U.S. patent application number 09/989796 was filed with the patent office on 2002-08-01 for balloon forming process.
This patent application is currently assigned to Advanced Cardiovascular Systems, Inc.. Invention is credited to Skinner, Johann J., Wang, Chicheng, Williams, Kerry J., Zhang, Michael Y..
Application Number | 20020103455 09/989796 |
Document ID | / |
Family ID | 23919859 |
Filed Date | 2002-08-01 |
United States Patent
Application |
20020103455 |
Kind Code |
A1 |
Zhang, Michael Y. ; et
al. |
August 1, 2002 |
Balloon forming process
Abstract
The present invention is directed to apparatus and method for
forming balloons with improved dimensional stability and balloons
formed by the same. The method of the present invention provides
for a very accurate control of the temperature profile of the
balloon material during its making. The attributes of the balloon
can be affected by how the balloon is treated during the blowing
stage and after the initial blowing, i.e., heat-setting. Using the
present method, the balloon will form more uniformly and evenly
(e.g., wall thickness and outer diameter of the balloon). The
present method significantly increases the dimensional stability of
the balloon which provides a balloon that is more predictable in
use. The present heat-set process also provides the means for the
working length to be located more accurately on dilation catheters
and stent delivery systems.
Inventors: |
Zhang, Michael Y.; (San
Diego, CA) ; Williams, Kerry J.; (Temecula, CA)
; Skinner, Johann J.; (Cupertino, CA) ; Wang,
Chicheng; (Sunnyvale, CA) |
Correspondence
Address: |
Edward J. Lynch
Coudert Brothers LLP
600 Beach Street, 3rd Floor
San Francisco
CA
94109
US
|
Assignee: |
Advanced Cardiovascular Systems,
Inc.
|
Family ID: |
23919859 |
Appl. No.: |
09/989796 |
Filed: |
November 20, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09989796 |
Nov 20, 2001 |
|
|
|
09483390 |
Jan 13, 2000 |
|
|
|
Current U.S.
Class: |
604/96.01 ;
264/535 |
Current CPC
Class: |
B29C 35/045 20130101;
B29C 2949/08 20220501; B29C 67/0014 20130101; B29C 55/24 20130101;
Y10S 264/903 20130101; Y10S 264/904 20130101; B29L 2031/7542
20130101; B29C 49/6472 20130101; B29K 2105/258 20130101; A61M
25/1029 20130101 |
Class at
Publication: |
604/96.01 ;
264/535 |
International
Class: |
A61M 029/00; B29C
049/64 |
Claims
What is claimed is:
1. A method for forming a balloon; comprising: disposing a
polymeric tubular product having an effective length with first and
second ends within a mold; applying internal pressure to the
tubular product; heating at least a portion of the tubular product
to a first elevated temperature for a first predetermined period of
time to form the tubular product into a balloon; maintaining the
temperature of the tubular product to a minimal temperature
differential from the first temperature; heating the tubular
product to a second elevated temperature for a second predetermined
period of time to heat set the formed balloon; cooling down the
tubular product to substantially ambient temperature; removing the
tubular product from the mold.
2. The method of claim 1 wherein the temperature differential is
less than about 100.degree. C.
3. The method of claim 1 wherein the temperature differential is
less than about 50.degree. C.
4. The method of claim 1 wherein the temperature differential is
less than about 20.degree. C.
5. The method of claim 1 wherein the first elevated temperature is
greater than the glass transition temperature of the polymeric
material forming the tubular product.
6. The method of claim 5 wherein the first elevated temperature is
at least 10.degree. C. greater than the glass transition
temperature of the polymeric material forming the tubular
product.
7. The method of claim 6 wherein the first elevated temperature is
at least 20.degree. C. greater than the glass transition
temperature of the polymeric material forming the tubular
product.
8. The method of claim 7 wherein the first elevated temperature is
at least 40.degree. C. greater than the glass transition
temperature of the polymeric material forming the tubular
product.
9. The method of claim 5 wherein the first elevated temperature is
less than the melting temperature of the polymeric material forming
the tubular product.
