One of the biggest problems in emergency situations, such as on battlefields and at the scene of a car accident, is blood.

Even relatively superficial wounds can be fatal if doctors don't have access to a fresh supply of blood for transfusions. Donated blood is always in short supply because it's good for only around 35 days. Plus, blood needs to be refrigerated, making it difficult to transport.

That may change, though, thanks to the work of researchers at the University of Sheffield, in England. Scientists there are developing a type of artificial blood for use in emergencies.

The blood is made from hollow, artificial molecules called porphyrins. Like hemoglobin found in real blood, these plastic molecules contain an iron atom. Like real blood, the atom allows the molecules to gather oxygen from air in the lungs and transport it throughout the body.

At least that's the idea. So far the blood exists only in test tubes. It remains to be seen how well plastic blood would work in the human body. Also, our kidneys normally get rid of foreign molecules cruising around in the blood stream. The researchers hope that their molecules are large enough to stay in the blood stream long enough to supply oxygen to the body's cells until a real blood transfusion is possible.

Despite the potential hurdles, though, plastic blood is promising. Unlike real blood, it won't spoil and doesn't require refrigeration. It's lightweight and easy to transport to accident scenes and battlefields. The researchers hope that with more funding, their blood will move out of test tubes and into people who need it.