JP3626097B2 - Improved stent configuration - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates generally to endovascular stents, and more particularly to special stent configurations for treating non-uniform intravascular vascular disease such as tapered arteries or arterial openings or arterial branches.
[0002]
[Prior art]
Stents or expandable grafts are implanted in these lumens in an effort to maintain the patency of the various lumens of the body. These devices are typically implanted in a lumen using a catheter. After the catheter is inserted into a position where it can be easily approached, it is advanced to the deployment site. The stent is initially maintained in a radially compressed or collapsed state so that the stent can be manipulated through the lumen. Once in place, the stent is deployed. Depending on the structure, the stent can be deployed automatically, for example, by removing the restraint, or it can be active, for example, by inflating a balloon supported on the catheter with the stent around it. To be done.
[0003]
Currently used intravascular stents are typically designed to expand or expand to a given nominal diameter within a diseased vessel. The nominal diameter is constant along the entire length of the stent. Further, a stent typically has a radial strength, a longitudinal flexibility, and a coverage of the stent material that defines the surface of the deployed stent, ie the vessel covered by the stent. The actual area relative to the area is uniform along its entire length. However, many blood vessels are not constant in diameter, and are naturally tapered or narrowed, especially at the branch. The blood vessel is taper over a short length (20 mm or less) as in the case of the carotid artery, or gradually taper over a long length (20 mm or more) as in the case of the iliac artery. ing. Examples of branch locations in the human circulatory system include vascular contours where the external and internal carotid arteries branch off from a common carotid artery. The common carotid artery diameter is 7 mm to 9 mm, while the internal carotid artery diameter is 4 mm to 6 mm. If disease is present at such a joint, the internally deployed stent must absorb changes in diameter of 3 mm to 5 mm over a length of about 20 mm to 30 mm. Another example is the placement of a stent in the renal artery. In order to cover the entire opening area, the stent must be configured identically to the inside of the renal artery and divergent into the larger aorta. Furthermore, the lesion site at the opening is typically hard and calcified, and it is necessary to increase the strength of the stent in that particular area. Similar demands arise in the treatment of natural coronary branch opening disease or bypass graft and aortic-opening disease of peripheral arteries (eg, carotid, renal, and iliac arteries) . Inhomogeneities are caused by the curved or tortuous shape of the blood vessels in the affected area.
[0004]
[Problems to be solved by the invention]
A number of problems have arisen from mounting conventional shaped stents, i.e., stents of uniform shape and diameter, at such locations. When such a stent is mounted on a tapered section of an artery, the artery is deformed into an unnatural shape or the stent is deformed to some extent during its deployment. When an artery is deformed into an unnatural shape, certain sections of tissue are over-extended or lack of support for other locations. The process performed in an effort to unevenly expand a uniformly structured stent provides the device with undesirable non-uniform features such as radial strength, flexibility, and non-uniform coverage. Another potential side effect associated with using a stent with a uniform structure is that when deployed within tortuous segments of the vasculature, such segments are undesirably straightened. It means that.
[0005]
Accordingly, there is a need for a stent that can uniformly support non-uniform blood vessels and provide consistency along its entire length with respect to coverage, radial strength, and longitudinal flexibility. In another aspect, specific for coverage, radial strength, and longitudinal flexibility at a particular location along the length to meet the need to vary along the length of a particular vessel There is a need for stents that can provide change.
[0006]
[Means for Solving the Problems]
The stent of the present invention provides a structure that provides uniform coverage, uniform radial strength, and / or uniform longitudinal flexibility to deployment sites of non-uniform shapes such as tapered or branched vessels. It has. In another aspect, such stents may be non-uniform at specific locations where flexibility, radial stiffness, or special changes in coverage are required at specific locations along such stents. It has a structure that meets the requirements.
[0007]
Desired functional specialization is obtained with a structurally specialized stent in a preselected manner. Both dimensional specialization or geometric specialization, or both dimensional specialization and geometric specialization, are performed by applying desired functional property changes to a particular stent. Such structural specialization may be performed gradually or suddenly, including several different types of specialization along the length of the stent.
