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Back in circulation: Why certain polymers improve blood flow

Simulation of a suspension of red blood cells with added polymer molecules flowing through a small channel. The polymer molecules are the thin lines and are color-coded by how highly stretched they are.
Simulation of a suspension of red blood cells with added polymer molecules flowing through a small channel. The polymer molecules are the thin lines and are color-coded by how highly stretched they are. Larger Image

With funding from the National Science Foundation, a University of Wisconsin-Madison engineer will study whether "drag-reducing" polymer molecules enhance flow through some of the tiniest blood vessels in the human body.

Smaller than the diameter of a human hair, capillaries are embedded within the body's organs and are important for distributing blood throughout the tissues.

"One of the issues is making sure that, under situations where there's a disease or injury, blood is still able to get to where it needs to be," says Michael Graham, Harvey D. Spangler Professor of Chemical and Biological Engineering at UW-Madison.

Drag-reducing polymers show particular promise for improving circulation in situations that involve blood loss. "Experiments in lab animals have demonstrated improvements in survival rates if the animals were resuscitated with a solution containing these polymer molecules," says Graham.

Drag-reducing polymer molecules dissolve in the blood. As red blood cells flow through blood vessels, they collide—an action that likely stretches the polymer molecules, says Graham. "If the polymer molecules are coiled, they don't do anything interesting," he says. "If they're stretched out, they can exert very large forces on the fluid and then alter the blood flow."

Graham has developed and uses a variety of computational and theoretical tools to study such complex fluids as gels and molten plastics, among others. He will apply these tools to study flowing blood—itself a complex fluid—and its individual components, and then compare the results with experimental observations. For the experiments, Graham will design novel methods for quantifying flow resistance through microenvironments such as capillaries.

The research could provide investigators greater understanding of how drag-reducing polymers modify blood flow and, as a result, help improve treatments for people with circulatory disorders.

However, Graham also plans to use his tools to study the fate of drug molecules in the bloodstream—for example, tracking a particle designed to deliver a drug to the coronary artery walls. Additionally, he will extend the methods to improving flow-based cell-separation techniques that enable researchers to study, for example, healthy versus cancerous cells.

Funded in 2009, Graham's proposal was among those that benefited from the American Recovery and Reinvestment Act, which provided nearly $3 billion to the National Science Foundation. NSF devoted about two-thirds of its stimulus allocation to increasing its percentage of highly rated research proposals that received funding.

In addition to the research, Graham's grant also will support an undergraduate student, who will develop educational outreach materials related to how organisms move in fluids of varying densities. These materials will build on "How to swim in corn syrup," a series of three YouTube videos an undergraduate and postdoctoral researcher created under Graham in 2007.

Renee Meiller
6/3/2010