Patent Application
20060142852
The present invention relates generally to low profile, reinforced PTFE or ePTFE composite graft. More particularly, the present invention relates to a thermally laminated PTFE or ePTFE composite graft.
Implantable prostheses are commonly used in medical applications. One of the more common prosthetic structures is a tubular prosthesis which may be used as a vascular graft to replace or repair damaged or diseased blood vessels.
One form of a conventional tubular prosthesis specifically used for vascular grafts includes a textile tubular structure formed by weaving, knitting, braiding or any non-woven textile technique processing synthetic fibers into a tubular configuration. Such conventional textile prostheses are often thick walled tubular vessels having wall thicknesses that exceed one millimeter, which limits intraluminal delivery due to the high profile of the graft.
It is also well known to form a nontextile prosthesis, especially a tubular graft, from polymers such as polytetrafluoroethylene (PTFE). Such a nontextile tubular graft may be formed by stretching and expanding PTFE into a structure referred to as expanded polytetrafluoroethylene (ePTFE). Tubes formed of ePTFE exhibit certain beneficial properties as compared with textile prostheses. The expanded PTFE tube has a unique structure defined by nodes interconnected by fibrils. The node and fibril structure defines micropores which facilitate a desired degree of tissue ingrowth while remaining substantially fluid-tight. Tubes of ePTFE may be formed to be exceptionally thin and yet exhibit the requisite strength necessary to serve in the repair or replacement of a body lumen. The thinness of the ePTFE tube facilitates ease of implantation and deployment with minimal adverse impact on the body. Such thinness, however, may result in a decrease in radial tensile strength, radial burst strength or suture retention strength.
It is therefore desirable to provide an implantable prosthesis, preferably in the form of a tubular vascular prosthesis, which achieves many of the above-stated benefits, such as low profile, without the resultant disadvantages associated therewith.
In one aspect a low profile, durable, reinforced composite implantable graft is provided. The composite graft includes (a) a first seamless tubular layer comprising biocompatible first polymeric material and having a luminal surface and an exterior surface; (b) a biocompatible reinforcing member arranged in a pattern to define a second tubular layer, the second tubular layer being disposed over the exterior surface of the first tubular layer; and (c) a third seamless tubular layer comprising biocompatible second polymeric material and having a luminal surface and an exterior surface, the luminal surface of the third tubular layer being securably disposed over the second tubular and over the first tubular layer; wherein the tubular layers define a wall of the graft, the wall having a wall thickness of less than 0.1 mm. Desirably, the graft wall thickness is less than 0.05 mm.
In this aspect of the present invention, the first polymeric material and the second polymeric materials may be the same polymeric material or the same class of polymeric material.
The biocompatible reinforcing members may comprise yarns. The yarns may be formed in a textile pattern, such as a braided textile pattern, a woven textile pattern, a knitted textile pattern, or combinations thereof. Further, the yams may be helically wrapped over the luminal layer to provide for the reinforcing layer. Moreover, the biocompatible reinforcing members may comprise helically wrapped tape, such as polymeric tape.
The first and the second polymeric materials may be selected from the group consisting of polytetrafluoroethylene, expanded polytetrafluoroethylene and combinations thereof. The graft layers may be laminated together without the presence of an adhesive. The reinforcing members comprise polymeric, such as polytetrafluoroethylene yarns or metallic yarns. The reinforcing members may also be monofilament strands or multifilament yarns.
Desirably, the first layer is an extruded tube and the third layer is an extruded tube. The graft may be a self-supporting graft. The graft may also be crimped.
