives have poor underwater adhesion and harm to human health and the environment during their use, which largely limits their practical applications. Herein, we synthesized cellulose-based adhesives with underwater adhesion and biocompatibility by grafting N-(3,4-dihydroxyphenethyl)methacrylamide into the cellulose chain via atom transfer radical polymerization (ATRP). FTIR, 1H NMR, and XPS analyses ensured the successful preparation of the cellulose-based adhesive polymers. The different properties of the prepared adhesives, including swelling ratio, adhesion strength, and biocompatibility are examined. Results found that the lap shear strength is enhanced by increasing the catechol content. When catechol content is 27.2 mol %, cellulose-based adhesive with the addition of Fe3+ possesses a strong lap shear strength of 2.13 MPa in a dry environment, 0.10 MPa underwater, and 0.16 MPa under seawater for iron substrate, respectively. In addition, the cell culture test demonstrated that the prepared adhesives have outstanding biocompatibility. The cellulose-based adhesives with underwater adhesion and biocompatibility have potential applications in biomedicine, electronic engineering, and construction fields.

Low-Viscous, Dilute Phase Adhesive from Dense Polyphenolic Coacervates of Poly(vinyl alcohol) and Tannic acid

This study explores a polyphenolic coacervate, named VATA, formed by poly(vinyl alcohol) (PVA) and tannic acid (TA). Distinct from conventional studies that have focused on the bottom, dense phase of coacervates, this research emphasizes the top, dilute phase, low-viscous coacervate liquid termed liquid-VATA (l-VATA). Due to TA's capability of intermolecular association as well as adhesiveness, phenomena not typically observed in the upper dilute phase of standard polyelectrolyte-based coacervates are revealed. At first glance, the dilute phase l-VATA coacervate resembles a water-like, low-viscous mixture solution of PVA, TA, and PVA/TA complexes. However, analysis shows that nearly all of the TA molecules associate with PVA chains, forming PVA/TA complexes. Furthermore, supraparticular association was observed between PVA/TA complex nanoparticles upon applying external shear force. A broad survey of shear rate and strain showed that the solution exhibited sequential shear-thickening, followed by shear-thinning behavior. The water-like, low viscosity of l-VATA unexpectedly reveals robust adhesiveness and thus able to lift an entire mouse using just a single human hair strand. Even in cases of failure, no interfacial failure was detected between mouse and human hair. In addition to enabling hair-to-hair bonding, our study also showcases the efficacy of l-VATA in facilitating hair-to-skin adhesion. The results illustrate how the lower viscosity of l-VATA can be exploited for a wide range of industrial and cosmetic applications, allowing the formulation of thin, uniform adhesive layers, something unachievable with the dense, viscous VATA glue. Thus, this study highlights the importance of investigating the top dilute phase of coacervates, shedding light on an area often underestimated compared to the bottom dense phase reported in prevalent coacervate studies.

Stretchable surface electromyography electrode array patch for tendon location and muscle injury prevention

Surface electromyography (sEMG) can provide multiplexed information about muscle performance. If current sEMG electrodes are stretchable, arrayed, and able to be used multiple times, they would offer adequate high-quality data for continuous monitoring. The lack of these properties delays the widespread use of sEMG in clinics and in everyday life. Here, we address these constraints by design of an adhesive dry electrode using tannic acid, polyvinyl alcohol, and PEDOT:PSS (TPP). The TPP electrode offers superior stretchability (~200%) and adhesiveness (0.58 N/cm) compared to current electrodes, ensuring stable and long-term contact with the skin for recording (>20 dB; >5 days). In addition, we developed a metal-polymer electrode array patch (MEAP) comprising liquid metal (LM) circuits and TPP electrodes. The MEAP demonstrated better conformability than commercial arrays, resulting in higher signal-to-noise ratio and more stable recordings during muscle movements. Manufactured using scalable screen-printing, these MEAPs feature a completely stretchable material and array architecture, enabling real-time monitoring of muscle stress, fatigue, and tendon displacement. Their potential to reduce muscle and tendon injuries and enhance performance in daily exercise and professional sports holds great promise.

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.

