U.S. patent application number 09/207867 was filed with the patent office on 2001-11-29 for stent with nested or overlapping rings.
Invention is credited to WIJAY, BANDULA.
Application Number | 20010047199 09/207867 |
Document ID | / |
Family ID | 22772307 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010047199 |
Kind Code |
A1 |
WIJAY, BANDULA |
November 29, 2001 |
STENT WITH NESTED OR OVERLAPPING RINGS
Abstract
A flexible stent is disclosed which reduced openings between
rings by two alternative techniques. In the first instance,
adjacent sinusoidally bending rings are nested to compact them
closer together to reduce the opening sizes therebetween. In
another embodiment, adjacent sinusoidal rings overlap each other to
achieve the same effect. The nested design can be fabricated from a
long continuous sinusoidal band having alternating high and low
peaks wrapped spirally around the mandrel and welded at crossties.
The assembly can be covered with a graft as a support therefor.
Inventors: |
WIJAY, BANDULA;
(FRIENDSWOOD, TX) |
Correspondence
Address: |
STEVE ROSENBLATT
ROSENBLATT & REDANO
ONE GREENWAY PLAZA
SUITE 500
HOUSTON
TX
77046
|
Family ID: |
22772307 |
Appl. No.: |
09/207867 |
Filed: |
December 8, 1998 |
Current U.S.
Class: |
623/1.15 |
Current CPC
Class: |
A61F 2/915 20130101;
A61F 2/88 20130101; A61F 2/91 20130101; A61F 2002/91541 20130101;
A61F 2002/91558 20130101; A61F 2002/91508 20130101; A61F 2230/0013
20130101 |
Class at
Publication: |
623/1.15 |
International
Class: |
A61F 002/06 |
Claims
1. A stent, comprising: a band made in an undulating form having a
plurality of high and low peaks such that when wound spirally, it
presents a high peak opposite a low peak; at least some of said
opposed high and low peaks are connected so as to give the effect
of nesting undulations due to said spiral winding.
2. The stent of claim 1, wherein: said nested undulations define
oblong openings between pairs of crossties.
3. The stent of claim 2, wherein: said oblong openings are spirally
disposed with respect to a longitudinal axis of the cylindrical
shape formed by said ring when spirally wound.
4. The stent of claim 1, wherein: said ring comprises alternating
high and low peaks connected by crossties.
5. The stent of claim 4, wherein: each said peak comprises a
crosstie; and each said high peak is equal in height to every other
high peak and each said low peak is equal in height to every other
low peak.
6. The stent of claim 5, wherein: said nested undulations define
oblong openings between pairs of crossties.
7. The stent of claim 6, wherein: said oblong openings are spirally
disposed with respect to a longitudinal axis of the cylindrical
shape formed by said ring when spirally wound.
8. A stent, comprising: a plurality of rings, each said ring
further comprising an undulating form with a plurality of high and
low peaks; at least one said ring disposed adjacent another said
ring in a manner where on at least one side, a high peak on one
ring is disposed opposite a low peak on the adjacent ring so as to
nest said adjacent rings; and said rings connected to each
other.
9. The stent of claim 8, wherein: said high and low peaks alternate
to define a plurality of valleys therebetween.
10. The stent of claim 9, wherein: at least one said ring disposed
adjacent another said ring in a manner where on at least one side,
a valley on one ring is disposed opposite a valley on the adjacent
ring.
11. The stent of claim 10, further comprising: crossties to connect
said rings; said opposed valleys are each connected by said
crossties; said crossties connect each pair of opposed high and low
peaks.
12. The stent of claim 8, wherein: said rings define oblong
openings therebetween whose minimum length is less than the
combined height of said high and low peaks.
13. The stent of claim 12, further comprising: crossties to connect
said rings; said minimum length also includes the length of a
crosstie.
14. The stent of claim 8, wherein: said crossties comprise
connecting a high peak directly to its opposing low peak.
