HK1021309A - Stented, radially expandable, tubular ptfe grafts - Google Patents

Description

Radially expandable tubular PTFE graft with stent

Technical Field

The present invention relates generally to medical devices and methods of making the same, and more particularly to tubular Polytetrafluoroethylene (PTFE) grafts for implantation in a body lumen or body passageway (e.g., various tubes or vessels) having a radially expandable stent integrally formed therewith.

Background of the invention A. fixed mold

The prior art includes a variety of radially expandable stents which may be first used in a radially collapsed condition suitable for insertion into a delivery lumen by an introducer catheter and then transitioned to a radially expanded condition whereby the stent contacts and adheres to the surrounding wall or anatomical conduit or lumen in which it is disposed. Stents as described above have been used to support and maintain the patency of a vessel lumen at a desired location within a body lumen or body passageway (e.g., as an adjunct to balloon angioplasty) and to structurally support and/or secure other devices, such as a tubular endovascular graft (e.g., a tubular endovascular graft secured to a vessel wall to form a catheter through the interior of an aneurysm or wound site).

Many stents of the prior art are made from a single element(s) that is bent, braided, interwoven or otherwise formed into a generally tubular shape, such as a wire, plastic, metal strip or mesh. These prior art stents generally fall into two broad categories: a) a "self-expanding" stent, and b) "a" crimped "stent.

I) self-expanding stents

Self-expanding stents are typically made of a resilient metal, a memory-shape alloy, or other material that returns to its original, radially fully expanded shape when biased, or in other words, self-expands to its radially fully expanded shape without the application of an outward radial force to the stent by some additional expansion means (e.g., an inflation tool or a mechanical expansion tool). These self-expanding stents may be first radially compressed and loaded into a small diameter introducer catheter or otherwise secured to the outer surface of the introducer catheter, with some means being provided on the introducer catheter to restrain or hold the stent in its radially compressed state. The introducer catheter is then inserted into the body and advanced to a position at or near which the stent is to be implanted. The stent is then detached (or withdrawn) from the introducer catheter, self-expanding to its original diameter. This expansion of the stent causes it to adhere by friction to the walls around the body lumen and body passageway in which it is placed. The introducer catheter is then withdrawn, leaving the self-expanding stent at the site of its intended implantation. Some examples of prior art self-expanding stents include those disclosed in U.S. Pat. No. 4,655,771 (Walstein et al); 4,954,126 (walstein): 5,061,275 (Walstein et al); 4,580,568 (giantco); 4,830,003 (Walf et al); 5,035,706 (Giardiac et al) and 5,330,400 (Mulberry).

Ii) a pressure-expandable stent

Prior art stents are typically made of wire, wire or other malleable or malleable deformable material formed into a generally tubular shape. Such a crimped stent is first deployed in a collapsed configuration having a diameter less than the desired final diameter of the stent when implanted in a blood vessel. The collapsed stent is then loaded or secured onto a small diameter introducer catheter. The introducer catheter is then inserted into the vasculature at the desired stent location, and an outward radial force is applied to the stent by means of an inflatable or other stent-expanding device (which may be integral with or disposed within the introducer catheter), whereby the stent is radially expanded and plastically deformed to its intended use diameter, whereby the stent frictionally adheres to the surrounding vessel wall. The material of the stent is plastically deformed during the pressure expansion. This plastic deformation of the stationary mold material keeps it in the radially expanded use shape. The balloon or other expansion device is then deflated and withdrawn from the body separately from or as part of the introducer catheter, leaving the inflated stent in its intended implantation position.

Some examples of prior art stents include those disclosed in U.S. patent No. 5,135,536 (hilted); 5,161,547 (torr); 5,292,331 (Bonun); 5,304,200 (Spelline) and 4,733,665 (Palmatz). PTFE vascular grafts

Heretofore, fluoropolymers such as polytetrafluoroethylene have been used to make various types of vascular repair grafts. These vascular grafts are generally tubular and may be used to replace a resected portion of a blood vessel.

Tubular PTFE vascular grafts of the prior art have traditionally been implanted using open surgical techniques whereby a diseased or damaged portion of a blood vessel is surgically removed and a tubular bioprosthetic graft is then anastomosed into the host vessel to replace the removed portion thereof. On the other hand, such tubular vascular grafts have also been used as bypass grafts, in which the opposite ends of the graft are sutured to the host vessel to form a bypass duct near the portion of the host vessel where the lesion, injury, or occlusion occurs.

Generally speaking, many tubular vascular repair grafts of the prior art are made from extruded porous PTFE tubes. In some prior art tubular grafts, PTFE tape is wrapped around and laminated to the outer surface of the tubular graft to provide reinforcement and increase burst strength. Some existing tubular vascular repair grafts also include (some) external support, such as fine grained PTFE bonded or laminated to the outer surface of the tubular graft to prevent the graft from compressing or buckling during implantation. These externally supported tubular vascular grafts have proven particularly suitable for replacing lengths of blood vessels that are threaded or passed over frequently moving or moving human joints or other sites.

One commercially available externally supported tubular vascular graft is made from a PTFE tube having PTFE monofilament (impera Flex) helically wound and bonded to its outer surface^TMGraft, IMPRA, Inc., Tanpey, Arizona).

Another commercially available externally supported tubular vascular graft comprises a regular circumferential PTFE tube having a helically wound and bonded outer surface PTFE stiff strip with a plurality of polyvinylfluoride propylene (FEP) single loops bonded to the outer surface of the stiff strip. (ePTFE vascular grafts with FEP loops, W.L. Gore & Associates, Inc., Fragranstafort, Arizona). C. Stent-equipped graft

The prior art also includes a variety of "stented grafts". These stented grafts typically comprise a self-expanding or a crimped stent that is fixed or fabricated within a flexible tubular graft. Because of their radial compressibility/expandability, these stented grafts are particularly well-suited for use in applications requiring insertion of the graft into an anatomical passageway (e.g., a blood vessel), with the graft being placed in a radially compressed state upon insertion and then expanded and secured to the wall surrounding the anatomical passageway. Recently, various methods have been developed for introducing and implanting a vascular graft for repair of a vessel into a vascular lumen using a percutaneous, minimal incision. Such intravascular implantation initially involves introducing the graft in a compressed state into a delivery lumen through a catheter or other introduction instrument that is capable of accessing the delivery lumen. The graft is then radially expanded and fixed to the surrounding vessel wall, thereby securing the graft in its intended implantation location within the host vessel. At least the opposite ends of the tubular graft are typically secured to the surrounding vessel wall using a securing device, such as a stent. One particular application of such endovascular grafts is in the treatment of vascular aneurysms without the need for surgical access and removal of the aneurysmal vessel. Moreover, such stented grafts may also be used to treat occlusive vascular disease, particularly where the stented graft is constructed in a manner such that the tubular graft material forms an integral barrier between the stent and the blood flowing through the vessel. In this manner, the material of the tubular graft serves as a lubricious, biocompatible inner "coating" of the stent to prevent a) disturbance of blood flow as blood flows through the wire elements or other structural materials comprising the stent, b) an immune response to the metal or other material from which the stent is made, and c) a barrier separating the diseased or damaged vessel from blood flow therethrough. Since it is believed that blood flow disturbances and/or immune responses to the stent material are associated with thrombus formation and/or vessel stenosis, it is believed that avoiding both of these phenomena is desirable.

Other applications of stented grafts may include re-clearing or re-cannulating other anatomical passageways, such as biliary, digestive and/or genitourinary tracts.

Many stents known in the art have utilized braided or knitted materials, such as polyester fibers, as the graft material.

There is a need to develop a radially expandable, stented graft made from a continuous tubular ePTFE tube because stented grafts in the prior art have previously employed woven polyester and other graft materials, and these inherent properties of PTFE tube may have a number of clinical advantages over these materials.

