U.S. patent application number 14/078225 was filed with the patent office on 2014-03-27 for non-shortening wrapped balloon.
This patent application is currently assigned to W. L. Gore & Associates, Inc.. The applicant listed for this patent is W. L. Gore & Associates, Inc.. Invention is credited to Sherif A. Eskaros, David R. King, Joseph E. Korleski, Lonzo C. McLaughlin, Kenneth R. Newcomb, Peter J. Roeber, John Streeter, Jeffrey C. Towler.
Application Number | 20140088683 14/078225 |
Document ID | / |
Family ID | 39082527 |
Filed Date | 2014-03-27 |
United States Patent
Application |
20140088683 |
Kind Code |
A1 |
Eskaros; Sherif A. ; et
al. |
March 27, 2014 |
NON-SHORTENING WRAPPED BALLOON
Abstract
A non-shortening catheter balloon having a longitudinal axis and
an inflatable balloon able to be affixed to a catheter shaft is
provided. The balloon has an uninflated length which remains
relatively unchanged upon inflation and is formed of least two
helically oriented wrapped passes of balloon materials at a
balanced force angle. Methods of making this balloon are also
provided.
Inventors: |
Eskaros; Sherif A.; (Elkton,
MD) ; King; David R.; (Wilmington, DE) ;
Korleski; Joseph E.; (Newark, DE) ; McLaughlin; Lonzo
C.; (Landenberg, PA) ; Newcomb; Kenneth R.;
(Middletown, DE) ; Roeber; Peter J.; (Oxford,
PA) ; Streeter; John; (Flagstaff, AZ) ;
Towler; Jeffrey C.; (Wilmington, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
W. L. Gore & Associates, Inc. |
Newark |
DE |
US |
|
|
Assignee: |
W. L. Gore & Associates,
Inc.
Newark
DE
|
Family ID: |
39082527 |
Appl. No.: |
14/078225 |
Filed: |
November 12, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12508695 |
Jul 24, 2009 |
8597566 |
|
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14078225 |
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11501249 |
Aug 7, 2006 |
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12508695 |
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Current U.S.
Class: |
623/1.11 ;
604/103.06 |
Current CPC
Class: |
A61M 25/1034 20130101;
A61M 2025/1086 20130101; A61M 2025/1004 20130101; A61M 2025/1075
20130101; A61F 2/958 20130101; A61M 25/10 20130101; A61M 25/1029
20130101 |
Class at
Publication: |
623/1.11 ;
604/103.06 |
International
Class: |
A61M 25/10 20060101
A61M025/10; A61F 2/958 20060101 A61F002/958 |
Claims
1. A balloon catheter comprising: a catheter shaft having a
longitudinal axis and a non-shortening radially symmetric
inflatable balloon affixed to said shaft, said balloon having an
uninflated length which remains relatively unchanged upon inflation
and comprising at least two helically wrapped passes of helically
oriented anisotropic balloon material.
2. The balloon of claim 1 wherein the length change upon inflation
is less than 20 percent.
3. The balloon of claim 1 wherein the length change upon inflation
is less than 10 percent.
4. The balloon of claim 1 wherein the length change upon inflation
is less than 5 percent.
5. The balloon of claim 1 wherein said helically wrapped passes of
a first balloon material are bonded to each other through the
application of heat.
6. The balloon of claim 1 wherein the first balloon material is
mechanically stress relieved through annealing with heat in the
inflated state.
7. The balloon of claim 1 wherein the helically wrapped passes of
the first balloon material are oriented and balanced in opposite
directions at an angle of less than or equal to about 55 degrees
with respect to the longitudinal axis and further comprising a
second balloon material oriented at an angle of greater than or
equal to about 55 degrees with respect to the longitudinal axis in
the inflated state.
8. The balloon of claim 7 wherein said helically wrapped passes of
a first balloon material are bonded to the second balloon material
through the application of heat.
9. The balloon of claim 1 wherein the helically wrapped passes are
at a balanced force angle.
10. The balloon of claim 7 wherein the first balloon material is
held at balanced force angle by second balloon material that is
helically wrapped at an angle greater than 54 degrees.
11. The balloon of claim 7 wherein the first balloon material is
held at balanced force angle by second balloon material pass that
is wrapped at an angle greater than 54 degrees.
12. The balloon of claim 7 wherein the second balloon material is
isotropic.
13. The balloon of claim 7 wherein the second balloon material is
anisotropic.
14. The balloon catheter of claim 1 wherein the un-inflated length
is changed by less than 2% upon inflation.
15. The balloon catheter of claim 1 wherein the balloon exhibits
essentially radial symmetry upon inflation.
16. The balloon catheter of claim 1 wherein the balloon exhibits
equal hydrostatic force on a vessel wall in clinical use.
17. The balloon catheter of claim 1 further comprising a stent with
uniform deployment capability.
18. The balloon catheter of claim 1 wherein the balloon is
non-compliant.
19. The balloon catheter of claim 1 wherein the balloon is
semi-compliant.
20. A balloon catheter of claim 1 wherein said first balloon
material or said second balloon material comprises a filler.
21. The balloon of claim 1 wherein at least one of the balloon
materials comprises a porous reinforcing polymer.
22. The balloon of claim 21 wherein the porous reinforcing polymer
comprises a fibrous reinforcement.
23. The balloon of claim 21 wherein the porous reinforcing polymer
is a PEEK.
24. The balloon of claim 21 wherein the porous reinforcing polymer
is a polyamide.
25. The balloon of claim 21 wherein the porous reinforcing polymer
is a polyurethane.
26. The balloon of claim 21 wherein the porous reinforcing polymer
is a polyester.
27. The balloon of claim 21 wherein the porous reinforcing polymer
is a fluoropolymer.
28. The balloon of claim 21 wherein the porous reinforcing polymer
is an olefin.
29. The balloon of claim 21 wherein the porous reinforcing polymer
is bio-resorbable.
30. The balloon of claim 22 wherein the porous reinforcing polymer
is expanded PTFE.
31. The balloon of claim 30 wherein the expanded PTFE has a matrix
tensile value in one direction of greater than 690 megapascals.
32. The balloon of claim 30 wherein the expanded PTFE has a matrix
tensile value in one direction of greater than 960 megapascals.
33. The balloon of claim 30 wherein the expanded PTFE has a matrix
tensile value in one direction of greater than 1,200
megapascals.
