Comparative Study of Printed and Laser-scribed Stretchable Conductors on Thin Elastomers for Soft and Wearable Electronics

As printed electronics is evolving towards applications in biosensing and wearables, the need of novel routes to fabricate flat, lightweight, stretchable conductors is increasing in importance. Here, combined to the necessary functionality and stretchability, new important requirements can come into play, such as good match with elastic properties of skin or other tissues, breathability, compatibility, high stability at temperatures used for processing of other components, among others.<br/>A suitable strategy for creating soft yet robust and stretchable interconnections in the aforementioned technological applications is to use print-related techniques to pattern conductors on top of elastomer substrates. In this study some thin elastomeric sheets – two forms of medical grade thermoplastic polyurethanes and a medical grade silicone – are considered as suitable substrates. Their mechanical, surface and moisture barrier properties – relevant for their application in soft and wearable electronics – are investigated. We tested various approaches to pattern conductors: screen printing of (i) conducting polymer (poly(3,4-ethylenedioxythiophene):polystyrene sulfonate, PEDOT:PSS), or (ii) stretchable Ag ink, and (iii) laser-scribing of Laser Induced Graphene (LIG). The electromechanical properties of these materials are thoroughly investigated by means of tensile testing and concurrent electrical measurements, up to a maximum strain of 100%. Performance of the different stretchable conductors is compared and rationalized, evidencing the differences in onset and propagation of failure. Selected materials are then used in a proof of concept application as connectors for a wearable tattoo biosensor.