Finding the right polymer coating was the key to the Taxus stent, a groundbreaking drug-delivery product from Boston Scientific Corp. used to treat coronary artery disease, top executive James Tobin said during Antec 2005.
Boston Scientific has sold more than 1 million Taxus stents, at an average price of $2,500 each, Tobin said. The Food and Drug Administration approved Taxus in early 2004.
Tobin, Boston Scientific's president and chief executive officer, was keynote speaker May 3 at the Society of Plastics Engineers annual conference. The company in Natick, Mass., does much of its own plastic processing. Tobin said Boston Scientific runs 100 injection molding machines and 75 extruders, plus equipment to make the balloons for angioplasty.
A stent is a tiny metal scaffolding used in angioplasty. Less invasive than bypass surgery, angioplasty uses a catheter that inflates a tiny balloon to open a clogged artery, leaving behind the stent. Tobin said in about a decade of using bare-metal stents, about 25 percent have failed and required new surgery.
The key to the drug-delivering stents - made today by only two companies, Boston Scientific and the much-larger Johnson & Johnson - is that they slowly release medicine that keeps the artery open. Tobin said the worldwide market is $5 billion to $6 billion.
Boston Scientific and other companies are studying all-plastic stents, but in his speech, Tobin only talked about polymer-coated, stainless-steel Taxus.
One big challenge, Tobin said, is that coronary arteries are extremely sensitive to foreign material. Boston Scientific looked at 20-30 different polymers before coming up with one called SIBS, which Tobin described as an elastomeric block copolymer of polystyrene and butyl rubber. The coating had to be stable, could not break down inside the body or cause inflammation, be able to be sterilized and be processible.
``The SIBS polymer was one of, if not the most critical element that made it all possible,'' Tobin said.
The polymer coating and drug are mixed together and coated on the surface of the stent.
Tobin said SIBS was originally developed by a professor at the University of Akron in Ohio, for industrial use as a thermoplastic elastomer.
A company obtained a license to use SIBS in medical applications, and Boston Scientific picked up that license when it bought the company in 1998.
When Boston Scientific was developing Taxus, SIBS was not commercially available, so the company worked with a supplier to begin production quickly. Tobin credited the University of Massachusetts at Lowell for helping with the process.
Tobin told the Antec audience that Boston Scientific plans to make SIBS in-house so it has a second supply of material. The company manufactures the stents at plants in Minnesota and Ireland.
SIBS, Tobin said, ``is arguably the most challenging part of our commercialization effort for Taxus.''
``It's actually easier to find a drug that works than it is to find a polymer that works.''