Near-infrared Light Triggered Titanium Dioxide Nanoparticles With Antibacterial Photodynamic Inactivation Against Periodontitis-related Pathogens

Background:Periodontitis is a common and frequently-occurring disease in human oral cavity characterized by loss of tooth-supporting structures,which eventually leads to tooth loss.According to the World Health Organization,10–15%of the global population suffers from severe periodontitis.Periodontitis has a great impact on the quality of life and general health of patients.At present,dental plaque biofilm formed by bacteria and their products are considered as the initial factors of periodontitis.Therefore,how to quickly and effectively inhibit plaque is the core issue in preventing the occurrence and progression of periodontitis.Periodontal basic treatment combined with drug treatment is a common method in clinical treatment of periodontitis.However,as the depth of the periodontal pocket increases,it becomes more difficult to remove subgingival plaque by mechanical debridement.Sustained drug treatment increases the drug resistance of bacteria from subgingival plaque,which makes treatment difficult.In recent years,antimicrobial photodynamic therapy?aPDT?has been gradually applied to the treatment of periodontitis.It has the advantages of easy operation,wide range and high efficiency,and can effectively inhibit the growth of plaque.Photosensitizers,light source and oxygen are the three elements of photodynamic therapy.However,the current commercial photosensitizers have problems with limited germicidal efficacy and gingival staining,and their excitation light source is mostly red light,which has limited penetrating power in tissues.Near-infrared light?NIR?has a greater depth of tissue penetration and less damage to the tissue.Therefore,it is of great clinical significance to explore a high-efficiency photosensitizer stimulated by near-infrared light to combat periodontitis pathogens.Objective:A near-infrared light-excited core-shell structured upconversion nanoparticle and titanium dioxide composite?UCNPs@TiO₂?was prepared,and its inhibitory effect on periodontitis-related pathogens was studied by aPDT.In addition,antibacterial properties of UCNPs@TiO₂ and commercial photosensitizer were compared.Methods:1.The core?-NaYF₄:Yb³⁺,Tm³⁺were synthesized via thermal decomposition and further modified with the TiO₂ shell via a hydrothermal method.2.The materials were characterized by transmission electron microscope?TEM?,Zeta potential,XRD ray diffraction,upconversion fluorescence spectrum,upconversion nanoparticle fluorescence lifetime,and ROS measurement in vitro.3.Dark-toxicity measurement in vitro was evaluated by CCK-8 method and cell staining method.4.The aPDT effect induced by UCNPs@TiO₂ under 980 nm NIR excitation was investigated.Three types of periodontitis-related bacteria:Streptococcus sanguinis?S.sanguinis?,Porphyromonas gingivalis?P.gingivalis?and Fusobacterium nucleatum?F.nucleatum?were investigated.The killing activity against planktonic bacteria was detected by a time-kill assay.Single species 4-day biofilms on dentin were tested by live/dead staining,colony-forming unit?CFU?counts,and metabolic activity.5.The bactericidal effects of commercial photosensitizer TBO and upconversion nanoparticles on periodontitis-related bacteria were compared.Results:1.The hexagonal shaped UCNPs@TiO₂ had an average diameter of 39.7 nm.UCNPs@TiO₂ nanoparticles had positively charged?+12.4 mV?surface and had strong luminous efficiency.2.UCNPs@TiO₂ nanoparticles had good biocompatibility.When the drug concentration was less than 2 mM,there was no obvious cytotoxicity.3.The time-kill curves results showed that the drugs in the dark groups had no bactericidal effect;the three suspension bacteria were killed within 12 hours in the Light+1 mM UCNPs@TiO₂ group;The three suspension bacteria were killed within 4 hours in the Light+2 mM UCNPs@TiO₂ group.4.Bacterial live/dead staining results showed that the bacteria in the UCNPs@TiO₂-aPDT groups were almost killed and showed red.The bacteria in the dark groups showed green.The commercial aPDT control group had a certain bactericidal effect in orange.5.Compared with the control group,the UCNPs@TiO₂-aPDT groups could significantly reduce the biofilm?p<0.05?.The UCNPs@TiO₂-aPDT groups reduced biofilm CFU by over 3 orders of magnitude,which was significantly higher than that of the dark groups and the commercial aPDT control group.6.The killing efficacy of the UCNPs@TiO₂-aPDT groups against the three species was ranked to be:S.sanguinis<F.nucleatum=P.gingivalis.Metabolic activities of biofilms were also greatly reduced via NIR-triggered aPDT?p<0.05?.Conclusions:This study synthesized core/shell-structured UCNPs@TiO₂ nanoparticles.UCNPs@TiO₂ possessed excellent biocompatibility with uniform size and positive charge on their surfaces.UCNPs@TiO₂ achieved strong inhibiting effects against all three species of periodontitis-related pathogens.This novel nanotechnology demonstrated a high promise to inhibit periodontitis.