Note: Descriptions are shown in the official language in which they were submitted.
CA 02179636 2006-03-07
76664-76
1
SLIP-LAYERED CATHETER BALLOON
BACKGROUND OF THE INTENTION
The present invention relates to balloons for
medical catheter applications, wherein a catheter with a
balloon at the proximal end is positioned within a bodily
conduit and inflated to expand the conduit, and to methods
of fabrication of such balloons.
Typical balloon catheters have a balloon fastened
around the exterior of a hollow catheter tube or shaft, with
the balloon in fluid flow relation with the interior of the
shaft. The shaft provides a fluid supply for inflating the
balloon.
Examples of such balloon catheters are catheters
for prostate therapy, TTS endoscopic catheters for
gastrointestinal use, and PTA and PTCA catheters for
angioplasty. For example, coronary angioplasty can involve
the insertion of a PTCA (percutaneous transluminal coronary
angioplasty) catheter through a patient's artery to an
arterial stenosis, and injecting a suitable fluid into the
balloon to inflate it. The inflation expands the stenosis
radially outwardly and compresses it against the artery wall
to increase the cross-sectional area of the artery so that
the artery has an acceptable blood flow rate.
Some known catheter balloons are fabricated from
non-compliant materials such as polyethylene terephthalate
(PET) or Nylon. Non-compliant balloons present the
advantages of high burst strength and predetermined maximum
diameter. These balloons can prevent damage to tissues due
to overinflation, since they do not increase in diameter
significantly beyond the point of full inflation. Their
disadvantages, however, include stiffness and poor
CA 02179636 2006-03-07
76664-76
2
foldability. Further, on deflation these balloons can
present sharp edges and corners which can cause trauma to
bodily tissues as the catheters are withdrawn.
Other known balloons are fabricated from compliant
materials such as polyethylene (PE) or ethylene vinyl
acetate (EVA). The diameter of these balloons is dependent
on the pressure of the inflation fluid. The compliant
balloons are easily folded, and are softer than the non-
compliant balloon, thus are less likely to cause trauma
during their passage through the body. However, the
variable diameter of the non-compliant balloons must be
carefully monitored to prevent tissue damage and
catastrophic failure of the balloon during inflation. They
can also present the disadvantages of lower tensile strength
than the non-compliant balloons. Increasing the wall
thickness to offset the lower tensile strength can present
an undesirably large profile in the folded balloon.
It would be desirable to have a medical catheter
balloon which combines the best properties of the compliant
and non-compliant balloons, with low compliance, high burst
strength, low folded profile, softness, and pliability. The
invention described herein was developed to address that
need.
SUMMARY OF THE INVENTION
In a first aspect, the invention is a soft,
pliable, inflatable and refoldable sliplayered balloon for
use with a medical catheter device, said balloon comprising
a wall defining a chamber, said wall comprising at least two
imperforate coextensive layers of a non-compliant polymeric
medical balloon material, said layers having therebetween a
low-friction substance imparting a low coefficient of
friction between facing surfaces of said layers, such that
CA 02179636 2006-03-07
76664-76
3
said layers become slip-layers which readily slide with
respect to one another as said balloon is inflated and
deflated.
A typical configuration for the balloon wall is a
generally cylindrical central portion between tapered
proximal and distal end portions.
In a narrower aspect, the balloon wall is unitary,
with layers joined to one another at a plurality of ridges,
each extending the length of the wall. Each ridge is
separated from other ridges by slip-layered segments in
which the layers become slip-layers which readily slide with
respect to one another as the balloon is inflated and
deflated.
In another narrower aspect, the balloon further
includes an elastic sleeve surrounding and coextensive with
the wall. The low-friction substance in such a sleeved
balloon can also be disposed between the elastic sleeve and
the outermost layer, so that a low coefficient of friction
is imparted between facing surfaces of the elastic sleeve
and the outermost layer and such that the elastic sleeve and
the outermost layer also become slip-layers which readily
slide with respect to one another as the balloon is inflated
and deflated.
