Impact of Superparamagnetic Iron-Oxide Nanoparticles and Magnetic Fields on Mixed-Species Oral Biofilm

Impact of Superparamagnetic Iron-oxide Nanoparticles and Magnetic Fields on Oral Biofilm

Jane Nguyen

University of New Mexico, Albuquerque, New Mexico

Data from the Center of Disease Control states that approximately 80% of the adult population in America are victims of periodontitis, an irreversible gingival disease that stems from the onset of gingivitis. The most common cause of gingivitis is poor oral hygiene which produces plaque and bacteria propagation in the human mouth through the establishment of primary and secondary colonizing bacteria. Without the proper oral care, plaque will harden under the gum line to produce tartar which serves as a protective shield for the bacteria and induces irritation along the gums. The continual gum agitation and growth of bacteria results in gingivitis. Therefore, it is imperative to prevent the aggregation of primary and secondary colonizers on the teeth and gingiva. Many attempts have been made to incorporate metal-oxide nanoparticles into dental care due to their promising bactericidal abilities, but a limitation is found in the need to develop non-toxic nanoparticles that still display high levels of antimicrobial potency.

To address this issue, saliva containing mixed bacterial species was collected from adult individuals and propagated to form biofilm. The biofilm was separated to form two samples. The control samples contained the biofilm in phosphate-buffered saline (PBS). The experimental samples subjected the biofilm to a two-fold concentration gradient of FDA-approved superparamagnetic iron-oxide nanoparticles suspended in PBS. The control and experimental samples were exposed to two different magnetic field treatments, static and alternating, induced by molybdenum magnets. A static magnetic field treatment induced magnetic fields with a strength of 4.44 kGs from the bottom of the samples for 6 hours. The alternating field treatment exposed the samples to two magnets. A magnet with a field strength of 4.44 kGs was placed below the samples and a magnet with a field strength of 0.12 kGs was placed above. Both magnets were alternated for 30 minutes over a total span of 6 hours. Analysis utilizing an XTT reduction assay indicated that both static and alternating magnetic field treatments significantly suppressed biofilm metabolic activity. Fluorescent confocal laser scanning microscopy was used to analyze the bacterial viability. Results displayed that the static magnetic treatment was more effective in disrupting the biofilm than the alternating treatment. This difference was more prominent when the treatments were used with nanoparticles. SPSS software was used to conduct a Mann-Whitney U-test to compare differences between the control and the experimental samples. The test yielded a p-value of less than 0.05, which concludes that the nanoparticles did disrupt the bacterial biofilm significantly. Overall, the nanoparticles were proven to effectively disrupt the biofilm, but their ability to kill any bacteria was minimal.

Future studies will apply the nanoparticles to an antimicrobial mouth rinse to penetrate the oral biofilm and increase the potency of the mouth rinse on oral bacteria. Two strains of bacteria will be used to simulate the formation of oral biofilm: Streptococcus gordonii, a primary colonizer, and Fusobacterium nucleatum, a secondary colonizer. The biofilm samples will be subject to a two-fold concentration gradient of iron oxide nanoparticles and a time-dependent matrix study will be conducted to observe the nanoparticles’ effect on the oral bacteria after sixty seconds with ten seconds increments. The predominance of poor oral hygiene and the biomedical limitations of nanoparticles have led to the need for a potent substance that is safe enough to be used in household dental care products. Iron-oxide nanoparticles have been used in a wide variety of in vivo biomedical applications such as MRI contrasting, therefore they are a promising candidate to use in conjunction with an antimicrobial mouth rinse to prevent gingivitis thus reduce the magnitude of the population suffering from periodontitis.