Fast Click Crosslinking Bio‐Inspired Adhesives With Tailored Hierarchical High Bonding and Exceptional Versatility

ABSTRACT

The sluggish room‐temperature curing kinetics and low‐temperature brittle failure of epoxy resins have long constrained their deployment in extreme environments. Although existing acceleration strategies can enhance curing rates, they are invariably accompanied by issues of intense exothermic heat release, cohesive embrittlement, and toxic emissions. Herein, inspired by mussel adhesive proteins, we present an interfacial–bulk synergistic optimization strategy that leverages triazolinedione–indole (TAD–indole) click chemistry to construct a room‐temperature, second‐scale curable epoxy adhesive (RTIA). This strategy exploits the TAD–indole cycloaddition reaction to form a high‐density C–N crosslinked network, while concurrently endowing the crosslinking sites with dicarbonyl hydrogen bond acceptor functionalities, thereby achieving synchronous enhancement of cohesive strength and interfacial adhesion. The RTIA adhesive exhibits a dry shear strength of 9.42 MPa and retains 3.12 MPa after boiling water treatment, demonstrating stable performance across a broad temperature window from −196°C to 80°C. Notably, the indole moieties confer intrinsic antibacterial properties that effectively suppress bacterial adhesion. This heat‐free curing mechanism fundamentally circumvents the adverse effects associated with conventional accelerators, enabling compatibility between instantaneous on‐site processing and deployment in extreme environments and thereby establishing a new paradigm for the design of high‐performance structural adhesives.

Ultrahigh bonding performance is achieved by using the biomimetic hierarchical design of interface–bulk synergistic optimization strategy that leverages triazolinedione–indole (TAD–indole) click chemistry to construct a room‐temperature, second‐scale curable epoxy adhesive. This promising, versatile, accessible, and high‐performance structural adhesive enables compatibility between instantaneous on‐site processing and deployment in extreme environments.

1. Introduction

Wood, as a naturally abundant and renewable structural material, possesses a hierarchical porous architecture and inherent anisotropy that provide a unique platform for the design of functional wood products [1, 2]. However, efficient manufacturing within the wood industry has long been constrained by performance limitations of adhesive systems [3]. Epoxy resin (EP) has become the material of choice for structural wood bonding and composite matrices by virtue of its exceptional mechanical strength, chemical resistance, and interfacial adhesion [4, 5, 6]. Nevertheless, its intrinsically sluggish curing kinetics at ambient temperatures and significantly compromised adhesive performance under low‐temperature conditions severely limit deployment in cold regions and field construction scenarios [7, 8, 9, 10, 11]. In recent years, to address the inherent trade‐off between curing rate and low‐temperature resistance, highly reactive accelerators—notably 2,4,6‐tris‐(dimethyl aminomethyl) phenol (DMP‐30) and 2‐methylimidazole (2‐MI)—are widely employed to facilitate rapid crosslinking by reducing the reaction activation energy [12]. Yet, these accelerators induce pronounced exothermic heat generation and high residual thermal stresses during the accelerated curing process, leading to cohesive embrittlement and compromised thermomechanical properties of the adhesive [13, 14, 15]. Additionally, volatile amine compounds pose risks of noxious odors and toxicity.

In the past few decades, click chemistry has become a key focus in synthetic chemistry because of its ability to efficiently create functional units through highly controllable reactions and cleaning mechanisms. Lately, thiol‐epoxy click polymerization driven by a base catalyst has gained significant attention due to its rapid curing, excellent regioselectivity, versatility, and high conversion, making it ideal for creating cross‐linked adhesives [16, 17]. Despite its potential benefits and widespread use, this system has significant drawbacks in industry. Notably, many thiols used frequently have a foul smell, complicating their handling in some situations [18]. More importantly, the stability of the thiol‐epoxy system, which is triggered by the nucleophilic attack of commonly used base catalysts, is constrained by rapid initial curing rates [19]. This contradiction exposes a fundamental oversight in existing research: a disproportionate emphasis on optimizing bulk reaction kinetics while neglecting microstructural engineering and stress management at the adhesive–wood interface. Adhesive failures typically stem from stress concentration within the interfacial phase and weak boundary layers rather than inadequate cohesive strength of the adhesive itself [20, 21].

