Making highly elastic and tough hydrogels from doughs

A hydrogel is often made from preexisting polymers by covalently crosslinking them into a polymer network. The crosslinks make the hydrogel swell-resistant but brittle. We present a method to resolve this conflict, making a hydrogel from a dough. The dough is formed by mixing long polymer chains with a small amount of water and photoinitiator. It is homogenized by kneading and annealing at elevated temperatures, during which the crowded polymer chains densely entangle. The polymer chains are then sparsely crosslinked into a polymer network under UV, and then swollen to equilibrium. The resulting hydrogel is both swell-resistant and tough, and shows near-perfect elasticity, high strength, high fatigue resistance, and low friction. We demonstrate the method with poly(ethylene glycol) and cellulose. The method is generally applicable to synthetic and natural polymers, and is compatible with industrial processing technologies, opening doors to the development of sustainable, high-performance hydrogels.