Note: Descriptions are shown in the official language in which they were submitted.
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CANADA
DIVISIONAL PATENT APPLICATION
PIASETZKI & NENNIGER
File No.: HB192/GAP
Title: SHAPED WOVEN TUBULAR SOFT-TISSUE PROSTHESES
AND METHODS OF MANUFACTURING
Inventors: Jose F. Nunez
Peter J. Schmitt
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SHAPED WOVEN TUBULAR SOFT-TISSUE PROSTHESES AND METHODS
OF MA . UFACTURING
FIELD OF THE INVENTION:
The present invention relates to shaped seamless woven tubular prostheses and
methods of manufacture. In particular, the present invention relates to
implantable
endoluminal prostheses used in the vascular system.
BACKGROUND OF THE INVENTION:
Tubular woven fabrics have been used for soft-tissue implantable prostheses to
replace or repair damaged or diseased lumens in the body. In particular,
endoprostheses are used in the vascular system to prevent the blood from
rupturing a
weakened section of the vessel. Such endoluminal conduits are generally
affixed in a
specified location in the vessel by means of stents, hooks or other mechanisms
which
serve to secure the device in place. Endoluminal tubular devices or conduits
can also
be used in other lumens in the body, such as in the esophagus and colon areas.
Vascular grafts have been used successfully for many years to replace segments
of the diseased vessel by open surgical methods. These techniques, however,
required
long and expensive procedures which have a high degree of risk associated with
them
due to the complexity of the surgical procedures. Presently, non-invasive
techniques
for treating body lumens, such as vessels in the vascular system, have become
more
prominent because they present less risk to the patient and are less complex
than open
surgery. Generally, a doctor will make an incision in the femoral artery and
introduce
an endoluminal device by means of a catheter delivery system to the precise
location of
the damaged or diseased vessel. The device will generally include a stent and
graft
combination which is deployed from the delivery system and affixed in place
usually
by use of a balloon catheter. The balloon catheter is used to expand the
stents which
are attached to and most often contained within the graft portion. Expansion
of the
stent serves to both anchor the graft and to maintain the graft and the body
lumen in the
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open state. In some cases, self-expanding stents or the like are used.
Stents made from shaped-memory materials, such as nitinol, are also
employed whereby radial expansion or contraction of the stent is designed
to occur at specified temperatures.
The use of tubular endoluminal prostheses, however, requires a high
degree of precision in the diameter of the tube, such that its external
diameter matches the internal diameter of the body lumen very closely,
thereby conforming to the internal surface of the body lumen. The vessels
or lumens in the body, however, often vary in diameter and shape from one
length to another, in addition to sometimes defining a tortuous path
therebetween. This is particularly true with the vessels in the vascular
system. Thus, tubular endoprostheses which are generally straight in
configuration cannot accurately conform to all portions of the lumen which
have these variations present. Often times, the prosthesis wall will require
a bunching or gathering within the lumen of the vessel which presents a
long-term potential for thrombosis and generally creates a more turbulent
environment for blood flow.
More recently, in recognition of certain problems in implanting and
delivering endoluminal prostheses, a thinly woven graft has been made
which is designed to closely fit the inner lumen of vessels. Such a graft is
described in co-assigned patent application EP 0 699 423 A2. The thinness
of this graft allows for it to be easily packed into a catheter delivery
system
and occupy less space within the lumen when deployed. However, these
grafts have been made in straight lengths or bifurcated structures using
traditional weaving techniques which have specific limitations as to the final
shape of the product and, in the case of bifurcated or multi-diameter grafts,
the transition from one diameter to another occurs at a single point in the
weave, creating a sudden change in the weaving pattern of the fabric. Such
sudden changes, as further discussed herein, are considered undesirable.
Weaving is commonly employed to fabricate various tubular shaped
products.
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For example, implantable tubular prostheses which serve as conduits, such as
vascular
grafts, esophageal grafts and the like, are commonly manufactured using
tubular
weaving techniques, wherein the tubular product is woven as a flat tube. In
such
weaving processes, a variety of yarns are interwoven to create the tubular
fabric. For
example, a set of warp yarns is used which represents the width of the product
being
woven, and a fill yarn is woven between the warp yarns. The fill yarn is woven
along
the length of the warp yams, with each successive pass of the fill yarn across
the warp
yarns for each side of the tube representing one machine pick. Thus, two
machine
picks represent one filling pick in a tubular woven structure, since weaving
one fill yam
along the entire circumference of the tube, i.e., one filling pick, requires
two picks of
the weaving machine. As such, in a conventional woven product, the fill yarn
is woven
along the length of the warp yams for a multiple number of machine picks, with
the
woven product produced defmed in length by the number of filling picks of the
fill yam
and defined in width by the number of warp yams in which the fill yarn is
woven
therebetween. Such terminology and processes are common in the art of textile
weaving.
Woven tubular prostheses such as vascular grafts, having tapered diameter
sections or tailored shapes such as those shown in the inventive figures
discussed
herein, have heretofore not been made without requiring manual customization
in the
form of cutting, splicing and/or tailoring with sutures. Continuous flat-
weaving
techniques have not been able to make diameter changes in a gradual manner,
having a
tapered tubular section transitioning from one diameter to another diameter.
Instead,
diameter changes in the woven product occur instantaneously, creating a sudden
split in
the warp yams. Such a sudden split, such as at the crotch section of a
bifurcated
endoluminal graft, leaves gaps or voids in the weave at the splitting point.
Thus,
conventional bifurcated woven grafts have required sewing of the crotch
section in
order to insure a fluid-tight character. Such sewing is labor intensive and is
generally
done manually, thereby introducing the potential for human error and reliance
on the
technique of the technician.
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Furthermore, the prior art techniques of forming tubular shapes have required
manual cutting and suturing of standard woven tubes to the desired size and
shape.
Continuous weaving of tubular grafts to produce seamless gradual diameter
transitions
in devices has not been previously known. For example, the change from a first
diameter to a second diameter in a single lumen, straight graft, in a
continuous weaving
process was not attempted due to the aforementioned limitations. Instead,
individual
grafts of different diameters would be individually woven and sutured together
to make
a continuous tube. The diameter change required customized cutting to
gradually
transition from one diameter to another. For example, in the case where a
bifurcated
graft having a 24 mm aortic section and leg sections with different diameters,
e.g. 12
mm and 10 mm, the surgeon would manually cut and tailor one of the legs of a
bifurcated graft which was formed having two equal leg sections with the same
diameters, and suture a seam along that leg to form a leg of the desired
different
diameter. This customization required cutting and suturing. Such customization
relied
heavily on the skill of the physician and resulted in little quality control
in the final
product. Additionally, such grafts could not always be made in advance for a
particular
patient, since the requirements for such customization may not be known until
the
doctor begins the surgery or procedure of introducing the device into the
body.
Additionally, as previously mentioned, the suture seams take up considerable
amounts
of space when packed into the delivery capsule or other catheter-like device
designed to
deploy the endoluminal prostheses.
There is currently no prior art means to satisfy the variation in requirements
from patient to patient for proper fit of the endoprosthesis. Prior art
continuously
woven bifurcated grafts not only suffered from the gap created at the warp
yarn split,
but they existed only with iliac leg portions having equal diameters. If
different
diameter iliac leg portions were required, this would again be accomplished
through
customization. One leg would be manually cut-off and another independently
formed
leg having a different diameter would be sutured on in its place.
