However, those materials have some characteristics that may limit their usefulness. "In some instances, the chemistry in the polymer is sensitive to moisture and heat, so whether it can be easily commercialized is one of the big issues," he said. In addition, the polymer coating must be very thin for most biomedical applications, which limits the amount of nitric oxide that can be stored and released from the thin coating on the sensor surface.

The new approach is to make polymers that generate nitric oxide from compounds called nitrosothiols found in the bloodstream. The key to doing this, the researchers found, is copper.

"It turns out that copper ions can act as catalysts to take nitrosothiols and generate nitric oxide from them," said Meyerhoff. So the U-M team has been creating polymers that include a copper ion-containing complex. They've demonstrated that complexed copper ions do have the desired catalytic effect when incorporated into a polymer and that they remain effective even after soaking in blood for up to three days, suggesting that sensors coated with nitric oxide-generating polymers might have longer lifespans than those that release nitric oxide. Next, the researchers plan to test the new polymers to see if these materials are as effective at preventing clots as the nitric oxide-releasing polymers they developed earlier.

Other questions to explore are how much of the raw materials for generating nitric oxide are present in blood, and whether the amount varies from one person to another. "The device might work with me, but if you don't have enough of the reactive species in your blood, then it may not generate adequate nitric oxide levels and it may not prevent clotting," said Meyerhoff. To get at these questions, the researchers have developed a way of measuring the amount
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Contact: Nancy Ross-Flanigan
rossflan@umich.edu
734-647-1853
University of Michigan
15-Mar-2005