Biocompatible Gel-Free Coconut Oil and Carbon Black Electrodes for ECG and Respiration Measurements

The current state of the art in telemedicine has increased the interest in long-term monitoring of physiological and bioelectric signals. This motivated the development of materials and techniques for the fabrication of biocompatible, user, and environmentally friendly alternatives to conventional resistive wet electrodes. Here, we report a method for the fabrication of dry flexible and stretchable electrodes based on coconut oil (CNO) and carbon black (CB) for the monitoring of electrophysiological signals without conductive gels. The highly stretchable material shows a specific resistance $\rho $ down to $33.2\pm 12.3 \Omega \text{m}$ , high conformability, and a stretchability up to 1500%. The epidermal electrodes were used to record electrocardiographic (ECG) signals and measure respiration in a three-lead configuration and compared with commercial wet electrodes. Even after being elongated by 100% for 100 stretch/release cycles, a reliable recording of the QRS complex is demonstrated without the need for any contact enhancer or substances that cause skin reaction, demonstrating the potential use of this material for long-term ECG monitoring applications.