Discreet wearable biopotential interfaces based on water-soluble biodegradable thermoplastics

Non-invasive wearable biopotential interfaces (WBIs), devices that enable recording of electrical signals from the body's surface, depend on electrodes that form a low impedance interface with the skin. Existing electrodes are often bulky, uncomfortable, slow to stabilize, and socially unacceptable due to their conspicuous appearance, or require complex conductive materials and fabrication processes. Here, we show that thin films of poly(vinyl alcohol) (PVA), a low-cost, transparent, electronically insulating biodegradable thermoplastic, can be used as a discreet, high-performance electrode when exposed to a water-based ionic gel. Water plasticizes PVA and makes it mechanically skin-like. Plasticized PVA also becomes ionically conductive to serve as an electrode that conforms to the skin to enable efficient ion transport at the skin's interface upon application, yielding 13× lower resistance than when the same gel is used with a plastic backing. This eliminates the stabilization delay of conventional wet or semi-wet electrodes, leading to a similar level of performance when compared to benchmark Ag/AgCl semi-wet electrodes for electrocardiography and electromyography, enabling the implementation of a wireless gesture recognition interface. Signal quality is maintained or improved over multi-hour recordings, and artificial sweat can replace the ionic gel to yield a comparable skin-electrode impedance. These results establish biodegradable thermoplastics as a scalable path towards socially acceptable, high-performance WBIs.