Superentangled polymer networks by stable acoustic cavitation

Entanglements of polymer chains are a crucial structural factor in determining the mechanical properties. However, entropic polymers cannot surpass the thermodynamic equilibrium, imposing an upper bound on the material property space. Here, we demonstrate a superentangled state, where polymer chains entangle beyond the thermodynamic equilibrium, through spatiotemporally controlled stable cavitation induced by focused ultrasound (FUS). Upon stable cavitation, microbubbles periodically expand and shrink with negligible sonochemical effects, generating stable yet strong micro acoustic streaming that further densifies entanglements. Using highly entangled polyacrylamide hydrogels as a model material, we demonstrate that the modulus exceeds the thermodynamic limit by about 34.7%, confirming the superentangled state. This physical approach demonstrates entanglement density as a programmable design parameter, unlocking new possibilities for developing high-performance soft materials.