34. The balloon of claim 30 wherein the maximum hoop stress of the
helically wrapped layers in greater than 400 megapascals.
35. The balloon of claim 30 wherein the maximum hoop stress of the
helically wrapped layers in greater than 600 megapascals.
36. The balloon of claim 1 wherein the helically wrapped passes
comprise a porous reinforcing polymer and a continuous polymer
layer.
37. The balloon of claim 36 wherein a layer is less than 0.0002''
thick.
38. The balloon of claim 36 wherein the continuous polymer layer is
imbibed throughout the porous reinforcing polymer.
39. The balloon of claim 36 where the continuous polymer layer is
comprised of a fluoropolymer.
40. The balloon of claim 36 where the continuous polymer layer is
an elastomer.
41. The balloon of claim 36 wherein the continuous polymer layer is
a urethane.
42. The balloon of claim 36 wherein the continuous polymer layer is
a silicone.
43. The balloon of claim 36 wherein the continuous polymer layer is
a styrene block copolymer.
44. The balloon of claim 36 wherein the continuous polymer layer is
a fluoro-elastomer.
45. The balloon of claim 36 wherein the continuous polymer layer is
bioresorbable.
46. The balloon catheter of claim 1 wherein said first balloon
material or said second balloon material comprises a filler.
47. The balloon catheter of claim 46 wherein the filler is radio
opaque.
48. The balloon catheter of claim 46 wherein the filler provides
therapeutic value.
49. The balloon catheter of claim 1 wherein the balloon contains an
integral non-distending wrapped seal region.
50. The balloon catheter of claim 49 wherein the integral
non-distending wrapped seal region is located between at least two
passes of balloon material.
51. The balloon catheter of claim 49 wherein the integral
non-distending wrapped seal region is located on the outer surface
of a balloon material.
52. The balloon catheter of claim 1 further comprising a reinforced
catheter shaft under the balloon to push out balloon after
deflation which prevents distended material from folding over the
seals.
53. The balloon catheter of claim 1 further comprising a stent
wherein the first balloon material pass and a second balloon
material pass flows into interstices of a stent to provide stent
embedment when used as a stent delivery system.
54. The balloon catheter of claim 53 wherein the stent is embedded
without the use of heat.
55. The balloon catheter of claim 54 wherein the stent is embedded
without balloon inflation.
56. The balloon catheter of claim 1 wherein the first balloon
material and the second balloon material are comprised of the same
materials.
57. The balloon catheter of claim 1 wherein the first balloon
material and the second balloon material are comprised of different
materials.
58. The balloon catheter of claim 56 wherein the first balloon
material pass and the second balloon material pass are less than 2
micrometers thick.
59. A balloon catheter comprising a catheter shaft having a
longitudinal axis and an inflatable balloon affixed to said shaft,
said balloon having an un-inflated length which remains relatively
unchanged upon inflation and comprising at least two helically
wrapped passes of a first balloon material which are wrapped in
opposing directions each with a wrap angle of less than 15 degrees
with respect to the longitudinal axis.
60. The balloon catheter of claim 59 wherein the helically wrapped
passes are at a balanced force angle in the inflated state.
61. The balloon catheter of claim 60 wherein the helically wrapped
passes are exposed to heat and inflation pressure to reach the
inflated state.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to balloon catheters and, more
particularly, to a non-shortening wrapped balloon configured to
expand with essential radial symmetry to a predetermined diameter
upon application of a predetermined pressure thereto.
[0002] Balloon catheters are well known in the art. Such catheters
are employed in a variety of medical procedures, including dilation
of narrowed blood vessels, placement of stents and other implants,
and temporary occlusion of blood vessels.
[0003] In a typical application, the balloon is advanced to the
desired location in the vascular system. The balloon is then
pressure-expanded in accordance with a medical procedure.
Thereafter, the pressure is removed from the balloon, allowing the
balloon to contract and permit removal of the catheter. The balloon
must be formed of a material which has a low profile to allow entry
through a vessel, yet is readily pressure-expanded and able to
contract upon removal of the inflation pressure.
[0004] Procedures such as these are generally considered minimally
invasive, and are often performed in a manner which minimizes
disruption to the patient's body. As a result, catheters are often
inserted from a location remote from the region to be treated.
However, previous wrapped balloons have suffered from problems such
as overexpansion during inflation and shortening of the balloon due
to inflation resulting in unreliable placement of the balloon in a
vessel. This is particularly concerning when large diameter balloon
are employed in medical procedures because the maximum hoop stress
of the inflated balloon material can more easily be exceeded
causing the balloon to rupture or burst.
[0005] Previous attempts to compensate for overexpansion have been
made.
[0006] However, only the present invention provides a
non-shortening balloon that expands to a maximum diameter in an
essentially radial symmetric fashion. While an advantage of a low
angle wrapped balloon is that the wrap is accomplished at the
deflated diameter making mounting to a catheter shaft possible. The
balloon then inflates to a larger diameter in use at which time the
wrap angle rotates to the neutral angle. A typical low angle
wrapped balloon will foreshorten as it is expanded. Compensation
for foreshortening by means of accordion-scrunching-length-storage
is limited in that the longitudinal folds push out and then the
angle moves to the neutral angle thus the foreshortening is not
eliminated during inflation. The devices and methods of the present
invention minimize foreshortening while maintaining an essentially
radial inflating balloon, and allow the balloon to be mounted on a
smaller diameter catheter shaft. The present invention solves the
clinical issues of accurate placement of a balloon or stent due to
foreshortening of traditional wrapped balloons. The present
invention also prevents undue trauma on vessel endothelial layers
and possibility of plaque fragmentation caused by inflation
movement of asymmetric inflating balloons.
SUMMARY OF THE INVENTION
[0007] The present invention is a balloon catheter comprising a
catheter shaft having a longitudinal axis and an inflatable balloon
affixed to said shaft, said balloon having an uninflated length
which remains relatively unchanged upon inflation and comprising at
least two helically oriented layers oriented at a balanced force
angle.
[0008] A non-shortening wrapped catheter balloon having a
longitudinal axis, comprising a first balloon material layer fused
to a second balloon material layer is provided, wherein the first
balloon material is oriented at an angle of less than or equal to
about 55 degrees and the second balloon material is oriented at an
opposing angle of less than or equal to about 55 degrees with
respect to the longitudinal axis. These opposing angle layers
create a balloon preform.
