AU757985B2 - Shaped woven tubular soft-tissue prostheses and methods of manufacture - Google Patents

Description

I.

P/00/011 28/5/91 Regulation 3.2(2)

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: SHAPED WOVEN TUBULAR SOFT-TISSUE PROSTHESES AND METHODS OF MANUFACTURE The following statement is a full description of this invention, including the best method of performing it known to us SHAPED WOVEN TUBULAR SOFT-TISSUE PROSTHESES AND METHODS OF MANUFACTURING 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.

S 15 Vascular grafts have been used successfully for many years to replace segments S. 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 I, For example, implantable tubular prostheses which serve as conduits, such as vascular grafts, esophagea! 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 yams are interwoven to create the tubular fabric. For example, a set of warp yams is used which represents the width of the product being woven, and a fill yam is woven between the warp yams. The fill yam is woven along the length of the warp yams, with each successive pass of the fill yam across the warp yams 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, one filling pick, requires two picks of the weaving machine. As such, in a conventional woven product; the fill yamrn is woven along the length of the warp yams 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 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 20 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 0:0 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.

'J (t 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 o. 20 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 •go• 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, S 25 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 cutroff and another independently formed leg having a different diameter would be sutured on in its place.

Complex shapes, such as tubular shaped or frustoconical shaped woven sections were not even attempted due to the impracticability, 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.

S. SUMMARY OF THE INVENTION An aspect of the present invention relates to flat-woven implantable tubular prostheses, and in particular endoluminal grafts, which have been continuously •Dog woven to form seamless tubular products having gradual changes in diameter along their length, as well as various shaped tubular sections. 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 and using a predetermined criteria to calculate the appropriate number of warp yarns required for different diameters and and/or using yarns having different heat shrinkage properties or heat setting temperatures. It has also been discovered that such a gradual transition can be accomplished using electronic jacquard looms controlled by computer software. By changing the diameter tube as such seamless and gradual transitions from one diameter to another can be created.

Additionally, these aspects of the invention can be used to create tubular vascular prostheses and the like which have any number of shapes as depicted and further described herein.

The present invention relates to several aspects, some of which are covered by the present specification, others of which are covered by parent Patent No. 729443 derived from parent Application No. 32087/97 and by possible further divisional applications.

In an aspect of the present invention covered by the appended claims there is provided a method of forming a flat-woven synthetic tubular implantable prosthesis having a precise pre-determined internal diameter comprising: choosing a desired weaving pattern and weaving type; (ii) providing a desired yarn and yarn size for said weaving pattern; (iii) providing a desired density at which said yarn is to be woven; (iv) providing a number of edge warp yarns required to weave a suitable tubing edge; choosing a desired internal diameter of said tubular prosthesis; and (vi) calculating the total number of warp yarns required to weave S-said tubular prosthesis having said internal diameter using the formula: S (D x p) 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 p represents the number of warp yarns per unit of diameter.

In another aspect of the present invention there is provided a method of forming a flat-woven synthetic tubular implantable prosthesis as described above further comprising: weaving a wall portion having a first longitudinal expanse portion comprising yarns of a first shrinkage property and defining a tubular shape of a first diameter; weaving a second longitudinal expanse portion of said wall portion comprising yarns of a second shrinkage property and defining a tubular shape of a second diameter; and heat-setting said prosthesis at a temperature to define a varying diameter thereof.

In a further aspect of the present invention there is provided a flat-woven synthetic tubular implantable prosthesis having a precise pre-determined internal diameter comprising: a weaving pattern and weaving type; a yarn and yarn size for said weaving pattern, said yarn having a density at which said yarn is to be woven; a number of edge warp yarns required to weave a suitable tubing edge; an internal diameter of said tubular prosthesis; and a total number of warp yarns conforming to the formula: *o N S (D x p); wherein p represents the number of warp yarns per unit of diameter.

