Near-infrared laser-activated PLGA-PDA core-shell nanohybrids for synergistic photothermal antibacterial therapy and sustained ion release in orthodontic white spot lesions prevention.

Objective: To develop near-infrared (NIR) laser-activated PLGA-PDA core-shell nanohybrids encapsulating Ag/CuO nanoparticles for simultaneous photothermal antibacterial therapy and sustained Ag/Cu release, and to evaluate their bactericidal efficacy against Streptococcus mutans and preventive potential in orthodontic white spot lesions.

Methods: Ag/CuO nanoparticles were encapsulated in PLGA/PDA nanospheres via a double-emulsion and self-polymerization approach. The resulting core-shell particles were fully characterized for composition, size distribution, zeta potential, morphology, photothermal performance, release kinetics, and cytocompatibility. Finally, we assessed their bactericidal efficacy under NIR laser irradiation against Streptococcus mutans and evaluated their potential to prevent orthodontic white-spot lesions.

Results: Synthesized Ag/CuONPs@PLGA/PDA nanoparticles exhibit uniform nanoscale distribution and stable zeta potential. Upon 0.5 W 980-nm NIR irradiation, the photoresponsive polydopamine coating rapidly converts light to thermal energy, enabling sustained antibacterial drug release for 16 days. This confers potent bactericidal activity against Streptococcus mutans, effectively preventing orthodontic white spot lesions. Crucially, in vivo analysis demonstrates near-absent IL-6 expression with polarized VEGF/TGF-β upregulation, enhancing anti-inflammatory responses while promoting angiogenesis and tissue regeneration. Histopathological examination of major organs reveals no significant inflammation, confirming systemic biocompatibility.

Conclusion: Triggered by brief near-infrared irradiation (0.5 W), Ag/CuONPs@PLGA/PDA sustained-release microspheres enable controlled drug release that effectively suppresses both Streptococcus mutans planktonic cells and dental plaque biofilm formation, thereby preventing orthodontic white spot lesions. Furthermore, these microspheres significantly attenuate wound-site inflammation, accelerate tissue regeneration, and demonstrate excellent biocompatibility.

Clinical Significance: The Ag/CuONPs@PLGA/PDA core-shell nanohybrids reported here can be readily formulated into antimicrobial coatings for orthodontic adhesives or clear aligner surfaces. Upon occasional NIR activation, they deliver a localized photothermal "burst" together with sustained Ag⁺/Cu²⁺ release, achieving potent, on-demand eradication of Streptococcus mutans while preserving surrounding tissues. By integrating this dual-mode defense into routine appliances, clinicians may substantially reduce the incidence of white spot lesions without compromising bonding strength or biocompatibility, ultimately improving treatment outcomes and patient satisfaction.