[0009] A method of creating a non-shortening catheter balloon with
increased burst pressures is provided, said balloon comprising:
wrapping a mandrel with an anisotropic film at a low angle to form
a balloon preform; removing the mandrel; exposing the balloon
preform to internal pressure at a temperature to soften or a melt
point for the film or imbibing material; and inflating the balloon
preform into a balloon as it is continued to be exposed to said
internal pressure at an increased temperature.
[0010] A method of creating a non-shortening catheter balloon with
increased burst pressures is provided comprising: wrapping a
mandrel with an anisotropic film at a low angle to form a balloon
preform; exposing the balloon preform to internal pressure at
temperatures below melting point of the film; inflating the balloon
as it is continued to be exposed to said internal pressure and
constant temperature; and wrapping the inflated balloon with an
overwrap at an angle between 54 and 90 degrees to form a high
pressure catheter balloon that is retractable.
[0011] A method of creating a non-shortening catheter balloon with
increased burst pressures is provided comprising: wrapping a
mandrel with an anisotropic film at a low angle to form a balloon
preform; removing the mandrel; exposing the balloon preform to
internal pressure at temperatures above ambient to soften or melt
the film, inflating the balloon as it is continued to be exposed to
said internal pressure and constant temperature; and wrapping the
inflated balloon helically with an anisotropic material at a high
angle of between 54 and 90 degrees to form a high pressure catheter
balloon.
DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows a schematic of a wrapped balloon of the present
invention.
[0013] FIG. 2 shows a balloon material with a single side
coating.
[0014] FIG. 3 shows a balloon material with a double sided
coating.
[0015] FIG. 4 shows a schematic of a partially wrapped balloon.
[0016] FIG. 5 shows a cross section of wrapped balloon on a
core.
[0017] FIG. 6 shows a cross section of wrapped balloon on a core
with a cigarette wrapped second balloon material pass.
[0018] FIG. 7 shows a cross section of wrapped balloon on a core
with a cigarette wrapped second balloon material pass and
non-distending regions.
[0019] FIG. 8 shows a cross section of wrapped balloon on a core
with an overlapped cigarette wrap of second balloon material
pass.
[0020] FIG. 9 shows a mold-shaped catheter balloon with
non-distensible regions.
[0021] FIG. 10 shows a cross-section view of a wrapped balloon with
non-distensible regions.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The balloon catheter of the present invention in its
simplest form comprises a catheter shaft having a longitudinal axis
and an inflatable balloon affixed thereto. The balloon is comprised
of at least two passes. An individual pass is comprised of one or
more layers of material which are laid at a similar angle in
relation to the longitudinal axis of the balloon. A layer is
considered to be one thickness of balloon material which may be
wrapped, folded, laid or weaved over, around, beside or under
another thickness. A longitudinal pass comprises a distinctive
layer or series of layers of material which are wound to form a
region or area distinct from surrounding or adjoining parts. For
instance a pass may comprise multiple layers of balloon material
wrapped at a 90 degree angle relative to the longitudinal axis.
This exemplary pass may then be flanked by layers of balloon
material wrapped at dissimilar angles in relation to the
longitudinal axis, thus defining the boundary of the pass.
[0023] A pass of balloon material may be oriented helically,
radially or longitudinally. By layers of balloon material it is
meant to include pieces, threads, layers, filaments, membranes, or
sheets of suitable balloon material. In helically oriented layers,
the material is oriented so to form a balanced force angle in
relation to each other upon inflation. The layers may further be
wound upon themselves in subsequent passes. A balanced force
balloon of the present invention is a balloon possessing a
combination of passes to create the strength to balance the radial
force exerted by inflation pressures on the balloon vessel with
respect to the longitudinal forces exerted by inflation so that the
balloon inflates to its desired diameter without any longitudinal
movement. One method of achieving a balanced-force-angle balloon is
to orient the helical layers to approach the geometrically derived
neutral angle value of 54.7 degrees. This neutral angle is derived
from balancing the forces in a thin walled pressure vessel where:
2.times.Axial stress=Hoop stress. The inflatable balloon of the
present invention exhibits both essentially radial symmetry upon
inflation and non-foreshortening. Radial symmetry is exhibited upon
inflation as the movement of the balloon material away from the
center point of the lumen in a direct radial fashion so that the
balloon maintains a relatively radial outward movement which
resists twisting of the balloon surface as the balloon inflates. By
non-foreshortening it is meant that the length of the balloon does
not change by more than ten percent upon inflation to a rated burst
pressure. In preferred applications, the balloon does not change
length by more than 5 percent upon inflation to a rated burst
pressure. In further preferred applications, the balloon does not
change length by more than 2 percent upon inflation to a rated
burst pressure. A radial symmetry upon inflation allows the balloon
to exhibit an equal hydrostatic force on a vessel wall in clinical
use. When used with a stent or stent graft, an equal hydrostatic
force allows uniform deployment capability. Uniform stent
deployment is preferred so that less trauma is inflicted on the
vessels and more efficient vessel scaffolding is achieved, as
compared to other types of deployment.
[0024] In one embodiment as shown in FIG. 1, an inflatable device
of the present invention comprises a catheter shaft 18 having a
longitudinal axis and an inflatable balloon 9 affixed to the shaft,
the balloon has an un-inflated length which remains relatively
unchanged as the balloon is inflated and comprises at least two
helical wrap passes of a balloon material 6. The at least two
passes may be fused together. The balloon has a working length 15,
shoulders 14, and wrapped balloon material 6 on the legs 50 of the
balloon. As shown in FIG. 2, the balloon material 6 comprises a
porous reinforcing polymer 1 and a polymer coating 2. The polymer
coating is imbibed into the porous reinforcing polymer to form a
continuous polymer layer 12. The porous reinforcing polymer may
comprise a fibrous reinforcement, a porous membrane such as, a
polyolefin, a fluoropolymer, a discontinuous phase of a polymer, or
an oriented microporous reinforcement, such as ePTFE. In the
present invention it is desirable to use expanded PTFE (ePTFE) as a
porous reinforcing polymer, allowing the balloon material to
realize a matrix tensile value in one direction greater than 690
megapascals; or preferably greater than 960 megapascals; more
preferably greater than 1,200 megapascals.
