US20090036971A1 - Ptfe layers and methods of manufacturing - Google Patents
Ptfe layers and methods of manufacturing Download PDFInfo
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- US20090036971A1 US20090036971A1 US12/250,915 US25091508A US2009036971A1 US 20090036971 A1 US20090036971 A1 US 20090036971A1 US 25091508 A US25091508 A US 25091508A US 2009036971 A1 US2009036971 A1 US 2009036971A1
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- ptfe
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
- A61L27/14—Macromolecular materials
- A61L27/16—Macromolecular materials obtained by reactions only involving carbon-to-carbon unsaturated bonds
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
- A61F2/82—Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
- A61L27/50—Materials characterised by their function or physical properties, e.g. injectable or lubricating compositions, shape-memory materials, surface modified materials
- A61L27/507—Materials characterised by their function or physical properties, e.g. injectable or lubricating compositions, shape-memory materials, surface modified materials for artificial blood vessels
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
- A61L27/50—Materials characterised by their function or physical properties, e.g. injectable or lubricating compositions, shape-memory materials, surface modified materials
- A61L27/56—Porous materials, e.g. foams or sponges
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C43/00—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
- B29C43/22—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor of articles of indefinite length
- B29C43/222—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor of articles of indefinite length characterised by the shape of the surface
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C43/00—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
- B29C43/22—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor of articles of indefinite length
- B29C43/24—Calendering
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
- B29C48/022—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the choice of material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
- B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
- B29C48/07—Flat, e.g. panels
- B29C48/08—Flat, e.g. panels flexible, e.g. films
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
- B29C55/005—Shaping by stretching, e.g. drawing through a die; Apparatus therefor characterised by the choice of materials
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2027/00—Use of polyvinylhalogenides or derivatives thereof as moulding material
- B29K2027/12—Use of polyvinylhalogenides or derivatives thereof as moulding material containing fluorine
- B29K2027/18—PTFE, i.e. polytetrafluorethene, e.g. ePTFE, i.e. expanded polytetrafluorethene
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/13—Hollow or container type article [e.g., tube, vase, etc.]
- Y10T428/1352—Polymer or resin containing [i.e., natural or synthetic]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/13—Hollow or container type article [e.g., tube, vase, etc.]
- Y10T428/1352—Polymer or resin containing [i.e., natural or synthetic]
- Y10T428/139—Open-ended, self-supporting conduit, cylinder, or tube-type article
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/13—Hollow or container type article [e.g., tube, vase, etc.]
- Y10T428/1352—Polymer or resin containing [i.e., natural or synthetic]
- Y10T428/139—Open-ended, self-supporting conduit, cylinder, or tube-type article
- Y10T428/1393—Multilayer [continuous layer]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
- Y10T428/24802—Discontinuous or differential coating, impregnation or bond [e.g., artwork, printing, retouched photograph, etc.]
Abstract
Description
- This application is a continuation of application Ser. No. 11/106,131, filed Apr. 13, 2005, the contents of which are incorporated herein by reference.
- Polytetrafluoroethylene (PTFE) layers have been used for the manufacture of various types of intracorporeal devices, such as vascular grafts. Such vascular grafts may be used to replace, reinforce, or bypass a diseased or injured body lumen. One conventional method of manufacturing “expanded” PTFE layers is described in U.S. Pat. No. 3,953,566 by Gore. In the methods described therein, a PTFE paste is formed by combining a PTFE resin and a lubricant. The PTFE paste may be extruded. After the lubricant is removed from the extruded paste, the PTFE article is stretched to create a porous, high strength PTFE article. The expanded PTFE layer is characterized by a porous, open microstructure that has nodes interconnected by fibrils.
- Such an expansion process increases the volume of the PTFE layer by increasing the porosity, decreasing the density and increasing the internodal distance between adjacent nodes in the microstructure while not significantly affecting the thickness of the PTFE layer. As such, the conventional methods expand the PTFE layer and impart a porosity and permeability while only providing a negligible reduction in a thickness of the PTFE layer. In situations where a thin PTFE layer, and specifically, a thin PTFE layer having a low fluid permeability is needed, conventional PTFE layers are largely unsatisfactory due to the porosity and highly permeable nature of the expanded PTFE layer.
- Therefore, what have been needed are improved PTFE layers and improved methods for manufacturing the PTFE layers. In particular, it would be desirable to have thin PTFE layers that have a controllable permeability to fluids (gases, liquids or both). It may also be desirable to have such thin PTFE layers that have a high degree of limpness and suppleness to allow mechanical manipulation or strain of such a PTFE layer without significant recoil or spring back.
- Embodiments of the present invention provide PTFE layers and films and methods of manufacturing the PTFE layers and films. Embodiments of the present invention may include one or more layers of a fluoropolymer, such as PTFE. Embodiments of PTFE layers may include at least a portion that does not have a significant node and fibril microstructure.
- In one embodiment, a method of processing PTFE includes providing a layer of PTFE, selectively applying a stretching agent to at least one lateral zone of the layer of PTFE in a predetermined pattern and stretching the layer of PTFE. In another embodiment, a method of processing PTFE includes providing a layer of PTFE having a stretching agent content level and selectively removing stretching agent from at least one lateral zone of the layer of PTFE in a predetermined pattern and stretching the layer of PTFE. In yet another embodiment of a method of processing PTFE, a layer of PTFE is provided. Stretching agent is applied to at least one lateral zone of a surface of the layer in a predetermined pattern until the lateral zone is saturated with stretching agent. Next, the layer of PTFE is stretched while the lateral zone of the layer of PTFE is saturated with stretching agent.
- In another embodiment, a PTFE layer includes a layer made by providing a layer of PTFE, selectively applying a stretching agent to at least one lateral zone of the layer of PTFE in a predetermined pattern and stretching the layer of PTFE. In another embodiment, a PTFE layer includes a layer made by providing a layer of PTFE having a stretching agent content level, selectively removing stretching agent from at least one lateral zone of the portion of the layer of PTFE in a predetermined pattern and stretching the layer of PTFE. In another embodiment, a PTFE layer includes a layer made by providing a layer of PTFE, applying a stretching agent to at least one lateral zone of a surface of the layer in a predetermined pattern until the lateral zone is saturated with stretching agent and stretching the layer of PTFE while lateral zone of the layer of PTFE is saturated with stretching agent.
- An embodiment of a multi-layered vascular graft includes a first tubular body having an outer surface and an inner surface that defines an inner lumen of the vascular graft. A second tubular body having an outer surface and an inner surface is coupled to the outer surface of the first tubular body. At least one of the first tubular body and the second tubular body includes a PTFE layer having a first lateral zone with a substantially low porosity, a low fluid permeability and no discernable node and fibril structure, and a second lateral zone which is fluid-permeable and has substantial node and fibril microstructure.
- In another embodiment, a tubular structure includes a layer of PTFE having a first lateral zone that is fluid-permeable and has a substantial node and fibril microstructure and a second lateral zone with a closed cell microstructure having high density regions whose grain boundaries are directly interconnected to grain boundaries of adjacent high density regions and having no discernable node and fibril microstructure. In another embodiment, an endovascular graft includes a PTFE layer having a first lateral zone that is fluid-permeable adjacent a second lateral zone with a closed cell microstructure having high density regions whose grain boundaries are directly interconnected to grain boundaries of adjacent high density regions and having no discernable node and fibril microstructure. In yet another embodiment, a PTFE layer includes a first lateral zone with a substantially low porosity, a low liquid permeability, no discernable node and fibril structure, and a high degree of limpness and suppleness to allow mechanical manipulation or strain of the PTFE layer without significant recoil or spring back. The PTFE layer also includes a second lateral zone which is fluid-permeable and has a substantial node and fibril microstructure.
- These features of embodiments will become more apparent from the following detailed description when taken in conjunction with the accompanying exemplary drawings.
