Graphene-based wearable piezoresistive physical sensors

In the last two decades, wearable piezoresistive physical sensors have attracted tremendous attention due to their broad applications in individual health-monitoring, human–machine interfaces, robotics, sports and therapeutics. Many different nanostructured materials, including nanowires, nanoparticles, nanoribbons, carbon black, carbon nanotubes and graphene, have been explored to construct stretchable piezoresistive sensors on an elastomer substrate. Thanks to its unique two-dimensional geometry, lightweight, flexibility, semi-transparency and outstanding transport and mechanical properties, graphene and its derivatives in particular are considered among the most suitable candidates as wearable sensors. This paper reviews various design strategies established for fabricating flexible, wearable sensors using graphene. The current state-of-the-art developments are discussed of flexible sensors made of 1D fibrous, 2D planar and 3D cellular interconnected graphene architectures for detecting physiological strains, tactile pressures and temperatures. The working mechanisms along with existing applications of flexible sensors are presented. The challenges these sensors are currently facing and potential opportunities for novel applications are revealed to offer new insights into future prospects in this field.