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April 7, 2004 — In the beginning, there was the stent. And it was good for clogged arteries — at least at first. Then came the drug-releasing stent. It not only kept arteries free of plaque, but also reduced the risk of scar tissue forming around the implanted, pop-up scaffolding.
Now, researchers have designed a “stentenna,” a micromachined stent integrated with microsensors for wireless monitoring of blood flow and pressure.
The battery-free devices could transmit advance notice of problems to patients and their doctors.
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The stentenna has been successfully placed in a mock artery by inflating a balloon used in angioplasty. It’s also designed to be compatible with standard stents and procedures, according to a team from the University of Michigan’s (U-M) Department of Electrical Engineering and Computer Science.
By adding a drug that is released — the industry term is “eluted” — from within special polymers placed on a stent, the rate of renarrowing, or restenosis, drops to between 5 and 10 percent. That’s a big improvement over first-generation bare-metal stents, which had restenosis in 30 to 35 percent of patients within six months. Still, the drug-eluting stent doesn’t eliminate all concerns, said Yogesh Gianchandani, a U-M associate professor and specialist in stent research and development.
“The problem they do not address is continuous monitoring,” he said. “Until the tissue has healed form the surgery … you need chronic monitoring; and (it could provide) extended health care for patients highly at risk.”
One key advantage of the stentenna is that it would be powered by radio waves, so a patient could check his blood flow or pressure on a hand-held radio-frequency device.
Gianchandani said the stentenna concept also is compatible with drug-eluting stents. That’s an important selling point for the new devices, given the trends: The U.S. stent market is expected to grow from about $2.5 billion in 2003 to $4.5 billion in 2005, with $4.4 billion of that coming from drug-eluting stents, according to Waltham, Mass.-based Decision Resources Inc. Current and future drug-eluting stent makers include Johnson & Johnson’s Cordis Corp. (News, Web), Boston Scientific Corp. (NYSE: BSX, News, Web), Medtronic Inc. (NYSE: MDT, News, Web), Guidant Corp. (NYSE: GDT, News, Web) and Abbott Laboratories.
The stentenna already has broadcast some strong signals to investors. Gianchandani said venture capital funds have expressed interest, and he and his colleagues are evaluating the options. They plan animal trials shortly and hope to be cleared for the market within five years.
At the same time, Gianchandani and his colleagues are developing new ways to make stents. Unlike the traditional approach, which involves laser machining stainless steel tubes, his team starts with a flat sheet of steel, and makes patterns by microelectrodischarge machining — a process whereby material is removed by a high energy discharge between an electrode and material while immersed in a dielectric fluid. The new method, compatible with integrated circuit technologies, allows them to make a large number of stents at the same time in the exact same way.
The stentenna combines the new fabrication approaches with cutting-edge pressure sensors developed by the research team of Ken Wise, an engineering professor and director of the National Science Foundation’s Wireless Integrated MicroSystems (WIMS) Engineering Research Center at U-M.
Although the result is a combination of the work by two professors and their students, the WIMS center played a key role in providing the right push — and pull, say Gianchandani and Joe Giachino, the center’s associate director.
“It shows some of the strength of the center in combining work by various groups … to assist a need,” Giachino said.
“Two years ago, we didn’t even have a basic stent.” Gianchandani said. “You’re looking at basically 24 months of work: We’ve gone from regular stents to flow-sensing stents — and we have many more things in the works.
“It wouldn’t have happened this fast if it wasn’t for the existence of this center pulling together people, minds and know-how.”