15. The stent of claim 13, wherein: said crossties comprise an
elongated member that spans a gap between said opposed high and low
peaks.
16. The stent of claim 10, further comprising: crossties to connect
said rings; said crossties comprise connecting a valley to its
opposing valley.
17. The stent of claim 10, further comprising: crossties to connect
said rings; said crossties comprise elongated members which span a
gap between opposing valleys and are not connected at said
valleys.
18. The stent of claim 8, further comprising: a graft supported by
said rings.
19. A stent, comprising: a plurality of undulating rings which
overlap each other, at least in part, and crossties to connect
them.
20. The stent of claim 19, wherein: each said ring comprises
alternating peaks and valleys; said crossties connect peaks on one
ring to peaks on an adjacent ring.
21. The stent of claim 19, wherein: each said ring comprises
alternating peaks and valleys; said crossties connect at least one
peak on one ring to a point between a peak and a valley on an
adjacent ring.
22. The stent of claim 19, wherein: each said ring comprises
alternating peaks and valleys; said crossties connect between a
peak and a valley on one ring to a location between a peak and a
valley on an adjacent ring.
23. The stent of claim 19, wherein: each said ring comprises at
least one multiply recurring high peak and at least one multiply
recurring low peak.
24. The stent of claim 23, wherein: said high peaks alternate with
said low peaks.
25. The stent of claim 19, wherein: said rings define a plurality
of heights.
26. The stent of claim 19, further comprising: at least a first,
second and third overlapping and undulating rings; each said ring
comprising alternating peaks and valleys; said crossties on said
first ring extend through said second ring to connect to said third
ring.
27. The stent of claim 26, wherein: said crossties connect said
valley on said first ring with a peak on said third ring.
28. The stent of claim 1, wherein: said high peaks have at least
two different values and said low peaks have at least two different
values.
29. The stent of claim 8, wherein: said high peaks have at least
two different values and said low peaks have at least two different
values.
Description
FIELD OF THE INVENTION
[0001] The field of this invention relates to vascular stents.
BACKGROUND OF THE INVENTION
[0002] Vascular stents are structures that are designed to maintain
the patency of a vessel in the body. The stent provides internal
support to allow the circulation to proceed therethrough. Stents
can be used in the vascular system in ureters, bile ducts,
esophagus, and in many other tubular structures in the human
body.
[0003] Stents can be tubular or can be made from wire. Stents are
typically made from a metal or polymeric substance or a metal
coated with polymers which are biocompatible or contain heparin to
reduce blood clotting or other tissue reactions. Many prior designs
have used a coil approach where a wire is helically wound on a
mandrel. Yet other designs have evolved-braided wire mesh and
angulated wire forms wrapped on a spindle to form a coil.
[0004] U.S. Pat. Nos. 5,292,331 by Boneau and U.S. Pat. No.
5,403,341 describe such wire forms. These devices have very poor
radial support to withstand the hoop strengths of the artery or
vein and further are not suitable for arteries that are bent or
curved or for long lesions; multiple stent are required. These
designs do not provide any support to hold the wall of the artery,
other than the memory of the metal.
[0005] Wall Stent, produced by Pfizer Inc., is a braided wire tube.
Although this stent is flexible so as to be placed in curved
arteries or veins and other body cavities, it does not have any
radial strength imparted to it by design.
[0006] Wiktor, U.S. Pat. Nos. 4,649,922; 4,886,062; 4,969,458; and
5,133,732 describe a wire form stent. He describes stents made of
wire helix made of a preformed wire which is in the sinusoidal
form, in which either all or some of the adjacent strands are
connected.
[0007] Arthus Fontaine, U.S. Pat. No. 5,370,683, also describes a
similar device where a flat wire form of sinusoidal shape is wound
on a mandrel to form a helical coil. The wire bends are "U" shaped
and are connected to alternate "U"-shaped bands.