Summary of The Invention

The present invention is directed to stented tubular PTFE grafts and methods of making the same. In general, the present invention can be any of the following three (3) separate embodiments, depending on whether the stent component of the graft is made integral with (i.e., within) the tubular PTFE graft or is made on the exterior of (i.e., on the exterior surface of) the tubular PTFE graft or is made on the interior of (i.e., on the surface of the lumen of) the tubular PTFE graft. Each of the three separate embodiments of the present invention may be self-expanding (i.e., having a self-expanding stent) or pressure-expanding (i.e., having a pressure-expanding stent).

In accordance with a first embodiment of the present invention, a stent-integrated PTFE graft is provided comprising a tubular PTFE-based graft (base graft), preferably having a density of less than 1.6g/cc, a radially expandable stent on the outer surface of the tubular base graft and an outer layer of PTFE having a density of less than 1.6 g/cc. The tubular outer layer is fused to the tubular substrate graft through side holes or side holes formed in the stent. A polymeric coating, such as a PTFE coating, may be provided over the stent to further facilitate fusion or bonding of the stent to the base layer tube and/or the tubular outer layer.

According to a second embodiment of the present invention, there is provided a tubular PTFE graft having a stent on the exterior thereof, comprising a radially compressible/expandable stent having an ePTFE tube of density less than 1.6g/cc coaxially disposed therein, the outer surface of the tubular ePTFE graft being fused or otherwise secured to the stent. A polymeric coating, such as PTFE or any other plastic that is fusible or bondable to PTFE, may be applied or formed over the stent to facilitate the necessary fusing or securing of the tubular graft to the stent and/or to enhance the biocompatibility of the stent.

According to a third embodiment of the present invention, there is provided a tubular PTFE graft having a stent inside thereof, comprising a tubular outer layer of ePTFE having a density of less than 1.6g/cc and a radially expandable stent. The stent is coaxially disposed within the lumen of the tubular outer layer and fused or otherwise secured thereto. The stent may be coated with a polymeric coating, such as PTFE or other biocompatible plastic that can be bonded or fused to PTFE to facilitate the necessary fusing or anchoring of the stent to the tubular outer layer and/or to enhance the biocompatibility of the stent. Alternatively, PTFE particles may be placed between the tubular outer layer and the tubular base graft to facilitate adhesion or fusion of the layers to each other and/or to the stent. The PTFE particles can be placed therebetween by applying or attaching a liquid dispersion of PTFE between the inner base graft and the tubular outer layer, or by attaching a dry resin powder of PTFE.

Any of the above three (3) separate embodiments of the present invention can be made using a process comprising the steps of: a) first a self-expanding or press-expanded, generally tubular stent is placed on a tubular mandrel or other suitable support surface in coaxial contact with the tubular ePTFE base graft and/or tubular ePTFE outer layer, and b) the stent-graft assembly (i.e., stent bonded to the inner base graft and/or tubular outer layer) is then fused (i.e., heated to a lamination temperature) to form an integral stent-graft structure. In the embodiment integrated with the stent, both a tubular ePTFE substrate graft and a tubular ePTFE outer layer are present, and the heating also fuses the tubular outer layer to the inner tubular substrate graft through side holes or eyes present in the stent. The surface of the stent may be treated, polished or coated with a plastic that adheres or fuses to the ePTFE to facilitate the stent's fixation to the adjoining outer and/or inner base graft upon subsequent application of heat, solvent or other suitable adhesive modification technique. In the case of a plastic coating formed over the stent, the coating may in fact be a tube or a die, which is applied to the stent prior to assembly and securement of the stent-bearing graft member to the mandrel or other support surface. Further, in embodiments employing tubular outer and tubular base grafts, an aqueous dispersion of PTFE, powdered PTFE resin, or other flowable plastic material may be attached between the tubular outer and inner tubular base grafts at the time of assembly (prior to heating) to further facilitate fusing the tubular outer and/or inner tubular base grafts to the stent and/or to each other.

Using the materials and methods of manufacture described above, the stented PTFE graft of the present invention is capable of radial expansion and contraction without excessive wrinkling, or invagination of the PTFE graft material. Moreover, in embodiments wherein the stent is fabricated from individual elements that move or return relative to one another during the corresponding expansion and contraction of the stented graft, the fabrication methods and materials of the present invention enable lamination or fusion of the PTFE sufficiently strong to permit the above-described relative movement of the stent individual elements without tearing or breaking the tubular PTFE graft.

Still other objects and advantages of the present invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description and the annexed drawings.

Brief Description of Drawings

FIG. 1 is a perspective view of a tubular PTFE graft of the present invention integrally formed with a stent, wherein a portion of the graft is inserted into a tubular catheter.

Fig. 1a is a partially enlarged perspective view of fig. 1.

Figure 2 is an enlarged longitudinal cross-sectional view of a preferred stent-integrated tubular PTFE graft of the present invention.

Figure 3a is an enlarged partial perspective view of the stent incorporated in the graft of figure 2.

Fig. 3b is an enlarged cross-sectional view through line 3b-3d in fig. 3 a.

Figure 4 a-4 f is a step-by-step illustration of a preferred method of making a stent-integrated PTFE graft of the present invention.

Figure 5 is a schematic illustration of an alternative electron beam attachment method suitable for attaching a PTFE coating to the stent portion of a stent-integrated PTFE graft of the present invention.

FIG. 6 is a perspective view of an alternative heating device suitable for use in making the stent-integrated PTFE graft of the present invention.

Detailed description of the preferred embodiments

The following detailed description is merely provided to describe and illustrate some of the presently preferred embodiments of the invention and is not intended to be exhaustive of all possible embodiments in which the invention may be practiced. A. Structure of stent-integrated PTFE graft

In fig. 1-3b, a tubular PTFE graft 10 of the present invention is shown integrated with a stent. The preferred stent-integrated graft 10 comprises a tubular PTFE-based graft 12, a stent 14 having a PTFE coating, and an outer layer 16 of PTFE.

In these figures, one of a plurality of stents is shown, which may be used to construct the component stent 14 in the stented graft 10 of the present invention. This particular stent 14 is made of individual elements or wires 18 that are covered with a PTFE coating 20. There are some gaps or side holes 19 between adjacent wires or bundles of wires 18. In U.S. Pat. No. 4,655,771 (Walstein); 4,954,126 (walstein); and 5,061,275 (Walstein et al), which are expressly incorporated herein by reference in their entirety. Such as shown in some of the figures of the present patent applicationThe particular stent 14 is formed of a plurality of stiff yet resilient flexible wire elements or wires 18. The wire elements or wires 18 are made of an alloy of a metal, such as cobalt, chromium, nickel or molybdenum, wherein the remainder of the alloy is iron. Elgiloy (Elgiloy) (Elgiloy, 1565 Fleetwood drive, Elgiline, Ill.) is a specific example of an alloy that is commercially available for use in the wire 18 used to form the stent 14. The wires 18 of the stent 14 are arranged in a helical shape around the common longitudinal axis LA such that the plurality of wires 18 are positioned substantially parallel to each other but are axially displaced from each other. So configured, some of the wires 18 are wound in a first helical direction and others are wound in a second or opposite helical direction so that they pass on opposite sides of adjacent wires wound in the first helical direction to form a helically braided wire stent as shown in some of the figures, thus forming a generally tubular braided wire stent 14 which is self-expanding and biased to its radially expanded diameter D₂. However, such a stent 14 can be compressed to a smaller diameter D in the radial direction₁And can be radially constrained by the wall surrounding the tubular introduction catheter 22 shown in FIG. 1, so that the stent 14 is held in the above-mentioned radially compressed state (diameter D)₁). Thereafter, when the radial restriction is released from the stent 14, the stent 14 is elastically restored to its radially expanded diameter D₂. The single helically wound wire 18 of this particular braided stent 14 is subject to shifting and articulation (articulale) to allow the angle of orientation of the wires 18 relative to one another to alter the radial expansion and compression of the stent 14. The longitudinal length of the stent 14 will also be compressed radially as it is compressed radially to its radially compressed shape D₁And this length increases as the stent 14 expands to its radially expanded shape D₂And is shortened. Thus, the wire 18 of the stent 14 is provided with an optional PTFE coating 20 that is sufficiently flexible (as described in more detail below) to resist bending and movement of the individual wires 18 without cracking or breaking.