10. The method of claim 1 wherein the second elevated temperature
is substantially equal to the first elevated temperature.
11. The method of claim 1 wherein the second elevated temperature
is greater than the first elevated temperature.
12. The method of claim 11 wherein the second elevated temperature
is sufficiently high to thermoset the polymeric material forming
the tubular product.
13. A method for forming a balloon; comprising: disposing a
polymeric tubular product having an effective length with first and
second ends within a mold; applying internal pressure to the
tubular product; heating at least a portion of the tubular product
to a first elevated temperature for a predetermined period of time
to form the tubular product into a balloon; heating the tubular
product uniformly between the first and second ends to a second
elevated temperature for a predetermined period of time to heat set
the formed balloon; cooling down the tubular product to
substantially ambient temperature; removing the tubular product
from the mold.
14. The method of claim 12 wherein the tubular product temperature
difference between the first and second ends is less than about
30.degree. C.
15. The method of claim 14 wherein the tubular product temperature
difference between the first and second ends is less than about
15.degree. C.
16. The method of claim 15 wherein the tubular product temperature
difference between the first and second ends is less than about
10.degree. C.
17. A method for forming a balloon; comprising: disposing a
polymeric tubular product having an effective length with first and
second ends within a mold; applying internal pressure to the
tubular product; heating at least a portion of the tubular product
to a first elevated temperature with a first heating member for a
predetermined period of time to form the tubular product into a
balloon; heating the tubular product to a second elevated
temperature with a second heating member having an effective length
at least substantially the same as the effective length of the
tubular product; cooling down the tubular product to substantially
ambient temperature; removing the tubular product from the
mold.
18. The method of claim 17 wherein the first heating member applies
heat to the tubular product as it traverses from one end of the
tubular product to the other end.
19. The method of claim 17 wherein the first heating member has an
effective length at least substantially the same as the effective
length of the tubular product.
20. The method of claim 19 wherein the first heating member applies
heat to the tubular product simultaneously across the effective
length of the tubular product.
21. The method of claim 17 wherein the second heating member
applies heat to the tubular product as it traverses from one end of
the tubular product to the other end.
22. The method of claim 17 wherein the second heating member
applies heat to the tubular product simultaneously across the
effective length of the tubular product.
23. The method of claim 17 wherein the first heating member and the
second heating member are integral with one another.
24. The method of claim 17 wherein the first heating member and the
second heating member are on different heating heads.
25. The method of claim 17 wherein the second elevated temperature
is different from the first elevated temperature.
26. A medical balloon having a reduced radial shrinkage and reduced
axial growth.
27. The balloon of claim 26 wherein the radial shrinkage is less
than about 10%.
28. The balloon of claim 27 wherein the radial shrinkage is less
than about 6%.
29. The balloon of claim 28 wherein the radial shrinkage is less
than about 4%.
30. The balloon of claim 26 wherein the axial growth is less than
about 10%.
31. The balloon of claim 29 wherein the axial growth is less than
about 6%.
32. The balloon of claim 30 wherein the axial growth is less than
about 4%.
Description
FIELD OF INVENTION
[0001] The invention relates to the field of intravascular
balloons, and more particularly to method and apparatus for forming
balloons.
BACKGROUND OF THE INVENTION
[0002] In percutaneous transluminal coronary angioplasty (PTCA)
procedures a guiding catheter is advanced until the distal tip of
the guiding catheter is seated in the ostium of a desired coronary
artery. A guidewire, positioned within an inner lumen of an
dilatation catheter, is first advanced out of the distal end of the
guiding catheter into the patient's coronary artery until the
distal end of the guidewire crosses a lesion to be dilated. Then
the dilatation catheter, having an inflatable balloon on the distal
portion thereof, is advanced into the patient's coronary anatomy
over the previously introduced guidewire until the balloon of the
dilatation catheter is properly positioned across the lesion. Once
properly positioned, the dilatation balloon is inflated with liquid
one or more times to a predetermined size at relatively high
pressures (e.g. greater than 8 atmospheres) so that the stenosis is
compressed against the arterial wall and the wall expanded to open
up the passageway. Generally, the inflated diameter of the balloon
is approximately the same diameter as the native diameter of the
body lumen being dilated so as to complete the dilatation but not
overexpand the artery wall. After the balloon is finally deflated,
blood flow resumes through the dilated artery and the dilatation
catheter can be removed therefrom.