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FIG. 1 illustrates a ram extruder extruding a PTFE ribbon being taken up on a spool. -
FIG. 2 illustrates a calendering process of the PTFE ribbon ofFIG. 1 . -
FIGS. 3 and 4 illustrate a tentering process with a stretching agent being applied to a PTFE layer during the stretching process and with portions of the tentering machine not shown for purposes of clarity of illustration. -
FIGS. 5 and 6 illustrate a stretching process in the machine direction of the stretched PTFE layer ofFIGS. 3 and 4 . -
FIGS. 7 and 8 illustrate a final calendering or densification process performed on a stretched PTFE layer. -
FIG. 8A illustrates a method of application of a stretching agent in a preselected pattern during a transverse stretching process in a direction that is substantially orthogonal to a machine direction by a tentering machine in order to produce PTFE layers having characteristics which may vary across the layer in a desired pattern. -
FIG. 8B illustrates as side view of the method ofFIG. 8A with portions of the tentering machine not shown for purposes of clarity of illustration. -
FIG. 8C is an enlarged view of an alternative embodiment of a portion of the PTFE layer ofFIG. 8A containing stretching agent in a preselected pattern, taken within the encircled portion 8C ofFIG. 8A . -
FIG. 8D is an enlarged view of an alternative embodiment of a portion of the stretched PTFE layer ofFIG. 8A having a pattern of varied permeability, taken within encircled portion 8D ofFIG. 8A . -
FIG. 8E is an enlarged view of an alternative embodiment of a portion of the PTFE layer ofFIG. 8A containing stretching agent in a preselected pattern, taken within the encircled portion 8C ofFIG. 8A . -
FIG. 8F is an enlarged view of an alternative embodiment of a portion of the stretched PTFE layer ofFIG. 8A having a pattern of varied fluid permeability, taken within encircled portion 8D ofFIG. 8A . -
FIG. 8G is an enlarged view of an alternative embodiment of a portion of the PTFE layer ofFIG. 8A containing stretching agent in a preselected pattern, taken within the encircled portion 8C ofFIG. 8A . -
FIG. 8H is an enlarged view of an alternative embodiment of a portion of the stretched PTFE layer ofFIG. 8A having a pattern of varied fluid permeability, taken within encircled portion 8D ofFIG. 8A . -
FIG. 8I is an enlarged view of an alternative embodiment of a portion of the PTFE layer ofFIG. 8A containing stretching agent in a preselected pattern, taken within the encircled portion 8C ofFIG. 8A . -
FIG. 8J is an enlarged view of an alternative embodiment of a portion of the stretched PTFE layer ofFIG. 8A having a pattern of varied fluid permeability, taken within encircled portion 8D ofFIG. 8A . -
FIG. 8K is an enlarged view of an alternative embodiment of a portion of the PTFE layer ofFIG. 8A containing stretching agent in a preselected pattern, taken within the encircled portion 8C ofFIG. 8A . -
FIG. 8L is an enlarged view of an alternative embodiment of a portion of the stretched PTFE layer ofFIG. 8A having a pattern of varied fluid permeability, taken within encircled portion 8D ofFIG. 8A . -
FIG. 9 is a scanning electron microscope (SEM) image of a PTFE layer at a magnification of 20,000. -
FIG. 10 is a SEM image of the PTFE layer ofFIG. 9 at a magnification ofFIG. 11 is a SEM image of the PTFE layer ofFIG. 9 at a magnification ofFIG. 12 is a SEM image of the PTFE layer ofFIG. 9 at a magnification ofFIG. 13 is a SEM image of the PTFE layer ofFIG. 9 at a magnification of 500. -
FIG. 14 schematically illustrates a composite PTFE film that comprises a PTFE layer having low or substantially no fluid permeability and a porous PTFE layer. -
FIG. 15 schematically illustrates a simplified tubular structure that comprises an outer layer having low or substantially no fluid permeability and a fluid-permeable inner layer. -
FIG. 16 schematically illustrates a simplified tubular structure that comprises a layer having low or substantially no fluid permeability and a fluid-permeable outer layer. -
FIG. 17 illustrates an embodiment of an endovascular graft having a network of inflatable conduits. -
FIGS. 18 to 20 are transverse cross sectional views of an inflatable conduit of the graft ofFIG. 17 . -
FIG. 21 is a transverse cross sectional view of an embodiment of a tubular inflatable conduit. -
FIG. 22 is an elevational view that illustrates another embodiment of an inflatable endovascular graft. -
FIG. 23 illustrates an embodiment of an inflatable bifurcated endovascular - Embodiments of the present invention relate generally to thin PTFE layers, PTFE films, composite films having two or more PTFE layers and methods of manufacturing the PTFE layers, films and composite films. Some particular embodiments are directed to thin PTFE layers having low or substantially no fluid permeability with a microstructure that does not include significant fibril and nodal structure as is common with expanded PTFE layers. It may also be desirable for some embodiments of such thin PTFE layers that have a high degree of limpness and suppleness so to allow mechanical manipulation or strain of such a PTFE layer without significant recoil or spring back. Such PTFE layers may be manufactured and used for construction of endovascular grafts or other medical devices. For some applications, embodiments of PTFE films may include one or more discrete layers of PTFE that are secured together to form a composite film. As used herein, the term “composite film” generally refers to a sheet of two or more PTFE layers that have surfaces in contact with each other, and in some embodiments, may be secured to each other such that the PTFE layers are not easily separated. The individual PTFE layers used in some of the PTFE composite film embodiments herein may have the thinness and low fluid permeability characteristics discussed above in combination with other layers having the same or different properties Some PTFE layer embodiments have a low fluid permeability while other PTFE layer embodiments have no or substantially no fluid permeability. A PTFE layer having a low fluid permeability may, for some embodiments, be distinguished from the permeability of a standard layer of expanded PTFE by comparing fluid permeability based on Gurley test results in the form of a Gurley Number or “Gurley Seconds”. The Gurley Seconds is determined by measuring the time necessary for a given volume of air, typically, 25 cc, 100 cc or 300 cc, to flow through a standard 1 square inch of material or film under a standard pressure, such as 12.4 cm column of water. Such testing may be carried out with a Gurley Densometer, made by Gurley Precision Instruments, Troy, N.Y. A standard porous fluid-permeable layer of expanded PTFE may have a Gurley Number of less than about 15 seconds, specifically, less than about 10 seconds, where the volume of air used is about 100 cc. In contrast, embodiments of layers of PTFE discussed herein having low fluid permeability may have a Gurley Number of greater than about 1500 seconds where 100 cc of air is used in the test. An embodiment of a PTFE layer discussed herein having no or substantially no fluid permeability may have a Gurley Number of greater than about 12 hours, or up to a Gurley Number that is essentially infinite, or too high to measure, indicating no measurable fluid permeability. Some PTFE layer embodiments having substantially no fluid permeability may have a Gurley Number at 100 cc of air of greater than about 1×106 seconds. Stretched PTFE layers processed by embodiments of methods discussed herein having no discernable node or fibril microstructure may initially have substantially no fluid permeability. However, such PTFE layer embodiments may subsequently be stretched during a manufacturing process, such as the manufacture of an inflatable endovascular graft, during which process the PTFE layer may become more fluid-permeable and achieve a level of low permeability as discussed above.
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FIGS. 1-8 illustrate processing of PTFE material to form a thin, stretched PTFE layer having low or substantially no liquid permeability for particular liquids, such as water based liquids. Such an embodiment may be useful where it is desirable to exclude water based fluids and other fluids, such as body fluids of a patient. Some PTFE layer embodiments discussed herein may also be substantially impermeable to air and other gases. As such, embodiments of the stretched PTFE layers are not “expanded” in the conventional sense as taught by Gore in U.S. Pat. No. 3,953,566. For example, the stretched PTFE layers may be substantially thinned during stretching whereas prior art “expansion” processes typically leave the thickness of the expanded material somewhat unchanged but generate distinct nodal and fibril microstructure along with increased porosity and permeability in order to accommodate the expansion of the layer in plane of the layer. - Referring to
FIG. 1 , a fine PTFE resin powder is compounded with an extrusion agent such as a liquid lubricant to form aPTFE compound 10. A variety of different PTFE resins may be used such as the lower extrusion ratio, higher molecular weight fine powder coagulated dispersion resins (available from 3M Corporation, Ausimont Corporation, Daikin Corporation, DuPont and ICI Corporation) The PTFE molecules used in these resins typically have an average molecular weight of from about 20 million to about 50 million or more. Optionally, an additive, such as powdered or liquid color pigment or other resin additive may be added to the PTFE resin and lubricant to change the properties of the final PTFE layer. For example, a fluorinated copolymer may be added (such as perfluoropropylvinylether-modified PTFE) to improve the bondability of the PTFE layer. Additive is typically provided in a mass amount that is less than 2% of the mass of the PTFE resin, but it may be provided in any amount that produces a desired result. Additive may be combined with the PTFE resin before the lubricant is added so as to ensure homogenous mixing of the additive throughout the PTFE resin. - A variety of different types of extrusion and stretching agents, or lubricants, may be compounded with the PTFE powder resin. Some examples of lubricants that may be mixed with the PTFE resin include, but are not limited to, isoparaffin lubricants such as ISOPAR® H, ISOPAR® K and ISOPAR® M all of which are manufactured by ExxonMobil Corporation. Additional lubricants include mineral spirits, naphtha, MEK, toluene, alcohols such as isopropyl alcohol, and any other chemical that is capable of saturating the PTFE resin. In addition, two or more lubricants may be blended together for some lubricant embodiments. The amount of lubricant added to the PTFE resin may vary depending on the type of lubricant used as well as the desired properties of a final PTFE layer. Typically, however, the percent mass of lubricant for some compound embodiments may vary from about 15% to about 25% of the compound mass; specifically, from about 17% to about 22% of the compound mass, and more specifically from about 18% to about 20% of the compound mass.