When the stent 14 is in its radially expanded configuration, the tubular base graft 12 is first placed coaxially within the hollow interior of the tubular stent 14, and the stent 14 is previously coated, if necessary, with a PTFE coating 20. The outer PTFE layer 16 is then formed by any suitable method, such as by winding a strip 17 of PTFE around the outer surface of the stent 14 having a PTFE coating, to form a generally tubular outer PTFE layer 16. The outer PTFE layer 16 is then fused to the inner base layer graft 12 by heat or other means through some gaps or perforations 19 present in the stent 14. In some embodiments in which the optional PTFE coating 20 is applied to the stent 14, such heating may also facilitate adhesion of the PTFE coating 20 of the stent 14 to the adjacent base graft 12 and outer PTFE layer 16. In this manner, a self-expanding tubular stent-integrated PTFE graft 10 of substantially unitary construction is formed. The stent 14 forms a framework of unitary construction within the tubular graft 10, and the fused graft PTFE matrix is of sufficiently low density to permit the stent 14 to be positioned within the graft 10 so as to continue to undergo substantially the same magnitude of radial expansion and contraction as would be achieved by the stent 14 prior to deployment of the PTFE graft on the stent 14. In this regard, the stent-integrated graft 10 is radially compressible to the stent and to a first diameter D₁And may be inserted into the lumen of the small diameter tubular catheter 22. The external constraint imposed by the wall of catheter 22 causes stented graft 10 to maintain its diameter D₁Until the graft 10 is extruded or ejected from the catheter 22. After the graft 10 is extruded or ejected from the catheter 22, the diameter of the graft self-expands to substantially equal the original expanded diameter D of the stent 14₂. B. Preparation of tubular basal layer grafts

i) Preparation of paste

The manufacture of the tubular substrate graft begins with the step of preparing a PTFE paste dispersion for subsequent extrusion. Such PTFE paste dispersions can be prepared by known methods by which fine, pure and PTFE powders (e.g., F104 or F103 pure) are made20 Olympic Drive, new york 10962) with a liquid lubricant, such as odorless mineral spirits (e.g., Isopar)^77253-.

Ii) extrusion of tubes

The PTFE-lubricating oil mixture dispersion is then passed through a tubular extrusion die to form a tubular extrusion product.

Iii.) drying

The wet tubular extrudate is then subjected to a drying step whereby the lubricating oil is removed. This drying step can be carried out either at room temperature or by placing the wet tubular extrudate in an oven at an elevated temperature at or near the dry point of the lubricant for a time sufficient to evaporate substantially all of the lubricant.

Iv) stretching

The dried tubular extrudate is then longitudinally stretched or longitudinally drawn at a temperature of less than 327 deg.C, typically 250 deg.C and 326 deg.C. Such longitudinal stretching of the extrudate can be carried out by known methods and can be carried out by means of what are known as batch stretchers. The tubular extrudate is generally stretched in the longitudinal direction to a stretch ratio greater than two to one (2: 1) (i.e., at least 2 times its original length).

The primary graft 12 is preferably made of a material having a density of less than 1.6g/cm³Is made of stretched, sintered PTFE.

V. sintering

After the longitudinal stretching step is completed, the stretched PTFE tube is subjected to a sintering step whereby it is heated above the sintering temperature of the PTFE (i.e., 350-. The methods by which the sintering step is carried out and the devices by which such methods are carried out are well known in the art.

Completion of the sintering step indicates that the preparation of the stretched, sintered PTFE-based graft 12 is complete.

The PTFE tape 16 may be made by any suitable method, including the conventional methods of making stretched PTFE tapes, as follows: preparation of PTFE strips

I.) preparation of paste dispersions

The manufacture of the stretched, sintered PTFE strip 17 typically begins with the preparation of a PTFE paste dispersion that can be used to form the PTFE outer layer 16 of the stented graft 10. This PTFE paste dispersion can be prepared in the same manner as described above for the PTFE paste dispersion used to make the tubular substrate graft.

Ii.) extrusion of the film

The PTFE paste dispersion is then passed through a film extrusion die to form a wet film-like extrudate. The wet film extrudate is removed or wound onto a spool to form a roll of wet film extrudate.

Iii.) calendering

The rolled wet film extrudate is then unwound and the film is passed through at least one set of stainless steel twin roll calenders with an initial cold (i.e. < 100 ℃) calendering step, the gap width (thickness) between the rolls being adjustable. The temperature of the calender rolls is preferably maintained at room temperature to 60 ℃. The width of the moist extrudate remains constant as it passes through the calender rolls. When the width of the film is held constant, the thickness of the wet film extrusion is reduced to its desired final thickness (e.g., 0.004-0.005 in). Obviously, passing the film through a calender causes the film to grow in the machine direction, keeping the width of the film constant. As the film passes between the calendering rolls, its increase in the machine direction is a function of the decrease in film thickness.

An example of a commercially available calender for this purpose is the small kilion 2 Roll Stack, (Killion extruder, llc, sardagleff, n.j. 07009.).

Iv) drying

The wet film is then subjected to a drying step. This drying step may be carried out by a method which enables the liquid lubricating oil to evaporate from the matrix of the film. Passing the film over a drum or roller facilitates evaporation of the liquid lubricant, and the drum or roller is maintained at a temperature sufficiently high to cause complete evaporation of the liquid lubricant from the substrate of the film.

V.) stretching

The film is subjected to the stretching step either alone or simultaneously with the drying step. The stretching step comprises stretching the PTFE membrane in at least one direction (e.g., the machine direction). The stretching of the membrane serves to a) increase the porosity of the membrane, b) strengthen the membrane, and c) orient the fibrils of PTFE in the direction of the axis of stretching.

This stretching step is typically accomplished by heating the film to some extent during the stretching process, but not above the melting point of the PTFE polymer crystals.

Vi.) sintering of films

After the drying and stretching steps are completed, the membrane is subjected to a sintering step in which the membrane is heated above the melting point temperature of the PTFE to effect sintering or amorphous orientation of the PTFE polymer. This sintering step may be carried out by passing the membrane through a drum or roller which is maintained at a high surface temperature (e.g., 350 c-420 c) and the PTFE membrane is maintained above the melting point of the PTFE polymer for a sufficient period of time and with the necessary heating to effect the desired sintering of the membrane.

Vii.) cutting the film into strips

After the film is dried, the film is cut into strips, each typically 0.25-0.50in width, to produce a plurality of stretched, sintered PTFE strips 14. D. Coating of stents and/or attaching PTFE between layers to enhance adhesion

The stent 14 may be coated with a polymer coating 20 prior to assembly of the stent-integrated graft 10 components.

The polymer coating formed on the stent 14 may be any suitable polymer that can bond to PTFE. Examples of polymers that may be used as the polymeric coating or cladding include Polytetrafluoroethylene (PTFE), Fluorinated Ethylene Propylene (FEP), polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polyvinyl chloride (PVC), polypropylene (PP), polyethylene terephthalate (PET), Polyvinylidenefluoride (PVDF), and other biocompatible plastics.