Eco-friendly photothermal hydrogel evaporator for efficient solar-driven water purification

The field of solar vapor generation has developed rapidly in recent years, but achieving the goals of a high evaporation rate, eco-friendliness and rapid preparation with low-cost raw materials is still a challenge. In this work, a type of photothermal hydrogel evaporator was prepared by blending eco-friendly poly(vinyl alcohol), agarose, Fe³⁺ and tannic acid (TA) together, in which the tannic acid-ferric ion (TA*Fe³⁺) complexes served as photothermal materials and effective gelators. The results indicate that the TA*Fe³⁺ complex exhibits excellent gelatinization ability and light-absorption performance, which leads to a compressive stress of 0.98 MPa at 80% strain and up to 85% light absorption ratio in the photothermal hydrogel. For interfacial evaporation, a high rate of 1.897 ± 0.11 kg·m^-2·h^-1 corresponding to an energy efficiency of 89.7 ± 2.73% under 1 sun irradiation is achieved. Moreover, the hydrogel evaporator exhibits high stability in a 12-hour test and a 20-cycle test without a decline in evaporation performance. The outdoor testing results show that the hydrogel evaporator can achieve an evaporation rate of > 0.70 kg/m² and effectively purify wastewater treatment and seawater desalination.

Tannic-Acid-Enriched Poly(vinyl alcohol) Nanofibrous Membrane as a UV-Shie lding and Antibacterial Face Mask Filter Material

Face masks are increasingly important in the battle against infectious diseases and air pollution. Nanofibrous membranes (NFMs) are promising filter layers for removing particulate matter (PM) without restricting air permeability. In this study, tannic-acid-enriched poly(vinyl alcohol) (PVA-TA) NFMs were fabricated by electrospinning PVA solutions containing large amounts of tannic acid (TA), a multifunctional polyphenol compound. We were able to prepare uniform electrospinning solution without coacervate formation by inhibiting the robust hydrogen bonding between PVA and TA. Notably, the NFM maintained its fibrous structure even under moist conditions after heat treatment without the use of a cross-linking agent. Further, the mechanical strength and thermal stability of the PVA NFM were improved by the introduction of TA. The functional PVA NFM with a high TA content showed excellent UV-shielding (UV-A: 95.7%, UV-B: 100%) and antibacterial activity against Escherichia coli (inhibition zone: 8.7 ± 1.2 mm) and Staphylococcus aureus (inhibition zone: 13.7 ± 0.6 mm). Moreover, the particle filtration efficiency of the PVA-TA NFM for PM_0.6 particles was 97.7% at 32 L min^-1 and 99.5% at 85 L min^-1, indicating excellent filtration performance and a low pressure drop. Therefore, the TA-enriched PVA NFM is a promising mask filter layer material with excellent UV-blocking and antibacterial properties and has the potential for various practical applications.

Bioglues Based on an Elastin-Like Recombinamer: Effect of Tannic Acid as an Additive on Tissue Adhesion and Cytocompatibility

More than 260 million surgical procedures are performed worldwide each year. Although sutures and staples are widely used to reconnect tissues, they can cause further damage and increase the risk of infection. Bioadhesives have been proposed as an alternative to reconnect tissues. However, clinical adhesives that combine strong adhesion with cytocompatibility have yet to be developed. In this study, we explored the production of adhesives based on protein-engineered polymers bioinspired by the sequence of elastin (i.e., elastin-like recombinamers, ELRs). We hypothesized that the combination of polyphenols (i.e., tannic acid, TA) and ELRs would produce an adhesive coacervate (ELR+TA), as reported for other protein polymers such as silk fibroin (SF). Notably, the adhesion of ELR alone surpassed that of ELR+TA. Indeed, ELR alone achieved adhesive strengths of 88.8 ± 33.2 kPa and 17.0 ± 2.0 kPa on porcine bone and skin tissues, respectively. This surprising result led us to explore a multicomponent bioadhesive to encompass the complementary roles of elastin (mimicked here by ELR) and silk fibroin (SF), and subsequently mirror more closely the multicomponent nature of the extracellular matrix. Tensile testing showed that ELR+SF achieved an adhesive strength of 123.3 ± 60.2 kPa on porcine bone and excellent cytocompatibility. To express this in a more visual and intuitive way, a small surface of only 2.5 cm2 was able to lift at least 2 kg of weight. This opens the door for further studies focusing on the ability of protein-engineered polymers to adhere to biological tissues without further chemical modification for applications in tissue engineering.

