Memristive Behavior of a Graphite-Hydrogel-Graphite Nanodevice

Iontronic nanofluidic memristors have garnered significant interest as promising platforms for mimicking energy-efficient neuromorphic functions by exploiting nonlinear ion transport in aqueous environments to emulate the signal transmission mechanisms of biological systems. In this study, we present a bipolar iontronic memristor composed of graphite-hydrogel-graphite layers functioning within an electrolyte environment, where the central hydrogel layer is composed of electrically neutral, soft, and biocompatible poly(lactic-co-glycolic acid) (PLGA) polymer. Our all-atom Molecular Dynamics (MD) simulations reveal that the proposed device exhibits distinctive memristive behavior, including a hysteretic current-voltage response under applied transmembrane voltages. Notably, the central dense hydrogel layer plays a pivotal role in inducing in-channel ion concentration polarization and also influences ion transport by selectively trapping cations through electrostatic interactions with the negatively charged oxygen atoms of the polymer. In addition, we systematically investigate the effects of electrolytes, nanopore surface charge, and hydrogel porosity on device performance. Stronger hysteresis in ionic current is observed with KCl compared to NaCl, while excessive nanopore charge reduces hysteresis due to ion saturation in the central hydrogel layer. Decreasing hydrogel porosity alters the ion mobility though it preserves the memristive behavior. Altogether, these findings offer molecular-level insights and design strategies for realizing and optimizing soft-matter-based iontronic memristors for relevant neuromorphic applications.