Modified bacterial retention to toothbrush nylon with combined easy-release and photocatalytic surface treatments
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The published literature indicates that toothbrushes retain viable, pathogenic microorganisms on toothbrush bristles, even after 5 days under dry conditions. There is concern that such toothbrush contamination can contribute to health complications suffered by, for instance, immunocompromised patients. Bacteria and organic debris that attach to high-surface-energy nylon (polyamide) toothbrush bristles may be more easily released from octadecylsilane (ODS)-modified nylon expressing low-surface-energy methyl groups outermost. The contamination also may be photocatalytically oxidized by ultraviolet-A illumination in the presence of titanium dioxide (titania) [TiO 2 ] at nylon bristle surfaces. The possible benefits from these two surface-modification approaches were examined utilizing live/dead fluorescence microscopy assays of oral bacteria retained by solvent-cast thin films of toothbrush bristle nylon, as compared to films of either ODS or nylon+titania, with or without additional UV-A illumination, before and after exposure to standardized hydrodynamic shear forces. Biomaterial surface characterization was accomplished by multiple attenuated internal reflection infrared spectroscopy to confirm the chemical compositions of the cast films, and by comprehensive contact angle measurements for determinations of critical surface tensions and polar/dispersive surface energy components. Parallel plate flow cells were used to impart increasing shear stresses to the microbial layers on test surfaces, followed by inspections of the fractions of the initial biological contamination retained in each case. Correlations were sought among the data sets collected, and challenged by ANOVA techniques for evidence of whether the applied surface modifications diminished retained and/or viable microbial contamination. Statistically significant reductions of all retained organisms were found for ODS coatings exposed to 3-minute laminar, 20-inverse-second shear rate flows of Brain Heart Infusion (BHI)-suspensions at 10 6 late-logarithmic growth phase cells/ml of Streptococcus gordonii (Sg) or Fusobacterium nucleatum (Fn) through single-pass rectangular parallel-plate flow cells containing 2 plates each of 4 different test substrata (glass, nylon, nylon+ titania particles and ODS) subsequently rinsed with distilled water at shear rates of 20 and 100 inverse seconds and stained with SYTO ® 9 and Propidium Iodide fluorescent stains to reveal numbers and live/dead ratios of retained microorganisms. Simple drying did not cause loss of bacterial viability for Fn or Sg organisms, but UV-A illumination of bacteria-exposed nylon+titania coatings did cause a significant reduction of viable Fn while there was no statistically significant reduction in number of viable Sg. Further, the UV-A activated titania apparently degraded the attached BHI microbial biofilm matrix, allowing more mass removal at the higher rinse flow rate. The results of these in vitro studies suggest that combination of easy-release, low-energy ODS surface chemistry with presence of UV-A photocatalytic titania in a toothbrush-bristle-nylon matrix could provide benefits of safe self-disinfection for used toothbrushes retaining oral microbes.