To overcome these limitations, we herein propose an interface–bulk synergistic optimization strategy that constructs hierarchical interfacial structures to simultaneously modulate curing kinetics and interfacial stress transfer efficiency [22, 23, 24, 25, 26]. By maximizing both the cohesive strength of the adhesive and the interfacial interactions between the adhesive and wood substrate, this approach enables ultrahigh bonding performance.

Herein, inspired by the hierarchical interaction of mussel adhesive proteins and the ultrafast click chemistry reaction between triazolinedione (TAD) and indole derivatives, we introduce TAD‐indole adducts as hierarchical interaction sites into the epoxy polymer to construct a new kind of adhesive (RTIA), endowing it with heat‐free and rapid adhesion, excellent bonding strength, good environmental suitability, water resistance, and antibacterial properties (Figure 1). In our strategy, the obtained adhesive system fulfills the following key objectives: firstly, the epoxy matrix rich in hydroxy groups and ether bonds could form abundant hydrogen bonds with the wood's substrate surface, improving the interfacial adhesion. Secondly, TAD, with its high reactivity to indole, enables efficient crosslinking and enhances the internal cohesive force of the adhesive. Moreover, TAD‐indole adducts with di‐carbonyl interaction sites are particularly effective as hydrogen acceptors, further promoting interfacial adhesion. This hierarchical design successfully results in the creation of an intrinsically hydrophobic and adhesive polymer. More interestingly, the incorporation of indole moieties further grants adhesives significant antibacterial performance, effectively inhibiting bacterial growth. These studies will help us to gain a deeper insight into how to develop multifunctional adhesives that could perform well in complex and extreme environments, such as Antarctica and the Arctic, where mechanical strength and environmental durability are essential.

FIGURE 1.

Design principle and application demonstrations of RTIA adhesive. (a) Wood adhesive inspired by mussel adhesive protein. (b) Schematic bonding mechanism including interfacial adhesion and internal cohesion of the RTIA adhesive on wood. (c) Summary of excellent performance and function for the heating‐free adhesive RTIA.

2. Results and Discussion

2.1. Synthesis and Characterization of RTIA Adhesive

As schematically illustrated in Figure 2a, a linear polymer EPI with indole in the side chains was first synthesized by copolymerizing diglycidyl ether of bisphenol A (E51) with tryptamine (Tryp) in a 1:1 molar ratio and then treated with a TAD crosslinker 4,4’‐(4,4’‐diphenylmethylene)‐bis‐(1,2,4‐triazoline‐3,5‐dione) via an ultrafast click reaction at room temperature to achieve a series of C‐N crosslinked heat‐free adhesives (RTIAs). The as‐prepared adhesives were denoted as RTIA‐x, where x was the molar fraction of TAD‐indole adduct in the feed (varied between 0 and 10 mol%). The experimental procedures were described in detail in the Supporting Information.

FIGURE 2.

Synthesis and characterization of RTIA adhesive. (a) Schematic diagram of the preparation process for the adhesive RTIA. (b) FTIR spectra of EPI, TAD, and RTIA. (c) TGA results of EPI and RTIA. (d) DTG results of EPI and RTIA. (e) XPS survey spectra of EPI and RTIA. (f) N 1s XPS spectral analysis of EPI and RTIA. (g) C 1s XPS spectral analysis of EPI and RTIA.

