A device for sealing an opening or puncture in the wall of a blood vessel, duct or other lumen of a living being. The device includes an elongated tubular body having an outlet at the distal end thereof and which is arranged to be inserted, such as percutaneously, through the puncture in the blood vessel so that the outlet is located within the vessel's interior. An expandible closure is disposed within the tubular body and is formed so as to be held in a compact configuration therein. The tubular body also includes ejecting means for forcing the closure out of the outlet into the interior of the blood vessel, whereupon the closure automatically expands to form an enlarged engagement surface. A retraction filament is secured to the closure for pulling it to the puncture after the tubular body has been withdrawn from the puncture so that the engagement surface of the closure means hemostatically engages the inner surface of the blood vessel contiguous with the puncture. The filament held taut and taped or otherwise secured in place on the patient's skin to hold the closure in position. The closure and filament are each formed of a biodegradable material to enable the closure to be left in place. Preferably the closure also includes a non-thrombogenic coating on its surface. The closure is constructed so that when it is opened and is in place sealing the puncture in the blood vessel it doesn't appreciably block the flow of any blood through the blood vessel.