U.S. patent application number 09/016770 was filed with the patent office on 2002-08-15 for process improvements for preparing catheter balllons.
Invention is credited to FRANK, DEBORAH A., HORN, DANIEL J., MILLER, PAUL JAMES, WANG, LIXIAO.
Application Number | 20020110657 09/016770 |
Document ID | / |
Family ID | 22730157 |
Filed Date | 2002-08-15 |
United States Patent
Application |
20020110657 |
Kind Code |
A1 |
WANG, LIXIAO ; et
al. |
August 15, 2002 |
PROCESS IMPROVEMENTS FOR PREPARING CATHETER BALLLONS
Abstract
A method for forming a balloon for a dilatation catheter
involving the steps of extruding a tubing preform of a polyester
resin and then blowing the tubing into an oriented balloon, wherein
the tubing preform is dried prior to blowing into the balloon form.
The addition of this drying step to the balloon forming method has
been observed to cause a reduction in the frequency of balloons
which are rejected because of visible defects in the balloon wall,
while producing the same or higher average wall strengths in the
non-defective balloons obtained. Balloon cone and waist thicknesses
are reduced by varying the axial tension and blowing pressure at
several stages as a mold containing the balloon preform is dipped
into a heating medium. Specifically, tubing of a thermoplastic
material is placed in a mold and blown by pressurizing and
tensioning the tubing and gradually dipping the mold into a heated
heat transfer media so as to sequentially blow a first waist, a
body and a second waist portion. The tubing is subjected to a
relatively lower pressure while the body portion is blown than
while the first and second waist portions are blown.
Inventors: |
WANG, LIXIAO; (MAPLE GROVE,
MN) ; MILLER, PAUL JAMES; (ST LOUIS PARK, MN)
; HORN, DANIEL J.; (SHOREVIEW, MN) ; FRANK,
DEBORAH A.; (ST LOUIS PARK, MN) |
Correspondence
Address: |
VIDAS, ARRETT & STEINKRAUS, P.A.
6109 BLUE CIRCLE DRIVE
SUITE 2000
MINNETONKA
MN
55343-9185
US
|
Family ID: |
22730157 |
Appl. No.: |
09/016770 |
Filed: |
January 30, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09016770 |
Jan 30, 1998 |
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08197634 |
Feb 17, 1994 |
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09016770 |
Jan 30, 1998 |
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08650222 |
May 20, 1996 |
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08650222 |
May 20, 1996 |
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08197634 |
Feb 17, 1994 |
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08197634 |
Feb 17, 1994 |
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08124238 |
Sep 20, 1993 |
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Current U.S.
Class: |
428/35.7 ;
428/36.9 |
Current CPC
Class: |
B29C 35/041 20130101;
A61M 25/1002 20130101; A61M 25/104 20130101; B29C 49/18 20130101;
Y10T 428/139 20150115; B29C 2949/08 20220501; A61M 25/1029
20130101; A61M 2025/1075 20130101; A61M 2025/1088 20130101; B29C
49/04 20130101; B29C 49/783 20130101; B29K 2067/00 20130101; Y10T
428/1331 20150115; B29L 2031/7542 20130101; Y10T 428/1352 20150115;
B29K 2905/12 20130101; B29K 2105/258 20130101; A61M 25/0045
20130101 |
Class at
Publication: |
428/35.7 ;
428/36.9 |
International
Class: |
B32B 001/08 |
Claims
What is claimed is:
1. An oriented balloon of thermoplastic material prepared by the
method of extruding a hollow tube of the balloon material, and
subsequently expanding the tube under heat and pressure in a mold
to produce an oriented balloon, wherein the tube is dried prior to
said expanding step.
2. An oriented balloon as in claim 1 wherein said tube is dried to
a moisture content of 0.15% or less.
3. An oriented balloon as in claim 2 wherein said tube is dried to
a moisture content of 0.10% or less.
4. An oriented balloon as in claim 3 wherein said tube is dried to
a moisture content of 0.075% or less.
5. An oriented balloon as in claim 1 wherein the thermoplastic
material is a polyethylene terephthalate homopolymer or
copolymer.
6. In a method of preparing an oriented balloon of thermoplastic
material comprising the extruding a hollow tube of the balloon
material, and subsequently expanding the tube under heat and
pressure in a mold to produce an oriented balloon, the improvement
wherein the tube is dried prior to said expanding step.
7. A method of preparing an oriented balloon as in claim 6 wherein
said tube is dried to a moisture content of 0.15% or less.
8. A method of preparing an oriented balloon as in claim 7 wherein
said tube is dried to a moisture content of 0.10% or less.
9. A method of preparing an oriented balloon as in claim 8 wherein
said tube is dried to a moisture content of 0.075% or less.
10. A method as in claim 6 wherein the extruded tube is subjected
to a stretching step before said expanding step and the tube is
dried before said stretching step.
11. A method of preparing an oriented balloon as in claim 6 wherein
the thermoplastic material is a polyethylene terephthalate
homopolymer or copolymer.
12. A method of forming a balloon for a catheter, the balloon
having a first waist portion, a body portion and a second waist
portion, the method comprising placing tubing of a thermoplastic
material in a mold and blowing the balloon by pressurizing and
tensioning the tubing and gradually dipping the mold into a heated
heat transfer media so as to sequentially blow the first waist, the
body and the second waist portions of the balloon, the tubing being
subjected to a relatively lower pressure than while the first and
second waist portions are blown.
13. A method as in claim 12 wherein the tubing is also subjected to
a relatively a lower tension while the body portion is blown than
while the first and second waist portions are blown.
14. A balloon made from the method of claim 12.
15. A catheter comprising an elongated flexible tube having a
distal end with a balloon mounted thereon wherein the balloon is a
balloon as in claim 14.
