Graphene-based e-tattoo takes strain to indicate pain

The human palm tends to sweat when people are excited or nervous and this reaction is used to measure emotional stress and help people with mental health issues. Current solutions, however, are bulky and unreliable.

Now, researchers at The University of Texas at Austin and Texas A&M University have applied emerging electronic tattoo (e-tattoo) technology to electrodermal (EDA) activity. In a paper published in Nature Communications, the researchers created a graphene-based e-tattoo that attaches to the palm, is nearly invisible and connects to a smart watch.

"It's so unobstructive that people sometimes forget they had them on, and it also reduces the social stigma of wearing these devices in such prominent places on the body," said Nanshu Lu, professor in the Department of Aerospace Engineering and Engineering Mechanics and leader of the project.

Lu and her collaborators have been advancing wearable e-tattoo technology for many years. Graphene has been a favoured material because of how thin it is and how well it measures electrical potential from human body, leading to very accurate readings.

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These ultra-thin materials cannot handle much, if any strain, which presents challenges when applying them to parts of the body that include a lot of movement.

Key to this latest research is how the palm-worn e-tattoo transfers data to a rigid circuit, in this case a commercially available smart watch, in out-of-lab, ambulatory settings. The team used a serpentine ribbon with two layers of graphene and gold partially overlapped. By snaking the ribbon back and forth, it can handle the strain that comes with movements of the hand for everyday activities.

Current palm monitoring tech uses bulky electrodes that fall off and are very visible, or EDA sensors applied to other parts of the body, which provide less accurate readings.

Other researchers have tried similar methods using nanometre-thick straight-line ribbons to connect the tattoo to a reader, but they could not handle the strain of constant movement.

Lu said the researchers were inspired by virtual reality (VR), gaming and the metaverse for this research. VR is used in some cases to treat mental illness; however, the human-aware capability in VR remains lacking in many ways.

"You want to know whether people are responding to this treatment," Lu said. "Is it helping them? Right now, that's hard to tell."