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Phosphorescent Bandage Helps Wound Assessment

Photonics.com
Nov 2014
CAMBRIDGE, Mass., Nov. 11, 2014 — A “smart” bandage can indicate oxygen concentration in severely damaged tissue, potentially increasing the success rate of surgeries to restore limbs and physical functions.

With wounded soldiers in mind, a team from the Wellman Center for Photomedicine at Massachusetts General Hospital and Harvard Medical School developed the see-through, paint-on bandage system. It provides direct, noninvasive measurement of tissue oxygenation using an imaging method that captures oxygen-dependent signals from the bandage.

“It allows for the visual assessment of the wound bed, so treatment-related wound parameters are readily accessible without the need for bandage removal, preventing unnecessary wound disruption and reducing the chance for bacterial infection,” said Wellman Center professor Dr. Conor L. Evans.


The transparent liquid bandage displays a quantitative, oxygenation-sensitive color map. Courtesy of Dr. Zongxi Li/Wellman Center for Photomedicine.


In a study, the bandage was created with an oxygen-sensitive phosphor and a green oxygen-insensitive reference dye to clearly demonstrate the changes in tissue oxygenation. It was painted onto the skin as a viscous liquid, which dried into a solid film in less than a minute. A second barrier layer was then applied to protect the film and slow the rate of oxygen exchange between the bandage and the air.

Electronic flash units with 400/70-nm bandpass filters provided a brief pulse of blue excitation light, after which a near-infrared CMOS camera collected light emitted by the bandage, which allowed the researchers to generate a 2-D oxygen map of the underlying tissue.

“How brightly our phosphorescent molecules emit light depends on how much oxygen is present,” said Dr. Zongxi Li, a research fellow at Harvard Medical. “As the concentration of oxygen is reduced, the phosphors glow both longer and more brightly.”

She added that, depending on the camera’s configuration, “we can measure either the brightness or color of the emitted light across the bandage or the change in brightness over time. Both of these signals can be used to create an oxygenation map.”

This system can be used to monitor patients at risk of developing ischemic conditions, where blood flow is restricted. It could also be used in postoperative monitoring of skin grafts or flaps and burn-depth determination as a guide for surgical removal of dead or damaged tissue.

Light emitted from the bandage is bright enough that in the future it could also be obtained using a regular camera or smartphone, the researchers said. They added that their ongoing work includes the potential expansion of the bandage’s sensing capabilities to include pH, bacterial load, oxidative states and specific disease markers.

“In the future, our goal for the bandage is to incorporate therapeutic release capabilities that allow for on-demand drug administration at a desired location,” Evans said.

The work was funded by the U.S. Department of Defense Military Medical Photonics Program and National Institutes of Health. The research was published in Biomedical Optics Express (doi: 10.1364/BOE.5.003748). 

For more information, visit www.massgeneral.org/wellman.


GLOSSARY
phosphorescence
Luminescence is the emission of light from a source that is delayed by more than 10-8 s following excitation.
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