US20150148885A1 - Stent with dual support structure - Google Patents

Abstract

A intraluminal stent comprises a reticulated tube having an un-deployed diameter and expandable to an enlarged diameter. The tube includes a structural beam extending between first and second ends. The structural beam changes from a first geometry to a second geometry when the tube changes from the un-deployed diameter to the enlarged diameter. The structural beam includes first and second longitudinal elements each extending at least partially between the first and second ends and with a spacing between the first and second elements. Each of said first and second elements changes from the first geometry to the second geometry when the tube changes from the un-deployed diameter to the enlarged diameter for the spacing to remain substantially unchanged as the tube changes from the un-deployed diameter to the enlarged diameter.

Description

I. CROSS-REFERENCE TO RELATED APPLICATION
• The present application is a continuation-in-part of copending and commonly assigned U.S. patent application Ser. No. 09/049,486 filed Mar. 27, 1998, entitled “STENT” and naming Paul J. Thompson as sole inventor.
II. BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• This invention pertains to stents for use in intraluminal applications. More particularly, this invention pertains to a novel structure for such stents.
• 2. Description of the Prior Art
• Stents are widely used for numerous applications where the stent is placed in the lumen of a patient and expanded. Such stents may be used in coronary or other vasculature, as well as other body lumens.
• Commonly, stents are cylindrical members. The stents expand from reduced diameters to enlarged diameters. Frequently, such stents are placed on a balloon catheter with the stent its the reduced-diameter state. So placed, the stent is advanced on the catheter to a placement site. At the site, the balloon is inflated to expand the stent to the enlarged diameter. The balloon is deflated and removed, leaving the enlarged diameter stent in place. So used, such stents are used to expand occluded sites within a patient's vasculature or other lumen.
• Examples of prior art stents are numerous. For example, U.S. Pat. No. 5,449,373 to Pinchasik et al. teaches a stent with at least two rigid segments joined by a flexible connector. U.S. Pat. No. 5,695,516 to Fischell teaches a stent with a cell having a butterfly shape when the stent is in a reduced-diameter state. Upon expansion of the stent, the cell assumes a hexagonal shape.
• In stent design, it is desirable for the stent to be flexible along its longitudinal axis to permit passage of the stent through arcuate segments of a patient's vasculature or other body lumen. Preferably, the stent will lave at most minimal longitudinal shrinkage when expanded and will resist compressive forces once expanded.
III. SUMMARY OF THE INVENTION
• According to a preferred embodiment of the present invention, an intraluminal stent is disclosed. The stent comprises a reticulated tube having an un-deployed diameter and expandable to an enlarged diameter. The tube includes a structural beam extending between first and second ends. The structural beam changes from a first geometry to a second geometry when the tube changes from the un-deployed diameter to the enlarged diameter. The structural beam includes first and second longitudinal elements each extending at least partially between the first and second ends and with a spacing between the first and second elements. Each of said first and second elements changes from the first geometry to the second geometry when the tube changes from the un-deployed diameter to the enlarged diameter for the spacing to remain substantially unchanged as the tube changes from the un-deployed diameter to the enlarged diameter.
IV. BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a perspective view of a first embodiment of a stent according to the present invention shown in a rest diameter state and showing a plurality of stent cells each having a major axis perpendicular to an axis of the stent;
• FIG. 2 is a plan view of the stent ofFIG. 1 as it would appear if it were longitudinally split and laid out flat;
• FIG. 3 is the view ofFIG. 2 following expansion of the stent to an enlarged diameter;
• FIG. 4 is a view taken along line4-4 inFIG. 2;
• FIG. 5 is a view taken along line5-5 inFIG. 2;
• FIG. 6 is an enlarged view of a portion ofFIG. 2 illustrating a cell structure with material of the stent surrounding adjacent cells shown in phantom lines;
• FIG. 7 is the view ofFIG. 2 showing an alternative embodiment of the present invention with a cell having five peaks per longitudinal segment;
• FIG. 8 is the view ofFIG. 2 showing an alternative embodiment of the present invention with a major axis of the cell being parallel to an axis of the stent;
• FIG. 9 is the view ofFIG. 5 following expansion of the stent to as enlarged diameter;
• FIG. 10 is a plan view of a first prior art stent as it would appear if it were longitudinally split and laid out flat;