[0008] Allen Tower, U.S. Pat. Nos. 5,217,483 and 5,389,106
describes a similar device where the wire is preformed to a
sinusoidal shape and subsequently wound on a mandrel to form a
helical coil.
[0009] All of the above-described art fails to provide radial
support. The pre-shaped wire form (sinusoidal in most of the prior
art) is wrapped on a mandrel to form a coil. However, the forces
imported by the vessel wall's hoop strength are radially inward. In
other words, the force is acting perpendicular to the plane of the
U-shaped wire form. This means that the bends that are in the wire
add no structural strength to the wire form to support the force
produced by the wall, which is radially inward.
[0010] When we examine the simple coils, such as taught in U.S.
Pat. Nos. 5,383,928 to Scott or Gene Samson 5,370,691 or Rolando
Gills 5,222,969, it is apparent that the spring coil will withstand
substantial radial forces due to the vessel wall; however, all
these stents are bulky in their pre-expanded form and are hard to
place in small and curved arteries or veins of the body. Also, a
major disadvantage of this design is that when the coil stent is
placed in a curved artery or vein, it forms an "accordion" shape
whereby some strands in the outer radius are spread and those of
the inner radius are gathered. Spring coils can also "flip" to form
a flat structure when a longitudinal force is applied on one side
of the stent.
[0011] The other types of stents that have been developed are tube
stents. Palmer, U.S. Pat. Nos. 4,733,665; 4,739,762; 7,776,337; and
4,793,348 describe such a tube stent of slotted metal tube. The
slotted metal tube is expanded by a high-pressure balloon to
implant the stent into the inside wall of the artery or vein.
[0012] Joseph Weinstein, U.S. Pat. No. 5,213,561 describes a
similar stent made of tubular materials with slots cut into it. On
expansion using a balloon, it forms a structure with diamond-shaped
slots.
[0013] Henry Wall, U.S. Pat. No. 5,266,073 also describes a stent,
tubular, that has slots machined into it. When expanded, the edges
of the stent lock to form a cylinder. Not only is this device stiff
and can only be used for short lesions, but also the diameter
cannot be adjusted to meet the exact needs of the particular vessel
but it is fixed to the predetermined sizes.
[0014] Lau and Hastigan, U.S. Pat. No. 5,344,426 describes a
slotted tubular stent that has a structure similar to Henry Wall's
but has provided prongs that will lock in as the stent is
expanded.
[0015] Michael Marin, U.S. Pat. No. 5,397,355 also describes a
tubular slotted stent with locking prongs.
[0016] All the above-described tube stents, although typically
providing substantial radial support when expanded, are not
flexible enough to be placed in curved vessels. Arteries and veins
in the human body are mostly curved and are tapered. As such, these
tube stents suffer from this main disadvantage.
[0017] European patent document 042172982 employs wires that are
doubled up and whose ends are snipped off to make a given joint.
Such doubling up at the junction of two elements with snipped off
free ends creates a potential puncture problem upon radial
expansion. The sheer bulk of the doubled up wires makes them rotate
radially outwardly away from the longitudinal center-line of the
stent, while the plain ends on such an arrangement which are
snipped off offer the potential of sharp points which can puncture
or damage the intima. On the other hand, the apparatus of the
present invention, employing sharp angles, as defined, avoids this
problem in an embodiment which illustrates a continuous wire or
wire-like member bent into a sharp angle. This type of structure
alleviates the concerns of sharp edges, as well as the tendency of
a doubled up heavy joint to rotate outwardly toward the intima upon
radial expansion of the stem, as would be expected in the EPO
reference 042172982.
[0018] Often these stents are layered with polymeric sheaths that
are impregnated with biocompatible substances or can be coated with
heparin or hydrogel. Most sheath-type coatings reduce endothelial
cell growth through the stent, which is a major requirement in
successful stenting of body cavities such as arteries and
veins.
