Balloon catheter device

Balloon catheters having the strength and maximum inflated diameter characteristics of an angioplasty balloon and having the recovery characteristics during deflation of an elastic embolectomy balloon. The balloon catheter can be made in very small sizes and has a lubricious and chemically inert outer surface. The balloon catheter is easy to navigate through tortuous passageways, is capable of rapid inflation and deflation and has high burst strengths. Balloon covers having these same characteristics are also described for use with conventional embolectomy balloons or angioplasty balloons.

FIELD OF THE INVENTION 
The present invention relates to catheter balloons used in a variety of 
surgical procedures and to balloon covers for use with catheter balloons. 
BACKGROUND OF THE INVENTION 
Balloon catheters of various forms are commonly employed in a number of 
surgical procedures. These devices comprise a thin catheter tube that can 
be guided through a body conduit of a patient such as a blood vessel and a 
distensible balloon located at the distal end of the catheter tube. 
Actuation of the balloon is accomplished through use of a fluid filled 
syringe or similar device that can inflate the balloon by filling it with 
fluid (e.g., water or saline solution) to a desired degree of expansion 
and then deflate the balloon by withdrawing the fluid back into the 
syringe. 
In use, a physician will guide the balloon catheter into a desired position 
and then expand the balloon to accomplish the desired result (e.g., clear 
a blockage, or install or actuate some other device). Once the procedure 
is accomplished, the balloon is then deflated and withdrawn from the blood 
vessel. 
There are two main forms of balloon catheter devices. Angioplasty catheters 
employ a balloon made of relatively strong but generally inelastic 
material (e.g., polyester) folded into a compact, small diameter cross 
section. These relatively stiff catheters are used to compact hard 
deposits in vessels. Due to the need for strength and stiffness, these 
devices are rated to high pressures, usually up to about 8 to 12 
atmospheres depending on rated diameter. They tend to be self-limiting as 
to diameter in that they will normally distend up to the rated diameter 
and not distend appreciably beyond this diameter until rupture due to 
over-pressurization. While the inelastic material of the balloon is 
generally effective in compacting deposits, it tends to collapse unevenly 
upon deflation, leaving a flattened, wrinkled bag, substantially larger in 
cross section than the balloon was when it was originally installed. 
Because of their tendency to assume a flattened cross section upon 
inflation and subsequent deflation, their deflated maximum width tends to 
approximate a dimension corresponding to one-half of the rated diameter 
times pi. This enlarged, wrinkled bag may be difficult to remove, 
especially from small vessels. Further, because these balloons are made 
from inelastic materials, their time to complete deflation is inherently 
slower than elastic balloons. 
By contrast, embolectomy catheters employ a soft, very elastic material 
(e.g., natural rubber latex) as the balloon. These catheters are employed 
to remove soft deposits, such as thrombus, where a soft and tacky material 
such as latex provides an effective extraction means. Latex and other 
highly elastic materials generally will expand continuously upon increased 
internal pressure until the material bursts. As a result, these catheters 
are generally rated by volume (e.g., 0.3 cc) in order to properly distend 
to a desired size. Although relatively weak, these catheters do have the 
advantage that they tend to readily return to their initial size and 
dimensions following inflation and subsequent deflation. 
Some catheter balloons constructed of both elastomeric and non-elastomeric 
materials have been described previously. U.S. Pat. No. 4,706,670 
describes a balloon dilatation catheter constructed of a shaft made of an 
elastomeric tube and reinforced with longitudinally inelastic filaments. 
This device incorporates a movable portion of the shaft to enable the 
offset of the reduction in length of the balloon portion as the balloon is 
inflated. The construction facilitates the inflation and deflation of the 
balloon. 
While balloon catheters are widely employed, currently available devices 
experience a number of shortcomings. First, as has been noted, the 
strongest materials for balloon construction tend to be relatively 
inelastic. The flattening of catheter balloons made from inelastic 
materials that occurs upon inflation and subsequent deflation makes 
extraction and navigation of a deflated catheter somewhat difficult. 
Contrastly, highly elastic materials tend to have excellent recovery upon 
deflation, but are not particularly strong when inflated nor are they 
self-limiting to a maximum rated diameter regardless of increasing 
pressure. This severely limits the amount of pressure that can be applied 
with these devices. It is also somewhat difficult to control the inflated 
diameter of these devices. 
Second, in instances where the catheter is used to deliver some other 
device into the conduit, it is particularly important that a smooth 
separation of the device and the catheter balloon occur without 
interfering with the placement of the device. Neither of the two catheter 
devices described above is ideal in these instances. A balloon that does 
not completely compact to its original size is prone to snag the device 
causing placement problems or even damage to the conduit or balloon. 
