Engineered double-network hydrogels for robust protection of fragile systems

Engineered double-network hydrogels for robust protection of fragile systems | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Engineered double-network hydrogels for robust protection of fragile systems Chandan Maity, Dineshkumar Bharathidasan This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9445757/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Hydrogels capable of rapid mechanical energy dissipation are highly attractive for impact protection and shock-absorbing applications, yet conventional systems often rely on viscoelastic damping or irreversible sacrificial bonds, resulting in slow recovery and mechanical fatigue. Herein, we report an engineered double-network hydrogel (AGK) that integrates covalent boronate ester crosslinks with supramolecular G4-quartet assemblies to achieve enhanced mechanical robustness and resilience. This synergistic architecture enables stress-induced network dissociation and reconfiguration, facilitating efficient energy dissipation alongside rapid, autonomous self-healing. The AGK hydrogel sustains compressive loads of up to ~ 5.4 kg, demonstrating significant mechanical strength. Coefficient of restitution measurements reveal a low rebound (COR ≈ 0.21), indicative of superior impact attenuation and energy absorption. Consequently, the hydrogel effectively protects fragile systems, such as glass substrates and eggs, under both static loading and free-fall impact without fracture. The combined covalent and supramolecular interactions further enable repeated damage–recovery cycles with minimal performance degradation. Overall, this work establishes a rational molecular design strategy that integrates dynamic crosslinking with hierarchical energy dissipation, providing a promising platform for mechanically robust, self-healing hydrogels in sustainable protective materials and advanced impact-mitigation applications. Physical sciences/Materials science/Soft materials/Gels and hydrogels Physical sciences/Chemistry/Polymer chemistry/Supramolecular polymers double-network hydrogel self-healing material energy dissipation supramolecular assembly boronate ester crosslinking G4-quartet impact protection Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction Hydrogels, three-dimensional polymer networks swollen with large amounts of water, have received tremendous interest across materials science, chemistry, and biomedical research due to their tunable mechanical properties, biocompatibility, and structural similarity to soft biological tissues. Beyond their widespread use in biomedical systems, there is growing interest in hydrogels for materials science applications that demand durability, impact resistance, and adaptability under dynamic mechanical conditions, such as protective layers, cushioning materials, and adaptive interfaces. [1,2,3,4] However, most conventional hydrogels, particularly those derived from natural polymers, remain mechanically weak and prone to irreversible damage, limiting their applicability in mechanically demanding environments. A promising strategy to overcome these limitations is the integration of dynamic covalent chemistry with supramolecular interactions, enabling polymer networks to reversibly break and re-form under stress while maintaining structural integrity. Recent advances in self-healing materials have demonstrated that reversible molecular interactions can endow polymer networks with the ability to autonomously recover after mechanical disruption. [5,6,7] Rational hydrogel design increasingly relies on combining dynamic covalent bonds with supramolecular interactions, allowing networks to reversibly dissociate and re-form under stress while maintaining functional integrity. Dynamic covalent chemistries such as imine bonds, disulfide exchange, and boronate ester linkages provide reversible covalent crosslinks that can reform to repair network defects and restore mechanical properties. [8,9,10] These mechanisms enable self-healing without external intervention and are widely used to improve hydrogel durability and service life. Among them, boronate ester bonds formed between borate ions and cis-diol-containing polymers offer rapid exchange kinetics and mechanical robustness, making them particularly attractive for self-healing hydrogels. [11] In parallel, supramolecular interactions such as hydrogen bonding, π–π stacking interaction, host–guest complexation, and metal–ligand coordination introduces dynamic physical crosslinks that enable efficient energy dissipation and rapid network reconfiguration. Notably, G4-quartet assemblies, formed through potassium ion ( K ⁺ )-templated stacking of guanosine units, generate extended supramolecular networks stabilized by hydrogen bonding and π–π interactions, contributing to enhanced cohesion and responsiveness. [12] Together, these reversible interactions form the foundation for hydrogels that integrate mechanical resilience with autonomous healing. [13,14] Despite significant progress, achieving simultaneous mechanical robustness, efficient self-repair, and high energy dissipation within a single hydrogel platform remains a key challenge. [15,16] Systems dominated by weak supramolecular interactions often lack sufficient mechanical strength, whereas permanently crosslinked networks sacrifice dynamic adaptability. Thus, there is a clear need for integrated design strategies that synergistically combine complementary dynamic interactions to meet the mechanical and functional demands of advanced soft materials. Herein, we report a mechanically robust, self-healing double-network hydrogel ( AGK , Figure 1 ) constructed from a natural polysaccharide scaffold, agarose ( Aga ), and reinforced through the integration of dynamic boronate ester covalent crosslinks and K⁺-templated guanosine ( Gua ) G4-quartet supramolecular assemblies. The diol-rich galactose units of Aga enable dynamic boronate ester formation, while Gua introduces additional physical crosslinks through supramolecular self-assembly. The resulting AGK hydrogel exhibits self-healing efficiency, superior energy dissipation, and impact-absorbing capability, positioning it as a promising platform for protective and adaptive materials in dynamic operating environments. This work provides a rational framework for developing sustainable soft materials that combine structural robustness with autonomous functional recovery. 2. Preparation of AGK hydrogel The supramolecular/polymer double-network AGK hydrogel was synthesized by dissolving Gua and boric acid in equimolar amounts (1:1 molar ratio) in water with continuous stirring at ~90 °C until a clear solution was obtained ( Figure 2a ). Subsequently, 3 wt % Aga was incorporated and fully dissolved under the same conditions, followed by the addition of K⁺ ions to trigger gelation. The resulting solution was cast into a mold and cooled at ambient conditions to obtain AGK-based hydrogels of the desired dimensions. Systematic optimization of the Gua concentration (12.5–100 mM) revealed that 25.0 mM was sufficient to impart noticeable self-healing capability to the hydrogel matrix. Increasing Gua content enhanced self-healing performance, indicating a positive correlation between supramolecular crosslink density and dynamic repair efficiency. However, higher concentrations (>100 mM) compromised structural integrity, presumably due to excessive supramolecular crosslinking or phase separation, resulting in mechanically weaker gels. These observations indicate the importance of balancing dynamic and mechanical interactions in double-network systems. The optimal formulation of AGK hydrogel was identified as 3 wt % Aga with Gua and boric acid each at 50.0 mM (1:1 molar ratio), ensuring a robust network with efficient self-healing and mechanical strength suitable for impact-absorbing applications. Introduction of a potassium ion source, either KCl or KOH, initiated gelation. It is worth mentioning that addition of KOH (as K + source) elevated the pH to ~8, accelerating gelation. However, the elevated pH resulting from the addition of KOH posed challenges to maintaining gel shape integrity. The rapid gelation kinetics under alkaline conditions hindered precise control over gel uniformity and molding, potentially resulting in irregular or poorly defined structures. In contrast, KCl maintained solution pH and allowed controlled morphology during gel formation and therefore, KCl was employed in all subsequent experiments. Successful network formation was confirmed through comprehensive spectroscopic and microscopic structural characterization. In the 1 H NMR spectra (recorded in DMSO-D 6 at room temperature), Aga displayed characteristic signals at δ ≈ 5.20–4.28 ppm. Upon addition of boric acid, these signals shifted downfield toδ ≈ 4.90–4.21 ppm, consistent with the formation of dynamic boronate ester linkages between borate ions and the diol functionalities of Aga ( Figure 2b ). Upon incorporation of Gua and K⁺, a new peak at δ ≈ 7.49 ppm emerged, indicative of a distinct chemical environment arising from Gua–borate complexation and G4-quartet assembly. FTIR spectra of the hydrogel exhibited combined features of both Aga and Gua, with O–H stretching at 3297 cm⁻¹, C–H stretching at 2919, and 2846 cm⁻¹, C=O and C=N vibrations of Gua at 1736 and 1650 cm⁻¹, and a B–O–C vibration at 1412 cm⁻¹ corresponding to borate–diol crosslinks ( Figure S1 ). The band at 1053 cm⁻¹ was assigned to C–O and C–O–C modes of the Aga backbone, collectively confirming covalent and supramolecular network integration. Powder X-ray diffraction (pXRD) analysis demonstrated that the crosslinked AGK hydrogel exhibited an amorphous structure, in contrast to the semi-crystalline diffraction pattern observed for Gua. This transformation indicates that crosslinking disrupted