One method by which the stent 14 may be coated is illustrated in FIG. 4a, and as shown in FIG. 4a, the stent 14 may be immersed in a container 30 containing an aqueous dispersion 32 of PTFE. One aqueous PTFE dispersion that may be used as a coating for the stent 14 is DuPont T-30 aqueous PTFE dispersion commercially available from the E.I. DuPont de Numori corporation (Wilmington, Del.). Another commercially available PTFE dispersion 32 that can be used as a stent coating is the Daikin-polytetrafluoroethylene TFE dispersion, available from Daikin industries, Inc. (Umeda Center Bldg.,4-12 Chome, Nakazaki-nishi; Kita-ku, Osaka, Japan).

The time that the stent 14 must remain immersed in the liquid dispersion 32 of PTFE may vary depending on the structure of the stent 14 and the chemical composition of the PTFE dispersion 32. However, in most cases, a soaking time of 10-15 seconds is sufficient to obtain a uniform adhesion of the PTFE coating 20 to the wire element 18 of the stent 14.

After the stent 14 is removed from the PTFE liquid dispersion 32, it is allowed to dry in the air, and the dried PTFE coating 20 remains adhered to the outer surface of each of the wires 18 of the stent 14.

After air drying is complete, the PTFE coated stent 14 may optionally be placed in an oven at 350 ℃ for about 10 minutes to sinter the coating and/or enhance the adhesion of the PTFE coating 20 to the wire element 18 of the stent 14. Sintering of the PTFE coating makes the coating more resistant to wear or shedding during subsequent stenting procedures and/or ensures the manufacture and use of stented grafts 10. It will be appreciated that various alternative non-immersion methods may be used to attach the PTFE coating 20 to the stent 14. An alternative method is the electron beam attachment illustrated in fig. 5. According to this alternative PTFE attachment method, the stent 14 is placed in a sealed vacuum chamber 36 containing a quantity of PTFE 38. The PTFE38 in the chamber 36 is then irradiated with an electron beam emitted from the electron beam device 40 to sublimate the PTFE to obtain the PTFE layer 20 adhered to the outer surface of the stent 14. The apparatus and specific method for attaching the PTFE coating 20 using such electron beams is well known to those skilled in the relevant art.

When the above-described dipping method is employed (FIG. 4a), the stent 14 having the PTFE coating 20 attached to its surface may optionally be heated at 350 ℃ for about 10 minutes to sinter the PTFE coating and/or enhance the adhesion of the PTFE coating 20 to the wire element 18 of the stent 14.

As an alternative to, or in addition to, the over-molding process, the aqueous PTFE dispersion described above may be applied to the outer surface of the base graft 12 or the inner surface of the tubular outer layer 16, or may be otherwise disposed between the base graft 12 and the tubular outer layer 16 to facilitate fusing or bonding of the inner base graft 12 to the tubular outer layer 16. Alternatively, the aqueous PTFE dispersion described above may be sprayed or otherwise applied to the outer surface of the tubular outer layer 16, provided that the particles of PTFE in the dispersion are small enough to migrate inwardly through the micropores of the tubular outer layer 16 and become attached between the tubular outer layer 16 and the underlying graft 12 within.

An alternative method or alternative means for facilitating or enhancing adhesion or fusion of the base graft 12, the tubular outer layer 16, and/or the stent 14 includes attaching a starting PTFE resin powder between the tubular outer layer 16 and the inner base graft 12 and/or to the stent 14.

It will be apparent that in many instances it will be desirable to have the stent 14 at its diameter D₂In a sufficiently radially expanded shape, the polymer coating 20 is applied to the stent 14. In this wayIn a method wherein the stent 14 is subsequently reduced to its diameter D after the coating 20 has been applied and formed on the stent 14 having been sufficiently radially expanded₁Without tearing or damaging the previously applied coating 20. In embodiments employing a stent 14, it may be desirable to first intentionally or intentionally expand the stent 14 to its fully radially expanded diameter D₂And then the coating 20 is applied. Alternatively, when the stent 14 is of the self-expanding type, it will automatically assume its diameter D in most cases₂Without said intentional or intentional pre-expansion of the stent.

Preferred methods by which a liquid dispersion of PTFE and/or solid powder of PTFE may be attached between the tubular outer layer 16 and the inner base layer graft 12 will be discussed in more detail below with reference to the method of manufacture. E. Assembly and manufacture of stent-integrated PTFE grafts

Figures 4b-4f illustrate in a step-wise fashion a preferred method for assembling and manufacturing the stent-integrated PTFE graft 10.

As shown in fig. 4b, the tubular substrate graft 12 is first disposed on a rod or mandrel 50. The rod or mandrel 50 may comprise a stainless steel rod having an outer diameter only slightly smaller than the inner diameter of the tubular substrate graft 12. In this way, the tubular substrate graft can be slid forward onto the outer surface of mandrel 50 without undue force or damage to substrate graft 12.

Thereafter, as shown in FIG. 4c, a PTFE coated stent 14 is axially advanced over the outer surface of the tubular substrate graft 12.

At this step in the process, a liquid dispersion of PTFE or powdered PTFE resin may also (optionally) be applied to the outer surface of the stent 14 and/or the base graft 12 to promote further adhesion and fusing of the base graft 12 to the stent 14 and/or the subsequently applied outer layer 16. In this regard, the tubular substrate graft 12 and stent 14 mounted on the mandrel may be rolled in powdered PTFE resin for the desired attachment of the PTFE powder thereto. Alternatively, the PTFE liquid dispersion described above can be sprayed or otherwise applied to the surface of the stent 14 and/or the outer surface of the tubular substrate graft 12 prior to subsequent application of the tubular outer layer 16.

Further, as shown in FIG. 4d, the strip 17 is first spirally wound in an overlapping manner in the first direction on the outer surface of the fixed mold 14. In a preferred embodiment, strips having a width of 1/2 inches are used. The strip is helically wound around the stent at an oblique angle such that 6-8 turns of the strip are wound per linear inch of the stent 14.

Thereafter, as shown in FIG. 4e, a second strip is wound in the opposite direction, preferably at the same angle of inclination using strips of the same width, to wind another 6-8 turns 17 per linear inch of stent 14. In this way, the two wound layers of tape 17 (fig. 4d and 4e) together form the tubular PTFE outer layer 16, preferably less than 0.1 inch thick, and this outer layer may be formed from 1-10 layers of tape 17 in sequence (e.g., laminated). For example, when using an ePTFE strip having a density of less than 1.6g/cc and a width of 1/2 inches, a first spiral wrap (FIG. 4d) may be wrapped sequentially around 4 layers of strip 17, while a second spiral wrap (FIG. 4e) may be wrapped around another 4 layers of strip 17 to form a tubular outer layer 16 comprised of a total of 8 layers of strip 17.

To further promote adhesion of the tubular outer layer 16 to the stent 14 and/or the inner substrate graft 12, a liquid dispersion of PTFE may optionally be sprayed or otherwise applied and dried onto the strips 17 prior to winding, or by any suitable method (spraying, coating, etc.) to adhere such a liquid dispersion of PTFE between the tubular outer layer 16 of helically wound strips 17 and the inner substrate graft 12. Alternatively, as described below, the PTFE liquid dispersion described above may be sprayed or otherwise applied to the outer surface of the helically wound strips 17 prior to subsequent heating of the assembly, such that the PTFE particles contained in the liquid dispersion migrate inwardly through the pores of each of the layers of strips 17 and become attached between the tubular outer layer 16 and the inner substrate graft 12. Another alternative (and optional) method of attaching polymer (e.g., PTFE) particles between the base graft 12 and the tubular outer layer 16 is to roll a mandrel 50 having the base graft 12 and stent 14 disposed thereon in a dry powdered polymeric resin (e.g., the PTFE resin described above) attached to the outer surface of the base graft 12 and/or stent 14 prior to winding the strip 17 as shown in fig. 4d and 4 e.

