A remove-remodel-repair strategy enabled by a spatiotemporally controlled hydrogel for integrative osteosarcoma therapy.

Postoperative management of osteosarcoma faces challenges such as tumor recurrence, bone defects, and infections due to the inability of conventional therapies to eradicate tumors and regenerate bone simultaneously. We developed a multifunctional hydrogel (CHGel) built on a curdlan (CUR) backbone that coloads Chlorella extract (CE) and hydroxyapatite (HAP). This platform couples a dual-stage therapeutic strategy to provide an integrated "remove-remodel-repair" (3R) paradigm for osteosarcoma. Stage I (weeks 0-2): Under ultrasound (US), CE in CHGel generates reactive oxygen species (ROS) via sonodynamic therapy (SDT) to remove tumors and bacteria, whereas HAP potentiates SDT by inducing mitochondrial Ca2+ overload (amplifying ROS) and lysosomal alkalinization (blocking autophagy and elevating MHC-I expression). These effects polarize macrophages toward the M1 phenotype, creating an anti-tumor and anti-infective immune niche. Stage II (weeks 2-6): With the US off, HAP establishes an alkaline microenvironment and releases Ca2+/PO43-, reprogramming macrophages to the M2 phenotype and remodeling the osteogenic niche. Combined with the mechanical support provided by the hydrogel, these actions collectively drive the final repair. These results demonstrated that CHGel + US removed 96.13% of the primary tumors (30.14% greater than did SDT with CE alone), removed more than 98.49% of the bacteria, and repaired the thickness of the trabecular bone and bone density by 2.8-fold and 1.8-fold, respectively. Moreover, CHGel mediated sequential programming of the M1 and M2 phenotypes of macrophages, reinforcing the 3R paradigm for osteosarcoma treatment. This multifunctional hydrogel links immediate tumor control with long-term bone recovery, offering a transformative approach for integrative osteosarcoma therapy.