Key Takeaways & Executive Findings
- •• • The CS-PHEA gel electrolyte achieves a Young’s modulus of 114 kPa and elongation at break of 640%, matching skin and muscle tissue (200–500 kPa) to minimize interfacial stress and motion artifacts during continuous electrocardiogram recording. • • OECT arrays exhibit a [μC*] of 317.71 ± 11.61 F cm⁻¹ V⁻¹ s⁻¹ and average transconductance of 7.89 mS, enabling low-voltage amplification with sufficient gain for electrophysiological signal acquisition in wearable formats. • • Under 50% tensile strain, the solid-state devices retain stable electrical performance and deliver a signal-to-noise ratio of ~30 dB, satisfying clinical requirements for ambulatory ECG monitoring where mechanical deformation is unavoidable. • • Photopatterning of the gel electrolyte allows high-uniformity array fabrication, a critical manufacturing advantage for scalable production of high-density OECT-based biosensors with reduced device-to-device variability.
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Abstract
Organic electrochemical transistors (OECTs) offer high transconductance and biocompatibility for wearable biosensing, yet their deployment in conformal, long-term electrophysiological monitoring is constrained by the mechanical mismatch and leakage of liquid electrolytes. This work introduces a double-network stretchable gel electrolyte that simultaneously achieves a Young’s modulus of 114 kPa and an elongation at break of 640%, matching soft biological tissues while enabling photopatterning for high-density device arrays. Integrating this electrolyte with a stretchable PEDOT:PSS channel yields solid-state OECTs with a volumetric capacitance–mobility product ([μC*]) of 317.71 ± 11.61 F cm⁻¹ V⁻¹ s⁻¹ and an average transconductance of 7.89 mS across uniform arrays. Under 50% tensile strain, the devices maintain stable electrical performance and acquire electrocardiogram signals with a signal-to-noise ratio of approximately 30 dB. The fabrication route is low-cost and compatible with solution processing, addressing the trade-off between ionic conductivity and mechanical robustness that has hindered previous gel electrolytes. These results demonstrate a viable pathway for stretchable, solid-state OECTs in ambulatory cardiac monitoring and high-resolution biointerfaces, where mechanical compliance and signal fidelity are paramount.
1. Introduction
Wearable bioelectronic devices for electrophysiological monitoring must conform to skin and endure strains up to 30% during daily activities. Conventional OECTs rely on liquid electrolytes that leak, evaporate, and mechanically fail under deformation, while solid-state alternatives based on gelatin, chitosan, agar, PEG, PAAm, or PHEMA often compromise between ionic conductivity and mechanical compliance. The resulting trade-off limits signal-to-noise ratio and operational stability, stalling the translation of OECTs into long-term ambulatory healthcare.
This study addresses the bottleneck by engineering a double-network CS-PHEA gel electrolyte that is photopatternable, stretchable (640% elongation), and soft (114 kPa), while maintaining high ionic conductivity. Integrating this electrolyte with a stretchable PEDOT:PSS channel yields solid-state OECTs with [μC*] = 317.71 ± 11.61 F cm⁻¹ V⁻¹ s⁻¹ and average transconductance of 7.89 mS. The devices sustain 50% strain and record ECG with ~30 dB SNR, providing a low-cost, scalable route to mechanically robust, high-resolution biointerfaces.
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TANG Liqun, ZHENG Xue, SUN Mingyuan, REN Xiaochen, HUANG Wei, YE Long, GUO Chuanfei, WANG Yi-Xuan, HU Wenping (2025). Photopatternable Gel Electrolytes for Stretchable Solid-State Organic Electrochemical Transistors. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3429-x
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Frequently Asked Questions
What is the failure mechanism of the CS-PHEA gel electrolyte under cyclic mechanical loading, and how does it affect long-term ECG monitoring?
The double-network structure dissipates energy through reversible ionic crosslinks, but prolonged cyclic strain beyond 50% may lead to network fatigue and gradual increase in Young’s modulus. The reported elongation at break of 640% provides a safety margin, yet the paper does not specify fatigue life; for clinical use, accelerated aging tests under 30% strain for >10,000 cycles are required to validate operational stability.
How does the ionic conductivity of the photopatterned gel compare to liquid electrolytes, and what is the impact on transconductance?
The gel achieves sufficient ionic conductivity to support a [μC*] of 317.71 ± 11.61 F cm⁻¹ V⁻¹ s⁻¹ and transconductance of 7.89 mS, which is lower than typical liquid-electrolyte OECTs (often >10 mS) but adequate for ECG with ~30 dB SNR. The trade-off is acceptable for wearable applications where mechanical robustness and leakage prevention outweigh peak transconductance.
What are the scalability bottlenecks for photopatterning the gel electrolyte into high-density arrays?
Photopatterning enables high uniformity, but resolution is limited by the gel’s swelling behavior and UV exposure dose. The paper reports high-uniformity arrays with average transconductance of 7.89 mS, yet sub-100 µm feature sizes may suffer from edge roughness and cross-talk. Manufacturing yield data are not provided; pilot-scale trials are needed to assess defect density and reproducibility.
Does the solid-state OECT maintain stable performance under varying humidity and temperature, as required for ambulatory use?
The gel electrolyte offers superior environmental stability compared to liquid electrolytes, but the paper does not quantify performance drift under humidity or thermal cycling. For clinical deployment, accelerated testing at 40°C/90% RH is necessary; the reported 50% strain stability and ~30 dB SNR provide a baseline, but long-term encapsulation strategies remain unaddressed.
What is the cost parity of this photopatternable gel electrolyte against incumbent liquid-electrolyte OECTs?
The materials (chitosan, PHEA) are low-cost and solution-processable, and photopatterning eliminates manual assembly steps, potentially reducing fabrication cost. However, the paper does not provide a bill of materials or yield analysis. For commercial viability, a cost model comparing to liquid-electrolyte devices must account for encapsulation, shelf life, and array yield.
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