• FIG. 11 is the view ofFIG. 10 with the stent modified for support beams to include parallel, spaced elements in accordance with the present invention;
• FIG. 12 is a plan view of a second prior art stent as it would appear if it were longitudinally split and laid out flat; and
• FIG. 13 is the view ofFIG. 12 with the stent modified for support beams to include parallel, spaced elements in accordance with the present invention.
V. DESCRIPTION OF THE PREFERRED EMBODIMENT
• Referring now to the several drawing figures in which identical elements are numbered identically, a description of the preferred embodiment of the present invention will now be provided. Where several embodiments are shown, common elements are similarly numbered and not separately described with the addition of apostrophes to distinguish the embodiments.
• As will be more fully described, the present invention is directed to a novel support beam for an expandable stent. The support beam is applicable to a wide variety of stent designs. In a preferred embodiment, the support beam will be used as a longitudinal segment in a stent as described in the aforementioned U.S. patent application Ser. No. 09/049,486 filed Mar. 27, 1998, entitled “STENT” and naming Paul J. Thompson as sole inventor. Therefore, such a stent will now be described with reference toFIGS. 1 to 9. Subsequently, the use of the novel beam will be described in use with other stent designs (i.e., those shown is U.S. Pat. No. 5,449,373 to Pinchasik et al. and U.S. Pat. No. 5,695,516 to Fischell) to illustrate the broad range of applicability of the novel support beam to a wide range of other stent designs.
• FIG. 1 illustrates astent10 having a rest length L, and an un-deployed or reduced diameter D_r. Thestent10 is of the design shown in the aforementioned U.S. patent application. The slot of the novel beam construction, as will be described, is not shown inFIG. 1.
• For ease of illustration, thestent10 is shown flat inFIG. 2 which illustrates a rest circumference C_r(C_r=πD_r). InFIG. 2, locations A, B, C, D and E are shown severed from their normally integrally formed locations A₁, B₁, C₁, D₁and E₁. This permits thestent10 to be shown as if it were severed at normally integrally formed locations A-A₁, B-B₁, C-C₁, D-D₁and E-E₁and laid flat.FIG. 6 is an enlarged portion of the view ofFIG. 2 to better illustrate a cell structure as will be described.
• Thestent10 is a reticulated, hollow tube. Thestent10 may be expanded from the rest diameter D_r(and corresponding rest circumference C_r) to an expanded or enlarged diameter.FIG. 3 is a view similar toFIG. 2 (i.e., illustrating the expandedstent10 as it would appear if longitudinally split and laid flat). SinceFIG. 3 is a two-dimensional representation, the enlarged diameter is not shown. However, the enlarged circumference C_eis shown as well as a length L_efollowing expansion. The expanded diameter is equal to C_e/π.
• As will be discussed length L_eis preferably not more than minimally smaller (e.g., less than 10% smaller) than length L_r. Ideally, L_eequals L_r.
• The material of thestent10 defines a plurality ofcells12. Thecells12 are bounded areas which are open (i.e., extend through the wall thickness of the stent10). Thestent10 may be formed through any suitable means including laser or chemical milling. In such processes, a hollow cylindrical tube is milled to remove material and form theopen cells12.
• Thecells12 have a longitudinal or major axis X_M-X_Mand a transverse or minor axis X_m-X_m. In the embodiments ofFIGS. 1-3, the major axis X_M-X_Mis perpendicular to the longitudinal cylindrical axis X-X of thestent10. In the embodiments ofFIGS. 8 and 9, the major axis X_M′-X_M′ is parallel to the longitudinal cylindrical axis X′-X′ of thestent10′. Thecell12 is symmetrical about axes X_M-X_Mand X_m-X_m.
• Thecell12 is defined by portions of the tube material including first and second longitudinal segments or support beams14. Thebeams14 each have a longitudinal axis X_a-X_a(shown inFIG. 6). The beams' longitudinal axes X_a-X_aare parallel to and positioned on opposite sides of the cell major axis X_M-X_M.
• Referring toFIG. 6, each oflongitudinal beams14 has an undulating pattern to define a plurality ofpeaks17,21,25 andvalleys19,23. Thepeaks17,21,25 are spaced outwardly from the longitudinal axes X_a-X_aand thevalleys19,23 are spaced inwardly from the longitudinal axes X_a-X_a. As used in this context, “inward” and “outward” mean toward and away from, respectively, the cell's major axis X_M-X_M.
• Each of thepeaks17,21,25 andvalleys19,23 is a generally semi-circular arcuate segment. Thepeaks17,21,25 andvalleys19,23 are joined by parallel and spaced-apartstraight segments16,18,20,22,24 and26 which extend perpendicular to the major axis X_M-X_M. Linearly alignedstraight end portions16,26 of opposingsegments14 are joined at first and secondlongitudinal connection locations27 spaced apart on me major axis X_M-X_M. First and secondtransverse connection locations28 are spaced apart on the minor axis X_m-X_m. The first and secondtransverse connection locations28 are positioned at the apices of the center peaks21 of the longitudinal beams14.
