Engineering hydrophobically associated hydrogels with rapid self‐recovery and tunable mechanical properties using metal‐ligand interactions

Abstract

In this contribution, hydrophobic association and metal‐ligand coordination have been employed in a dual physical crosslinking strategy to access hydrogels based on micellar copolymerization of acrylamide and a hydrophobic acrylic monomer (containing terpyridine (terpy) for metal‐ligand interaction). The mechanical properties of these hydrogels are strongly influenced by the thermodynamic stability and kinetic lability of the metal‐terpy crosslinks present in these materials. While the hydrogel tensile strength and stability on water exposure are enhanced by choosing stronger Fe2+‐terpy crosslinks, the weaker and more kinetically labile Zn2+‐terpy coordination bonds enable significantly higher energy dissipation under tensile loading and self‐healing in the resultant hydrogels.

Dynamic metal–ligand cross‐link promoted mechanically robust and pH responsive hydrogels for shape memory, programmable actuation and resistive sensing application

“…These results are consistent with more elastic nature of the D‐X‐(10%) hydrogels and indicate that the hydrogen bonding interactions present in the S‐X‐(10%) hydrogel can dissociate and re‐associate during the application of the strain. Similar frequency sweep behaviors have been previously observed for ionically cross‐linked alginate based hydrogels, 38 hydroxyethyl cellulose based hydrogels having H‐bonding cross‐linking associations 39 as well as terpyridine‐metal ion cross‐linked polymer hydrogels 40 . Step strain experiment was undertaken to study the self‐healing behavior of the hydrogels.…”

“…Similar frequency sweep behaviors have been previously observed for ionically cross-linked alginate based hydrogels, 38 hydroxyethyl cellulose based hydrogels having H-bonding cross-linking associations 39 as well as terpyridine-metal ion cross-linked polymer hydrogels. 40 Step strain experiment was undertaken to study the self-healing behavior of the hydrogels. Consecutive cycles (duration: 100 s) of low strain (10%) and large strain (5000%) at 1 Hz frequency were applied to the S-X-(10%) hydrogels.…”

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

“…Nonetheless, the preparation process of this PDN hydrogel was sophisticated, and the employment of organic solvent might be harmful to the environment. Hence, many efforts [33][34][35] have been conducted to develop hydrogels with high strength, toughness, and excellent self-recoverability via convenient approaches without using any organic solvent.…”

Poly(acrylamide‐co‐acrylic acid)/chitosan semi‐interpenetrating hydrogel for pressure sensor and controlled drug release

“…Many strategies have been explored to enhance the mechanical properties of hydrogels through the incorporation of specific structures, such as nanocomposite hydrogels, 16 topological slide‐ring hydrogels, 17 and double‐network hydrogels 18 . One practical method to enhance the comprehensive mechanical properties of synthetic hydrogels is to introduce a dynamic crosslinking network or reversible sacrificial bonds to the network 19 . The chemical crosslinks work as permanent crosslinking points, imparting strength to hydrogel, while the weak bonds with reversibility, broken by loading and reformed by unloading, serve as sacrificial bonds that dissipate energy to endow hydrogel with high toughness 19,20 …”

“…One practical method to enhance the comprehensive mechanical properties of synthetic hydrogels is to introduce a dynamic crosslinking network or reversible sacrificial bonds to the network 19 . The chemical crosslinks work as permanent crosslinking points, imparting strength to hydrogel, while the weak bonds with reversibility, broken by loading and reformed by unloading, serve as sacrificial bonds that dissipate energy to endow hydrogel with high toughness 19,20 …”