New material illuminates when exposed to chemicals on the body

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Researchers have found that the hydrogel’s mostly watery environment helps keep nutrients and programmed bacteria alive and active. When the bacteria reacts to a certain chemical, the bacteria are programmed to light up, as seen on the left. [Photo courtesy of the researchers]

MIT engineers and biologists teamed up and designed a living-cell-injected hydrogel that can illuminate when exposed to certain chemicals.

The MIT team made wearable sensors using the hydrogel with living cells that lit up after touching a surface with certain chemicals. The new material has the potential to detect chemicals in the environment and the human body.

“With this design, people can put different types of bacteria in these devices to indicate toxins in the environment, or disease on the skin,” said Timothy Lu, associate professor of biological engineering and electrical engineering and computer science, in an MIT news release. “We’re demonstrating the potential for living materials and devices.”

Lu specializes in reprogramming the biological parts of living cells to do what he wants them to do, like performing certain tasks like sensing and signaling the presence of viruses and toxins.

Xuanhe Zhao and his team of engineers at MIT have spent the past 5 years creating a combination of polymers and water to make the stretchable, biocompatible hydrogels. It contains 95% water and is able to support living cells. Zhao also recently created a robot with the hydrogels that could be used in surgical applications.

Lu and Xuanhe combined their expertise and infused Lu’s genetically programmed bacteria into Zhao’s hydrogel material. Using 3D printing, they made small channels in the first layer of the hydrogels. Then they merged the hydrogel to a layer of elastomer that could let in oxygen. The reprogrammed E. coli cells were programmed to detect the natural compound DAPG and were injected into the channels. The hydrogel material was submerged in nutrients that infused through the hydrogels and kept the bacteria alive for several days. Each channel lit up when exposed to the chemical compounds.

The team also created a bandage that had the same type of channels with bacteria that was sensitive to the naturally occurring sugar rhamnose. They swabbed a volunteer’s wrist with rhamnose and put the hydrogel bandage on the area. The bandage lit up in response to the rhamnose.

They also created a hydrogel glove with swirling channels on the fingertips that also glowed when exposed to certain chemicals.

The researchers have also supplied a theoretical model to guide other researchers who might be interested in designing living materials and devices.

“The model helps us to design living devices more efficiently,” Zhao said. “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 research was supported by the Office of Naval Research, the National Science Foundation and the National Institutes of Health and was published online in the Proceedings of the National Academy of Sciences of the United States of America.

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