U.S. patent application number 10/742278 was filed with the patent office on 2005-06-23 for molds and related methods and articles.
Invention is credited to Lindquist, Jeffrey S., Schewe, Scott.
Application Number | 20050137619 10/742278 |
Document ID | / |
Family ID | 34678408 |
Filed Date | 2005-06-23 |
United States Patent
Application |
20050137619 |
Kind Code |
A1 |
Schewe, Scott ; et
al. |
June 23, 2005 |
Molds and related methods and articles
Abstract
Low polymer stress balloons are made by expanding a tube
radially while allowing the ends of the tube to move axially in
response to the radial expansion.
Inventors: |
Schewe, Scott; (Eden
Prairie, MN) ; Lindquist, Jeffrey S.; (Maple Grove,
MN) |
Correspondence
Address: |
FISH & RICHARDSON PC
225 FRANKLIN ST
BOSTON
MA
02110
US
|
Family ID: |
34678408 |
Appl. No.: |
10/742278 |
Filed: |
December 19, 2003 |
Current U.S.
Class: |
606/192 |
Current CPC
Class: |
B29K 2067/00 20130101;
B29K 2105/258 20130101; B29L 2022/022 20130101; B29B 2911/14653
20130101; B29C 33/56 20130101; B29K 2077/00 20130101; B29B
2911/14713 20130101; B29C 2049/4655 20130101; B29L 2031/7542
20130101; B29C 33/42 20130101; B29C 49/00 20130101; B29C 49/22
20130101; A61M 25/1029 20130101; B29C 2049/0089 20130101; B29L
2023/22 20130101; B29C 33/306 20130101; B29C 49/14 20130101; B29C
49/0005 20130101 |
Class at
Publication: |
606/192 |
International
Class: |
A61M 029/00 |
Claims
What is claimed is: claims
1. A method of making a medical balloon, comprising: providing a
polymer tube suitable for being formed into the medical balloon,
the tube having two ends; drawing the tube axially; and expanding
the tube radially while allowing the ends of the tube to move
axially in response to said radial expansion.
2. The method of claim 1, wherein the tube is below a glass
transition temperature of a material of the tube during
drawing.
3. The method of claim 2, wherein the tube is below about
100.degree. C. during drawing.
4. The method of claim 1, wherein the tube is internally
pressurized during drawing.
5. The method of claim 1, wherein expanding the tube comprises
heating the tube.
6. The method of claim 5, wherein the tube is heated to a
temperature about equal to or greater than a glass transition
temperature of a material of the tube.
7. The method of claim 1, wherein the tube is expanded to an
expanded diameter about 5 to 9 times larger than an unexpanded
diameter of the tube.
8. The method of claim 1, wherein expanding the tube comprises
simultaneously heating and pressurizing the tube.
9. The method of claim 1, wherein expanding the tube comprises:
positioning the tube into a mold; and simultaneously heating and
pressurizing the tube.
10. The method of claim 1, wherein expanding the tube comprises
contacting the tube with a liquid.
11. The method of claim 10, wherein the liquid comprises water.
12. The method of claim 1, wherein the ends of the tube are allowed
to move axially a distance between about 5 and about 30 percent of
an original length of the tube.
13. The method of claim 1, wherein the tube is formed of a polymer
having regions of different hardnesses.
14. The method of claim 1, wherein the tube comprises a block
copolymer including hard segments and soft segments.
15. The method of claim 14, wherein the block copolymer comprises a
material selected from a group consisting of a polyether-ester
elastomer, a polyester elastomer, and a polyether block amide.
16. The method of claim 14, wherein the block copolymer comprises a
polyether-ester elastomer.
17. The method of claim 1, wherein the tube comprises a material
selected from a group consisting of a polyester and a
polyamide.
18. The method of claim 1, wherein the tube is a multilayer
tube.
19. The method of claim 1, wherein the tube is a coextruded tube
having layers of different hardnesses.
20. The method of claim 1, further comprising characterizing the
balloon by birefringence.
21. The method of claim 1, further comprising attaching the balloon
to a catheter to form a balloon catheter device.
22. The method of claim 1, further comprising sterilizing the
balloon by heating between about 32.degree. C. and about 60.degree.
C.
23. The method of claim 1, wherein expanding the tube radially
comprises allowing the ends of the tube to move inwardly in
response to said radial expansion.