the ordered molecular packing of Gua ( Figure S2 ). Morphological analysis via fluorescence microscopy, using Thioflavin T (ThT) [17] as a G4-quartet probe, demonstrated minimal fluorescence in the absence of K⁺ ( Figure S3 ), consistent with isolated Gua assemblies. [18] With K⁺, a continuous fluorescent network was observed ( Figure 2c ), confirming extensive K⁺-templated supramolecular crosslinking. FESEM imaging revealed a transition from a layered polymer morphology in Aga alone ( Figure S4 ) to a dense, fibrillar network in the presence of K⁺ ( Figure 2d ), highlighting the role of G4-quartet assembly in reinforcing the hydrogel matrix. In contrast, Gua-Aga gel lacking G4-quartet exhibited a non-homogeneous morphology in the FESEM image ( Figure S5 ), consistent with their static network architecture. [19] 3. Self-healing with AGK hydrogel Following the successful fabrication of the AGK hydrogel from readily available building blocks and its thorough structural characterization, we proceeded to investigate its self-healing behavior and the specific role of K⁺ ions. These ions promote the formation of G4-quartet structures that act as dynamic physical cross-links within the network. By bridging polymer chains, they enhance network connectivity, which is essential for mechanical strength and efficient self-repair. These supramolecular motifs, stabilized by hydrogen bonding and π–π stacking in the presence of K⁺, are known to strengthen guanosine-based supramolecular hydrogel networks. [20] To directly assess the role of K⁺ in self-healing, hydrogel materials were prepared with and without K⁺ in the presence of the G4-responsive fluorophore ThT, followed by mechanical incision ( Figure 3a ). In the absence of K⁺, fluorescence microscopy revealed discrete ThT-emissive domains confined to disconnected guanosine assemblies ( Figure 3b ), indicating disrupted network continuity and no healing. Dense ThT fluorescence at the disconnected site and no fluorescence at non-affected sites represent absence of G4-quarete. By contrast, K⁺-containing hydrogels displayed a bright fluorescent network spanning the cut interface ( Figure 3c ), evidencing re-established G4-quartet cross-links and rapid restoration of structural integrity. To visualize this process dynamically, a diffusion assay was performed in which K⁺ solution (25 mM) was introduced into wells within a preformed AGK gel (3 wt% Aga with 25 mM Gua:H₃BO₃), while ThT in water served as a control ( Figure 3d ). Time-lapse imaging and ImageJ analysis demonstrated a linear K⁺ diffusion front ( Figure 3e ), accompanied by a transition from an opaque to a transparent hydrogel matrix ( Figure S6a and Video SV1 ). ThT diffusion alone caused only dye transport without structural change, confirming that network reorganization arises specifically from K⁺-induced G4 assembly. In a complementary experiment, K⁺ diffusion across a preformed crack promoted interfacial closure and restoration of homogeneity ( Figure S6b ). Collectively, these results demonstrate that K⁺ diffusion drives G4-quadruplex reassembly, enabling recovery of transparency, structural continuity, and mechanical integrity. To further demonstrate the self-healing behaviour, four AGK-based hydrogel specimens (two coloured red and two blue) were individually cut and brought into contact ( Figure 3f ). Spontaneously hydrogel fragments fused at their interfaces in ~3 minutes without external intervention, forming a single, mechanically cohesive construct capable of supporting its own weight upon lifting. This robust restoration of structural integrity highlights the dynamic and reversible nature of K⁺-mediated G4-quartet cross-links, which permit network rearrangement and reconnection after damage. These observations highlight the central role of K⁺-induced supramolecular interactions in imparting resilience and repeatable self-healing to the hydrogel system. 4. Rheological and mechanical characterization of AGK hydrogel The viscoelastic behaviour of the double-network AGK hydrogel was systematically evaluated using oscillatory shear rheology. Disc-shaped samples (25 mm diameter, 1 mm thickness) were subjected to strain-sweep and frequency-sweep experiments to probe network stability and deformation tolerance. In the strain sweep, the storage modulus (G′) consistently exceeded the loss modulus (G″) for both Aga ( Figure 4a ) and AGK hydrogel ( Figure 4b ) across a broad strain range, confirming dominant elastic behaviour typical of solid-like hydrogel networks. The linear viscoelastic regime extended from 0.1 % to 10 % strain for Aga and 0.1 % to 30 % strain for AGK, indicating enhanced mechanical resilience and resistance to deformation in the composite network relative to pure Aga. Based on these observations, a nominal strain of 0.1 % within the linear viscoelastic regime was selected for subsequent frequency sweep analyses ( Figure 4c ). Frequency sweeps revealed parallel, strain-independent profiles for G′ and G″ across the tested range, reflecting a consistent viscoelastic balance and network stability. The loss tangent (tan δ = G″/G′), a key indicator of the relative contributions of viscous and elastic components, remained <1 for both gels, confirming that elastic, solid-like behaviour predominates and that the networks maintain their structural integrity under deformation. The slightly higher tan δ value for AGK (0.113) compared to Aga (0.085) suggests increased viscous dissipation in the composite gel, consistent with its enhanced strain tolerance and dynamic network rearrangement. Compression testing further differentiated the mechanical profiles of the gels ( Figure 4d, Figure S7 ). Aga exhibited a compressive stress of ~0.06 MPa at 15 % strain, characteristic of a softer, more compliant material. In contrast, AGK sustained nearly double the stress (~0.11 MPa) at larger strains (~25 %), demonstrating superior load-bearing capacity and stiffness. Correspondingly, AGK withstood a maximum force of ~53 N (≈5.4 kgf) at 4.7 mm displacement, compared to ~29 N (≈2.9 kgf) at 2.7 mm for Aga, highlighting its enhanced compressive toughness and energy dissipation that are critical parameter for impact-absorbing materials. [21] The interfacial attachment strength was further assessed using a load-holding capacity test. In this experiment, two gel segments (Gel 1 and Gel 2; Figure 4e ) were stacked with a third gel segment (Gel 3), allowed to stick via healing, and subsequently suspended vertically. The upper end of the assembly was secured with a clip, while calibrated weights were attached to the free end via a 10 cm nylon string affixed to Gel 2. For a healed junction length (d) of 3 cm, the construct sustained loads of 50, and 100 g, with the 100 g load maintained for over 7 min, as indicated by stable height profiles ( Figure 4f ). Reducing the junction length to 1.5 cm diminished load-bearing performance. The assembly reliably supported 20 g, whereas 50 g was sustained for ~2 min. These results demonstrate that increasing the self-healed interfacial area significantly enhances load-holding capacity and mechanical stability, likely due to the increased material volume and more effective stress distribution at the interface. Altogether, these rheological and mechanical data demonstrate that the AGK hydrogel exhibits robust viscoelasticity, enhanced compressive strength, and effective load-bearing and energy-dissipating characteristics, attributable to its dynamic boronate ester and G4-quartet‐reinforced double network. These characteristics are essential for advanced protective materials and resilient soft interfaces. 5. Impact-mitigation performance of AGK hydrogel Agarose (Aga) hydrogels at low polymer content (≤1.5 wt %) are known to exhibit viscoelastic damping and adjustable stiffness, making them effective for basic impact absorption applications. [22,23] However, their inherent brittleness and lack of self-healing compromise shape retention and structural integrity under repeated loading, and increasing Aga content to ~3 wt % enhances elasticity at the cost of increased rebound on impact, rendering them less suitable for energy dissipation tasks. The dual-network design of the AGK hydrogel overcomes these limitations by combining a dynamic boronate ester polysaccharide network with Gua-derived supramolecular assemblies, enabling the material to deform, absorb kinetic energy, and recover via rapid reformation of dynamic bonds. Impact dissipation was quantified by coefficient of restitution (COR) using a standardized ball-drop test. [ 24] When a 53.6 g marble was dropped from 25 cm ( Figure 4g, Video SV2 ), the bare surface exhibited a COR of ~0.83, and 3 wt % Aga gel showed moderate energy loss (COR ≈ 0.58, Figure 4h ). In contrast, the AGK (50 mM) hydrogel yielded a significantly lower COR (~0.21), indicating efficient energy absorption with minimal rebound and highlighting its potential as an effective shock-absorbing medium. Such low COR values reflect the material’s ability to dissipate impact energy rather than elastically reflect it, a characteristic desirable for protective packaging and cushioning applications. [25,26] To further evaluate impact absorption, load cell tests were conducted. [27] The load cell was assembled and operated (see load cell setup in Supporting Information and Figure S8a-c ). The system was calibrated using standard weights from 1 to 100 g ( Figure S8d ). Gel discs (4 cm diameter, 5 mm thickness) were placed on the impact plate, and weights of 20, 50, and 100 g were dropped from heights of 15 and 30 cm through a hollow plastic tube to ensure controlled vertical impact. The impact response was recorded in real time and converted into weight (g) versus time (ms) profiles. For impacts from 15 cm, the hydrogel exhibited significant impact absorption across all tested weights compared