U.S. patent application number 11/356522 was filed with the patent office on 2006-07-13 for medical device balloons with improved strength properties and processes for producing the same.
This patent application is currently assigned to BOSTON SCIENTIFIC SCIMED, INC.. Invention is credited to John Jianhua Chen, Douglas A. Devens, Nao Pao Lee, Jeffrey S. Lindquist, Lixiao Wang.
Application Number | 20060151921 11/356522 |
Document ID | / |
Family ID | 27787552 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060151921 |
Kind Code |
A1 |
Wang; Lixiao ; et
al. |
July 13, 2006 |
Medical device balloons with improved strength properties and
processes for producing the same
Abstract
A tubular parison for forming a medical device balloon. The
parison is formed of a polymeric material, for instance a
thermoplastic elastomer. The parison has an elongation at break
which is not more than 80% of the elongation of the bulk polymeric
material. The elongation of the parison is controlled by altering
extrusion conditions. Balloons prepared from the parisons provide
higher wall strength and/or higher inflation durability than
balloons prepared from conventional parisons of the same
material.
Inventors: |
Wang; Lixiao; (Long Lake,
MN) ; Chen; John Jianhua; (Plymouth, MN) ;
Lindquist; Jeffrey S.; (Maple Grove, MN) ; Lee; Nao
Pao; (Brooklyn Park, MN) ; Devens; Douglas A.;
(St. Paul, MN) |
Correspondence
Address: |
VIDAS, ARRETT & STEINKRAUS, P.A.
6109 BLUE CIRCLE DRIVE
SUITE 2000
MINNETONKA
MN
55343-9185
US
|
Assignee: |
BOSTON SCIENTIFIC SCIMED,
INC.
Maple Grove
MN
|
Family ID: |
27787552 |
Appl. No.: |
11/356522 |
Filed: |
February 17, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10087653 |
Feb 28, 2002 |
7029732 |
|
|
11356522 |
Feb 17, 2006 |
|
|
|
Current U.S.
Class: |
264/464 |
Current CPC
Class: |
C09K 2323/06 20200801;
B29C 48/832 20190201; Y10T 428/1086 20150115; B29C 48/022 20190201;
B29C 48/09 20190201; A61M 25/1029 20130101; A61L 31/125 20130101;
B29C 48/919 20190201; A61L 31/06 20130101; B29L 2031/7542 20130101;
B29C 48/865 20190201; B29C 48/86 20190201 |
Class at
Publication: |
264/464 |
International
Class: |
H05B 6/00 20060101
H05B006/00 |
Claims
1. A method of making a parison for forming a medical device
balloon, the method comprising extruding a tube of polymeric
material to form the tube, wherein the extrusion is controlled to
provide the extruded tube with an elongation at break which is not
more than 80% of the elongation at break of the bulk polymeric
material.
2. A method as in claim 1 wherein the elongation at break of the
extruded tube is not more than about 70% of the elongation at break
of the bulk polymeric material.
3. A method of making a parison for forming a medical device
balloon, the method comprising extruding a tube of polymeric
material to form the tube, the extrusion having a draw down ration
of about 8 or higher.
4. A method of making a parison for forming a medical device
balloon, the method comprising extruding a tube of polymeric
material from an extruder having a barrel where the mixture is kept
in molten state at a barrel temperature and a die zone where the
molten material is pushed through a die to form the tube, wherein
the die zone is kept at a temperature at least 5.degree. F. below
the barrel temperature.
5. A method as in claim 4 wherein said die zone temperature is
10-40.degree. F. below the barrel temperature.
6. A method as in claim 4 wherein said die zone temperature is
20-30.degree. F. below the barrel temperature.
7-24. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] Medical devices comprising catheter balloons are used in an
increasingly widening variety of applications including vascular
dilatation, stent delivery, drug delivery, delivery and operation
of sensors and surgical devices such as blades, and the like. The
desired physical property profile for the balloons used in these
devices vary according to the specific application, but for many
applications a high strength robust balloon is necessary and good
softness and trackability properties are highly desirable.
[0002] Commercial high strength balloons having wall strengths in
excess of 20,000 psi, have been formed of a wide variety of
polymeric materials, including PET, nylons, polyurethanes and
various block copolymer thermoplastic elastomers. U.S. Pat. No.
