Fighting Cavities With Nanoparticles

Silicon nanoparticles soaked with disinfectants can inhibit bacterial growth for up to three days and could be used to prevent oral biofilm formation.

AsianScientist (Feb. 18, 2015) – A team led by researchers from the Faculty of Dentistry of the University of Hong Kong (HKU) has applied nanotechnology to improve the effectiveness of a commonly used antiseptic against the growth of harmful bacteria found in the mouth.

In a study published in PLoS ONE, the researchers created a slow-release and long-lasting source of antiseptic by pre-soaking porous nanoparticles of silica in a solution of chlorhexidine in its pure chemical form. Chlorhexidine is the active ingredient in disinfectants widely used in medicine and dentistry.

In laboratory tests, the nanoparticles containing the pure chlorhexidine curbed the growth of several types of bacteria that are linked to dental infection, cavities, and gum disease. This antibacterial effect lasted for three days. By contrast, the antibacterial effect of mouth rinse containing a low concentration of chlorhexidine as a chemical compound lasts only six to ten hours.

Furthermore, the chlorhexidine-loaded nanoparticles not only killed free-floating, or planktonic, bacteria but also prevented bacteria from growing over a plastic surface to form an attached colony called a biofilm. Because bacteria can cause diseases in humans by forming biofilms, the authors conclude that their new nanoparticle product “may be developed as a novel and promising anti-biofilm agent for clinical use.”

The key to the product’s effectiveness is the way in which the silica nanoparticles quickly absorb but slowly release the chlorhexidine. This property relies on the small diameter of the nanoparticles, on average about 140 nm (1 nanometre, or nm, is a millionth of a millimetre), as well as the presence of many narrow, hollow channels called mesopores, each with a width of about 2.5 nm.

After overnight immersion in a solution of pure chlorhexidine dissolved in an alcohol (ethanol), the porous nanoparticles took up more than a fifth (21.8 percent) of their own weight in chlorhexidine.

Relatively low concentrations of the chlorhexidine-loaded nanoparticles were able to stop the visible growth of bacteria in one day, when added to each of five liquid samples of harmful oral bacteria in free-floating form (minimum inhibitory concentration of 50-100 μg/mL against Streptococcus mutans, Streptococcus sobrinus, Fusobacterium nucleatum, Aggregatibacter actinomycetemcomitans, and Enterococcus faecalis).

In addition, low concentrations (100-200 μg/mL) inhibited visible growth in one day when added to the five different bacteria as preformed single-species biofilms living on a plastic surface. By contrast, empty nanoparticles had no antibacterial effect.

In a further experiment, the researchers added chlorhexidine-loaded nanoparticles to three different combinations of bacteria—all including Porphyromonas gingivalis, an important bacterial species underlying gum disease—and then allowed them to grow on a plastic surface to form so-called mixed biofilms. Low concentrations of the nanoparticles (12.5 – 100 μg/mL) prevented the development of mixed biofilms for up to three days.

The team concludes that their “proof of concept” study shows that their new product has “potent antibacterial effects.” Noting that the type of silica in the nanoparticles is approved in the US for use in implants, the team comments that depending on more studies, the chlorhexidine-loaded nanoparticles could be developed for use against oral biofilms in humans.

The article can be found at: Seneviratne et al. (2014) Nanoparticle-Encapsulated Chlorhexidine against Oral Bacterial Biofilms.

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Source: The University of Hong Kong.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

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