In another aspect, the invention is a catheter for
insertion into a bodily conduit. The catheter includes a
shaft with a lumen for delivery of fluid inflation media, a
balloon having a wall concentric with the shaft and defining
a chamber. The chamber is in fluid communication with the
CA 02179636 2006-03-07
76664-76
3a
lumen for inflation of the balloon. The balloon wall
includes at least two non-adhering layers of a polymeric
medical balloon material. Between the layers is a low-
friction substance imparting a low coefficient of friction
between facing surfaces of the layers, so that the layers
become slip-layers which readily slide with respect to one
another as the balloon is inflated and deflated.
In yet another aspect, the invention is a method
for fabricating a slip-layered balloon for use with a
medical
R'O 95117920 PCTIUS94114199
217963,
4
catheter device. The method involves providing on a first
layer of a medical balloon material at least one additional
layer to form a balloon wall including at least two layers
of a medical balloon material. The wall defines a chamber.
A low-friction substance is disposed between said layers
imparting a low coefficient of friction between facing
surfaces of the layers, so that the layers become slip-
layers which readily slide with respect to one another as
the balloon is inflated and deflated.
In a narrower aspect of this method, the additional
layer on said first layer is provided by extruding the
medical balloon material to form the first layer and the
additional layer of the balloon wall. In a preferred
method, a polymeric medical balloon material and a second
polymeric material are coextruded so that the medical bal-
loon material forms a continuous phase providing a generally
tubular balloon blank and the second material forms a dis-
crete phase. The discrete phase is surrounded by the con-
tinuous phase and provides strands extending lengthwise
within the blank. The strands are then removed from the
blank and the strand-removed blank is shaped to form a
balloon including a unitary wall defining a chamber. The
balloon wall includes at least two layers of a the medical
balloon material joined to one another at a plurality of
ridges, each of the ridges extending the length of the wall
and being separated from other ridges by layered segments of
the wall. A low-friction substance is disposed between the
layers of the segments, imparting a low coefficient of
friction between facing surfaces of the layers, so that the
layers become slip-layers which readily slide with respect
to one another as the balloon is inflated and deflated. In
a most preferred method, the second material is softer than
the medical balloon material, and the strands are removed by
scoring the balloon blank to form a score-line in the
circumferential direction along the outermost surface of the
medical balloon material near an end of the blank, without
WO 95117920 PCTIIJS94114199
~:~'~9~36
affecting the second material. The medical balloon material
is then broken at the score-line to separate the medical
balloon material of the end of the blank from the remainder
of the medical balloon material. The separated medical
y 5 balloon material is removed from the blank by pulling the
separated medical balloon material off of the strands,
thereby exposing an end of each strand. The strand ends are
then gripped and pulled to remove the strands from the
blank.
~F' DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-sectional view of a balloon cathe-
ter in an inflated condition in accordance with one embodi-
went of the present invention.
Figure 2 is a cross-sectional view of the balloon shown
in Figure 1, taken along the line 2-2.
Figure 3 is a cross-sectional view of a coextruded
balloon blank for fabricating a balloon in accordance with
I
an alternate embodiment of the present invention.
' Figure 4 is an elevation view of the balloon blank of
i
Figure 3, illustrating the withdrawal of the second phase
strands to leave open channels in the balloon blank.
( Fi a 5 is a cross-sectional view of a
gur portion of the
balloon fabricated from the balloon blank of Figures 3
i and 4.
Figure 6 is a cross-sectional view of a portion of a
balloon in accordance with another alternate embodiment of
the present invention.
~ DETAINED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An exemplary embodiment of the balloon in accordance
with the invention utilizes a non-compliant balloon in which
the balloon wall encloses a chamber. The balloon has two or
more boncentric thin layers of high strength medical balloon
~ material, with provision made to overcome the normally
occurring high coefficient of friction existing between the
R'O 95/17920 PCT/US94114199
_ X1'79636
Y
6
interfacial surfaces of the balloon layers. That is, a
sufficiently low coefficient of friction between the layers ,
exists for the layers to be very slippery against each
other. The number of layers in the balloon wall typically .
is 2 to about 10 layers, preferably 3 - 5 layers, with
provision made for a low coefficient of friction between
adjacent pairs of layers.
