U.S. patent application number 10/013633 was filed with the patent office on 2002-06-27 for laminate catheter balloons with additive burst strength and methods for preparation of same.
Invention is credited to Chen, Jiahua, Lee, Nao, Wang, Lixiao.
Application Number | 20020081406 10/013633 |
Document ID | / |
Family ID | 24449941 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020081406 |
Kind Code |
A1 |
Wang, Lixiao ; et
al. |
June 27, 2002 |
Laminate catheter balloons with additive burst strength and methods
for preparation of same
Abstract
A laminate balloon comprising at least two layers of separately
oriented thermoplastic polymer material, which are coextensive over
the body of the balloon. The two layers may be made of different
polymer materials, including an underlying layer made of a low
compliant, high strength polymer, such as PET, and an overlying
layer of a softer and more flexible polymer material relative to
the first polymer material, such as a polyester-polyether block
copolymer. The balloon structures have an additive burst pressure,
meaning that they are stronger than a single-layer reference
balloon corresponding to the underlying polymer layer. The balloons
are characterized by a combination of flexibility and surface
softness which allows catheters to track down into lesions
relatively easily, puncture resistance, abrasion resistance and
refoldability, in addition to low compliance and high burst
strength. The balloons may be prepared with generally linear or
with stepped compliance profiles. Methods of preparation of such
balloons are also disclosed.
Inventors: |
Wang, Lixiao; (Long Lake,
MN) ; Chen, Jiahua; (Plymouth, MN) ; Lee,
Nao; (Brooklyn Park, MN) |
Correspondence
Address: |
VIDAS, ARRETT & STEINKRAUS, P.A.
6109 BLUE CIRCLE DRIVE
SUITE 2000
MINNETONKA
MN
55343-9185
US
|
Family ID: |
24449941 |
Appl. No.: |
10/013633 |
Filed: |
December 10, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10013633 |
Dec 10, 2001 |
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09670074 |
Sep 26, 2000 |
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6328925 |
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09670074 |
Sep 26, 2000 |
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08611664 |
Mar 6, 1996 |
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6124007 |
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Current U.S.
Class: |
428/35.2 ;
428/212 |
Current CPC
Class: |
B29K 2995/005 20130101;
B32B 27/281 20130101; B32B 2535/00 20130101; B32B 2379/08 20130101;
B32B 27/285 20130101; Y10T 428/24942 20150115; B32B 27/08 20130101;
B32B 2038/0028 20130101; Y10T 428/1393 20150115; B32B 7/022
20190101; B32B 2367/00 20130101; B29C 2949/08 20220501; Y10S 428/91
20130101; B32B 2377/00 20130101; B32B 27/40 20130101; B32B 2375/00
20130101; A61M 25/1029 20130101; B32B 2371/00 20130101; B29C 49/24
20130101; B29L 2031/7542 20130101; B29K 2105/258 20130101; Y10T
428/1334 20150115; B32B 1/08 20130101; B32B 27/34 20130101; B32B
27/36 20130101 |
Class at
Publication: |
428/35.2 ;
428/212 |
International
Class: |
B32B 001/02 |
Claims
What is claimed is:
1. A process for producing a laminate balloon for mounting on an a
catheter, the process comprising the steps of: a) providing a first
tubing segment of a first polymer material; b) stretching the first
tubing segment at a first stretch ratio to produce a first
stretched tube having an outer diameter; c) providing a second
tubing segment of a second polymer material having an inner
diameter greater than the outer diameter of the first stretched
tube; d) inserting the first stretched tube into the second tubing
segment; e) stretching the second tubing segment at a second
stretch ratio to produce a second stretched tube, the first and
second stretched tubes being brought into direct annular contact
during the stretching of said second tubing segment, to form a
laminate stretched tubing structure; and f) forming the laminate
balloon by pressurizing the laminate stretched tubing structure at
a temperature and pressure above ambient so as to expand the
laminate stretched tubing structure.
2. A process as in claim 1 wherein the first and second polymer
materials are different.
3. A process as in claim 2 wherein the first polymer material is a
low compliant, high strength polymer and the second polymer is a
softer and more flexible polymer material relative to the first
polymer material.
4. A process as in claim 3 wherein the first polymer material is
selected from the group consisting of polyesters, polyamides,
thermoplastic polyimides, liquid crystal polymers and high strength
engineering thermoplastic polyurethanes and the second polymer
material is a thermoplastic elastomer.
5. A process as in claim 4 wherein said thermoplastic elastomer is
a polyester/polyether segmented block copolymer.