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Complex shapes, such as tubular "S" shaped or frustoconical shaped woven
sections were not even attempted due to the impractibility, intensive labor
and
subsequent cost. Such shaped tubes could not practically be woven using prior
art
techniques.
In addition to requiring manual sewing steps, sutures used in prior art
customized grafts create seams which are to be avoided in endoluminal
prostheses,
particularly because of the space which they take up when tightly packed into
a catheter
delivery system. Furthermore, such seams contribute to irregularities in the
surface of
the graft and potential weakened areas which are obviously not desirable.
Due to the impracticalities of manufacturing tubular grafts and
endoprostheses,
straight and bifurcated tubular grafts often required customization by doctors
using
cutting and suturing for proper size and shape.
With the present invention, designs are now possible which heretofore have not
been realized. Thus, the weaving of gradually shaped tubular grafts in a
continuous
process to create seamless and void-free conduits for implantation in the body
has
heretofore not been possible. The present invention provides a process of
producing
such grafts, as well as providing the weaving structure inherent in products
formed
therefrom.
SUMMARY OF THE INVENTION=
The present invention relates to flat-woven implantable tubular prostheses,
and
in particular endoluminal grafts, which have been continuously woven to form
seamless
tubular products having gradual changes in diameter along their length, as
well as
various shaped tubular sections formed from gradual changes in the number of
warp
yams engaged or disengaged with the fill yarns during the weaving process.
Changes
in diameter and/or shape are accomplished by gradually engaging and/or
disengaging
selected warp yams with the fill yams in the weave pattern. It has been
discovered that
such a gradual transition can be accomplished using electronic jacquard looms
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controlled by computer software. Such engaging and/or disengaging of warp
yarns can
change the diameter of the tube in a manner which creates a seamless and
gradual
transition from one diameter to another. Additionally, such engagement and/or
disengagement can be used to create tubular vascular prostheses and the like
which
have any number of shapes as depicted and further described herein.
Thus, in one embodiment of the present invention there is provided, a flat-
woven implantable tubular prosthesis having warp yarns and fill yarns
including first
and second spaced apart portions which define therebetween a transition
tubular wall
extent, the first portion having a first diameter and the second portion
having at least a
second diameter different from the first diameter. The tubular prosthesis
further
includes a weaving pattern along the transition tubular wall extent, said
weaving pattern
having a gradual change in the number of warp yarns to provide a seamless
transition
between the first and second portions.
In another embodiment of the present invention there is provided, a flat-woven
implantable tubular prosthesis including first and second ends defining a
tubular wall
therebetween, with the tubular wall including warp yams and fill yarns. The
tubular
wall is defined by a first elongate woven section with a first selected number
of warp
yarns therealong to define a first tubular internal diameter, and a second
elongate
woven section seamlessly contiguous with the first woven section and having a
gradual
change in the number of warp yams therealong to define at least a second
tubular
internal diameter.
In an alternative embodiment of the present invention, there is provided, a
flat-
woven tubular implantable prosthesis having warp yarns and fill yarns
including first
and second ends defining a tubular wall therebetween, with the tubular wall
having a
first woven extent with a first selected number of warp yams therealong to
define a first
tubular intemal diameter, a transitional second woven extent contiguous with
the first
woven section with at least a second selected number of warp yarns therealong
to
define at least a second tubular internal diameter which is different from the
first
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tubular internal diameter, and at least a third woven extent contiguous with
the second
woven extent with a third selected number of warp yarns which is different
from the
first and said second selected number of warp yarns, with the third woven
extent
defining a third tubular internal diameter which is different from the first
and second
tubular internal diameters.
Additionally, methods of forming such endoluminal prostheses are also
provided. In one of such methods, there is provided a method of forming a
seamless
flat-woven implantable tubular prosthesis including the steps of weaving a
tubular wall
having transitional diameter along a longitudinal extent thereof, such weaving
including
gradually engaging or disengaging additional warp yams along the extent to
transition
from a first diameter to a second diameter different from the first diameter.
Another embodiment of the methods of the present invention includes a method
of making a seamless flat-woven implantable tubular prosthesis including
weaving a
first section of the prosthesis having a first diameter using a first selected
number of
warp yarns, and transitioning to a second section of the prosthesis having a
second
diameter different from the first diameter by gradually engaging or
disengaging warp
yams.
Additionally included in the present invention is a method of forming a flat-
woven synthetic tubular implantable prostheses having a precise pre-determined
internal diameter (D) including the steps of: (i) choosing a desired weave
pattern;
(ii)providing a desired yam and yarn size for the weaving pattern; (iii)
providing a
desired density (p) at which the yam is to be woven; (iv) providing a number
of warp
yams (S) required to weave a suitable tubing edge; (v) choosing a desired
internal
diameter (D) of the tubular prosthesis; (vi) calculating the total number of
warp yams
(N) required to weave the tubular prosthesis having the intemal diameter (D)
using the
formula:
N = S + (D x p)
wherein N represents the total number of warp yarns required, S represents the
number
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of warp yarns required to weave a suitable tubing edge , D represents the
desired
internal diameter and p represents the number of warp yarns per unit of
diameter.
BRIEF DESCRIPTION OF THE DRAWINGS:
Figures I a, I b and 1 c depict perspective views of a graft constructed in
accordance with the prior art.
Figures 2, 3, 4, 5, 6 and 7 depict perspective views of shaped grafts
constructed
in accordance with various embodiments of the present invention.
Figure 8 is a perspective view of a graft of the present invention having a
first
diameter tapering to a second diameter shown in a flat, radially compressed
form after
weaving but prior to heat setting.
Figure 9 is a cross-sectional view of the graft shown in Figure 8.
Figure 10 is a cross-sectional view of the graft of Figure 8 after heat
setting.
Figures I I a and 11 b are perspective views of weave patterns in accordance
with
the present invention.
Figure 12 is a perspective view of grafts being continuously flat-woven in
accordance with the present invention, showing warp yarns gradually disengaged
from
the weave during weaving of one of the graft sections.
Figure 13 shows a photomicrograph of the internal woven portion of a crotch
section of a bifurcated graft of the prior art at a magnification of l Ox.
Figure 14 shows a photomicrograph of the internal portion of a crotch section
of
a bifurcated graft made in accordance with the present invention at a
magnification of
I Ox.
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Figures 15, 16 and 17 depict perspective views of bifurcated grafts
constructed
in accordance with alternative embodiments of the present invention.
Figure 18 depicts a perspective view of a trifurcated graft constructed in
accordance with an alternative embodiment of the present invention.
Figure 19 shows a scanning electron micrograph of the internal portion of a
crotch section of a bifurcated graft of the prior art at a magnification of
30x.
Figure 20 shows a scanning electron micrograph of the intemal portion of the
crotch section of a bifurcated graft made in accordance with the present
invention at a
magnification of 45x.
Figure 21 is a perspective view of a bifurcated graft of the present invention
shown in a flat, radially compressed form after weaving, but prior to heat-
setting.
Figure 22 is a cross-sectional view of the graft shown in Figure 21.
Figure 23 is a cross-sectional view of the graft of Figure 21 after heat
setting.
Figure 24 is a perspective view of bifurcated grafts being continuously
seamlessly flat-woven in accordance with the present invention, showing warp
yams
gradually disengaged from the weave during weaving of the iliac sections.