The specification also pertains to other aspects of the invention which may be covered by claims of one or more related divisional applications.

S. In another aspect of the present invention not included in the appended claims there is provided a flat-woven, varying diameter tubular prosthesis comprising a wall portion having a first longitudinal expanse portion comprising S yarns that are heat-setting at a first temperature and defining a tubular shape of a first diameter and a second longitudinal expanse portion comprising yarns that are heat-setting at a second temperature and defining a tubular shape of a second diameter, wherein said varying diameter is heat-set at said first and said second temperatures to shape said prosthesis.

In yet another aspect of the present invention not included in the appended claims there is provided a method of forming a flat-woven, varying diameter tubular prosthesis comprising: weaving a wall portion having a first longitudinal expanse portion comprising yarns of a first shrinkage property and defining a tubular shape of a first diameter; weaving a second longitudinal expanse portion comprising yarns of a .second shrinkage property and defining a tubular shape of a second diameter; 8 heat-setting said first and said second expanse portions at a temperature to shape said varying diameter of said prosthesis.

BRIEF DESCRIPTION OF THE DRAWINGS The following description of exemplary embodiments relates to several aspects of the invention, some but not all of which are covered by the appended claims. Some aspects of the invention are covered by claims which may be included in one or more related divisional applications.

References to "the invention" in the following description pertain to exemplary embodiments of the invention.

Figures la, Ib, and Ic depict perspective views of a graft construction 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 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-section 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 11 a and 11 b are perspective views of graft weave patterns that may be utilised in forming prosthesis in accordance with the present invention.

Figure 12 is a perspective view of grafts being continuously flat-woven, 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 10 Ox.

Figure 14 shows a photomicrograph of the internal portion of a crotch section of a bifurcated graft made by engaging or disengaging warp yarns at a magnification of 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 ata magnification of Figure 20 shows a scanning electron micrograph of the internal portion of the crotch section of a bifurcated graft made in accordance with the present invention at a magnification of 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 15 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 S. gradually disengaged from the weave during weaving of the aortic section.

20 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.

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.

20 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, "000 25 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 use 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 years 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 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.

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 go a a its length, as demonstrated in Figures I a, 1 b and I 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 I 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 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 postfabrication 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 99 9:.9 therebetween an inner lumen 18 which permits passage of blood once graft 10 is 20 implanted in the body. Graft 10 includes continuous transitional woven portion 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 *999 inner diameter which is different than the inner diameter of first end 12. For example, 25 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 gradually tapers from the 12 millimeter inner diameter of first end 12 to the 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 using yarns with different heat setting temperatures or heat shrinkage properties and/or by varying the number of warp yarns for the different diameters 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 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 S. 20 woven portion 130 through the length of transitional woven portion 125.

In this regard the required internal diameters are effected by conforming the total number of warp yarns to the formula N S (D x where S in the number of edge warp yams required to weave a suitable tubing edge, D is the internal diameter and p is the number of warp years per unit of diameter and/or 25 using yarns of different shrinkage properties.

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 30 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). Once again the internal diameters are effected by conforming the total number of warp yarns to the formula N 5 (D x and/or utilising yams of different shrinkage properties.

Figure 5 shows a further variation 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.

Once again the internal diameters are effected using the formula N S (D x and/or yarns of varying shrinkage properties.

S 20Figures 6 and 7 show further shapes which can be formed according to 20 embodiments of 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

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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 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 30 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 shape again changes direction, the opposite may be true, 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 other to maintain to 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.

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

S.

i 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 configuration similar to the manner in Figure 6, 9l** 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 the 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.

Though the present invention it is now possible 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 changes must be accomplished gradually 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 fluidtight 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.