The chemical structure of RTIA has been characterized by utilizing Fourier‐transform infrared (FTIR) spectroscopy and X‐ray photoelectron spectroscopy (XPS). FTIR spectra analysis (Figure 2b) verified an obvious cycloaddition click reaction between the indole ring of EPI and TAD, indicating the successful formation of cross‐linking networks. TAD exhibited a peak characteristic of carbonyl in the TAD moiety at 1748 cm⁻¹. The characteristic peak at 2268 cm⁻¹ was associated with the stretching vibration of the TAD azo bond (‐N = N‐). Compared to TAD, the carbonyl absorption peak of TAD at 1746 cm⁻¹ was confirmed in the RTIA spectrum. Meanwhile, the peak belonging to ‐N = N‐ disappeared, suggesting the occurrence of TAD‐indole adducts in the epoxy polymer matrix. Moreover, the hydroxyl and N‐H absorption peak of EPI at 3508 cm⁻¹ was red‐shifted to 3480 cm⁻¹ and intensified, implying an increase in N‐H content and enhanced hydrogen bonding interactions. In addition, the C‐H stretching vibration peaks of methylene (‐CH₂‐) groups in the range of 2950–2900 cm⁻¹ remained almost the same, demonstrating the preservation of the integral epoxy polymer structures in RTIA. The alterations in the above spectra showed that the TAD‐indole adducts acting as the energetic crosslinking points play an important role in the construction of the adhesive RTIA.

The elemental composition and changes in chemical bonding within RTIA were investigated via XPS analysis (Figure 2e–g). As depicted in Figure 2e, distinctive peaks corresponding to O 1s (532 eV), N 1s (399.5 eV), and C 1s (285 eV) across EPI were aligned with the molecular constitution of the adhesive RTIA. In contrast to what is seen with EPI, the introduction of TAD led to an increase in the peak area ratio of C–N (400 eV) / N–H (399.3 eV), and a new ‐N–N‐ (398.71 eV) characteristic peak appeared in the N 1s spectrum (Figure 2f). This change was ascribed to the consumption of the TAD azo‐bond (‐N = N‐) upon the click reaction to form adduct structures (N–NH). At the same time, the stable C–N covalent bonds were formed of TAD‐indole moieties within the network [27]. In the C 1s spectrum, the peak area ratio of C–N (286.10 eV) decreased, and the peak area ratio of C−C/C═C (284.8 eV) dramatically increased. Moreover, the appearance of a carbonyl (C═O) characteristic peak at 287.12 eV in the C 1s region of RTIA further confirmed the successful incorporation of TAD into the system (Figure 2g).

Subsequently, thermogravimetric analysis (TGA) was employed to assess the thermal decomposition behavior of the adhesive RTIA at high temperatures. At 300°C, both EPI and RTIA showed slight mass loss, which was due to the hydration of hydroxyl groups generated during the epoxidation reaction and the indole rings present on polymers (Figure 2c). DTG curves of Figure 2d revealed that the maximum thermal decomposition temperature (T_max) of EPI was 356.4°C, largely owing to the loose, linear polymer structures. In contrast, after TAD modification, the T_max obviously increased to 363.8°C, while the residual char yield at 700°C also improved from 21.5% to 23.82%, meaning that the crosslinking network structure enhanced the thermal stability of the adhesive (Figure 2c–d; Table S1).

2.2. Adhesion Properties of RTIA Adhesive

The mechanical properties of the adhesive significantly influence the balance between cohesive force and adhesive force, determining the bonding strength of the adhesives [28]. Notably, an effective approach for improving adhesive durability against mechanical stress is to develop adhesives with superior bonding performance. As we know, the cohesive force refers to the internal strength that upholds the structure of the adhesive. The mechanical tensile tests could be conducted to assess the resistance of adhesives to stress failure, which may help estimate the cohesive force [29]. Initially, the mechanical properties were recorded with tensile tests at a stretching rate of 10 mm/min to provide insight into the effects of different TAD ratios on the RTIA adhesives. The stress‐strain curves were shown in Figure S5. It can be clearly seen that RTIA‐0% exhibited the lowest tensile strength owing to its linear polymer structure. In contrast, the tensile strength initially increased and then slightly decreased with different crosslinking ratios from 2% to 10%, with an optimal tensile strength of 9.37 ± 0.46 MPa observed for RTIA‐3.5%. Such findings led us to consider that the construction of a crosslinking network via the click modification of TAD successfully relieved stress concentration and maintained the integrity of the networks, strengthening the cohesive force of the polymer and advancing the material's mechanical strength. However, the impact of adding a small amount of TAD crosslinker itself on the mechanical properties was negligible [30]. Here, we chose RTIA‐3.5% as a representative example to demonstrate our strategy.

