The answer, according to the review, is a family of electrodeless RED and electrodialysis (ED) systems that operate as closed ionic circuits, in which charge transport is mediated solely by ions and no Faradaic reactions occur anywhere in the device. Veerman surveys the existing applications of these electrode-free generators and desalinators and introduces several conceptual designs presented for the first time, including an acid/base generator, a preconcentration unit that couples RED with assisted RED (ARED), and an alternating current RED generator. The unifying principle is elegant: because ED and RED employ essentially identical stack architectures of alternating cation exchange membranes (CEMs) and anion exchange membranes (AEMs), two or more such stacks can be wired together ionically, so that one stack’s electrical output drives the other stack’s ion pumping directly, without ever touching a wire.

The operating envelope of a RED stack explains why this coupling works. When current density is plotted against power density, three characteristic points stand out. At short-circuit condition, ion transport proceeds without any external power supply. At the maximum power point, RED systems are conventionally operated. At open-circuit condition, ion transport ideally vanishes, although incomplete membrane permselectivity leaves a small leakage current. Push the current density beyond the conventional RED range into strongly negative territory and the stack enters the ARED regime, where an external field assists the salinity-gradient-driven transport. ARED can be applied for pre-desalination of seawater when a lower-salinity stream, such as wastewater, is available. In an electrodeless coupled system, one RED stack can supply exactly that assisting field to another, closing the ionic loop between generator and desalinator.

The historical roots of this idea reach back to the 1950s. Manecke, regarded as the founder of RED technology, described a Membranakkumulator in 1952, a device based on ED and RED that could store electrical energy. A few years later, Pattle pointed out that the RED principle could tap an enormous energy source by controlled mixing of river water and seawater. In 1958, Murphy proposed what he called Osmionic Demineralization, using a salinity gradient to further desalinate a dilute solution, in essence a direct coupling between a RED and an ED device. Murphy and Matthews published the thermodynamic foundations of ion transport for osmotic demineralization in 1967. Unaware of Murphy’s work, Veerman independently described a similar system in 1994, motivated by elevated salinity in the Rhine River caused by discharges from potash mines in Alsace, France, which hampered the cultivation of salt-sensitive crops in the Westland region near the Rhine delta. He constructed and tested a four-compartment system in which the D-A-B segment functioned as the RED generator powering the ED unit B-C-D, with NaCl concentrations of 30 g/L in the generator feed and 1 g/L in the other compartments. Under idealized assumptions, the equilibrium calculation predicts that 0.88 g/L of salt is transferred, leaving the desalinated compartment at roughly 0.12 g/L, a substantial desalination achieved with essentially no external energy input.

For seawater desalination, where the driving force is weaker because the concentration ratio between brine and seawater is lower, Murphy proposed increasing the number of RED cell pairs relative to the ED section. In the modern configuration, the stack is fed alternately with high-concentration brine and lower-concentration seawater, and at selected positions a desalination compartment contains seawater instead of brine, marking the product compartments. The principle was later redeveloped by Chen and colleagues as an energy self-sufficient desalination stack for small islands, although their design still employed electrodes. The electrodeless variant removes the last electronic component, making the entire desalination train a purely ionic machine.

Perhaps the most striking existing application is medical. Pharmaceutical drugs can enter the body through the skin via transdermal administration, and medicated patches allow this without medical supervision, but conventional diffusion-based delivery is slow. Kwon and colleagues developed a method based on RED for ionized drugs, positioned at one end of the stack depending on their charge. Crucially, in this configuration the RED stack operates without electrodes, because the electrical circuit is closed and charge transport is facilitated by ionic species, both cations and anions. The authors tested lidocaine hydrochloride, a cationic anesthetic, and sodium risedronate, an anionic anti-osteoporosis drug, in vitro on mouse skin. Transport rates were several times faster than diffusion-based topical administration without an electric field, and the complete RED stack was miniaturized to the size of a standard patch. A salinity gradient between two harmless salt solutions becomes, in effect, a built-in ionic power source for pushing medicine through the skin.