[0025] The oriented microporous reinforcement may be a
fluoropolymer, a polyamide, a polyurethane, a polyester, a PEEK, a
reinforced polymer, or any other suitable materials or combination
of materials. The polymer coating 2 is imbibed throughout the
porous reinforcing polymer and may comprise a fluoropolymer, an
elastomer, a urethane, a silicone, a styrene block copolymer, a
fluoro-elastomer, a bioresorbable material or any other suitable
polymer. As further shown in FIG. 1, the balloon comprises a
working length 15 between two shoulders 14 of the balloon. In a
preferred embodiment, the balloon comprises at least one hoop pass
wrapped over the working length and a shoulder pass having a
thickness ratio between the hoop layer and the shoulder layer of
2:1. The balloon material layers forming the individual passes may
be heated or set in position relative to each other after each
pass.
[0026] Typical low angle wrapped balloons tend to foreshorten as
they inflate and the wrap angle rotates towards the neutral angle.
Less obvious is that the wrap layers also strain perpendicular to
the wrap angle during the rotation caused by inflation. The growth
in the wrap layer width follows this geometrically derived
equation: (Width.sub.F=Width.sub.I.times.(cos .theta..sub.F/cos
.theta..sub.I).sup.2.times.(tan .theta..sub.F/tan .theta..sub.I)
where F is final and I is initial, and .theta. is the angle of the
helical wrap relative to the longitudinal axis of the balloon. This
strain can exceed 500 percent in some balloons depending on the
deflated to inflated ratio. Highly anisotropic materials are
necessary to allow this perpendicular stain. The wrap layers when
configured in accordance with the present invention, reset a low
angle wrapped balloon at or near a balanced force angle which
prevents the layers from incurring transverse strain in subsequent
balloon inflations. Additionally, the balloon exhibits essentially
radial symmetry upon inflation. The balloon is wrapped by winding
layers at opposing directions to one another until a desired
thickness is obtained. The balloon material passes may be comprised
of the same materials or different materials. While the thickness
of the materials may vary, for vascular use it is advantageous to
use balloon material that is about 4-6 micrometers thick.
[0027] As shown in FIGS. 2 and 3, a balloon material comprising a
polymer layer 2 is coated on the porous reinforcement polymer 1
allowing the polymer coating to fill the void spaces of the porous
reinforcement polymer 1. The polymer layer 2 may desirably fill the
void spaces in the porous reinforcement polymer 1 to form a filled
polymer layer 12. The polymer layer 2 may be formed on one side of
the porous reinforcing polymer 1 (FIG. 2) or on both sides of the
porous reinforcing polymer 1 (FIG. 3). The composite film 3 may
further comprise a filler. The filler may provide benefits such as
radio opaque marking or therapeutic value. The balloon material may
be cut into more narrow widths if necessary to form wrapping layers
used in the balloon. An anisotropic material is used as a wrap
layer in balloon passes consisting of wrap layer angles of less
than about 55 degrees. However, if an overwrap pass is employed it
may comprise isotropic or anisotropic material depending on desired
applications.
[0028] The composite film 3 of the present invention comprises a
porous reinforcing layer and a continuous polymer layer as depicted
in FIGS. 2 and 3. The porous reinforcing polymer layer 1 is
preferably a thin strong porous membrane that can be made in sheet
form. The porous reinforcing polymer can be selected from a group
of polymers including but not limited to: olefin, PEEK, polyamide,
polyurethane, polyester, polyethylene, and polytetrafluoroethylene.
In a preferred embodiment the porous reinforcing polymer is
expanded polytetrafluoroethylene (ePTFE) made in accordance with
the general teachings of U.S. Pat. No. 5,476,589 and U.S. patent
application Ser. No. 11/334,243. In this preferred embodiment, the
ePTFE membrane is anisotropic such that it is highly oriented in
the one direction. An ePTFE membrane with a matrix tensile value
(matrix tensile stress or MTS) in one direction of greater than 690
megapascals is preferred, and greater than 960 megapascals is even
more preferred, and greater than 1,200 megapascals is most
preferred. The exceptionally high MTS of ePTFE membrane allows the
composite material to withstand very high hoop stress in the
inflated balloon configuration. In addition, the high matrix
tensile value of the ePTFE membrane makes it possible for very thin
layers to be used which reduces the deflated balloon profile. A
small profile is necessary for the balloon to be able to be
positioned in small arteries or veins or orifices. In order for
balloons to be positioned in some areas of the body, the balloon
catheter must be able to move through a small bend radius, and a
thinner walled tube is typically much more supple and capable of
bending in this manner without creasing or causing damage to the
wall of the vessel.
[0029] The continuous polymer layer 2 of the present invention is
coated onto at least one side of the porous reinforcing polymer 1
as depicted in FIGS. 2 & 3. The continuous polymer layer is
preferably an elastomer, such as but not limited to, aromatic and
aliphatic polyurethanes including copolymers, styrene block
copolymers, silicones, preferably thermoplastic silicones,
fluoro-silicones, fluoroelastomer, THV and latex. In one embodiment
of the present invention, the continuous polymer layer 2 is coated
onto only one side of the porous reinforcing polymer 1, as shown in
FIG. 2. As depicted in FIG. 3, the continuous polymer layer 2 is
coated onto both sides of the porous reinforcing polymer 1. In one
aspect, the continuous polymer layer 2 is imbibed into the porous
reinforcing polymer 1 and the imbibed polymer 2 fills the pores of
the porous reinforcing polymer 1 to form a composite 12.
[0030] The continuous polymer layer can be applied to the porous
reinforcing polymer through any number of conventional methods
including but not limited to, lamination, transfer roll coating,
wire-wound bar coating, reverse roll coating, and solution coating
or solution imbibing. In a preferred embodiment, the continuous
polymer layer is solution imbibed into the porous reinforcing
polymer. In this embodiment, the continuous polymer layer polymer
is dissolved in a suitable solvent and coated onto and throughout
the porous reinforcing polymer using a wire-wound rod process. The
coated porous reinforcing polymer is then passed through a solvent
oven and the solvent is removed leaving a continuous polymer layer
coated onto and throughout the porous reinforcing polymer. In some
cases, such as when silicone is used as the continuous polymer
layer, the coated porous reinforcing polymer may not require the
removal of solvent. In another embodiment, the continuous polymer
layer is coated onto at least one side of the porous reinforcing
polymer and maintained in a "green" state where it can be
subsequently cured. For example, an ultraviolet light (UV) curable
urethane may be used as the continuous polymer layer and coated
onto the porous reinforcing polymer. The composite film comprising
the porous reinforcing polymer and the UV curable urethane
continuous polymer layer can then be wrapped to form at least one
layer of the balloon and subsequently exposed to UV light and
cured.