This slip-layered balloon deforms easily, since little
force is necessary to cause the layers to slide against
(move relative to) one another. This sliding movement is
principally in the circumferential direction, and may be
likened to the sliding against one another of the pages of a
paperback booklet when the booklet is bent into a curve.
Although the booklet may be the same thickness as a similar
sized piece of paperboard, it is softer and more flexible.
Similarly, even if each individual layer is stiff and
strong, the slip-layered balloon described herein feels soft
and pliable, and folds down easily. This improvement in
properties is achieved even in a balloon having a total
2o thickness greater than is normally used for a particular
medical purpose.
The balloon layers may be fabricated from any high
strength material known to be suitable for medical balloons,
and preferably from a non-compliant material. Examples of
preferred non-compliant materials suitable for fabrication
of the balloon are polyethylene terephthalate (PET), most
preferably biaxially oriented PET, Nylon, polypropylene
(PP), and other non-compliant engineering resins known to be
suitable for medical balloon applications. Suitable compli-
ant materials are polyethylene (PE), particularly biaxially _
oriented PE (irradiated), polyvinyl chloride (PVC), and
other compliant polymers known to be suitable for medical
balloons.
The low coefficient of friction between layers may be
provided by coating the interfacial surfaces of the balloon
layers with a low-friction substance, or otherwise inserting
WO 95/17920 PCTlUS94/14199
7
a low-friction substance between the layers. Examples of
such a low-friction substance include silicone, silicone
oil, fluorocarbons, and other lubricants known to be suit-
able for medical uses. The softness, pliability, and
foldability of such a slip-layered balloon is significantly
greater than that of a single layer balloon of the same
total thickness, and even than that of a multi-layered
balloon of the same total thickness without the low-friction
substance between the layers.
The coextensive layers of the slip-layered balloon
described herein may be fabricated by separately forming
(e. g., by extrusion) tubular balloon blanks, either formed
with or stretched to progressively larger diameters, and
sliding progressively larger tubes over the smaller tubes to
assemble the individual layers into a multi-layered balloon
blank. If necessary, the larger tubes may be shrink-fitted
over the smaller diameter tubes. In a preferred alterna-
tive, however, the layers are extruded simultaneously (co-
extruded) to form the balloon blank. If desired, the inner-
most and/or outermost layers of a multi-layered balloon may
be thicker than the intermediate layers) for improved
abrasion resistance. The balloon blank may then be shaped
by conventional means to form the balloon. In one exemplary
shaping process, the blank is heated and inflated to form,
e.g., a cylindrical balloon body with tapered portions
between the body and the balloon proximal and distal ends.
As part of such a shaping process, the blank may be
stretched to orient the material and/or to form thinner
layers and/or ends.
The low-friction substance may be coated on or other-
wise inserted between the layers by any one of several
means. For example, separately fabricated layers may be
coated with the low-friction substance, e.g., by dipping,
wiping, or spraying with the substance alone or in solution
before assembling the layers to form the balloon blank.
Alternatively, the assembled or commonly extruded layers of
VVO 95/17920 PC1'IITS94/14199
8
the blank may be coated, e.g., by soaking the blank in a
solution of the substance or by forcing the substance or its
solution between the layers under pressure. One example of
a suitable solution of a low friction substance is a solu-
tion of about 2% - 10% silicone oil in Freon. The blank may
then be shaped by conventional methods to form a medical
balloon for use with a catheter. Preferably, the low fric-
tion substance is applied before shaping to prevent adhering
of the layers together during the shaping process. Most
preferably, the low-friction material is applied both before
and after shaping.
A catheter utilizing the herein-described slip-layered
balloon may be similar to any conventional balloon catheter
assembly, with the herein-described novel balloon substitut-
ed for the conventional balloon. The catheter includes a
shaft, and the proximal end of the slip-layered balloon
typically is joined to the shaft at the shaft distal end.
