Development of Self-Healing Double-Network Hydrogels: Enhancement of the Strength of Wheat Gluten Hydrogels by In Situ Metal–Catechol Coordination

Wheat gluten, a byproduct of the wheat starch industry, is widely used as a dough strengthener and gelling agent. In this research, we developed novel double-network hydrogels by gelation of gluten using in situ metal–catechol coordination. The first network consisted of physically associated gluten molecules, while the second network consisted of Fe 3+ -cross-linked proanthocyanidins (PACs). Dynamic shear rheology experiments suggested that coordination of Fe 3+ and PACs greatly enhanced the mechanical properties of the gluten hydrogels. The double-network hydrogels exhibited a 3-fold higher shear modulus than pure gluten hydrogels. The formation of bis- and tris-catechol–Fe 3+ complexes between Fe 3+ and PACs in the hydrogels was confirmed by ultraviolet–visible spectrometry and isothermal titration calorimetry (ITC). The ITC measurements of Fe 3+ binding to PACs indicated a molar stoichiometry of 1:4 and a dissociation constant ( K D ) of 24.9 × 10 –9 . When subject to repeated shear deformation–compression cycles, the hydrogels exhibited strong and rapid recovery of their rheological properties. The strong, self-healing characteristics of the double-network gluten hydrogels produced in this study may be useful for certain applications in the food, agriculture, biomedicine, and tissue-engineering industries.