a secure stent for maintaining a lumenal opening constructed preferably as a tubular structure of niti material or bioabsorbable polymers . the circumference of the tube is preferably in the shape of a polygon in contrast to the circular or oval shape of a body lumen into which the stent is to be placed . the polygon shape and ribs provides interference with the lumen wall and resists stent migration . the diameter of the stent tube is configured with each end enlarged providing flanges for interference with a lumen wall . the central portion of the stent is also bulged out to an increased diameter to provide an enhanced lumen wall resistance to avoid migration . in addition , the locking feature of a ribbed structure prevents the stent from collapsing , and thereby maintains the lumen opening . the stent is preferably constructed from polymers , including bioabsorbable polymers , and / or super elastic materials . the bioabsorbable polymer construction aids removal by causing the tube diameter to collapse . removal of the stent can therefore be accomplished by simply grasping the proximal end of the stent . alternatively , a stent constructed entirely of bioabsorbable material will eventually be entirely absorbed , avoiding the need for removal . alternatively , the stent can be preferably constructed of niti or other shape memory material and set in the desired shape at a high temperature . installation is accomplished by cooling the stent to the malleable martensite state and winding it on a small diameter mandrel of an insertion / removal tool . the compacted stent is then placed in a probe and inserted in a body lumen , whereupon it is heated to an austenite state where it regains its spring tension , forcing it back toward the set shape . removal is accomplished by cooling the stent to the malleable martensite state and pulling it out . if the selected material is bioabsorbable , the stent generally does not have to be removed .