16. In a process for forming an elongated balloon having a
longitudinal body portion, first and second waist portions of
reduced diameter relative to the body portion at opposite ends of
the balloon and first and second cone portions connecting
corresponding waist portions and respective ends of the
longitudinal body portion, the process comprising the steps of
placing an extruded and stretched tubular preform in a mold having
an internal form corresponding to the desired outer configuration
of the balloon, and blowing the balloon by applying axial tension
and internal pressure to the preform upon dipping of the mold into
a heated heat transfer media, the improvement comprising that the
blowing step comprises: pressurizing the stretched tubing to a
first pressure in the range of 150-320 psi and applying a first
tension in the range of 5-150 g; dipping the mold to a first depth
in the range of from the transition (C) from the first waist to the
first cone to the transition (D) from the first cone to the body
portion of the balloon; reducing the pressure to a second pressure
between 80 and 170 psi and setting a second tension in the range of
the first tension; dipping the mold to a second depth in the range
of from the transition (E) from the body portion to the second cone
portion to the transition (F) from the second cone to the second
waist; increasing the pressure to a third pressure higher than the
second pressure and between 150 and 320 psi and increasing the
tension to a third tension, higher than the first tension, and
then, dipping the mold to a third depth (H) beyond the depth of the
second waist.
17. A method as in claim 16 wherein the third tension is in the
range of 50 to 700 g.
18. A method as in claim 16 wherein: the mold is held at the first
depth for a predetermined first time interval while maintaining
said first tension and first pressure before said pressure reducing
step; the mold is held at the second depth while maintaining the
second tension and the second pressure for a predetermined second
time interval before said pressure increasing step; and, the mold
is held at the third depth for a predetermined third time interval
while maintaining said third tension and third pressure.
19. The method as in claim 18 wherein said first time interval is
between 1 and 40 seconds, the second time interval is between 1 and
40 seconds and the third time interval is between 10 and 100
seconds.
20. The method of claim 18 wherein the difference between said
second and third pressures is at least 100 psi.
21. The method of claim 18 wherein the thermoplastic material is a
polyethylene terephthalate homopolymer or copolymer.
22. The method of claim 21 wherein said heat transfer media is
heated to a temperature of 90.degree. C. to 100.degree. C.
23. The method of claim 16 wherein the extruded tubular preform is
dried prior to being stretched.
24. The method of claim 23 wherein the extruded tubular preform is
dried to a moisture content of less than 0.15%.
25. The method of claim 16 wherein the second tension is the same
as the first tension.
26. The method of claim 16 wherein the second tension is less than
the first tension.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a method for making
balloons for catheters used in medical dilatation procedures.
[0002] Balloon catheters are being used extensively in procedures
related to the treatment of blood vessels. For example, arterial
stenosis is commonly treated by angioplasty procedures which
involve inserting balloon catheters into specific arteries. Balloon
catheters have also been found useful in procedures involving
dilation of body cavities.
[0003] The most widely used form of angioplasty makes use of a
dilatation catheter which has an inflatable balloon at its distal
end. Using fluoroscopy, a physician guides the catheter through the
vascular system until the balloon is positioned across the
stenoses. The balloon is then inflated by supplying liquid under
pressure through an inflation lumen to the balloon. The inflation
of the balloon causes stretching of a blood vessel and pressing of
the lesion into the blood vessel wall to reestablish acceptable
blood flow through the blood vessel.
[0004] In order to treat very tight stenoses with small openings,
there has been a continuing effort to reduce the profile of the
catheter so that the catheter can reach and pass through the small
opening of the stenoses. There has also been an effort to reduce
the profile of the catheter after an initial use and deflation of
the balloon to permit passage of the catheter through additional
lesions that are to be treated or to allow entry and retreatment of
lesions that reclose after initial treatment.
[0005] One factor manipulated to reduce the profile of the
dilatation catheter is the wall thickness of the balloon material.
Balloons for dilatation balloon catheters have been made from a
wide variety of polymeric materials. Typically the balloon wall
thicknesses have been on the order of 0.0004 to 0.003 inches for
most materials. There have been continuing efforts, however, to
develop ever thinner walled balloon materials, while still
retaining the necessary distensibility and burst pressure rating,
so as to permit lower deflated profiles.
[0006] It is possible to make balloons from a variety of materials
that are generally of the thermoplastic polymeric type. Such
materials may include: polyethylenes and ionomers,
ethylene-butylene-styrene block copolymers blended with low
molecular weight polystyrene and, optionally, polypropylene, and
similar compositions substituting butadiene or isoprene in place of
the ethylene and butylene; poly(vinyl chloride); polyurethanes;
copolyesters; thermoplastic rubbers; silicone-polycarbonate
copolymers; polyamides; and ethylene-vinyl acetate copolymers.
Orientable polyesters, especially polyethylene terephthalate (PET),
are among the preferred materials for forming catheter
balloons.
[0007] References illustrating the materials and methods of making
catheter balloons include: U.S. Pat. No. 4,413,989 and U.S. Pat.
No. 4,456,000 to Schjeldahl et al, U.S. Pat. No. Re 32,983 and Re
33,561 to Levy, and U.S. Pat. No. 4,906,244, U.S. Pat. No.
5,108,415 and U.S. Pat. No. 5,156,612 to Pinchuck et al. The Levy
patents, teach that a high tensile strength polyethylene
terephthalate balloon can only be formed from a high intrinsic
viscosity polymer, specifically, high molecular weight polyethylene
terephthalate having a requisite intrinsic viscosity of at least
1.0.
[0008] High tensile strengths are important in angioplasty balloons
because they allow for the use of high pressure in a balloon having
a relatively small wall thickness. High pressure is often needed to
treat some forms of stenosis. Small wall thicknesses enable the
deflated balloon to remain narrow, making it easier to advance the
balloon through the arterial system.
[0009] Polyesters possessing a lower intrinsic viscosity are easier
to process, and hence balloon manufacturers have desired to use
polyesters possessing an intrinsic viscosity below 1.0. However, it
was thought that using such material would sacrifice the strength
of the balloon. Recently it has been discovered that angioplasty
catheter balloons, having a wall strength of greater than 30,000
psi and a burst strength of greater than 300 psi, can be prepared
from a PET polymer of an intrinsic viscosity of 0.64-0.8. This,
high strength, non-compliant balloon, made from a standard
intrinsic viscosity polyester, has been a significant improvement
in the art. There remains, however, a need to continue to improve
balloon wall strengths while simultaneously reducing their wall
thickness.