A ligature 51 of stainless steel wire is then tied over the opposite end of the graft 10 to securely hold the base graft 12, the PTFE coated stent 14 and the outer layer 16 on the mandrel 50, as shown in figure 4 f. The mandrel with the graft 10 disposed thereon is then heated to a temperature of 363 ° ± 2 ℃ for 30 min. This heating heats the outer PTFE layer 16 and fuses to the inner base graft 12 through the perforations 19 present in the stent 14, and also facilitates bonding or fusing of the stent 14 PTFE coating 20 to the adjacent base graft 12 and outer strip layer 16. In this way, the desired stent-integrated tubular PTFE graft 10 is formed.

The heating step illustrated schematically in figure 4f may be carried out by any suitable method. For example, the mandrel 50 with the graft 10 and ligature 52 disposed thereon may be placed in an oven preheated to a desired temperature for a desired time. Alternatively, the mandrel with the graft 10 and ligature 52 disposed thereon may be rolled on a hot plate or heated surface to effect the desired heat fusion or bonding of the outer layer 16, base graft 12 and PTFE coating 20 of the stent 14.

An alternative heating step, schematically illustrated in figure 4f, may be used, which is an aluminium block heater (U-plate heater) as shown in figure 6. The aluminum plate heater is formed from a solid aluminum plate 54 formed into a generally U-shaped configuration with a plurality of bores 60 formed longitudinally therein extending at least partially therethrough. An elongated tubular electric heater 62, such as those commercially available from Watlow electric company (12001 Lackland road, St. Louis, 63146), is inserted into the bore 60 and the heater 62 is heated to maintain the inner surface of the U-shaped aluminum panel heater 54 at a temperature above about 300 ℃. It will be appreciated that other types of heating devices, such as strip-type electric heaters mounted on the outer surface of the U-shaped plate 54, may be used in place of the bore 60 and tubular heater 62 described herein.

After the U-shaped plate 54 is heated to the desired temperature, the mandrel 50 with the graft 10 and ligature 52 disposed thereon is inserted into the area inside the U-shape of the plate 54 and rotated therein to effect the desired thermal fusion of the tubular base graft 12, outer strip 16 and PTFE coating 20 of the stent 14.

In many applications, a stented graft 10 that is capable of post-bending and re-expanding is desirable to ensure that the stented graft 10 is capable of sufficient radial compression and sufficient radial expansion over its full range of two predetermined diameters.

To allow the stented graft 10 to undergo such post-bending and re-expansion, the stented graft 10 is removed from the mandrel 50 and stored in a heated environment, such as the interior space of a U-shaped heating apparatus as shown in figure 6. The opposite ends of the stent 14 are then pulled longitudinally away from each other, thereby radially contracting the stent graft 10 to its minimum radially compressed diameter D₁. The stented graft 10 is then self-expanding. If this self-expansion of the stented graft 10 does not return it to its fully radially expanded diameter D₂The stented graft 10 may then be replaced on the mandrel 50, forcing it to assume the diameter D₂Is substantially radially expanded.

Thereafter, when the graft is removed again from the mandrel 50, the stented graft 10 will be radially compressed to its fully compressed diameter D₁Then self-expand to its fully radially expanded diameter D₂. F. With fixed mouldsAssembly and manufacture of unitary PTFE tubular grafts

In a first alternative embodiment of the present invention, the inner base graft 12 may be eliminated or eliminated, thereby providing a modified stented graft 10 comprising only a stent 14 and a tubular outer layer 16.

In this first alternative embodiment, the above-described method of manufacture is performed as described without the tubular base graft 12, thereby producing a modified stent graft 10 in which the tubular outer PTFE layer 16 is fused to the stent 14 only.

In embodiments in which the stent 14 is coated with a polymeric coating, such as PTFE, the presence of the coating on the stent 14 provides lubricity and biocompatibility that may render the stent-graft with an internal stent suitable for use in applications in which the exposed stent 14 may come into direct contact with biological fluids or blood flowing through the graft, thereby eliminating the need for the internal base layer graft 12.

Thus, this first alternative embodiment of the present invention includes all possible embodiments in which a stent-graft 10 is prepared using only a tubular outer layer 16 in combination with a stent 14, the graft being devoid of an inner tubular base graft 12. G. Assembly and manufacture of externally stented PTFE tubular grafts

In a second alternative embodiment of the invention, the tubular outer layer 16 may be eliminated or eliminated, thereby producing an externally stented PTFE tubular graft comprising only the stent 14 and the inner base tube 12.

In this second alternative embodiment, the above-described manufacturing method is carried out as described, without the tubular outer layer 16. This results in a modified stent graft 10 which contains only the inner base graft 12 and stent 14.

In some versions in which the stent 14 is coated with a polymeric coating, such as PTFE, the presence of such a coating on the stent 14 may enhance biocompatibility, which may render such externally stented grafts suitable for implantation in blood vessels and other tubular anatomical passageways, wherein the exposed portion of the coated stent 14 may be in direct contact with vascular or other tissue of the human body, thereby eliminating the need for the tubular outer layer 16.

This second alternative embodiment of the present invention therefore includes all possible embodiments in which a stent graft 10 is prepared having an outer stent, using only an inner base graft 12 in combination with a stent 14, which graft does not have a tubular outer layer 16.

It will be apparent that the invention has been described above with reference to some embodiments of the invention which are presently preferred. Various additions, deletions, modifications and improvements may be made to the above-described embodiments without departing from the spirit and scope of the invention. Accordingly, it is intended that all such reasonable additions, deletions, modifications and variations to the above-described embodiments be included within the scope of the following claims.

Claims (115)

1. A tubular stented graft that can be used alternately in a radially compressed configuration having a first diameter and in a radially expanded configuration having a second diameter, the stented graft comprising:

a) a stent comprising:

i) at least one generally tubular member having a cavity extending longitudinally therethrough;

ii) said stent diameter is radially collapsible to substantially equal said first stent graft diameter and then radially expandable to substantially equal said second stent graft diameter; and

iii) a plurality of side holes are present in said stent at said second radially expanded diameter thereof;

b) a continuous tubular PTFE coating formed on said stent, said PTFE coating comprising:

i) a tubular substrate graft of stretched, sintered PTFE having an outer surface and an inner surface, said tubular substrate graft being coaxially disposed within the stent lumen such that the outer surface of the tubular substrate graft contacts the inner stent surface, whereby the inner surface of the tubular substrate graft defines a luminal passageway through the stent graft; and

ii) a tubular outer layer of stretched, sintered PTFE disposed on the outer surface of said stent such that said stent is sandwiched between said outer layer and said tubular base graft;

securing said tubular outer layer to said tubular base graft through said side openings in said stent to form a continuous PTFE tube integral with the stent, said tube being used alternately in said radially compressed configuration of said first diameter and in said radially expanded configuration of said second diameter.

2. The stented graft of claim 1 wherein the tubular outer layer is formed from a strip of stretched, sintered PTFE having a width of less than about 1 inch, the strip being wound around the stent to form the tubular outer layer thereon.

3. The stented graft of claim 2 wherein the strip of PTFE having a thickness of less than 0.015 inch is wrapped around the stent in an overlapping manner such that the outer tubular layer comprises from 1 to 10 layers of the strip.

4. The stent graft of claim 2 wherein said strip is helically wound around said stent.

5. The stented graft of claim 4 wherein the strip has a width of 1/2 inches, and wherein the strip is helically wound such that 6-8 turns of the strip are longitudinally wound per inch of stented graft.

6. The stented graft of claim 5 wherein said helical winding of said strip is co-wound first in one direction and then in the opposite direction two times.

7. The stent graft of claim 6 wherein said helical winding of said strip forms a tubular outer layer of 8 sequential layers of the strip.

8. The stented graft of claim 1 wherein the stent is a self-expanding stent.

9. The stent graft of claim 1 wherein the stent is a crimped stent.

10. The stent graft of claim 1 wherein said self-expanding stent is formed from a plurality of wire elements woven into said generally tubular shape, and wherein said side openings in the stent are formed by gaps existing between adjacent ones of the wire elements.

