Autonomous self-healing and damage monitoring in protective coatings are of great significance for marine energy devices, ocean-going vessels, and offshore engineering equipment. However, realizing multimodal damage sensing and real-time monitoring of healing dynamics still faces considerable challenges, which arise from the unpredictable nature of microdamage initiation and dynamic property of interfacial healing. Herein, a supramolecular self-healing coating with multimodal damage sensing capability is designed by integrating a conductive polymer layer with a polyurethane (PU) substrate, which enables efficient self-healing and sensitive dynamic electrical signal monitoring. By rationally regulating the PEDOT:PSS conductive network and supramolecular structure, the microfailure information on coating damage (wear, impact, crack) and interfacial healing dynamic behaviors can be converted and amplified into easily detectable electrical signals, enabling the real-time and dynamic monitoring of interfacial evolution behavior, capable of sensing cracks as small as 0.33 mu m in width. Based on multiple hydrogen bonds and dynamic disulfide bonds in the polyurethane (PU) matrix, the smart coating possessed superior self-healing efficiency (93%), high tensile strength (41.49 MPa), and a relatively high impedance value (1.66 & times; 1010 Omega & centerdot;cm2). Therefore, this smart coating system not only possesses damage-healing capabilities and anticorrosion performance but also breaks through the technical limitations of traditional coatings that cannot dynamically track interface failures, providing a material solution with application potential for coating health monitoring and life prediction in marine environment.

Hydrogel-based flexible wearable devices and physiological electrodes have garnered increasing attention owing to their biocompatibility and comfort. However, accurate sensitivity for tiny deformation and low electrical conductivity are still limitations for ideal hydrogel sensors and electrodes. In this work, a multifunctional conductive polyelectrolyte hydrogel was prepared with cationic monomer 3- (methacryloylamino) propyl-trimethylammonium chloride, at the same time, polyphenolic compound tannic acid and glycerol were introduced to the hydrogel network to enhance the adhesion performance and environmental tolerance. The polyelectrolyte hydrogel showed low hysteresis (below 10%), good self-adhesion (∼50 kPa), excellent biocompatibility and antibacterial activity, satisfactory conductivity (8.5 mS m-1), long-term stability (∼10 000 repeated cycles), wide strain sensing range (0.1%-100%), and accurate sensitivity even for human pulse monitoring. A flexible wearable device was designed for real-time monitoring of multiple movements and outdoor sports. In addition, a reusable self-adhesive electrode was designed based on the polyelectrolyte hydrogel for physiological signal monitoring, including electroencephalogram (EEG), electrocardiogram (ECG), and electromyogram (EMG). The electrode exhibited a superior signal-to-noise ratio, long-term stability, and sensitivity compared to traditional commercial electrodes. This study provides a promising material platform for long-term stable and accurate signal monitoring in flexible wearable electronics.

The equilibrium shear modulus of some swollen polymer networks decreases with increasing temperature, even when the corresponding dry network shows the classical positive temperature coefficient of entropic elasticity. This sign reversal cannot be explained by the conventional Frenkel-Flory-Rehner framework, in which the mixing free energy is assumed independent of deformation. We show that allowing the Flory-Huggins parameter χ to depend on isochoric strain invariants, a thermodynamically general but previously unexplored possibility, resolves this inconsistency. Within continuum thermodynamics, this yields, to leading order under commonly encountered conditions, an affine modulus-temperature relation, Geq = θ(X - Y) +ΘY, which separates the dry-network contribution X from a solvent-mediated contribution Y. The resulting structure defines an experimental strategy: measure dry and swollen networks over temperature and concentration, then test the consistency of Y inferred from slope and intercept, or directly when Θ is known independently. We apply this framework to poly(n-butyl acrylate) swollen in butyl benzoate and poly(ethylene glycol) swollen in dimethylformamide, obtaining Y < 0 and Y > 0, respectively. For the latter system, the fitted Θ agrees with the known crystallization temperature of poly(ethylene glycol) in dimethylformamide. The present work establishes a thermodynamic framework and validation strategy for solvent-deformation coupling in swollen networks, while leaving molecular identification to future study.

