Mechanically Strong Metal–Organic Framework Nanoparticle-Based Double Network Hydrogels for Fluorescence Imaging

Tough and multicolor-changing hydrogels have shown great potential in sensing devices, wearable electronics, and human–machine interfaces. However, most of these hydrogels are either mechanically weak or lack the multi-responsive color-change property. Here, we designed and fabricated gelatin/pHEAA hydrogels crosslinked by metal–organic framework (MOF) nanoparticles (NPs) and with a nanocomposite and double-network structure using a facile, one-pot method. The presence of vinyl-functional zeolitic imidazole framework-8 MOF NPs in hydrogels provided not only multiple chemical and physical interactions with polymer networks to strengthen their mechanical properties (a tensile strength of ∼2.4 MPa, a fracture strain of ∼14, and a fracture energy of ∼14.10 MJ/m3) but also UV-triggered multi-fluorescence changes ranging from primary red–green–blue to secondary yellow, magenta, cyan, and white colors. More importantly, MOF/gelatin/pHEAA hydrogels can be further fabricated to possess different fluorescence-responsive patterns for QR codes or potential information storage. This work provides a design concept and hydrogel systems for developing tough, multi-color-changing hydrogels for imaging and other optical applications.