Chitosan/oxidized dextran hydrogel decorated with recycled antibiotic-derived carbon dots for synergistic antimicrobial and antioxidant activity.

A functional chitosan/oxidized dextran hydrogel (CS-MCDs/ODex) with enhanced antimicrobial and antioxidant properties was developed by incorporating carbon dots (MCDs) derived from recycled antibiotic waste. MCDs prepared from moxifloxacin hydrochloride via attapulgite adsorption and one-step hydrothermal carbonization exhibited enhanced antimicrobial activity and newly acquired strong antioxidant capacity that the precursor lacked. The hydrogel network was formed through dynamic imine bonding between CS and ODex, with additional hydrogen bonding between MCDs and the polymer matrix further stabilizing the structure. The composite hydrogel exhibited excellent injectability, self-healing ability, and pH-responsive swelling, degradation, and release behavior, with faster degradation and MCDs release under mildly acidic conditions due to the acid-labile Schiff-base bonds. Incorporation of MCDs enhanced the mechanical stability of the hydrogel, with improved compressive strength and rupture strain. The resulting CS-MCDs/ODex hydrogel exhibited synergistic antimicrobial and antioxidant effects in a fresh produce model. This work offers an eco-friendly strategy to upcycle pharmaceutical waste into value-added nanomaterials while enhancing the bioactivity of polysaccharide-based hydrogels for antimicrobial and antioxidant coating applications.