Stretchable Substrate Surface-Embedded Inkjet-Printed Strain Sensors for Design Customizable On-Skin Healthcare Electronics

Stretchable strain sensors have been proposed for personalized healthcare monitoring or human motion detection in a skin-mountable form factor. For customization and stretchable substrate-compatible low-temperature processing, various printing technologies have been utilized to fabricate strain sensors. Hydrophobic stretchable polymers and low viscosity conductive inks are typically used in printed high resolution strain sensor fabrications. However, directly printed strain sensors on hydrophobic stretchable substrates have shown limited printability in pattern continuity, spatial resolution, stretchability, and linearity. Therefore, there is still a need to develop a simple printing process that can fabricate high-resolution stretchable strain sensors for skin-mountable healthcare electronics. In this work, we developed a simple inkjet printing and substrate transfer process for stretchable strain sensors by optimizing a polymer coating layer for enhancing the printed pattern formation, spatial resolution, and substrate transfer efficiency simultaneously while maintaining the benefits of inkjet printing, such as customizability and large-area applicability. The printed stretchable strain sensors are embedded into a stretchable substrate, improving stretchability up to 45% of strain, which successfully detects various parts of our body, such as wrists, fingers, and arms. Further, the printing process scales down the sensors to 150 μm × 6 mm, and the miniaturization enables distinguishing subtle movements of different fingers.