6. A process as in claim 1 wherein the first and second stretch
ratios are different.
7. A process as in claim 6 wherein in said balloon forming step (f)
said laminate stretched tubing structure is expanded to a
preselected diameter.
8. A process as in claim 7 wherein said balloon forming step (f) is
performed in a mold.
9. A process as in claim 7 wherein said first and second stretch
ratios are individually selected to produce in said laminate
balloon at least one preselected strength or compliance
characteristic.
10. A process as in claim 9 wherein said first polymer material is
a low compliant, high strength polymer, said second polymer is a
softer and more flexible polymer material relative to the first
polymer material, whereby said laminate balloon comprises an
underlayer of said first polymer and an overlayer of said second
polymer material, said at least one preselected characteristic
includes a laminate balloon burst strength value greater than the
burst strength of a first reference balloon of said first polymer
formed at a wall thickness, a stretch ratio and a hoop expansion
ratio substantially the same as the wall thickness, stretch ratio
and hoop expansion ratio of said laminate balloon underlayer.
11. A process as in claim 10 wherein said laminate balloon burst
strength value exceeds the burst strength of the first reference
balloon by an amount which is at least 50% of the burst strength of
a second reference balloon of said second polymer formed at a wall
thickness, a stretch ratio and a hoop expansion ratio substantially
the same as the wall thickness, stretch ratio and hoop expansion
ratio of said laminate balloon overlayer.
12. A process as in claim 11 wherein said laminate balloon burst
strength value exceeds the burst strength of said first reference
balloon by an amount which is at least 75% of the burst strength of
said second reference balloon.
13. A laminate balloon produced by the process of claim 1.
14. A laminate balloon produced by the process of claim 10.
15. A laminate balloon comprising at least two layers of separately
oriented thermoplastic polymer material, which are coextensive over
the body of the balloon.
16. A laminate balloon as in claim 15 wherein said two layers are
made of different polymer materials.
17. A laminate balloon as in claim 16 a first of said polymer
materials is a low compliant, high strength polymer and a second of
said polymer materials is a softer and more flexible polymer
material relative to the first polymer material.
18. A laminate balloon as in claim 17 comprising a first layer of
said first polymer material and an adjacent second layer of said
second polymer material.
19. A laminate balloon as in claim 18 having a central axis, said
second layer being located outwardly from said central axis
relative to said first layer.
20. A laminate as in claim 18 wherein said second layer defines the
outer surface of the balloon.
21. A laminate balloon as in claim 18 wherein the first polymer
material is selected from the group consisting of polyesters,
polyamides, thermoplastic polyimides, liquid crystal polymers and
high strength engineering thermoplastic polyurethanes and the
second polymer material is a thermoplastic elastomer.
22. A laminate balloon as in claim 21 wherein said thermoplastic
elastomer is a polyester/polyether segmented block copolymer.
23. A laminate balloon as in claim 19 wherein said balloon has a
burst strength value greater than the burst strength of a first
reference balloon of said first polymer formed at a wall thickness,
a stretch ratio and a hoop expansion ratio substantially the same
as the wall thickness, stretch ratio and hoop expansion ratio of
said first layer.
24. A laminate balloon as in claim 23 wherein said laminate balloon
burst strength value exceeds the burst strength of the first
reference balloon by an amount which is at least 50% of the burst
strength of a second reference balloon of said second polymer
formed at a wall thickness, a stretch ratio and a hoop expansion
ratio substantially the same as the wall thickness, stretch ratio
and hoop expansion ratio of said second layer.
25. A laminate balloon as in claim 24 wherein said laminate balloon
burst strength value exceeds the burst strength of said first
reference balloon by an amount which is at least 75% of the burst
strength of said second reference balloon.
26. A laminate balloon as in claim 15 wherein at least two of said
layers are made of the same polymer material.
27. A laminate balloon as in claim 15 wherein said layers are
sufficiently adherent to each other so that the balloon maintains a
unitary structure at rest.
28. A laminate balloon as in claim 1 5 having a generally linear
compliance curve.
29. A laminate balloon as in claim 15 having a stepped compliance
curve.
30. A process for forming a laminate balloon which includes the
steps of. a) providing a first tubing segment of a first polymer
material; b) stretching the first tubing segment at a first stretch
ratio to produce a first stretched tube; c) blowing the first
stretched tube in a mold to produce a first layer structure, said
first layer structure including waist, cone and body portions, the
waist portion having an inner diameter; c) providing a second
tubing segment of a second polymer material; d) stretching the
second tubing segment at a second stretch ratio to produce a second
stretched tube having an outer diameter less than the inner
diameter of the waist portion of said first layer structure; e)
inserting the second stretched tube into the first layer structure
and f) forming the laminate balloon by pressurizing the second
stretched tube at a temperature and pressure above ambient to
expand the second layer tube, forming a second layer which is in
direct annular contact with the first layer structure.
