Medical Tattoos

If you suffer from diabetes, you’d probably do just about anything to end the pain and drudgery of sticking your fingers with needles several times a day to draw blood for glucose testing. A group of researchers at the University of Illinois, Northwestern University, and Dailan University of Technology in China that is exploiting the techniques used in making temporary tattoos and transferring them to the skin may someday make that wish come true.

In a paper published today in the online edition of Science magazine, the group reports that it has developed ultrathin nanoscale electronics such as sensors for measuring a patient’s brain or heart activity and transmitters and receivers for wirelessly reporting vital signs. Incorporating these devices in tattoos would enable biological readings to be remotely and unobtrusively recorded day and night, so important events such as a heart arrhythmia or a spike in blood sugar levels are sure to be noticed.

All the makings of a tabletop device you’d find in a doctor’s office—including sensors, circuits, and elements for drawing power and transmitting data—are stuck to the surface of a 30-micrometer-thick, breathable plastic sheet. The electronic components, which are made of materials such as silicon and gallium arsenide, are in the form of “filamentary serpentine nanoribbons.” That’s another way of saying that the researchers made thin, wavy rods and strips that they arranged in an open mesh structure. The result is an electronics layer atop the plastic sheet that is less than 10 micrometers thick and can bend and stretch without breaking. This mechanical arrangement and the pick-and-place printing of circuits on flexible substrates was a breakthrough made a few years ago by University of Illinois researchers.

This small scale provides a few other advantages. Because a patch weighs less than a tenth of a gram, breathes and stretches, and, at less than 50 µm, is thinner than the diameter of a strand of human hair, it is hardly noticeable by the wearer or anyone else. In fact, the researchers are confident that they will be able to hide the stretchable mesh patches in plain sight beneath a commercial temporary tattoo. Thinness also lets electronic device adhere to the skin because of electrostatic surface interactions instead of glue that might be an irritant or inhibit some potential sensor functions such as chemical sensing, wound treatment, and dispensing of medicine.

Devices on that scale can also get by on negligible amounts of energy. The researchers are hopeful that the devices can pick up the power they need wirelessly, through magnetic induction or from solar cells.

All these advantages notwithstanding, epidermal electronics systems (EES) would not be adopted by the medical community if they didn’t work. But the signal-to-noise ratios of the devices the group rigged up in the lab were just as high as those achieved using big, rigid electrodes and conductive gels. Subjects wore the devices for 24 hours or more with no noticeable irritation of the skin and no decrease in the devices’ performance in taking heart and brain readings.

And in a test of a potential function for which conventional monitoring devices are poorly suited, the team recorded the muscle activity of a subject’s throat during speech. The signal archived for each word was distinct enough to suggest “opportunities for EES-based human-machine interfaces,” said the team members in the Science paper. It’s easy to imagine people who have lost their voices because of surgery having words put back into their mouths. It’s just as easy to see would-be performers using a patch linked to a synthesizer to make themselves sound like songbirds.

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