Stents are responsible for making angioplasty a viable alternative to bypass surgery for many patients with coronary artery disease. After pushing plaque out of the way with a balloon, doctors insert one of these tiny metal mesh tubes inside the artery to prevent the vessel from closing. But now that so many heart patients have stents, issues have emerged. Plaque or scar tissue sometimes grows inside bare-metal stents, requiring repeat revascularization. Coating the stent with a slow-release medication to make a drug-eluting stent retards tissue regrowth, but attracts life-threatening blood clots (thrombi), requiring patients to take anti-clotting medications indefinitely.