Note: Descriptions are shown in the official language in which they were submitted.
CA 02575032 2007-02-09
Balloon For A Dilation Catheter and Method for Manufacturing a Balloon
[0001] This application is a divisional application of Canadian patent
application
serial number 2,232,250, filed on April 23, 1998.
FIELD OF THE INVENTION
[0002] The present invention relates generally to a device for treating a
blockage or stenosis in a vessel of a patient and a method for making the
device.
More specifically, the present invention relates to a balloon for a dilation
catheter
that is useful for performing medical dilation procedures such as angioplasty,
and/or delivering a stent and a method for manufacturing the balloon.
BACKGROUND
[0003] It is well known that many medical complications are caused by a
partial
or total blockage or stenosis of a blood vessel in a patient. Depending on the
location of the stenosis, the patient can experience cardiac arrest, stroke,
or
necrosis of tissues or organs.
[0004] Several procedures have been developed to treat stenoses, including
angioplasty, incising and dilating the vessel, and stenting. These procedures
typically utilize a dilation catheter having a balloon to dilate the vessel or
deliver
the stent. The desired size and physical characteristics of the balloon depend
largely upon the size of the vessel and the intended use of the balloon.
[0005] Generally, balloons for dilation catheters are classified according to
their
"compliance" or expandability relative to other balloons. Typically, a balloon
is
rated as being either "compliant," "semi-compliant," or "non-compliant." A
comprehensive definition of these terms is provided in U.S. Pat. No.
5,556,383,
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CA 02575032 2007-02-09
issued to Wang et al. and entitled "Block Copolymer Elastomer Catheter
Balloons".
[0006] The physical characteristics of the balloon are primarily influenced by
how the balloon is formed and by the material utilized in the balloon.
Presently,
most balloons are formed from a tube that is heated to above its glass
transition
temperature and radially expanded in a blow mold. Often, the tube is also
subjected to an axial stretch so that the resulting balloon is bi-axially
oriented.
[0007] Typically, non-compliant balloons are made from materials, such as
polyethylene terephthalate. These non-compliant balloons are often relatively
inflexible, are prone to develop pin holes, and the balloon does not rewrap
well
after inflation in the vessel. As a result thereof, these balloons are often
difficult to
remove from the delivery catheter. Further, if these balloons are used to
position a
stent in the vessel, the balloon frequently catches on the stent and
repositions the
stent in the vessel. On the other extreme, compliant balloons are typically
made of
materials, such as polyvinyl chlorides. However, compliant balloons often have
a
relatively low tensile strength, do not expand in a predictable fashion, and
are
subject to rupture during high pressure applications.
[0008] Recently, a number of semi-compliant balloons have been
manufactured using materials, such as nylon and polyamide-polyether
copolymers. These balloons exhibit many desirable characteristics including
relatively thin walls, a soft texture, a low uninflated crossing profile,
thermal
stability, and good tensile strength. However, present semi-compliant balloons
are
not completely satisfactory, since these semi-compliant balloons are made by
standard blow molding processes. For example, the wall thickness of a balloon
manufactured by standard processes may be inconsistent and/or the balloon may
have a compliance curve which is too steep or too flat. This can lead to
unpredictable balloon inflation and/or over-inflation of the balloon in the
vessel.
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CA 02575032 2009-08-07
[0009] Further, it has been discovered that certain polymers, which exhibit
desirable physical properties, cannot be formed into a balloon using the
present
blow molding processes. In fact, these materials, namely certain polyester
block
copolymers will rupture during a typical blow molding process. Thus, it is
believed
that these polyester block copolymers have not been used for balloons.
SUMMARY
[0010] In light of the above, it is an object of the present invention to
provide a
balloon having improved physical characteristics for a wide variety of
applications.
[0011] It is another object of the present invention to provide a balloon
having
relatively thin, consistent walls, a soft texture, and a low uninflated
crossing profile
and a low rewrap profile after inflation in the vessel.
[0012] Another object of the present invention is to provide a balloon that is
thermally stable, semi-compliant, expands in a predictable fashion, and has
improved tensile strength. Still another object of the present invention is to
provide
a balloon made from certain polyester block copolymers.
[0013] Yet another object of the present invention is to provide a simple
method
for manufacturing a balloon that has greater control over the physical
properties of
the balloon.
