When a soldier is wounded on an extremity such as an arm or leg, applying a bandage and/or tourniquet to stop the bleeding is typically a fairly straight-ahead process. However, in cases where an injury is received right at the junction between an extremity and the torso – places such as the neck, shoulder or groin – things get a lot trickier. Gauze pads treated with clotting agents are often packed into the wound, although they're not always sufficient for staunching the flow. A group of students from Johns Hopkins University are working on a better alternative, in the form of a hardening foam that's injected into the wound.

The treatment system is based around a syringe-style device that contains two liquids, namely polyol and a diisocyanatein, that are kept in separate compartments – it's not unlike one of those two-part epoxy applicators.

The idea is that when a medic is treating an injured soldier on the battlefield, they use a single plunger on the device to simultaneously inject the two liquids into the wound. As the liquids mix, a chemical reaction occurs. This causes them to transform into a polyurethane foam that expands to fill the wound cavity, and then hardens.

That hardened foam basically acts as a "plug," plus it applies pressure from within to help stop the bleeding. Additionally, while still in its liquid state, the foam is able to run deep and thoroughly into the cavity. This is important, as it's often difficult to find the sources of blood loss in such injuries, and then apply clotting agents to them.

Once the soldier reaches a hospital, it should be fairly easy to remove the foam. "Since the wound will have to be debrided extensively anyway [have its damaged tissue removed], we are not anticipating any issue in that regard," student team leader Sydney Rooney told us. "We are still testing it so we don't know the final answer, but our physicians aren't anticipating for it to be a problem. Ideally, most of the block will be removed in one chunk."

DARPA is in fact also working on a wound-filling foam, although it's intended more for use on abdominal injuries. "Their foam expands to a way larger size and more aggressively than many a junctional bleed permits," said Rooney. "Since the stomach expands, their foam expands by 30 times and it doesn't matter, whereas if you put it in, say, a junctional neck wound, it could apply too much pressure."

Meanwhile, Oregon-based RevMedX has developed yet another variation on the same basic idea. Its XStat system uses an oversized syringe to inject tiny sponges into the wound, which expand as they absorb blood. It is currently awaiting FDA approval.

The Johns Hopkins device has so far been tested on flesh-simulating gel containing artificial blood vessels, with animal trials planned to take place next.

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