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Injuries can not heal without a constant intake of the main ingredient of blood, oxygen.
A new flexible sensor developed by UC Berkeley engineers can map blood oxygen levels over large areas of skin, tissues and organs, providing physicians with a new way to to monitor in real time the wounds during healing.
A new sensor consisting of an alternating array of printed light emitting diodes and photodetectors can detect oxygen levels in the blood from anywhere in the body. The sensor sends red and infrared light into the skin and detects the ratio of the reflected light. (UC Berkeley Photo by Yasser Khan, Arias Research Group)
"When you hear the word oximeter, you have in mind the name of blood oxygen sensors, rigid and bulky finger sensors," said Yasser Khan, a graduate student in electrical engineering and computer science at the university. University of Berkeley. "We wanted to break with that and show that the oximeters can be light, thin and flexible."
The sensor, described this week in the newspaper Proceedings of the National Academy of Sciences, is composed of organic electronic material printed on flexible plastic that conforms to the shape of the body. Unlike fingertip oximeters, it can detect blood oxygen levels at nine points of a grid and can be placed anywhere on the skin. It could possibly be used to map the oxygenation of skin grafts or to look through the skin to monitor the levels of oxygen in the transplanted organs, the researchers say.
"All medical applications using oxygen monitoring could benefit from a portable sensor," said Ana Claudia Arias, a professor of electrical engineering and computer science at the University of Berkeley. "Patients with diabetes, respiratory diseases and even sleep apnea could use a sensor that could be worn anywhere to monitor blood oxygen levels 24/7." / 7. "
Existing oximeters use light-emitting diodes (LEDs) to shine the red and near-infrared light through the skin and then detect the amount of light scattered on the other side. Oxygen-rich red blood absorbs more infrared light, while darker, oxygen-poor blood absorbs more red light. By examining the transmitted light ratio, the sensors can determine the amount of oxygen in the blood.
These oximeters only work on partially transparent body areas, such as fingertips or ear lobes, and can only measure the rate of oxygen in the blood at a single point in the body.
The sensor is assembled from a printed sheet of organic photodetectors (top) and organic red and infrared LEDs (bottom). (UC Berkeley Photo by Yasser Khan, Arias Research Group)
"Thick areas of the body, such as the forehead, arms and legs, barely let in visible or near infrared light, which makes the measurement of oxygenation at these places really difficult Khan said.
In 2014, Arias and a team of graduate students showed that printed organic LEDs could be used to create thin, flexible oximeters for fingertips or ear lobes. Since then, they have pushed their work further, developing a way to measure tissue oxygenation using reflected light rather than transmitted light. The combination of these two technologies allows them to create the new portable sensor capable of detecting oxygen levels in the blood anywhere on the body.
The new sensor consists of a set of alternating red and quasi-infrared organic LEDs and organic photodiodes printed on a flexible material. The team used the sensor to track the overall level of oxygen in the forehead blood of a volunteer who was breathing in air with progressively lower concentrations of oxygen – such as during a climb to altitude – and found that it was consistent with those using a standard oximeter. They also used the sensor to map the levels of oxygen in the blood in a three by three grid on the forearm of a volunteer wearing an armband.
"After transplantation, surgeons want to measure that all parts of an organ are receiving oxygen," Khan said. "If you have a sensor, you have to move it to measure the oxygenation at different places. With a chart, you can know right away if there is a point that is not healing properly. "
The authors of this work are Han Donggeon, Adrien Pierre, Jonathan Ting, Xingchun Wang and Claire M. Lochner of UC Berkeley; and Gianluca Bovo, Nir Yaacobi-Gross, Chris Newsome and Richard Wilson of Cambridge Display Technology Limited.
This work was funded in part by Cambridge Display Technology Limited (CDT, company number 2672530) and Intel Corporation through Semiconductor Research Corporation grant 2014-IN-2571.
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