Biocompatible Interface for Organic Electrochemical Transistors Enables Bioadhesion and Over‐Swelling Suppression

ABSTRACT Bioelectronic interfaces necessitate devices that not only align mechanically with biological tissues but also adhere effectively to wet surfaces and maintain electrochemical stability over extended periods. However, glycolated conjugated polymer (g‐CP) channels in organic electrochemical transistors (OECTs) face challenges due to mechanical incompatibility and swelling‐induced degradation. We propose a versatile interfacial design employing a conformal hydrogel coating that transforms various p‐type and n‐type g‐CPs into bioelectronic interfaces that can harmonize with tissue and maintain adhesion. This innovative coating ensures seamless interaction between the device and biological tissues, while concurrently mitigating channel swelling. As a result, the coated OECTs exhibit a figure‐of‐merit µ C* roughly double that of uncoated OECTs and show enhanced stability over 1800 operational cycles. When utilized within a flexible, complementary circuit, these coated OECTs deliver a substantial voltage gain of 210 V V −1 and consume an exceptionally low power of 20 nW. Validated through in vivo electrocorticographic recordings, the platform achieves a signal‐to‐noise ratio of 28 dB—significantly surpassing that of conventional electrodes—highlighting its potential for high‐fidelity neural interfacing. This study elegantly combines the mechanics of soft hydrogels with the superior performance of organic electronics through deliberate interface engineering, providing a comprehensive strategy for cutting‐edge biointegration.