Description
BACKGROUND OF THE INVENTION
[0001] Balloons mounted on the distal ends of catheters are widely
used in medical treatment. The balloon may be used to widen a
vessel into which the catheter is inserted or to force open a
blocked vessel. The requirements for strength and size of the
balloons vary widely depending on the balloon's intended use and
the vessel size into which the catheter is inserted. Perhaps the
most demanding applications for such balloons are in balloon
angioplasty in which catheters are inserted for long distances into
extremely small vessels and used to open stenoses of blood vessels
by balloon inflation. These applications require extremely thin
walled, high strength, relatively inelastic balloons of predictable
inflation properties. Thin walls are necessary because the
balloon's wall and waist thicknesses limit the minimum diameter of
the distal end of the catheter and therefore determine the limits
on vessel size treatable by the method and the ease of passage of
the catheter through the vascular system. High strength is
necessary because the balloon is used to push open a stenosis and
so the thin wall must not burst under the high internal pressures
necessary to accomplish this task. The balloon must have some
elasticity so that the inflated diameter can be controlled,
enabling the surgeon to vary the balloon's diameter as required to
treat individual lesions, but that elasticity must be relatively
low so that the diameter is easily controllable. Small variations
in pressure must not cause wide variation in diameter.
[0002] The compliance characteristics of angioplasty balloon
materials are described in U.S. Pat. No. 5,447,497, incorporated
herein by reference. A variety of low-compliant materials have been
employed in angioplasty balloons, including polypropylene,
polyimides, polyamides, and polyesters, such as PET and PEN. Such
low compliant materials can generally be fabricated into higher
strength balloons than balloons made of more compliant materials.
The use of low compliant materials, however, has been associated
with a number of minor but undesirable problems, such as poor
refold characteristics, pinhole development, difficulty in bonding
to the catheter structure and high friction coefficient.
[0003] To address some of these problems a number of balloon
structures have been proposed in which a layer of low compliant
polymer material is coated or coextruded with an over or underlying
layer of another polymer material less prone to one or more of the
problems occasionally encountered with low compliant balloons.
Exemplary of this approach are U.S. Pat. No. 5,270,086 (Hamlin),
U.S. Pat. No. 5,195,969 (J. Wang, et al.) and U.S. Pat. No.
5,290,306 (Trotta, et al), which pertain to co-extruded structures
and U.S. Pat. No. 5,490,839 (L. Wang, et. al) which pertains to
coated balloon structures wherein the balloon coating imparts
refold and soft pliable surface characteristics. The balloons of
these references are unitary structures whose compliance and burst
profiles are determined primarily by the non-compliant polymer
layer, with little or no contribution by the second polymer layer.
However, balloons made from coextruded tubes with soft polymer
material on the top layer do provide rewrap, abrasion and puncture
resistance, and reduced tracking resistance.
[0004] It is also known to prepare catheter balloon structures
which include two separate concentrically arranged balloon elements
mounted on a catheter. References which describe such structures
include U.S. Pat. No. 4,608,984, in which an outer balloon element
of a highly elastic material such as latex having a deflated
circumference less than the diameter of the associated catheter is
disclosed for use in refolding the inner working balloon after it
has been inflated and deflated; and U.S. Pat. Nos. 5,447,497,
5,358,487 and 5,342,305, in which a non-linear compliance curve is
obtained from two different sized balloon elements or from use of
an inner balloon which bursts at some pressure below the burst
pressure of the outer element. The dual concentric balloon
structures, are made of materials of quite different strength
characteristics and tend to give balloons whose burst strength is
little different from to the burst strength of the strongest member
element (typically PET or nylon).
SUMMARY OF THE INVENTION
[0005] This invention will provide a linear and noncompliant
balloon expansion curves. In the case both balloons have almost the
same diameters.
