Rapid photocontrollable dopamine polymerization for instant adaptive wet adhesion

Domain: chemistry
Published: 2026-01-07
Editorial outcome: major_revision

Abstract
Dopamine-based adhesives offer strong, versatile adhesion through diverse interactions but are limited by slow, poorly controlled oxidative polymerization and dopamine’s inhibition of radical polymerization. We present an efficient photochemical strategy for in-situ fabrication of high-performance polydopamine-containing hydrogels with instant wet adhesion. By integrating a scalable synthesis of a protected dopamine derivative with rational photochemical design, we enable simultaneous, light-controlled oxidative and radical polymerizations, forming interpenetrated hydrogel networks within seconds. The resulting tough adhesives exhibit high polydopamine content and strong adhesion across diverse wet and dry substrates, outperforming conventional polydopamine-coated systems. This rapid, light-driven process is compatible with extrusion-based 3D printing, allowing spatially programmable adhesion and the creation of complex biomimetic architectures. Furthermore, the instant, robust adhesion enables integration of flexible electroluminescent devices that remain stable under large deformations. This work establishes a versatile platform for rapid, programmable adhesion in soft electronics and biointerfacing systems.

Introduction
Adhesion, the interaction between two surfaces, is a fundamental behavior observed across nature and daily life1–4. In biological systems, wet adhesion is particularly vital for tissue integration, enabling complex functions and enhancing biological processes in high-humidity or underwater environments5–8. For instance, fibronectin and collagen proteins facilitate strong muscle-to-bone attachments in humans, allowing coordinated movement during large-scale or high-frequency physiological motions9–11. Similarly, marine organisms such as mussels, sandcastle worms, and barnacles exhibit remarkable adhesion capabilities in saline and turbulent waters, which are essential for survival, reproduction, and nutrient acquisition12–14. In these systems, dopamine residues of proteins play a pivotal role, mediating adhesion through multiple covalent and noncovalent interactions with diverse substrates15–17.

Drawing inspiration from these biological systems, synthetic dopamine-containing adhesives have garnered significant attention, particularly when combined with porous, water-rich hydrogel matrices18–20. These polydopamine-containing hydrogel adhesives (PDCHAs) combine biocompatibility with inherent wet adhesion, enabling radical scavenging, antimicrobial activity, and enhanced wound healing and tissue regeneration21–23. Furthermore, PDCHAs facilitate the stable integration of wearable devices with soft tissues, preserving their performance under substantial mechanical deformations24,25. Their intrinsic conductivity and mechanical strength also position them as promising candidates for applications in human-machine interfaces, artificial tissues, and mechanical sensors with reliable signal transduction26–28. Despite these advantages, the development of high-performance PDCHAs remains limited by two long-standing fundamental challenges: their inhibitory effect on radical polymerization and slow, inadequately controlled oxidative polymerization under standard conditions (e.g., alkaline environments).

From a materials chemistry perspective, direct incorporation of polydopamine (PDA) into polymer networks is straightforward, but its moderate solubility and aggregation tendencies often result in non-uniform dispersion and reduced adhesion performance29,30. An alternative strategy involves homogenously loading dopamine monomers into preformed hydrogels, followed by post-polymerization oxidation31. While this method improves PDA distribution, it lacks spatial and temporal control, limiting its applicability in scenarios demanding rapid adhesion and compatibility with advanced manufacturing techniques. Efforts toward in situ copolymerization of dopamine with other monomers have achieved moderate adhesion strengths (tens of kilopascals)32,33. Despite these improvements, these systems remain limited by prolonged curing times and insufficient bonding strength for practical applications. Grafting dopamine onto polymer backbones followed by oxidative crosslinking provides faster curing34,35; however, these systems typically contain low dopamine content, far below the levels found in natural adhesive proteins (avg. ~10 wt.%). This low content, coupled with the prevalence of characteristic cyclized PDA units, limits adhesion enhancement. Their slow and unsatisfactorily controlled polymerization of catechol residues also reduces compatibility with additive manufacturing.

Recent advances in photochemistry, using ultraviolet, visible, or two-photon light, offer non-contact, spatiotemporal control over dopamine polymerization36–38. While promising, PDA’s broadband light absorption attenuates light penetration, and dopamine’s radical-scavenging behavior continues to impede hydrogel network formation. To overcome these limitations, an ideal photochemical strategy for PDCHA fabrication should meet the following criteria: (i) dopamine must undergo efficient oxidative polymerization while preserving its characteristic structure to enable multiple interactions; (ii) the photochemical system is compatible with conventional hydrogel polymerization mechanisms, enabling in-situ adhesive formation with dopamine content comparable to biological systems; and (iii) the process should be rapid, controllable reactivity suitable for on-demand adhesion and complex architectural fabrication via extrusion or light-based printing. To date, meeting all of these requirements poses a significant challenge for the development of fast, efficient, and broadly applicable photochemical strategies for PDCHA preparation with instant adhesion.

In this work, we present a rapid photocontrollable dopamine polymerization (RPDP) strategy that enables the in-situ formation of printable, high-performance PDCHAs with instant wet adhesion. Central to this approach is the rational design of a photolabile dopamine derivative and a photochemical system that allows for simultaneous deprotection and oxidative polymerization of dopamine while suppressing its inhibitory effects on conventional radical polymerization. This enables one-pot, light-controllable formation of interpenetrated PDA-containing multinetwork adhesives. The resulting tough PDCHAs exhibit rapid, strong, and durable adhesion to a wide range of porous and non-porous substrates, outperforming traditional PDA-coating approaches. Importantly, this RPDP approach is fully compatible with extrusion-based printing techniques, enabling precise fabrication of hierarchical biomimetic architectures. Adhesion performance can be tuned through contact topology, making these materials highly suitable for structured adhesives and flexible electronics. As proof of concept, RPDP-fabricated electroluminescent displays maintain stable light output under repeated and large mechanical deformation. It is anticipated that the RPDP strategy and high-performance PDCHAs have broadly applicable potential in chemistry and materials science, engineering, and flexible electronics.

Results
Design principle of polydopamine-containing instant adhesives
Dopamine is an oxygen- and pH-sensitive molecule that undergoes slow oxidative polymerization under alkaline conditions and in open air environments. In acidic or neutral environments, it can polymerize more rapidly in the presence of strong oxidants, biocatalysts, or via electrochemical and plasma treatments39–42. However, these methods typically rely on specialized equipment, offer limited reaction control, and are often incompatible with conventional hydrogel polymerization conditions. Recent protection strategies43,44, such as catechol-boronate complexation, nitrobenzyl and silyl protection, have been developed to stabilize dopamine during polymer synthesis for the fabrication of polydopamine-containing polymer materials. Yet, these protection/deprotection approaches are often multistep, labor-intensive, and incompatible with one-pot hydrogel formation. Moreover, the synthesis of such protected dopamine derivatives is often limited to small-scale yields and is more expensive than commercially available dopamine. Thus, there is a pressing need to rationally design a low-cost and practical strategy that enables the efficient preparation of high-performance PDCHAs via photochemical methods. As such, the protected dopamine is rationally designed for cheap and tens-of-gram scalable production. The deprotection and oxidative polymerization of dopamine could occur sequentially in a single pot, allowing hydrogel networks to form simultaneously under light irradiation. The process completes within tens of seconds, ensuring uniform PDA dispersion and enabling rapid formation of high-performance PDCHAs.

To this end, the RPDP strategy is rationally developed, which enables both the deprotection of dopamine (DA) derivatives and their subsequent polymerization in a single process. In advance, the key component, a photolabile DA derivative, is synthesized through sequential protection reactions with di-tert-butyl dicarbonate and ethylenediaminetetraacetic dianhydride (Supplementary Figs. 1–5). Upon acid-mediated deprotection of the amine groups, the derivative (ethylenediaminetetraacetic acid-protected dopamine, EDA) is obtained in high yield (>90%) at a scalable amount (~30 g), demonstrating its practicality and cost-effectiveness. As shown in Fig. 1a, the PDCHA precursor is composed of EDA, vinyl monomers, and a catalyst system of ruthenium complex Ru(bpy)3 2+/persulfate. Upon visible light exposure, persulfate decomposes into sulfate radicals that initiate the radical polymerization of vinyl monomers to form the hydrogel matrix with ruthenium-based redox photochemistry45–47. Meanwhile, the ruthenium complex Ru(bpy)3 2+ is oxidized to Ru(bpy)3 3+, which facilitates EDA deprotection and co-initiates DA polymerization with persulfate as the oxidant. As a result, this photochemical process enables simultaneous hydrogel crosslinking and in-situ PDA formation within tens of seconds in a single step. The incorporation of PDA directly within the hydrogel network significantly enhances adhesion performance, enabling instant wet adhesion and robust sealing on both tissue and hydrophobic interfaces, far exceeding the performance of traditional DA-containing hydrogels prepared via post-polymerization coating within the same hydrogel matrix (Fig. 1b–d, and Supplementary Figs. 6, 7). Furthermore, such a rapid and precisely controllable RPDP approach is compatible with extrusion-based 3D printing, allowing the fabrication of complex hydrogel architectures (Fig. 1e). The RPDP process exhibits hallmark characteristics of orthogonality, controllability, and rapid polymerization, yielding PDCHAs with superior adhesion and mechanical performance compared to previous approaches using oxidants such as ClO-, S2O8 2-, and H2O2 (Fig. 1f and Supplementary Fig. 8).