[0019] One of the problems with prior designs of slotted tube and
wire stents is that in their expanded state, the openings in them
become fairly large. This allows tissue to protrude through these
openings or windows. When there are protrusions into the body
cavity through the stent, it causes disturbances to the blood flow,
causing activation of platelets causing blood clotting. This
phenomenon can also enhance the process of restenosis due to the
large area exposed for neointimal formation.
[0020] FIG. 1 depicts two rings of a stent of a design known in the
prior art. Rings 10 and 12 are each sinusoidal, having respective
peaks 14 and 16 joined together by crossties such as 18. Respective
valleys 20 and 22 are deposed opposite each other to create a
lengthy elongated opening 24, which has a length 26 nearly as long
as the distance from opposing valleys 20 and 22. FIG. 2 illustrates
what happens to the oblong openings 24 when the rings 10 and 12 are
expanded radially to set the stent of the prior art shown in FIG.
1. As shown in FIG. 2, each of the openings 24 is quite large,
allowing tissue growth to enter therethrough, as shown in FIG. 3,
which shows more rings than the rings 10 and 12 illustrated in FIG.
1. The tissue growth 28 significantly constricts the blood flow
passage through the stent of the prior art shown in FIGS. 1-3.
[0021] One of the objectives of the present invention is to provide
a stent which overcomes this problem. Alternative solutions are
illustrated to achieve the objective of making the opening smaller
to provide better resistance to tissue growth into the blood flow
passage through the stent. Thus, in one embodiment, the objective
is accomplished by nesting adjacent rings which have sinusoidal
bending so as to more closely pack them to reduce the opening sizes
between them. In yet another embodiment, adjacent sinusoidal rings
are made to be overlapping to again accomplish the objective of
deceasing opening sizes in the expanded state for a stent of a
given diameter and length. These and other objectives will be
readily apparent to those skilled in the art from a description of
the preferred embodiments of the invention below.
SUMMARY OF THE INVENTION
[0022] A flexible stent is disclosed which reduced openings between
rings by two alternative techniques. In the first instance,
adjacent sinusoidally bending rings are nested to compact them
closer together to reduce the opening sizes therebetween. In
another embodiment, adjacent sinusoidal rings overlap each other to
achieve the same effect. The nested design can be fabricated from a
long continuous sinusoidal band having alternating high and low
peaks wrapped spirally around the mandrel and welded at crossties.
The assembly can be covered with a graft as a support therefor.
DETAILED DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a partial flattened view of a stent of the prior
art, showing sinusoidal rings with crossties connecting adjacent
peaks.
[0024] FIG. 2 is a view of one of the openings formed between
adjacent rings in the prior art stent shown in FIG. 1.
[0025] FIG. 3 is a section view through the stent shown in FIG.
1.
[0026] FIG. 4 illustrates two rings of a stent of one of the
embodiments of the present invention shown in a flattened form.
[0027] FIG. 5 illustrates one of the elongated openings of the
stent of FIG. 4 after expansion.
[0028] FIG. 6 is a section view of the stent of FIG. 4.
[0029] FIG. 7 shows how adjacent rings are connected to each other
to form the stent of FIG. 4.
[0030] FIG. 8 shows an alternative embodiment to the stent of FIG.
4 and the technique for connecting adjacent rings.
[0031] FIG. 9 shows the stent of FIG. 8 with two overlapping rings
connected.
[0032] FIG. 10 is the stent of FIGS. 8 and 9 showing four
overlapping rings.
[0033] FIG. 11 is the stent of FIG. 4 with a graft around the
outside.
[0034] FIG. 12 illustrates a technique for making the stent of FIG.
4 which is an alternative to the technique of FIG. 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0035] Referring to FIG. 4, the preferred embodiment is
illustrated. A portion of a stent S is shown in FIG. 4. More
specifically, adjacent undulating rings 30 and 32 are illustrated.
