Shaped woven tubular soft-tissue prostheses and methods of manufacturing

Continuously flat-woven implantable tubular prostheses have seamless woven sections which gradually change the number of warp yarns to smoothly transition, i.e., taper, from one diameter to another. Multi-diameter endoluminal grafts having a variety of shapes and configurations are made using a seamless weaving process without unacceptable voids or gaps in the tubular wall.

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 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. Oftentimes, 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 and copending U.S. Ser. No. 08/285,334 filed 
on Aug. 2, 1994, herein incorporated by reference. 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 on e 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. 
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 yarns, 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 yarns for a multiple number of machine picks, 
with the woven product produced defined in length by the number of filling 
picks of the fill yam and defined in width by the number of warp yarns 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 yarns. 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. 
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 an 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. 
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 yarns 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 
yarns with the fill yarns in the weave pattern. It has been discovered 
that such a gradual transition can be accomplished using electronic 
jacquard looms 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 
yarns 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 yarns 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 yarns therealong to define a first tubular internal 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 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 yarns 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 yarns. 
Additionally included in the present invention is a method of forming a 
flat-woven synthetic tubular implantable prostheses having a precise 
predetermined internal diameter (D) including the steps of: (i) choosing a 
desired weave pattern; (ii)providing a desired yarn and yarn size for the 
weaving pattern; (iii) providing a desired density (.rho.) at which the 
yam is to be woven; (iv) providing a number of warp yarns (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 yarns 
(N) required to weave the tubular prosthesis having the internal diameter 
(D) using the formula: 
EQU N=S+(D.times..rho.) 
wherein N represents the total number of warp yarns required, S represents 
the number of warp yarns required to weave a suitable tubing edge, D 
represents the desired internal diameter and .rho. represents the number 
of warp yarns per unit of diameter.

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 FIG. 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 yarns 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 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 yarns in half at the crotch area in order to form iliac leg 
portions in prior art processes resulted in an incorrect number of warp 
yarns 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 yam 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 yarns 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 
yarn 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 pattern 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. Oftentimes, 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 
its length, as demonstrated in FIG. 1a, 1b and 1c. In FIG. 1a, 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 FIG. 1b, 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 FIGS. 
2 through 7. 
With reference to FIG. 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 FIG. 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 FIG. 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 portion 25. The gradual tapering of 
transitional woven portion 25 is accomplished 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. 
FIGS. 3, 4, 5, 6 and 7 show various shapes of grafts that can be formed 
according to the present invention. FIG. 3 shows a variation of the 
configuration of FIG. 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 
FIG. 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 FIG. 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. 
FIG. 4 shows a further variation on the step-tapered configuration of FIG. 
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 FIG. 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 gradual tapering can be either 
an inward taper or an outward taper (flared). 
FIG. 5 shows a further variation on the configuration of graft 10 of FIG. 
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 FIG. 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. 
FIGS. 6 and 7 show further shapes which can be formed according to the 
present invention. FIG. 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 FIG. 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 yarns 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 yarns are engaged or 
disengaged at this edge. Thus, as warp yarns at one edge of the graft are 
disengaged as that edge and shape of the graft gradually curves, the 
corresponding warp yarns 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 yarns at the other edge on the same pick may be 
disengaging. In order to maintain a constant diameter, the warp yarns at 
each of the edges of the tubular graft must simultaneously change by 
additionally adding or engaging an equal number of warp yarns 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. 
FIG. 7 depicts a variation of the sinusoidal shaped graft 400 shown in FIG. 
6. Graft 500 in FIG. 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 FIG. 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 
FIG. 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 yarns 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 yarns may be of the monofilament, multifilament, or spun type. 
The yarns 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 yam type and yam denier can be selected to 
meet specific properties desired for the prosthesis, such as porosity, 
flexibility and compliance. The yarn denier represents the linear density 
of the yam (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 
yam with a larger denier, e.g., 1000, would correspond to a heavy yarn. 
The yarns 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 yarns 
are one ply, 50 denier, 48 filament flat polyester. 