to the no-gel control ( Figure 4h ). A similar trend was observed for impacts from 30 cm ( Figure S9 ). It is worth noting that comparable experiments could not be performed with pristine Aga gels, as they fractured upon impact, highlighting the superior impact-dissipation capability of the AGK hydrogel. The enhanced impact performance can be attributed to the synergistic interaction between the boronate ester network and K⁺-stabilized G4-quartet supramolecular assemblies, which enable large deformations and efficient energy dissipation via reversible bond rupture and re-formation. Rapid reassembly of these dynamic interactions upon unloading facilitates swift shape recovery and self-healing. This combination of effective energy dissipation and autonomous repair positions the AGK hydrogel as a promising soft material for impact mitigation in applications including protective packaging, [ 24 ,28] cushioning, [29] wearable protection, and soft robotics. [30,31,32] 5. Impact Protection Performance of AGK Hydrogel For protective applications, soft materials must efficiently dissipate kinetic energy and minimize rebound to safeguard fragile contents during handling and transport. Hydrogels with pronounced viscoelasticity are particularly promising in this context, as their capacity for energy absorption and damping can surpass that of many conventional cushioning materials. [33] The AGK hydrogel can exhibit markedly superior impact-mitigation performance relative to conventional Aga gels, due to its enhanced deformation capacity and self-healing network architecture that facilitates energy dissipation upon mechanical loading. To evaluate protective functionality, controlled impact experiments were performed using custom-fitted hydrogel enclosures for fragile model objects, including a glass slide, glass bottle, egg, and grape. Two complementary impact scenarios were employed: (i) a foreign load impact, wherein a 100 g weight was dropped from a fixed height of 30 cm onto the hydrogel-covered object ( Figure 5a ), and (ii) a free-fall test, in which the entire hydrogel-encapsulated specimen was dropped from the same height to mimic real-world transport hazards ( Figure 5c ). In the load-drop test set-up, 100 g weight was dropped from 30 cm height above the lab-desk to check the capability of protecting the fragile material by the hydrogel material. Unprotected glass specimens such as glass slide shattered upon impact, whereas specimens protected with the AGK hydrogel remained intact, confirming effective shock absorption and dissipation of impact energy by the gel layer ( Figure 5b and Video SV3 ). Similarly, glass bottles enclosed in the hydrogel withstood three consecutive impacts without damage, in stark contrast to the destruction observed for unprotected controls. Similarly, delicate items such as eggs preserved their structural integrity only when enclosed within the hydrogel layer, whereas unprotected samples were readily damaged upon impact ( Video SV4 ). A comparable protective effect was observed for grapes, which also remained intact when shielded by the hydrogel. These results demonstrate that the hydrogel significantly reduces force transmission to enclosed objects, consistent with a low coefficient of restitution that minimizes rebound and enhances energy dissipation. In order to simulate mechanical stresses encountered during routine transportation and handling, a controlled free-fall test was performed from a height of 30 cm, representing moderate impact energy typical of accidental drops ( Figure 5c ). Fragile objects such as glass bottles were selected as model systems due to their low fracture toughness and high susceptibility to brittle failure under sudden loading ( Video SV5 ). In control experiments, unprotected samples fractured immediately upon free fall onto a rigid surface, reflecting rapid kinetic energy transfer and localized stress concentrations exceeding the material’s tensile strength. In contrast, specimens encapsulated within the AGK hydrogel exhibited no visible damage after impact ( Figure 5d ). A similar protective effect was observed for eggs, which also remained intact when shielded by the hydrogel. These observations indicate that the hydrogel layer effectively attenuates peak stress through viscoelastic deformation and energy dissipation, thereby preventing structural failure of both the encapsulated object and the gel matrix. Altogether, these results demonstrate effective energy absorption, stress distribution, and mechanical damping of the hydrogel material under impact, demonstrating its potential as a protective material for fragile goods during transportation and handling. 6. Sustainability and recyclability of AGK hydrogel Conventional polymer-based gel packing materials often composed of superabsorbent polymers such as sodium polyacrylate, polyacrylamide, and other synthetic copolymers pose significant environmental challenges due to their limited biodegradability and recyclability. [34 ,35] These synthetic hydrogels are typically non-degradable and persist in the environment, contributing to soil and water contamination and exacerbating microplastic pollution when disposed of improperly. In contrast, the AGK hydrogel is formulated from predominantly natural and biodegradable constituents, including Aga and Gua, with boric acid and K⁺ ions that are benign at low concentrations and can contribute nutrients in soil contexts. Aga, a polysaccharide derived from renewable resources, has documented biocompatibility and gradual biodegradation under physiological conditions, reinforcing its suitability for sustainable applications. Importantly, the AGK hydrogel demonstrates reusability through a simple aqueous thermal reprocessing protocol. Used gel materials can be dried, re-dissolved in water at ~90 °C, and recast into moulds to reform hydrogel structures ( Figure S10 ). This approach enables multiple reuse cycles with minimal processing energy and without generating persistent waste, aligning with principles of circular materials design and addressing key sustainability concerns in soft materials technology. Such recyclability not only reduces material waste but also enhances resource efficiency relative to single-use polymer gel packs. Moreover, the predominantly biodegradable nature of the AGK hydrogel components mitigates long-term environmental accumulation, making this dual-network system a promising candidate for sustainable, impact-mitigating applications where environmental safety is crucially important. 7. Conclusion In conclusion, we have developed an engineered, dynamically crosslinked double-network AGK hydrogel that integrates mechanical robustness, self-healing capability, and impact-absorbing functionality within a biodegradable platform. By coupling dynamic covalent crosslinks with supramolecular interactions, the hydrogel network can reversibly dissociate and reconstruct under external stress, enabling rapid structural recovery and efficient mechanical energy dissipation. This adaptive architecture successfully reconciles mechanical strength with network mobility, overcoming the traditional trade-off between stability and recoverability in protective hydrogel systems. The AGK hydrogel withstands compressive loads up to 5.4 kg, nearly twice that of pristine agarose, and exhibits a significantly reduced coefficient of restitution, confirming its superior impact attenuation capacity. Importantly, these mechanical advantages translate into practical protective performance, effectively safeguarding fragile materials such as glass substrates, bottles, eggs, and fruits under both static compression and dynamic free-fall conditions. The synergistic interplay between supramolecular crosslinking and diffusion-mediated molecular rearrangement ensures sustained resilience over repeated damage–recovery cycles without pronounced mechanical fatigue. Altogether, this work establishes a rational molecular design strategy for dynamically crosslinked double-network hydrogels that combine mechanical robustness with autonomous self-repair. The demonstrated protective performance and biodegradability position the AGK hydrogel as a promising candidate for sustainable packaging, transportation cushioning, and next-generation protective materials, while offering broader insights into the development of adaptive soft matter systems for advanced materials engineering. 8. Experimental Section/Methods Diffusion experiment A diffusion assay was designed to visualize K⁺-mediated network reorganization within the AGK hydrogel Aga solution (3 wt%) was mixed with Gua:H 3 BO 3 (25 mM each), and heated to 60°C to obtain transparent solution that was cast into a 3.5 cm Petri dish, and cooled to form a stable gel. Small wells were introduced using pipette tip, and K⁺ solution (25 mM) was added to two diagonal wells, while ThT in water (300 µM) was introduced into the remaining wells. Time-lapse imaging at 1-min intervals, followed by ImageJ analysis, enabled quantification of diffusion profiles. Load cell setup A 1 kg load cell, HX711 module, and Arduino Uno board were procured from Amazon India. To assemble the 1 kg load cell system, the load cell was mounted between two plywood bases with a load plate positioned on top ( Figure S8a ), and connected with a measurement setup comprising an HX711 module ( Figure S8b ) and an Arduino Uno ( Figure S8c ). The four load cell wires were connected to the HX711 as follows: black to E+, red to E−, green to A+, and white to A−. The HX711 was then connected to the Arduino Uno by wiring VCC to 5V, GND to GND, DT (DOUT) to digital pin 7, and SCK to digital pin 2 ( Figure S8d ). The Arduino was programmed with Code S1 , and the system was calibrated using a known standard weight. Upon application of load, the ‘Wheatstone bridge’ within the load cell generates a small millivolt-level signal, which is amplified and digitized into 24-bit data by the HX711. The Arduino reads this digital output at 100 millisecond intervals (timer-based sampling), enabling continuous data acquisition. The recorded data were exported as a .txt file to a specified directory on a PC using Visual Studio (open-source) software with Code S2 . Calibration of the instrument: The calibration was done using the Arduino software (calibration factor: -1673.8). And the calibration was crosschecked using the know weight from 1 g to 100 g ( Figure S8e ). Declarations Conflict of Interest A part of this work has been filed as Indian patent application (application no.: IN202641018722) with all the authors as inventor. 