Self-Adhesive, Stretchable, Biocompatible, and Conductive Nonvolatile Eutectogels as Wearable Conformal Strain and Pressure Sensors and Biopotential Electrodes for Precise Health Monitoring

Conductive stretchable hydrogels and ionogels consisting of ionic liquids can have interesting application as wearable strain and pressure sensors and bioelectrodes due to their soft nature and high conductivity. However, hydrogels have a severe stability problem because of water evaporation, whereas ionogels are not biocompatible or even toxic. Here, we demonstrate self-adhesive, stretchable, nonvolatile, and biocompatible eutectogels that can always form conformal contact to skin even during body movement along with their application as wearable strain and pressure sensors and biopotential electrodes for precise health monitoring. The eutectogels consist of a deep eutectic solvent that has high conductivity, waterborne polyurethane that is an elastomer, and tannic acid that is an adhesive. They can have an elongation at a break of 178%, ionic conductivity of 0.22 mS/cm, and adhesion force of 12.5 N/m to skin. They can be used as conformal strain sensors to accurately monitor joint movement and breath. They can be even used as pressure sensors with a piezoresistive sensitivity of 284.4 kPa–1 to precisely detect subtle physical movements like arterial pulses, which can provide vital cardiovascular information. Moreover, the eutectogels can be used as nonvolatile conformal electrodes to monitor epidermal physiological signals, such as electrocardiogram (ECG) and electromyogram (EMG).