[0014] According to one aspect of the invention, there is provided a balloon
for
a dilation catheter, the balloon being made from a polyester block copolymer.
[0015] According to another aspect of the invention, there is provided a
single
layer dilation balloon comprising a hard aromatic polyester segment and a soft
aliphatic polyester segment and including a block copolymer comprising:
polybutylene terephthalate segment; and a soft segment selected from the group
consisting of polyether glycol or polyester. According to this aspect, the
balloon is
formed by: positioning a preform tube in a precondition mold, the precondition
3
CA 02575032 2009-08-07
mold having a precondition mold inner diameter; stretching and expanding the
preform tube within the precondition mold to form a uniformly reduced parison;
positioning the uniformly reduced parison in a balloon mold, the balloon mold
having a balloon mold inner diameter which is larger than the precondition
mold
inner diameter; and stretching and expanding the parison within the balloon
mold
to form the balloon.
100161 According to a further aspect of the invention, there is provided a
single
layer dilation balloon comprising a hard aromatic polyester segment and a soft
aliphatic polyester segment and including a block copolymer comprising: a
polybutylene terephthalate segment; and a soft segment selected from the group
consisting of polyether glycol or polyester. According to this aspect, the
balloon is
formed by: providing a preform tube, the preform tube having a preform tube
inner
diameter and a preform tube outer diameter; positioning the preform tube in a
precondition mold, the precondition mold having a pair of opposed precondition
mold openings; stretching and expanding the preform tube within the
precondition
mold to form a parison, the parison having a parison outer diameter, the
parison
outer diameter being larger than the tube outer diameter; preconditioning the
tube
within the precondition mold to form a parison by stretching and expanding the
tube; positioning the parison in a balloon mold, the balloon mold having a
balloon
mold inner diameter which is larger than the precondition mold inner diameter,
the
balloon mold having a pair of opposed balloon mold openings; and stretching
and
expanding the parison within the balloon mold to form the balloon.
[00171 Another aspect of the invention provides a single layer balloon for a
dilation catheter, the balloon being prepared by a process comprising the
steps
of: providing a tube consisting essentially of a polyester block copolymer
material
having a tube outer diameter, the tube being made of a polyester block
copolymer
comprising a hard aromatic polyester segment and a soft aliphatic polyester
segment; expanding the tube to form a parison, the parison having a parison
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CA 02575032 2009-08-07
outer diameter which is between approximately one and one-half (1.5) to two
and
one-half (2.5) times larger than the tube outer diameter; and expanding the
parison to form a balloon, the balloon having a balloon outer diameter which
is
between approximately one and one-half (1.5) to two and one-half (2.5) times
larger than the parison outer diameter.
[00181 A further aspect of the invention provides a single layer dilation
balloon
comprising a hard aromatic polyester segment and a soft aliphatic polyester
segment and including a block copolymer comprising: polybutylene terephthalate
segment; and a soft segment selected from the group consisting of polyether
glycol or polyester, wherein the balloon is formed by: positioning a single
layered
block copolymer preform tube in a precondition mold, the preform tube having a
tube wall thickness of TWT; stretching and expanding the tube in the
precondition
mold to form a work hardened parison, the parison having a parison wall
thickness, PWT, approximately 0.25TWT; positioning the uniformed reduced
parison in a balloon mold; and stretching and expanding the parison in the
balloon
mold to form a balloon, the balloon having a balloon wall thickness, BWT,
approximately 0.33PWT.
[00191 The present invention is directed to a balloon for a dilation catheter
and
a method for manufacturing a balloon that satisfy these objectives. The method
for
forming the balloon includes the steps of providing a tube, positioning the
tube in a
precondition mold, preconditioning the tube within the precondition mold to
form a
parison, positioning the parison in a balloon mold, and expanding the parison
within the balloon mold to form the balloon.
[00201 As provided in detail below, the unique use of the precondition mold to
form the parison from the tube provides for greater control over the
dimensions
and properties of the balloon. Further, certain materials which could not be
formed
into a balloon using prior art blow molding processes can be formed into a
balloon
using the process provided by the present invention.
CA 02575032 2007-02-09
[0021] As used herein, the term "parison" means and describes the preform
that results from preconditioning the tube in the precondition mold.
