Researchers print flexible electronic tattoo directly onto human skin

From the research lab that brought us stick-on electronic tattoos, and recently the stretchable battery, we now have the first electronic sensor that has been printed directly onto human skin. These sensors can directly measure skin hydration and temperature, and electric signals from muscle and brain activity.

The skin-printable sensors, created by the Rogers research group at the University of Illinois at Urbana-Champaign, are a natural evolution of the lab’s electronic tattoos. The electronic tattoos are circuits that are affixed to an elastic polymer backing, which is then stuck to the skin (pictured above). Like temporary tattoos, though, these electronic tattoos are easily washed off in the shower or swimming pool, making them unsuitable for extended use. Now, by removing the polymer backing and printing the sensor directly onto the skin, the researchers have made a device that is one thirtieth as thick and better at conforming to the natural bumpiness of skin. ”What we’ve found is that you don’t even need the elastomer backing,” John Rogers tells Technology Review. “You can use a rubber stamp to just deliver the ultrathin mesh electronics directly to the surface of the skin.”

Once on the skin, the researchers use a commercially available spray-on bandage to protect the electronics in a “very robust way.” Because of the skin’s natural exfoliation process, though, the device flakes off after two weeks — an inherent flaw of any surface-mounted skin-based electronics (epidermal electronics). To achieve a longer lifespan we will need to embed devices under the skin, like real tattoos.

As for how the Rogers group created a computer that’s flexible enough to move and stretch with your body, we look no further than the stretchable battery that the same researchers unveiled in February. In essence, the stretchable battery and electronic tattoos are standard computer circuits, fashioned from normal silicon processes — but each of the components are connected by special, serpentine wires that are capable of flexing and stretching gracefully (pictured right). In the case of the battery, which has a liquid electrolyte, the components are encased in stretchy silicone — but with this new electronic tattoo, your skin is the stretchy substrate.

Moving forward, the researchers say they will work on improving their flexible wireless charging circuitry (which debuted in the stretchable battery) and communications circuitry — after all, what good is an electronic tattoo that can’t connect to other sensors, or some kind of wearable computer/smartphone?

Eventually, the goal is to produce sensors and simple computers that might aid with healthcare (m-health), or more generally with quantified health/body hacking (using technology to track your body’s state and performance throughout the day). You can easily imagine an electronic tattoo that keeps track of a surgical wound and alerts doctors if it doesn’t heal as expected. On the elective front, you might install an electronic tattoo that tells you when your heart or brain activity is spiking, or interacts in interesting ways with other wearable sensors and computers that you might be wearing.

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