• Slots30 are formed through the complete thickness of each of thebeams14. Theslots30 extend between first and second ends31,32. The first ends31 are adjacent thelongitudinal connection locations27. The second ends32 are adjacent thetransverse connection locations28. Theslots30 divide thebeams14 into first and secondparallel elements14₁,14₂.
• Except as will be described, thebeams14 have uniform cross-sectional dimensions throughout their length as illustrated inFIG. 4. By way of non-limiting example, the width W and thickness T of thestraight line segments16,18,20,22,24 and26 are about 0.0065 inch (about 0.16 mm) and about 0.0057 inch (about 0.14 mm), respectively. The width W includes the widths (each of equal width) of the twoelements14₁,14₂plus the width W_Sof theslot30. By way of a non-limiting example, the width W_Sis in the range of 0.001 to 0.0025 inch. By way of another non-limiting example, the width W_Sis less than 0.005 inch.
• For reasons that will be described, the width W′ (FIG. 5) at the apices of thepeaks17,21,25 andvalleys19,23 is narrower than width W (in the example given, narrow width W′ is about 0.0055 inch or about 0.13 mm). The width of thepeaks12,21,25 andvalleys19,23 gradually increases from width W′ at the apices to width W at thestraight segments16,18,20,22,24 and26. At the longitudinal andtransverse connection locations27,28, the width W_C(shown inFIG. 2) is preferably equal to or less than the common width W. Preferably, the width W_Sofslot30 remains constant throughout its length.
• The combined lengths of segments16-20 to the apex ofpeak21 represent apath length50 fromlongitudinal connection location27 totransverse connection location28. Similarly the combined lengths of the other arcuate and straight segments22-26 to the apex ofpeak21 represent identicallength path lengths51 of identical geometry fromlongitudinal connection locations27 totransverse connection locations28. Each of thepath lengths50,51 is longer than a straight-line distance between the transverse andlongitudinal connection locations27,28. As will be described, the straight-line distance between the transverse andlongitudinal connection locations27,28 increases as the diameter of thestent10 is expanded. Thepath lengths50,51 are sized to be not less than the expanded straight-line distance.
• Thestent10 includes a plurality ofidentical cells12. Opposite edges of thesegments14 define obliquely adjacent cells (such ascells12₁,12₂inFIG. 2).Cells12 having major axes X_M-X_Mcollinear wife the major axis X_M-X_Mofcell12 are interconnected at thelongitudinal connection locations27. Cells having minor axes collinear with the minor axis X_m-X_mofcell12 are interconnected at thetransverse connection locations28.
• As mentioned, thestent10 in the reduced diameter ofFIG. 1 is advanced to a site in a lumen. Thestent10 is then expanded at the site. Thestent10 may be expanded through any conventional means. For example, thestent10 in the reduced diameter may be placed on the balloon tip of a catheter. At the site, the balloon is expanded to generate radial forces on the interior of thestent10. The radial forces urge thestent10 to radially expand without appreciable longitudinal expansion or contraction. Plastic deformation of the material of the stent10 (e.g., stainless steel) results in thestent10 retaining the expanded shape following subsequent deflation of the balloon. Alternatively, thestent10 may be formed of a super-elastic or shape memory material (such as nitinol—a well-known stent material which is an alloy of nickel and titanium).
• As thestent10 expands, thepath lengths50,51 straighten to accommodate the expansion. During such change in geometry of thepath lengths50,51, each of theelements14₁,14₂similarly changes in geometry so that. At all times, theelements14₁,14₂are mutually parallel and separated by spacing30.
• FIG. 3 illustrates the straightening of thepath lengths50,51. InFIG. 3, thestent10 has been only partially expanded to an expanded diameter less than a maximum expanded diameter. At a maximum expanded size, thepath lengths50,51 are fully straight. Further expansion of thestent10 beyond the maximum expanded size would result in narrowing of the minor axis X_m-X_m(i.e., a narrowing of a separation between the transverse connection locations and a resulting narrowing of the length L_rof the stent) or would require stretching and thinning of the stent material.
• As shown inFIG. 3, during expansion of thestent10, thestraight segments16,18,20,22,24 and26 are substantially unchanged. The straightening of thepath lengths50,51 results in bending of thearcuate peaks17,21,25 andvalleys19,23. Since the width W′ of thepeaks17,21,25 andvalleys19,23 is less than the width W of thestraight segments16,18,20,22,24 and26, thearcuate peaks17,21,25 andvalleys19,23 are less stiff than thestraight segments16,18,20,22,24 and26 and, therefore, more likely to deform during expansion.
