|Publication number||US20090036971 A1|
|Application number||US 12/250,915|
|Publication date||Feb 5, 2009|
|Filing date||Oct 14, 2008|
|Priority date||Apr 13, 2005|
|Also published as||CA2604918A1, EP1885545A1, US8840824, US20060233990, US20110125255, US20140356588, WO2006113082A1|
|Publication number||12250915, 250915, US 2009/0036971 A1, US 2009/036971 A1, US 20090036971 A1, US 20090036971A1, US 2009036971 A1, US 2009036971A1, US-A1-20090036971, US-A1-2009036971, US2009/0036971A1, US2009/036971A1, US20090036971 A1, US20090036971A1, US2009036971 A1, US2009036971A1|
|Inventors||Joseph W. Humphrey, Jeffry B. Skiba|
|Original Assignee||Trivascular2, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Referenced by (8), Classifications (26), Legal Events (1)|
|External Links: USPTO, USPTO Assignment, Espacenet|
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.
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.
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 ISOPARŽ H, ISOPARŽ K and ISOPARŽ 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, the compound 10 may be placed in an extruder, such as the ram extruder 12 shown in
Once the PTFE resin compound is loaded, the piston 14 is advanced towards the output end 18 of the extruder 12, as indicated by arrow 21 which increases the chamber pressure and forces the PTFE compound 10 to be extruded through an orifice 22 of the die 16 to form an extrudate 24. The extrudate 24 may be in the form of a ribbon or tape that is then wound onto a take up spool 26 as indicated by the arrow adjacent the take up spool in
Processing conditions may be chosen to minimize the amount of lubricant that is evaporated from the PTFE extrudate ribbon 24. For example, the PTFE compound 10 may be extruded at a temperature that is above the glass transition temperature, and typically above 90° F. The PTFE extrudate ribbon 24 is generally fully densified, non-porous and typically has approximately 100% of its original amount of lubricant upon extrusion from the die 16. The die 16 may also be configured to produce an extrudate 24 having other configurations, such as a tubular configuration. Also, for some methods, the PTFE compound 10 may be processed to form a preform billet before it is placed in the extruder 12. In addition, a de-ionizing air curtain may optionally be used to reduce static electricity in the area of the extruder 12. In one example, the ram extruder 12 has a barrel 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 have orifices 22 configured to produce an extrudate ribbon or tape 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 by arrow 27, to reduce the thickness of the PTFE extrudate ribbon 24 into a PTFE layer 28 as shown in
While it may be possible to store the PTFE extrudate ribbon 24 for an extended period of time after extrusion, lubricant in the PTFE extrudate ribbon 24 will evaporate from the ribbon 24 during the storage period. As such, it may be desirable in some instances to calender the PTFE extrudate ribbon 24 almost immediately after extrusion so as to better control the lubricant level in the PTFE extrudate ribbon 24. For some embodiments, the PTFE 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 a PTFE layer 28 of any suitable thickness. The reduction ratio of an embodiment of the calendering process, which is a ratio of the thickness of the PTFE extrudate ribbon 24 to the thickness of the calendered PTFE 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 a PTFE 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, the PTFE ribbon 24 may be calendered to a PTFE layer 28 which has a thickness that is slightly greater than a final desired thickness, so that the final stretch of the PTFE ribbon 24 causes the final 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, the adjustable 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 the PTFE 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 produce PTFE 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 the PTFE 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 in
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 or lubricant 40 may optionally be applied to the calendered PTFE layer 28 during the stretching process as shown in
The stretching agent 40 may be the same lubricant used to form the PTFE 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 the PTFE layer 28 to saturate the PTFE layer 28 during the stretching process. The stretching agent may be applied by a variety of methods to a surface, such as the upper surface 38, of the PTFE layer 28 during the stretching process. For example, the stretching agent 40 may be sprayed over the entire layer 28, or only on selected portions of the PTFE layer 28 by a spray mechanism 42 to the upper surface 38 of the PTFE layer 28. The stretching agent 40 is applied to the PTFE layer 28 after the PTFE layer 28 unwinds from spool 32 and passes under the spray mechanism 42. The stretching agent 40 may be applied uniformly over one or both sides of the PTFE layer 28, on only one side of the PTFE layer 28, or only on selected portions of the PTFE 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 the PTFE layer 28 is stretched, the capacity of the resulting stretched PTFE layer 36 to absorb stretching agent 40 increases. As such, if it is desirable to maintain a saturated status of the PTFE layer 28 and stretched PTFE 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 the PTFE layer 36 and the effect of the stretching agent 40 temperature (about 110° F. to about 120° F.) for a period of time. As such, stretching agent 40 may be added prior to the initiation of the stretching process or at any time during the stretching process. A method whereby stretching agent 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 stretching agent 40 to the PTFE layer; however, thinning of the PTFE layer will still take place once the stretching agent 40 has been applied and stretching continues.
