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A nut used in herbal tea has become a hydrogel perfect for a variety of biomedical uses in new research from the University of Chicago Pritzker School of Engineering (UChicago PME) and UChicago Chemistry Department.

In a study, "Sustainable Conversion of Husk into Viscoelastic Hydrogels for Value-Added Biomedical Applications," in Matter, researchers created a malva nut hydrogel for medical uses ranging from wound care to ECG readings. The research doesn't rely on the rumored health benefits of the nuts—in China, they're known as the sore throat remedy Pangdahai (PDH)—but for their ability to swell in water.

"You never saw the fruit from a tree expand in that kind of volume," said first author Changxu Sun, a UChicago PME Ph.D. student.

Where others saw gooey tea residue, Sun saw possibility.

"It is a remarkable discovery from a remarkable student," said Sun's principal investigator, University of Chicago Chemistry Prof. Bozhi Tian. "Changxu looked at herbal tea and saw a world of sustainable biomedical applications ready to be built."

From tea...

In traditional Chinese medicine, malva nuts are known as Pangdahai, often used in tea as a sore throat remedy, similar to adding ginger or lemon. A sniffling person pops the small, dried nut in hot water and watches the magic unfold.

"Originally, it's an oval shape one centimeter in width. Once you soak it in the water, it will expand about eight times in volume and 20 times by weight, turning into a gelatinous mass, like a jelly," Sun said. "After you drink the beverage, you're left with the jelly as a waste. People usually throw that out."

For comparison, rice swells by about three times by weight when cooked. Chia seeds swell to 10 times their weight when added to water; the snow fungus used in many Asian soups has a similar rate.

But the malva nuts' 20-fold increase leaves them all behind. Sun and Tian saw potential in the gelatinous food waste thrown out with yesterday's tea.

"We said, 'Okay, that's a natural hydrogel,'" Sun said.

... to hydrogel

Hydrogels are gooey water-based substances noted for their many applications in health care. As soft and water-loving as human tissue itself, hydrogels are used in wound care, fighting infection and spurring healing beyond what a bandage can do. They're used in drug delivery systems, implantable bioelectronics like pacemakers, tissue repair, ECG and EKG readings, and other uses.

Turning nuts into medical devices takes more work than just popping them in tea.

First, the nuts are crushed in a blender and then run through a centrifuge to extract as much of the soft, expanding polysaccharide hydrocolloid as possible while getting rid of the hard structural lignins that give nuts their shells.

They then freeze-dry the hydrocolloid solution, removing all the water to create a dry scaffolding of pure malva nut polysaccharide. Picture a dried-out kitchen sponge popping back into shape under the kitchen tap.

"If we hydrate those scaffolds again, that becomes a gel," Sun said.

The team began testing their malva nut hydrogel in a variety of medical uses, from wound care to biomonitoring.

"We found it demonstrated superior performance and qualities compared to commercial ECG patches. And then we also applied to the tissue surface in vivo, demonstrating great recording of biosignals," Sun said. "We wanted to show people should shift their attention to the unexplored properties and unexplored resources of natural plants."

Sun hopes the new, naturally derived hydrogel will provide a new source of powerful but less-expensive medical resources across the globe, but particularly in the Southeast Asian nations where the malva tree grows.

"They're low-income countries. Their health care systems are always limited by this lack of resources," Sun said. "Here we have a local, native material that can be used to create valuable health care solutions while providing these impoverished areas with some economic stability."