[0010] Prior art PET balloon forming techniques involve blowing or
stretching and blowing of the balloon in a segment of extruded PET
tubing. It has been recognized that control of moisture in the PET
resin, prior to extrusion, is important and prior art techniques
have embodied a drying step prior to extrusion of PET tubing from
which the balloon is formed by stretch blow molding techniques.
However it has not been previously suggested that drying of
extruded tubing would provide any benefit properties of the
balloons produced from the extruded tubing.
[0011] Balloons produced by stretching and blowing a tubular
preform or "parison" typically have much thicker waist and cone
walls than the wall thickness of their body portions. The thicker
cone walls contribute to the overall thickness of the catheter,
making tracking, crossing and recrossing of lesions more difficult.
Further, thick cones interfere with refolding of the balloon on
deflation so that the deflated balloon can only be further inserted
or withdrawn with difficulty, occasionally even damaging the blood
vessel.
[0012] There have been several solutions proposed for reducing the
cone or waist thickness of catheter balloons in U.S. Pat. No.
4,906,241, U.S. Pat. No. 4,963,313, and EP 485,903. However, the
procedures involved in these references are quite cumbersome and so
it is desirable that simplified methods be developed to provide
cone and waist walls with reduced thicknesses.
SUMMARY OF THE INVENTION
[0013] The present invention in one aspect is an improved method
for forming a balloon for a dilatation catheter involving the steps
of extruding a tubing preform of a polyester resin and then blowing
the tubing into an oriented balloon, the improvement comprising
that the tubing preform is dried prior to blowing into the balloon
form. The addition of this novel step to the balloon forming method
has been observed to cause a reduction in the frequency of balloons
which are rejected because of defects in the balloon wall while
producing the same or higher wall strengths in the non-defective
balloons obtained.
[0014] It has also been discovered that the problem of thick
balloon cones and waists can be substantially improved by varying
the axial tension and blowing pressure at several stages as a mold
containing the balloon preform is dipped into a heating medium. A
further aspect of the invention therefore is an improved method of
forming a balloon for a catheter, comprising placing tubing of a
thermoplastic material in a mold and blowing the balloon by
pressurizing and tensioning the tubing and gradually dipping the
mold into a heated heat transfer media so as to sequentially blow
the first waist, the body and the second waist portions of the
balloon, the tubing being subjected to a relatively lower pressure,
and preferably a relatively a lower tension, while the body portion
is blown than while the first and second waist portions are
blown.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a perspective view of an angioplasty catheter
having a balloon of the invention mounted thereon.
[0016] FIGS. 2a, 2b and 2c illustrate the results of various
process steps in forming a catheter balloon, depicting
respectively, side elevational views of an extruded tube of polymer
material used to form the balloon, a stretched tubing preform
prepared from the extruded tube, and a formed balloon prepared from
the stretched tubing preform.
[0017] FIG. 3 is a schematic view of a stretching device that may
be useful in practicing the method of the invention.
[0018] FIG. 4 is a cross-sectional view of a preferred mold used in
the method of the invention.
[0019] FIG. 5 is a side elevation view of a molding station that
may be useful in practicing the method of the invention.
[0020] FIG. 6 is a perspective schematic representation of relevant
portions of the molding station of FIG. 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] A dilatation balloon catheter of the present invention,
illustrated generally at 10 in FIG. 1, includes an inflatable
balloon 14 mounted at the distal end of an elongated flexible shaft
11. Catheter 10 is conventional in its construction, providing a
lumen communicating with the interior of balloon 14, for inflation
and deflation of the balloon, and other optional features
conventional in the dilatation catheter art. The balloon 14 is in
its inflated configuration. The balloon 14 is formed of a
thermoplastic polymer material which provides the balloon with its
essential compliance characteristics. The balloon may be
noncompliant and made of stiff materials such as PET or nylon, or
it may be compliant, made of polyester copolymers, blends of
polyesters or blends of a polyester with a minor portion of another
thermoplastic polymer which disrupts the crystalinity of the
polyester. Other thermoplastic materials such as previously
described for catheter balloons may be employed. Most
advantageously the balloon material is a polyester, a polyamide or
similar highly orientable polymer material.
[0022] The balloon of this invention, in one aspect, is obtained by
extruding tubing of a thermoplastic polymer comprising a polyester,
drying the tubing, suitably for at least 4 hours, and preferably at
least 24 hours, and then expanding the extruded tubing axially and
radially. In this drying step the tubing is suitably dried to a
level of 0.15% or less, by any suitable means, including vacuum
drying with or without heat and with or without a desiccant.
[0023] Any conventional extruder may be employed to perform the
extrusion process. After the resin has been extruded into tube form
and dried, it preferably undergoes a prestretch which axially
elongates the tubing. Referring to FIGS. 2a-2c, the prestretching
process comprises applying an axial stretching force to the
extruded tubing 12, heating the extruded tubing, allowing the
extruded tubing to stretch while maintaining the axial stretching
force and finally cooling the stretched tubing 13. Once the
prestretch is complete, the stretched tubing 13 is radially
expanded into the form of a balloon 14, using a molding process.
The molding process comprises placing the stretched tubing 13 in a
mold, heating the mold and expanding the stretched tubing radially
by means of internal pressure. After sufficient time has passed for
the balloon to form, the mold is cooled and the balloon 14 is
removed.
[0024] The starting resin used to produce the balloon of this
invention is most preferably a PET homopolymer or copolymer. The
resin should be relatively free of foreign material and other
contaminants. Polyethylene terephthalate in pellet form may be
employed. Suitable examples are Shell Chemical's Cleartuf 7207 and
Traytuf 7357, and DuPont's Selar X260. The intrinsic viscosity of
the PET resin is preferably between 0.64-0.80, more preferably
between 0.68-0.76 and most preferably between 0.72-0.74. Intrinsic
viscosity, which is a function of the molecular weight, may be
determined by means of manufacturer standard processes, or
ANSI/ASTM D 2857-70.
[0025] Well controlled processing of the PET resin is important to
attaining the desired strength and compliance characteristics in
the final balloon. The PET resin is preferably dried to less than
10 ppm moisture content prior to extrusion. Drying to this level
prevents excessive degradation of the material during extrusion and
also reduces other defects such as tubing haziness or bubbles.
