Ptfe layers and methods of manufacturing

Abstract

Thin PTFE layers are described having little or no node and fibril microstructure and methods of manufacturing PTFE layers are disclosed that allow for controllable permeability and porosity of the layers. In some embodiments, the PTFE layers may act as a barrier layer in an endovascular graft or other medical device.

1 . A method of processing PTFE, comprising:
 providing a layer of PTFE;   applying a stretching agent to at least a portion of the layer of PTFE; and   stretching the layer of PTFE while the layer of PTFE is wet with the stretching agent to form a stretched layer of PTFE.   
     
     
         2 . The method of  claim 1  wherein the stretching agent is applied to substantially all of the layer of PTFE prior to stretching. 
     
     
         3 . The method of  claim 1  wherein stretching the layer of PTFE comprises stretching the layer of PTFE by a stretch ratio of about 2:1 to about 20:1. 
     
     
         4 . The method of  claim 1  wherein the stretching of the layer of PTFE comprises stretching in a machine direction. 
     
     
         5 . The method of  claim 1  wherein the stretching of the layer comprises stretching the layer of PTFE in a direction transverse to the machine direction. 
     
     
         6 . The method of  claim 1  further comprising calendering the stretched layer of PTFE to densify and compress the layer of PTFE. 
     
     
         7 . The method of  claim 1  wherein the stretching agent comprises an isoparaffin. 
     
     
         8 . The method of  claim 1  wherein the stretching agent is selected from the group consisting of naphtha, mineral spirits, alcohol, MEK, toluene and alcohol. 
     
     
         9 . The method of  claim 1  wherein a lubricant content of the layer of PTFE prior to application of the stretching agent is about 0 percent by weight to about 22 percent by weight. 
     
     
         10 . The method of  claim 1  further comprising spreading the stretching agent after application to the layer of PTFE with a skimming member disposed adjacent the layer of PTFE. 
     
     
         11 . The method of  claim 1  wherein stretching of the layer of PTFE is performed at a temperature of about 80° F. to about 100° F. 
     
     
         12 . The method of  claim 1  wherein stretching of the layer of PTFE is performed at a temperature of about 85° F. to about 95° F. 
     
     
         13 . The method of  claim 1  wherein the stretching agent is applied to the layer of PTFE at a temperature of about 110° F. to about 130° F. 
     
     
         14 . The method of  claim 13  wherein the stretching agent is applied to the layer of PTFE at a temperature of about 115° F. to about 125° F. 
     
     
         15 . The method of  claim 1  wherein stretching the layer of PTFE is performed at a temperature that is just above the glass transition temperature of the PTFE layer material. 
     
     
         16 . The method of  claim 1  wherein the provided layer of PTFE is produced by extruding a compounded PTFE resin through an extruder to form a PTFE ribbon extrudate. 
     
     
         17 . The method of  claim 16  wherein the compounded resin is extruded to an extrudate having a ribbon configuration and having a thickness of about 0.020 inch to about 0.040 inch. 
     
     
         18 . The method of  claim 16  wherein the PTFE ribbon extrudate is calendered to a reduced thickness of about 0.001 inch to about 0.005 inch prior to stretching. 
     
     
         19 . The method of  claim 1  wherein the stretching agent is applied to the layer of PTFE in sufficient quantity such that at least a portion of the layer of PTFE is saturated with stretching agent at the time of stretching. 
     
     
         20 . The method of  claim 1  further comprising stretching the stretched layer of PTFE a second time with no stretching agent added to the stretched layer of PTFE during the second stretch. 
     
     
         21 . The method of  claim 20  wherein the stretched layer of PTFE has a sufficiently low stretching agent content so to form a discernable node and fibril microstructure in the stretched layer of PTFE during the second stretch. 
     
     
         22 . The method of  claim 1  further comprising sintering the stretched layer of PTFE. 
     
     
         23 . A method of processing PTFE, comprising:
 providing a layer of PTFE;   applying a stretching agent to at least a portion of the layer of PTFE until a portion of the layer of PTFE is saturated with the stretching agent to form a saturated portion; and   stretching the layer of PTFE while the saturated portion of the layer of PTFE is saturated with the stretching agent.   
     
     
         24 . The method of  claim 23  wherein substantially all of the layer of PTFE is saturated with stretching agent to form a saturated portion prior to stretching. 
     
     
         25 . The method of  claim 24  further comprising sintering the layer of PTFE. 
     
     
         26 . A method of processing PTFE, comprising:
 providing a stretched layer of PTFE that has been stretched in at least a first direction;   applying a stretching agent to at least a portion of the stretched layer of PTFE; and   stretching the stretched layer of PTFE while the stretched layer of PTFE is wet with the stretching agent.   
     
     
         27 . The method of  claim 26  wherein the stretching agent is applied to substantially all of the stretched layer of PTFE prior to the stretching of the stretched layer. 
     
     
         28 . The method of  claim 26  wherein the stretched layer of PTFE has a lubricant content of below about 3% by weight prior to application of the stretching agent. 
     
     
         29 . The method of  claim 26  wherein the stretched layer of PTFE has been stretched in the first direction with a sufficiently low stretching agent content so to form a discernable node and fibril microstructure in the stretched layer of PTFE during the stretch in the first direction. 
     
     
         30 . The method of  claim 26  wherein the stretching of the stretched layer is performed in a direction different than the first direction. 
     
     
         31 . The method of  claim 30  wherein the first direction is a machine direction and the stretching of the stretched layer is performed in a transverse direction. 
     
     
         32 . The method of  claim 30  wherein the stretching of the stretched layer of PTFE material is performed in a transverse direction by a stretch ratio of about 2:1 to about 30:1. 
     
     
         33 . The method of  claim 26  wherein the stretching of the stretched layer is performed in substantially the same direction as the first direction. 
     