Textile products 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 and textured, and according to one embodiment of the present invention, have shrinkage properties. Additionally, the yarn type and yarn 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 yarn (number of grams mass divided by 9,000 meters in length). Thus, a yarn with a small denier would correspond to a very fine yarn whereas a yarn with a larger denier, 1000, would correspond to a heavy yarn. The yarns used with the present invention may have a denier from about 20 to about 1000, .i* 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, 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 0.16mm, with the most preferable wall thickness being from about 0.07mm to about 0.14mm. These thicknesses, facilitate the folding of the graft into an appropriate delivery system. Moreover, the seamless sutureless) feature of the present invention further facilitates packing and folding of the graft into the delivery system.

Wherein 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) ibeing used for weaving of each of the iliac leg sections. When such a graft was flat-woven of polyester in tubular from and then heat set, however, the exact 20 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 then 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 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 provides, 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: N S (D x p) wherein N represents the total 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 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 20 28 when the diameter is an odd number. In such a preferred embodiment, the .oo.density p is 23 using a 1 ply/50 denier/48 filament polyester yarn.

A transition from one diameter to another can 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 S. 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. Figure 8 shows such edges at 117c.

As previously noted, two machine picks represents one filling pick of tubular fabric, one tubular, fill yarn. Thus, four machine picks represents two tubular fill yarns.

According to a particular embodiment of the invention, the tubular-woven graft of the present invention is constructed of polyester which is capable of shrinkage during a heat set process. For instance, such grafts are typically flatwoven 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 invention as a flatwoven in a tubular step-tapered form as shown in Figure 3. As shown in crosssectional view in Figure 9, such a flat-woven tubular graft subsequent to weaving in a generally elliptical-shape. Such grafts, however, when constructed of heatsettable polyester yarn, can be heat set on a mandrel to form a generally circular shape, as depicted in Figure 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 i 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 190-2000 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 to top tubular body portion 117a and "bottom tubular body portion 117b, which connect at tubular body edges, 117c.

Figure 11 a 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 18a yarns 160a and bottom warp yars 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 yars 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 yar shuttle (not shown) passes across warp yarns 160 while selected warp yams 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 yar 170a by passing across warp yars 160 while certain warp yars 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 yars 170a from interweaving with bottom warp yams 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 yams 160a are always lifted such that bottom fill yars 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 yams to create tapers and/or shapes.

S 20 For example, the plain weave pattern shown in Figure 1 la and described above is formed by continuously passing top and bottom fill yars 170a and 170b back and forth across warp yams 160 to form first woven portion 120 of graft 100 shown in Figure 12.

Figure 11 b shows a plain tubular weave pattern having a gradual disengaging of warp yams. As seen in Figure 11 b, warp yams 160' have been disengaged from the pattern and are no longer interwoven beginning at the fill yam 170'. Likewise, the next t* set of picks shows an additional warp yam being disengaged. As noted, the pattern is within the maximum disengagement of three warp yams 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 than 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 flatweaving process. 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. In this regard the number of warp yarns for each portion is calculated using the formula N S (D x where S is the number of edge warp yarns, D the desired internal diameter and p the number of warp yarns per unit diameter, and/or yarns of different shrinkage properties are used in order to attain different internal diameters.

20 At transitional portion 125, the warp yarns are gradually disengaged from weave, as depicted by disengaged warp yams 160'. Since the grafts 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 being 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, when the 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, graphs produced in such a manner resulted on 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 postfabrication suturing resulted in voids in the graft wall from the needle which was used for suturing. Figure 13 shows a photomicrograph of and 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.

Split grafts such as bifurcated grafts can be flat-woven in a tubular form S* with varying diameters in the iliac portions and the aortic portion, without the need 20 for such post-fabrication suturing, 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 ooo° 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 leg in the prior legs in the prior art grafts are not present in the graft produced in Figure 14.

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 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 640b each having an inner diameter which is different than the inner diameter of aortic woven portion of 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. In this regard according to present invention the various diameters are effected by conforming the total number of warp yarns to the formula N S (D x and/or utilising yarns of varying shrinkage properties.

