Engineers and biologists at Massachusetts Institute of Technology MIT have teamed up to design a new “living material” — a tough, stretchy, biocompatible sheet of hydrogel injected with live cells that are genetically programmed to light up in the presence of certain chemicals.
In a paper published this week in the Proceedings of the National Academy of Sciences, the researchers demonstrate the new material’s potential for sensing chemicals, both in the environment and in the human body. 
The team fabricated various wearable sensors from the cell-infused hydrogel, including a rubber glove with fingertips that glow after touching a chemically contaminated surface, and bandages that light up when pressed against chemicals on a person’s skin.
Xuanhe Zhao, the Robert N. Noyce Career Development associate professor of mechanical engineering at MIT, says the group’s living material design may be adapted to sense other chemicals and contaminants, for uses ranging from crime scene investigation and forensic science, to pollution monitoring and medical diagnostics.
“With this design, people can put different types of bacteria in these devices to indicate toxins in the environment, or disease on the skin,” says Timothy Lu, associate professor of biological engineering and of electrical engineering and computer science. “We’re demonstrating the potential for living materials and devices.”
The paper’s co-authors are graduate students Xinyue Liu, Tzu-Chieh Tang, Eleonore Tham, Hyunwoo Yuk, and Shaoting Lin.
“The challenge to making living materials is how to maintain those living cells, to make them viable and functional in the device,” Lu says. “They require humidity, nutrients, and some require oxygen. The second challenge is how to prevent them from escaping from the material.”
“The model helps us to design living devices more efficiently,” Zhao says. “It tells you things like the thickness of the hydrogel layer you should use, the distance between channels, how to pattern the channels, and how much bacteria to use.”
The group has also developed a theoretical model to help guide others in designing similar living materials and devices.
Ultimately, Zhao envisions products made from living materials, such as gloves and rubber soles lined with chemical-sensing hydrogel, or bandages, patches, and even clothing that may detect signs of infection or disease.
This research was supported, in part, by the Office of Naval Research, the National Science Foundation, and the National Institutes of Health.
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