Red blood cells live for up to 100 days

The technique could prove a better way to help people who are at risk of strokes or deep vein thrombosis.

Scientists already know that a chemical called tissue plasminogen activator (tPA) has the ability to "dissolve" clots.

However, when simply injected into the bloodstream, the drug has a short lifespan and can cause potentially dangerous side-effects.

Experts from the Pennsylvania School of Medicine hit upon the idea of coating red blood cells with the chemical in order to prolong its effectiveness.

They found that not only did the drug persist in the bloodstream for far longer as a result, as potentially dangerous clots formed, it was carried into the heart of them, from where it could begin working to destroy them from within.

Hundreds of thousands of people every year are at increased risk of a blood clot following surgery.

Dr Vladimir Muzykantov, who led the research, said: "If developed for humans, the method could provide an ideal way of delivering clot-busting drugs, with fewer side effects.

"In theory, patients could donate blood before surgery and receive their own cells bound to tPA following surgery, providing a safer alternative to blood-thinning medication."

He said that the treatment held promise as a way of helping people who had already suffered strokes or heart attacks.

Old clots

Animal tests showed that not only was it effective, but it did not break up "old" clots which may actually have a beneficial role, perhaps by sealing damage to blood vessels.

The team is interested in the potential of binding other drugs to red blood cells.

Dr Muzykantov said: "Red blood cells can travel hundreds of kilometers throughout the blood vessels during their 100 or so day lifespan.

"That fact alone makes the idea of red blood cell-bound therapeutics very interesting.

"Red blood cells are relatively large, which makes it very difficult for drugs bound to them to burrow their way out of the bloodstream where they could potentially do damage."