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Polyacrylamide degradation and its implications in environmental systems. npj Clean Water 2018, 1, 17. (https://doi.org/10.1038/s41545-018-0016-8) K. D. Nixon, Z. O. G. Schyns, Y. Luo, M. G. Ierapetritou, D. G. Vlachos, L. T. J. Korley, T. H. Epps III, Analyses of circular solutions for advanced plastics waste recycling. Nat. Chem. Eng. 2024, 1, 615– 626. (https://doi.org/10.1038/s44286-024-00121-6) Additional Declarations There is a conflict of interest A part of this work has been filed as Indian patent application (application no.: IN202641018722) with all the authors as inventor. Supplementary Files VideoSV1.mp4 Video SV1 VideoSV2.mp4 Video SV2 VideoSV3.mp4 Video SV3 VideoSV4.mp4 Video SV4 VideoSV5.mp4 Video SV5 Supportinginformation.docx Supporting information Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9445757","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":626835094,"identity":"6dda7122-ff7f-4781-a7e1-d240959e3708","order_by":0,"name":"Chandan Maity","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+ElEQVRIiWNgGAWjYDACCSDmAbMYGxgYKqBsBgPitDQ2MJxh4OEhQQvQGsY2OAc34J/d/OzBm5o7DLrth9sf8847LGPPwPzwA0PBHdyW3Dlmbjjn2DMGszOJjc282w4DHcZmLMFg8AynFgOJBDNpHrbDDGYHwFrSQH4xA4ofxqMl/Zs0zz+glvMPgVrmgLSwfyOgJcdMmrcNqOUGyJYGG6AWHvy2SNzIKZOc23eYx+zGw8aZc44BtRzmKZZIwKOFf0b6Nok33w7LmZ1Pf/DhTY2EPXt7+8YPH/7g1gID4NhgApPMQJxAUAMUMP4gVuUoGAWjYBSMKAAAvVNObgXAVc8AAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0002-8963-3175","institution":"Vellore Institute of Technology, Vellore Campus","correspondingAuthor":true,"prefix":"","firstName":"Chandan","middleName":"","lastName":"Maity","suffix":""},{"id":626835095,"identity":"621fbb52-6c2e-4859-9563-6454b9b86333","order_by":1,"name":"Dineshkumar Bharathidasan","email":"","orcid":"","institution":"Vellore Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Dineshkumar","middleName":"","lastName":"Bharathidasan","suffix":""}],"badges":[],"createdAt":"2026-04-17 07:51:21","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9445757/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9445757/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108095598,"identity":"e2114de0-49f1-4b7b-b8af-888247b3b3da","added_by":"auto","created_at":"2026-04-29 09:59:55","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":120681,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustration of the AGK double-network hydrogel preparation and its multifunctional performance. The diagram depicts the formation of boronate ester crosslinks between the diol unit of Aga and borate ions, and the K⁺-templated self-assembly of Gua into G4-quartet supramolecular structures, leading to additional physical crosslinking. The integrated network configuration enables self-healing, and effective impact absorption, demonstrating the potential of the hydrogel material for protective material applications.\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9445757/v1/535548919a16d7ee3feb893f.jpg"},{"id":108095600,"identity":"c77a6e1a-b5e2-4cf9-ad31-ea6be71d03cd","added_by":"auto","created_at":"2026-04-29 09:59:55","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":190289,"visible":true,"origin":"","legend":"\u003cp\u003eAGK-based supramolecular hydrogel. (a) Chemical structures of the molecular building blocks used to assemble AGK supramolecular scaffold, together with a schematic illustration of hydrogel fabrication by casting the precursor mixture into a mould to yield a freestanding hydrogel. (b) Comparative \u003csup\u003e1\u003c/sup\u003eH NMR spectra of the assembled AGK scaffold and its individual organic components, Aga and Gua. (c) Fluorescence microscopy image of the AGK hydrogel (scale bar = 100 µm). (d) FESEM image of the AGK material (scale bar = 5 µm).\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9445757/v1/cf194d0c3c422e0a9db5afd5.jpg"},{"id":108095602,"identity":"a2b24844-c0cc-4379-8e0f-a4328a2a39e3","added_by":"auto","created_at":"2026-04-29 09:59:55","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":149982,"visible":true,"origin":"","legend":"\u003cp\u003eK⁺-mediated G4-quadruplex assembly drives healing in AGK hydrogel. (a) Schematic illustration of a hydrogel after mechanical incision, showing a clearly separated interface. (b) Fluorescence microscopy image of the cut hydrogel in the absence of K⁺, displaying discontinuous ThT emission indicative of disrupted network connectivity. (c) Fluorescence image following K⁺ addition, showing merging of the cut surfaces and restoration of a continuous fluorescent network at the interface. (d) Schematic of the diffusion assay: opaque Gua–Aga gel containing wells loaded with K⁺ solution or aqueous ThT. Representative photographs show ion/dye diffusion and the K⁺-induced transition from an opaque Gua–Aga gel to a transparent matrix. (e) Quantification of diffusion by ImageJ analysis, measuring the width of the transparent region from the well centre (dotted line in d) over time. The dotted line is drawn to guide the eyes. (f) Autonomous self-healing of four separately cut hydrogel segments (two red, two blue). Initial separation (left), contact (middle), and formation of a single cohesive construct after healing (right).\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9445757/v1/3cb4f6e75d3803b25fe774f5.jpg"},{"id":108095604,"identity":"fbed581d-6b9d-4208-9354-2770a10e311d","added_by":"auto","created_at":"2026-04-29 09:59:55","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":263263,"visible":true,"origin":"","legend":"\u003cp\u003eRheological and mechanical characterization of Aga- and AGK-based hydrogels. (a, b) Strain sweep measurements of (a) Aga and (b) AGK hydrogels, showing storage (G′) and loss (G″) moduli as a function of applied strain. (c) Frequency sweep analysis comparing the viscoelastic responses of Aga and AGK hydrogels. (d) Compression force–displacement curves highlighting the enhanced mechanical strength of the AGK hydrogel relative to Aga. (e) Photograph of the load-bearing test setup using a 20 g applied load. (f) Load-holding performance and corresponding height profiles over time under varying applied loads (20, 50, and 100 g) and healed junction lengths (1.5 and 3.0 cm). (h) Coefficient of restitution (COR) values derived from the ball-drop test for Aga and AGK hydrogels. (i) Weight–time impact profiles of Aga (control) and AGK hydrogels subjected to 20, 50, and 100 g loads dropped from a height of 15 cm.\u003c/p\u003e","description":"","filename":"Figure4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9445757/v1/fa8be0deb5c28fee2be53f6b.jpg"},{"id":108182679,"identity":"c35e555f-a2af-4153-ac0f-e7f6ace338f4","added_by":"auto","created_at":"2026-04-30 08:59:29","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":299048,"visible":true,"origin":"","legend":"\u003cp\u003eImpact-mitigation performance of the AGK hydrogel under load-drop and free-fall conditions. (a) Schematic illustration of the load-drop test setup, in which a defined weight (100 g) was released from a fixed height of 30 cm onto the specimens. (b) Representative photographs of fragile objects (glass slide, glass bottle, egg, and grape) before, during, and after impact. Unprotected controls exhibited visible fracture or deformation upon impact, whereas hydrogel-encapsulated specimens remained intact, demonstrating effective shock absorption. (c) Schematic of the free-fall test configuration simulating accidental drop conditions from a height of 30 cm. (d) Post-impact photographs of glass bottle and egg subjected to free-fall tests, comparing unprotected controls (showing catastrophic damage) with AGK hydrogel-protected samples (remaining structurally intact). Scale bars = 1 cm.