• As the geometry of thebeams14 changes during expansion, the geometry of the first andsecond elements14₁,14₂similarly changes so that theelements14₁,14₂remain in mutually parallel relation both before and after expansion. As used in this application, the term “mutually parallel” means the spacing30 between theelements14₁,14₂is substantially constant throughout the length of theelements14₁,14₂. Theelements14₁,14₂andbeam14 may be curved or straight throughout their lengths.
• As thestent10 expands, thecells12 assume a diamond shape shown inFIG. 3. Since the expansion forces are radial, the length of the major axis X_M-X_M(i.e., the distance between the longitudinal connection locations27) increases. The length of the minor axis X_m-X_m(and hence the length of the stent10) remains unchanged.
• Thestent10 is highly flexible. To advance to a site, the axis X-X of thestent10 must bend to navigate through a curved lumen. Further, for placement at a curved site in a lumen, thestent10 must be sufficiently flexible to retain a curved shape following expansion and to bend as the lumen bends over time. Thestent10, as described above, achieves these objections.
• When bending on its axis X-X, thestent10 tends to axially compress on the inside of the bend and axially expand on the outside of the bend. The present design permits such axial expansion and contraction. Thenovel cell geometry12 results in an accordion-like structure which is highly flexible before and after radial expansion. Further, the diamond shape of thecells12 after radial expansion resists constricting forces otherwise tending to collapse thestent10.
• The dual support structure of the elements separated by the slots increases flexibility without reducing resistance to compression forces. Further, during expansion and during flexing of the stent on its axis, the use of parallel, spacedelements14₁,14₂results in lower stress levels than would be experienced by a solid beam.
• Numerous modifications are possible. For example thestent10 may be lined with either an inner or outer sleeve (such as polyester fabric or ePTFE) for tissue growth. Also, the stent may be coated with radiopaque coatings such as platinum, gold, tungsten or tantalum. In addition to materials previously discussed, the stent may be formed of any one of a wide variety of previous known materials including, without limitation, MP35N, tantalum, platinum, gold, Elgiloy and Phynox.
• While threecells12 are shown inFIG. 2 longitudinally connected surrounding the circumference C, of the stent, a different number could be so connected to vary the properties of thestent10 as a designer may elect. Likewise, while each column ofcells12 inFIG. 2 is shown as having three longitudinally connectedcells12, the number of longitudinally connectedcells12 could vary to adjust the properties of the stent. Also, while eachlongitudinal segment14 is shown as having threepeaks17,21,25 perlongitudinal segment14, the number of peaks could vary.FIG. 7 illustrates astent10″ with acell12″ having fivepeaks117″,17″,21″,25″ and125″ perlongitudinal segment14″. Preferably, the longitudinal segment will have an odd number of peaks so that the transverse connection points are at art apex of a center peak. InFIG. 7, no slot is shown in thebeams14″ for ease of illustration.
• FIGS. 8 and 9 illustrate an alternative embodiment where the major axis X_M′-X_M′ of thecells12′ are parallel with the cylindrical axis X′-X′ of thestent10′. InFIG. 9, the expandedstent10′ is shown at a near fully expanded state where thepath lengths50′,51′ are substantially linear. InFIGS. 1 and 9, no slots are shown in thebeams14′ for ease of illustration.
• FIGS. 10 and 12 illustrate prior art stent designs.FIG. 10 is astent10aas shown in U.S. Pat. No. 5,449,373 to Pinchasik et al. andFIG. 12 is astent10bas shown in U.S. Pat. No. 5,695,516 to Fischell.Stent10ais shown flat as if longitudinally split at locations Aa-Aa₁through Pa-Pa₁. Similarly,Stent10bis shown flat as if longitudinally split at locations Ab-Ab₁through Eb-Eb₁.
• Both of the designs ofFIGS. 10 and 12 include solidstructural beams14a,14b.Beams14aare curved when thestent10ais in a reduced diameter state. Thebeams14acooperate to define cells12a.The curved beams14astraighten when thestent10aexpands. Thebeams14bare straight and cooperate to define a butterfly-shapedcell12b.Upon expansion, thebeams14bremain straight but pivot for thecell12bto assume a hexagon shape upon expansion.
• The dual support structure aspect of the present invention is applicable to prior art stents such as those shown inFIGS. 10 and 12.FIGS. 11 and 13 show the prior art stents ofFIGS. 10 and 11, respectively, modified according to the dual support structure aspect of the present invention. Specifically, beams14a′,14b′ are provided withslots30a,30bto divide the beams into parallel, spaced first andsecond elements14a₁′,14a₂′ and14b₁′,14b₂′ having the benefits previously described.
• From the foregoing, the present invention has been shown in a preferred embodiment. Modifications and equivalents are intended to be included within the scope of the appended claims.