- The PTFE resin and lubricant may be mixed until a substantially
homogenous PTFE compound 10 is formed. Compounding of the PTFE resin and lubricant is typically carried out at a temperature below the glass transition temperature of the PTFE resin which is typically from about 55° F. to about 76° F. Compounding of the PTFE resin may be carried out at a temperature below about 50° F., and specifically, at a temperature of from about 40° F. to about 50° F., so as to reduce shearing of the fine PTFE particles. Once mixed, the PTFE compound maybe stored at a temperature of above approximately 100° F., and typically from about 110° F. to about 120° F. for a time period that ensures that the lubricant has absorbed through the PTFE resin particles. The storage time period typically may be greater than about six hours, and may vary depending on the resin and lubricant used. - Once the compounded PTFE resin and
lubricant 10 have been suitably prepared, thecompound 10 may be placed in an extruder, such as theram extruder 12 shown inFIG. 1 . Theram extruder 12 includes abarrel 13 and apiston 14 that is configured to slide within a chamber of thebarrel 13 and form a seal against an inner cylindrical surface of thebarrel 13. Thecompound 10 is placed in the chamber of theextruder 12 between the distal end of thepiston 14 and an extruder die 16 sealed to theoutput end 18 of theextruder 12. Theram extruder 12 may also includeheat elements 20 disposed about theoutput end 18 of thebarrel 13 which are configured to uniformly heat theoutput end 18 of theextruder 12. In some methods, theoutput end 18 of the extruder is heated before the compoundedPTFE resin 10 is loaded into the chamber. An embodiment of aram extruder 12 may include a Phillips Scientific Corporation vertical three inch hydraulic ram extruder. - Once the PTFE resin compound is loaded, the
piston 14 is advanced towards theoutput end 18 of theextruder 12, as indicated byarrow 21 which increases the chamber pressure and forces thePTFE compound 10 to be extruded through anorifice 22 of the die 16 to form anextrudate 24. Theextrudate 24 may be in the form of a ribbon or tape that is then wound onto a take upspool 26 as indicated by the arrow adjacent the take up spool inFIG. 1 . The ram extrusion process represents a mechanical working of thecompound 10, and introduces shear forces and pressure on thecompound 10. This working of the compound results in a more cohesive material in the form of an extrudate ribbon ortape 24. - Processing conditions may be chosen to minimize the amount of lubricant that is evaporated from the
PTFE extrudate ribbon 24. For example, thePTFE compound 10 may be extruded at a temperature that is above the glass transition temperature, and typically above 90° F. ThePTFE extrudate ribbon 24 is generally fully densified, non-porous and typically has approximately 100% of its original amount of lubricant upon extrusion from thedie 16. The die 16 may also be configured to produce anextrudate 24 having other configurations, such as a tubular configuration. Also, for some methods, thePTFE compound 10 may be processed to form a preform billet before it is placed in theextruder 12. In addition, a de-ionizing air curtain may optionally be used to reduce static electricity in the area of theextruder 12. In one example, theram extruder 12 has abarrel 13 with a chamber having an inside transverse diameter of about 1 inch to about 6 inches in diameter. Embodiments of the die 16 may haveorifices 22 configured to produce an extrudate ribbon ortape 24 having a width of about 1 inch to about 24 inches and a thickness of about 0.020 inch to about 0.040 inch, specifically, about 0.025 inch to about 0.035 inch. - After extrusion, the wet
PTFE extrudate ribbon 24 may be calendered in a first direction or machine direction, as indicated byarrow 27, to reduce the thickness of thePTFE extrudate ribbon 24 into aPTFE layer 28 as shown inFIG. 2 . During the calendering process, the width of thePTFE extrudate ribbon 24 and calenderedPTFE layer 28 changes little while thePTFE extrudate ribbon 24 is lengthened in the machine direction. In one embodiment, thePTFE extrudate ribbon 24 and calenderedPTFE layer 28 may be about 6 inches to about 10 inches in width. The calendering process both lengthens and reduces the thickness of thePTFE ribbon 24 to formPTFE layer 28 which is taken up byspool 32. During calendering, thePTFE extrudate ribbon 24 may be calendered between adjustableheated rollers 30 to mechanically compress and reduce the thickness of thePTFE ribbon 24. As such, the calendering process also encompasses a second mechanical working of thecompound 10. Suitable equipment for the calendering process includes acustom 12 inch vertical calendar machine manufactured by IMC Corporation, Birmingham, Ala. - While it may be possible to store the
PTFE extrudate ribbon 24 for an extended period of time after extrusion, lubricant in thePTFE extrudate ribbon 24 will evaporate from theribbon 24 during the storage period. As such, it may be desirable in some instances to calender thePTFE extrudate ribbon 24 almost immediately after extrusion so as to better control the lubricant level in thePTFE extrudate ribbon 24. For some embodiments, thePTFE ribbon 24 will have a lubricant content of about 15% to about 25% immediately prior to calendering. - Depending on the calendering speed and roller positioning, the
PTFE ribbon 24 may be calendered down to produce aPTFE layer 28 of any suitable thickness. The reduction ratio of an embodiment of the calendering process, which is a ratio of the thickness of thePTFE extrudate ribbon 24 to the thickness of the calenderedPTFE layer 28, may be between about 3:1 to about 75:1, and specifically between about 7.5:1 to about 15:1. In one particular embodiment, for aPTFE extrudate ribbon 24 having a thickness of about 0.030 inches, calendering may reduce the thickness to about 0.001 inch to about 0.006 inch, specifically, between about 0.002 inch to about 0.004 inch. In some instances, thePTFE ribbon 24 may be calendered to aPTFE layer 28 which has a thickness that is slightly greater than a final desired thickness, so that the final stretch of thePTFE ribbon 24 causes thefinal PTFE layer 28 to have its desired thickness. - The calendering temperatures and processing parameters may be chosen so that the calendered
PTFE layer 28 still has a significant amount of residual lubricant after the calendering process. For this embodiment, theadjustable rollers 30 may be heated to a temperature between about 100° F. and about 200° F., and specifically between about 120° F. and about 160° F. during the calendering process. After calendering, a residual amount of lubricant will remain in thePTFE layer 28 which may typically be between about 10% to about 22% lubricant by weight remaining, specifically about 15% to about 20% lubricant by weight. - Once the
PTFE ribbon 24 has been calendered to producePTFE layer 28,PTFE layer 28 may then be mechanically stretched transversely (also called the cross machine direction), in the longitudinal direction (also called the machine direction), both of these directions or any other suitable direction or combination of directions, in order to thin thePTFE layer 28, generate a suitable microstructure and mechanically work the PTFE. It should be noted that although this specification describes a process whereby a PTFE layer is stretched transversely, then stretched longitudinally and then densified, the order these steps are performed in may be changed. For example, a PTFE layer may be first stretched longitudinally, then stretched transversely. Such a layer may optionally then be densified, as discussed below. For the transverse stretching process shown inFIGS. 3 and 4 , atentering machine 34 may be used to mechanically stretch the calenderedPTFE layer 28 into a stretchedPTFE layer 36. One embodiment of asuitable tentering machine 34 includes a 60 inch wide by 28 foot long tenter having a T-6 10 horsepower drive unit, manufactured by Gessner Industries, Concord, N.C. - For some embodiments, in order to produce desired thickness, porosity, permeability as well as mechanical properties, process parameters such as temperature, stretch ratios and material lubricant content of
PTFE layer 28, may be controlled before and during the stretching process. As such, for some embodiments, a stretching agent orlubricant 40 may optionally be applied to the calenderedPTFE layer 28 during the stretching process as shown inFIGS. 3 and 4 . Applying the stretchingagent 40 to thePTFE layer 28 prior to or during the stretching process of thePTFE layer 28 may be used to control the lubricant content of the stretchedPTFE layer 36. This technique may be used to provide characteristics to the stretchedPTFE layer 36 such as thinness, low porosity and low or substantially no permeability. This method embodiment also allows for the stretchedPTFE layer 36 to have a high degree of limpness and suppleness to allow mechanical manipulation or strain of such a PTFE layer without significant recoil or spring back which may be particularly useful for some applications. If a high density, liquid and gas-impermeable PTFE layer 28 is desired, thePTFE layer 28 may be saturated throughout the thickness of thePTFE layer 28 with one or more stretchingagents 40 during stretching. If a moreporous PTFE layer 28 is desired, a lesser amount of stretchingagent 40 will be applied onto thePTFE layer 28. Stretching thePTFE layer 28 may be carried out for some embodiments at a temperature of about 80° F. to about 100° F., specifically, about 85° F. to about 95° F. - The stretching
agent 40 may be the same lubricant used to form thePTFE compound 10 or it may be a different lubricant or combination of lubricants. In some embodiments, the stretching agent may be applied in sufficient quantities to thePTFE layer 28 to saturate thePTFE layer 28 during the stretching process. The stretching agent may be applied by a variety of methods to a surface, such as theupper surface 38, of thePTFE layer 28 during the stretching process. For example, the stretchingagent 40 may be sprayed over theentire layer 28, or only on selected portions of thePTFE layer 28 by aspray mechanism 42 to theupper surface 38 of thePTFE layer 28. The stretchingagent 40 is applied to thePTFE layer 28 after thePTFE layer 28 unwinds fromspool 32 and passes under thespray mechanism 42. The stretchingagent 40 may be applied uniformly over one or both sides of thePTFE layer 28, on only one side of thePTFE layer 28, or only on selected portions of thePTFE layer 28 at a temperature of typically about 70° F. to about 135° F., specifically, about 105° F. to about 125° F., and more specifically, about 110° F. to about 120° F. - If a PTFE layer having low or substantially no fluid permeability is desired, the