\u003c/p\u003e","description":"","filename":"Figure5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9445757/v1/16273ba0e2fb4a3b3f6c89db.jpg"},{"id":108806957,"identity":"d7cc247c-67b8-4072-aa91-e3449db6e9df","added_by":"auto","created_at":"2026-05-08 15:29:45","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1256297,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9445757/v1/66d51b74-46e6-46d7-8c5c-afaa65a7593a.pdf"},{"id":108095599,"identity":"8d76aefe-9736-4ade-a649-6bd0beea2abb","added_by":"auto","created_at":"2026-04-29 09:59:55","extension":"mp4","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":11786689,"visible":true,"origin":"","legend":"Video SV1","description":"","filename":"VideoSV1.mp4","url":"https://assets-eu.researchsquare.com/files/rs-9445757/v1/f01a65a93dbe39ef260479e8.mp4"},{"id":108182243,"identity":"fa602819-1b11-411a-87a4-af312734171f","added_by":"auto","created_at":"2026-04-30 08:59:16","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":11430703,"visible":true,"origin":"","legend":"Video SV2","description":"","filename":"VideoSV2.mp4","url":"https://assets-eu.researchsquare.com/files/rs-9445757/v1/75ed924fd79aa710065cd344.mp4"},{"id":108182379,"identity":"b8dac392-a627-4683-9cd2-c77a393c1b4a","added_by":"auto","created_at":"2026-04-30 08:59:20","extension":"mp4","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":31146372,"visible":true,"origin":"","legend":"\u003cp\u003eVideo SV3\u003c/p\u003e","description":"","filename":"VideoSV3.mp4","url":"https://assets-eu.researchsquare.com/files/rs-9445757/v1/ce4ba436e3fb171e2b6260e0.mp4"},{"id":108095605,"identity":"5e09b2a8-9544-4658-ad56-1ffc84ee2a8c","added_by":"auto","created_at":"2026-04-29 09:59:55","extension":"mp4","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":15059866,"visible":true,"origin":"","legend":"\u003cp\u003eVideo SV4\u003c/p\u003e","description":"","filename":"VideoSV4.mp4","url":"https://assets-eu.researchsquare.com/files/rs-9445757/v1/6591aca9204f63175c9e3765.mp4"},{"id":108095606,"identity":"1d266892-2cfe-412c-8c51-4d0f9a8ddfd2","added_by":"auto","created_at":"2026-04-29 09:59:55","extension":"mp4","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":2939335,"visible":true,"origin":"","legend":"\u003cp\u003eVideo SV5\u003c/p\u003e","description":"","filename":"VideoSV5.mp4","url":"https://assets-eu.researchsquare.com/files/rs-9445757/v1/c184a5e65207e8d90ca691ed.mp4"},{"id":108095607,"identity":"6203196f-b0a0-4f5c-ad09-c2257b5d098f","added_by":"auto","created_at":"2026-04-29 09:59:55","extension":"docx","order_by":6,"title":"","display":"","copyAsset":false,"role":"supplement","size":3949715,"visible":true,"origin":"","legend":"\u003cp\u003eSupporting information\u003c/p\u003e","description":"","filename":"Supportinginformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-9445757/v1/c6f3a08401f9c8cba7befef5.docx"}],"financialInterests":"There is a conflict of interest\nA part of this work has been filed as Indian patent application (application no.: IN202641018722) with all the authors as inventor.","formattedTitle":"Engineered double-network hydrogels for robust protection of fragile systems","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eHydrogels, three-dimensional polymer networks swollen with large amounts of water, have received tremendous interest across materials science, chemistry, and biomedical research due to their tunable mechanical properties, biocompatibility, and structural similarity to soft biological tissues. Beyond their widespread use in biomedical systems, there is growing interest in hydrogels for materials science applications that demand durability, impact resistance, and adaptability under dynamic mechanical conditions, such as protective layers, cushioning materials, and adaptive interfaces.\u003csup\u003e[1,2,3,4]\u003c/sup\u003e However, most conventional hydrogels, particularly those derived from natural polymers, remain mechanically weak and prone to irreversible damage, limiting their applicability in mechanically demanding environments. A promising strategy to overcome these limitations is the integration of dynamic covalent chemistry with supramolecular interactions, enabling polymer networks to reversibly break and re-form under stress while maintaining structural integrity. Recent advances in self-healing materials have demonstrated that reversible molecular interactions can endow polymer networks with the ability to autonomously recover after mechanical disruption.\u003csup\u003e[5,6,7]\u003c/sup\u003e Rational hydrogel design increasingly relies on combining dynamic covalent bonds with supramolecular interactions, allowing networks to reversibly dissociate and re-form under stress while maintaining functional integrity. Dynamic covalent chemistries such as imine bonds, disulfide exchange, and boronate ester linkages provide reversible covalent crosslinks that can reform to repair network defects and restore mechanical properties.\u003csup\u003e[8,9,10]\u003c/sup\u003e These mechanisms enable self-healing without external intervention and are widely used to improve hydrogel durability and service life. Among them, boronate ester bonds formed between borate ions and cis-diol-containing polymers offer rapid exchange kinetics and mechanical robustness, making them particularly attractive for self-healing hydrogels.\u003csup\u003e\u0026nbsp;[11]\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn parallel, supramolecular interactions such as hydrogen bonding, \u0026pi;\u0026ndash;\u0026pi; stacking interaction, host\u0026ndash;guest complexation, and metal\u0026ndash;ligand coordination introduces dynamic physical crosslinks that enable efficient energy dissipation and rapid network reconfiguration. Notably, G4-quartet assemblies, formed through potassium ion (\u003cstrong\u003eK\u003c/strong\u003e\u003cstrong\u003e⁺\u003c/strong\u003e)-templated stacking of guanosine units, generate extended supramolecular networks stabilized by hydrogen bonding and \u0026pi;\u0026ndash;\u0026pi; interactions, contributing to enhanced cohesion and responsiveness.\u003csup\u003e\u0026nbsp;[12]\u003c/sup\u003e Together, these reversible interactions form the foundation for hydrogels that integrate mechanical resilience with autonomous healing.\u003csup\u003e\u0026nbsp;[13,14]\u003c/sup\u003e Despite significant progress, achieving simultaneous mechanical robustness, efficient self-repair, and high energy dissipation within a single hydrogel platform remains a key challenge.\u003csup\u003e\u0026nbsp;[15,16]\u003c/sup\u003e Systems dominated by weak supramolecular interactions often lack sufficient mechanical strength, whereas permanently crosslinked networks sacrifice dynamic adaptability. Thus, there is a clear need for integrated design strategies that synergistically combine complementary dynamic interactions to meet the mechanical and functional demands of advanced soft materials.\u003c/p\u003e\n\u003cp\u003eHerein, we report a mechanically robust, self-healing double-network hydrogel (\u003cstrong\u003eAGK\u003c/strong\u003e, \u003cstrong\u003eFigure 1\u003c/strong\u003e) constructed from a natural polysaccharide scaffold, agarose (\u003cstrong\u003eAga\u003c/strong\u003e), and reinforced through the integration of dynamic boronate ester covalent crosslinks and K⁺-templated guanosine (\u003cstrong\u003eGua\u003c/strong\u003e) G4-quartet supramolecular assemblies. The diol-rich galactose units of Aga enable dynamic boronate ester formation, while Gua introduces additional physical crosslinks through supramolecular self-assembly. The resulting AGK hydrogel exhibits self-healing efficiency, superior energy dissipation, and impact-absorbing capability, positioning it as a promising platform for protective and adaptive materials in dynamic operating environments. This work provides a rational framework for developing sustainable soft materials that combine structural robustness with autonomous functional recovery.\u003c/p\u003e"},{"header":"2. Preparation of AGK hydrogel","content":"\u003cp\u003eThe supramolecular/polymer double-network AGK hydrogel was synthesized by dissolving Gua and boric acid in equimolar amounts (1:1 molar ratio) in water with continuous stirring at\u0026nbsp;~90 \u0026deg;C until a clear solution was obtained (\u003cstrong\u003eFigure 2a\u003c/strong\u003e). Subsequently, 3 wt % Aga was incorporated and fully dissolved under the same conditions, followed by the addition of K⁺\u0026nbsp;ions to trigger gelation. The resulting solution was cast into a mold and cooled at ambient conditions to obtain AGK-based hydrogels of the desired dimensions. Systematic optimization of the Gua concentration (12.5\u0026ndash;100 mM) revealed that 25.0 mM was sufficient to impart noticeable self-healing capability to the hydrogel matrix. Increasing Gua content enhanced self-healing performance, indicating a positive correlation between supramolecular crosslink density and dynamic repair efficiency. However, higher concentrations (\u0026gt;100 mM) compromised structural integrity, presumably due to excessive supramolecular crosslinking or phase separation, resulting in mechanically weaker gels. These observations indicate the importance of balancing dynamic and mechanical interactions in double-network systems. The optimal formulation of AGK hydrogel was identified as 3 wt % Aga with Gua and boric acid each at 50.0 mM (1:1 molar ratio), ensuring a robust network with efficient self-healing and mechanical strength suitable for impact-absorbing applications. Introduction of a potassium ion source, either KCl or KOH, initiated gelation. It is worth mentioning that addition of KOH (as K\u003csup\u003e+\u003c/sup\u003e source) elevated the pH to\u0026nbsp;~8, accelerating gelation.\u0026nbsp;However, the elevated pH resulting from the addition of KOH posed challenges to maintaining gel shape integrity. The rapid gelation kinetics under alkaline conditions hindered precise control over gel uniformity and molding, potentially resulting in irregular or poorly defined structures.\u0026nbsp;In contrast, KCl maintained solution pH and allowed controlled morphology during gel formation and\u0026nbsp;therefore, KCl was employed in all subsequent experiments.\u003c/p\u003e\n\u003cp\u003eSuccessful network formation was confirmed through comprehensive spectroscopic and microscopic structural characterization. In the \u003csup\u003e1\u003c/sup\u003eH NMR spectra (recorded in DMSO-D\u003csub\u003e6\u003c/sub\u003e at room temperature), Aga displayed characteristic signals at \u0026delta; \u0026asymp; 5.20\u0026ndash;4.28 ppm. Upon addition of boric acid, these signals shifted downfield to\u0026delta; \u0026asymp; 4.90\u0026ndash;4.21 ppm, consistent with the formation of dynamic boronate ester linkages between borate ions and the diol functionalities of Aga (\u003cstrong\u003eFigure 2b\u003c/strong\u003e). Upon incorporation of Gua and K⁺, a new peak at \u0026delta; \u0026asymp; 7.49 ppm emerged, indicative of a distinct chemical environment arising from Gua\u0026ndash;borate complexation and G4-quartet assembly. FTIR spectra of the hydrogel exhibited combined features of both Aga and Gua, with O\u0026ndash;H stretching at 3297 cm⁻\u0026sup1;, C\u0026ndash;H stretching at 2919, and 2846 cm⁻\u0026sup1;, C=O and C=N vibrations of Gua at 1736 and 1650 cm⁻\u0026sup1;, and a B\u0026ndash;O\u0026ndash;C vibration at 1412 cm⁻\u0026sup1; corresponding to borate\u0026ndash;diol crosslinks (\u003cstrong\u003eFigure S1\u003c/strong\u003e). The band at 1053 cm⁻\u0026sup1; was assigned to C\u0026ndash;O and C\u0026ndash;O\u0026ndash;C modes of the Aga backbone, collectively confirming covalent and supramolecular network integration.