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Description  |
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TECHNICAL FIELD OF THE INVENTION
The present invention relates to supports for collapsed or occluded blood
vessels, and more particularly, to a coiled wire stent for insertion and
expansion in a collapsed or occluded blood vessel. Still more
particularly, the present invention relates to a coiled, bifurcated stent
which supports a Y-shaped juncture of two blood vessels.
The present invention further relates to methods and apparatus for
manufacturing artificial supports for blood vessels and more particularly,
to methods for making a wire coil having certain desired properties. Still
more particularly, the present invention discloses methods and apparatus
for preparing a continuous loop and forming the loop into a cylindrical
shape having a desired configuration.
BACKGROUND OF THE INVENTION
A typical wire stent for insertion and expansion in a collapsed or occluded
blood vessel is shown in U.S. Pat. No. 4,800,882 and includes a coiled
wire having a plurality of curved sections that are formed into a
generally circular configuration. Adjacent curved sections are joined by a
bend so that a series of alternating opposing loops are formed. The stent
has a cylindrical shape with a longitudinal opening through which a folded
balloon catheter is inserted. The opposing loops are tightly contracted
about the catheter so that the cylindrical shape has an overlapping region
in which portions of adjacent loops circumferentially overlap. The loops
are arranged so that when the balloon catheter is inflated, adjacent loops
diverge circumferentially relative to each other, thereby decreasing the
width of the overlapping region while increasing the diameter of the
cylindrical shape. As the diameter of the cylindrical stent increases, the
stent engages the inner surface of the blood vessel.
In operation, the stent is deployed at its desired position within the
vessel in its collapsed state, by threading the balloon catheter up the
vessel from an incision some distance away, and then expanded to its
expanded state, for supportive engagement with the interior of the vessel
wall.
The prior art stents have several deficiencies. As shown in FIG. 7 of U.S.
Pat. No. 4,800,882, the alternating bends are aligned in relation to the
longitudinal axis of the stent such that upon expansion of the stent as
shown in FIG. 8, the opposing loops may be expanded such that a
longitudinal gap appears between the opposing bends of the loops, leaving
a longitudinal unsupported area along the occluded blood vessel. Such an
unsupported area is undesirable. Further, when it is desired to support a
branched section of a blood vessel without obstructing the passageway of
the vessel, it is necessary to utilize several conventional stents to
support the main vessel and the adjacent two branch vessels. Deployment of
multiple stents requires an extended medical procedure, and may produce
unsatisfactory results if any of the stents migrates away from the
juncture, leaving one leg of the Y-shaped juncture of the vessels
unsupported. Additionally, the stents of the prior art often require the
application of heat, torsional three, or a shortening in length in order
to attain their expanded state.
Alternatively, stents having no longitudinal gap may be comprise spiral
coils, or other configurations that are radially expandable and provide
the desired circumferential support for a collapsed vessel.
Because of the asymmetrical nature of many of the desired coil
configurations, standard manufacturing methods are inapplicable. Thus,
stents such as that disclosed in U.S. Pat. No. 4,800,882, involve a high
degree of labor to produce. The present invention discloses means and
apparatus for producing a desired stent quickly and easily.
The present invention overcomes the deficiencies of the prior art.
SUMMARY OF THE INVENTION
The stent of the present invention comprises a coil including a plurality
of arcuate sections that alternate clockwise and counterclockwise
directions around a central longitudinal axis. Each arcuate section
includes a pair of curved turns joined by a cusp. The cusps of adjacent
arcuate sections intermesh, thereby defining at least one region of
overlap, which in turn describes a helix around and along the length of
the coil. In the preferred embodiment, there are two regions of overlap,
which together form a double helix.
The present invention further discloses a Y-shaped, bifurcated stent. The
bifurcated stent comprises three coils, each constructed according to a
preferred coil pattern, joined so as to form an unobstructed support for a
branched vessel.
The stent of the present invention is radially expandable without the use
of heat, torsional forces, or shortening of the stent, and is constructed
to provide a region of enhanced support which wraps helically around the
stent. The branched stent fills the need for a reliable device which is
simple to install and effectively supports a branched blood vessel.
