Human Skin Turns Into Display For Biological Information

Human Skin Turns Into Display for Biological InformationA wearable sensor that uses a human arm to display biological information has come much closer to realization.
A research group led by Takao Someya, professor of the Department of Electrical and Electronic Engineering, School of Engineering, the University of Tokyo, developed a flexible OLED light source as an ultra-thin sheet and succeeded in stably operating it in the atmosphere.
Also, the group verified that it is possible to form organic photodiodes on the sheet, attach the sheet to human skin and measure oxygen saturation, pulse rate, etc.

The sheet uses a biocompatible base material and is expected to be attached to skin by using an adhesive material and used as a disposable device.

The group developed an ultra-thin OLED light source sheet in 2013. However, at that time, it had a structure that easily transmits water and oxygen and cannot be stably operated in the atmosphere. Thus, it was operated in nitrogen.

This time, the group stably operated the new sheet in the atmosphere for about 30 hours. The sheet is 3μm in thickness and does not break even when it is crumpled. Its brightness is 10,000cm/m2, which is about 100 times higher than in 2013, and its external quantum efficiency is 6.3-13.9%, which is about 10 times higher than in 2013.

The OLED light source with excellent optical properties can be stably operated in the atmosphere for the following three reasons. First, it became possible to form ITO electrodes on an ultra-thin polymeric material (parylene). The group reduced surface roughness by stacking a smoothed layer on parylene and optimized the energy that generates plasma at the time of sputter-depositing an ITO film.

Second, by using the layered structure of the SiON layer and parylene, the group realized a sealing film that does not easily transmit oxygen and water. Third, a high-quality organic luminescent material for industrial use was employed.

'Super-flexible photonic skin' collects biological information

The research group developed a "super-flexible photonic skin" by using the OLED light source sheet. It is a device made by forming red and green OLED light sources and organic photodiodes on the same ultra-thin sheet. When it is wrapped around a fingertip, etc, it can measure oxygen saturation and pulse rate.

The measurement principle of the device is the same as that of conventional pulse oximeters. Lights with certain wavelengths are applied so that they are absorbed by hemoglobins combined with oxygen and uncombined hemoglobins, respectively, to measure oxygen saturation and pulse rate based on the intensity of the reflected lights. In an experiment, the group confirmed that oxygen saturation can be measured within a range of 90-99% and pulse rate can be stably measured for five days or more.

Measured by skin, displayed on skin

For the future, the research group is planning to realize a display using an OLED light source on the super-flexible photonic skin. It will be a device that is directly attached to human skin, measures oxygen saturation and pulse rate without making the wearer feel discomfort and shows measurement results on the display in real time.

For example, a jogger can see his/her real-time oxygen saturation and pulse rate displayed on the arm (with displayed values changing in real time). The group has already prototyped a segment display that can show numbers from 0 to 9 and a device that can display an indicator with a light-emitting area of 10cm2 on human skin.

The display can potentially show a map, manual, etc in addition to biological information so that it can be used for checking body condition and predicting risks in sports, workplace and so forth.

Communication tool for showing emotions

To realize practical applications, it is necessary to develop a high-resolution display equipped with organic transistor arrays (active matrix), integrate a power source with a drive circuit and improve the durability of the entire system including wiring.

"The new technology can potentially be used for changing the way of communication by intentionally exposing inner feelings," Someya said.

For example, a pulse rate can be indicated by the brightness of an indicator attached to the cheek, telling the wearer's feelings to the other person and facilitating conversation.