Flexible Sensor Maps Wound Oxygenation Levels

A novel organic reflectance oximeter maps blood-oxygen levels over large areas of skin, tissue, and organs, helping to monitor healing wounds in real time.

Developed at the University of California (UC; Berkeley, USA) and Cambridge Display Technology (CDT; Godmanchester, United Kingdom), the innovative oximetry device is based on multiple organic printed optoelectronics organized in a flexible printed array configuration that can sense reflected light. The array uses organic light-emitting diodes (OLEDs) that emit light in both the red and near-infrared (NIR) bandwidths and organic photodiodes that sense the reflected light from tissues in order to determine oxygen saturation.

The researchers used the sensor to track the overall blood-oxygen levels on the forehead of a volunteer who breathed air with progressively lower concentrations of oxygen--similar to going up in altitude--and found that it matched those using a standard fingertip oximeter within 1.1%. They also used the sensor to create oxygenation maps of adult forearms under pressure-cuff induced ischemia. The mathematical models used can also determine oxygenation in the presence and absence of a pulsatile arterial blood signal. The study was published on November 7, 2018, in Proceedings of the National Academy of Sciences (PNAS).

“When you hear the word oximeter, the name for blood-oxygen sensors, rigid and bulky finger-clip sensors come into your mind. We wanted to break away from that, and show oximeters can be lightweight, thin, and flexible,” said lead author graduate student Yasser Khan, MSc, of UC. “If you have one sensor, you have to move it around to measure oxygenation at different locations. With an array, you can know right away if there is a point that is not healing properly.”

Existing oximeters use LEDs to shine red and NIR light through the skin and then detect how much light makes it to the other side. Oxygen-rich blood absorbs more NIR light, while darker, oxygen-poor blood absorbs more red light. By looking at the ratio of transmitted light, the sensors can determine how much oxygen is in the blood. But such oximeters only work on areas of the body that are partially transparent, such as the fingertips or the earlobes, and can only measure blood-oxygen levels at a single point in the body.

Related Links:
University of California
Cambridge Display Technology