Edelman and HST postdoctoral associates developed a mathematical model that helps to forcast whether particular size and shape of stents affects blood flow and drug distribution.
The model "helps explain why some stents are better than others, and could predict which stents are predisposed to cause clotting," said Elazer Edelman, the Thomas D. and Virginia W. Cabot Professor of Health Science and Technology (HST) and senior author of a paper on the work appearing as the cover story of the Jan. 5 issue of the Journal of Controlled Release.
The drugs such as paclitaxel and rapamycin effectively obstruct tissue growth that could slow down flow, but can lead to unforeseen side effect of increasing the risk of blood clots and heart attacks. However, drug-releasing stents have been proven a "double-edged sword," Edelman said.
This paper explains why: Stents affect the fluid dynamics of blood flowing past them and cause drugs to accumulate in certain areas. Too much drug buildup promotes clot formation.
The MIT researchers model shows that the dynamics of blood flowing around a stent is similar to whitewater rapids, said Edelman. When water in a river flows over a rock, some of the water strikes the base of the rock, flies up in the air and comes back down, instead of flowing over the rock. This water continuously recirculates in the same area.
The same thing happens when blood flows across a stent: Drugs tend to accumulate and spin around in the recirculation zone. This is most likely to happen with stents that protrude further into the artery. "Until now, the degree to which recirculation zones impact the distribution of drugs was not appreciated," said Edelman.
The mathematical model established for the first time successfully predicted stent performance based on changes in arterial blood flow and design. The MIT researchers developed a model to design stents that allow drugs to be more evenly distributed throughout the area.
The model could also help the FDA in its approval processes, by helping regulators figure out which stents are most likely to be safe or harmful, based on their size and shape, which controls how they will affect blood flow.
Davis Arifin, a graduate student in the MIT-Singapore Alliance, is also an author of the paper. This research was funded by the National Institutes of Health.
