A self-healing multispectral transparent adhesive peptide glass.

Despite its disordered liquid-like structure, glass exhibits solid-like mechanical properties1. The formation of glassy material occurs by vitrification, preventing crystallization and promoting an amorphous structure2. Glass is fundamental in diverse fields of materials science, owing to its unique optical, chemical and mechanical properties as well as durability, versatility and environmental sustainability3. However, engineering a glassy material without compromising its properties is challenging4-6. Here we report the discovery of a supramolecular amorphous glass formed by the spontaneous self-organization of the short aromatic tripeptide YYY initiated by non-covalent cross-linking with structural water7,8. This system uniquely combines often contradictory sets of properties; it is highly rigid yet can undergo complete self-healing at room temperature. Moreover, the supramolecular glass is an extremely strong adhesive yet it is transparent in a wide spectral range from visible to mid-infrared. This exceptional set of characteristics is observed in a simple bioorganic peptide glass composed of natural amino acids, presenting a multi-functional material that could be highly advantageous for various applications in science and engineering.

Bonding wood with uncondensed lignins as adhesives.

Plywood is widely used in construction, such as for flooring and interior walls, as well as in the manufacture of household items such as furniture and cabinets. Such items are made of wood veneers that are bonded together with adhesives such as urea-formaldehyde and phenol-formaldehyde resins1,2. Researchers in academia and industry have long aimed to synthesize lignin-phenol-formaldehyde resin adhesives using biomass-derived lignin, a phenolic polymer that can be used to substitute the petroleum-derived phenol3-6. However, lignin-phenol-formaldehyde resin adhesives are less attractive to plywood manufacturers than urea-formaldehyde and phenol-formaldehyde resins owing to their appearance and cost. Here we report a simple and practical strategy for preparing lignin-based wood adhesives from lignocellulosic biomass. Our strategy involves separation of uncondensed or slightly condensed lignins from biomass followed by direct application of a suspension of the lignin and water as an adhesive on wood veneers. Plywood products with superior performances could be prepared with such lignin adhesives at a wide range of hot-pressing temperatures, enabling the use of these adhesives as promising alternatives to traditional wood adhesives in different market segments. Mechanistic studies indicate that the adhesion mechanism of such lignin adhesives may involve softening of lignin by water, filling of vessels with softened lignin and crosslinking of lignins in adhesives with those in the cell wall.

Instant tough adhesion of polymer networks.

Generating strong rapid adhesion between hydrogels has the potential to advance the capabilities of modern medicine and surgery. Current hydrogel adhesion technologies rely primarily on liquid-based diffusion mechanisms and the formation of covalent bonds, requiring prolonged time to generate adhesion. Here, we present a simple and versatile strategy using dry chitosan polymer films to generate instant adhesion between hydrogel-hydrogel and hydrogel-elastomer surfaces. Using this approach we can achieve extremely high adhesive energies (>3,000 J/m2), which are governed by pH change and non-covalent interactions including H-bonding, Van der Waals forces, and bridging polymer entanglement. Potential examples of biomedical applications are presented, including local tissue cooling, vascular sealing, prevention of surgical adhesions, and prevention of hydrogel dehydration. We expect these findings and the simplicity of this approach to have broad implications for adhesion strategies and hydrogel design.

Mimicking natural deterrent strategies in plants using adhesive spheres.

With a continuous increase in world population and food production, chemical pesticide use is growing accordingly, yet unsustainably. As chemical pesticides are harmful to the environment and developmental resistance in pests is increasing, a sustainable and effective pesticide alternative is needed. Inspired by nature, we mimic one defense strategy of plants, glandular trichomes, to shift away from using chemical pesticides by moving toward a physical immobilization strategy via adhesive particles. Through controlled oxidation of a biobased starting material, triglyceride oils, an adhesive material is created while monitoring the reactive intermediates. After being milled into particles, nanoindentation shows these particles to be adhesive even at low contact forces. A suspension of particles is then sprayed and found to be effective at immobilizing a target pest, thrips, Frankliniella occidentalis. Small arthropod pests, like thrips, can cause crop damage through virus transfer, which is prevented by their immobilization. We show that through a scalable fabrication process, biosourced materials can be used to create an effective, sustainable physical pesticide.

Dry double-sided tape for adhesion of wet tissues and devices.