The length of the catheter is sufficient to be threaded
through the bodily cavity or cavities to the area to be
treated with a sufficient length remaining outside the body
to permit manipulation of the catheter. The shaft includes
at least one internal lumen for inflating the balloon with a
fluid inflation medium. Typically, a guidewire extends
through the balloon, and may extend distally from the bal-
loon. Alternatively, a wire may extend proximally through
the shaft (via an additional lumen) to provide greater
stiffness and strength to the shaft.
The catheter may be fabricated by conventional means,
except for the fabrication of the novel slip-layered bal-
loon, described above, and the joining of the balloon to the
catheter at the balloon s proximal and distal ends. The
proximal joint may be accomplished by adhering the layers to
one another at the balloon ends and adhering the innermost
layer to the shaft. Alternatively, the layers may be
trimmed to overlap one another and successively adhered to
the shaft, or only the innermost and outermost layers may be
WO 95/17920 PCTlUS94114199
X1'7963
9
adhered. Heat sealing and/or adhesive are suitable for this
joining process. An improved seal may be achieved by adher-
ing the innermost layer to the shaft, slipping a flexible
polymeric sleeve cover over the shaft with its distal end
overlapping the balloon end, then adhering the sleeve cover
to both the outermost layer and the shaft. Similar joining
methods may be used to anchor the proximal end of the bal-
loon to, e.g., the guidewire. Optionally, the outer surface
of the balloon or the entire catheter may be further coated
with a conventional slip coating, for example silicone or a
hydrophilic coating, to ease passage of the catheter through
the body.
In a particularly preferred embodiment of the slip-
layered balloon, a unitary balloon wall is fabricated in
which regions of slip-layered wall extend lengthwise between
"ridges'°, i.e. long, narrow regions in which the layers of
the balloon are joined to one another through the thickness
of the balloon, the joined regions normally visible as
ridges or stripes on the outside surface of the balloon
wall. The unitary nature of the ridged slip-layered balloon
provides better quality control and simplifies joining of
the balloon ends to the catheter, since the layers are
already fixed to one another at the ridges.
The ridged design also results in differential stiff-
ness about the circumference of the balloon, encouraging
regular, multiple-fold collapse of the balloon during defla-
tion and ensuring a smaller diameter for the collapsed
balloon. On deflation, multiple folds form in a regular
pattern about the circumference of the balloon wall as the
balloon wall collapses. The regular fold pattern, in turn,
provides a smaller collapsed profile than is usual with the
prior art balloons, especially the stiffer non-compliant
balloons. This smaller profile can ease passage of the
deflated balloon through the arteries during withdrawal of
the catheter.
The ridged slip-layered balloon may be fabricated by
WO 95117920 PCT/US94114199
heat-sealing or otherwise joining together the separate
layers of the above described mufti-layered balloons along ,
the ridges, leaving layered segments between the ridges.
(Preferably, each heat-sealed ridge is continuous along the _.
5 length of the balloon.) However, the preferred method of
fabricating such a ridged slip-layered balloon is to extrude
a balloon blank with open channels extending lengthwise
through the wall of the blank to divide regions of the wall
into mufti-layered segments. For example, the wall of a
10 blank for a ridged two-layered balloon is fabricated with a
single cylindrical array of a plurality of radially dis-
posed, axially extending channels within the thickness of
the wall. The channels are separated by ridges formed by
the non-channeled portions of the wall. After shaping of
the balloon from the blank, the channels effectively divide
the single balloon wall into inner and outer walls in the
regions between the ridges. The channels and ridges may
extend in a straight line parallel to the balloon axis, or
they may be "wrapped" in a helical pattern about the balloon
axis.
A balloon with more than two layers in the layered
segments between ridges is similarly fabricated, except that
at least one additional array of channels is formed, each
array at a different radial position within the wall of the
balloon blank. The channels of each array preferably are
superimposed over one another to provide mufti-layered
segments sharing a common ridge between each pair of adja-
cent segments. The surfaces enclosing each channel are
coated with the low-friction substance described above to
provide a slip-layered balloon, but with the advantages of _
unitary construction, as described below.