Tuning Water-Resistant Networks in Mussel-Inspired Hydrogels for Robust Wet Tissue and Bioelectronic Adhesion

Hydrogels with robust wet adhesion are desirable for applications in aqueous environments. Wet adhesion arising from synergy between hydrophobic and catechol components in mussel foot proteins has been highlighted. However, optimizing hydrogels with multiple components is challenging because of their complex structure-property relationships. Herein, high-throughput screening of a series of hydrophobic alkyl monomers and adhesive catechol derivatives was used to systematically develop wet adhesive hydrogels. Short alkyl chains promote wet adhesion by repelling water at the adhesive interface, whereas long alkyl chains form strong hydrophobic interactions inside the hydrogel network that impede or dissipate energy for wet adhesion. The optimized wet adhesive hydrogel, containing short alkyl chain, was applied for rapid hemostasis and wound healing because of the synergistic effect of catechol and alkyl groups and its immunomodulation ability, which is revealed through a transcriptomic analysis. Conductive nanocomponents were incorporated into the optimized hydrogel to produce a wearable device, which was used for continuous monitoring human electrocardiogram (ECG) during swimming, and in situ epicardial ECG on a porcine living and beating heart. This study demonstrated an efficient and generalized molecular design strategy for multifunctional wet adhesive hydrogels.

Reversible tissue sticker inspired by chemistry in plant-pathogen relationship

Plants release phenolic molecules to protect against invading pathogens. In plant-microorganism relationships, phenolics bind to surface oligosaccharides, inactivating microorganism activities. Inspired by phenol-saccharide interactions in plant defense systems, we designed an adhesive sealant. By screening 16 different saccharides, the O-acetyl group, rich in glucomannan (GM), exhibited rapid, robust binding with the galloyl moiety of a model phenolic molecule, tannic acid (TA). Furthermore, the interaction showed both pH and temperature (upper critical solution temperature) sensitivities. Utilizing O-acetyl-galloyl interactions, materials of all dimensions from beads (0D) to strings (1D), films (2D), and objects (3D) could be prepared, as a suitable platform for printing techniques. GMTA films are elastic, adhesive, water-resistant, and effectively sealed perforations, as demonstrated by (1) a lung incision followed by an air inflation model and (2) a thoracic diaphragm model. STATEMENT OF SIGNIFICANCE: In nature, phenolic molecules are 'nearly always' physically bound with polysaccharides, indicating that the phenolics widen the functions of polysaccharides. An example includes that phenolic-polysaccharide interactions are key defense mechanisms against microbial infection in plants whereas polysaccharide alone functions poorly. Despite the ubiquitous biochemistry of polysaccharide-phenolic interactions, efforts on understanding binding chemistry focusing on phenol/polysaccharide interactions is little. This study is important because we found for the first time that O-acetyl group is the moiety in polysaccharides to which phenolic cis-diol and/or cis-triol is spontaneously bound. The phenol-polysaccharide interaction is non-covalent yet robust, kinetically fast, and reversible. Inspired by the interaction chemistry, a simple mixture of phenolic molecules and O-acetyl group containing polysaccharides such as glucomannan opens a promising fabrication strategy toward functional polysaccharide-based material.

Povidone-iodine enhanced underwater tape

Realizing rapid and stable bonding under humid conditions has remained a challenge in adhesion science and wound dressing. In this study, polyacrylate-based underwater tape with water-enhanced adhesion and antimicrobial performance was designed and synthesized. Good underwater adhesion performance is achieved through the reasonable selection of comonomers, among which 4-hydroxybutyl acrylate (4-HBA) and isobornyl acrylate (IBOA) provide rich hydrogen bond interactions and a rigid side chain stable structure, respectively. The former effectively increases the interface strength between the tape and the substrate, while the latter ensures that the tape can maintain a good cohesion strength under water. Besides, povidone iodine (PVP-I₂) as a reinforcing filler and germicidal factor endows the tape with tunable mechanical properties and impressive antimicrobial abilities. This work provides a facile approach to prepare a wet adhesive for medical and industrial fields which can be used as wound dressing and underwater adhesive materials.