Two dry surfaces can instantly adhere upon contact with each other through intermolecular forces such as hydrogen bonds, electrostatic interactions and van der Waals interactions1,2. However, such instant adhesion is challenging when wet surfaces such as body tissues are involved, because water separates the molecules of the two surfaces, preventing interactions3,4. Although tissue adhesives have potential advantages over suturing or stapling5,6, existing liquid or hydrogel tissue adhesives suffer from several limitations: weak bonding, low biological compatibility, poor mechanical match with tissues, and slow adhesion formation5-13. Here we propose an alternative tissue adhesive in the form of a dry double-sided tape (DST) made from a combination of a biopolymer (gelatin or chitosan) and crosslinked poly(acrylic acid) grafted with N-hydrosuccinimide ester. The adhesion mechanism of this DST relies on the removal of interfacial water from the tissue surface, resulting in fast temporary crosslinking to the surface. Subsequent covalent crosslinking with amine groups on the tissue surface further improves the adhesion stability and strength of the DST. In vitro mouse, in vivo rat and ex vivo porcine models show that the DST can achieve strong adhesion between diverse wet dynamic tissues and engineering solids within five seconds. The DST may be useful as a tissue adhesive and sealant, and in adhering wearable and implantable devices to wet tissues.

Archaeological adhesives made from Podocarpus document innovative potential in the African Middle Stone Age.

Studying the earliest archaeological adhesives has implications for our understanding of human cognition. In southern Africa, the oldest adhesives were made by Homo sapiens in the Middle Stone Age. Chemical studies have shown that these adhesives were made from a local conifer of the Podocarpaceae family. However, Podocarpus does not exude resin, nor any other substance that could have been recognized as having adhesive properties. Therefore, it remains unknown how these adhesives were made. This study investigates how Podocarpus adhesives can be made, comparing their mechanical properties with other naturally available adhesives. We found that Podocarpus tar can only be made by dry distillation of leaves, requiring innovative potential, skill, and knowledge. This contrasts with our finding that the Middle Stone Age environment was rich in substances that can be used as adhesives without such transformation. The apparent preference for Podocarpus tar may be explained by its mechanical properties. We found it to be superior to all other substances in terms of its adhesive properties. In addition, the condensation method that allows producing it can be recognized accidentally, as the processes take place above ground and can be triggered accidentally. Our findings have implications for establishing a link between technology and cognition in the Middle Stone Age.

Fast, strong, and reversible adhesives with dynamic covalent bonds for potential use in wound dressing.

Adhesives typically fall into two categories: those that have high but irreversible adhesion strength due to the formation of covalent bonds at the interface and are slow to deploy, and others that are fast to deploy and the adhesion is reversible but weak in strength due to formation of noncovalent bonds. Synergizing the advantages from both categories remains challenging but pivotal for the development of the next generation of wound dressing adhesives. Here, we report a fast and reversible adhesive consisting of dynamic boronic ester covalent bonds, formed between poly(vinyl alcohol) (PVA) and boric acid (BA) for potential use as a wound dressing adhesive. Mechanical testing shows that the adhesive film has strength in shear of 61 N/cm2 and transcutaneous adhesive strength of 511 N/cm2, generated within 2 min of application. Yet the film can be effortlessly debonded when exposed to excess water. The mechanical properties of PVA/BA adhesives are tunable by varying the cross-linking density. Within seconds of activation by water, the surface boronic ester bonds in the PVA/BA film undergo fast debonding and instant softening, leading to conformal contact with the adherends and reformation of the boronic ester bonds at the interface. Meanwhile, the bulk film remains dehydrated to offer efficient load transmission, which is important to achieve strong adhesion without delamination at the interface. Whether the substrate surface is smooth (e.g., glass) or rough (e.g., hairy mouse skin), PVA/BA adhesives demonstrate superior adhesion compared to the most widely used topical skin adhesive in clinical medicine, Dermabond.

Self-Adhesive, Stretchable, and Thermosensitive Iontronic Hydrogels for Highly Sensitive Neuromorphic Sensing-Synaptic Systems.