Figure 25 is a perspective view of bifurcated grafts being continuously
seamlessly flat-woven in accordance with the present invention, showing warp
yarns
gradually disengaged from the weave during weaving of the aortic section.
Figure 26 is a perspective view of the bifurcated graft of Figure 17 used in
connection with the tapered graft of Figure 5, with an internal stent shown at
one
portion of the graft.
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Figure 27 is a perspective view of the bifurcated graft of Figure 17 including
an
internal stent extending therethrough.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT:
It has been discovered through the present invention that tubular woven
textile
products such as vascular grafts can be seamlessly woven into a variety of
shapes and
sizes, without the need for any post-weaving fabrication techniques such as
cutting,
sewing, suturing and the like.
A recurrent problem and limitation in prior art techniques of tubular weaving
can be evidenced through the prior art techniques for manufacturing split
grafts, such as
bifurcated grafts, trifurcated grafts, and the like. A split graft consists of
a tubular graft
section of a certain diameter, which splits at a crotch area into a plurality
of tubular
graft sections or members of a different diameter than the first graft
section. For
example, a bifurcated graft, as depicted in Figure 15, includes an aortic
woven portion
620 with a crotch 627, and splits into first and second iliac woven portions
630a and
630b. For the purposes of the present invention, split grafts are designated
as having a
first graft section referred to as an aortic woven portion and second graft
sections
referred to as iliac woven portions or iliac leg sections, since in preferred
embodiments,
such split grafts, i.e. bifurcated grafts, are meant for implantation within
the aorta at the
branch of the iliac arteries, for instance, for use in repairing an aortic
aneurism.
In conventional manufacturing processes for tubular weaving of bifurcated
grafts, it was necessary to split the number of warp yarns at the crotch area
during the
weaving process in order to split the tubular woven graft from the first
aortic woven
portion 620 into the first and second iliac woven portions 630a and 630b. This
splitting
of warp yams was necessary in order to accomplish the transition at the crotch
627,
where the diameter of the graft transitions from a first inner diameter of the
aortic
woven portion 620 to two separate inner diameters representing the first and
second
iliac woven portions 630a and 630b . In prior art processes, however, such
transition in
split grafts from a first diameter to two equal second diameters was
accomplished by
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splitting the warp yarns evenly at the crotch 627 during the weaving process.
It is
known that it is desired to us an odd number of warp yarns in order to form a
continuous plain weave pattern for tubular weaving. Thus, such splitting of
the number
of warp yams in half at the crotch area in order to form iliac leg portions in
prior art
processes resulted in an incorrect number of warp yams in one of the iliac leg
portions,
since the number of warp yarns required in the tubular weaving of the aortic
portion
was of an odd number, and splitting this odd number in half results in an odd
number
and an even number. Thus, in prior art processes, at least one of the iliac
leg portions
of a tubular woven graft often included an incorrect weave pattern at the flat-
woven
edge.
In an effort to correct this problem resulting in the wrong number of warp
yarns
in one of the iliac leg portions, the present inventors discovered that it is
possible to
disengage a warp yarn from the weave pattern for that portion of the weaving
process
required to weave the iliac leg portions without deleterious effects. In the
prior art
weaving processes the number of warp yams generally remained constant
throughout
the weaving pattern, due to the inefficiencies and impracticability of
disengaging a
warp yarn for only a portion of the weaving pattern. The present invention
utilizes
specially designed software and a customized electronic tubular weaving
machine for
disengaging a warp yam for a portion or portions of the weaving pattern. Thus,
by
disengaging one warp yam from the weave pattern at the crotch area during the
weaving process, an odd number of warp yarns could be utilized during the
weaving of
the iliac leg sections of the graft, and the correct weave pattem would be
produced
throughout the entire graft.
As previously discussed, a further problem with prior art processes in the
manufacture of tubular woven grafts related to achieving precise diameters of
the graft.
Often times, the portion of a damaged blood vessel to be repaired included a
taper or
diameter change, wherein the blood vessel changes from one diameter to a
second
diameter over the area to be repaired. In the prior art, in order to
compensate for such
changes in diameters, a surgeon commonly cuts a seamless tubular woven graft
along
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its length, as demonstrated in Figures 1 a, 1 b and 1 c. In Figure 1 a, a
seamless tubular
woven graft 10' is depicted, having a first end 12' and a second end 14', with
an internal
diameter extending through the tubular graft. As shown in Figure 1 b, a cut in
the wall
of the graft was made, leaving cut edges 13'. Thereafter, the cut edges 13'
were sutured
together by a surgeon with edge sutures 15', thereby providing a tubular woven
graft 10'
with one diameter at first end 12' which gradually tapers to a second diameter
at second
end 14' by way of taper seam 16'. Such a tapering process, however, involved a
post-
fabrication technique, resulting in a tubular woven graft which was no longer
seamless
and required additional steps after fabrication of the graft. -
In order to overcome these problems, the present inventor discovered that such
a
tubular-woven graft could be tapered during the weaving process, producing a
seamless
tubular-woven graft having a tapered configuration, as well as a variety of
other tapers,
flares, and shapes as shown in Figures 2 through 7.
With reference to Figure 2, a typical seamless tubular-woven textile graft 10
in
accordance with the present invention is shown generally as a tapered graft in
a
generally frustoconical shape. Graft 10 is a textile product formed of a woven
synthetic
fabric. Graft 10 is depicted in one embodiment in Figure 2 which includes a
generally
tubular body 17 having a first end 12 and an opposed second end 14, defining
therebetween an inner lumen 18 which permits passage of blood once graft 10 is
implanted in the body. Graft 10 includes continuous transitional woven portion
25
extending between first end 12 and second end 14, and extending along the
entire
length of graft 10. Graft 10 of Figure 2 has a generally frustoconical shape,
with first
end 12 having a first tubular inner diameter and second end 14 having a second
tubular
inner diameter which is different than the inner diameter of first end 12. For
example,
first end 12 may have an inner diameter of 12 millimeters and second end 14
may have
an inner diameter of 10 millimeters, with transitional woven portion 25
forming a
gradual taper having successive changes in diameter throughout such that graft
10
gradually tapers from the 12 millimeter inner diameter of first end 12 to the
10
millimeter inner diameter of second end 14 along the length of transitional
woven
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portion 25. The gradual tapering of transitional woven portion 25 is
accomplished by
gradually disengaging and/or engaging a selected number of warp yams from the
weaving pattern during weaving of the graft, as will be discussed in more
detail herein.
Figures 3, 4, 5, 6 and 7 show various shapes of grafts that can be formed
according to the present invention. Figure 3 shows a variation of the
configuration of
Figure 2, with graft 100 in the form of a step-tapered graft having a tubular
body 117
with a first end 112 and an opposed second end 114 defining an inner lumen 118
therebetween. In the embodiment of Figure 3, graft 100 includes first woven
portion
120 which defines a portion of tubular wall 117 having a continuous first
inner
diameter and second woven portion 130 which defines a portion of tubular wall
117
having a continuous second inner diameter which is different than the inner
diameter of
first woven portion 120. Graft 100 of Figure 3 further includes transitional
woven
portion 125 adjacent and contiguous with first and second woven portions 120
and 130.
In such an embodiment, graft 100 includes a constant diameter extending
through first
woven portion 120 and a constant diameter which is different than the inner
diameter of
first woven portion 120 which extends through second woven portion 130, and
gradually tapers from the inner diameter of first woven portion 120 to the
inner
diameter of second woven portion 130 through the length of transitional woven
portion
125.