[0006] In one aspect the invention comprises a laminate balloon
comprising at least two layers of separately oriented thermoplastic
polymer material, which are coextensive over the body of the
balloon. The two layers are preferably made of different polymer
materials. Suitably, the layers are sufficiently adherent to each
other so that the laminate balloon is a unitary structure even when
the balloon is deflated. Most preferably the balloon has an
underlying layer made of a low compliant, high strength polymer and
an overlying layer of a softer and more flexible polymer material
relative to the first polymer material. The inventive balloon
structures have an additive burst pressure, meaning that they are
stronger than a first single-layer reference balloon corresponding
to the underlying polymer layer. The additive strength of the
balloons of the invention is exhibited typically by burst strengths
greater than the first reference balloon by at least 50%, and
commonly at least 75%, of the strength of a second single-layer
reference balloon corresponding to the overlying relatively soft
flexible polymer layer. Optimal balloons of the invention give
burst strengths which exceed the strength of the first reference
balloon by about 100% or even more of the strength of the second
reference balloon.
[0007] The preferred inventive balloons have good flexibility and
surface softness, allowing catheters to track down into lesions
relatively easily, good puncture resistance, good abrasion
resistance and good refold characteristics, all contributed by the
soft material top layer. Furthermore they also have a low
compliance profile with a burst strength which exceeds the
strongest PET angioplasty balloons currently commercially
available.
[0008] A second aspect of the invention comprises a preferred
method of making a laminate balloon which includes the steps of
[0009] a) providing a first tubing segment of a first polymer
material;
[0010] b) stretching the first tubing segment at a first stretch
ratio to produce a first stretched tube having an outer
diameter;
[0011] c) providing a second tubing segment of a second polymer
material having an inner diameter greater than the outer diameter
of the first stretched tube;
[0012] d) inserting the first stretched tube into the second tubing
segment;
[0013] e) stretching the second tubing segment at a second stretch
ratio to produce a second stretched tube, the first and second
stretched tubes being brought into direct annular contact during
the stretching of said second tubing segment, to form a laminate
stretched tubing structure; and
[0014] f) forming the laminate balloon by pressurizing the laminate
stretched tubing structure at a temperature and pressure above
ambient so as to expand the laminate stretched tubing
structure.
[0015] A still further aspect of the invention is an alternative
process for forming a laminate balloon which includes the steps
of:
[0016] a) providing a first tubing segment of a first polymer
material;
[0017] b) stretching the first tubing segment at a first stretch
ratio to produce a first stretched tube;
[0018] c) blowing the first stretched tube in a mold to produce a
first layer structure, said first layer structure including waist,
cone and body portions, the waist portion having an inner
diameter;
[0019] c) providing a second tubing segment of a second polymer
material;
[0020] d) stretching the second tubing segment at a second stretch
ratio to produce a second stretched tube having an outer diameter
less than the inner diameter of the waist portion of said first
layer structure;
[0021] e) inserting the second stretched tube into the first layer
structure and
[0022] f) forming the laminate balloon by pressurizing the second
stretched tube at a temperature and pressure above ambient to
expand the second layer tube, forming a second layer which is in
direct annular contact with the first layer structure.
[0023] Balloons of the invention ordinarily have generally linear
compliance curves, however, if desired, the balloons can be
provided with stepped compliance curves can be prepared by use of a
post-blowing annealing process to shrink the balloon.
[0024] Further aspects of the invention will become apparent from
the following description, claims and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIGS. 1-5 depict various stages in the preferred process for
forming a balloon of the invention.
[0026] FIG. 1 is a side plan view of a portion of an extruded
tubing segment for use in forming a first layer of the inventive
balloon according to the preferred process of the invention.
[0027] FIG. 2 is a side plan view of the portion of tubing depicted
in FIG. 1 after it has been stretched to form the first stretched
tube.
[0028] FIG. 3 is a cross-sectional view showing the first stretched
tube of FIG. 2 inserted into a second tubing segment.
[0029] FIG. 4 is a cross-sectional view as in FIG. 3 after the
second tubing segment has been stretched down onto the first
stretched tube.
[0030] FIG. 5 is a side sectional view of a balloon of the
invention.
[0031] FIG. 6 is a graph of the compliance curve of a balloon
prepared in accordance with Example 5.
[0032] FIG. 7 is a graph of the compliance curve of a balloon
prepared in accordance with Example 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] In the preferred embodiments the balloon is formed of two
layers of different polymer material, one of which is a low
compliant, high strength thermoplastic polymer and the other of
which is a relatively soft and flexible polymer material. However,
other combinations of polymer materials can also be used, including
dual layers of the same polymer material. Furthermore, balloons of
the invention can also be prepared using more than two laminae
without departing from the principles of the invention hereof.
