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October 27, 2008
Animal studies show polymer beads deliver drugs safely to heart

By Quinn Eastman

Researchers at Emory and Georgia Tech have developed tiny polymer beads that can slowly release anti-inflammatory drugs and break down into non-toxic components.

When injected into rats’ hearts after a simulated heart attack, the drug-embedded “microparticles” reduce inflammation and scarring, the researchers found.

The results are scheduled for publication in the November issue of Nature Materials.

Doctors believe that certain anti-inflammatory drugs, if delivered directly into the heart after a heart attack, could prevent permanent damage and reduce the probability of heart failure later in life.

Getting those drugs to the right place at the right time is more challenging than simply swallowing an aspirin, says biomedical engineer Michael Davis.

“If you look at previous studies to see what it would take to get enough of these drugs into the heart, they did things like direct injections twice a day,” he says. “And there are clear toxicity issues if the whole body is exposed.”

As an alternative, Davis and graduate student Jay Sy turned to microscopic (1/50 of a millimeter wide) particles made of a material called polyketals, developed by Georgia Tech engineer Niren Murthy.

The microparticles break down over a few weeks in the body, releasing an experimental drug that inhibits an inflammatory enzyme.

Davis said the drug gradually leaches out of the polyketal particles. In addition, they are eaten by white blood cells called macrophages.

“These are actually cells we’re trying to reach with the drug, because they’re involved in the inflammatory response in the heart,” he says. “The macrophages can surround and eat the particles, or fuse together if the particles are too big.”

Davis said polyketals have an advantage over other biodegradable polymers, in that they break down into neutral, excretable compounds that aren’t themselves inflammatory.

In contrast, when polyesters used in sutures and grafts are made into particles small enough to be broken down in the body, they cause inflammation — exactly what the drugs are supposed to stop, he says.