Mechanically Heterogeneous Architecture Enables Robust and Ultrathin Bioelectronics for High-Fidelity Biosignal Monitoring.

High-fidelity biosignal monitoring is essential for daily health tracking and the diagnosis of chronic diseases. However, developing bioelectrodes capable of withstanding repeated use and mechanical deformation on wet tissue surfaces remains a significant challenge. Here, we present a robust and ultrathin bioelectrode (RUB), featuring a mechanically heterogeneous architecture and a thickness of ∼3 μm. In this design, a hydrophobic and stretchable polymer microfiber network is embedded within the brittle poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) matrix, significantly enhancing both mechanical integrity and electrical stability. The RUB exhibits excellent tolerance to repeated use and mechanical deformation on wet tissue surfaces, enabled by noncovalent adhesion. Significantly, the RUB retains ∼94.2% of its initial signal-to-noise ratio in electromyography monitoring after 100 reuse cycles with ethanol cleaning, showing a 4.3-fold enhancement compared to the uncleaned electrode (∼17.9% after 50 cycles). Additionally, the RUB reliably captures electrocardiogram (ECG) signal variations in response to different intensities of physical activity and isoproterenol hydrochloride treatment, offering valuable data for health analysis. Moreover, the RUB can reliably monitor high-fidelity ECG signals on tissue surfaces, even under ∼20% deformation. The ultrathin bioelectronics, enhanced by mechanically heterogeneous architecture, demonstrate strong potential for biointerface applications.