The present invention further discloses a double-spiral stent that may
comprise either a single coil or a bifurcated coil, and a rib-cage type
stent that includes a longitudinal spine supporting a plurality of looped
ribs thereon.
Also disclosed is a method for making the foregoing stents that is rapid,
repeatable and economical. The method of the present invention is not
labor intensive and is capable of producing even stents that do not have a
linear axis of symmetry. The present method includes creating a continuous
loop, or blank, by photoetching a sheet of material. The blank produced by
the photoetching technique has no ends or joints and is therefore superior
for internal applications because the likelihood of a puncture or other
damage is minimized.
The present method further includes rolling the continuous blank between a
series of rollers, to form a cylindrical coil. According to the present
invention, the precise configuration of the coil is determined by the
shape of the blank that is rolled. Thus, single-helix, double-helix and
spiral configured stents may be constructed by rolling according to the
present invention.
Alternatively, a method for constructing the desired coil shape by hand is
disclosed. The manual method comprises forming each loop of the coil
around a mandril by individually pulling the cusps of the coil into place.
This manual method may of course be automated to increase speed and
efficiency of production.
Other objects and advantages of the present invention will appear from the
following description.
BRIEF DESCRIPTION OF THE DRAWINGS
For a detailed description of a preferred embodiment of the invention,
reference will now be made to the accompanying drawings wherein:
FIG. 1 is a perspective view of a double-helix nonbifurcated stent
according to the present invention.
FIG. 2 is an end view of the double-helix nonbifurcated stent of FIG. 1.
FIG. 3 is an enlarged view of two full loops of the double-helix stent of
FIG. 1.
FIG. 4 is a close-up view of two full loops of the double-helix stent of
FIG. 1.
FIG. 5 is a perspective view of a single-helix nonbifurcated stent.
FIG. 6 is a perspective view of a double-helix bifurcated stent according
to the present invention.
FIG. 7 is a perspective view of a bifurcated stent in which the major coil
is a double-helix and the two minor coils are single-helix.
FIG. 8 is a side elevational view of the stent of FIG. 6 in a collapsed
state, mounted on a balloon catheter within a blood vessel.
FIG. 9 is a side elevational view of the stent of FIG. 6 deployed within a
bifurcated vessel and partially expanded.
FIG. 10 is a perspective view of a first nonbifurcated cross-over stent.
FIG. 11 is a perspective view of a second nonbifurcated cross-over stent.
FIG. 12 is a perspective view of a bifurcated zig-zag stent according to
the present invention.
FIG. 13 is an enlarged view of two of the loops of the zig-zag stent of
FIG. 12,
FIG. 14 is an isometric view of a nonbifurcated ribbon stent.
FIG. 15 is an isometric view of a bifurcated ribbon stent.
FIG. 16 is a perspective view of a double-spiral stent made according to
the present invention;
FIG. 17 is a perspective view of a bifurcated double-spiral stent made
according to the present invention;
FIG. 18 is a perspective view of a bifurcated stent in which the major coil
is a double-spiral and the minor coils are single spirals;
FIG. 19 is an perspective view of a continuous loop blank that may be used
to form the stents of FIGS. 16 and 17;
FIG. 19A is a cross section of the blank of FIG. 19 taken along lines A--A
of FIG. 19;
FIG. 20 is an elevational view of a continuous loop blank that may be used
to form the stems of FIGS. 1 and 6;
FIG. 21 is a perspective view of a backbone blank;
FIG. 22 is an end view of an apparatus that can be used according to the
present invention to produce the stents of FIGS. 1, 5, 6, 7, 16, 17, and
21;
FIG. 23 is a perspective view of the apparatus of FIG. 22 forming the loop
of FIG. 19 into the stent of FIG. 16;
FIG. 24 is a perspective view of the apparatus of FIG. 22 forming the loop
of FIG. 20 into the stent of FIG. 1; and
FIG. 25 is a perspective view of a stent formed from the rib-cage blank of
FIG. 21.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Double Helix Stent
Referring initially to FIGS. 1 and 2, there is shown a preferred embodiment
of a stent 10 according to the present invention. Stent 10 is made of a
single length of wire having a mid-point at 12 forming two wire legs 14,
16 of approximately equal length. Legs 14, 16 are bent into a double-helix
coil 22 as shown, forming individual spiral wire shell halves 18, 20
respectively. One end 24 of coil 22 includes mid-point 12, and the other
end 26 of coil 22 includes the terminal ends 28, 30 of wire legs 14, 16.