In a most preferred method, a blank for the ridged
slip-layered balloon is fabricated by coextruding a hollow
tube of two or more dissimilar polymeric materials using
conventional extrusion techniques. A discrete phase, that
is a phase which serves as the precursor of the channels
WO 95/I7920 PCT/ITS94I14199
~1~9636
(and which dictates their location and shape) is formed of,
for example, high density polyethylene, Nylon, low density
polyethylene, or polyethylene copolymers. A continuous
_ phase, that is the phase that will form the balloon blank
with the discrete phase enclosed within the walls thereof,
can be formed of polyethylene terephthalate or high or low
density polyethylene. High density polyethylene, low densi-
ty polyethylene and polyethylene copolymers can be extruded
within polyethylene terephthalate. Nylon can be extruded
within a high or low density polyethylene. Typically, the
material of the continuous phase is harder and more brittle
than the softer, more pliable discrete phase material.
Normally, the strands of all arrays are formed of the same
second-phase material. However, arrays of different strand
materials as well as strands of different materials in the
same array are within the scope of the invention.
After the phases are coextruded, the discrete phase is
withdrawn from the continuous phase to leave open channels
internal to the continuous phase, as described above.
Coextrusion of two polymeric materials is well known, and
conventional techniques are used for this process. Criteria
for matching of two polymeric materials for the above-de-
scribed coextrusion are that they not adhere to each other
after extrusion and that the discrete phase can be withdrawn
from the continuous phase leaving channels therein.
In one method for removing the strands from the co-
extruded balloon blank, the material of the continuous phase
of the balloon blank is harder and more brittle than that of
the discrete phase strands. .A notch is scratched into the
outer surface of the blank, extending in a circumferential
direction. (The notch need not extend about the entire
circumference of the balloon wall.) The blank then can be
fractured cross-sectionally by exerting tensile stress at
the notch (for example, by bending the balloon blank) with-
out breaking the strands, and the fractured continuous phase
is separated from the blank.
WO 95!17920 PCT/US94114199
t- _
~~,"~g63s
12
The discrete phase strands then can be withdrawn from
the continuous phase, forming a tubular balloon blank of,
e.g., polyethylene terephthalate with a plurality of open
channels within its wall. The shape, number, and arrange-
s ment of the channels can be varied as desired by the opera-
for by varying the design of the extrusion die. For exam-
ple, the strands described above may be round, ovoid,
square, rectangular, etc. in cross-section. Also, any
number of arrays between 1 and about 10, preferably about
3 - 7, is possible through the total thickness of the bal-
loon, n-1 arrays producing n layers in each shaped, ridged,
slip-layered balloon. Any number of channels in each array
between 1 and about 24 is possible, preferably about 3 - 10.
Normally, the ridges are of a circumferential width smaller
than that of the slip-layered segments.
The open channel balloon blank is then shaped by con-
ventional means, e.g. heating and inflation, to form a
ridged balloon. During the shaping process, the chamber
enclosed by the inner surface of the heated balloon is
inflated, but the channels within the wall itself are not
pressurized. Thus, the layers formed by the inner and outer
walls of the channels are stretched to a greater extent than
the walls joining the channels in each array, creating a
plurality of layered wall segments separated by ridges. If
desired, the innermost and/or outermost layers may be thick-
er than any intermediate layers present, providing increased
toughness and strength. The channels are coated with sili-
cone oil or other low-friction substance such that the
layered segments are slip-layered segments which readily
slide relative to one another, as described above. This
ridged balloon is a strong, soft medical balloon in which
ridges and slip-layered segments provide differential stiff-
ness about the circumference of the balloon for improved
foldability. Additionally, the ridges anchor the layers to
, one another providing easierjoining of the balloon to the
catheter.