[0026] Once the pellets have been sufficiently dried, they are
extruded under carefully controlled conditions. As stated
previously, any conventional extruder may be employed to perform
the extrusion. Suitably, a Killion extruder with a 1.25 inch
diameter barrier flight screw is used.
[0027] In order to obtain optimal results, the processing
temperatures applied to transform the raw resin into balloon
preform tubing are meticulously maintained. A preheater may be
employed that permits the use of a small extruder while still
maintaining normal torque levels. The preheater heats the resin to
370.degree. F. Thereafter, the pellets move to the feedthroat which
is maintained at a temperature of 140-180.degree. F. Next, the PET
material passes through three extruder zones, the first of which is
preferably maintained at 490.degree. F. (+/-5.degree. F.) while the
following two are maintained at 500.degree. F. (+/-5.degree. F.).
The PET material then passes through a clamp and a melt filter
before it reaches the die. The clamp, melt filter and two
temperature zones within the die are all maintained at 500.degree.
F. (+/-5.degree. F.). The melt filter removes foreign matter from
the PET material, thereby ensuring a correct failure mode in the
final balloons. Optimally, the residence time in the extruder is
kept to a minimum. The preferred die size is in the range of
0.060-0.080 inches.
[0028] After the PET material extrudes out of the die in tube form,
it must be cooled. One way to perform the cooling process is to
pass the extruded tubing from the extruder, through a small air gap
and into a water bath maintained at approximately 60-70.degree. F.
A puller may be used to pull the tube from the cooled end through
the water bath. Thereafter, the tubing is cut into lengths. The
area draw down ratio of the extruded tubing (which is the area
defined by the die and mandrel divided by the cross-sectional area
of the extruded tubing) should be less than 10.
[0029] After the tubing has been extruded and cut, it is preferably
prestretched to axially elongate the tubing prior to its radial
expansion. In the past it was considered important to prestretch
and mold the balloon soon after the tube had been extruded, to
reduce the chance that the tube would not be degraded by
atmospheric moisture. Immediate prestretching and blowing is
sometimes inefficient in a commercial manufacturing operation,
however, and was not a fully reliable method of assuring a uniform
yield of high quality balloons. It has now been discovered that the
negative effects of exposure to atmospheric moisture can readily
avoided or reversed by desiccating the extruded tubing, preferably
to a moisture content of no more than 0.15%. In accordance with one
aspect of the invention, therefore, the preform is dried between
the extrusion and blowing steps, suitably between extrusion and
prestretching. Drying may be accomplished by heating the extruded
tubing at 50.degree. C.-60.degree. C. in a vacuum oven, suitably at
a pressure of 10.sup.-6 atm or less; or in a desiccator containing
a conventional desiccant suitably at a pressure of 600-760 mm Hg,
at ambient temperature. The tubing is suitably dried for a period
of at least 24 hours, preferably at least 48 hours, or until a
sample preform of a batch introduced simultaneously into the
desiccator is measured to have a moisture content of no more than
0.15%, preferably less than 0.10%, more preferably less than
0.075%, water. Examples of suitable desiccants which may be
employed to aid in drying the tubing include silica gel, molecular
sieves, for instance molecular sieves 3A and 4A, calcium chloride,
phosphorus pentoxide, and Drierites. A combination of heat, vacuum
and desiccant may be used to obtain the necessary dryness in a
shorter period of time if desired.
[0030] The prestretch step stretches a section of a cut length of
tubing to a predetermined length by applying an axial stretching
force to the tube while the tube is heated. Once the tube is
exposed to the higher temperature, the axial stretching force is
maintained and the tubing is stretched at a specific rate.
Desirably, the tube is heated just prior to stretching.
[0031] FIG. 3 illustrates one device useful in performing the
prestretch. The device 18 of FIG. 3 possesses two jaws 20 and 22
capable of gripping at least one cut length of extruded tubing 12.
The stretching device 18 lowers the tubing 12 into a bath 24
containing heated media maintained at a temperature above the glass
transition temperature of the extruded tubing 12. A suitable
temperature is the range extending from 85-95.degree. C. However,
the preferred media is water at a temperature of 90.degree. C.
(+/-2.degree. C.). The first gripping jaw 20 may remain stationary
while the second gripping jaw 22 moves horizontally at a set rate
to a predetermined final position, thereby achieving the desired
final stretch. The preferred rate of stretching is 25% per second.
The desired amount of axial elongation prior to radial expansion is
in the range of 75-150%. Preferably, however, the axial elongation
occurring in this phase is 125%. Therefore, the stretch ratio,
calculated by dividing the final length of the stretched section of
tubing (the portion between jaws 20 and 22) by the initial length
of that section, is 2.25.
[0032] After the tubing 12 is stretched to the desired stretch
ratio and length, it is cooled. This may be accomplished with a
device such as the device 18 of FIG. 3 by controlling the jaws 20
and 22 such that they finish stretching the tubing 12 and
automatically lift up out of the bath 24. The stretched tubing 13
may then be moved to a cooling water bath (not shown), preferably
maintained at room temperature. During this cooling process, the
stretched tubing portion 13 of tubing 12 is held on both ends in
order to apply sufficient tension to ensure that the tube does not
relax and shrink or recover from the stretch.
[0033] After cooling, the stretched tubing 13 is removed from the
water bath and expanded radially using internal pressure. The
dimensions to which it is stretched are preferably controlled by
performing the radial stretching while the tubing 13 is in a mold
having the shape of the desired balloon. A suitable mold 28 is
shown in FIG. 4. Heating the stretched tubing 13 while radially
expanding it may best be accomplished by dipping the mold 28 into
hot water while internal pressure is applied.
[0034] To perform the radial expansion step one end of the
stretched tube inside of the area where it was gripped by jaws 20
and 22 is cut off to provide an opening to the lumen of the tubing
13. The stretched tube 13 then fed through the mold 28 which
consists of three parts: the proximal portion (top) 30, the body 40
and the distal (bottom) portion 50. These three sections fit
tightly together and provide the tubing 13 a form to blow to.