4,490,421, Levy and U.S. Pat. No. 5,264,260, Saab describe PET
balloons. U.S. Pat. No. 4,906,244, Pinchuk et al, and U.S. Pat. No.
5,328,468, Kaneko, describe polyamide balloons. U.S. Pat. No.
4,950,239, Gahara, and U.S. Pat. No. 5,500,180, Anderson et al
describe balloons made from polyurethane block copolymers. U.S.
Pat. No. 5,556,383, Wang et al and U.S. Pat. No. 6,146,356, Wang et
al, describes balloons made from polyether-block-amide copolymers
and polyester-block-ether copolymers. U.S. Pat. No. 6,270,522
Simhambhatla, et al, describes balloons made from
polyester-block-ether copolymers of high flexural modulus. U.S.
Pat. No. 5,344,400, Kaneko, describes balloons made from
polyarylene sulfide. All of these balloons are produced from
extruded tubing of the polymeric material by a blow-forming radial
expansion process. U.S. Pat. No. 5,250,069, Nobuyoshi et al, U.S.
Pat. No. 5,797,877, Hamilton et al, and U.S. Pat. No. 5,270,086,
Hamlin, describe still further materials which may be used to make
such balloons.
[0003] Different balloon materials provide different properties. In
general, materials with high elongation and low flexural modulus
give relatively greater resistance to pin hole formation and to
winging upon deflation and also provide better trackability through
body lumens, but such materials tend to give balloons with lower
burst strengths and higher distensibility. Conversely, polymer
materials with relatively high tensile strengths and hardness tend
to give balloons with low distension and high burst strengths, but
at a sacrifice of susceptibility to pin holing, winging and/or loss
of trackability.
[0004] A variety of blow forming techniques have been utilized. The
extruded parison may be radially expanded as is into a mold or by
free-blowing. Alternatively, the parison may be pre-stretched
longitudinally before expansion or reformed in various ways to
reduce thickness of the balloon cone and waist regions prior to
radial expansion. The blowing process may utilize pressurization
under tension, followed by rapid dipping into a heated fluid; a
sequential dipping with differing pressurization; a pulsed
pressurization with compressible or incompressible fluid, after the
material has been heated. Heating may also be accomplished by
heating the pressurization fluid injected into the parison.
Examples of these techniques may be found in the patent documents
already mentioned or in U.S. Pat. No. 4,963,313, Noddin et al, U.S.
Pat. No. 5,306,246 Sahatjian, U.S. Pat. No. 4,935,190, Tennerstedt,
U.S. Pat. No. 5,714,110, Wang et al.
[0005] Following blow-forming the balloons may be simply cooled,
heat set at a still higher pressure and/or temperature or heat
shrunk at an intermediate pressure and/or temperature, relative to
the blow forming temperature and pressure. See U.S. Pat. No.
5,403,340, Wang et al, EP 540858 Advanced Cardiovascular Systems,
Inc., WO 98/03218, Scimed Life Systems.
[0006] Thus a great deal of attention has been paid to blow forming
processing conditions and to balloon materials. Less attention has
been paid to extrusion conditions for preparing the polymer tubing
used as the parison: In general, dry polymer has been used. It has
been recognized that a single die can be used to produce different
tubing diameters by varying the draw down ratio, but, at least
since-the advent of PET balloons, relatively low draw down ratios
have been recommended to provide an amorphous state and thereby
facilitate the subsequent blow-forming step. See S. Levy,
"Improved. Dilatation Catheter Balloons," J. Clinical Engineering,
Vol. 11, No. 4, July-August 1986, 291-295, at p 293.
[0007] Balloons made from thermoplastic elastomers are desirable
because they are relatively soft and robust, have good trackability
and still provide adequate strength for many applications. However,
as demands for balloon performance have increased, a need has
arisen to find a way to improve wall strength of thermoplastic
elastomer balloons without requiring still further increases in
hoop ratios, and/or to provide more robust balloons without
sacrificing wall strength.
SUMMARY OF THE INVENTION
[0008] The present invention is directed to methods of forming
balloons and parisons therefor.