[0003] In such angioplasty procedures, there may be restenosis of
the artery, i.e. reformation of the arterial blockage, which
necessitates either another angioplasty procedure, or some other
method of repairing or strengthening the dilated area. To reduce
the restenosis rate and to strengthen the dilated area, physicians
frequently implant an intravascular prosthesis, generally called a
stent, inside the artery at the site of the lesion. Stents may also
be used to repair vessels having an intimal flap or dissection or
to generally strengthen a weakened section of a vessel. Stents are
usually delivered to a desired location within a coronary artery in
a contracted condition on a balloon of a catheter which is similar
in many respects to a balloon angioplasty catheter, and expanded to
a larger diameter by expansion of the balloon. The balloon is
deflated to remove the catheter and the stent left in place within
the artery at the site of the dilated lesion. Thus, stents are used
to open a stenosed vessel, and strengthen the dilated area by
remaining inside the vessel.
[0004] In either procedure, substantial, uncontrolled or
unpredictable expansion of the balloon against the vessel wall can
cause trauma to the vessel wall. For example, although stents have
been used effectively for some time, the effectiveness of a stent
can be diminished if it is not properly implanted within the
vessel. Additionally, the final location of the implanted stent in
the body lumen may be beyond the physician's control where
longitudinal growth of the stent deploying balloon causes the
stent's position on the balloon to shift during deployment. As the
balloon's axial length grows during inflation, the stent may shift
position along the length of the balloon, and the stent may be
implanted upstream or downstream of the desired location in the
body lumen. Thus, balloons which have a large amount of
longitudinal growth during inflation can frequently provide
inadequate control over the location of the implanted stent. Thus,
it is important for the balloon to exhibit dimensional
stability.
[0005] Therefore, what has been needed is an improved method for
forming catheter balloons. The present invention satisfies these
and other needs.
SUMMARY OF THE INVENTION
[0006] The present invention is directed to an apparatus and method
for forming balloons with improved dimensional stability and
balloons formed by the same.
[0007] The method of the present invention provides for a very
accurate control of the temperature profile of the balloon material
during its making. The attributes of the balloon can be affected by
how the balloon is treated during the blowing stage and after the
initial blowing, i.e., heat-setting. Using the present method, the
balloon will form more uniformly and evenly (e.g., wall thickness
and outer diameter of the balloon). The present method
significantly increases the dimensional stability of the balloon
which provides a balloon that is more predictable in use. The
present heat-set process also provides the means for the working
length to be located more accurately on dilation catheters and
stent delivery systems.
[0008] In one embodiment, the method for forming the balloon
comprises disposing a polymeric tubular product having an effective
length with first and second ends within a mold. The interior of
the tubular product is then pressurized. At least a portion of the
tubular product is heated to a first elevated temperature for a
first predetermined period of time to form the tubular product into
a balloon. Preferably, the temperature of the tubular product is
maintained to a minimal temperature differential from the first
temperature. The tubular product is heated to a second elevated
temperature for a second predetermined period of time to heat set
the formed balloon. The tubular product (i.e., formed balloon) is
then cooled down to substantially ambient temperature and may be
subsequently removed. In an embodiment, the temperature
differential is less than about 100.degree. C., preferably, less
than about 50.degree. C., and more preferably, less than about
20.degree. C. In one embodiment, the first elevated temperature is
greater than the glass transition temperature of the polymeric
material forming the tubular product, preferably, by at least
10.degree. C., more preferably, by at least 20.degree. C., and most
preferably, by at least 40.degree. C. Preferably, the first
elevated temperature is less than the melting temperature of the
polymeric material forming the tubular product. The second elevated
temperature may be equal or greater than the first elevated
temperature, and is preferably sufficiently high to thermoset the
polymeric material forming the tubular product.