The bonding strength of an adhesive depends on its ability to transfer and dissipate stress at the interface [31]. To evaluate the bonding performance of the adhesives, we proposed a standardized protocol for shear testing. The poplar wood specimens were fabricated by uniformly applying the obtained adhesive onto one end of the poplar veneers with a bonding area of 20 × 8 mm². Then the bonding strength was studied through lap shear tests (Figure 3a). To identify the best aging time for mechanical strength, RTIA‐3.5% was next treated with different aging times for comparison (Figure 3b). It was found that both the dry and wet shear strengths were low at first, suggesting that the crosslinked curing process was a complex and long process. After the click reaction, the crosslinking occurred, but not all functional groups in the system had reacted, and the curing process was still going on [32]. With the extension of time, the strength gradually increased due to the continuous improvement of the curing crosslinking degree of the adhesive. As the aging time lengthened to 4 h, the dry shear strength of the adhesive rose steadily from 5.45 ± 0.35 MPa to 9.42 ± 0.32 MPa, while the wet shear strength increased from 3.35 ± 0.21 to 5.26 ± 0.21 MPa. We speculated that the increase of the crosslinking degree promoted the formation of a stronger mechanical interlock and better interfacial contact with the veneer surfaces [32]. However, after 4 h, both the dry and wet shear strength enhanced slowly and remained basically unchanged, meaning that the click reaction sites were nearly consumed completely. Thus, a relatively stable aging time (4 h) was chosen for the following experiments.

FIGURE 3.

Adhesion properties of RTIA adhesive. (a) Schematic illustration of the lap‐shear test. (b) Lap shear strength of the adhesive RTIA‐3.5% at different epoxidation aging times. (c) Dry and wet strengths of the RTIA‐3.5% adhesive. (d) Comparison of bonding strength of RTIA‐3.5% and commercial adhesives. (e) Photographs of RTIA‐3.5% adhering to diverse substrates in air. (f) Bonding strength of RTIA‐3.5% and EPI on different substrates. (g) Demonstration of lap shear strength of RTIA‐3.5%. (h) Exhibition of wooden bench repaired with RTIA‐3.5% at room temperature.

As illustrated in Figure 3c, RTIA‐3.5% possessed excellent bonding capability with dry and wet strengths; even at 100°C in water for 3 h, the wet strength was still as high as 3.12 ± 0.14 MPa. These results led us to further conclude that the synergy between C–N crosslinking and functional hydrogen bond activation in the crosslinking networks plays a key role in the achievement of strong and stable adhesion. Simultaneously, we carefully checked the water resistance of the RTIA‐3.5% layer through moisture absorption experiments. Figure S6 depicted that RTIA‐3.5% adhesive layer had only a moisture absorption rate of 9.55% for 35 days, suggesting that the hydrophobic crosslinking structure effectively resisted moisture erosion, ensuring strong wet shear strength. Importantly, the dry bonding strength and wet bonding strength of RTIA‐3.5% were distinctly superior to those of commercial phenol formaldehyde adhesive PF2130 (PF) and epoxy adhesive Pattex (Epoxy) (Figure 3d; Table S2). These characteristics make RTIA‐3.5% a promising candidate adhesive for complex humid environments.