\u0026nbsp;Powder X-ray diffraction (pXRD) analysis demonstrated that the crosslinked AGK hydrogel exhibited an amorphous structure, in contrast to the semi-crystalline diffraction pattern observed for Gua. This transformation indicates that crosslinking disrupted the ordered molecular packing of Gua (\u003cstrong\u003eFigure S2\u003c/strong\u003e).\u0026nbsp;Morphological analysis via fluorescence microscopy, using Thioflavin T (ThT)\u003csup\u003e\u0026nbsp;[17]\u003c/sup\u003e as a G4-quartet probe, demonstrated minimal fluorescence in the absence of K⁺\u0026nbsp;(\u003cstrong\u003eFigure S3\u003c/strong\u003e), consistent with isolated Gua assemblies.\u003csup\u003e\u0026nbsp;[18]\u003c/sup\u003e With K⁺, a continuous fluorescent network was observed (\u003cstrong\u003eFigure 2c\u003c/strong\u003e), confirming extensive K⁺-templated supramolecular crosslinking. FESEM imaging revealed a transition from a layered polymer morphology in Aga alone (\u003cstrong\u003eFigure S4\u003c/strong\u003e) to a dense, fibrillar network in the presence of K⁺\u0026nbsp;(\u003cstrong\u003eFigure 2d\u003c/strong\u003e), highlighting the role of G4-quartet assembly in reinforcing the hydrogel matrix. In contrast, Gua-Aga gel lacking G4-quartet exhibited a non-homogeneous morphology in the FESEM image (\u003cstrong\u003eFigure S5\u003c/strong\u003e), consistent with their static network architecture.\u003csup\u003e\u0026nbsp;[19]\u003c/sup\u003e\u003c/p\u003e"},{"header":"3. Self-healing with AGK hydrogel","content":"\u003cp\u003eFollowing the successful fabrication of the AGK hydrogel from readily available building blocks and its thorough structural characterization, we proceeded to investigate its self-healing behavior and the specific role of K⁺\u0026nbsp;ions. These ions promote the formation of G4-quartet structures that act as dynamic physical cross-links within the network. By bridging polymer chains, they enhance network connectivity, which is essential for mechanical strength and efficient self-repair. These supramolecular motifs, stabilized by hydrogen bonding and \u0026pi;\u0026ndash;\u0026pi; stacking in the presence of K⁺, are known to strengthen guanosine-based supramolecular hydrogel networks.\u003csup\u003e\u0026nbsp;[20]\u003c/sup\u003e To directly assess the role of K⁺\u0026nbsp;in self-healing,\u0026nbsp;hydrogel materials were prepared with and without K⁺\u0026nbsp;in the presence of the G4-responsive fluorophore ThT, followed by mechanical incision (\u003cstrong\u003eFigure 3a\u003c/strong\u003e). In the absence of K⁺, fluorescence microscopy revealed discrete ThT-emissive domains confined to disconnected guanosine assemblies (\u003cstrong\u003eFigure 3b\u003c/strong\u003e), indicating disrupted network continuity and no healing. Dense ThT fluorescence at the disconnected site and no fluorescence at non-affected sites represent absence of G4-quarete. By contrast, K⁺-containing hydrogels displayed a bright fluorescent network spanning the cut interface (\u003cstrong\u003eFigure 3c\u003c/strong\u003e), evidencing re-established G4-quartet cross-links and rapid restoration of structural integrity.\u0026nbsp;To visualize this process dynamically, a diffusion assay was performed in which K⁺\u0026nbsp;solution (25 mM) was introduced into wells within a preformed AGK gel (3 wt% Aga with 25 mM Gua:H₃BO₃), while ThT in water served as a control (\u003cstrong\u003eFigure 3d\u003c/strong\u003e). Time-lapse imaging and ImageJ analysis demonstrated a linear K⁺\u0026nbsp;diffusion front (\u003cstrong\u003eFigure 3e\u003c/strong\u003e), accompanied by a transition from an opaque to a transparent hydrogel matrix (\u003cstrong\u003eFigure S6a\u003c/strong\u003e and \u003cstrong\u003eVideo SV1\u003c/strong\u003e). ThT diffusion alone caused only dye transport without structural change, confirming that network reorganization arises specifically from K⁺-induced G4 assembly. In a complementary experiment, K⁺\u0026nbsp;diffusion across a preformed crack promoted interfacial closure and restoration of homogeneity (\u003cstrong\u003eFigure S6b\u003c/strong\u003e). Collectively, these results demonstrate that K⁺\u0026nbsp;diffusion drives G4-quadruplex reassembly, enabling recovery of transparency, structural continuity, and mechanical integrity.\u003c/p\u003e\n\u003cp\u003eTo further demonstrate the self-healing behaviour, four AGK-based hydrogel specimens (two coloured red and two blue) were individually cut and brought into contact (\u003cstrong\u003eFigure 3f\u003c/strong\u003e). Spontaneously hydrogel fragments fused at their interfaces in ~3 minutes without external intervention, forming a single, mechanically cohesive construct capable of supporting its own weight upon lifting. This robust restoration of structural integrity highlights the dynamic and reversible nature of K⁺-mediated G4-quartet cross-links, which permit network rearrangement and reconnection after damage. These observations highlight the central role of K⁺-induced supramolecular interactions in imparting resilience and repeatable self-healing to the hydrogel system.\u003c/p\u003e"},{"header":"4. Rheological and mechanical characterization of AGK hydrogel","content":"\u003cp\u003eThe viscoelastic behaviour of the double-network AGK hydrogel was systematically evaluated using oscillatory shear rheology. Disc-shaped samples (25 mm diameter, 1 mm thickness) were subjected to strain-sweep and frequency-sweep experiments to probe network stability and deformation tolerance. In the strain sweep, the storage modulus (G\u0026prime;) consistently exceeded the loss modulus (G\u0026Prime;) for both Aga (\u003cstrong\u003eFigure 4a\u003c/strong\u003e) and AGK hydrogel (\u003cstrong\u003eFigure 4b\u003c/strong\u003e) across a broad strain range, confirming dominant elastic behaviour typical of solid-like hydrogel networks. The linear viscoelastic regime extended from 0.1 % to 10 % strain for Aga and 0.1 % to 30 % strain for AGK, indicating enhanced mechanical resilience and resistance to deformation in the composite network relative to pure Aga. Based on these observations, a nominal strain of 0.1 % within the linear viscoelastic regime was selected for subsequent frequency sweep analyses (\u003cstrong\u003eFigure 4c\u003c/strong\u003e). Frequency sweeps revealed parallel, strain-independent profiles for G\u0026prime; and G\u0026Prime; across the tested range, reflecting a consistent viscoelastic balance and network stability. The loss tangent (tan \u0026delta; = G\u0026Prime;/G\u0026prime;), a key indicator of the relative contributions of viscous and elastic components, remained \u0026lt;1 for both gels, confirming that elastic, solid-like behaviour predominates and that the networks maintain their structural integrity under deformation. The slightly higher tan \u0026delta; value for AGK (0.113) compared to Aga (0.085) suggests increased viscous dissipation in the composite gel, consistent with its enhanced strain tolerance and dynamic network rearrangement.\u003c/p\u003e\n\u003cp\u003eCompression testing further differentiated the mechanical profiles of the gels (\u003cstrong\u003eFigure 4d, Figure S7\u003c/strong\u003e). Aga exhibited a compressive stress of\u0026nbsp;~0.06 MPa at 15 % strain, characteristic of a softer, more compliant material. In contrast, AGK sustained nearly double the stress (~0.11 MPa) at larger strains (~25 %), demonstrating superior load-bearing capacity and stiffness. Correspondingly, AGK withstood a maximum force of\u0026nbsp;~53 N (\u0026asymp;5.4 kgf) at 4.7 mm displacement, compared to\u0026nbsp;~29 N (\u0026asymp;2.9 kgf) at 2.7 mm for Aga, highlighting its enhanced compressive toughness and energy dissipation that are critical parameter for impact-absorbing materials.\u003csup\u003e\u0026nbsp;[21]\u003c/sup\u003e The interfacial attachment strength was further assessed using a load-holding capacity test. In this experiment, two gel segments (Gel 1 and Gel 2; \u003cstrong\u003eFigure 4e\u003c/strong\u003e) were stacked with a third gel segment (Gel 3), allowed to stick via healing, and subsequently suspended vertically. The upper end of the assembly was secured with a clip, while calibrated weights were attached to the free end via a 10 cm nylon string affixed to Gel 2. For a healed junction length (d) of 3 cm, the construct sustained loads of 50, and 100 g, with the 100 g load maintained for over 7 min, as indicated by stable height profiles (\u003cstrong\u003eFigure 4f\u003c/strong\u003e). Reducing the junction length to 1.5 cm diminished load-bearing performance. The assembly reliably supported 20 g, whereas 50 g was sustained for\u0026nbsp;~2 min. These results demonstrate that increasing the self-healed interfacial area significantly enhances load-holding capacity and mechanical stability, likely due to the increased material volume and more effective stress distribution at the interface.\u003c/p\u003e\n\u003cp\u003eAltogether, these rheological and mechanical data demonstrate that the AGK hydrogel exhibits robust viscoelasticity, enhanced compressive strength, and effective load-bearing and energy-dissipating characteristics, attributable to its dynamic boronate ester and G4-quartet‐reinforced double network. These characteristics are essential for advanced protective materials and resilient soft interfaces.