U.S. patent application number 14/924278 was filed with the patent office on 2016-04-28 for methods of manufacturing nested balloons utilizing pressurized constrained annealing.
The applicant listed for this patent is Interface Associates, Inc.. Invention is credited to Kevin Justin Herrera, Eric Mabry, Don Ngo-Chu, Matthew F. Tonge.
Application Number | 20160114141 14/924278 |
Document ID | / |
Family ID | 55791137 |
Filed Date | 2016-04-28 |
United States Patent
Application |
20160114141 |
Kind Code |
A1 |
Mabry; Eric ; et
al. |
April 28, 2016 |
METHODS OF MANUFACTURING NESTED BALLOONS UTILIZING PRESSURIZED
CONSTRAINED ANNEALING
Abstract
A nested balloon is provided where each balloon is formed from
tubing that optimizes the inner wall stretch thus providing maximum
balloon strength. The high pressure, nested balloon is provided
with layers that allow for slipping, such that the balloon has a
very high pressure rating and toughness, yet excellent folding
characteristics. Methods for producing such nested balloons using
existing balloon forming equipment are also provided. The nested
balloons can have layers with low-friction surfaces. The nested
balloons are preferably manufactured using a variety of methods,
including pressurized constrained annealing.
Inventors: |
Mabry; Eric; (Trabuco
Canyon, CA) ; Tonge; Matthew F.; (Costa Mesa, CA)
; Ngo-Chu; Don; (Milpitas, CA) ; Herrera; Kevin
Justin; (Sherman Oaks, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Interface Associates, Inc. |
Laguna Niguel |
CA |
US |
|
|
Family ID: |
55791137 |
Appl. No.: |
14/924278 |
Filed: |
October 27, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62069303 |
Oct 27, 2014 |
|
|
|
Current U.S.
Class: |
604/101.02 ;
156/221 |
Current CPC
Class: |
A61M 2025/1075 20130101;
B29L 2031/7543 20130101; A61M 2025/1031 20130101; A61M 2025/1013
20130101; A61M 25/1029 20130101; B29C 49/00 20130101; A61M 25/1011
20130101 |
International
Class: |
A61M 25/10 20060101
A61M025/10; B29D 23/00 20060101 B29D023/00 |
Claims
1. A method of manufacturing a nested balloon, comprising the steps
of: providing a first balloon layer; providing a second balloon
layer; inserting the first balloon layer into the second balloon
layer; annealing the first balloon layer and the second balloon
layer in a mold at a temperature of between about 200.degree. F.
and about 300.degree. F. for a time period of between about 10
minutes and about 90 minutes; wherein annealing comprises
pressurizing the nested balloon at a pressure of between about 2
atm and about 30 atm.
2. The method of claim 1, wherein the first balloon layer comprises
nylon.
3. The method of claim 1, wherein the second balloon layer
comprises nylon.
4. The method of claim 1, wherein the annealing temperature is
between about 215.degree. F. and about 255.degree. F.
5. The method of claim 1, wherein the annealing temperature is
about 235.degree. F.
6. The method of claim 1, wherein the pressure is between about 10
atm and about 25 atm.
7. The method of claim 1, wherein the pressure is between about 15
atm and about 25 atm.
8. The method of claim 1, further comprising stretching the balloon
with a stretch force of between about 1 pound and about 5
pounds.
9. The method of claim 1, wherein the time period is between about
15 minutes and about 45 minutes.
10. The method of claim 1, wherein the time period is between about
30 minutes.
11. The method of claim 1, further comprising the step of
sterilizing the nested balloon after the annealing step at a
temperature of between about 40.degree. C. and about 60.degree. C.
for a time period of between about 1 hour and about 3 hours.
12. The method of claim 1, further comprising the step of
blow-molding the first balloon layer and the second balloon layer
prior to the annealing step, wherein the blow molding occurs no
more than about 48 hours prior to the annealing step.
13. The method of claim 1, further comprising the step of
blow-molding the first balloon layer and the second balloon layer
prior to the annealing step, wherein the blow molding occurs no
more than about 24 hours prior to the annealing step.
14. The method of claim 1, further comprising the step of welding
the nested balloon to a catheter shaft to form a balloon
catheter.
15. The method of claim 1, wherein the first balloon layer is a
co-extruded balloon layer.
16. The method of claim 1, wherein the second balloon layer is a
co-extruded balloon layer.
17. The method of claim 1, further comprising the step of inserting
the second balloon layer into a third balloon layer.
18. A nested balloon formed by the method of claim 1.
Description
RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C.
.sctn.119(e) as a nonprovisional of U.S. Prov. Patent Application
No. 62/069,303 filed Oct. 27, 2014. The entire disclosure of the
foregoing priority application is hereby incorporated by reference
herein for all purposes.
[0002] The entire disclosure of U.S. patent application Ser. No.
11/611,748 filed Dec. 15, 2006, (now U.S. Pat. No. 7,942,847 issued
May 17, 2011), is also incorporated by reference its entirety.
BACKGROUND
[0003] 1. Field
[0004] Embodiments relate generally to balloon catheters and
methods for making balloon catheters for medical applications. In
particular, embodiments relate to a nested balloon having at least
two balloons having different properties. The balloons may have
multiple layers such as a layer comprising a low coefficient of
friction.
[0005] 2. Description of the Related Art
[0006] An increasing number of surgical procedures involve
percutaneously inserted devices that employ an inflatable thin wall
polymer balloon attached to the distal end of a small diameter
hollow shaft called a catheter. The device can be advanced to the
treatment site via an artery, vein, urethra, or other available
passage beneath the skin. The shaft usually exceeds 130 cm in
length so that the balloon can be positioned deep within the
patient's body. The opposite (proximal) end of the shaft, typically
having an inflation connector, remains external to the patient.
[0007] When a balloon is advanced to a treatment site, the balloon
is deflated and tightly wrapped around the shaft to minimize its
cross-section and facilitate easy insertion and navigation through
the passage. After reaching the desired location, the balloon is
slowly inflated with a high pressure saline solution. The balloon
walls unfold and expand radially. During this process a substantial
radial force can be exerted by or on the balloon walls. This
hydraulically generated radial force can be utilized for a number
of different medical procedures such as, for example, vessel
dilation, stent deployment, passage occlusion, and bone compression
or distraction (such as distraction of vertebrae in the spinal
column).
[0008] Several factors can limit the force a balloon can exert
while within a patient. For example, for a particular
cross-sectional balloon size, the design of a balloon, the material
used to construct the balloon, and the structural integrity of a
balloon can limit the force a balloon can exert without failing
(e.g., bursting). Minimizing the risk of balloon bursting can be
important in many medical procedures because, upon bursting,
balloon debris may become lodged within a patient causing
potentially severe trauma. Additional, higher pressures may be
needed to affect the treatment.
[0009] The hydraulically generated pressure, as noted above,
typically exerts two types of stress on the balloon. Radial stress
(or hoop stress) pushes a cylindrically-shaped balloon radially
outward. Radial stress can lead to axial bursting of the balloon
parallel to its longitudinal axis. Axial stress, on the other hand,
pushes a cylindrically-shaped balloon axially outward. Axial stress
can lead to radial bursting of the balloon somewhere along the
balloon's circumference (e.g., complete fracture of the
balloon).
[0010] Both radial stress and axial stress have a linear
relationship in pressure to the balloon's wall thickness and the
ratio of the balloon's diameter to the balloon's wall thickness. As
a result, any increase in pressure or diameter size requires an
equally proportional increase in the balloon's thickness to avoid a
critical pressure level (i.e., burst pressure) that will cause the
balloon to burst. Generally, radial stress is twice as large as
axial stress, so balloons will frequently burst axially absent some
deformity or preprocessing. However, in the presence of balloon
deformities, a balloon may burst radially. Such a radial bursting
could disadvantageously leave separated sections of the balloon
inside the patient after the catheter is removed.
[0011] Increasing balloon wall thickness also increases the
cross-section of the balloon when deflated and wrapped for
insertion. Consequently, a balloon having an increased balloon wall
thickness might have limited access to certain areas in a patient
due to the balloon's increased size. Typically, the balloon's
stiffness varies as a cube of the balloon's thickness. For example,
doubling the balloon's wall thickness to increase the burst
pressure will increase the stiffness by a factor of eight. This
added wall stiffness impairs one's ability to tightly wrap the
balloon around the catheter shaft, which is necessary to limit the
size of the balloon's cross-sectional area. If the balloon is bent
too much beyond its stiffness, undesirable deformities may result.
Usually, a balloon having a wall thickness of less than 0.0030
inches must be used to avoid the above-mentioned problems.
[0012] A number of techniques are being used to modify balloon
properties in order to improve balloon functionality. These
techniques include blending different types of polymers, adding
plasticizers to balloons, and modifying parameters of the balloon
forming process. These methods are often not entirely successful in
creating a more desirable balloon with improved mechanical
characteristics. Typically, these known techniques improve one
balloon performance parameter while deteriorating another
parameter.
[0013] Some have attempted to resolve this problem by using
multi-layer balloons. For the reasons described below, these prior
art multi-layer balloons also have serious deficiencies.
SUMMARY
[0014] Disclosed in some embodiments are commercially viable, high
pressure, nested balloon catheters. One aspect of embodiments
involves creating nested balloons. The nested balloon comprises at
least two balloons, wherein each may have stretch properties that
optimize the inner wall stretch thus providing maximum balloon
strength. The nested balloons have, in some cases, very high
pressure ratings and toughness, yet excellent folding
characteristics. Methods for producing such nested balloons using
existing balloon forming equipment are also provided.
[0015] In some embodiments, a method of manufacturing a nested
balloon is provided. The method can include the step of providing a
first balloon layer. The method can include the step of providing a
second balloon layer. The method can include the step of inserting
the first balloon layer into the second balloon layer. The method
can include the step of annealing the first balloon layer and the
second balloon layer in a mold at a temperature of between about
200.degree. F. and about 270.degree. F. for a time period of
between about 10 minutes and about 60 minutes. In some embodiments,
annealing comprises pressurizing the nested balloon at a pressure
of between about 5 atm and about 30 atm and stretching the balloon
with a stretch force of between about 1 pound and about 5
pounds.
[0016] In some embodiments, the first balloon layer comprises
nylon. In some embodiments, the second balloon layer comprises
nylon. In some embodiments, the annealing temperature is between
about 215.degree. F. and about 255.degree. F. In some embodiments,
the annealing temperature is about 235.degree. F. In some
embodiments, the pressure is between about 15 atm and about 25 atm.
In some embodiments, the pressure is between about 15 atm and about
25 atm. In some embodiments, the stretch force is between about 1
pound and about 2 pounds. In some embodiments, the time period is
between about 15 minutes and about 45 minutes. In some embodiments,
the time period is between about 30 minutes. The method can include
the step of sterilizing the nested balloon after the annealing step
at a temperature of between about 40.degree. C. and about
60.degree. C. for a time period of between about 1 hour and about 3
hours. The method can include the step of blow-molding the first
balloon layer and the second balloon layer prior to the annealing
step, wherein the blow molding occurs no more than about 48 hours
prior to the annealing step. The method can include the step of
blow-molding the first balloon layer and the second balloon layer
prior to the annealing step, wherein the blow molding occurs no
more than about 24 hours prior to the annealing step. The method
can include the step of welding the nested balloon to a catheter
shaft to form a balloon catheter. In some embodiments, the first
balloon layer is a co-extruded balloon layer. In some embodiments,
the second balloon layer is a co-extruded balloon layer. In some
embodiments, a nested balloon having a plurality of layers (e.g.,
2, 3, or more layers) that may be either co-extruded or non
co-extruded layers can be formed via methods as disclosed herein,
including annealing the nested balloon under a relatively high
pressure.
[0017] In some embodiments, a nested balloon is provided. The
nested balloon can include a first balloon having an inner layer
and an outer layer. In some embodiments, each balloon layer of the
first balloon has a first biaxial molecular orientation at its
inner wall. The nested balloon can include a second balloon
configured to be disposed within the first balloon. The nested
balloon can include a second balloon having an inner layer and an
outer layer. In some embodiments, each balloon layer of the second
balloon has a second biaxial molecular orientation at its inner
wall. In some embodiments, the expansion ratio of at least one of
the inner wall of the inner layer and the outer layer of the first
balloon are optimized such that the inner layer and the outer layer
of the first balloon resist further stretching. In some
embodiments, the expansion ratio of at least one of the inner wall
of the inner layer and the outer layer of the second balloon are
optimized when disposed within the first balloon such that the
inner layer and the outer layer of the second balloon resist
further stretching. In some embodiments, the inner and outer layers
of the first balloon and/or the second balloon are formed from
co-extruded tubing. In some embodiments, the first balloon and the
second balloon are formed from co-extruded tubing. In some
embodiments, the average burst pressure is substantially greater
than that of a single balloon having the double wall thickness
equal to combined thickness of the first balloon and the second
balloon.
[0018] In some embodiments, the expansion ratio of both of the
inner walls of the inner layers and the outer layer of the first
balloon are optimized such that the inner layers and the outer
layer of the first balloon resist further stretching. In some
embodiments, the expansion ratio of both of the inner walls of the
inner layers and the outer layer of the second balloon are
optimized such that the inner layers and the outer layer of the
first balloon resist further stretching. In some embodiments, the
first balloon and the second balloon are each formed from
co-extruded tubing with at least two different materials having
different stretch properties.
[0019] In some embodiments, the average burst pressure is at least
about 10% greater than that of a single balloon having the double
wall thickness equal to combined thickness of the first balloon and
the second balloon. In some embodiments, the average burst pressure
is at least about 25% greater than that of a single balloon having
the double wall thickness equal to combined thickness of the first
balloon and the second balloon. In some embodiments, the average
burst pressure is at least about 60% greater than for a single
balloon having the double wall thickness equal to the combined
thickness of the first balloon and the second balloon. In some
embodiments, the average burst pressure is between about 25% and
about 75% greater than that of a single balloon having the double
wall thickness equal to combined thickness of the first balloon and
the second balloon.
[0020] In some embodiments, the average burst pressure is about or
at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%,
55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%, greater than
that of a single balloon having the double wall thickness equal to
combined thickness of the first balloon and the second balloon. In
some embodiments, the average burst pressure is between about
10%-20%, 15%-25%, 20%-30%, 25%-35%, 30%-40%, 35%-45%, 40%-50%,
45%-55%, 50%-60%, 55%-65%, 60%-70%, 65%-85%, 70%-80%, 75%-85%,
80%-90%, 85%-95%, or 90%-100%, greater than that of a single
balloon having the double wall thickness equal to combined
thickness of the first balloon and the second balloon. In some
embodiments, the average burst pressure is between about 10%-30%,
15%-35%, 20%-40%, 25%-45%, 30%-50%, 35%-55%, 40%-60%, 45%-65%,
50%-70%, 55%-75%, 60%-80%, 65%-85%, 70%-90%, 75%-95%, or 80%-100%,
greater than that of a single balloon having the double wall
thickness equal to combined thickness of the first balloon and the
second balloon. In some embodiments, the average burst pressure is
between about 10%-40%, 15%-45%, 20%-50%, 25%-55%, 30%-60%, 35%-65%,
40%-70%, 45%-75%, 50%-80%, 55%-85%, 60%-90%, 65%-95%, or 70%-100%,
greater than that of a single balloon having the double wall
thickness equal to combined thickness of the first balloon and the
second balloon. In some embodiments, the average burst pressure is
between about 10%-50%, 15%-55%, 20%-60%, 25%-65%, 30%-70%, 35%-75%,
40%-80%, 45%-85%, 50%-90%, 55%-95%, or 60%-100%, greater than that
of a single balloon having the double wall thickness equal to
combined thickness of the first balloon and the second balloon. In
some embodiments, the average burst pressure is between about
10%-40%, 15%-45%, 20%-50%, 25%-55%, 30%-60%, 35%-65%, 40%-70%,
45%-75%, 50%-80%, 55%-85%, 60%-90%, 65%-95%, or 70%-100%, greater
than that of a single balloon having the double wall thickness
equal to combined thickness of the first balloon and the second
balloon. In some embodiments, the average burst pressure is between
about 10%-100%, 15%-95%, 20%-90%, 25%-85%, 30%-80%, 35%-75%,
40%-70%, 45%-55%, greater than that of a single balloon having the
double wall thickness equal to combined thickness of the first
balloon and the second balloon.