Na+ saltiness perception strongly depends on its diffusion and retention within the salivary layer, processes modulated by mucoadhesive polysaccharides. However, the underlying saltiness-enhancing mechanism of soy hull polysaccharide (SHP) remains unclear due to its compositional and structural heterogeneity. SHP was separated into neutral (SHP-N, hemicellulose) and acidic (SHP-A, RG-I-enriched pectin) fractions. Salivary mucoadhesion of Na+ and SHP were investigated. Compared to SHP-N, negatively charged SHP-A exhibited a stronger saltiness-enhanced effect by accelerating Na+ diffusion and prolonging retention, which is not mainly attributed to viscosity changes. The electrostatic screening effect of Na+ promoted stable mucoadhesion of SHP-A on the mucin layer. Strong hydrophobic interaction as the dominant force is primarily mediated by protein domains within the rhamnogalacturonan I (RG-I) region of SHP-A. Strong SHP-mucin affinity may influence Na+ adsorption-desorption dynamics and accelerate its penetration. This work reveals key structural domains of polysaccharides responsible for saltiness enhancement and their mucoadhesive driving forces in salivary layer.

Spectrally selective transmission of solar radiation is vital to balance energy efficiency, visual comfort, and UV protection in the human environment. Thermochromic materials regulate solar spectral transmission through temperature-dependent optical transitions, but their single thermal responsiveness limits precise spectral control, leading to inefficient utilization of light and insufficient UV protection. To overcome these limitations, we implement a dual-responsive strategy that synergizes photochromic and thermochromic mechanisms by developing a nanocomposite organohydrogel integrating photochromic perovskite nanosheets and a thermochromic poly(N-isopropylacrylamide-co-acrylamide) network in a water-glycerol matrix, forming a photo/thermal dual-responsive smart window (PTSW). Acrylamide and glycerol synergistically enhance dimensional stability and environmental tolerance, ensuring reliable performance under diverse climatic conditions. The perovskite nanosheets efficiently absorb and scatter UV light, blocking UV transmittance greatly while maintaining high visible transparency. The PTSW with a 1 mm-thick gel layer exhibits pronounced solar modulation, reducing indoor temperature by up to 17.3 degrees C relative to double glazing in outdoor experiments, and achieves similar to 20% simulated annual energy savings in high-irradiance regions. Climatic wind-tunnel experiments further confirm the PTSW's excellent weather adaptability and cycling durability. This dual-responsive smart window establishes a general pathway for intelligent selective solar-spectrum management, UV protection, and sustainable thermal regulation toward carbon-neutral building technologies.

We mapped the isothermal (25 degrees C), isohydric (pH 7.0) phase diagram of soy-glycinin/NaCl/water and combined it with small-strain and large-amplitude oscillatory shear (LAOS) rheometry to relate salt-driven structural transitions to viscoelastic behavior. The diagram shows classic re-entrance-two single-phase regions separated by a protein-rich coacervate corridor-yet its boundaries are asymmetric: coacervates harvested at low salt (50 mM-100 mM) contain percolating 7S-trimer networks, whereas those formed at high salt (150 mM-200 mM) are populated by dispersed 11S-hexamers. Consequently, low-salt samples are solid-like (G ' > G '' for omega greater than or similar to 10 rad/s) and exhibit pronounced non-linearities (I-3/1 >= 0.1), while high-salt samples behave as weak power-law fluids (G ' proportional to G '' proportional to omega(0.8)) with frequency-dependent shear thinning. Pipkin diagrams confirm a shift from frequency-independent plasticity at 50 mM to viscous flow at 200 mM. These results establish a direct link between glycinin's salt-controlled quaternary structure and the mechanics of its self-coacervates, providing design guidelines for plant-protein adhesives, encapsulants and other soft, sustainable materials.

We distinguish two rheological routes to the liquid-solid transition (LST) in soft materials by tracking the linear viscoelastic spectrum under small-amplitude oscillatory shear. Type I (dynamical arrest) shows the growth of a low-frequency elastic plateau without a reversal in the loss-tangent trend; Type II (percolation with criticality) features scale-free spectra at a well-defined time and a reversal in the loss-tangent trend. In synthetic hectorite suspensions spanning broad clay and salt concentrations, freshly prepared samples consistently follow Type II. After aging and pre-shear, the pathway becomes history-dependent: a map in composition-shear space reveals a boundary where high clay concentrations undergo Type I only, whereas lower clay concentrations evolve from Type I to Type II; increasing pre-shear rate shifts this boundary to higher clay content. A unified mechanism links these routes to aggregation kinetics: early particle-cluster growth yields peaked cluster-size distributions and Type I arrest; later depletion-enhanced cluster-cluster aggregation produces heavy-tailed distributions and Type II percolation. These results explain why "shear rejuvenation" does not restore the fresh state and provide a spectrum-based framework relevant to colloids and polymer systems undergoing physical or chemical gelation.