[0009] In one embodiment, the tubular product is heated uniformly
between the first and second ends to the second elevated
temperature for a predetermined period of time to heat set the
formed balloon. Preferably, the temperature difference between the
first and second ends is less than about 30.degree. C., more
preferably, less than 15.degree. C., and most preferably, less
than
[0010] In a preferred embodiment, the tubular product is heated to
the first elevated temperature with a first heating member, and to
the second elevated temperature with a second heating member. The
first heating member may apply the heat as it traverses along the
length of the mold. Alternatively, the first heating member has an
effective length which is at least substantially the same as the
effective length of the tubular product. In this embodiment, the
first heating member may then apply the heat to the mold
simultaneously across the effective length of the tubular
product.
[0011] In one embodiment, the second heating member applies heat to
the tubular product as it traverses from one end of the tubular
product to the other end. Alternatively, the second heating member
may apply the heat to the tubular product simultaneously across the
effective length of the tubular product.
[0012] In another embodiment, the first and second heating members
are integral with one another. Alternatively, the first heating
member and the second heating member may be on different heating
heads. The second heating member may apply the heat to the mold as
it traverses along the length of the mold or it may apply the heat
simultaneously across the effective length of the mold, and thus,
the tubular product.
[0013] Balloons formed from the process of the present invention,
preferably, have either or both a reduced radial shrinkage and
reduced axial growth. Such reduction, being in radial shrinkage or
axial growth, preferably, is less than about 10%, more preferably,
less than about 6%, and most preferably, less than about 4%.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a top elevational view, partially cut away, of a
balloon forming apparatus.
[0015] FIG. 2 is a partial top elevational view of the apparatus of
FIG. 1 showing a first heating element.
[0016] FIG. 3 is a front, partially cut away, elevational view of
the apparatus of FIG. 2 taken along lines 3.
[0017] FIG. 4 is a cross sectional view of the apparatus of FIG. 3
taken along lines 4.
[0018] FIG. 5 is a partial top elevational view of the apparatus of
FIG. 1 showing a second heating element.
[0019] FIG. 6 is a front, partially cut away, view of the apparatus
of FIG. 5 taken along lines 6.
[0020] FIG. 7 is a cross sectional view of the apparatus of FIG. 6
taken along lines 7.
[0021] FIG. 8 is a bottom view of the apparatus in FIG. 6 taken
along lines 8.
[0022] FIG. 9 is an alternate embodiment of another heating
element.
[0023] FIG. 10 is an alternate embodiment of another heating
element having heating cartridges.
[0024] FIG. 11 is an alternate embodiment of another heating
element having a heating head configured in a "C" shape.
[0025] FIG. 12 is a side elevational view, partially cut away, of
an alternate embodiment of the balloon forming apparatus of FIG.
1.
[0026] FIG. 13 is an alternate embodiment of an integral heating
element.
DETAILED DESCRIPTION OF THE INVENTION
[0027] The invention relates to a method of making a balloon and
apparatus for carrying out the same. The method generally comprises
extruding a polymeric tubular product having a first outer
diameter. The tubular product is then radially expanded and,
preferably axially drawn, to a second outer diameter by heating at
least a portion of the tubular product to a first elevated
temperature while subjecting the interior of the tubular product to
an expansion pressure. While still under pressure, the expanded
tubular product is heated to a second elevated temperature.
Preferably, the first elevated temperature is greater than the
glass transition temperature of the polymeric material forming the
tubular product. Preferably, the first elevated temperature is at
least 10.degree. C., more preferably at least 20.degree. C., and
most preferably at least 40.degree. C., greater than the glass
transition temperature of the polymeric material forming the
tubular product. The second elevated temperature is sufficiently
high to thermoset the polymeric material forming the tubular
product. The second elevated temperature may be less, equal or
greater than the first elevated temperature. Preferably, the second
elevated temperature is equal to or greater than the first elevated
temperature.
