Theory of non-equilibrium signal processing in hydrogels

Living organisms store and differentiate information by processing complex dynamic environmental signals. Current hydrogel-based systems are constrained to an in-phase coupling between environmental changes and swelling or contraction. In order to integrate non-equilibrium complex signal processing capabilities into hydrogels, we model the interplay between transport of multiple chemical signals, their complexation with the hydrogel network, and the resulting dynamic poroelastic responses. The theory guides the design of a bio-inspired experimental hydrogel system that can detect and report features of the environment it would otherwise be unable to differentiate. In particular, it (i) distinguishes between signals and their propagation direction, converts (ii) transient stimuli to continuous responses or (iii) continuous stimuli to transient responses, and (iv) filters signals or amplifies them. Our combined theoretical and experimental approach provides new functionalities for engineering applications where complex signal processing is critical, ranging from sensors to soft robotics.