\u003c/p\u003e"},{"header":"5. Impact-mitigation performance of AGK hydrogel","content":"\u003cp\u003eAgarose (Aga) hydrogels at low polymer content (\u0026le;1.5 wt %) are known to exhibit viscoelastic damping and adjustable stiffness, making them effective for basic impact absorption applications.\u003csup\u003e\u0026nbsp;[22,23]\u003c/sup\u003e However, their inherent brittleness and lack of self-healing compromise shape retention and structural integrity under repeated loading, and increasing Aga content to\u0026nbsp;~3 wt % enhances elasticity at the cost of increased rebound on impact, rendering them less suitable for energy dissipation tasks. The dual-network design of the AGK hydrogel overcomes these limitations by combining a dynamic boronate ester polysaccharide network with Gua-derived supramolecular assemblies, enabling the material to deform, absorb kinetic energy, and recover via rapid reformation of dynamic bonds. Impact dissipation was quantified by coefficient of restitution (COR) using a standardized ball-drop test.\u003csup\u003e\u0026nbsp;[\u003c/sup\u003e\u003csup\u003e24]\u003c/sup\u003e When a 53.6 g marble was dropped from 25 cm (\u003cstrong\u003eFigure 4g, Video SV2\u003c/strong\u003e), the bare surface exhibited a COR of\u0026nbsp;~0.83, and 3 wt % Aga gel showed moderate energy loss (COR \u0026asymp; 0.58, \u003cstrong\u003eFigure 4h\u003c/strong\u003e). In contrast, the AGK (50 mM) hydrogel yielded a significantly lower COR (~0.21), indicating efficient energy absorption with minimal rebound and highlighting its potential as an effective shock-absorbing medium. Such low COR values reflect the material\u0026rsquo;s ability to dissipate impact energy rather than elastically reflect it, a characteristic desirable for protective packaging and cushioning applications.\u003csup\u003e\u0026nbsp;[25,26]\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eTo further evaluate impact absorption, load cell tests were conducted.\u003csup\u003e\u0026nbsp;[27]\u003c/sup\u003e The load cell was assembled and operated (see load cell setup in Supporting Information and \u003cstrong\u003eFigure S8a-c\u003c/strong\u003e). The system was calibrated using standard weights from 1 to 100 g (\u003cstrong\u003eFigure S8d\u003c/strong\u003e). Gel discs (4 cm diameter, 5 mm thickness) were placed on the impact plate, and weights of 20, 50, and 100 g were dropped from heights of 15 and 30 cm through a hollow plastic tube to ensure controlled vertical impact. The impact response was recorded in real time and converted into weight (g) versus time (ms) profiles. For impacts from 15 cm, the hydrogel exhibited significant impact absorption across all tested weights compared to the no-gel control (\u003cstrong\u003eFigure 4h\u003c/strong\u003e). A similar trend was observed for impacts from 30 cm (\u003cstrong\u003eFigure S9\u003c/strong\u003e). It is worth noting that comparable experiments could not be performed with pristine Aga gels, as they fractured upon impact, highlighting the superior impact-dissipation capability of the AGK hydrogel.\u003c/p\u003e\n\u003cp\u003eThe enhanced impact performance can be attributed to the synergistic interaction between the boronate ester network and K⁺-stabilized G4-quartet supramolecular assemblies, which enable large deformations and efficient energy dissipation via reversible bond rupture and re-formation. Rapid reassembly of these dynamic interactions upon unloading facilitates swift shape recovery and self-healing. This combination of effective energy dissipation and autonomous repair positions the AGK hydrogel as a promising soft material for impact mitigation in applications including protective packaging,\u003csup\u003e\u0026nbsp;[\u003c/sup\u003e\u003csup\u003e24\u003c/sup\u003e\u003csup\u003e,28]\u003c/sup\u003e cushioning,\u003csup\u003e\u0026nbsp;[29]\u003c/sup\u003e wearable protection, and soft robotics.\u003csup\u003e\u0026nbsp;[30,31,32]\u003c/sup\u003e\u003c/p\u003e"},{"header":"5. Impact Protection Performance of AGK Hydrogel","content":"\u003cp\u003eFor protective applications, soft materials must efficiently dissipate kinetic energy and minimize rebound to safeguard fragile contents during handling and transport. Hydrogels with pronounced viscoelasticity are particularly promising in this context, as their capacity for energy absorption and damping can surpass that of many conventional cushioning materials.\u003csup\u003e[33]\u003c/sup\u003e The AGK hydrogel can exhibit markedly superior impact-mitigation performance relative to conventional Aga gels, due to its enhanced deformation capacity and self-healing network architecture that facilitates energy dissipation upon mechanical loading. To evaluate protective functionality, controlled impact experiments were performed using custom-fitted hydrogel enclosures for fragile model objects, including a glass slide, glass bottle, egg, and grape. Two complementary impact scenarios were employed: (i) a foreign load impact, wherein a 100 g weight was dropped from a fixed height of 30 cm onto the hydrogel-covered object (\u003cstrong\u003eFigure 5a\u003c/strong\u003e), and (ii) a free-fall test, in which the entire hydrogel-encapsulated specimen was dropped from the same height to mimic real-world transport hazards (\u003cstrong\u003eFigure 5c\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003eIn the load-drop test set-up, 100 g weight was dropped from 30 cm height above the lab-desk to check the capability of protecting the fragile material by the hydrogel material. Unprotected glass specimens such as glass slide shattered upon impact, whereas specimens protected with the AGK hydrogel remained intact, confirming effective shock absorption and dissipation of impact energy by the gel layer (\u003cstrong\u003eFigure 5b\u0026nbsp;\u003c/strong\u003eand\u003cstrong\u003e\u0026nbsp;Video SV3\u003c/strong\u003e). Similarly, glass bottles enclosed in the hydrogel withstood three consecutive impacts without damage, in stark contrast to the destruction observed for unprotected controls. Similarly, delicate items such as eggs preserved their structural integrity only when enclosed within the hydrogel layer, whereas unprotected samples were readily damaged upon impact (\u003cstrong\u003eVideo SV4\u003c/strong\u003e). A comparable protective effect was observed for grapes, which also remained intact when shielded by the hydrogel. These results\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003edemonstrate that the hydrogel significantly reduces force transmission to enclosed objects, consistent with a low coefficient of restitution that minimizes rebound and enhances energy dissipation.\u003c/p\u003e\n\u003cp\u003eIn order to simulate mechanical stresses encountered during routine transportation and handling, a controlled free-fall test was performed from a height of 30 cm, representing moderate impact energy typical of accidental drops (\u003cstrong\u003eFigure 5c\u003c/strong\u003e). Fragile objects such as glass bottles were selected as model systems due to their low fracture toughness and high susceptibility to brittle failure under sudden loading (\u003cstrong\u003eVideo SV5\u003c/strong\u003e). In control experiments, unprotected samples fractured immediately upon free fall onto a rigid surface, reflecting rapid kinetic energy transfer and localized stress concentrations exceeding the material\u0026rsquo;s tensile strength. In contrast, specimens encapsulated within the AGK hydrogel exhibited no visible damage after impact (\u003cstrong\u003eFigure 5d\u003c/strong\u003e). A similar protective effect was observed for eggs, which also remained intact when shielded by the hydrogel. These observations indicate that the hydrogel layer effectively attenuates peak stress through viscoelastic deformation and energy dissipation, thereby preventing structural failure of both the encapsulated object and the gel matrix. Altogether, these results demonstrate effective energy absorption, stress distribution, and mechanical damping of the hydrogel material under impact, demonstrating its potential as a protective material for fragile goods during transportation and handling.\u003c/p\u003e"},{"header":"6. Sustainability and recyclability of AGK hydrogel","content":"\u003cp\u003eConventional polymer-based gel packing materials often composed of superabsorbent polymers such as sodium polyacrylate, polyacrylamide, and other synthetic copolymers pose significant environmental challenges due to their limited biodegradability and recyclability.\u003csup\u003e[34\u003c/sup\u003e\u003csup\u003e,35]\u003c/sup\u003e These synthetic hydrogels are typically non-degradable and persist in the environment, contributing to soil and water contamination and exacerbating microplastic pollution when disposed of improperly. In contrast, the AGK hydrogel is formulated from predominantly natural and biodegradable constituents, including Aga and Gua, with boric acid and K⁺\u0026nbsp;ions that are benign at low concentrations and can contribute nutrients in soil contexts. Aga, a polysaccharide derived from renewable resources, has documented biocompatibility and gradual biodegradation under physiological conditions, reinforcing its suitability for sustainable applications. Importantly, the AGK hydrogel demonstrates reusability through a simple aqueous thermal reprocessing protocol. Used gel materials can be dried, re-dissolved in water at\u0026nbsp;~90 \u0026deg;C, and recast into moulds to reform hydrogel structures (\u003cstrong\u003eFigure S10\u003c/strong\u003e). This approach enables multiple reuse cycles with minimal processing energy and without generating persistent waste, aligning with principles of circular materials design and addressing key sustainability concerns in soft materials technology. Such recyclability not only reduces material waste but also enhances resource efficiency relative to single-use polymer gel packs. Moreover, the predominantly biodegradable nature of the AGK hydrogel components mitigates long-term environmental accumulation, making this dual-network system a promising candidate for sustainable, impact-mitigating applications where environmental safety is crucially important.