[0021] In some embodiments, the maximum hoop stress of the nested
balloon is substantially greater than that of a single balloon
having the double wall thickness equal to combined thickness of the
first balloon and the second balloon. In some embodiments, the
maximum hoop stress is approximately 30% greater than for a single
balloon having the double wall thickness equal to combined
thickness of the first balloon and the second balloon. In some
embodiments, the maximum hoop stress is approximately 40% greater
than for a single balloon having the double wall thickness equal to
combined thickness of the first balloon and the second balloon. In
some embodiments, the maximum hoop stress is approximately 50%
greater than for a single balloon having the double wall thickness
equal to combined thickness of the first balloon and the second
balloon. In some embodiments, the maximum hoop stress is between
about 25% and about 55% greater than that of a single balloon
having the double wall thickness equal to combined thickness of the
first balloon and the second balloon.
[0022] In some embodiments, the maximum hoop stress is about or at
least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%,
60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%, greater than that
of a single balloon having the double wall thickness equal to
combined thickness of the first balloon and the second balloon. In
some embodiments, the maximum hoop stress is between about 10%-20%,
15%-25%, 20%-30%, 25%-35%, 30%-40%, 35%-45%, 40%-50%, 45%-55%,
50%-60%, 55%-65%, 60%-70%, 65%-85%, 70%-80%, 75%-85%, 80%-90%,
85%-95%, or 90%-100%, greater than that of a single balloon having
the double wall thickness equal to combined thickness of the first
balloon and the second balloon. In some embodiments, the maximum
hoop stress is between about 10%-30%, 15%-35%, 20%-40%, 25%-45%,
30%-50%, 35%-55%, 40%-60%, 45%-65%, 50%-70%, 55%-75%, 60%-80%,
65%-85%, 70%-90%, 75%-95%, or 80%-100%, greater than that of a
single balloon having the double wall thickness equal to combined
thickness of the first balloon and the second balloon. In some
embodiments, the maximum hoop stress is between about 10%-40%,
15%-45%, 20%-50%, 25%-55%, 30%-60%, 35%-65%, 40%-70%, 45%-75%,
50%-80%, 55%-85%, 60%-90%, 65%-95%, or 70%-100%, greater than that
of a single balloon having the double wall thickness equal to
combined thickness of the first balloon and the second balloon. In
some embodiments, the maximum hoop stress is between about 10%-50%,
15%-55%, 20%-60%, 25%-65%, 30%-70%, 35%-75%, 40%-80%, 45%-85%,
50%-90%, 55%-95%, or 60%-100%, greater than that of a single
balloon having the double wall thickness equal to combined
thickness of the first balloon and the second balloon. In some
embodiments, the average burst pressure is between about 10%-40%,
15%-45%, 20%-50%, 25%-55%, 30%-60%, 35%-65%, 40%-70%, 45%-75%,
50%-80%, 55%-85%, 60%-90%, 65%-95%, or 70%-100%, greater than that
of a single balloon having the double wall thickness equal to
combined thickness of the first balloon and the second balloon. In
some embodiments, the maximum hoop stress is between about
10%-100%, 15%-95%, 20%-90%, 25%-85%, 30%-80%, 35%-75%, 40%-70%,
45%-55%, greater than that of a single balloon having the double
wall thickness equal to combined thickness of the first balloon and
the second balloon.
[0023] Additionally, the nested balloon can have greater
flexibility than that of a single balloon having the double wall
thickness equal to combined thickness of the first balloon and the
second balloon. In some embodiments, the flexibility is
approximately 25% greater than for a single balloon having the
double wall thickness equal to combined thickness of the first
balloon and the second balloon. In some embodiments, the
flexibility is approximately 50% greater than for a single balloon
having the double wall thickness equal to combined thickness of the
first balloon and the second balloon. In some embodiments, the
flexibility is approximately 75% greater than for a single balloon
having the double wall thickness equal to combined thickness of the
first balloon and the second balloon. In some embodiments, the
flexibility is between about 25% and about 75% greater than that of
a single balloon having the double wall thickness equal to combined
thickness of the first balloon and the second balloon.
[0024] In some embodiments, the flexibility is about or at least
about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%,
65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%, greater than that of a
single balloon having the double wall thickness equal to combined
thickness of the first balloon and the second balloon. In some
embodiments, the flexibility is between about 10%-20%, 15%-25%,
20%-30%, 25%-35%, 30%-40%, 35%-45%, 40%-50%, 45%-55%, 50%-60%,
55%-65%, 60%-70%, 65%-85%, 70%-80%, 75%-85%, 80%-90%, 85%-95%, or
90%-100%, greater than that of a single balloon having the double
wall thickness equal to combined thickness of the first balloon and
the second balloon. In some embodiments, the flexibility is between
about 10%-30%, 15%-35%, 20%-40%, 25%-45%, 30%-50%, 35%-55%,
40%-60%, 45%-65%, 50%-70%, 55%-75%, 60%-80%, 65%-85%, 70%-90%,
75%-95%, or 80%-100%, greater than that of a single balloon having
the double wall thickness equal to combined thickness of the first
balloon and the second balloon. In some embodiments, the
flexibility is between about 10%-40%, 15%-45%, 20%-50%, 25%-55%,
30%-60%, 35%-65%, 40%-70%, 45%-75%, 50%-80%, 55%-85%, 60%-90%,
65%-95%, or 70%-100%, greater than that of a single balloon having
the double wall thickness equal to combined thickness of the first
balloon and the second balloon. In some embodiments, the
flexibility is between about 10%-50%, 15%-55%, 20%-60%, 25%-65%,
30%-70%, 35%-75%, 40%-80%, 45%-85%, 50%-90%, 55%-95%, or 60%-100%,
greater than that of a single balloon having the double wall
thickness equal to combined thickness of the first balloon and the
second balloon. In some embodiments, the flexibility is between
about 10%-100%, 15%-95%, 20%-90%, 25%-85%, 30%-80%, 35%-75%,
40%-70%, 45%-55%, greater than that of a single balloon having the
double wall thickness equal to combined thickness of the first
balloon and the second balloon.
[0025] The outer layer of the first balloon can be configured to
slide relative to the inner layer of the second balloon. At least
one of the inner layers and the outer wall of the first balloon can
include a stress crack mitigating layer for the outer layer of the
first balloon. In some embodiments, the inner layer comprises
Pebax. The stress crack mitigating layer can have a lower
coefficient of friction relative to nested balloons of the same
material to permit sliding of the balloons relative to each other.
The inner layer of the second balloon can include a stress crack
mitigating layer. In some embodiments, the outer layer of the first
and the second balloon comprises Nylon and the inner layer of the
first and the second balloon comprises Pebax. In some embodiments,
the ratio of Nylon to Pebax is about 70:30. In some embodiments,
the outer layer of the first and the second balloon comprises Nylon
and the inner layer of the first and the second balloon comprises
Pebax. In some embodiments, the ratio of Nylon to Pebax is about
60:40. In some embodiments, the outer layer of the first and the
second balloon comprises Nylon and the inner layer of the first and
the second balloon comprises Pebax. In some embodiments, the ratio
of Nylon to Pebax is about 50:50. In some embodiments, the ratio of
Nylon to Pebax is between about 90:10-80:20, 80:20-70:30;
70:30-60:40 or 60:40-50:50. In some embodiments, the ratio of Nylon
to Pebax is between about 90:10-70:30; 80:20-60:40, or 70:30-50:50.
In some embodiments, the ratio of Nylon to Pebax is between about
90:10-60:40 or 80:20-50:50.
[0026] In some embodiments, the neck of the first balloon is fused
to a neck of the second balloon at a location spaced from the
proximal end of a catheter. In some embodiments, at least one end
of a neck of the first balloon is staggered from the corresponding
end of a neck of the second balloon. In some embodiments, at least
one end of a neck of the first balloon is axially offset from the
corresponding end of a neck of the second balloon.
[0027] In some embodiments, a method for creating a nested balloons
for medical applications is provided. The method can include the
step of providing a first balloon having a first proximal neck and
a first distal neck and a second balloon having a second proximal
neck and a second distal neck. The method can include the step of
inserting the second balloon into the first balloon. The method can
include the step of heating and stretching the first balloon to
optimize the stretch of an inner wall of the first balloon. The
method can include the step of heating and stretching the second
balloon to optimize the stretch of an inner wall of the second
balloon. In some embodiments, the second balloon has different
stretch properties than the first balloon.
[0028] In some embodiments, a method of making a nested balloon is
provided. The method can include the step of selecting a first
co-extruded tubular section comprising a first inner layer and a
first outer layer, the first inner layer and the first outer layer
having either the same or different materials with the same or
different stretch properties. The method can include the step of
selecting a second co-extruded tubular section comprising a second
inner layer and a second outer layer, the second inner layer and
the second outer layer having the same or different materials with
the same or different stretch properties. The method can include
the step of stretching each layer of the first and second
co-extruded tubular sections to within approximately 15% of its
optimal radial stretch, the optimal radial stretch for each layer
determined based upon the inner surface of the layer. The method
can include the step of positioning the first co-extruded tubular
section within the second co-extruded tubular section to form a
nested balloon.
[0029] In some embodiments, the stretching step is accomplished
before the positioning step. In some embodiments, the stretching
step is accomplished after the positioning step. The method can
include the step of fluting the first co-extruded tubular section.
The method can include the step of wrapping the first co-extruded
tubular section. In some embodiments, the fluting and wrapping
steps are accomplished before the positioning step. In some
embodiments, a radially inwardly facing surface of the second inner
layer is provided with a slip layer. In some embodiments, the slip
layer comprises carbon nanoparticles. In some embodiments, at least
one layer comprises nylon. In some embodiments, the second outer
layer comprises nylon. In some embodiments, the stretching step
comprises stretching each layer to within approximately 10% of its
optimal radial stretch. In some embodiments, the stretching step
comprises stretching each layer to within approximately 5% of its
optimal radial stretch. In some embodiments, the first co-extruded
tubular section and second co-extruded tubular section fail at
approximately the same pressure when a pressure is applied to the
nested balloon. In some embodiments, the first and second
co-extruded tubular sections are configured to withstand at least
about 40 atmospheres of applied pressure. In some embodiments, the
first and second co-extruded tubular sections are configured to
withstand at least about 50 atmospheres of applied pressure. In
some embodiments, the first and second co-extruded tubular sections
have substantially the same inner diameter and substantially the
same outer diameter.
[0030] In some embodiments, the average burst pressure is at least
30% greater than that of a single balloon having the double wall
thickness equal to combined thickness of the nested balloon. In
some embodiments, the average burst pressure is at least 40%
greater than that of a single balloon having the double wall
thickness equal to combined thickness of the nested balloon. In
some embodiments, the average burst pressure is at least 50%
greater than that of a single balloon having the double wall
thickness equal to combined thickness of the nested balloon. In
some embodiments, the average burst pressure is at least 60%
greater than that of a single balloon having the double wall
thickness equal to combined thickness of the nested balloon. In
some embodiments, the maximum hoop stress is at least 30% greater
than that of a single balloon having the double wall thickness
equal to combined thickness of the nested balloon. In some
embodiments, the maximum hoop stress is at least 40% greater than
that of a single balloon having the double wall thickness equal to
combined thickness of the nested balloon. In some embodiments, the
maximum hoop stress is at least 50% greater than that of a single
balloon having the double wall thickness equal to combined
thickness of the nested balloon. In some embodiments, the maximum
hoop stress is at least 60% greater than that of a single balloon
having the double wall thickness equal to combined thickness of the
nested balloon.
[0031] In some embodiments, a method of making a nested balloon is
provided. The method can include the step of selecting a first
co-extruded balloon comprising a first inner layer and a first
outer layer, the first inner layer and the first outer layer having
different materials with different stretch properties. The method
can include the step of selecting a second co-extruded balloon. The
method can include the step of expanding the first balloon to
within approximately 15% of the optimal radial stretch of an inner
surface of the first inner layer. The method can include the step
of expanding the second balloon to within approximately 15% of the
optimal radial stretch of an inner surface of the second balloon.
The method can include the step of nesting the first co-extruded
balloon within the second co-extruded balloon. In some embodiments,
the first inner layer comprises a lower strength and lower hardness
material than nylon.
[0032] In some embodiments, a method of making a nested balloon is
provided. The method can include the step of selecting a first
co-extruded balloon comprising a first inner layer and a first
outer layer. The method can include the step of selecting a second
co-extruded balloon comprising a second inner layer and a second
outer layer, the second inner layer and the second outer layer
having different material with different stretch properties. The
method can include the step of expanding the first balloon to
within approximately 15% of the optimal radial stretch of an inner
surface of the first inner layer. The method can include the step
of expanding the second balloon to within approximately 15% of the
optimal radial stretch of an inner surface of the second inner
layer. The method can include the step of nesting the first
co-extruded balloon within the second co-extruded balloon. In some
embodiments, the second outer layer comprises nylon.
[0033] In some embodiments, a nested balloon is provided. The
nested balloon can include a first balloon having an inner layer
and an outer layer, each balloon layer of the first balloon having
a first biaxial molecular orientation at its inner wall. The nested
balloon can include a second balloon configured to be disposed
within the first balloon, the second balloon having an inner layer
and an outer layer, each balloon layer of the second balloon having
a second biaxial molecular orientation at its inner wall. In some
embodiments, the expansion ratio of the inner wall of at least one
of the inner layers is substantially optimized such that the inner
layer resists further stretching. In some embodiments, at least one
end of a neck of the first balloon is axially offset from the
corresponding end of a neck of the second balloon.
[0034] In some embodiments, the expansion ratio of both of the
inner walls of the inner layers is optimized such that the inner
layers a resist further stretching. In some embodiments, the first
balloon and the second balloon are each formed from co-extruded
tubing with at least two different materials having different
stretch properties. In some embodiments, the outer layer of the
first balloon is configured to slide relative to the inner layer of
the second balloon. In some embodiments, at least one of the inner
layers comprises a stress crack mitigating layer. In some
embodiments, a neck of the first balloon is fused to a neck of the
second balloon at a location spaced from the proximal end of a
catheter. In some embodiments, at least one end of a neck of the
first balloon is staggered from the corresponding end of a neck of
the second balloon. In some embodiments, the neck of the second
balloon has a small diameter than the neck of the first balloon. In
some embodiments, the neck of the second balloon has a longer
length than the neck of the first balloon. In some embodiments, the
neck of the second balloon is configured to be welded to a
catheter. In some embodiments, the neck of the first balloon is
configured to be welded to the neck of the second balloon at a
location along the neck of the second balloon.
[0035] In some embodiments, a method of making a nested balloon is
provided. The method can include the step of selecting a first
co-extruded tubular section comprising a first inner layer and a
first outer layer, the first inner layer and the first outer layer
having different materials with different stretch properties. The
method can include the step of selecting a second co-extruded
tubular section comprising a second inner layer and a second outer
layer, the second inner layer and the second outer layer having
different materials with different stretch properties. The method
can include the step of positioning the first co-extruded tubular
section within the second co-extruded tubular section to form a
nested balloon. In some embodiments, at least one end of a neck of
the first balloon is axially offset from the corresponding end of a
neck of the second balloon.
[0036] The method can include the step of stretching each layer of
the first and second co-extruded tubular sections to within
approximately 15% of its optimal radial stretch, the optimal radial
stretch for each layer determined based upon the inner surface of
the layer. The method can include the step of fluting the first
co-extruded tubular section. The method can include the step of
wrapping the first co-extruded tubular section. In some
embodiments, a radially inwardly facing surface of the second inner
layer is provided with a slip layer. In some embodiments, at least
one layer comprises nylon. In some embodiments, the second outer
layer comprises nylon. In some embodiments, the first co-extruded
tubular section and second co-extruded tubular section fail at
approximately the same pressure when a pressure is applied to the
nested balloon. The method can include the step of welding the neck
of the second balloon to a catheter. The method can include the
step of welding the neck of the first balloon to the neck of the
second balloon at a location along the neck of the second
balloon.
[0037] Another aspect comprises a nested balloon with two balloons
having the same or different material properties. In some
embodiments, the outer layer of at least one of the balloons can
comprise a material of high strength and hardness. In yet another
aspect, the outer layer can be polyamides, polyesters,
polyethylenes, polyurethanes and their co-polymers. One suitable
material is polyamide (nylon). It will be apparent that further
variations are possible involving structural layers of other
material or chemical composition.