The same metal-free logic powers the emerging field of iontronics, in which ions rather than electrons act as charge carriers, analogous to electronics. Information transfer in biological systems relies on the transport of ions through nerves, and fully iontronic systems interfacing with living tissue offer improved biocompatibility over metallic electrodes. In 2017, Han and colleagues demonstrated the first iontronic logic gate powered by RED, creating a fully metal-free system. A logical OR gate was embedded in a microchip, with inputs connected to a RED generator via capillary tubes. Input interruption, representing a logical zero, was achieved by pinching the tubes, and fluorescein in the output indicated current flow, turning yellow when current passed and remaining colorless otherwise. Closely related is Donnan dialysis, which uses a salinity-gradient-induced electric field to drive ions against their concentration gradient. In a water-softening application, a sweep phase of 0.5 M NaCl exchanges magnesium and calcium ions for sodium, removing undesirable ions or recovering valuable ones, all without electrodes.

The new concepts proposed in the perspective push the electrodeless principle into industrial territory. The first couples two RED stacks directly for a coastal drinking water supply. The numerical example is designed for a drinking water production of 3,000 cubic meters per day, sufficient for a city of 10,000 inhabitants consuming 300 liters per capita per day, with a reverse osmosis (RO) unit operating at 50 percent recovery. Wastewater from the town, at 0.5 g/L salinity, is used in two ways: in RED-1, energy is recovered from controlled mixing of a wastewater fraction with incoming seawater, partially desalinating the RO feed and improving RO performance, and RED-1 can be operated in ARED mode, where the additional energy input is more than compensated by the reduction in RO energy demand. In RED-2, energy is extracted from another wastewater fraction combined with the RO concentrate. The novel step is the direct, electrodeless coupling of RED-1 and RED-2, in which electrodes and associated electrical equipment are no longer required. The stack specifications show RED-1 handling 1,000 L/min of seawater-side flow with 10 kg/min of salt transport, and RED-2 handling 500 L/min with 7.3 kg/min of salt transport. Because the ratio of high to low concentration is higher in RED-2, its electromotive force exceeds that of RED-1, and its higher salt concentrations yield a lower internal resistance, so RED-2 can effectively drive the ARED operation of RED-1. In practice, the number of cell pairs in each stack should be adjusted for proper electrical matching.

The second new concept produces acid and base using a bipolar membrane, a sandwich of a CEM and an AEM. Under forward bias in NaCl solutions, water dissociates in the extremely narrow junction compartment into hydrogen and hydroxide ions; the hydroxide migrates through the AEM part toward one compartment, forming NaOH, while the hydrogen ions move through the CEM part, forming HCl. Under reverse bias with NaCl, the junction quickly becomes saturated and the current is blocked, so the bipolar membrane behaves like a semiconductor diode. Under reverse bias with NaOH and HCl, the ions recombine to form water and electrical power is generated. If the acid and base were previously produced by forward bias, this creates an acid-base battery with an energy storage capacity roughly ten times higher than that of a salinity gradient battery. The key technical challenge is ensuring sufficiently fast water diffusion to prevent delamination of the bipolar membrane. The perspective proposes powering this acid/base production system with an electrode-free RED generator, opening the way to bipolar-membrane applications including ammonia production, sulfur dioxide capture and carbon dioxide capture, all driven by salinity gradients alone.

The third concept is the most futuristic: an alternating current RED generator. A ring-shaped RED stack generates an ionic loop current in the primary winding of a transformer, and a mechanical shutter periodically interrupts the current, transferring electrical power to the secondary winding. Adding a second circular RED stack generating current in the opposite direction can produce a square-wave electric field, advantageous over interrupted direct current. Because the weight of a transformer is inversely proportional to frequency, efficient operation requires a shutter frequency of at least 50 to 60 hertz. Replacing the mechanical shutter with an iontronic interrupter remains challenging, although emerging research on ionic transistors using ion exchange membranes and self-supported ion-conductive membrane-based transistors may provide solutions, provided a large active membrane transistor area can be realized. Closed-loop systems, as used in heat-to-power schemes that regenerate the salinity gradient with waste heat, may allow the addition of chemical aids, whereas natural feed water systems must operate without additives.

The outlook, as Veerman frames it, extends from macroscale water treatment to microscale medicine and beyond. Electrodeless RED systems may provide a versatile platform for powering industrial processes involving bipolar membranes, using feed waters of natural or industrial origin, while closed-loop concepts in which ionic streams are continuously regenerated using low-grade industrial waste heat could enable sustainable and circular process designs. The electrodeless RED generator also points toward a new class of iontronic systems, serving as a conceptual stepping stone toward ionic transistors and other controllable ion-based switches, and ultimately toward fully ionic circuits that operate without electronic components. Pursuing these directions will require addressing fundamental challenges in materials, system integration and process control, but history suggests that progress in this field will not be linear, and the unexpected insights that accompany it may redefine both the scope and the impact of RED-based technologies.