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 length, as shown at 830a and 830b in Figure 17. Bifurcated graft 600 further includes bifurcated transitional woven portion 625 contiguous with aortic woven potion 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 .i woven portion 620 to the inner diameters of first and second iliac woven portions 20 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.

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.

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 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.

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 .i 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 example, during weaving of the bifurcated graft 600, as shown in Figure 15, the warp yarns 160 which are being interwoven by the fill yarns 170 25 are gradually transferred from the aortic woven section 620 and the transitional S woven section 625 to each of the iliac 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.

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.

Further, figures 24 and 25 show a plurality of bifurcated grafts 600 being woven in a continuous flat-weaving process. 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 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 Figure 25, iliac woven portions 630a and 630b require more warp yarns for :.°°.weaving than aortic woven portion 620, and thus 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, 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 alternative embodiment of the present invention, having stent 50 substantially along the entire length of the tubular wall 617, positioned with 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 know 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 present invention.

EXAMPLES

Unless otherwise noted, the grafts of all of the following examples were flat-woven in a tubular configuration using and electronic jacquard weaving machine. All of the grafts were flat-woven using a plain tubular 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, 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 i number of warp yarns required to achieve the true desired diameters upon heat shrinkage as follows: N S (D x p) N =29 (12 x 23) 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 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, at a single machine pick, in order to produce the 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 yams were not disengaged at once transitioning to the 10 millimeter diameter portion. Instead, 4 or more warp yams were disengaged for every 2 machine picks. The graft thus produced included a 12 millimeter inner 15 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.

S

Example 3 This example demonstrates the requirement for a maximum of three warp yams 20 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 flatwoven 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 yams 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 Sshrinkage. 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 method of gradually changing the warps was not employed. Instead, the number of warp yams were split all at once, at a given pick, with one warp yam being disengaged as necessary for one leg of the iliac leg section in order to produce the correct weave pattern (obtain an odd 15 warp yarn number). The number of warp yarns used for each graft is shown in Tables o* 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 yar numbers were calculated in accordance with the formula stated therein.

C

C.

Table 1 NUMBER OF WARP YARNS USED NUMBER OF WARP YARNS USED FOR 24 mm AORTIC SECTION FOR EACH 12 mm ILIAC SECTION 583 291 587 293 591 295 595 297 Table 2 NUMBER OF WARP YARNS USED FOR 26 mm AORTIC SECTION Graft 2A 657 NUMBER OF WARP YARNS USED FOR EACH 13 mm ILIAC SECTION 313 Graft 2B 631 315 Graft 2C 635 317 Graft 2D 639 319 Table 3 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, 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.

Example 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.

Aset 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 millimneter inner diameter for each leg section, respectively. The aortic section of the grafts were first flat-woven. When the weave reached the bifurcatio n portion, the number of warp yarns was adjusted by disengaging warp yarns from the weave pattern at a rate of 4 warp yams 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 NUMEROF WARP YARNS USDINMBER OF WARP YARNS USED FOR 24 rmm AORTIC SECTION FR EACH 12'mm ILIAC SECTION9 Graft 4f 581 305 Table NUMBER OF WARP YARNS USED NUMBER OF WARP YARNS USED FOR 26 rum AORTIC SECTION FOR EACH 13 mmi ILIAC SECTION.

Garaft 5 627 327 Table 6 NUMBER OF WARP YARNS USED NUMBER OF WARP YARNS USED FOR 28 mum 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 190-2000 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 gradually disengaged warp yarns to transition 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 o the grafts from the mandrels, the inner diameters of the aortic section of each of 20 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.

"Comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

es

Claims (19)

1. A method of forming a flat-woven synthetic tubular implantable prosthesis having a precise pre-determined internal diameter comprising: i) choosing a desired weaving pattern and weaving type; ii) providing a desired yarn and yarn size for said weaving pattern; iii) providing a desired density at which said yarn is to be woven; iv) providing a number of edge warp yarns required to weave a suitable tubing edge; v) choosing a desired internal diameter of said tubular prosthesis; and vi) calculating the total number of warp yarns required to weave *e said tubular prosthesis having said internal diameter using the formula: "N S +(Dx p) 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 o represents the desired internal diameter and p represents the number of warp yarns per unit of diameter.