Controllable polymerization mechanism of EDA with ruthenium photochemistry
The chemical mechanism underlying the RPDP strategy is systematically investigated using UV-vis spectroscopy, leveraging the distinct color change associated with PDA formation (Fig. 2a). EDA solutions remain chemically stable under ambient conditions and show no significant color change unless both the catalyst and light irradiation are present (Supplementary Fig. 9). In contrast, DA solutions darken with transmittance sharply dropping to nearly 0% within 4 min only upon catalyst addition, due to the spontaneous polymerization initiated by the oxidative persulfate component (Supplementary Movie 1). This comparison highlights the importance of RPDP in enabling controlled, photochemical deprotection of the ethylenediaminetetraacetic acid group48,49, thereby allowing successful oxidative polymerization of EDA under the same conditions with high conversion efficiency (Fig. 2b and Supplementary Fig. 10). This key deprotection process is further confirmed in the di-tert-butyl decarbonate-protected EDA intermediate, where characteristic peaks of the ethylenediaminetetraacetic acid moiety disappeared after the same deprotection treatment (Supplementary Figs. 11, 12). In contrast, the similar protection group of succinic acid is not photochemically cleaved with the RPDP strategy; protected DA is therefore chemically stable and insensitive to oxidative persulfates (Supplementary Fig. 13). No significant color change is observed even with prolonged irradiation under the same conditions (Supplementary Fig. 14 and inset images in Fig. 2a). Moreover, XPS characterization in Fig. 2c and Supplementary Fig. 15 reveals a higher content of C-O bonds and lower C=O bonds in those synthesized via RPDP compared to those formed under alkaline conditions. This suggests a higher abundance of hydroxyl groups and a more distinct functional PDA structure. In combination with mass spectrometry analysis in Fig. 2d, e, these findings support two primary polymerization pathways for PDA formation via the RPDP strategy: Under light irradiation, both Ru(III) intermediates and persulfates act as strong oxidants in the acidic condition: (i) Ru(III) enables dominantly rapid phenol coupling and dimerization of DA, and (ii) deprotected EDA (now functionally equivalent to DA) undergoes spontaneous oxidative polymerization with persulfates.

Importantly, Fig. 2f and Supplementary Fig. 16 exhibit that this process is broadly pH-tolerant and proceeds efficiently across acidic, neutral, and alkaline pH values, achieving nearly 100% conversion within minutes. The improved phenol deprotonation slightly enhances the reaction rate of EDA (~1.5 times) in alkaline conditions17,50. As shown in Supplementary Figs. 17, 18, increasing EDA contents raises oxidative reaction rates. Meanwhile, increasing the persulfate-to-EDA molar ratio improves the conversion to 100% (Supplementary Figs. 19, 20). This enhancement is attributed to higher persulfate concentrations generating more Ru(III), which accelerates both deprotection and polymerization processes. However, excessive oxidant levels can cause over-oxidation and partial degradation of the PDA product. Notably, Fig. 2g and Supplementary Figs. 21–28 reveal that this RPDP strategy is readily applicable to other typical catechols and their derivatives, which can be similarly protected with ethylenediaminetetraacetic acid and undergo light-triggered polymerization, as confirmed by changes in solution transmittance.

Polymerization process and mechanical properties of PDCHA adhesives
As shown in Fig. 3a, rheology characterization is conducted to assess the sol-gel transition behavior of PDCHAs with RPDP and previously reported strategies. Initially, the precursor appeared as a yellow liquid, which rapidly solidified and darkened upon light exposure, indicating successful radical and oxidative polymerizations via the RPDP strategy. Gelation occurred within ~60 s, as evidenced by the storage modulus surpassing the loss modulus (G‵ ≥ G‵‵). Real-time Fourier-transform infrared spectra in Fig. 3b and Supplementary Figs. 29–31 confirmed the rapid polymerization rates, with radical polymerization, EDA deprotection, and subsequent DA oxidative polymerization each achieving over 95% conversion. Notably, radical polymerization proceeded more rapidly than the EDA-mediated processes, exhibiting a higher exponential rate constant (k=180) compared to the slower deprotection and oxidation steps (k=50 and 80) in fitting curves, thereby establishing a clear temporal separation among the reaction pathways (Fig. 3c and Supplementary Table 1). This sequential progression is critical, as the formation of an initial polymer network must precede extensive DA oxidation to ensure effective gelation and mechanical integrity. In contrast, precursors containing DA or PDA in place of EDA exhibited only visible color changes under light, but negligible modulus increases, indicating that DA oxidation occurred without effective radical polymerization. This inhibition is likely due to DA’s and PDA’s radical-scavenging activity and broad-spectrum light absorption, which reduce photoinitiation efficiency (Supplementary Fig. 32). These findings are corroborated by EPR analysis (Fig. 3d and Supplementary Fig. 33), which revealed significant suppression of radical generation in DA-containing systems, whereas radicals were effectively generated and sustained in EDA-containing formulations, facilitating efficient and controllable polymerization of typical vinyl monomers in PDCHAs (Supplementary Figs. 34, 35). Figure 3e and Supplementary Figs. 36–38 illustrate that this temporal disparity between radical polymerization and DA oxidation also contributes to a significant enhancement in mechanical performance with increasing DA content. At a concentration of 10 wt.%, the adhesives exhibit a maximum tensile stress of ~0.35 MPa at a strain of 850% and a toughness of 1500 kJ m−3.

As shown in Fig. 3f and Supplementary Fig. 39, toughness assessments, including crack propagation, fracture energy and fatigue resistance tests revealed a marked improvement in mechanical performance for PDCHAs prepared via the RPDP strategy: This enhancement is attributed to the in-situ formation of covalently crosslinked polymer matrices and the synergistic contribution of multiple supramolecular interactions with PDA, including electrostatic forces, hydrogen bonding, π-π stacking, cation-π interactions, and hydrophobic associations51–53. These reversible interactions effectively dissipate mechanical energy under stress, enabling PDCHAs to reach a high fracture energy (3.3 kJ m−2) and a fatigue threshold of up to 550 J m−2. In contrast, PDA-coated hydrogels lack sufficient energy-dissipating interactions54–56. Consequently, they exhibit markedly lower fracture energy (2.2 kJ m−2), a reduced fatigue threshold (270 J m−2), rapid crack propagation, and failure at strains below 150%. Furthermore, as illustrated in Fig. 3g, PDCHAs with pre-existing cracks also exhibit excellent cyclic stretchability, maintaining structural integrity through 1000 loading cycles at 50% strain. In comparison, PDA-coated control samples exhibit rapid crack propagation and fail after <300 cycles, exhibiting mechanical behavior similar to that of PDA-free hydrogels (Supplementary Figs. 39, 40). This indicates that post-polymerized PDA contributes minimally to mechanical reinforcement in the PDA-coated samples (Supplementary Fig. 41). Notably, previous studies have shown that high dopamine-to-monomer ratios can lead to hydrogel formation via spontaneous DA oxidation in air, even without light or alkaline conditions, achieving ~80% monomer conversion after 12 h57. However, such hydrogels exhibit ~60% lower mechanical strength and stretchability than those produced via the RPDP strategy (Supplementary Fig. 42). Based on these results, it is anticipated that the RPDP strategy is readily available for designing high-performance PDCHAs that can combine the advantages of the RPDP strategy, PDA features, their hierarchical multiple interactions and networks in diverse areas (Fig. 3h and Supplementary Fig. 43)54.