Subject of Research: Science & Technology

Article Title: Electrodeless reverse electrodialysis

Article References: Veerman, J. (2026). Electrodeless reverse electrodialysis. Frontiers in Membrane Science and Technology, 5, Article 1812910. https://doi.org/10.3389/frmst.2026.1812910

Image Credits: AI Generated

DOI: 10.3389/frmst.2026.1812910

Keywords: reverse electrodialysis, electrodeless systems, salinity gradient energy, ion exchange membranes, desalination, iontronics, bipolar membrane, assisted reverse electrodialysis, renewable energy, membrane technology, Electrodeless, reverse

The inspiration comes directly from living cells. Biological ion channels are not rigid sieves; they are dynamic molecular machines that couple their local electrostatic environment to the hydration state of the interface, achieving selectivity and transport rates that approach the diffusion limit. Potassium channels, for example, use coordinated amino acid residues to strip the hydration shell from ions as they pass. Synthetic solid-state nanochannels have long tried to imitate this behavior by decorating rigid channel walls with stimuli-responsive molecules, converting molecular recognition events directly into measurable ionic currents. The problem has always been that these functionalizations are essentially two-dimensional, painting the sensing chemistry onto a flat surface where physiological salt can neutralize it.

The new platform, developed by Liu Shi, Genxi Li and colleagues, flips that geometry. Instead of modifying the channel surface, the team assembled a peptide-DNA hybrid hydrogel asymmetrically on the exterior of an anodic aluminum oxide membrane, creating a volumetric functional zone roughly 25 to 30 micrometers thick that acts as an active ion trap. The hydrogel is superhydrophilic and densely charged, so it pre-concentrates bulk ions through macroscopic Donnan enrichment while simultaneously generating a substantial Donnan potential. Because this charge reservoir occupies a volume orders of magnitude larger than the compressed Debye length, it keeps working even in the harshest ionic environments the body can supply.

The molecular architecture of the gate is a piece of careful supramolecular engineering. Single-stranded linker DNA is covalently anchored to the nanochannel surface, then a bridging strand and polyacrylamide conjugates are hybridized stepwise into the network. At the heart of the assembly sits a peptide-DNA complex cross-linker, synthesized through orthogonal thiol-maleimide coupling and strain-promoted alkyne-azide cycloaddition. The peptide backbone physically tethers the polymer-nucleic acid strands in close proximity, and this localized proximity effect entropically stabilizes the short DNA duplexes that hold the whole gel together. The elegance of the design is that the same tether that builds the network becomes its Achilles heel: a specific enzyme can cut it, and the entire structure falls apart on command.

That enzyme is Granzyme B, a serine protease released by cytotoxic T lymphocytes and a pivotal biomarker for gauging whether lung cancer patients are responding to immune checkpoint blockade therapy. When Granzyme B cleaves the peptide cross-linkers, the hydrogel undergoes a macroscopic gel-to-sol phase transition. Rheological measurements captured the collapse dramatically, with the storage modulus falling below the loss modulus as the elastic network vanished. Confocal microscopy showed fluorescently labeled gels fading after enzymatic treatment, while spectroscopy confirmed the loss of amide and hydrogen-bonding signatures. The gate does not merely weaken; it switches off.

The shutdown is synergistic, and that synergy is where the signal amplification comes from. As the gel disassembles, its volumetric charge reservoir dissipates, with the effective surface charge density dropping from -5.26 to -0.92 millivolts per square centimeter, an 82.5 percent loss in charge capacity. At the same time, the interface loses its superhydrophilicity, with the water contact angle rising from about 7.6 degrees to 39.0 degrees. Finite-element simulations governed by the Poisson-Nernst-Planck equations, fed with these experimentally measured parameters, showed the cation enrichment zone vanishing and the energy barrier for ion entry soaring. In a two-compartment electrochemical cell, the device swung from a high-current ON state of roughly 17.8 microamperes to an OFF state of about 3.07 microamperes, a gating ratio of approximately 5.8.