[0028] The transformation of the tubular product into the balloon
is performed in a mold having a longitudinal dimension including an
effective length with first and second ends, the mold's effective
length and the ends substantially corresponding to an effective
length and first and second ends of the tubular product which in
turns corresponds to the resulting balloon's longitudinal
dimension; and a radial dimension suitable for forming the desired
size balloon.
[0029] Preferably, the temperature of the tubular product along its
effective length is maintained to a minimal temperature
differential from the first temperature. Preferably, the
temperature differential is less than about 100.degree. C.; more
preferably, less than about 50.degree. C.; and most preferably,
less than about 20.degree. C. It should be noted, that when
referring to the temperature of the tubular product, such
temperature may be measured directly, or indirectly by correlation,
as for example, when measuring the temperature of the heat source
or the in mold temperature.
[0030] Preferably, the second elevated temperature is uniformly
applied to the effective length of the tubular product. Preferably,
the tubular product's temperature difference between the first and
second ends is less than about 30.degree. C.; more preferably, less
than about 15.degree. C.; and most preferably, less than about
10.degree. C.
[0031] The expanded, heat-treated tubular product is then cooled to
form a balloon.
[0032] For example, the formed balloon has a minimal radial
shrinkage (for example, as measured by the % change in the outer
diameter of the working length of an inflated balloon as part of a
catheter system versus as formed after the present process), and
minimal axial growth (for example, as measured by the % change in
the axial dimension of an inflated balloon as part of a catheter
system versus as formed after the present process). Preferably,
balloons formed as a result of the present process will exhibit a %
shrinkage less than about 10%, more preferably, less than about 6%,
and most preferably, less than about 4%. The balloons made
according to the present method, may additionally have reduced
axial growth of less than about 10%, more preferably, less than
about 6%, and most preferably, less than about 4%, as for example
when balloons formed from polyurethane.
[0033] The balloon is typically formed within a mold having
dimensions close to the dimensions of the desired balloon. The blow
up ratio, i.e., the balloon outer diameter divided by the balloon
tubing inner diameter, is typically about 5.0 to about 8.0, and
preferably about 7.0 to about 8.0.
[0034] In a presently preferred embodiment, to heat the tubular
product to the first elevated temperature during the radial
expansion, a first heating member such as a heat nozzle is
displaced along a length of the tubular product within the mold, to
thereby apply heat to portions of the tubular product adjacent to
the first heating member. The expanded tubular product is then heat
treated at a second elevated temperature. The heat treatment at the
second elevated temperature may be achieved by the first heating
member or a second heating member. In either way, the heating
member for applying the heat treatment at the second elevated
temperature, preferably, applies the heat in such manner as to
sufficiently provide a uniform temperature profile across at least
substantially the entire length of the mold corresponding to the
balloon member (i.e., the effective length). The balloon is then
cooled within the mold under pressure.
[0035] By way of example, when using a polyurethane tubular
product, the first elevated temperature is reached by heating the
mold to about 80.degree. C. to about 120.degree. C., and preferably
about 95.degree. C. to about 105.degree. C.; and the second
elevated temperature is reached by heating the mold to about
100.degree. C. to about 160.degree. C., and preferably about
110.degree. C. to about 140.degree. C. In a presently preferred
embodiment, regardless of the material of choice for the tubular
product, the second temperature is greater than the first
temperature. By way of example, when using a polyurethane tubular
product, the second temperature is typically no more than about
10.degree. C. to about 50.degree. C., preferably no more than about
10.degree. C. to about 20.degree. C., greater than the first
temperature.
[0036] FIGS. 1 through 7, illustrate features of a balloon forming
apparatus 10 for transforming a tubular product 13 into a balloon
16 (FIG. 6) for medical devices according to the present invention.
The apparatus 10 achieves longitudinal stretching, biaxial
orientation, heating, and cooling, in addition to means for
monitoring radial expansion or biaxial orientation through suitable
means such as hard circuitry, a microprocessor, or other
computerized controlling arrangements. For simplicity, many of the
details of such apparatus which are commonly known and used in the
art are not illustrated. The tubular product 13 is disposed within
a mold 19 by inserting the distal and proximal ends of the tubular
product 13 through the mold 19 and into corresponding distal and
proximal collets, 22 and 25. The mold 19 is then closed and held in
place. The tubular product 13 is then subjected to axial tension
and pressurized air as is commonly practiced in the art.