[0038] In some embodiments, the inner layer of at least one of the
balloons can comprise a material of lower strength and hardness.
One suitable material is Pebax (Arkema polyether block amide).
Another aspect comprises a balloon, wherein at least one layer of
at least one of the balloons has at least one low friction surface.
The inner layer of one of the balloons can have a low coefficient
of friction to advantageously allow sliding between adjacent
balloons. As a result, flexibility of the nested balloon is
increased over single balloons having an equal wall thickness.
Other aspects involve a different number of structural layers for
each individual balloon, such as, for example, three structural
layers, four structural layers, and five structural layers.
[0039] Another aspect involves a nested balloon where each balloon
has a different size (e.g., diameter and/or wall thickness). In
some embodiments, each balloon is comprised of the same material or
materials having substantially identical mechanical properties. In
some embodiments, each balloon has the same degree of molecular
orientation in the body portion of the balloon.
[0040] Another aspect involves a method for creating balloons with
low friction interfaces by nesting multiple balloons. It will be
apparent that these methods can be combined with each other and
other balloon forming methods to produce stronger balloons.
[0041] In one aspect, the bodies of the balloons can be formed
separately on the different molds to ensure that they have the
proper size. The necks may be specifically designed to ensure
optimal welding and/or attachment to the catheter. It will be
apparent that other methods can be used. It will also be apparent
that similar results can be achieved by making the outer balloon
wider than the inner balloon.
[0042] In another aspect, separately formed balloons can be nested
after altering the orientation of one balloon to make it thinner,
facilitating insertion.
[0043] Balloons need not be formed and processed identically to
obtain equivalent burst strengths, and/or molecular orientations.
This is especially true for balloons of different materials. Other
suitable methods can also be used to achieve uniform molecular
alignment among the balloons.
[0044] In another aspect of some embodiments, already nested
balloons can be treated as a single balloon. As a result, one can
manufacture nested balloons with a greater numbers of balloons
(about or at least about 2, 3, 4, 5, 6, or more balloons) than
those specifically disclosed herein.
[0045] Some important parameters for performance assessment of high
pressure balloon catheters include the rated burst pressure, the
balloon compliance, the size of the introducer, the flexibility of
the folded balloon section of the catheter and the production cost.
In some embodiments, the rated burst pressure is about or greater
than about 20, 25, 30, 35, or more atmospheres. In some
embodiments, the balloon compliance is less than about five percent
as measured between nominal pressure and rated burst pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] These and other features, aspects, and advantages of the
present invention will now be described in connection with
preferred embodiments of the invention shown in the accompanying
drawings. The illustrated embodiments, however, are merely an
example and are not intended to limit the invention. The drawings
are briefly described as follows:
[0047] FIG. 1A is a perspective view of an exemplary prior art
balloon catheter.
[0048] FIG. 1B is an enlarged perspective view of a cross-section
of a prior art balloon catheter shaft.
[0049] FIG. 2 is a perspective view of a balloon catheter having a
plurality of flutes.
[0050] FIG. 3A is a cross-sectional view of a fluted balloon
catheter before wrapping has been performed.
[0051] FIG. 3B is a cross-sectional view of a fluted balloon
catheter after wrapping.
[0052] FIGS. 3C through 3E are enlarged cross-sectional views of
three different fluted balloon catheters after wrapping.
[0053] FIG. 3F is an enlarged cross-sectional view of a fluted
balloon catheter after wrapping and compression.
[0054] FIG. 4 is an enlarged cross-sectional view of a fluted
balloon catheter that has developed a crack deformity upon
wrapping.
[0055] FIG. 5 is a perspective view of a balloon catheter that has
developed an axial tear.
[0056] FIG. 6 is a perspective view of a balloon catheter that has
developed a fish-eye deformity.
[0057] FIG. 7A is an enlarged cross-sectional view of a fluted
nested balloon catheter after wrapping.
[0058] FIG. 7B is an enlarged cross-sectional view of a fluted
single balloon catheter after wrapping.
[0059] FIG. 8A is a cross-sectional view of a nested balloon
catheter after inflation.
[0060] FIG. 8B is a cross-sectional view of a single balloon
catheter after inflation.
[0061] FIG. 9 is a schematic showing the stretching of polymers to
align their molecular chains through a blow molding process.
[0062] FIG. 10 is a stress-strain curve with strain, or the amount
that a balloon will stretch during formation, on the x-axis and
stress, or the applied pressure, on the y-axis. FIG. 10 shows that
once optimal stretch is achieved, a balloon material will have its
greatest strength and will resist further growth.
[0063] FIG. 11 is a diagram illustrating the inner diameter stretch
and the outer diameter stretch of single balloon tubing when
expanded and showing that the outer diameter stretch is less than
the inner diameter stretch.
[0064] FIG. 12 is a stress-strain curve showing that when the inner
wall stretch of single balloon tubing is optimized, the outer wall
stretch is sub-optimal and will continue to expand when applied
pressure is increased.
[0065] FIG. 13 is a diagram illustrating the inner and outer radii
of single balloon tubing in an unexpanded and an expanded
state.
[0066] FIG. 14 is a graph showing single balloon catheters having
diameters of 2 mm, 4 mm, 6 mm, 8 mm, and 10 mm with wall thickness
on the x-axis and the ratio of outer wall stretch to inner wall
stretch on the y-axis.
[0067] FIG. 15 is a schematic showing the wall profile of a single
balloon catheter that is represented in the graph of FIG. 16.
[0068] FIG. 16 is a graph of a single balloon catheter showing the
relative stretch ratio as a function of wall slice with wall
position on the x-axis and percentage of inner balloon stretch on
the y-axis.
[0069] FIG. 17 is a graph of a single balloon catheter showing the
relative wall strength with wall thickness on the x-axis and wall
thickness adjusted by the relative ratio of outer wall stretch to
inner wall stretch on the y-axis.
[0070] FIG. 18 is a schematic showing the inner/outer stretches for
nested tubing of the same material in forming a dual layer
balloon.
[0071] FIG. 19 is a graph of the inner stretch of wall slices of
the nested balloon having two non-identical balloons formed from
the nested tubing from FIG. 18 in which inner wall stretch is not
optimized on the outer extrusion relative to the inner stretch of
corresponding wall slices of the single balloon.
[0072] FIG. 20 is a stress-strain curve with strain, or the amount
that a balloon will stretch during formation for the nested tubing
of FIG. 18, on the x-axis and stress, or the applied pressure, on
the y-axis. FIG. 20 shows optimal stretch is only achieved for the
inner wall of the inner balloon.
[0073] FIG. 21 is a graph of numerous balloon lots showing average
burst pressure increasing with thickness with double wall thickness
on the x-axis and average burst pressure on the y-axis.
[0074] FIG. 22 is a graph showing maximum hoop stress of the
balloon lots shown in FIG. 21 deviating from the maximum hoop
stress of a uniform material with double wall thickness on the
x-axis and hoop stress on the y-axis.
[0075] FIG. 23 is the graph of FIG. 21 showing average burst
pressure deviating from the average burst pressure of a uniform
material with double wall thickness on the x-axis and average burst
pressure on the y-axis.
[0076] FIG. 24 is a diagram illustrating the inner diameter stretch
and the outer diameter stretch of coextruded tubing from materials
possessing different maximum stretch properties to form a dual
layer balloon.
[0077] FIG. 25 is the graph from FIG. 21 with the addition of a
nested balloon with double wall thickness on the x-axis and average
burst pressure on the y-axis.
[0078] FIG. 26 is the graph of FIG. 22 with the addition of a
nested balloon with double wall thickness on the x-axis and hoop
stress on the y-axis.
[0079] FIG. 27 is a graph of a single balloon catheter and
dual-layer balloon catheter manufactured from tubing in which the
inner wall stretch has been optimized for maximum strength. Both
the single balloon and dual-layer balloon have the same overall
wall thickness. The dual-layer balloon can be a nested balloon or a
balloon which is blown from extruded tubing as shown in FIG. 24.
FIG. 27 shows the inner stretch of wall slices of each layer of the
dual-layer balloon relative to the inner stretch of corresponding
wall slices of the single balloon.
[0080] FIG. 28A is a perspective view of a balloon catheter having
an element shown aligned in a longitudinal direction and in a
lateral direction.
[0081] FIG. 28B is an enlarged perspective view of the
longitudinally-aligned element of the balloon catheter as shown in
FIG. 28A.
[0082] FIG. 29A is a diagram of an element with a small thickness
bending like a cantilevered beam shown with an applied force and a
maximum deflection.
[0083] FIG. 29B is a diagram of an element with a large thickness
bending like a cantilevered beam shown with an applied force and a
maximum deflection.
[0084] FIG. 29C is a diagram of an element comprising three
balloons each having small thicknesses bending like a cantilevered
beam shown with an applied force and a maximum deflection.
[0085] FIG. 29D is an enlarged side elevational view of the element
shown in FIG. 29C.
[0086] FIG. 30A is a side elevational view of an inner balloon used
in a method for nesting balloons to form a nested balloon.
[0087] FIG. 30B is a side elevational view of the inner balloon
after heating and stretching (shown exaggerated) of the method for
nesting balloons of FIG. 30A.
[0088] FIG. 30C is a side elevational view of the inner balloon
after fluting of the method for nesting balloons of FIG. 30A.
[0089] FIG. 30D is a side elevational view of a nested balloon
wherein the inner balloon is inserted into the outer balloon used
in the method for nesting balloons of FIG. 30A.
[0090] FIG. 31 is a side elevational view of a catheter with a
nested balloon.
[0091] FIG. 32A is a side elevational view of a balloon weld
configured for a single balloon with equivalent strength.
[0092] FIG. 32B is a side elevational view of a balloon weld
configured for multi-layer balloons.
[0093] FIG. 32C is a side elevational view of a balloon weld
configured for nested balloons.
[0094] FIGS. 33A-33B are graphs of a single balloon catheter and
nested balloon catheter illustrating and comparing the superior and
unexpected wall stretch properties of a nested balloon comprising a
co-extruded inner layer and a co-extruded outer layer at a given
wall thickness with respect to a single layer balloon having the
same wall thickness. As noted, each balloon in the nested balloon
catheter is dual-layer balloon manufactured from co-extruded
tubing. Both the single balloon and nested balloon have the same
overall wall thickness. FIG. 33A shows an embodiment where the
stress crack mitigating inner layer is not optimized. FIG. 33B
shows an embodiment where the stress crack mitigating inner layer
is optimized.
[0095] FIG. 34 is a graph of standard deviation for the average
burst pressure of nylon balloons, according to some
embodiments.
[0096] FIG. 35 is a graph of compliance of nylon balloons, wherein
compliance is the percent change in balloon diameter from the
nominal pressure to the Rated Burst Pressure, according to some
embodiments.
[0097] FIG. 36 is a graph of compliance of a nested balloon showing
that the initial diameter for calculating the standard balloon
compliance is lower, resulting in a greater compliance value,
according to some embodiments.
[0098] FIG. 37 is a graph of the change in diameter due to a change
in pressure for non-annealed nested balloons, according to some
embodiments.
[0099] FIG. 38 is a graph of the change in diameter due to a change
in pressure for annealed nested balloons, according to some
embodiments.
DETAILED DESCRIPTION
[0100] Embodiments of the present invention will now be described
more fully hereinafter with reference to accompanying drawings, in
which preferred embodiments are shown. This invention may, however,
be embodied in many different forms and should not be construed as
limited to the embodiments set forth herein; rather, these
embodiments are provided so that this disclosure will be thorough
and exemplary of the scope of the invention to those skilled in the
art.
[0101] FIGS. 1A and 1B show an exemplary embodiment of a prior art
balloon catheter system 1. A balloon 2 is attached to the distal
end of a catheter shaft 3 and is inflated through an inflation
lumen 4. A guide wire lumen 5 is provided on the catheter system 1,
which allows for external control of the balloon 2 and the catheter
3 when the system 1 is disposed within a patient. It should be
noted that further variations (e.g., rapid exchange, concentric
lumen, etc.) are possible for this structure.
[0102] FIG. 2 illustrates a perspective view of an embodiment of a
prior art catheter balloon 2 in an unwrapped and deflated
configuration. The balloon 2 is folded into a plurality of flutes
6, typically ranging from three to eight flutes. The plurality of
flutes 6 are formed in a direction substantially parallel to a
longitudinal direction of the balloon 7. The plurality of flutes 6
are folded with a slight curvature in order to facilitate
subsequently wrapping the fluted balloon 2 around the catheter
shaft 3 (as shown in FIG. 1A). The balloon 2 attaches to the
catheter shaft 3 both at a proximal neck of the balloon 50 and at a
distal neck of the balloon 51. The balloon 2 also includes a body
portion 52, which can be inflated and deflated when the balloon 2
is disposed within the body of a patient during a particular
medical procedure.
[0103] FIG. 3A shows a cross-section of an embodiment of a prior
art fluted balloon 2 on a catheter shaft 3. The fluted balloon 2
has a plurality of flutes 6. In the illustrated embodiment, the
plurality of flutes 6 comprises six flutes. The deflated fluted
balloon 2 has a relatively small cross-sectional area, but can have
a relatively wide diameter because the thin flutes 6 stretch
radially outward from the catheter shaft 3. Upon inflation, the
balloon 2 can expand to have a much larger diameter and
cross-sectional area 8, as shown in the circular phantom lines in
FIG. 3A.
[0104] FIG. 3B shows a cross-section of an embodiment of a prior
art fluted balloon 2 after it has been wrapped. The plurality of
flutes 6 are folded down and about the catheter shaft 3 such that
they are in close contact with each other and the catheter shaft 3.
Once the balloon 2 is wrapped, the deflated balloon's diameter and
cross-sectional area 9 (sometimes referred to as the crossing
profile) is much smaller than the inflated balloon's diameter and
cross-sectional area 8 (as seen in the circular phantom lines in
FIG. 3B). Having a balloon 2 with a small diameter and
cross-sectional area 9 allows the catheter 2 to be guided through
smaller passageways within a patient's body. Inflating the balloon
2 to have a larger diameter and cross-sectional area 8
advantageously allows for the placement of a larger stent,
occlusion of a larger passageway, and generally greater versatility
once the catheter 2 has reached a particular treatment site within
a patient's body.
[0105] FIGS. 3C through 3E generally illustrate enlarged views of
several configurations of balloon folding patterns. FIG. 3C
illustrates an enlarged side elevational view of a cross-section of
a prior art fluted balloon 2c after wrapping. As shown in FIG. 3C,
the reduction in size of the wrapped balloon 2c about the catheter
shaft 3 is limited by the balloon's bend radius 10c. In general, a
balloon's bend radius increases with the thickness and toughness of
the balloon, as can be seen by comparing FIG. 3C with FIGS. 3D and
3E. FIG. 3D shows a balloon 2d that is thicker than the balloon 2c
shown in FIG. 3C. As can be seen in FIG. 3D, the bend radius 10d
for the thicker balloon 2d is larger than the bend radius of the
balloon 2c in FIG. 3C. FIG. 3E shows a balloon 2e having the same
thickness as the balloon 2c of FIG. 3C, but being composed of a
tougher or less flexible material than that of the balloon in FIG.
3C. As can be seen in FIG. 3E, the bend radius 10e for the tougher
balloon 2e is also larger than the bend radius of the balloon 2c in
FIG. 3C. Accordingly, both a thicker balloon 2d and a tougher
balloon 2e typically cannot be folded into as small a cross-section
as the balloon 2c of FIG. 3C. The bend radius of a balloon is
important because bending a balloon beyond its bend radius can
cause deformities which will lower the balloon's resistance to
bursting when inflated.
[0106] FIG. 3F shows a balloon 2f wrapped about a catheter shaft 3.
The balloon 2f has a negligible bend radius and can, therefore, be
tightly wrapped about the catheter shaft 3 without any protrusions
developing on the outer surface of the folded and wrapped balloon
2f Advantageously, this configuration permits the diameter and the
cross-section of the balloon 2f to be minimized prior to, and
during, insertion of the balloon catheter system into a patient's
body. In addition, as discussed in further detail below, this
configuration minimizes failure of the balloon 2f during a medical
application due to a deformity developing on the balloon's outer
surface.