The comparison with a conventional two-dimensional control is what makes the result compelling. A monolayer of the same peptide chemistry on the channel surface showed only minor changes in wettability and charge after cleavage, and its sensing performance suffered accordingly, with a constrained dynamic range and reduced linearity. More tellingly, when the researchers varied the background ionic strength from 10 to 200 millimolar, the 2D device’s gating ratio collapsed sharply around 50 millimolar, exactly where Debye screening takes over. The 3D hydrogel platform, by contrast, maintained robust signal modulation all the way to 200 millimolar. In a physiological 150 millimolar buffer, the device still achieved a limit of detection of 133.60 femtomolar, while in low-salt conditions it reached an extraordinary 0.830 femtomolar across a range spanning six orders of magnitude.

The modularity of the building blocks opened a further, almost playful dimension: molecular computing. By incorporating cross-linkers responsive to both Granzyme B and matrix metalloproteinase 2 into a single hydrogel, the team built a cascaded logic circuit with two parallel INHIBIT sub-circuits feeding an OR gate. Each enzyme can independently trigger the phase disassembly and generate a current response, but a specific inhibitor for each enzyme vetoes the process. The device executed a full truth table of Boolean operations on biochemical inputs, supported by molecular docking simulations of the enzyme-inhibitor pairs. It is a small demonstration, but it points toward sensors that do not merely detect a molecule but compute a diagnosis from a panel of interacting biological signals.

Robustness in messy biological fluids proved equally impressive. The intact hydrogel doubles as a physical shield against non-specific fouling, and the sensor held its performance in 10 percent fetal bovine serum and 10 percent human serum, showing strict selectivity against a panel of interfering proteins. The device survived five regeneration cycles with consistent current switching, showed negligible degradation over 15 days of storage, and achieved batch-to-batch reproducibility with a relative standard deviation of just 1.62 percent. These are the unglamorous metrics that decide whether a laboratory curiosity can ever become a clinical instrument, and the platform passed them.

The clinical proof of concept is the most striking part of the story. Working with serum samples from healthy donors and lung cancer patients collected before and after immune checkpoint blockade therapy, under a protocol approved by the Medical Ethics Committee of Shanghai Pulmonary Hospital, the team measured Granzyme B directly in unpurified specimens. Healthy individuals averaged around 0.8 picomolar, while pre-treatment patients showed suppressed levels of roughly 0.3 to 0.5 picomolar, reflecting the immunosuppressive microenvironment of advanced malignancies. After immunotherapy, concentrations surged to 2.0 to 2.5 picomolar, signaling restored T-cell cytotoxicity. Benchmarked against a commercial ELISA, the sensor achieved a correlation coefficient of 0.962, a negligible mean bias of 0.0423 picomolar by Bland-Altman analysis, and an area under the ROC curve of 0.980 for distinguishing healthy from pre-treatment patients, with near-perfect discrimination of therapeutic response. The researchers acknowledge that translation will require packing the electrochemistry into automated microfluidic cassettes and expanding the logic gates to wider biomarker panels, but the core demonstration stands: by thinking in three dimensions, a dissolving gel has done what flat chemistry could not, carrying ultrasensitive nanochannel sensing out of the buffer and into the blood.

Subject of Research: A three-dimensional hydrogel soft-gating strategy for solid-state nanochannel biosensors that circumvents Debye screening to enable ultrasensitive detection of Granzyme B for immunotherapy monitoring.

Article Title: Hydrogel Phase Transition‐Driven Soft Gating Circumvents Debye Screening for Advanced Biosensing

Article References: Shi, L., Zhang, Z., Li, B., Gao, Y., Zhang, R., Mu, Z., Ni, J., Bo, B., & Li, G. (2026). Hydrogel Phase Transition‐Driven Soft Gating Circumvents Debye Screening for Advanced Biosensing. Advanced Science, Article e78049. https://doi.org/10.1002/advs.78049

Image Credits: AI Generated

DOI: 10.1002/advs.78049

Keywords: nanochannel biosensing, hydrogel, Debye screening, Donnan enrichment, Granzyme B, peptide-DNA hybrid, iontronics, immune checkpoint blockade, lung cancer, biocomputing, phase transition, clinical diagnostics

The central challenge the team set out to address concerns scalability and flexibility in ionic neuromorphic devices. Neuromorphic nanofluidics, which harness ionic rather than electronic transport to emulate neural dynamics, have generally depended on nanoconfinement—squeezing ionic motion into channels with dimensions comparable to the electrical double layers that form at solid-liquid interfaces. This confinement gives researchers exquisite control over how quickly ions accumulate, dissipate, and relax, which in turn determines whether a device exhibits the short-term and long-term memory effects characteristic of biological synapses. But the inherent scales of the spatial interactions at nanoconfined interfaces impose hard limits: fabricating angstrom-scale or nanometer-scale channels across large areas is difficult, integrating them into soft, stretchable, or biologically coupled systems is harder still, and the spatial scale of the governing physics cannot easily be tuned after fabrication.