[0022] The step of preconditioning of the tube to form the parison typically
includes radially expanding the tube within the precondition mold to form the
parison. Radial expansion of the tube can be accomplished by heating the tube
to
a first temperature (71") and pressurizing a lumen of the tube to a first
pressure
("P1"). For the polyester-block copolymers provided herein, the first pressure
P1 is
at least approximately five hundred (500) psi.
[00231 The amount of preconditioning of the tube can vary according to the
material utilized for the tube and the desired physical characteristics of the
balloon.
For example, the precondition mold can be sized so that the parison has a
parison
outer diameter, which is at least over one (1) times larger than a tube outer
diameter of the tube. Typically, however, the precondition mold is sized so
that the
tube radially expands within the preconditioning mold to form a parison having
a
parison outer diameter, which is between approximately one and one-half (1.5)
and two and one-half (2.5) times larger than the tube outer diameter. More
specifically, for some of the embodiments provided herein, the precondition
mold
is sized so that the parison outer diameter is approximately one and seven-
tenths
(1.7) times larger than the tube outer diameter.
[0024] Preferably, the step of preconditioning of the tube to form the parison
also includes axial stretching of the tube in the precondition mold. As
provided
herein, the tube can be axially stretched between approximately one and one-
half
(1.5) to two and one-half (2.5) an original tube length of the tube. This
results in a
highly oriented and work hardened parison, which is ready to be formed into
the
balloon. Further, a wall thickness of the tube is substantially uniformly
reduced
within the precondition mold.
[0025] The balloon mold is typically sized so that parison can be radially
expanded in the balloon mold to form a balloon having a balloon outer
diameter,
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CA 02575032 2007-02-09
which is between approximately one and one-half (1.5) and two and one-half
(2.5)
times larger than the parison outer diameter. More specifically, for some of
the
embodiments provided herein, the balloon mold is sized so that the parison is
radially expanded into a balloon having a balloon outer diameter, which is
approximately two (2) times larger than the parison outer diameter.
[00261 Preferably, the parison is also axially stretched in the balloon mold
so
that the resulting balloon is highly bi-axially oriented. As provided herein,
the
parison can be axially stretched between approximately one (1.0) to one and
one-
half (1.5) times the parison length of the parison.
[00271 Additionally, it has been discovered that a balloon exhibiting superior
physical characteristics, including a low crossing profile, a low rewrap
profile, a
soft texture, thermal stability, and semi-compliant expansion can be formed
from
polyester block copolymers. Specifically, it has been discovered that a
superior
balloon can be manufactured from a block copolymer, which consists of an
aromatic polyester hard segment and an aliphatic polyester soft segment. For
example, an excellent balloon can be made from the copolymer sold under the
trade-mark "Pelprene," by Toyobo, located in Osaka, Japan. This copolymer
consists of an aromatic polyester hard segment and an aliphatic polyester soft
segment. Additionally, it is believed that an excellent balloon can be made
from
the copolymer sold under the trade-mark "Hytrel," by DuPont, located in
Wilmington, Del. This copolymer consists of a polybutylene terephalate hard
segment and a long chain of polyether glycol soft segment.
[00281 Importantly, the softening point for the specific polyester block
copolymers identified above is very close to the melting point of the
material. For
these materials, little strength of the material is lost and little softening
occurs
during a standard blow mold process. With these materials, the pressure needed
to initiate expansion of the tube is very high, typically, at least
approximately five
hundred (500) psi. With these polyester block copolymers, this would cause the
7
CA 02575032 2007-02-09
tube to rupture prior to forming the balloon using a standard blow molding
process.
However, these materials can be formed into a balloon utilizing the unique
process
provided herein.
[0029] Additionally, the present invention relates to a device for
manufacturing
a balloon. The device includes a precondition mold suitable for expanding the
tube
into a parison and a balloon mold suitable for expanding the parison into a
balloon.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The novel features of this invention, as well as the invention itself,
both
as to its structure and its operation, will be best understood from the
accompanying drawings, taken in conjunction with the accompanying description,
in which similar reference characters refer to similar parts, and in which:
[0031] FIG. 1 is a side plan view of a dilation catheter having features of
the
present invention;
[0032] FIG. 2 is a cross-sectional view of a precondition mold, a parison and
a
tube (shown in phantom) having features of the present invention;
[00331 FIG. 3 is a cross-sectional view of a balloon mold, a balloon, and a
parison (shown in phantom) having features of the present invention;
100341 FIG. 4 is a cross-sectional view of a parison having features of the
present invention;
[0035] FIG. 5 is a cross-sectional view of a balloon having features of the
present invention;
[0036] FIG. 6 is a graph which outlines one (1) example of the relationship
between time, temperature, axial stretch, and pressure during the expansion of
the
tube in the precondition mold to form the parison;
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[0037] FIG. 7 is a graph which outlines one (1) example of the relationship
between time, temperature, axial stretch, and pressure during the expansion of
the
parison in the balloon mold to form the balloon; and
[0038] FIG. 8 is a graph that outlines the compliance curve for a balloon made
in accordance with the present invention.