Similarly, the use of a balloon that is constructed of tacky material will 
likewise cause snagging problems and possible displacement of the device. 
Latex balloons are generally not used for device placement in that they 
are considered to have inadequate strength for such use. Accordingly, it 
is a primary purpose of the present invention to create a catheter balloon 
that is small and slippery for initial installation, strong for 
deployment, and returns to its compact size and dimensions for ease in 
removal and further navigation following deflation. It is also believed 
desirable to provide a catheter balloon that will remain close to its 
original compact pre-inflation size even after repeated cycles of 
inflation and deflation. Other primary purposes of the present invention 
are to strengthen elastic balloons, to provide them with distension limits 
and provide them with a lubricious outer surface. The term "deflation" 
herein is used to describe a condition subsequent to inflation. 
"Pre-inflation" is used to describe the condition prior to initial 
inflation. 
SUMMARY OF THE INVENTION 
The present invention is an improved balloon catheter device for use in a 
variety of surgical procedures. The balloon catheter device of the present 
invention comprises a catheter tube having a continuous lumen connected to 
an inflatable and deflatable balloon at one end of the catheter tube. The 
catheter tube may have additional lumens provided for other purposes. The 
balloon can have a burst strength equal to or greater than that of 
conventional PTA catheter balloons. The balloon also has a maximum 
inflation diameter in a similar fashion to conventional PTA catheter 
balloons. The inventive balloon offers the recovery characteristics of a 
latex balloon that when deflated is of about the same maximum diameter as 
it was prior to inflation. This allows the inventive balloon to be 
withdrawn following deflation more easily than conventional PTA balloons 
which assume a flattened, irregular cross section following deflation and 
so have a deflated maximum diameter much larger than the pre-inflation 
maximum diameter. The balloon also has a smooth and lubricious surface 
which also aids in insertion and withdrawal. The inventive balloon 
possesses all of the above attributes even when made in small sizes 
heretofore commercially unavailable in balloon catheters without a movable 
portion of the catheter shaft or some other form of mechanical assist. The 
present invention eliminates the need for a movable portion of the shaft 
and associated apparatuses to aid in balloon deflation. 
The present invention is made from polytetrafluoroethylene (hereinafter 
PTFE) materials and elastomeric materials. The PTFE is preferably porous 
PTFE made as taught by U.S. Pat. Nos. 3,953,566 and 4,187,390, both of 
which are incorporated by reference herein. An additional optional 
construction step, longitudinally compressing a porous PTFE tube prior to 
addition of the elastomeric component, allows the balloon or balloon cover 
to sufficiently change in length to enable the construction of higher 
pressure balloons, again without the need for mechanical assist. 
Particularly small sizes (useful in applications involving small tortuous 
paths such as is present in brain, kidney, and liver procedures) can be 
achieved by decreasing the wall thickness of the balloon via impregnation 
of a porous PTFE tube with silicone adhesive, silicone elastomer, silicone 
dispersion, polyurethane or another suitable elastomeric material instead 
of using a separate elastomeric member. Impregnation involves at least 
partially filling the pores of the porous PTFE. U.S. Pat. No. 5,519,172 
teaches in detail the impregnation of porous PTFE with elastomers. In that 
this patent relates primarily to the construction of a jacket material for 
the protection of electrical conductors, the suitability of each of the 
various described materials for in vivo use as catheter balloon materials 
must be considered. 
The balloon may be made from the materials described herein as a complete, 
stand-alone balloon or alternatively may be made as a cover for either 
conventional polyester PTA balloons or for latex embolectomy balloons. The 
use of the balloon cover of the present invention provides the covered 
balloon, regardless of type, with the best features of conventional PTA 
balloons and renders viable the use of elastic balloons for PTA 
procedures. That is to say, the covered balloon will have high burst 
strength, a predetermined maximum diameter, the ability to recover to 
substantially its pre-inflation size following deflation, and a lubricious 
exterior surface (unless it is desired to construct the balloon such that 
the elastomeric material is present on the outer surface of the balloon). 
The balloon cover substantially reduces the risk of rupture of an elastic 
balloon. Further, if rupture of the underlying balloon should occur, the 
presence of the balloon cover may serve to contain the fragments of the 
ruptured balloon. Still further, the inventive balloon and balloon cover 
can increase the rate of deflation of PTA balloons thereby reducing the 
time that the inflated balloon occludes the conduit in which it resides. 
