Engineers at the Massachusetts Institute of Technology (MIT) have designed a "smart” wound dressing that releases medicine in response to changes in skin temperature. It can be designed to light up if medicine runs low.

The sticky, stretchy, gel-like material can incorporate temperature sensors, LED lights and other electronics, as well as drug-delivering reservoirs and channels. When the dressing is applied to a flexible area such as an elbow or knee it stretches with the body, keeping the embedded electronics functional and intact.

The stretchy hydrogel can be embedded with various electronics. Image credit: Melanie Gonick/MIT.The stretchy hydrogel can be embedded with various electronics. Image credit: Melanie Gonick/MIT.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. It is designed to bond strongly to surfaces such as gold, titanium, aluminum, silicon, glass and ceramic.

"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," Zhao says. Typical synthetic hydrogels may be brittle, barely stretchable and adhere weakly to other surfaces.

To overcome these limitations, the team came up with a strategy to create robust hydrogels by mixing water with a small amount of selected biopolymers. This created soft, stretchy materials with a stiffness of 10 to 100 kilopascals, about the range of human soft tissues. They also devised a method to bond the hydrogel to various nonporous surfaces.

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 that it maintained constant electrical conductivity.

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 deformable areas such as the knee and elbow.

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. The researchers also created pathways for drugs to flow through the hydrogel, either by inserting patterned tubes or drilling holes through the matrix. They placed the dressing over various parts 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.

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

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