Intrinsically conducting polymers in flexible and stretchable resistive strain sensors: a review

Flexible and stretchable strain sensors are in great demand in advanced health care, human–machine interface, stretchable electronics, electronic skin, etc. Of the various strain sensing mechanisms, the piezoresistive technique has many advantages over other methods such as capacitive, piezoelectric, and optical sensing techniques. A typical flexible/stretchable resistive sensor is realized using an insulating polymer substrate with conducting filler materials. Intrinsically conducting polymers (ICPs) such as polypyrrole (PPy), polyaniline (PANI), and poly(3,4-ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS) are used as primary or secondary filler in the polymeric or fibrous substrates to fabricate stretchable composite sensors. This review comprehensively discusses the development of flexible and stretchable strain sensors using conducting polymers. The material combinations, fabrication methods, quantitative metrics such as maximum sensitivity, stretchability, durability, and salient features of various stretchable resistive strain sensors are summarized, which would serve as a vademecum to the researchers developing ICP-based stretchable strain sensors.