Each year, more than a million patients have their blocked coronary arteries opened with balloon angioplasty, making it one of the most common medical procedures performed in the United States. The majority of these patients also have a drug-eluting stent put in at the time of the procedure. These stents are tiny, wire-mesh tubes that not only physically prop open the blood vessel but are coated with drugs that prevent the artery from narrowing again--a problem called restenosis. But recent studies have questioned the effectiveness and long-term safety of these stents, suggesting that they might lead to fatal blood clots in certain patients.

Now, a company called Pervasis Therapeutics, based in Cambridge, MA, is testing a technology to prevent restenosis without the need for a stent. The product is designed to be wrapped around the artery at the site of the procedure and to release biochemical factors to promote the healing of the vessel's inner lining, or endothelium.

"The blood-vessel wall is a complicated structure," says Elazer Edelman, director of the Harvard-MIT Biomedical Engineering Center and cofounder of Pervasis. When the endothelium is damaged, it leads to a condition called intimal hyperplasia--an abnormal growth of smooth muscle cells. The vessel walls then scar and thicken, leading to restenosis.

The Pervasis product contains endothelial cells grown from culture. The factors released by the cells "send the signal that the endothelium is okay, that it's in control," says Pervasis CEO Steve Bollinger. It gives the endothelium time to heal itself. The gel biodegrades after 30 to 60 days.

While the technology has been tested in cardiovascular patients, it could have applications in several other conditions, says Bollinger. "It's a mistake to say it's just a 'stentless stent,'" he says.

For example, the technology is being tested in patients undergoing kidney dialysis, which involves removing blood through an artery, filtering it through a machine, and then returning it through a vein. In order to get high blood flows, surgeons often make an access point by connecting an artery directly to a vein, creating a so-called arteriovenous fistula. The vessels can also be connected with a plastic tube, or shunt.

However, the surgical trauma can damage the endothelium and cause intimal hyperplasia. Patients with shunts are particularly vulnerable to the problem. As a result, blockages often form where the grafts attach to the vein after just a few months. "The biggest cause of hospital admissions for patients with end-stage renal disease is the issue of access," says Alejandro Alvarez, an interventional nephrologist at Saint Louis University. Expecting technologies like Pervasis's gel "to make fistulas last 20 years is unreasonable," he says. "But if you can delay admission by six months in the majority of patients, that is a huge savings."

For cardiovascular patients, Bollinger says that the gel could "potentially work hand in hand with a stent or without a stent."