PTFE layer 28 will be stretched in one or more directions while fully saturated until the desired thickness is achieved. It should be noted that as thePTFE layer 28 is stretched, the capacity of the resulting stretchedPTFE layer 36 to absorb stretchingagent 40 increases. As such, if it is desirable to maintain a saturated status of thePTFE layer 28 and stretchedPTFE layer 36, it may be necessary to add stretching agent multiple times or over a large area in order to maintain that saturated state of thePTFE layer 36 and the effect of the stretchingagent 40 temperature (about 110° F. to about 120° F.) for a period of time. As such, stretchingagent 40 may be added prior to the initiation of the stretching process or at any time during the stretching process. A method whereby stretchingagent 40 is applied to the PTFE layer during the stretching process may allow for the formation of discernable node and fibril microstructure creation during the stretching process prior to application of the stretchingagent 40 to the PTFE layer; however, thinning of the PTFE layer will still take place once the stretchingagent 40 has been applied and stretching continues. -
FIG. 4 illustrates the stretchingagent 40 being applied toupper surface 38 of thePTFE layer 28 byspray mechanism 42 as thePTFE layer 28 is being stretched transversely. For saturated stretching embodiments, it may be necessary to apply sufficient stretching agent so as to pool or puddle the stretching agent on theupper surface 38 of thePTFE layer 28. In such a case, the pooled or puddled stretching agent may be spread over theupper surface 38 of thePTFE layer 28 by a skimmingmember 44 that has asmooth contact edge 46 adjacent theupper surface 38 of thePTFE layer 28. The skimmingmember 44 is disposed adjacent thespray mechanism 42 displaced from the spray mechanism in the machine direction of thePTFE layer 28 such that the stretchingagent 40 applied by thespray mechanism 42 runs into the skimmingmember 44 and is spread by the motion of the stretchingagent 40 andPTFE layer 28 relative to the skimmingmember 44. The skimmingmember 44 may be in contact with theupper surface 38 of thePTFE layer 28 or may also be disposed above theupper surface 38, depending on the desired configuration of the set up, the type of stretching agent being used as well as other factors. Multiple skimming members may be used with some or all of the skimming members having a smooth contact edge or alternatively a grooved/patterned contact edge. - Embodiments of methods discussed herein may be useful to reduce a thickness of the
PTFE layer 28 to a stretchedPTFE layer 36 of any thickness down to about 0.00005 inch, but typically from about 0.00005 inch and 0.005 inch. Typical transverse stretch ratios may be from about 3:1 to about 20:1. In one embodiment, a calenderedPTFE layer 28 having a width of about 3 inches to about 6 inches, may be transversely stretched, as shown inFIGS. 3 and 4 , into a stretchedPTFE layer 36 having a width of about 20 inches to about 60 inches. This represents a stretch ratio of about 3:1 to about 12:1. In another embodiment, a calenderedPTFE layer 28 having a width of about 3.5 inches to about 4.5 inches, may be transversely stretched, as shown inFIGS. 3 and 4 , into a stretchedPTFE layer 36 having a width of about 20 inches to about 60 inches. This represents a stretch ratio of about 7.8:1 to about 13:1. - As discussed above, the thickness, porosity, average pore size and fluid permeability of the PTFE layers 36 may be affected by the amount and temperature of stretching
agent 40 applied to thelayer 36 prior to or during stretching. In addition, the temperature of the PTFE layer, the type of stretching agent that is applied to the PTFE layer, and the stretch rate may also affect the thickness, porosity, average pore size and fluid permeability of thePTFE layer 36. By adjusting these parameters, these characteristics may be optimized in order to produce a PTFE layer that is suited to a particular application. For example, if thePTFE layer 36 is used as a moisture barrier for clothing, the parameters may be adjusted to produce an average pore size of less than about 6.0 microns. Alternatively, if thePTFE layer 36 is used in an endovascular graft that benefits from tissue in-growth, the average pore size is adjusted to be greater than 6.0 microns. In other embodiments, where thePTFE layer 36 is a barrier layer for use in an endovascular graft, the pore size may be smaller, such as between about 0.01 microns and about 5.0 microns. In addition, embodiments of the stretchedPTFE layer 36 are fusible and deformable and may easily be fused with other PTFE layers having different properties. At any point after thePTFE layer 28 is stretched, the stretchedPTFE layer 36 may be sintered to amorphously lock the microstructure of thePTFE layer 36. Sintering may be performed to combine the stretchedPTFE layer 36 with other layers of PTFE to form multi-layer films, such as those used for endovascular grafts and the like discussed below. - The stretched PTFE layer optionally may be subjected to a second stretching process, as shown in
FIGS. 3 , 4, 5 and 6, wherein the stretchedPTFE layer 36 is formed into a twice-stretchedPTFE layer 46. Once again, as discussed above, it is important to note that although the method embodiments discussed herein are directed to a first transverse stretch and subsequently to a longitudinal or machine direction stretch, the order of the stretch direction steps may be reversed and other combinations of stretch directions and numbers are also contemplated. For example,PTFE layer 28 may be stretched twice in the machine or longitudinal direction without any transverse stretching.PTFE layer 28 may be stretched first in a longitudinal or machine direction and then in a transverse direction. In addition, aPTFE layer 28 may be stretched three or more times. Some or all of the speeds, stretch ratios, temperatures, lubricant parameters and the like as discussed herein may be the same or similar to those previously described, but need not necessarily be so. Moreover, these parameters typically will not be the same for any of these various stretching steps, regardless of the order in which they are undertaken. - This optional second stretching process subjects the
PTFE layer 36 to yet another mechanical working. The second stretching process shown inFIGS. 5 and 6 is being carried out in the machine direction; however, the second stretching process may also be carried out in any other suitable direction, such as transversely. The twice-stretchedPTFE layer 46 is wound ontospool 48 after undergoing the second stretching process.Additional stretching agent 40 optionally may be applied to a surface of the stretchedPTFE layer 36 as thelayer 36 is being stretched a second time. If higher porosity and fluid permeability are desired, the second stretch may be performed with the stretchedlayer 36 in a dry state without the addition of lubricant during the second stretch. If the stretchedPTFE layer 36 has residual lubricant without additional lubricant added, the second stretching process will generate a microstructure having significant nodes connected by fibrils. The second stretching process may be carried out at a temperature of about 85° F. to about 95° F. for some embodiments. The stretch ratio for the second stretch may be up to about 20:1, specifically, about 6:1 to about 10:1. - If the
PTFE layer 28 is stretched in two or more directions, the rate of stretching in the two directions; e.g., the machine direction and the off-axis or transverse direction, may have different or the same stretch rates. For example, when thePTFE layer 28 is being stretched in the machine direction (e.g., first direction), the rate of stretching is typically in the range from about two percent to about 100 percent per second; specifically, from about four percent to about 20 percent per second, and more specifically about five percent to about ten percent per second. In contrast, when stretching in the cross machine or transverse direction, the rate of stretching may be in the range from about one percent to about 300 percent per second, specifically from about ten percent to about 100 percent per second, and more specifically about 15 percent to about 25 percent per second. - Stretching in the different directions may be carried out at the same temperatures or at different temperatures. For example, stretching in the machine direction is generally carried out at a temperature below about 572° F., and for some embodiments, below about 239° F. In contrast, stretching in the transverse direction is typically carried out at a temperature above the glass transition temperature, and usually from about 80° F. to about 100° F. Stretching PTFE layers 28 at lower temperatures will reduce stretching
agent 40 evaporation and retain the stretchingagent 40 in thePTFE layer 28 for a longer period of time during processing. - Either the stretched
PTFE layer 36 or the twice-stretchedPTFE layer 46 optionally may be calendered in order to further thin and density the material. The twice-stretchedPTFE layer 46 is shown being calendered inFIGS. 7 and 8 . In this example, the twice-stretchedPTFE layer 46 is unwound fromspool 48, passed throughcalender rollers layer 54, then taken up onspool 54. The calender machine may be the same machine or a different machine as that indicated inFIG. 2 and discussed above. This final calendering or densification ofPTFE layer 46 generally produces a highly densifiedPTFE layer 54 that has no discernable microstructure features, such as pores, and has low or substantially no fluid permeability. The methods of compressing and stretching PTFE layers may both be used to control thinning of the PTFE layer and the microstructure that results from the thinning process. The densifiedPTFE layer 54 may also lack the suppleness and limpness mechanical properties of the stretched PTFE layers 36 and 46 discussed above. Therollers PTFE layer 54 having a thickness of about 0.00005 inch to about 0.005 inch. Therollers - The following example describes specific methods of manufacturing of the stretched PTFE layers 36. In this embodiment, 1000 grams of resin are compounded with an isoparaffin based lubricant; specifically, ISOPAR® M, in a mass ratio of lubricant-to-PTFE compound from about 15% to about 25%. Compounding of the PTFE resin and lubricant is carried out at a temperature below 50° F., which is well below the glass transition temperature of the PTFE resin of between about 57° F. to about 75° F.
