Conductive, Tough, Transparent, and Self-Healing Hydrogels Based on Catechol–Metal Ion Dual Self-Catalysis

Abstract

Tough and conductive hydrogels are the promising materials for various applications. However, fabrication of these hydrogels at room or low temperatures, without external stimuli, is a challenge. Herein, a novel dual self-catalytic system composed of a variety of metal ions and catechol-based molecules was developed to efficiently trigger the free-radical polymerization of tough, conductive, transparent, and self-healing hydrogels at low temperature without any external stimuli. Ferric ions (Fe3+) and dopamine (DA) were chosen as model compounds, which form stable redox pairs that act as a dual self-catalytic system to activate ammonium persulfate to generate free radicals. Consequently, the radicals could rapidly trigger the hydrogel self-gelation at low temperatures (6 °C) within 5 s. The dual self-catalytic system opens up a facile route to synthesize multifunctional hydrogels at mild conditions for a broad range of applications, especially in tissue engineering and wearable electronics.

Physical Double‐Network Hydrogel Adhesives with Rapid Shape Adaptability, Fast Self‐Healing, Antioxidant and NIR/pH Stimulus‐Responsiveness for Multidrug‐Resistant Bacterial Infection and Removable Wound Dressing

“…For the adhesion mechanism, both oxidation and coordination exist in the catechol−Fe 3+ based adhesive, and the coordination effect is dominant due to metal ions' stabilizing deprotonated catechol groups. [ 33 ] Besides, the catechol was oxidation‐resistant as the siderophores exhibited robust adhesion energy from pH 3.5 to pH 7.5. [ 34 ] Actually, in the catechol−Fe 3+ based adhesive, the bidentate hydrogen bond and catechol–metal coordination bond were recognized as the major factors that contribute to the adhesive properties, [ 22a ] as well as other noncovalent bonding (hydrophobic interaction and π/cation–π stacking) and covalent bonding (substrates containing amine or thiol groups through Schiff base or Michael addition reactions).…”

4D Printed Hydrogels: Fabrication, Materials, and Applications

“…For example, a number of hydrogels having high electrical conductivity and good mechanical strength have been reported. [ 34,120,121 ] The conductive and stretchable hydrogel has the potential for application as the matrix of electrical‐ and mechanical‐responsive hydrogel composites. On the other hand, the output signal for current 4D printed hydrogel devices is limited mainly to the mechanical and biological; the output signals of hydrogels in other areas are seldom employed for 4D printing.…”

Soft and Ion‐Conducting Materials in Bioelectronics: From Conducting Polymers to Hydrogels

“…Hydrogels can conduct electrons, ions, and even small molecules . Moreover, self‐healing and self‐adhesive hydrogels are ideal candidates for skin‐attached electronics …”