DESCRIPTION
[0039] Referring initially to FIG. 1, the present invention is directed to a
dilation
catheter 10 which utilizes a balloon 12 to treat a vessel (not shown) of a
patient
(not shown). The balloon 12 provided herein, has improved physical
characteristics, including a relatively high tensile strength, a relatively
thin wall, a
relatively low initial crossing profile, and a relatively low rewrap profile.
Preferred
embodiments of the balloon 12 provided herein are semi-compliant, soft, and
expand in a predictable manner.
[0040] The improved physical characteristics of the balloon 12 are a result of
the unique process used to manufacture the balloon 12 and the material used in
forming the balloon 12. However, it is anticipated that the unique process can
be
used with other materials to form compliant or non-compliant balloons 12.
[0041] As shown in FIG. 1, the dilation catheter 10 includes a relatively
thin,
flexible length of tubing 14. The balloon 12 is positioned at the desired
location
along the length of tubing 14. In the embodiment shown in FIG. 1, the balloon
is
positioned proximate a distal tip 16 of the dilation catheter 10. The dilation
catheter
is particularly useful for dilating a vessel, incising a vessel, and/or
positioning a
stent in a vessel of a patient. However, it is believed that the dilation
catheter 10
and balloon 12 may be useful for other intravascular medical procedures.
[0042] The balloon 12 is manufactured utilizing a unique process that allows
for
greater control over the physical characteristics of the balloon 12. Referring
to
FIGS. 2 and 3, as an overview, the unique process includes preconditioning a
tube
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18 (shown in phantom in FIG. 2) in a precondition mold 20 to form a parison 22
and subsequently expanding the parison 22 in a balloon mold 24 to form the
balloon 12. Because the tube 18 is preconditioned in the precondition mold 20,
there is greater control over the physical characteristics of the resulting
balloon 12
and the balloon 12 can be manufactured from materials which would rupture
during a normal, prior art, blow molding process.
[0043] For example, it has been discovered that an excellent, semi-compliant
balloon 12 can be made from polyester block copolymers such as a polyester-
polyester block copolymer consisting of an aromatic polyester as the hard
segment and an aliphatic polyester as the soft segment. An example of a
suitable
block copolymer consisting of an aromatic polyester hard segment and an
aliphatic
polyester soft segment is manufactured by Toyobo, under the trade-marks
"PELPRENE S6001," "PELPRENE S9001." Additionally, it is believed that other
polyester block copolymers could be used for the balloon. For example, it is
believed that the polymer manufactured by DuPont under the trade-mark "Hytrel"
will make an excellent balloon 12.
[0044] Importantly, some polyester block copolymers such as "PELPRENE
S6001" and "PELPRENE S9001" could not be manufactured using prior art
balloon blow molding processes. This is because the pressure required to
initiate
expansion of the tube 18 is relatively high, i.e., at or above five hundred
(500) psi.
If a prior art blow molding process was used, the pressure required to
initiate
expansion would rupture the tube 18 prior to the balloon 12 expanding into its
final
configuration. With the process provided herein, the precondition mold 20
prevents
radial expansion of the tube 18 prior to rupture of the tube 18.
[0045] Moreover, the unique manufacturing process provided above provides
greater control over the physical characteristics of the balloon 12.
Importantly, the
dimensions, shape, and physical characteristics of the balloon 12 can be more
closely varied and controlled utilizing the manufacturing process provided
herein.
CA 02575032 2007-02-09
[0046] Additionally, it is believed that other materials such as PET, nylon,
polymers, and other block copolymers can be used for the balloon with the
unique
process provided herein. With the use of alternate materials, it is believed
that a
compliant balloon 12, a non-compliant balloon 12, or a semi-compliant balloon
12
can be manufactured using the process provided herein.
