Nanostructured Selenium – A Novel Biologically-Inspired Material for Antibacterial Medical Device Applications - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 207

of the probiotics. In the in vivo studies, Kunming mice were allocated to
different groups supplemented with selenium-enriched and other probiot-
ics. After 28 days, the mice were inoculated with pathogenic Escherichia
coli so that we could compare mortality rates and inspect other indexes of
each treatment. It was found that the mortality of the group with selenium-
enriched probiotics was the lowest. Thus, selenium-enriched probiotics
can strongly antagonize pathogenic Escherichia coli in vitro and in vivo .
What is more, a synthesized organoselenium compound was shown
to be as effective as penicillin in inhibiting Pseudomonas aeruginosa and
Staphylococcus aureus growth in solution in vitro [65]. Specifi cally, organo-
selenium molecules (N-substituted benzisoselenazol-3(2H)-ones, ana-
logues of ebselen, whose name was unrevealed for proprietary reasons)
covalently bonded to silicone hydrogel contact lenses to transform the
lenses into antibacterial materials. The contact lenses were coated with the
organo-selenium molecules and tested against colonization of Pseudomonas
aeruginosa and Staphylococcus aureus . The results showed little or no bacte-
rial biofi lm formation on the coated lenses after 4 days of incubating the
lenses in bacteria solutions. In contrast, uncoated lenses showed exten-
sive bacterial biofi lm formation. The safety of the organo-selenium coated
lenses was also tested by placing them into the eyes of New Zealand albino
rabbits for up to 2 months. There was no sign of toxicity for the eyes wear-
ing the coated lenses as well as the eyes wearing uncoated lenses.

8.4.2 Selenium Nanoparticles Inhibit Staphylococcus Aureus

Growth

A previous study [66] tested the growth of Staphylococcus aureus in the pres-
ence of selenium nanoparticles. Selenium nanoparticles were synthesized
by the reduction of sodium selenite by glutathione and stabilized by bovine
serum albumin. Transmission electron microscopy (TEM) images of sele-
nium nanoparticles showed that the particles were spherical and approxi-
mately 40-60 nm in diameter (Figure 8.4). Further investigation of the size
distribution of the selenium nanoparticles by Dynamic light scattering (DLS)
revealed that most of the particles had hydrodynamic diameters around
100 nm. The sizes observed by DLS were larger than those determined by
TEM images because BSA molecules bound to the surface of the selenium
nanoparticles created a layer that made the particles appear larger [67, 68].
Nanoscale sizes of the synthesized selenium nanoparticles promoted a desir-
able large surface area important for increasing interactions with bacteria.
Importantly, the bacterial assays in this study clearly showed a slow,
inhibited growth profi le of Staphylococcus aureus in the presence of sele-
nium nanoparticles. Bacterial growth was inhibited approximately
20 times (compared with controls) after 3 hours, 50 times after 4 hours,
and 60 times after 5 hours (Figure 8.5). It was the fi rst time it was shown