Figure 4 shows a further variation on the step-tapered configuration of Figure
3,
with graft 200 having a tubular body 217 with a first end 212 and an opposed
second
end 214 defining an inner lumen 218 therebetween. In the embodiment of Figure
4,
graft 200 includes a first woven portion 220 and a transitional woven portion
225, with
the first woven portion 220 defining first end 212 and including a continuous
inner
diameter along the length thereof, and the transitional woven portion 225
defining
second end 214 and including a gradual taper such that graft 200 gradually
tapers from
the inner diameter of first woven portion 220 to a second diameter at second
end 214
which is different than the inner diameter of first woven portion 220. It is
contemplated
that such gradually tapering can be either an inward taper or an outward taper
(flared).
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WO 97/43y33 PCT/US97/08602 Figure 5 shows a further variation on the
configuration of graft 10 of Figure 2,
with graft 300 having a tubular body 317 with a first end 312 and an opposed
second
end 314 defining an inner lumen 318 therebetween. In the embodiment of Figure
5,
graft 300 includes a transitional woven portion 325 and a second woven portion
330,
with the transitional woven portion 325 defining first end 312 and the second
woven
portion 330 including a continuous inner diameter along the length thereof,
and
defining second end 314. Further, transitional woven portion 325 includes a
gradual
taper such that graft 300 gradually tapers outwardly from the inner diameter
of first end
312 to a second diameter at second end 314 which is different than the inner
diameter
of first end 312.
Figures 6 and 7 show further shapes which can be formed according to the
present invention. Figure 6 depicts a sinusoidal shaped graft 400 having a
tubular body
417 with a first end 412 and an opposed second end 414 defining an inner lumen
418
therebetween. In the embodiment of Figure 6, graft 400 includes a continuous
first
woven portion 420, with the first woven portion 420 defining both first and
second
ends 412 and 414. First woven portion 420 has a continuous inner diameter
along the
length thereof, such that first end 412 and second end 414 have the same inner
diameter. Graft 400 is shaped along its length in an "S" configuration, with
tubular
body 417 gradually changing direction as warp yams on one edge of graft 400
during
the weaving process are engaged or disengaged while the same portion of
tubular body
417 on the other edge of graft 400 equally changes in the same direction as
warp yams
are engaged or disengaged at this edge. Thus, as warp yams at one edge of the
graft are
disengaged as that edge and shape of the graft gradually curves, the
corresponding warp
yams at the opposite edge on the same pick are engaged. As the "S" shape again
changes direction, the opposite may be true, i.e., warp yarns at a given pick
on one edge
may be engaging as corresponding warp yams at the other edge on the same pick
may
be disengaging. In order to maintain a constant diameter, the warp yams at
each of the
edges of the tubular graft must simultaneously change by additionally adding
or
engaging an equal number of warp yams on one edge as the other edge loses or
disengages warps. Thus, the total number of warp yarns within the tubular wall
remains constant during the weaving process.
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Figure 7 depicts a variation of the sinusoidal shaped graft 400 shown in
Figure
6. Graft 500 in Figure 7 includes a tubular body 517 with a first end 512 and
an
opposed second end 514 defining an inner lumen 518 therebetween. In the
embodiment of Figure 7, graft 500 includes first woven portion 520 having a
first inner
diameter and second woven portion 530 having a second inner diameter which is
different than the inner diameter of first woven portion 520. Graft 500
further includes
transitional woven portion 525 adjacent first and second woven portions 520
and 530.
For example, first woven portion 520 may include a woven graft section having
an
inner diameter of 12 millimeters and second woven portion 530 may include a
woven
graft section having an inner diameter of 10 millimeters, with transitional
woven
portion 525 forming a gradual taper such that graft 500 gradually tapers from
the 12
millimeter inner diameter of first woven portion 520 to the 10 millimeter
inner diameter
of second woven portion 530 along the length of transitional woven portion
525. Graft
500 is shaped along its length in an "S" configuration similar to the manner
in Figure 6,
with tubular body 517 gradually tapering in on one side of graft 500 during
the weaving
process while the same portion of tubular body 517 on the other side of graft
500 tapers
outwardly.
While a variety of shapes and configurations are shown in the drawings and
described herein, any seamless tubular flat-woven graft incorporating a
gradual
transitional continuously woven portion is contemplated by the present
invention. The
gradual tapering of the transitional woven portion is accomplished in each of
the
inventive embodiments by gradually disengaging and/or engaging a selected
number of
warp yarns from the weaving pattern during weaving of the graft, as will be
discussed
in more detail herein.
Through the present invention it is now possible to accomplish disengaging
and/or engaging of selected warp yarns to create gradual changes with size,
shape or
configuration of the graft during weaving of the graft. It has been discovered
through
the present invention, however, that such disengaging and/or engaging of the
warp
CA 02422915 2003-03-25
WO 97/43983 PCT/US97/08602 yams must be accomplished in a gradual transition
in order to prevent holes or voids
between the contiguous sections of the woven graft. It is known that a
delicate balance
exists between porosity of the graft for proper ingrowth and the need in many
applications for fluid-tight walls. It has been determined that a void greater
than the
diameter of about three warp yarns results in a graft with a porosity which is
unacceptable as a fluid-tight conduit and may be incapable of sufficiently
maintaining
blood pressure therein. Thus, the transition from a graft section of one
diameter to a
graft section of another diameter must be accomplished in fluid-tight
applications
without creating such voids between the contiguous weave sections which are
generally
greater than the diameter of three warp yarns. In applications where fluid-
tight walls
are not crucial, the size of such voids may of course be greater.
Any type of textile product can be used as the warp yarns and fill yarns of
the
present invention. Of particular usefulness in forming the woven prostheses of
the
present invention are synthetic materials such as thermoplastic polymers.
Thermoplastic yarns suitable for use in the present invention include, but are
not
limited to, polyesters, polypropylenes, polyethylenes, polyurethanes and
polytetrafluoroethylenes. The yams may be of the monofilament, multifilament,
or
spun type.
The yams used in forming the woven grafts of the present invention may be
flat,
twisted or textured, and may have high, low or moderate shrinkage properties.
Additionally, the yarn type and yam denier can be selected to meet specific
properties
desired for the prosthesis, such as porosity, flexibility and compliance. The
yam denier
represents the linear density of the yarn (number of grams mass divided by
9,000
meters of length). Thus, a yam with a small denier would correspond to a very
fine
yarn whereas a yarn with a larger denier, e.g., 1000, would correspond to a
heavy yam.
The yams used with the present invention may have a denier from about 20 to
about
1000, preferably from about 40 to about 300. Preferably, the warp and fill
yarns are
polyester, and most preferably the warp and fill yams are one ply, 50 denier,
48
filament flat polyester.
16
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WO 97/43983 PCT/US97/08602
The graft of the present invention can be woven using any known weave pattern
in the art, including, simple weaves, basket weaves, twill weaves, velour
weaves and
the like, and is preferably woven using a flat plain tubular weave pattern,
most
preferably with about 170-190 warp yarns (ends) per inch per layer and about
86-90 fill
yams (picks) per inch per layer. The wall thickness of the graft may be any
conventional useful thickness, but is preferably no greater than about 0.16
mm, with the
most preferable wall thickness being from about 0.07 mm to about 0.14 mm.
