Skin-Inspired Multifunctional Luminescent Hydrogel Containing Layered Rare-Earth Hydroxide with 3D Printability for Human Motion Sensing

The development of multifunctional hydrogels is gaining a lot of attention owing to its application in electronic skins, wearable electronics, and soft robotics. In this study, an effective and facile one-step preparation strategy is developed to fabricate a multifunctional nanocomposite hydrogel consisting of sodium alginate/sodium polyacrylate/layered rare-earth hydroxide (LRH), where LRH plays multiple roles as a co-cross-linker and ionic carrier and is also the origin of fluorescence. The obtained LRH-based composite hydrogel exhibits excellent three-dimensional printing performance at room temperature. When exposed to different humidity conditions, the hydrogel exhibits humidity-dependent electro-mechanical properties. The multiple functions of the resultant hydrogel are easily realized by just relying on the addition of cationic LRH nanoplates. A skinlike motion sensor with transparency is fabricated based on the printed hydrogel and is used to monitor human motion. Owing to the fluorescence characteristics of lanthanide ions (Eu3+ and Tb3+) from LRH, the hydrogel shows highly tunable multicolored photoluminescence by adjusting the LRH constituent. This study reveals that the multifunctional hydrogels have potential for applications in sensing.