[0047] The tube 18 is typically extruded from the material using methods known
by those skilled in the art. The tube 18 includes a lumen 28, a tube inner
diameter
30, a tube outer diameter 32, a tube wall thickness 34, and a tube length 36
which
can be varied according to the desired size and strength characteristics of
the
balloon 12.
[0048] The preconditioning mold 20 preconditions the tube 18 to create the
parison 22. Basically, the precondition mold 20 is used to ready or
precondition the
tube 18 for expansion in the balloon mold 24. The required design of the
precondition mold 20 depends upon the desired design of the balloon 12. In the
embodiment shown in FIG. 2, the precondition mold 20 includes a pair of
opposed
precondition mold openings 38 and a precondition mold cavity 40 for forming
the
parison 22. The precondition mold openings 38 are each sized and shaped to
receive the tube 18 and are typically right circular cylinder shaped.
[0049] The size and shape of the precondition mold cavity 40 varies according
to the desired size and shape of the parison 22. In the embodiment shown in
FIG.
2, the shape of the precondition mold cavity 40 is that of a pair of opposed,
truncated right circular cones, which are separated by a right circular
cylinder.
However, those skilled in the art will recognize that the precondition mold
cavity 40
can have an alternate shape. For example, the opposed, truncated right
circular
cone could be replaced with a pair of opposed spherical segments (not shown).
[0050] The precondition mold cavity 40 restricts the expansion of the tube 18
and includes a precondition mold inner diameter ("PMID") 42 for restricting
the
expansion of the tube 18. The size of the precondition mold cavity 40 depends
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CA 02575032 2007-02-09
upon the size of balloon 12 to be manufactured, the material utilized, and the
size
of the tube 18. For example, in some instances, it may be beneficial for the
PMID
42 to be only slightly larger, i.e., more than one (1) times larger than the
tube outer
diameter 32. Typically, however the precondition mold 20 has a PMID 42 that is
approximately between one and one-half (1.5) to two and one half (2.5) times
larger than the tube outer diameter 32. Therefore, for a tube 18 having a tube
outer diameter 32 of about 0.035 inches, the precondition mold 20 has a PMID
42
of between approximately 0.052 inches and 0.0875 inches. However, it is
anticipated that a PMID 42 larger than approximately two and one-half (2.5)
times
the tube outer diameter 32 may be useful.
[00511 Preferably, the tube 18 is axially stretched and radially expanded in
the
precondition mold 20 so that the parison 22 is bi-axially oriented. The amount
of
axial stretching and radial expansion can vary according to the requirements
of the
balloon 12. Referring to FIG. 4, the parison 22 that is formed from the tube
18 in
the precondition mold 20 has a parison outer diameter 44, a parison inner
diameter 46, a parison wall thickness 48, and a parison length 50.
[00521 Typically, the tube 18 is: (i) axially stretched between approximately
one
and one-half (1.5) to two and one-half (2.5) times the original tube length
36; and
(ii) radially expanded so that the parison outer diameter 44 is between
approximately one and one-half (1.5) to two and one-half (2.5) times larger
than
the tube outer diameter 32. The resulting parison 22 is highly oriented and
has a
parison wall thickness 48 that is approximately one-fourth (0.25) the tube
wall
thickness 34.
100531 Referring back to FIG. 3, the balloon mold 24 is used to form the
balloon
12 from the parison 22. Thus, the design of the balloon mold 24 also varies
according to the desired design of the balloon 12. In the embodiment shown in
FIG. 3, the balloon mold 24 includes a pair of opposed balloon mold openings
62
and a balloon mold cavity 64. The balloon mold openings 62 are generally right
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circular, cylinder shaped. The balloon mold cavity 64 forms the shape of the
balloon 12. Accordingly, the balloon mold cavity 64 is shaped similar to the
desired
shape of the balloon 12. In the embodiment shown in FIG. 3, the shape of the
balloon mold cavity 64 is that of a pair of opposed, truncated right circular
cones
which are separated by a right circular cylinder. However, those skilled in
the art
will recognize that the balloon mold cavity 64 could have an alternate shape.