The present invention also enables the distension of a vessel and side 
branch or even a prosthesis within a vessel and its side branch without 
exerting significant force on the vessel or its branch. Further, it has 
been shown to be useful for flaring the ends of prostheses, thereby 
avoiding unwanted constrictions at the ends of the prostheses. Prostheses 
can slip along the length of prior art balloons during distension; the 
present invention not only reduces such slippage, it also can be used to 
create a larger diameter at the end of the graft than prior art materials. 
The inventive balloon and balloon cover also maintain a substantially 
circular cross section during inflation and deflation in the absence of 
external constraint. Plus, the balloon and balloon cover can be designed 
to inflate at lower pressure in one portion of the length than another. 
This can be accomplished, for example, by altering the thickness of the 
elastomer content along the length of the balloon in order to increase the 
resistance to distension along the length of the balloon. Alternatively, 
the substrate tube may be constructed with varying wall thickness or 
varying amounts of helically-applied film may be applied along the tube 
length in order to achieve a similar effect. 
Balloons of the present invention can also be constructed to elute fluids 
at pressures exceeding the balloon inflation pressure. Such balloons could 
have utility in delivering drugs inside a vessel. 
A catheter balloon of the present invention is anticipated to be 
particularly useful for various surgical vascular procedures, including 
graft delivery, graft distension, stent delivery, stent distension, and 
angioplasty. It may have additional utility for various other surgical 
procedures such as, for example, supporting skeletal muscle left 
ventricular assist devices during the healing and muscle conditioning 
period and as an intra-aortic balloon.

DETAILED DESCRIPTION OF THE INVENTION 
The catheter balloon and catheter balloon cover of the present invention 
are preferably made from porous PTFE films having a microstructure of 
interconnected fibrils. These films are made as taught by U.S. Pat. Nos. 
3,953,566 and 4,187,390. The balloon and balloon cover may also 
incorporate a porous PTFE substrate tube in the form, for example, of an 
extruded and expanded tube or a tube constructed of film containing at 
least one seam. Also, the balloon may be impregnated with an elastomeric 
material. 
To form the balloon or balloon cover, both of which are made in the shape 
of a tube, a thin, porous PTFE film of the type described above is slit 
into relatively narrow lengths. The slit film is helically wrapped onto 
the surface of a mandrel in two opposing directions, thereby forming a 
tube of at least two layers. FIGS. 1A, 1B and 1C describe this procedure. 
FIG. 1A shows the first layer 14 of porous PTFE film helically wrapped 
over the mandrel 12 with the traverse direction of the wrap applied in a 
first direction 20 parallel to the longitudinal axis 18. The longitudinal 
axis of a balloon is defined as coincident with the longitudinal axis of 
the balloon catheter shaft, that is along the length of the shaft. 
Substantially parallel is defined as between about 0.degree. and 
45.degree., or between about 135.degree. and 180.degree., with respect to 
the longitudinal axis of the catheter shaft and substantially 
circumferential is defined as between about 45.degree. and 135.degree. 
with respect to the longitudinal axis of the catheter shaft. FIG. 1B 
describes the application of the second layer of porous PTFE film 16 
helically wrapped over the top of the first layer 14, wherein second layer 
16 is wrapped in a second traverse direction 22 parallel to longitudinal 
axis 18 and opposite to the first traverse direction 20. 
Preferably both layers 14 and 16 are wrapped with the same pitch angle 
measured with respect to the longitudinal axis but measured in opposite 
directions. If, for example, film layers 14 and 16 are applied at pitch 
angles of 70.degree. measured from opposite directions with respect to 
longitudinal axis 18, then included angle A between both 70.degree. pitch 
angles is 40.degree.. 
More than two layers of helically wrapped film may be applied. Alternate 
layers of film should be wrapped from opposing directions and an even 
number of film layers should be used whereby an equal number of layers are 
applied in each direction. 
Following completion of film wrapping, the helically wrapped mandrel is 
placed into an oven for suitable time and temperature to cause adjacent 
layers to heat-bond together. After removal from the oven and subsequent 
cooling, the resulting film tube may be removed from the mandrel. The film 
tube is next placed over the balloon, tensioned longitudinally and affixed 
in place over the balloon. 
During use, the inflated balloon or balloon cover 10 of the present 
invention has an increased diameter which results in included angle A 
being substantially reduced as shown by FIG. 2. The balloon or balloon 
cover thus reaches its pre-determined diametrical limit as included angle 
A approaches zero. 
The inventive balloon or balloon cover 10 is reduced in diameter following 
deflation by one of two ways. First, tension may be applied to the balloon 
or balloon cover parallel to longitudinal axis 18 to cause it to reduce in 
diameter following deflation to the form described by FIG. 1C. The 
application of tension is necessary if low profile is desired. 
