Multi-functional and multi-responsive layered double hydroxide-reinforced polyacrylic acid composite hydrogels as ionic skin sensors

With the rapid development of artificial intelligence and other fields, flexible devices with various functions and response capabilities have become necessary for human–computer interaction. Hydrogels have a bionic three-dimensional elastic crosslinked aqueous polymer network, making them ideal biocompatible flexible sensing materials. In this study, the conductive composite hydrogels with enhanced mechanical properties, transparency, UV shielding, and adhesion were prepared using the interaction between the alternating ionic layer structure of layered double hydroxide nanosheets and acrylic acid. The conductive composite hydrogels were mechanically sensitive and could monitor human motion, such as finger bending, wrist bending, and swallowing movements, and they could also achieve near-linear and self-powered temperature sensing. Moreover, the strong absorption of UV light led to different degrees of photoelectrochemical reactions in the hydrogels, resulting in the formation of ion concentration differences and spontaneous ion diffusion, thus realizing self-powered UV light detection in only a hydrogel material for the first time. Therefore, the as-prepared multi-functional composite hydrogel ionic skin sensors could sense force, temperature, and UV light, respectively, which is expected to facilitate the development of functionalization and the expansion of application fields of layered double hydroxides and hydrogels. Graphical Abstract