WO 95/17920 ,. PCTlf1594114199
13
3Jhile coextrusion is generally the preferred method for
forming the ridged balloons, it is also possible to extrude
tubes having the channels already formed therein using a
_ known type of extrusion die. However, the thickness of the
channels within the blank is extremely small, typically
about 0.025 - 0.5 mm within a tubular balloon blank having a
total wall thickness between about 0.07 and 1.0 mm and
outside diameter between about 0.25 and 5.0 mm. Therefore,
extrusion with the desired preformed channels can be more
difficult than coextrusion, and coextrusion is generally
preferred.
The foldability and surface characteristics of any of
the balloons described herein, and particularly of the
ridged balloons, may be improved by providing an elastomeric
or elastic sleeve surrounding the balloon wall. The sleeve
may be fabricated of such materials as silicone rubber,
polyurethane elastomer, polyamide elastomer, polyolefin
elastomer, thermoplastic elastomers (e. g., an engineering
thermoplastic elastomer), or any elastomer considered suit-
able for use in medical catheters.
The elastic sleeve is of a size, thickness, and elastic
modulus such that it fits closely around the slip-layered
balloon wall in its completely deflated or collapsed state,
expands with the balloon wall as the balloon is inflated to
its maximum diameter, and contracts as the pressure in the
balloon is decreased during deflation, collapsing the slip-
layered balloon wall into a tight, compact, generally cylin-
drical bundle. A typical thickness for the elastic sleeve
is about 0.003" - 0.020". To further encourage the collapse
of the balloon wall, as well as to permit more even expan-
sion of the elastic sleeve, a coating of silicone oil or
other low-friction substance may be disposed between the
slip-layered balloon wall and the elastic sleeve. The
elastic sleeve and low-friction coating cooperate with the
slip layers, and in the ridged balloon with the ridges to
refold the balloon in, e.g., a helical wrap about the axis
WO 95117920 PCTIUS94114199 -
14
of the balloon. Ridges in the sleeved balloon assure that
the folding will occur along predetermined lines along the
length of the balloon. The sleeve is fabricated, applied to
the balloon, and joined to the catheter by known means.
Referring now to Figures-1 and 2, catheter 10, not
drawn to scale, includes slip-layered balloon 1l, shown in
its inflated state, in which Blip-layered balloon wall 12
encloses chamber 13. Balloon wall 12 includes inner layer
14 and outer layer 15. Layers 14 and 15 are coextensive,
and are disposed with interfacial surfaces 16 and 17, re-
spectively, facing one another. Surface 16 and/or surface
17 are coated with silicone oil 18, and layer 15 is heat
treated to shrink-fit layer 15 over inflated layer 14 such
that no air bubbles are enclosed between surfaces 16 and 17.
Thus, silicone oil coating 18 causes layers 14 and 15 to
slide with respect to one another, such that slip-layered
balloon 11 is softer and more pliable than prior art bal-
loons. In Figures 1 and 2, balloon wall 12 is shown with
two layers with a silicone oil coating between the two
layers. Alternatively, the balloon wall may have up to
about 10 layers, with silicone oil or other low-friction
substance between facing surfaces of the layers.
Balloon 11 is shown in Figure 1 with its proximal end
19 fixed to distal end 20 of shaft 21 by sleeve cover 22 and
adhesive (not shown). Balloon distal end 23 is fixed to
wire 24 in a similar manner by sleeve cover 25. Balloon
chamber 13 is in communication via lumens 26 with a source
(not shown) of an inflation medium for inflation of balloon
11. In the embodiment of Figure 1, wire 24 extends proxi-
mally through balloon chamber 13 and through lumen 27 of
catheter l0.
Inflation of chamber 13 causes balloon wall 12 to
expand from a folded arrangement around wire 24 to being
spaced therefrom. This expansion causes proximal and distal
ends 19 and 23 to assume generally conical shapes and allow
for an increase in the diameter of balloon 11 and for press-
WO 95!17920 PC17US94114199
ing of balloon wall 12 against the lesion being addressed.
A typical balloon diameter when the balloon chamber is
fully inflated is about 0.04 - 2 in. The thickness of each
of layers 14 and 15 typically is about 0.0001 - 0.004 in,
. 5 with 0.0003 - 0.002 in being preferred. The deflated pro-
file of balloon 11 typically is about 0.03 - 0.25 in.