Adhesion properties of PDCHA adhesives
Figure 4a and Supplementary Fig. 44 illustrate that the rapid and controllable formation of PDCHAs via the RPDP strategy enables instant and strong adhesion to a wide range of substrates, achieving adhesion strengths between 0.1 and 0.4 MPa, approximately times higher than those obtained through conventional PDA-coating methods. The adhesion process is completed within several tens of seconds through a sequence of precursor application, surface contact, and light exposure (Fig. 4b and Supplementary Movie 2). On a 2 cm × 2 cm contact area, the adhesion strength can reach up to 1.2 MPa, sufficient to support a 4 kg load (Supplementary Fig. 45). Raman spectra in Fig. 4c reveal that in the RPDP system, EDA remains mobile before polymerization and adsorbs uniformly onto substrate surfaces. This promotes intimate interfacial contact and alignment, leading to strong adhesion (Fig. 4d). In contrast, free DA undergoes uncontrolled oxidative aggregation, forming disordered PDA structures that weaken interfacial bonding. Atomic force microscopy analysis in Fig. 4c, Supplementary Figs. 46, 47 further support these findings, showing that increasing EDA concentration accelerates PDA film deposition while maintaining low surface roughness. Film thickness increases progressively over time, with surface roughness initially increasing and then stabilizing at ~3.2 nm. By contrast, conventional PDA coatings are significantly thicker, rougher, and more aggregated, with larger average particle sizes, as shown in Fig. 4d and Supplementary Fig. 48. These results highlight the superior uniformity, controllability, and interfacial compatibility of PDA films formed via the RPDP strategy.

Moreover, Fig. 4e, f demonstrates that the RPDP strategy allows liquid precursor to infiltrate porous substrates and polymerize in situ, forming interlocking networks with superior interfacial bonding (Supplementary Fig. 49). On highly porous hydrogel substrates, PDCHAs achieve interfacial toughness values as high as 1300 J m−2. In comparison, PDA-coated hydrogels exhibit limited contact and only one-fourteenth to one-fourth of the toughness of RPDP-derived adhesives. As shown in Figs. 3h and 4g, this synergistic adsorption-polymerization mechanism boosts supramolecular interactions58–60, resulting in substantial increases in interfacial toughness thresholds, for example, from 87 J m−2 to 173 J m−2 and from 98 J m−2 to 469 J m−2 across various interface types (Supplementary Figs. 50, 51). Figure 4h highlights PDCHAs’ potential applications for biomedical use: their rapid adhesion, mechanical resilience, and water resistance enable effective sealing of wounds even under deformation or fluid flow conditions. In contrast, PDA-coated hydrogels are easily detached by washing and mechanical twisting. Furthermore, the introduction of zwitterionic monomers imparts antifreeze properties, allowing PDCHAs to retain strong adhesion over a broad temperature range. Even after storage at −10°C for five days, adhesion remains stable (Supplementary Fig. 52). This monomer also improves water retention: PDCHAs exposed to 30% humidity for 12 h retain ~60% water content and >90% of their initial adhesion strength (Supplementary Fig. 53).

Additive manufacturing and applications of PDCHA adhesives
Figure 5a demonstrates that the rapid and controllable RPDP strategy is well-suited for precise 2D and 3D fabrication using additive manufacturing61,62. Viscous precursors can be extruded through a black syringe and cured at the nozzle tip under blue light, enabling layer-by-layer construction of complex structures. In contrast, traditional PDA precursors with low viscosity lack sufficient shape fidelity due to inadequate polymerization. More importantly, inspired by nature, hierarchical adhesive architectures mimicking the microstructures of gecko feet, octopus suckers, and tree frog pads were designed using the RPDP strategy (Fig. 5b). As shown in Fig. 5c, structured samples have adhesion strengths of >0.1 MPa, and adhesives with ring-shaped patterns outperform flat or stripe-like structures, achieving approximately double the adhesion strength. These biomimetic PDCHAs exhibit rapid, repeatable, and stable adhesion during multiple attachment-detachment cycles (Fig. 5d). Moreover, the adhesive performance of these structures can be further tuned by altering ring geometry (Fig. 5e), demonstrating the versatility of the RPDP method for customized and application-specific designs.

As a proof of concept, this RPDP strategy is employed to fabricate flexible electronic devices with intricate architectures. A multilayer electroluminescent device was fabricated by integrating a ZnS:Cu emission layer with printed PDCHAs (Supplementary Fig. 54). In this device, patterned PDCHAs serve dual functions as adhesives and electrodes. The in-situ formation of PDA ensures strong bonding with the hydrogel matrix and thermoplastic elastomer substrates, resulting in stable conductivity and consistent performance under mechanical deformation (Supplementary Fig. 55). Figure 5f demonstrates that a butterfly-shaped device produced via this method maintained consistent performance during repeated stretching, folding and twisting. Moreover, PDCHA-based devices retained >95% brightness over 1000 deformation cycles, confirming their mechanical resilience and conductivity stability (Fig. 5g and Supplementary Fig. 56). In contrast, devices made with PDA via surface coating exhibit non-uniform PDA distribution and aggregation under strain, leading to weakened adhesion and declining conductivity after prolonged use (e.g., 100 cycles at 50% strain). The devices using PDA-coated electrodes suffer from rapid performance degradation, losing 50% of their brightness after only 400 cycles and nearly failing by 700 cycles under identical test conditions.

Methods
Materials
Dopamine hydrochloride (DA), sulfobetaine methacrylate (SBMA), hydroxyethyl acrylate (HEA), di-tert-butyl dicarbonate, poly(ethylene glycol) diacrylate (PEGDA), ethylenediaminetetraacetic dianhydride, succinic anhydride, tris(2,2′-bipyridyl) dichlororuthenium (II) [Ru(bpy)3 2+], gallic acid, pyrogallol, tyramine, protocatechuic acid, ammonium persulfate, trifluoroacetic acid, triethylamine, anhydrous dimethylformamide, polystyrene-b-polybutadiene-b-polystyrene and other chemicals were chemically pure and purchased from Sigma-Aldrich (St. Louis, USA) and Tansoole (Shanghai, China) Co., Ltd. All other reagents were used as received. Moreover, we obtained informed consent from the research participant and confirmed that the ethics committee waived the requirement for ethics approval.

Synthesis of tert-butyl (3,4-dihydroxyphenyl) carbamate (Boc-protected DA)
Under a nitrogen atmosphere, DA (20.00 g, 0.10 mol) was suspended in 200 mL of dichloromethane. Di-tert-butyl dicarbonate (27.6 mL, 0.12 mol) was then added to the suspension. The reaction mixture was cooled to 0 °C in an ice-water bath, after which a solution of triethylamine (22.0 mL, 0.16 mol) in 15 mL of dichloromethane was added dropwise at a rate of 0.01 mL s−1. The mixture was allowed to warm to room temperature and stirred for 6 h. After completion, the reaction mixture was poured into 200 mL of 1.0 M HCl and extracted. The organic layer was separated, washed with an additional 200 mL of 1.0 M HCl, dried over anhydrous magnesium sulfate, and concentrated by rotary evaporation to give a white Boc-protected DA solid (26.70 g, yield: 95%). 1H-NMR (400 MHz, DMSO-d6): δ 8.73 (s, 1H), 8.63 (s, 1H), 6.80 (t, J=2 Hz, 1H), 6.62 (d, J=4 Hz, 1H), 6.55 (s, 1H), 6.41 (d, J=8 Hz, 1H), 3.04 (q, J=8 Hz, 2H), 2.48 (t, J=8 Hz, 2H), 1.38 (s, 9H); 13C-NMR (100 MHz, DMSO-d6): δ 156.1, 145.5, 144.0, 130.8, 119.7, 116.5, 115.9, 78.0, 42.5, 35.6, 28.8; HRMS (m/z) = [M]+ Calcd for C13H18NO4: 252.1236. Found 252.1238.

Synthesis of Boc- and ethylenediaminetetraacetic acid-protected dopamine (Boc-protected EDA)
Under a nitrogen atmosphere, Boc-protected DA (10.13 g, 40.0 mmol) was dissolved in 25 mL of anhydrous DMF with stirring until a clear solution was obtained. TEA (6.47 g, 64.0 mmol) was then added, and the mixture was stirred for 30 min. Subsequently, ethylenediaminetetraacetic acid dianhydride (4.70 g, 20.0 mmol) was added, and the reaction was heated in a 70 °C water bath for 36 h. After removal of the solvent by rotary evaporation, the crude product was purified by flash chromatography using dichloromethane to afford the target Boc-protected EDA as a white solid (12.61 g, yield: 90%). 1H-NMR (400 MHz, DMSO-d6): δ 8.70 (m, 2H), 6.74 (m, 2H), 6.62 (d, J=4 Hz, 2H), 6.55 (s, 2H), 6.41 (d, J=8 Hz, 2H), 3.94 (s, 4H), 3.65 (s, 4H), 3.01 (t, J=6 Hz, 4H), 2.60 (t, J=8 Hz, 4H), 2.48 (t, J=8 Hz, 4H), 1.38 (s, 18H); 13C-NMR (100 MHz, DMSO-d6): δ 172.5, 170.0, 156.0, 145.5, 144.0, 130.8, 119.7, 116.5, 116.0, 78.0, 54.9, 51.8, 42.5, 42.1, 35.5, 28.8; HRMS (m/z) = [M]+ Calcd for C36H49N4O14: 761.3251. Found 761.3260.