Rational design of adhesives for effective underwater bonding

Underwater adhesives hold great promises in our daily life, biomedical fields and industrial engineering. Appropriate underwater bonding can reduce the huge cost from removing the target substance from water, and greatly lift working efficiency. However, different from bonding in air, underwater bonding is quite challenging. The existence of interfacial water prevents the intimate contact between the adhesives and the submerged surfaces, and water environment makes it difficult to achieve high cohesiveness. Even so, in recent years, various underwater adhesives with macroscopic adhesion abilities were emerged. These smart adhesives can ingeniously remove the interfacial water, and enhance cohesion by utilizing their special physicochemical properties or functional groups. In this mini review, we first give a detail introduction of the difficulties in underwater bonding. Further, we overview the recent strategies that are used to construct underwater adhesives, with the emphasis on how to overcome the difficulties of interfacial water and achieve high cohesiveness underwater. In addition, future perspectives of underwater adhesives from the view of practical applications are also discussed. We believe the review will provide inspirations for the discovery of new strategies to overcome the obstacles in underwater bonding, and therefore may contribute to designing effective underwater adhesives.

Biomineralization-Inspired Intermediate Precursor for the Controllable Gelation of Polyphenol-Macromolecule Hydrogels

Hydrogels composed of polyphenols and various macromolecules have been widely reported to have the advantage of facile preparation, mainly through the formation of hydrogen bonds. However, the traditional preparation method involves the direct mixing of polyphenols and macromolecules, which generally occurs too quickly and uncontrollably, and results in poor homogeneity, injectability, and shape designability. Here, inspired by the intermediate precursor during biomineralization, to facilitate transformation in a controllable way, we propose a novel and universal internal gelation method that creates an intermediate precursor by controlling the pH value to manipulate the elimination and generation of hydrogen bonds between a polyphenol and macromolecules. The precursor strategy greatly improves the homogeneity, injectability, and shape designability of the hydrogel while also achieving a controllable gelation process, and the gelation time can be accurately adjusted. The hydrogels prepared with this method exhibited superior capability to seal leaks, provided complete wound coverage, and showed the potential to be a shape-designable wearable strain sensor. Our study opens up a new way to construct and apply polyphenol-macromolecule hydrogels in a more controllable manner.

Biodegradable Block Copolymer-Tannic Acid Glue

Bioadhesives are becoming an essential and important ingredient in medical science. Despite numerous reports, developing adhesive materials that combine strong adhesion, biocompatibility, and biodegradation remains a challenging task. Here, we present a biocompatible yet biodegradable block copolymer-based waterborne superglue that leads to an application of follicle-free hair transplantation. Our design strategy bridges self-assembled, temperature-sensitive block copolymer nanostructures with tannic acid as a sticky and biodegradable polyphenolic compound. The formulation further uniquely offers step-by-step increases in adhesion strength via heating-cooling cycles. Combining the modular design with the thermal treating process enhances the mechanical properties up to 5 orders of magnitude compared to the homopolymer formulation. This study opens a new direction in bioadhesive formulation strategies utilizing block copolymer nanotechnology for systematic and synergistic control of the material's properties.

Probing and Manipulating Noncovalent Interactions in Functional Polymeric Systems

Noncovalent interactions, which usually feature tunable strength, reversibility, and environmental adaptability, have been recognized as driving forces in a variety of biological and chemical processes, contributing to the recognition between molecules, the formation of molecule clusters, and the establishment of complex structures of macromolecules. The marriage of noncovalent interactions and conventional covalent polymers offers the systems novel mechanical, physicochemical, and biological properties, which are highly dependent on the binding mechanisms of the noncovalent interactions that can be illuminated via quantification. This review systematically discusses the nanomechanical characterization of typical noncovalent interactions in polymeric systems, mainly through direct force measurements at microscopic, nanoscopic, and molecular levels, which provide quantitative information (e.g., ranges, strengths, and dynamics) on the binding behaviors. The fundamental understandings of intermolecular and interfacial interactions are then correlated to the macroscopic performances of a series of noncovalently bonded polymers, whose functions (e.g., stimuli-responsiveness, self-healing capacity, universal adhesiveness) can be customized through the manipulation of the noncovalent interactions, providing insights into the rational design of advanced materials with applications in biomedical, energy, environmental, and other engineering fields.

