Boston Scientific Corp has received approval from the FDA to market its new WallFlex Biliary RX covered stents. The stents are designed to treat clogged bile ducts in cancer patients. The liver excretes bile, which the body uses to help digest food. The WallFlex Biliary RX uncovered stent was cleared by the FDA in 2006. The new covered version of the stents was also approved by European regulators.