Electrically Conductive and Highly Stretchable Piezoresistive Polymer Nanocomposites via Oxidative Chemical Vapor Deposition

Electrically conductive polymer nanocomposites have been the subject of intense research due to their promising potential as piezoresistive biomedical sensors, leveraging their flexibility and biocompatibility. Although intrinsically conductive polymers such as polypyrrole (PPy) and polyaniline have emerged as lucrative candidates, they are extremely limited in their processability by conventional solution-based approaches. In this work, ultrathin nanostructured coatings of doped PPy are realized on polyurethane films of different architectures via oxidative chemical vapor deposition to develop stretchable and flexible resistance-based strain sensors. Holding the substrates perpendicular to the reactant flows facilitates diffusive transport and ensures excellent conformality of the interfacial integrated PPy coatings throughout the 3D porous electrospun fiber mats in a single step. This allows the mechanically robust (stretchability > 400%, with fatigue resistance up to 1000 cycles) nanocomposites to elicit a reversible change of electrical resistance when subjected to consecutive cycles of stretching and releasing. The repeatable performance of the strain sensor is linear due to dimensional changes of the conductive network in the low-strain regime (ε ≤ 50%), while the evolution of nano-cracks leads to an exponential increase, which is observed in the high-strain regime, recording a gauge factor as high as 46 at 202% elongational strain. The stretchable conductive polymer nanocomposites also show biocompatibility toward human dermal fibroblasts, thus providing a promising path for use as piezoresistive strain sensors and finding applications in biomedical applications such as wearable, skin-mountable flexible electronics.