By Joe Carlson •

The skinny spring trapped inside the tube on the conference table in front Jay Kokate may someday prevent thousands of diabetic patients from having their legs and feet amputated.

At least, that's the hope. The "spring" is not a spring, of course, but an advanced medical device designed by Boston Scientific Corp. engineers in Maple Grove. Clinical testing of a metal mesh tube called Eluvia has come back with some of the best performance data ever seen in a stent intended to be used in the legs.

The reason that the stent is confined to a tube, and the reason hopes for the device are running high is because the Eluvia is coated with a generic drug called paclitaxel embedded in a specialized polymer that allows the chemical to be slowly released for up to a year. Kokate, one of the engineers who designed the stent, doesn't want to get it on his hands.

"We wanted to make sure that it was a sustained release for at least six months to a year," he says, noting that Boston Scientific officials believe this slow-release system is the reason why a recent clinical trial found that 94 percent of patients with an Eluvia in their leg avoided the common complication of having to return to the hospital for reopening of their arteries within nine months.

An estimated 202 million people worldwide have a health condition called peripheral artery disease (PAD), in which arteries in the legs narrow or become blocked, limiting or even cutting off blood supply. Symptoms include pain, throbbing and swelling of the legs. Many of the worst cases can lead to amputation in the lower extremities, particularly in patients with diabetes.

A study published in 2012 in the Journal of the American College of Cardiology reported that about 3 million Americans were hospitalized for PAD between 2000 and 2008, and 186,000 of them had lower extremities amputated as a result. The proportion of PAD patients getting amputations dropped steadily over the span of years in the study, but as of 2008, the rate of incidence still stood at 5,790 per 100,000 patients with PAD.

Stents are some of the most common medical devices in procedure rooms across the world, but most are used to open and repair arteries on or near the heart. Typically a doctor makes a small incision in the leg and then snakes a thin wire called a delivery catheter to the damaged or blocked artery site, where the stent is unsheathed from the tube and inflated inside the vessel using a narrow medical balloon. Most are permanent once they become covered with scar tissue, leaving them to become a kind of metal scaffold holding the vessel open.

To combat the common problem of stented vessels re-closing, medical device companies have developed the "drug-eluting" stent, releasing drugs like paclitaxel that can prevent re-narrowing.

While many of the medical concepts are the same with narrowed arteries in the legs, designing a device to fit them is much more challenging because of the weirdly contorted shapes of people's peripheral leg arteries and the long blockages that can form in them. The first drug-eluting peripheral vascular stent in the U.S. — the Zilver PTX, made by Indiana's Cook Medical — wasn't approved by the Food and Drug Administration until 2012.

Last month, Boston Scientific saw its first patient implanted with the company's new peripheral stent, called Innova, in a procedure performed in the Chicago suburb of Oak Lawn. The device comes in many sizes, including one that is up to 8 inches long, but Innova is a bare metal stent.

An Eluvia stent is the same as an Innova, except it's covered with a paclitaxel-embedded polymer. Boston Scientific officials think their device is showing stronger rates of "patency" — vessels remaining open after procedure — because the Zilver releases its drug over the course of a month or so. Most re-narrowing of the arteries is reported between six months to a year after the procedure.

"We had this goal of getting to 90 percent patency. Now that we've shown this 94 percent, we've exceeded that goal," said Jeff Mirviss, president of Boston Scientific's peripheral interventions business. Restenosis, or re-narrowing of arteries, "is a pretty well-known part of the disease state. And we think that we have designed a device that could potentially solve restenosis in the leg."

Later this month, Boston Scientific is expected to publish Eluvia's one-year patency rates from its ongoing trial of 57 patients in Europe and Australia. The company plans to launch its much larger pivotal trial of Eluvia in the U.S. and other countries later this year, with the goal of getting FDA approval within three years.

Joe Carlson • 612-673-4779

Twitter: @_JoeCarlson