Terminal ends 28, 30 are connected at juncture 32 on coil end 26, such as
by soldering or the like. Upon the joining of terminal ends 28, 30, coil
22 effectively consists of a single continuous wire 34. The two wire shell
halves 18, 20 are curved, as shown in the end view of FIG. 2, so that
stent 10 is generally cylindrical in shape with a generally circular
opening 36 formed therein. Stent 10 is shown having a central longitudinal
axis 38. Referring now to FIGS. 1, 3, and 4, each individual spiral wire
shell half 18, 20 includes a series of alternating clockwise and
counterclockwise arcuate sections. For purposes of description, the
arcuate sections have been severed in FIG. 3 to better illustrate such
sections. The clockwise direction relative to the axis 38 has been
arbitrarily selected and is indicated by the arrow CW. Wire shell half 18
includes alternating clockwise and counterclockwise arcuate sections 40,
42, respectively, and opposed wire shell half 20 includes alternating
counterclockwise and clockwise arcuate sections 50, 52, respectively.
Clockwise arcuate section 40 is typical of the other arcuate sections and
includes two adjacent curved turns 44, 46 of wire joined by a bend or cusp
48. Likewise, counterclockwise arcuate section 50 of shell half 20
includes two adjacent curved turns 54, 56 joined by a cusp 58.
As best seen in FIG. 1, wire leg 14 forms shell half 18, comprising
clockwise arcuate sections 40a, 40b, 40c, etc., with cusps 48 pointing in
the clockwise direction and counterclockwise arcuate sections 42a, 42b,
42c, etc., with cusps 48 pointing in the opposite counterclockwise
direction. Likewise, wire leg 16 forms shell half 20 comprising
counterclockwise arcuate sections 50a, 50b, 50c, etc. with cusps 58 and
clockwise arcuate sections 52a, 52b, 52c, etc. with cusps 58. The
clockwise arcuate sections 40 of shell half 18 are in phase with the
counterclockwise arcuate sections 50 of shell half 20 so that the
clockwise arcuate sections 40 of half 18 intermesh and extend between
counterclockwise arcuate sections 50 of half 20. The same is true for
counterclockwise arcuate sections 42 of half 18 and clockwise arcuate
sections 52 of half 20.
Referring now to FIG. 4, the intermeshing of arcuate sections 40, 50 and
42, 52 creates two regions of overlap in coil 22. Clockwise arcuate
sections 40 and counterclockwise arcuate sections 50 create a first
overlap region 60 and counterclockwise arcuate sections 42 and clockwise
arcuate sections 52 create a second overlap region 70. Regions of overlap
60, 70 have diametrically opposed centerlines 62, 72, respectively.
Referring now to FIGS. 1 and 4, the extent of the regions of overlap 60, 70
will vary with the size of the blood vessel in which the stent 10 is
deployed. The extent of the region of overlap 60, 70 is maximized in the
contracted position of the stent 10 and is minimized in the expanded
position of the stent 10. The intermeshing of adjacent arcuate sections
40, 50 and 42, 52 defines an angle .alpha. at axis 38, shown in FIG. 1.
Preferably, in the contracted position, .alpha. is at least five
longitudinal degrees. In the Figures, an intermeshing of only a few
longitudinal degrees is shown, but it will be understood that the degree
of intermeshing can be increased without departing from the spirit of the
invention and is actually increased when the stent is used. Cusps 48, 58
of arcuate sections 40, 42, 50, 52 shift circumferentially with each turn.
In this manner, regions of overlap 60, 70 describe a double-helix around
coil 22, best demonstrated by reference centerlines 62, 72, shown in FIG.
1. The advantages of this construction will become apparent from the
discussion below.