[0107] FIGS. 4 through 6 generally show deformities that can
develop on a balloon's outer surface. As shown in FIG. 4, a wrapped
balloon 2 is folded and compressed beyond its bend radius 10
creating a crack 11 in the outer surface of the wrapped balloon 2
near the site of a fold. Such cracking is more likely for less
compliant materials, which also generally have higher burst
strengths. Thus, there is a general tradeoff between burst strength
and flexibility. Once the crack 11 has formed, stress will
concentrate near the crack 11 when the balloon 2 is inflated,
causing the crack 11 to expand and ultimately causing failure of
the balloon 2 (e.g., by bursting).
[0108] FIG. 5 shows another deformity that occurs in balloons. When
a medical device such as a stent is applied over a balloon 2, it
can create a scratch or axial tear 12. The scratch or axial tear 12
generally extends in the longitudinal direction of the balloon 2.
Again, the likelihood of scratching can be minimized by using a
more compliant material, which also has a lower burst strength.
Once the scratch 12 has formed, stress will concentrate near the
scratch 12 when the balloon 2 is inflated, causing the scratch 12
to expand and ultimately causing failure of the balloon 2 (e.g., by
bursting).
[0109] FIG. 6 illustrates yet another type of deformity. When a
balloon is formed, there may be regions of low molecular density or
imperfections in the molecular lattice. As a result, a small hole
13 can form upon stretching the balloon 2. The hole 13 can grow as
the balloon 2 is stretched further, often resembling a "fish-eye."
Stress concentrates near the edges of the fish-eye deformity 13.
Since the balloon 2 is stretched during inflation, this can also
lead to failure of the balloon 2 (e.g., by bursting).
[0110] FIGS. 7A and 8A show an enlarged cross-section of an
embodiment of a nested balloon 2 having a first balloon 20, a
second balloon 22, and a third balloon 24. Each balloon can be
formed by the same process or a different process. In some
embodiments, one or more of the first balloon 20, the second
balloon 22, and the third balloon 24 are formed from parisons or
co-extrusion. While the nested balloon 2 is shown with three
balloons, 20, 22, 24, other configurations are contemplated (e.g.,
two balloons, four balloons, five balloons, six balloons, etc.)
[0111] In some embodiments, in which the nested balloon 2 comprises
multiple balloons, one or more of the balloons can comprise one,
two, or more layers, as described herein. In some embodiments, each
balloon in a nested balloon can comprise one or more layers. In
some embodiments, each balloon in a nested balloon can comprise two
or more layers. In some embodiments, two or more layers of the same
balloon have different properties. In some embodiments, two or more
layers of the same balloon have the same properties. In some
embodiments, two or more layers of a single balloon are bonded
together. In some embodiments, two or more layers of a single
balloon are integrally formed.
[0112] The properties of the layer can depend on the location of
the layer within the nested balloon. For instance, the first
balloon 20 can comprise an outer layer, such as a material of high
strength and hardness. The first balloon 20 can comprise an inner
layer, such as a material having a low coefficient of friction. The
outer layer and the inner layer can be bonded together. Other
layers can be disposed between the outer layer and the inner layer
of the first balloon 20. Each layer can have an inner wall. The
properties of the inner wall can be optimized, as disclosed herein.
The material selection of the layers of the first balloon 20, the
second balloon 22, and the third balloon 24 are described in
greater detail herein.
[0113] The nested balloon 2 is shown in the wrapped position in
FIG. 7A. The wrapped position is described with respect to FIGS. 3A
and 3B. In comparison, a single balloon 2' is also shown in the
wrapped position in FIG. 7B. The cumulative thickness of the
balloons 2, 2' shown in FIGS. 7A and 7B are equal.
[0114] In some embodiments with three balloons, the first balloon
20 of the nested balloon 2 has a thickness that is approximately
one-third the thickness of the single balloon 2' shown in FIG. 7B.
The second balloon 22 and the third balloon 24 also each have a
thickness that is approximately one-third the thickness of the
single balloon 2' shown in FIG. 7B. In other embodiments, the
balloons 20, 22, 24 have unequal thicknesses that equal the
cumulative thickness of the single balloon 2'. While three balloons
20, 22, 24 are shown in FIG. 7A, other configurations are possible,
such as two balloons or four balloons. In some embodiments, each
balloon of a two balloon nested balloon 2 has one-half the
thickness of the single balloon 2'. In some embodiments, each
balloon of a four balloon nested balloon 2 has one-fourth the
thickness of the single balloon 2'. Because each balloon 20, 22, 24
of the nested balloon 2 is thinner than the single balloon 2' of
FIG. 7B, the bend radius 10 is smaller. Because the cumulative
thickness of the nested balloon 2 of FIG. 7A is substantially the
same as the thickness of the single balloon 2' of FIG. 7B, the
burst pressure P could in some cases be the substantially the same
as long as adjacent balloons 20, 22, 24 of the nested balloon 2 can
slide relative to each other. However, in some embodiments,
depending on the materials and other parameters and the desired
clinical result the burst pressure of a nested balloon can be
greater than the single balloon having the same cumulative
thickness.
[0115] In some embodiments, a nested balloon 2 comprises a first
balloon 20 and a second balloon 22 but not the third balloon 24. In
some embodiment, the first balloon 20 has one-half the thickness of
the single balloon 2' and the second balloon 22 has one-half the
thickness of the single balloon 2'. Because each balloon 20, 22 is
thinner than the single balloon 2' of FIG. 7B, the bend radius 10
is smaller.
[0116] As shown in FIGS. 7B and 8B, the single balloon 2' has a
total thickness 3t that is equivalent the thickness of the nested
balloon 2 shown in FIGS. 7A and 8A. In this example, each balloon
20, 22, 24 has a thickness t. As shown in FIG. 7B, the single
balloon 2' has a larger bend radius 10', and thus cannot be folded
as closely to the catheter shaft 3. In FIG. 7A, adjacent balloons
20, 22, 24 of the nested balloon 2 can slide relative to each
other. The nested balloon has a smaller bend radius, and thus can
be folded closer to the catheter shaft 3.
[0117] Because the nested design is more flexible, as discussed
below, deformities as shown in FIGS. 4-6 are less likely to occur.
Further, the material of the balloon or the material of the layers
of the nested balloon 2 can be selected to reduce the risk of
deformities. In some embodiments, the first balloon 20 or the outer
layer of the first balloon 20 can resist scratches.
[0118] Meanwhile, the burst pressure P for a nested balloon 2 is
substantially greater as will be shown as that for an equivalent
thickness single balloon 2', as described herein. It will be
apparent that similar effects can be achieved by varying the
material in each balloon layer, varying the number of balloons, and
varying other aspects of this embodiment.
[0119] In some embodiments, the first balloon 20 of the nested
balloon 2 has an outer layer which is preferably scratch and
puncture resistant. When a device such as a stent is applied to the
catheter system, it is typically crimped onto the nested balloon 2.
The applied crimping force should be such as to provide a
sufficiently strong attachment force, yet it should also not
scratch, pierce, or otherwise damage the nested balloon 2. By
selecting the material of the first balloon 20 or the outer layer
of the first balloon 20, (which can comprise an outer surface of
the nested balloon 2), the risk of failure due to scratching can be
decreased.
[0120] The second balloon 22 and the third balloon 24 (which
comprise inner balloons of the nested balloon 2) can be made of the
same material as the first balloon 20 or a different material than
the first balloon 20. In some embodiments, the second 22 and the
third balloon 24 comprise the same material. These balloons 22, 24
can be protected from scratching by the first balloon 20, and can
provide additional strength to the nested balloon 2. It should be
noted that the above-described effects need not always be achieved
simultaneously, and they are not necessarily sensitive to the
number of balloon, composition of other balloon, form of device
carried by the catheter, or other aspects of this embodiment.
[0121] As is discussed in greater detail below, each balloon 20,
22, 24 may be differently sized and shaped in the body portion, in
order to optimize the burst characteristics of the balloon. As the
nested balloon 2 is inflated, each balloon 20, 22, 24 is stretched,
causing the thickness of each balloon 20, 22, 24 to shrink. The
nested balloon 2 can be designed such that the inner wall of each
balloon 20, 22, 24 reaches the point of optimal stretch, as
described herein. When the inner wall of each balloon 20, 22, 24
reaches the point of optimal stretch, the stretch of the outer wall
of each balloon 20, 22, 24 is more optimal than the outer wall of
the single balloon 2'. Referring back to FIGS. 7A and 7B, each
balloon 20, 22, 24 is has a thickness t and the single balloon 2'
has a thickness 3t. There is a smaller gradient of stretch from the
inner wall to the outer wall of each balloon 20, 22, 24 than the
gradient of stretch from the inner wall to the outer wall of the
single balloon 2'.
[0122] In some embodiments, incorporating different material for
each of the balloons 20, 22, 24 can allow the nested balloon 2
reach the optimal stretch of each inner wall at the required
diameter. In some embodiments, incorporating different sizes for
each of the balloons 20, 22, 24 can allow the nested balloon 2
reach the optimal stretch of each inner wall at the required
diameter. In some embodiments, the design of each layer of each
balloon 20, 22, 24 can allow the nested balloon 2 reach the optimal
stretch of each inner wall at the required diameter.
[0123] In the nested configuration, the inner wall of the first
balloon 20 needs to stretch to a distance between the diameter of
the tube (deflated) and the required diameter (inflated). The inner
wall of the second balloon 22, disposed inside the first balloon
20, needs to stretch to a larger distance than the first balloon 20
between the diameter of the tube (deflated) and the required
diameter (inflated). The inner wall of the third balloon, if
present, disposed inside the second balloon 22, needs to stretch to
a larger distance than the first balloon 20 and the second balloon
between the diameter of the tube (deflated) and the required
diameter (inflated). The inner wall of the third balloon 24, if
present, needs to stretch the greatest distance. The configuration
is shown in FIG. 8A. The balloons 20, 22, 24 can be formed from the
same, or different diameter tubing to allow tailoring of the
stretch of the inner wall of each balloon. The balloons 20, 22, 24
can be formed from the same, or different materials to allow
tailoring of the stretch of the inner wall of each balloon.
[0124] With reference to FIGS. 9 and 10, an objective of blow
molding in balloon formation is to stretch the polymer material in
order to achieve maximum strength and semi-compliance. In blowing
molding balloons used in high pressure PTA and PTCA catheters, the
intent is to stretch the tubing polymer in biaxial fashion so as to
align the polymer molecules along the length and circumference of
the balloon. This alignment of the molecular chains is shown in
FIG. 9. During the stretching process, the material will grow until
the polymer chains are aligned. Once the polymer chains are
aligned, the material resists further growth and provides maximum
strength. Such orientation provides the greatest strength for the
material and resistance to further stretching. The extreme strength
of thin polymer films that form balloons comes from biaxial
molecular orientation. The ultimate tensile strength of fully
oriented material increases by a factor of four to five as compared
to as-extruded tubing. The extent of molecular orientation is
proportional to amount of stretch (e.g., deformation, strain)
imparted to the walls of the balloon.
[0125] Theoretically there is an optimal stretch for each material.
This is shown on the idealized stress-strain curve in FIG. 10. In
response to the strain caused by stretching, the material exhibits
relatively even stress, shown by the flat region in FIG. 10. Once
the polymer chains are aligned at the optimal stretch point, the
material resists further growth as shown by an increase in stress.
In the ideal cases, all polymer chains will be uniformly stretched
at the optimal stretch point. Various polymer materials will have
different ideal stretch ratios in order to achieve uniform
molecular alignment. For instance, if the tube is under-stretched,
such as any point along the flat region shown in FIG. 10, then the
polymers do not achieve the optimal alignment and strength.
Pressurizing such a balloon will result further growth and stretch
of the polymer chains in an uncontrolled fashion, especially in
absence of proper temperature and dimensional control. The expected
result is reduced burst pressure, reduced fatigue (ability to
inflate to maximum pressure repeatedly) and lack of recovery in
compliance. For instance, if the tube is over-stretched, such as
any point above the optimal stretch point, the polymers become
strained, resulting in bursting at lower pressures and reduced
fatigue.
[0126] Optimum stretch for a balloon is dependent upon a number of
variables. For a given material, there is a calculated optimum
stretch that provides optimum strength of the balloon. The
calculated optimum stretch is dependent upon, for example, the
diameter of the balloon and the thickness of the layers which
comprise the balloon. Practically, it can be very difficult to
stretch a balloon to its exact optimum stretch. Thus, for most
applications, stretching a material to within 15% of its optimum
stretch, such as to within less than 10%, will provide optimum
balloon strength.
[0127] During the balloon forming process, the polymer material is
stretched both radially and longitudinally in order to achieve
biaxial orientation of the polymer chains. As balloons are
typically cylindrical, there are two key areas of stress that come
into play. The first key area of stress is hoop or radial stress,
resulting from pressure aligned along the circumference of the
cylinder. Hoop stress of the inflated balloon equals the pressure
multiplied by the radius of the inflated balloon divided by the
thickness of the inflated balloon. The polymer stretch around the
circumference of the balloon provides strength against bursting
from hoop stress. The polymers act much like the bands around a
barrel to prevent bursting. The second key area of stress is axial
or longitudinal stress, which is aligned along the central axis.
Axial stress of the inflated balloon equals the pressure multiplied
by the radius of the inflated balloon divided by twice the
thickness of the inflated balloon. Therefore, hoop or radial stress
is twice that of axial or longitudinal stress. As a result,
optimizing the radial stretch is more important to burst resistance
than longitudinal stretch. For medical balloons, the critical
attribute is often the maximum hoop strength.
[0128] With reference to FIGS. 11 and 12, radial stretch confounds
the goal to achieve a uniform stretch of the polymer material. The
reason for this is that balloons are blow molded from tubing having
thicker walls. As shown in FIG. 11, a confounding factor in balloon
forming is that the stretch of the circumference of the inner wall
of the tubing to the inner wall of the inflated balloon will always
be greater than that of the outer wall of the tubing to the outer
wall of the inflated balloon. The difference in wall thickness
between the tubing and the inflated balloon will cause the stretch
of the inner wall of the initial tubing to be greater than that of
the respective outer wall. This disparity between the stretch of
the inner wall and the outer wall increases with the increase in
the thickness of the initial tubing.
[0129] In some embodiments, the outer wall of the balloon will have
a lower level of molecular orientation than the inner wall of the
same balloon. The lower level of molecular orientation of the outer
wall is related to the shorter distance from outer diameter of the
tube to the balloon mold wall as compared to distance from inner
diameter of the tube to balloon mold wall (assuming thickness of
the balloon is negligible). For example, a balloon is produced from
nylon tubing having an outer diameter of 0.031 and an inner
diameter of 0.019. The mold has an inner diameter of 0.118 and the
thickness of the balloon is negligible when inflated for ease of
calculation. The expansion ratio for the outer wall is 3.8
(0.118/0.031) and the expansion ratio of the inner wall is 6.2
(0.118/0.019).
[0130] The mold can be designed such that the inner wall reaches
full molecular orientation. In the example above, let us assume
that full molecular orientation occurs at an expansion ratio of
6.2. The outer wall which only expanded by a ratio of 3.8, not the
optimal 6.2, has not reached full molecular orientation. A thicker
tubing causes a greater disparity in the level of molecular
orientation between the outer wall and the inner wall. A thinner
tubing causes, in some cases, less disparity in the level of
molecular orientation between the outer wall and the inner wall.
The smaller the difference between the outer diameter and the inner
diameter of the tubing, the greater the expansion ratio for the
outer wall. The smaller the difference between the outer diameter
and the inner diameter of the tubing, the outer wall experiences
greater molecular orientation.
[0131] A problem encountered in the art is optimizing the radial
stretch of the balloon tubing. In view of the non-uniform stretch
between the inner wall and the outer wall of the tubing, some
embodiments aim to optimize the molecular orientation of the inner
wall. The highest hoop stress is on the inner wall of the balloon
where the molecules are at the maximum orientation level. On the
inner wall, there is very little radial stretchability. While
moving through the balloon towards the outer wall, the molecules
are not at the maximum orientation level. On the outer wall, there
is more radial stretchability since the outer wall was expanded
radially by a lesser amount (e.g., expansion ration of 3.8 compared
to the optimal expansion ratio of 6.2 in the previous example).
