Qi Wang swirls a solution of selenium nanoparticles in the laboratory. Coatings of the nanoparticles appear effective in fighting staph bacteria in medical device materials, according to a new study. Credit: Webster Lab/Brown University |
Selenium is an inexpensive element that naturally belongs in the body. It
is also known to combat bacteria. Still, it had not been tried as an antibiotic
coating on a medical device material. In a new study, Brown University
engineers report that when they used selenium nanoparticles to coat
polycarbonate, the material of catheters and endotracheal tubes, the results
were significant reductions in cultured populations of Staphylococcus aureus
bacteria, sometimes by as much as 90%.
“We want to keep the bacteria from generating a biofilm,” said Thomas
Webster, professor of engineering and orthopaedics, who studies how
nanotechnology can improve medical implants. He is the senior author of the paper,
published online in the Journal
of Biomedical Materials Research A.
Biofilms are notoriously tough colonies of bacteria to treat because they
are often able to resist antibiotic drugs.
“The longer we can delay or inhibit completely the formation of these
colonies, the more likely your immune system will clear them,” Webster said. “Putting selenium on there could buy more time to keep an endotracheal tube in
a patient.”
Meanwhile, Webster said, because selenium is actually a recommended
nutrient, it should be harmless in the body at the concentrations found in the
coatings. Also, it is much less expensive than silver, a less biocompatible
material that is the current state of the art for antibacterial medical device
coatings.
Webster has been investigating selenium nanoparticles for years, mostly for
their possible anticancer effects. As he began to look at their antibiotic
properties, he consulted with Hasbro Children’s Hospital pediatrician Keiko
Tarquinio, assistant professor of pediatrics, who has been eager to find ways
to reduce biofilms on implants.
Studying selenium
For this study, Webster and first author Qi Wang grew selenium nanoparticles of
two different size ranges and then used solutions of them to coat pieces of
polycarbonate using a quick, simple process. On some of the polycarbonate, they
then applied and ripped off tape not only to test the durability of the
coatings but also to see how a degraded concentration of selenium would perform
against bacteria.
On coated polycarbonate—both the originally coated and the tape-tested
pieces—Wang and Webster used electron and atomic force microscopes to measure
the concentration of nanoparticles and how much surface area of selenium was
exposed to interact with bacteria.
One of their findings was that after the tape test, smaller nanoparticles
adhered better to the polycarbonate than larger ones.
Then they were ready for the key step: experiments that exposed cultured
staph bacteria to polycarbonate pieces, some of which were left uncoated as
controls. Among the coated pieces, some had the larger nanoparticles, and some
had the smaller ones. Some from each of those groups had been degraded by the
tape, and others had not.
All four types of selenium coatings proved effective in reducing staph
populations after 24, 48, and 72 hours compared to the uncoated controls. The
most potent effects—reductions larger than 90% after 24 hours and as much as
85% after 72 hours—came from coatings of either particle size range that had
not been degraded by the tape. Among those coatings that had been subjected to
the tape test, the smaller nanoparticle coatings proved more effective.
Staph populations exposed to any of the coated polycarbonate pieces peaked
at the 48-hour timeframe, perhaps because that is when the bacteria could take
fullest advantage of the in
vitro culture medium. But levels always fell back dramatically by
72 hours.
The next step, Webster said, is to begin testing in animals. Such in vivo experiments, he
said, will test the selenium coatings in a context where the bacteria have more
available food but will also face an immune system response.
The results may ultimately have
commercial relevance. Former graduate students developed a business plan for
the selenium nanoparticle coatings while in school and have since licensed the
technology from Brown for their company, Axena Technologies.
Source: Brown University
