Ventilating flaps lined with live cells open and close in response to an athlete’s sweat. Image: Hannah Cohen

Ventilating flaps lined with live cells open and close in response to an athlete’s sweat. Image: Hannah Cohen

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US researchers have developed a breathable workout suit with ventilating flaps lined with live microbial cells that shrink and expand in response to changes in humidity to keep the wearer cool and dry.

According to the team of scientists at the Massachusetts Institute of Technology (MIT), the cells act as tiny sensors and actuators, driving the flaps to open when an athlete works up a sweat, and pulling them closed when the body has cooled off.

In nature, biologists have observed that living things and their components, from pine cone scales to microbial cells and even specific proteins, can change their structures or volumes when there is a change in humidity. The MIT team predicted that natural shape-shifters such as yeast, bacteria, and other microbial cells might be used as building blocks to construct moisture-responsive fabrics.

The researchers first worked with the most common nonpathogenic strain of E coli, which was found to swell and shrink in response to changing humidity. The cells were then engineered to express green fluorescent protein, enabling the cell to glow when it senses humid conditions, before using a cell-printing method to print E coli onto sheets of rough, natural latex.

This biofabric was then worked into a wearable garment, with cell-lined latex flaps patterned across the back of the suitback, with each flap tailored to the degree to which they open and based on previously published maps of where the body produces heat and sweat.

"People may think heat and sweat are the same, but in fact, some areas like the lower spine produce lots of sweat but not much heat," explains former graduate student Lining Yao, who co-led the project, dubbed bioLoic, with Wen Wang, a former research scientist in MIT's Media Lab and Department of Chemical Engineering. "We redesigned the garment using a fusion of heat and sweat maps to, for example, make flaps bigger where the body generates more heat."

Support frames underneath each flap keep the fabric's inner cell layer from directly touching the skin, while at the same time, the cells are able to sense and react to humidity changes in the air lying just over the skin. In trials to test the running suit, study participants donned the garment and worked out on exercise treadmills and bicycles while researchers monitored their temperature and humidity using small sensors positioned across their backs.

After five minutes of exercise, the suit's flaps started opening up, right around the time when participants reported feeling warm and sweaty. According to sensor readings, the flaps effectively removed sweat from the body and lowered skin temperature, more so than when participants wore a similar running suit with nonfunctional flaps.

The researchers say that moisture-sensitive cells require no additional elements to sense and respond to humidity. The microbial cells they have used are also proven to be safe to touch and even consume. What's more, with new genetic engineering tools available today, cells can be prepared quickly and in vast quantities, to express multiple functionalities in addition to moisture response, the team says.

To demonstrate this last point, the researchers engineered moisture-sensitive cells to not only pull flaps open but also light up in response to humid conditions.

"We can combine our cells with genetic tools to introduce other functionalities into these living cells," adds Wang. "We use fluorescence as an example, and this can let people know you are running in the dark. In the future we can combine odour-releasing functionalities through genetic engineering. So maybe after going to the gym, the shirt can release a nice-smelling odour."

Meanwhile, the researchers have also integrated the moisture-responsive fabric into a rough prototype of a running shoe, with an inner layer of similar cell-lined flaps to air out and wick away moisture.

Where the bottom of the foot touches the sole of the shoe, the researchers sewed multiple flaps, curved downward, with the cell-lined layer facing toward — though not touching — a runner's foot. They again designed the size and position of the flaps based on heat and sweat maps of the foot.

"In the beginning, we thought of making the flaps on top of the shoe, but we found people don't normally sweat on top of their feet," Wang explains. "But they sweat a lot on the bottom of their feet, which can lead to diseases like warts. So we thought, is it possible to keep your feet dry and avoid those diseases?"

As with the workout suit, the flaps on the running shoe opened and lit up when researchers increased the surrounding humidity and faded and closed in dry conditions.

Looking ahead, the team hopes to collaborate with sportswear companies to commercialise their designs.

"This work is an example of harnessing the power of biology to design new materials and devices and achieve new functions," adds Xuanhe Zhao, the Robert N. Noyce career development associate professor in the department of mechanical engineering and a co-author on the paper. "We believe this new field of 'living' materials and devices will find important applications at the interface between engineering and biological systems."

The research was supported, in part, by MIT Media Lab and the Singapore-MIT Alliance.