Synthesis of ethylenediaminetetraacetic acid-protected dopamine (EDA) and typical catechols
In an ice/water bath (0~5 °C), Boc-protected EDA (7.63 g, 10.0 mmol) was dissolved in 40 mL of DMF to form a homogeneous solution under magnetic stirring. Trifluoroacetic acid (5.2 mL, 68.0 mmol) was added dropwise, and the reaction mixture was stirred at 0~5 °C for 12 h. The mixture was then transferred to a separatory funnel, and 150 mL of diethyl ether was slowly added to induce precipitation. The resulting precipitate was collected and dried in a vacuum oven at 40 °C for 6 h, affording white EDA solid (5.35 g, yield: >95%). 1H-NMR (400 MHz, DMSO-d6): δ 6.82 (s, 2H), 6.68 (d, J=8 Hz, 2H), 6.61 (s, 2H), 6.47 (d, J=6 Hz, 2H), 4.03 (t, J=4 Hz, 4H), 3.71 (m, 4H), 3.05 (s, 4H), 2.78 (q, J=8 Hz, 4H), 2.66 (t, J=8 Hz, 4H); 13C-NMR (100 MHz, DMSO-d6): δ 168.2, 159.5, 145.8, 144.6, 128.5, 119.8, 116.5, 115.6, 54.7, 41.0, 40.7, 33.0, 32.5; HRMS (m/z) = [M]+ Calcd for C26H33N4O10: 561.2051. Found 561.2058.

Preparation for PDA coatings via the RPDP strategy
EDA was dissolved in 10 mL of deionized water to a final concentration of 4 wt.% (0.4 g, 0.53 mmol). Ammonia persulfate (0.48 g, 2.1 mmol), and Ru(bpy)3 2+ (2.5 mg, 3.3 μmol) were then added to the EDA solution. After that, an aliquot (0.2 mL) of the homogeneous precursor solution was drop-cast onto clean glass slides and irradiated with visible light (λ=452 nm, 50 mW cm−2, distance: 5 cm) for 5 min to induce EDA deprotection and oxidative polymerization. Following irradiation, the coverslip was carefully removed, and the slide was left to dry under ambient conditions (~22 °C) for 12 h to allow solvent evaporation.
For comparison, PDA-coated samples were prepared using unprotected dopamine (4 wt.%, 0.21 M) with persulfate (48 g L−1, 210 mM) as the oxidant. Dopamine and persulfate were dissolved in deionized water and briefly stirred. The precursor solution (0.2 mL) was drop-cast onto clean glass slides and left under ambient conditions (open air, pH ~6.8, ~22 °C) for 12 h, during which oxidative polymerization and solvent evaporation occurred simultaneously.

Preparation of PDCHAs via the RPDP strategy
EDA (0.4 g, 0.53 mmol) was dissolved in 10 mL of deionized water under magnetic stirring. SBMA (2.0 g, 8.0 mmol), HEA (2.0 g, 17.3 mmol), PEGDA (0.7 g, 1.0 mmol), NaCl (0.58 g, 10 mmol), persulfate (0.48 g, 2.1 mmol), and Ru(bpy)3 2+ (2.5 mg, 3.3 μmol) were then sequentially added. The mixture was stirred at room temperature until a clear, homogeneous precursor solution was obtained, followed by brief centrifugation to remove air bubbles. The degassed precursor was poured into a mold or applied to the desired surface and irradiated with blue light (λ=452 nm, 50 mW cm−2, distance: 5 cm) for ~3 min to yield PDCHAs. DA hydrogels were prepared following the same procedure, with EDA replaced by an equivalent amount of DA.
3D printing was carried out using a custom-designed printer at a printing speed of 40 mm min−1, applied pressure of 0.1 MPa, and a nozzle diameter of 200 μm. During printing, precursor solutions were stored in 15 mL dark syringes and extruded onto target substrates in a layer-by-layer manner. Extrusion volume, printing speed, and trajectory were computer controlled. Blue light irradiation was applied during printing to induce photogelation of the PDCHA precursors.

Preparation of PDA-free and coated hydrogels via the conventional coating process
For PDA-free hydrogels, the precursor solution, comprising SBMA (2.0 g, 8.0 mmol), HEA (2.0 g, 17.3 mmol), PEGDA (0.7 g, 1.0 mmol), NaCl (0.58 g, 10 mmol), persulfate (0.48 g, 2.1 mmol), and Ru(bpy)3 2+ (2.5 mg, 3.3 μmol), was stirred until a clear, homogeneous solution was obtained. After degassing, the solution was poured into a mold and irradiated with blue light for 3 min to form PDA-free hydrogels. To prepare PDA-coated hydrogels, a fresh Tris-buffered dopamine solution (5 wt.%, pH 8.5) was manually applied to the surface of the cured PDA-free hydrogels in a predetermined amount, ensuring the final PDA content matched that of the PDCHAs. The hydrogels were then allowed to polymerize for 12 h, followed by air-drying at room temperature to remove excess water, yielding PDA-coated hydrogels.

Adhesion of diverse surfaces
To achieve robust adhesion on both porous and nonporous surfaces, the PDCHA precursor was prepared by homogeneously mixing EDA (0.4 g, 0.53 mmol), SBMA (2.0 g, 8.0 mmol), HEA (2.0 g, 17.3 mmol), PEGDA (0.7 g, 1.0 mmol), NaCl (0.58 g, 10 mmol), persulfate (0.48 g, 2.1 mmol), and Ru(bpy)3 2+ (2.5 mg, 3.3 μmol) in the dark for 20 min at room temperature. The precursor was then cast or painted onto the target substrates. After a predetermined waiting period, the samples were exposed to blue light irradiation, triggering PDCHA formation and strong bonding to diverse surfaces.
For comparison, PDA-coated hydrogels were prepared by first forming PDA-free hydrogels using SBMA (2.0 g, 8.0 mmol), HEA (2.0 g, 17.3 mmol), PEGDA (0.7 g, 1.0 mmol), NaCl (0.58 g, 10 mmol), persulfate (0.48 g, 2.1 mmol), and Ru(bpy)3 2+ (2.5 mg, 3.3 μmol) under blue light irradiation. A freshly prepared Tris-buffered dopamine solution (5 wt.%, pH 8.5) was then manually applied to the surface of the cured PDA-free hydrogels in a controlled amount to match the PDA content of the PDCHAs. The DA-loaded hydrogels were subsequently placed in contact with target substrates for 12 h to enable PDA-mediated adhesion.

Characterizations
The polymerization of vinyl groups and dopamine was monitored using in-situ FT-IR (Bruker, INVENIOR), with scans collected every 10 s at a resolution of 4 cm−1. Ultraviolet spectra were recorded using a UV-Vis spectrophotometer (PRESEE, TU-1810) at a scan rate of 50 mm min−1. The gelation process of hydrogel precursors under blue light was evaluated using a rotational rheometer (Anton Paar MCR302) equipped with optical modules and a 20-mm steel parallel-plate geometry. Measurements were performed at room temperature with 1% strain at 10 Hz, following 1 min of equilibration.
EPR measurements were conducted on a Bruker spectrometer at room temperature, with Ru(bpy)3 2+, persulfate, and EDA dissolved in water and DMPO added; samples were irradiated with light for varying durations before testing. 1H-NMR spectra were acquired on a Bruker 400 MHz instrument at 25 °C. XPS analysis (ULVAC PHI) was performed to characterize polydopamine structure under different conditions, using a monochromatic Al Kα X-ray source (1486.6 eV) at 15 kV and 25 W, with a pass energy of 26 eV for high-resolution scans. TOF-SIMS (IONTOF, TOF-SIMS-5) was used to analyze molecular weight changes during dopamine polymerization.
AFM (Bruker, Dimension Icon) characterized the surface morphology and roughness of polydopamine coatings over areas of 5×5 μm2 or 10×10 μm2, with scan rates of 0.5~1.0 Hz. Raman spectroscopy (Horiba, LabRAM HR Evolution) assessed coating uniformity using a 532 nm laser, with spectra collected over 400~2000 cm−1 and an integration time of 10 s. Optical microscopy (Nikon Eclipse Ni) was used to observe the adhesion effects of PDCHAs.
Electrical conductivity of PDCHAs was measured using a two-probe setup with a digital multimeter (Keithley 6517B), testing three samples per composition. Mechanical properties were evaluated using an MTS Insight 50 tensile tester at 50 mm min−1 at room temperature for samples measuring 8×40×2 mm3. Fracture energy was determined via tearing tests on hydrogels with 2 mm notches, stretched at 50 mm min−1; a humidifier maintained hydration during testing. Fatigue thresholds were assessed through cyclic loading of notched samples at 50 mm min−1, with cyclic strain increased until crack propagation and sample fracture, while maintaining a humid environment.
For shear adhesion tests, PDCHA precursor solutions were applied between surfaces of 25×25×0.1 mm3, affixed to glass slides (2.5×7.5 cm2), and irradiated with visible light (452 nm, 15 mW cm−2) for ~2 min. Adhesive strength was measured by tensile loading at 50 mm min⁻¹ until detachment, recording the ultimate adhesive strength.
Interfacial toughness was measured using a 90° peel test with a mechanical testing machine and a 90° peeling fixture. PDCHAs were bonded onto surfaces, and peeling was performed at a constant speed of 20 mm min−1. Interfacial toughness was calculated by dividing the plateau force (F) by the hydrogel width (W). Control samples were tested using the same procedure, and all tests were repeated for reproducibility.