[0008]
The stent of the present invention having a structure that deploys within a tapered vessel has an expansion ratio that gradually increases along its length. Such specialization can be accomplished by an assembly that includes an axially aligned ring. Each ring has a serpentine structure, and each of the repeating patterns of the serpentine structure defines a single unit cell. By selecting a continuous ring unit cell size that is progressively wider, the amount of material available for expansion is increased. Such a stent, when expanded, assumes a tapered frustoconical shape that matches the shape of the tapered artery. Despite its tapered shape, the stent uniformly covers the tapered vessel wall and exhibits uniform radial strength and longitudinal flexibility along its entire length. In another aspect, the stent may have a structure that expands to any of a variety of shapes and contours and is adapted to a particular application. Such functional changes can be made using the shape or size of the unit cell and changes in shape and size.
[0009]
As another variation, the stent of the present invention is uniform in diameter along its entire length, but the coverage, radial strength, or longitudinal flexibility is preselected along its length. It is preferable to have a non-uniform structure so as to change at This can be done, for example, by changing the thickness of the serpentine element while keeping the width of each serpentine element constant, or by changing the number of unit cells of a particular serpentine element. Similar results can be obtained by simultaneously changing the dimensions of individual unit cells (ie strut width and / or unit cell thickness) or geometry, or both dimensions and geometry.
[0010]
These and other features and advantages of the present invention will become apparent upon reading the following detailed description of the preferred embodiments in conjunction with the accompanying drawings which illustrate the principles of the invention.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The stent of the present invention has a special structure for a particular deployment location, thereby solving the inherent drawbacks of attempting to load a uniform stent at a non-uniform location. Location non-uniformities include tapers, branches, openings, or any other change in size or support requirements. The collapsed stent is sent to a predetermined place by a conventional method using a catheter or the like disposed around the stent. Once in place, the stent is expanded by inflating one or more balloons, or in the case of self-expanding stents, the restraining sheath is removed and the stent is automatically expanded. After withdrawal of the catheter and associated deployment device, the stent is left in place to maintain vessel patency.
[0012]
By providing a tapered stent for deployment in a tapered artery, it is nevertheless possible to have uniform coverage, radial strength, and stiffness along the entire length of the stent. In another aspect, the flexibility of the system of the present invention provides non-uniformity that increases coverage, strength, or rigidity at preselected locations, for example, to provide the necessary support requirements for diseased affected areas. Simple stents can be formed.
[0013]
FIG. 1 shows a stent 12 incorporating features of the present invention, and more particularly a stent for deployment within a tapered artery. The stent is typically tubular in its overall shape, but in the accompanying drawings, the stent is shown cut and flattened lengthwise to clearly show the structure of the stent. The stent structure includes a series of generally serpentine elements (14, 16,..., 30) extending generally circumferentially, and these elements are interconnected by links 32 extending between adjacent serpentine elements. Each serpentine element is characterized by a number of individual unit cells 34, each of which includes a link 32 attached to two adjacent U-shaped or V-shaped ribs 36,38. In the illustrated embodiment, a total of four unit cells define each serpentine element. Adjacent serpentine elements are arranged such that their respective series of tops are in phase and are longitudinally aligned with each other. All links extend from the same side of the serpentine element. In the illustrated embodiment, all links extend between the left edges of individual serpentine elements.
[0014]
In the embodiment shown in FIG. 1, each serpentine element is specialized with respect to adjacent serpentine elements with respect to the width of the serpentine pattern, ie with respect to the length of each rib element as well as the length of each link element. In the particular embodiment shown, each of the continuous serpentine elements is gradually wider than the previous element, and thus the rib elements and link elements of each unit cell are longer. However, the number of unit cells for each serpentine element remains unchanged as is the thickness and width of all ribs and serpentine elements.
[0015]
FIG. 2 is a perspective view showing the actual appearance of the stent 12 before deployment in use. The overall tubular structure is uniform in diameter and each of the serpentine elements extends around the entire circumference of the device. Individual serpentine elements can be recognized as rings, whereas individual links 32 extend only between adjacent rings. The diameter of the stent is selected to be small enough to be delivered through the patient's vasculature to the deployment site.
[0016]
FIG. 3 shows the stent shown in FIGS. 1 and 2 in its deployed state. This device is also shown cut and flattened lengthwise to show the structure more clearly. As can be clearly seen, when the device is inflated it tapers and the wide serpentine element shown towards the right side of the device expands more than the narrow serpentine element shown towards the left side of the device. Is done. Such expansion results in a frustoconical shape as shown in the perspective view of FIG. The U-shaped or V-shaped ribs 36, 38 are wide and have a more open angle, in which case the link 32 remains essentially stationary and aligned. Rib deformation and expansion increases the diameter of the device, but the overall length of the stent remains essentially unchanged during stent deployment. This is because the links connect only the adjacent rings. This is a highly desirable property of a stent. This is because shortening not only reduces the total area supported by the device, but can also damage the surrounding tissue during deployment. In addition, the larger diameter ring has more stent material due to the same number of long ribs, so the radial strength, coverage, and stiffness of the stent remain approximately constant along its entire length. is there.