[0054] The size of the balloon mold cavity 64 depends upon the desired size of
balloon 12 to be manufactured. Typically, the balloon mold cavity 64 has a
balloon
mold inner diameter 66 ("BMID"), which is approximately between one and one-
half (1.5) to two and one-half (2.5) times larger than the PMID 42 of the
precondition mold 20. For example, for a parison 22 having a parison outer
diameter 44 of about 0.065 inches, the balloon mold 24 has a BMID 66 of
between
approximately 0.0975 inches and 0.1625 inches. However, it is anticipated that
a
BMID 66 which is less than approximately one and one-half (1.5) times the PMID
42 can be utilized. Similarly, it is also anticipated that a BMID 66 which is
greater
than approximately two and one-half (2.5) times the PMID 42 can be used.
[0055] Typically, the parison 22 is axially stretched and radially expanded in
the
balloon mold 24 to form the balloon 12. The amount of axial stretch and radial
expansion depends upon the requirements of the balloon 12. Referring to FIG.
5,
the balloon 12 that is formed from the parison 22 in the balloon mold 24 has a
balloon outer diameter 70, a balloon inner diameter 72, a balloon wall
thickness 74
and a balloon length 76. Typically, the parison 22 is: (i) axially stretched
between
approximately one (1) to one and one-half (1.5) times longer than the parison
length 50. The resulting balloon 12 is highly oriented and has a balloon wall
thickness 74 which is approximately one-third (1/3) the parison wall thickness
48.
[0056] To facilitate radial expansion and axial stretching, the precondition
mold
20 and the balloon mold 24 are preferably heated to heat the tube 18 or the
parison 22. This can be accomplished with a heating element (not shown) in the
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CA 02575032 2007-02-09
mold 20, 24 or by directing a hot fluid proximate the molds 20, 24. The axial
stretching and the radial expansion typically occur when the material is at or
above
the glass transition temperature of the material that is being used.
[0057] Devices and methods for radially expanding and axially stretching a
piece of tubing are well known by those skilled in the art. For example, as
shown
in FIG. 2, a first clamp 56 and a second clamp 58 can be used to grasp the
tube
18 on each side of the precondition mold 20 and axially stretching the tube
18. The
first clamp 56 also seals one (1) end of the tube 18 by compressing the tube
18.
For axially stretching of the tube 18, the first clamp 56 and/or the second
clamp 58
can be moved apart by a stepper motor (not shown).
[0058] Again referring to FIG. 2, the tube 18 can be radially expanded by
releasing pressurized fluid from a container 60 into the lumen 28 of the tube
18.
The pressurized fluid can be nitrogen gas, oxygen, or some other suitable
fluid
that is under pressure.
[0059] Typically, the axial stretching and the radial expansion occur
substantially simultaneously. However, in certain instances, it may be
beneficial for
axial stretching to occur before the radial expansion or radial expansion to
occur
before the axial stretching.
[0060] Method of Manufacture
[0061] The following procedure describes how to form what is designed as a
three millimeter (3 mm) by twenty millimeter (20 mm) balloon 12 from a
polyester-
polyester block copolymer sold under the trade-mark of "Pelprene S6001." It
should be understood that the following procedure is merely provided as an
example of a manufacturing process utilizing the precondition mold 20 and the
balloon mold 24.
[0062] The relationship between time, temperature, axial stretch, and
pressure,
for this particular example, is provided in FIGS. 6 and 7. Importantly, the
times,
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CA 02575032 2007-02-09
temperatures, pressures, and amount of axial stretching can be varied for a
different material, a different size of balloon 12, or to alter
characteristics of the
balloon 12.
[00631 Initially, the tube 18 is extruded from the polyester-polyester block
copolymer to form a tube 18 having a tube inner diameter 30 of approximately
0.017 inches, a tube outer diameter 32 of approximately 0.035 inches, a tube
wall
thickness 34 of approximately 0.009 inches, and a tube length 36 of
approximately
26 centimeters. Subsequently, the tube 18 is placed inside the preconditioning
mold 20. For this example, the preconditioning mold 20 has a PMID 42 which is
approximately 0.06 inches. Referring to FIG. 6, the temperature of the tube 18
is
ramped from approximately ambient temperature to a first temperature T1, which
is between approximately one hundred and thirty degrees Fahrenheit (130 F) to
one hundred and eighty degrees Fahrenheit (180 F) and preferably,
approximately one hundred and fifty degrees Fahrenheit (150 F). The increase
in
temperature only slightly softens the tube 18 made from the polyester-
polyester
block copolymer. After an initial, approximate fifteen (15) second delay, the
tube
18 is radially expanded by applying a first pressure P1 to the lumen 28. The
P1 is
typically between approximately five hundred (500) to six hundred (600) psi.
