Water-based “Band-Aid” that can sense temperature by lighting up and potentially could deliver medicine to the skin has been designed my MIT engineers. According to researchers, Xuanhe Zhao, the Robert N. Noyce Career Development Associate Professor in MIT’s Department of Mechanical Engineering the gel-like material can incorporate temperature sensors, LED lights, and other electronics, as well as tiny, drug-delivering reservoirs and channels. They illustrated how the “smart wound dressing” will release medicine in response to changes in skin temperature and can be designed to light up if, for instance the medicine is running low.
In a research funded, in part, by the Office of Naval Research, the MIT Institute for Soldier Nanotechnologies, and the National Science Foundation, the hydrogel, described by Zhao is a rubbery material, mostly composed of water, designed to bond strongly to surfaces such as gold, titanium, aluminum, silicon, glass, and ceramic. 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.
In a new paper published in the journal Advanced Materials, the researchers report 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,” 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.
“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.
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. Yuk says an immediate application of the technology may be as a stretchable, on-demand treatment for burns or other skin conditions.
“It’s a very versatile matrix,” Yuk says. “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. Delving deeper, Zhao envisions hydrogel to be an ideal, biocompatible vehicle for delivering electronics inside the body. He is currently exploring hydrogel’s potential as a carrier for glucose sensors as well as neural probes. Conventional glucose sensors, implanted in the body, typically spark a foreign-body response from the immune system, which covers the sensors with dense fibers, requiring the sensors to be replaced often. While various hydrogels have been used to coat glucose sensors and prevent such a reaction, the hydrogels are brittle and can detach easily with motion. Zhao says the hydrogel-sensor system his group is developing would likely be robust and effective over long periods. He says a similar case might be made for neural probes.
“The brain is a bowl of Jell-O,” Zhao says. “Currently, researchers are trying different soft materials to achieve long-term biocompatibility of neural devices. With collaborators, we are proposing to use robust hydrogel as an ideal material for neural devices, because the hydrogel can be designed to possess similar mechanical and physiological properties as the brain.”
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