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 yarns (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 yarns can be accomplished in any combination of numbers. For example, 
up to three warp yarns 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 yarns 
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. FIG. 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 FIG. 8, 
which shows a graft 100 in one embodiment of the present invention as 
flat-woven in a tubular step-tapered form as shown in FIG. 3. As shown in 
cross-sectional view in FIG.9, such a flat-woven tubular graft subsequent 
to weaving is generally eliptical. Such grafts, however, when constructed 
of heat-settable polyester yam, can be heat set on a mandrel to form a 
generally circular shape, as depicted in FIG. 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 yarns of the graft to heat set to the shape and diameter of 
the mandrel. Preferably polyester yarns are used as the warp and fill 
yarns, and the heat setting is accomplished at time and temperatures 
appropriate for the material. For example, heat setting can be 
accomplished at about 190.degree.-200.degree. 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 FIG. 9. The post-fabrication 
flat shape of tubular wall 117 is comprised of top tubular body portion 
117a 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 FIG. 10, 
graft 100 can be provided as a finished product in the generally flat 
shape shown in FIG. 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. 
FIG. 11a 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 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 FIG. 11a in a manner known in the art. For example, a 
filling yam 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 FIG. 11a, 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 yarns 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 yarns 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 FIG. 11a 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 FIG. 12. 
FIG. 11b shows a plain tubular weave pattern having a gradual disengaging 
of warp yarns. As seen in FIG. 11b, warp yarns 160' have been disengaged 
from the pattern and are no longer interwoven beginning at the fill yam 
170'. Likewise, the next set of picks shows an additional warp yarn being 
disengaged. As noted, the pattern is within the maximum disengagement of 
three warp yarns per four machine picks. 
The disengaging of the warp yarns is accomplished by dropping the desired 
warp yarns 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 pattern. Such dropping of warp yarns in a gradual 
manner forms the transitional portion of the graft. In continuous 
flat-weaving processes, the warp yarns 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. 
FIG. 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 yarns 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 yarns 
160' 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 yarns 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 seamless manner. 
Typically, when a tubular woven bifurcated graft with two different 
diameter iliac leg portions 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. FIG. 13 shows a photomicrograph of an 
enlarged view of the internal portion of a prior art bifurcated graft 
woven of warp yarns 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 yarns 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 yarns 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 FIG. 14. FIG. 14 shows a bifurcated graft having 
first and second iliac woven portions 630a and 630b. As compared with the 
prior art graft shown in FIG. 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 FIG. 15, a typical tubular woven bifurcated graft 
600 includes a generally tubular body 617 having a first end 612 and 
opposed second ends 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 FIG. 15, or can be different, as depicted 
in 730a and 730b of FIG. 16. Further, iliac woven portions 630a and 630b 
can be of the same general length as shown in FIGS. 15 and 16, or can be 
of different general lengths, as shown at 830a and 830b in FIG. 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. 
FIG. 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 FIG. 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. 
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 FIG. 19, representing the prior art. 
FIG. 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 yarns 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 FIG. 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 example, during weaving of the bifurcated graft 600, as shown in FIG. 
15, the warp yarns 160 which are being interwoven by the fill yarns 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 shuttle designated for weaving of iliac woven 
portion 630a selectively and gradually engages warp yarns designated for 
weaving of iliac woven portion 630b. Likewise, the shuttle designated for 
weaving iliac woven portion 630b selectively and gradually engages warp 
yarns 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 yarns such as polyester 
for the weaving yarns, the actual diameter after heat setting of the yarns 
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 yarns were split in half in order to 
weave the iliac leg sections, with 627 warp yarns 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 
26.times.13.times.13 set of diameters. 
As noted above, the invention employs customized, programmable electronic 
jacquard weaving machines to gradually engage and/or disengage selected 
warp yarns 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-woven synthetic tubular implantable prosthesis having a precise 
pre-determined internal diameter 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 diameter can be calculated using the 
following formula: 
EQU N=S+(D.times..rho.) 
wherein N represents the total number of warp yarns required, S represents 
the number of edge warp yarns required to weave a suitable tubing edge , D 
represents the desired internal diameter and .rho. 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 .rho. is 23 using a 1 
ply/50 denier/48 filament polyester yarn. 
