A graduate student and her colleagues from Scotland developed a new way to test artificial cardiac valves using curdled milk as a blood substitute. The results look encouraging:
In 2000, Aimee Martin set out to find a research project for her graduate studies in bioengineering and stumbled upon a group of Scottish engineers looking for a way to test medical devices with a cheap substitute for human blood. Since the mid-1980s, the group had been testing a protein-rich liquid that flowed like blood, splattered like blood and–crucially–congealed like blood.
The mystery ingredient? Milk.
Scotland is a long way from her native Massachusetts, but Martin was intrigued. With the help of an NSF Graduate Research Fellowship, she joined the group of researchers at the Institute for Materials and Processes at Scotland’s University of Edinburgh. They were beginning to study whether pumping milk through an artificial heart chamber could pinpoint flaws in mechanical valves.
Existing methods for testing heart valves were expensive and sometimes failed to detect problems that surfaced later in clinical trials.
Using blood outside the body, Martin says, is tricky. “Blood wants to clot when it’s exposed to air. To prevent it from doing that, you have to add an anticoagulant, and then you have to add a chemical right back into [the blood] before the experiment to initiate clotting,” she explains. At that point, “you’re no longer working with human blood in the native state.”
To avoid these problems, researchers have traditionally tested artificial valves in large mammals like sheep before conducting human clinical trials. But raising the test animals is expensive, and they provide an imperfect substitute for the human cardiovascular system.
By the time Martin joined the lab, the Edinburgh researchers had already shown that milk–after the addition of a curdling agent like rennet–flows and clots like blood. One of Martin’s first contributions was to improve the device for testing artificial valves. She designed a breadbox-sized machine rigged to circulate blood much like the heart does.
“I made it much more like a heart, in terms of shape and flexibility,” than previous heart chamber models, Martin says. “It could expand and contract like the human heart.”
Next, Martin tested 12 valve models inside the heart simulator, paying special attention to the positions on each valve where milk tended to clump. After testing each valve, Martin compared her results with what was already known from human clinical trials.
In each case, milk congealed in the same locations on the valves where blood had been shown to clot in clinical trials. By testing future heart valve models with the milk system, Martin hopes, researchers will spot defects before clinical trials begin–saving money and reducing the risk to patients.
Full statement by the National Science Foundation…