During this radial expansion, the tube 18 is also axially stretched
approximately
between one and one-half (1.5) to two and one-half (2.5) times the original
tube
length 36.
[00641 The axial stretch and pressure on the tube 18 in the precondition mold
cavity 40 expands the tube 18 to form the parison 22. Importantly, the size of
the
precondition mold cavity 40 prevents the tube 18 from bursting during this
procedure. Subsequently, the parison 22 is cooled until the temperature of the
precondition mold 20 is below approximately one hundred degrees Fahrenheit
(100 F).
CA 02575032 2007-02-09
=
[0065] The result is a highly oriented, work hardened parison 22 having a
parison outer diameter 44 of approximately 0.06 inches and a parison wall
thickness 48 which is approximately one-fourth (0.25) times the original wall
thickness.
[0066] Next, the parison 22 is positioned in the balloon mold 24. In this
example, the balloon mold 24 has a BMID 66 that is approximately two (2) times
larger than the PMID 42. In the balloon mold 24, the parison 22 is subjected
to a
first pressure cycle 78 and a second pressure cycle 80 to form the balloon 12.
[0067] During the first pressure cycle 78, the parison 22 is quickly heated
from
approximately ambient temperature to a second temperature ("T2"), which is
between approximately one hundred and eighty degrees Fahrenheit (180 F) to
two hundred and ten degrees Fahrenheit (210 F). After approximately a fifteen
(15) second delay, the lumen 28 is pressurized to approximately a second
pressure ("P2") which is between approximately two hundred and seventy (270)
to
three hundred and ten (310) psi and the parison 22 is axially stretched. After
approximately seventy-five (75) seconds, the pressure is reduced to
approximately
one hundred and fifty (150) psi for approximately five (5) seconds.
[0068] Subsequently, in the second pressure cycle 80, the pressure in the
lumen 28 is increased to a third pressure ("P3") which is between
approximately
three hundred and fifty (350) to five hundred and fifty (550) psi. The second
pressure cycle 80 lasts approximately twenty (20) seconds.
[00691 At this time, the dimensions of the balloon 12 are substantially
established and the balloon 12 is then subjected to the anneal cycle 82. The
anneal cycle 82 prepares the balloon 12 for use by internally stabilizing the
balloon
12 and relaxing the stress in the balloon 12. The anneal cycle 82 includes
raising
the temperature of the balloon mold 24 to a third temperature ("T3") which is
between approximately one hundred and ninety degrees Fahrenheit (190 F) to
two hundred and twenty degrees Fahrenheit (220 F) for forty-five (45) seconds
16
CA 02575032 2007-02-09
and reducing the internal pressure on the lumen 28 to a fourth pressure ("P4")
which is approximately one hundred and ninety (190) to two hundred and ten
(210)
psi.
[0070] Finally, the balloon 12 is cooled to ambient temperature. During the
cooling of the balloon 12, the internal pressure on the lumen 28 is reduced to
between approximately one hundred thirty (130) and one hundred eighty (180)
psi
and the balloon 12 is cooled until the temperature of the balloon 12 is below
approximately one hundred degrees Fahrenheit (100 F).
[0071] A compliance curve for a balloon 12 made in accordance with the
procedure outlined above is provided in FIG. 8. Importantly, the balloon 12
formed
by this procedure has improved physical characteristics, such as being semi-
compliant, soft, low crossing profile, and relatively high tensile strength.
[0072] Again, it should be noted that the above steps are merely exemplary.
The temperatures, pressures, and amount of axial stretch can be varied
according
to the balloon material utilized and the desired physical characteristics of
the
dilation catheter 10.
[0073] While the particular balloon 12 and method for manufacturing a balloon
12, as herein shown and disclosed in detail, is fully capable of obtaining the
objects and providing the advantages herein before stated, it is to be
understood
that it is merely illustrative of the presently preferred embodiments of the
invention
and that no limitations are intended to the details of construction or design
herein
shown other than as described in the appended claims.
17
