Bioinspired learning and memory in ionogels through fast response and slow relaxation dynamics of ions

Introduction

Biological intelligence arises from the seamless integration of rapid sensing, associative learning, and long-term memory, processes fundamentally controlled by the selective transport and dynamic relaxation of ions^{1, 2, 3–4}. These ion-regulated mechanisms allow biological systems to respond, adapt, and store information with efficiency. Inspired by these natural processes, synthetic ionic materials such as hydrogels and ionogels have garnered significant attention for their potential to mimic sensory functions. Recent advances have enabled these materials to replicate basic sensory behaviors, demonstrating their utility in bioinspired systems^{5, 6, 7, 8–9}. However, their ability to achieve higher-order functions such as learning and memory remains severely limited, falling far short of the capabilities of their biological counterparts. Bridging this gap is critical to advance the development of intelligent soft materials that integrate perception, learning, and memory, offering transformative opportunities in wearable devices, soft robotics, and adaptable systems¹⁰.

To compensate the limitations of soft ionic materials, traditional solid-state semiconductors are used for signal processing and data storage due to their tunable electronic properties, including rectification and non-linear current-voltage characteristics¹¹. More recently, semiconductor heterostructures have also been combined with ionic interfacial layers to enable environmental sensing and signal processing within these hybrid devices^12,13. While these approaches achieve high efficiency, they fundamentally rely on the charge injection and storage properties of inorganic semiconductors, rather than fully utilizing the intrinsic capabilities of the ionic materials. The reliance on solid-state components inherently lacks the flexibility, stretchability, and self-healing properties that are features of biological tissues, ultimately restricting their mechanical compatibility and adaptability for real-time interaction with soft biological and ionic systems⁹. In the search for more biologically compatible solutions, people have explored polyelectrolyte fluids within confined micro- or nanochannels to develop fluidic ionic diodes, transistors, and memristors^2,14,15. While promising, these approaches are often hampered by stability issues, particularly the risk of leakage associated with aqueous media¹⁶. Quasi-solid ionogels offer an alternative, as they can mitigate leakage while translating external stimuli into changes in ion distribution, enabling the stimulus sensing and signal rectification observed in biological systems^{5,7,17, 18, 19–20}. However, existing ionogels still face a challenging trade-off between fast response and slow relaxation dynamics of ions, which...