Patients with sickle cell disease often suffer from painful attacks known as vaso-occlusive crises, during which their sickle-shaped blood cells get stuck in tiny capillaries, depriving tissues of needed oxygen. A team of researchers from MIT and Carnegie Mellon University have developed a microfluidic device that can analyze the behavior of blood from sickle cell disease patients. This device can measure how long it takes blood cells to become dangerously stiff, making them more likely to get trapped in blood vessels. The researchers say that future versions of this device could be used to predict and prevent vaso-occlusive crises. It could also help researchers test the efficacy of new drugs for sickle cell disease, which occurs in about 300,000 newborns per year, more than 75 percent of them in Africa. The best drug now available, hydroxyurea, works for only about two-thirds of patients.