Embodiments of methods discussed herein may be useful to reduce a thickness of the PTFE layer 28 to a stretched PTFE 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 calendered PTFE layer 28 having a width of about 3 inches to about 6 inches, may be transversely stretched, as shown in
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 the layer 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 the PTFE 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 the PTFE 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 the PTFE 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 the PTFE 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 stretched PTFE layer 36 are fusible and deformable and may easily be fused with other PTFE layers having different properties. At any point after the PTFE layer 28 is stretched, the stretched PTFE layer 36 may be sintered to amorphously lock the microstructure of the PTFE layer 36. Sintering may be performed to combine the stretched PTFE 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
This optional second stretching process subjects the PTFE layer 36 to yet another mechanical working. The second stretching process shown in
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 the PTFE 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 stretching agent 40 in the PTFE layer 28 for a longer period of time during processing.
Either the stretched PTFE layer 36 or the twice-stretched PTFE layer 46 optionally may be calendered in order to further thin and density the material. The twice-stretched PTFE layer 46 is shown being calendered in
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, ISOPARŽ 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, the PTFE compound 10 is placed in an extruder 12, as shown in
The PTFE extrudate ribbon 24 is then calendered, as shown in
Referring again to
Wet tentering with the stretching agent 40 allows the PTFE layer 28 to be thinned without creating substantial porosity and fluid permeability in the stretched PTFE layer 36. While the stretched PTFE 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 stretched PTFE 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 or layer 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 stretching agent 40. The predetermined horizontal spatial pattern may be formed from various lateral zones or sections which may each have varying levels of stretching agent 40 content or stretching agent 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 stretching agent 40 content whereby the content of stretching agent 40 varies stepwise or continuously through the thickness of a layer of PTFE. Selective application of the stretching agent 40 by spray 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 stretching agent 40 contained within the various lateral zones of the PTFE layer 28 may vary from about 0 percent stretching agent content by weight to a level of substantial saturation of stretching agent 40.
PTFE layer 28 having a predetermined pattern of stretching agent 40 may be stretched in at least one direction such that the lateral zones of the stretched PTFE layer 36 that contained more stretching agent 40 during stretching will have a lower permeability (e.g., substantially impermeable), while the lateral zones of the stretched PTFE layer 36 that contained less stretching agent 40 during stretching will have a higher permeability. Typically, the lateral zones of the stretched layer 36 that contained more stretching agent 40 may also have a reduced thickness relative to the lateral zones that contained less stretching agent 40 during the stretching process. In some embodiments, it may be desirable to have lateral zones or regions of the PTFE layer 28 that are substantially saturated with stretching agent 40 adjacent lateral zones or regions of PTFE 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 the PTFE layer 28 radially about a point.
As discussed above, the stretching agent 40 content of lateral zones 62 may be chosen such that standard expansion takes place for the PTFE material within lateral zones 62 upon stretching. Standard expansion of PTFE may produce expanded PTFE (ePTFE) within lateral 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 stretching agent 40 such that expansion of the PTFE layer 28 within lateral zones 60 produces PTFE material of lateral zones 64 which is thinner and less permeable than the material of lateral zones 66. For some embodiments, the PTFE material of lateral 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 in
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 stretching agent 40 may be selectively applied to the PTFE layer 28 by a spray mechanism 42 that may be controlled through computer or manual control. The spray mechanism 42 shown in
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 the PTFE layer 28 in a predetermined pattern may be used as opposed to selective addition of stretching agent 40. In such a method, a PTFE layer 28 could be produced having a high level of stretching agent 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 the PTFE layer 28. In such an embodiment, an array of LED lasers 60, or the like, could be disposed adjacent the PTFE layer 28, as shown in
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
At a magnification of 20,000, as seen in
Though PTFE film or layer 110 is configured to have low or substantially no fluid permeability, PTFE layer 110 nonetheless has a porosity. The PTFE layer 110 typically has an average porosity from about 20% to about 80%, and specifically from about 30% and about 70%. In one embodiment, a PTFE film 110 has a porosity of about 30% to about 40%. In another embodiment, a PTFE 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 the PTFE film 110. An average pore size in the PTFE layer 110 is may be less than about 20 microns, and specifically less than about 0.5 micron. In one embodiment, a PTFE 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, the PTFE film 110 may have an average pore size of greater than about 6.0 microns. As described below, depending on the desired properties of the resultant PTFE layer 110, embodiments of methods may be modified so as to vary the average porosity and average pore size of the PTFE 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 the PTFE 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 the PTFE layer 110 may be densified to a higher density level so that the density of the PTFE layer 110 is comparable to a fully densified PTFE layer.
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
As shown in
Tubular structures 130 or 140 may define an inner diameter ID which is the diameter of the inner surface, which may define the area of flow through tubular structure 130 or 140. An outer diameter OD, which is the diameter of the outer surface 139 or 149 of the outer tubular layer 138 or 148. The inner diameter ID and outer diameter OD may be any desired diameter. For use in an endovascular graft, the inner diameter ID but is typically from about 10 mm to about 40 mm and the outer diameter OD is typically from about 12 mm to about 42 mm. The tubular layers may have any suitable thickness, however, fluid-impermeable PTFE layers 138 and 142 have a thickness from about 0.0005 inch and about 0.01 inch thick, and specifically from about 0.0002 inch to about 0.001 inch. Similarly, fluid-permeable PTFE layers 132 or 148 may also be any thickness desired, but typically have a thickness from about 0.0001 inch and about 0.01 inch, and specifically from about 0.0002 inch to about 0.001 inch. As can be appreciated, the thicknesses and diameters of the tubular structures 130 or 140 will vary depending on the use of the tubular structures.