The new system sidesteps nanoconfinement altogether by introducing what the researchers call cascaded-heterointerfacial ion traps within a multiphasic gel ion transporter, or GIT. Rather than a single confining channel, the device consists of multiple gel phases joined at heterointerfaces—boundaries between chemically distinct soft phases with differing ionic environments. When ions attempt to cross these interfaces, they encounter what the authors describe as interionic hierarchical cross-interface retardation and dissipation. In practical terms, the coupled dynamics of ion accumulation, crowding, and relaxation on either side of each boundary slow and scatter ionic flux in a hierarchy of timescales. Each interface therefore behaves like a trap: it can hold ionic charge transiently, release it gradually, and modulate the transmission of subsequent ionic spikes. By cascading several such interfaces in series, the system multiplies these trapping effects, creating rich temporal dynamics from macroscopically scalable soft materials.

One of the clearest signatures of this design is a pronounced ionic bipolar rectification effect, with rectification ratios exceeding one thousand. Rectification means that ionic current flows far more readily in one polarity than the other, analogous to the behavior of a diode in an electronic circuit. In biological terms, it resembles the one-way gating of signals at synapses and ion channels. Achieving ratios above 10^3 in an entirely soft, gel-based architecture indicates that the cascaded traps do not merely attenuate signals but actively sculpt their directionality. The rectification arises because ion enrichment and depletion at successive heterointerfaces depend strongly on the polarity of the applied bias, so the same physical structure can either promote or suppress transmission depending on which way the ionic spike travels through the system.

Beyond directionality, the device exhibits what the researchers characterize as spike-strength-dependent and timing-dependent dual-order plasticity. This is a cornerstone of neural computation. In the brain, synapses strengthen or weaken depending both on how strongly they are activated and on the precise relative timing of pre- and postsynaptic spikes—a phenomenon known as spike-timing-dependent plasticity, which is widely believed to underpin learning and memory formation. By reproducing both amplitude-dependent and timing-dependent forms of plasticity within a single ionic platform, the cascaded-heterointerface system captures two distinct but intertwined orders of synaptic adaptability. The interionic retardation and dissipation at each trap accumulate across the cascade, so the device’s response to any given spike depends on its own recent history—exactly the property that distinguishes a memristive, memory-bearing element from a passive conductor.

Particularly significant is the integration of both short-term and long-term memory effects within the same material system. Short-term plasticity, in which synaptic efficacy transiently changes over milliseconds to seconds, enables computational functions such as filtering, adaptation to stimulus statistics, and temporal differentiation. Long-term plasticity, persisting over much longer durations, provides the substrate for durable memory and learned associations. Biological synapses blend the two seamlessly, and neuromorphic engineers have long struggled to replicate that blend with adequate dynamic range. The hierarchical trapping timescales of the multiphasic gel naturally generate both regimes, allowing the team to demonstrate complex ion-based synaptic adaptability and multiple biologically grounded learning rules, including forms of spike-timing-dependent behavior implemented through purely ionic dynamics.

The energy figures reported are remarkable for a soft material system: multistate ionic neuromorphic processing at as little as 0.61 picojoules per spike. For context, individual synaptic transmission events in the human brain are often estimated to consume on the order of tens of femtojoules to picojoules, and modern semiconductor-based artificial synapses frequently require far more energy per operation, particularly when overheads of converting signals between electronic and ionic or chemical domains are counted. Operating in the picojoule regime means the gel system is not merely a conceptual demonstration but approaches the energy budgets at which practical, body-attached, or even body-implanted neuromorphic hardware becomes feasible. Soft matter also offers mechanical compliance and chemical compatibility that silicon cannot match, which points directly toward the study’s most eye-catching experiment.

