December 7, 2015

Stretchable hydrogel electronics

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.

read entire press  release >>