[0035] Referring to FIG. 4, the distal portion 50 of the preferred
mold 28 is generally between 0.6 and 1.4 inches long, which
includes the enlarged end section 51 used to hold the mold 28 in
the molding fixture 62 (FIG. 5). The distal cone section 52 is
formed at an angle of between 15.degree. and 45.degree. with the
axis of the mold 28. The cup 54 of the distal portion, which
interfaces with the distal insert portion 42 of body 40, generally
has a length of 0.120 inches. The proximal portion 30 of the
preferred mold 28 is generally between 1.1 and 2.0 inches long. The
proximal cone section 32 is also formed at an angle of between
15.degree. and 45.degree. with the axis of the mold 28. The cup 34
of the proximal portion interfaces with the proximal insert portion
44, symmetrical with the distal insert mold portion 42 of body 40.
The length for the balloon body 40 is generally between 0.4 and 2
inches long. The inner and outer diameter of the mold sections 30,
40 and 50, and the angles of each cone 32, 52 are both dependent on
the desired balloon size. The mold 28 for the balloon will be
different when producing different sized balloons, which is
necessary to meet the preference or needs of those who will perform
medical treatments with the balloon.
[0036] The molds 28 of the present invention are preferably made of
303 stainless steel with a smooth mirror finish to provide a smooth
finish on the balloon surface. The surface roughness average should
be in the range of 5-10 microns or less.
[0037] The appropriate mold 28, with the stretched tubing 13
inside, may be heated while pressure is applied using a device 60
such as the one depicted in FIGS. 5 and 6. With this device 60, the
mold 28 is placed in a holder 62. The tubing 13 extends out from
the top of the mold 28 and is fed into a Touhy clamp 64 through
which a pressurized fluid, preferably nitrogen gas, is applied to
the inner lumen of the tubing 13. The tubing at the bottom of the
mold 28 is clamped off such that no gas can flow through it. The
pressure applied is suitably in the range of 210-280 psi.
[0038] One advantage of using a device 60 is that tension may be
applied to the tubing 13 during the molding phase. A string 65
trained over pulley 66 (shown in FIG. 6 but deleted from FIG. 5 for
sake of clarity) may be attached to a tension clamp 67 adjacent the
Touhy clamp 64. The tension clamp 67 holds the tubing 13 to apply
tension to it without closing off the flow path of pressurized
fluid into tubing 13. Weights 68 attached to the end of string 65
may thus provide tension to the tubing 13. Generally, 0-500 g of
tension may be applied. Tension may be applied during the molding
process to better control the wall thickness of certain areas of
the balloon, primarily the waist sections. The tension decreases
the cross sectional area of the balloon waists, thereby increasing
flexibility in those regions.
[0039] The tubing 13, subjected to specific interior pressures, is
then heated. As depicted by dashed lines in FIG. 5, the mold 28 is
dipped into a water bath 70, suitably at a rate of 4 mm/sec., with
the total process of submerging the mold 2.3 inches into the bath
70 taking approximately 15 seconds. Preferably, the bath 70 is a
hot water bath maintained at a temperature range of 85-98.degree.
C., with 95.degree. C. (+/-1.degree. C.) being the most preferred
temperature. Once the entire mold 28 has been submerged it is held
stationery for a period of time, suitably 40 seconds, while the
balloon and waist portions yield completely and stabilize. The
radial expansion, or hoop ratio (calculated by dividing the inner
diameter of the balloon by the inner diameter of the extruded
tubing), should be in the range of 6-8.5. However, the preferred
hoop ratio is approximately 8.0. A lower hoop ratio may result in
compliance which is higher. than desired. A higher hoop ratio may
result in preforms which will not blow out fully. During this phase
of radial expansion, the tubing 13 will further elongate, i.e.
expand further in the axial direction, such that the total
elongation of the tubing 13 in the finished balloon body will range
from 175-275% of the length of the unstretched tubing used to form
the body of the balloon.
[0040] In accordance with a further aspect of the invention the
stretched tubing 13 is blown during a programmed dipping cycle, for
dipping into hot water bath 70, during which the pressure and axial
tension are varied at several stages so that the balloon is
sequentially blown from one end to the other (proximal, body and
distal, or vice versa). By this method, a reduced waist and cone
thickness is obtained without the necessity of introducing a
separate processing operation directed specifically to cone and
waist reduction.
[0041] FIG. 4 has been labeled to show depth regions at which
transitions of pressure and/or tension occur in this aspect of the
invention as mold 28 is dipped into bath 70. Corresponding
locations on the balloon 14 are labeled in FIG. 1. The region B-C
comprises the proximal waist portion, the region C-D comprises the
proximal cone portion, the region D-E comprises the body portion,
the region E-F comprises the distal cone portion and the region F-G
comprises the distal waist portion of the mold. The balloon blowing
process of the invention involves the steps of:
[0042] pressurizing the stretched tubing to a first pressure in the
range of 150-320 psi and applying a first tension in the range of
5-150 g;
[0043] dipping the mold to a first depth in the range of from the
transition (C) from the first waist to the first cone to the
transition (D) from the first cone to the body portion of the
balloon;
[0044] reducing the pressure to a second pressure between 80 and
170 psi and setting a second tension in the range of the first
tension;
[0045] dipping the mold to a second depth in the range of from the
transition (E) from the body portion to the second cone portion to
the transition (F) from the second cone to the second waist;
[0046] increasing the pressure to a third pressure higher than the
second pressure and between 150 and 320 psi and increasing the
tension to a third tension, higher than the first and second
tensions, and then,
[0047] dipping the mold to a third depth (H) beyond the depth (G)
of the second waist.
[0048] Although the process may be accomplished with substantially
continuous dipping, it is preferred that the mold be held at each
of the first, second and third depths for predetermined time
intervals before changing pressure/tension parameters and moving to
the next depth. Suitable hold time intervals are between 1 and 40
seconds at the first depth, between 1 and 40 seconds at the second
depth and between 10 and 100 seconds at the third depth. A typical
dipping program for a PET polymer balloon, beginning at an initial
depth (A) before the depth (B) of the first waist of the balloon,
and using a 95.degree. C. hot water bath as heating media, will
take a total of approximately 60-90 seconds. Typical programs for
PET balloons are illustrated in Examples 4-9.
