A new stretchy
hydrogel can be embedded with various electronics. Here, a sheet of hydrogel
is bonded to a
matrix of polymer islands (red) that can encapsulate electronic components
such as
semiconductor chips, LED lights, and temperature sensors. Credit: Melanie
Gonick/MIT
(December 7, 2015) Water-based
“Band-Aid” senses temperature, lights up, and delivers medicine to the skin.
MIT engineers have designed what may be the Band-Aid of the
future: a sticky, stretchy, gel-like material that can incorporate temperature
sensors, LED lights, and other electronics, as well as tiny, drug-delivering
reservoirs and channels. The “smart wound dressing” releases medicine in
response to changes in skin temperature and can be designed to light up if,
say, medicine is running low.
A stretchable,
smart, hydrogel wound dressing includes temperature sensors and drug-delivery
channels and
reservoirs, embedded in a robust hydrogel matrix. Mock drugs can be released
at various locations
on demand, based on the measured temperatures.
Courtesy of the
researchers
When the dressing is applied to a highly flexible area, such
as the elbow or knee, it stretches with the body, keeping the embedded
electronics functional and intact.
The key to the design is a hydrogel matrix designed by
Xuanhe Zhao, the Robert N. Noyce Career Development Associate Professor in
MIT’s Department of Mechanical Engineering. The hydrogel, which Zhao detailed
earlier this month, is a rubbery material, mostly composed of water, designed
to bond strongly to surfaces such as gold, titanium, aluminum, silicon, glass,
and ceramic.
In a new paper published in the journal Advanced Materials,
the team reports embedding various electronics within the hydrogel, such as
conductive wires, semiconductor chips, LED lights, and temperature sensors.
Zhao says electronics coated in hydrogel may be used not just on the surface of
the skin but also inside the body, for example as implanted, biocompatible
glucose sensors, or even soft, compliant neural probes.
“Electronics are
usually hard and dry, but the human body is soft and wet. These two systems
have drastically
different properties,” says professor Xuanhe Zhao (pictured here).
Credit: Melanie
Gonick/MIT
“Electronics are usually hard and dry, but the human body is
soft and wet. These two systems have drastically different properties,” Zhao
says. “If you want to put electronics in close contact with the human body for
applications such as health care monitoring and drug delivery, it is highly
desirable to make the electronic devices soft and stretchable to fit the
environment of the human body. That’s the motivation for stretchable hydrogel
electronics.”
Zhao’s co-authors on the paper are graduate students
Shaoting Lin, Hyunwoo Yuk, German Alberto Parada, postdoc Teng Zhang, Hyunwoo
Koo from Samsung Display, and Cunjiang Yu from the University of Houston.
A strong and stretchy
bond
Typical synthetic hydrogels are brittle, barely stretchable,
and adhere weakly to other surfaces.
“They’re often used as degradable biomaterials at the
current stage,” Zhao says. “If you want to make an electronic device out of
hydrogels, you need to think of long-term stability of the hydrogels and
interfaces.”
To get around these challenges, his team came up with a
design strategy for robust hydrogels, mixing water with a small amount of selected
biopolymers to create soft, stretchy materials with a stiffness of 10 to 100
kilopascals — about the range of human soft tissues. The researchers also
devised a method to strongly bond the hydrogel to various nonporous surfaces.
In the new study, the researchers applied their techniques
to demonstrate several uses for the hydrogel, including encapsulating a
titanium wire to form a transparent, stretchable conductor. In experiments,
they stretched the encapsulated wire multiple times and found it maintained
constant electrical conductivity.
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