Ptfe layers and methods of manufacturing

Abstract

Single, continuous PTFE layers having lateral zones of varied characteristics are described. Some of the lateral zone embodiments may include PTFE material having little or no nodal and fibril microstructure. Methods of manufacturing PTFE layers allow for controllable permeability and porosity of the layers, in addition to other characteristics. The characteristics may vary from one lateral zone of a PTFE layer to a second lateral zone of a PTFE layer. 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;
 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.   
     
     
         2 . The method of  claim 1  wherein the layer of PTFE is stretched while the at least one lateral zone is wet with the stretching agent. 
     
     
         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 in a direction transverse to the machine direction. 
     
     
         6 . The method of  claim 1  further comprising calendering the stretched layer of PTFE to compress and densify the PTFE layer. 
     
     
         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 sprits, alcohol, MEK, toluene and alcohol. 
     
     
         9 . The method of  claim 1  wherein the stretching agent content of the layer of PTFE prior to selective 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 stretching the stretched layer of PTFE a second time. 
     
     
         11 . A method of processing PTFE, comprising:
 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.   
     
     
         12 . The method of  claim 11  wherein the layer of PTFE is stretched while at least a portion of the layer of PTFE is wet with stretching agent. 
     
     
         13 . The method of  claim 11  wherein stretching the layer of PTFE comprises stretching the layer of PTFE by a stretch ratio of about 2:1 to about 20:1. 
     
     
         14 . The method of  claim 11  wherein the stretching of the layer of PTFE comprises stretching in a machine direction. 
     
     
         15 . The method of  claim 11  wherein the stretching of the layer comprises stretching the layer in a direction transverse to the machine direction. 
     
     
         16 . The method of  claim 11  further comprising calendering the stretched layer of PTFE to compress and densify the PTFE layer. 
     
     
         17 . The method of  claim 11  wherein the stretching agent comprises an isoparaffin. 
     
     
         18 . The method of  claim 11  wherein the stretching agent is selected from the group consisting of naphtha, mineral sprits, alcohol, MEK, toluene and alcohol. 
     
     
         19 . The method of  claim 11  further comprising applying stretching agent to the layer of PTFE prior to selective removal of the stretching agent. 
     
     
         20 . The method of  claim 19  wherein the stretching agent content of the layer of PTFE prior to application of the stretching agent is about 3 percent by weight to about 22 percent by weight. 
     
     
         21 . The method of  claim 19  further comprising spreading the stretching agent after application to the layer of PTFE with a skimming member disposed adjacent the layer of PTFE. 
     
     
         22 . The method of  claim 11  further comprising stretching the stretched layer of PTFE a second time. 
     
     
         23 . A method of processing PTFE, comprising:
 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 the stretching agent; and   stretching the layer of PTFE while lateral zone of the layer of PTFE is saturated with the stretching agent.   
     
     
         24 . The method of  claim 23  further comprising stretching the stretched layer of PTFE a second time. 
     
     
         25 . A PTFE layer comprising 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.   
     
     
         26 . A PTFE layer comprising 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.   
     
     
         27 . A PTFE layer comprising 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 the stretching agent; and   stretching the layer of PTFE while lateral zone of the layer of PTFE is saturated with the stretching agent.   
     
     
         28 . 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 at least one of the first tubular body and the second tubular body comprises a PTFE layer having a first lateral zone with a substantially low porosity, a low fluid permeability and no discernable node and fibril microstructure, and a second lateral zone which is fluid-permeable and has substantial node and fibril microstructure.   
     
     
         29 . A tubular structure comprising a layer of PTFE having a first lateral zone which is fluid-permeable and which has 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. 
     
     
         30 . An endovascular graft comprising a PTFE layer having a first lateral zone with a liquid-permeable, expanded PTFE layer adjacent a second lateral zone having (a) a closed cell microstructure having high density regions whose grain boundaries are directly interconnected to grain boundaries of adjacent high density regions and (b) substantially no node and fibril microstructure. 
     
     
         31 . The endovascular graft of  claim 30  wherein the endovascular graft comprises an inflatable endovascular graft having at least one inflatable channel and wherein the second lateral zone bounds at least a portion of the inflatable channel. 
     
     
         32 . A thin, continuous PTFE layer, comprising:
 a first lateral zone with a substantially low porosity, a low fluid 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; and   a second lateral zone which is fluid-permeable and has a substantial node and fibril microstructure.   
     
     
         33 . A method of processing a layer of PTFE, comprising:
 providing a layer of PTFE;   stretching the layer of PTFE; and   applying a stretching agent to the PTFE layer during the stretching process.   
     
     
         34 . The method of  claim 33  wherein the formation of a discernable node and fibril microstructure is created during the stretching process prior to application of the stretching agent to the PTFE layer.