Bioresorbable polymeric stents near clinical stage

After more than 20 years of development, bioresorbable coronary stents are close to commercialization, setting up what is sure to be a hotly contested battle for a multi-billion dollar market.

One of the key players is the Absorb bioresorbable vascular scaffold (BVS) that restores blood flow by opening a blocked artery and providing support to the vessel until the device dissolves. Once in place, Absorb dissolves in approximately two years, leaving patients with a treated vessel free of a permanent metallic implant, according to Abbott Laboratories (Abbott Park, IL).

Abbott's bioresorbable stent has received an important regulatory clearance in Europe.

"Absorb represents the best in scientific innovation, as it has the potential to change the way physicians practice medicine and improve outcomes for their patients," says Robert B. Hance, senior vice president, vascular, Abbott.

Absorb is being evaluated in more than 40 clinical centers in 20 countries around the world. Earlier this year, Absorb received the CE Mark in Europe for the treatment of coronary artery disease. In the United States, Absorb currently is under development and is not available for sale.

Another important polymeric contender comes from Reva Medical (San Diego, CA).

The Brazilian Ministry of Health and a German health authority, this year authorized clinical trials to evaluate the safety of Reva's ReZolve Bioresorbable Coronary Stent, which is also designed to restore blood flow and promote arterial healing, then gradually dissolve, leaving nothing behind. "We are extremely pleased to have accomplished this very important regulatory milestone and look forward to entering the clinic soon," says Robert Stockman, CEO of Reva.

Proprietary polymer

The ReZolve stent combines a proprietary design with a proprietary polymer that is metabolized and cleared from the body. The ReZolve stent is designed to offer full x-ray visibility, providing clinically relevant sizing. In addition, by early encapsulation of the stent in the artery tissue coupled with the loss of stent structure over time, the ReZolve stent may reduce the incidence of late-forming blood clots, or thrombosis, a rare but serious problem associated with drug-eluting metal stents currently in wide use.

Reva is backed by Medtronic and Boston Scientific, major players in stents and medical devices.

Final regulatory approval of the technology in the United states could still be years off, but they could be in widespread use elsewhere in the world within two years if the clinical trials are successful. Stents help stabilize diseased arteries by propping them open and restoring blood flow.

The first bioresorbable stent was developed by researchers at Duke University in the early 1980s.

Reva scientists designed a proprietary polymer that could withstand the expansion of the stent inside a coronary artery. In a filing with the Securities and Exchange Commission, Reva states: "Our proprietary 'slide and lock' design enables the ReZolve stent to be expanded with minimal deformation of the polymer; therefore, maintaining the strength of the material. Our proprietary polymer is also less prone to breaking than other polymers that have been tested for this application, and we believe the strength is maintained during the critical 90-day healing period following stent placement."  Degradation rates can be programmed in the polymeric formulation.

Reva's polymer is an iodinated, tyrosine-derived polycarbonate that was originally developed at Rutgers University in New Jersey. A target dose of 80 µg of sirolimus is coated onto the outside surface of the ReZolve stent using a polymer solution containing the drug. The purpose of the drug is to reduce the risk of restenosis, or restriction of blood flow.

Abbott's Absorb is made of polylactide, a bioplastic widely used in medical applications.




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