. . . . . "A positioning element may be a hook or claw-like structure that may penetrate into or catch on the surface of the lumen wall, as in FIG. 5B, an expanding element that causes the lumen-traveling device to form a pressure-fit with the lumen, as in FIG. 8B, an adhesive material or glue, as in FIG. 5A, or other structure or material that may engage the lumen wall." .