24. A method of making a medical balloon, comprising: providing a
polymer tube suitable for being formed into the medical balloon,
the tube having two ends; and expanding the tube radially while
allowing the ends of the tube to move axially in response to said
radial expansion.
25. The method of claim 24, further comprising axially orienting a
material of the tube.
26. The method of claim 25, wherein axially orienting the material
comprises axially drawing the tube.
27. The method of claim 26, wherein axially orienting the material
further comprises internally pressurizing the tube.
28. The method of claim 24, wherein expanding the tube comprises
contacting the tube with a liquid.
29. The method of claim 28, wherein the liquid comprises water.
30. The method of claim 24, wherein expanding the tube comprises:
heating the tube to a temperature about equal to or greater than a
glass transition temperature of a material of the tube; and
introducing a gas into the tube.
31. The method of claim 24, wherein expanding the tube further
comprises placing the tube into a mold.
32. The method of claim 24, wherein the tube comprises a block
copolymer.
33. The method of claim 24, further comprising characterizing the
balloon by birefringence.
34. The method of claim 24, further comprising attaching the
balloon to a catheter to form a balloon catheter device.
35. The method of claim 1, further comprising positioning a stent
on the balloon.
36. The method of claim 24, further comprising positioning a stent
on the balloon.
37. A medical balloon product made according to the method of claim
1.
38. A medical balloon product made according to the method of claim
24.
39. A medical balloon comprising a block copolymer having a
cylindrically-shaped region exhibiting a birefringence pattern of
substantially parallel lines before and after an exposure to
temperatures of about 32.degree. C. to about 60.degree. C.
40. The balloon of claim 39, wherein the cylindrically-shaped
region has a length between about 1.5 cm and about 14 cm.
41. The balloon of claim 39, wherein the cylindrically-shaped
region has an outer diameter between about 1 mm and about 12
mm.
42. The balloon of claim 39, formed of a polymer having regions of
different hardness.
43. The balloon of claim 39, wherein the block copolymer includes
hard segments and soft segments.
44. The balloon of claim 39, wherein the block copolymer comprises
a material selected from a group consisting of a polyether-ester
elastomer, a polyester elastomer, and a polyether block amide.
45. The balloon of claim 39, wherein the block copolymer comprises
a polyether-ester elastomer.
46. The balloon of claim 39, comprising a material selected from a
group consisting of a polyester and a polyamide.
47. The balloon of claim 39, formed of multiple layers.
48. The balloon of claim 47, formed of multiple coextruded layers
having different hardnesses.
Description
TECHNICAL FIELD
[0001] This invention relates to medical balloons, such as dilation
balloons and catheters using such balloons, and methods of making
and using the same.
BACKGROUND
[0002] Medical balloons can be deflated and inflated about their
long supporting devices and placed in bodily conduits to administer
treatments, for example, deployment of stents or widening of
constricted passages during angioplasty, valvuloplasty, or
urological procedures.
[0003] In angioplasty, for example, coronary angioplasty, a balloon
can be used to treat a stenosis by collapsing the balloon and
placing it in a bodily conduit, e.g., a coronary artery. The
balloon is then inflated, e.g., by injecting a fluid, at a region
of the artery that has been narrowed to such a degree that blood
flow is restricted. Inflating the balloon can expand the stenosis
radially so that the vessel will permit an acceptable rate of blood
flow. This procedure can be a successful alternative, for example,
to coronary arterial bypass surgery. After use, the balloon is
deflated or collapsed and withdrawn.
[0004] Medical balloons can be manufactured by extruding a
cylindrical tube of polymer and then pressurizing the tube while
heating to expand the tube into the shape of a balloon. The balloon
can be fastened around the exterior of a hollow catheter shaft to
form a balloon catheter. The hollow interior of the balloon is in
fluid communication with the hollow interior of the shaft. The
shaft may be used to provide a fluid supply for inflating the
balloon or a vacuum for deflating the balloon.
[0005] It is important that the balloon have a generally
predictable shape on inflation. Typically, the balloon, such as a
regular balloon, should have proximal and distal taper regions with
closely matched taper angles and a uniformly cylindrical dilatation
region. A deformed regular balloon, however, may have an irregular
profile, such as a taper extending along the length of the
dilatation region or portions with non-uniform cross sectional
diameters. As a result, during use, deformed regular balloons may
undesirably provide unpredictable, and thus unreliable,
inflations/deflations or stent deployments. It is believed that
deformed balloon shapes can be caused by locking the polymeric
chains in undesirable configurations during manufacture, referred
to as polymeric stress. The release or partial release of this
stress, e.g., during heat sterilization, can also cause
deformation.
