Skin‐interfaced electrochemical sensing devices are widely developed for biochemical sensing at molecular levels. However, the sensing electrodes fabricated with photolithography or printing technique are hard to achieve high stretchability without special designs like serpentine shape. Also, most of them require wired connections with external electrochemical workstations for data acquisition or on‐board batteries to power the circuits, which largely restrain the flexibility, simplification, and miniaturization of the devices. Here, a battery‐free, wireless, and epidermal electrochemical system is presented for in situ biochemical sensing. The sensing component of the system is a stretchable electrode array all‐printed with soft polymer and conductive silver nanowires. The electrodes show stable electrical properties within strain range of 0–50%, without serpentine designs. The electronic component of the system is a fully integrated flexible circuit board with near field communication module, which enables wireless energy harvesting and data transmission with smartphones. The system demonstrates good performance in real‐time on‐body sweat analysis for simultaneous quantitative detections of glucose, hydrogen, sodium, and potassium. This battery‐free and wireless epidermal electrochemical system provides a simplified, miniaturized, and flexible solution for a wide range of biochemical platforms, including wearable and implanted bioelectronics.

A direct inkjet printing process was developed to fabricate patterned elastic microstructures for pressure sensors using n-butyl acetate diluted polymethylsiloxane (PDMS). The diluted PDMS precursor mixture with a cross-linker exhibited a controllable viscosity below 14 cP in 48 h at 25 °C, and the PDMS film had lower elastic modulus and hardness values than the non-diluted PDMS precursor after curing. The capacitor using the printed PDMS film as the microstructured dielectric layer showed a very high pressure sensitivity of up to 10.4 kPa−1 under the pressure below 70 Pa, and the pressure sensitivity would be dramatically decreased to 0.043–0.052 kPa−1 under the pressure between 2 and 8 kPa. Furthermore, the triboelectric sensors could be structured with an inkjet printed PDMS film and controllably generate the voltage signals up to 1.23 V without any amplification. The results suggest that mechanical properties and patterned elastic microstructures play the key roles in PDMS-based sensor devices, and the PDMS dielectric layer with controlled mechanical properties and microstructures fabricated via directly inkjet printing opens up the applications of the PDMS and its composites in functional devices.

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