That experiment involved creating a biohybrid neural circuit by interfacing the in vivo neuro-iontronic processor with the transected sciatic nerve of a rat. The sciatic nerve, the major peripheral nerve running down the hind limb, was cut and the processor was connected across the transection, allowing nerve-generated spikes to drive ionic processing in the gel and, reciprocally, allowing the processor’s output to stimulate downstream nerve segments. The result was bioneuron-driven ionic neuromorphic processing: the device’s synaptic states were updated by genuine biological action potentials, and in turn the device reconfigured the interneural signals passing through the injured nerve. The experiment, approved by the Animal Protection Ethics Committee of Capital Medical University, suggests a route toward prosthetic or regenerative interfaces in which a soft computational material does not simply relay nerve signals but adaptively reshapes them according to neuromorphic learning rules.

The theoretical underpinnings of the system were developed in parallel with the experiments, with collaborators at Tsinghua University performing calculations that connect the observed macroscopic behavior to the microscopic interionic dynamics at each heterointerface. This modeling work clarifies how hierarchical cross-interface retardation and dissipation give rise to the device’s memristive characteristics and provides a design framework for tuning trap strength, cascade depth, and phase chemistry. The work builds on a rapidly maturing field of iontronics and nanofluidic computing, in which recent years have seen fluidic memristors, droplet-based modular iontronics, and mechano-ionic logic switches emerge from laboratories around the world. What distinguishes the present contribution is the deliberate move away from spatial confinement as the sole control lever and toward interfacial design in soft, multiphasic matter—a shift that promises devices that are cheaper to fabricate, easier to scale, and far more amenable to integration with living tissue.

The implications extend across several frontiers. For brain-inspired computing, the system offers a hardware substrate in which the informational carriers, the physical dynamics, and the material compliance all resemble biology far more closely than conventional transistors do, potentially enabling machine learning implementations that exploit the same temporal plasticity principles the brain uses. For medicine, a soft iontronic processor that can learn from and modulate peripheral nerve activity hints at adaptive neural prostheses, smart neuro-repair scaffolds, and closed-loop bioelectronic therapies that reconfigure damaged signaling pathways in real time. And for the broader materials community, the demonstration that cascaded heterointerfaces can substitute for nanoconfinement opens a design space in which chemistry, phase architecture, and interfacial engineering replace lithographic miniaturization. Much work remains before such devices leave the laboratory—long-term biostability, manufacturing reproducibility, and integration with clinical hardware all present substantial hurdles—but the convergence of picojoule energy consumption, dual-order synaptic plasticity, and verified in vivo biohybrid operation marks a genuinely notable step toward computing materials that think the way biology does.

The choice of gel-based ion transporters also reflects a broader trend in which soft ionic conductors are increasingly viewed as viable active materials rather than passive wiring. Because ions are the native charge carriers of living systems, devices that process signals ionically can, in principle, couple to tissue without the transduction penalties that arise when electronic implants must convert ionic bioelectricity into electron flow and back again. The multiphasic architecture takes advantage of this by letting phase chemistry, rather than channel geometry, define the functional behavior, which means trap dynamics can in principle be tuned through material formulation.

The dual-order plasticity reported here is also notable from a computational standpoint. Spike-strength dependence and timing dependence together enable learning rules that resemble Hebbian and predictive forms of adaptation studied in neuroscience, and memristive hardware implementing such rules has been proposed as a route to energy-efficient spatiotemporal learning. Demonstrating both orders of plasticity in a purely ionic, soft-matter platform suggests that such rules need not depend on solid-state electronics.

The in vivo sciatic nerve experiment, conducted under ethics approval AEEI-2025-036, additionally illustrates how a processor driven by genuine biological action potentials could serve as a testbed for studying signal reconfiguration in injured nerves, complementing conventional cuff electrodes and stimulation implants.

Subject of Research: Soft-matter iontronic devices using cascaded-heterointerface ion traps for multistate ionic neuromorphic processing and biohybrid neural interfacing.

