Construction of a dual-drug delivery system based on oxidized alginate and carboxymethyl chitosan for chemo-photothermal synergistic therapy of osteosarcoma

•A smart dual-responsive DDDS based on the hydrogel of OxAlg and CMCS is developed.•The DDDS can be used for co-delivery of MTX and Nar for treatment of osteosarcoma.•The –N=C– bond between OxAlg and CMCS is prone to be hydrolyzed in an acidic medium.•GO in this DDDS is an outstanding photothermal agent.•The therapeutic efficacy is improved via the chemo-photothermal synergistic mode.