[0037] To blow the balloon (FIGS. 2 through 4), the interior of the
tubular product 13 is pressurized at the desired pressure and a
first heating member 37 providing heat at a first elevated
temperature is moved from a first position substantially radial to
a distal end 40 of an effective length 43 of the mold 19 (i.e.,
what will be a distal shaft of the balloon 16), over the working
length 43, to a second position substantially radial to a proximal
end 46 of the effective length 43 of the mold 19 (i.e., what will
be a proximal shaft of the balloon 16). During the movement of the
first heating member 37, the tubular product 13 is also being
subjected to radial expansion, preferably, also axial stretching.
At this time, the tubular product 19 is blown up and formed to
substantially its ultimate shape. The blow cycle may include one or
more passes of the first heating member 37 along the effective
length 43 of the mold 19. Alternatively, as the first heating
member 37 traverses along the effective length 43 of the mold, the
second heating member 49 may also traverse along this length
following the first heating member.
[0038] After the completion of the blowing cycle (may include one
or more passes of the first heating member), the tubular product 13
is then subjected to a second elevated temperature as a second
heating member 49 applies heat to the tubular product 13 through
the mold 19 (FIGS. 5 through 7). Preferably, the second heating
member 49 is of such longitudinal dimension and design so as to
apply heat to substantially the entire effective length 43 of the
mold 19 at the same time. In other words, preferably, the second
heating member 49 is long enough to provide a uniform temperature
profile across substantially the entire length of the mold 19, and
in effect substantially the entire effective length 43 of the
tubular product 13 corresponding to the balloon 16 within the mold
19.
[0039] Now referring to FIGS. 8A, 8B, the second heating member 49
includes a heating head 52 having one or more heating nozzles 55.
The heating head 52 may have one large nozzle such as slot 58 (FIG.
8A) or a multiple of smaller nozzles such as 61 (FIG. 8B). The
heating nozzles 55, may have any shape and number as may be
required to heat the mold in the uniform manner desired. The
heating nozzles 55 as shown in FIGS. 7, 8A, 8B, 9 and 10 are
fluidically connected to a source of hot air 64. The air source 64
may be heated in connecting bodies 67 before exiting the heating
nozzles 55.
[0040] FIG. 10 illustrates features of an alternate embodiment of a
second heating member 70. In this embodiment, the second heating
member 70 includes one or more heating heads 73 formed of
conductive material such as stainless steel and further includes
cartridge heaters 76. To apply heat to the mold 19, the heating
cartridges 76 heat the heating head 73. The heating head 73 is
brought into physical contact with the mold 19 and the mold 19 is
heated by conduction. At points such as 79 where the heating head
73 is not in physical contact with the mold 19, the mold 19 may be
heated as heat radiates from the heating head 73 through air and to
the mold 19.
[0041] In order to uniformly heat the mold 19 from all directions,
the second heating member 49, may include one or more individual
heating members such as 82, each possibly having a separate heat
source (e.g. air) which can heat the mold 19 from two opposite
sides, as shown in FIG. 7. Alternatively, the second heating member
49, may be one such as that illustrated in FIGS. 9 and 11, where
the heating head 85 is formed in a semi-circular shape or "C"
shaped and receiving its heat from a single source. It should be
appreciated that the same configuration may also be used for the
first heating member 37.
[0042] Now referring to FIG. 12, wherein like references refer to
like members, apparatus 100 includes a single integral heating
member 103 for both the blowing and heat setting of the tubular
product 13 as it is formed into balloon 16. In this embodiment, the
integral heating member 103 includes a single heating head 106 with
one or more leading nozzles 109 (one as is shown in FIG. 12, and
13) for heating the tubular product 13 during the blowing stage. As
a leading edge 112 of the integral heating member 103 moves from
the first position to the second position, the tubular product 13
is blown as described in reference to FIG. 1. When the one or more
leading nozzles 109 reach the second position, one or more trailing
nozzles 115 apply heat to the mold 19 to heat set the balloon 16.
