Magnetically guided iron nanoparticles represent a new approach to drug delivery for using magnetic fields to drive therapeutic agents, such as pharmaceuticals, genetic material, even whole cells to disease sites in the body. Researchers at The Children's Hospital of Philadelphia have now demonstrated that the approach can target metal stents inserted surgically into injured blood vessels.

Patients with heart disease commonly receive such stents, narrow metal scaffolds that widen a partly clogged blood vessel. The stents are inserted using a catheter fed along a blood vessel. Commonly, the stents are coated with an antiproliferative agent, such as paclitaxel, which inhibits the replication of smooth muscle cells within the stent, which would otherwise block the device.

Robert Levy and colleagues made magnetic nanoparticles just 290 nm across from a biodegradable polymer impregnated with magnetite, an iron oxide. They loaded the nanoparticles with paclitaxel and used a magnetic field, about a tenth the strength of an MRI machine, to drive the particles through the bloodstream to a stent implanted in the carotid artery of laboratory rats. Five days after receiving the nanoparticle infusion, the magnetically treated animals had four to 10 times as many particles in their stented arteries as the control animals.

By delivering the drug paclitaxel, commonly known as the anticancer agent Taxol which prevents cell proliferation, the treatment can prevent blockages forming in those vessels. In the animal tests, the technique was more successful than conventional non-magnetic stent therapy.

Levy's magnetically guided system broadens the possibilities for stents, since magnetic targeting permits the use of higher doses without increasing side-effects. It also offers the possibility of applying additional doses later or using more than one type of agent.

“This could become a major platform technology for delivering drugs and other agents to specific sites where they can produce benefits in diseased or injured blood vessels,” according to study leader Levy. His team worked on the technique with engineers and scientists from Drexel, Northeastern, and Duke Universities.

The researchers inserted stents and nanoparticles into a group of control rats, but without using a magnetic field.

Moreover, using magnetic fields to concentrate the treatment had a lasting effect. Fourteen days after using the magnetic field and a single dose of magnetic nanoparticle-encapsulated paclitaxel, the researchers found the rat arteries had significantly lower restenosis than found in arteries of control rats that had no magnetic treatment.