Abstract

Facile stiffness switching enables adaptive flexible smart materials. However, conventional hydrogels exhibit fixed mechanical properties once formed, struggling to flexibly switch between fluid and solid states, while lacking damage repair and rapid dissociation capabilities. Here, we propose a “solvent-regulated coacervate-gel transition” strategy. In this strategy, a reinforced reversible hydrogen-bond network between the polymer chains is formed after the hydration layer is disrupted by the poor solvent ethanol. This hydrogen-bond network can be densified or progressively dissociated by modulating the solvent and temperature. Ultimately, a liquid coacervate with an initial modulus of 12.69 Pa can be gradually programmed into stiff hydrogels and further into a dense xerogel with a modulus exceeding 15.10 MPa and compressive strength of 26.47 MPa. Importantly, these distinct mechanical states are reversibly interconvertible. Materials across this broad mechanical range exhibit rapid state-adaptive healing capability. They simultaneously maintain environmental stability under extreme pH and ionic environments, together with favorable biocompatibility. This work offers a new paradigm of performance-programmable smart materials for intelligent logistics monitoring, flexible wearable sensors, and biointegrated adaptive systems.