Realising it would be some time before the ambulance arrived, Johnson opened a packet of sand-like material and poured it into the wound. Within seconds the bleeding had practically stopped, and the man survived. "The medic told me that had I not put the substance in there, the guy would probably have bled out and died," he says.
The material, called QuikClot, which is issued routinely to police officers in Hillsborough county, Florida, was developed for the US military to cut down the number of soldiers who bleed to death on the battlefield. More than 85 per cent of soldiers killed in action die within an hour of being wounded. Improved haemorrhage control "could probably save 20 per cent of the soldiers who are killed in action", says Hasan Alam, a trauma surgeon at Massachusetts General Hospital in Boston.
The material is already used by the navy and a few US police departments. Researchers would like to see it used more widely, but one major safety problem has prevented this happening. Now developers are hoping that advances in the material and the design of new substances could see blood clotting treatments used by ambulance crews, in operating theatres, and even in the home.
Every US marine and navy soldier in Iraq and Afghanistan carries QuikClot. Its maker, Z-Medica of Wallingford, Connecticut, claims it has saved 150 lives so far. The porous mineral powder is poured into the wound, where pores quickly absorb water, which concentrates the blood's clotting factors and so speeds up clotting. In lab tests, blood treated with QuikClot clots in less than 2 minutes, compared with the 10 minutes or so for untreated blood. In studies on pigs with severed arteries, the survival rate was 100 per cent; with a standard gauze dressing, more than half the animals died.
The safety problem in the way of QuikClot's wider use arises because of the large amount of heat the material releases when it absorbs water, sometimes enough to cause second-degree burns. In the face of a life-threatening injury, this may be a price worth paying.
Being a powder, QuikClot can be poured into any shape of wound, but if it is to be used more widely it cannot harm those it treats. Researchers Galen Stucky and Todd Ostomel at the University of California, Santa Barbara, who are collaborating with Z-Medica, have found a way to tune the material to control the amount of heat it releases. They have also learned that there is much more to how the substance accelerates clotting than just water absorption, and are using this knowledge to develop a new generation of materials that work even faster and should prove more acceptable for civilian use.
QuikClot releases heat when positively charged calcium ions in its pores react with water molecules. Other positive ions release less heat when they react with water, so Stucky and Ostomel swap some of the calcium ions in the material for silver ions by soaking the material in a silver-containing solution. They can control how much of the calcium they replace, allowing them to tune the material to release as much or as little heat as they choose. "Having some heat is good," Stucky says. "It facilitates the clotting process."
Although a variety of ions can be used, silver is particularly good because it has antibacterial properties, even at very low concentrations. The drawback is that silver is expensive and significantly raises the cost from the existing military price of $10 a packet. Z-Medica plans to commercialise two versions of the new material, one with silver and another containing a less expensive heat-reducing formulation the company does not yet want to name.
Stucky's group is building on this work to develop new materials to control bleeding during surgery. For a material to be most effective it must have a large surface area like QuikClot, and since calcium acts as a cofactor in many clotting reactions some calcium ions must be present.
The team's new material, a bioactive glass made of silica and calcium, has larger pores than QuikClot and a different consistency. Its large surface area, and efficiency in releasing calcium ions, makes it clot blood even faster. The large pores allow bigger molecules, such as enzymes found in the blood's clotting cascade, to be incorporated in the material and released into the wound, which could further improve clotting.
Unlike QuikClot, which is hard to make in anything but powder form, the bioglass can be squeezed out of a syringe, like a paste, which would be easier to apply during surgery. Bioglass can also be left in the body after surgery, where it will eventually be absorbed unlike the QuikClot particles, which have to be removed from the wound after bleeding has stopped, a fiddly and time-consuming process.
Meanwhile Z-Medica is hoping that its new, safer version of QuikClot will be taken up not only by surgeons and emergency crews, but also by individuals. "Ultimately, we hope everybody will have a first-aid kit with a pack in their car," says Huey.
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THIS ARTICLE APPEARS IN NEW SCIENTIST MAGAZINE ISSUE: 18 MARCH 2006
AUTHOR: JESSICA MARSHALL, REPORTER IN SAN FRANCISCO
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