Triboelectrification is an inherent phenomenon associated with friction, involving mechanisms of charge generation and evolution closely linked to tribological behavior. However, there is insufficient systematic understanding of how tribological behavior regulates electrostatic charging and how interfacial charges reciprocally influence friction. This limitation constrains the development of related technologies in fields such as energy harvesting and condition monitoring. This review investigates the interaction mechanism between interfacial friction and triboelectrification, thoroughly examines how factors such as interfacial contact, adhesion, friction, and lubrication influence triboelectrification, and further elucidates the regulatory mechanism of friction based on interfacial charges. By controlling the generation, transmission, and dissipation of electrical charges, charge accumulation could be effectively reduced, thereby optimizing friction behavior. Additionally, this review introduces triboelectric-based sensor designs and their applications in monitoring interfacial properties and lubrication states during friction processes. This review contributes to an in-depth understanding of the interaction mechanism between interface friction and triboelectrification, providing theoretical support for the development of novel tribological sensing technologies and the optimization of tribological control methods.

Two-dimensional (2D) materials have demonstrated immense potential in electronic devices, optoelectronic devices, and micro electro mechanical systems due to their unique structures and exceptional physicochemical properties. However, the tribological properties of 2D materials under carrier transportation conditions possess a significant impact on the reliability and lifespan of electronic devices, which poses a critical challenge for practical applications. Traditional macroscopic tribology theories are inadequate in explaining friction mechanisms at the nanoscale. Electric fields, as an effective control method, could dynamically regulate the interface friction behavior through various pathways such as carrier concentration, lattice strain, electron–phonon coupling, electric field-induced redox, and mechanical resonance. They have important potential in the fields of intelligent lubrication and friction sensing. However, the microscopic mechanism of friction energy dissipation under the action of electric fields is still unclear, especially the essence of the interaction between electrons and phonons. This review systematically reviews the modulation mechanisms of current-carrying friction in 2D materials, which includes electronic interactions, electrically induced strain, electron–phonon coupling, electric field-induced redox effects, and mechanical resonance. The relevant research indicates that applied electric fields could dynamically alter interfacial adhesion and energy dissipation pathways by modulating carrier concentration, lattice deformation, and surface chemical reactions. This capability enables precise control over friction coefficients. Furthermore, environmental factors (humidity) and multi-physical field coupling (electric and magnetic fields) exert additional influences on frictional behavior. This review exhibits the application potential of these mechanisms in low-power devices and intelligent lubrication systems. Additionally, it underscores the necessity of integrating multi-scale simulations with experimental validation in future studies. These researches would deepen mechanistic understanding and facilitate the development of novel modulation strategies.

Steel cables serving in offshore energy systems are prone to rapid degradation under the coupled effects of friction-induced wear and marine corrosion, leading to severe safety and reliability concerns. Early recognition of micro-defect initiation and real-time damage monitoring remain formidable challenges due to the difficulty in detecting sub-surface micro-damage. Herein, we present a sandwich-structured thermochromic smart coating that enables preemptive, visual detection of frictional heating prior to irreversible damage. The coating integrates silica-encapsulated thermochromic microcapsules (TC@SiO2) comprising crystal violet lactone (CVL), bisphenol A (BPA), and n-hexadecanol as a responsive sensing layer between polyurea (top) and epoxy (bottom) matrices. Upon frictional heating, electron transfer between CVL and BPA induces C─O─C bond cleavage and chromophore disruption, triggering a solid-liquid phase transition and color fading that visually warning micro-damage events. Meanwhile, hydrogen-bond interactions between the microcapsules and the polymer network further enhance mechanical robustness and coating integrity, yielding superior tribological performance (5.86 × 10-5 mm3 N-1 m-1) and long-term corrosion resistance (5.144 × 109 Ω·cm2 after 70 days immersion). This work establishes a cost-effective and intuitive strategy for early friction monitoring, offering a new paradigm for intelligent protection of marine structural materials.

