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

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.