Researchers have been puzzled in recent years by observations that drug-releasing stents (mesh-like tubes implanted to hold patients' coronary arteries open) can increase the likelihood of blood clots and heart attacks. Now, a mathematical model developed by MIT engineers can predict whether particular types of stents are likely to cause life-threatening side effects. The model helps explain why some stents are better than others, and could predict which stents are predisposed to cause clotting.