SUMMARY
[0006] This invention relates to medical balloons, such as dilation
balloons and catheters using such balloons, and methods of making
and using the same.
[0007] In one aspect, the invention features a method of making
medical balloons that relieves and minimizes stress in the balloon.
The invention also features balloon devices such as, for example,
balloon catheters and stent deployment systems.
[0008] In another aspect, the invention features a method of making
a medical balloon including providing a polymer tube having two
ends and suitable for being formed into the medical balloon, and
expanding the tube radially while allowing the ends of the tube to
move axially in response to said radial expansion. The method can
further include axially orienting a material of the tube, e.g., by
axially drawing the tube. Axially orienting the material can
further include internally pressurizing the tube.
[0009] In another aspect, the invention features a method of making
a medical balloon including providing a polymer tube having two
ends and suitable for being formed into the medical balloon,
drawing the tube axially, and expanding the tube radially while
allowing the ends of the tube to move axially in response to said
radial expansion.
[0010] Embodiments of aspects of the invention may include one or
more of the following features. The ends of the tube are allowed to
move freely as the balloon is formed. In some embodiments, the ends
of the tube moves inwardly, for example, a distance between about 1
and about 40 percent, e.g., between about 5 and about 30 percent of
an original length of the tube, between about 10 and about 25
percent, or between about 15 and about 22 percent. The tube is
below a glass transition temperature of a material of the tube
during drawing, e.g., below about 100.degree. C. The tube is
internally pressurized during drawing.
[0011] Expanding the tube can include heating the tube, e.g., to a
temperature about equal to or greater than a glass transition
temperature of a material of the tube. The tube can be expanded to
an expanded diameter of the balloon being made. In certain
embodiments, the tube can be expanded to an expanded diameter about
1 to about 15 times, e.g., about 5 to about 9 times, larger than an
unexpanded diameter of the tube, e.g., by introducing a gas into
the tube. Expanding the tube can include simultaneously heating and
pressurizing the tube. Expanding the tube can include positioning
the tube into a mold, and simultaneously heating and pressurizing
the tube. Expanding the tube can include contacting the tube with a
liquid, e.g., one including water.
[0012] The tube can be formed of a polymer having regions of
different hardness. The tube can include a block copolymer having
hard segments and soft segments. The block copolymer can be a
polyether-ester elastomer, a polyester elastomer, or a polyether
block amide. The tube can include a material such as a polyester
and a polyamide. The tube can be a multilayer tube, such as a
coextruded tube having layers of different hardness. The tube can
be formed of a polymer that is not a block copolymer.
[0013] The method can further include characterizing the balloon by
birefringence.
[0014] The method can further include attaching the balloon to a
catheter to form a balloon catheter device. The method can further
include sterilizing the balloon, e.g., by heating the balloon
between about 32.degree. C. and about 60.degree. C.
[0015] The method can further include attaching the balloon to a
catheter to form a balloon catheter device and/or positioning a
stent on the balloon.
[0016] In another aspect, the invention features medical balloon
product made according to the above methods.
[0017] Embodiments of the invention include one or more of the
following features. The medical balloon can include a block
copolymer having a cylindrically-shaped region exhibiting a
birefringence pattern of substantially parallel lines before and
after an exposure to sterilization temperatures. In certain
embodiments, the balloon can be exposed to about 32.degree. C. to
about 60.degree. C. The cylindrically-shaped region can have a
length between about 1.5 cm and about 14 cm and/or an outer
diameter between about 2 mm and about 30 mm, e.g., about 2 mm and
about 20 mm, or about 2 mm and about 12 mm. The polymer can have
regions of different hardness, e.g., hard segments and soft
segments. The block copolymer can include a material such as, for
example, a polyether-ester elastomer, a polyester elastomer, a
polyether block amide, a polyester, or a polyamide. The balloon can
be formed of multiple layers, e.g., multiple coextruded layers
having different or the same hardness.
