The research will be reported in the Feb. 12 print edition of Nano Letters, a peer-reviewed journal of the American Chemical Society, the world's largest scientific society.
"If you were bleeding and a paramedic came up to you on the street, what would he do?" asks Gary Bowlin, Ph.D., a professor of biomedical engineering at VCU and lead author of the paper. "He'd probably whip out a gauze, slap it on and hold pressure on it. When you get to the hospital, they're going to rip that gauze off and start the bleeding all over again."
The new mat could be placed directly on the bleeding site to start the clotting process, then, depending on the nature and severity of the wound, it could be left there to promote healing and eventually be absorbed by the body, according to the researchers. It could potentially be used for anything from a minor cut to a battlefield wound, where it is vital to stop bleeding immediately while waiting for transport to a distant hospital.
"Or sometimes in surgery there are small bleeders that surgeons can't control," Bowlin says. "In this case, they can just take a small piece of this mat, slap it down, stop the bleeding and leave it. Similar to what people use when they cut themselves shaving — just put a little dab on there and it's done."
The researchers made the mat out of fibrinogen, a natural compound found in the bloodstream. When you get cut, your body activates its clotting mechanism — a cascade of reactions where fibrinogen is broken down and converted to fibrin. "Fibrin is the meshwork, the netting," Bowlin says. "It's like throwing a net over the clot that holds it together and keeps it from dissolving quickly." After the clot is formed and stabilized by the fibrin meshwork, that same meshwork sets the stage for the natural healing processes.
To make the fibers, the researchers used a technique called electrospinning. The process begins with a solution of fibrinogen attached to a nozzle, which is then pointed at a metal target. An electric field is created between the nozzle and the target, and it is gradually increased until the force of the electric field overcomes the surface tension of the solution. This forms a liquid jet that is transformed into a dry fiber before it reaches the target.
The solution is made with a high concentration that causes the polymer chains to intertwine. Instead of breaking into droplets just after the jet forms (which occurs in electrospray ionization — a similar technique that earned a Nobel Prize in chemistry last year for another VCU researcher, John Fenn), the jet continues as a continuous liquid stream. By the time it hits the target, the solvent has largely evaporated and fibers are formed.
"When the jet comes out, the polymer chains are all tangled up and help to form the fiber, just like if you were to pour a boiling pot of spaghetti into a strainer," Bowlin says. "If you let it sit there for a minute, then grab a piece of spaghetti and try to lift it, a bunch of them come out together. The same thing is happening here."
"The key is that we're making these fibers at basically the same dimensions you would find in a natural clot," Bowlin continues. "So when the body sees it, it sees it as normal, and it's going to promote normal things to happen." Natural fibrinogen fibers form in the body at diameters between 82 and 91 nanometers, and the researchers have closely mimicked these dimensions by creating fibers of about 80 nanometers in diameter, Bowlin says. For reference, the average human hair is about 100,000 nanometers in diameter.
The researchers have successfully made the mats in a wide range of sizes using this technique. The texture of the material is akin to that of a flannel shirt, Bowlin says. They have also used electrospinning to make synthetic blood vessels from collagen that are six times smaller than those available to doctors now. These are just two of the many potential applications for this technology, according to Bowlin.
VCU has licensed this technology to NanoMatrix, Inc., and both the process and products are protected by pending United States and international patents.
— Jason Gorss