Shapeshifting microrobots can brush and floss teeth
University of Pennsylvania
Image: Minjun Oh/Penn Dental Medicine
A
shapeshifting robotic microswarm may one day act as a toothbrush, rinse, and
dental floss in one. The technology, developed by a multidisciplinary team at
the University of Pennsylvania, is poised to offer a new and automated way to
perform the mundane but critical daily tasks of brushing and flossing. It's a
system that could be particularly valuable for those who lack the manual
dexterity to clean their teeth effectively themselves.
The
building blocks of these microrobots are iron oxide nanoparticles that have
both catalytic and magnetic activity. Using a magnetic field, researchers could
direct their motion and configuration to form either bristle-like structures
that sweep away dental plaque from the broad surfaces of teeth, or elongated
strings that can slip between teeth like a length of floss. In both instances,
a catalytic reaction drives the nanoparticles to produce antimicrobials that
kill harmful oral bacteria on site.
Experiments
using this system on mock and real human teeth showed that the robotic
assemblies can conform to a variety of shapes to nearly eliminate the sticky
biofilms that lead to cavities and gum disease. The Penn team shared their
findings establishing a proof-of-concept for the robotic system in the
journal ACS Nano.
"Routine oral care is cumbersome and can pose challenges for many people, especially those who have hard time cleaning their teeth" says Hyun (Michel) Koo, a professor in the Department of Orthodontics and divisions of Community Oral Health and Pediatric Dentistry in Penn's School of Dental Medicine and co-corresponding author on the study. "You have to brush your teeth, then floss your teeth, then rinse your mouth; it's a manual, multi-step process. The big innovation here is that the robotics system can do all three in a single, hands-free, automated way."
"Nanoparticles
can be shaped and controlled with magnetic fields in surprising ways,"
says Edward Steager, a senior research investigator in Penn's School of
Engineering and Applied Science and co-corresponding author. "We form
bristles that can extend, sweep, and even transfer back and forth across a
space, much like flossing. The way it works is similar to how a robotic arm
might reach out and clean a surface. The system can be programmed to do the
nanoparticle assembly and motion control automatically."
Disrupting
oral care technology
"The
design of the toothbrush has remained relatively unchanged for millennia,"
says Koo.
While
adding electric motors elevated the basic 'bristle-on-a-stick format', the
fundamental concept has remained the same. "It's a technology that has not
been disrupted in decades."
Several
years ago, Penn researchers within the Center for Innovation & Precision
Dentistry (CiPD), of which Koo is a co-director, took steps toward a major
disruption, using this microrobotics system.
Their innovation arose from a bit of serendipity. Research groups in both Penn Dental Medicine and Penn Engineering were interested in iron oxide nanoparticles but for very different reasons. Koo's group was intrigued by the catalytic activity of the nanoparticles.
They can activate hydrogen peroxide to release free
radicals that can kill tooth-decay-causing bacteria and degrade dental plaque
biofilms. Meanwhile Steager and engineering colleagues, including Dean Vijay
Kumar and Professor Kathleen Stebe, co-director of CiPD, were exploring these
nanoparticles as building blocks of magnetically controlled microrobots.
With
support from Penn Health Tech and the National Institutes of Health's National
Institute of Dental and Craniofacial Research, the Penn collaborators married
the two applications in the current work, constructing a platform to
electromagnetically control the microrobots, enabling them to adopt different
configurations and release antimicrobials on site to effectively treat and
clean teeth.
"It
doesn't matter if you have straight teeth or misaligned teeth, it will adapt to
different surfaces," says Koo. "The system can adjust to all the
nooks and crannies in the oral cavity."
The
researchers optimized the motions of the microrobots on a small slab of
tooth-like material. Next, they tested the microrobots' performance adjusting
to the complex topography of the tooth surface, interdental surfaces, and the
gumline, using 3D-printed tooth models based on scans of human teeth from the
dental clinic. Finally, they trialed the microrobots on real human teeth that
were mounted in such a way as to mimic the position of teeth in the oral
cavity.
On
these various surfaces, the researchers found that the microrobotics system
could effectively eliminate biofilms, clearing them of all detectable
pathogens. The iron oxide nanoparticles have been FDA approved for other uses,
and tests of the bristle formations on an animal model showed that they did not
harm the gum tissue.
Indeed,
the system is fully programmable; the team's roboticists and engineers used
variations in the magnetic field to precisely tune the motions of the
microrobots as well as control bristle stiffness and length. The researchers
found that the tips of the bristles could be made firm enough to remove
biofilms but soft enough to avoid damage to the gums.
The
customizable nature of the system, the researchers say, could make it gentle
enough for clinical use, but also personalized, able to adapt to the unique
topographies of a patient's oral cavity.
To
advance this technology to the clinic, the Penn team is continuing to optimize
the robots' motions and considering different means of delivering the
microrobots through mouth-fitting devices.
They're
eager to see their device help patients.
"We
have this technology that's as or more effective as brushing and flossing your
teeth but doesn't require manual dexterity," says Koo. "We'd love to
see this helping the geriatric population and people with disabilities. We
believe it will disrupt current modalities and majorly advance oral health
care."
Hyun
(Michel) Koo is a professor in the Department of Orthodontics and divisions of
Community Oral Health and Pediatric Dentistry in the School of Dental Medicine
and co-director of the Center for Innovation & Precision Dentistry at the
University of Pennsylvania.
Edward
Steager is a senior research investigator in Penn's School of Engineering and
Applied Science.
Koo
and Steager's coauthors on the paper are Penn Dental Medicine's Min Jun Oh,
Alaa Babeer, Yuan Liu, and Zhi Ren and Penn Engineering's Jingyu Wu, David A.
Issadore, Kathleen J. Stebe, and Daeyeon Lee.
This work was supported in part by the National Institute for Dental and Craniofacial Research (grants DE025848 and DE029985), Procter & Gamble, and the Postdoctoral Research Program of Sungkyunkwan University.