[0018] Embodiments may have one or more of the following
advantages. During balloon formation, the balloon is not
constrained in movement or axially drawn. Instead, the balloon is
allowed to recover or relax, e.g., contract and/or expand axially
and radially. As a result, the balloons can be formed uniformly and
with a minimal level of residual stress. Subsequently, the balloons
can then be exposed to a post-formation heat treatment, such as
sterilization at temperatures of about 32.degree. C. to about
60.degree. C., without incurring substantial irregularities or
deformations. The balloons can be produced consistently and
predictably, thereby providing reliable results during use. The
balloons may also be mechanically stable and have enhanced
properties, such as burst strength and hoop strength. The method
can also be performed without the need for certain production
steps, such as annealing, thereby reducing manufacturing cost and
time. The process can be useful for forming relatively large size
balloons. The process can be useful for forming balloons about
1.5-14 cm or more in length and/or about 1-30 mm, e.g., about 1-20
mm, or about 1-12 mm, or more in diameter, where small amounts of
residual polymeric stress may be manifested as relatively large
physical deformations. Other balloon sizes are possible.
[0019] Other features and advantages of the invention will be
apparent from the description of the preferred embodiments thereof
and from the claims.
DESCRIPTION OF DRAWINGS
[0020] FIG. 1 is a schematic of an embodiment of a method of making
a medical balloon;
[0021] FIG. 2A is a photograph of a medical balloon having a
substantially straight birefringence pattern;
[0022] FIG. 2B is a photograph of medical balloons having a "bump"
birefringence pattern and a "bowtie" birefringence pattern;
[0023] FIG. 2C is a photograph of medical balloons having a
proximal to distal taper birefringence pattern and a distal to
proximal taper birefringence pattern;
[0024] FIGS. 3A-3B are schematic views of an embodiment of a
drawing machine during use;
[0025] FIGS. 4A-4C are schematic views of an embodiment of a
blow-molding assembly during use;
[0026] FIG. 5 is a front view of an embodiment of a gripper
assembly;
[0027] FIG. 6 is a top view of the gripper assembly of FIG. 5;
[0028] FIG. 7 is an end view of the gripper assembly of FIG. 5;
[0029] FIG. 8 is an exploded perspective view of an embodiment of a
gripper;
[0030] FIG. 9 is a plot of applied internal pressure (psi) vs. time
(sec) during axial drawing of a 6-4 balloon; and
[0031] FIG. 10 is a plot of parison internal temperature (Celsius)
vs. time (second) and pressure (psi) vs. time (second) during
fabrication of a 6-4 medical balloon; and
[0032] FIG. 11 is a plot of parison internal temperature (Celsius)
vs. time (second) and pressure (psi) vs. time (second) during
fabrication of an 8-4 medical balloon.
DETAILED DESCRIPTION
[0033] Referring to FIG. 1, a method of fabricating a medical
balloon 20 includes the steps of drawing a tube 22 axially to form
a parison 28 having a stretched portion 24, and forming the balloon
in the stretched portion. During formation of balloon 20, both ends
26 of parison 28 are allowed to move axially, e.g., contract in the
direction of the balloon (shown by arrows 27). The balloon exhibits
no or relatively small undesirable deformation, both after
formation and after a post-formation heat treatment, such as heat
sterilization in ethylene oxide. Consequently, the balloon provides
enhanced performance. In certain embodiments, the balloon exhibits
accurate sizing, good abrasion resistance, and/or consistent
deflations and inflations.
[0034] The amount of residual stress retained by a balloon can be
measured by observing the birefringence of polarized light passing
through the balloon. Referring to FIG. 2A, one example of a balloon
in which stress has been substantially relieved can exhibit a
birefringence pattern of generally parallel lines 23 across the
dilatation portion, or body, 21 of the balloon and generally
symmetric taper birefringence. Referring to FIGS. 2B and 2C, a
balloon in which stress is retained can show wavy-line
birefringence 25, asymmetric split line birefringence 27, and
birefringence lines 29 that are not parallel with the cylindrical
surfaces of the balloon. Upon release of this stress, e.g., by heat
sterilization, the balloon may deform unpredictably into an
undesired shape.
[0035] Without wishing to be bound by theory, it is believed that
the deformed shapes in medical balloons can be the result of
residual stresses imposed in the polymer during manufacture, e.g.,
during blowing and heating. Irregular balloon shapes can be
particularly problematic when the balloons are formed of a material
having molecular portions or segments capable of having different
physical properties.
[0036] For example, a block copolymer can include molecular
segments that are relatively hard or rigid and other segments that
are softer or more elastic. The rigidity of the hard regions is
believed to be caused by the intermolecular interaction of the
polymer chains in these regions, which lock the segments in a
particular orientation. In the soft segments, on the other hand,
the molecular chains are more mobile, e.g., they can expand or
contract. The sections can distribute themselves differently in
response to stretching and temperature changes.