Turning now to FIGS. 21-23, bifurcated graft 600 of FIG. 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 FIGS. 8-10. 
Further, FIGS. 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 
FIGS. 24 and 25, are woven in a similar manner as grafts 100, depicted in 
FIG. 12. In FIG. 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 yarns 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 FIG. 25, iliac woven portions 630a and 630b 
require more warp yarns for weaving than aortic woven portion 620, and 
thus the disengaged warp yarns 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, FIG. 
26 shows a bifurcated graft in accordance with one embodiment of the 
present invention, including a stent 50 affixed thereto at one portion of 
bifurcated graft 600. FIG. 27 shows a bifurcated graft in accordance with 
an alternative embodiment of the present invention, having stent 50 
substantially along the entire length of tubular wall 617, positioned 
within the inner lumen of bifurcated graft. 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 Application No. PCT/US95/01466, incorporated 
herein by reference. 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. 
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 yarns 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: 
EQU N=S+(D.times..rho.) 
EQU N=29+(12.times.23) 
EQU N=305 
The number of warp yarns required for weaving the 10 millimeter inner 
diameter portion of the graft was similarly calculated as follows: 
EQU N=29+(10.times.23) 
EQU N=259 
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. 
Example 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 transition between the two portions included a gradual 
transition with no holes between the weave sections of the graft. 
Example 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 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 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 yarn numbers were calculated in accordance with the formula 
stated therein. 
TABLE 1 
______________________________________ 
NUMBER OF NUMBER OF 
WARP YARNS USED 
WARP YARNS USED 
FOR 24 mm FOR EACH 12 mm 
AORTIC SECTION 
ILIAC SECTION 
______________________________________ 
Graft 1A 583 291 
Graft 1B 587 293 
Graft 1C 591 295 
Graft 1D 595 297 
______________________________________ 
TABLE 2 
______________________________________ 
NUMBER OF NUMBER OF 
WARP YARNS USED 
WARP YARNS USED 
FOR 26 mm FOR EACH 13 mm 
AORTIC SECTION 
ILIAC SECTION 
______________________________________ 
Graft 2A 657 313 
Graft 2B 631 315 
Graft 2C 635 317 
Graft 2D 639 319 
______________________________________ 
TABLE 3 
______________________________________ 
NUMBER OF NUMBER OF 
WARP YARNS USED 
WARP YARNS USED 
FOR 28 mm FOR EACH 14 mm 
AORTIC SECTION 
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.degree.-200.degree. 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. 
Example 5 
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 yarns per 4 machine, unacceptable 
voids are present in the weave. 
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 graft were first flat-woven. When 
the flat-woven. When the weave reached the bifurcation portion, the number 
of wrap 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. 
EQU N=S+(D.times..rho.) 
The calculated warp yarn numbers for each diameter section is set forth in 
the tables below. 
TABLE 4 
______________________________________ 
NUMBER OF WARP NUMBER OF WARP 
YARNS USED FOR YARNS USED FOR 
24 mm AORTIC SECTION 
EACH 12 mm ILIAC SECTION 
______________________________________ 
Graft 4 
581 305 
______________________________________ 
TABLE 5 
______________________________________ 
NUMBER OF WARP NUMBER OF WARP 
YARNS USED FOR YARNS USED FOR 
26 mm AORTIC SECTION 
EACH 13 mm ILIAC SECTION 
______________________________________ 
Graft 5 
627 327 
______________________________________ 
TABLE 6 
______________________________________ 
NUMBER OF WARP NUMBER OF WARP 
YARNS USED FOR YARNS USED FOR 
28 mm AORTIC SECTION 
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.degree.-200.degree. 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, 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 the inventive embodiment, 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 yarns 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 yarns 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 yarns necessary to account for heat 
set shrinkage. Moreover, when the disengaged warp yarns 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 yarns as claimed herein. 
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.