[0132] The differences in molecular orientation relate to balloon
failure. In some instances, balloon rupture starts from the inner
wall. The inner wall experiences the highest radial stresses (e.g.,
maximum expansion). Before final burst failure, micro tears or
stress cracks will start forming on the inner wall of the balloon.
Any additional forces, shear stresses or uneven force transfer from
inner wall will accelerate the micro tear forming. The outer wall
is not at the maximum orientation level (e.g., expansion ration of
3.8 compared to the optimal expansion ratio of 6.2 in the previous
example). Therefore, any additional forces, shear stresses or
uneven force transfer will cause the outer wall to stretch thus
providing no additional strength to the balloon. Balloon burst
strength can be substantially improved by modifying the inner wall.
In some embodiments, the balloon is formed from layers having
different material properties. The inner wall can be a surface of
an inner layer of softer, more stretchable material to act as
stress crack mitigating layer. The inner layer can also be radially
stretched to optimize the strength and orientation of the inner
layer. For instance, the balloon mold can be designed such that the
inner wall reaches full or substantially full molecular
orientation. By delaying or mitigating stress crack formation, the
balloon burst strength can be substantially increased. Magnitude of
the increase can be as much as 25% or more depending on the
thickness of the tubing, diameter of the balloon, and the material
selected, among other characteristics of the balloon.
[0133] As shown in the stress-strain curve in FIG. 12, the outer
wall is under-stretched when optimizing radial stretch based upon
the inner wall of the balloon. When the inner wall achieves optimal
alignment of its polymer chains, as shown on the stress-strain
curve, the outer wall has not yet reached optimal alignment of its
polymer chains, as shown by being further down the stress-strain
curve of FIG. 12. If the inner wall of the balloon fails, the outer
wall will continue to stretch thus providing no additional strength
to the balloon. In contrast, if the outer wall stretch is
optimized, then the inner wall is over-stretched. Consequently, the
inner wall will develop micro-tears which can lead to premature
failure of the balloon. Therefore, in some embodiments, the design
of the balloon optimizes the radial stretch based on the inner wall
rather than the outer wall.
[0134] The relative under-stretching of the outer wall can be
substantial. This can be shown using a mathematical model relating
the radial expansion of a smaller-diameter hollow cylinder with a
given wall thickness (the initial extruded tube) to a hollow
cylinder with a larger diameter and thinner walls (the blow molded
balloon body). FIG. 13 shows the various radii to be taken into
account from a cross section of the tube and balloon. Of particular
interest will be the inner wall stretch (S.sub.i=R.sub.i/r.sub.i)
and the outer wall stretch (S.sub.o=R.sub.o/r.sub.o). As S.sub.i is
given as being the optimized radial stretch, the relative ratio of
S.sub.o/S.sub.i will used to demonstrate the confounding effect of
radial stretch on uniform wall strength. The stretch of the
circumference can also be described as radial stretch. The inner
wall stretch can be denoted as
(S.sub.i=2.pi.R.sub.i/2.pi.r.sub.i=R.sub.i/r.sub.i) and the outer
wall stretch (S.sub.o=2.pi.R.sub.o/2.pi.r.sub.o=R.sub.o/r.sub.o).
As the best approach to balloon design is to optimize the inner
wall stretch, S.sub.i is considered to be a given. We must now
determine r.sub.o and S.sub.o for the balloon.
[0135] To fully understand the effect of biaxial stretching on the
cross section, both the tubing and the balloon are considered
cylindrical. Formula I, set forth below, shows the equation for the
mass (M) of a hollow cylinder based on outer radius of the tube
(r.sub.o), inner radius of the tube (r.sub.i), length (L) and
density (.rho.).
[0136] In expanding the hollow cylinder represented by the tube to
a balloon, the mass remains the same, as shown in Formula II set
forth below. The parameters with the subscripted t refer to the
tubing and the subscripted B refers to the balloon. The length,
outer radius, inner radius and possibly the density may change.
Since the mass remains the same, there is a fixed relationship
between the radii of tube to that of the balloon as shown in
Formula III.
M=.pi.(r.sub.o.sup.2-r.sub.i.sup.2)L.rho. I.
M.sub.t=M.sub.B II.
.pi.(r.sub.o.sup.2-r.sub.i.sup.2)L.sub.t.rho..sub.t=.pi.(R.sub.o.sup.2-R-
.sub.i.sup.2)L.sub.B.rho..sub.B III.
[0137] Thus, for a balloon of a given diameter (2R.sub.o) and wall
thickness (W.sub.b) with an optimized inner wall stretch (S.sub.i),
there is a specific tube size that must be used as a starting
condition. For a given balloon, the required inner radius for the
tubing is simply the balloon outer radius less the wall thickness
divided by the optimal stretch for the polymer used:
r.sub.i=(R.sub.o-W.sub.b)/S.sub.i. Determining the outer tubing
radius, r.sub.o, is more complicated but can be derived from the
equation in Formula III.
[0138] As set forth below, Formula IV shows such a derivation with
S.sub.L being used to express the longitudinal stretch
(S.sub.L=L.sub.B/L.sub.t). The relative longitudinal stretch,
S.sub.L, can be expressed as the ratio of balloon body length to
tube length. The variable .rho. represents the relative change in
density (.rho.=.rho..sub.B/.rho..sub.t). With these two equations,
S.sub.o and S.sub.i can be calculated and the confounding effect of
radial stretch shown. Formula IV can determine the outer diameter
of the tubing based on the outer diameter of the balloon and the
wall thickness.
r.sub.o= {square root over
(S.sub.L.rho.(2R.sub.oW.sub.B-W.sub.B.sup.2)+(R.sub.o-W.sub.B).sup.2/S.su-
b.i.sup.2)}{square root over
(S.sub.L.rho.(2R.sub.oW.sub.B-W.sub.B.sup.2)+(R.sub.o-W.sub.B).sup.2/S.su-
b.i.sup.2)} IV.
[0139] Formula V can determine the degree of outer wall stretch,
S.sub.o, as a function of wall thickness for a given balloon with
specific outer radius (R.sub.o), longitudinal stretch (S.sub.L),
density (.rho.), wall thickness (W.sub.b), and inner wall stretch
(S.sub.i).
S 0 = R o S L .rho. ( 2 R o W B - W B 2 ) + R o - W B ) 2 / S i 2 V
##EQU00001##
[0140] Formula V can be used to evaluate the ratio of the outer
wall stretch to the inner wall relative to increasing wall
thickness for a variety of balloons. FIG. 14 shows the ratio of
S.sub.o/S.sub.i as a function of wall thickness for different
diameters of balloons. As can be seen, the relative
under-stretching of the outer wall can be substantial. For example,
the outer wall for a 2 mm balloon with a wall thickness of 0.001
inches has been stretched less than 40% relative to the inner wall.
Any increase in wall thickness to try to strengthen the wall shows
a further decrease in relative stretching. The same 2 mm balloon
with a 0.002 inch wall thickness shows an outer wall stretch of
less than 30%. The net result is that trying to increase wall
thickness to increase bursting pressure gives diminishing returns
in relation to outer wall stretch. Further, a thicker balloon wall
causes a greater disparity in the level of molecular orientation
between the outer wall and the inside wall, as described herein.
Therefore, increasing the wall thickness for a specific balloon
diameter causes a decrease in the ratio of outer wall stretch to
inner wall stretch (S.sub.o/S.sub.i). This suggests a diminishing
return for increasing wall thickness to achieve a higher burst
pressure.
[0141] FIG. 14 also shows that thin walled balloons (e.g., with
thicknesses approximately 0.005) have a greater ratio of
S.sub.o/S.sub.i for larger diameter balloons. For instance, 2 mm
balloon has a relative outer wall stretch of greater than 50%. The
10 mm balloon has a relative outer wall stretch of greater than
80%. The larger diameter balloons (e.g., 10 mm or more) have a
better distribution of stretch ratios between the inner and outer
walls. This distribution may help to counter-balance the increasing
hoop stress that comes with increasing diameter.
[0142] The formulas can also be used to view the relative stretch
within the balloon wall itself. Turning now to FIGS. 15 and 16, the
confounding effect of radial stretch can be shown in more detail by
examining the distribution of relative stretch within the wall.
This can be done by "mapping" the respective wall slice in the tube
to that of the balloon. FIG. 15 shows such a map in which the inner
wall has a position of 0% and the outer wall has a position of
100%. By calculating the stretch of a slice for the tube wall, for
example the 20% line, to the equivalent slice in the balloon, the
distribution of relative radial stretch can be shown. FIG. 16 shows
a graph of a representative balloon with the relative stretch ratio
as a function of wall slice. As can be seen, the falloff in
relative stretch is not linear. The relative stretch in fact
decreases more quickly from the inner wall.
[0143] The following model evaluates the effect of decreasing the
ratio outer wall stretch to inner wall stretch (S.sub.o/S.sub.i)
with increasing wall thickness on wall strength, W.sub.s. Formula
VI shows the relationship.
W.sub.s=W.sub.b*S.sub.o/S.sub.i VI.
[0144] FIG. 17 shows an ideal wall, where wall strength increases
proportionally with increasing thickness. However, the stretch
ratio of the balloons decreases with the increase of thickness, as
shown in FIG. 14. Therefore, due to the influence of the stretch
ratio, the wall strength is substantially reduced relative to the
ideal wall. For smaller diameter balloons, (e.g., 2 mm balloons),
wall strength is reduced relative to the ideal wall even at the
smallest wall thickness (e.g., below 0.0005 in). For all balloon
diameters, wall strength is reduced relative to the ideal wall
strength at larger wall thicknesses. This is due in part to the
under-optimization of the stretch of the outer wall for larger wall
thicknesses. This suggests a diminishing return for increasing wall
thickness to increase wall strength.
[0145] Some embodiments of nested balloons described herein
emphasize the use of tubes of the same material, stretch properties
and/or size. FIG. 18 shows one example of a nested balloon 2. The
nested balloon comprises outer balloon A and inner balloon B. The
balloons can be produced from nested tubing of the same material or
different material. As such, the tubes initially can have the same
or a different inner radius (r.sub.i) and outer radius (r.sub.o).
In some embodiments, the tubes initially can have the same inner
radius (r.sub.i). In some embodiments, the tubes initially can have
different inner radii (r.sub.i). In some embodiments, the tubes
initially can have the same outer radius (r.sub.o). In some
embodiments, the tubes initially can have different outer radii
(r.sub.o). In some embodiments, nesting could in some cases produce
significantly a weaker outer balloon based on the confounding
effect of radial stretch.
[0146] In the manufacturing of the balloon, an outer diameter D of
the balloon is selected based on the mold. The diameter can be
selected to optimize the stretch of the inner wall of the inner
balloon B, as described herein.
[0147] The inner wall of the inner balloon B reaches the point of
optimal stretch. The inner balloon B cannot be further stretched
without causing the inner balloon B to burst. Therefore the outer
walls of the inner balloon B can be under-stretched. Additionally,
the balloons A, B can be identical. Therefore, the inner walls and
the outer walls of the outer balloon A can be under-stretched.
[0148] This problem may not be solved in some cases by co-extruding
the balloon such that balloons A, B are integrally formed. The
problem of inner balloon bursting can sometimes occur with
co-extruded multi-layer balloons because the inner layer
necessarily has a more optimized inner wall stretch compared to
that of outer layer. This is shown in detail on FIG. 19, in which
the relative stretch of the wall slices of a dual layer balloon
made from co-extruded tubing is shown relative to a single wall
balloon having the same overall wall thickness. As shown in FIG.
19, the outer layer shown with triangular markers is significantly
less stretched than that of the inner layer, as shown by the square
markers. Some methods of creating multi-layer balloons primarily
focus on co-extruding balloon elements in order to create a
multi-layer balloon. The confounding effect of radial stretch may
not be considered when co-extruding a multi-layer balloon.
[0149] FIG. 20 shows the stress-strain curve for the nested balloon
2 having two balloons A, B similar to FIG. 18 above. The inner
balloon, inner wall is at the point of optimal stretch. The inner
balloon, outer wall is under stretched. The inner wall of the outer
balloon is under stretched and the outer wall of the outer balloon
is under stretched. Only the inner wall of the inner balloon has
polymer chains that are aligned at the optimal stretch point.
Pressurizing such a balloon will result further growth and stretch
of the polymer chains in an uncontrolled fashion, especially in
absence of proper temperature and dimensional control.
[0150] The effect of the differential of inner wall stretch and
outer wall stretch on burst strength can be demonstrated from
internal production data, shown in FIGS. 21-23. Data including the
average double wall thickness (DWT), hoop stress and burst pressure
is produced for every lot. The graphs shown in FIGS. 21-23 are
produced from production data. To simplify the following analysis,
balloon lots are restricted to 6.times.40 balloons, each made from
nylon 12 but with varying wall thickness. Each data point is the
average value for a production lot.
[0151] FIG. 21 shows that the average burst pressure relative to
the double wall thickness for 6 mm Nylon 12 balloons. The average
burst pressure increases with wall thickness in approximately a
linear manner as shown by the best fit line. The average burst
pressure (ABP) represents a specific property of the material.
[0152] FIG. 22 shows the maximum hoop stress relative to the double
wall thickness for 6 mm Nylon 12 balloons. Formula VII represents
the maximum hoop stress, which normalizes the average burst
pressure to the balloon diameter and the double wall thickness.
Max .sigma. .theta. = ABP * D DWT VII ##EQU00002##
[0153] For a material with uniform properties, the maximum hoop
stress (Max.sigma..sub..theta.) is a constant. However, as shown in
FIG. 22, there is a significant decrease in maximum hoop stress due
to the confounding effect of radial stretch with respect to
orientation as compared with a material with uniform properties.
The dashed line shows the expected uniform hoop stress. Each data
point represents average value of the hoop stress for a production
lot. The maximum hoop stress decreases with wall thickness in
approximately a linear manner as shown by the best fit line.
[0154] FIG. 23 shows the average burst pressure relative to the
double wall thickness for 6 mm Nylon 12 balloons. The dashed line
shows the expected average burst pressure given uniform hoop
stress. Each data point represents average value of the burst
pressure for a production lot. The average burst pressure decreases
with wall thickness in approximately a linear manner as shown by
the best fit line.
[0155] As shown in FIG. 23, there is a significant decrease in
average burst pressure as compared with a material with uniform
properties shown in the dashed lines. The molecules in the
outermost layers of the balloon wall can be only partially oriented
and thus contribute less and less to the load bearing capacity of
the material. This can have a significant impact on balloon design.
The decreasing maximum hoop stress and average burst pressure
confirms a diminishing return on increasing the wall thickness to
achieve higher burst pressures, as described herein. Additionally,
thicker walls increase the catheter profile as well as decrease the
flexibility of the balloon, as described herein.
[0156] The nested balloons 2 described herein, in some embodiments,
can overcome these deficiencies in a variety of ways. In some
embodiments, the outer balloon A and the inner balloon B shown in
FIG. 18 comprise different materials. In some embodiments, the
outer balloon A and inner balloon B shown in FIG. 18 have different
inner radii. In some embodiments, the outer balloon A and inner
balloon B shown in FIG. 18 have different outer radii. In some
embodiments, the inner wall of the outer balloon A and the inner
wall of the inner balloon B are both optimized. In FIG. 20, the
inner wall of the outer balloon A and the inner wall of the inner
balloon B both reach the point of optimization near the bend in the
stress-strain curve shown in FIG. 20. In some embodiments, the
outer balloon A and the inner balloon B have a small thickness
(e.g., double wall thickness less than 0.0005'', less than
0.0010'', less than 0.0015'', less than 0.0020'', etc.). The wall
thickness can be selected to minimize the difference in
optimization between the inner wall and the outer wall of each
balloon A, B. For smaller thicknesses, the outer wall stretch can
be closer to the bend in the stress-strain curve shown in FIG.
20.
[0157] In some embodiments, each balloon A, B of a nested balloon 2
is formed from a co-extruded tubing. FIG. 24 shows an embodiment of
a co-extruded tube with each layer made from different materials.
The co-extruded tube can comprises a plurality of layers, such as
an inner layer and an outer layer, or an inner, middle, and outer
layer in some embodiments with a tri-layer balloon. In some
embodiments, the co-extruded tube can include at least 3, 4, 5, or
more layers. The layers can have different materials or the same
material. In some embodiments, the outer layer is formed from
nylon. In some embodiments, the inner layer is formed from Pebax
(polyether block amide). Other combinations are contemplated.
