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.