- The
PTFE compound 10 may be formed into a billet and stored at a temperature of about 105° F. to about 125° F. for six or more hours to ensure that the lubricant substantially has penetrated and absorbed through the resin. Thereafter, thePTFE compound 10 is placed in anextruder 12, as shown inFIG. 1 . ThePTFE compound 10 may then be paste extruded from theorifice 22 of thedie 16 of theextruder 12 at a temperature above the resin glass transition temperature. In one embodiment, the paste is extruded at a temperature from about 80° F. to 120° F. A reduction ratio, e.g., a ratio of a cross sectional area of thePTFE compound 10 before extrusion to the cross section area of thePTFE extrudate 24 after extrusion, may be from about 10:1 to about 400:1, and specifically may be from about 80:1 to about 120:1. Theextruder 12 may be a horizontal extruder or a vertical extruder. Theorifice 22 of the extrusion die 16 determines the final cross sectional configuration of theextruded PTFE ribbon 24. Theorifice 22 shape or configuration of the extrusion die 16 may be tubular, square, rectangular or any other suitable profile. It may be desirable to preform the PTFE compound (resin and lubricant) into a billet. - The
PTFE extrudate ribbon 24 is then calendered, as shown inFIG. 2 , at a temperature from about 100° F. to about 160° F. to reduce a thickness of thePTFE ribbon 24 and form a PTFE layer orfilm 28. The temperature at calendering may be controlled by controlling the temperature of therollers 30 of the calender machine. The PTFE layer may be calendered down to a thickness from about 0.001 inch to about 0.006 inch, and specifically, down to a thickness of about 0.002 inch to about 0.003 inch. At the end of the calendering, the calenderedPTFE layer 28 may have a lubricant content of about 10% by weight to about 20% by weight. - Referring again to
FIGS. 3 and 4 , after calendering, one side or both sides of the calenderedPTFE layer 28 are sprayed with an isoparaffin-based stretchingagent 40 at a prescribed temperature so that the PTFE film orlayer 28 is flooded and fully saturated through the thickness of thePTFE layer 28. The saturated, calendered PTFE layer may then be stretched in a direction that is substantially orthogonal to the calendering direction by atentering machine 34 to reduce a thickness of thePTFE layer 28 and form a stretchedPTFE layer 36. The stretchedPTFE layer 36 may have a thickness of about 0.00005 inch to about 0.005 inch; specifically, the stretchedPTFE layer 36 may have a thickness of about 0.0002 inch to about 0.002 inch. ThePTFE layer 28 typically is tentered or stretched at an elevated temperature above the glass transition temperature, specifically, from about 80° F. to about 100° F., more specifically, about 85° F. to about 95° F. - Wet tentering with the stretching
agent 40 allows thePTFE layer 28 to be thinned without creating substantial porosity and fluid permeability in the stretchedPTFE layer 36. While the stretchedPTFE layer 36 will have a porosity, its porosity and pore size typically will not be large enough to be permeable to liquids, and often will be small enough to have substantially no fluid permeability. In addition, the stretchedPTFE layer embodiment 36 does not have the conventional node and fibril microstructure but instead has a closed cell microstructure in which boundaries of adjacent nodes are directly connected with each other. The fluid-impermeable stretched PTFE film orlayer 36 typically may have a density from about 0.5 g/cm3 to about 1.5 g/cm3, but it may have a larger or smaller density for some embodiments. In addition, with regard to all of the methods of processing layers of PTFE discussed above, any of the PTFE layers produced by these methods may also be sintered at any point in the above processes in order to substantially fix the microstructure of the PTFE layer. A typical sintering process may be to expose the PTFE layer to a temperature of about 350° C. to about 380° C. for several minutes; specifically, about 2 minutes to about 5 minutes. - In another aspect of the methods and PTFE layers discussed herein, the
PTFE layer 28 may be selectively lubricated in a predetermined horizontal or lateral spatial pattern with a stretchingagent 40. The predetermined horizontal spatial pattern may be formed from various lateral zones or sections which may each have varying levels of stretchingagent 40 content or stretchingagent 40 content gradients within and/or between lateral zones. Lateral zones of a PTFE layer can extend in any direction across a layer of PTFE, including transversely, longitudinally or any direction in between these directions. Lateral zones of a layer of PTFE are distinguishable from a thickness gradient of stretchingagent 40 content whereby the content of stretchingagent 40 varies stepwise or continuously through the thickness of a layer of PTFE. Selective application of the stretchingagent 40 byspray mechanism 42 to a surface of a layer of PTFE may be carried out using the methods described herein or using other conventional methods. The levels of stretchingagent 40 contained within the various lateral zones of thePTFE layer 28 may vary from about 0 percent stretching agent content by weight to a level of substantial saturation of stretchingagent 40. -
PTFE layer 28 having a predetermined pattern of stretchingagent 40 may be stretched in at least one direction such that the lateral zones of the stretchedPTFE layer 36 that containedmore stretching agent 40 during stretching will have a lower permeability (e.g., substantially impermeable), while the lateral zones of the stretchedPTFE layer 36 that contained less stretchingagent 40 during stretching will have a higher permeability. Typically, the lateral zones of the stretchedlayer 36 that containedmore stretching agent 40 may also have a reduced thickness relative to the lateral zones that contained less stretchingagent 40 during the stretching process. In some embodiments, it may be desirable to have lateral zones or regions of thePTFE layer 28 that are substantially saturated with stretchingagent 40 adjacent lateral zones or regions ofPTFE layer 28 that have a low enough stretching agent content to allow expansion of the PTFE layer so as to produce a substantial node and fibril microstructure with relatively high fluid permeability. Stretching may be carried out in the machine direction, in a direction that is substantially transverse or orthogonal to the machine direction, or any direction in between. Alternatively, it may be possible to stretch thePTFE layer 28 radially about a point. - Referring to
FIGS. 8A-8D ,PTFE layer 28 may have stretchingagent 40 applied in a predetermined pattern to thePTFE layer 28, such as the exemplary checker board pattern shown inFIG. 8C (which shows an enlarged view of a portion of the PTFE layer 28). This checker board pattern includes rectangularlateral zones 60 which are substantially saturated with stretchingagent 40 throughout the thickness of thelateral zones 60 and which are visible on the surface of the layer of PTFE. The checker board pattern also includes rectangularlateral zones 62 which have a significantly lower stretchingagent 40 content throughout the thickness of thezones 62. Upon stretching,lateral zones lateral zones PTFE layer 36, as shown inFIG. 8D .Lateral zones zones PTFE layer 28 in the transverse direction during the tentering process shown inFIGS. 8A and 8B . Lateral zones 60-66 represent areas on thePTFE layer 28 that extend across the surface of thePTFE layer 28 in any direction or in any shape or configuration. The checker board pattern ofFIG. 8C is provided for exemplary purposes only. In general, the stretching agent content level may be substantially constant throughout a thickness of thePTFE layer 28 at any point on thePTFE layer 28 or within a particular lateral zone; however, a stretching agent content level gradient may also be present across the thickness of thePTFE layer 28 if desired. In addition, while thelateral zones FIGS. 8C and 8D as being defined by substantially discrete stretching agent content levels, other embodiments of lateral zones could include areas of thePTFE layer 28 which include a stretching agent content level gradient in any desired direction or pattern. -
FIGS. 8E-8L illustrate alternative embodiments of the effect of applying predetermined patterns and amounts of stretchingagent 40 on a layer of PTFE before and after a stretching process, whereinlateral zones 60 are substantially saturated with stretchingagent 40 andlateral zones 62 has a relatively low level of (or substantially no) stretchingagent 40. After stretching,lateral zones lateral zones FIGS. 8E and 8F show circles of relatively high or substantially saturated stretchingagent 40 content and the elliptical shape the circles may assume after stretching.FIGS. 8G and 8H show, in another example, a pattern in which the rectangular cells of relatively high or substantially saturated stretchingagent 40 content become square in shape after stretching.FIGS. 8I and 8J show elliptical patterns of relatively high or substantially saturated stretchingagent 40 content that become circular after stretching. Finally,FIGS. 8K and 8L illustrate a bull's eye pattern that is stretched into an elliptical shape during stretching. - As discussed above, the stretching
agent 40 content oflateral zones 62 may be chosen such that standard expansion takes place for the PTFE material withinlateral zones 62 upon stretching. Standard expansion of PTFE may produce expanded PTFE (ePTFE) withinlateral zones 64 after stretching, which typically has a substantial node and fibril microstructure that is discernable when viewed in by SEM.Lateral zones 60 may be substantially saturated with stretchingagent 40 such that expansion of thePTFE layer 28 withinlateral zones 60 produces PTFE material oflateral zones 64 which is thinner and less permeable than the material oflateral zones 66. For some embodiments, the PTFE material oflateral zones 64 may be substantially impermeable and may have a closed cell microstructure. The closed cell microstructure may have a plurality of interconnected nodes but is substantially free of fibrils between the nodes (when viewed at a SEM magnification of 20,000 such as shown inFIG. 9 ). Put another way, the material oflateral zones 64, which may be the same as or similar to the material shown inFIG. 9 , shows no discernable node and fibril microstructure when viewed by SEM at a magnification of 20,000. In addition, the stretching agent content oflateral zones lateral zones PTFE layer 36 may vary with respect to density, thickness, and/or porosity. - The stretching
