Ugi four-component-crosslinked chitosan-graphene quantum dots as pseudo-peptide-functionalized photoluminescent carriers for potential active and passive targeting delivery of methotrexate

In this study, graphene quantum dots (GQDs) were introduced innovatively as multifunctional nano-crosslinkers to construct chitosan-based hydrogels (CS-GQDs) via an Ugi four-component reaction (Ugi-4CR), enabling the formation of a covalently crosslinked pseudo-peptidic network through a facile, green, and one-pot synthetic strategy. This work represents a novel application of Ugi chemistry in polysaccharide-based hydrogel engineering, where GQDs simultaneously act as structural crosslinkers and photoluminescent nanofillers with tunable content. In vitro release studies demonstrated a pronounced pH-responsive and sustained methotrexate (MTX) release behavior, with significantly higher release under acidic conditions (pH 4.5) than at physiological pH (7.4), which became more prominent as the GQD content increased. Kinetic modeling showed that the release profiles were best fitted by the Weibull model (R² > 0.95), suggesting a combined diffusion–polymer relaxation-controlled release mechanism. Cytotoxicity assessments revealed that blank CS-GQDs hydrogels maintained good cytocompatibility toward HUVEC cells (cell viability >75% even at the highest GQD content), whereas MTX-loaded CS-GQDs exhibited enhanced and selective cytotoxicity against MCF-7 breast cancer cells compared to normal cells. The results highlight the innovation and therapeutic potential of Ugi-crosslinked CS-GQDs hydrogels as a multifunctional platform for MTX delivery, with prospective applicability in both passive and active targeting cancer therapies.