A stent is a medical device introduced to a body lumen and is well known in the art. Typically, a stent is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called “minimally invasive techniques” in which the stent in a radially reduced configuration, optionally restrained in a radially compressed configuration by a sheath and/or catheter, is delivered by a stent delivery system or “introducer” to the site where it is required. For example, the introducer may enter the body from an access location outside the body, such as through the patient's skin, or by a “cut down” technique in which the entry blood vessel is exposed by minor surgical means.
Stents, grafts, stent-grafts, vena cava filters, expandable frameworks, and similar implantable medical devices are radially expandable endoprostheses which are typically intravascular implants capable of being implanted transluminally and enlarged radially after being introduced percutaneously or through a natural orifice. Stents may be implanted in a variety of body lumens or vessels such as within the vascular system, urinary tracts, bile ducts, fallopian tubes, coronary vessels, secondary vessels, gastrointestinal tract, airways, etc. They may be self-expanding, expanded by an internal radial force, such as when mounted on a balloon, or a combination of self-expanding and balloon expandable (hybrid expandable).
One of the main problems with stenting, especially with partially covered and fully covered stents, is migration. Though the exact reasons leading to stent migration are not well known, it is important to prevent stent migration for many reasons. The main reason is that if the stent moves away from the stenosis in which it was implanted, the vessel blockage may reoccur, also a migrated stent can cause problems for the patients. For instance a migrated duodenal stent can cause an obstruction of the small bowel. Migration can occur shortly after stent implantation or several months afterwards. Bare stents tends to have a lower migration rate than partially covered or fully covered stents because tissue grows through the stent mesh and keep the stent from moving. Several techniques are used to prevent stent migration, the main one is to use a flared end to anchor the stent at the stricture. However, there is still a significant amount of migration even with flared stents. Spikes or barbs have also been used to prevent stent migration.
In a few applications, it is also important to have a stent that can be retrieved after implantation, either immediately or even a few months after implantation. For instance, the stent may be used to treat a benign stenosis like a corrosive stricture of the esophagus. It is expected that the tissue would remodel under the constant pressure applied by the stent and therefore, the stent should be removed after a few weeks. Typically, esophageal stents would move downwards, therefore the stent should be designed to prevent downwards migration but allow for endoscopic removal through the mouth. Therefore it is important to have spikes of barbs oriented in one direction in order to prevent migration in one direction but allow for stent removal in the other direction.
The art referred to and/or described above is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. §1.56(a) exists.
All US patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
Without limiting the scope of the invention a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.