Preferably, stent 10 is constructed of wire, although any suitable material
may be substituted. The wire comprising stent 10 is malleable, preferably
from the group consisting of annealed stainless steel, tungsten and
platinum. This malleable material must be sufficiently deformable to allow
shell halves 18, 20 to expand radially when radially outward pressure is
applied by the inflation of the membrane that comprises the standard
balloon catheter. Because the stent material deforms plastically, rather
than elastically, the stent 10 retains the enlarged diameter after the
balloon is deflated.
The material has sufficient strength and stiffness, however, to avoid the
stent 10 being displaced during insertion and to avoid the adjacent
arcuate sections 40, 50 and 42, 52 being forced into an overlying
relation. Further, the stent 10 has sufficient strength and stiffness to
allow it to maintain its position in the vessel passageway and to resist
being dislodged after the catheter has been deployed. One example of a
suitable wire has an outer diameter of 0.018 inches and is stainless steel
AISI 315 alloy. Alternately, the stent 10 of the present invention can be
constructed of a memory metal, such as Nitinol, that resumes a particular
original shape, following deformation, when heat is applied.
In a preferred embodiment, the surface of the stent is coated with a
biocompatible substance, preferably a biolized collagen/gelatin compound
such as those discussed in Characterization of Rehydrated Gelatin Gels,
Emoto, et al., Artificial Organs, 15(1):29-34, 1991 and incorporated
herein by reference. The coating serves to increase biocompatibility of
the stent and aid in blood flow around the device. The coating is a 5%
glutaraldehyde cross-linked dried gelatin coating which can be applied to
a texturized surface, dehydrated, sterilized, and stored dry. This type of
gel, when applied as a film, provides a smooth, biochemically stable
protein coating with non-pseudointima properties, very little platelet
adhesion, and high blood compatibility.
To deploy a stent such as the stent 10 of FIG. 1 in a blood vessel, the
stent is radially contracted or compressed until it assumes a outer
diameter which is calibrated to allow insertion into a particular vessel
passageway. Typically, this means an outer diameter on the order of 3
millimeters. With regard to stent 10, as the stent is compressed, regions
of overlap 60, 70 widen and the cusps 48, 58 are forced into deeper
intermeshing relationship. The stent 10 in its contracted state is
threaded onto a balloon catheter (not shown) prior to deployment in the
vessel. The compressed stent 10 and catheter are inserted at an incision
in the vessel and threaded up the vessel on a wire guide to the place of
deployment. At that point, pressure is applied to the balloon to expand it
within the stent. As the balloon is inflated, the clockwise and
counter-clockwise arcuate sections 40, 50 and 42, 52 expand radially,
reducing the width of overlap regions 60, 70 until the desired
circumference is attained. Thus, the effective diameter of stent 10 is
increased without thermal expansion, application of torsional forces to
the stent, or a reduction in overall length of the stent.
Single Helix Stent
Referring now to FIG. 5, there is shown an alternate nonbifurcated stent 61
comprising a single helix coil 64. According to this embodiment, a wire is
bent into a series of alternating clockwise and counterclockwise arcuate
sections 63, 65, formed by turns 66 and cusps 68, such that one region of
overlap 71 is formed. The ends 67, 69 of the wire are located at opposite
ends of coil 64. As described above with regard to stent 10, arcuate
sections 63, 65 are constructed so that region of overlap 71 shifts
longitudinally with each successive turn 66 and forms a spiral around coil
64. Because there is only one region of overlap, 71, coil 64 is referred
to as a single-helix coil. Stent 61 can be deployed in the manner
discussed above with regard to stent 10.
Referring now to FIG. 6, there is shown a preferred bifurcated stent 80
according to the present invention. Bifurcated stent 80 includes a major
coil 82 and two minor coils 84, 86. In practice, major coil 82 may be
placed, for example, in the aortic vessel and minor coils 84, 86 in the
iliac vessels. As with stent 10, bifurcated stent 80 comprises a single
continuous wire 34, and each of coils 82, 84, 86 comprises a part of the
wire 34. Major coil 82 has the same double helix pattern as coil 22 of
stent 10, with the exception that wire legs 14, 16 are extended to form
minor coils 84, 86, respectively, which are also coiled in the double
helix pattern of coil 22. As in coil 22, the terminal ends 88, 90 of wire
legs 14, 16 are joined at a juncture 92. Hence, a single wire loop is able
to define and flexibly support a branched vessel without obstructing flow
therethrough.
