E-tattoo research makes its mark on the wearable tech scene

Doctoral student Ajay Pratap (left) and Professor David Estrada look into an electrospinning machine. "The electrospinner is used to create nanofiber mats, which form the foundation of the E-tattoo," Estrada said. "It basically uses a high electric field between a needle and the drum to pull the polymer into these nanoscale fibers while they fly towards the drum and are collected in random mat of fibers that look a bit like spaghetti on a plate." Photo by Priscilla Grover.

Peel and stick tattoos have been a childish fad for decades. Any shape, color and design can be applied directly to the skin, and removed with simple household ingredients. Despite its playful origin, Boise State researchers have taken this concept to the next level with "electronic tattoos" that hold promise for the growing field of wearable technology.

Ajay Pratap, a doctoral student in materials science and engineering, led the "E-tattoo" research team under the mentorship of Materials Science and Engineering Professor David Estrada. This interdisciplinary team included the expertise from 17 research faculty and staff representing fields such as physics, electrical engineering, biomolecular sciences, biomedical engineering and materials engineering.

"E-tattoo is a fancy word for skin electronics," Pratap said, "and we can cut them into any kind of designs we want. They directly go on the skin like a tattoo, but they are removable. Because they are functionalized material, they can do a lot of things; for example, energy harvesting or sensing, electrocardiogram monitoring, and monitoring muscle activity through electromyography."

Ajay Pratap applies an ultra-thin, flexible electric tattoo to his hand in the E-tattoo research lab. Photo by Priscilla Grover

In their testing, the team demonstrated the E-tattoo's ability to capture electrocardiogram (ECG) and electromyography (EMG) signals, all while staying flexible and adhering to the skin even while stretching, compressing and twisting. Outfitted with special nano-scale generators, these E-tattoos can harvest energy directly from human motion and prolong the battery life of other wearable systems.

"According to research and available data, the average human walks 5,000 to 10,000 steps per day, and that generates one to two kilojoules of energy," Pratap said. "So our target is to harvest that energy for the low-powered electronics: for example, LED sensors, your heart sensors or your smartwatch."

In the E-tattoo research lab, Pratap measures energy flow through the tattoo using an oscilloscope. Photo credit Priscilla Grover

The team's E-tattoo uses two materials in a novel way: a new polymer that is electrospun into fibers, coated with titanium carbide MXenes (pronounced 'MAX-enes'). Titanium carbide MXenes are two-dimensional inorganic compounds that have specific material properties, making them ideal for energy harvesting, and wearable technologies being placed against skin and being formed into 'E-tattoos'. Essentially, these MXenes are coated onto the fibers, and then can be applied directly to skin, and removed with alcohol.

These E-tattoos also break the mold in another way. Unlike current electronic tattoo materials being used, these can be removed with rubbing alcohol and will create less waste.

"We're one of the few groups in the world working with this polymer for this application," Estrada said. "We are exploring this new polymer in a lot of fields right now, as we believe it is more environmentally friendly compared to other polymers that are typically used within this domain. That's one of the big advantages of Ajay's research."

When asked the challenges faced while conducting this research, Pratap concluded that the extremely supportive and multi-disciplined team made all challenges insignificant.

In the E-tattoo research lab with doctoral student Ajay Pratap (left), and Professor David Estrada of the Micron School of Materials Science and Engineering. Photo by Priscilla Grover

"I got help all the time," Pratap said. "I got help from Professor Estrada. I got help from my team - amazing. Whenever I had any questions, Dr. Tony, Dr. Josh, Haley, Fereshteh - you name it - they always came up with some solution. That's why I did not feel any kind of struggle in the whole project."

The E-tattoo research was published in Advanced Science journal and was conducted by authors Pratap; Estrada; and Fereshteh Rajabi Kouchi; Tony Valayil-Varghese; Hailey Burgoyne; Attila Rektor; Michael Curtis; Miranda Lea Nelson; Francis N. Mokogwu; Corey M. Efaw; Josh Eixenberger; Allyssa Bateman; Benjamin C. Johnson; Brian Jaques; Zhangxian Deng; Kurtis Cantley; and Christopher E. Shuck.

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