Artificial sensory afferent nerves that emulate receptor nanochannel perception and synaptic ionic information processing in chemical environments are highly desirable for bioelectronics. However, challenges persist in achieving life-like nanoscale conformal contact, agile multimodal sensing response, and synaptic feedback with ions. Here, a precisely tuned phase transition poly(N-isopropylacrylamide) (PNIPAM) hydrogel is introduced through the water molecule reservoir strategy. The resulting hydrogel with strongly cross-linked networks exhibits excellent mechanical performance (∼2000% elongation) and robust adhesive strength. Importantly, the hydrogel's enhanced ionic conductance and heterogeneous structure of the temperature-sensitive component enable highly sensitive strain information perception (GFmax = 7.94, response time ∼ 87 ms), temperature information perception (TCRmax = -1.974%/°C, response time ∼ 270 ms), and low energy consumption synaptic plasticity (42.2 fJ/spike). As a demonstration, a neuromorphic sensing-synaptic system is constructed integrating iontronic strain/temperature sensors with fiber synapses for real-time information sensing, discrimination, and feedback. This work holds enormous potential in bioinspired robotics and bioelectronics.

Surface Passivation of Norland Optical Adhesive Improves the Guiding Efficiency of Gliding Microtubules in Microfluidic Devices.

The microtubule-kinesin biomolecular motor system, which is vital for cellular function, holds significant promise for nanotechnological applications. In vitro gliding assays have demonstrated the ability to transport microcargo by propelling microtubules across kinesin-coated surfaces. However, the uncontrolled directional motion of microtubules has posed significant challenges, limiting the system's application for precise cargo delivery. Microfluidic devices provide a means to direct microtubule movement through their geometric features. Norland Optical Adhesive (NOA) is valued for its mold-free application in microfluidic device fabrication; however, microtubules often climb up channel walls, limiting controlled movement. In this study, a surface passivation method for NOA is introduced, using polyethylene glycol via a thiol-ene click reaction. This technique significantly improved the directional control and concentration of microtubules within NOA microchannels. This approach presents new possibilities for the precise application of biomolecular motors in nanotechnology, enabling advancements in the design of microfluidic systems for complex biomolecular manipulations.

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.

Wheat-Based Glues in Conservation and Cultural Heritage: (Dis)solving the Proteome of Flour and Starch Pastes and Their Adhering Properties.

Plant-based adhesives, such as those made from wheat, have been prominently used for books and paper-based objects and are also used as conservation adhesives. Starch paste originates from starch granules, whereas flour paste encompasses the entire wheat endosperm proteome, offering strong adhesive properties due to gluten proteins. From a conservation perspective, understanding the precise nature of the adhesive is vital as the longevity, resilience, and reaction to environmental changes can differ substantially between starch- and flour-based pastes. We devised a proteomics method to discern the protein content of these pastes. Protocols involved extracting soluble proteins using 0.5 M NaCl and 30 mM Tris-HCl solutions and then targeting insoluble proteins, such as gliadins and glutenins, with a buffer containing 7 M urea, 2 M thiourea, 4% CHAPS, 40 mM Tris, and 75 mM DTT. Flour paste's proteome is diverse (1942 proteins across 759 groups), contrasting with starch paste's predominant starch-associated protein makeup (218 proteins in 58 groups). Transformation into pastes reduces proteomes' complexity. Testing on historical bookbindings confirmed the use of flour-based glue, which is rich in gluten and serpins. High levels of deamidation were detected, particularly for glutamine residues, which can impact the solubility and stability of the glue over time. The mass spectrometry proteomics data have been deposited to the ProteomeXchange, Consortium (http://proteomecentral.proteomexchange.org) via the MassIVE partner repository with the data set identifier MSV000093372 (ftp://MSV000093372@massive.ucsd.edu).

Biocompatible Tough Ionogels with Reversible Supramolecular Adhesion.

Cohesive and interfacial adhesion energies are difficult to balance to obtain reversible adhesives with both high mechanical strength and high adhesion strength, although various methods have been extensively investigated. Here, a biocompatible citric acid/L-(-)-carnitine (CAC)-based ionic liquid was developed as a solvent to prepare tough and high adhesion strength ionogels for reversible engineered and biological adhesives. The prepared ionogels exhibited good mechanical properties, including tensile strength (14.4 MPa), Young's modulus (48.1 MPa), toughness (115.2 MJ m-3), and high adhesion strength on the glass substrate (24.4 MPa). Furthermore, the ionogels can form mechanically matched tough adhesion at the interface of wet biological tissues (interfacial toughness about 191 J m-2) and can be detached by saline solution on demand, thus extending potential applications in various clinical scenarios such as wound adhesion and nondestructive transfer of organs.