[0034] The materials used for strong layer are low compliant, high
strength thermoplastic polymers. Suitably the balloon polymer is
poly(ethylene terephthalate) (PET) of initial intrinsic viscosity
of at least 0.5, more preferably 0.7-1.3, as reported by the
polymer manufacturer. Other high strength polyester materials, such
as poly(ethylene napthalenedicarboxylate) (PEN); polyamides such as
nylon 11, nylon 12 and aromatic/aliphatic polyamides; thermoplastic
polyimides; liquid crystal polymers and high strength engineering
thermoplastic polyurethanes such as Isoplast 301 sold by Dow
Chemical Co., are considered suitable alternative materials.
Physical blends and copolymers of such materials may also be used.
Examples of thermoplastic polyimides are described in T. L. St.
Clair and H. D. Burks, "Thermoplastic/Melt-Pro- cessable
Polyimides,"NASA Conf. Pub. #2334 (1984), pp. 337-355. A suitable
thermoplastic polyimide is described in U.S. Pat. No. 5,096,848 and
is available commercially under the tradename Aurum.RTM. from
Mitsui Toatsu Chemicals, Inc., of Tokyo, Japan. Examples of liquid
crystal polymers include the products Vectra.RTM. from Hoechst
Celanese, Rodrun.RTM. from Unitika, LX or HX series polymers from
DuPont and Xydar from Amoco. Suitably the liquid crystal polymer
materials are blended with another thermoplastic polymer such as
PET.
[0035] The soft materials used for soft and flexible layer are
suitably thermoplastic elastomers, especially segmented
polyester/ether block copolymers, such as available under the
trademarks Arnitel.RTM. and Hytrel.RTM.; flexible polyurethanes,
such as sold under the trademark Pellethane.RTM.; and
polyamide/ether block copolymers, such as sold under the Pebax.RTM.
trademark.
[0036] The preferred balloons of the invention are
polyester/polyether segmented block copolymers. Such polymers are
made up of at least two polyester and at least two polyether
segments.
[0037] The polyether segments of the polyester/polyether segmented
block copolymers are aliphatic polyethers having at least 2 and no
more than 10 linear saturated aliphatic carbon atoms between ether
linkages. More preferably the ether segments have 4-6 carbons
between ether linkages, and most preferably they are
poly(tetramethylene ether) segments. Examples of other polyethers
which may be employed in place of the preferred tetramethylene
ether segments include polyethylene glycol, polypropylene glycol,
poly(pentamethylene ether) and poly hexamethylene ether). The
hydrocarbon portions of the polyether may be optionally branched.
An example is the polyether of 2-ethylhexane diol. Generally such
branches will contain no more than two carbon atoms. The molecular
weight of the polyether segments is suitably between about 400 and
2,500, preferably between 650 and 1000.
[0038] The polyester segments are polyesters of an aromatic
dicarboxylic acid and a two to four carbon diol. Suitable
dicarboxylic acids used to prepare the polyester segments of the
polyester/polyether block copolymers are ortho-, meta- or para-
phthalic acid, napthalenedicarboxylic acid or
meta-terphenyl-4,4'-dicarboxylic acids. Preferred
polyester/polyether block copolymers are poly(butylene
terephthalate)-block-poly(tetramethylene oxide) polymers such as
Arnitel EM 740, sold by DSM Engineering Plastics. Hytrel polymers,
sold by DuPont which meet the physical and chemical specifications
set out herein can also be used.
[0039] Polyamide/polyether block copolymers may also be used as the
soft layer polymer. The polyamide/polyether block copolymers are
commonly identified by the acronym PEBA (polyether block amide).
The polyamide and polyether segments of these block copolymers may
be linked through amide linkages, however, most preferred are ester
linked segmented polymers, i.e. polyamide/polyether polyesters.
Such polyamide/polyether/ polyester block copolymers are made by a
molten state polycondensation reaction of a dicarboxylic polyamide
and a polyether diol. The result is a short chain polyester made up
of blocks of polyamide and polyether. The polyamide and polyether
blocks are not miscible. Thus the materials are characterized by a
two phase structure: one is a thermoplastic region that is
primarily polyamide and the other is elastomer region that is rich
in polyether. The polyamide segments are semicrystalline at room
temperature. The generalized chemical formula for these polyester
polymers may be represented by the following formula: 1
[0040] in which PA is a polyamide segment, PE is a polyether
segment and the repeating number n is between 5 and 10.
[0041] The polyamide segments are suitably aliphatic polyamides,
such as nylons 12, 11, 9, 6, 6/12, 6/11, 6/9, or 6 16. Most
preferably they are nylon 12 segments. The polyamide segments may
also be based on aromatic polyamides but in such case significantly
lower compliance characteristics are to be expected. The polyamide
segments are relatively low molecular weight, generally within the
range of 500-8,000, more preferably 2,000-6,000, most preferably
about 3,000-5,000.
