Cuttlefish Ink-Derived Melanin Nanoparticles Enabling NIR-Responsive Electrospun Nanofibrous Mats for On-Demand Selective Antibacterial Disinfection of Orthodontic Braces

Fixed orthodontic appliances facilitate bacterial accumulation on brackets and wires, increasing the risk of enamel demineralization and periodontal inflammation. To address this challenge, near-infrared (NIR) responsive nanofibrous mats were developed for on-demand antibacterial disinfection of orthodontic brackets by incorporating cuttlefish ink-derived melanin nanoparticles (MNPs) into a poly(vinyl alcohol)/poly(ethylene oxide) (PVA/PEO) matrix. The incorporation of MNPs improved physicochemical properties, including enhanced thermal stability (∼77 °C increase in decomposition temperature), increased swelling capacity (∼2-fold compared with melanin-free fibers), and improved wettability. After thermal cross-linking, the fibrous network remained structurally stable in aqueous conditions with morphology preserved for up to 1 month and low melanin loss. Strong antioxidant performance was observed, reaching ∼60% 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging after 10 h. In vitro evaluation using L929 fibroblasts confirmed good cytocompatibility, supporting adhesion, viability, and proliferation. Under NIR irradiation at 808 nm (1.5 W/cm2, 10 min), efficient photothermal heating was achieved under wet conditions (∼55–60 °C) with stable performance across repeated cycles. Antibacterial efficacy was demonstrated, reducing Escherichia coli survival to 0.55% and disinfecting bacteria-contaminated bracket surfaces, while only minor inhibition of Lactobacillus acidophilus was detected. Overall, a biocompatible, marine-derived, and sustainable nanofibrous mat are presented for on-demand orthodontic disinfection.