Hi-tech tattoo that acts as heart, brain and muscle monitor

By Dr. Ananya Mandal, MDAug 12 2011

Researchers have designed a wireless electronic monitoring device so thin it can be applied to the skin like a temporary tattoo. It could one day be used to monitor heart, brain and muscle activity of patients without their even noticing.

The researchers released their findings Thursday in the journal Science added that this electronic tattoo could rid hospitals of the unwieldy, outdated monitoring systems, which often involve needles, webs of wires and conductive gels.

Zhenqiang Ma, an engineering professor at the University of Wisconsin who was not involved in the research, wrote in a commentary on the study, “Such complicated wiring can be inconvenient and distressing for both patients and physicians.” Patients with heart disease may have to wear bulky monitors for a month to try to catch rare cardiac events, he explained. A more streamlined, wearable, integrated system would appear to be a relief to all.

But designing a chip flexible enough to stretch, squeeze and twist with the skin is no easy task, said study co-author John Rogers, a materials scientist with the University of Illinois at Urbana-Champaign. He explained that silicon the key ingredient in electronic devices, is very rigid. Manufactured in the form of a relatively thin silicon wafer, he said, “it’s like a plate of glass” and shatters when dropped. The solution was in the design. The researchers first used extremely thin slices of silicon -- about 50 to 100 nanometers deep -- to increase their flexibility. They used the silicon to create S-shaped chains whose snaky contours were able to conform to skin and layered the structure onto membranes that closely match skin’s properties and movement.

Testing the device, the researchers found that it gave readings for brain, heart and muscle activity just as well as did traditional electrode-based systems. The chips could even be hidden under conventional temporary tattoos.

The devices stick to the skin’s surface in much the same way geckos are believed to cling to walls, by taking advantage of a phenomenon called the Van der Waals force. But Rogers said that for longer-term adhesion -- or in the event that, say, a patient sweats heavily - adhesives
like those built into temporary tattoos could provide more a durable option.

The technology could also be used for voice-commanded software, Rogers added, by mounting the device on a person’s throat and training it to recognize and transmit simple commands. There are also tiny solar cells which can generate power or get energy from electromagnetic radiation. The device is small, less than 50 micrometres thick - less than the diameter of a human hair.

Smaller, less invasive, sensors could be especially useful for monitoring premature babies or for studying patients with sleep apnoea without them wearing wires through the night, researchers say.

Prof Todd Coleman, from the University of Illinois, said, “If we want to understand brain function in a natural environment, that's completely incompatible with studies in a laboratory. The best way to do this is to record neural signals in natural settings, with devices that are invisible to the user.” The device was worn for up to 24 hours without loss of function or skin irritation.

However, there are problems with longer-term use, as the skin constantly produces new cells, while those at the surface die and are brushed off, meaning a new sensor would need to be attached at least every fortnight.

Prof Zhenqiang Ma, added, “An electronic skin will help solve these problems and allow monitoring to be simpler, more reliable and uninterrupted. It has proved to be viable and low-cost in this demonstration which will greatly facilitate the practical clinical use of the electronic skin.”