A Dual Physical Cross‐Linking Strategy to Construct Tough Hydrogels with High Strength, Excellent Fatigue Resistance, and Stretching‐Induced Strengthening Effect

Abstract

Hydrogels with excellent stiffness, toughness, anti‐fatigue, and self‐recovery properties are regarded as promising water‐containing materials. In this work, a dual physically cross‐linked (DPC) sodium alginate (SA)/poly[acrylamide (AAm)‐acrylic acid (AAc)‐octadecyl methacrylate (OMA)]‐Fe3+ hydrogel is reported, which is constructed by hydrophobic association (HA) and ionic coordination (IC). The optimal DPC hydrogel demonstrates excellent mechanical performance: tensile modulus of 0.65 MPa, tensile strength of 3.31 MPa, elongation at break of 1547%, and toughness of 27.8 MJ m–3. SA/P(AAm‐AAc‐OMA)‐Fe3+ DPC hydrogels also exhibit prominent anti‐fatigue and self‐recovery performance (99.1–109.7% modulus recovery and 90.4–108.9% dissipated energy recovery after resting for 5 min without additional stimuli at ambient temperature) through the reconstruction of reversible physical cross‐linking. Some of the SA/P(AAm‐AAc‐OMA)‐Fe3+ DPC hydrogels even exhibit a stretching‐induced strengthening effect, which is similar to the performance of muscle—“the more training, the more strength.” Hence, the combination of HA and IC will provide an effective approach to design DPC hydrogels with desirable mechanical performances and a longer service life for wider applications of soft materials.

Research Advances in Mechanical Properties and Applications of Dual Network Hydrogels

“…High-density electrostatic interaction and the formation of coordination bonds between Ag + and amino and carboxyl groups in PEC give the hydrogel strength up to 24 MPa and toughness up to 84.7 MJm −3 . Yang [ 22 ], by combining reversible hydrophobic binding (HA) with low binding energy and ion coordination (IC) with high binding energy, prepared sodium alginate/polyacrylamide acrylate-octadecyl methacrylate Fe 3+ (SA/P(AAM-AAC-OMA)-Fe 3+ ) hydrogel ( Figure 2 D). The former provides high tensile properties, while the latter offers high tensile modulus and strength.…”

“…2018, Wiley; ( D ) Preparation mechanism of sodium alginate/polyacrylamide-acrylate-octadecyl methacrylate Fe 3+ (SA/P(AAM-AAC-OMA)-Fe 3+ ) hydrogel. Reprinted with permission from [ 22 ]. 2021, Wiley.…”

Preparation of high‐strength, high‐modulus PVA fiber by synthesis of syndiotacticity‐rich high molecular weight PVA polymers with VAc and VBz via emulsifier‐free emulsion polymerization

“…At the same time, the PVA polymer with a high S‐diad has a high hydrogen bond concentration between molecules. As the number of intermolecular hydrogen bonds increases, a robust and durable network connection structure is generated between macromolecular chains, preventing the entanglement of macromolecules themselves, 37,52 PVA macromolecular chains with a low‐entanglement degree are more effective at stretching and can be straightened more quickly. After better stretching, the macromolecules in the PVA fiber tended to align along the axial direction, and the PVA fiber's crystallinity, orientation, and mechanical properties were subsequently enhanced 4,39 .…”

Design of a DNA‐Based Double Network Hydrogel for Electronic Skin Applications

“…constructed a fully physically cross‐linked alginate (SA)/poly(acrylamide‐acrylic acid ‐octadecyl methacrylate)‐Fe 3+ (SAp(AAm‐AAc‐OMA)‐Fe 3+ ) DN hydrogel using hydrophobic association and ionic coordination. [ 20 ] The hydrogel exhibited a tensile strength of 3.31 MPa, prominent anti‐fatigue properties, and a self‐recovery efficiency of ≈100% after 5 min.…”

“…[19] Recently, Gao et al constructed a fully physically cross-linked alginate (SA)/poly(acrylamide-acrylic acid -octadecyl methacrylate)-Fe 3+ (SAp(AAm-AAc-OMA)-Fe 3+ ) DN hydrogel using hydrophobic association and ionic coordination. [20] The hydrogel exhibited a tensile strength of 3.31 MPa, prominent anti-fatigue properties, and a self-recovery efficiency of ≈100% after 5 min.DNA is a biological macromolecule with a double-helix structure that can be reversibly switched by external stimuli, Electronic skin (e-skin) is widely studied for its ability to detect physiological information and provide feedback through electrical signals. Biocompatible stimulus-responsive DNA-based hydrogels exhibit high sensitivity, which makes them outstanding candidates for biomedical applications.…”