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Open access Jul 2026

An Ionically Crosslinked Hyperelastic Hydrogel With Extreme Environmental Tolerance and Self-Strengthening Capability.

Hyperelastic hydrogels have broad application prospects in coatings and flexible sensors. However, these flexible polymer networks often suffer from severe water loss and performance degradation under long-term use and extreme environmental conditions. Here, ionic interactions were used to fabricate a superelastic hydrogel with long-term stability. By modulating the calcium chloride (CaCl2)-chitosan (CTS) ionic cross-linking network, the formation of a "pearl necklace" structure in methacryloyloxyethyltrimethylammonium chloride (DMC) was promoted. Grazing incidence small-angle x-ray scattering (GISAXS) and atomic force microscopy (AFM) confirmed the formation of this structure. Acrylamide provides anchoring sites for the chloride salts, which enhance the ion adhesion and hygroscopic-moisture balance of the hydrogel network. This mechanophysical interaction confers excellent stability to the hydrogel through self-strengthening. The non-oriented hyperelastic network allows the hydrogel to recover quickly after stretching to an areal strain greater than 12 000% and to remain flexible at temperature extremes from -50°C to 120°C. Differential Scanning Calorimetry (DSC) shows that more than 90% of the water in the hydrogel does not undergo a phase transition during this process. Our work provides new insights into the fabrication of flexible hydrogels that can be stably used under extreme conditions.

Yuxuan He, Zhihong Yu, Xian Zhang et al. · 0 citations
Aug 2026

CaCl2-Enhanced Interpenetrating Polymer Network Hydrogels with Stable Freeze Resistance and Sensing Durability Performance.

Hydrogels are attractive for flexible electronics and wearable sensors, yet their performance is severely limited at subzero temperatures due to ice crystallization, dehydration, and mechanical embrittlement. Here, we report a CaCl2-enhanced double-network (DN) hydrogel (BNP-x) that integrates excellent anti-freezing, mechanical, and adhesive properties with reliable strain-sensing capabilities. The hydrogel combines a covalently crosslinked P(NIPAm-co-HEA) network and an ionically coordinated poly(acrylic acid) network, in which Ca2+ ions regulate water states and suppress ice formation. The optimized BNP-6 hydrogel exhibits excellent low-temperature performance, maintaining a tensile strength of 0.16 MPa and an elongation at break of ∼849% at -30 °C with minimal mass loss and stable properties over repeated freeze-thaw cycles. Owing to the synergistic DN structure and mobile Ca2+ ions, BNP-6 retains high ionic conductivity (44.1 mS cm-1 at -10 °C), representing only a 17.9% decrease compared to its room-temperature value. Moreover, the hydrogel demonstrates stable adhesion, rapid strain response, and reliable sensing performance under subzero conditions-even during cyclic deformation and self-healing processes-highlighting its potential for robust low-temperature wearable electronics and bioelectronic interfaces operating in harsh environments.

Jizhe Feng, Yumeng Li, Xiaoai Yang et al. · 0 citations
Aug 2026

Cellulose Nanofibril-Reinforced Triple Physically Cross-Linked Double-Network Hydrogels

The introduction of reversible physical cross-linking constitutes a viable strategy for fabricating hydrogels with excellent mechanical properties, efficient self-recovery, and shape-memory capability. In this study, tannic acid-functionalized cellulose nanofibrils (TA@CNF) served as the core functional filler and were incorporated into a polyacrylamide-acrylic acid-stearyl methacrylate (P(AAm-AAc-SMA)) matrix to construct a nanocomposite hydrogel. In this system, TA@CNF not only served as a nanoscale reinforcing phase but also synergistically participated in the construction of multiple physical cross-linking networks through its abundant phenolic hydroxyl functional groups on the surface. Specifically, the polymeric network was stabilized by the incorporation of four distinct physical reinforcement mechanisms. These include (i) nanoparticle reinforcement provided by TA@CNF; (ii) hydrophobic associations among the PSMA segments; (iii) hydrogen bonding, which occurs both between TA@CNF and PSMA and within each individual component; and (iv) multiple metal-coordination bonds formed between Fe3+ ions and the phenolic groups of TA@CNF, as well as the carboxyl groups of PAAc segments. Benefiting from the pivotal bridging role of TA@CNF across the aforementioned multiple physical cross-linking networks, the resulting TA@CNF/P(AAm-AAc-SMA)/Fe3+ hydrogels (THFs) exhibited significantly improved mechanical properties. The optimal hydrogels demonstrated excellent mechanical performance, with a high tensile strength (8.31 MPa), elongation at break (700%), and toughness (39.59 MJ·m–3). Owing to reversible physical cross-links and TA@CNF flexibility, the hydrogels also showed self-recovery (achieving 52% toughness recovery within 10 min), outstanding fatigue resistance, and reliable shape-memory performance. The mechanical properties and multifunctional performance of these tough hydrogels made them well-suited for use in load-bearing and soft actuator applications.