These
thicknesses facilitate the folding of the graft into an appropriate delivery
system.
Moreover, the seamless (i.e., sutureless) feature of the present invention
further
facilitates packing and folding of the graft into the delivery system.
As noted, transition from one diameter to another diameter is accomplished by
gradually engaging and/or disengaging selected warp yarns from the weave
pattern. In
the present invention, it has been discovered that such a transition can be
effectively
accomplished by engaging or disengaging a maximum of three warp yarns per four
successive machine picks for a given weave pattern on each edge of the graft.
Such
disengaging or engaging of -warp yams can be accomplished in any combination
of
numbers. For example, up to three warp yams can be disengaged or engaged at
any of
the four successive machine picks, as long as the total number of warp yarns
engaged
and/or disengaged does not exceed a maximum of three warp yams per four
machine
picks on each edge of the tubular flat-woven product. An edge is defined as an
outer
limit of the graft width as taken along the longitudinal axis as the graft is
flat-woven on
the loom. Figure 8 shows such edges at 117c. As previously noted, two machine
picks
represents one filling pick of tubular fabric, i.e., one tubular fill yarn.
Thus, four
machine picks represents two tubular fill yarns.
As noted above, preferably the tubular-woven graft of the present invention is
constructed of polyester which is capable of shrinking during a heat set
process. For
instance, such grafts are typically flat-woven in a tubular form. Due to the
nature of the
flat-weaving process, the tubular graft is generally flat in shape after
weaving, as
depicted in Figure 8, which shows a graft 100 in one embodiment of the present
17
CA 02422915 2003-03-25
WO 97/43983 PCT/US97/08602 invention as flat-woven in a tubular step-tapered
form as shown in Figure 3. As shown
in cross-sectional view in Figure 9, such a flat-woven tubular graft
subsequent to
weaving a generally elliptical-shape. Such grafts, however, when constructed
of heat-
settable polyester yarn, can be heat set on a mandrel to form a generally
circular shape,
as depicted in Figure 10.
Such a heat setting process is accomplished by first flat-weaving the graft in
a
tubular form out of a material capable of shrinking during a heat setting
process. After
the graft is woven, the graft is placed on a mandrel, and heated in an oven at
a
temperature and time capable of causing the yams of the graft to heat set to
the shape
and diameter of the mandrel. Preferably polyester yarns are used as the warp
and fill
yams, and the heat setting is accomplished at time and temperatures
appropriate for the
material. For example, heat setting can be accomplished at about 190-200 C
for a
period of about 14-16 minutes. Other methods of heat setting known in the art
may be
employed. After such a heat setting process, the graft can be formed into a
shape
desired for implantation, having a generally circular inner lumen.
As noted above, due to the nature of the flat-weaving process, while graft 100
is
tubular, it is generally flat in shape during weaving and prior to the
aforementioned heat
setting, as shown in Figure 9. The post-fabrication flat shape of tubular wall
117 is
comprised of top tubular body portion I 17a and bottom tubular body portion
117b,
which connect at tubular body edges 117c. While reference has been made to a
heat
setting process for forming graft 100 into a generally cylindrical shape as
shown in
Figure 10, graft 100 can be provided as a finished product in the generally
flat shape
shown in Figure 9, or can be made cylindrical in shape by any known methods.
Further, crimping of the graft 100 along the length of tubular wall 117 to
provide
structural integrity is contemplated.
Figure 1 la shows a conventional plain tubular weave pattern known in the art.
Warp yarns 160 are further shown as 160a indicating they are in the top layer
of the
weave and 160b indicating their presence in the bottom layer of the weave. Top
warp
18
CA 02422915 2003-03-25
WO 97143983 PCT/US97/08602
yarns 160a and bottom warp yarns 160b run in a lengthwise direction in the
graft and
define the width of the graft. Fill yarns 170 are further shown as top fill
yarns 170a and
bottom fill yarns 170b. These fill yarns are woven with the top and bottom
warp yarns
160a and 160b as shown in Figure 11 a in a manner known in the art. For
example, a
filling yarn shuttle (not shown) passes across warp yarns 160 while selected
warp yarns
160 are lifted according to a specific weave pattern. In electronic weaving
machines,
such weave patterns can be programmed using software into the machine. In a
typical
plain tubular weave as depicted in Figure 11 a, the shuttle first weaves top
fill yarn 170a
by passing across warp yarns 160 while certain warp yarns 160 are lifted.
During travel
of top fill yarns 170a (direction X) for weaving of the top tubular body
portion such as
top tubular body portion 117a of graft 100, the bottom warp yarns 160b are not
lifted to
prevent top fill yarns 170a from interweaving with bottom warp yarns 160b.
Likewise,
during passage of bottom fill yams 170b (direction Y) for weaving of the
bottom
tubular body portion such as the bottom tubular body portion 117b of graft
100, the top
warp yarns 160a are always lifted such that bottom fill yarns 170b are not
interwoven
with top warp yams 160a. The plain tubular weave pattern as just described can
be
used to form straight portions of the inventive grafts which have a constant
diameter.
This pattern is then modified by gradually engaging or disengaging warp yarns
to create
tapers and/or shapes.
For example, the plain weave pattern shown in Figure 11 a and described above
is formed by continuously passing top and bottom fill yarns 170a and 170b back
and
forth across warp yarns 160 to form first woven portion 120 of graft 100 shown
in
Figure 12.
Figure l lb shows a plain tubular weave pattern having a gradual disengaging
of
warp yarns. As seen in Figure 11 b, warp yarns 160' have been disengaged from
the
pattem and are no longer interwoven beginning at the fill yarn 170'. Likewise,
the next
set of picks shows an additional warp yarn being disengaged. As noted, the
pattem is
within the maximum disengagement of three warp yams per four machine picks.
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WO 97/43983 PCT/US97/08602
The disengaging of the warp yams is accomplished by dropping the desired
warp yams from the end of the tubular flat-woven graft during the weaving
process,
such that the fill yarns are not interwoven across the warp yarns for that
section of the
pattem. Such dropping of warp yarns in a gradual manner forms the transitional
portion of the graft. In continuous flat-weaving processes, the warp yams are
then re-
engaged during the weave pattern once the transitional section has been
completed.
Once the complete graft has been woven, the weave pattern may be repeated
creating
the next graft to be woven in a continuous process.
Figure 12 shows a plurality of grafts 100 being woven in a continuous flat-
weaving process, in accordance with the present invention. First woven portion
120 is
of one inner diameter, for instance 24 millimeters, while second woven portion
130 is
of another inner diameter different than that of first woven portion 120, for
instance 18
millimeters. As such, first woven portion 120 requires more warp yams 160 for
weaving than does second woven portion 130. Thus, at transitional portion 125,
the
warp yarns are gradually disengaged from the weave, as depicted by disengaged
warp
yarns 160'. Since the grafts of the present invention are preferably
fabricated using a
continuous flat-weaving process, disengaged warp yams I60' must be re-engaged
into
the weave pattern after completion of the second woven portion in order to
begin
weaving the first woven portion of the subsequent graft to be produced.
Through such
a continuous flat-weaving process, a plurality of grafts 100 can be woven in a
continuous manner, and can be cut apart along line C after fabrication.
Furthermore,
disengaged warp yams 160' are removed subsequent to weaving.
