Copper-Coordination Engineered Glassy Hydrogels Featuring Ultrastiffness and Structural Programmability

Abstract

Glassy hydrogels, which maintain a distinctive glassy state at ambient temperature, are appealing for engineering applications. Nevertheless, the existing glassy hydrogels often suffer from inferior strength, inadequate stiffness, and environmental stability caused by weak physical cross-linking. Herein, we present an ultrastiff and ultrastrong glassy hydrogel by introducing robust coordination bonds into a network composed of polyacrylic acid (PAA) and polyvinyl alcohol (PVA), using a copper acetate-assisted strategy. The presence of acetate anions creates a relatively alkaline environment, which deprotonates the carboxyl groups of PAA. This deprotonation exposes carboxylate groups that readily coordinate with copper ions, establishing a densely cross-linked network in the glassy state. The resultant glassy hydrogel exhibits record-breaking Young's modulus (469.7 MPa), tensile strength (19.2 MPa), and exceptional environmental stability. Moreover, the reversible softening and vitrification induced by the breakage and reforming of coordination bonds endows glassy hydrogel with structural programmability, allowing for the construction of integrated auxetic hydrogel (IAH). The IAH demonstrates enhanced mechanical properties compared to the auxetic skeleton alone while maintaining a negative Poisson's ratio over a wide strain range of 0–29%. This study provides a promising engineering route for the development of advanced glassy hydrogels.