[0049] The third tension is suitably in the range of 50 to 700 g,
and is higher than the second tension, suitably higher than both
the first and second tensions. For balloons of 4.00 mm diameter or
less, the third tension will usually not exceed 500 g. The second
tension may be the same or different from the first tension and if
different will usually be less than the first tension. In general
the tension employed at all depths will be higher as the diameter
of the balloon is increased. For balloons having nominal diameters
of at least 2.25 mm it is preferred that the third tension be
higher than both the first and second tensions by at least 150
grams and at all typical angioplasty balloon diameters it is
preferred that the difference between the second and third
pressures be at least 100 psi, usually at least 150 psi.
[0050] It should be noted that this aspect of the invention can
also be practiced by inserting the end of mold 28 which forms the
distal end of the balloon into the heating bath first.
[0051] The balloon formed in the mold is next cooled. One way to
cool the balloon is to remove the mold 28 from the hot water bath
70 and place it in a cooling bath 72. As shown in FIG. 5, this step
may be accomplished through use of a machine 60 having a pivot arm
74 capable of transferring the mold 28 from the hot 70 to the cold
water bath 72. The cooling bath 72 is preferably maintained at
7-15.degree. C. In the preferred embodiment, the balloon remains in
the cooling bath 72 for approximately 10 seconds.
[0052] Finally, the ends of the tubing 13 extending from the mold
28 are cut off and the balloon is removed from the mold 28 by
removing either the distal end 50 or proximal end 30 from the body
section 40 of mold 28, then gently pulling the balloon from the
remaining mold sections. To mount on a catheter 10, balloon 14 is
cut at B and G and adhered to the catheter in conventional
manner.
[0053] The various aspects of the invention are illustrated by the
following non-limiting examples. In the examples wall thickness
measurements single wall thicknesses unless specifically specified
as double wall thicknesses.
EXAMPLE 1 (POST EXTRUSION DRYING)
[0054] The product of this example is a 3.00 mm balloon. Shell
Chemical Cleartuf 7207 PET pellets, reported as having an intrinsic
viscosity of 0.73 as determined by Goodyear R100E intrinsic
viscosity test method, were dried to approximately 10 ppm moisture
content. The dried resin was extruded into tubing and cut into 8
inch sections. The tubing sections had an OD of 0.0425 in. and an
ID of 0.0183 in.
[0055] The extruded tubing sections were next stretched to a
predetermined length by applying an axial stretching force to the
individual tubing sections and heating them. Each tubing section
was placed in an automated prestretching device possessing two
gripping mechanisms capable of concurrent vertical motion. The
prestretching device lowered the tubing section into a deionized
water bath 24 heated to 90.degree. C. (.+-.2.degree. C.). One of
the two gripping mechanisms remained stationary while the other
moved horizontally at a rate of 25%/sec. for 5 seconds. The
resulting axial elongation, due to the 2.25 stretch ratio, was
approximately 125%.
[0056] After the prestretch was complete, the tubing section was
manually removed from the pre-stretching device and cooled for a
few seconds in a deionized water bath maintained at room
temperature. The tubing section was held in order to apply
sufficient tension to ensure that the tube 12 did not recover from
the stretch. The stretched tubing section was then removed from the
water bath.
[0057] After cooling, the stretched tubing section was expanded
radially using internal pressure. One end of the stretched tube was
cut to provide an opening to the lumen of the tubing. In order to
form a 3.75 mm balloon with a 20 mm body length, a mold having
dimensions that allowed the stretched tube to blow out to the
appropriate body size and balloon waist inner diameters was
used.
[0058] After the tubing section was securely inside the mold, the
mold was placed in a holder. The tubing section extended out the
top of the mold and was fed into a Touhy clamp through which
nitrogen gas was applied to the inner lumen of the tubing at 260
psi. No tension was applied to the tubing. The tubing section at
the bottom of the mold was clamped off such that the pressure was
maintained inside the tubing section. The mold was then gradually
dipped, at a rate of 4 mm/sec., into a deionized hot water bath
maintained at 95.degree. C. (.+-.1.degree. C.) to a point just
above the proximal waist portion of the mold. The entire dipping
process consumed 15 sec. and the mold was held stationary in the
bath 70 for 40 sec. Then the mold was removed from the hot water
bath and cooled for approximately 10 sec. in a deionized water bath
maintained at about 11.degree. C. The balloon axially expanded
during the molding by an additional 50% of its original tubing
length, resulting in a total axial elongation of 175%.
[0059] Thirty balloons prepared in this manner from a single lot of
tubing were used as controls.
[0060] Balloons of the invention were made in the same manner from
the same lot of tubing as the controls except that the prior to the
prestretching step, the tubing sections were dried in a vacuum
desiccator. Five marked and preweighed tubes were used to monitor
weight loss after 24 and 48 hour desiccation intervals. After 24
hours the balloons had lost an average of 0.38% of their
undesiccated weight. After 48 hours the average weight loss was
0.44%.
[0061] Meanwhile, in the same desiccator, 80 unmarked tubes were
dried. After 24 hours 30 tubes were removed and processed into
balloons in the manner of the controls. An additional 30 balloons
were made from tubes which were kept in the desiccator for 48
hours.
[0062] All balloons were inspected for "bubble" defects and
observed defects were categorized as small (<0.004 inch dia.),
medium (0.004-0.01 inch) and large (>0.01 inch). "Bubble"
defects are typically tear shaped or American football shaped
visible distortions which are sometimes, but not always,
hollow.
[0063] Results were as follows:
[0064] Controls:
[0065] 18 "bubbles". 1 Large, 7 medium, 10 small. Four balloons had
more than one "bubble".
[0066] 24 hours:
[0067] 11 "bubbles". 0 Large, 1 medium, 10 small. No balloons with
more than one "bubble".
[0068] 48 hours:
[0069] 7 "bubbles". 0 Large, 3 medium, 4 small. No balloons with
more than one "bubble".
[0070] Six balloons from each batch which displayed no defects were
then subjected to standard burst tests by measuring the double wall
thickness of the deflated balloon, inflating the balloon at
incrementally increasing pressures and measuring the outside
diameter at each increment until the balloon burst. Typical and
average results for each batch are given in Table 1 where Dnom is
diameter at nominal inflation (118 psi), Pburst and Dburst are,
respectively, average burst diameter and average burst
pressure.
