Injectable gellan gum hydrogel systems with Doxorubicin and melanin nanoparticles for chemo-photothermal osteosarcoma treatment.

Osteosarcoma remains one of the most aggressive bone malignancies, with limited advances in effective therapies. Herein, we developed injectable, in situ gel-forming hydrogels based on gellan gum (GG, 0.75% and 1.25% w/v), naturally extracted melanin nanoparticles (MNPs, 0-500 μg/mL), and Doxorubicin (Dox, 20 μg/mL) for localized chemo-photothermal therapy. Therapeutic efficacy was assessed using a physiologically relevant 3D osteosarcoma model mimicking post-surgical bone defects, generated by encapsulating Saos-2 cells within collagen hydrogels. Cells fully colonized the constructs within 7 days, remaining viable, proliferative, and expressing osteoblastic markers (Runx-2 and ALP). GG concentration modulated hydrogel rheology, injectability, water uptake, and degradation. Upon near-infrared (NIR) irradiation, MNP-loaded hydrogels reached temperatures above 60 °C within 5 min, reducing tumor cell viability to 43% after 24 h. Dox release profiles depended on MNP incorporation: GG(Dox) exhibited a burst release (~30% within 1 h), whereas GG(Dox-MNPs) enabled sustained release (~20% over 48 h). After 7 days of treatment, GG(Dox) reduced tumor viability to 11%, while GG(Dox-MNPs) achieved 27%. Overall, these hydrogels demonstrate strong chemo- and photothermal antitumor efficacy in a 3D osteosarcoma model, offering a versatile platform adaptable through controlled NIR irradiation and drug delivery.