Hybrid Hydrogel-Based Skin Health Monitor for Tracing Solar UV Radiation in Aqueous Environments

Inspired by the Chinese wood oil coating on umbrella, an ionic polymer layer is coated onto hybrid hydrogels to realize monitoring of the solar ultraviolet (UV) radiation dose in aqueous environments. The hybrid hydrogels are synthesized by introducing the photocatalyst graphitic-carbon nitride (g-C₃N₄) nanosheets into the radically polymerized hydrogels from the monomer di(ethylene glycol) methyl ether methacrylate (MA) and oligo(ethylene glycol) methyl ether methacrylate (MA₃₀₀). Thus, g-C₃N₄ are physically embedded in the hydrogels. Owing to the existence of inorganic nanoparticles (g-C₃N₄ nanosheets) and hydrogels, the obtained hydrogels containing g-C₃N₄ nanosheets are named as hybrid hydrogels. Because g-C₃N₄ can decompose the dye methylene blue (MB) by photodegradation and the decomposition capability is correlated to the absorbed UV radiation dose from the sunshine, the solar UV radiation dose can be easily traced by the discoloration extent of dyed hybrid hydrogels. To avoid the possible dye leakage during aquatic sports activities, such as swimming in a lake or surfing in the seaside, the acetamide/zinc perchlorate hexahydrate (AC/ZPH)-based ionic polymer is coated onto the hybrid hydrogels. Owing to the combined effects of the dense structure as well as the existence of positive and negative ions in the AC/ZPH layer, the coated hybrid hydrogels present excellent resistance against dye leakage. To overcome the frangibility of the hydrogels, microfiber nonwoven fabrics (MFNF) are used as a substrate for the sensor. The obtained hybrid hydrogel-based UV radiation monitor presents excellent dye leakage resistance as well as flexibility and strength. Thus, it is very suitable for wearable devices to monitor skin health in the aqueous environment under sunshine.