A method of forming a composite graft includes the steps of (a) providing an elongate tubular mandrel; (b) placing a first seamless tubular layer over the mandrel, the first layer comprising biocompatible first polymeric material and having a luminal surface and an exterior surface; (c) providing reinforcing members over the exterior surface, the yarns arranged in a pattern to define a second tubular layer; (d) providing a third seamless tubular layer over the yarns, the third layer comprising biocompatible second polymeric material and having a luminal surface and an exterior surface, the luminal surface being securably disposed over the reinforcing members and over the first tubular layer; (e) heat laminating the layers together to form a graft wall having a wall thickness of less than 0.1 mm. The step of providing the reinforcing members may be selected from the group consisting of braiding, knitting, weaving, helically winding and combinations thereof. Desirably, the step of heat laminating the layers is done in the absence of an adhesive.
When the elongate members 24 are yarns, the yarns are desirably made from a textile material. The textile material may be formed from synthetic yarns that may be flat, shaped, twisted, textured, pre-shrunk or un-shrunk. Synthetic biocompatible yarns suitable for use in the present invention include, but are not limited to, polyesters, including polyethylene terephthalate (PET) polyesters, polypropylenes, polyethylenes, polyurethanes, polyolefms, polyvinyls, polymethylacetates, polyamides, naphthalane dicarboxylene derivatives, natural silk and polytetrafluoroethylenes. Moreover, at least one of the synthetic yarns may be a metallic yarn or a glass or ceramic yarn or fiber. Useful metallic yarns include those yarns made from or having stainless steel, platinum, gold, titanium, tantalum and Ni—Co—Cr-based alloy. The yarns may further comprise carbon, glass or ceramic fibers. Preferably, the yarns are made from thermoplastic materials including, but not limited to, polyesters, polypropylenes, polyethylenes, polyurethanes, polynaphthalenes, polytetrafluoroethylenes and the like. The yams may be of the multifilament, monofilament or spun types. As is well known, the type and denier of the yarn chosen may be selected in a manner which forms a prosthesis and, more particularly, a vascular structure have desirable properties.
As depicted in
Braiding machines, including circular braiding machines that form a braided textile over a mandrel, are useful with the practice of the present invention. An example of such a braiding machine is described in U.S. Pat. No. 6,652,571, the content of which is incorporated herein by reference. A braiding machine capable of forming the interlocked three-dimensional braid used to form the textile tube of the present invention is described in International Patent Publication No. WO 91/10766, which is incorporated herein by reference.
Generally, a braided structure is formed having a braid angle from about 30° to about 90° with respect to the longitudinal axis of the braided structure, desirably about 54.5° to about 75°. The yarns of the braid tend to seek equilibrium at a braid angle of about 54.5°, which is a neutral angle for tubular vessels under pressure. Thus, when the braid angle is larger than the neutral angle, when pressure is exerted from within, for example due to fluid flow, the yarns will tend to scissor and decrease the braid angle thereby elongating or stretching the braided structure in order to reach the neutral angle.
Useful weaves include, but are not limited to, a plain or regular weave 36 as depicted in
Knitting involves the interlooping of one yarn system into vertical columns and horizontal rows of loops called wales and courses, respectively, with fabric coming out of the machine in the wale direction. Useful knits include, but are not limited to a high stretch knit, a locknit knit, which is also referred to as tricot or jersey knit (e.g., knit 38 as depicted in
As depicted in
Desirably, the exterior layer 18 and the interior layer 22 are formed from polytetrafluoroethylene (PTFE) and/or expanded polytetrafluoroethylene (ePTFE). An ePTFE layer may be produced from the expansion of PTFE formed in a paste extrusion process. The PTFE extrusion may be expanded and sintered in a manner to form ePTFE having a microporous structure defined by nodes interconnected by elongate fibrils. The distance between the nodes, referred to as the intemodal distance, may be varied by the parameters employed during the expansion and sintering process. The resulting process of expansion and sintering yields pores within the structure of the ePTFE layer. The sizes of the pores are defmed by the internodal distance of the ePTFE layer. Additional details for extruding thin-walled PTFE and ePTFE seamless tubes is disclosed in U.S. Patent Application Publication 2003/0082324 A1, the contents of which are incorporated by reference herein.
