Carbon Dot-Based Mechanofluorescent Hydrogel with Tunable Fluorescence for Bioengineering Applications

Fluorescent hydrogels are emerging as versatile platforms for tissue engineering and soft robotics due to their ability to transduce mechanical stimuli into optical signals. However, existing systems respond only to large stresses, suffer from fluorescence quenching, and lack bioactive functionalities, limiting their ability to detect and quantify subtle mechanical forces. This study reports on a stimuli-responsive hydrogel with robust mechanics, pH sensitivity, biocompatibility, and pronounced mechano-responsive fluorescence for sensitive, quantitative readout of low mechanical stress.  Hydrogels were synthesized from gelatin methacryloyl (GelMA), acrylamide (AM), and polyethylene glycol diacrylate (PEGDA) and infused with carbon-based quantum dots (CQDs) derived from citric acid (GAPC) and cysteine-modified citric acid (GAPCys). Under low compressive forces (250-1250 Pa), the operating range of soft grippers for delicate tissues, hydrogels showed a concentration-dependent linear decrease in photoluminescence, establishing a quantitative correlation between fluorescence intensity and applied stress. The integration of CQDs with tunable hydrogel matrices overcomes fluorescence quenching while maintaining mechanical robustness and bioactivity. These mechanofluorescent hydrogels offer a platform for applications including soft robotic grippers, tissue engineering scaffolds monitoring forces during growth, and implantable sensors for quantitative strain tracking in organs, joints, or vasculature.