The dressing uses 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. 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 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 paper published in the journal Advanced Materials, the research team reported embedding various electronics within the hydrogel, such as conductive wires, semiconductor chips, LED lights, and temperature sensors. The 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 Zhao. "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 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 meet the challenges, the research team devised 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.