11. The stented graft of claim 10 wherein the wire elements are formed of a metal alloy wherein the remainder of the alloy is iron and wherein at least one other element alloyed with iron is selected from the group consisting of:

a) cobalt;

b) chromium;

c) nickel; and

d) molybdenum.

12. The stent graft of claim 1 wherein said stent is formed from a plurality of plastic members woven into said generally tubular shape, and wherein said side openings in the stent are formed by gaps existing between adjacent plastic members.

13. The stented graft of claim 12 wherein the plastic from which the plastic element is made is selected from the group consisting of:

polytetrafluoroethylene;

fluorinated ethylene propylene;

polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymers;

polyvinyl chloride;

polypropylene;

polyethylene terephthalate;

various fluoroplastics (brood fluoride); and

other biocompatible plastics.

14. The stent graft of claim 10 wherein some of said stent wire elements are helically wound around a longitudinal axis in a first direction and the remainder of said wire elements are helically wound around said longitudinal axis in a second direction such that they pass on opposite sides of some of the wire elements wound in the first helical direction to form a helically braided tubular wire stent.

15. The stent graft of claim 8 wherein said self-expanding stent comprises a memory shape alloy that exists in alternating first and second crystalline states, and wherein when said memory shape alloy is in its first crystalline state, the stent assumes its radially expanded shape, and when said memory shape alloy is in its second crystalline state, the stent assumes its radially compressed shape.

16. The stented graft of claim 1 wherein the tubular base graft comprises stretched, sintered PTFE having a thickness of less than 0.10 inch.

17. The stented graft of claim 1 wherein the tubular base graft comprises stretched, sintered PTFE having a density less than 1.6 g/cc.

18. The stented graft of claim 1 wherein the tubular based graft comprises stretched, sintered PTFE having a thickness of less than 0.10 inch and a density of less than 1.6 g/cc.

19. The stented graft of claim 1 wherein the tubular outer layer comprises stretched, sintered PTFE having a thickness of less than 0.10 inch.

20. The stented graft of claim 1 wherein the tubular outer layer comprises stretched, sintered PTFE having a density less than 1.6 g/cc.

21. The stented graft of claim 1 wherein the tubular outer layer comprises stretched, sintered PTFE having a thickness of less than 0.10 inch and a density of less than 1.6 g/cc.

22. The stented graft of claim 19 wherein said tubular outer layer having a thickness of less than 0.1 inch is formed from a stretched, sintered PTFE strip having a thickness of less than 0.015 inch which is wrapped around said stent in overlapping relation to form said tubular outer layer.

23. The stented graft of claim 1 wherein the stent further comprises:

iv) a polymeric coating formed on said stent.

24. The stent graft of claim 23 wherein the polymeric material forming the polymeric coating on the stent is selected from the group consisting of:

polytetrafluoroethylene;

fluorinated ethylene propylene;

polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymers;

polyvinyl chloride;

polypropylene;

polyethylene terephthalate;

polyvinylidene fluoride; and

other biocompatible plastics.

25. The stent graft of claim 23 wherein the step of applying said polymer coating to said stent is as follows:

immersing the stent in a liquid dispersion of a polymer;

removing the stent from the liquid dispersion of the polymer;

drying the liquid dispersion of the polymer remaining on the stent to form said polymer coating thereon.

26. The stent graft of claim 23 wherein the polymer coating is formed on the stent by electron beam attachment.

27. The stent graft of claim 23 wherein the stent is formed from a plurality of elongate elements and wherein the polymer coating is formed on each of the elongate elements by placing a polymer tube over the elongate elements.

28. The stented graft of claim 23 wherein said base graft and said tubular outer layer are bonded to a polymer coating formed on said stent.

29. The stented graft of claim 1 wherein the graft further comprises:

iv) attaching a quantity of polymeric particles between said inner substrate graft and said tubular outer layer and then melting to facilitate the anchoring of said tubular substrate graft to said tubular outer layer.

30. The stented graft of claim 29 wherein the polymer particle is PTFE.

31. The stented graft of claim 29 wherein the polymer particles are melted by heating.

32. The stented graft of claim 30 wherein the polymer particles are solvent-melted.

33. The stented graft of claim 29 wherein the polymer particles are attached by applying a liquid dispersion of polymer particles to one of the base graft and the tubular outer layer prior to assembly.

34. The stent graft of claim 29 wherein said polymer particles are attached between said tubular base graft and said tubular outer layer by applying a liquid dispersion of polymer particles to the exterior of said tubular outer layer such that the polymer particles contained within the dispersion migrate inwardly through the tubular outer layer.

35. A stented tubular graft for use alternately in a radially compressed configuration having a first diameter and in a radially expanded configuration having a second diameter, said stented tubular graft comprising:

a) a stent comprising:

i) at least one generally tubular member having a cavity extending longitudinally therethrough;

ii) said stent diameter is radially collapsible to substantially equal said first stent graft diameter and radially expandable to substantially equal said second stent graft diameter; and

iii) a plurality of side holes are present in said stent at a radially expanded diameter thereof.

b) A continuous tubular PTFE coating formed on said stent, said PTFE coating comprising a tubular base graft of stretched, sintered PTFE, said tubular base graft having an outer surface and an inner surface, said tubular base graft being coaxially disposed within the lumen of said stent such that the outer surface of the tubular base graft contacts the stent such that the inner surface of the tubular base graft defines a luminal passageway through the lumen of the stent;

said tubular base graft being secured to said stent to form an externally stented continuous PTFE tube which can be used alternately in said radially compressed configuration of said first diameter and in said radially expanded configuration of said second diameter.

36. The externally stented graft of claim 35 wherein the stent is a self-expanding stent.

37. The externally stented graft of claim 35 wherein the stent is a stent that is a crimped stent.

38. The externally stented graft of claim 36 wherein the self-expanding stent is formed from a plurality of wire elements woven into the generally tubular shape, and wherein the side openings in the stent are gaps between adjacent ones of the wire elements.

39. The externally stented graft of claim 38 wherein the wire element is formed of an alloy wherein the remainder of the alloy is iron, and wherein the at least one other element alloyed with iron is selected from the group consisting of:

a) cobalt;

b) chromium;

c) nickel; and

d) molybdenum.

40. The stent graft of claim 35, wherein said stent is made of a plurality of plastic members woven into said generally tubular shape, and wherein said side holes in the stent are formed by gaps existing between adjacent ones of the plastic members.

41. The stented graft of claim 40 wherein the plastic from which the plastic element is made is selected from the group consisting of:

polytetrafluoroethylene;

fluorinated ethylene propylene;

polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymers;

polyvinyl chloride;

polypropylene;

polyethylene terephthalate;

polyvinylidene fluoride; and

other biocompatible plastics.

42. The externally stented graft of claim 38 wherein some of said stent wire elements are helically wound in a first direction and others of said wire elements are helically wound in a second direction so that they cross on opposite sides of adjacent ones of the wire elements wound in the first helical direction to form a helically braided wire stent.

43. The externally stented graft of claim 36, wherein said self-expanding stent comprises a memory shape alloy alternately existing in a first crystalline state and a second crystalline state, such that said stent substantially assumes a radially compressed shape of said first diameter when said memory shape alloy is in its first crystalline state and a radially expanded shape of said second diameter when said memory shape alloy is in its second crystalline state.

44. The externally stented graft of claim 35 wherein the tubular base graft comprises stretched, sintered PTFE having a thickness of less than 0.10 inch.

45. The externally stented graft of claim 35 wherein the tubular base graft comprises stretched, sintered PTFE having a density less than 1.6 g/cc.

46. The externally stented graft of claim 35 wherein the tubular base graft comprises stretched, sintered PTFE having a thickness of less than 0.10 inch and a density of less than 1.6 g/cc.

