Stretchable hydrogel electronics

Stretchable hydrogel electronics

6:51 AM, 9th December 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.

CAMBRIDGE, US: 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.

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, associate professor in MIT’s department of mechanical engineering.

The hydrogel is a rubbery material, mostly composed of water, designed to bond strongly to surfaces such as gold, titanium, aluminium, silicon, glass, and ceramic.

This study is published in the journal Advanced Materials.

“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,” said Zhao.

“Electronics are usually hard and dry, but the human body is soft and wet. These two systems have drastically different properties,” he added. “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.”

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 said. “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.

In the new study, the researchers applied their techniques to demonstrate several uses for the hydrogel.

Zhao also created an array of LED lights embedded in a sheet of hydrogel. When attached to different regions of the body, the array continued working, even when stretched across highly deformable areas such as the knee and elbow.

A versatile matrix

Finally, the group embedded various electronic components within a sheet of hydrogel to create a “smart wound dressing,” comprising regularly spaced temperature sensors and tiny drug reservoirs. They placed the dressing over various regions of the body and found that even when highly stretched the dressing continued to monitor skin temperature and release drugs according to the sensor readings.

Yuk said an immediate application of the technology may be as a stretchable, on-demand treatment for burns or other skin conditions.

“It’s a versatile matrix,” Yuk said. “The unique capability here is, when a sensor senses something different, like an abnormal increase in temperature, the device can on demand release drugs to that specific location and select a specific drug from one of the reservoirs, which can diffuse in the hydrogel matrix for sustained release over time.”

Zhao said the hydrogel-sensor system his group is developing would likely be robust and effective over long periods. He said a similar case might be made for neural probes.

This research was funded, in part, by the Office of Naval Research, the MIT Institute for Soldier Nanotechnologies and the National Science Foundation.

© MIT News

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