Alternatively, a layer of elastomer, applied to the luminal surface of the 
balloon 10 and allowed to cure prior to use of the balloon, will cause the 
balloon to retract to substantially its pre-inflation size shown by FIG. 
1C following deflation. The elastomer may take the form of a coating of 
elastomer applied directly to the luminal surface of the balloon or 
balloon cover 10, or an elastomeric balloon such as a latex balloon or a 
silcone tube may be adhered to the luminal surface of the inventive 
balloon 10 by the use of an elastomeric adhesive. Alternatively, elastomer 
can be impregnated into the porous material to create a balloon or balloon 
cover. 
FIG. 3A describes a cross sectional view of a balloon cover 10 of the 
present invention in use with a conventional balloon catheter of either 
the angioplasty or embolectomy type. The figure describes a balloon cover 
without an elastomeric luminal coating. The balloon cover 10 is closed at 
distal end 26 of the balloon catheter 11. Balloon cover 10 extends in 
length part of the way to the proximal end 27 of balloon catheter 11 
whereby balloon cover 10 completely covers catheter balloon 25 and at 
least a portion of the catheter 11. FIG. 3B describes the same balloon 
catheter 11 with catheter balloon 25 in an inflated state. Layers 14 and 
16 of balloon cover 10 allow the cover to increase in diameter along with 
catheter balloon 25. During or following deflation of catheter balloon 25, 
tension is applied to the balloon cover 10 at the proximal end 27 of 
balloon catheter 11 as shown by arrows 28, thereby causing balloon cover 
10 to reduce in diameter and substantially return to the state described 
by FIG. 3A. FIG. 4A describes a cross sectional view of a balloon cover 10 
of the present invention wherein the balloon cover 10 has a liquid-tight 
layer of elastomer 34 applied to the inner surface of helically wrapped 
porous PTFE film layers 14 and 16. Balloon cover 10 is closed at distal 
end 26. The figure describes a ligated closure, such as by a thread or 
filament, however, other suitable closing means may be used. Proximal end 
27 of balloon cover 10 is affixed to the distal end 32 of catheter 24. 
Balloon 25 may be of either the angioplasty or embolectomy type. If an 
elastomeric embolectomy balloon is used, it is preferred that the cover be 
adhered to the balloon by the use of an elastomeric adhesive to 
liquid-tight layer of elastomer 34. During inflation of balloon 25 as 
shown by FIG. 4B, helically wrapped porous PTFE film layers 14 and 16 and 
liquid-tight elastomer layer 34 increase in diameter along with balloon 
25. During subsequent deflation, liquid-tight elastomer layer 34 causes 
helically wrapped porous PTFE film layers 14 and 16 to reduce in diameter 
as described previously, thereby returning substantially to the state 
described by FIG. 4A. 
FIGS. 5A and 5B describe cross sectional views of a catheter balloon 10 
made in the same fashion as the balloon cover described by FIGS. 4A and 
4B. The presence of liquid-tight elastomer layer 34 allows this 
construction to function as an independent balloon 42 as described 
previously without requiring a conventional angioplasty or embolectomy 
balloon. 
FIGS. 6A, 6B and 6C describe cross sectional views of an alternative 
embodiment of the catheter balloon 10 of the present invention. According 
to this embodiment helically wrapped porous PTFE film layers 14 and 16 are 
provided with a luminal coating 44 which is liquid-tight but is not 
elastomeric. The resulting balloon behaves in the fashion of a 
conventional angioplasty balloon but offers the advantages of a lubricious 
and chemically inert exterior surface. FIG. 6A describes the appearance of 
the balloon prior to inflation. FIG. 6B describes the balloon in an 
inflated state. As shown by FIG. 6C, following deflation, collapsed 
balloon 46 has a somewhat wrinkled appearance and an irregular transverse 
cross section in the same fashion as a conventional angioplasty balloon 
made from polyester or similar inelastic material. 
It is also anticipated that the balloon and balloon cover of the present 
invention may be provided with an additional reinforcing mesh or braid on 
the exterior or interior surface of the balloon (or balloon cover), or 
more preferably between layers of the film whereby the mesh or braid is in 
the middle. 
Alternatively, a mesh or braid of PTFE may be used as a balloon cover 
without including a continuous tube. A continuous tube does not include 
openings through its wall as does a conventional mesh or braid. 
The following examples describe in detail the construction of various 
embodiments of the balloon cover and catheter balloon of the present 
invention. Evaluation of these balloons is also described in comparison to 
conventional angioplasty and embolectomy balloons. FIG. 7 is provided as a 
description of the maximum dimension 72 and minimum dimension 74 (taken 
transversely to the longitudinal axis of the balloon) of a flattened, 
deflated angioplasty balloon 70 wherein the figure describes a transverse 
cross section of a typical flattened angioplasty balloon. The transverse 
cross section shown is meant to describe a typical deflated, flattened 
inelastic angioplasty balloon 70 having a somewhat irregular shape. 
