ARCHIVED - Advanced material shows promise for replacing diseased arteries
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March 02, 2009— Boucherville, Quebec
NRC has developed a novel biocompatible material that may allow surgeons to replace diseased coronary arteries and other narrow, blocked blood vessels with synthetic grafts.
Coronary artery and peripheral vascular diseases are the leading cause of death and hospitalization in Canada, at a total annual cost of $19 billion. The standard treatment for patients with blocked peripheral blood vessels of less than 6 mm in diameter is a bypass operation, involving transplanted veins. However, this is not an option when vital coronary arteries (located inside the heart) get blocked.
When diseased blood vessels exceed 6 mm in diameter, such as arteries found in the lower limbs, they can be replaced by artificial blood vessels. "These perform fairly well, but they're not a long-term solution," says Dr. Martin Bureau, leader of the Advanced Polymer Composites Group at the NRC Industrial Materials Institute (NRC-IMI) in Boucherville, Quebec. "Currently available graft materials tend to be stiffer than real blood vessels and more prone to occlusion" he explains.
"The 'holy grail' in this field is to achieve a small-diameter synthetic graft that will not be prone to occlusion (non-thrombogenic) with mechanical properties similar to a real artery, so the blood flows smoothly," adds Dr. Bureau. "Between the systolic and the diastolic pressure, our arteries contract and dilate. If you can't reproduce that rhythm in a synthetic graft, there will be turbulence, which will eventually lead to an arterial blockage, a phenomenon called 'intimal hyperplasia'. The walls of an artificial artery need to be flexible enough to prevent this."
"Another challenge is to design materials on which platelets will not adhere, so the synthetic grafts won't become obstructed," says Dr. Bureau. So far, no one has achieved these goals for smaller-diameter artificial blood vessels, such as for coronary grafts of 1-2 mm diameter. "This is a huge and virtually unexplored market."
Now, NRC-IMI researchers led by Dr. Abdellah Ajji have developed a unique process with potential for making narrow artificial grafts using the same type of polyester fibres, such as Dacron, currently found in large-diameter grafts. "We use a manufacturing process based on 'melt blowing' to fabricate webs of non-woven fibres," says Dr. Bureau.
"Building on this, we can make very thin webs and then adjust their orientation to make a stack, which measures from 1 to 10 microns in thickness," he says. "This technique allows us to construct grafts that perfectly match the flexibility of normal human arteries. We then treat the surface with polyethylene glycol to give these grafts non-thrombogenic (non-clotting) characteristics."
The NRC team, which includes Dr. Maria Moreno of the NRC Institute for Biological Sciences in Ottawa, filed a patent in June 2008. "So far, we've done animal studies for biocompatibility and we hope over the next year to begin testing our grafts in pigs," says Dr. Bureau. He and his colleagues are working closely with École Polytechnique; the Montréal Heart Institute (University of Montréal); Coronéo, a Montréal-based company interested in using their non-woven technology to replace aortic arteries; and Tissue Growth Technologies, a U.S. company developing bioreactors for tissue engineering. The NRC team recently obtained funding from the NSERC Strategic Partnership Program to develop tissue-engineered vascular grafts.
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National Research Council of Canada
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