The integral heating member 103 may be formed from multiple single
heating heads 106 (as shown in FIG. 13) or multiple heads
configured to correspond to the leading nozzle 109 and the trailing
nozzle 115 separately.
[0043] This embodiment, enables the blowing of the tubular product
13 in a number of desirable fashions. For example, during the
blowing stage of the tubular product 13, the integral heating
member 103 may be displaced along the effective length 43 of the
mold 19 as it traverses from one end to the other. Alternatively, a
heating member such as that of FIG. 8A or 8B may be brought into
position (as that illustrated in FIG. 5) so as to provide uniform
heating of the entire effective length 43 of the mold 19 for both
blowing and heat-setting.
[0044] The balloon may be formed of any material, preferably,
compliant material, including thermoplastic and thermoset polymers.
The presently preferred compliant polymeric materials include
polyurethanes such as TECOTHANE from Thermedics. TECOTHANE is a
thermoplastic, aromatic, polyether polyurethane synthesized from
methylene disocyanate (MDI), polytetramethylene ether glycol
(PTMEG) and 1,4 butanediol chain extender. TECOTHANE grade 1065D is
presently preferred, and has a Shore durometer of 65D, an
elongation at break of about 300%, and a high tensile strength at
yield of about 10,000 psi. However, other suitable grades may be
used, including TECOTHANE 1075D, having a Shore D of 75. Balloons
produced from the TECOTHANE materials are particularly preferred
because the axial growth of the balloon during inflation is
minimized, and the axial and radial size of the balloon deflates to
the original preinflation size following inflation and deflation of
the balloon. Thus, inflation produces little or no axial or radial
growth, so that the deflated balloons elastically recoil to the
preinflation size. Other suitable compliant polymeric materials
which deflate so that at least the radial size of the balloon
returns to the original preinflation radial size, and which
therefore have a substantially elastic recoil after deflation,
include ENGAGE from DuPont Dow Elastomers (an ethylene alpha-olefin
polymer) and EXACT, available from Exxon Chemical, both of which
are thermoplastic polymers and are believed to be polyolefin
elastomers produced from metallocene catalysts. Other suitable
compliant materials include, but are not limited to, elastomeric
silicones, latexes, and urethanes. The type of compliant material
may be chosen to provide compatibility with the catheter shaft
material, to thereby facilitate bonding of the balloon to the
catheter.
[0045] The compliant material may be cross linked or uncrosslinked,
depending upon the balloon material and characteristics required
for a particular application. The presently preferred polyurethane
balloon materials are not crosslinked. However, other suitable
materials, such as the polyolefinic polymers ENGAGE and EXACT, are
preferably crosslinked. By crosslinking the balloon compliant
material, the final inflated balloon size can be controlled.
Conventional crosslinking techniques can be used including thermal
treatment and E-beam exposure. After crosslinking, initial
pressurization, expansion, and preshrinking, the balloon will
thereafter expand in a controlled manner to a reproducible diameter
in response to a given inflation pressure, and thereby avoid
overexpanding the stent (when used in a stent delivery system) to
an undesirably large diameter.
[0046] The length of the compliant balloon may be about 0.8 cm to
about 8 cm, preferably about 1.5 cm to about 3.0 cm, and is
typically about 2.0 cm. The wall thickness is generally about 0.004
in (0.1 mm) to about 0.016 in (0.4 mm), and is typically about
0.008 in (0.2 mm). In an expanded state, the balloon diameter is
generally about 0.06 in (1.5 mm) to about 0.22 in (5.5 mm), and the
wall thickness is about 0.0005 in (0.012 mm) to about 0.0025 in
(0.06 mm).
[0047] While particular forms of the invention have been
illustrated and described, it will be apparent that various
modifications can be made without departing from the spirit and
scope of the invention. Accordingly, it is not intended that the
invention be limited, except as by the appended claims.
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