Materials

This Sports Bra Checks Your Heart Rate and Recharges as You Move

Scientists have invented an electrically conductive coating that turns any fabric into a simple circuit.

In the not-too-distant future, our shirts, shorts and shoes will all be “smart,” embedded with subtle circuitry that might collect sunlight to power our smartphones or continuously monitor our vital signs like a full-body Fitbit. Researchers recently brought this wearable electronics future one step closer to reality with the creation of a stretchable, washable, non-metal coating that transforms any piece of clothing into a robust electrical conductor.

One of the biggest obstacles in wearable electronics is making smart clothing that people actually want to wear. That means cotton T-shirts that feel like cotton T-shirts — soft, lightweight and bendable, instead of stiff, heavy and threaded with metal wires.

A team of scientists and engineers at the University of Massachusetts at Amherst may have solved the wearability problem by inventing an impossibly thin conductive coating that can be applied at room temperature to any textile or material — cotton, wool, silk, polyester, leather, or plastic — without altering the look and feel of the garment.

Coated with this conductive polymer, which measures only 500 nanometers thick (one-tenth the thickness of a human hair), the fabrics can now act as their own simple circuits. The researchers have already turned an inexpensive sports bra into a wearable heart rate monitor with eight strategically placed sensors versus Fitbit’s one.

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Trisha Andrew runs the Wearable Electronics Lab at UMass Amherst where the conductive coating was developed. She said that her research team took inspiration from the reactive vapor deposition process used in the semiconductor industry to make the silicon chips in all of our devices.

But instead of using 500-degree ovens and caustic chemical reactants to lay down nanolayers of material, Andrew’s lab used a room-temperature vacuum tube pumped with more environmentally friendly compounds from organic chemistry. They detailed their process in a recent issue of the journal Advanced Functional Materials

The result of the lab’s vapor deposition technique is highly conductive polymer called poly (3,4-ethylenedioxythiophene) — nickname PEDOT — that channels electricity as efficiently as the copper wiring in your house. Andrew said that the flexible PEDOT coating overcomes the challenge of trying to design wearable circuitry for different types of materials with varying surface roughness and surface chemistries.

“Our method doesn't care what you give us,” said Andrew, “whether it’s a sports bra from a big box store or a silk tulle dress from a very fancy boutique. If you want that transformed into something electronic, we can put a conductive coating on it.”

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The sports bra heart monitor works exactly like an EKG. The thin circuitry on the bra touches the skin and registers the small changes in conductivity that accompany the sound waves generated by every heartbeat. Andrew’s lab is getting the sports bra ready for the human testing stage and developing software that will analyze data from its eight sensors to produce a “smarter” picture of heart health.

Andrew’s lab has made other simple circuits that generate small amounts of heat and recently made a breakthrough on a separate method for actually generating electricity through your clothes.

The science is called the triboelectric effect. It happens whenever two materials rub against each other and create a surface charge, like rubbing your socks across a thick carpet. Andrew and her team created a second polymer coating that acts as an insulator and wove together both insulating and conducting threads to make a triboelectric textile patch.

“As you tug or pat the material, it actually generates power,” said Andrew. “With all of your small body motions — bending, stretching, walking, twisting an arm — you’ll actually be generating power.” Right now, the electricity is measured in microwatts, enough to run a Fitbit, but the long-term goal is to create a self-charging fabric that could one day power your smartphone.

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