Blood loss kills a lot of people; one-third of deaths related to traumatic injuries are caused by bleeding. But a lab-made polymer could change that, as it was able to stop bleeding in rats whose femoral artery was cut, according to a study published today in Science Translational Medicine — the procedure essentially saved their lives.
"We designed a polymer that we can inject into the bloodstream and that’s able to integrate in the forming of clots, and it stabilizes them," says Suzie Pun, a bioengineer at The University of Washington and a co-author of the study. "I think this has real power to save people in the battlefield."
Doctors and paramedics often use tourniquets to stop someone from bleeding out, but when injuries are internal, its hard to know where to apply pressure without making things worse. In those situations, a strong blood clot can be life-saving.
forming blood clots isn’t easy when blood is pouring out of an organ
Clots are formed when platelets, a type of blood cell, group together to make a "platelet plug." This plug is reinforced thanks to a fibrous protein called fibrin. But forming blood clots isn’t easy when blood is pouring out of an organ, because the components that are needed to strengthen clots are located in the blood that spills out. Thus, when major blood loss occurs internally, clots become weak — so weak that they break down when doctors supply patients with blood transfusions. To solve this problem, researchers decided to make a polymer that could strengthen clots inside the body, even as the patient suffers massive amounts of internal bleeding.
In the study, researchers made a 3-millimeter cut in the femoral artery of 40 rats. Of those rats, about half were given an injection of the polymer solution as they were bleeding out. The rats that didn't receive the drug didn't do very well — over 50 percent of them died. But "100 percent of the rats treated with the polymer survived," Pun says.
Chan et al. 2015
The polymer, called PolySTAT, looks like a "white fluffy powder" before it’s dissolved in saline solution, Pun explains. It was engineered using the same polymer that makes up contact lenses, in addition to a peptide that’s built to seek out and attach to fibrin. When it’s injected, PolySTAT detects fibrin and weaves itself throughout the forming clot. This strengthens it, and could help the clot stay in place in humans when doctors inject blood or saline solution to increase a patient’s blood pressure. Moreover, the fact that it only binds to fibrin means that it shouldn’t suddenly start forming clots all over the place. "We designed this to only work after the initial clot has formed," says Nathan White, an emergency physician at the University of Washington and a co-author of the study.
"100 percent of the rats treated with the polymer survived."
The method is completely novel, Pun says. "People have tried to make artificial platelets, but in terms of a synthetic polymer like this, we think it’s the first."
The researchers think the polymer could be used in the emergency room, as well as by paramedics in the field. "Most people who die of bleeding die very quickly, before they make it to the medical facility," White says. Being able to use PolySTAT in the field could make a big difference in those cases. It may also help people who have blood disorders that prevent them from forming clots. And, because it only binds to fibrin, it might one day be possible to employ this strategy to break down clots that form during a stroke, by adding other drugs to the formula that can break down clots, White says.
"PolySTAT reduced blood loss, abolished rebleeding at the injury site, and increased survival," writes Karim Brohi, a trauma science researcher at Queen Mary University in London who didn't participate in the study, in a Science news article about the experiment. But "drugs need to survive the rigors of the emergency environment," and questions about the drug’s safety remain.
The polymer doesn’t appear to be toxic — "it doesn’t cause organ damage," White says — but researchers still need to perform long-term safety tests to see what happens after the clot is formed. Using PolyStat will probably slow the natural breakdown of clots, but that still needs to be determined. The components that make up PolyStat have been used in humans before, but "what we don’t know is what effect the combination will have," White says.
"Unless it actually saves a life, making clots stronger is meaningless."
The researchers plan to try it on larger animals soon. They will also have to try it on different types of wounds. A nice clean cut to the femoral artery doesn’t necessarily represent what doctors see in the emergency room — or what soldiers see in the field. "Some laceration models take out a quarter of the liver," so researchers will have to test PolySTAT on bigger wounds, Pun says.
Still, the polymer looks promising. Unlike blood and plasma, the powder can be stored in a simple container; it doesn’t need to be refrigerated. That means that it might one day make its way into the kinds of first-aid kits that paramedics and soldiers employ. Until then, the increased survival rate seen in the rats in very exciting, Pun says — "it’s new paradigm for treating trauma." But the polymer still has a long way to go. "Unless it actually saves a life, making clots stronger is meaningless," she says.