Moreover, the RTIA‐3.5% adhesive was intended to be used as a room‐temperature‐curing adhesive for the adhesion of a variety of substrates. Figure 3e showed the adhesion and bonding performance of RTIA‐3.5% on different substrate surfaces, including glass, ceramic, wood, steel, polypropene (PP) Eppendorf Tube, and polytetrafluoroethylene (PTFE), with the adhesion strengths of 0.64 ± 0.11, 1.78 ± 0.13, 9.42 ± 0.20, 3.06 ± 0.15, 0.58 ± 0.13, and 0.28 ± 0.13 MPa, respectively (Figure 3f; Table S3). In contrast, EPI indicated much worse adhesion to various substrates (Table S3). These observations demonstrated that the unique hierarchical bonding cross‐linked network with active sites such as hydroxyl and carbonyl groups and indole rings could greatly favor the synergy of the multiple supramolecular interactions between RTIA and various substrate surfaces via hydrogen bonding, cation‐π and hydrophobic interactions, etc., facilitating the interfacial adhesion and the internal cohesive force of the adhesive and making it more effective in bonding than some other reported adhesives [29, 33].

To exhibit the adhesion strength of RTIA‐3.5% and EPI clearly and visually, two poplar boards were overlapped and glued with the two different adhesives together with a bonding area of 2 cm² and the adhesive layer thickness of approximately 0.2 mm. Then we found that RTIA‐3.5% could successfully support the weight of an adult (around 50 kg) (Figure 3g), while EPI failed in lifting a load of 23.5 kg (Figure S7). Furthermore, to investigate the practical woodwork maintenance applications of the adhesive RTIA‐3.5%, the restoration of the structurally broken wooden bench was tested by ambient adhesion processes. From Figure 3h, we can see that the one repaired joint still could withstand 26 kg loads. For comparison, the adhesive‐bonded joint repaired with EPI cannot bear the weight of 23.50 kg (Figure S8), further confirming the exceptional adhesion strength of RTIA‐3.5% by its strong multiple hydrogen bonding with the surface of the wood.

2.3. Interfacial Structure Analysis and Adhesion Mechanism

The strong bond of the adhesive is primarily due to high adhesion of the adhesive nail structures created during infiltration [34]. Investigating the interfacial wettability of adhesives across various substrates to understand the nail formation mechanism was crucial. To further shed light on the mechanism behind the excellent adhesion strength of RTIA‐3.5% during this process, the contact angles of RTIA‐3.5% and water on different substrates, including PTFE, PP, glass, ceramic, steel, and wood, were carried out, respectively. As shown in Figure 4a, the contact angles of RTIA‐3.5% were consistently smaller than that of water on the surfaces of the above substrates, illustrating its superior wettability. Interestingly, RTIA‐3.5% had the lowest contact angle of 47.4° on wood, indicating the efficient wetting behavior of RTIA allowed it to easily penetrate the wood substrate and ensure an intimate contact between the adhesive and surfaces [35]. This enhanced wettability promoted deep substrate infiltration and facilitated the proximity of interaction sites in RTIA‐3.5% molecules to improve the adhesion strength [36]. In addition, the contact angles of RTIA‐3.5% and EPI with deionized water were measured, respectively to investigate the effect of hierarchical interactions on the interfacial wetting properties. After the hierarchical modification of TAD click crosslinking, the polarity of RTIA‐3.5% was lower than that of linear epoxy polymer EPI, resulting in a marked decrease in contact angle from 102.60° to 55.93° (Figure S9) [37]. This indicated the enhancement of water resistance after crosslinking, thereby improving the durability of the adhesive RTIA‐3.5% in humid environments. The rheological properties of RTIA and EPI were also systematically studied (Figure S10). RTIA demonstrated distinct non‐Newtonian shear‐thinning behavior, implying that the adhesive maintained high viscosity at the low shear rates to prevent itself bleed‐through during lapping, effectively balancing viscosity adjustment and manufacturing requirements. Notably, viscosity showed positive correlation with the content of interaction sites at equivalent shear rates. The observed rheological response validated that hierarchical hydrogen bonding interactions amplified the internal cohesive force.

FIGURE 4.

Interfacial structure analysis and adhesion mechanism. (a) Contact angles of the RTIA‐3.5% adhesive and water on different substrates. (b) SEM image of the fracture surface of the cured EPI adhesive. (c) SEM image of the fracture surface of the cured RTIA‐3.5% adhesive. (d) SEM image for obtaining the wood fracture morphology. (e) Wood failure rates of EPI and RTIA‐3.5% in both air and water. (f) The electrostatic potential maps of EPI and RTIA‐3.5%. (g) Weak interactions and (h) the corresponding scatter figure within the bonded model.