\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"7. Conclusion","content":"\u003cp\u003eIn conclusion, we have developed an engineered, dynamically crosslinked double-network AGK hydrogel that integrates mechanical robustness, self-healing capability, and impact-absorbing functionality within a biodegradable platform. By coupling dynamic covalent crosslinks with supramolecular interactions, the hydrogel network can reversibly dissociate and reconstruct under external stress, enabling rapid structural recovery and efficient mechanical energy dissipation. This adaptive architecture successfully reconciles mechanical strength with network mobility, overcoming the traditional trade-off between stability and recoverability in protective hydrogel systems. The AGK hydrogel withstands compressive loads up to 5.4 kg, nearly twice that of pristine agarose, and exhibits a significantly reduced coefficient of restitution, confirming its superior impact attenuation capacity. Importantly, these mechanical advantages translate into practical protective performance, effectively safeguarding fragile materials such as glass substrates, bottles, eggs, and fruits under both static compression and dynamic free-fall conditions. The synergistic interplay between supramolecular crosslinking and diffusion-mediated molecular rearrangement ensures sustained resilience over repeated damage\u0026ndash;recovery cycles without pronounced mechanical fatigue.\u003c/p\u003e \u003cp\u003eAltogether, this work establishes a rational molecular design strategy for dynamically crosslinked double-network hydrogels that combine mechanical robustness with autonomous self-repair. The demonstrated protective performance and biodegradability position the AGK hydrogel as a promising candidate for sustainable packaging, transportation cushioning, and next-generation protective materials, while offering broader insights into the development of adaptive soft matter systems for advanced materials engineering.\u003c/p\u003e"},{"header":"8. Experimental Section/Methods","content":"\u003cp\u003e \u003cb\u003eDiffusion experiment\u003c/b\u003e \u003c/p\u003e \u003cp\u003eA diffusion assay was designed to visualize K⁺-mediated network reorganization within the AGK hydrogel Aga solution (3 wt%) was mixed with Gua:H\u003csub\u003e3\u003c/sub\u003eBO\u003csub\u003e3\u003c/sub\u003e (25 mM each), and heated to 60\u0026deg;C to obtain transparent solution that was cast into a 3.5 cm Petri dish, and cooled to form a stable gel. Small wells were introduced using pipette tip, and K⁺ solution (25 mM) was added to two diagonal wells, while ThT in water (300 \u0026micro;M) was introduced into the remaining wells. Time-lapse imaging at 1-min intervals, followed by ImageJ analysis, enabled quantification of diffusion profiles.\u003c/p\u003e \u003cp\u003e \u003cb\u003eLoad cell setup\u003c/b\u003e \u003c/p\u003e \u003cp\u003eA 1 kg load cell, HX711 module, and Arduino Uno board were procured from Amazon India. To assemble the 1 kg load cell system, the load cell was mounted between two plywood bases with a load plate positioned on top (\u003cb\u003eFigure S8a\u003c/b\u003e), and connected with a measurement setup comprising an HX711 module (\u003cb\u003eFigure S8b\u003c/b\u003e) and an Arduino Uno (\u003cb\u003eFigure S8c\u003c/b\u003e). The four load cell wires were connected to the HX711 as follows: black to E+, red to E\u0026minus;, green to A+, and white to A\u0026minus;. The HX711 was then connected to the Arduino Uno by wiring VCC to 5V, GND to GND, DT (DOUT) to digital pin 7, and SCK to digital pin 2 (\u003cb\u003eFigure S8d\u003c/b\u003e). The Arduino was programmed with \u003cb\u003eCode S1\u003c/b\u003e, and the system was calibrated using a known standard weight.\u003c/p\u003e \u003cp\u003eUpon application of load, the \u0026lsquo;Wheatstone bridge\u0026rsquo; within the load cell generates a small millivolt-level signal, which is amplified and digitized into 24-bit data by the HX711. The Arduino reads this digital output at 100 millisecond intervals (timer-based sampling), enabling continuous data acquisition. The recorded data were exported as a .txt file to a specified directory on a PC using Visual Studio (open-source) software with \u003cb\u003eCode S2\u003c/b\u003e.\u003c/p\u003e \u003cp\u003eCalibration of the instrument: The calibration was done using the Arduino software (calibration factor: -1673.8). And the calibration was crosschecked using the know weight from 1 g to 100 g (\u003cb\u003eFigure S8e\u003c/b\u003e).\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eConflict of Interest\u003c/h2\u003e \u003cp\u003eA part of this work has been filed as Indian patent application (application no.: IN202641018722) with all the authors as inventor.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor contributions\u003c/h2\u003e \u003cp\u003eC.M. and D.B. conceived the idea and designed the research. D.B. performed the experiments. D.B. and C.M. analyzed the data, and C.M. supervised the overall project. C.M. and D.B. wrote the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eAll authors acknowledge the central instrumental facility of VIT Vellore to carry out the work.\u003c/p\u003e\u003ch2\u003eData Availability Statement\u003c/h2\u003e \u003cp\u003eSupporting figures and videos are provided in the Supporting Information. Additional data supporting this study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eS. Fuchs, K. Shariati, M. Ma. Specialty tough hydrogels and their biomedical applications. Adv. Healthcare Mater. 2020, 9, 1901396. (https://doi.org/10.1002/adhm.201901396)\u003c/li\u003e\n\u003cli\u003eX. Kuang, M. O. Arıcan, T. Zhou, X. Zhao, Y. S. Zhang. Functional tough hydrogels: design, processing, and biomedical applications. Acc. Mater. Res. 2023, 4, 101\u0026ndash;114. (https://doi.org/10.1021/accountsmr.2c00026)\u003c/li\u003e\n\u003cli\u003eN. Petelin\u0026scaron;ek, S. Mommer. Tough hydrogels for load-bearing applications. Adv. Sci. 2024, 11, 2307404. (https://doi.org/10.1002/advs.202307404) \u003c/li\u003e\n\u003cli\u003eY. Liu, Z. Guo. Small functional hydrogels with big engineering applications. Mater. Today Phy. 2024, 43, 101397. 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(https://doi.org/10.1038/s44286-024-00121-6)\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"double-network hydrogel, self-healing material, energy dissipation, supramolecular assembly, boronate ester crosslinking, G4-quartet, impact protection","lastPublishedDoi":"10.21203/rs.3.rs-9445757/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9445757/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHydrogels capable of rapid mechanical energy dissipation are highly attractive for impact protection and shock-absorbing applications, yet conventional systems often rely on viscoelastic damping or irreversible sacrificial bonds, resulting in slow recovery and mechanical fatigue. Herein, we report an engineered double-network hydrogel (AGK) that integrates covalent boronate ester crosslinks with supramolecular G4-quartet assemblies to achieve enhanced mechanical robustness and resilience. This synergistic architecture enables stress-induced network dissociation and reconfiguration, facilitating efficient energy dissipation alongside rapid, autonomous self-healing. The AGK hydrogel sustains compressive loads of up to ~\u0026thinsp;5.4 kg, demonstrating significant mechanical strength. Coefficient of restitution measurements reveal a low rebound (COR\u0026thinsp;\u0026asymp;\u0026thinsp;0.21), indicative of superior impact attenuation and energy absorption. Consequently, the hydrogel effectively protects fragile systems, such as glass substrates and eggs, under both static loading and free-fall impact without fracture. The combined covalent and supramolecular interactions further enable repeated damage\u0026ndash;recovery cycles with minimal performance degradation. Overall, this work establishes a rational molecular design strategy that integrates dynamic crosslinking with hierarchical energy dissipation, providing a promising platform for mechanically robust, self-healing hydrogels in sustainable protective materials and advanced impact-mitigation applications.\u003c/p\u003e","manuscriptTitle":"Engineered double-network hydrogels for robust protection of fragile systems","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-29 09:59:47","doi":"10.21203/rs.3.rs-9445757/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"1e2945f0-2c34-4f68-8785-51dc727c3eb7","owner":[],"postedDate":"April 29th, 2026","published":true,"recentEditorialEvents":[{"type":"decision","content":"Reject after peer review","date":"2026-05-08T10:03:18+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"This content is not available.","date":"2026-05-07T14:44:56+00:00","index":2,"fulltext":"This content is not available."},{"type":"editorInvitedReview","content":"This content is not available.","date":"2026-05-06T15:21:56+00:00","index":3,"fulltext":"This content is not available."}],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":66709550,"name":"Physical sciences/Materials science/Soft materials/Gels and hydrogels"},{"id":66709551,"name":"Physical sciences/Chemistry/Polymer chemistry/Supramolecular polymers"}],"tags":[],"updatedAt":"2026-05-08T10:06:02+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-29 09:59:47","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9445757","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9445757","identity":"rs-9445757","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}