The exterior layer 18 and the interior layer 22 and/or the reinforcing layer 20 may be adhesively bonded to form a composite prosthesis. The bonding agent may include various biocompatible, elastomeric bonding agents such as urethanes, styrene/isobutylene/styrene block copolymers (SIBS), silicones, and combinations thereof. Other similar materials are contemplated. Desirably, the bonding agent may include polycarbonate urethanes sold under the trade name CORETHANE®. This urethane is provided as an adhesive solution with preferably 7.5% Corethane, 2.5 W30, in dimethylacetamide (DMAc) solvent. Additional details of suitable adhesives and methods for adhesively bonding graft layers are disclosed in U.S. Patent Application Publication No. 2003/0139806 A1, the content of which is incorporated herein by reference.
Alternatively, the exterior layer 18 and the interior layer 22 and/or the reinforcing layer 20 may be thermally bonded to form a composite prosthesis. Desirably, the exterior layer 18 and the interior layer 22 and/or the reinforcing layer 20 are made from the same polymeric material, such as polytetrafluoroethylene, including expanded polytetrafluoroethylene, to facilitate the heat fusing of similar polymeric materials. Advantageously, the interior layer 22, the reinforcing layer 20 and the exterior layer 18 are placed sequentially over a tubular mandrel. A silicone tube may be placed over the composite graft components to apply a pressure from about 1 psig to about 10 psig, which facilitates the bonding process. The graft components may then be placed in an oven to thermally bond the components to one and the other. When the components' material is polytetrafluoroethylene, useful heating or laminating conditions include a temperature from about 300° C. to about 400° C. for a period of about 5 minutes to about 30 minutes. Other useful heating durations include from about 10 minutes to about 20 minutes, desirably about 15 minutes. Other useful temperatures include from about 330° C. to about 370° C., desirably, from about 340° C. to about 360° C. Additional details of pressure lamination techniques for tubular grafts may be found in U.S. Pat. No. 6,139,573 and U.S. patent application Ser. No. 10/741,209, filed Dec. 19, 2003, the contents of which are incorporated herein by reference.
In one aspect of the present invention, a composite implantable graft is provided. The composite graft may include (a) a first seamless tubular layer comprising biocompatible first polymeric material and having a luminal surface and an exterior surface; (b) biocompatible reinforcing member arranged in a pattern to define a second tubular reinforcing layer, the second tubular layer being disposed over the exterior surface; and (c) a third seamless layer comprising biocompatible second polymeric material and having a luminal surface and an exterior surface, the luminal surface being securably disposed over the reinforcing members and over the first tubular layer; wherein the tubular layers define a wall of the graft, the wall having a wall thickness of less than 0.1 mm. Desirably, the wall thickness is less than 0.05 mm.
The graft may be crimped to provide kink resistance and or to provide the graft with longitudinal flexibility and or a self-supporting wall feature. The present invention, however, is not limited to crimping to provide such mechanical features, such as a self-supporting graft wall. For example, the reinforcing members may be metallic yarns or strands arranged in a pattern to provide the self-supporting feature of this aspect of the present invention. The reinforcing members may also comprise metallic yarns. The yarns may be monofilament strands or multifilament yarns.
Desirably, the first polymeric material and the second polymeric material are the same, for example polytetrafluoroethylene or expanded polytetrafluoroethylene. The biocompatible reinforcing members may include yarns. The yarns may be formed in a textile pattern, such as a braided textile pattern, a woven textile pattern, a knitted textile pattern, or combinations thereof. Further, the yarns may be arranged as a helical wrap of the yarns to provide the reinforcing layer. Moreover, the biocompatible reinforcing members may comprise a helically wrapped tape. The biocompatible reinforcing members comprise a third polymeric material which may be the same or different from the first and the second polymeric materials. Desirably, these polymeric materials are the same, for example, polytetrafluoroethylene, expanded polytetrafluoroethylene and combinations thereof. The layers may be laminated together without the presence of an adhesive.
The graft wall of the composite graft of the present invention may be substantially fluid tight.
