The seamless and adaptive interactions between functional devices and their environment (e.g. the human body) are critical for advancing emerging technologies, e.g. wearable devices, consumer electronics, and healthcare. Although non-electrical signals such as mechanical stimuli are inherent in these applications, electrical control of device operation dominates existing technologies. This scheme of operation not only requires a complex integration of heterogeneous components but also lacks a direct interface between the (opto)electronics and the working environment. Moreover, all existing technologies require a power source, which complicates the system design and limits operation schemes.
Stretchable electronic devices are particularly desirable for practical applications because of the high mechanical deformability and adaptability enabling their integration with three-dimensional biological systems. In this work, we demonstrate for the first time a monolithic integration of piezoelectric nanogenerator system with 3D printed electrodes as self-powered wearable devices for physiological sensing on human body. The stretchable electrodes were directly printed on soft substrates with designed patterns. Subsequently, two-dimensional ZnO nanosheets were selectively grown on electrodes without any decrease of electrode conductivity. ZnO nanosheets with controlled atomic thickness are more flexible compared with ZnO nanowires, which can generate distinguishable electrical signals under tiny mechanical deformation and sustainably perform non-invasive physiological functions, e.g. pulses detection, by harvesting power from human body. This research is expected to have a positive impact and immediate relevance to many societally pervasive areas, e.g. biomedical monitoring, consumer electronics, and human-machine interface.