By Jean Balchin 14/02/2018

“Close your eyes, give me your hand, darlin’
Do you feel my heart beating
Do you understand”

You know what else can record heart beats? That’s right, an electronic tattoo! Temporary tattoos may no longer be as popular as they once were, but researchers at Huazhong University of Science and Technology and the University of Texas at Austin have come up with a cheap way of using their sophisticated tech to fix electronic tattoos onto your skin that can record body temperature and heart rate.

Although it’s probably not a design you wanted permanently imprinted, this new method is much thinner and more breathable than a previous cut-n-paste version which also required tape to be stuck on. An extremely thin plastic sheet was attached to temporary tattoo transfer paper and then coated with a thin film of gold particles. The design was then cut out, to create a wearable electronic sensor that can be pasted onto human skin just like a temporary tattoo.

A temporary tattoo.

As described in a paper published online in npj Flexible Electronics this week, the inexpensive metallic sensors are so thin — about one thousandth of a millimetre — that they can be pasted directly onto skin, conforming to the skin’s texture without blocking normal perspiration, or being affected by body movement.

“Noninvasive wearable devices mounted on skin, the largest organ of human body, provide a versatile means to acquire information about the body or to deliver stimulation and drugs to the body. They are believed to have the potential to revolutionize mobile health, assistive technology, athletic training, human machine interaction, and many other fields” said the researchers.

Typically, fabricating electronic tattoos created from inorganic electronic materials are expensive and time-consuming, but a recently developed cut-and-paste method has cheapened and simplified the process. However, the cut-and-paste method requires pasting the electronic tattoo sensors onto medical tape, which actually increases the tattoo’s thickness and decreases its breathability.

The researchers, led by Nanshu Lu, YongAn Huang and colleagues rectified these problems by modifying the cut-and-paste approach to make low-cost, open-mesh electronic tattoos with a total thickness of 1.5μm (0.0015mm).

First, they laminated a thin (1.4μm) plastic sheet (made from polyethylene terephthalate) onto a piece of temporary tattoo transfer paper, before depositing a thin film of gold particles onto the plastic sheet.

Then, they cut winding filaments into the e-tattoo using a computer-controlled knife of the kind used to cut paper, vinyl and other materials in custom shapes. The resulting e-tattoo can then be pasted onto human skin like a temporary tattoo.

This tape-free design is highly breathable and flexible, and can be used to measure skin hydration and temperature, as well as electrocardiogram signals — from which heart and respiratory rates can be extracted. Tape-free e-tattoos represent another step towards disposable wearable technology.

You can read the research here.