Data availability
The data that support the findings of this study are available from the corresponding author on request.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Dopamine is a fundamentally important molecule for bioinspired materials, yet the development of polydopamine-based hydrogels has long been hindered by two major challenges over the past decades: (i) the slow and uncontrollable oxidative polymerization process, and (ii) intrinsic inhibitory effects on conventional radical polymerization of vinyl monomers. These barriers have significantly limited progress in designing high-performance polydopamine hydrogel adhesives.\nI am pleased to see that this study effectively addresses these long-standing issues. The authors present an innovative strategy for fabricating dopamine-containing instant adhesives via a well-designed RPDP process, coupled with a visible-light-driven ruthenium photochemical system. The RPDP strategy effectively overcomes the aforementioned limitations by enabling simultaneous dopamine polymerization and hydrogel network formation within seconds. This approach ensures efficient dopamine incorporation and produces hydrogels with strong wet adhesion, interfacial toughness, and mechanical durability. Particularly noteworthy is its full compatibility with extrusion-based 3D printing, broadening potential applications in biomimetic material design, soft electronics, and adhesive chemistry.\nThe manuscript is comprehensive, rigorously validated, and demonstrates both fundamental and applied significance. While dopamine-containing gels have recently attracted considerable attention, much of the work has been incremental. In contrast, this study introduces a genuinely novel concept and achieves a level of performance that represents a major advance. The design is simple yet powerful, addressing a classic problem in dopamine research. In my view, this represents the most significant progress in the field over the past decade and will substantially advance our understanding of dopamine adhesion and the development of biomimetic materials.\nI am happy to recommend publication of this paper in Nature Communications, more-or-less in its current form. Addressing the following points would further enhance clarity and strengthen the manuscript:\n(1) The authors state that under ruthenium photochemistry, EDA undergoes deprotection to release dopamine molecules. A schematic illustration of this deprotection process would help readers better visualize and understand this key mechanism.\n(2) The RPDP strategy is compared with the coating method for preparing polydopamine-containing hydrogels. However, the coating process is not fully described. I suggest that the authors include schematic illustrations of both preparation methods in the Supporting Information to provide readers with a clearer understanding of the differences.\n(3) In Figure S31, the authors compare the RPDP strategy with the direct initiation of monomers using DA. However, the manuscript does not provide data on the differences in adhesion performance between hydrogels prepared by these two methods. Additional experiments quantifying these differences would be valuable.\n(4) In Figure 3, the authors mention that supramolecular interactions exist between dopamine and the polymer network, and the mechanical tests indeed demonstrate a toughening effect. Direct spectroscopic evidence (e.g., FT-IR or related techniques) would help confirm these interactions.\n(5) In Figure 5, the authors state that PDCHAs exhibit stable conductivity and consistent performance under mechanical deformation. However, the manuscript does not provide corresponding experimental data to support this claim. Measurements during repeated stretching, bending, or twisting would substantiate this important claim.", "reviewer_2": "Yu et al. report a simple and general method to achieve rapid and controllable polymerization of dopamine through the rational design of a photolabile dopamine derivative in combination with ruthenium photochemistry. This photochemical strategy not only enables fast dopamine polymerization but also mitigates its inhibitory effects on conventional radical polymerization of vinyl monomers, thereby allowing instant wet adhesion. Furthermore, the approach is compatible with extrusion-based 3D printing, enabling performance modulation through structural design. The experiments are carefully conducted, the data are systematically discussed, and the results convincingly support the authors’ claims. I believe this work addresses critical bottlenecks in polydopamine and polyphenol research and provides valuable insights into wet adhesion and related applications. In my view, the novelty and significance of this study meet the high standards of Nature Communications, and therefore, I recommend publication after the authors address the following minor issues:\n1. The authors claim that the dopamine polymerization process is controllable, as shown in Fig. 2a. I suggest the authors to really demonstrate the control of the reaction under varied conditions. In addition, it remains unclear whether such controllability extends to the preparation of polydopamine-containing PDCHA hydrogels. Although Fig. 3a demonstrates rapid gelation using the RPDP strategy. There is no direct evidence of controllability. I suggest performing real-time rheological measurements to monitor storage modulus changes under intermittent irradiation.\n2. The deprotection of EDA is a critical step for achieving both controllable dopamine polymerization and compatibility with radical polymerization. In Fig. 2b, the authors use SDA as a control to demonstrate the deprotection or degradation of the ethylenediaminetetraacetic acid residue under the same ruthenium photochemistry. Stronger evidence or additional literature support should be provided to substantiate this conclusion.\n3. Fig. 3a shows a gelation time of ~50 s for the PDCHA precursor, whereas the gelation times reported in Fig. S25 is closer to 2 min. This discrepancy needs clarification. The authors should carefully re-examine the experimental conditions and provide an explanation for the apparent conflict.\n4. The authors introduce the coating method as a control approach for preparing polydopamine-containing adhesives. However, the description of this process is insufficient. Please clarify the specific steps of the coating approach and explain whether it differs from the commonly used immersion process.\n5. In Fig. S28, the effects of various components on the mechanical properties of PDCHAs are investigated. However, the addition of salts such as LiCl, NaCl, and KCl appears to provide no significant improvement in maximum stress compared to salt-free samples. The authors should discuss this result and provide possible explanations.\n6. In Fig. S39, the authors aim to evaluate specific interactions between PDCHAs and surfaces (e.g., electrostatic, pi-pi, cation-pi, and metal chelation). However, the methodology for measuring these interactions in the adhesion process is not clearly described. Additional experimental details are needed to help readers understand how these specific interactions were assessed.", "reviewer_3": "The authors synthesized photolabile dopamine derivatives and demonstrated the instant adhesion. The demonstrations are beautiful but I have several concerns as below. The authors claim in this manuscript that “These results demonstrate that RPDP is a simple, cost-effective, and general method for the controlled polymerization of various polyphenols, offering promising applications in the fabrication of polyphenol-containing materials.” However, these are not fully validated by the experiments. For example, although the curing process is actually a simple one-step, the synthetic procedures are not so simple. Furthermore, the synthetic procedure looks not so cost-effective and Ruthenium is used in the adhesive formulation. It is also too early to conclude that this is general method by just applying to four phenolics shown in Figure 2g. Further detail investigation is necessary. I recommend to resubmit to a more specialized journal.\n(1) In Figure 1a, it is written “1.2 USD/g”. The detail of this cost estimation should be described.\n(2) In the section of “Synthesis of Boc-protected EDA” in SI, the authors wrote “After rotary evaporation and chromatography, 12.61 g (yield: 90%) of the target Boc-protected EDA product was obtained.” The condition of chromatography is missing.\n(3) The NMR spectra provided in Figure S2 and S3 look identical while the compounds are different (Boc-protected EDA and EDA).\n(4) How the authors identified which -OH is esterified among the two -OHs in the catechol group? The “d,e,f” peaks in Figures S2 must be carefully assigned. Also the peak of OH group should be directly checked by using DMSO-d6 (instead of D2O) as a solvent.\n(5) The results of mass spectroscopy should be provided for Boc-protected DA, Boc-protected EDA, EDA, and ethylenediaminetetraacetic acid-protected pyrogallol (and the other three phenolics shown in Figure 2g)."}, "author_response": "Response to Reviewer #1:\nDopamine is a fundamentally important molecule for bioinspired materials, yet the\ndevelopment of polydopamine-based hydrogels has long been hindered by two major\nchallenges over the past decades: (i) the slow and uncontrollable oxidative polymerization\nprocess, and (ii) intrinsic inhibitory effects on conventional radical polymerization of vinyl\nmonomers. These barriers have significantly limited progress in designing high-performance\npolydopamine hydrogel adhesives.\nI am pleased to see that this study effectively addresses these long-standing issues. The\nauthors present an innovative strategy for fabricating dopamine-containing instant adhesives\nvia a well-designed RPDP process, coupled with a visible-light-driven ruthenium\nphotochemical system. The RPDP strategy effectively overcomes the aforementioned\nlimitations by enabling simultaneous dopamine polymerization and hydrogel network\nformation within seconds. This approach ensures efficient dopamine incorporation and\nproduces hydrogels with strong wet adhesion, interfacial toughness, and mechanical durability.