[0037] In forming a balloon, a portion of a tube of block copolymer
is heated, typically above the glass transition temperature
(T.sub.g) of the tube material, and the polymer is stretched, e.g.,
radially, by blowing. This process orients the polymer. As the
polymer is cooled, the chains become locked in given
orientations.
[0038] In the present technique, the ends of the polymer tube are
free to contract, expand, etc. as the inflated portion is formed so
that the polymeric chains are able to orient in desirable
configurations, thus reducing polymeric stress. In addition, in
some embodiments, it is preferred that the tube is axially
stretched and plastically deformed at low temperatures prior to
blowing. The low temperature stretching is believed to axially
orient the polymer. By carrying this step out at low temperatures,
e.g., less than T.sub.g, the polymer orientation is not modified by
heat-induced phenomena. As a result, the balloon is biaxially
oriented with reduced stress.
[0039] Balloon 20 can be formed of a resilient material, such as a
polymer, that is capable of being inflated and deflated in a
patient. Preferably, the material is relatively stable upon
crystallization. As discussed above, the method is particularly
applicable to polymers or polymer combinations in which stress
produced during manufacture is subsequently released, e.g., during
heat sterilization. Deformation problems can be most severe when
soft polymers are used in combination with hard or rigid, highly
crystalline polymers, such as polyethylene terephthalate (PET). For
example, block copolymers having soft and rigid blocks or
combinations of different polymers in coextruded layers having
different stress release characteristics can be effectively
manufactured with reduced deformations. Examples of suitable
materials include block copolymers such as a polyether-ester
elastomer (e.g., Amitel.RTM. EM740, from DSM Engineering Plastics,
Evansville, Ind.), a thermoplastic polyester elastomer resin (e.g.,
Hytrel.RTM. from E. I. du Pont de Nemours and Co.), or a polyether
block amide (e.g., Pebax.RTM. from Atofina). Other materials can
also be used, for example, organic or synthetic polymers such as
polyimides, nylons, rubbers, latex, or engineered resins. In some
embodiments, the material can have a hardness, measured in Shore D
hardness, between about 50 and about 75.
[0040] Referring to FIGS. 3A and 3B, in one embodiment, parison 28
may be formed in a drawing machine 30. Drawing machine 30 stretches
tube 22, which axially orients the polymer. The stretching
preferably is done below the glass transition temperature of the
polymer, e.g., at room temperature (typically about 15 to about
30.degree. C.), so the parison is not exposed to high temperatures
during stretching. Drawing machine 30 includes a pair of opposed
gripping assemblies 38, 40 between which tube 22 can be stretched.
Gripping assembly 38 is fixed, e.g., using a bolting arrangement
44, to a support table 46 and includes a pressured tube gripper 48
that clamps a sealed end of tube 22. Gripping assembly 40 is
moveable. Assembly 40 can be translated along table 46 (arrow 50)
by coupling the assembly to a translation device 52, such as a
planetary gear coupled to a servo motor. Moveable gripping assembly
40 includes a pressurized gripper 58 that grips an open end of the
tube 22 and permits a coupling 60 for introduction of pressurized
fluid, such as a gas, from a fluid source into the tube. Suitable
grippers are available from, for example, SMC Corp., Indianapolis
Ind. (Model MGQ2-25S). The servo motor and gas source may be
interfaced to a computer to draw an end of tube 22 a predetermined
distance at a predetermined rate while providing a predetermined
pressure profile. Multiple sets of gripper assemblies may be
arranged in adjacent rows to simultaneously stretch multiple tubes.
Parison 28 may also be stretched by translating both ends 26.
Pressurized gas may be introduced from both ends 26.
[0041] Tube 22 is generally a cylindrical member dimensioned to be
suitable for being fabricated into a medical balloon. For example,
tube 22 can have a length of about 5 cm to about 42 cm; an inner
diameter of about 0.2 mm to about 3 mm; and an outer diameter of
about 1 mm to about 4 mm, depending on the size of the balloon to
be fabricated and the material of the tube. Other tube sizes can be
used.