1 TABLE 1 0 Hours 24 Hours 48 Hours Single wall thickness 0.00062"
0.00067" 0.00068" Pressure (psi) Measured body diameter (mm) 40
3.65 3.66 3.66 88 3.75 3.75 3.75 Dnom 118 3.79 3.78 3.78 132 3.80
3.79 3.79 147 3.82 3.80 3.80 180 3.84 3.83 3.82 206 3.86 3.84 3.84
235 3.89 3.86 3.86 260 3.92 3.88 3.87 270 3.95 3.90 3.88 280 3.98
3.92 3.90 290 4.01 3.93 3.92 300 4.05 3.95 3.93 310 4.10 3.98 3.96
320 4.14 4.00 3.99 330 4.21 4.04 4.02 340 4.07 4.05 350 4.10 4.10
360 4.11 4.13 370 4.18 Average Results Pburst 323 352 353 Dburst
4.13 4.11 4.09 Distention dnom-280 5.0% 3.7% 3.2%
EXAMPLE 2 (POST EXTRUSION DRYING
[0071] The procedures of example 1 were repeated. Average weight
loss on desiccation for 24 hours was 0.34% and for 48 hours was
0.52%. Results of defect inspections were as follows:
[0072] Controls:
[0073] 12 "bubbles". 3 Large, 5 medium, 4 small. Three balloons had
more than one "bubble".
[0074] 24 hours:
[0075] 9 "bubbles". 0 Large, 4 medium, 5 small. No balloons with
more than one "bubble".
[0076] 48 hours:
[0077] 5 "bubbles". 0 Large, 3 medium, 2 small. No balloons with
more than one "bubble".
[0078] Typical and average results of burst testing are shown in
Table 2:
2 TABLE 2 0 Hours 24 Hours 48 Hours Single wall thickness 0.00062"
0.00067" 0.00068" Pressure (psi) Measured body diameter (mm) 40
3.65 3.67 3.65 88 3.76 3.75 3.76 Dnom 118 3.79 3.78 3.79 132 3.81
3.79 3.80 147 3.82 3.80 3.81 180 3.85 3.82 3.83 206 3.87 3.84 3.85
235 3.90 3.86 3.87 260 3.94 3.88 3.89 270 3.97 3.90 3.91 280 4.01
3.91 3.92 290 4.04 3.93 3.94 300 4.08 3.95 3.96 310 4.13 3.98 3.98
320 4.15 4.01 4.01 330 4.05 4.04 340 4.09 4.07 350 4.13 4.10 360
4.12 Average Results Pburst 318 349 350 Dburst 4.13 4.12 4.12
Distention dnom-280 5.6% 3.4% 3.5%
EXAMPLE 3 (POST EXTRUSION DRYING)
[0079] Four lots of balloons (25 in each lot) were stretched and
blown from extruded PET tubing at a mold pressure of 180 psi. The
molds were for 4.0 mm balloons. Mold dimensions were: length 100
mm; proximal ID 0.421"; distal ID 0.0315"; body ID 0.1600". The
tubing lots were subjected to the following conditions before
stretching and blowing:
3 A Tubing allowed to equilibrate in a dry room to a moisture
content of 0.3%. The stretch ratio before blowing was 2.15. B
Tubing vacuum dried to moisture content of 0.05% in a desiccator
prior to stretching. The stretch ratio prior to blowing was 2.15. C
Tubing allowed to equilibrate in a dry room to a moisture content
of 0.3%. The stretch ratio before blowing was 2.25. D Tubing vacuum
dried to moisture content of 0.05% in a desiccator prior to
stretching. The stretch ratio prior to blowing was 2.25.
[0080] In blowing each lot of stretched tubing a tension was
selected to assure an axial lengthening (growth) of 17-22 mm during
the blowing stage and to keep the double body wall thickness
between 0.00095" and 0.00125". All balloons were inspected for
"bubbles" and foreign materials. Ten of the best balloons from each
lot were burst tested and distal and proximal waists were measured
on one balloon from each lot. Blowing conditions and test results
are shown in Table 3.
4 TABLE 3 A B C D Comparative Invention Comparative Invention
Pressure (psi) 180 180 180 180 Tension 133 161 137 152 Average
growth 19.7 18.9 19.2 17.5 (mm) Body double wall 0.00110 0.00116
0.00108 0.00116 thickness (in) Small "bubbles" 3 0 2 0 (<0.010
mm) Medium "bubbles" 1 0 0 0 (0.004-0.10 mm) Large "bubbles" 0 0 2
0 (>0.010 mm) Burst diameter 4.3 4.3 4.3 4.3 (mm) Burst pressure
(psi) 328 336 327 337 Distal wall thickness 0.0037 0.0037 0.0034
0.0041 Proximal wall 0.0023 0.0027 0.0028 0.0026 thickness
EXAMPLE 4 (PROGRAMMED DIP CYCLE)
[0081] Balloons were made in a manner similar to Examples 1 and 2
except that a programmed dip cycle was used and the device of FIG.
6 was modified by replacing the pulley 66 and weight 68 with a
metal cylinder containing a pressure driven piston. String 65 was
attached to the piston rod so that tension could be varied by
changing the pressure in the cylinder so as to move the cylinder up
or down. The program was as follows, where pressures applied to the
cylinder have been converted to equivalent tensions applied to the
tubing.
5 Mold specification: Proximal waist ID 0.0352 inches Body ID
0.1195 inches Distal waist ID 0.0280 inches Cone angle 15.degree.
Prestretch stretch ratio: 2.25 Program: bath at 95.degree. C. (1)
pressure to 295 psi tension to 60 g hold at A 5 seconds dip to D 5
seconds hold at D 5 seconds (2) pressure to 120 psi tension to 60 g
dip to F 10 sec hold at F 5 seconds (3) pressure to 295 psi tension
to 200 g dip to G 1 sec hold at G 1 sec dip to H 10 sec hold at H
25 seconds
[0082] Average wall thickness of the balloons produced in this way
were: body single wall, 0.00045 inches; proximal wall, 0.00141
inches; distal wall, 0.00169 inches.
