Army of micro-robots can wipe out dental plaque

Scientists have developed microscopic robots that can non-invasively clean up dental plaques.

With two types of robotic systems -- one designed to work on surfaces and the other to operate inside confined spaces -- the scientists showed that robots with catalytic activity could ably destroy biofilms, sticky amalgamations of bacteria enmeshed in a protective scaffolding.

Such robotic biofilm-removal systems could be valuable in a wide range of potential applications, from keeping water pipes and catheters clean to reducing the risk of tooth decay, dental infections, and implant contamination.

"We're leveraging the expertise of microbiologists and clinician-scientists as well as engineers to design the best microbial eradication system possible," said Hyun Koo, from University of Pennsylvania in the US.

"This is important to other biomedical fields facing drug-resistant biofilms as we approach a post-antibiotic era," said Koo, who led the study published in the journal Science Robotics.

"Treating biofilms that occur on teeth requires a great deal of manual labor, both on the part of the consumer and the professional," said Edward Steager, from University of Pennsylvania.

"We hope to improve treatment options as well as reduce the difficulty of care," Steager said in a statement.

Biofilms can arise on biological surfaces, such as on a tooth or in a joint or on objects, like water pipes, implants, or catheters.

Wherever biofilms form, they are notoriously difficult to remove, as the sticky matrix that holds the bacteria provides protection from antimicrobial agents.

In previous work, researchers made headway at breaking down the biofilm matrix by employing iron-oxide-containing nanoparticles that work catalytically, activating hydrogen peroxide to release free radicals that can kill bacteria and destroy biofilms in a targeted fashion.

Iron-oxide nanoparticles were used as building blocks for microrobots. The engineers control the movement of these robots using a magnetic field, allowing a tether-free way to steer them.

The team designed, optimised, and tested two types of robotic systems, which the group calls catalytic antimicrobial robots (CARs) capable of degrading and removing biofilms.

The first involves suspending iron-oxide nanoparticles in a solution, which can then be directed by magnets to remove biofilms on a surface in a plow-like manner.

The second platform entails embedding the nanoparticles into gel molds in three-dimensional shapes. These were used to target and destroy biofilms clogging enclosed tubes.

Both types of CARs effectively killed bacteria, broke down the matrix that surrounds them, and removed the debris with high precision.

After testing the robots on biofilms growing on either a flat glass surface or enclosed glass tubes, the researchers tried removing biofilm from hard-to-reach parts of a human tooth.

The CARs were able to degrade and remove bacterial biofilms not just from a tooth surface but from one of the most difficult-to-access parts of a tooth, the isthmus, a narrow corridor between root canals where biofilms commonly grow.

"Existing treatments for biofilms are ineffective because they are incapabale of simultaneously degrading the protective matrix, killing the embedded bacteria, and physically removing the biodegraded products," says Koo. "These robots can do all three at once very effectively, leaving no trace of biofilm whatsoever."
"We think about robots as automated systems that take actions based on actively gathered information," says Steager. In this case, he says, "the motion of the robot can be informed by images of the biofilm gathered from microcameras or other modes of medical imaging."