[0042] The dimensions of stretched portion 24, e.g., length, and
end tapers, are a function of the drawing parameters, such as the
rate of drawing, the distance of drawing, the initial dimensions of
tube 22, the material of the tube, the internal pressure, inner
diameter, and outer diameter. Generally, the larger the balloon to
be fabricated, the more tube 22 is drawn and the longer the
stretched portion. The rate of drawing can be relatively slow or
relatively fast, e.g., about 0.02 cm/sec to about 0.6 cm/sec.
Faster draw rates can improve production throughput.
[0043] The rate and distance of drawing are generally balanced with
the applied internal pressure to form a substantially uniform
stretched portion 24. Relatively low pressure is typically applied
at relatively slow draw rates to avoid bulging stretched portion 24
and/or bursting tube 22. Conversely, at relatively high draw rates,
relatively high pressure is applied to maintain the integrity of
the lumen of tube 22 and to minimize crystallization in stretched
portion 24, which could later appear as defects during balloon
formation.
[0044] Referring to FIGS. 4A-4C, in one embodiment, parison 28 is
formed into a balloon by expanding stretched portion 24 under
pressure while heating. During expansion, both ends of parison 28
can contract axially to relieve stress introduced during the axial
stretching or radial expansion. In one embodiment, balloon 20 can
be formed using a blow-molding assembly 70, which includes a heated
mold 72 and two opposing gripper assemblies 74, 76 that are
translateably mounted on a support table 78 using low friction
couplings 80, 82. The mass of the grippers and the low friction
couplings 80, 82 are arranged to allow the parison to move freely
or with minimal inhibition. In some embodiments, the mass of the
grippers and the low friction couplings 80, 82 are arranged to
provide a small frictional resistance, e.g., having a coefficient
of friction of about 0.003, to axial motion compared to the force
of the relaxing polymer. Suitable couplings include ball slides. In
other embodiments, the ends of the balloon can be mechanically
urged inwardly, e.g., using a motor to release stress.
[0045] Mold 72 may be a clamshell-type mold having an upper portion
84 and a lower portion 86 that can be positioned about stretched
portion 24, and includes a mold cavity 85 of desired shape. Mold 72
can be made of any material that is stable, e.g., does not melt, at
balloon forming temperatures and that can be heated, e.g., by an
infrared lamp or by a resistive or inductive heater. Suitable
materials include those with relatively high thermal conductivity
such as, e.g., aluminum, stainless steel, beryllium copper alloys,
and glass.
[0046] Gripper assemblies 74, 76 include pressurized grippers to
grip the ends of the parison and couplings 79 to permit the
introduction of pressurized gas. Throughout balloon formation,
pressure is applied in the parison. The amount of applied pressure
depends, for example, on the size of the balloon and the properties
of the parison such as hoop stress. For example, larger balloons
tend to require less pressure. Too much pressure can burst the
balloon, while too little pressure can produce incomplete balloon
formation.
[0047] To form balloon 20, parison 28 is positioned between gripper
assemblies 74, 76 and mold 72 is positioned about the central
portion of the parison (FIG. 4A). Mold 72 is then heated, typically
above the glass transition temperature of the parison polymer(s),
while pressurized gas is introduced into the parison lumen, causing
the central portion of the parison to expand into the shape of the
mold (FIG. 4B). As evident, the ends of the parison engaged by the
grippers are not substantially heated. As the temperature of the
mold is increased and the polymer heats above T.sub.g and is
pressurized, stresses induced during blow molding and axial
stretching are allowed to relax by permitting the ends of the
parison to be drawn inward (arrows 88, 90) (FIG. 4C). The parison
can axially relax between about 5 to about 30 percent of its
length. The ends of the parison move inwardly during blowing since
the grippers are mounted on low friction couplings 80, 82, which
are slideable inwards. The stress release may be gradual as the
balloon forms. Typically, the balloon expands to a diameter of
about 5-9 times the inner diameter of tube 22. After reaching the
desired diameter, mold 72 is cooled.
[0048] Referring again to FIG. 1, after formation of balloon 20,
the balloon is cooled, the end portions are cut away, e.g., the
portions extending outwardly from the smallest diameter of the
parison, and the balloon is assembled upon a suitable catheter 92
that has a balloon inflation lumen 94 for inflation of the balloon
and a through lumen 96 for receiving a guidewire. Radiopaque
markers 98 can be provided on catheter 92 near the ends of the main
body of balloon 20. Catheter 92, including balloon 20, can then be
sterilized.