\nParticularly noteworthy is its full compatibility with extrusion-based 3D printing, broadening\npotential applications in biomimetic material design, soft electronics, and adhesive chemistry.\nThe manuscript is comprehensive, rigorously validated, and demonstrates both fundamental\nand applied significance. While dopamine-containing gels have recently attracted considerable\nattention, much of the work has been incremental. In contrast, this study introduces a genuinely\nnovel concept and achieves a level of performance that represents a major advance. The design\nis simple yet powerful, addressing a classic problem in dopamine research. In my view, this\nrepresents the most significant progress in the field over the past decade and will substantially\nadvance our understanding of dopamine adhesion and the development of biomimetic materials.\nI am happy to recommend publication of this paper in Nature Communications, more-or-less\nin its current form. Addressing the following points would further enhance clarity and\nstrengthen the manuscript.\nA: Thanks for your positive comments. We have revised the Manuscript according to your\nsuggestions and hope that it, in its current state, can meet the high standard of Nature\nCommunications.\nQ1. The authors state that under ruthenium photochemistry, EDA undergoes deprotection to\nrelease dopamine molecules. A schematic illustration of this deprotection process would help\nreaders better visualize and understand this key mechanism.\nA: Thank you for your helpful comments. We have added the proposed deprotection process of\nEDA catalyzed by ruthenium photochemistry. We believe this new illustration will help readers\nclearly understand the key photochemical mechanism underlying the controllable\npolymerization of dopamine in this study. Please see the updated Figure S10 in the revised\nSupplementary Information.\nQ2. The RPDP strategy is compared with the coating method for preparing polydopamine-\ncontaining hydrogels. However, the coating process is not fully described. I suggest that the\nauthors include schematic illustrations of both preparation methods in the Supporting\nInformation to provide readers with a clearer understanding of the differences.\nA: We are sorry for the unclear description regarding the preparation of the two types of\npolydopamine-containing hydrogels. We also recognize that these details are critical for\nreproducing the RPDP strategy and for appreciating the key novelty of this study. To address\nthis, we have added a schematic illustration of the adhesion processes for both the RPDP and\ncoating strategies, which will help readers clearly understand the differences between these two\ntypical approaches. In addition, we have demonstrated a similar process for the preparation of\nbulk polydopamine-containing hydrogels. Please see the updated Figures S6 and S7 in the\nrevised Supplementary Information.\n(i) The schematic illustration of adhesion processes (Figure S6).\n(ii) The schematic illustration of preparing bulk hydrogels (Figure S7).\nQ3. In Figure S31, the authors compare the RPDP strategy with the direct initiation of\nmonomers using DA. However, the manuscript does not provide data on the differences in\nadhesion performance between hydrogels prepared by these two methods. Additional\nexperiments quantifying these differences would be valuable.\nA: Thank you for your helpful suggestion. We have conducted additional experiments to\ncompare the adhesion performance of these two types of hydrogel adhesives. The results\nindicate that DA-initiated hydrogels exhibit poor mechanical properties, which consequently\nlead to weaker adhesion strength compared to PDCHAs. These findings have been included in\nthe updated Figure S39. Please see the revised Supplementary Information for the related\ncontents.\nQ4. In Figure 3, the authors mention that supramolecular interactions exist between dopamine\nand the polymer network, and the mechanical tests indeed demonstrate a toughening effect.\nDirect spectroscopic evidence (e.g., FT-IR or related techniques) would help confirm these\ninteractions.\nA: Thank you for your kind comments. We have performed in-situ FT-IR characterization of\nthe two types of hydrogel samples prepared by different methods under varied temperatures.\nThe stretching vibration of N-H (3200~3400 cm-1) gradually shifted to higher wavenumbers\n(blue shift) as the temperature increased from 30 to 90 oC, indicating that hydrogen bonds\ninvolving dopamine weaken at elevated temperatures (Figures a and b). In addition, the\ncharacteristic peaks corresponding to the aromatic C=C skeleton vibration (~1660 cm-1) and\nthe S=O stretching vibrations of sulfonate groups (~1180 and 1050 cm-1) also showed distinct\ntemperature-dependent shifts and intensity variations.\nThese reversible changes provide strong evidence for hydrogen bonding and electrostatic\ninteractions between dopamine moieties and SBMA units within the polymer network. By\ncontrast, such supramolecular interactions are absent in the coating-mediated hydrogels, where\nno significant spectral changes were observed under the same heating conditions (Figures c and\nd). Please see the updated Figure S38 in the revised Supplementary Information.\nQ5. In Figure 5, the authors state that PDCHAs exhibit stable conductivity and consistent\nperformance under mechanical deformation. However, the manuscript does not provide\ncorresponding experimental data to support this claim. Measurements during repeated\nstretching, bending, or twisting would substantiate this important claim.\nA: We have evaluated the conductive responsiveness and stability of PDCHAs under different\nmechanical deformations, according to your valuable suggestion. As shown in the updated\nfigure, PDCHAs exhibit high responsiveness under both small and large strains, as well as\nduring finger-bending tests. Moreover, the adhesive maintains excellent stability even after\nmore than 1000 cycles of repeated stretching. Please see the updated Figure S54 and related\ncontent in the revised Supplementary Information.\nResponse to Reviewer #2:\nYu et al. report a simple and general method to achieve rapid and controllable polymerization\nof dopamine through the rational design of a photolabile dopamine derivative in combination\nwith ruthenium photochemistry. This photochemical strategy not only enables fast dopamine\npolymerization but also mitigates its inhibitory effects on conventional radical polymerization\nof vinyl monomers, thereby allowing instant wet adhesion. Furthermore, the approach is\ncompatible with extrusion-based 3D printing, enabling performance modulation through\nstructural design. The experiments are carefully conducted, the data are systematically\ndiscussed, and the results convincingly support the authors’ claims. I believe this work\naddresses critical bottlenecks in polydopamine and polyphenol research and provides valuable\ninsights into wet adhesion and related applications. In my view, the novelty and significance of\nthis study meet the high standards of Nature Communications, and therefore, I recommend\npublication after the authors address the following minor issues:\nA: Thanks for your positive comments. We have revised the Manuscript according to your\nsuggestions and hope that it, in its current state, can meet the high standard of Nature\nCommunications.\nQ6. The authors claim that the dopamine polymerization process is controllable, as shown in\nFig. 2a. I suggest the authors to really demonstrate the control of the reaction under varied\nconditions.\nA: Thanks for your kind comments. We have characterized the UV-Vis spectra changes of the\nreaction under various conditions, including standard conditions as well as conditions without\nruthenium and persulfate. As shown in the figure below, without light irradiation, the\nabsorbance remains constant across all samples. However, under light irradiation, only the\nsample under standard conditions shows changes in absorption. This comparison clearly\ndemonstrates that both light irradiation and the catalyst are essential for controlling the\ndopamine polymerization process. Please refer to the updated Figure S9 in the revised\nSupporting Information.\nQ7. In addition, it remains unclear whether such controllability extends to the preparation of\npolydopamine-containing PDCHA hydrogels. Although Fig. 3a demonstrates rapid gelation\nusing the RPDP strategy, there is no direct evidence of controllability. I suggest performing\nreal-time rheological measurements to monitor storage modulus changes under intermittent\nirradiation.\nA: Thanks for your kind comments. We have evaluated the controllability of PDCHA\npreparation via rheological characterization under intermittent irradiation. As shown in the\nfollowing Figure, this result indicates that both storage and loss moduli increase during\nirradiation but remain constant in the dark. This trend is consistent with the UV–vis results in\nFig. 2a, further confirming the excellent controllability enabled by ruthenium photochemistry.\nPlease see the updated Figure S31 in the revised Supplementary Information.\nQ8. The deprotection of EDA is a critical step for achieving both controllable dopamine\npolymerization and compatibility with radical polymerization. In Fig. 2b, the authors use SDA\nas a control to demonstrate the deprotection or degradation of the ethylenediaminetetraacetic\nacid residue under the same ruthenium photochemistry. Stronger evidence or additional\nliterature support should be provided to substantiate this conclusion.