[0031] In another aspect of this invention, the helically wrapped
passes of balloon material are bonded to each other. A preferred
bonding technique is heat although other types of bonding may be
used. The balloon material is then annealed in the inflated state
through the application of heat to reset the low angle wrap balloon
perform at or near a balanced force angle.
[0032] As shown in FIGS. 4 and 5, the first balloon material 6 may
be wrapped around a core wire 4. The core wire 4 may be coated with
a release agent 5, such as an FEP coating or other suitable agent.
The helical wrap layers are first laid across the longitudinal axis
in one direction or pass. A second pass lays another helical wrap
layer in the opposing direction. Both passes 6 are oriented at an
angle of less than or equal to about 55 degrees with respect to the
longitudinal axis but in opposing directions. FIG. 5 shows that
non-distensible layers 7 may be present to form non-distensible
regions 8. The helically wrap layers of a first balloon material
pass may be bonded to a second balloon material pass through the
application of heat, or another suitable bonding technique. These
balloon preforms are wrapped at a low angle to facilitate sealing
to a catheter shaft. The distensible region of the preform is then
inflated and the helical wrapped layers of the first material are
reset at a balanced force angle through heating, solvating,
annealing, or through a second material added while in the inflated
state. The second material may be comprised of the same or
different materials as the first material.
[0033] In one preferred embodiment as shown in FIGS. 6 and 8, a
balloon material 6 is wrapped into at least two passes to form a
balloon preform and then is fused and inflated to form the shape of
a catheter balloon. The balloon material 6 is then held at balanced
force angle by second balloon material layer 11 which is cigarette
wrapped around the first balloon material at an angle greater than
54 degrees relative to the longitudinal axis of the catheter
balloon. It is preferred that two ends of the second balloon
material overlap to form a longitudinally oriented seam 13, as
shown in FIG. 8.
[0034] In another preferred embodiment as shown in FIGS. 7 and 9, a
balloon material 6 is wrapped into a low angle balloon preform. The
balloon is inflated in an inflation mold 10 as shown in FIG. 9. The
inflation mold 10 is of a desired shape to form a catheter balloon
which is then held at balanced force angle by second pass of
balloon material 11 that is helically wrapped around the molded
catheter balloon at an angle greater than 54 degrees but not
greater than 90 degrees relative to the longitudinal axis of the
catheter balloon. A non-distensible region 8 may be included in the
balloon as shown in FIGS. 5, 7, and 9. The non-distending regions 8
are focal regions which are more resistant to radial dilatation
allowing for reduction of load or sealing of an inflated balloon to
an underlying catheter shaft. A non-distending region 8 comprises a
plurality of non-distensible layers 7 which wind around the balloon
material 6 and overlap to form an angle of between 0 degrees to 90
degrees relative to the longitudinal axis of the balloon. The
non-distending regions 8 are incorporated or integrated into the
surface of the balloon wall, into the balloon wall, or under the
outer most surface of the balloon wall. The non-distending regions
8 are in direct continuity with the balloon wall and are virtually
indistinguishable in form from the balloon wall in an un-inflated
state.
[0035] The second balloon material 11 may be isotropic, having a
relatively equal strength in all directions or anisotropic having
an oriented longitudinal strength.
[0036] The balloons of the present invention expand from a
low-profile delivery configuration to an inflated configuration in
a uniform concentric manner over substantially its entire working
length. The present invention is applicable for use with
non-compliant or semi-compliant balloons.
[0037] In another embodiment, the inventive balloon comprises a
balloon material 6 wrapped into a low angle preform and inflated to
form the shape of a catheter balloon which is then further wrapped
and held at a balanced force angle by a pass or passes of second
balloon material oriented at an angle greater than 54 degrees with
respect to the longitudinal balloon axis. It is desirable to orient
the second balloon material helically in direction of the maximum
hoop stress to create a high pressure balloon. It is desirable to
use ePTFE as the porous reinforcing polymer in the composite film
of a balloon layer to achieve a maximum hoop stress of the
helically wrapped layers in greater than 400 megapascals. Even more
desirable is achieving a maximum hoop stress of the helically
wrapped layers in greater than 600 megapascals.
[0038] The balloon materials may comprise a filler if desired to
alleviate leakage of the membrane or to deliver therapeutic agents.
The filler may be radio opaque or provide therapeutic value. The
balloon may further comprise one or more integral non-distending
regions, as described above. An integral non-distending region may
be located between two or more layers of balloon material or
located on the surface of a balloon material 6 to form a
non-distending region 8 (see FIGS. 5 and 10). FIG. 10 shows a core
wire 4 with a release agent 5, a balloon material 6 and a surface
mounted non-distensible layer 7 forming a seal. The non-distending
region, as depicted in FIG. 5, is formed by changing the wrapping
angle of the balloon material layers to create a build up of
non-distending passes. The non-distending passes overlap each other
either wholly or partially to form one or more non-distending
regions 8 on the wrapped distensible balloon. The non-distending
regions 8 are significantly less compliant under distention force
than a distensible main body of the balloon. The non-distending
region may comprise the same material as a distensible balloon
material 6 or a different material. It is preferable that the
non-distending region 8 undergoes little or no change in radial
diameter upon introduction of distention force.
[0039] The present invention further contemplates that a balloon
catheter comprising a catheter shaft with a longitudinal axis and
an inflatable balloon of the present invention affixed to the
shaft. A catheter balloon of the present invention may be used in
conjunction with a stent. When at least the second balloon material
exhibits a low modulus, the balloon material is able to pillow into
the stent interstices. Thus, the pillow areas which fill in the
interstices of a stent provide stent embedment prior to stent
delivery. In this manner the stent is embedded without the use of
heat, and without balloon inflation.
[0040] A method of creating a non-shortening catheter balloon with
increased burst pressures is also provided, comprising wrapping a
wire core with a plurality of balloon material layers or pieces at
a angle of between 3 and 54 degrees relative to the longitudinal
axis of the balloon to form a balloon preform; exposing the
plurality of balloon material layers to heat to bond them together;
removing the core; and then further exposing the balloon preform to
internal pressure at a reflow temperature. The reflow temperature
is the temperature to soften or a melt point for the film or
imbibing material; and inflating the balloon preform into a balloon
as it is continued to be exposed to said internal pressure at an
increased temperature. At this point if desired the balloon may be
wrapped with a second balloon material layer at a high angle of
between 54 and 90 degrees. The second balloon material may be fused
to the inflated balloon by the application of heat or other desired
bonding technique. The balloon is then removed from exposure to
reflow temperature and internal pressure to create a non-shortening
balloon. When a second balloon material is used it may be fused to
the inflated balloon by the application of heat or other desired
bonding technique. Further, an inflation mold may be used to
inflate the balloon using heat and pressure so that a desired
balloon shape results prior to passing the second balloon material
layer. The second balloon material may be cigarette wrapped or
helically wrapped.
