Construction and properties of a carbon dots-decorated gelatin-dialdehyde starch hydrogel with pH response release and antibacterial activity

An antibacterial carbon dot hydrogel (GDS S-PCD ) was constructed based on gelatin, dialdehyde starch (DS) and carbon dots (S-PCDs). The formation mechanism of GDS S-PCD hydrogels was attributed to the synergistic cross-linking of hydrogen bonds and dynamic covalent bonds . With increasing S-PCD content, the mechanical and rheological properties of GDS S-PCD hydrogels can be improved, and the micropore size becomes denser. GDS S-PCD hydrogels had pH-dependent swelling and degradation behavior, with a high swelling rate under acidic conditions and relatively low swelling under neutral and alkaline conditions. The cumulative release of S-PCDs from the same hydrogel in an acidic environment was higher than that in an alkaline environment, indicating that the GDS S-PCD hydrogel had a pH-dependent controlled release ability. The release behavior of S-PCDs conformed to the first-order kinetic release model (R 2  > 0.95), and the release mechanism was related to Fickian diffusion. The synergistic antibacterial mechanism of GDS S-PCD hydrogels against Staphylococcus aureus suggested that bacterial metabolism leads to an acidic culture environment, which releases S-PCDs and destroys the bacterial cell membrane for antibacterial purposes. In GDS S-PCD hydrogels, S-PCDs play the main antibacterial role, and the hydrogel plays a synergistic role in trapping bacteria. Carbon dot hydrogels are promising materials to fulfil the functions of antibacterial and controlled release in the food and biomedical fields.