Figures 3 and 4 illustrate coextruded balloon blank 30,
from which an alternate embodiment of the balloon described
herein is fabricated. In Figures 3 and 4, like features to
10 those shown in Figures 1 and 2 are indicated by the same
reference numerals.
In Figure 3, balloon blank 30 has continuous phase
balloon wall 12a of non-compliant polyethylene terephthalate
balloon material. Balloon wall 12a includes channels 31
15 filled by discrete phase strands 32 of a high density poly-
ethylene. Channels 31 are disposed in inner and outer
cylindrical arrays 33 and 34, respectively, around an axis,
not shown, which can be similar to wire 24. Each of chan-
nels 31 share a common "connector" wall, wall 35 or 36, with
the next adjacent of channels 31 in array 35 or 36, respec-
tively. Thus, in this embodiment, innermost layer 14a,
outermost layer 15a, and intermediate layer 37 are each
present as segments joined by connector walls 35 and 36.
After coextrusion, strands 32 are removed from balloon
blank 30 by withdrawing the strands from channels 31, as
illustrated in Figure 4. A notch or groove (not shown) is
scratched into the outer surface of continuous phase balloon
wall 12a at 38, the notch extending in a short
circumferential arc about the balloon wall. The hard,
brittle continuous phase balloon wall 12a is fractured
cross-sectionally by bending the balloon blank to exert
tensile stress at the notch. The soft, pliable strands
remain unbroken during this process. The fractured continu-
ous phase 12a may then be separated into portions 30a and
30b. Shorter portion 30a is pulled away from longer portion
30b, permitting part of each strand 32 to be withdrawn from
WO 95/17920 PCT/US94114199
16
channels 31 in shorter portion 30a, and to extend from
cross-sectional surface 39 of longer portion 30b. The
exposed parts of strands 32 are then gripped and pulled,
withdrawing strands 32 from channels 31 in longer portion
30b to form a balloon blank with open channels. The open
channels of the balloon blank are then coated with, e.g.,
silicone oil, as described above, and the balloon blank is
shaped by conventional means, e.g. heating and inflation, to
form a ridged balloon, described in more detail below.
The coextruded balloon blank of Figures 3 and 4, as
mentioned above, is fabricated from two dissimilar materi-
als, the harder, more brittle polyethylene terephthalate
continuous phase forming the balloon wall and the softer,
more pliable high density polyethylene discrete phase form-
ing the removable strands. However, other dissimilar mate
rial combinations may be used, as described above.
As the discrete phase is withdrawn from the continuous
phase, a tubular balloon blank is formed having a plurality
of open channels within its wall. For the balloon blank of
Figures 3 and 4, the discrete phase is extruded such that
the channels within the shaped balloon are disposed to
define two cylindrical arrays, as shown in Figure 5. The
shape and arrangement of the channels can be varied as
desired by the operator by varying the design of the extru-
sion die.
Figure 5 illustrates in cross-section a portion of
ridged balloon 30c. In Figure 5, like features to those
shown in Figures 1-4 are indicated by the same reference
numerals. Balloon 30c is fabricated from coextruded balloon
blank portion 30b of Figure 4 (after withdrawal of strands
32 from channels 31) by heating and inflation of balloon
blank portion 30b, in a conventional manner, to form a
balloon similar in shape to balloon 1i of Figure 1. (The
cross-section shown in Figure 5 is taken at a position on
the balloon similar to cross-section 2-2 of Figure 1.)
