What are Electronic Tattoos?
Human skin provides invaluable information that health care professionals and researchers can use to monitor, prevent and treat health conditions. Devices placed in direct contact with the human skin are referred to as bioelectronics — or electronic tattoos. They can monitor the electrical activity of the brain, heart, muscles, blood pressure, glucose monitoring, and the hydration level of the skin.
Wearable bioelectronics have evolved to be patches that are soft, stretchable and flexible. Researchers currently face the challenge of how to control “motion artifacts” caused when wearing these bioelectronic devices. These artifacts occur when the patch does not conform to, or is weakly adhered to the skin. As the person moves, motion artifacts result which can lead health care professionals to misinterpret the recorded data, or even misdiagnose an illness. Drawn-on-Skin (DoS) electronic tattoos is a technique that address this challenge.
DoS electronics have many uses, such as a wireless DoS electrocardiogram (ECG) monitoring system. This can be used at home for daily monitoring, or in a clinical hospital setting for 24/7 or on-demand monitoring.
How Is It Applied To The Skin?
Biosensors can now be used to replace traditional inks, where the colors will change in response to a variation in the skin. Two types of inks are traditionally used in this process: a) a conductive Ag-PEDOT:PSS ink and b) a semiconducting P3HT-NF ink.
Stencils are created and adhered to the target skin area. Next, the inks are drawn directly into the outlines of the stencils on the skin using a modified ballpoint pen with a 1-mm diameter tip. By varying the tip diameter of the pen or stencils, this allows one to control the line width and resolution. After three to five minutes, the stencil is then removed, leaving a thin, dry film of ink on the skin. This can then be used to provide motion-free sensing. The electronic tattoos typically last for several days, even weeks, and can record vital health information.
Researchers at Harvard and the Massachusetts Institute of Technology developed a series of color-changing digital electronic tattoos. These tattoos can measure the concentration of sodium, pH, and glucose in the skin. This is demonstrated in the following images.
For more information about the science behind DoS electronic tattoos, see the article here in Nature magazine.