FeetBeat: A Flexible Iontronic Sensing Wearable Detects Pedal Pulses and Muscular Activities

Objective: Human feet have long been considered in close association with whole-body health, from which abundant cardiovascular and skeletomuscular information can be extracted. In this study, we aim to develop the world's first foot-based wearable system that can detect both pedal pulses and muscular activities, referred to as FeetBeat. Methods: Utilizing the flexible iontronic sensing technology, we have constructed and characterized a five-unit sensing array for detection of both pedal pulse signals and muscular activities. It is integrated into the tongue of an athletic shoe for real-time signal acquisition. Additionally, the linear array allows alignment-free capture of pulse signals and also provides a spatial reference to muscular activities. Results: An ultrahigh sensitivity of up to 1 nF/mmHg has been achieved for individual units, with a range of 1 to 200 mmHg. The pedal pulse waveforms have been detected to derive vital health signs, such as heart rates (HR) and respiratory rates, of which the pulse-derived HR is compared with the electrocardiogram. Moreover, individual tendon responses have been acquired to analyze different pedal gestures, from which multi-channel signals can be used to distinguish different activities. Conclusion: The FeetBeat device has shown the potential to be the world's first wearable platform to simultaneously analyze both vital signals and body activities from the measurable pedal pulse waveforms and muscular responses in a natural and unobtrusive fashion. The data-collecting wearable system provides a highly valuable means to assess the personalized health as well as daily activities on a continuous basis.