During the shaping process, layers 14a, 37, and 15a of
WO 95II7920 PCTlITS94114199
21'~963G
17
balloon wall 12a (Figure 3) are stretched to a greater
extent than connecting walls 35 and 36 (Figure 3), creating
a plurality of layered wall segments 40 (of shaped balloon
wall 12b) separated by ridges 41. Each layered segment 40
is made up of innermost thin balloon wall layer 14b, outer-
most thin balloon wall layer 15b, and intermediate thin
balloon wall layer 37a. In the embodiment shown in Figure
5, intermediate layer 37a is thinner than either of layers
14b and 15b. Layers 14b and 37a and layers 37a and 15b are
separated by channels 31, which have been coated with sili-
cone oil 42 such that segments 4o are slip-layered segments
which readily slide relative to one another, as described
above. Thus, balloon 30c is a strong, soft, ridged medical
balloon in which ridges 41 and slip-layered segments 40
provide differential stiffness about the circumference of
the balloon for improved foldability. Additionally, ridges
41 anchor the layers to one another providing easier joining
of the balloon to the catheter.
Figure 6 illustrates in cross-section a portion of yet
another embodiment of the balloon described herein. In
Figure 6, like features to those shown in Figures 1-5 are
indicated by the same reference numerals.
&idged balloon 50 of Figure 6 includes non-compliant
balloon wall 12c made up of slip-layered segments 40a sepa-
rated by ridges 41. Segments 40a include channels 31 ar-
ranged in single cylindrical array 33a. Channels 31 sepa-
rate inner layer 14c and outer layer 15c, and are coated
with silicone oil 42 as described above. Surrounding bal-
loon wall 12c is elastomeric sleeve or elastic sleeve 51,
fabricated of silicone rubber. Elastic sleeve 51 is of a
size, thickness, and elastic modulus such that it fits
closely around slip-layered balloon wall 12c in its com-
pletely deflated or collapsed state, expands with balloon
wall 12c as balloon 50 is inflated to its maximum diameter,
and contracts as the pressure in balloon 50 is decreased
during deflation, collapsing slip-layered balloon wall 12c
WO 95/17920 PCT/US94114199 ,
18
into a tight, compact, generally cylindrical bundle. To
further encourage the collapse of balloon wall 12c, as well- ,
as to permit more even expansion of elastic sleeve 51,
coating 52 of silicone oil or other low-friction substance
is disposed between sleeve 51 and balloon wall 12c. Elastic
sleeve 51 and silicone oil coating 52 cooperate with slip
layered segments 40a and ridges 41 to refold balloon 50 in a
helical wrap about its axis.
Balloon wall 12c is fabricated by a process similar to
that described above for balloon wall 12b. Elastic sleeve
51 may be applied to balloon wall 12c by, for example,
prefabricating tubular elastic sleeve 51 by known means,
e.g., extrusion, then swelling sleeve 51 by immersing in,
e.g., Freon. Prefabricated balloon wall 12c may then be
inserted into the enlarged sleeve, and the Freon evaporated
to shrink sleeve 51 about balloon wall 12c.
Elastic sleeve 51 is shown in Figure 6 surrounding a
ridged, non-compliant balloon wall having a single array of
channels filled with a low-friction substance. However, a
similar elastic sleeve may be utilized as part of any com-
pliant or non-compliant slip-layered balloon embodiment in
accordance with the present invention. The elastic sleeve
of Figure 6 is described as silicone rubber. Other suitable
materials for the sleeve are polyurethane elastomer, polyam-
ide elastomer, polyolefin elastomer, thermoplastic elasto-
mers (e.g., an engineering thermoplastic elastomer), or any
elastomer considered suitable for use in medical catheters,
as described above.
The slip-layered balloons described herein and the
catheters made therefrom present many advantages over those
of the prior art. For example, the balloons can combine
small folded profiles, high burst pressures, and, optional-
ly, low compliance with improved foldability, pliability,
and softness, and high tensile strength. In particular, the
ridged slip-layered balloon presents the advantages of
fabrication by simple, commercially viable techniques,
WO 95/17920 ; PCTJITS94114199
~1'~~63~
19
further improved foldability, and easier joining without
significantly sacrificing softness and pliability. Also,
the addition of the elastic sleeve described herein even
further improves foldability and minimizes folded profile
y
while eliminating sharp folded edges and adding considerable
abrasion resistance to the balloon.
It is apparent that modifications and changes can be
made within the spirit and scope of the present invention.
It is our intention, however, only to be limited by the
scope of the appended claims.