For flat-weaving of bifurcated tubular grafts, prior art processes typically
involved splitting of the warp yarns in half at the portion of the weave
pattern where-the
graft splits from the aortic graft portion to the iliac leg portions, with the
iliac leg
sections of the graft therefore being woven with half the number of warp yarns
as the
aortic section of the graft. With such techniques, however, variations in the
diameters
of the iliac leg sections could not be accomplished in a seamiess manner.
Typically,
when a tubular woven bifurcated graft with two different diameter iliac leg
portions
CA 02422915 2003-03-25
WO 97/43983 PCT/US97/08602
was required, i.e., when a tubular woven bifurcated graft having iliac leg
portions with
diameters different than that which would be formed by splitting the number of
warp
yarns in half was desired, the bifurcated graft would have to be first woven
in a
conventional manner, followed by cutting and suturing of the iliac to achieve
the
desired diameter. As discussed above, grafts produced in such a manner
resulted in
many drawbacks. For instance, the suture seam added to the wall thickness of
the graft
and added a discontinuity to the internal wall surface of the graft. Further,
grafts
requiring such post-fabrication suturing resulted in voids in the graft wall
from the
needle which was used for suturing. Figure 13 shows a photomicrograph of an
enlarged view of the internal portion of a prior art bifurcated graft woven of
warp yams
161 and fill yarns 171 at the crotch area 627' of the graft, where the two
iliac leg
portions branch off from the aortic portion. Needle holes 140 are present in
the wall of
the graft, representing holes through the graft wall which were made by a
needle during
suturing of the iliac leg portions to the aortic portion.
Through the present invention, split grafts such as bifurcated grafts can be
flat-
woven in a tubular form with varying diameters in the iliac portions and the
aortic
portion, without the need for such post-fabrication suturing. This is
accomplished by a
gradual transition in the number of warp yams in the weave of the graft, as
accomplished in the tapered grafts discussed above. Such gradual transition is
accomplished by gradually engaging or disengaging warp yams during the
fabrication
of the graft at the transition from the aortic graft portion to the iliac leg
portions of the
graft. A bifurcated graft produced in this manner is shown in an enlarged view
at
Figure 14. Figure 14 shows a bifurcated graft having first and second iliac
woven
portions 630a and 630b. As compared with the prior art graft shown in Figure
13, the
needle holes 140 which were created from the suturing needle required for
attachment
of the iliac legs in the prior art grafts are not present in the graft
produced in accordance
with the present invention.
Referring generally to Figure 15, a typical tubular woven bifurcated graft 600
includes a generally tubular body 617 having a first end 612 and opposed
second ends
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CA 02422915 2003-03-25
WO 97/43983 PCT/US97/08602 614a and 614b, defining therebetween an inner lumen
618 which permits passage of
blood once bifurcated graft 600 is implanted in a blood vessel. Bifurcated
graft 600
includes aortic woven portion 620 having a first inner diameter, and further
includes
first and second iliac woven tubular wall portions 630a and 630b each having
an inner
diameter which is different than the inner diameter of aortic woven portion
620. The
inner diameters of first and second iliac woven portions 630a and 630b can be
the same,
as depicted in Figure 15, or can be different, as depicted in 730a and 730b of
Figure 16.
Further, iliac woven portions 630a and 630b can be of the same general length
as
shown in Figures 15 and 16, or can be of different general lengths, as shown
at 830a
and 830b in Figure 17. Bifurcated graft 600 further includes bifurcated
transitional
woven portion 625 contiguous with aortic woven portion 620 and first and
second iliac
woven portions 630a and 630b at crotch 627 forming a bifurcated arch.
Bifurcated
transitional woven portion 625 forms a gradual taper such that bifurcated
graft 600
gradually tapers from the inner diameter of aortic woven portion 620 to the
inner
diameters of first and second iliac woven portions 630a and 630b along the
length of
bifurcated transitional woven portion 625. The gradual tapering of bifurcated
transitional woven portion 625 is accomplished by gradually disengaging and/or
engaging a selected number of warp yarns from the weaving pattern during
weaving of
the graft, as accomplished in the preferred embodiment discussed above.
Figure 18 depicts a trifurcated graft 900 in accordance with an alternative
embodiment of the present invention. Trifurcated graft 900 is of the same
general
configuration as bifurcated graft 600 shown in Figure 17, including a
generally tubular
body 917 having first end 912, second ends 914a, 914b and 914c with first
woven
portion 920, transitional woven portion 925, first and second iliac woven
portions 930a
and 930b, and further includes an additional iliac leg as iliac woven portion
930c.
Further, trifurcated graft 900 also includes crotches 927a, 927b and 927c (not
shown),
extending between transitional woven portion 925 and each of iliac woven
portions
930a, 930b and 930c.
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WO 97/43983 PCTIUS97/08602
Prior art processes for tubular weaving of split grafts such as bifurcated and
trifurcated grafts and the like resulted in holes or voids in the crotch area
of the grafts,
which in certain applications further resulted in undesirable porosity for the
graft. The
porosity of grafts is of vital importance, since such grafts are to be
implanted into the
body as fluid conduits and therefore must be of a porosity which prevents
undesirable
fluid leakage through the wall of the graft. The voids which were formed in
the crotch
area of bifurcated grafts produced by the prior art tubular weaving techniques
resulted
in high porosity of the graft at the crotch area and required suturing before
they were
acceptable for implantation. A bifurcated graft woven of warp yarns 161 and
fill yarns
171 having such reinforcement sutures is depicted in Figure 19, representing
the prior
art. Figure 19 is a scanning electron micrograph of a prior art bifurcated
graft showing
the crotch area in an enlarged view. Warp yarns 161 and fill yarns 171 are
seen
generally in the micrograph. Crotch sutures 150 are shown, which undesirably
create
an added area of wall thickness in the graft.
The present inventor has discovered that such voids in the crotch area of a
split
graft can be avoided by gradually transferring the warp yams during the
weaving
process from one woven section to another woven section contiguous thereto,
thereby
avoiding the necessity for post-fabrication suturing of voids. Thus, as
depicted in
Figure 20, a closed weave is established in crotch 627 of a bifurcated graft
600, by
gradually transferring the warp yarns during the weaving process from one
woven
section to another woven section contiguous therewith.
For exampie, during weaving of the bifurcated graft 600, as shown in Figure
15,
the warp yarns 160 which are being interwoven by the fill yams 170 are
gradually
transferred from the aortic woven section 620 and the transitional woven
section 625 to
each of the iliac woven portions 630a and 630b.
Further, during weaving of bifurcated graft 600, two separate filling yarn
shuttles (not shown) are required for weaving of the two distinct iliac woven
portions
630a and 630b. To form the gradual transition in the crotch 627 avoiding
holes, the
23
CA 02422915 2003-03-25
WO 97/43983 PCT/US97/08602
shuttle designated for weaving of iliac woven portion 630a selectively and
gradually
engages warp yams designated for weaving of iliac woven portion 630b.
Likewise, the
shuttle designated for weaving iliac woven portion 630b selectively and
gradually
engages warp yams designated for weaving of iliac woven portion 630a. In this
manner, the crotch 627 is woven using a simultaneous tapering effect at the
interface
between the aortic woven portion 620 and iliac woven portions 630a and 630b.
As
such, a smooth contiguous surface transition is obtained.
