Injectable pH-Responsive Cross-Linked Chitosan Hydrogel Co-Delivering Methotrexate and Diaminoperylene Bisimide: Enhanced Targeted Chemo-Photodynamic Therapy for Breast Cancer Cells with Reduced Systemic Toxicity

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 with a quantum yield of Φ Δ = 0.22 ± 0.02 upon light irradiation. The system provided controlled, pH-sensitive MTX release, reaching 90.0 ± 2.5% at pH 5.2 compared to 70.0 ± 3.0% at pH 7.2 over 72 h. Rheological analysis confirmed excellent injectability and mechanical stability, with an elastic-dominant behavior (G′ ≈ 300 Pa) and pronounced shear-thinning and self-healing properties. In vitro studies showed that the combined chemo-photodynamic treatment reduced the viability of MDA-MB-231 breast cancer cells to 23.68 ± 1.8% at 3 µg/mL MTX and 12 µg/mL DA-PBI under light irradiation, while maintaining high biocompatibility toward normal MCF-10A cells (>85% viability). These results demonstrate that low-dose chemotherapy combined with photodynamic activation can achieve potent and selective anticancer efficacy with reduced systemic toxicity.