[0158] Each layer can be selected to optimize the inner wall
stretch. For instance, the material, inner radius, and outer radius
of each layer can be selected to optimize the inner wall stretch of
each layer. The inner wall of the nylon layer can be optimized as
shown in the double arrow line. The inner wall of the pebax layer
can be optimized as shown in the double arrow line. The outer wall
of each layer can be closer to the optimized stretch. This is due
in part to each layer having a smaller thickness than an equivalent
single layer balloon.
[0159] In some embodiments, each balloon A, B is formed from a
co-extruded tubing and the balloons A, B can be nested. In some
embodiments, the inner wall of the inner layer (e.g., Pebax layer)
of the inner balloon B is optimized. The inner wall of outer layer
(e.g., Nylon layer) of the inner balloon B is optimized. In some
embodiments, the inner wall of the inner layer (e.g., Pebax layer)
of the outer balloon A is optimized. The inner wall of outer layer
(e.g., Nylon layer) of the outer balloon B is optimized. In some
embodiments, only one balloon is formed from co-extruded tubing. In
some embodiments, both the outer balloon A and the inner balloon B
are formed from co-extruded tubing. In some embodiments, a third
balloon is provided, see FIG. 7A. Each balloon 20, 22, 24 can be
formed from co-extruded tubing. Each balloon 20, 22, 24 can have
one or more layers. The inner wall of each layer can be optimized.
The material, inner radius, or outer radius of each layer can be
selected to optimize the inner wall of each layer. Each co-extruded
balloon can be produced using techniques known in the art. In some
embodiments, one or more balloons can be made of a plurality of
layers, e.g., produced using co-extrusion techniques. In some
embodiments, both layers can be made of the same material, such as
both Nylon layers or both Pebax layers.
[0160] In the example above, discussing optimizing the radial
stretch, a single balloon can be produced from nylon tubing having
an outer diameter of 0.031'' and an inner diameter of 0.019'', with
a wall thickness of 0.006''. The mold has an inner diameter of
0.118'' and the thickness of the balloon is negligible when
inflated for ease of calculation. The expansion ratio for the outer
wall is 3.8 and the expansion ratio of the inner wall is 6.2.
[0161] For a nested balloon 2 having an outer balloon A and an
inner balloon B, the expansion ratios could be altered. In this
example, the outer balloon A and the inner B have a wall thickness
of approximate half of a single balloon. The two balloons A, B
could be produced from nylon tubing having an outer diameter of
0.025'' and an inner diameter of 0.019'', for a wall thickness of
0.003''. The wall thickness is half because two balloons are used.
In the case of three balloons 20, 22, 24 shown in FIG. 7A, the wall
thickness could be cut by a third.
[0162] As in the previous examples, the expansion ratio of the
inner wall is optimized at 6.2. In the example of two balloons A,
B, the expansion ratio for the outer wall is 4.2, which is higher
than the expansion ratio for the outer wall of the single balloon
(e.g., 3.8).
[0163] The nested balloon 2 has many potential synergistic
advantages, in some embodiments. The nested balloon 2 has two
balloons A, B, each having an optimized inner wall. The nested
design produces highly oriented material on the two inner walls.
The nested balloon 2 has two balloons A, B, each having outer walls
with a higher expansion ratio than a single balloon having the same
overall thickness. The nested design produces a higher level of
molecular orientation of the two outer walls. The higher expansion
ratio relates to the increased stretching which aligns molecular
chains. Further, each tube which forms the balloon A, B has a
smaller thickness (e.g., half of the overall thickness as compared
to a single balloon). A thinner tube causes less disparity in the
level of molecular orientation between the outer wall and the inner
wall of the balloon. Thus multiple thin balloons nested together
will unexpectedly and advantageously provide greater strength due
in part to the higher level of molecular orientation of the outer
wall, than a single balloon of equal thickness.
[0164] The properties of each balloon A, B within a nested balloon
2 are selected to optimize the stretch of the inner wall. In some
embodiments, three balloons are provided, balloons 20, 22, 24 as
shown in FIG. 7A. In some embodiments, each balloon comprises two
or more layers as shown in FIG. 24. The properties of each layer
are selected to optimize the stretch of the inner wall of each
layer. For instance, the balloons A, B, 20, 22, 24 or balloon
layers may be sized differently. In some embodiments, the balloons
A, B, 20, 22, 24 or balloon layers have different diameters. In
some embodiments, the balloons A, B, 20, 22, 24 or balloon layers
have different lengths. In some embodiments, the balloons A, B, 20,
22, 24 or balloon layers have different tube thicknesses. In some
embodiments, the balloons A, B, 20, 22, 24 or balloon layers have
different inner radii of the tube. In some embodiments, the
balloons A, B, 20, 22, 24 or balloon layers have different outer
radii of the tube. In some embodiments, the balloons A, B, 20, 22,
24 or balloon layers have different inner radius of the inflated
balloon. In some embodiments, the balloons A, B, 20, 22, 24 or
balloon layers have different outer radius of the inflated
balloon.
[0165] Therefore, the inner wall of each balloon or the inner wall
of each balloon layer can reach a point of optimal stretch. The
outer walls of each balloon are more optimal than a single balloon
having the same thickness as the nested balloon 2. The outer walls
of each layer are more optimal than a single balloon having the
same thickness as the nested balloon 2.
[0166] The balloons A, B, 20, 22, 24 or balloon layers may have
different material properties. In some embodiments, the balloons A,
B, 20, 22, 24 or balloon layers have different materials. In some
embodiments, the balloons A, B, 20, 22, 24 or balloon layers have
different densities. The present application, in some embodiments,
contemplates selecting different stretch properties for the
balloons A, B, 20, 22, 24 or balloon layers, one greater than the
other, to allow one balloon to be nested in another balloon.
Utilizing different balloons allows the stretch of the inner wall
of each balloon or balloon layer to be optimized, while making the
stretch of the outer wall as optimal as possible. Therefore, the
nested balloon 2 will have at least a first balloon A, 20 and a
second balloon B, 22. Nesting one balloon within the other balloon
produces two optimized inner walls and two highly-oriented outer
walls.
[0167] If the first balloon and the second balloon comprise
co-extruded balloons having two layers each, then the number of
optimized walls can increase. The first balloon A, 20 can have an
inner layer with an optimized inner wall and an outer layer with an
optimized inner wall. The second balloon B, 22 can have an inner
layer with an optimized inner wall and an outer layer with an
optimized inner wall. The first balloon A, 20 can have two
optimized inner walls. The second balloon B, 22 can have two
optimized inner walls. Each balloon layer of the balloons A, B, 20,
22 can have an optimized inner wall.
[0168] If the first balloon and the second balloon comprise
co-extruded balloons having two layers each, then the number of
highly orientated walls can increase. The first balloon A, 20 can
have two highly-oriented outer walls. The second balloon B, 22 can
have two highly oriented outer walls. Each balloon layer of the
balloons A, B, 20, 22 can have an highly oriented outer wall.
Nesting one co-extruded balloon within the other co-extruded
balloon can produce four optimized inner walls and four
highly-oriented outer walls. This, in some cases, greatly increases
the strength of the nested balloon 2. In some embodiments, the
stretch and/or orientation of inner layers can be optimized. In
some embodiments, the stretch and/or orientation of outer layers
can be highly-oriented. However, in some embodiments, only the
stretch and/or orientation of one of the inner and/or outer layers
are optimized.
[0169] FIG. 25 shows data related to a nested co-extruded balloon
2. FIG. 25 shows that the average burst pressure relative to the
double wall thickness for 6 mm Nylon 12 balloons. The average burst
pressure increases with wall thickness in approximately a linear
manner as shown by the bolded best fit line. FIG. 25 includes the
data presented in FIG. 21. FIG. 25 includes additional data points.
One data point represents the average burst pressure of a 6 mm
Nylon 12 single balloon with a double wall thickness of
approximately 0.005'', shown as a diamond symbol. The reference
single balloon had a burst pressure of 31 atm. The other data
points represents the average burst pressure of the nested
co-extruded balloon 2, shown as triangles. One data point
corresponds with a nested co-extruded balloon with a double wall
thickness approximately 0.005'', similar to the reference single
balloon. The nested balloon resulted in burst pressure of 49
atm--almost 60% greater than the reference single balloon. FIG. 25
includes another data point for a nested co-extruded balloon with a
thinner double wall thickness of approximately 0.0036''. The 38 atm
average burst pressure is approximately 40% higher than the
extrapolated burst pressure from the single layer balloons at a
similar double wall thickness. FIG. 25 suggests that nested
co-extruded balloons have higher burst pressure than single layer
balloons having the same wall thickness. In some embodiments, the
increase in burst pressure is at least 5%, at least 10%, at least
15%, at least 20%, at least 25%, at least 30%, at least 35%, at
least 40%, at least 45%, at least 50%, at least 55%, at least 60%,
at least 65%, at least 70%, at least 75%, at least 80%, at least
85%, at least 90%, at least 95%, at least 100%, greater than that
of a single balloon having the double wall thickness equal to
combined thickness of the nested co-extruded balloon.
[0170] FIG. 26 shows data related to a nested co-extruded balloon
2. FIG. 26 shows the maximum hoop stress relative to the double
wall thickness for 6 mm Nylon 12 balloons. The maximum hoop stress
decreases with wall thickness in approximately a linear manner as
shown by the best fit line. FIG. 26 includes the data presented in
FIG. 22. FIG. 26 includes additional data points. One data point
represents the maximum hoop stress of a 6 mm Nylon 12 single
balloon with a double wall thickness approximately 0.005'', shown
as a square symbol. The reference single balloon had a maximum hoop
stress around 1,450 atm. The other data points represents the
maximum hoop stress of the nested co-extruded balloon 2, shown as
triangles. One data point corresponds with a nested co-extruded
balloon with a double wall thickness equal to the reference single
balloon. The nested balloon resulted in a maximum hoop stress of
2,350 atm--almost 40% greater than the reference single balloon.
FIG. 26 includes an additional data point for a nested balloon with
a thinner wall thickness of approximately 0.0036''. The
.apprxeq.2,500 atm maximum hoop stress is approximately 40% higher
than the extrapolated maximum hoop stress from the single layer
balloons at a similar double wall thickness. FIG. 26 indicates that
nested co-extruded balloons, in some cases, can have higher maximum
hoop stress than single layer balloons having the same wall
thickness. In some embodiments, the increase in maximum hoop stress
is between about, or at least about, 25%-55%, 30%-50%, 35%-45%, or
more greater than that of a single balloon having the double wall
thickness equal to combined thickness of the nested co-extruded
balloon. In some embodiments, the increase in maximum hoop stress
is at least 5%, at least 10%, at least 15%, at least 20%, at least
25%, at least 30%, at least 35%, at least 40%, at least 45%, at
least 50%, at least 55%, at least 60%, at least 65%, at least 70%,
at least 75%, at least 80%, at least 85%, at least 90%, at least
95%, at least 100%, or more greater than that of a single balloon
having the double wall thickness equal to combined thickness of the
nested co-extruded balloon.
[0171] As shown in FIGS. 25 and 26, the majority of 6 mm Nylon 12
balloons have a double wall thickness in the range of 0.0015'' to
0.0030''. Balloons having a double wall thickness greater than
0.0030'' are in some cases not desirable as they can be difficult
to flute and wrap due to the stiffness of the wall. The individual
balloons of the nested balloon 2 can in some embodiments have a
double wall thickness of 0.0025. In some embodiments, the first
balloon 20, A of the nested balloon 2 has a thickness that is
approximately one-half the thickness of the single balloon. In some
embodiments, the second balloon 22, B has a thickness that is
approximately one-half the thickness of the single balloon. Other
configurations are contemplated.
[0172] In accordance with some embodiments, in order to
substantially increase the overall wall strength of a nested
balloon, each balloon or balloon layer is molded from tubing in
which in the inner wall stretch has been optimized for maximum
strength. FIG. 27 shows the relative stretch of wall slices for a
single wall balloon compared to a co-extruded balloon having two
layers. The first layer of the co-extruded balloon has an inner
wall that has been optimized, shown with square symbols. The second
layer of the co-extruded balloon has an inner wall that has been
optimized, shown with triangle symbols. Each layer has been
designed to optimize the stretch of the inner wall. This is in
contrast to FIG. 19. In FIG. 19, the second layer of the
co-extruded balloon was not designed to optimize the inner wall of
the second layer. As can been seen, the relative amount of
optimally stretched material is greater than shown in FIG. 19.
[0173] The graph would be similar for two balloons molded from
tubing in which in the inner wall stretch has been optimized for
maximum strength (not shown). The first balloon of the nested
balloon would have an inner wall that has been optimized, similar
to the square symbols. The second balloon of the nested balloon
would have an inner wall that has been optimized, similar to the
triangle symbols. Each balloon can be selected to optimize the
stretch of the inner wall.
[0174] Each balloon or balloon layer is made such that the inner
wall has been stretched for maximum strength, with the stretch
ratio specific for that particular material. As described above,
the inner wall can be stretched to within about 15% of its optimal
stretch and, in some applications, such as to within less than 10%
of its optimal stretch. As the wall strengths are additive, the
burst pressure will be higher than that for any individual
balloon.
[0175] A drawback of increasing balloon wall thickness to reach
higher burst strength is reduced flexibility. The flexibility of
the balloon can be drastically reduced with increasing wall
thickness. Nested balloons can have several times better
flexibility then a single wall balloon of equivalent thickness, as
shown in FIGS. 7A, 7B, 8A, and 8B. An ideal nested balloon would
have an infinite number of infinitely thin balloons. This would
provide maximum achievable strength and maximum achievable
flexibility. For practical purposes, such as complexity of assembly
and manufacturing cost, the number of balloons is typically limited
to a few balloons (e.g., less than five, between two and five, less
than four, between two and four, less than three, two or three).
Substantial performance improvement over prior art balloons can be
achieved with a nested balloon being made of two or more balloons.
In some embodiment, each balloon to be nested can be made of one,
two, or more layers. If a balloon to be nested is made of two or
more layers, it can be formed via a co-extrusion process.
[0176] FIGS. 28A and 28B illustrate a balloon wall element 14 of a
nested balloon catheter 2. To maintain flexibility, friction
between each balloon 20, 22, 24 should be minimized. To illustrate
this point we consider a balloon wall element 14. This element 14
has a thickness t, and a small width b and a length 1. The element
14 can be configured either axially or radially. Taking one end of
the element 14 as fixed, the element 14 can be viewed as a
cantilevered beam for analytical purposes, as described below in
FIGS. 29A through 29D.
[0177] FIG. 29A shows the balloon element 14 with thickness t. A
balloon element 14 with thickness t requires a force F.sub.1 to
bend the element 14 a set distance y. FIG. 29B shows the balloon
wall element 14' with thickness 3t. This thicker element 14'
requires a force F.sub.2, which is twenty-seven times larger than
F.sub.1, to bend the element 14' the same distance y as the element
14 in FIG. 29A (that is, because the force required varies as a
cube of the element thickness).
[0178] FIG. 29C shows a nested element 14'' comprised of a first
element 15 corresponding to the first balloon 20, a second element
16 corresponding to the second balloon 22, and a third element 17
corresponding to the third balloon 24. Each of the elements 15, 16,
and 17 has an individual thickness t. As a result, the nested
balloon element 14'' has a cumulative thickness 3t. Each
sub-element 15, 16, and 17 is individually as thick as the balloon
element 14 in FIG. 29A, but collectively as thick as the balloon
element 14' in FIG. 29B. Each individual element in FIG. 29C
requires a force F.sub.1 to bend a single balloon element a given
distance y. Collectively, the balloon element 14'' requires a force
F.sub.3 to bend the element 14'' a given distance y, which is three
times as large as the force F.sub.1 in FIG. 29A, but only one third
as large as the force F.sub.2 in FIG. 29B. As shown in FIG. 29C,
each element 15, 16, and 17 preferably slides relative to the other
elements a distance .DELTA.l. If the balloon element 15, 16, and 17
are not permitted to slide, then the nested balloon 14 will likely
require the equivalent force F.sub.3 shown in FIG. 29B.
