Capacitive Coupling of Conducting Polymer Tattoo Electrodes with the Skin

• Published in: Advanced materials interfaces Vol. 8; no. 15
• Main Authors: Ferrari, Laura M., Ismailov, Usein, Greco, Francesco, Ismailova, Esma
• Format: Journal Article
• Language: English
• Published: Weinheim John Wiley & Sons, Inc 01.08.2021; Wiley
• Subjects: Bioengineering; Biomonitoring; biosignal transduction; Condensed Matter; Conducting polymers; conformable biosensors; Coupling; Electrodes; Equivalent circuits; Interfaces; Life Sciences; Materials Science; New technology; Physical properties; Physics; Silver chloride; skin impedance; Stability analysis; tattoo electrodes; Tattoos; Conformable biosensors; biosignal transduction; tattoo electrodes; conducting polymers; skin impedance
• DOI: 10.1002/admi.202100352
• ISSN: 2196-7350

Tattoo electronics is one of the emerging technologies in skin compliant biosensing. The growing interest in their large application in health monitoring raises several interrogations on how these sensors interface with the skin. In this paper, the bioimpedance at the interface of the skin and ultra‐conformable tattoo electrodes made of conducting polymers are focused on. The electrochemical characteristics of these electrodes differ from traditional gelled Ag/AgCl electrodes. The modeling of equivalent circuits in different skin‐electrode configurations proposes the explanation of the biopotentials transduction mechanism. The strong agreement between the circuit model and experimental values reveals the capacitive coupling of conducting polymer tattoo electrodes where circuit's values reflect the electrodes’ and skin physical characteristics. Additional studies underline an enhanced signal stability in inter/intra‐subject evaluations using dry tattoos beneficial for broad long‐term recordings. This study provides a comprehensive explanation of the skin/tattoo electrode interface model. The understanding of this interface is essential when designing next generation wearable biomonitoring devices using imperceptible interfaces. Tattoo electrodes are dry sensors that provide outstanding conformability to the skin thanks to their ultralow thickness. These electrodes interact with the skin via capacitive coupling where the upper layers act as a dielectric. Tattoos made of conducting polymer poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) display great mechanical stability and a long‐term performance in detecting biopotentials from the skin despite their considerably large impedance.