Localized corrosion, poor wear and corrosion resistance of biphasic magnesium-lithium alloys limit their engineering applications. In this study, a WO3-containing micro-arc oxidation (MAO) coating was constructed in alkaline silicate electrolyte on Mg-9Li-1Al (LA91) alloy, and the effects of sodium citrate and sodium tungstate as electrolyte additives on corrosion and wear resistance of the MAO coatings were investigated. The corrosion behavior of the samples was evaluated by electrochemical and hydrogen evolution experiments in simulated sweat, as well as salt spray test. Vickers hardness and friction coefficient of the MAO coating were also appraised. The results indicated that both additives participated in the MAO reaction process, reduced the porosity and increased the compactness and thickness of the MAO coating. The corrosion current density of the obtained MAO coating was decreased from 17.52 mu A/cm2 (LA91 alloy) to 0.1 mu A/cm2, and the salt spray test could last for 96 h. The surface hardness and friction coefficient were 352.45 HV and 0.12, exhibiting a significantly enhanced wear resistance than LA91 alloy. The improved corrosion and wear resistance can be ascribed to the addition of sodium citrate and sodium tungstate, leading to the formation of carboxylate-based complexes and WO3, respectively, which will promote the application of biphasic magnesium-lithium alloys in electronic 3 C products and smart wearable devices.

It is urgent to achieve the in-situ monitoring of the wear for MAO-Al/resin coatings during frictional wear. However, there are few effective monitoring methods at present. This work examined the wear state of the resin coatings through friction testing with a steel ball, which further evaluated the relationship between friction current and friction coefficient. There is an evident correspondence between the time corresponding to mutation of the friction current and the time corresponding to the wear through of the resin coating under different loads, frequencies, and thicknesses of the resin coating, which provides an effective method for real time monitoring of wear state. The experimental results revealed that the friction current between steel ball and resin coating is considerably higher than that between steel ball and micro-arc oxidized aluminum layer. When the steel ball is friction with the resin coating, the friction current could reach 370 nA, and the current after the coating is worn through is merely 3 nA. This is attributed to that the difference in electric properties between friction electrodes of metal and polymer are significantly larger than the difference in electric properties between friction electrodes of metal and metal oxide. It is demonstrated that the mutation of friction current is more sensitive than that of friction coefficient at the critical point of wear through for coating, and the mutation of friction current could realize real-time monitoring for the frictional wear of resin coating. This friction wear sensing and monitoring technology is simple, sensitive, and possesses broad applications in the mechanical friction field.

Finding a way to prevent corrosion while also stopping scale buildup is a big challenge for sustainable energy systems. Traditional methods that use inhibitors often lead to environmental problems and waste energy because of the uncontrolled release of chemicals. Here, we present an eco-conscious coating design that integrates superhydrophobic surfaces and controlled inhibitor release to form dual passive-active protection strategies. A highly ordered, porous, superhydrophobic anodic alumina (PSAA) coating incorporated with 2-Phosphonobutane-1,2,4-Tricarboxylic Acid (PBTCA) was developed. This coating works in two ways: it provides a solid barrier while also using chemical methods to prevent issues. This gas-liquid-solid interface stabilised by the superhydrophobic matrix physically blocks Cl- permeation and promotes a reduction in CaCO3 nucleation through the trapping air layer. At the same time, the prolonged release of PBTCA from the porous structure chemically chelates with Ca2+ ions and prevents the binding of CO32-and, at the same time, neutralizes Cl-aggressiveness. The dual mode of operation allows the coating to achieve greater than 98.2 % CaCO3 scale in-hibition efficiency and a 4-orders-of-magnitude reduction in corrosion current density compared to bare sub-strates. The work establishes a new approach for multifunctional coatings that reconcile environmental sustainability with long-term anti-fouling performance through spatially and temporally coordinated protection mechanisms.

The introduction of monomers containing a hydrophobic group endows the polyion complex (PIC) hydrogels with enhanced mechanical strength and salt resistance without sacrificing their original functions. However, the synergistic mechanism between ionic interactions and hydrophobic associations as well as the relationship between network structure and performance remain unclear. In this study, we employed a model system: a PIC hydrogel composed of positively charged poly(2-(diethylamino)ethyl methacrylate) and negatively charged poly(4-styrenesulfonic acid) to investigate the influence of ionic interactions and hydrophobic associations on their structure and mechanical behavior. Notably, we observed that pH can induce a mechanical transition in these PIC hydrogels from a stiff and tough state to a soft but still tough one. When the hydrogel is immersed in NaOH for a short time, the breakage of ionic bonds is expedited, resulting in a weakening of the ionic interactions between the polymer chains. However, increasing the immersion time further leads to an increase in the modulus and work of extension of the hydrogel. Through a systematic investigation of the network structure evolution during immersion in NaOH and the utilization of various hydrophobic monomers, it was discovered that the pH-induced mechanical transition can be attributed to a shift from ionic association to hydrophobic association in the gel network. Furthermore, it was found that the mechanical properties and the deformation capacity of the PIC hydrogels can be adjusted facilely through controlling the hydrophobicity of the side groups, which can further affect the pH-induced shape-changing behavior. This novel strategy of combining ionic association and hydrophobic association can be used to develop smart PIC hydrogels with multiple functions and outstanding performance.

