Li Wang

Soft iontronic devices, which utilize ions as charge carriers and integrate flexibility and stretchability, exhibit diverse carrier species, high biocompatibility, multimodal stimulus responsiveness, and strong resistance to electromagnetic interference. These features make them highly promising for applications in ionic circuits, flexible sensing, implantable systems, and neuromorphic information processing. Among them, soft iontronic diodes have attracted sustained attention over the past two decades as fundamental building blocks of functional circuits. This review systematically summarizes the material types of soft iontronic diodes and their influence on key device performance. It further elucidates the mechanisms underlying ionic rectification and highlights recent advances in logic gate implementation, energy harvesting, flexible sensing, and neuromorphic computing. Finally, we discuss key challenges and future opportunities in this field, aiming to provide design principles and mechanistic insights for the development and application of soft iontronic diodes.

The depletion of fossil resources and environmental pollution issues have accelerated the development of biomass-based lightweight porous materials. Cellulose-based lightweight porous materials (CLPMs) have emerged as ideal alternatives to petroleum-based porous materials owing to their advantages of renewability and biodegradability. Ambient pressure drying has become an ideal solution for the large-scale production of CLPMs; owing to its low cost, short processing time, and ease of operation. However, challenges such as strong capillary forces, reorganization of intermolecular hydrogen bonds, and insufficient framework strength can lead to the collapse of the porous structure during the drying process. This review systematically summarizes the research progress of ambient pressure drying techniques for CLPMs, providing an in-depth analysis of the intrinsic mechanisms underlying structural collapse in terms of capillary pressure, hydrogen bond reorganization, and structural strength. Based on this analysis, five major control strategies for ambient pressure drying, such as solvent substitution and surface hydrophobic modification, are outlined. Furthermore, this review comprehensively discusses the practical application prospects of such materials in adsorption, thermal insulation, and other fields. This review aims to provide theoretical references for the development and industrialization of CLPMs.

Biological perception represents a sophisticated process that seamlessly integrates adaptive sensory processing with neural computation. The core mechanism involves transforming external stimuli into potential signals with receptor–synapse synergy enabled by precise ion transport. Inspired by nature’s paradigm, we present an adaptive neuromorphic tactile perception system that couples piezoionic sensing with synaptic computing functions via nanochannel-mediated ion transport. The biomimetic tactile device is a composite of two ionic hydrogel films separated by a PET nanochannel membrane. Similar to mechanosensitive ion channels, applied pressure drives ions to selectively traverse the nanochannels, producing fast-adaptive transmembrane potential in single units and slow-adaptive potential maintenance via force-driven coupling of piezoionic signaling with electrical relaxation across interconnected units. Leveraging adaptive sensory signaling within interconnected units, the neuromorphic system reduces the recording consumption of pressure information by 75% and achieves 92.3% texture recognition accuracy. This capability offers a promising pathway toward overcoming integration and computation bottlenecks in wearable intelligent sensing.

This review summarizes advances in neuromorphic iontronic devices based on soft ionic conductors, highlighting ion transport mechanisms, design principles, structure–function relationships, and challenges to guide their future development.

The signal transmission utilizing ions as carriers provides the brain with efficient and outstanding computational capability. The controllable ion transport in neurons relies on a multiplicity of ion channels, which have ångström (Å) dimensions. The interactions between ions and channel walls contribute to their nonlinear ion transport behavior, which can be manifested as natural memory resistors, i.e., memristors. However, it remains a great challenge to understand the relationship between the nonlinear ion transport behaviors of different solid-state ionic memristors and artificial ion channel properties. Here, we present two different unipolar and bipolar ionic memristors based on artificial Å-scale channels in polymeric membranes with varying surface charge densities. The resistive switching mechanism of ionic memristors is attributed to synergistic energy barriers arising from size exclusion and interactions between ions and channel walls. The synaptic functions were mimicked by configuring synaptic devices using ionic memristors, which can be used to stimulate artificial neural network algorithms for energy-efficient image recognition. Our results open a pathway for revealing the nonlinear dynamics of fluidic memristors based on artificial Å-scale channels and realizing neuromorphic computation in aqueous media.

