Textile substrates, coatings and conductive inks used in fabrication and characterization of printed dry electrodes for bio-impedance sensing

Abstract This study discusses the development of dry electrodes on stretchable textile substrates, addressing the limitations of traditional wet electrodes in bio-impedance (BI) sensing applications. Wet electrodes require conductive gels that cause skin irritation, offer limited usability, and produce inconsistent measurements, underscoring the need for reusable, gel-free electrodes. A systematic approach was adopted to optimize materials and methods for textile-based dry BI sensors to solve these problems. Various characterization tests, including mechanical, adhesion, and surface profilometry tests, were performed to validate the selected materials. Of the five different textile substrates studied in this work, a polyester + spandex blend textile was chosen for its superior stretchability, comfort, and compatibility with coating materials. Heat-transfer vinyl poly vinyl chloride (HTV PVC) and heat-transfer vinyl polyurethane (HTV PU) coatings were tested as an additional coating layer on textile substrates to improve surface roughness, ink adhesion, and printability. Stretchable conductive inks were used to print electrodes and conductive tracks via screen printing and stencil printing techniques. Polydimethylsiloxane (PDMS) and HTV PU were tested for the encapsulation of the electrodes and track lines to increase the longevity of the fabricated sensor. These fabricated sensors were subjected to bending tests to check for any loss in the electromechanical properties of the sensors, conductivity of the sensor was maintained even after 1000 cycles of bending tests. Dry electrodes were tested for contact resistance and BI measurements from human subjects. The results show a reliable, durable and wearable BI sensor platform that maintains consistent skin contact without adhesives. This work represents an advancement in the development of long-term, noninvasive health monitoring systems, paving the way for more efficient and comfortable biomedical diagnostic tools.