MnO_x-armored magnesium implants for anti-osteosarcoma and biofilm eradication by charge-transfer interference

Frequent tumor recurrence and postoperative bacterial infections after osteosarcoma surgery have increased the demand for advanced bone implants. Although magnesium and its alloys are considered promising candidates for next-generation bone implants, their clinical application remains limited due to inadequate corrosion resistance. In this work, manganese oxide (MnO_x) nano-coatings with varying Mn³⁺/Mn²⁺ ratios were fabricated on the surface of ZE21C alloys via heat treatment, effectively enhancing corrosion resistance. The MnO_x nano-coatings consisted of multiple semiconductors with different Mn³⁺/Mn²⁺ ratios, and Mn₂O₃ with a narrower band gap became the dominant phase with heat treatment, resulting in a significant improvement in the photothermal conversion performance. In vivo and in vitro experiments demonstrated that samples with higher Mn³⁺/Mn²⁺ ratios disrupted redox homeostasis, inducing lipid peroxidation of biological membranes. Additionally, valence electrons in the semiconductors could be excited by NIR irradiation to generate photogenerated carriers, forming transmembrane electron-transfer channels with adhered tumor and bacterial cells, leading to structural membrane disruption and sustained antibacterial and tumor cell ablation. Furthermore, Mg alloys modified with MnO_x nano-coatings exhibited excellent biocompatibility and did not inhibit mitochondrial function of normal cells. This work provides a broader range of options and practical solutions for developing intelligent bone tissue-engineering materials for postoperative osteosarcoma.