Electronics designed to stick to skin and transmit the body’s electric signals could improve the sensitivity of prosthetics or help doctors monitor patients’ vital signs. Unfortunately, conventional electrodes used for this purpose trap air and sweat against skin, causing irritation or inflammation when used for an extended period.
Now, a team of researchers from the University of Tokyo, the Japan Science & Technology Agency, and Riken have developed a conductive gold nanomesh that is flexible and breathable while relaying electric signals (Nat. Nanotechnol. 2017, DOI: 10.1038/nnano.2017.125).
To make the material, researchers led by Takao Someya at the University of Tokyo electrospun nanofibers of biocompatible polyvinyl alcohol (PVA) and interwove them to form a mesh. They then coated the top of the nanomesh with a layer of gold 70- to 100-nm thick. After applying this mesh to a person’s skin, researchers sprayed it with water to dissolve the PVA and form an adhesive layer several tens of nanometers thick to hold the gold conductors in place. A person can easily remove the nanomesh in the shower or bath because the PVA is very water soluble.
The nanomesh easily conformed to skin irregularities, fingerprints, and wrinkles, and was both gas and water permeable. A panel of 18 participants rated the nanomesh as more comfortable than conventional plastic and elastomer films used as electrode adhesives. The nanomesh also caused no clinical signs of skin irritation after participants wore it for one week.
Despite its thinness, the nanomesh was flexible enough to retain function when stretched repeatedly to 40% of its original length—about as much as the skin on your knuckle stretches when going from straight to bent. The researchers successfully used the nanomeshes to relay electric signals from tiny fingertip sensors for touch, temperature, and pressure to a fingerless glove capable of wirelessly transmitting the data to a laptop. The nanomesh could also perform electromyogram recordings directly from skin, detecting the electric signals from a flexing muscle.
Zhenan Bao, a chemical engineer at Stanford University, says the nanomesh’s breathability and the way it conforms to skin are the material’s main advantages. And although the nanomesh did not outperform conventional gel electrodes in recording electromyograms, she says the nanomesh was still able to detect a comparable signal.
Someya and the study’s co-lead author, Akihito Miyamoto, think the nanomesh has two major applications. “The first is long-term monitoring of patient vital signs without causing any stress or discomfort,” Miyamoto says. “The second is the continuous, precise monitoring of athletes’ physiological signals and motions without impeding their performance.”
Someya thinks reducing the nanomesh’s cost—possibly by replacing gold with a different, less costly conductor—could yield disposable sensors that would easily be replaced during long-term monitoring.