3D-printed microstructured ionic hydrogels for enhanced electric double-layer pressure sensing

Hydrogel-based pressure sensors have attracted increasing attention for wearable sensing applications due to their intrinsic softness, flexibility, biocompatibility, and permeability. However, the influence of surface microstructure geometry on the electromechanical response of hydrogels remains insufficiently understood, and scalable fabrication strategies for engineering such structures are limited. In this study, we investigate the effect of surface microstructure geometry on the pressure-sensing performance of ionic hydrogel sensors fabricated using a low-cost digital light processing (DLP) 3D printing. A chitosan/poly(ethylene glycol) diacrylate hydrogel was assembled and printed with different microstructures by integrating surface protrusion array configurations. The pressure-sensing behavior was characterized using capacitive measurements. The results showed that microstructured hydrogels exhibit enhanced pressure sensitivity compared to solid hydrogels due to deformation-induced changes in the electric double-layer (EDL) capacitance at the hydrogel-electrode interface. The hydrogel with more densely distributed protrusions (17×17) demonstrated the highest-pressure sensitivity of 0.42 kPa-1, compared to 0.082 kPa-1 for the solid hydrogel. Furthermore, increasing ionic concentration by incorporating LiCl significantly improved sensitivity to 1.46 kPa-1. Wireless sensing experiments confirmed that pressure-dependent resonant frequency shifts, with the 17×17 structure exhibiting higher sensitivity than the 7×7 structure. These results demonstrate that engineering hydrogel surface microstructures provides a strategy to enhance the performance of soft pressure sensors for wearable and wireless sensing applications.