[0041] A yet further embodiment of creating a non-shortening
catheter balloon with increased burst pressures is also provided,
comprising wrapping a mandrel with a plurality of anisotropic first
balloon material layers at a low angle of between 3 and 54 degrees
relative to the longitudinal axis to form a balloon preform, these
first balloon layers may be oriented in opposing directions
relative to the longitudinal balloon axis; exposing the plurality
of balloon material layers to heat to bond them together creating a
preform; placing the balloon preform in a mold and exposing the
balloon preform to internal pressure; inflating the balloon preform
as it is continued to be exposed to said internal pressure creating
a balloon; and removing the balloon from the mold; and wrapping the
inflated balloon with a second balloon material layer at an angle
between 54 and 90 degrees to form a high pressure catheter balloon.
The second balloon material may be isotropic or anisotropic. The
mandrel may be a wire or any other suitable core material to
provide a hollow body upon removal from the balloon material. In
this method a balloon may be created with the addition of heat and
pressure so that no mold is needed. Alternatively, as heat and
pressure are added, the balloon may be inflated into a mold.
[0042] Additionally, it may be desirable in some shaped balloons to
have a catheter shaft comprising a reinforced inner member located
adjacent to the longitudinal axis of the balloon and between the
shaft and the balloon wherein the reinforced inner member is
modulated to compensate for shape shifting or pressure changes in
the balloon so as to prevent movement of the catheter balloon upon
inflation. The catheter shaft may also comprise an expandable
pleated shaft section located adjacent to the longitudinal axis of
the balloon wherein the expandable pleated shaft section is formed
to compensate for movement or shifting in the balloon upon
inflation. To increase the bonding of the seals of the shaped
balloon, a catheter shaft comprising an outer seal dimension having
both convex portions and concave portions which provide an
increased surface area and increased seal strength when attached to
the balloon ends.
[0043] The following examples are provided to illustrate the
present invention. While particular embodiments of the present
invention have been illustrated and described herein, the present
invention should not be limited to such illustrations and
descriptions. It should be apparent that changes and modifications
may be incorporated and embodied as part of the present invention
within the scope of the following claims and examples.
EXAMPLES
Example 1
[0044] The ePTFE membrane used to make the composite film was made
in accordance with the teaching in U.S. Pat. No. 5,476,589 to
Bacino. Specifically, the ePTFE membrane was longitudinally
expanded to a ratio of 55 to 1 and transversely expanded
approximately 2.25 to 1, to produce a thin strong membrane with
fibrils oriented substantially in the longitudinal direction, and a
mass of approximately 3.5 g/m 2 and a thickness of approximately
6.5 micrometers.
[0045] The composite film was made by using a saturation coating
process whereby a solution of Tecothane TT-1085A polyurethane and
tetrahydrofuran (THF) was coated onto the ePTFE membrane using a
wire-wound rod coating process. A 3% to 8% by weight solution of
Tecothane TT-1085A polyurethane in THF was saturation coated onto
the ePTFE membrane to produce a composite film with approximately
equal amounts of Tecothane TT-1085A polyurethane on either side of
the ePTFE membrane and a total polymer weight application of
approximately 50% to 60% of the total final composite film
weight.
Example 2
[0046] A mechanically balanced composite film was made by using a
wire-wound rod coating process whereby a solution of Tecothane
TT-1085A polyurethane and tetrahydrofuran (THF) was coated onto an
ePTFE membrane. The ePTFE membrane used to make the composite film
was made in accordance with the teachings of U.S. patent
application Ser. No. 11/334,243. Specifically, the ePTFE membrane
was longitudinally expanded to a ratio of 15 to 1 and transversely
expanded approximately 28 to 1, to produce a thin strong membrane
with a mass of approximately 3.5 g/m.sup.2 and a thickness of
approximately 8 micrometers. A 3% to 8% by weight solution of
Tecothane TT-1085A polyurethane in THF was coated onto the ePTFE
membrane to produce a composite film with Tecothane TT-1085A
polyurethane on one side of the ePTFE membrane and throughout the
ePTFE membrane, and a total polymer weight application of
approximately 40% to 60% of the total final composite film
weight.
Example 3
[0047] A mechanically balanced composite film was made by using a
saturation coating process whereby a solution of Tecothane TT-1085A
polyurethane and tetrahydrofuran (THF) was coated onto an ePTFE
membrane using a wire-wound rod coating process. The ePTFE membrane
used to make the composite film was made in accordance with the
teachings in Example (2). Specifically, the ePTFE membrane was
longitudinally expanded to a ratio of 15 to 1 and transversely
expanded approximately 28 to 1, to produce a thin strong membrane
with an mass of approximately 3.1 g/m.sup.2 and a thickness of
approximately 8 micrometers. A 3% to 8% by weight solution of
Tecothane TT-1085A polyurethane in THF was saturation coated onto
the ePTFE membrane to produce a composite film with approximately
equal amounts of Tecothane TT-1085A polyurethane on either side of
the ePTFE membrane and a total polymer weight application of
approximately 40% to 50% of the total final composite film
weight.
Example 4
[0048] The composite balloons of the present invention were
evaluated on an inflation tester (Interface Associates model
PT3070, Laguna Nigel, Calif.). The inflation tester was filled with
distilled, de-ionized water. A balloon was connected to the
inflation tester and equilibrated in a water circulation bath
(Polyscience Model 210, Niles, Ill.) at 37 C for 5 minutes. The
balloons were cycled three times to 5 atmospheres of pressure at a
rate of 6 atmospheres per minute, held at 5 atmospheres of pressure
for 10 seconds, and then ramped back down at 6 atmospheres per
minute. After cycling the pressure was increased in increments of 1
atmosphere every 10 seconds. The diameter was recorded at each
pressure increment with a laser micrometer (Keyence Model LS-7501,
Woodcliff Lake, N.J.). The length was manually measured with a
micrometer (Mitutoyo Absolute Digimatic 500-196, Aurora, Ill.)
several times during the pressure ramp, and the pressure value was
recorded for each length measurement taken.