\nA: Thanks for your comments. The photodegradation of ethylenediaminetetraacetic acid under\nredox-active ruthenium photochemistry has been independently identified by Prof. Itamar\nWiller (Nature, 1979, 280, 823) and our group (Nat. Commun., 2020, 11, 4694). Furthermore,\nDaniel E. Falvey and co-workers have demonstrated similar photochemical degradation using\nriboflavin as a sensitizer (Photochem. Photobiol. Sci., 2017, 16, 1003). We have added relevant\nreferences and a schematic illustration to help readers understand this process. Please see the\nupdated Ref. 49 and Figure S10 in the revised Supplementary Information.\nQ9. Fig. 3a shows a gelation time of ~50 s for the PDCHA precursor, whereas the gelation times\nreported in Fig. S25 are closer to 2 min. This discrepancy needs clarification. The authors\nshould carefully re-examine the experimental conditions and provide an explanation for the\napparent conflict.\nA: We have carefully re-examined the discrepancy between these results according to your\nhelpful comments. We have removed the equilibration time on the rheological Peltier boards\nfrom the characterization process. Only the time corresponding to the photochemical process is\nnow shown in these Figures, and the gelation times are approximately 50 s, which are consistent\nwith the value presented in Figure 3a. Please see the updated Figure S32 in the revised\nSupplementary Information.\nQ10. The authors introduce the coating method as a control approach for preparing\npolydopamine-containing adhesives. However, the description of this process is insufficient.\nPlease clarify the specific steps of the coating approach and explain whether it differs from the\ncommonly used immersion process.\nA: We apologize for the earlier lack of clarity regarding the preparation of the two types of\npolydopamine-containing hydrogels. We also recognize that these details are critical for\nreproducing the RPDP strategy and for appreciating the key novelty of this study. To address\nthis, we have added a schematic illustration of the adhesion processes for both the RPDP and\ncoating strategies, which will help readers clearly understand the differences between these two\ntypical approaches.\nFurthermore, as shown in the updated illustration, compared with the conventional\nimmersion process, the coating method enables more precise loading of the polydopamine\ncomponent into the adhesives and significantly reduces the influence of content variations\non their comparison. Please see the updated Figures S6 and S7 in the revised Supplementary\nInformation. In addition, we have demonstrated a similar process for the preparation of bulk\npolydopamine-containing hydrogels.\n(i) The schematic illustration of adhesion processes (Figure S6).\n(ii) The schematic illustration of preparing bulk hydrogels (Figure S7).\nQ11. In Fig. S28, the effects of various components on the mechanical properties of PDCHAs\nare investigated. However, the addition of salts such as LiCl, NaCl, and KCl appears to provide\nno significant improvement in maximum stress compared to salt-free samples. The authors\nshould discuss this result and provide possible explanations.\nA: Thanks for your helpful comments. In this study, as sulfobetaine methacrylate (SBMA) is\nthe matrix of PDCHAs, the solubility and configuration of SBMA-based polymers strongly\ndepend on the ionic environment. Thus, salts must be considered in optimizing mechanical and\nadhesion properties.\nIn the updated Figure, we show that although maximum stress remains similar, the critical strain\nincreases from ~200% to ~400% upon adding NaCl. The further tests demonstrate that\nincreasing NaCl concentration (0.1~1.0 mol L-1) significantly improves both mechanical and\nadhesion performance. Please see the updated Figure S35 and related content in the revised\nManuscript and Supplementary Information.\nQ12. In Fig. S39, the authors aim to evaluate specific interactions between PDCHAs and\nsurfaces (e.g., electrostatic, π-π, cation-π, and metal chelation). However, the methodology for\nmeasuring these interactions in the adhesion process is not clearly described. Additional\nexperimental details are needed to help readers understand how these specific interactions were\nassessed.\nA: To evaluate the specific interactions, glass substrates were chemically modified with the\ncorresponding silanes by immersion in 1 wt.% ethanol solutions for 12 h, followed by rinsing\nwith ethanol and water, and drying in air. The silanes used were N-[3-\n(trimethoxysilyl)propyl]ethylenediamine, 2-(carboxymethylthio)ethyltrimethylsilane,\nphenyltriethoxysilane, and N-trimethoxysilylpropyl-N, N, N-trimethylammonium chloride,\nwhich were employed to construct electrostatic, π-π, and cation-π interactions, respectively. In\naddition, iron sheets were used to evaluate metal chelation interactions. The detailed procedures\nhave been added to the caption of the updated Figure S47. Please see the related content in the\nrevised Supplementary Information.\nResponse to Reviewer #3:\nThe authors synthesized photolabile dopamine derivatives and demonstrated the instant\nadhesion. The demonstrations are beautiful but I have several concerns as below.\nA: Thanks for your positive comments. We have revised the Manuscript according to your\nsuggestions and hope that it, in its current state, can meet the high standard of Nature\nCommunications.\nQ13. The authors claim in this manuscript that “These results demonstrate that RPDP is a\nsimple, cost-effective, and general method for the controlled polymerization of various\npolyphenols, offering promising applications in the fabrication of polyphenol-containing\nmaterials.” However, these are not fully validated by the experiments.\nA: Thank you for your valuable comments. We recognize that our original claim may mislead\nreaders and obscure the novelty and main contributions of this study. Accordingly, we have\ndeleted this description from the Manuscript (Please see Page 13, Paragraph 2).\nIn addition, we performed further characterizations and experiments on both the intermediate\nand final products, as you and other referees suggested, and incorporated the related discussions\ninto the revised Manuscript and Supplementary Information. We believe these improvements\nenhance the clarity of the study and align with the high standards of Nature Communications.\nPlease see our detailed responses, particularly Q14-Q21, and the corresponding revisions in the\nManuscript and Supplementary Information.\nQ14. For example, although the curing process is actually a simple one-step, the synthetic\nprocedures are not so simple.\nA: Thanks for your helpful comments. For the synthesis of EDA, three key steps are involved:\n(i) protection of the amine and phenol groups using di-tert-butyl dicarbonate and\nethylenediaminetetraacetic dianhydride, and (ii) deprotection of di-tert-butyl dicarbonate.\nThese reactions are well-established and widely applied for efficient group protection in organic\nand dopamine chemistry (Greene’s Protective Groups in Organic Synthesis, 5th Edition; J.\nAm. Chem. Soc. 126, 15030). Although three steps are required, the procedure is\nstraightforward, and both intermediate and final products can be easily separated and purified,\nleading to high overall efficiency and scalability.\nMoreover, several representative studies have proposed strategies to protect dopamine, such as\nemploying nitrobenzyl or silyl groups, followed by polymerization with functional components\nto obtain dopamine-based polymers (Angew. Chem. Int. Ed. 61, e202113929; Nat. Mater. 13,\n867-872). However, these approaches require a deprotection step after polymerization. In\ncontrast, the method developed in this study can be carried out under mild, standard conditions\nwithout the need for stringent environmental controls. Furthermore, the deprotection step\nproceeds during the polymerization process and is fully compatible with one-step polymer and\nadhesive preparation.\nTaken together, these advantages highlight that our proposed RPDP strategy offers an efficient\nand practical method for synthesizing dopamine derivatives, which can be easily deprotected\nand are well-suited for preparing high-performance polydopamine adhesives.\nAdditionally, we have carefully revised the Manuscript and replaced terms such as “simple”\nand “general” with more appropriate alternatives according to your valuable comments. We\nbelieve these revisions provide a clearer and more accurate description of the RPDP strategy\nand PDCHA adhesives.\nQ15. Furthermore, the synthetic procedure looks not so cost-effective and Ruthenium is used\nin the adhesive formulation.\nA: Thanks for your valuable comments. As described in the Materials Section, all chemicals\nare commercially available from Sigma-Aldrich (St. Louis, USA) and Tansoole (Shanghai,\nChina) Co., Ltd. For the synthesis of EDA, two key reagents are used: dopamine hydrochloride\n(0.58 USD/g) and ethylenediaminetetraacetic dianhydride (0.4 USD/g). Other solvents and\nreagents, including dimethylformamide, dichloromethane, triethylamine, trifluoroacetic acid,\nand di-tert-butyl dicarbonate, are inexpensive and commonly used. Considering the high\nsynthetic efficiency, the overall procedure is cost-effective and can be completed in three steps\nwith excellent yield.\nMoreover, the ruthenium complex, a well-established and highly efficient photocatalyst, is\nemployed in this study. Although its unit price is relatively higher than that of other commercial\nchemicals (16 USD/g from Tansoole, Shanghai, China), its high catalytic activity allows it to\nbe used at very low concentrations (~0.33 mM). Under these conditions, the estimated cost is\nabout 2.5 USD/L of PDCHA precursor solution, which is comparable to the cost of\ncommercially available ethanol (analytically pure grade). Therefore, despite the relatively high\nprice of the ruthenium complex, the actual cost contribution in this work remains low.\nQ16. It is also too early to conclude that this is general method by just applying to four phenolics\nshown in Figure 2g. Further detail investigation is necessary. I recommend to resubmit to a\nmore specialized journal.