Topological transitions in Reversible and Active Hydrogels

We investigate two classes of swollen polymer networks whose organization and mechanics are governed by topology.

 In the first part, we study reversible gels formed by transient binding of long polymer chains via short linkers, designed to mimic protein–RNA mixtures with specific binding interactions. Depending on the number of binding sites per chain, the system exhibits either liquid–liquid phase separation or gelation without macroscopic demixing. Coarse-grained simulations quantitatively match the mean-field theory of Danielsen, Semenov, and Rubinstein [Macromolecules 56, 5661 (2023)].  Notably, heterogeneity in sticker  sequence has little effect on overall phase behavior but does influence the microstructure of the dense phase.

 In the second part, we examine irreversibly crosslinked gels  containing light-driven molecular rotors as active crosslinkers. Upon irradiation, these gels contract via irregular chain twisting, reminiscent of artificial muscle actuation. Simulations reproduce experimental trends and reveal a universal scaling behavior, providing insights into possible mechanical responses to activity in topological soft materials.