Referring now to FIG. 7, an alternate bifurcated stent 81 comprises one
major coil 83 constructed in the manner of double-helix coil 22 of stent
10 shown in FIG. 1, and two minor coils 85, 87 constructed in the manner
of single-helix coil 64 of stent 61 shown in FIG. 5. As with bifurcated
stent 80, bifurcated stent 81 can be constructed from a single piece of
wire. In stent 81, wire legs 14, 16 terminate at ends 88, 90, which may be
joined to coils 85, 87, as shown at 91, individually formed into loops
(not shown), or otherwise prevented from puncturing the vessel wall.
Deployment of a bifurcated stent is shown in FIGS. 8 and 9, using the stent
80 shown in FIG. 6. Stent 80, in a contracted state on balloon catheter
112, is threaded up one of the iliac vessels 108, 110 from an incision in
the leg, as shown in FIG. 8. When it reaches the juncture 106 of vessels
108, 110, the stent 80 is pushed up into the aortic vessel 100 by a guide
wire 104, until one of the minor coils 84, 86 of the stent 80 is clear of
the juncture 106. Then the stent 80, still in a compressed state, is
backed down the iliac vessel 108 until it is in its proper position for
expansion. FIG. 9 shows stent 80 in position for deployment within the
vessel juncture 106 and partially expanded. Bifurcated stents of the
present invention having a variety of coil patterns may be deployed in the
manner described above with respect to stent 80.
As shown in FIGS. 8 and 9, a tri-wing balloon 112 may be used to inflate
stent 80, so that uniform pressure is applied to each coil of stent 80 and
the coils expand simultaneously. The balloon material is flexible, so
that, once deflated, it may be easily removed through any opening in the
stent 80. Preferably, it is removed through an opening where the aortic
section branches to form the iliac sections, or through the end of one of
the iliac sections.
Cross-Over Stents
Referring now to FIG. 10, an additional single-helix, nonbifurcated coil
120, is shown. In coil 120, both wire ends 88, 90 are at one end of the
coil 120, and one region of overlap 130 is formed. In alternate
embodiments of coil 120 (not shown), wire ends 88, 90 may be joined as at
32 in FIG. 1, formed into loops, or extended to form integral adjacent
minor coils. Region of overlap 130 describes a helix around coil 120, as
discussed above with respect to coil 22. Unlike coil 22, however, where
the material forms two opposing individual shell halves that do not cross,
the material of coil 120 forms two generally cylindrical legs 124, 126,
each comprising of a series of alternating clockwise and counter-clockwise
sections 132, 134 having clockwise and counter-clockwise cusps 133, 135,
respectively. Each leg 124, 126 has its own region of overlap, and legs
124, 126 are intermeshed so that the regions of overlap coincide. When
intermeshed, legs 124, 126 cross each other at a series of cross-overs
128. For this reason, coils such as coil 120 are hereinafter referred to
as cross-over coils. It should be noted that in coil 120 clockwise cusps
133 and counterclockwise cusps 135 alternate along region of overlap 130.
Coil 120 provides a radially expandable coil with an asymmetrical region of
overlap. The fact that both wire ends 88, 90 are at one end of coil 120
makes coil 120 suitable for the construction of either a closed loop,
nonbifurcated stent or a bifurcated stent in which the minor coils are
formed from, and are therefore integral with, ends 88 and 90.
Referring now to FIG. 11, an alternate single-helix, cross-over,
nonbifurcated coil 120, is shown. In coil 122, as in coil 120, both wire
ends 88, 90 are at one end of the coil 122, and one region of overlap 130
is formed. Region of overlap 130 describes a helix around coil 122, as
discussed above with respect to coil 120. As in coil 120, the material of
coil 122 forms two generally cylindrical legs 124, 126, each comprising of
a series of alternating clockwise and counter-clockwise sections 132, 134
having clockwise and counter-clockwise cusps 133, 135, respectively. Each
leg 124, 126 has its own region of overlap, and legs 124, 126 are
intermeshed so that the regions of overlap coincide. When intermeshed,
legs 124, 126 cross each other at a series of | | |
