Sensors for monitoring human body movements have gained much attention in the recent times especially in the health-care sector as these devices offer real-time monitoring of vital physiological signs, enabling health-care professionals to evaluate health conditions and provide remote feedback. In this work, we have fabricated carbon-nanotube (CNT)/ polydimethylsiloxane (PDMS) composite sensor through simple dispersion and freezing method for monitoring flexion movements in humans. Sensors with different CNT loadings, namely 0.1 wt %, 0.5 wt %, and 1 wt % were fabricated and analyzed to find the best performing sensor. Several characterizations like Raman, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), tensile strength measurements, and piezoresistive studies were carried out to study the features of the sensors. Among the fabricated sensors, the one with the loading concentration of 0.5 wt% is found to be most sensitive for flexion applications with higher gauge factor of 533 at 60% strain level, response time of ~ 140 ms and lower hysteresis loss. The feasibility of the sensor for monitoring flexion like finger bending, wrist bending, elbow bending, and knee bending is also analyzed making it ideal for use in sports for athletes, physicians, and trainers to investigate physical performance and well-being.

CNT–PDMS film-based flexion sensor for examining physical activity in humans
    Abstract
        Graphical abstract
    1 Introduction
    2 Experimental section
        2.1 Synthesis of MWCNTs
        2.2 Fabrication of the MWCNT–PDMS epidermal sensor
        2.3 Characterization and sensing property measurement
    3 Results and discussion
    4 Conclusion
    Acknowledgements 
    References

• Indu Elizabeth(Surface Engineering Division, CSIR-National Aerospace Laboratories, Bangalore 560017, India) Corresponding author
• C. Athira(Surface Engineering Division, CSIR-National Aerospace Laboratories, Bangalore 560017, India)
• Sharon J. Paul(CSIR-National Physical Laboratory, New Delhi 110012, India)
• Bhanu P. Singh(CSIR-National Physical Laboratory, New Delhi 110012, India)