If you’ve ever been plugged into a wearable device at the doctor’s office, then you’re familiar with the electrodes that are attached to your body to monitor their electrical signals. The problem with these electrodes made of metal or hydrogel is that they do not stay in place when moving, for long periods of time or on sweaty or hairy skin.
Engineers at Penn State University aim to change this with painted tattoos that use flexible ink to power the sensors of wearable devices such as EEGs, ECGs and EMGs that track the brain, heart and muscles respectively.
As reported in a paper published on Monday in the Proceedings of the National Academy of Sciences , a team of engineers filed a provisional patent for this ink, a water-based solution mixed with polymers and acidic additives that start clear with a glue-like consistency. It can be colored with food dye to create different colors of a cute fox or a shark that opens its mouth when you open your hand, and dries to the skin in less than 10 minutes. It can be reused or washed.
Due to its customizable, fun nature, these paintable electrodes can be especially beneficial for children who may be wearing a medical device if it is powered by a temporary tattoo of their favorite character or animal.
Because of its customizable design, the ink can be used as face paint in any design you desire.
How ink works on wearables
To connect the ink to the sensors, there is a perforated silver cloth with electrodes that can be connected. Before your painted tattoo dries, a cloth is placed over the design to adhere to the skin. Then, the fabric is connected to a port in a wearable monitoring device. The latter is attached to the skin under the clothes.
The electrical signals collected by the ink are sent through the fabric to a monitoring device, which then transmits the data to a computer via Bluetooth.
If the conductive ink is paired with a silver cloth, it can be connected to a wearable medical device.
“The big idea behind this is that in the future, you may have a very expensive sensing module that stays separate from the system, but the electrodes themselves are disposable. One bottle of ink can provide enough material to paint multiple electrodes within a few days or a week,” said Larry Cheng, co-author of the paper along with James L. Henderson Jr.
The hope is that these temporary electrode tattoos could help detect heart attacks early, read brain waves or power prosthetic robots.
In addition, since it is painted directly on the skin, the ink is stronger and more accurate than sensors attached to the skin, as there may be an air gap between them and the skin. As for the silver cloth, because it is porous, the connecting electrodes can grow to more than 150% of their original size. This means that sweat can pass through the fabric without adversely affecting adhesion, accuracy or comfort.
What the team found during the test
When testing the ink, the Penn State team found that the painted electrodes could monitor ECG signals for 12 hours. They also sit during exercise. When applied to a team member’s arm, the electrodes effectively track muscle signals using an EMG device, allowing for remote control of the robotic arm.
Using an EMG device, human muscle signals can be monitored to control a robot hand.
Since the electrodes can be washed and reused, 12 hours is not the limit of their use.
Finally, painted electrodes can power sensors that track cortisol or glucose. The team is looking at the commercial use of doctors, such as pediatricians. Or, creating “smart plants” that provide information about chemical exposures in their environment and their impact on plant health.
As it has become common to see people wearing health trackers smart watches again smart ringsmaybe one day no one will bat an eye when they see someone leaving the doctor’s office with a temporary tattoo.