Antibacterial Hydrogel Adhesives Based on Bifunctional Telechelic Dendritic-Linear-Dendritic Block Copolymers.

Antibiotic-resistant pathogens have been declared by the WHO as one of the major public health threats facing humanity. For that reason, there is an urgent need for materials with inherent antibacterial activity able to replace the use of antibiotics, and in this context, hydrogels have emerged as a promising strategy. Herein, we introduce the next generation of cationic hydrogels with antibacterial activity and high versatility that can be cured on demand in less than 20 s using thiol-ene click chemistry (TEC) in aqueous conditions. The approach capitalizes on a two-component system: (i) telechelic polyester-based dendritic-linear-dendritic (DLDs) block copolymers of different generations heterofunctionalized with allyl and ammonium groups, as well as (ii) polyethylene glycol (PEG) cross-linkers functionalized with thiol groups. These hydrogels resulted in highly tunable materials where the antibacterial performance can be adjusted by modifying the cross-linking density. Off-stoichiometric hydrogels showed narrow antibacterial activity directed toward Gram-negative bacteria. The presence of pending allyls opens up many possibilities for functionalization with biologically interesting molecules. As a proof-of-concept, hydrophilic cysteamine hydrochloride as well as N-hexyl-4-mercaptobutanamide, as an example of a thiol with a hydrophobic alkyl chain, generated three-component networks. In the case of cysteamine derivatives, a broader antibacterial activity was noted than the two-component networks, inhibiting the growth of Gram-positive bacteria. Additionally, these systems presented high versatility, with storage modulus values ranging from 270 to 7024 Pa and different stability profiles ranging from 1 to 56 days in swelling experiments. Good biocompatibility toward skin cells as well as strong adhesion to multiple surfaces place these hydrogels as interesting alternatives to conventional antibiotics.

Solvent-Triggered, Ultra-Adhesive, Conductive, and Biocompatible Transition Gels for Wearable Devices.

The development of robust adhesive, conductive, and flexible materials has garnered significant attention in the realm of human-machine interface and electronic devices. Conventional preparation methods to achieve these exceptional properties rely on incorporating highly polar raw materials, multiple components, or solvents. However, the overexposure of functional groups and the inherent toxicity of organic solvents often render gels non-stick or potentially biocompatible making them unsuitable for human-contact devices. In this study, a straightforward three-step strategy is devised for preparing responsive adhesive gels without complex components. Structurally conductive poly(N-(2-hydroxyethyl)-acrylamide-co-p-styrene sulfonate hydrate) (PHEAA-NaSS) gels are synthesized by integrating ionic and hydrophilic networks with distinct solvent effects. Initially, the in-suit formed PHEAA-NaSS networks are activated by dimethyl sulfoxide, which substantially increases intramolecular hydrogen bonding and enhances the matrix stretchability and interfacial adhesion. Subsequently, ethanol exchange reduced solvent impact and led to a compact network that limited surface exposure of ionic and hydrophilic groups, resulting in nonstick, robust for convenient storage. Finally, upon contacting with water, the network demonstrates rehydration, resulting in favorable adhesion, biocompatibility, and conductivity. The proposed PHEAA-NaSS/W gels can stably and reliably capture joint motion and electrophysiological signals. Furthermore, this uncomplicated gel preparation method is also applicable to other electrolyte monomers.

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.

Swift Covalent Gelation Coupled with Robust Wet Adhesive Powder: A Novel Approach for Acute Massive Hemorrhage Control in Dynamic and High-Pressure Wound Environments.

The quest for efficient hemostatic agents in emergency medicine is critical, particularly for managing massive hemorrhages in dynamic and high-pressure wound environments. Traditional self-gelling powders, while beneficial due to their ease of application and rapid action, fall short in such challenging conditions. To bridge this gap, the research introduces a novel self-gelling powder that combines ultrafast covalent gelation and robust wet adhesion, presenting a significant advancement in acute hemorrhage control. This ternary system comprises ε-polylysine (ε-PLL) and 4-arm polyethylene glycol succinyl succinate (4-arm-PEG-NHS) forming the hydrogel framework. Na2HPO4 functions as the "H+ sucker" to expedite the amidation reaction, slashing gelation time to under 10 s, crucial for immediate blood loss restriction. Moreover, PEG chains' hydrophilicity facilitates efficient absorption of interfacial blood, increasing the generated hydrogel's cross-linking density and strengthens its tissue bonding, thereby resulting in excellent mechanical and wet adhesion properties. In vitro experiments reveal the optimized formulation's exceptional tissue compliance, procoagulant activity, biocompatibility and antibacterial efficacy. In porcine models of heart injuries and arterial punctures, it outperforms commercial hemostatic agent Celox, confirming its rapid and effective hemostasis. Conclusively, this study presents a transformative approach to hemostasis, offering a reliable and potent solution for the emergency management of massive hemorrhage.