Stretchable and Self-Adhesive PEDOT:PSS Blend with High Sweat Tolerance as Conformal Biopotential Dry Electrodes

Dry epidermal electrodes that can always form conformal contact with skin can be used for continuous long-term biopotential monitoring, which can provide vital information for disease diagnosis and rehabilitation. But, this application has been limited by the poor contact of dry electrodes on wet skin. Herein, we report a biocompatible fully organic dry electrode that can form conformal contact with both dry and wet skin even during physical movement. The dry electrodes are prepared by drop casting an aqueous solution consisting of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), poly(vinyl alcohol) (PVA), tannic acid (TA), and ethylene glycol (EG). The electrodes can exhibit a conductivity of 122 S cm^-1 and a mechanical stretchability of 54%. Moreover, they are self-adhesive to not only dry skin but also wet skin. As a result, they can exhibit a lower contact impedance to skin than commercial Ag/AgCl gel electrodes on both dry and sweat skins. They can be used as dry epidermal electrodes to accurately detect biopotential signals including electrocardiogram (ECG) and electromyogram (EMG) on both dry and wet skins for the users at rest or during physical movement. This is the first time to demonstrate dry epidermal electrodes self-adhesive to wet skin for accurate biopotential detection.

Effective Antifogging Coating from Hydrophilic/Hydrophobic Polymer Heteronetwork

Fogging on optical devices may severely impair vision, resulting in unacceptable adverse consequences. Hydrophilic coatings can prevent surface fogging by instantly facilitating pseudo-film water condensation but suffer from short antifogging duration due to water film thickening with further condensation. Here, an innovative strategy is reported to achieve longer antifogging duration via thickening the robust bonded hydrophilic/hydrophobic polymer heteronetwork coating to enhance its water absorption capacity. The combination of strong interfacial adhesion and hydrophilic/hydrophobic heteronetwork structure is key to this approach, which avoids interfacial failure and swelling-induced wrinkles under typical fogging conditions. The developed antifogging coating exhibits prolonged antifogging durations over a wide temperature range for repetitious usages. Eyeglasses coated with this coating successfully maintained fog-free vision in two typical scenarios. Besides, the coating recipes developed in this study also have potential as underwater glues as they demonstrate strong adhesions to both glass and polymer substrates in wet conditions.

Ternary Complex Coacervate of PEG/TA/Gelatin as Reinforced Bioadhesive for Skin Wound Repair

Bioadhesives have attracted more attention in surgery due to their easy operability and abilities of promoting wound closure and tissue healing. However, it is still a great challenge to develop a robust and biocompatible bioadhesive through a facile preparation method. Herein, a ternary complex coacervate comprised of tannic acid (TA), polyethylene glycol (PEG), and gelatin (TPG) is proposed as a novel bioadhesive, which is fabricated by simple physical blending method. The adhesion capacity of TPG was reinforced through programming the cross-linking network of TPG matrix and tailoring the interfacial interactions between matrix and tissue. Curing parameters (pH, temperature, and period) and gelatin content in TPG have crucial impacts on the final comprehensive adhesion performance. The adhesion strength of the optimized formulation, fabricated with 10% (m/m) gelatin (TPG10), was over 3 folds of TPG0 (without gelatin inclusion) after 24 h curing at pH 6 and 37 °C. The mechanism of the reinforced comprehensive adhesion was also investigated, suggesting TA provided tough interfacial adhesion, covalent cross-link of TA-gelatin improved mechanical properties, and the hydrogen bonds mediated dynamic cross-link between TA and PEG enabled the bulk matrix to dissipate energy upon deformation. Furthermore, the additional antibacterial activity, biocompatibility, and suitable degradability endowed TPG10 with desirable wound closure and tissue repairing efficacy on rat skin wound model. Such low-cost, readily prepared, and function-efficient bioadhesive could provide a versatile platform for tissue repair and regeneration.