The adhesive bonding performance was assessed by examining the fractured surfaces of the cured adhesive and the fracture patterns of the ruptured wood veneers. SEM analysis showed extensive fracture patterns, surface damage, and fiber breakage in wood (Figure 4b–d). The fracture surface of the wood bonded by EPI was smooth and loose, and there was almost no adhesive residue in the wood tissue (Figure 4b), suggesting that it depended only on weak hydrogen bonds and physical entanglement inside, giving rise to poor interfacial bonding strength. In contrast, RTIA‐3.5% showed strengthened interfacial interaction with the wood, evidenced by wood tissue being pulled out on the shear fracture surface (Figure 4c). The microscopic morphology revealed that the modified adhesive formed a stronger bond, allowing for efficient stress transfer and leading to wood failure (Figure 4d). The improved mechanical properties likely stemmed from the constitution of stable and high‐crosslinked networks in the adhesive. Furthermore, the wood failure rate was evaluated to look into the quality of the bond and the site of failure (Figure 4e). We can see from Figure 4e that a stark contrast in the extent of damage inflicted on the wood substrate during the lap‐shear tests on EPI and RTIA‐3.5%. Adhesion using EPI resulted in an absence of wood failure rates due to the cohesive failure of the wood. Whereas the poplar wood bonded with RTIA‐3.5% had a high wood failure rate at 80% in air (or 70% in water) accompanied by the formation of rough fracture surfaces, representing strong interfacial adhesion.

The molecular polarity changes before and after the hierarchical modification was further explored from a theoretical perspective through density functional theory (DFT). Figure 4f displayed a comparison of the electrostatic potential maps of RTIA‐3.5% with that of linear EPI, revealing a significant local color change. The findings lent support to the inference that the polarity of the molecular segments was increased to improve the non‐covalent interactions between the adhesive and the wood interface [37]. Consequently, the interfacial wetting ability of RTIA‐3.5% was enhanced, aligning with the experimental results.

In addition, the isosurface and scatter graphs of the bonded model between RTIA‐3.5% and cellulose in the wood were conducted by the Multiwfn package [38, 39] by using the independent gradient model (IGM) method [40, 41] (Figure 4g,h). The blue area in the scatter plot indicated interactions that were stronger than the van der Waals forces represented in the green area, such as hydrogen bonding (Figure 4h). The interactions in the bonded model were mainly hydrogen bonds and van der Waals forces, with hydrogen bonding dominating. Furthermore, we could also determine the atomic composition of the hydrogen bonds by examining their directionality and saturability. As shown in Figure 4g, not only do O–H···O hydrogen bonding interactions exists in the model, but also ─C═O···H hydrogen bonds between the electron‐donating carbonyl groups on the indole‐TAD adduct and the electron‐deficient H atoms of hydroxyl on cellulose skeletons are present. Binding energy calculations were carried out for the model. It can be found that the binding energy was as high as −119.67 kJ/mol, suggesting that the interactions between RTIA‐3.5% and the wood substrate were strong and exceeded the energy of traditional hydrogen bonds observed in other polymer systems [42, 43], which was further supported by the studies mentioned above. In summary, the contact angle tests exhibited that the polar structure of RTIA‐3.5% enhanced its interfacial adhesion. Moreover, theoretical calculations confirmed the changes in the electrostatic potential of the adhesive molecules before and after the hierarchical modification. This wood adhesive was expected to provide stable adhesion at low temperatures, thanks to its outstanding interfacial adhesion and wetting properties.

