Stress in daily life has become a significant issue due to health risks. Because many sources of stress are unavoidable, management of stress is critical. Recent wearable devices, detecting physiological signals such as electrodermal activity, have been developed for quantitative and practical stress management assessment. However, they rely on a rigid and bulky system that is uncomfortable to wear during daily activities and has significant motion artifact issues. Here, we introduce a wireless skin-conformal bioelectronic system that evaluates daily stress management. Ultrathin, stretchable circuit system incorporated with a silicone elastomer enables a soft lamination on the skin, providing portable, continuous monitoring of stress. Printed, biocompatible nanomembrane electrodes on a breathable silicone tape provide long-term wearability and skin compatibility, enabling seamless monitoring of galvanic skin response at home with daily activities. Demonstration of stress management practice with human subjects shows the effectiveness of stress alleviation with a promising, non-invasive, and portable wearable system.
Recent advances in materials engineering, chip miniaturization, wireless communication, power management, and manufacturing technologies have shaped our perspectives on wearable electronics in ways that wearing a Fitbit is as casual as driving to work. However, establishing a robust sensor-to-skin interface remains as a significant challenge due to the drastic contrast in soft, dynamic human skin and rigid electronics, limiting the adoption of technology to leisurebased applications. Here, we present an engineering solution by combining the respective merits of thin-film nanostructures, soft materials, and miniature electronic components and developing a soft, hybrid, wireless, wearable platform. We exploit conventional CMOS processes to fabricate metal/polymer nanostructures, implemented as dry contact electrodes (thickness ~3 μm) as well as a flexible interconnection system (thickness ~10 μm). The electrodes are further optimized by incorporating an open-mesh network geometric features allowing for prolonged, intimate contact throughout repeated and dynamic deformation of human skin. The skin-electrode impedance and the signal-to-noise ratio are ~18 kΩ and 29.52 dB, respectively, from electromyogram (EMG) recordings, matching the qualities of Ag/AgCl hydrogel electrodes. The stretchable circuit layer contains pad metal structures compatible for integration of surface mount chip components using a conventional reflow soldering process, allowing for easy integration of commercially available integrated circuit solutions. Silicone-based elastomer is used as both the carrier substrate for the thin-film structures and the backing layer providing the necessary adhesiveness to the skin. We verify that the completed system can be stretched up to 10% based on computational and experimental analysis. Finally, we demonstrate the robustness of the system functionality by showcasing human-machine interfaces (HMI) based on a single-channel forearm EMG with a real-time classification distinguishing four different hand gestures (accuracy: 95.9%) as well as the control of a robotic hand using three devices simultaneously.
Heart disease is the most common cause of death, so there is a great need for non-invasive continuous monitoring of heart activities in daily life for early diagnosis and treatment. However, existing devices are not suitable for long-term use since they are uncomfortable to wear and heavy due to rigid plastics and thick metals. Here, we introduce a low-profile, comfortable, skin-wearable multifunctional biopatch, capable of wireless monitoring of heart and motion activities. The combination of a thin, tacky elastomeric membrane, skin-like stretchable electrodes, and a small form factor flexible circuit ensures the intimate integration of the device on the skin in adhesive and gel electrolyte-free environment. The results are not only enhanced user comfort and minimized motion artifacts during normal activities but also accurate classifications for various arrhythmias based on R-R interval and ST-segment analysis. In addition, the integrated motion sensor is available to track human activities and alert an emergency when a fall event occurs. This multifunctional soft wearable system would serve as a new wearable tool to advance human healthcare.