Each of these rings has an undulating, preferably sinusoidal shape
with alternating high and low peaks. For example, in ring 30
alternating high peaks 34 exist between low peaks 36. Between peaks
34 and 36 are valleys 35. The height is defined as the distance
from valleys 35 to peaks 34. The crossties 38 connect ring 30 to
ring 32. Crossties 38 are optional as ring 30 can be connected
directly to ring 32 without them. Crossties can connect peaks to
peaks, valley to valley, or at least one peak or one valley to
another location on the next ring. Ring 32 has alternating high
peaks 40 and low peaks 42. The high peaks 40 of ring 32 are
juxtaposed against the low peaks 36 of ring 30. Similarly, the low
peaks 42 of ring 32 are juxtaposed against the high peaks 34 of
ring 30. The result of this construction is that the oblong
openings 44 get smaller as adjacent rings such as 30 and 32 in a
typical stent S get nested into each other. The minimum length of
opening 44 is less than the combined height of peaks 34 and 42,
including the material. FIG. 5 illustrates the resultant shape of
the opening 44 after radial expansion of the rings such as 30 and
32 which make up the stent S. FIG. 5 can be compared to FIG. 2 to
illustrate that the typical opening in the stent S of the preferred
embodiment of the present invention is smaller than the large
oblong openings 24, which necessarily arise when rings such as 10
and 12 are aligned adjacent peak 14 to peak 16 with a crosstie 18
in between. In a sense, the rings 10 and 12 of the prior art get no
closer to each other then the length of the crosstie 18 and there
is no nesting or overlapping between rings 10 and 12 of the design
in the prior art. Referring to FIG. 11, additional rings are shown
besides rings 30 and 32. These rings 46 and 48 reflect a
continuation of a pattern. As can be seen from FIG. 11, the peaks
50 of ring 46 extend in alignment but in the opposite direction
from the low peaks 42 of ring 32 to create an opening 44' which is
the same size as opening 44. In the embodiment shown in FIG. 11, a
graft 52 is mounted over the stent S. Those skilled in the art will
appreciate that, in the preferred embodiment, the openings 44 and
44' are identical and form a spiral pattern around the periphery of
the stent S. The spiral pattern is continued with openings 44"
which exist between rings 46 and 48. Those skilled in the art will
appreciate that each ring does not need to be identical to its
adjacent ring. It is within the scope of the invention that the
greatest peak-to-valley height is varied from one ring to the next.
The preferred embodiment is to make such height longer at ends of
the stent and shorter in between. Also, the degree of nesting of
adjacent rings such as 30 and 32 can be varied along with the width
of openings such as 44 by adjusting the heights of the
corresponding peaks and valleys. The prior art FIG. 1 depicts an
extreme in the spacing between adjacent rings which provides the
maximum width of openings 24. At the other extreme, adjacent rings
such as 30 and 32 in effect become a single ring. The present
invention is directed to the range of designs in between the two
stated extremes which result in narrowing the longitudinal gap such
as 44, 44', and 44", etc., while maintaining the rings such as 30,
32, 46, and 48 distinct and connected with crossties such as 38.
Referring to FIG. 12, an alternative technique to making individual
rings such as 30, 32, 46, and 48, and connecting such as by welding
the crossties such as 38 in between is illustrated. Here in FIG.
12, a single elongated band is produced having alternating peaks
and valleys as described previously, with at least some but
preferably each of the high peaks and low peaks such as 34 and 36
having a crosstie 38 thereon. The assembly shown in the top part of
FIG. 12 is then wrapped around a mandrel 54 in a spiral fashion
such that the crossties 38 bridge between a low peak 36 and a high
peak 34, as illustrated in the lower part of FIG. 12. In essence,
the same stent S is produced as is shown in FIGS. 4 and 11, with
the difference being that the elongated openings such as 44 are
skewed with respect to the longitudinal axis 56 but are still
disposed in a generally spiral pattern akin to that shown in FIG.
