Transparent Bandage Allows Scientists to Detect Suffocating Wounds

Scientists have developed a paint-on bandage capable of mapping oxygen levels in injuries. They hope that these oxygen maps will help doctors make important clinical decisions from when to amputate limbs, to how much charred flesh to remove from a burn.

“It’s not often in science that you essentially get a prescription for exactly what you need to make,” says Conor Evans, Harvard Medical School professor and investigator at Massachusetts General Hospital Wellman Center for Photomedicine. Evans led the multi-institutional team of scientists developing the bandage.

But this was one of those rare instances. The team modified the commercially available New-Skin liquid bandage to fill their scientific prescription for a non-invasive, quantifiable, tissue oxygen detector that could be painted onto skin and rapidly interpreted by caregivers. They published their results earlier this month in The Optical Society’s open-access publication Biomedical Optics Express.

redbloodcells_1024x576
The experienced eye can tell how approximately many oxygen-carrying red blood cells perfuse soft tissue, but a new transparent bandage could give a more definitive measure.

Every human cell in the body needs oxygen to turn fuel into energy, but healing increases the energy demands of cells cleaning and repairing the injury. At best, wounds with impaired oxygen supplies fail to heal; at worst, living tissue dies—raising the stakes for determining, and intervening, when oxygen levels drop.

Dr. James Thornton, a reconstructive surgeon at University of Texas Southwestern who was not involved in developing the bandage, says clinical observations can tell the experienced eye how much oxygen-carrying blood perfuses soft tissue. “You can kind of tell if you’ve done it enough. You can poke it with a needle and see how red the blood comes out, and you can look at the color and the capillary refill,” he says. There are also quantitative—histological, PET imaging, and electrode-based—methods of detecting tissue oxygenation, but they can be invasive and spatially nonspecific.

The bandage Evans and colleagues developed uses phosphorescence to quantitatively detect oxygen in, and under, the skin it covers. Phosphorescence is the same phenomenon that allows glow-in-the-dark stickers and toys to continue emitting their own light after the lights go out. The scientists added two different phosphorescent dyes to the New-Skin bandage: a green reference dye, and a red oxygen sensor.

Lloyd Rose, an author of the paper, says the bandage is “like nail polish…it starts out a liquid and you just kind of brush it on. As it dries, it solidifies.” Once it solidifies, an additional plastic film is applied over the top of it to keep the bandage from mistakenly detecting ambient oxygen. A camera’s flash and a filter provide the charging pulse of blue light for both dyes—but unlike the reference dye, the charged red oxygen-sensing molecules glow only until they collide with oxygen and lose the energy they need to phosphoresce.

In the absence of oxygen, the red color glows more brightly. After the first, charging flash, the camera takes a second picture on a timer. The scientists can then use the ratios between green (oxygenated) and red (deoxygenated) phosphorescence to create oxygenation maps of the covered tissue.

Although the research team used pig skin grafts to prove the bandage’s function, Thornton is not convinced that these are the best use for it. “Whether or not there’s adequate oxygenation at the time is absolutely going to affect the final result, but it’s not necessarily going to change your action because there’s not much else you can do,” he says. But, Thornton does believe it could inform skin flap surgeries—which differ from grafts in that they maintain the transferred skin’s original blood supply—as well as procedures as simple as casting broken bones. Constricting casts can cut off circulation in the extremities leading to a rare but dangerous condition called compartment syndrome.

Evans says human studies will start in 2015, and hopes to see the bandage in hospitals 5–10 years from now; he couldn’t comment specifically yet on expected prices. He teases with hints about fully developing an all-in-one SMART bandage—one that Senses, Monitors, And Releases Therapeutics to the wound it covers. In the meantime, Evans hopes that tweaking the existing bandage’s chemistry to increase its brightness enough for devices like the iPhone or Google Glass to detect will make it easier for doctors like Thornton to test the bandage in the clinic—to which Thornton says, “We’d try it in a heartbeat.”