Neuromorphic iontronic devices based on soft ionic conductors

The human brain efficiently processes external information using ions as information carriers, inspiring the development of ionic brain-like intelligence. Central to such systems are neuromorphic iontronic devices (NIDs), including artificial axons, synapses, and neurons, which employ ions as charge carriers. Recently, NIDs based on soft ionic conductors (SICs), such as ionic hydrogels, ionogels, and ionic elastomers, have attracted growing attention due to their ionic compatibility, flexibility, biocompatibility, and facile fabrication and integration, making them promising candidates for next-generation neuromorphic technologies. Despite their potential, research remains in its infancy, with key challenges in elucidating fundamental mechanisms, establishing design principles, and realizing practical applications. To address these issues and guide future research, this review first introduces the functional roles and electrical signalling of axons, synapses, and neurons, thereby defining the performance requirements for NIDs. It then summarizes means for controlling ion transport in SICs and discusses feasible approaches for constructing SIC-based NIDs, including structural and interfacial engineering, device architectures, and dropletronic techniques. Finally, recent advances in SIC-based NIDs are reviewed, and their prospects in human-machine interaction and brain-like computing are discussed along with the remaining challenges.