Desirably, the first layer is an extruded tube. The third layer may also be an extruded tube.
In another aspect of the present invention, an ePTFE or PTFE composite implantable graft is provided. The graft comprises (a)a first seamless tubular layer consisting essentially of a biocompatible polymeric material selected from the group consisting of polytetrafluoroethylene, expanded polytetrafluoroethylene and combinations thereof and having a luminal surface and an exterior surface; (b) a biocompatible reinforcing layer comprising a thin, elongate member arranged in a noncontiguous pattern to define a non-continuous second tubular layer, the elongate member consisting essentially of the biocompatible polymeric material, the second tubular layer being disposed over the exterior surface of the first tubular layer; and (c) a third seamless tubular layer consisting essentially of the biocompatible polymeric material and having a luminal surface and an exterior surface, the luminal surface of the third tubular layer being securably disposed over the second tubular layer and over the first tubular layer; wherein the layers are laminated together without the presence of an adhesive.
A method of forming the composite graft of the present invention includes the steps of (a) providing an elongate tubular mandrel; (b) placing a first seamless tubular layer over the mandrel, the first layer comprising biocompatible first polymeric material and having a luminal surface and an exterior surface; (c) providing reinforcing members over the exterior surface, the yarns arranged in a pattern to define a second tubular layer; (d) providing a third seamless tubular layer over the yarns, the third layer comprising biocompatible second polymeric material and having a luminal surface and an exterior surface, the luminal surface being securably disposed over the reinforcing members and over the first tubular layer; (e) heat laminating the layers together to form a graft wall having a wall thickness of less than 0.1 mm.
The step of providing the reinforcing members may be selected from the group consisting of braiding, knitting, weaving, helically winding and combinations thereof. Further, the step of heat laminating the layers is advantageously done in the absence of an adhesive.
With any embodiment of the graft 10 may be formed as a self-supporting prosthesis and usable to maintain patency of a bodily vessel, such as in the coronary vasculature, esophagus, trachea, colon, biliary tract, urinary tract, prostate, and brain. Also, stent-graft 10 may be treated with any of the following: anti-thrombogenic agents (such as heparin, heparin derivatives, urokinase, and PPack (dextrophenylalanine proline arginine chloromethylketone); anti-proliferative agents (such as enoxaprin, angiopeptin, or monoclonal antibodies capable of blocking smooth muscle cell proliferation, hirudin, and acetylsalicylic acid); anti-inflammatory agents (such as dexamethasone, prednisolone, corticosterone, budesonide, estrogen, sulfasalazine, and mesalamine); antineoplastic/antiproliferative/anti-miotic agents (such as paclitaxel, 5-fluorouracil, cisplatin, vinblastine, vincristine, epothilones, endostatin, angiostatin and thymidine kinase inhibitors); anesthetic agents (such as lidocaine, bupivacaine, and ropivacaine); anti-coagulants (such as D-Phe-Pro-Arg chloromethyl keton, an RGD peptide-containing compound, heparin, antithrombin compounds, platelet receptor antagonists, anti-thrombin antibodies, anti-platelet receptor antibodies, aspirin, prostaglandin inhibitors, platelet inhibitors and tick antiplatelet peptides); vascular cell growth promotors (such as growth factor inhibitors, growth factor receptor antagonists, transcriptional activators, and translational promotors); vascular cell growth inhibitors (such as growth factor inhibitors, growth factor receptor antagonists, transcriptional repressors, translational repressors, replication inhibitors, inhibitory antibodies, antibodies directed against growth factors, bifunctional molecules consisting of a growth factor and a cytotoxin, bifunctional molecules consisting of an antibody and a cytotoxin); cholesterol-lowering agents; vasodilating agents; and agents which interfere with endogenous vascoactive mechanisms.
Various changes to the foregoing described and shown structures will now be evident to those skilled in the art. Accordingly, the particularly disclosed scope of the invention is set forth in the following claims.
