A surprisingly simple microparticle could help doctors stop uncontrolled bleeding from serious wound sites. A team of researchers led by Christian J. Kastrup of the University of British Columbia, in Vancouver, made self-propelled microparticles that can transport thrombin—against the flow of blood—to a wound site, where the thrombin initiates blood clotting (Sci. Adv. 2015, DOI: 10.1126/sciadv.1500379). The researchers mixed thrombin-loaded calcium carbonate microparticles with the solid organic acid tranexamic acid, an agent used clinically to stabilize clots. When they applied the microparticle mixture to a test animal’s wound, the carbonate reacted to release carbon dioxide bubbles that propelled the particles into the blood vessels surrounding the wound. With these microparticles, “you don’t need to see where the damaged blood vessels are,” Kastrup says. “If you can get the microparticles in proximity of the damaged vessels, the particles will do the rest of the work. They’ll expand and push the agent throughout the blood and find the damaged blood vessels.” The researchers tested the particles in three animal models of intraoperative and traumatic bleeding.