\nA: Thank you for your helpful comments. (i) We have deleted the previous conclusion in the\nrevised Manuscript to avoid any potential confusion and to better guide the readers in\nunderstanding the main content of this study (Please see Page 13, Paragraph 2). Additionally,\nwe have performed more detailed investigations as per the referees’ suggestions, and the\ncorresponding results have been incorporated into both the updated Manuscript and\nSupplementary Information. We believe these revisions improve the quality of the Manuscript\nand provide a clearer description of the RPDP strategy and PDCHA adhesives.\nDopamine, gallic acid, pyrogallol, tyramine, and protocatechuic acid are representative\nphenolic derivatives commonly used for preparing polyphenol-containing adhesives (Adv.\nFunct. Mater., 31, 2008821; Prog. Polym. Sci., 82, 34-91). These four molecules are therefore\nused in this study to demonstrate the feasibility of the proposed RPDP strategy. We fully agree\nwith your suggestion to explore additional phenolic derivatives. Moving forward, we plan to\nemploy and synthesize a broader range of phenolic derivatives to further demonstrate the\ngenerality of the RPDP strategy and expand its applications beyond adhesive preparation.\n(ii) Moreover, in this study, our goal is to rationally develop a strategy to address two long-\nstanding challenges in polydopamine and other polyphenol-based adhesives: the slow and\nuncontrollable oxidative polymerization process, and the intrinsic inhibitory effects on\nconventional radical polymerization of vinyl monomers. These barriers have significantly\nlimited progress in designing high-performance polydopamine hydrogel adhesives.\nTo overcome these issues, we present an RPDP strategy for fabricating dopamine-containing\ninstant adhesives via a photolabile dopamine derivative design, combined with a visible-light-\ndriven ruthenium photochemical system. The results demonstrate that the proposed RPDP\nstrategy effectively addresses the above challenges by enabling simultaneous dopamine\npolymerization and hydrogel network formation within seconds. This ensures efficient\ndopamine incorporation and yields hydrogels with strong wet adhesion, interfacial toughness,\nand mechanical durability. Importantly, the method is fully compatible with extrusion-based 3D\nprinting, thereby broadening potential applications in biomimetic material design, soft\nelectronics, and adhesive chemistry.\nCompared with existing approaches, this ethylenediaminetetraacetic acid-based protection\nmethod relies on the efficient esterification between phenol groups and anhydride compounds.\nThe subsequent deprotection is efficiently triggered by ruthenium photochemistry, suggesting\nthat this approach can be broadly extended to other catechols and polyphenolic systems for\nrapid material development. Furthermore, the RPDP strategy significantly mitigates\ndopamine’s inhibitory effect on radical polymerization, enabling seamless integration not only\nwith free-radical polymerization but also with diverse methodologies such as cationic\npolymerization, reversible transfer radical polymerization, and radical-based click chemistry.\nThis versatility provides a foundation for designing advanced PDA-based materials with finely\ntailored properties.\nIn addition, the rapid and controllable photochemistry of RPDP is highly compatible with\nstandard extrusion-based printing techniques, making it feasible to construct complex device\narchitectures using established additive manufacturing technologies (e.g., stereolithography,\nlaminated object manufacturing). Finally, the blue-light-mediated process and the hydrogel\ncomponents are nontoxic and biocompatible, rendering PDCHAs suitable not only for\nelectronic adhesives but also for biomedical applications such as multifunctional tissue tapes\nand photothermal platforms leveraging the intrinsic properties of PDAs.\nBased on these revisions and clarifications, we believe that the Manuscript now more clearly\nconveys the novelty, significance, and broad applicability of the RPDP strategy and that it meets\nthe high standards of Nature Communications.\nQ17. In Figure 1a, it is written “1.2 USD/g. The detail of this cost estimation should be\ndescribed.\nA: In summary, the cost of EDA synthesis is estimated based on the commercial prices of\ndopamine hydrochloride (0.58 USD/g) and ethylenediaminetetraacetic dianhydride (0.4\nUSD/g), both sourced from Tansoole (Shanghai, China) Co., Ltd. The synthesis efficiency is\nalso considered in the estimation. The cost of EDA is approximately twice that of dopamine\nhydrochloride. This estimation has been incorporated into the caption in response to your\nvaluable suggestions. Please refer to the updated caption in Figure 1a of the revised Manuscript.\nQ18. In the section of “Synthesis of Boc-protected EDA” in SI, the authors wrote “After\nrotary evaporation and chromatography, 12.61 g (yield: 90%) of the target Boc-protected EDA\nproduct was obtained.” The condition of chromatography is missing.\nA: Thanks for your kind comments. In this experiment, flash chromatography with\ndichloromethane is used to purify the Boc-protected EDA product. We have revised the\ndescription of the Boc-protected EDA purification procedure, and the details have been added\nto the Experimental Section. Please see the related content in the revised Manuscript (Page 26,\nParagraph 1).\nQ19. The NMR spectra provided in Figure S2 and S3 look identical while the compounds are\ndifferent (Boc-protected EDA and EDA).\nA: We are very sorry for this mistake, as the same figures were inadvertently provided in\nFigures S2 and S3. We have corrected this fault according to your helpful comments. Please see\nthe updated Figures S3 and S4 in the revised Supporting Information.\nThe NMR spectrum of Boc-protected EDA (Figure S3).\nThe NMR spectrum of EDA (Figure S4).\nQ20. How the authors identified which -OH is esterified among the two -OHs in the catechol\ngroup? The “d,e,f” peaks in Figures S2 must be carefully assigned. Also the peak of OH group\nshould be directly checked by using DMSO-d6 (instead of D2O) as a solvent.\nA: Thanks for your helpful comments. (i) We have carefully reassigned all peaks of Boc-\nprotected EDA, with particular attention to the d, e, and f peaks. Please see the updated Figure\nS3 in the revised Supplementary Information.\nAlso, the OH groups in these materials were examined according to your suggestion. As shown\nin the 1H NMR spectra in Figures S3 and S4, characteristic peaks corresponding to OH groups\nwere observed when DMSO-d was used instead of D O. Moreover, the characteristic OH peaks\n6 2\nin the 1H NMR spectra (Figure S3) indicate that the two OH groups exhibit comparable\nchemical reactivity toward ethylenediaminetetraacetic dianhydride, leading to the formation of\nthree Boc-protected EDA derivatives with similar chemical structures (as shown in Figure S2).\nConsequently, it remains challenging to unambiguously determine which specific OH group is\nmodified in these materials. Please refer to the updated Figures S1-S4 in the revised\nSupplementary Information.\nThe proposed three Boc-protected EDA derivatives (Figure S2).\n(ii) Moreover, as shown in the following Figure, although the precise modification process of\nOH groups has not been fully elucidated, it is reasonably predicted that the deprotection process\nis identical. Both OH groups in polydopamine contribute similarly to adhesion and other\nproperties, thereby enabling controllable dopamine polymerization and facilitating instant wet\nadhesion.\nNevertheless, we fully agree with your valuable comment that identifying specific OH\nmodification is crucial for exploring the potential functions of dopamine derivatives. In future\nwork, we plan to design more specialized model structures to gain deeper insights into the\nmodification process, for example, by employing theoretical calculations to evaluate phenolic\nderivatives with different functional substituents and to investigate how the modification\nposition of OH groups influences their subsequent photodegradation and polymerization\nbehaviors.\nQ21. The results of mass spectroscopy should be provided for Boc-protected DA, Boc-\nprotected EDA, EDA, and ethylenediaminetetraacetic acid-protected pyrogallol (and the other\nthree phenolics shown in Figure 2g).\nA: Thanks for your kind suggestions. We have performed the mass spectroscopy\ncharacterization of these molecules and added the corresponding spectra in the updated Figures.\nThese results can provide more structural information about these molecules and help readers\ndeeply understand the novelty of this study. Please see the updated Figures S5 and S23 in the\nrevised Supplementary Information.\n(i) The mass spectra of protected dopamine derivatives (Figure S5).\n(ii) The mass spectra of ethylenediaminetetraacetic acid-protected typical polyphenols\n(Figure S23)."}, {"round": 2, "reviewer_comments": {"reviewer_1": "[Note from the Editor: Reviewer #1 was asked to assess also the response given to comment 4 of reviewer #3 who was not\navailable to review the revised manuscript.]\nThe review comments of mine and reviewer #3 have all been well addressed, including the pt 4 on how to identify which -\nOH is esterified among the two -OHs in the catechol group. Overall, this research tackles an important problem (traditional\ndopamine (DA)inhibiting radical polymerization for obtaining DA-based composites) with a novel and effective method,\nshowing great performance. The manuscript is in a good shape now and recommended for publication on Nature\nCommunications.", "reviewer_2": "My comments have been considered carefully by the authors. I am satisfied with their response and corresponding revisions.\nI fully support the acceptance of this manuscript in its current form."}, "author_response": ""}]

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