Triboelectric nanogenerators (TENGs), as a new strategy for harvesting energy from nature, have attracted widespread attention in the field of water droplet energy capture. As a friction layer material, the solidliquid electrification phenomenon of coatings has been studied. However, little attention is paid to the influence of the surface wettability of the coating itself on the electrical signal of the droplet generator. In this study, alkyl/phenyl pure silicone resin was utilized as a substitute for fluorine-containing polymer materials. This substitution not only mitigated the risk of environmental pollution from TENG friction materials but also resulted in varying wettability of the silicone resin coating through plasma and surface structure treatment. The droplet-based Double-electrode (D-TENG) and Single-electrode (S-TENG) coating-based triboelectric nanogenerators were fabricated. Through the integration of a high-speed camera and ammeter, the motion state of water droplets on surfaces with different wettability closely correlates with their charged behavior. This correlation is utilized to observe the motion state of water droplets on hydrophilic-hydrophobic surfaces in four stages: contact, spreading, contraction, and sliding. Under the double-electrode structure, as the water contact angle of the coating increased from 6.84° to 139.77°, the short-circuit current initially increased and then decreased, peaking at 466µA when the contact angle was 98.48°, representing a 677-fold increase from the initial 0.689µA. In the single electrode structure, the short-circuit current increased from 2.66nA to 700nA, indicating a 263-fold increase. Studying the varied wettability of the surface of silicone resin coating aids in comprehending the application of the coating material in solid-liquid friction electrification for energy collection. Furthermore, it offers insight into selecting appropriate coating materials for friction coatings in future applications.

Double physical network (DPN) hydrogels exhibit superior performance compared with other hydrogel types due to their unique crosslinking structure. However, certain mechanical properties, such as self -recovery and fatigue resistance, still need improvement, and stimuli -responsiveness can be expanded for a wider range of applications. In this study, we presented a facile strategy for designing multifunctional DPN hydrogels based on a polycyclodextrin (PCD) and adamantane (Ad) host -guest supramolecular crosslinked polyacrylamide (PAAm) network and a low-methoxyl pectin (LMP) network established through Ca2+ or H+. 'Egg box' junction zones between Ca2+ and COO- on the LMP chains, as well as hydrogen bonding and hydrophobic association junction zones, could be formed during this process. The synergistic effect of the flexible supramolecular network and the stiff LMP network imparted remarkable stress tolerance, fatigue resistance, ductility, and anti -piercing capacities to the DPN hydrogels. The thermal reversible DPN structure also endowed the hydrogel with thermal -accelerated rapid self -recovery, as the hydrogel can virtually recover to its original state within 40 min at 80 degrees C. Multistimuliresponsive including chemical- and thermal -induced shape memory behavior was achieved based on the versatile LMP network. The temporary shape of the LMP hydrogel could be fixed with the introduction of Ca2+ or H+, while spontaneous shape recovery was observed under near infrared (NIR) radiation or immersion in K2CO3 or NaOH solutions, respectively. Additionally, the DPN hydrogels exhibited notable self -healing behavior when the cut surfaces were contacted and stored at 80 degrees C. More importantly, green natural resources derived raw materials of cyclodextrin (CD) and LMP also offered a sustainable strategy to prepare functional hydrogels. The combination of the above features of the LMP DPN hydrogel provided a new method for designing smart materials with ideal functions for soft actuators and biomedical applications.

