A membrane for covering a peripheral surface of a stent is provided, the membrane including a plurality of line openings formed therein. Each line opening may be a straight line opening, for example in the form of a slit, a curved line opening, or any line opening of a suitable shape or curvature, e.g. U-shaped or V-shaped. Blood pressure opens the slits to allow blood to flow through the membrane, while curved line openings create a flap in the membrane that can open to allow blood to pass through. According to further embodiments of the present invention, a method of forming a membrane on a stent and a device for use in a blood vessel are provided.