agent 40 may be applied in any preselected lateral spatial pattern and in any desired amount or concentration level within the lateral zones of that pattern. For some embodiments, the stretchingagent 40 may be selectively applied to thePTFE layer 28 by aspray mechanism 42 that may be controlled through computer or manual control. Thespray mechanism 42 shown inFIGS. 8A and 8B may be configured to be controllable to a substantial degree of spatial resolution so that fine preselected patterns of stretchingagent 40 may be applied to thePTFE layer 28. In some embodiments, thespray mechanism 42 may include an inkjet head, such as is commonly used on an inkjet printer device. Other embodiments of applying the stretchingagent 40 may include, but are not limited to, a contact roller which may be smooth, textured or grooved. Droplets or stream application may be used with an optional skimming member or blade that may also be smooth, textured or grooved. A squeegee that is smooth, textured or grooved may also be used to spread stretching agent delivered by droplets or stream spray. Also, a sponge that is smooth, textured or grooved may be used as well as a rotating drum having a pattern disposed thereon. Silk screen type of methods and the like may also be used to apply the stretchingagent 40. - For other embodiments of methods of producing PTFE layers having lateral zones of varied fluid permeability as well as other characteristics, selective removal or reduction of stretching
agent 40 content from thePTFE layer 28 in a predetermined pattern may be used as opposed to selective addition of stretchingagent 40. In such a method, aPTFE layer 28 could be produced having a high level of stretchingagent 40 content, up to a saturated level, with subsequent removal of some of the stretching agent by the selective application of heat or other energy in a predetermined lateral spatial pattern. The selective application of heat selectively evaporates or boils the stretching agent from thePTFE layer 28. In such an embodiment, an array ofLED lasers 60, or the like, could be disposed adjacent thePTFE layer 28, as shown inFIGS. 3 and 4 . TheLED laser array 60 could be controlled manually, by a computer or any other suitable means so as to apply laser energy to thePTFE layer 28 as it passes by thelaser array 60. As such, stretchingagent 40 is uniformly applied to thePTFE layer 28 by thespray mechanism 42 andoptional skimming member 44 as shown inFIGS. 3 and 4 so as to produce aPTFE layer 28 having a substantiallyuniform stretching agent 40 content level. Then, as thePTFE layer 28 passes adjacent theLED laser array 60, the individual LED lasers of the array are selectively activated to as to produce a pattern of lateral zones, such as the lateral zones shown inFIGS. 8C-8L . In addition to laser energy, any other suitable form of energy that can be spatially controlled could also be used. For example, radiofrequency energy, ultrasound energy and the like could also be used for selective removal or reduction of stretchingagent 40 from thePTFE layer 28. In addition, air jets or nozzles dispensing air or other gases at a specified temperature, pressure and direction may be used to selectively remove the stretchingagent 40 from the PTFE layer by spraying the gas from the air jet onto the PTFE layer to either blow the stretching agent from the PTFE layer or through the PTFE layer. Also, the gas expelled from such air jets could be heated to facilitate evaporation of the stretching agent from the point of impact of the compressed or high velocity gas from the air jets. - As discussed above, the PTFE layers 36 may or may not include a discernable node and fibril microstructure. If the stretched PTFE layers 36 or lateral zones of the stretched PTFE layers include a discernable node and fibril microstructure, the stretched PTFE layers 36 or lateral zones thereof may have a uniaxial fibril orientation, a biaxial fibril orientation, or a multi-axial fibril orientation. The stretched PTFE layers 36 or twice-stretched PTFE layers 46 within a multi-layer PTFE film may be positioned in any configuration, such that the fibrils in one PTFE layer (if any) are parallel, perpendicular, or at other angles relative to the fibrils of an adjacent PTFE layer. The stretched PTFE layers with lateral zones can be used on any of the stent graft embodiments discussed below. In some embodiments, it may be desirable to use a stretched PTFE layer with impermeable lateral zones disposed about or bordering inflatable channels and permeable lateral zones in other areas of the stent graft.
- The various methods discussed above may be used to produce PTFE layers having a variety of desirable properties. The scanning electron microscope (SEM) images shown in
FIGS. 9 to 13 illustrate different magnifications of a microstructure of a PTFE film orlayer 110 made in accordance with embodiments of the present invention.PTFE layer 110 has a generallyclosed cell microstructure 112 that is substantially free of the conventional node and fibril microstructure commonly seen in expanded PTFE layers. Embodiments of thePTFE film 110 may have low fluid-permeability, or no or substantially no fluid-permeability. One or more ofPTFE layer 110 may be used as a barrier layer to prevent a fluid such as a liquid or gas from permeating or escaping therethrough. - At a magnification of 20,000, as seen in
FIG. 9 , the microstructure of the stretchedPTFE layer 110 resembles a pocked-like structure that comprises interconnectedhigh density regions 114 and pockets orpores 116 between some of thehigh density regions 114. ThePTFE film 110 may be considered to have a closed cell network structure with interconnected strands connectinghigh density regions 114 in which a high density region grain boundary is directly connected to a grain boundary of an adjacent high density region. Unlike conventional expanded PTFE which typically has a substantial node and fibril microstructure that is discernable when viewed at a SEM magnification of 20,000,PTFE layer 110 lacks the distinct, parallel fibrils that interconnect adjacent nodes of ePTFE and has no discernable node and fibril microstructure when viewed at a SEM magnification of 20,000, as shown inFIG. 9 . The closed cell microstructure of thePTFE layer 110 provides a layer having low or substantially no fluid permeability that may be used as “a barrier layer” to prevent liquid from passing from one side of the PTFE layer to the opposite side. - Though PTFE film or
layer 110 is configured to have low or substantially no fluid permeability,PTFE layer 110 nonetheless has a porosity. ThePTFE layer 110 typically has an average porosity from about 20% to about 80%, and specifically from about 30% and about 70%. In one embodiment, aPTFE film 110 has a porosity of about 30% to about 40%. In another embodiment, aPTFE layer 110 has a porosity of about 60% to about 70%. Porosity as described in these figures is meant to indicate the volume of solid PTFE material as a percentage of the total volume of thePTFE film 110. An average pore size in thePTFE layer 110 is may be less than about 20 microns, and specifically less than about 0.5 micron. In one embodiment, aPTFE layer 110 has an average pore size of from about 0.01 micron to about 0.5 micron. As can be appreciated, if tissue ingrowth is desired, thePTFE film 110 may have an average pore size of greater than about 6.0 microns. As described below, depending on the desired properties of theresultant PTFE layer 110, embodiments of methods may be modified so as to vary the average porosity and average pore size of thePTFE film 110 in a continuum from 10 microns to 50 microns down to substantially less than about 0.1 micron. -
PTFE layer 110 may have a density from about 0.5 g/cm3 to about 1.5 g/cm3, and specifically from about 0.6 g/cm3 to about 1.5 g/cm3. While the density of thePTFE film 110 is typically less than a density for a fully densified PTFE layer (e.g., 2.1 g/cm3), if desired, the density of thePTFE layer 110 may be densified to a higher density level so that the density of thePTFE layer 110 is comparable to a fully densified PTFE layer.FIGS. 9 to 13 illustrate aPTFE film 110 having a closed micro structural network and that is substantially impermeable to liquid and gas; other embodiments of PTFE layers may be manufactured using the methods discussed herein to have other suitable permeability values and pore sizes. -
PTFE film 110 may have an average thickness that is less than about 0.005 inch, specifically from about 0.00005 inch to about 0.005 inch, and more specifically from about 0.0001 inch to about 0.002 inch. While embodiments of methods discussed herein are directed to manufacturing PTFE layers, it should be appreciated that the methods discussed may also be useful in the manufacture of other fluoropolymer-based films having substantial, low or substantially no fluid permeability. As such, the methods discussed herein are not limited to the processing of PTFE materials. For example, the processing of other fluoropolymer resin-based materials, such as copolymers of tetrafluororethylene and other monomers, is also contemplated. - The PTFE layer and PTFE films may be used in a variety of ways. For example, the PTFE layers and PTFE films of the present invention may be used for prosthetic devices such as a vascular graft, breast implants and the like. Other applications include tubing, protective clothing, insulation, sports equipment, filters, membranes, fuel cells, ionic exchange barriers, gaskets as well as others. For some of these applications, it may be desirable to include PTFE layers that have variable characteristics with respect to lateral zones of the PTFE layers, which may be produced by the methods discussed above. Specifically, some applications may require PTFE layers that have a high permeability in one lateral zone and low or substantially no permeability in an adjacent lateral zone. PTFE films having at least two PTFE layers combined may overlap the predetermined patterns of the lateral zones of the PTFE layers to achieve a more complex patterns of varied characteristics. As such, any of the embodiments discussed below may incorporate PTFE layers, stretched PTFE layers or PTFE films that have lateral zones of varied characteristics as discussed above.
