A Wearable Platform for Monitoring Wrist Flexion and Extension in Biomedical Applications Using Organic Transistor-Based Strain Sensors

In this paper, a wearable platform for monitoring the wrist flexion and extension is reported. Differently, from similar devices already presented in literature, organic field-effect transistors will be effectively employed as strain sensors. We propose a novel device, fabricated over flexible plastic substrates, and capable to operate at low voltages (≤2 V). Thanks to these properties, the proposed devices can be integrated into a custom-made Lycra® glove for wrist motion monitoring without affecting the naturalness of movements, and interfaced with a portable readout electronic module. The readout electronics is able to transduce the current variation in the transistor structure into a voltage signal, opportunely conditioned and converted for proper acquisition by the elaboration unit. Control software allows users to set different control signals, including sensor polarization and overall amplification, to carry out sensor calibration and to finally record and real-time signal visualization. A complete electrical characterization of fabricated strain sensors is reported, as well as the evaluation of their functionality when mounted on the glove. The readout circuit is described, with details about the analog front-end design and simulation. Finally, the correct functionality of the complete system is demonstrated by the experimental acquisition of wrist movements and resolution evaluation. Thanks to the intrinsic properties of organic electronics in terms of lightweight, the platform represents a valuable system for non-invasive, imperceptible, and comfortable evaluation of wrist motion in real time, thus being effective for different applications such as rehabilitation and occupational health.