Actively Deployable Balloon Electrodes with High Omnidirectional Stretchability for Enhanced Interfacing with Luminal Organs

Luminal organs such as the gastrointestinal tract, auditory canal, and urogenital tract exhibit complex, folded, and dynamic architectures, presenting significant challenges for stable and conformal electrophysiological monitoring. Conventional soft electrodes, while effective on flat surfaces, often fail to adapt to the deep-seated, narrow, and irregular environments of endoluminal tissues. Here, a balloon electrode incorporating a semi-embedded Ag–Au core–shell nanowire (Ag@AuNW) composite is developed to enable active and reversible interfacing with endoluminal tissues of various sizes. The Ag@AuNW composite is fabricated using tape-assisted masking and vacuum filtration, followed by partial embedding in elastomer to form a percolated conductive network with high conductivity, mechanical durability, chemical stability, and omnidirectional stretchability (600% area strain). When integrated onto a catheter, the balloon electrode undergoes a reversible tubular-to-balloon transformation during inflation, actively expanding to conform to folded tissue surfaces and reduce interfacial impedance. It maintains stable electro-mechanical performance over 1000 inflation-deflation cycles. For proof-of-concept, the device is deployed into human ear canals and rabbit vaginas, where it achieves conformal adaptation and enables the acquisition of high-quality electroencephalography (EEG) and electromyography (EMG) signals, outperforming conventional electrodes. These results highlight the potential of an omnidirectionally stretchable balloon electrode for minimally invasive, high-fidelity electrophysiological monitoring within complex luminal organs.