The oral environment harbors both benign and malign bacteria, just like everywhere else in the body. The chances of developing dental cavities increase when one of these malicious bacteria called “Streptococcus mutans” (aka S. mutans) becomes dominant.
This situation occurs if the bacteria live in a highly-structured community where they can send out signals to one another and protect themselves from outside hazards. These communal cities are called “dental biofilm,” or more popularly known as “dental plaques.” If either the bacteria or the niche they are living in get disrupted, the plaque can be less problematic. It is also important to detect the biofilms at an early stage. If left untreated, more severe diseases such as bacterial pneumonia, diabetes mellitus, abnormal pregnancy outcomes, and atherosclerosis may arise.
A team of researchers at the University of Illinois at Urbana Champaign led by Prof. Pan, have worked on finding a “nano” solution to identify and fight the biofilms of S. mutans. Their strategy is based on using Hafnium Oxide nanoparticles, which are synthesized to be monodispersed less than 5 nm in size. These nanoparticles are developed from a sol-gel chemistry route where they are nucleated in the tiny water in oil emulsion. Their surface chemistry is further tuned to target S. mutans in the complex varieties of bacteria and then kill them by attacking the cell membrane of S. mutans. Because these particles are made of a “heavy element,” they can block X-ray efficiently and therefore would lighten up in the X-ray field (just as the bone does).
Intraoral X-ray is a mainstay device for many dental clinics. The team envisions that with the help of these radiopaque nanoparticles, the dentist may apply a suspension or paste of the Hafnium oxide nanoparticles for one minute and then image the teeth. The plaque can be detected in the X-ray image as bright regions. In the case of S. mutans plaque buildup, the patient can be prescribed the therapeutic variant of nanoparticles.
“The therapeutic nanoparticles work based on a “latch and kill” mechanism where the Hafnium oxide nanoparticles will attach to the S. mutans membrane and disrupt the bacterial cell wall; hence they lose cellular integrity” adds Fatemeh Ostadhossein, who is a Ph.D. candidate under the supervision of Professor Dipanjan Pan at the Bioengineering department. “We could observe this behavior of nanoparticles in our electron microscopy investigations in time frames as short as 20 minutes. Not only did we observe the damage to the bacteria in suspension, we also could verify the nanoparticles’ benefit in fighting the biofilm. We have tested these nanoparticles in the dental biofilm model of rats and indicated their efficiency when applied topically for only 8 days.”
Interestingly, they found that Hafnium oxide nanoparticles turned out to be safer than the clinically used chemical, chlorhexidine when tested in cells. Importantly, the method does not rely on using any drug and therefore is self-contained.
The team hopes to apply these nanoparticles in the future in conjunction with more advanced X-ray based technologies to diagnose systemic bacterial infection at the early stage in conditions such as gastrointestinal and periodontal diseases while treating them more effectively by targeting the contributing bacterial strain of interest.
These findings are described in the article entitled Dual purpose hafnium oxide nanoparticles offer imaging Streptococcus mutans dental biofilm and fight it In vivo via a drug-free approach, recently published in the journal Biomaterials. This work was conducted by Fatemeh Ostadhossein, Santosh K. Misra, Indu Tripathi, Valeriya Kravchuk, Gururaja Vulugundam, Denae LoBato, Laura E. Selmic, and Dipanjan Pan from the University of Illinois at Urbana-Champaign.