[0049] In other embodiments, balloon 20 can be used with a balloon
expandable stent to form a stent delivery system. For example, the
stent is crimped to its reduced diameter over a delivery catheter,
positioned at a deployment site, and then expanded in diameter by
fluid inflation of the balloon positioned between the stent and the
delivery catheter.
[0050] In other embodiments, the step of axially drawing tube 22
can be eliminated. For example, tube 22 can be pre-formed axially
oriented and/or include a segment having a diameter equal to
stretched portion 24. Alternatively, a hypotube having an outer
diameter equal to the inner diameter of stretched portion 24, can
be inserted into tube 22 prior to axial stretching to maintain the
lumen of the stretched portion.
[0051] In other embodiments, during axial drawing, both ends of
tube 22 can be drawn. During balloon formation, the pressuring
fluid can be introduced through only one end of parison 28. Other
balloon formation techniques may be used. For example, free blowing
without a mold may be used.
[0052] In some embodiments, mold 72 includes an indicator, e.g., a
hash mark, that can be used to place parison 28 in the mold at a
predetermined position. The indicator can minimize systematic
error.
[0053] In other embodiments, the methods described above can be
applied to other balloon configurations, such as, for example,
step, or non-regular, balloons.
[0054] Further embodiments are illustrated in the following
examples, which are not intended to be limiting.
EXAMPLE 1
[0055] FIGS. 5-7 illustrate a particular gripper assembly and low
friction coupling.
[0056] Each gripper assembly 100 includes a gripper 102 that is
connected, e.g., by brackets 104, to a vertically-mounted ball
slide, or crossed roller slide, 106 and a horizontally-mounted ball
slide 108. Each gripper 102 connects to one end of a parison and
allows a pressurizing gas to be introduced into the lumen of the
parison. Slides 106 and 108 allow the parison to move freely, e.g.,
contract axially and/or move vertically within a mold, during
balloon formation. Slides 106 and 108 are commercially available
from, for example, PIC Design Corp., Middlebury, Conn. (Part No.
PNBT-1080A).
[0057] Referring to FIG. 8, gripper 102 includes a cube-like
housing 110. On a first face of housing 110, gripper 102 receives a
silicone grommet 112 and a grommet cap 114. On a second face
opposite the first face, housing 110 receives a balloon guide 116
having an opening 118 through which the parison is fitted. On a
third face, housing 110 receives a piston 120, including O-rings
122, and a piston cap 124. Generally, gripper 102 mates with the
ends of the parison by applying pressure to piston 120 to lock the
parison in place. Simultaneously, pressure is applied around
grommet 112 to allow the inflation pressure to flow into the
parison without leaking.
EXAMPLE 2
[0058] The following illustrates formation of a 6-4 (i.e., 6 mm
O.D. and 4 cm long) Amitel.RTM. (EM740 from DSM Engineering
Plastics, Evansville, Ind.) balloon.
[0059] A tube of Arnitel.RTM. was provided having an inner diameter
of about 0.086 cm (0.034 in), an outer diameter of about 0.177 cm
(0.07 in), and a length of about 30.48 cm (12 in). The tube was
sealed on one end by heating and pressing the end with pliers. The
tube was formed into a parison by axially drawing the open end of
the tube at room temperature. The draw rate was about 0.41 cm/sec
(0.16 in/sec); the draw length was about 10.16 cm (about 4 in); and
the maximum internal nitrogen pressure was about 450 psi (FIG. 9).
A stretched portion about 10.16 cm (about 4 in) long and having an
O.D. of about 0.152 cm (0.06 in) was produced. The sealed end of
the tube was removed.
[0060] The parison was formed into a balloon using an aluminum
clamshell mold positioned between a gripper assembly described in
Example 1. The lower half shell included a thermocouple positioned
at the center to monitor the temperature of the mold during
use.
[0061] Before forming the balloon, the lower half of the mold was
sprayed with a liquid, such as water, until the lower half was
uniformly coated. It is believed that the liquid acted as a surface
lubricant for the balloon and/or a plasticizer for the polymer in
the balloon. The liquid may also help to maintain a uniform heat
profile along the mold. The parison was then placed on the lower
half of the mold at a predetermined position, e.g., by placing an
end of the parison at an indicator mark, and connected to the
grippers. The horizontally-mounted ball slide allowed the parison
to move horizontally within the mold. The upper half of the mold
was then lowered onto the lower half. The parison was then
pressurized by introducing N.sub.2 gas into both ends of the
parison, and heated to form the balloon. The parison was not drawn
axially during balloon formation. Instead, the parison was allowed
to move freely such that as the balloon was formed and needed more
material to expand, the balloon drew adjacent material toward
itself.