[0009] Surprisingly, it has been found that improved balloon
properties can be obtained by controlling the parison extrusion in
a manner which restricts the elongation of the parison material in
the longitudinal direction. In one aspect the invention is a method
of extruding a parison useful for forming a medical balloon by a
radial expansion process, the method comprising extruding the
parison in a manner which provides the parison material with an
elongation which is not more than 80% of the elongation of the bulk
material. In another aspect the invention is a method of extruding
a parison, the method comprising extruding a tube of polymeric
material to form the tube at a cross-sectional area draw down ratio
of about 8 or higher.
[0010] In still another aspect, the invention is directed to
improved balloons characterized by a particular high strength
property; to medical devices comprising such balloons; and to
surgical procedures employing such devices. A particular embodiment
is a balloon formed from a thermoplastic elastomer and having a
wall strength of at least 34,000 psi, especially at least 37,000
psi, in pre-sterilized condition. A further embodiment is such a
balloon, in post-sterilized condition, having a wall strength of
32,000 psi or more.
[0011] Further aspects of the invention are described in the
following detailed description of the invention or in the
claims.
DETAILED DESCRIPTION OF THE INVENTION
[0012] All published documents, including all US patent documents,
mentioned anywhere in this application are hereby expressly
incorporated herein by reference in their entirety. Any copending
patent applications, mentioned anywhere in this application are
also hereby expressly incorporated herein by reference in their
entirety.
[0013] It has been found that the distention and the burst pressure
of a balloon are affected by the elongation properties of the
extruded parison, as well as by the hoop ratio and the tube wall
thickness. It is believed the elongation affects the balloon
properties through its effect on the balloon wall thickness. Thus,
for a given hoop ratio and tube size, as parison elongation
decreases, the balloon wall thickness increases, the balloon
distention decreases and the burst pressure increases.
[0014] Thus, while an increase in the hoop strength and modulus
comes at the expense of thinner balloon walls, which can increase
distention and decrease burst pressure, it is also possible to
extrude tubes with lower elongation to break. This allows one to
provide even stronger walls than were previously been obtained with
a given polymer. Alternatively, the invention can allow one to
thicken the balloon wall, while affecting the hoop strength and
distension very little, thereby obtaining a balloon which is more
suited to stent or other surgical device delivery operations.
[0015] In one aspect the invention involves modifying the parison
processing so as to provide the parison material with an elongation
which is not more than 80% of the elongation of the bulk material.
In particular, when 3 inch length of the extruded tube is stretched
until it breaks, the length of the tube when it breaks will
correspond to a percentage increase which is not more than 80% of
the elongation value obtained by determining elongation of the bulk
material per ASTM D-638. In some embodiments the parison is
processed so as to provide the parison material with an elongation
which is not more than 70% of the elongation of the bulk material,
and in still others the parison elongation is less than 60% of the
elongation of the bulk material.
[0016] The parison processing techniques described herein, alone or
in combination can provide balloon wall strength improvements of as
much as 10-25% over those obtainable in their absence, for
non-sterilized balloons. Sterilization, depending on the technique
chosen, may reduce this benefit somewhat. The invention may be used
with any known balloon materials, however high strength
thermoplastic elastomers are preferred, especially polyamide
polyether block copolymers, including
polyamide/polyether/polyesters such as sold under the PEBAX
trademark, in particular PEBAX 7033 and PEBAX 7233;
polyester/polyether block copolymers such as sold under the HYTREL
and ARNITEL trademarks, in particular ARNITEL EM 740 and HYTREL
8238; and polyurethane block copolymers such as PELLETHANE
2363-75D. The parison may be extruded as a single layer or in
multiple layers, for instance 3, 5, 7, or even more alternating
layers of PEBAX 7033 and Pebax 7233. Blends of such polymers may
also be used.
[0017] Parison elongation may be controlled by varying one or more
of the following extrusion parameters:
Extrusion Temperature:
[0018] The temperature at the extrusion head, die temperature, is
lowered relative to the temperature in the extruder barrel.. Heat
loss begins even as the material is passing through the die head.
The resulting tubing has a higher degree of crystallization. In
general the die head temperature reduction should be about 5 to
about 50.degree. F., suitably 10.degree. F. to 40.degree. F., and
preferably about 20-30.degree. F. below the barrel temp.