11, despite the skew shown in FIG. 12 due to the method of
assembly. The stent S of FIG. 11 is assembled in a technique shown
in FIG. 7, which involves taking adjacent rings such as 30 and 32,
aligning them as previously described, and welding the crossties 38
to join ring 30 to ring 32 in alternating locations. Each opening
44 is identified by a welded crosstie 38 above and below.
[0036] Accordingly, those skilled in the art can see that when the
stent S of the preferred embodiment illustrated in FIG. 4 is
inserted into a vessel as shown in FIG. 6, the gaps, such as
between rings 30 and 32 which define the width of openings 44, are
significantly smaller than the oblong openings 24 between rings 10
and 12 of the prior art as shown in FIG. 3. Thus, the central
passage 58 is not obstructed by an invasion of tissue 28 in the
design of FIG. 4, illustrated in section in FIG. 6. This should be
contrasted to the constriction and internal roughness of the
passage 60 as illustrated in FIG. 3.
[0037] Yet another embodiment of the present invention is shown in
FIGS. 8 through 10. Here, adjacent rings 62 and 64 are built
identically with an undulating, preferably sinusoidal shape, with
each bend preferably having the same height 65 as the adjacent band
akin to the individual rings 10 and 12 illustrated in the prior
art. Varying heights can also be used. However, the method of
connection of adjacent rings 62 and 64 is substantially different
wherein the crossties 66 are connected to an opposing valley 68.
Thus, for example, as shown in FIG. 8, the crossties 66 from a peak
70 connect to valley 68 of ring 62. The crossties can be connected
to other locations. FIG. 9 illustrates the appearance of rings 62
and 64 after the crossties 66 are positioned for welding. As can
readily be seen, the ring 64 overlaps ring 62. The amount of
overlap can be varied with a variety of techniques, such as
variation of the length of the crossties 66 or the peak-to-valley
heights of either of the rings 62 or 64. FIG. 10 illustrates rings
62 and 64 with additional rings 70 and 72. As seen in FIG. 10,
crossties 74 extend from ring 62 at its various peaks 76 to be
connected to peaks 78 of ring 70. The crossties 74 literally extend
between the undulations of ring 64 to reach the peak 78 of ring 70.
Ring 72 is connected to ring 70 by crossties 80, putting ring 72 in
an overlapping relationship with ring 70, while ring 70 overlaps
ring 64 and, in turn, ring 64 overlaps ring 62. As shown in FIG.
10, it can be seen that a series of oblong openings of different
sizes are provided. Openings 82 are the widest in this design and
their width is affected by the configuration of the individual
rings as well as the length of the crossties connecting them so
that the width of opening 82 can be lengthened or shortened as
desired. Those skilled in the art will appreciate that the smaller
the width of opening 82, the stiffer the stent and the more
difficult the stent can become to maneuver. The stent of FIG. 10 is
generally stiffer than the stent of FIG. 4 in view of the fact that
the rings 62, 64, 70, and 72 overlap each other, generally
increasing the thickness of the stent being formed and somewhat
decreasing its central passage when compared to a comparable design
using the nesting technique shown in FIG. 4. The advantage of the
design in FIG. 10 is that the size of the openings, particularly
their width, can be more carefully controlled and reduced to
present the stent with a smaller opening area so as to take maximum
advantage of the smaller openings to obtain the desired effect
shown in FIG. 6. Thus, either of the two designs can be used
alternatively, depending on the application and the accessability
to the location for setting the particular stent. The desirable
advantage of either design is that the intrusion of tissue due to
overly large openings, which present themselves after expansion in
the designs of the prior art such as shown in FIG. 1, are
dramatically reduced with either of the alternative designs
illustrated.
[0038] The foregoing disclosure and description of the invention
are illustrative and explanatory thereof, and various changes in
the size, shape and materials, as well as in the details of the
illustrated construction, may be made without departing from the
spirit of the invention.
* * * * *