2.4. Excellent Environmental Suitability and Antibacterial Properties

To explore the possibility of engineering applications for extreme environments, such as Antarctica (−20.7°C to −94.2°C) and the Arctic (−20°C to −140°C), the resistance of RTIA‐3.5% to low temperatures was verified by simulated lap shear strength tests. The results demonstrated that RTIA‐3.5% had much better low‐temperature adhesive stability than conventional wood adhesives [37]. As exhibited in Figure 5a, the adhesive RTIA‐3.5% on the poplar interface could sustain a 10 kg load without interface delamination at −196°C in a liquid nitrogen environment, while the EPI‐bonded joint failed under a load of 10 kg (Figure S11). The cross‐temperature wood lap shear tests were also investigated to evaluate the environmental tolerance of RTIA‐3.5% quantitatively (Figure 5b). All samples were kept at their specified temperatures for one week. Across temperatures ranging from −196°C to 80°C, the adhesion strength of RTIA‐3.5% showed an increasing, followed by a decreasing trend, and the maximum adhesion strength reached up to 9.42 ± 0.20 MPa at room temperature. Then the shear strength decreased very significantly when the temperature exceeded T_g of RTIA‐3.5% (75.87°C, Figure S12). We assumed that heating RTIA‐3.5% to 80°C above its T_g activated the movement of the polymer segments. Thus, the material transformed from a glassy to a rubbery state, and the internal morphology changed so that the strength of the material at room temperature could no longer be maintained [44]. After soaking in liquid nitrogen for 6 h, the adhesive still retained a strength of 5.05 ± 0.42 MPa (Figure S13). These results were attributed to the embrittlement of the material's internal structure and stress concentration by the excessive immersion time, finally reducing its strength. It was suggested that RTIA‐3.5% indeed had excellent low and high‐temperature resistance and could be preferable to real‐world applications.

FIGURE 5.

Environmental suitability and antibacterial properties. (a) Macroscopic adhesion tests of RTIA‐3.5% in liquid nitrogen. (b) Adhesion strengths of the RTIA adhesive at various temperatures (on wood). (c) Swelling resistance of RTIA‐3.5% lap joint samples in different solvents. (d) Comprehensive comparison of the performance of RTIA‐3.5% adhesive and representative adhesives reported in terms of preparation, adhesion strength, temperature resistance, water resistance, solvent adaptability, and antibacterial property. (e) Antibacterial activity evaluation of RTIA‐3.5% and EPI against E. coli and S. aureus. (f) Comparison of the antibacterial activities of RTIA‐3.5% and EPI.

RTIA‐3.5% not only possessed outstanding dry and wet lap shear strength as well as low‐temperature bonding performance but also had excellent stability and environmental adaptability. As we know, the organic solvent resistance of adhesives was of paramount importance in fields such as oil platform construction and shipbuilding. To study the performance of RTIA‐3.5% in different organic solvents (including both polar and non‐polar solvents), lap shear samples were immersed in dimethylacetamide (DMAC), silicone oil, and ethanol for 30 days, and the strength changes were recorded (Figures S14 and S15). After immersion in all three solvents, the RTIA samples maintained ultra‐high strengths of 5.40 ± 0.28 MPa, 5.15 ± 0.21 MPa, and 5.55 ± 0.35 MPa, with no significant cracking or swelling of the adhesive. To assess the solvent resistance, the solvent immersion tests of adhesive films were performed, and the status was documented every 18 days (Figures S16 and S17). After soaking in dichloromethane (DCM), ethanol (EtOH), ethyl acetate (EtOAc), chloroform (TCM), toluene (Tol), and dimethyl sulfoxide (DMSO) for 36 days, RTIA‐3.5% films showed only slight swelling in chloroform and toluene, while other solvents had ignorable changes. Figure 5c presented the calculated swelling rates of RTIA‐3.5% and EPI in various solvents. More importantly, the swelling rate of RTIA‐3.5% was enhanced by 42.4% (chloroform) and 39.6% (toluene), respectively, owing to its denser crosslinking network structure that improved the solvent resistance. The stable adhesion in solvent environments resulted from the robust adhesive structure and the crosslinking network that prevented swelling of the adhesive layer.

