3-D Printing of PAM Hydrogel-Based Iontronic for Dual-Mode Epidermal Sensors

The advancement of hydrogel-based epidermal sensors that integrate multifunctionality, high transparency, rapid processing, and heightened sensitivity is of significant interest. Herein, we present an efficient approach for the fabrication of flexible dual-mode epidermal sensors through the ultraviolet (UV)-curing 3-D printing of polyacrylamide (PAM)-based ionic hydrogels. The hydrogel precursor incorporates sodium dodecyl sulfate (SDS) monomers to augment the water dispersibility of the 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) photoinitiator, thereby substantially increasing the photocuring efficiency of the ionic hydrogel. As a result, the distinctive surface microstructures of PAM-based ionic hydrogels can be engineered for sensors with varying sensing modalities to improve detection performance. The piezoelectric tactile sensor, incorporating a concentric ring microstructure, demonstrates a sensitivity coefficient of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.39~\text {mV}\cdot \text { kPa}^{-{1}}$ </tex-math></inline-formula>. Conversely, the resistive strain sensor, characterized by a high-density reticular hollow structure, exhibits the highest gauge factor of 24.87. Furthermore, each sensor modality demonstrates excellent temporal response and stability, confirming its applicability in motion monitoring and Morse code transmission.