Bioinspired Heat-Induced Viscoelasticity-Switchable Electrodes for Conformal Brain-Computer Interfaces

Electroencephalography is a promising noninvasive modality for brain-computer interfaces (BCIs), yet its widespread adoption is constrained by electrode limitations: dry electrodes yield unstable signals, whereas wet electrodes require laborious setup and are ill-suited to wearable devices. Inspired by honeybees that locally heat beeswax to reversibly switch it between rigid and moldable states for comb construction, this work introduces a heat-induced viscoelasticity-switchable electrode (HIVE) that enables conformal contact on hairy scalps and user-friendly operation in wearable systems. HIVE integrates a thermoresponsive gelatin gel confined in a sponge matrix with an on-electrode microheater. Its temperature is actively modulated on demand, enabling autonomous switching between the gel and sol states. As a flowable sol, it permeates hair, conforms to the skin. At body temperature, it remains in a viscoelastic state, providing strong adhesion. Moreover, heating duration is closed-loop controlled using real-time electrode-skin impedance. In steady-state visual evoked potential paradigm, HIVE delivers high classification accuracy comparable to gold-standard wet electrodes while supporting wearable BCI devices for vision-based wheelchair navigation and high-speed text entry. By translating honeybee viscoelasticity-modulation strategy into bioelectronic interfaces, this work provides a practical solution for wearable BCI devices and a new design paradigm for conformal biointerfaces on hairy or piliferous surfaces.