Aligned flexible conductive fibrous networks for highly sensitive, ultrastretchable and wearable strain sensors

Microstructure design is an essential procedure to realize high performance wearable strain sensors. In this paper, we proposed a simple and effective assembly approach to prepare a reduced graphene oxide (RGO) nanosheet-wrapped aligned thermoplastic polyurethane (TPU) fibrous mat through ultrasonication to construct a uniform 3D conductive network. By combining the advantages of this conductive network and elastomers, a highly stretchable and ultrasensitive strain sensor was prepared by embedding this aligned fibrous network in flexible polydimethylsiloxane (PDMS). In comparison with vertical directional conductive RGO/TPU networks, the parallel directional fibrous network-based flexible sensor exhibited remarkable mechanical strength and responsivity, showing an interesting anisotropic response behavior. Our flexible strain sensors possessed a broad sensing range (0-150% with reversible responses), high sensitivity (the gauge factor was 593), excellent cycling stability, fast response and stable resistance to humidity and temperature stimuli, thus fulfilling the requirements of remarkable strain sensors. As a prototype, the parallel directional fiber-based flexible strain sensor was assembled onto various parts of the human body to monitor the motions via the response of electrical signals, indicating its tremendous potential applications in wearable electronics and intelligent robots.