[0179] Referring now to FIG. 29D, because the elements 15, 16, and
17 are in close contact with each other and there is a potentially
strong force pushing them together, frictional effects can be very
significant and prevent sliding between the balloons. To minimize
friction between adjacent balloons and to allow sliding, layers 12,
13, 14 can be added to elements 15, 16, and 17. In some
embodiments, the layers are formed in a co-extrusion process such
that the balloons 20, 22, 24 are co-extruded balloons. In some
embodiments, the inner layer of the first balloon 20 includes a
sliding layer. In some embodiments, the inner layer of the second
balloon 22 includes a sliding layer. In some embodiments, the outer
layer of the second balloon 22 includes a sliding layer. In some
embodiments, the outer layer of the third balloon 24 includes a
sliding layer. Other configurations are contemplated. The layers
12, 13, 14 can be made of any suitable substance, nonexclusively
including biocompatible material. In some embodiments, the material
is Pebax (Arkema polyether block amide). It should be noted that
layers are not necessary when friction between balloons is
allowable and, in some applications, desirable.
[0180] To produce the layers, one or more of the balloons 20, 22,
24 may be formed from co-extrusion. The primary goal of the tubing
coextruded from different types of material is to provide different
surface properties either on the outside or the inside of the
balloon. For example, the tubing can be coextruded in a combination
of materials. In some embodiments, a coextruded balloon comprises
an outer layer of Pebax for strength. In some embodiments, a
coextruded balloon comprises an middle bonding layer of Plexar. In
some embodiments, a coextruded balloon comprises an inner layer of
HDPE for low coefficient of friction. FIG. 24 shows another
embodiment. In some embodiments, a coextruded balloon comprises an
outer layer of nylon. In some embodiments, a coextruded balloon
comprises an inner layer of Pebax. Other configurations are
contemplated. Additionally, the application of the balloon may
dictate the material. For instance, dilation balloons for heavily
calcified lesions or areas where fine bone fragments may be
encountered, such as rhinoplasty, may require balloons with a tough
outer layer that has high abrasion, scratch and cut resistance.
This can be accomplished by co-extruding an outer layer made of
polyurethane. Stent delivery balloons may require balloons with a
softer outer layer with a high coefficient of friction to improve
the stent retention.
[0181] One goal is to provide the highest achievable burst strength
with balloon compliance below about 10, 9, 8, 7, 6, 5, 4, 3%, or
less and balloon wall thickness that is compatible with the
smallest size of introducer for that specific balloon size. To
achieve this goal, each individual balloon can have a high burst
pressure to wall thickness ratio. This can be accomplished via
material selection. In some embodiments, a coextruded balloon
comprises Nylon 12 tubing with the stress crack mitigation layer of
Pebax on the inside. The Pebax layer also provides a secondary
benefit of reduced friction at a boundary where the inner balloon
touches the outer balloon. There can be alignment between the inner
balloon and outer balloons both radially and axially with no
twisting of balloons with respect to each other. The low balloon
compliance is related to the level of material orientation. Two or
more thin walled balloons can have much higher average orientation
than one thick walled balloon, as described herein.
[0182] The balloons 20, 22, 24, A, B that form the nested balloon
can be formed from parisons or from coextruded tubing. The outer
layer of the balloon can be made of high strength and hardness
polyamide (nylon) that serves as the main load bearing layer. The
inner layer can be made of lower strength and lower hardness
material that also has a low coefficient of friction. One suitable
material is Pebax (Arkema polyether block amide). In some
embodiments, the material selected for the outer layer of the
balloon and the inner layer of the balloon have the same or
substantially the same melt temperature. The outer layer and inner
layer of a single balloon can have a strong fused bond. The
materials polyamide and Pebax are closely related, and therefore
coextrude well and fuse together at the boundary layer. In some
embodiments, the Pebax layer is radially stretched and optimally
oriented. This type of tubing provides advantageous properties for
forming individual balloons to be used in the nested balloon
design.
[0183] During extensive testing, individual balloon formed from
coextruded tubing with outer main layer of Nylon 12 and inner layer
of Pebax showed superior and unexpected results. The relative
thickness can include, for example, Nylon 12 70%, Pebax 30% (e.g.,
Nylon 12 50%, Nylon 12 greater than 50%, Nylon 12 60%, Nylon 12
greater than 60%, Nylon 12 70%, Nylon 12 greater than 70%, Nylon 12
80%, Nylon 12 greater than 80%, Nylon 12 90%, Nylon 12 greater than
90%, Nylon 12 between 60% and 80%, Nylon 12 between 50% and 90%).
The inner layer of Pebax functions as a stress crack mitigation
layer that delays the onset of micro tear formation. The inner
layer of Pebax also functions as a lubricious layer due to its
lower hardness and lower coefficient of friction as compared to
Nylon 12. Other suitable materials are contemplated.
[0184] FIGS. 30A through 30D generally depict a method for nesting
balloons to form a nested balloon. Each balloon can be made, in
some embodiments, of one material, a blend, or co-extruded to
comprise two or more layers as described herein. As shown in FIG.
30A, an inner balloon 30 is provided having a proximal neck 50A and
a distal neck 51A. The inner balloon 30 can be heated and stretched
so that the diameter and cross-sectional area of the inner balloon
30 is decreased, while the length of the inner balloon 30 is at
least partially increased, as shown in FIG. 30B. Heating and
stretching the inner balloon 30 in this manner typically alters the
alignment of the polymer molecules comprising the body of the
balloon 30. In some methods, the inner balloon 30 can be then
fluted using known fluting methods so that the balloon 30 comprises
a plurality of flutes. In some methods, the inner balloon 30 can be
then wrapped about a catheter shaft. The fluted and wrapped inner
balloon 30 is illustrated in FIG. 30C. The balloon 30 can be fluted
and wrapped, for example, using known fluting and wrapping
machines. Embodiments of such machines can be found in U.S. Pat.
No. 7,762,804 entitled "Balloon Catheter Folding and Wrapping
Devices and Methods," the contents of which are hereby incorporated
by reference in their entirety. Other suitable balloon fluting and
wrapping devices, however, can also be used.
[0185] With reference to FIG. 30D, the fluted and wrapped inner
balloon 30 can be inserted into an outer balloon 31. The outer
balloon 31 may have the same or different properties of the inner
balloon 30. For instance, the outer balloon 31 may comprise
different materials or reach the point of optimal stretch at a
larger diameter. In some embodiment, the balloons 30, 31 are
comprised of tube stock that optimizes the inner wall stretch of
the balloons 30, 31. In some embodiment, the balloons 30, 31 are
comprised of co-extruded tubing that optimizes the inner wall
stretch of inner layers of the balloons 30, 31 and the inner wall
stretch of the outer layers of the balloons 30, 31.
[0186] The outer balloon 31 has a proximal neck 50B and a distal
neck 51B. In some embodiments, the proximal neck 50B and the distal
neck 51B of the outer balloon 31 have larger diameters than the
proximal neck 50A and distal neck 51A of the inner balloon 30. In
some embodiments, the inner balloon 30 can be inserted into the
outer balloon 31 by drawing it through the outer balloon 31 such
that the inner balloon 30 is substantially contained within the
outer balloon 31. Other suitable methods can also be used to insert
the inner balloon 30 into the outer balloon 31.
[0187] The nested balloons 30, 31 are next heated, stretched, and
inflated to bring the respective body portions of the inner balloon
30 and the outer balloon 31 into the same, or a substantially
similar, molecular and geometric alignment. Embodiments of devices
capable of inflating and heating a balloon can be found in U.S.
Pat. No. 7,578,165 entitled "Measurement Apparatus and Methods for
Balloon Catheters," the contents of which are hereby incorporated
by reference in its entirety. The embodiments presented can be
modified to stretch the balloon as well, and also can be used to
verify that the balloons have been stretched to an optimal size and
shape. Other embodiments can be used to heat, stretch, and inflate
the nested balloons disclosed herein.
[0188] In some embodiments of the nesting method, one can heat and
stretch the balloon and then begin inflating the balloon while
continuing to heat and stretch the balloon. Inflation of the
balloon can commence, for example, when approximately thirty
percent of the stretching remains to be completed. The balloons are
preferably stretched to 3-6.times., 4-5.times., about 4.times.,
about 4.5.times., or about 5.times. their initial length in some
cases. This amount of stretching is meant to optimize biaxial
molecular alignment, and it will be apparent that a different
method will be suitable for different applications.
[0189] The nested balloon comprising the inner balloon 30 and the
outer balloon 31 can be fluted and wrapped in preparation for
attachment to a catheter shaft. In some embodiments, the nested
balloon is fluted and wrapped in preparation for insertion into
another balloon. In another embodiment, the nested balloon is
fluted and wrapped in preparation for having another balloon
inserted into a cavity defined by the nested balloon.
[0190] The above-disclosed nesting method is particularly suitable
for ultra-high pressure balloons having large neck diameters
relative to their body size. In some embodiments, one or more of
the balloons to be nested can have a neck diameter that is between
about 10-80%, 20-70%, 30-60%, 40-50%, 20-50% with respect to its
balloon diameter at its midpoint, or at least about 10%, 15%, 20%,
25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% of the
balloon diameter at its midpoint while still being less than the
balloon diameter at its midpoint. Further variations to the nesting
method are possible such as, for example, repetition of this
process to produce nested balloons having multiple balloons (e.g.,
exactly or at least three, four, five, six, etc.).
[0191] In some embodiments of the present nesting method, the inner
balloon 30 and the outer balloon 31 are blow-molded on different
molds. The balloons 30, 31 can have substantially similar shapes
along a body portion of the balloons 30, 31. In some embodiments,
the balloons 30, 31 can have proximal necks having different sizes
or configurations. In some embodiments, the balloons 30, 31 can
have distal necks having different sizes or configurations. That
is, the proximal and distal necks 50A, 51A of the inner balloon 30
can have a different diameter than the proximal and distal necks
50B, 51B of the outer balloon 31, as described herein.
[0192] The above-disclosed method comprising independent formation
of an inner balloon and an outer balloon and then nesting the
balloons allows for a variety of balloon sizes and shapes.
Therefore, this method can advantageously allow for ideal balloon
parameters for each individual balloon. However, in some instances,
independent formation of balloons could be a slower and more costly
process, particularly for balloons with small necks relative to
their bodies. Typically, the body of the balloon is wider than its
neck. However, the body of the inner balloon should still be
capable of fitting through the neck of the outer balloon. The body
of a balloon can be narrowed by heating, stretching, fluting, and
wrapping. The neck of a balloon can possibly be widened by heating
and inflating or stretching the balloon radially, but these methods
are limited. As a result, it is often practical to form balloons
independently and then nest them to create nested balloons with a
balloon body diameter to neck diameter ratio of about 7:1, 6:1,
5:1, 4:1, 3:1, or less.
[0193] FIG. 31 shows a typical catheter for a nested balloon 2. The
catheter size is affected by the cross section area of the folded
balloon and/or the size of the proximal balloon neck weld. The
introducer size can be minimized by minimizing the overall size of
the catheter. Thus, to minimize the introducer and/or access
greater regions of the human anatomy, the designer may try to
minimize the balloon thickness and/or the neck weld. The neck of
the balloon may be specifically designed to ensure optimal welding
and/or attachment to the catheter. The location of the proximal
neck weld 4 relative to the nested balloon 2 and the catheter 3 is
shown in FIG. 31.
[0194] FIGS. 32A-32C show embodiments of the weld between the
balloon and the catheter. FIG. 32A shows a single balloon 2' having
an inner wall and an outer wall. In some embodiments, the thickness
of the balloon 2' neck is 2t, and the thickness of the weld for the
balloon neck and the proximal shaft is 3t, as shown. The thickness
of the weld increases the size of the introducer needed for the
balloon catheter. FIG. 32B shows a nested balloons 2'' having two
balloons. Each balloon can have an outer layer and an inner layer
as shown. In some embodiments, the thickness of the balloon 2''
neck is 2t, and the thickness of the weld for the balloon neck and
the proximal shaft is 3t, as shown. The thickness of the weld
increases the size of the introducer needed for the balloon
catheter. The nested balloons 2'' can have multiple balloons and/or
multiple layers, providing benefits over the single layer balloon
2' shown in FIG. 32A and described herein. However, the balloons 2'
and 2'' shown in FIG. 32A and FIG. 32B would require the same size
of introducer.
[0195] FIG. 32C shows the weld of an embodiment of the nested
balloon 2. The nested balloon 2 comprises the first balloon 20 and
the second balloon 22, each with thickness t. Each balloon can have
an outer layer and an inner layer, as described herein. The neck of
the second balloon 22 can have a smaller diameter and/or longer
length than the neck of the first balloon 20. The neck of the first
balloon 20 can have a larger diameter and/or shorter length than
the neck of the second balloon 22. The neck of the second balloon
22 can be welded to the catheter 3. The first balloon 20 can be
welded to the second balloon 22 at a location along the neck of the
second balloon 22. The necks are partially or completely staggered
(e.g., offset). Therefore, the thickness of the balloon and the
catheter is 2t, not 3t as shown in FIGS. 32A-32B. The balloon
catheter shown in FIG. 32C would require a smaller introducer. The
configuration of the necks of the balloons 20, 22 produces a
smaller, in some cases about 33% smaller bulge than the previous
examples. Other configurations of staggering the neck welds of the
nested balloons are contemplated.
[0196] FIGS. 33A-33B are graphs illustrating concepts described
herein. The graphs compare a single balloon and a nested balloon.
The nested balloon comprises two balloons. Each balloon can be
formed from co-extruded tubing, having a first layer and a second
layer. The graphs illustrate the superior and unexpected wall
stretch properties of a nested balloon comprising a co-extruded
inner layer and a co-extruded outer layer at a given wall thickness
with respect to a single layer balloon having the same wall
thickness. As noted, each balloon in the nested balloon is
dual-layer balloon manufactured from co-extruded tubing. Both the
single balloon and nested balloon have the same overall wall
thickness.
[0197] FIG. 33A shows an embodiment where the inner layer of the
first balloon and the inner layer of the second balloon are not
optimized. As shown, the inner wall of the inner layer of the first
balloon is only 80% of the optimized stretch. The inner wall of the
inner layer of the second balloon is only 80% of the optimized
stretch. The inner layer can comprise a stress crack mitigating
layer, as described herein. The inner walls of the inner layers are
not optimized. The inner wall of the outer layer of the first
balloon is optimized. The inner wall of the outer layer of the
second balloon is optimized. The inner walls of the outer layers
are 100% of the optimized stretch.
[0198] FIG. 33A shows an embodiment where the inner wall of the
outer layer of each balloon is optimized. The inner wall of the
inner layer of each balloon, which may be a stress crack mitigating
inner layer, is not optimized. In some embodiments, the inner wall
of the inner layer of one or more of the balloons forming a nested
balloon need not necessarily have its wall stretch optimized. In
such cases, the co-extruded nested balloon can still retain the
advantageous stress crack mitigating and/or lubricious properties
of the inner layer.
[0199] In some embodiments, each inner wall of each inner layer of
the nested balloon is optimized. In some embodiments, each inner
wall of each outer layer of the nested balloon is optimized. In
some embodiments, some inner walls of the inner layers of the
nested balloon are optimized. In some embodiments, some inner walls
of the outer layers of the nested balloon are optimized.
[0200] FIG. 33B shows an embodiment where the inner layer of the
first balloon and the inner layer of the second balloon are
optimized. As shown, the inner wall of the inner layer of the first
balloon is close to, or at 100% of the optimized stretch. The inner
wall of the inner layer of the second balloon is close to, or at
100% of the optimized stretch. The inner walls of the inner layers
are optimized. The inner wall of the outer layer of the first
balloon and the inner wall of the outer layer of the second balloon
are also optimized. Each of the four inner walls is close to, or at
100% of the optimized stretch. FIG. 33B shows an embodiment where
both the outer layer and the inner layer of each balloon is
optimized.
[0201] Nested balloons can have several times better flexibility
then a single wall balloon of equivalent thickness. As shown in
FIG. 29C, each element 15, 16, and 17 preferably slides relative to
the other elements a distance .DELTA.l. If the balloon element 15,
16, and 17 are permitted to slide, then the nested balloon will
likely require less force to bend. For three elements of equal
thickness, the force needed can approach the limit of three times
the force needed to bend a single element. For three elements of
equal thickness, the force can approach the limit of a third less
force than needed to bend a balloon with a single layer of
equivalent thickness to the three elements.