It is well‐known that the antibacterial quality of adhesives is essential for maintaining their long‐term efficiency and ensuring sustained performance in environments that are humid and conducive to bacterial growth. Here, the plate counting method, a standard technique in microbiology for evaluating the antibacterial efficacy, was used to assess the antibacterial activities of RTIA‐3.5% and EPI against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Strikingly, almost no bacterial colonies were observed on plates containing RTIA‐3.5%, in sharp contrast to EPI and the blank group, which were fully covered in bacteria (Figure 5e). In Figure 5f, RTIA‐3.5% further displayed superior antibacterial performance with an inhibition rate reaching 99%, significantly better than EPI. Subsequently, EPI and RTIA‐3.5% films were separately placed in E. coli and S. aureus suspensions and incubated for 24 h to study the antiadhesion ability of adhesives to bacteria. Bacterial attachment on the surfaces of EPI and RTIA‐3.5% was examined using SEM (Figure S18). As exhibited in Figure S19, many E. coli adhered significantly on the surface of EPI. Like E. coli, S. aureus also aggregated more readily to the surface of EPI. On the contrary, the RTIA‐3.5% surface showed much lower bacterial coverage, demonstrating its effectiveness in inhibiting bacterial growth and reproduction. The antibacterial activity of RTIA was primarily attributed to the presence of indole rings. Indole and its derivatives had antibacterial properties that could disrupt bacterial DNA replication or cell wall synthesis, thus leading ultimately to bacterial death [45]. The ability of the adhesive RTIA to resist bacterial growth identified it as an ideal candidate for long‐term application in infection‐sensitive environments.

Furthermore, we found the obtained adhesive achieved excellent bonding strength and outstanding durability across various harsh environments (water, organic solvents, extreme temperatures, and bacterial growth), offering a practical balance between bonding strength and multifunctionality, including excellent performance in heat‐free and rapid adhesion, excellent bonding strength, good environmental suitability, water resistance, and antibacterial property. RTIA‐3.5% showed a combination of properties that were superior to those of other reported adhesives (Figure 5d; Table S4) [46, 47, 48, 49, 50, 51, 52]. These merits made it a promising, versatile, accessible, and high‐performance adhesive through a biomimetic hierarchical design strategy, being suitable for diverse applications such as deep space exploration, polar scientific research, special industries, and daily life.

3. Conclusion

Inspired by the hierarchical interfacial interactions of mussel adhesive proteins, we herein report an interfacial–bulk synergistic molecular engineering strategy that enables the development of a room‐temperature, heat‐free, rapidly curable high‐performance wood adhesive (RTIA) through the integration of TAD–indole click chemistry into epoxy systems. The central tenet of this strategy leverages the ultrafast cycloaddition reaction between TAD and indole derivatives (enabling second‐scale crosslinking at ambient temperature) to construct a high‐density C–N covalent network while concurrently endowing the crosslinking sites with di‐carbonyl hydrogen bond acceptor functionalities. This singular molecular architecture achieves synchronous enhancement of cohesive strength and interfacial adhesion. The RTIA adhesive exhibits breakthrough comprehensive performance metrics. Furthermore, the incorporation of indole moieties imparts intrinsic broad‐spectrum antibacterial properties, with significantly enhanced inhibition of E. coli and S. aureus adhesion compared to unmodified systems, ensuring long‐term serviceability in high‐humidity, high‐bacterial‐load environments. Distinct from conventional rapid‐curing systems reliant on highly reactive amine accelerators, the heat‐free click‐curing mechanism of RTIA fundamentally circumvents cohesive embrittlement and thermal residual stress induced by exothermic heat release, while simultaneously achieving compatibility between instantaneous room‐temperature processing and deployment in extreme scenarios such as polar and deep‐space environments. This research provides a paradigm for the convergence of biomimetic hierarchical interfacial engineering and efficient click chemistry, establishing a new design paradigm for high‐performance adhesives targeting complex environments, with broad engineering application prospects in deep‐space exploration, polar scientific research, marine engineering, and emergency repair operations.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Supporting File: smll74255‐sup‐0001‐SuppMat.docx.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.