On the battlefield, severe blood loss is a leading cause of death. So in the last decade or so, the military has pushed solution after solution to the problem of exsanguination—especially in the initial ten minutes after a first responder like a medic gets to a wounded soldier. Better tourniquets, kaolin-impregnated bandages that pull excess water out of clotting blood, and chitin-infused bandages that seal to the edges of wounds have all improved results and saved lives—in battle, and then migrating into civilian medical care. Now, to that list, add another tricky bandage with a lifesaving extra feature: bubbles.
The problem with those other chemical-enhanced bandages is that blood is powerful stuff. It spurts or oozes from wounds with enough force to carry the chemicals away instead of letting them work on damaged vessels. And the chemicals can't reach into deeper wounds at all—they're stuck on the surface. The trick is getting clotting agents where they need to go, and fizzing, popping bubbles are great at transporting stuff around.
“If you can get the particles in the general area of the wound, they will do the work and get the drugs to the damaged vessels,” says Christian Kastrup, a biomedical engineer at the University of British Columbia who wrote a paper on the new work in Science Advances. Instead of using a drying agent like kaolin or a clumping agent like chitin, his bandages combine powdered calcium carbonate—marble—with tranexamic acid, which blocks a clot-dissolving enzyme, and the clotting enzyme thrombin.
As soon as the bandage touches an open wound, the water in the blood sets off a reaction and the powder starts to fizz and bubble, releasing carbon dioxide. "It's similar to when a grenade goes off and fragments go in all directions," Kastrup says. The acid and calcium carbonate reaction propels the thrombin deep into the bloodstream, like salmon swimming upstream. “As they're reacting and propelling, they're dissolving away like a comet,” says Kastrup.
The particles can get deep into the tissue, all the way to damaged internal blood vessels feeding the wound. Bandages like QuikClot Combat Gauze, the one with the kaolin, may clot a severe wound, but the vessels inside can burst the seal. These bubble-powered particles get to those deeper vessels, making the clot more stable. At least, that's the idea—Kastrup has only tested it in mice and pigs.
Scientists have tried to use self-propelled particles for things like removing pollutants from water or capturing cancer cells, but never in living animals. “As chemists and engineers, we’re just not trained to do those kinds of studies,” says Ayusman Sen, a chemist at Pennsylvania State University who works on propelled particles. “The stars were lined up—these people knew how to do those studies and about self-propelled particles and combined the two.”
The next step, says Sen, will be self-propelled particles that scientists and doctors can intelligently direct towards specific areas. Right now, Kastrup's particles shoot off in all directions. By applying enough of the powder—about a gram for a really severe wound—the particles do end up throughout the wound but lots head in the wrong direction. "In the future, we envision being able to push the powder through an endoscope so you get to the actual area where there's blood," says Kastrup. On the battlefield or in an emergency room, every advantage helps.