When weaving materials for implantation such as vascular grafts, however, it
is
necessary to provide exact inner diameters for the woven grafts. It has been
discovered
that, when using heat setting yams such as polyester for the weaving yarns,
the actual
diameter after heat setting of the yams is not easily predictable using
conventional
techniques. For example, in the prior art weaving of a tubular bifurcated
graft having
an aortic graft section of 26 millimeter inner diameter and two iliac leg
sections of 13
millimeter inner diameter, the warp yams were split in half in order to weave
the iliac
leg sections, with 627 warp yams required for weaving of the aortic graft
section, and
313 warp yarns (half of 627) being used for weaving of each of the iliac leg
sections.
When such a graft was flat-woven of polyester in tubular form and then heat
set,
however, the exact diameters of 26 millimeters for the aortic section and 13
millimeters
for each of the iliac leg sections was not accomplished. Although the aortic
section
achieved the 26 millimeter diameter, the iliac leg portions shrunk to a
smaller diameter
than 13 millimeters, making the graft difficult to remove from the mandrel.
Thus, the
graft was not a true 26x13x13 set of diameters.
As noted above, the invention employs customized, programmable electronic
jacquard weaving machines to gradually engage and/or disengage selected warp
yams
from the weaving pattern during weaving of a flat-woven tubular product. With
such
capabilities, the present inventor has discovered that the number of warp
yarns required
for each of the tubular segments having different diameters can be pre-
determined to
account for the variation in heat shrinkage from one diameter to the next.
Thus, in yet
another alternate embodiment of the present invention, a method of forming a
flat-
24
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'NO 97/43983 PCT/US97/08602
woven synthetic tubular implantable prosthesis having a precise pre-determined
internal
diamter is provided. In the method, a desired weaving pattern is first
selected for
constructing the prosthesis. Preferably, the weaving pattern is selected from
the group
consisting of a simple weave (plain weave), a basket weave, a twill weave, and
velour
weaves. A desired yarn size and yarn diameter is then provided for the weaving
pattern. The density at which the yarn is to be woven in the weave is then
chosen,
represented by a specific number of warp yarns per unit diameter.
Additionally, a
selected number of warp yarns is provided for weaving a suitable tubing edge.
The
desired internal diameter of the tubular prosthesis is then selected. Based
upon
knowing these parameters, the total number of warp yarns required to weave the
tubular
prosthesis with such a desired internal diarneter can be calculated using the
following
formula:
N = S + (D x p)
wherein N represents the total number of warp yarns required, S represents the
number
of edge warp yams required to weave a suitable tubing edge, D represents the
desired
internal diameter and p represents the number of warp yarns per unit of
diameter. By
applying the aforementioned steps, it has been discovered that an exact inner
diameter
for a given synthetic tubular woven product can be predetermined to account
for
variation in shrinkage due to heat setting. In a preferred embodiment, S is 29
when the
diameter D is an even number, and S is 28 when the diameter is an odd number.
In
such a preferred embodiment, the density p is 23 using a I ply/50 denier/48
filament
polyester yam.
Turning now to Figures 21-23, bifurcated graft 600 of Figure 21 is depicted in
a
generally flat tubular shape subsequent to weaving, with top tubular wall
portion 617a
and bottom tubular wall portion 617b connecting at tubular edges 617c in a
similar
means as graft 100, previously discussed with relation to Figures 8-10.
CA 02422915 2006-07-26
Further, Figures 24 and 25 show a plurality of bifurcated grafts 600
being woven in a continuous flat-weaving process, in accordance with one
embodiment of the present invention. Bifurcated grafts 600, as shown in
Figures 24 and 25, are woven in a similar manner as grafts 100, depicted in
Figure 12. In Figure 24, however, bifurcated graft 600 includes aortic woven
portion 620 and first and second iliac woven portions 630a and 630b, with
aortic woven portion 620 requiring more warp yams for weaving than the
iliac woven portions 630a and 630b. As such, during weaving of the iliac
woven portions 630a and 630b, selected warp yarns are gradually
disengaged from the weave at transitional woven portion 625 as represented
by disengaged warp yarns 660'. In Figure 25, iliac woven portions 630a and
630b require more warp yarns for weaving than aortic woven portion 620,
and thus the disengaged warp yams 660' are disengaged during weaving of
the aortic woven section.
The tubular prostheses formed in accordance with the present
invention can be used in surgical procedures as well as non-invasive
procedures. Alternatively, the tubular prostheses of the present invention
can be used in conjunction with a variety of stents in order to maintain the
prostheses within the lumen of the body to be repaired. For example, Figure
26 shows a bifurcated graft 600 in accordance with one embodiment of the
present invention, including a stent 50 affixed thereto at one portion of
bifurcated graft 600. Figure 27 shows a bifurcated graft 600 in accordance
with an altemative embodiment of the present invention, having stent 50
substantially along the entire length of tubularwall 617, positioned within
the
inner lumen of bifurcated graft 600. Such a stent 50 is well known in the art,
and can be constructed in any desired shape and of any material known in
the art, for example, a shaped memory alloy, as disclosed in International
Publication No. WO 95/21592 Al. It is contemplated by the present
invention that stent 50, as well as other stent types, can be used in such a
manner with any of the tubular woven grafts of the present invention.
26
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WO 97/43983 PCT/US97/08502
EXAMPLES
Unless otherwise noted, the grafts of all of the following examples were flat-
woven in a tubular configuration using an electronic jacquard weaving machine.
All of
the grafts were flat-woven using a plain tubular weave pattern. The warp yarns
and the
fill yams were constructed of single ply, 50 denier, 48 filament polyester
with 170-190
warp ends per inch per layer and 86-90 fill yarns per inch per layer.
Example 1
The purpose of Examples 1 and 2 are to demonstrate that even when the
electronic jacquard loom is used, unless the gradual engagement or
disengagement of
warp yarns is employed in accordance with the present invention, acceptable
void free
grafts will not be obtained.
A stepped graft (no taper) was flat-woven on an electronic jacquard loom in a
tubular configuration to produce a 12 millimeter inner diameter section of the
graft and
a 10 millimeter inner diameter portion of the graft. The number of warp yarns
required
for weaving the 12 millimeter inner diameter portion of the graft was
calculated using
the above-mentioned method for pre-determining the number of warp yarns
required to
achieve the true desired diameters upon heat shrinking as follows:
N=S+(Dxp)
N=29+(12x23)
N = 305
The number of warp yarns required for weaving the 10 millimeter inner
diameter portion of the graft was similarly calculated as follows:
N = 29 + (10 x 23)
N=259
27
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WO 97/43983 PCT/US97/08602
The 12 millimeter inner diameter portion of the graft was first flat-woven to
a
desired length. During the flat-weaving process, 46 warp yarns were disengaged
from
the weaving pattern all at once, i.e., at a single machine pick, in order to
produce the 10
millimeter inner diameter portion of the graft. The graft thus produced
included a 12
millimeter inner diameter portion and a 10 millimeter inner diameter portion.
The
transition between the two portions, however, included large holes between the
weave
sections of the graft which were visible to the naked eye.
Example 2
A graft having a 12 millimeter inner diameter portion and a 10 millimeter
inner
diameter portion was flat-woven in a manner similar to that of Example 1.
During the
transition from the 12 millimeter inner diameter portion to the 10 millimeter
inner
diameter portion, however, all 46 warp yarns were not disengaged at once
transitioning
to the 10 millimeter diameter portion. Instead, 4 or more warp yarns were
disengaged
for every 2 machine picks. The graft thus produced included a 12 millimeter
inner
diameter portion and a 10 millimeter inner diameter portion. The transition
between
the two portions, however, also included unacceptable holes between the weave
sections of the graft which were visible to the naked eye.