47. The externally stented graft of claim 35 wherein the stent further comprises:

iv) a polymeric coating formed on said stent.

48. The externally stented graft of claim 35 wherein the polymer material forming the polymer coating on the stent is selected from the group consisting of:

polytetrafluoroethylene;

fluorinated ethylene propylene;

polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymers;

polyvinyl chloride;

polypropylene;

polyethylene terephthalate;

polyvinylidene fluoride; and

other biocompatible plastics.

49. The externally stented graft of claim 47 wherein the polymer coating is a polymer coating applied to the stent by the steps of:

immersing the stent in a liquid dispersion of a polymer;

removing the stent from the liquid dispersion of the polymer;

drying the liquid dispersion of the polymer remaining on the stent to form a coating thereon.

50. The externally stented graft of claim 47 wherein the polymer coating is formed over the stent using electron beam attachment.

51. The externally stented graft of claim 47 wherein the stent is formed from a plurality of elongate elements and wherein the polymer coating is formed by mounting a preformed polymer tube over each of the elongate elements.

52. The externally stented graft of claim 47 wherein both said base graft and said tubular outer layer are additionally fused to a polymer coating formed over said stent.

53. A stented tubular graft usable first in a radially compressed configuration having a first outer diameter and then expanded to a radially expanded configuration having a second outer diameter, said stented graft comprising:

a) a stent comprising:

i) at least one generally tubular member having a cavity extending longitudinally therethrough;

ii) said stent diameter is radially collapsible to substantially equal said first stent graft diameter and then radially expandable to substantially equal said second stent graft diameter; and

iii) a plurality of side holes are present in said stent when said stent is at its radially expanded diameter;

b) a continuous tubular outer PTFE coating formed over said stent, said outer PTFE coating comprising a tubular stretched sintered PTFE outer layer disposed coaxially over the tubular stent;

said tubular outer layer being secured to the stent to form a continuous PTFE tube having a stent therein, the tube being alternately usable in said radially compressed shape of said first diameter and in said radially expanded shape of said second diameter.

54. The stented graft of claim 53 having a stent within the interior of said stent, wherein said stent is a self-expanding stent.

55. The stented graft of claim 53 having a stent within the interior of said stent, wherein said stent is a stent of the compressed stent type.

56. The stented graft of claim 54 wherein said self-expanding stent is formed from a plurality of wire elements woven into said generally tubular shape, and wherein some of said side holes in the stent are some of the gaps that exist between some of the adjacent ones of said wire elements.

57. The stented graft of claim 52 wherein the wire element is formed of a metal alloy wherein the remainder of the alloy is iron and wherein the at least one other element alloyed with iron is selected from the group consisting of:

a) cobalt;

b) chromium;

c) nickel; and

d) molybdenum.

58. The stent graft of claim 53 wherein said stent is formed from a plurality of plastic elements woven into said generally tubular shape, and wherein said side openings in said stent are formed by gaps existing between adjoining plastic elements.

59. The stented graft of claim 58 wherein the plastic from which said plastic elements are made is selected from the group consisting of:

polytetrafluoroethylene;

fluorinated ethylene propylene;

polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymers;

polyvinyl chloride;

polypropylene;

polyethylene terephthalate;

polyvinylidene fluoride; and

other biocompatible plastics.

60. The stent-graft of claim 56 wherein some of said stent wire elements are helically wound around a longitudinal axis in a first direction and the remainder of said stent wire elements are helically wound around said longitudinal axis in a second direction such that they pass on opposite sides of the wire elements wound in the first helical direction to form a helically braided tubular wire stent.

61. The stented graft of claim 53 wherein said self-expanding stent comprises a memory shape alloy which exists in alternating first and second crystalline states, and wherein the stent assumes its radially expanded shape when said memory shape alloy is in its first crystalline state and assumes its radially compressed shape when said memory shape alloy is in its second crystalline state.

62. The stented graft of claim 53 wherein said tubular outer layer is formed from a stretched, sintered PTFE strip having a width of less than about 1 inch, wound around the stent outer surface to form said tubular outer layer.

63. The stented graft of claim 62 wherein said strip of PTFE has a thickness of less than 0.015 inch and wherein the strip is wrapped around said stent in an overlapping manner such that said outer layer comprises from 1 to 10 layers of the strip.

64. The stented graft of claim 62 wherein said strip is helically wound around said stent.

65. The stent graft of claim 64 wherein the width of said strip is 1/2 inches, and wherein the strip is helically wound such that the stent is longitudinally wound 6 to 8 turns per inch of the strip.

66. The stented graft of claim 65 wherein said helical winding of said strip is co-wound first in one direction and then in the opposite direction two times.

67. The stented graft of claim 66 wherein said helical winding of said strip forms a tubular outer layer of 8 sequential layers of the strip.

68. The stented graft of claim 66 wherein said helical winding of said strip occurs first in one direction and then in a second direction opposite said first direction.

69. The stented graft of claim 53 having a stent within the interior, wherein said stent further comprises:

iv) a polymeric coating formed on said stent.

70. The stent-bearing graft in the interior of claim 69, wherein the polymeric material forming the polymeric coating on the stent is selected from the group consisting of:

polytetrafluoroethylene;

fluorinated ethylene propylene;

polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymers;

polyvinyl chloride;

polypropylene;

polyethylene terephthalate;

polyvinylidene fluoride; and

other biocompatible plastics.

71. The stent-graft of claim 69, wherein said polymer coating is applied to said stent by the steps of:

immersing the stent in a liquid dispersion of a polymer;

removing the stent from the liquid dispersion of the polymer;

drying the liquid dispersion of the polymer remaining on the stent to form a coating thereon.

72. The stented graft of claim 69 wherein the polymer coating is formed on the stent using electron beam attachment.

73. The stented graft of claim 69 wherein said stent comprises a plurality of elongated wire elements and wherein said polymer coating is formed on said stent by mounting a preformed polymer tube over said wire elements.

74. The stented graft of claim 69 wherein said outer layer is fused to a polymer coating formed over said stent.

75. A method of making a tubular PTFE graft stented internally, the graft being alternately usable in a radially compressed shape having a first diameter and in a radially expanded shape having a second diameter, the method comprising the steps of:

a) preparing a tubular base graft comprising stretched sintered PTFE having a density of less than 1.6 g/cc;

b) placing a tubular substrate graft over a tubular mandrel;

c) preparing a generally tubular stent which is alternately radially compressed to a first diameter and radially expanded to a second diameter, said stent having a longitudinal lumen therethrough and having a plurality of side openings therein when radially expanded to its second diameter;

d) mounting a common tubular stent on a tubular base graft placed on a mandrel so that the tubular base graft is coaxially arranged in a longitudinal cavity of the stent and is in close contact with the stent;

e) forming a tubular PTFE outer layer outside the stent so that the stent is coaxially placed in the tubular outer layer and is in close contact with the stent;

f) after the substrate graft, stent and tubular outer layer are fitted over the mandrel, they are heated to fix the tubular outer layer and tubular substrate graft to each other through the side holes present in the stent, thereby producing the stent tubular PTFE graft.

76. The method of claim 75, further comprising the additional steps of:

g) removing the stented tubular PTFE graft from the mandrel;

h) radially reducing the stented tubular PTFE graft to a radially compressed shape of said first diameter; and

i) then re-expanding the stented tubular PTFE graft to its radially expanded shape of said second diameter.

77. The method of claim 76 wherein step i) is performed by placing the stented tubular PTFE graft on a mandrel having an outer diameter substantially equal to the diameter of the lumen of the stented tubular PTFE graft in its radially expanded shape having said second diameter.

78. The method of claim 75, wherein step c) of the method further comprises coating the stent with a plastic coating that will adhere to the PTFE when heated, and wherein step f) further comprises adhering the tubular outer layer and the tubular base graft to the plastic coating formed on the stent.