Triboelectric nanogenerators (TENGs), as a new strategy for harvesting energy from nature, have attracted widespread attention in the field of water droplet energy capture. As a friction layer material, the solid-liquid electrification phenomenon of coatings has been studied. However, little attention is paid to the influence of the surface wettability of the coating itself on the electrical signal of the droplet generator. In this study, alkyl/ phenyl pure silicone resin was utilized as a substitute for fluorine-containing polymer materials. This substitution not only mitigated the risk of environmental pollution from TENG friction materials but also resulted in varying wettability of the silicone resin coating through plasma and surface structure treatment. The droplet-based Double-electrode (D-TENG) and Single-electrode (S-TENG) coating-based triboelectric nanogenerators were fabricated. Through the integration of a high-speed camera and ammeter, the motion state of water droplets on surfaces with different wettability closely correlates with their charged behavior. This correlation is utilized to observe the motion state of water droplets on hydrophilic-hydrophobic surfaces in four stages: contact, spreading, contraction, and sliding. Under the double-electrode structure, as the water contact angle of the coating increased from 6.84 degrees to 139.77 degrees, the short-circuit current initially increased and then decreased, peaking at 466 mu A when the contact angle was 98.48 degrees, representing a 677-fold increase from the initial 0.689 mu A. In the single electrode structure, the short-circuit current increased from 2.66 nA to 700 nA, indicating a 263-fold increase. Studying the varied wettability of the surface of silicone resin coating aids in comprehending the application of the coating material in solid-liquid friction electrification for energy collection. Furthermore, it offers insight into selecting appropriate coating materials for friction coatings in future applications.

Due to cyclic loading, clays composed of different mineral compositions exhibit non-linear viscoelastic characteristics. This study quantified the effect of the mineral composition on the non-linear viscoelastic properties of clays. Large-amplitude oscillatory shear rheological tests and cryo-electron microscopy tests were conducted on clays containing quartz, feldspar, montmorillonite, and kaolinite (Q, F, Mt., and Kaol). The results indicated that as the clay content in the soil sample increased, so did the value of relative intensity(I3/1), the Lissajous curves shifted from elliptical to rectangular, and the absolute values of the overall non-linear viscoelasticity parameters (NEand NV) were also larger. In addition, its non-linear viscoelasticity was more prominent, supported by the cryo-electron microscopy test outcomes. Montmorillonite played a more significant role than kaolinite in increasing the nonlinear viscoelasticity of the soil samples. The study findings have significant academic and practical value, facilitating an in-depth understanding of the viscoelastic behavior of clays, rheological studies of other types of clay soils, and geotechnical engineering applications.

Solid-liquid triboelectric nanogenerators (S-L TENGs) are extensively researched for their capability to harvest mechanical energy from natural sources. Nevertheless, some TENGs based on friction electrification and electrostatic induction are partially limited, and liquids exhibit slow separation speeds upon contact with solid interfaces, resulting in lower output currents and voltages. This limitation hinders their ability to satisfy real-world electricity demands. This study introduces a wave-driven closed polytetrafluoroethylene tube TENG (PT-TENG) and enhances the conventional tank car model by applying the principle of interface charge transfer. The improvements enable the output current and voltage to reach 900 mu A and 150 V, respectively, with a power output of 17.74 mW. This represents a thirteen-fold increase over the traditional model's performance, effectively capturing the kinetic energy of water flow. The mechanism and influencing factors of the PT-TENG are analysed, including the effect of external conditions on the movement state of water flow within the device, to enhance PT-TENG's output. This novel S-L TENG efficiently gathers low-frequency energy, offering a straightforward manufacturing process and elevated output. It enhances charge transfer at the solid-liquid interface and offers a new strategy for harvesting ocean wave energy. A wave-driven closed polytetrafluoroethylene tube TENG (PT-TENG) with enhanced output is proposed, utilizing interface charge transfer principles, which can generate stable high output current and be used to design a new cathodic protection system.

Underwater adhesion of hydrogels is essential for their applications in liquid environment. However, green raw materials, facile preparation process and multiple environmental adaptability are still issues that need to be improved. Inspired by the protein-based underwater bio-adhesion phenomena in nature, an effective stepwise immersion method is developed without any polymerization to prepare a green underwater adhesive hydrogel by combining gelatin and tannic acid (TA), two common materials from nature yet difficult to obtain their homogenous compound. By facile treatments in urea solution or heating, the hydrogels can realize stable immediate adhesion on various substrates and in different liquids in addition to water with a wide range of adjustable adhesion strength of 100-103 kPa. The evolution of the hydrogel network structure and the adhesion mechanism are systematically studied. Furthermore, several typical portable products based on the adhesive hydrogels are demonstrated to show the commercialization possibility. This work presented a novel, facile, and distinctive strategy for designing environmentally friendly, multiple adaptive adhesives. Bioinspired green underwater adhesive hydrogel is prepared by a stepwise immersion method with gelatin hydrogel in tannic acid solution without any polymerization. Underwater adhesion is realized by treating the hydrogel with urea solutions or heating with the adhesion strength adjustable at a wide range of 100-103 kPa. The hydrogel shows multiple environmental adaptability in different liquids and on different substrates. image