Medical Design Briefs - March 2024 - 34

Squishy, Metal-Free Magnets to Power Robots and
Guide Medical Implants
The magnets are strong
enough to move soft
robots and medical
capsules, weak enough to
not ruin MRI images.
University of Michigan
Ann Arbor, MI
" Soft robots, " medical devices and implants,
and next-generation drug delivery
methods could soon be guided with
magnetism - thanks to a metal-free
magnetic gel developed by researchers
at the University of Michigan and the
Max Planck Institute for Intelligent Systems
in Stuttgart, Germany.
The material is the first in which
carbon- based, magnetic molecules are
chemically bonded to the molecular network
of a gel, creating a flexible, longlived
magnet for soft robotics. The study
describing the material was published in
the journal Matter.
Creating robots from flexible materials
allows them to contort in unique ways,
handle delicate objects and explore places
that other robots cannot. More rigid robots
would be crushed by the deep ocean's
pressure or could damage sensitive tissues
in the human body, for example.
" If you make robots soft, you need to
come up with new ways to give them power
and make them move so that they can
do work, " says Abdon Pena-Francesch, assistant
professor of materials science and
engineering affiliated with the Robotics
Institute at the University of Michigan
and a corresponding author of the study.
Today's prototypes typically move with
hydraulics or mechanical wires, which require
the robot to be tethered to a power
source or controller, also limiting where
they can go. Magnets could unleash these
robots, enabling them to be moved by magnetic
fields.
Conventional, metallic magnets introduce
their own complications, however.
They could reduce the flexibility of soft
robots and be too toxic for some medical
applications.
The new gel could be a nontoxic alternative
for medical operations, and further
modifications to the magnet's chemical
structure could help it degrade in the envi34
Pena-Francesch
holds the soft gel before it is treated
with chemicals that give the material its magnetic properties.
(Credit: Brenda Ahearn, Michigan Engineering)
Pena-Francesch holds the soft gel capsule after it
has been given its magnetic properties. Once the
tempo molecules in the material are activated, the
material turns orange. (Credit: Brenda Ahearn,
Michigan Engineering)
ronment and human body. Such biodegradable
magnets could be used in capsules
that are guided to targeted locations
of the body to release medicine.
" If these materials can safely degrade in
your body, you don't have to retrieve them
with another surgery later, " Pena- Francesch
says. " This is still pretty exploratory, but
these materials could enable newer, cheaper
medical operations some day. "
The team's gel consists solely of carbon-based
molecules. The key ingredient is
TEMPO, a molecule with a " free " electron
that is not paired up with another electron
inside an atomic bond. The spin of every
unpaired TEMPO electron in the gel aligns
under a magnetic field, which attracts the
gel to other magnetic materials.
Additional " cross-linking molecules " in
the gel act like a frame that connects the
TEMPO molecules to a solid network structure
while forming a protective cage
around the TEMPO electrons. That cage
prevents the unpaired electrons from
forming bonds, which would remove the
gel's magnetic properties.
" Earlier studies soaked these small,
magnetic molecules into a gel, but they
could leak out of the gel, " says Zane
Zhang, a doctoral student in materials
science and engineering and co-author
of the study. " By integrating the magnetic
molecules into the cross-linked gel
network, they are fixed inside. "
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Locking the TEMPO molecules inside
the material ensures that the gel does
not leak potentially harmful TEMPO
molecules into the body and allows the
material to retain its magnetic properties
for more than a year.
While weaker than metallic magnets, the
TEMPO magnets are strong enough to be
pulled and bent with another magnet.
Their weaker magnetism also has some upsides
- TEMPO magnets can be photographed
by an MRI, unlike stronger magnets
that can distort MRI images to the
point of uselessness.
" Medical devices using our magnets
could be used to deliver drugs to target locations
and measure tissue adhesion and
mechanics in the GI tract under MRI imaging, "
says Metin Sitti, former director of the
Physical Intelligence Department at Max
Planck Institute for Intelligent Systems and
a corresponding author of the study.
The research is funded by the American
Chemical Society Petroleum Research
Fund, Max Planck Society and the
European Research Council Advanced
Grant Soft-bodied Miniature Mobile Robots
program. The material was built in
the BioInspired Materials Laboratory
and characterized in the Michigan Center
for Materials Characterization.
Pena-Francesch is also an assistant professor
of chemical engineering and macromolecular
science and engineering.
This article was written by Derek Smith,
University of Michigan. For more information,
contact Abdon Pena-Francesch at
abdon@umich.edu or visit https://news.
umich.edu. A video of the technology is
available at https://www.youtube.com/
watch?v=NTAWzVN5pNg&t=1s.
Medical Design Briefs, March 2024
https://news.umich.edu https://news.umich.edu https://www.youtube.com/watch?v=NTAWzVN5pNg&t=1s https://www.youtube.com/watch?v=NTAWzVN5pNg&t=1s http://www.medicaldesignbriefs.com
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