Conductive Nanocomposite-Based Soft Electronic Interfaces for Continuous Physiological Monitoring

Abstract

Soft electronic interfaces that match our skin properties show great potential in various applications, such as health monitoring, human-machine interface, and the Internet of Things. Both inorganic and organic conductive materials offer unique advantages for their use in soft electronics. In this thesis, we introduced soft conductive nanocomposites comprised of an interpenetrating network of highly conductive metal nanowires and an intrinsically soft conductive polymer to achieve high conductivity, electromechanical stability, and low modulus. The nanocomposite can be patterned via a simple, low-cost micro-molding process and transferred onto various adhesives for skin-interfaced electrophysiological sensing. We validated the performance of nanocomposite-based wearable sensors by comparing them with gold standard gel electrodes for continuous recording of biophysical signals. The nanocomposite sensors exhibit a higher signal-to-noise ratio than the gel electrodes in the recording of an electrocardiogram (ECG), electromyogram (EMG), and electrical bioimpedance (EBI). The nanocomposite-based electronic interface can also address the connection challenges between soft electrodes and rigid data acquisition circuitry for reliable continuous recording. The bioimpedance continuously recorded with such a connection shows a signal-to-noise ratio of 37.0 dB, higher than the ratio of 25.9 dB obtained with the gel electrodes. We developed nanocomposite-based bioimpedance sensors for continuously recording heart rate, systolic, and diastolic blood pressures. Although the sample set is low, the continuously measured systolic and diastolic blood pressure offer accuracy of 0.1 ± 3.3 mmHg and 1.3 ± 3.7 mmHg, respectively, confirming the grade A performance based on the IEEE standard for wearable, cuffless blood pressure measuring devices. In summary, the nanocomposite design and fabrication approach can be employed to create a wide range of soft and stretchable devices, showing great potential in biomedical applications.