[0202] Nested balloons can be formed from co-extruded tubing. The
tubing outer layer can be made of high strength and hardness
material. In some embodiments, the material is polyamide (nylon).
In some embodiments, the structural layers comprise a polyamide
such as Nylon 12. The tubing inner layer can be made of lower
strength and lower hardness material. The tubing inner layer can
have a low coefficient of friction. In some embodiment, the
lubricating layers comprise 0.0001 to 0.00015 inch high-density
polyethylene. To maintain flexibility in the nested balloon,
friction between these balloons 20, 22, 24, A, B can be
minimized.
[0203] Nested balloon can provide an additive strength of
individual balloons. FIGS. 7A and 8A show an enlarged cross-section
of an embodiment of the nested balloon 2 having the first balloon
20, the second balloon 22, and the third balloon 24. In some
embodiments, one or more of the balloon 20, 22, 24 can comprise
multiple layers. For instance, the first balloon can comprise two
or more layers, the second balloon can comprise two or more layers
and/or the third balloon can comprise two or more layers. In some
embodiment, in which the nested balloon 2 comprises a balloon
having three structural layers, the balloon comprises an outer
layer, a middle layer, and an inner layer.
[0204] Because each balloon 20, 22, 24 is thinner than the
single-layer balloon of FIGS. 7B and 8B, the bend radius 10 is
smaller for an equal cumulative thickness 3t. Because the
cumulative thickness of the nested balloon 2 of FIG. 7A is
substantially the same as the thickness of the single-layer balloon
2', the burst pressure P would be anticipated to be the
substantially the same as long as adjacent balloon layers of the
nested balloon can slide relative to each other. However, as shown
in FIG. 25, the burst pressure is greater than the burst pressure
of a single-layer balloon having an equivalent thickness. FIG. 25
suggests that nested co-extruded balloons have higher burst
pressure than single layer balloons having the same wall thickness.
In some embodiments, the increase in burst pressure is between
about 25%-75%, 30%-70%, 35%-65%, 40%-60% greater than that of a
single balloon having the double wall thickness equal to combined
thickness of the first balloon and the second balloon.
[0205] The nested balloon can comprise two or more balloons, each
blown from a co-extrusion. Disclosed herein is a method for
creating nested balloons with low friction interfaces by nesting
multiple balloons or by nesting co-extruded tubing. It will be
apparent that these methods can be combined with each other and
other balloon forming methods to produce larger multi-layer
balloons. Similarly, the balloons need not be formed and processed
identically to obtain equivalent burst strengths, sizes, and/or
molecular orientations. This is especially true for balloons of
different materials. In accordance with embodiments, each balloon
is molded from tubing in which in the inner wall stretch of each
layer has been optimized for maximum strength.
[0206] In some embodiment, each co-extruded tube can have at least
two inner walls of optimized stretch. Each co-extruded tube can
have at least two outer walls of highly oriented stretch. In some
embodiments, materials are selected with different stretch
properties for the co-extrusion, one greater than the other. In
some embodiments, the co-extruded tubing is sized based on
optimizing that stretch. It will be apparent that balloons of
different material may require different sizes and shapes to
optimize the inner wall stretch. It will also be apparent that,
because the balloons still do not stretch to exactly equal
diameters upon inflation, it may be practical to make the inner
balloons slightly smaller such that each layer stretches to
substantially near its optimal stretch. Using this design, it is
not necessary that the layers be made from the same material or
have the same wall thickness. Each layer is made such that the
inner wall has been stretched for maximum strength, with the
stretch ratio specific for that particular material. The method of
nesting contemplates use of non-identically sized or shaped
balloons.
[0207] In accordance with some embodiments, in order to
substantially increase the overall wall strength of a nested
balloon, each balloon or balloon layer is molded from tubing in
which in the inner wall stretch has been optimized for maximum
strength. FIGS. 33A-33B show the relative stretch of wall slices
for such a nested balloon having two balloons formed from
co-extruded tubing.
[0208] Each balloon in the nested balloon can be manufactured from
co-extruded tubing. Each balloon in the nested balloon catheter has
an outer layer and an inner layer, as described herein. In some
embodiments, the inner layer can be a lubricious, stress crack
mitigating inner layer as described herein. Other configurations
are contemplated.
[0209] Embodiments of the nested balloon disclosed herein can
provide a significant and unexpected performance improvement over
current high pressure balloons. The disclosed embodiments allow for
balloon catheters to be used in new applications. For example,
nested balloons can be used in ultra-high pressure applications
such as 50 atmospheres or more for up to 10 mm diameter balloons,
and for high pressure applications for very large balloons such as
12 atmospheres or more for up to 30 mm diameter balloons. The
advantages provided by the nested balloons disclosed herein can be
attributed, at least in part, to forming each balloon from tubing
where the inner wall stretch has been optimized for maximum
strength, as well as the particular material choice for each
balloon making up the nested balloon.
[0210] As noted herein, there is a distinction between balloons
produced from nested tubing of the same material and nested
balloons comprising a plurality of individual balloons. There can
be a difference in performance between the two as well as targeted
applications.
[0211] Coextruded balloon tubing does not address the differences
in material molecular orientation between the inner wall and the
outer wall of the balloon. Some embodiments as disclosed herein
improve the strength of the coextruded balloon by achieving more
uniform orientation through the balloon wall. Multilayer balloons
produced from coextruded tubing, in some embodiments, suffer from
the same drawbacks as any single layer balloon in terms of
disparities in orientation and lack of flexibility. In some
embodiments, each layer of a co-extruded balloon is selected to
optimize the inner wall of each layer.
[0212] A nested balloon comprises two or more balloons formed
independently and subsequently inserted within each other. For
nested balloon design, careful consideration must be given to the
individual balloon dimensions, including balloon cones and necks.
The design enables efficient and uniform load transfer from the
inner balloon to the outer balloon with a minimum friction between
balloon walls. Some important elements include balloon sizing,
alignment of the balloons, reduced friction between balloon walls,
and a stress crack mitigation layer. The issue of stress crack
(micro tear) formation is magnified by the interaction of the inner
and outer balloons during the force transfer.
[0213] Nested balloons can advantageously provide the additive
strength of individual balloons. For example, if you have two
balloons each with burst strength of 25 atm, then these balloons
nested within each other shall provide theoretical strength of 50
atm. In reality this number can be lower by 10% to 30% due to small
inefficiencies in load transfer or load sharing by the individual
balloons. In order to maximize the results the balloons can be very
precisely sized and aligned during the nesting process. In some
embodiments, it is preferred to have a uniform contact between the
complete surfaces of inner and outer balloon without any voids or
air pockets. Furthermore, it can be desirable to have certain
amount of lubricity between the layers so the balloons can
self-align and compensate for small irregularities without creating
additional stresses in the wall. The material selection of layers
of the balloons can reduce friction. For example, the inner layer
made of, for example, Pebax as described herein can provide
lubricity.
[0214] Nested balloons can provide benefit with respect to burst
strength and flexibility. However they present unique challenges
compared to single layer balloons. Two such challenges are Rated
Burst Pressure (RBP) and compliance.
[0215] The challenge with respect to RBP is that increased
deviation in average burst that can occur with nested balloons will
result in a lower value for RBP. RBP is defined as the pressure at
which 99.9% of balloons can survive with 95% statistical
confidence. Failure of a balloon to maintain integrity at the RBP
could result, in device failure or luminal damage. Typically a
Minimum Burst Strength (MBS) is used which is greater than the RBP
to provide some cushion. MBS is calculated from the Average Burst
Pressure (ABP) less the Standard Deviation (SD) for the ABP
multiplied by the K factor. The K factor is based on one-sided
tolerance limits for normal distribution and is a function of
confidence level, probability and sample size. For 95% confidence
with 99.9% probability and a sample size of 30 the K factor is
4.022. As a result small increases in SD can significantly impact
the resulting MBS even if the ABP is the same:
MBS=ABP-(K*SD)
[0216] Historically, the SD for nylon balloons is approximately
4.5% and can range from approximately 2% to 7% according to some
embodiments, as shown in FIG. 34.
[0217] From a design point of view it can be desirable in some
cases to design for the top end to ensure lot to lot success.
% SD=SD/ABP.
ABP=MBS/(1-K*% SD)
[0218] One consequence is that SD increases with ABP, which can be
significant for high burst pressure requirements. Another is that
nesting balloons can increase the % SD.
[0219] Nested balloons increase the complexity over monolayer
balloons. Each layer will have an ABP along with a SD. In addition
the nesting itself contributes to the overall SD.
[0220] Nesting Effectiveness (NE) is a way of expressing the degree
to which nesting is effective. In the ideal case the ABP for the
nested balloons will be the sum of the ABP of two individual
layers. Assuming both layers have the same ABP, the NE would be 2.
If the NE is less than about 2, this indicates loss of burst
strength. For example if the individual balloon layers have an ABP
of 25 atm and the nested balloon ABP is 50 atm, this would be an NE
of 2. If in the same case the ABP of the nested balloon is 40 atm,
the NE is 1.6. Such loss in balloon strength might result from a
combination misalignment, micro-welds between layers acting as
stress risers or small differences in size, for example.
[0221] The NE will not be a constant and will have its own standard
deviation if measured across a population. This deviation will
contribute to the overall standard deviation of the nested balloon
ABP. Compensating for a higher % SD to achieve a specific MBS will
require increasing the ABP. This is done by increasing the balloon
wall thickness, which will offset the value of the nested
balloons.
[0222] As noted, another challenge is that nested balloons can
increase the compliance of the balloon, which on the surface
appears counter-intuitive as increased layers is expected to
decrease the compliance due to increased level of highly oriented
polymers. This decreased compliance is a result of how compliance
is stated for balloon catheters and the typical compliance curve
for a balloon.
[0223] Compliance is specifically the percent change in balloon
diameter from the nominal pressure (NP) to RBP. By changing the NP
and RBP for a given balloon it's possible to increase or reduce the
compliance without changing the balloon itself. The values of NP
and RBP are often manipulated so as to achieve specific
requirements for compliance. This can be seen in the graph below
where for a given RBP of 18 atm, the compliance is 8.4% for an 8
atm nominal pressure while it is 6.6% for a 10 atm nominal
pressure. The graph below also sets the stage for explaining why
the compliance can decrease for a nested balloon.
[0224] The compliance curve shown in FIG. 35 is typical for nylon
balloons, according to some embodiments. The compliance is bimodal
in that the initial compliance at lower pressures is higher than
the primary compliance curve at the higher pressures. The point at
which these points meet can be referred to as the Deflection Point
(DP). Note that the DP is approximately 6 atm. Typically nominal
pressures are in the range of 6 to 10 atm, so the higher initial
compliance is not a factor with respect to standard balloon
compliance. However this is not the case with respect to nested
balloons.
[0225] FIG. 36 shows the compliance curve for nested balloons,
according to some embodiments. Since the pressure seen by the
individual layers is effectively halved, the initial compliance
curve is spread over twice the pressure range. In FIG. 36 the DP is
at 12 atm, higher than the targeted 10 atm nominal pressure. As a
consequence the initial diameter for calculating the standard
balloon compliance is lower, resulting in a greater compliance
value.
[0226] In some embodiments, both the balloon burst deviation and
compliance issues have been mitigated to a substantial extent by a
process herein described, which can involve annealing a nested
balloon under relatively high pressures and/or temperatures, which
advantageously and unexpectedly can allow for two, three, or more
balloon layers nested together, which can increase strength and
improve (increase or decrease) compliance of the nested balloon, in
some cases relative to a non-nested balloon having the same
properties (e.g., materials, diameter, etc.)
[0227] The process can include, in some embodiments, any number of
the following steps:
[0228] (a) Balloons blown and nested within a relatively short time
period, such as within the same day (FN Fast Nesting), such as
within about 48, 36, 24, 20, 18, 16, 14, 12, 10, 8, 7, 6, 5, 4, 3,
2, 1, or less hours of each other.
[0229] (b) Nested balloons annealed in a mold can be annealed
involving one, two, or more of the following parameters in some
embodiments: temperature of: about 235.degree. F., (or from about
100.degree. F. to about 300.degree. F., from about 200.degree. F.
to about 300.degree. F., from about 120.degree. F. to about
270.degree. F., from about 215.degree. F. to about 255.degree. F.,
or from about 215.degree. F. to about 255.degree. F. in some
embodiments, or ranges includes any two of the foregoing values),
or below the upper end of the glass transition temperature of the
balloon materials; pressure: about or at least about 2 atm, 5 atm,
10 atm, 15 atm, or 20 atm (or about 2 to about 40 atm, about 5 to
about 30 atm, or about 15 to about 25 atm in some embodiments, at a
minimum above the nominal pressure of the balloon, or ranges
including any two of the foregoing values); 1-2 lbs stretch (about
0.5 to about 10 lbs, about 1 to about 5 lbs, or about 1 to about 3
lbs in some embodiments, or ranges including any two of the
foregoing values); for about or at least about 30 minutes (about 5
to about 180 minutes, about 5 to about 90 minutes, about 10 to
about 60 minutes, about 15 to about 45 minutes, or ranges including
any two of the foregoing values). Such techniques such as described
in some embodiments herein can be hereby referred to herein as PCA
or Pressurized Constrained Annealing. In some embodiments, the
annealing can occur in an enclosed, high pressure, balloon heating
chamber configured with a controller to allow for any number of the
parameters described herein. A variety of balloon materials,
diameters, and other characteristics can be utilized such as
described elsewhere herein in some embodiments.
[0230] (c) Nested balloons can be welded to the inner and/or outer
shaft of a catheter.
[0231] (d) "Sterilization" annealing at an appropriate temperature
at an appropriate time, such as about 50.degree. C. (for example,
about 40.degree. C. to about 60.degree. C.) for about 2 hours (for
example, about 1 hour to about 3 hours) in some embodiments.
[0232] The unexpectedly advantageous result can be a nested balloon
that with a lower compliance, both before and/or after annealing,
and higher MBS as a result of lower % SD. FIG. 37 shows the change
in diameter due to a change in pressure for non-annealed nested
balloons, and FIG. 38 shows the change the in diameter due to a
change in pressure for annealed nested balloons. The difference in
the curve indicates that the balloon burst deviation and compliance
issues can be mitigated to a substantial extent by annealing under
relatively high pressures as disclosed herein.
[0233] In comparison, balloons without constrained pressurized
annealing have lower burst pressure and higher compliance, as
listed in the table below:
TABLE-US-00001 Nested balloons not employing Fast Nesting,
Constrained Pressurized Annealing Annealed Yes No Nominal o 10 10
RBP 32 32 DWT 0.0062 0.0054 Avg BP 36.7 45.0 Compliance 12.7% 6.1%
DP 19.26 16.89
[0234] It is contemplated that various combinations or
subcombinations of the specific features and aspects of the
embodiments disclosed above may be made and still fall within one
or more of the inventions. Further, the disclosure herein of any
particular feature, aspect, method, property, characteristic,
quality, attribute, element, or the like in connection with an
embodiment can be used in all other embodiments set forth herein.
Accordingly, it should be understood that various features and
aspects of the disclosed embodiments can be combined with or
substituted for one another in order to form varying modes of the
disclosed inventions. Thus, it is intended that the scope of the
present inventions herein disclosed should not be limited by the
particular disclosed embodiments described above. Moreover, while
the invention is susceptible to various modifications, and
alternative forms, specific examples thereof have been shown in the
drawings and are herein described in detail. It should be
understood, however, that the invention is not to be limited to the
particular forms or methods disclosed, but to the contrary, the
invention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the various
embodiments described and the appended claims. Any methods
disclosed herein need not be performed in the order recited. The
ranges disclosed herein also encompass any and all overlap,
sub-ranges, and combinations thereof. Language such as "up to," "at
least," "greater than," "less than," "between," and the like
includes the number recited. Numbers preceded by a term such as
"approximately", "about", and "substantially" as used herein
include the recited numbers, and also represent an amount close to
the stated amount that still performs a desired function or
achieves a desired result. For example, the terms "approximately",
"about", and "substantially" may refer to an amount that is within
less than 10% of, within less than 5% of, within less than 1% of,
within less than 0.1% of, and within less than 0.01% of the stated
amount.
* * * * *