Sprayed antibacterial layer on titanium implants to eradicate biofilms by photoelectrons under near-infrared light

Infection induced by bacteria through biofilms can lead to implantation failure. Antibacterial implants against biofilms are being investigated, but the preparation conditions are sometimes challenging, especially when reactions occur on the implant surface. In this work, a pre-synthesized nanoparticle suspension is prepared that consists of rare earth compounds and Au nanoparticles (RE NPs/Au NPs), which are active under near-infrared light (NIR). The seed-assisted growth method allows intimate contact between Au NPs and RE NPs, which maximizes energy transfer from NIR by the upconversion effect. The suspension is deposited on titanium implants by a sonication-assisted spray that includes commercial SLA Ti and anodic Ti (with TiO₂ nanotubes on the surface) with controlled density of particles. The biofilm can be removed using the sprayed implants with NIR treatment both in vitro and in vivo through extracellular photoelectron therapy (PET) mechanism, and the implants exhibit high biocompatibility and physical stability for implantation. The antibacterial efficiency of anodic Ti implants surpasses that of SLA Ti, possibly due to the immobilization of RE NPs/Au NPs and improved charge transfer kinetics at the interface. Such a methodology could be applicable for a wide range of uses of biomaterial surfaces.