[0042] The polyether segments are the same as previously described
for the polyester/polyether segmented block copolymers block
copolymers usefull in the invention.
[0043] The weight ratio of polyamide to polyether in the
polyamide/polyether polyesters used in the invention desirably
should be in the range of 50/50 to 95/S, preferably between 60/30
and 95/5, more preferably, between 70/30 and 92/8.
[0044] Polyamide/polyether polyesters are sold commercially under
the Pebax.RTM. trademark by Atochem North America, Inc.,
Philadelphia Pa. Examples of suitable commercially available
polymers are the Pebax.RTM. 33 series polymers with hardness 60 and
above, Shore D scale, especially Pebax .RTM. 7233, 7033 and 6333.
These polymers are made up of nylon 12 segments and
poly(tetramethylene ether) segments in different weight ratios and
segment lengths.
[0045] It is also possible to use other PEBA polymers with the
physical properties specified herein and obtain similar compliance,
strength and softness characteristics in the finished balloon.
[0046] It is preferred that the block copolymers have a hardness,
Shore D scale, of at least 60 and a flexural modulus of no more
than about 150,000, in order to obtain optimal strength, compliance
and softness characteristics. Preferably the Shore D hardness is in
the range of 65-75 and the flexural modulus is in the range of
50,000-120,000. The preferred polymers useful in the invention are
also characterized by a high ultimate elongation of about 300% or
higher and an ultimate tensile strength of at least 6,000 psi
[0047] The preferred process of forming balloons of the invention
will be described with reference to FIGS. 1-5.
[0048] Referring to FIG. 1 there is shown an extruded tubing
segment 12, preferably made of a strong non-compliant material,
such as PET. The tubing segment 12 is stretched longitudinally,
typically at an elevated temperature, in conventional manner for
PET balloons to produce an elongated stretched tube 13 shown in
FIG. 2. The stretch ratio is one which will provide good strength
properties in the blown balloon. A typical stretch ratio for a PET
material is about 1.5-6 times the length of the original extruded
length. An extruded segment 14 of the second polymer material,
suitably a polyester/polyether block copolymer, is then provided
having an ID greater than the OD of stretched tube 13. Tube 13 is
inserted into tube 14 as shown in FIG. 3. Preferably without
further stretching of the tube 13, tube 14 is stretched to produce
a second stretched tube 15 whose ID is necked down, bringing tube
15 into direct contact with tube 13, as shown in FIG. 4. For the
preferred embodiment a "cold-neck" (i.e. at or below ambient
temperature) stretch at a ratio of 3-6 may be employed for this
step. The composite tubing structure shown in FIG. 4 is then blown
at elevated pressure in a manner conventional for single layer
balloons, for instance by a process as described in WO 95/22367.The
resulting laminate balloon 20, depicted in FIG. 5 has two
intimately contacting layers, the inner layer 16 being PET and the
outer layer 17 being the polyester/polyether block copolymer
material. Although they can easily be pealed apart when the balloon
is dissected, layers 16 and 17 are sufficiently adherent that the
balloon 20 is a unitary structure even when the balloon is deflated
and wrapped onto a catheter.
[0049] By this process, and unlike balloons formed from coextruded
tubing, the layers 16 and 17 of balloon 20 have been formed with
separate stretch ratios applied to the tubes 12 and 14 so that
optimal strength properties can be obtained from both layers.
[0050] Multi-laminate balloon structures having three or more
laminae can be prepared, for instance, by the additional steps of
inserting a composite tubing structure of FIG. 4 into a third
extruded tube which is necked down onto the outer surface of
stretched tube 15 before performing the balloon blowing step.
Structures with higher numbers of laminae can be prepared by
repetition of these additional steps before blowing the balloon.
With such multi-layer laminates it may be desirable to further
stretch the composite structure of FIG. 4 or any successive
composite stretched tubing structure to reduce the thickness of the
composite to be blown and achieve a desired hoop expansion
ratio.
[0051] An alternative, less preferred process for forming a balloon
of the invention is illustrated in Example 9.
[0052] After being blown, the dual element balloon of the invention
may be provided with a stepped compliance curve by annealing the
balloon for a short time after blowing at a pressure at or only
slightly above ambient and at a temperature which causes the blown
balloon to shrink. The process is described in U.S. Pat. No.
5,348,538. However, the balloons of the invention are desirably
constructed with a greater difference between the low pressure and
high pressure linear regions of the compliance curve so that the
transition between the two regions results in a step-up of diameter
of the balloon of at least 0.4 mm. This is accomplished by blowing
the balloon to the larger diameter and then shrinking to a greater
extent than was done in the specific illustrative examples of U.S.
