Implanted devices made from flexible transistors can wrap around
28 May 2014
Electronic devices that become soft when implanted inside the
body can reshape to grip body parts, such as large tissues, nerves
and blood vessels.
These biologically adaptive, flexible transistors might one day
help doctors learn more about what is happening inside the body, and
stimulate the body for treatments.
The research, by the University of Texas at Dallas and the
University of Tokyo is published online and in an upcoming print
issue of Advanced Materials.
It is one of the first demonstrations of transistors that can
change shape and maintain their electronic properties after they are
implanted in the body, said Jonathan Reeder, a graduate student in
materials science and engineering and lead author of the work.
“Scientists and physicians have been trying to put electronics in
the body for a while now, but one of the problems is that the
stiffness of common electronics is not compatible with biological
tissue,” he said. “You need the device to be stiff at room
temperature so the surgeon can implant the device, but soft and
flexible enough to wrap around 3-D objects so the body can behave
exactly as it would without the device. By putting electronics on
shape-changing and softening polymers, we can do just that.”
Shape memory polymers developed by Dr Walter Voit, assistant
professor of materials science and engineering and mechanical
engineering and an author of the paper, are key to enabling the
The polymers respond to the body’s environment and become less
rigid when they’re implanted. In addition to the polymers, the
electronic devices are built with layers that include thin, flexible
electronic foils first characterized by a group including Reeder in
work published last year in Nature.
The Voit and Reeder team from the Advanced Polymer Research Lab
in the Erik Jonsson School of Engineering and Computer Science
fabricated the devices with an organic semiconductor but used
adapted techniques normally applied to create silicon electronics
that could reduce the cost of the devices.
“We used a new technique in our field to essentially laminate and
cure the shape memory polymers on top of the transistors,” said Voit,
who is also a member of the Texas Biomedical Device Center. “In our
device design, we are getting closer to the size and stiffness of
precision biologic structures, but have a long way to go to match
nature’s amazing complexity, function and organization.”
The rigid devices become soft when heated. Outside the body, the
device is primed for the position it will take inside the body.
During testing, researchers used heat to deploy the device around
a cylinder as small as 2.25mm in diameter, and implanted the device
in rats. They found that after implantation, the device had morphed
with the living tissue while maintaining excellent electronic
“Flexible electronics today are deposited on plastic that stays
the same shape and stiffness the whole time,” Reeder said. “Our
research comes from a different angle and demonstrates that we can
engineer a device to change shape in a more biologically compatible
The next step of the research is to shrink the devices so they
can wrap around smaller objects and add more sensory components,