Article Title: Soft-matter multistate ionic neuromorphic processing based on cascaded-heterointerface ion traps

Article References: Wu, Z., Zhang, S., Zhai, L., Zhang, A., Zhu, X., Xu, J., Liu, H., Xu, Z., Jiang, L., & Zhao, Z. (2026). Soft-matter multistate ionic neuromorphic processing based on cascaded-heterointerface ion traps. Nature Electronics. https://doi.org/10.1038/s41928-026-01688-z

Image Credits: AI Generated

DOI: 10.1038/s41928-026-01688-z

Keywords: neuromorphic computing, iontronics, soft matter, ionic memory, synaptic plasticity, nanofluidics, biohybrid circuits, gel ion transporter, ion traps, energy-efficient computing, neural interfaces, Nature Electronics

The central idea is that a gel need not be a passive, homogeneous medium. In a multiphasic gel, the material is structured into distinct phases with different chemical compositions, ionic mobilities and interfacial properties. When an electrical signal is applied, ions do not simply drift through the material in a straight, Ohmic fashion. Instead, they accumulate, deplete and redistribute at the boundaries between phases, giving rise to transient behaviors that depend on the history of the applied voltage. This memory of past stimulation, embedded directly in the spatial distribution of ions, is precisely the property that neuromorphic engineers prize, because it allows a single material element to perform operations that would otherwise require many transistors.

To appreciate why this matters, it helps to consider the limitations of conventional electronics. Silicon transistors move electrons through crystalline semiconductors with extraordinary speed and reliability, but they are fundamentally decoupled from the chemistry of the environments in which they operate. Biological neural systems, by contrast, process signals in wet, soft, salt-laden surroundings, and they do so at energies orders of magnitude lower than digital hardware performing comparable tasks. The commentary by Peng and Zhang situates the new ionic gel work within a broader landscape of iontronic research that has been rapidly consolidating in recent years, including reviews of bioelectronic and iontronic technologies in Nature Reviews Bioengineering and a dedicated iontronics journal literature that has emerged to catalog the field’s accelerating progress.

The physics underlying ionic signal processing is rich and, in some respects, counterintuitive. Because ions are much heavier and slower than electrons, ionic currents respond to voltage changes on time scales ranging from microseconds to seconds, depending on the mobility of the charge carriers, the geometry of the channels and the viscosity of the medium. Far from being a defect, this slowness can be exploited. It introduces natural temporal dynamics, such as gradual charging of interfacial capacitances, diffusion-limited transport and concentration-polarization effects, that mimic the integration and decay behaviors of biological synapses. In a multiphasic gel, the interfaces between phases act as internal barriers and reservoirs, so the effective response of the device becomes a convolution of transport, partitioning and interfacial reaction processes, each with its own characteristic time constant.

Researchers in the field have assembled a substantial body of evidence that such dynamics can be harnessed for computation. A landmark demonstration published in Science in 2023 showed that nanofluidic systems, in which ions are forced through channels comparable in size to the electrical double layers that screen charged surfaces, can display memory and even long-term memory behaviors, providing a physical basis for memristive operation driven entirely by ions. The memristor, a circuit element whose resistance depends on the history of current flow through it, has become the canonical building block of neuromorphic hardware, and its ionic realization suggests that synapse-like elements could be fabricated from soft materials rather than rigid oxide films. Peng and Zhang’s commentary draws on this lineage, emphasizing that the cross-interface dynamics observed in multiphasic gels extend the same conceptual framework into a new class of soft, multiphase media.

Work published in Science in 2024 by Zhang, Tan, Toepfer, Lu and Bayley, several of whom are central figures in the bio-iontronics community, demonstrated that droplet-based ionic architectures can support sophisticated signal processing functions, pointing toward computational primitives built entirely from aqueous phases separated by lipid or polymer membranes. The multiphasic gel described in the Nature Electronics commentary represents a conceptual cousin of these droplet interfacial systems, but with the phases locked into a continuous solid-like scaffold. This distinction matters for applications. Droplet networks are exquisite for fundamental studies but fragile, whereas gels can be handled, patterned and potentially integrated with electrodes, wires and biological tissue, opening a route from laboratory curiosity toward practical soft devices.

The relationship between ionic transport and neuromorphic function can be made concrete by considering what happens when a voltage pulse crosses one of the internal interfaces in the gel. Initially, the ionic current is dominated by the mobile carriers in the phase connected to the driving electrode. As ions pile up at the interface, the local concentration rises, the interfacial electric field redistributes, and counter-diffusion begins to flatten the gradient. If the pulse ends before the system reaches equilibrium, some of the accumulated charge relaxes back, producing a short-term memory trace; if pulses arrive repeatedly, the accumulation can persist, strengthening the effective coupling across the interface in a manner analogous to synaptic facilitation. Two-terminal elements built on this principle naturally implement paired-pulse facilitation, temporal filtering and thresholded switching, all canonical operations of biological synapses.