[0083] In the remaining examples the modified version of the device
of FIG. 6 which is described in the previous example was employed
and a simplified programmed dipping and blowing cycle was used. In
this program the mold was dipped from the initial position, A in
FIG. 4, to a first depth approximately at the midpoint of the first
cone i.e. midway between C and D, held and then after reducing the
pressure, dipped to a second depth approximately at the midpoint of
the second cone, i.e. between E and F, held and then after
increasing pressure and tension, dipped to the final position H,
slowing down near the final position, and then holding for a third
interval before being removed and dipped in the cooling bath.
EXAMPLE 5 (PROGRAMMED DIP CYCLE)
[0084] 2.5 mm balloons were made from 0.0125".times.0.0272" PET
extruded tubes. The extruded tubes were stretched 2.25 times of the
original length at 90.degree. C. The stretched tubes were then
blown into balloons at 95.degree. C. The mold pressure was 250 psi
at proximal end, 130 psi at body, 290 psi at distal end. The
pulling tension was 25 grams at proximal end and body, 180 grams at
distal end. The dip cycle was 5 seconds hold at initial position, 5
sec. dip to first depth, 5 sec hold at first depth; 10 seconds dip
to second position, 8 seconds hold at second position; 6 seconds to
dip to the final position, holding for 30 seconds before removing
and quenching in a cooling bath. The balloon has a body wall
(single wall) of 0.00039", proximal waist wall of 0.0010", distal
waist wall of 0.0012", pressure burst at 343 psi. The compliance at
118-279 psi is less than 7%. The result is shown in Table 4.
EXAMPLE 6 (PROGRAMMED DIP CYCLE)
[0085] 3.0 mm balloons were made from 0.0149.times.0.0311 PET tube.
Stretching and blowing temperatures were the same as example 1. The
mold pressure was 280 psi at proximal end, 130 psi at body, 290 psi
at distal end. The pulling tension was 50 grams at proximal end and
35 grams at body, 250 grams at distal end. The dip cycle was as in
Example 5. The balloon has a body wall of 0.00040", proximal waist
wall of 0.0010", distal waist wall of 0.0011", pressure burst at
320 psi. The compliance at 118-279 psi was less than 7%. The result
is shown in Table 4.
EXAMPLE 7 (PROGRAMMED DIP CYCLE)
[0086] 4.0 mm balloons were made from 0.0195.times.0.0395" PET
tube. Stretching and blowing temperatures were the same as example
1. The mold pressure was 280 psi at proximal end, 130 psi at body,
290 psi at distal end. The pulling tension was 90 grams at proximal
end and 90 grams at body, 350 grams at distal end. The dip cycle
was as in Example 5. The balloon has a body wall of 0.00046",
proximal waist wall of 0.0022", distal waist wall of 0.0023",
pressure burst at 295 psi. The compliance at 118-279 psi was less
than 7%. The result is shown in Table 4.
6 TABLE 4 Comparative Invention Balloon* Balloon % Reduction Size:
2.5 mm Balloon wall/inch .00056" .00039" 30 Distal waist wall
.0031" .0012" 61 Prox. waist wall .0028" .0010" 64 Profile
reduced** .0038" Size: 3.0 mm Balloon wall/inch .00056" .00040" 29
Distal waist wall/inch .0041" .0010" 76 Prox. waist wall/inch
.0035" .0011" 69 Profile reduced .0062" Size: 4.0 mm Balloon
wall/inch .00062 .00046" 26 Distal waist wall/inch .0051" .0023 55
Prox. waist wall/inch .0049" .0022" 55 Profile reduced .0056"
*Comparative balloons were commercial balloons of comparable body
diameter and body wall thickness employed on NC-Shadow .TM.
catheters sold by SciMed Life Systems Inc., Maple Grove MN, USA and
prepared by a process using constant pressure and tension.
**Profile reduced is calculated from distal waist wall thicknesses
of the comparative balloons.
EXAMPLE 8
[0087] Balloons as prepared in example 6 were mounted on catheters
of comparable configuration to the NC-Shadow.TM. catheter of the
same balloon body dimension and the resulting catheters were
compared for recrossing force, pulling force, trackability and
surface friendship. Recrossing force is the force to push a
deflated balloon through a 0.049 inch lesion after the balloon has
been inflated to 12 atm. for 1 min. Pulling force is the force to
pull a deflated balloon catheter back through a 7F guide catheter
after balloons were inflated to 12 atm for 1 min. All of the
measurements were done at 37.degree. C. Results are provided in
table 5.
7 TABLE 5 Comparative catheter Invention catheter % Reduction
Recrossing Force 0.29 0.16 45 (lb) Pulling force from 0.13 0.10 23
guide (lb) Trackability greatly improved Surface friendship rough
good
EXAMPLE 9
[0088] 3.0 mm balloons were made from 0.0149.times.0.0307" PET
tube. The tubes were dried up to 100 ppm moisture (in the range of
10-200 ppm) before stretching and blowing. The tube was stretched
2.15 times of the original length at 90.degree. C. The stretched
tube was then blown into balloon at 95.degree. C. The mold pressure
was 270 psi at proximal end, 110 psi at body, 270 psi at distal
end. The pulling tension was 22 grams at proximal end and body, 50
grams at distal end. The dip cycle was as in Example 5. The balloon
has a body wall of 0.00040", proximal waist wall of 0.0013", distal
waist wall of 0.0013", pressure burst at 330 psi. The compliance at
118-279 psi was less than 7%.
EXAMPLE 10 (PROGRAMMED DIP CYCLE)
[0089] 3.0 mm polyethylene copolymer balloons were made from tubing
having an OD of 0.032" and an ID of 0.0215". The tubes were not
stretched before blowing. The tubes were treated with E-beams to
crosslink the polymer material. The blowing temperature was
90.degree. C. Mold pressure was 120 psi at both ends, 80 psi at
body. Pulling tension was 500 grams at the second end, 0 grams at
body. Balloon wall thickness of 0.0250"-0.0275" and burst pressure
of 188 psi were the same as those with fixed pressure and without
tension. However, the waist walls of the second ends of the
resulting balloons were reduced 10-30%.
[0090] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
* * * * *