Angioplasty remains one of those marvels of medicine: A doctor snakes a tube through the body, inflates a tiny balloon to break up a blood clot and then usually leaves behind tiny metal scaffolding, a stent, to keep the artery open.
There's always been one problem, though. The body treats the stent as a foreign invader. It tries to cover it up, and over time, that can wind up clogging the artery all over again.
Some scientists and medical-device companies think they see a way to use plastics to overcome that. Several firms are working on a polymer stent that remains in place for a while and harmlessly dissolves into the bloodstream after it has done its job.
There's a lot of interest: Boston Scientific Corp. of Natick, Mass., in November invested in a new California firm working on a plastic stent, scientists in Japan are developing their own biodegradable design from poly-l-lactic acid plastic and Indianapolis-based Guidant Corp. in April bought the remaining stake of its own bioabsorbable stent joint venture.
The interest isn't limited to plastic: A German company is working on a bioabsorbable model made from metal.
``The whole idea of having a device in the body that solves an issue at a particular time and then reabsorbs away, that's the Holy Grail,'' said Mark Landy, a medical-device analyst with Susquehanna International Group in Bala Cynwyd, Pa.
While investment is flowing into the technology, it's far from certain that the reabsorbable plastic stents will work, and some firms seem to be making defensive investments to protect their existing stent business, Landy said.
The companies say they are working intently, however, and if they do succeed, the market potential is sizable. One stent maker estimates reabsorbable designs could capture $1 billion of the $5 billion U.S. market.
Bioabsorbable designs may be able to expand the use of stents. Since arteries sometimes can clog up again after angioplasty, reabsorbable stents could be used repeatedly in the same location, something that's difficult with permanent stents.
For now, the work generally is being done quietly. Beyond the few companies that have gone public, Landy said there are others that have contacted him but have yet to publicly acknowledge what they are doing.
Reva Medical Inc. of San Diego has been testing its plastic stents in pigs, and hopes to start human trials in 18 months, said President Robert Schultz. Boston Scientific made an undisclosed investment in Reva in November, and has an option to buy the company.
``We're confident we'll have a game-changing technology,'' he said. ``Of course, we're proving out the technology now.''
The company uses a proprietary laser process to cut the stents from a flat sheet of plastic, but if the product takes off, it's looking at injection molding and other processes to produce commercial-scale numbers, he said.
The U.S. government reports that about 1 million stents are used in coronary artery patients annually. About 2 million angioplasty surgeries are performed each year around the world.
Molding interest
The potential market is starting to attract plastics companies as well.
Injection molder and medical-device manufacturer Midwest Plastic Components in Minneapolis has experimented with using poly-l-lactic acid for an injection molded bioabsorbable stent, and is working with unspecified companies that are trying to develop the technology, said Kyle Nevala, account executive for medical/ biomaterials.
Nevala, who was interviewed at the Medical Design & Manufacturing West show, held Jan. 10-12 in Anaheim, said MPC started exploring the market because it has a background in using PLA to make implantable products. During the past five years, the company has manufactured more than 25 bioabsorbable components for procedures ranging from screws that anchor sutures for ligament repairs to products used in cosmetic and reconstructive facial surgery.
The company designed a rough prototype of a bioabsorbable stent and was running it on an Engel press at the show.
MPC sees more sophisticated molding projects like that one as examples of the kind of manufacturing work that will remain in the United States.
``The way to stay alive is by hitting unique markets,'' Nevala said. ``A unique item is bioabsorbable polymers.''
Mimicking PC
While MPC is experimenting with PLA, Reva's stent takes a common amino acid in the body, tyrosine, and marries it to a polymer structure that mimics polycarbonate, as a way to create a strong material. The polymer was developed over nine months at the New Jersey Center for Biomaterials at Rutgers University.
``We combined the positive properties of a polycarbonate, which is its strength and stiffness, with the use of a biocompatible and biodegradable monomer,'' said Rutgers Professor Joachim Kohn. ``We can take the design of an industrial plastic and replace the monomer with a biologically derived monomer.''
Kohn said the polymer design process has broad implications for developing other plastic biomaterials. He said he took computer models used by the pharmaceutical industry to speed up drug development and applied it for the first time to plastics.
There were about 10,000 possible compositions of the material, he said, meaning that researchers would have had a one in 10,000 chance of finding the right combination randomly. But applying the computer models reduced that to nine very likely compositions.
``We only needed to synthesize nine materials to find what we would consider a polymer that is very close to ideal,'' he said. ``The discovery phase was six months. You sometimes search many, many years trying to find a polymer that could fit your application.''
Researchers had to make some changes, like modifying the material so it could be viewed using an X-ray. But Kohn said the research method has the potential to reduce the cost and risk of developing new biomaterials.
Kohn's work earned him the 2003 Clemson Award for Basic Research from the Society of Biomaterials, and he wrote an article on the stent project for the November issue of Nature Materials magazine.
Another advantage of the plastic stent is potential for better drug delivery, Reva's Schultz said.
While it now is common to have plastic-coated metal stents plastic as a way to dispense drugs in the body - the plastic is laced with pharmaceuticals and engineered to release them slowly - an all-plastic stent could mean better drug delivery, he said.
While analysts like Landy said it remains to be seen whether the technology will prove itself and absorbable stents will capture a big chunk of the market, Schultz said interest is picking up.
``It's one of those things that three years ago, if you talked to someone about a plastic reabsorbable stent, they would say, `Why do you want one?' '' Schultz said. ``A year later, they said maybe, and now, yes.''