- Referring now to
FIG. 14 ,PTFE layer 110 may be combined with, bonded to, or otherwise coupled, affixed or attached, partially or completely, to at least oneadditional layer 118 to form acomposite film 120. Depending on the use ofcomposite film 120,layer 118 may be chosen to have properties that combine with the properties oflayer 110 to give the desired properties incomposite film 120. Theadditional layer 118 may include a porous PTFE layer, a substantially non-porous PTFE layer, a gas- or liquid-permeable PTFE layer, a gas- or liquid-impermeable layer, an ePTFE layer, a non-expanded PTFE layer, a fluoropolymer layer, a non-fluoropolymer layer, or any combination thereof. In one embodiment,layer 118 is a porous, fluid-permeable, expanded PTFE layer having a conventional node and fibril microstructure. If desired, one or more reinforcing layers (not shown) optionally may be coupled to thecomposite PTFE film 120. The reinforcing layer may be disposed betweenlayers PTFE layer 110,PTFE layer 118, or both.PTFE layer 110 andlayer 118 may be combined, bonded to, or otherwise coupled, affixed or attached, partially or completely, to one another using any suitable method known in the art. For example, an adhesive may be used to selectively bond at least a portion oflayers layers -
FIGS. 15 and 16 are transverse cross-sectional views of two compositetubular structures Tubular structures FIG. 15 ,tubular structure 130 includes an innertubular body 132 that comprises aninner surface 134 and anouter surface 136.Tubular body 132 may comprise one or more layers of fluid-permeable PTFE. Such a fluid-permeable layer of PTFE may have a Gurley measurement of less than about 10 Gurley seconds.Tubular structure 130 further comprises an outertubular body 138 that comprises aninner surface 137 and anouter surface 139.Inner surface 137 of outertubular body 138 is coupled to theouter surface 136 of the innertubular body 132.Tubular body 138 may comprise one or more PTFE layers having low fluid-permeability or substantially no fluid-permeability. In this configuration,inner surface 134 of thetubular body 132 defines aninner lumen 135 oftubular structure 130 and theouter surface 139 of thetubular body 138 defines anouter surface 139 of thetubular structure 130.Tubular body 138 may be combined, bonded to, or otherwise coupled, affixed or attached, partially or completely, to thetubular body 132 through any suitable method known in the art. For example, an adhesive may be used to selectively bond at least a portion oftubular body 138 andtubular body 132 to each other. Alternatively, heat fusion, pressure bonding, sintering, and the like, or any combination thereof, may be used to bond at least a portion oftubular body 138 andtubular body 132 to each other. - As shown in
FIG. 16 ,tubular structure 140 includes an innertubular body 142 that comprises aninner surface 144 and anouter surface 146.Tubular body 142 may comprise one or more layers of PTFE having low or substantially no fluid permeability.Tubular structure 140 further comprises an outertubular body 148 that comprises aninner surface 147 and anouter surface 149.Inner surface 147 of outertubular body 148 is coupled to theouter surface 146 of the innertubular body 142. Outertubular body 148 may comprise one or more layers of fluid-permeable PTFE. Embodiments of fluid-permeable layers of PTFE may have a Gurley measurement of less than about 10 Gurley seconds. In this configuration,inner surface 144 of the innertubular body 142 defines aninner lumen 145 oftubular structure 140 and theouter surface 149 of the outertubular body 148 defines anouter surface 149 of thetubular structure 140.Tubular body 148 maybe combined, bonded to, or otherwise coupled, affixed or attached, partially or completely, to thetubular body 142 through any suitable method known in the art. For example, an adhesive may be used to selectively bond at least a portion oftubular body 148 andtubular body 132 to each other. Alternatively, heat fusion, pressure bonding, sintering, and the like, or any combination thereof, may be used to bond at least a portion oftubular body 148 andtubular body 142 to each other. -
Tubular structures tubular structure outer surface tubular layer permeable PTFE layers tubular structures -
Tubular structures tubular structures PTFE layers FIG. 14 , that are folded on a shape forming mandrel over each other so that ends of the layers are overlapped and bonded. As another alternative, PTFE layers 110 or 118 may be helically wound about the shape forming mandrel to form the tubular structure. Some exemplary methods of forming a tubular PTFE structure is described in commonly owned, copending U.S. patent application Ser. No. 10/029,557 (which published as US 20030116260 A1) and entitled “Methods and Apparatus for Manufacturing an Endovascular Graft Section” and Ser. No. 10/029,584 and entitled “Endovascular Graft Joint and Method of Manufacture”, both filed on Dec. 20, 2001 to Chobotov et al., and U.S. Pat. No. 6,776,604 to Chobotov et al., the complete disclosures of which are incorporated herein by reference. - The films and layers discussed herein are not limited to a single
porous PTFE layer 118 and a single PTFE layer orfilm 110 having low or substantially no fluid permeability. Thecomposite films 120 andtubular structures PTFE layer 110 having low or substantially no fluid permeability may be disposed between an inner and outer porous PTFE film or layer. The inner and outer porous PTFE layers may have varying porosities or the same porosities. In such embodiments, thePTFE layer 110 may have a reduced thickness relative to the porous PTFE layers. In other embodiments, however, thePTFE layer 110 may have the same thickness or larger thickness than the porous PTFE layers. As an alternative embodiment toFIGS. 15 and 16 ,tubular structures - Referring now to
FIG. 17 , a tubular structure that is in the form of an inflatableendovascular graft 50 is shown. For the purposes of this application, with reference to endovascular graft devices, the term “proximal” describes the end of the graft that will be oriented towards the oncoming flow of bodily fluid, typically blood, when the device is deployed within a body passageway. The term “distal” therefore describes the graft end opposite the proximal end.Graft 150 has aproximal end 151 and adistal end 152 and includes a generally tubular structure orgraft body section 153 comprised of one or more layers of fusible material, including such materials as PTFE and ePTFE. The inner surface of the tubular structure defines an inner diameter and acts as a luminal surface for flow of fluids therethrough. The outer surface of the tubular structure defines an abluminal surface that is adapted to be positioned adjacent the body lumen wall, within the weakened portion of the body lumen, or both. Note that althoughFIG. 17 shows an inflatable endovascular graft, the layers and films of the present invention may be used in non-inflatable endovascular grafts as well, in addition to other medical and non-medical applications. - A proximal
inflatable cuff 156 may be disposed at or near aproximal end 151 ofgraft body section 153 and a distalinflatable cuff 157 may be disposed at or near a graft body sectiondistal end 152.Graft body section 153 forms a longitudinal lumen that is configured to confine a flow of fluid, such as blood, therethrough.Graft 150 may be manufactured to have any desired length and internal and external diameter but typically ranges in length from about 5 cm to about 30 cm; specifically from about 10 cm to about 30 cm. If desired, astent 159 may be attached at theproximal end 151 and/or thedistal end 152 of thegraft 150. Depending on the construction of thecuffs graft body section 153, inflation ofcuffs cuffs Inflatable cuffs - At least one
inflatable channel 158 may be disposed between and in fluid communication with proximalinflatable cuff 156 and optional distalinflatable cuff 157.Inflatable channel 158 in theFIG. 17 example has a helical configuration and provides structural support to graftbody section 153 when inflated to contain an inflation medium.Inflatable channel 158 further prevents kinking and twisting of the tubular structure or graft body section when it is deployed within angled or tortuous anatomies as well as during remodeling of body passageways, such as the aorta and iliac arteries, within whichgraft 150 may be deployed. Together with proximal anddistal cuffs inflatable channel 158 forms an inflatable network over the length of thebody 153. Depending on the desired characteristics of theendovascular graft 150, at least one layer of the graft may be a PTFE layer having low or substantially no fluid permeability such as PTFE layer orfilm 110. The PTFE layer may be one of the layers that forms theinflatable channels 158, or the PTFE layer may surround or be underneath theinflatable channel 158 andcuffs - In addition, it may be desirable for some embodiments to include a
PTFE layer 110 that has varied permeability across lateral zones of thePTFE layer 110 whereby the characteristic of a lateral zone of thePTFE layer 110 corresponds to the function of the PTFE layer in the lateral zone. For example, instead of including asingle PTFE layer 110 of PTFE material that has substantially no fluid permeability, the layer may include lateral zones of PTFE material that has substantially no fluid permeability that correspond to the portion of thePTFE layer 110 that will be adjacent theinflatable channel 158 andcuffs inflatable channel 158 andinflatable cuffs inflatable channel 158 andinflatable cuffs -
Graft body 153 may be formed of two or more layers or strips of PTFE that are selectively fused or otherwise adhered together as described herein, to form theinflatable cuffs inflatable channel 158 therebetween. A detailed description of some methods of manufacturing a multi-layered graft are described in co-pending and commonly owned U.S. patent application Ser. No. 10/029,557 (which published as US 20030116260 A1); Ser. No. 10/029,584; U.S. patent application Ser. No. 10/168,053, filed Jun. 14, 2002 and entitled “Inflatable Intraluminal Graft” to Murch, and U.S. Pat. No. 6,776,604 to Chobotov et al., the complete disclosures of which are incorporated herein by reference. -
