University of Tokyo researchers develop breathable on-skin biosensor

It has been reported by the Tech-on website that Researchers at the University of Tokyo, led by Takao Someya, Professor at the School of Engineering, have developed a nano-mesh electrode that is lightweight, thin and does not cause inflammation even after being attached to human skin for a long time.

The team developed the electrode in cooperation with Masayuki Amagai, professor at the Graduate School of Medicine, Keio University, Riken and Japan Science and Technology Agency (JST).

The nano-mesh electrode can be used as a sensor electrode for measuring biological information for a long period of time in the fields of healthcare, medicine, nursing, etc. The team has already confirmed that it is possible to use the electrode to measure myoelectricity, temperature, pressure and so forth. The results of the research were published on the website in the July issue of Nature Nanotechnology magazine.

The team led by Takao Someya has been engaged in the development of a light-weight, thin biosensor that can be attached to human skin without causing discomfort. However, what the team had previously developed only achieved a device with low breathability. So when the biosensor was attached to human skin it often caused inflammation, inching and redness of the skin.

The new nano-mesh electrode has a higher breathability and so less prone to causing inflammation, as it allows the skin to breath.

The newly-developed nano-mesh electrode was made by:

• using the "electro-spinning" method to form nanofiber-like polyvinyl alcohol
• vapour-depositing gold on its surface

With its nano-size mesh structure, it has a high breathability and a moisture vapour transmission rate of 96.5%.

When the sheet-like electrode is placed on human skin and a small amount of water is sprayed on it, the polyvinyl alcohol melts and sticks to the skin, forming metal electrodes along the uneven skin surface.

Also, it can be easily removed from the skin by, for example, rubbing it.

To examine whether the nano-mesh electrode causes inflammatory reaction on skin, the research team conducted a patch test on 20 subjects. In the test, one week after silicon and parylene were attached to skin in addition to the nano-mesh electrode, the condition of the skin was examined by dermatologists. This test was carried out mainly by Amagai.

As a result, it was found that silicon and parylene caused a light inflammatory reaction but no inflammatory reaction was found on the skin under the nano-mesh electrode. Also, according to the questionnaires about discomfort, itching, reddish skin, etc, the nano-mesh electrode caused the least discomfort.

The research team also confirmed that the nano-mesh electrode can actually measure biological information. When the electrode was attached to an arm to measure myoelectricity, it was measured with a signal/noise ratio equivalent to that of measurement conducted with a conventional gel electrode.

Furthermore, the team combined the nano-mesh electrode with a wireless unit, sensor device and succeeded in measuring temperature, pressure and change in resistance at the time of attaching it to (and detaching it from) a metal object.

Even when the nano-mesh electrode is expanded and contracted in with skin movements, it does not lose its electric conductivity. Its resistance value hardly changed even after being expanded/contracted 10,000 times on the skin.

"We have removed negative elements, namely inflammatory reaction (from a biosensor to be attached to human skin)."

"We can now use it for experiments (for measuring biological information) at ease."

Professor Takao Someya, University of Tokyo