Building Safer, Superior Stents

A computer model simulates how drug-eluting stents behave in arteries, enabling the design of better devices.

Millions of drug-eluting stents are implanted in coronary arteries worldwide, yet little is understood about how the drugs are actually distributed to the surrounding tissue. The drug coatings can cause the formation of blood clots in the arteries--an often fatal condition. Now researchers at MIT have built a computer model to predict the performance of different types of stents under a variety of conditions.

Stent profiling: The image above is taken from a computer model that simulates the flow of drugs from stents--metal meshes that keep arteries open. Inside the arterial wall of this 3-D image (blood flow is from left to right), the stent is releasing the drugs at a uniform concentration, but the cells closest to the upstream region of the arterial vessel receive less of the drugs than other areas do. Red represents the highest concentration of drug release, blue the lowest. This kind of differential drug-distribution pattern can sometimes contribute to blood clots. Credit: Vijaya Kolachalama, MIT

Multimedia   Watch a demonstration of the stent computer model.

"The model allows us to change the stent--the design, dimensions, materials, drug, and the way it is released," says Elazer Edelman, a professor of Health Science and Technology (HST) at MIT and the principal investigator of the project. "Then we can place the stent, alone or adjacent to other stents, in arteries with different diseases or in different natural states. By rapidly considering thousands of different design features, the model can do things that can otherwise not be done."

Kinam Park, a professor of biomedical engineering at Purdue University, in West Lafayette, IN, says that Edelman is a "pioneer" in modeling drug-eluting stents--metal meshes coated with drugs, such as anti-scarring or anti-inflammatory medication. In addition to releasing drugs, the stents act as physical supports to help keep an artery open. The drugs tend to diffuse into the bloodstream at an unpredictable rate, despite many efforts to build polymer compounds to control drug release. "There are some areas with too much drug, and areas where there are no drugs," says Park. "Tissue can be damaged, and patients can die. The model is the first to test the drug-releasing profiles of stents and is critical for the design and development of new, better stents."

Story continues below

The computer model simulates the dynamics of blood flowing around a stent in order to evaluate how the drug is released from the stent and dispersed in the arterial wall. The researchers started with a two-dimensional stent and vessel design and created an algorithm that solves the fluid-flow and drug-delivery equations for each tiny segment of the domain. Now, they can do 3-D simulations to better show the stent's drug-eluting profile.

"The model can show exactly what the drug distribution is as a function of time," says Park. So researchers can model the different states of the arteries, visualizing where the drug will be deposited and what will happen.