Graphene Quantum Dots for Fluorescent Labeling of Gelatin-Based Shear-Thinning Hydrogels

The efficiency of injectable biomaterials as minimally invasive therapeutics significantly relies on biomaterial's characteristics, such as stability, biodegradation rate, and interaction with the host tissue, which requires real-time tracking of the biomaterials. Fluorescence imaging is considered as a noninvasive technique for monitoring biomaterials; however, the commonly used fluorescent agents are often accompanied by photobleaching and toxicity. Herein, graphene quantum dots (GQDs) are introduced as a biocompatible and stable fluorophore for imaging and noninvasive monitoring of a physically cross-linked injectable shear-thinning biomaterial (STB) of gelatin-silicate nanoplatelets. Silicate nanoplatelets and GQDs serve as the physical cross-linkers of gelatin making electrostatic interaction with gelatin chains. Different STB-GQDs formulations are assessed in terms of fluorescence intensity, injectability, thermal stability, and cellular biocompatibility. STB-GQDs with 0.06% GQDs, 6% solid material, and 50% silicate in the solid material show the strongest in vitro fluorescence and the highest thermal stability. In vivo monitoring of STB-GQDs is also achieved through fluorescent imaging where incorporated GQDs exhibit a robust and stable signal, suggesting their promising applications in long-term tracking of gelatin-based STBs.