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.

Adhesive Nanoparticle-in-Microgel System with ROS Scavenging Capability and Hemostatic Activity for Postoperative Adhesion Prevention.

Postoperative adhesion is a noteworthy clinical complication in abdominal surgery due to the existing physical barriers are unsatisfactory and inefficient in preventing its occurrence. In this work, an elaborate nanoparticle-in-microgel system (nMGel) is presented for postoperative adhesion prevention. nMGel is facilely formed by crosslinking manganese dioxide (MnO2) nanoparticles-loaded gelatin microspheres with polydopamine using a modified emulsification-chemical crosslinking method, generating a nano-micron spherical hydrogel. After drying, powdery nMGel with sprayability can perfectly cover irregular wounds and maintains robust tissue adhesiveness even in a wet environment. Additionally, nMGel possesses prominent antioxidant and free radical scavenging activity, which protects cell viability and preserves cell biological functions in an oxidative microenvironment. Furthermore, nMGel displays superior hemostatic property as demonstrated in mouse tail amputation models and liver trauma models. Importantly, nMGel can be conveniently administrated in a mouse cecal defect model to prevent adhesion between the injured cecum and the peritoneum by reducing inflammation, oxidative stress, collagen synthesis, and angiogenesis. Thus, the bioactive nMGel offers a practical and efficient approach for ameliorating postsurgical adhesion.

Adhesive technology based on biomass tar documents engineering capabilities in the African Middle Stone Age.

The foragers of the southern African Middle Stone Age were among the first humans to adapt their environment and its resources to their needs. They heat-treated stone to alter its mechanical properties, transformed yellow colorants into red pigments and produced moldable adhesive substances from plants. Until now, only Podocarpus conifers have been identified as the botanical origin of Middle Stone Age adhesives. This is curious as these conifers do not produce sticky exudations that could be recognized as potential adhesives. To obtain an adhesive, tar must be made with a technical process based on fire. However, the nature of these technical processes has remained unknown, hampering our understanding of the meaning of this adhesive technology for the cultural evolution of early Homo sapiens. Here, we present the first evidence of a technique used for tar making in the Middle Stone Age. We created an experimental reference collection containing naturally available adhesives along manufactured tars from plants available in the Middle Stone Age and compared these to artifacts using gas chromatography-mass spectrometry and infrared spectroscopy. We found that, in the Howiesons Poort at Sibhudu Cave, tar was made by condensation, an efficient above-ground process. Even more surprisingly, the condensation method was not restricted to Podocarpus. The inhabitants of Sibhudu also produced tar from the leaves of other plants. These tars were then used, either without further transformation or were processed into ochre-based compound adhesives, suggesting that people needed different moldable substances with distinct mechanical properties. This has important implications for our understanding of Middle Stone Age H. sapiens, portraying them as skilled engineers who used and transformed their resources in a knowledgeable way.

Design of Stretchable and Conductive Self-Adhesive Hydrogels as Flexible Sensors by Guar-Gum-Enabled Dynamic Interactions.

The limited elasticity and inadequate bonding of hydrogels made from guar gum (GG) significantly hinder their widespread implementation in personalized wearable flexible electronics. In this study, we devise GG-based self-adhesive hydrogels by creating an interpenetrating network of GG cross-linked with acrylic, 4-vinylphenylboronic acid, and Ca2+. With the leverage of the dynamic interactions (hydrogen bonds, borate ester bonds, and coordination bonds) between -OH in GG and monomers, the hydrogel exhibits a high stretchability of 700%, superior mechanical stress of 110 kPa, and robust adherence to several substrates. The adhesion strength of 54 kPa on porcine skin is obtained. Furthermore, the self-adhesive hydrogel possesses stable conductivity, an elevated gauge factor (GF), and commendable durability. It can be affixed to the human body as a strain sensor to obtain precise monitoring of human movement behavior. Our research offers possibilities for the development of GG-based hydrogels and applications in wearable electronics and medical monitoring.