Extensile Active Hydrogels Driven by Living FtsZ Polymers

Embedding living polymers that consume chemical energy into synthetic gels offers a route to soft materials that self-regulate their mechanical state. Here, The bacterial cytokinetic protein FtsZ is integrated within a polyacrylamide network to create an active extensile hydrogel. Upon post-gelation activation with Mg²⁺ and GTP, FtsZ filaments treadmill and exert internal stresses that drive isotropic swelling and mechanical softening. These responses is described using a Flory-Rehner swelling framework, where activity-induced volume expansion lowers the polymer volume fraction and, consequently, the elastic modulus. Normalizing the measured moduli to the FR baseline isolates an additional, rate-dependent softening that arises from living FtsZ polymer dynamics. Rheological analysis reveals that biochemical energy input modulates the elastic state of a pre-formed network through active swelling and strain-dependent fluidization, establishing a minimal model for living-polymer-driven soft materials.