2. The method of claim 1 wherein said weaving type is selected from the group consisting of a plain weave, a basket weave, a twill weave, and velour weave.

3. The method of claim 1 wherein said yarn is 1 ply, 50 denier, 48 filament polyester yarn.

4. The method of claim 3 wherein said density is 23. The method of claim 4 wherein said number of edge warp yarns is 29 when said diameter is an even number and 28 wherein said diameter is an odd number.

6. The method of claim 1 further comprising: weaving a wall portion having a first longitudinal expanse portion comprising yarns of a first shrinkage property and defining a tubular shape of a first diameter; weaving a second longitudinal expanse portion of said wall portion comprising yarns of a second shrinkage property and defining a tubular shape of a second diameter; and heat-setting said prosthesis at a temperature to define a varying diameter thereof.

7. The method of claim 6 wherein said temperature is from about 190 to about 200 0 C. *l 0. 0

8. The method of claim 1 further comprising: weaving a wall portion having a first longitudinal expanse portion comprising yarns that are heat-setting at a first temperature and defining a tubular shape of a first diameter; weaving a second longitudinal expanse portion of said wall portion comprising yarns that are heat-setting at a second temperature and defining a tubular shape of a second diameter; and heat-setting said prosthesis at said first and said second temperatures to define a varying diameter thereof.

9. The method of claim 8 wherein said first and said second temperatures are from about 190 to about 200 0 C. The method of claims 6 or 8 further comprising seamlessly transitioning said first and said second expanse portions.

11. The method of claims 6 or 8 wherein said yarns are thermoplastic polymers selected from the group consisting of polyesters, polypropylenes, polyethylenes, polyurethanes, polytetrafluoroethylenes and combinations thereof.

12. The method of claims 6 or 8 wherein said yarns are selected from the group consisting of flat yarns, textured yarns, twisted yarns, and combinations thereof.

13. The method of claims 6 or 8 wherein said first diameter is substantially constant along said first expanse portion and further wherein said second diameter is substantially constant along said second expanse portion.

14. The method of claims 6 or 8 wherein said second diameter is variable along the longitudinal expanse of said second portion.

15. The method of claims 6 or 8 wherein said second diameter increases longitudinally along said second expanse portion to define an outwardly tapered shape of said second expanse portion.

16. A flat-woven synthetic tubular implantable prosthesis having a precise pre- determined internal diameter comprising: a weaving pattern and weaving type; a yarn and yarn size for said weaving pattern, said yarn having a density at which said yarn is to be woven; a number of edge warp yarns required to weave a suitable tubing edge; an internal diameter of said tubular prosthesis; and a total number of warp yarns conforming to the formula: N S (D x p); wherein p represents the number of warp yarns per unit of diameter.

17. The prosthesis of claim 16 wherein said weaving type is selected from the group consisting of a plain weave, a basket weave, a twill weave, and velour weave.

18. The prosthesis of claim 16 wherein said yarn is 1 ply, 50 denier, 48 filament polyester yarn.

19. The prosthesis of claim 18 wherein said density is 23. The prosthesis of claim 19 wherein said number of edge warp yarns is 29 when said diameter is an even number and 28 wherein said diameter (D) is an odd number.

21. A method of claim 1 substantially as hereinbefore described and illustrated with reference to any one of Figures 2 to 27.

22. A prosthesis of claim 16 substantially as hereinbefore described and as illustrated with reference to the any one of Figures 2 to 27. :o DATED this 4 t h day of December 2002 BOSTON SCIENTIFIC LIMITED 0.0 WATERMARK PATENT TRADE MARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA e P5254AU01 RLT/MAP