Consistent and Reproducible Direct Ink Writing of Eutectic Gallium–Indium for High-Quality Soft Sensors

Given the need for stretchable sensors, many studies have been conducted on eutectic gallium–indium, which has superior properties as a conductive ink. However, it has remained a challenge to manufacture sensors in a consistent and reproducible manner because conventional mold-based fabrication still depends highly on manual techniques. To overcome this limitation, the direct ink writing was used in this study, focusing on improving the stability of writing by exploring issues related to failure and ensuring the consistency of the microchannel by selecting appropriate process variables, including the syringe material. As a result, multiple sensors produced under the same manufacturing conditions had similar behaviors. This fabrication technique improved the accuracy of manufacturing a microchannel, and its behavior was predicted successfully by a simple mathematical model, which was confirmed by nondestructive inspections of the microchannel. In developing a one-piece glove-type sensor without an assembly process, the efficiency of the fabrication technique was also emphasized.