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University of Pennsylvania researchers develop microscopic robots for removing plaque

July 03, 2019

By Mary Beth Versaci

Philadelphia –– Microscopic robots could mean the end of scraping away plaque on dental patients.

A team of University of Pennsylvania researchers have developed robots made of iron oxide nanoparticles that they have shown can kill, degrade and remove biofilm under laboratory conditions.

"This is the first time that 'kill-degrade-remove' is achieved simultaneously for complete biofilm eradication," said Dr. Hyun (Michel) Koo of the school of dental medicine, one of the lead researchers. "It directly tackles all facets of biofilm resistance mechanisms, both the antimicrobial drug resistance and resistance to mechanical clearance of these sticky structures."
Nanoparticle robots 1
Cleaning crew: With a precise, controlled movement, microrobots clean biofilms on a glass surface, as shown in this time-lapse image. Photo courtesy of Geelsu Hwang and Edward Steager
The research was published in the April 24 issue of Science Robotics and led by Drs. Koo and Edward Steager of the school of engineering and applied science. It was funded in part by the National Institutes of Health’s National Institute of Dental and Craniofacial Research and the National Science Foundation.

Biofilms are made up of bacteria that are encapsulated in a protective, sticky matrix. They adhere firmly to surfaces such as teeth and implants, causing infections that are difficult to treat. Currently, plaque biofilm is treated chemically with antimicrobials, manually with dental instruments or conjointly with the two.

"Existing treatments are ineffective because they are incapable of simultaneously degrading the protective matrix, killing the embedded bacteria and physically removing the biodegraded products," Dr. Koo said. "These robots can do all three at once very effectively, leaving no trace of biofilm whatsoever."

Researchers developed two types of robotic systems. One system suspends iron oxide nanoparticles in a solution of hydrogen peroxide and enzymes. The nanoparticles activate the hydrogen peroxide to release free radicals that can kill microbes and break down matrix. Once that catalytic disruption of the biofilm is initiated, the nanoparticles are controlled by a magnetic field to precisely plow through and remove the biofilm debris without damaging nearby host tissues or disrupting the healthy microbiota, Dr. Koo said.
 
For the second, researchers embedded nanoparticles into a gel to form 3D robots molded into specialized shapes to remove biofilms from confined spaces.
Nanoparticle robots 2
Moving along: This time-lapse image shows a 3D-molded, helicoidal robot traveling inside a tooth canal. Photo courtesy of Alaa Babeer, Elizabeth E. Hunter and Hyun Koo
After the systems were tested on flat glass surfaces and enclosed glass tubes, researchers tested them on extracted human teeth. Researchers used automated magnetic fields to move the nanoparticle solution through the isthmus and 3D helicoidal robots through the tooth canal.

Although in vivo studies and clinical testing still need to be conducted, the researchers are excited about possible applications. The systems eventually could be used in dental prophylaxis, root canals and the cleaning of dental equipment, Dr. Koo said.