Example 5
[0049] The inflatable balloon of the present invention was made by
wrapping a composite film of Tecothane TT-1085A polyurethane
(Thermedics, Inc, Woburn, Mass.), and ePTFE membrane, as described
in Example 1, over a FEP coated silver plated copper wire (Putnam
Plastics LLC, Dayville, Conn.).
[0050] The 0.394 mm diameter wire core was deadsoft copper with
silver plating and a 0.2 mm fluorinated ethylene-propylene (FEP)
coating.
[0051] The composite film was slit to 5 mm wide and wrapped around
the wire at a 4 to 5 degree angle from the longitudinal axis of the
wire. The wrapped wire was heated for approximately 5 to 30 seconds
at 180 C after wrapping. The wire was then wrapped with the
composite film in the opposite direction at a 4 to 5 degree angle
from the longitudinal axis of the wire and subsequently heated for
approximately 5 to 30 seconds at 180 C. The process of wrapping the
wire in opposite directions and heating after each pass was
repeated until a total of four passes of wrapping was complete. The
wrapped wire was wrapped around a pin frame with approximately 30
cm spaces between pins and approximately 180 degrees of wrap around
each pin and tied at the ends before being placed into an oven and
heated for approximately 30 minutes at 150 C, removed, and
permitted to cool to ambient.
Example 6
[0052] From the balloon detailed in Example 5, approximately a 2.54
cm section of the composite hollow balloon tube was removed from
either end of a longer section of the balloon. The exposed ends of
the wire were clamped with hemostats and pulled by hand until the
wire had been stretched approximately 5 cm, at which point it was
removed from the center of the tube. The plastic FEP coating was
removed in a similar fashion, but was stretched approximately 50 cm
before it was removed from the balloon.
[0053] The hollow balloon was clamped on one side with a hemostat,
and Monoject blunt needle with Aluminum luer lock hub (model
#8881-202389, Sherwood Medical, St. Louis Mo.) was inserted
approximately 2 cm into the open end of the balloon. The hemostatic
valve was tightened to seal the balloon, and was then attached to a
Balloon Development Station #210A (Beahm Designs, Inc., Campbell,
Calif.) with nozzle airflow is set to 25-30 units, temperature to
140 C, air pressure to 2.0 atmospheres.
[0054] A piece of composite film as described in Example 1 was cut
to 22 mm by 47 mm in the longitudinal and transverse directions
respectively. The composite film was positioned with the
longitudinal axis to run around the circumference of the balloon
and the edge running along the length of the balloon was lightly
tacked to the balloon by gently touching a Weller EC1002 solder
iron (Cooper Industries, Inc. Raleigh, N.C.) using a Apollo Seiko
power source (Model PPM, Apollo Seiko, Inc. Chatsworth, Calif.).
The balloon was then allowed to cool for approximately 10 seconds
and the pressure was increased to approximately 4.0 atmospheres.
The composite film was then carefully wrapped around the inflated
balloon in a cigarette fashion. The section of the composite film
that protruded from the ends of the inflated balloon were pressed
and twisted gently around the shoulder of the balloon. A second
piece of composite film was cut 12 mm by 47 mm in the transverse
and longitudinal direction respectively. The composite film was
positioned with the transverse axis to run around the circumference
of the balloon and the edge running along the length of the balloon
was lightly tacked to the balloon as described above. The section
of the composite film that protruded from the ends of the inflated
balloon were pressed and twisted gently around the shoulder of the
balloon.
[0055] A 7 mm wide by 50 mm long strip of composite film was
wrapped snuggly around either end of the shoulders. The entire
balloon was then subjected to the heat zone of the heat box at 140
C for about 1 minute while maintaining approximately 4.0
atmospheres of pressure. Any visual imperfection such as a wrinkle
was pressed down by hand from the outside while the balloon was
still hot and pressurized from the inside.
[0056] Using a Monoject blunt needle with AI Luer Lock Hub (Model
8881-202389, Sherwood Medical, St. Louis, Mo.), the wrapped balloon
was subjected to an internal pressure of approximately 5.4
atmospheres at room temperature for 0.5-2.0 hours, and was
subsequently removed from the pressure and cut to size by slicing
both uninflated ends to their desired length.
Example 7
[0057] A 30.5 cm long section of the composite balloon as described
in Example 5 was cut and mounted onto a wrapper consisting of two
chuck ends capable of clamping to the ends of the wire and a means
for rotating the wire at variable speed. The balanced composite
film as described in Example 2 was slit into a 6.35 mm wide strip
and six layers were wrapped over the balloon in two locations
leaving a 33 mm wide section between the over-wrapped areas. These
over-wrapped regions or non-distensible seals were used to
terminate the inflated balloon region. The over-wrapped balloon was
then heated in a convection oven at 150.degree. C. for 30 minutes
unrestrained and subsequently removed from the oven and allowed to
cool to room temperature.
[0058] The wire and the FEP coating over the wire were removed from
the balloon over wire construction. Approximately a 2.54 cm section
of the composite hollow balloon tube was removed from either end of
a 30.5 cm long section of the balloon. The exposed ends of the wire
were clamped with hemostats and pulled by hand until the wire had
been stretched approximately 5 cm, at which point it was removed
from the center of the tube. The plastic FEP coating was removed in
a similar fashion, but was stretched approximately 50 cm before it
was removed from the balloon.
[0059] The composite hollow balloon was then connected to an Encore
26 inflation device (Boston Scientific Scimed, Maple Grove, Minn.,
Catalog #15-105). The balloon was located in a 2.0 mm diameter
polycarbonate mold and pressurized to 10 atmospheres and held at
pressure for 5 minutes. The balloon was deflated, removed from the
2.0 mm diameter mold and positioned in a 2.5 mm diameter
polycarbonate mold and re-inflated to 10 atmospheres and held for 5
minutes. The process of inflating the balloon in the mold provided
a more uniform surface on the balloon.
[0060] The composite balloon was then mounted onto a small gauge
needle and connected to a rotary union (Dynamic Sealing
Technologies, Inc, Ham Lake, Minn.), and the other end was
connected to the rotating end of the wrapper described above. The
balloon was inflated through the rotary union using the Encore 26
inflation device to 10 atmospheres with water. The composite film
described was slit to approximately 7.6 mm and was used as the
second balloon material layer wrapping. The slit composite film was
helically wound around the inflated balloon at approximately 75 to
85 degrees relative to the longitudinal axis of the balloon. The
process of wrapping the balloon was repeated at the same angle but
in the opposite direction.
