Originally Published MDDI May 2005

R&D DIGEST

Heather Thompson

Plastic tubing that emits nitric oxide could be beneficial for replacing blood vessels. According to researchers from the Institute of Bioengineering at Rice University (Houston), the nitric oxide gas helps stimulate growth in the blood-vessel lining and discourages blood clots from forming. The team has been experimenting with modified plastics and has built tubes that are less than 6 mm across.

The team used polyurethane, which is already used in coronary artery bypass surgery. However, tubes that are less than 6 mm in diameter often give rise to the formation of blood clots. If such clots break off, they can damage the brain or other organs.

To minimize this potential risk, the polyurethane used by the Rice team was modified with a chemical group. As the chemicals decompose in water, they produce a nitric oxide byproduct.

Bioengineer Jennifer West, one of the project's researchers, notes that anticoagulants such as nitric oxide are commonly used. She explains that nitric oxide stops platelets from sticking together and strengthens the cells lining blood vessel walls. “That's the remarkable thing about nitric oxide,” she says. “It has all these beneficial effects on different types of tissue.”

But West also believes that there is a need for more-localized effects, as nitric oxide and other anticoagulants can easily lead to unwanted bleeding in other parts of the body. By using the artificial vessel tube to deliver the gas, the researchers can be assured that only the affected areas get a dose of nitric oxide.

For the experiment, the researchers studied the plastic's effect on platelets and cultures of blood-vessel and muscle cells over a two-month period. The release of nitric oxide gas was high during the first two days and then faded slowly with time. According to the group, nitric oxide kept platelets from sticking together, boosted blood-vessel cell numbers, and limited muscle-cell growth.

During the experiment, the team reported an increase in cyclic guanosine monophosphate (GMP) in cell cultures. The GMP compound affects enzyme activity and gene expression. Because no GMP levels were reported to increase after the tubing had shed the nitric oxide, the team concluded that nitric oxide, and not polyurethane, triggered the release.

The team chose polyurethane because it can be used for multiple applications and is inert. According to West, it may also be able to integrate easily with surrounding tissues. “Polyurethane is more flexible than other plastics used in grafts,” she says.

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