79. The method of claim 78 wherein the plastic coating on the stent is a PTFE coating.

80. The method of claim 79, wherein the step of forming said PTFE coating on said stent is as follows:

immersing the stent in an aqueous dispersion of PTFE;

removing the stent from the aqueous dispersion of PTFE; and

drying the aqueous PTFE dispersion remaining on the stent to form said PTFE coating thereon.

81. The process of claim 75, wherein step e) of the process is carried out by:

preparing a plurality of stretched, sintered PTFE strands;

the stretched sintered PTFE strand was wound around the outside of the stent to form the tubular outer layer thereon.

82. The method of claim 81 wherein the step of winding said stretched sintered PTFE strip around the stent to form said tubular outer layer thereon comprises:

a PTFE strip is spirally wound around the outside of the stent in an overlapping manner.

83. The method of claim 82 wherein said strip of PTFE has a width of 1/2 inches, wherein the strip is helically wound about 6 to 8 turns of the strip per inch of stented graft in the longitudinal direction.

84. The method of claim 77, wherein said helically winding of said strip is performed a total of two times, first in one direction and then in the opposite direction.

85. The method of claim 82, wherein said helical winding of said strip produces a tubular outer layer comprising 8 layers of said strip.

86. The method of claim 78 wherein said helically winding of said strip is first performed in one direction and then in a second direction opposite said first direction.

87. The method of claim 75, further comprising the additional step of:

attaching a plurality of polymer particles between said tubular base graft and said tubular PTFE outer layer to facilitate securement of said tubular base graft to said tubular PTFE outer layer and said stent.

88. The method of claim 87, wherein said polymer particles are PTFE.

89. The method of claim 87, wherein said attaching of said polymer particles is performed by attaching an aqueous suspension of polymer between a tubular inner layer and said tubular PTFE outer layer.

90. The method of claim 87, wherein said polymer particles are attached by rolling the mandrel having the inner substrate graft and stent disposed thereon in a powdered polymeric resin, such that some of the polymer particles attach to the stent and the outer surface of the tubular substrate graft.

91. The method of claim 90 wherein said powdered polymeric resin is a starting PTFE resin powder.

92. The method of claim 75, further comprising the step of:

the tubular outer layer and the tubular base graft are secured at both ends to the mandrel to prevent longitudinal foreshortening during subsequent heating of step f.

93. A method of making an externally stented tubular PTFE graft alternately usable in a radially compressed shape having a first diameter and in a radially expanded shape having a second diameter, said method comprising the steps of:

a) preparing a tubular base graft comprising stretched, sintered PTFE having a density of less than 1.6 g/cc;

b) placing a tubular substrate graft over a tubular mandrel;

c) preparing a generally tubular stent which is alternately radially compressed to a first diameter and radially expanded to a second diameter, the stent having a plurality of side holes therein when the stent is at the radially expanded second diameter;

d) placing a generally tubular stent over the tubular base graft on the mandrel such that the tubular base graft is coaxially disposed within and in intimate contact with the stent; and

e) the tubular base graft is fixed to the stent by heating the base graft and the stent mounted on the mandrel, thereby producing a tubular PTFE graft having a stent inside.

94. The method of claim 93, further comprising the additional steps of:

f) removing the tubular PTFE graft, having the stent on the outside, from the mandrel;

g) reducing the internally stented tubular PTFE graft to a radially compressed shape of said first diameter thereof; and

h) the stented tubular PTFE graft is then fully re-expanded to the radially expanded shape of the second diameter.

95. The method of claim 94 wherein step h is performed by placing the externally stented PTFE tubular graft over a mandrel having an outer diameter substantially equal to the diameter of the inner lumen of the externally stented PTFE tubular graft in its radially expanded configuration of said second diameter.

96. The method of claim 93, wherein step c) of the method further comprises coating the stent with a polymer coating that will adhere to the PTFE when heated, and wherein step f) causes the tubular substrate graft to adhere to the polymer coating formed on the stent.

97. The method of claim 96, wherein the polymer coating on the stent is a PTFE coating.

98. The method of claim 96, wherein the steps of forming said polymer coating on said stent are as follows:

immersing the stent in an aqueous dispersion of particles;

removing the stent from the aqueous dispersion of particles; and

drying the aqueous dispersion of the polymer retained on the stent to form said polymer coating thereon.

99. The method of claim 98, wherein the aqueous dispersion of polymer particles is an aqueous dispersion of PTFE particles.

100. The method of claim 96, wherein said polymer coating is formed on the stent by electroaffixation.

101. The method of claim 93, further comprising the step of:

securing the ends of the base graft and the stent to the mandrel to prevent longitudinal foreshortening during the heating of step e).

102. A method of making a tubular PTFE graft stented internally, the graft being alternately usable in a radially compressed configuration having a first diameter and in a radially expanded configuration having a second diameter, said method comprising the steps of:

a) preparing a generally tubular stent which is alternately radially compressed to a first diameter and radially expanded to a second diameter, the stent having a plurality of side holes therein when at the radially expanded second diameter;

b) placing a generally tubular stent over a tubular mandrel;

c) forming a tubular PTFE outer layer around the stent so that the tubular PTFE outer layer is in close contact with the stent; and

d) the stent and the tubular outer layer mounted on the mandrel are heated to fix the tubular outer layer to the stent, thereby producing a tubular PTFE graft having a stent inside.

103. The method of claim 102, further comprising the additional steps of:

e) removing the tubular PTFE graft with the stent inside from the mandrel;

f) reducing the internally stented tubular PTFE graft to a radially compressed shape of said first diameter thereof; and

g) the tubular PTFE graft, with the stent inside, is then re-expanded sufficiently to the radially expanded shape of the second diameter.

104. The method of claim 103 wherein step g) is performed by placing the stented tubular PTFE graft on a mandrel having an outer diameter substantially equal to the diameter of the inner lumen of the stented tubular PTFE graft when in its radially fully expanded shape having said second diameter.

105. The method of claim 104, wherein step a) of the method further comprises covering the stent with a plastic coating that will bond to the PTFE when heated, and wherein step d) further comprises bonding a tubular outer layer to the polymeric coating formed on the stent.

106. The method of claim 105, wherein the polymer coating on the stent is a PTFE coating.

107. The method of claim 106, wherein said polymer coating is formed on said stent by the steps of:

immersing the stent in an aqueous dispersion of a polymer;

removing the stent from the aqueous dispersion of the polymer; and

drying the aqueous polymer dispersion remaining on the stent to form said polymer coating thereon.

108. A method of claim 107, wherein said aqueous dispersion of polymer particles is an aqueous dispersion of PTFE particles.

109. The method of claim 106, wherein the polymer coating is formed on the stent by electroaffixation.

110. The method of claim 103, further comprising the step of:

securing the ends of the base graft and the stent to the mandrel to prevent longitudinal foreshortening during the heating of step e).

111. The method of claim 103, wherein step c of the method is performed by:

preparing a plurality of stretched, sintered PTFE strands;

the stretched, sintered PTFE strip is wound around the outside of the stent to form the tubular outer layer thereon.

112. The method of claim 111, wherein the step of winding said stretched, sintered PTFE strip around the stent to form said tubular outer layer thereon comprises:

a PTFE strip is spirally wound around the outside of the stent in an overlapping manner.

113. The method of claim 111, wherein said strip of PTFE has a width of 1/2 inches, and wherein said strip is helically wound such that 6 to 8 turns of the strip are wound per inch of stent in the longitudinal direction.

114. The method of claim 112, wherein said helically winding of said strip is performed a total of two times, first in one direction and then in the opposite direction.

115. The method of claim 112, wherein said helical winding of said strip produces a tubular outer layer comprising 8 layers of said strip.