[0061] Using a Weller WSD81 solder gun unit (Cooper Industries,
Inc. Raleigh, N.C.), equipped with a large blunt solder tip set to
a 250 set-point, the second balloon material layer wrapping was
fused to the first balloon material layer wrapping. The solder tip
was pressed lightly against the surface of the balloon while the
balloon rotated at 20 rpm, and was slowly traversed along the
length of the inflated balloon. The rotation of the balloon was
stopped and the solder tip was then pressed lightly against the
surface of the inflated balloon and traversed along the length of
the balloon at four locations each 90 degrees around the
circumference of the balloon. Pressure was relieved and balloon
removed from rotary union chucks and trimmed to final length.
[0062] This procedure produced a non-shortening wrapped balloon
that when inflated to 10 or more atmospheres of pressure created a
3.0 mm diameter and 25 mm long balloon between the non-distensible
over-wrapped regions.
Example 8
[0063] The core wire and the FEP coating over the core wire were
removed from the composite balloon over wire construction described
in Example 5.
[0064] Approximately a 2.54 cm long section of the composite hollow
balloon tube was removed from either end of a 30.5 cm long section
of the balloon over wire construction. The exposed ends of the wire
were clamped with hemostats and pulled by hand until the wire had
been stretched approximately 5 cm, at which point it was removed
from the center of the tube. The plastic FEP coating was removed in
a similar fashion, but was stretched approximately 50 cm before it
was removed from the balloon. A composite hollow balloon tube was
produced with a first layer wrapping material at a low (4 to 5
degree) angle of wrap.
[0065] A 15.25 cm long section of the composite hollow balloon tube
was tied into a knot and clamped with a hemostat on one end. The
opposite end was slipped through a Qosina male touhy borst with
spin lock fitting (#80343, Qosina Corporation, Edgewood, N.Y.), and
a Monoject blunt needle with Aluminum luer lock hub (model
#8881-202389, Sherwood Medical, St. Louis Mo.) was inserted
approximately 2.0 cm into the balloon. The hemostatic valve was
tightened to seal the balloon, and was then attached to a Balloon
Development Station Model 210A (Beahm Designs, Inc., Campbell,
Calif.). The nozzle airflow was set to 25-30 units and the
temperature was set to 140 C, air pressure to 2.58 atmospheres. The
air pressure was turned on, the center 40 mm long region to be
inflated, was subjected to heat for about 2-3 minutes resulting in
a balloon with a diameter of 2.85 mm and a length of. The diameter
was checked with a Mitutoyo Laser Scan Micrometer Model LSM-3100
(Mitutoyo America Corp, Aurora, Ill.) while in the inflated state.
The resulting balloon had a diameter of 2.85 mm and an inflated
length of 27 mm.
[0066] Using an Monoject blunt needle with Aluminum luer lock hub
(model #8881-202389, Sherwood Medical, St. Louis Mo.) dispensing
needle, the balloon was subjected to an internal pressure of 5.44
atmospheres at room temperature for approximately 1 hour. The
Inflation Pressure and length results are shown below.
TABLE-US-00001 A 426-49-3G 4th Cycle Pressure (atm) Length (mm)
Diam (mm) 0 26.38 2.54 0.07 26.15 2.53 1 26.15 2.89 2 24.75 3.04
2.99 24.75 3.05 3.99 24.75 3.05 4.98 24.75 3.04 5.99 24.75 3.03
6.97 25.35 3.04 7.97 25.35 3.08 8.91 24.41 3.17 9.93 25.43 3.27
11.01 25.76 3.42 B 1419-101A-2 4th Cycle Pressure (atm) Length (mm)
Diam (mm) 0 30.04 1.71 0.06 30.05 1.66 0.99 30.3 2.14 1.98 30.51
2.65 2.97 30.58 2.66 3.97 30.58 2.67 4.97 30.12 2.66 5.96 30.12
2.68 6.97 30.12 2.72 7.97 29.93 2.74 8.97 29.93 2.76 9.96 29.75
2.78 10.96 29.75 2.83 11.96 29.49 2.84 12.95 29.32 2.88 13.97 29.19
2.89 14.94 28.92 2.91 15.96 29.92 2.93 16.97 29.16 2.95 17.95 28.93
3 18.91 28.93 3.03 19.93 28.93 3.05 20.92 28.93 3.07 21.96 28.93
3.1 22.92 29.02 3.18 C 1419-102-6B 4th Cycle Pressure (atm) Length
(mm) Diam (mm) 0 25.64 2.72 0.06 25.57 2.72 0.99 25.57 2.88 1.98
25.57 2.91 2.97 25.57 2.91 3.97 25.57 2.92 4.96 25.57 2.93 5.97
25.57 2.95 6.96 25.57 2.95 7.94 25.57 2.96 8.95 25.69 2.97 9.96
26.06 2.98 10.95 26.06 3 11.94 26.06 3.02 12.93 26.06 3.02 13.92
26.08 3.04 14.9 26.39 3.06 15.89 26.4 3.1 16.9 26.39 3.11 17.8
26.39 3.17
Example 9
[0067] Tensile break load was measured using in INSTRON 1122
tensile test machine equipped with flat-faced grips and a 0.445 kN
load cell. The gauge length was 5.08 cm and the cross-head speed
was 50.8 cm/min. The sample dimensions were 2.54 cm by 15.24 cm.
For longitudinal MTS measurements, the larger dimension of the
sample was oriented in the machine, also known as the down-web
direction. For the transverse MTS measurements, the larger
dimension of the sample was oriented perpendicular to the machine
direction, also known as the cross-web direction. Each sample was
weighed using a Mettler Toledo Scale Model AG204, then the
thickness of the samples was taken using the Kafer FZ1000/30
thickness gauge. The samples were then tested individually on the
tensile tester. Three different sections of each sample were
measured. The average of the three maximum load (i.e., the peak
force) measurements was used. The longitudinal and transverse MTS
were calculated using the following equation:
MTS(psi)=(maximum load/cross-section area)*(bulk
density(PTFE))/density of the porous membrane), wherein the bulk
density of PTFE is taken to be 2.2 g/cc.
* * * * *