[0062] The parison was heated to balloon forming temperatures about
equal to or greater than a glass transition temperature (T.sub.g)
of the parison material, e.g., about 45-50.degree. C. for
Amitel.RTM.. Due to heat loss, e.g., radiative heat loss to air,
the mold was heated to a temperature greater than the glass
transition temperature of the parison material, e.g., about
110-115.degree. C., as measured by the thermocouple positioned in
the lower half of the mold. The parison was maintained at the
balloon forming temperatures for a time sufficient for the balloon
to fully form. Then, the heater was turned off, the mold was force
quenched to room temperature by spraying the mold with water, and
the upper half of the mold was lifted. Referring FIG. 10,
temperature and pressure profiles during fabrication of the 6-4
balloon are shown. The temperature profile shows an internal
parison temperature, as measured by a thermocouple inserted through
one end of the parison and positioned in the center of the parison.
At to, the parison was connected to the grippers, and the applied
pressure was relatively low, e.g., about 37 psi. At t.sub.1, which
corresponds to the closing of the upper half of the mold, the
pressure was increased to a first balloon forming pressure
(P.sub.1), here, about 265 psi. Then, at t.sub.2, the heater was
turned on and controlled to provide balloon forming temperatures,
here, an internal parison temperature of about 101.degree. C., to
form the balloon. About midway through balloon formation (t.sub.3),
here, about 35 seconds, the pressure was increased to a second
balloon forming pressure (P.sub.2), here, about 273 psi. In the
present example, about midway through balloon formation, the
temperature, as measured by the thermocouple of the lower half
shell, was also increased, e.g., stepped from about 123.degree. C.
to about 132.degree. C., to maintain the internal parison
temperature of about 101.degree. C. Other manufacturing
configurations may not require a change in pressure and/or
temperature. It is believed that the changes in pressure and
temperature helped to fully expand the parison to contact the mold
and complete balloon formation. The parison was held at the balloon
forming pressures and temperatures for a time sufficient to form
the balloon. At a predetermined time (t.sub.4), the temperature was
decreased, e.g., to room temperature, while the pressure was
maintained at the second balloon forming pressure, P.sub.2. At
t.sub.5, the pressure was decreased. The balloon was then removed
from the mold and the grippers.
[0063] To qualitatively characterize the degree of stress in the
balloon, the formed balloon was evaluated by directing
polychromatic white light through the balloon, and viewing the
balloon with a polarizing lens. In some embodiments, the
birefringence pattern generally contains straight and uniform
strain lines with minimal taper. FIG. 2A shows the bireflingence
pattern of a 6-4 balloon formed by the methods described above. In
comparison, as shown in FIGS. 2B and 2C, 6-4 balloons in which
axial movement was restricted during blowing, e.g., by mechanically
restricting the ends of the parison, have birefringence patterns
that are non-uniform and not straight, indicating that the balloons
have residual stress and/or are tapered.
EXAMPLE 3
[0064] The following illustrates formation of an 8-4 (i.e., 8 mm
O.D. and 4 cm long) Arnitel.RTM. (EM740 from DSM Engineering
Plastics) balloon.
[0065] A tube of Arnitel.RTM. was provided having an inner diameter
of about 0.108 cm (0.0425 in), an outer diameter of about 0.203 cm
(0.080 in), and a length of about 30.48 cm (12 in). The tube was
sealed on one end by heating and pressing the end with pliers.
Similar to Example 2, the tube was formed into a parison by axially
drawing the open end of the tube at room temperature. The draw rate
was about 0.41 cm/sec (0.16 in/sec); the draw length was about
12.065 cm (4.75 in); and the maximum internal nitrogen pressure was
about 410 psi. A stretched portion about 12.065 cm (4.75 in) long
and having an O.D. of about 0.175 cm (0.069 in) was produced.
[0066] The parison was formed into a balloon using generally the
same assembly and method as described in Examples 1 and 2 (with a
different mold). FIG. 11 shows the temperature and pressure
profiles during blowing of the 84 balloon.
[0067] The formed balloon was characterized using birefringence to
qualitatively evaluate the degree of stress in the balloon.
[0068] Other embodiments are within the claims.
* * * * *