Patent Application
20050038501
The present invention relates generally to stents, and more particularly to stents providing dynamic support of a vessel after implantation.
Stenting is a non-surgical treatment used with balloon angioplasty to treat coronary artery disease. Right after angioplasty has widened a coronary artery, a stent (one example being a small, expandable wire mesh tube) is inserted within the artery. The purpose of the stent is to help hold the newly treated artery open, reducing the risk of the artery re-closing (restenosis) over time.
Although stents have been widely used as solid mechanical, structural supports to maintain a vessel in a non-collapsed state following balloon angioplasty, they are not without their problems. Studies on the response of the artery wall to a stent demonstrate that the artery wall responds in distinct phases, displaying varying behaviors during certain time intervals after implantation. The earliest response, thrombus formation, is followed by ramping up inflammatory responses, smooth muscle cell proliferation, and finally, remodeling. Re-endothelization of the intima occurs on the time frame of weeks.
Research has demonstrated that stent design influences these actions through biomechanically mediated responses. For example, blood flow patterns dictate that platelet deposition is lowest when stent strut spacing is small, whereas endothelial cell regrowth is fastest when stent strut spacing is large. Stent-induced artery wall stresses (which depend heavily on strut configuration) also play a role in the inflammatory and proliferative responses. While each of these responses have distinctly different characteristic times of action, previously developed stents are either static and do not change over time, or are fully degradable and may fail to provide sufficient structural support for supporting the artery. Thus, there exists a need for a stent which is reliable, easy to manufacture, and which is dynamic such that the properties of the stent change over time to correspond to the changing responses and needs of the vessel.
One embodiment of a stent formed in accordance with the present invention is disclosed. The stent includes a support frame for supporting a vessel in a non-collapsed state. The support frame includes a degradable component for at least initially supporting the vessel in the non-collapsed state when the stent is first implanted in the vessel. The degradable component is degradable after implantation such that support provided by the degradable component decreases a selected amount after a predetermined time after implantation. The support frame further includes a durable component for supporting the vessel in the non-collapsed state. The durable component is resistant to degradation over time such that support provided by the durable component remains substantially constant after implantation.
Another embodiment of a stent formed in accordance with the present invention for supporting a vessel in a non-collapsed state is disclosed. The stent includes a plurality of durable struts for supporting the vessel in the non-collapsed state. The stent further includes a plurality of temporary struts for initially aiding in the support of the vessel in the non-collapsed state. The temporary struts break down over time after implantation such that they no longer substantially aid in supporting the vessel in the non-collapsed state.
Still another embodiment of a stent formed in accordance with the present invention for supporting a vessel in a non-collapsed state is disclosed. The stent includes a support frame having a durable component and a degradable component, the support frame providing a variable level of support for supporting the vessel in the non-collapsed state. Upon implantation, the support frame initially provides a predetermined amount of support for supporting the vessel in the non-collapsed state. After implantation, the support frame changes due to exposure to environmental conditions such that after passage of a selected duration, the support frame provides a selected lessened amount of support for supporting the vessel in the non-collapsed state.
The foregoing aspects and many of the attendant advantages of this invention will become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
Referring to
Moreover, in the early stages after implantation, both the permanent and temporary components 102 and 104 are present in the dynamic stent 100, such as shown in
Referring to
The support frame 106 includes a plurality of struts or annular links 108. The annular links 108 of the illustrated embodiment are sinusoidal in shape and are generally equally spaced along the length of the dynamic stent 100. The sinusoidal shape of the annular links 108 provides a blunt end profile for the dynamic stent 100 in order minimize the risk of puncturing the vessel and provides increased support of the artery wall over a straight annular link. Further, the sinusoidal shape of the annular links 108 permits the dynamic stent 100 to be expanded from a small diameter to a larger diameter once the dynamic stent is properly positioned within the artery. The dynamic stent 100 may be expanded by any suitable technique, such as by balloon expansion or self expansion.
Although a sinusoidal shape of the annular links 108 is described and depicted, it should be apparent to those skilled in the art that other shapes of the links are suitable for use with the present invention, some suitable examples being links formed from repeating geometric shapes, such as triangles, squares, circles, polygons, arcuate shapes, parabolic shapes, oval shapes, linear shapes, and non-sinusoidal shapes. In the illustrated embodiment, the dynamic stent 100 includes a series of twenty-three (23) annular links 108 spaced equidistant from one another along the longitudinal length of the dynamic stent 100. The annular links 108 are spaced from one another such that adjacent annular links 108 are disposed in a nested relationship relative to one another, such that a crest of the sinusoidal wave of one annular link 108 is nested at least partially between a pair of troughs of the sinusoidal wave of an adjacent annular link 108.
The spacing of the annular links 108 from one another is maintained by an array of longitudinally oriented struts 110. The struts 110 are linear in form and are preferably oriented parallel with the longitudinal axis of the dynamic stent 100. The struts 110 pass through and are connected to each of the annular links 108. In the illustrated embodiment, six (6) longitudinal struts 110 are used, spaced equidistant from each other about the circumference of the dynamic strut 100. Further, although a specific number, orientation, and shape of the longitudinal struts 110 is described and depicted, it should be apparent to those skilled in the art that alternate numbers, orientations, and shapes of longitudinal struts 110 are suitable for use with and within the spirit and scope of the present invention. Although the longitudinally oriented struts 110 are depicted and described as extending continuously from one end of the dynamic stent 100 to the other, it should be apparent to those skilled in the art that the longitudinally oriented struts 110 may be intermittently disposed along the length of the dynamic stent 100, such as to connect only a few annular links 108 to one another.
