Breast cancer therapy continues to face major challenges due to drug resistance and the severe side effects of conventional chemotherapy. To address these issues, an injectable and pH-responsive chitosan hydrogel was designed for the co-delivery of methotrexate (MTX) and diaminoperylene bisimide (DA-PBI), enabling a synergistic combination of chemotherapy and photodynamic therapy. The hydrogel matrix, cross-linked with glutaraldehyde, successfully maintained DA-PBI in its monomeric state, enabling efficient singlet oxygen generation
