Highly stretchable strain sensors based on graphene nanoplatelet-doped ecoflex for biomedical purposes

Ultrasensitive and highly stretchable strain sensors based on graphene nanoplatelet (GNP) doped Ecoflex are proposed. First, the electrical and electromechanical properties are deeply studied. It has been observed that the electrical conductivity significantly increases with GNP content, indicating that the saturation of the electrical network is not reached, even for the samples with 10 wt. % GNP, confirmed by SEM analysis. Furthermore, the analysis of the electromechanical behavior reveals a very high electrical sensitivity, with a gauge factor (GF) of around 25 at epsilon = 1 % and 3 center dot 10(4) at epsilon = 30 % in tensile and around 12 at epsilon = 1 % and 10(4) at epsilon = 30 % in compression. Furthermore, the electrical response was found to be stable under medium and long-term cycling tests, proving the high robustness of the proposed sensors. Finally, several proof-of-concept tests are carried out with the optimized sensor, proving the high applicability of the proposed material as pressure sensors, for breathing and wrist pulse monitoring, where the electromechanical responses in a relaxed or tired state are clearly distinguishable, proving the high potential of the developed sensors for biomedical purposes.