Biomedicine

Stopping Battlefield Bleeding

A polymer-filled pouch that expands when exposed to blood can quickly halt bleeding.

Researchers at Aurora Flight Sciences have developed a pouch that can be put inside a large, open wound to halt life-threatening bleeding within minutes. The pouch, called a swelling hemostat, resembles a beanbag and is made of a polymer-fiber mesh encased in spandex fabric. The polymer absorbs the blood, and as it does, it expands, putting sufficient pressure on the walls of the wound to stem the flow of blood. Preliminary tests have also shown that the pouch promotes clotting: only the water from the blood is absorbed, hence the natural clotting factors that exist in blood become concentrated.

A lifesaver: The swelling hemostats (above) are designed to absorb blood and stop bleeding in severe wounds. A superabsorbent polymer inside each pouch soaks up the blood and expands, putting pressure on the walls of the wound and stemming the flow of blood.

The pouch would be most useful for treating wounds in areas of the body where a tourniquet could not be applied and for wounds too large and severe for haemostatic bandages. One of the main causes of soldier death in Iraq and Afghanistan is bleeding, and there are many instances on the battlefield in which this device would prove lifesaving, says Javier de Luis, chief scientist at Aurora and the principal investigator for the swelling hemostat. Furthermore, it can be worn for long periods of time without any side effects, and it can be easily removed.

Conventional methods for controlling external bleeding include applying direct pressure. This can be done by a medic or another individual compressing the wound, stuffing it with haemostatic gauzes, or applying a tourniquet. “Each one presents a unique problem, and I am not sure any of them are very effective,” says George Velmahos, a professor of surgery at Harvard Medical School and chief of the division of trauma, emergency surgery, and surgical critical care at Massachusetts General Hospital (MGH). A tourniquet, for example, stops the blood circulation below the point on which it is applied, which leaves the rest of the extremity susceptible to becoming “dead muscle,” says Velmahos. Recently, the U.S. Army developed an ultrasonic tourniquet to stem the flow of blood using focused beams of ultrasound. (See “An Ultrasonic Tourniquet to Stop Battlefield Bleeding.”) But this method, along with others, has thermal side effects that cause damage to the surrounding tissue.

It is also very difficult to compress deep wounds, especially when bullets are flying, says Velmahos. “We need smart devices and smart materials that can stop bleeding without cutting circulation off, and without the need of a paramedic or another body being physically present. To that extent, the swelling hemostat is very useful.”

The pouch initially measures about three square inches and only weighs a couple of ounces, making it easy to stuff into a first-aid kit, a backpack, or even a soldier’s pocket. It is made of a polyacrylic-acid-based superabsorbent polymer powder, a standard material known to greatly swell when exposed to water, hence it can absorb the aqueous components of blood and expand. However, when the pouch is used in a wound, the expansion of the polymer particles is easily blocked by the particulates in the blood, which significantly reduces the effectiveness of the polymer in the device.

To combat this, Aurora researchers mixed the polymer with a polypropylene fiber. The fiber keeps the polymer particles evenly spaced so that they can soak up the blood quickly while expanding uniformly. The outside material is a micro-mesh spandex fabric that stretches to accommodate gel expansion. The pouch, in turn, puts pressure on the walls of the wound and stems the flow of blood through a mechanical fluid-blocking effect.

“The device has a total absorption of approximately 30 times its initial weight within two minutes,” says Liping Sun, a senior scientist at Aurora. Depending on the size of the wound, multiple pouches can be used. Each one can swell to about the size of a couple of grapefruits, says de Luis. But ideally, a pouch would not expand all the way–only enough to stop the flow of blood. The pouch also works like a diaper: it locks in the fluid so that the blood can’t be squeezed out. Tests on pigs at MGH yielded promising results: all of the test subjects treated with the pouch survived their injuries, versus only 40 percent for the controls, which were tested with a standard army-issued gauze roll.

The swelling hemostat pouch could provide a good way to stop bleeding for a few hours, so that a soldier or a patient can be transported to a medical center, says Ali Khademhosseini, an assistant professor in the Harvard-MIT division of health sciences and technology, and a winner of the TR35. “Unlike similar devices, it works to minimize the amount of liquid that would come out of the wound,” says Khademhosseini.

Two other types of devices already used by the U.S. military are made by HemCon and Z-Medica. HemCon, based in Portland, OR, makes bandages from chitosan, a naturally occurring, biocompatible polysaccharide derived from shrimp shells. When applied to a wound, the positively charged chitosan attracts negatively charged blood cells, which seals the wound and allows the body to form a clot that stops hemorrhaging.

Z-Medica, based in Wallingford, CT, makes a pourable product called QuickClot that uses zeolite-based agents to soak up the blood and adhere to the tissue at and around the wound site.

But for traumatic injuries, one needs to have a fast system that can prevent bleeding in large wounds, says Khademhosseini. HemCon bandages, for example, only cover a four-by-four-inch area.

“The main benefit to our device is that it is purely a mechanical application, so we don’t have any complications with chemical reactions or exothermic reactions,” says de Luis.

Researchers at MIT, led by Rutledge Ellis-Behnke, are also working on an innovative solution: a biodegradable liquid that can quickly stop bleeding. (See “Nanosolution Halts Bleeding” and “TR10: Nanohealing.”) It could also be used to promote healing particularly for wounds inside the body. The biodegradable liquid is still three to five years from being approved for use in humans, however, and MIT researchers say that it will first be used in surgical procedures. Its impact on large wounds and in other areas is unknown.

According to de Luis and Velmahos, the swelling hemostat can be developed for less than $10 per pouch, and it could be on the battlefield within a year. “These kinds of things are very useful not just for the battlefield, but for biomedical treatment anywhere,” says Khademhosseini. “They use standard polymers that are cheap and commercially available.”

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