Tubular structures 130 or 140 may be formed as tubes through conventional tubular extrusion processes. Typically, however, tubular structures 130 or 140 may be formed from PTFE layers 110 or 118, as shown in
The films and layers discussed herein are not limited to a single porous PTFE layer 118 and a single PTFE layer or film 110 having low or substantially no fluid permeability. The composite films 120 and tubular structures 130 or 140 may include a plurality of porous fluid-permeable PTFE layers (having the same or different node and fibril size and orientation, porosity, pore size, and the like), one or more non-porous, densified PTFE layers, and/or one or more PTFE layers 110 having low or substantially no fluid permeability. For example, 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, the PTFE layer 110 may have a reduced thickness relative to the porous PTFE layers. In other embodiments, however, the PTFE layer 110 may have the same thickness or larger thickness than the porous PTFE layers. As an alternative embodiment to
Referring now to
A proximal inflatable cuff 156 may be disposed at or near a proximal end 151 of graft body section 153 and a distal inflatable cuff 157 may be disposed at or near a graft body section distal 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, a stent 159 may be attached at the proximal end 151 and/or the distal end 152 of the graft 150. Depending on the construction of the cuffs 156 and 157 and graft body section 153, inflation of cuffs 156 and 157, when not constrained (such as, e.g., by a vessel or other body lumen), may cause the cuffs 156 and 157 to assume a generally annular or toroidal shape with a generally semicircular longitudinal cross-section. Inflatable cuffs 156 and 157 may be designed to generally, however, conform to the shape of the vessel within which it is deployed. When fully inflated, cuffs 156 and 157 may have an outside diameter ranging from about 10 mm to about 45 mm; specifically from about 16 mm to about 42 mm.
At least one inflatable channel 158 may be disposed between and in fluid communication with proximal inflatable cuff 156 and optional distal inflatable cuff 157. Inflatable channel 158 in the
In addition, it may be desirable for some embodiments to include a PTFE layer 110 that has varied permeability across lateral zones of the PTFE layer 110 whereby the characteristic of a lateral zone of the PTFE layer 110 corresponds to the function of the PTFE layer in the lateral zone. For example, instead of including a single 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 the PTFE layer 110 that will be adjacent the inflatable channel 158 and cuffs 156 and 157. In this way, the inflatable channel 158 and inflatable cuffs 156 and 157 can be made resistant to fluid loss, while the graft body retains its fluid-permeable character adjacent the inflatable channel 158 and inflatable cuffs 156 and 157. This type of arrangement could be included in any of the graft embodiments discussed herein.
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 the inflatable cuffs 156 and 157 and 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.
In the embodiment shown in
In an alternative configuration shown in
As shown in
Referring now to
In addition to the substantially tubular grafts of
Graft 180 comprises a first bifurcated portion 182, a second bifurcated portion 184 and main body portion 186. The size and angular orientation of the bifurcated portions 182 and 184 may vary to accommodate graft delivery system requirements and various clinical demands. The size and angular orientation may vary even between portion 182 and 184. For instance, each bifurcated portion or leg is shown in
While not shown, it should be appreciated, that instead of circumferential channels and longitudinal channels, the bifurcated graft 180 may comprise a helical inflatable channel 158, similar to that of the graft embodiment shown in
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 the graft 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.
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|US8083789||Nov 16, 2007||Dec 27, 2011||Trivascular, Inc.||Securement assembly and method for expandable endovascular device|
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|US8563879 *||Apr 9, 2010||Oct 22, 2013||Sierra Instruments||Inertial microbalance filter assembly|
|US8663309||Sep 26, 2007||Mar 4, 2014||Trivascular, Inc.||Asymmetric stent apparatus and method|
|US8992595||Mar 13, 2013||Mar 31, 2015||Trivascular, Inc.||Durable stent graft with tapered struts and stable delivery methods and devices|
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|U.S. Classification||623/1.15, 264/291, 526/255, 428/36.9|
|International Classification||C08F14/26, A61F2/06, B32B1/06, B29C55/00|
|Cooperative Classification||Y10T428/24802, Y10T428/1393, Y10T428/139, Y10T428/1352, A61F2/82, A61L27/56, B29C47/0021, B29C43/222, B29C43/24, B29C47/0004, A61L27/507, B29K2027/18, A61L27/16, B29C55/005|
|European Classification||A61L27/16, B29C55/00B, A61L27/50E, A61L27/56|
|Jul 13, 2010||AS||Assignment|
Owner name: TRIVASCULAR, INC., CALIFORNIA
Free format text: CHANGE OF NAME;ASSIGNOR:TRIVASCULAR2, INC.;REEL/FRAME:024672/0321
Effective date: 20091202