FIGS. 18 to 21 illustrate transverse cross sectional views of different embodiments ofinflatable channel 158. As can be appreciated, the embodiments ofFIGS. 18 to 21 may also be applicable to the proximal anddistal cuffs Inflatable channel 158 defines aninflatable space 162 that is created between aninner layer 164 andouter layer 166. If desired aninflation medium 167 may be delivered into thespace 162 to inflateinflatable space 162.Inflation medium 167 optionally may include adeliverable agent 168 as shown inFIGS. 18 to 21 , such as atherapeutic agent 168 that may be configured to be diffused in a controlled manner or otherwise transmitted through pores (not shown) ininner layer 164,outer layer 166 or both. The embodiments shown inFIGS. 18-21 are merely exemplary, as it may be desirable to have preferential diffusion of thedeliverable agent 168 throughlayer 164 orlayer 166. In addition, bothlayers deliverable agent 168, but with one of the two layers having a greater permeability to thedeliverable agent 168 than the other layer. Whileinner layer 164 andlayer 166 are shown as having only a single layer of material, it should be appreciated that each oflayers - In the embodiment shown in
FIG. 18 ,outer layer 166 is permeable to fluids so as to allow thetherapeutic agent 168, which may be a liquid, to diffuse over time in the direction ofarrow 169 throughouter layer 166. In such embodiments,inner layer 164 typically has a low or substantially no fluid permeability, and could therefore be considered a “barrier layer.” Because the inner “barrier”layer 164 has low or substantially no fluid permeability andouter layer 166 is fluid-permeable, the therapeutic agent will preferentially diffuse fromspace 162 in the direction ofarrow 169. The use of one (or more) porous fluid-permeable outer PTFE layers and aninner layer 164 having low or substantially no fluid permeability provides for improved release of a therapeutic agent through liquid-permeableouter layer 166. Varying the porosity or pore size across at least a portion ofouter layer 166 may provide even more localized delivery of thetherapeutic agent 168 throughouter layer 166. - In an alternative configuration shown in
FIG. 19 ,inner layer 164 may be substantially fluid-permeable to allow thetherapeutic agent 168 to selectively diffuse in the direction ofarrow 169 throughinner layer 164 and into the lumen of the tubular structure (e.g.,lumen FIGS. 15 and 16 ). In such embodiments,outer layer 166 typically has no or substantially no fluid-permeability and acts as a “barrier layer.” As such, the therapeutic agent will preferentially diffuse fromspace 162 in the direction ofarrow 169. The use of porous fluid-permeable PTFE layers andouter layer 166 having low or substantially no fluid permeability provides for improved release of a therapeutic agent into the inner lumen through fluid-permeableinner layer 164. Varying the permeability and/or porosity or pore size across at least a portion ofinner layer 164 may provide even more localized delivery of thetherapeutic agent 168 throughlayer 164. - As shown in
FIG. 20 , if it is desired to prevent theinflation medium 167 from escaping frominflatable space 162, both theinner layer 164 andouter layer 166 may comprise a “barrier” layer having low or substantially no fluid permeability. In such embodiments, the inner andouter layers inflation material 167 typically will not contain a therapeutic agent. Referring toFIG. 21 , the inflatable channel may be a substantiallytubular channel 170 that is fused or otherwise adhered to layer 164 that defines an inner lumen of the graft. If delivery of atherapeutic agent 168 is desired,tubular channel 170 will be liquid-permeable and will allow diffusion of thetherapeutic agent 168 through pores intubular channel 170. If however, it is desired to prevent theinflation fluid 167 from escaping frominflatable space 162, thentubular channel 170 will act as a barrier layer and may comprise at least one layer of PTFE having low or substantially no fluid permeability. - Referring now to
FIGS. 22 and 23 , therespective graft embodiments inflatable channel 158 has portions with a circumferential configuration as opposed to the helical configuration of theinflatable channel 158 shown inFIG. 17 . The circumferential configuration of portions of theinflatable channel 158 maybe particularly effective in providing the needed kink resistance for endovascular graft for effectively treating diseased body passageways such as a thoracic aortic aneurysm (TAA), abdominal aortic aneurysm (AAA), in which highly angled and tortuous anatomies are frequently found. In alternative embodiments, other cuff and channel configurations are possible.Inflatable channel 158 may be configured circumferentially as shown inFIGS. 22 and 23 . - In addition to the substantially tubular grafts of
FIG. 22 , bifurcated endovascular grafts as shown inFIG. 23 , are also contemplated. The bifurcatedendovascular graft 180 may be utilized to repair a diseased lumen at or near a bifurcation within the vessel, such as, for example, in the case of an abdominal aortic aneurysm in which the aneurysm to be treated may extend into the anatomical bifurcation or even into one or both of the iliac arteries distal to the bifurcation. In the following discussion, the various features of the graft embodiments previously discussed maybe used as necessary in the bifurcated graft 80 embodiment unless specifically mentioned otherwise. -
Graft 180 comprises a firstbifurcated portion 182, a secondbifurcated portion 184 andmain body portion 186. The size and angular orientation of thebifurcated portions portion FIG. 23 to optionally have a different length. First and secondbifurcated portions bifurcated portions main body portion 186 and first and secondbifurcated portions FIG. 22 , which is configured to confine a flow of fluid therethrough. A complete description of some desirable sizes and spacing of inflatable channels may be found in commonly owned, copending U.S. patent application Ser. No. 10/384,103 (which published as US 20040176836 A1), entitled “Kink-Resistant Endovascular Graft” and filed Mar. 6, 2003 to Kari et al., the complete disclosure of which is incorporated herein by reference. - While not shown, it should be appreciated, that instead of circumferential channels and longitudinal channels, the
bifurcated graft 180 may comprise a helicalinflatable channel 158, similar to that of the graft embodiment shown inFIG. 17 (or other channel geometries to achieve desired results), or a combination of helical and circumferential channels. A complete description of some embodiments of endovascular grafts that have helical and cylindrical channel configurations may be found in co-pending and commonly owned U.S. patent application Ser. No. 10/384,103 (which published as US 2004/0176836 A1). Other endovascular grafts that the liquid-impermeable PTFE film may be used with are described in U.S. Pat. No. 6,395,019 to Chobotov, U.S. Pat. No. 6,132,457 to Chobotov, U.S. Pat. No. 6,331,191 to Chobotov, and U.S. patent application Ser. Nos. 10/327,711 (which published as US 2003/0125797 A1), entitled “Advanced Endovascular Graft” to Chobotov et al. and filed Dec. 20, 2002, Ser. No. 10/168,053, the complete disclosures of which are incorporated herein by reference. - As can be appreciated, the inflatable portions of the
graft 180 optionally may be configured to have varying levels of fluid permeability and/or porosity, either within or between particular cuffs, channels or cuff/channel segments, so as to provide for controlled drug delivery, programmed drug delivery or both, into the vessel wall or lumen of the graft via elution of the agent from pores in the layers. For example, any desired portion of thegraft 180 may include PTFE layers having low or substantially no fluid permeability. Such a configuration would be useful in applications in which the drug delivery rate and other properties of the graft or stent-graft (e.g. mechanical properties) may be selected for the particular clinical needs and indication that is contemplated for that device. In addition, the fluid permeability and/or porosity may be uniform within a particular cuff or channel but different between any given channel and/or cuffs. In addition to improved drug delivery, the variable porosity of the outer surface of the graft may also be beneficial for promoting tissue in-growth into the graft. It may be possible to make portions of the graft that are in direct contact with the body lumen to have a higher porosity and/or larger pore size so as to promote tissue in-growth. In particular, tissue in-growth may be beneficial adjacent to the proximal and distal ends of the graft. - With regard to the above detailed description, like reference numerals used therein refer to like elements that may have the same or similar dimensions, materials and configurations. While particular forms of embodiments have been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the embodiments of the invention. Accordingly, it is not intended that the invention be limited by the forgoing detailed description.
Claims (34)
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Also Published As
Publication number | Publication date |
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WO2006113082A1 (en) | 2006-10-26 |
CA2604918A1 (en) | 2006-10-26 |
US8840824B2 (en) | 2014-09-23 |
EP1885545A1 (en) | 2008-02-13 |
JP2008537914A (en) | 2008-10-02 |
US20140356588A1 (en) | 2014-12-04 |
US20060233990A1 (en) | 2006-10-19 |
US20110125255A1 (en) | 2011-05-26 |
US9549829B2 (en) | 2017-01-24 |
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