Siyu Chen, Chengqian Gao, D. Yin · 0 citations
Aug 2026

Double-modified guar gum dual-network hydrogels with balanced mechanical and swelling properties.

Polysaccharide-based hydrogels suffer from an inherent trade-off between mechanical strength and swelling capacity, along with poor structural stability under complex conditions, which severely restricts their industrial scalability. Herein, a targeted dual-side-chain modification strategy (hydroxypropylation combined with phosphation) was developed, and a rigid-flexible dual-network (DN) hydrogel was constructed via the interpenetrating of modified guar gum derivatives with polyacrylamide (PAM). A critical crosslinking density threshold of 0.1 g/10 g system was identified, where the rigid modified guar gum backbone and flexible PAM network formed a homogeneous interpenetrating structure. This unique structure enabled the hydrogel to achieve a compressive strength exceeding 500 ± 26 kPa and swelling ratio of 46-fold, realizing an excellent balance between mechanical performance and swelling behavior. For extreme agricultural scenarios, the borate-ion-crosslinked B(OH)4--HPG/PAM hydrogel retained 85% of its mechanical properties under high temperature and salinity. For acidic complex wounds, the phosphorylated Ca2+-PGG/PAM hydrogel (esterification degree 0.12 ± 0.01) exhibited a superior swelling ratio via pH-responsive dissociation of coordination bond. This scenario-adaptive bio-based hydrogel constructed via rational molecular modification provides a feasible solution for agricultural water retention in extreme environments and advanced dressings for complex wounds, and offers a design paradigm for polysaccharide-based hydrogels with balanced mechanical-swelling properties.

Wenhao Zhang, Lun Chen, Chao Tian et al. · 0 citations
Open access Jul 2026

Poly(itaconic Acid) Hydrogels with Dynamic Covalent and Supramolecular Cross-Links for High and Tunable Mechanical Properties

Aiming toward sustainability, poly(itaconic acid) has been considered as an alternative to the widely used fossil-based poly(acrylic acid). Its application has been, however, limited by its lower mechanical properties due to challenges in the polymerization processes. Herein, we report photopolymerizable and thermoreversible hydrogels based on poly(itaconic acid) allowing tunability from high strength (∼1000 kPa) plastically yielding materials to soft elastomeric-like stretchability, also allowing thermoresponsive flow, and a relatively high water absorption of 384 g/g. The thermal gel melting stems from the dynamic covalent bonds, in combination with metal-ion-mediated supramolecular connections. The materials facilitate on-demand water stability while allowing gel-to-sol melting for thermal extrusion for 3D-printing, a combination not observed in classic permanent covalent networks. To promote sustainability, biosourceable starting materials are used without additional solvents or purification steps. Given the biocompatibility of the components, potential applications can be foreseen, such as tissue growth scaffolds, medical and hygienic superabsorbents, and tough hydrogels for soft robotics.

H. Savolainen, Maximilian J. L. Hagemann, Mika Salmi et al. · 0 citations
Aug 2026

Enhanced Mechanical Properties of PVA-Based Multifunctional Conductive Hydrogel Sensors with Cyclodextrin Slide-Ring as a Crosslinker

Developing hydrogels that simultaneously combine high mechanical robustness, antifreezing capability, and stable conductivity remains a substantial challenge for flexible sensing materials. Herein, we report a multifunctional conductive rotaxane-crosslinked hydrogel constructed from a γ-cyclodextrin/poly(ethylene glycol) diacrylate (γ-CD/PEGDA) slide-ring crosslinker embedded in a poly(vinyl alcohol) (PVA)/acrylamide (AM)/xanthan gum (XG)/Zn2+ network. The threaded crosslinker introduces movable junctions into the network, allowing stress redistribution through a pulley effect and thereby improving the mechanical performance of the hydrogel. Together with hydrogen bonding, Zn2+ coordination, and the physically crosslinked PVA network, this design generates a robust multicomponent architecture. The optimized hydrogel exhibited a tensile stress of 3.2 MPa, an elongation at break of 254%, and a toughness of 40 MJ m−3, together with high puncture resistance and cyclic stability. The hydrogel also showed a freezing point of −20.59 °C and a low equilibrium swelling ratio in water, indicating favorable antifreezing and antiswelling performance. Owing to interconnected ionic conduction pathways, the material further displayed stable ionic conductivity and reliable strain-sensing behavior over a broad strain range, with rapid response/recovery and effective monitoring of human motion and subtle physiological activities. This work provides a practical strategy for constructing mechanically robust, antifreezing, and conductive hydrogels for wearable sensing and related bioelectronic applications.

Jie Ren, Ziqiong Zhou, Wenjing Zhang et al. · 0 citations