An intraluminary prosthesis is a medical device used in the treatment of diseased bodily lumens. One type of intraluminary prosthesis used in the repair and/or treatment of diseases in various body vessels is a stent. A stent is generally a longitudinal tubular device formed of biocompatible material which is useful to open and support various lumens in the body. For example, stents may be used in the bodily vessel, such as in the coronary or peripheral vasculature, esophagus, trachea, bronchi colon, biliary tract, urinary tract, prostate, brain, as well as in a variety of other applications in the body. These devices are implanted within the vessel to open and/or reinforce collapsing or partially occluded sections of the lumen.
Stents generally include an open lattice configuration. This configuration allows the stent to be inserted through curved vessels. Furthermore, this configuration allows the stent to be configured in a radially compressed state for intraluminary catheter implantation. Once properly positioned adjacent the damaged vessel, the stent is radially expanded so as to support and reinforce the vessel. Radial expansion of the stent may be accomplished by inflation of a balloon attached to the catheter or the stent may be of the self-expanding variety which will radially expand once deployed. Tubular shaped structures, which have been used as intraluminary vascular stents, have included helically wound coils which may have undulations or zig-zags therein, slotted stents, ring stents, braided stents and open mesh wire stents, to name a few. Super-elastic materials and metallic shape memory materials have also been used to form stents.
While stents are often made from metallic materials, the use of plastic stents is not uncommon, especially in non-vascular applications. For example, plastic stents have been used to treat malignant or benign strictures throughout the gastrointestinal tract because of, among other things, ease of placement and non-permanency of the stents. In the case of biliary applications, re-intervention of a plastic stent after three months is typical for malignant tumors where after the plastic stent is replaced with another plastic stent or perhaps a metallic stent. Benign strictures in biliary applications are often treated every three months with a plastic stent for up to about a year. In duodenal applications, a plastic stent is often placed as a bridge to surgery. In esophageal applications, a plastic stent may be placed as an adjunct treatment to radiation.
While plastic stents offer many advantages, a drawback of a typical plastic stent is its patency rate as compared to a metallic stent. A metallic stent generally has much larger radial force and a longer patency rate, especially when the stent is covered. Metal stents, however, have generally not been used in benign applications due to the difficulty of removing an implanted metallic stent.
In biliary applications, re-intervention may be required in about twenty-five percent of the time due to tumor in-growth through the open lattice portions of the implanted stent. Covering the stent, for example with a layer of silicone, may reduce the re-intervention due to tumor in-growth less than two percent of the time.
U.S. Pat. No. 5,603,722 to Phan et al describes a stent made from plastic, more particularly a shape memory polymer. The stent includes elongate strips of shape memory polymer overlapping wound to form a closed-wall stent structure in a contacted state of the stent. When the stent is expanded portions of the strip segments separate from each other to provide a stent with an open lattice structure. U.S. Pat. No. 5,163,952 to Froix describes a stent made from plastic, more particularly a shape memory polymer, which is in the shape of a coil or a solid-walled tubular cylinder. While the coil is a flexible structure, it has gaps into which tumor in-growth may occur. The solid-walled tubular cylinder may avoid the tumor in-growth concerns associated with open lattice stent structures, but such a stent is not highly flexible, making delivery and placement into curved lumens difficult.
Thus, there is a need for a plastic stent which has improved patency by reducing re-intervention rates due, for example, to tumor in-growth, while still being flexible so that it can used in curved lumens.