The concept of a toothbrush -- essentially bristles on a stick -- hasn't changed much as a technology since the Babylonians and ancient Egyptians walked the earth more than 5,000 years ago. Now, scientists at the University of Pennsylvania aim to transform tooth cleaning with a swarm of microscopic "robots" that can do the job of a toothbrush, dental floss, and oral rinse all in one.
A new study published in the journal ACS Nano and supported by the U.S. National Institute of Dental and Craniofacial Research (NIDCR) demonstrates the feasibility of the robotic system, which could one day be adapted for use in humans.
"We want to improve oral health for people with disabilities and geriatric populations who don't have the manual dexterity to perform routine oral care," says dentist-scientist and senior author Dr. Hyun (Michel) Koo, PhD. "It's an unmet need in oral health care, and it's time to disrupt the technology."
The robots are actually nanosized iron oxide particles, each roughly 100 times smaller than a grain of pollen. In the presence of a magnet, the nanoparticles cluster into a series of strands -- aka bristles -- that align along the direction of the magnetic field. By making finely tuned adjustments to the field, the researchers could precisely direct the bristles' movements, adjust their stiffness, and shorten or lengthen them.
"One of the great things about working with magnetic fields is that they penetrate tissues and are harmless at the level we use them, meaning the system can reach difficult-to-access spaces," says microrobotics engineer and co-senior author Edward Steager, PhD.
The researchers tested the robots' scrubbing powers on several surfaces, including a 3D-printed model of human front teeth, real human front teeth mounted on artificial gums, and a section of a pig jaw containing gums and teeth.
As the video above shows, these robotic structures can be automated to shape-shift from bristlelike extensions to flosslike strings that conform to tooth surfaces and scrub the nooks and crannies between teeth. A separate experiment showed that they are soft enough to leave pig gums undamaged, but strong enough to break up biofilms, also known as plaque.
When it comes to busting biofilms, these robotic nanoparticles have another trick up their sleeves. They have a natural ability to trigger chemical reactions that release microbe-killing molecules, essentially creating an antimicrobial rinse onsite. In the experiments, this allowed the tiny robotic armies to both break apart biofilms and kill the bacteria within, leaving behind no detectable live pathogens.
Left: Biofilms grown on human teeth and stained pink for visibility. Right: Teeth scrubbed almost entirely clean by the microbots. Image courtesy of Minjun Oh.The robots could also sweep up and collect dead-pathogen-containing debris. According to the scientists, the microbial contents of this material can be analyzed to detect pathogens and other disease indicators, which one day could prove useful for predicting and diagnosing disease in the oral cavity and elsewhere in the body.
But before dispatching a platoon of tiny robots into our mouths, the researchers say clinical trials are needed. To optimize the robotic system and make it affordable for everyday use, the team plans to design prototypes that fit inside the mouth. They envision a programmable, fully automated system that can adapt to the unique features of a person's oral cavity, enabling personalized oral care.
The group is exploring other applications as well. In a proof-of-concept study recently published in the Journal of Dental Research, the researchers showed that microrobots can be magnetically guided through the root canal to remove biofilms and potentially carry and deliver drugs. Beyond dentistry, the scientists see a role for the technology in cleaning inside biofilm-contaminated catheters, surgical implants, and even water pipes.
"When you see this kind of result that opens a whole new area and applications, it's as exciting as it gets in research," says Steager.
Reprinted from the U.S. National Institutes of Health's National Institute of Dental and Craniofacial Research.
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