Researchers developed a paint-on, see-through, "smart" bandage that glows to indicate a wound's tissue oxygenation concentration.
The bandage created by team of researchers led by Assistant Professor Conor L. Evans at the Wellman Center for Photomedicine of Massachusetts General Hospital (MGH) and Harvard Medical School (HMS), which is inspired by a desire to help wounded soldiers, provides direct, noninvasive measurement of tissue oxygenation by combining three simple, compact and inexpensive components: a bright sensor molecule with a long phosphorescence lifetime and appropriate dynamic range; a bandage material compatible with the sensor molecule that conforms to the skin's surface to form an airtight seal; and an imaging device capable of capturing the oxygen-dependent signals from the bandage with high signal-to-noise ratio.
The bandage's not-so-secret key ingredient is phosphors-molecules that absorb light and then emit it via a process known as phosphorescence.
Phosphorescence is encountered by many on a daily basis-ranging from glow-in-the-dark dials on watches to t-shirt lettering. "How brightly our phosphorescent molecules emit light depends on how much oxygen is present," said Li. "As the concentration of oxygen is reduced, the phosphors glow both longer and more brightly." To make the bandage simple to interpret, the team also incorporated a green oxygen-insensitive reference dye, so that changes in tissue oxygenation are displayed as a green-to-red colormap.
The bandage is applied by "painting" it onto the skin's surface as a viscous liquid, which dries to a solid thin film within a minute. Once the first layer has dried, a transparent barrier layer is then applied atop it to protect the film and slow the rate of oxygen exchange between the bandage and room air-making the bandage sensitive to the oxygen within tissue.
The final piece involves a camera-based readout device, which provides a burst of excitation light that triggers the emission of the phosphors inside the bandage, and then it records the phosphors' emission.
Scientists said that depending on the camera's configuration, they can measure either the brightness or color of the emitted light across the bandage or the change in brightness over time and both of these signals can be used to create an oxygenation map. The emitted light from the bandage is bright enough that it can be acquired using a regular camera or smartphone-opening the possibility to a portable, field-ready device.
The study published in The Optical Society's (OSA) open-access journal Biomedical Optics Express.