Galinstan-based flexible microfluidic device for wireless human-sensor applications

Liquid-metal-based wearable technologies are one of the promising ways to realize soft-skin flexible electronics. Here, we report a flexible microfluidic device that injects Galinstan liquid-metal alloy through the microchannels of a polydimethylsiloxane (PDMS) substrate, targeting an inductor-capacitor (LC) resonant circuit for wireless power transmission and sensing. The surface inside PDMS microchannels is chemically modified using sulfuric acid (H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e) solution, making it easier for the liquid metal to flow through the microfluidic channel. Electromechanical characteristics of the capacitive pressure sensors were evaluated by loading and unloading the external pressure continuously in the range of 0–200 mmHg for 300 cycles. After that, the characterization of Galinstan-based flexible microfluidic sensors consisting of the LC circuit conducted in a strain range of up to 30 %. Finally, monitoring of various human motion (e.g., wrist flexion and finger motion) was demonstrated using a wireless sensing platform with an external antenna. Electrical and mechanical performances confirm that the Galinstan-based sensors are reliable, reproducible, repeatable, and flexible with a sensitivity of 5 kHz/mmHg. The proposed flexible microfluidic device has the potential to become an exceptionally reliable candidate for wireless human-machine applications.