As mentioned above, the dynamic stent 100 includes a permanent component 102 and a temporary component 104 which are interwoven/interlaced with one another, and in combination, to form the support frame 106. Referring to
The permanent component 102 is formed from any suitable rigid or semi-rigid material which is resistant to degradation in the body and which is compatible with the human body and bodily fluids that the dynamic stent 100 may contact. Further, preferably the dynamic stent 100 should be made from a material that allows for expansion of the dynamic stent 100 and which is able to retain its expanded shape while disposed within the lumen of the body passage. A few examples of suitable materials include stainless steel, tantalum, titanium, chromium cobalt, and nitinol.
The permanent component 102 may be formed using traditional techniques such as laser machining of tube stock, Electrical Discharge Machining (EDM), etc. The permanent component 102 may be self-expanding or balloon expandable. As should be apparent to those skilled in the art, a relatively sparse mesh pattern for the permanent component 102 may provide benefits with regard to delivery profile. A less dense mesh pattern for the permanent component 102 may mean that a ratio of a first collapsed diameter to a second expanded diameter may be smaller.
Referring to
The temporary component 104 is formed from any suitable rigid or semi-rigid material which is amenable to degradation in the body and which is compatible with the human body and bodily fluids that the dynamic stent 100 may contact. Further, preferably the temporary component 100 is made from a material that allows for expansion of the dynamic stent 100 and which is able to retain its expanded shape while disposed within the lumen of the body passage. A few examples of suitable materials include polymers, such as the polylactide (PLA) polymer or the polymers disclosed in U.S. Pat. No. 6,461,631, the disclosure of which is hereby expressly incorporated by reference, hydrogels, and magnesium alloys. The material used may include therapeutic substances which are selectively released once the dynamic stent is implanted to aid rehabilitation of the artery wall, one such suitable material disclosed in U.S. Pat. No. 6,506,437, the disclosure of which is hereby expressly incorporated by reference.
The temporary component 104 may be formed on the permanent component 102 by dipping the permanent component 102 in a liquid polymer. The liquid polymer is then cured upon the permanent component 102. The dynamic stent 100 may then be made into custom shapes by selective physical cutting and removal of certain pieces. Other selective removal techniques may be used as well, such as laser machining. Preferably, the permanent and temporary components 102 and 104 are each formed in a geometric array, mesh, chain, interlinking pattern, etc. Preferably, the permanent and temporary components 102 and 104 are coupled to one another, such as by interconnecting and/or interweaving one to the other. Alternately, the meshwork of polymer may also be produced by lining the inside and/or outside of the permanent component 102 with a weave of polymer fibers.
In still another alternate embodiment, the temporary component 104 may be a substantially complete covering, rather than a meshwork. In still yet another embodiment, the temporary component 104 may be a substantially complete covering made of a porous, biodegradable material. The porosity may come from laser machining, from physical hole punching, or from other traditional techniques of making porous polymers.
Preferably, the temporary component 104 is formed from a biodegradable mesh of sufficient density to hold back intimal flaps and other wall/plaque components that have intruded into the lumen. The need to prop these flaps against the wall likely goes away after partial healing; presumably occurring on the order of weeks after implantation.
In light of the above description of the structure of the dynamic stent 100, the use of the dynamic stent 100 will now be described. The dynamic stent 100 is inserted within a blood vessel using well known techniques. The permanent component 102 and temporary component 104 may be delivered together into the blood vessel. Alternately, the permanent component 102 would be delivered, and then the temporary component 104 would be extruded into the artery via a catheter approach. The extrusion geometry may be a standard geometry, or a custom geometry based on the plaque geometry and composition, as imaged by intravascular ultrasound or optical coherence tomography.
As time after implant progresses, the temporary component 104 preferably degrades, resulting in a stent geometry that adjusts over time to match the changing needs of the artery wall during the remodeling process. When initially inserted, both the permanent and temporary components 102 and 104 are fully present, as shown in
Referring to
Referring to
After implementation, the annular links 108 of the degradable component 104 disposed at the ends of the dynamic stent 100 degrade at an elevated rate and accordingly disappear first. The annular links 108 of the degradable component 104 located at the midpoint of the dynamic stent 100 degrade at a slower rate, and therefore remain in place for a longer duration. This variable degradation of the degradable component 104 results in a variable stiffness of the support frame 106 along a longitudinal length of the support frame 106 such that a stiffness at a pair of ends of the support frame 106 is less than a stiffness at a middle of the support frame 106 after a selected period after implantation.
Although this detailed description depicts and describes two separate embodiments, wherein in one, materials of different degradation rates are used to provide variable stiffness characteristics and wherein in a second, the spacing/shape of the support frame is modified to provide variable stiffness characteristics, it should be apparent that combinations thereof are within the spirit and scope of the present invention.
While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.
This application claims the benefit of U.S. Provisional Patent Application No. 60/494,476 filed on Aug. 12, 2003, the disclosure of which is hereby expressly incorporated by reference, and priority from the filing date of which is hereby claimed under 35 U.S.C. § 119(e).
| Number | Date | Country | |
|---|---|---|---|
| 60494476 | Aug 2003 | US |
