Synthesis of LiYbF ₄ : Tm-Based Core–Shell Upconversion Nanoparticles for Biofilm Eradication on Titanium Implants via Dominated Photoelectron Therapy

Bacterial biofilm-induced inflammation can corrode implant surfaces and is the main reason for implantation failures. Considering that conventional mechanical treatments show limited efficacy, prolonged antibiotic therapy carries certain risks as well. Here, we developed NIR-active antibacterial Ti implant surfaces. LiYbF 4 -based core–shell upconversion nanoparticles (UCNPs) were synthesized with controlled core size (∼10 nm) and shell thickness (∼2 nm). These UCNPs were homogeneously coated onto sandblasted and acid-etched titanium (SLA Ti) implants by ultrasonic spraying following the prior deposition of a conformal polydopamine (PDA) coating. Upon NIR excitation (λ = 980 nm), the UCNPs generate upconverted ultraviolet (UV) light, which can be absorbed by PDA and natural TiO 2 layers on Ti implants. The PDA layer not only mediates localized energy transfer but also enhances light absorption through the aromatic structures. Both in vitro and in vivo experiments demonstrated excellent biofilm eradication rate (98.9% in vitro and 99.99% in vivo ) and potentially high biocompatibility. This approach combines the high efficiency of LiYbF 4 core–shell UCNPs with PDA, providing antibacterial functionality based on photoelectron therapy on Ti implants. The deep-tissue penetration of NIR light and the localized UV generation minimize off-target effects, making this system a promising and clinically translatable strategy for infection-resistant implants.