[0017]
The accompanying drawings illustrate the structure and strain applied during deployment of a single embodiment of the present invention, but it is understood that numerous modifications are possible that can be tailored to the specific requirements of a particular application. It should be. By changing or specializing the geometry of the stent structure or the geometry of the individual unit cells, the same criteria changes or deformations are made. Furthermore, functional specialization can be performed by changing the thickness or width of the individual ribs. The desired functional differences can be obtained by changing the number of unit cells gradually along the length of the stent or at isolated locations on the stent. A particular functional effect can be obtained by changing the number of unit cells, the geometry of such cells, and the dimensions of such cells in any combination.
[0018]
The changes described above are selected so that the resulting stent can be tailored specifically for very specific anatomical requirements such as taper, branching, twisting, and vascular opening. it can. Furthermore, in addition to meeting specific anatomical heterogeneity dimensional requirements, the resulting stent provides the desired radial strength, longitudinal flexibility, or coverage specialization. The same variables can be selected so that they are specially made to order.
[0019]
The stent of the present invention can be formed using any number of well-known techniques. Preferably, the stainless steel tube is laser cut into the desired stent pattern well known in the art. Digital angiography and state-of-the-art computational algorithms are important tools that can be easily used to form structurally different stents that, when deployed, take the same form as the natural contours of blood vessels. The well-known chemical etching or electropolishing technique can then be used to selectively change the wall thickness of such stents.
[0020]
Deployment can be done with a shaped balloon in the case of a balloon inflatable stent, and a tapered balloon is used to expand the tapered stent within the tapered vessel. In another embodiment, multiple balloons of different sizes can be used to achieve the same effect as a tapered section of one oversized balloon. In another aspect, the stent can be self-expanding by any of a variety of techniques well known in the art. Deployment of self-expanding stents can be obtained by applying a specific temperature to expand the stent to a collapsed stent made of shape memory alloy. A stent made of an elastic material can be crushed by force and accommodated in a sheath. When the sheath is removed, the stent automatically expands.
[0021]
Balloon inflatable stents can be made from any ductile metal and alloy, including coated or uncoated stainless steel, tantalum, and platinum-iridium alloys. Self-expanding stents are made of NiTi alloys including Nitinol, shape memory alloys including Cu-Zn alloys or superelastic materials or alloys.
[0022]
While particular forms of the invention have been illustrated and described, it will also be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, the above description is not intended to be limiting except as by the appended claims.
[Brief description of the drawings]
FIG. 1 is an enlarged plan view of a stent of the present invention cut in length and flattened before deployment.
FIG. 2 is a perspective view of the stent shown in FIG. 1 before deployment.
FIG. 3 is an enlarged plan view of the stent of FIG. 1 in the deployed state, cut in the length direction and flattened.
4 is a perspective view of the stent shown in FIG. 3 in a deployed state. FIG.
[Explanation of symbols]
12 Stent 14, 16, 18, 20, 22, 24, 26, 28, 30 Meander element 32 Link 34 Unit cell 36, 38 Rib

Claims (5)

In a stent for supporting a tube region with non-uniform support requirements,
A tubular structure of circumferentially extending meander elements, each of said meander elements including a plurality of equal length ribs, said meander elements being longitudinally aligned to define the length of the structure, and adjacent Meandering elements connected to each other by links extending between them,
The structure is specialized to provide support in a non-uniform manner to meet the non-uniform support requirements by gradually lengthening the ribs of successive serpentine elements, and all serpentine elements have the same number A stent having ribs. The stent according to claim 1, wherein the structure is specialized to expand into a frustoconical shape and conform to a similarly tapered artery. The stent of claim 1, wherein the structure expands to a constant diameter along its length, but is specialized to exhibit a preselected change in radial strength along its length. The stent of claim 1, wherein the structure expands to a constant diameter along its length, but is specialized to provide a preselected change along its length for coverage. . The stent according to claim 1, wherein the structure is formed by providing a cavity in the tube by laser cutting.

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