Chemical reviews published over the past two years have begun to systematize this design space. A comprehensive survey in Chemical Reviews in 2025 examined ionic materials and devices for neuromorphic and bioelectronic applications, while a 2024 review in Chemical Society Reviews mapped the physics of ion transport and rectification in engineered nanostructures. Together with a further Chemical Society Reviews article in 2026 surveying the state of iontronic materials, these works chart a field that is moving from proof-of-concept demonstrations toward systematic design rules, in which the choice of polymer matrix, ionic species, phase composition and interface chemistry can be tuned to produce a desired dynamic response. The multiphasic gel strategy sits squarely within this trend, treating the internal structure of the material itself as an engineering variable.

The companion research article highlighted in the commentary, published by Wu and colleagues in Nature Electronics, provides the experimental substance behind the conceptual discussion. Although the full analytical details are available to readers of the journal, the commentary frames the work as demonstrating that ions in the multiphasic gel exhibit the complex cross-interface dynamics required for neuromorphic processing, and the accompanying figure, titled ‘Ion transporters based on multiphasic gels,’ illustrates the device concept in which ionic transporters, the structural and functional units that shuttle charge between phases, underpin the observed signal processing behavior. Framing a material platform in terms of transporters rather than passive channels reflects a shift in how the field describes ionic devices, emphasizing active, directed, history-dependent charge management rather than simple conduction.

The possible applications of soft ionic processors extend well beyond replacing silicon. Because ionic gels are mechanically compliant, chemically compatible with aqueous environments and operable at low voltages, they are natural candidates for integration with living tissue. Implantable and wearable bioelectronics could, in principle, incorporate local neuromorphic elements that preprocess electrophysiological signals in situ, reducing the bandwidth and power demands on external hardware. Artificial synapses built from multiphasic gels might one day interface directly with neurons, whose native signaling currency is the same ionic flux that the devices process. Researchers have also proposed ionic systems for reservoir computing, in which the rich internal dynamics of a physical medium perform temporal computation, with the gel itself serving as the reservoir. The commentary’s authors, based at a laboratory explicitly dedicated to bio-iontronics, underscore that the convergence of soft materials science, electrochemistry and neural engineering is what gives this direction its momentum.

Significant challenges remain before ionic gels can rival established technologies. Ionic devices are inherently slow compared with electronic ones, which limits their usefulness for high-frequency computation even as it suits them for biological time-scale tasks. Scaling from single junctions to large integrated networks requires reproducible fabrication of multiphase architectures, stable electrode contacts and materials that resist dehydration, fatigue and fouling over long lifetimes. The theoretical toolkit for describing coupled ionic transport across heterogeneous interfaces is still maturing, and researchers acknowledge that the field benefits from continued cross-disciplinary synthesis, as reflected in the breadth of the literature the commentary engages, spanning nanofluidics, memristive physics, droplet interfacial science and bioengineering. Peng and Zhang declare no competing interests, and their perspective, published in September 2026, arrives at a moment when iontronics is acquiring the journals, citations and design principles of a mature discipline.

What the multiphasic gel work ultimately illustrates is that computation need not be confined to crystalline silicon or even to electrons. Matter structured at the mesoscale, with phases that sort, store and release ions across their interfaces, can perform operations that look strikingly neural, and it can do so in a material that is soft, wet and biologically congenial. As the commentary concludes in spirit if not in a single sentence, the complex cross-interface dynamics of ions in such gels are not a nuisance to be engineered away but the very resource from which neuromorphic function is built. If the past decade belonged to memristive oxides and spintronic devices, the next may belong to materials that compute the way life does, one ion at a time, and the ionic gel now stands as one of the clearest demonstrations of that possibility.

Subject of Research: Neuromorphic signal processing using ionic transport across interfaces in a multiphasic gel

Article Title: Neural signal processing in an ionic gel

Article References: Peng, P., & Zhang, Y. (2026). Neural signal processing in an ionic gel. Nature Electronics. https://doi.org/10.1038/s41928-026-01684-3

Image Credits: AI Generated

DOI: 10.1038/s41928-026-01684-3

Keywords: iontronics, multiphasic gel, neuromorphic computing, ionic transport, memristor, soft materials, bioelectronics, nanofluidics, synaptic dynamics, Nature Electronics, Neural, signal