Carbon dot/WS2 heterojunctions for NIR-II enhanced photothermal therapy of osteosarcoma and bone regeneration

•CD/WS2 was fabricated by assembling NIR-II-responsive CDs and WS2 nanosheets.•CD/WS2 exhibited high photothermal conversion efficiency of 56.3% at 1064 nm.•CD/WS2 exhibited excellent deep-tissue photothermal effect to ablate osteosarcoma.•Hyperthermia generated by CD/WS2 greatly enhanced bone regeneration. Osteosarcoma as an aggressive malignant neoplasm is commonly treated by surgical resection, chemotherapy, and radiotherapy, but surgery induces bone defects and chemo/radiotherapy causes severe systemic toxicity. We have designed a novel low-toxic bifunctional 0D/2D heterojunction (HJ) that can be used to generate effective photothermal effects in the second NIR window (NIR-II, 1000–1350 nm) for simultaneous osteosarcoma treatment and bone regeneration. To construct this 0D/2D nanostructure, biocompatible, positively charged NIR-II-responsive carbon dots (CDs) were synthesized by an ultrafast microwave-assisted hydrothermal method, followed by electrostatically driven assembly on both sides of negatively charged WS2 nanosheets. We found that the HJs exhibited enhanced NIR-II absorption and photothermal conversion efficiency. Due to the deep-tissue penetration ability of 1064 nm laser, complete osteosarcoma ablation was realized at a low power density even when being covered by a 10-mm-thick additional tissue. Furthermore, osteogenic differentiation was remarkably enhanced by mild photothermal effects of CD/WS2 HJs, which significantly up-regulated bone-related gene expressions, particularly, heat shock protein expression. Designed CD/WS2 HJs can be used in osteosarcoma treatment and bone-tissue engineering.