~mlile 3
This example demonstrates the requirement for a maximum of three warp yarns
which can be engaged or disengaged for every 4 machine picks. A graft having a
12
millimeter inner diameter portion and a 10 millimeter inner diameter portion
was flat-
woven in a manner similar to that of Example'2. During the transition from the
12
millimeter inner diameter portion to the 10 millimeter inner diameter portion,
either 1
or 2 warp yarns were disengaged for every 4 machine picks, with a maximum of 3
warp
yarns being disengaged for every 4 machine picks. The graft thus produced
included a
12 millimeter inner diameter portion and a 10 millimeter inner diameter
portion. The
28
CA 02422915 2003-03-25
WO 97/43983 PCT/US97/08602
transition between the two portions included a gradual transition with no
holes between
the weave sections of the graft.
X~ amn1g 4
This example demonstrates than the selection of the number of warp yarns for
each desired diameter of a bifurcated graft must be made using the inventive
method
steps in order to obtain the true desired diameters and account for variation
in heat
shrinkage. A set of bifurcated grafts were flat-woven in a tubular
configuration to
prodiuce an aortic section having a 24, 26 and 28 millimeter inner diameter
and two
iliac leg sections having a 12, 13 and 14 millimeter inner diameter for each
leg section,
respectively. The aortic section of the grafts were first flat-woven. When the
weave
reached the bifurcation portion, the previously described inventive method of
gradually
changing the warps was not employed. Instead, the number of warp yarns were
split all
at once, i.e., at a given pick, with one warp yarn being disengaged as
necessary for one
leg of the iliac leg section in order to produce the correct weave pattern
(obtain an odd
warp yarn number). The number of warp yarns used for each graft is shown in
Tables
1-3.
None of the number of warp yarns for the aortic or the iliac sections were
determined using the aforementioned inventive method, and as such, none of the
warp
yann numbers were calculated in accordance with the formula stated therein.
Table 1
NUMBER OF WARP YARNS USED NUMBER OF WARP YARNS USED
FOR 24 mm AORTIC SECTION FOR EACH 12 mm ILIAC SECTION
Graft lA 583 291
Graft 1 B 587 293
Graft 1 C 591 295
Graft 1D 595 297
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Table 2
NUMBER OF WARP YARNS USED NUMBER OF WARP YARNS USED
FOR 26 mm AORTIC SECTION FOR EACH 13 mm ILIAC SECTION
Graft 2A 657 313
Graft 2B 631 315
Graft 2C 635 317
Graft 2D 639 319
Tablg3
NUMBER OF WARP YARNS USED NUMBER OF WARP YARNS USED
FOR 28 mm AORTIC SECTION FOR EACH 14 mm ILIAC SECTION
Graft 3A 675 337
Graft 3B 679 339
Graft 3C 683 341
Graft 3D 687 343
After the grafts were woven, they were placed on steel mandrels and heat set
in
an oven for a sufficient time and temperature to heat-set their shapes and
size, i.e., at a
temperature of 190-200 C for 14-16 minutes. After removing the grafts from
the
mandrels, the aortic section of each of the grafts was properly heat set to an
inner
diameter of 24, 26 and 28 millimeters. The iliac leg sections, however, were
heat set
too tightly on the mandrels, making it difficult to remove the leg sections
from the
mandrels. The actual inner diameter of each of the iliac leg sections was less
than the
desired 12, 13 and 14 millimeters, respectively.
Ex~mlile5
The following example demonstrates the use of the inventive method of forming
a bifurcated graft of a desired diameter. This invention also shows, however,
that when
the 'rate of changing (disengaging or engaging) the warp yarns is greater than
3 warp
yams per 4 machine, unacceptable voids are present in the weave.
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A set of bifurcated grafts were flat-woven in a tubular configuration in a
similar
manner as in Example 4, to produce an aortic section having a 24, 26 and 28
millimeter
inner diameter and two iliac leg sections having a 12, 13 and 14 millimeter
inner
diameter for each leg section, respectively. The aortic section of the grafts
were first
flat-woven. When the weave reached the bifurcation portion, the number of warp
yarns
was adjusted by disengaging warp yarns from the weave pattern at a rate of 4
warp
yarns being disengaged for every 4 machine picks. The total number of warp
yarns
used for each graft was calculated by the formula as described herein.
N = S + (D x p)
The calculated warp yarn numbers for each diameter section is set forth in the
tables
below.
Table 4
NUMBER OF WARP YARNS USED NUMBER OF WARP YARNS USED
FOR 24 mm AORTIC SECTION FOR EACH 12 mm ILIAC SECTION
Graft 4 581 305
Table 5
NUMBER OF WARP YARNS USED NUMBER OF WARP YARNS USED
FOR 26 mm AORTIC SECTION FOR EACH 13 mm ILIAC SECTION
Graft 5 627 327
Table 6
NUMBER OF WARP YARNS USED NUMBER OF WARP YARNS USED
FOR 28 mm AORTIC SECTION FOR EACH 14 mm ILIAC SECTION
Graft 6 673 351
After the grafts were woven, they were placed on steel mandrels and heat set
in
an oven at a temperature of 190-200 C for 14-16 minutes. After removing the
grafts
from the mandrels, the aortic section of each of the grafts was properly heat
set to an
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inner diameter of 24, 26 and 28 millimeters, respectively. The iliac leg
sections were
also properly heat set to an inner diameter of 12, 13 and 14 millimeters,
respectively.
When the disengaged warp yarns were removed from the exterior portion of the
aortic
graft section, however, holes visible to the naked eye were present in the
tubular wall of
the graft at the transition between the aortic portion and the iliac leg
portions.
Example 6
This example demonstrates the use of this inventive embodiments, i.e., using
gradually disengaged warp yarns to transition from the aortic section to the
iliac
sections, and the use of the inventive method of calculating the number of
warp yams
required for a given diameter.
A set of bifurcated grafts were flat-woven in a tubular configuration in the
same
manner as in Example 5, to produce an aortic section having a 24, 26 and 28
millimeter
inner diameter and two iliac leg sections having a 12, 13 and 14 millimeter
inner
diameter for each leg section, respectively. When the weave reached the
bifurcation
portion, however, the number of warp yarns was adjusted by disengaging warp
yams
from the weave pattern at a rate of no more than 3 warp yarns being disengaged
for
every 4 machine picks. After the grafts were woven, they were heat set in the
same
manner as in Example 5. After removing the grafts from the mandrels, the inner
diameters of the aortic section of each of the grafts measured 24, 26 and 28
millimeters,
respectively, and diameters of the iliac leg sections measured 12, 13 and 14
millimeters, respectively. The precise desired inner diameters were thus
obtained using
the inventive method of determining the proper number of warp yams necessary
to
account for heat set shrinkage. Moreover, when the disengaged warp yams were
subsequently removed from the exterior portion of the aortic graft section, no
holes
were present in the tubular wall of the graft at the transition between the
aortic portion
and the iliac leg portions. This clearly demonstrates the necessity for the
gradual
change in warp yams as claimed herein.
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The invention being thus described, it will now be evident to those skilled in
the
art that the same may be varied in many ways. Such variations are not to be
regarded
as a departure from the spirit and scope of the invention and all such
modifications are
intended to be included within the scope of the following claims.
33
