A stretchable epidermal sweat sensing platform with an integrated printed battery and electrochromic display

Wearable electronic devices are of potential use in various health monitoring applications including non-invasive chemical sensing. However, such platforms are typically limited by the need to connect to external devices for power and data visualization. Here we report a stretchable epidermal sweat sensing platform that integrates a stretchable battery and a low-power digital electrochromic display. The patch can operate as a standalone device to directly display the concentration of various electrolytes or metabolites in sweat, such as glucose and lactate, without any wired or wireless connection to external devices. It consists of electrochemical sensors, a stretchable Ag2O–Zn battery, ten individually addressable electrochromic pixels and a small microcontroller unit. All the components and interconnections, except the microcontroller, are fabricated via the high-throughput screen printing of customized elastomeric or silver inks. The integrated system is robust to mechanical deformation and is unaffected by 1,500 stretching cycles at 20% strain. The electrochromic display exhibits stability for 10,000 on/off cycles, and the battery can power 14,000 sensing sessions over a week-long use. A wearable epidermal sweat sensing platform that contains a printed low-power electrochromic display and a stretchable Ag2O–Zn battery can collect, analyse and present electrochemical data in real time without the need to connect to external devices.