Multiple-Language-Responsive Conductive Hydrogel Composites for Flexible Strain and Epidermis Sensors

Conductive hydrogels are considered highly promising materials for developing skin-like sensors due to their excellent biocompatibility and mechanical flexibility. However, their limited stretchability, low toughness, and low fatigue resistance hinder their sensing capabilities and durability. To overcome these limitations, we developed a conductive hydrogel composite with high mechanical performance and the ability to respond to and identify different languages. The hydrogels are prepared by incorporating functionalized multiwalled carbon tubes (F-CNTs) into hydrophobically associated polyacrylamide (AM) and lauryl methacrylate (Lmc) hydrogels. To ensure the uniform dispersion of F-CNTs in the hydrogel network, the cationic surfactant cetyldimethylethylammonium bromide (CDAB) is used; the carboxylic group on F-CNTs cross-links the micelles and polymer chains through electrostatic interactions. The surfactant also facilitates the formation of hydrophobic interactions between the hydrogel matrix and the F-CNT surface. This greatly improves the mechanical properties of the hydrogel, resulting in excellent stretchability of 2016%, a toughness of 551.56 kJ m–3, and an antifatigue property. The hydrogel also exhibits high tensile strain sensitivity with a gauge factor of 4.69 at 600% strain. The hybrid hydrogel-based sensors demonstrate excellent sensing capabilities, not only detecting full-range human activities but also differentiating different languages (English, Urdu, and Pushto) in both speaking and writing. Besides strain sensing, the hybrid hydrogel has the capability to mimic human skin for a touchable screen like a metal. These results highlight the potential of the F-CNT-based hybrid hydrogel as a wearable strain sensor for flexible devices.