     
         34 . The method of  claim 33  wherein the first direction is a machine direction and the stretching of the stretched layer is performed in the machine direction. 
     
     
         35 . The method of  claim 26  wherein the stretched layer of PTFE has been stretched in the first direction while the layer of PTFE was wet with stretching agent applied to the layer of PTFE. 
     
     
         36 . The method of  claim 26  further comprising sintering the layer of PTFE. 
     
     
         37 . A method of processing PTFE, comprising:
 providing a layer of PTFE;   applying a stretching agent to at least a portion of the layer;   stretching the layer of PTFE while the layer of PTFE is wet with the stretching agent to form a stretched layer of PTFE;   stretching the stretched layer of PTFE a second time; and   calendering the twice-stretched layer of PTFE so as to densify and further thin the twice-stretched layer of PTFE.   
     
     
         38 . The method of  claim 37  wherein the stretching agent is applied to substantially all of the surface of the layer prior to stretching. 
     
     
         39 . A PTFE layer comprising a layer made by providing a layer of PTFE;
 applying a stretching agent to a surface of the layer; and   stretching the layer of PTFE while the layer of PTFE is wet with the stretching agent.   
     
     
         40 . A PTFE layer comprising a layer made by providing a layer of PTFE;
 applying a stretching agent to a surface of the layer;   stretching the layer of PTFE while the layer of PTFE is wet with the stretching agent; and   stretching the stretched layer of PTFE a second time.   
     
     
         41 . A PTFE layer comprising a layer made by providing a layer of PTFE;
 applying a stretching agent to a surface of the layer;   stretching the layer of PTFE while the layer of PTFE is wet with the stretching agent;   stretching the stretched layer of PTFE a second time; and   calendering the twice-stretched layer of PTFE so as to densify and further thin the twice-stretched layer of PTFE.   
     
     
         42 . A thin PTFE layer comprising substantially low porosity, low permeability, no discernable node and fibril structure, and having a thickness of about 0.00005 inch to about 0.005 inch. 
     
     
         43 . A composite PTFE film comprising:
 a first layer comprising a stretched layer of PTFE that has a closed cell microstructure with a plurality of interconnected high density regions having no discernable node and fibril microstructure between the high density regions; and   a second layer of expanded PTFE which is secured to the first layer and which includes a substantial node and fibril microstructure.   
     
     
         44 . A thin, substantially liquid-impermeable PTFE layer produced by:
 providing a PTFE layer;   adding a stretching agent to the PTFE layer; and   stretching the PTFE layer in at least one direction to reduce a thickness of the PTFE layer without substantially creating a liquid permeability in the stretched PTFE layer.   
     
     
         45 . The thin layer of  claim 41  wherein the stretched PTFE layer comprises a closed cell microstructure that comprises a plurality of interconnected high density regions with no discernable node and fibril microstructure. 
     
     
         46 . A multi-layered vascular graft comprising:
 a first tubular body having an outer surface and an inner surface that defines an inner lumen of the vascular graft; and   a second tubular body having an outer surface and an inner surface coupled to the outer surface of the first tubular body,   wherein one of the first tubular body and the second tubular body comprises a fluid-permeable PTFE layer and the other tubular body comprises a PTFE layer having low fluid permeability.   
     
     
         47 . The multi-layered vascular graft of  claim 46  wherein the PTFE layer having low fluid permeability comprises a closed cell microstructure that comprises a plurality of interconnected high density regions wherein the closed cell microstructure has no discernable node and fibril microstructure. 
     
     
         48 . The multi-layered vascular graft of  claim 46  wherein the PTFE layer having low fluid permeability comprises a thin PTFE layer having substantially low porosity, no discernable node and fibril structure, and a high degree of limpness and suppleness so to allow mechanical manipulation or strain of the PTFE layer without significant recoil or spring back. 
     
     
         49 . An inflatable endovascular graft comprising a body portion having an inflatable channel that defines an inflatable space, wherein the inflatable space is at least partially surrounded by a thin, PTFE layer having substantially no fluid permeability. 
     
     
         50 . The inflatable endovascular graft of  claim 49  wherein the PTFE layer having substantially no fluid permeability comprises a closed cell microstructure that comprises a plurality of interconnected high density regions and wherein the closed cell microstructure has no discernable node and fibril microstructure. 
     
     
         51 . The inflatable endovascular graft of  claim 49  wherein the PTFE layer having substantially no fluid permeability comprises a thin PTFE layer having substantially low porosity, 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. 
     
     
         52 . A stretched, PTFE layer that comprises 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 and having substantially no fluid permeability. 
     
     
         53 . A composite film comprising a fluid-permeable, expanded PTFE layer secured to a surface of a thin stretched PTFE layer having 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. 
     
     
         54 . A tubular structure comprising a composite film comprising a fluid-permeable, expanded PTFE layer secured to a surface of a thin, stretched PTFE layer having 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. 
     
     
         55 . An endovascular graft comprising a composite film with a fluid-permeable, expanded PTFE layer secured to a surface of a thin stretched PTFE layer having 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. 
     
     
         56 . A thin PTFE layer, comprising substantially low porosity, low liquid permeability, no discernable node and fibril structure, and a high degree of limpness and suppleness so to allow mechanical manipulation or strain of the PTFE layer without significant recoil or spring back. 
     
     
         57 . A thin layer of PTFE comprising a stretched layer of PTFE that has a closed cell microstructure with a plurality of interconnected high density regions having no discernable node and fibril microstructure between the high density regions. 
     
     
         58 . A method of controlling the porosity, density or both of a PTFE layer, comprising:
 stretching the PTFE layer at least one time at a preselected temperature while using a preselected stretching agent content for the at least one stretch.