Claims (10)

What is claimed is:

1. An intraluminal stent comprising:

a reticulated tube having an un-deployed diameter and expandable to an enlarged diameter, said tube having a stent axis;

said tube including a structural beam extending between first and second ends;

said structural beam changing from a first geometry to a second geometry when said tube changes from said un-deployed diameter to said enlarged diameter;

said structural beam including first and second longitudinal elements each extending at least partially between said first and second ends and with a spacing between the first and second elements;

each of said first and second elements changing from said first geometry to said second geometry when said tube changes from said un-deployed diameter to said enlarged diameter for said spacing to remain substantially unchanged as said tube changes from said un-deployed diameter to said enlarged diameter.

2. An intraluminal stent according toclaim 1 wherein said first and second elements are mutually parallel both before and after changing of said tube from said un-deployed diameter to said enlarged diameter.

3. An intraluminal stent according toclaim 1 wherein said first and second elements each extend substantially an entire length of said structural beam between said first and second ends.

4. An intraluminal stent according toclaim 1 wherein a plurality of disconnected slots are formed through said structural beam to define a plurality of parallel first and second elements between said first and second ends.

5. An intraluminal stent according toclaim 1 wherein said beam and said first and second elements are curved.

6. An intraluminal stent according toclaim 1 wherein said beam and said first and second elements are straight.

7. An intraluminal stent according toclaim 1 wherein:

said beam is one of a plurality of beams with opposing surfaces defining an open cell bounded by said beams, said cell having a major axis and a minor axis;

said plurality of beams including first and second longitudinal beams each having:

a. a longitudinal axis extending parallel to and positioned on opposite sides of said cell major axis; and

b. an undulating pattern to define a plurality of peaks and valleys spaced outwardly and inwardly, respectively, from said longitudinal axes;

said first and second longitudinal beams interconnected at opposite ends thereof.

8. A stent according toclaim 7 further comprising:

first and second longitudinal connection locations at interconnection points of said interconnected first and second longitudinal beams for connection of said cell to first and second longitudinally adjacent cells, respectively; and

first and second transverse connection locations on said first and second longitudinal beams, respectively, for connection of said cell to first and second transversely adjacent cells, respectively.

9. A stent according toclaim 7 wherein path lengths of said longitudinal beams from said first and second transverse connection locations in said first and second longitudinal connection locations following expansion of said stent is substantially equal to or less than said lengths prior to said expansion.

10. A stent according toclaim 7 wherein:

said cell is substantially identical to adjacent cells;

said major axis of said cell is linearly aligned with major axes of said first and second longitudinally adjacent cells;

said minor axis of said cell is linearly aligned with minor axes of said first and second transversely adjacent cells;

opposing surfaces of cell defining portions of said cell, said longitudinally adjacent cells and said transversely adjacent cells cooperate to define at least in part obliquely adjacent cells.

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