Pat. No. 5,348,538. The amount of shrinkage is controlled by the
pressure maintained in the balloon during annealing and the
temperature and time of the annealing. The annealing pressure is
suitably in the range of 0-20, preferably 5-10 psi at
70-100.degree. C. for 3 seconds to 3 hours.
[0053] The invention is illustrated by the following non-limiting
examples.
EXAMPLE 1
[0054] A PET tube was extruded with an inner diameter of 0.0136
inch and an outer diameter of 0.0288 inch from Traytuf 7357 (Shell
Chemical, Akron) PET resin. The PET tube was stretched to 2.25 x
its original length (2.25 stretch ratio) at 90.degree. C. The
stretched tube was then inserted into a tube of extruded
polyester-polyether block copolymer resin (Amitel EM 740, DSM
Engineering Plastics, Evansville IN) of 0.0260 inch ID and 0.0340
inch OD. The polyester-polyether resin tube was cold necked
(stretched at ambient temperature) at 4.0 stretch ratio over the
PET tube, without further stretching of the PET tube. The resulting
coaxially arranged tube assembly was then inserted into a 3.0 mm
balloon mold and blown. The mold temperature was 97.degree. C. and
the blowing pressure was 350 psi with 30 gms tension applied during
the blowing process. The measured balloon double wall thickness
(i.e. two layers of PET and two layers of polyester-polyether) was
0.00145 inch, corresponding to a single wall thickness (one layer
each of PET and polyester-polyether) of 0.00073 inch. The
compliance curve showed balloon growth from 8 to 18 atm of 2.6%,
and 6.25% from 8 to 28 atm. The balloon burst pressure was 529 psi
(36 atm). When the balloons prepared in this manner were dissected,
the double wall thickness of the PET element was 0.00085 inch and
of the polyester-polyether element was 0.0006 inch.
EXAMPLE 2
Reference Example
[0055] An extruded tube of the same Arnitel EM 740
polyester/polyether resin with the same dimension used in Example 1
was made into a single layer balloon having a double wall thickness
0.0006 inch by stretching and blowing the balloon under similar
conditions to those of Example 1. The burst pressure of this
balloon was 147 psi (10 at m).
EXAMPLE 3
Reference Example
[0056] A PET tube with the same dimension as used in Example 1 was
made into a single layer balloon having a double wall thickness of
0.00085 inch by stretching and blowing under similar conditions as
in Example 1 The burst pressure of this balloon was 338 psi. (23
atm).
[0057] Comparison of the burst strengths of the two reference
balloons produced in Examples 2 and 3 with the burst strength of
the inventive balloon of Example 1 shows that the strength of the
inventive balloon was more than the sum of the strengths of the two
reference balloons.
EXAMPLE 4
[0058] A PET tube was extruded with an inner diameter of 0.0134
inch and an outer diameter of 0.0325 inch from Traytuf 7357 PET
resin. The PET tube was stretched at a 2.25 stretch ratio at
90.degree. C. The stretched tube was then inserted into a tube of
extruded Arnitel EM 740 polyester-polyether block copolymer resin.
The extruded tube had dimensions of 0.0245 inch ID and 0.0405 inch
OD. The polyester-polyether resin tube was stretched at ambient
temperature at 4.0 stretch ratio over the PET tube, without further
stretching of the PET tube. The resulting coaxially arranged tube
assembly was then inserted into a balloon 3.0 mm mold and blown.
The mold temperature was 97.degree. C and the blowing pressure was
460 psi with 150 gms tension applied during the blowing process.
The measured balloon double wall thickness was 0.0016 inch,
corresponding to a single wall thickness (one layer each of PET and
polyester-polyether) of 0.0008 inch. The compliance curve showed
balloon growth from 8 to 18 atm of 4%, and 9% from 8 to 28 atm. The
balloon burst pressure was 426 psi (29 atm). When similarly
prepared balloons were dissected, the double wall thickness of the
PET element was 0.0009 inch and of the polyester-polyether element
was 0.0008 inch.
EXAMPLE 5
[0059] A PET tube was extruded with an inner diameter of 0.0147
inch and an outer diameter of 0.0291 inch from Traytuf 7357 PET
resin. The PET tube was stretched at a 2.25 stretch ratio at
90.degree. C. The stretched tube was then inserted into a tube of
extruded Arnitel EM 740 polyester-polyether block copolymer resin.
