Cyborgs calling? It seems a logical extension from the work being described in Michael Berger’s August 28, 2025 Nanowerk Spotlight article, Note: A link has been removed,
Electronic devices that can sense, process, and respond to biological signals are reshaping how researchers approach medicine, neuroscience, and human–machine interaction [emphasis mine]. These systems, often soft, flexible, and powered by organic materials, promise to monitor brain activity, stimulate nerves, and control prosthetics with a level of precision and integration that rigid silicon electronics cannot match. The ambition is clear: build circuits that are not just compatible with the body, but functionally embedded within it.
Yet at the core of many of these bioelectronic systems lies a persistent technical obstacle. Organic electrochemical transistors—or OECTs—have emerged as one of the most promising components for such interfaces. They operate at low voltages, work well in wet environments, and can amplify faint biological signals. But their performance has depended almost entirely on liquid electrolytes—saline-based solutions that shuttle ions in and out of the transistor channel. While effective at driving fast switching and strong responses, these liquids are difficult to confine. They spread, leak, evaporate, and cause interference between closely packed devices. They make miniaturization harder, circuit integration more complex, and long-term implantation more fragile.
Solid-state electrolytes have been explored as a replacement. Some are made from ionic gels or charged polymers, others from hydrogels with modified compositions. But each compromise has created new limitations: reduced ion mobility, patterning challenges, long response times, or incompatibility with both p-type and n-type transistor operation. These tradeoffs have made it difficult to build dense, fast, reliable circuits for real use in living systems.
Now, researchers in Sweden report a material system that brings this goal closer. Writing in Advanced Materials (“A Photo‐Patternable Solid‐State Electrolyte for High‐Performance, Miniaturized, and Implantable Organic Electrochemical Transistor‐Based Circuits”), the team presents a hydrogel-based solid-state electrolyte that is both photopatternable and fast enough to match the performance of liquid systems.
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This turns out to be a hydrogel and seaweed story, from Berger’s August 28, 2025 article,
Using a naturally derived polymer from seaweed and a light-activated crosslinker, they’ve built a platform that enables high-speed operation, micrometer-scale precision, and compatibility with flexible, implantable devices. The system supports both logic circuits and spiking neural mimics, all operating on a solid-state foundation—offering a solution to a long-standing bottleneck in bioelectronic circuit design.
This work introduces a solid-state hydrogel based on ι-carrageenan, a charged polysaccharide extracted from red seaweed, crosslinked with poly(ethylene glycol) diacrylate (PEGDA). When exposed to ultraviolet light, PEGDA forms a permanent network that locks the ι-carrageenan into a soft, water-stable gel. The result is a solid-state electrolyte that can be patterned with high precision, while maintaining ionic conductivity at levels comparable to liquid saline.
The hydrogel can be processed as a liquid and selectively hardened using light exposure. Before crosslinking, it spreads easily for coating or printing. After UV exposure, it forms a water-insoluble gel that can be patterned down to 15 micrometers. This resolution is sufficient for building densely packed circuits on flexible substrates. Crucially, the material retains ionic conductivity above 10 millisiemens per centimeter—on par with 0.1 molar sodium chloride. That conductivity enables fast ion movement through the gel, preserving the switching speed and signal fidelity expected of high-performance OECTs.
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To move beyond digital logic, the researchers designed a circuit that mimics the behavior of a spiking neuron. This organic electrochemical neuron (OECN) was based on the leaky integrate-and-fire model used in artificial neural networks. It combines complementary OECTs with a reset transistor and integrates them into a spiking architecture that converts a continuous input into transient voltage pulses. The circuit was encapsulated using a biocompatible layer of parylene and fabricated on an ultrathin flexible substrate.
To demonstrate biological relevance, the team implanted this device in mice. They connected it to flexible stimulation electrodes coated with PEDOT:PSS, a conductive polymer that lowers electrode impedance. The system was wrapped around the cervical vagus nerve, a major nerve involved in autonomic regulation of the heart and digestive system. When inactive, the device produced no physiological effect. When activated to spike at frequencies between 1 and 20 hertz, it induced a measurable drop in heart rate of 2 to 4 percent—consistent with the known effects of vagus nerve stimulation.
Unlike previous systems based on liquid electrolytes, this device remained stable after implantation, with no fluid reservoirs or leakage pathways. Its function did not degrade after encapsulation, and spiking behavior remained consistent. The reduction in spiking frequency observed after implantation was attributed to the mouse acting as an external load, not to any failure of the circuit.
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The platform introduced in this study enables a new level of complexity and stability in soft bioelectronics. It demonstrates that solid-state, hydrogel-based circuits can meet the electrical demands of real-world applications without sacrificing manufacturability or implant safety. By bridging the gap between ionic transport and scalable circuit design, this work sets the foundation for future generations of bioelectronic therapies and neural interfaces.
Berger’s August 28, 2025 article offers a lot more detail and his explanations tend to be accessible (relatively speaking).
Here’s a link to and a citation for the paper,
A Photo-Patternable Solid-State Electrolyte for High-Performance, Miniaturized, and Implantable Organic Electrochemical Transistor-Based Circuits by Miao Xiong, Chi-Yuan Yang, Junpeng Ji, April S. Caravaca, Qi Guo, Qifan Li, Mary J. Donahue, Dace Gao, Han-Yan Wu, Adam Marks, Yincai Xu, Deyu Tu, Iain McCulloch, Peder S. Olofsson, Simone Fabiano. Advanced Materials DOI: https://doi.org/10.1002/adma.20250931 First published: 22 August 2025
This paper is open access.