Draw Down Ratio:
[0019] Die configuration, extruder pressure and/or line speeds can
be adjusted to provide a cross-sectional area draw down ratio in
excess of 5:1. Ratios as high as 17:1 have been employed, and even
higher ratios may be advantageous because they reduce extruder
pressure demands. Typically the draw down ratios will be in the
range of about 8:1 to about 17:1.
[0020] Quench Time:
[0021] Decreasing the gap between the extrusion head and the
cooling bath tank can also lower parison elongation by shortening
the quench time. Quench time can also be shortened by increasing
the line speed.
[0022] Bath Temperature:
[0023] Maintaining the cooling bath at a lower temperature also can
lower the elongation of the parison.
[0024] A surprising benefit of at least some embodiments of the
invention is that balloons prepared from parisons of the invention
have improved resistance to repeat inflation bursts versus controls
utilizing the same polymer, but prepared using typical extrusion
parameters for commercial balloons. The improvement may permit
three times, or even more, the number of inflations to rated
pressure, compared to the controls.
[0025] The invention is illustrated by the following non-limiting
examples.
EXAMPLES
[0026] In the following examples the following abbreviations are
used. [0027] Ex Example No. Alphabetic series are comparative,
numeric series are invention examples. [0028] OD Outer diameter, as
extruded. [0029] Die temp Extruder die zone temperature in degrees
Fahrenheit. The extruder barrel was kept at 395.degree. F. in these
examples. [0030] Line speed Speed in feet/min of the puller. [0031]
DDR Draw down ratio of the cross-sectional area from extrusion head
opening to final tube dimensions. DDR=[(Die ID).sup.2-(Tip
OD).sup.2]/[(Tubing OD)-(Tubing ID)2] [0032] Elong@ break Given as
percentage elongation determined on a 3'' long extruded tube which
is stretched to break. [0033] Balloon 2x wall Thickness in inches
of the balloon double wall as measured with a micrometer. [0034]
Hoop Hoop ratio determined as balloon OD (mold diameter)/parison ID
(as extruded). [0035] Distension The change in diameter as a % of
start diameter for the stated ranges of 6:12 (6 atm to 12 atm) and
12:18 (12 atm to 18 atm) inflation pressure. [0036] Burst Pressure
in psi at which the balloon burst [0037] Burst strength Wall
strength at burst as calculated by the equation: T.sub.s=PD/2t
[0038] where: T.sub.s is the wall tensile strength; [0039] P is the
balloon burst pressure; [0040] D is the nominal diameter of the
balloon; and [0041] t is the wall thickness.
[0042] All values are averages of at least 6 balloons. Balloon
blowing conditions used the same times, temperatures and sequences,
except where indicated.
[0043] All data is for balloons having a nominal diameter of 3.0 mm
at 6 atm. The balloons were made from PEBAX 7033. The published
elongation value for the bulk polymer, per ASThM D-638, is 400%.
The balloons were made from conventionally extruded parisons using
a very high hoop ratio and a step-wise dipping process similar to
that described in Wang et al, Example 3, U.S. Pat. No. 5,714,110. A
typical program is as follows: TABLE-US-00001 Program: bath at
95.degree. C. (1) pressure to 100 psi tension to 50 g dip to D 8
seconds hold at D 6 seconds (2) pressure to 450 psi tension to 20 g
dip to C 4 sec hold at C 6 seconds (3) pressure to 550 psi tension
to 200 g dip to B 20 sec hold at B 6 seconds
where D, C and B are locations, as described in U.S. Pat. No.
5,714,110. The parison formation conditions and formed balloon
results are described in Table 1. Die configuration was not
varied-between examples. Tank gaps, die temperatures and speeds
were varied as needed to obtain parison elongation targets.
Extruder pressure was not independently controlled and varied as a
result of changing these conditions.
[0044] Table 1 provides an example of a balloon formed using
conventional tube processing at a high hoop ratio. TABLE-US-00002
TABLE 1 Control Elong Tube Tube Die Line @ Balloon Distension
Distension Burst Ex ID OD Temp Speed DDR break 2.times. wall Hoop
6:12 12:18 Burst Strength A .0177 .0321 395 24 3.5 367 .00116 6.9
5.6 4.4 301 31056
[0045] The elongation at breaks of this parison corresponds to
about 91% of the published value for the bulk polymer.