The effective and precise processing of visual information by the human eye primarily relies on the diverse contrasting functions achieved through synaptic regulation of ion transport in the retina. Developing a bio‐inspired retina that uses ions as information carriers can more accurately replicate retina's natural signal processing capabilities, enabling high‐performance machine vision. Herein, an ion‐confined transport strategy is proposed to construct a bio‐inspired retina by developing artificial synapses with inhibitory and excitatory contrasting functions. By fine‐tuning the ionic hydrogel structures to control ion transport across the heterogeneous interfaces, inhibitory and excitatory synapses are realized to negatively or positively modulate the optical signal. The integration of these synapses facilitates advanced tasks such as image recognition and motion analysis. Moreover, as a proof of concept, guiding robot vehicles to perform path planning is demonstrated. This work offers a new idea for constructing the bio‐inspired retina by precisely regulating ion transport, allowing it to reach a level closer to the biological retina.

Living organisms with diverse perceptual functions interact with their environment through ion activity, a feature that bestows them with integrated processing, parallel operations, and efficient energy utilization. Inspired by this, an ionic hydrogel device is presented that seamlessly integrates multimodal sensing and synaptic properties, creating a simplified architecture for self‐powered tactile‐visual fusion perception. The precise control of ion transport through piezoionic and ionic thermodiffusion effects in the bilayer asymmetric hydrogel facilitates self‐driven multimodal sensing. The ionic relaxation effect, arising from differing mobilities between anions and cations, contributes to synaptic characteristics, including short‐term and long‐term plasticity. Consequently, this device alone constitutes a self‐powered tactile‐visual perception fusion system with signaling pathways similar to those of the skin and retina, endowing robotic arms with intelligent grasping capabilities and reflexive behaviors akin to human danger avoidance. Moreover, the device exhibits minimum pressure and light intensity detection limits of 3.6 KPa and 35.7 mW cm⁻², respectively, and operates without the need for an external power supply for information writing and reading, highlighting its practical applicability. This work offers valuable insights for developing neuronal sensing information integration devices facing humanoid robots and human‐robot interactions.

Neuromorphic devices are designed to replicate the energy‐efficient information processing advantages found in biological neural networks by emulating the working mechanisms of neurons and synapses. However, most existing neuromorphic devices focus primarily on functionally mimicking biological synapses, with insufficient emphasis on ion transport mechanisms. This limitation makes it challenging to achieve the complexity and connectivity inherent in biological systems, such as ephaptic coupling. Here, an ionic biomimetic synaptic device based on a flexible ion‐gel nanofiber network is proposed, which transmits information and enables ephaptic coupling through capacitance formation by ion transport with an extremely low energy consumption of just 6 femtojoules. The hysteretic ion transport behavior endows the device with synaptic‐like memory effects, significantly enhancing the performance of the reservoir computing system for classifying the MNIST handwritten digit dataset and demonstrating high efficiency in edge learning. More importantly, the devices in an array establish communication connections, exhibiting global oscillatory behaviors similar to ephaptic coupling in biological neural networks. This connectivity enables the array to perform working memory tasks, paving the way for developing brain‐like systems characterized by high complexity and vast connectivity.

The next-generation brain-like intelligence based on neuromorphic architectures emphasizes learning the ionic language of the brain, aiming for efficient brain-like computation and seamless human-computer interaction. Ionic neuromorphic devices, with ions serving as information carriers, provide possibilities to achieve this goal. Soft and biocompatible ionic conductive hydrogels are an ideal substrate for constructing ionic neuromorphic devices, but it remains a challenge to modulate the ion transport behavior in hydrogels to mimic neuroelectric signals. Here, we describe an ionic potential relaxation effect in a hydrogel device prepared by sandwiching a layer of polycationic hydrogel (CH) between two layers of neutral hydrogel (NH), allowing this device to simulate various electrical signal patterns observed in biological synapses, including short- and long-term plasticity patterns. Theoretical and experimental results show that the selective permeation and hysteretic diffusion of ions caused by the anion selectivity of the CH layer are responsible for potential relaxation. Such an effect allows us with hydrogels to enable synapse-like information processing functions, including tactile perception, learning, memory, and neuromorphic computing. Additionally, the hydrogel device can operate stably even under 180° bending and 50% tensile strain, expanding the pathway for implementing advanced brain-like intelligent systems.