Self-Healing and Moldable Poly(2-isopropenyl-2-oxazoline) Supramolecular Hydrogels Based on a Transient Metal Coordination Network

Materials that are capable of autonomous healing upon damage is the focus of many research groups because of the numerous potential applications of these materials, such as coatings, actuators for robotic applications, and wound healing. Although significant progress in the area has been achieved, the synthesis and large-scale applications of self-healing and moldable materials continue to be challenging. The present study highlights the use of poly(2-isopropenyl-2-oxazoline) partially modified with 2,2':6',2 ''-terpyridine-4'-carboxylic acid (TPy) for the synthesis of self-healing and moldable metallo-supramolecular hydrogels by metal coordination. The hydrogelation was triggered by the addition of divalent transition metal ions (e.g., Fe2+, Ni2+, Co2+, and Zn2+). Using this approach, metallo-supramolecular hydrogels with tunable rheological properties could be obtained, while evidencing the correlation between the hydrogel mechanical properties and the binding strength and kinetic lability of the supramolecular cross-linking motifs. The resulting hydrogels exhibited rapid self-healing properties at room temperature as confirmed by rheological measurements. Moreover, hydrogels cross-linked with Co2+ and Zn2+ showed a gel-sol transition, indicative of the higher kinetic lability of their complexes. The hydrogels exhibited fast and excellent repeatable autonomic healing capacity even at higher cross-linking density, making them useful as autonomously repairing materials and coatings. Compared to the conventional metallo-hydrogels, the herein developed hydrogels can be molded into a variety of complex geometrical shapes, which could be potentially applied in various areas from soft robotics to dynamic self-healing coatings.