An Electric Sock For the Heart

The titles of scientific papers can be a bit intimidating. For example, I’m currently reading “3D multifunctional integumentary membranes for spatiotemporal cardiac measurements and stimulation across the entire epicardium”.

In other words: electric heart socks.

A team of scientists led by John Rogers at the University of Illinois at Urbana-Champaign has created a web of electronics that wraps around a living heart and measures everything from temperature to electrical activity. It’s an ultra-thin and skin-like sheath, which looks like a grid of tiny black squares connected by S-shaped wires. Its embrace is snug and form-fitting, but gentle and elastic. It measures the heart’s beats, without ever impeding them.

Its goal is to monitor the heart in unprecedented detail, and to spot the unusual patterns of electrical activity that precede a heart attack. Eventually, it might even be able to intervene by delivering its own electrical bursts.

Cardiac socks have been around since the 1980s but the earliest ones were literal socks—fabric wraps that resembled the shape of the heart, with large electrodes sewn into place. They were crude devices, and the electrodes had a tough time making close and unchanging contact with the heart. After all, this is an organ known for constantly and vigorously moving.

The new socks solve these problems. To make one, graduate students Lizhi Xu and Sarah Gutbrod scan a target heart and print out a three-dimensional model of it. They mould the electronics to the contours of the model, before peeling them off, and applying them to the actual heart. They engineer the sock to be ever so slightly smaller than the real organ, so its fit is snug but never constraining.

This is all part of Rogers’ incredible line of flexible, stretchable electronics. His devices are made of mostly made of the usual brittle and rigid materials like silicon, but they eschew right angles and flat planes of traditional electronics for the curves and flexibility of living tissues. I’ve written about his tattoo-like “electronic-skin”, curved cameras inspired by an insect’s eye, and even electronics that dissolve over time.

The heart sock is typical of these devices. The tiny black squares contain a number of different sensors, which detect temperature, pressure, pH, electrical activity and LEDs. (The LEDs shine onto voltage-sensitive dyes, which emit different colours of light depending on the electrical activity of the heart.) Meanwhile, the flexible, S-shaped wires that connect them allow the grid to stretch and flex without breaking. As the heart expands and contracts, the web does too.

So far, the team have tested their device on isolated rabbit hearts and one from a deceased organ donor. Since these organs are hooked up to artificial pumps, the team could wilfully change their temperature or pH to see if the sensors could detect the changes. They could. They could sense when the hearts switched from steady beats to uncoordinated quivers.

Rogers thinks that tests in live patients are close. If anything, the doctors he is working with are more eager to push ahead. “We’re scientists of a very conservative mindset. They have patients who are dying,” he says. “They have a great appetite for trying out good stuff.”

The main challenge is to find a way of powering the device independently, and communicating with it wirelessly, so that it can be implanted for a long time. Eventually, Rogers also wants to add components that can stimulate the heart as well as recording from it, and fix any aberrant problems rather than just divining them.

It’s a “remarkable accomplishment” and a “great advance in materials science”, says Ronald Berger at Johns Hopkins Medicine, although he is less sure that the device will be useful is diagnosing or treating heart disease. “I don’t quite see the clinical application of these sensors.  There might be some therapy that is best implemented with careful titration using advanced sensors, but I’m not sure what that therapy is.”

But Berger adds that the sock has great promise as a research tool, and a couple of other scientists I contacted agree. After all, scientists can use the device to do what other technologies cannot: measure and match the heart’s electrical activity and physical changes, over its entire surface and in real-time.

For more on John Rogers’ flexible electronics, check out this feature from Discover that I co-wrote with Valerie Ross.

Reference: Xu, Gutbrod, Bonifas, Su, Sulkin, Lu, Chung, Jang, Liu, Lu, Webb, Kim, Laughner, Cheng, Liu, Ameen, Jeong, Kim, Huang, Efimov & Rogers. 2014.  3D multifunctional integumentary membranes for spatiotemporal cardiac measurements and stimulation across the entire epicardium. Nature Communications. http://dx.doi.org/ 10.1038/ncomms4329