The extruded tube had dimensions of 0.026 inch ID and 0.043 inch
OD. The polyester-polyether resin tube was stretched at ambient
temperature at 4.0 stretch ratio over the PET tube, without further
stretching of the PET tube. The resulting coaxially arranged tube
assembly was then inserted into a balloon 3.25 mm mold and blown.
The mold temperature was 97.degree. C. and the blowing pressure was
500 psi with 600 gms tension applied during the blowing process.
The measured balloon double wall thickness was 0.0022 inch. The PET
layer double wall thickness was 0.0012 inch and the Amitel layer
double wall thickness was 0.0010 inch. The compliance curve showed
balloon growth from 8 to 18 atm of 3%, and 5% from 8 to 28 atm. The
balloon burst pressure was 573 psi (39 atm). The compliance curve
for this balloon is shown in FIG. 6.
EXAMPLE 6
Reference Example
[0060] A tube of Arnitel EM 740 resin with the same dimensions as
example 2 was made into a single balloon with double wall thickness
0.0007 inch. The burst pressure of the resulting balloon was 221
psi (15 atm).
EXAMPLE 7
Reference Example
[0061] A PET tube with the same dimensions as example 3 was made
into a single layer balloon with double wall thickness 0.0008 inch.
The burst pressure was 330 psi (22 atm).
EXAMPLE 8
[0062] A PET tube of 0.0147 inch ID and 0.0275 inch OD was extruded
from Traytuf 7357 PET resin. The PET tube was stretched at a 2.25
ratio at 90.degree. C. The stretched tube was then inserted into a
tube of extruded Arnitel EM 740 resin. Then, the Arnitel tube was
stretched at ambient temperature over the PET tube at a 4.0 stretch
ratio, without further stretching the PET tube. The combined tube
was then inserted into a mold with body dimension of 3.0 mm. The
mold process was similar to that described in WO95/22367, using a
mold temperature of 97.degree. C. and blowing pressure/tension
settings (psi fgms) of 530140, 150/40 and 580/100, respectively, to
blow the proximal, body and distal portions of the balloon
respectively. The balloon was then shrunk by annealing at
82.degree. C. for 2 hours at 5 psi inflation pressure. The balloon
double wall thickness was 0.0018 inch. The balloon had a hybrid or
step compliance curve as demonstrated in FIG. 7. The average
balloon burst pressure for 3 balloons prepared in this manner was
417 psi (28.5 atm).
EXAMPLE 9
[0063] This example illustrates an alternative laminate balloon
blowing procedure of the invention and produces a balloon in which
the soft flexible polymer is the under layer.
[0064] Extruded tubes of PET having dimensions of 0.0136 ID and
0.0288 OD and Arnitel EM 740 having dimensions of 0.0210 ID and
0.0370 OD were used in this example. Single layer PET balloons were
prepared by stretching the PET tubes at 2.25 stretch ratio and then
blowing the stretched tubes in a 2.8 mm mold using a mold
temperature of 97.degree. C. and blowing pressure/tension settings
(psi/gms) of 210/20, 100/20 and 210/20, respectively, to blow the
proximal, body and distal portions of the balloons respectively.
The Arnitel EM 740 tubes were stretched at ambient temperature at a
4.0 stretch ratio and each inserted into a PET balloon, still in
the mold. The Arnitel tubing was blown at 80.degree. C. and 400 psi
pressure without applying tension, yielding laminate balloons which
had an average double wall thickness of 0.0023 inch and an average
burst pressure of 398 psi (27 atm).
[0065] Balloons of the invention may be prepared for use on medical
devices in various interventional medical specialties including
cardiology, gastroenterology, pulmonary medicine, radiology,
urology and vascular surgery. Examples of useful applications
include catheters used in coronary and vascular percutaneous
transluminal angioplasty, catheters used for ultrasound or laser
imaging systems, catheters used to deliver and implant vascular
prostheses, devices used to diagnose and treat gastrointestinal
disorders, biliary interventional products used in endoscopic
procedures in the gall bladder and bile ducts, and prostrate
dilatation catheters. Depending on the particular application, the
balloons may be prepared with a wide range of inflated diameters,
typically in the range of 1 mm to about 30 mm, and more typically
1.5 mm to about 20 mm, with typical lengths ranging from 5 mm to
about 100 mm.
[0066] Although the present invention has been described in terms
of specific embodiments, it is anticipated that alterations and
modifications thereof will no doubt be come apparent to those
skilled in the art. . It is therefore intended that the following
claims be interpreted as covering all such alterations and
modifications as fall within the true spirit and scope of the
invention.
* * * * *