Journal Article

Organic electrochemical transistors (OECTs) are increasingly recognized as high-performance, flexible platforms for bioelectronics, owing to their ultra-low voltage operation, high transconductance, and biocompatibility. The integration of gels, such as hydrogels and ionogels, with robust 3D polymer networks has progressed from traditional solid-state electrolytes to functional gate and semiconducting gel channels, with mobility exceeding 1 cm2 V-1 s-1, transconductance over 80 mS, and stretchability surpassing 100%. This enables the development of inherently flexible, stretchable OECTs with mechanical resilience, high transconductance, and dynamic functionality. Despite the significant progress, challenges remain in understanding hydrogel properties and interfaces for synergistic optimization of device performance and scaling up fabrication. This review provides a systematic overview of gel-based OECTs, and discusses the gel design strategies with their performance trade-offs. Hydrogels and ionogels are then compared across various device components, highlighting their gel optimization and different strengths. Significant device engineering strategies for optimizing gel-based OECTs, such as material enhancements and structural innovations, are discussed, alongside emerging applications in wearable health monitoring, bioelectronic medicine, biomimetic electronics, and environmental sensing. The review concludes by summarizing the current research landscape, identifying persistent challenges, and outlining potential solutions for the development of gel-based OECTs.