[0046] Table 2 gives the results of the same balloon wall thickness
made in accordance with the invention by increasing the DDR. The
increased draw down ratio reduced the elongation of this tube to
about 48% of the published elongation value. TABLE-US-00003 TABLE 2
High Draw Down Elong Tube Tube Die Line @ Balloon Distension
Distension Burst Ex ID OD Temp Speed DDR break 2.times. wall Hoop
6:12 12:18 Burst Strength 1 .0176 .0310 395 50 12.1 190 0.00118 6.9
5.4 4.5 331 34411
[0047] Table 3 shows extrusion parameters and balloon property
results when, after extrusion, the parison was modified by one of
the following steps before it was blow-formed into a balloon.
Example 2
[0048] A freeze spray process was used to selectively reduce
parison cone and waists as per Example 1 of U.S. Pat. No.
5,807,520.
Example 3
[0049] Cones and waists were selectively reduced by a grinding and
necking process which did not stretch the body-forming portion of
the parison. Similar to Example 2, first paragraph of
PCT/US01/26140, filed Aug. 22, 2001, attorney docket no S63.3-9928,
corresponding to U.S. application Ser. No. 09/672330 filed Sep. 28,
2000.
Example 4
[0050] the entire parison was stretched longitudinally at ambient
temperature under internal pressurization to maintain ID at the
extruded dimension (.+-.4%) at a stretch ratio 3x, where x is
starting length. See control in Example 1 of PCT/US01/26140.
TABLE-US-00004 TABLE 3 Parison Modifications Elong Tube Tube Die
Line @ Balloon Distension Distension Burst Ex ID OD Temp Speed DDR
break 2.times. wall Hoop 6:12 12:18 Burst Strength 2 0.176 .0290
395 50 12:1 193 .00105 6.9 5.3 4.7 309 36101 3 .0176 .0290 395 50
12:1 193 .00098 6.9 4.8 4.8 297 37423 4 .0176 .0290 395 50 12:1 193
.00097 6.9 4.9 4.7 300 37577
[0051] In examples 2-4, the burst pressure in all cases was
comparable to the control balloon, but with thinner walls so the
wall strength is much improved over the control balloon.
Example 5
[0052] Balloons were made using PEBAX 7033 parisons stretched at
ambient temperature at a stretch ratio of 1.5x and a hoop ratio of
7.0. Parisons, extruded to keep the parison elongation at break
above 80% of the published elongation of the polymer, were used as
controls. Parisons, extruded to provide a parison elongation at
break of about 50% or less of the published elongation of the
polymer, were prepared as invention examples. The balloons were
inflated to 211 psi and deflated repeatedly. Four balloons were
present in each group. The control balloon group, on average,
failed at about 80 repeats. All of the balloons of the invention
group survived 235 repeats without failure, at which point the test
was discontinued.
[0053] The above examples and disclosure are intended to be
illustrative and not exhaustive. These examples and description
will suggest many variations and alternatives to one of ordinary
skill in this art. All these alternatives and variations are
intended to be included within the scope of the claims, where the
term "comprising" means "including, but not limited to". Those
familiar with the art may recognize other equivalents to the
specific embodiments described herein which equivalents are also
intended to be encompassed by the claims. Further, the particular
features presented in the dependent claims can be combined with
each other in other manners within the scope of the invention such
that the invention should be recognized as also specifically
directed to other embodiments having any other possible combination
of the features of the dependent claims. For instance, for purposes
of claim publication, any dependent claim which follows should be
taken as alternatively written in a multiple dependent form from
all prior claims which possess all antecedents referenced in such
dependent claim if such multiple dependent format is an accepted
format within the jurisdiction (e.g. each claim depending directly
from claim 1 should be alternatively taken as depending from all
previous claims). In jurisdictions where multiple dependent claim
formats are restricted, the following dependent claims should each
be also taken as alternatively written in each singly dependent
claim format which creates a dependency from a prior
antecedent-possessing claim other than the specific claim listed in
such dependent claim below.
* * * * *