Balloon 70 includes a catheter tube 76 having a guidewire lumen 78 and a 
balloon inflation lumen 79 and two opposing sides 82 and 84 of balloon 70. 
Maximum dimension 72 may be considered to be the maximum width of the 
flattened balloon 70 while minimum dimension 74 may be considered to be 
the maximum thickness across the two opposing sides 82 and 84 of the 
flattened balloon 70. All balloon and catheter measurements are expressed 
in terms of dimensions even if the shape is substantially circular. 
Example 1 
This example illustrates the use of a balloon cover of the present 
invention over a commercially available angioplasty balloon. The balloon 
cover provides a means of returning the angioplasty balloon close to its 
original compact geometry after inflation and subsequent deflation, as 
well as providing the known chemical inertness and low coefficient of 
friction afforded by PTFE. 
The balloon used was a MATCH 35.RTM. Percutaneous Transluminal Angioplasty 
(PTA) Catheter model number B508-412, manufactured by SCHNEIDER 
(Minneapolis, Minn.). This balloon when measured immediately after being 
removed from the protective sheath provided by the manufacturer had a 
minimum dimension of 2.04 mm and a maximum dimension of 2.42 mm. These 
measurements were taken from approximately the center of the balloon, as 
defined by the midpoint between the circumferentially-oriented radiopaque 
marker bands located at both ends of the balloon. A Lasermike model 183, 
manufactured by Lasermike, (Dayton, Ohio) was used to make the 
measurements while the balloon was rotated about its longitudinal axis. 
The shaft onto which the balloon was attached had a minimum dimension of 
1.74 mm and a maximum dimension of 1.77 mm measured adjacent to the point 
of balloon attachment closest to the center of the length of the shaft. 
The balloon, when inflated to 8 atmospheres internal water pressure, had a 
minimum dimension of 8.23 mm and a maximum dimension of 8.25 mm at the 
center of the length of the balloon. When deflated by removing the entire 
volume of water introduced during the 8 atmosphere pressurization, the 
balloon at its mid-length, had a minimum dimension of 1.75 mm, and a 
maximum dimension of 11.52 mm as measured using Mitutoyo digital caliper 
model CD-6"P. Upon completion of the measurements the balloon portion of 
the PTA catheter was carefully repackaged into the protective sheath. 
The inventive balloon cover was made from a length of porous PTFE film made 
as described above cut to a width of 2.5 cm. The film thickness was 
approximately 0.02 mm, the density was 0.2 g/cc, and the fibril length was 
approximately 70 microns. Thickness was measured using a Mitutoyo snap 
gauge model 2804-10 and density was calculated based on sample dimensions 
and mass. Fibril length of the porous PTFE films used to construct the 
examples was estimated from scanning electron photomicrographs of an 
exterior surface of film samples. 
This film was helically wrapped onto the bare surface of an 8 mm diameter 
stainless steel mandrel at an angle of approximately 70.degree. with 
respect to the longitudinal axis of the mandrel so that about 5 
overlapping layers of film cover the mandrel. Following this, another 5 
layers of the same film were helically wrapped over the first 5 layers at 
the same pitch angle with respect to the longitudinal axis, but in the 
opposite direction. The second 5 layers were therefore also oriented at an 
approximate angle of 70.degree., but measured from the opposite end of the 
axis in comparison to the first 5 layers. Following this, another 5 layers 
of the same film were helically wrapped over the first and second 5 layers 
at the same bias angle with respect to the longitudinal axis as the first 
5 layers, and then another 5 layers of the same film were helically 
wrapped over the first, second, and third 5 layers at the same bias angle 
with respect to the longitudinal axis as the second 5 layers. This 
resulted in a total of about 20 layers of helically wrapped film covering 
the mandrel. 
The film-wrapped mandrel was then placed into an air convection oven set at 
380.degree. C. for 10 minutes to heat bond the layers of film, then 
removed and allowed to cool. The resulting 8 mm inside diameter film tube 
formed from the helically wrapped layers was then removed from the mandrel 
and one end was ligated onto a self-sealing injection site (Injection Site 
with Luer Lock manufactured by Baxter Healthcare Corporation, Deerfield, 
Ill.). A hole was created through the injection site, and the balloon end 
of the previously measured PTA catheter was passed through this hole, 
coaxially fitting the film tube over the balloon portion as well as a 
portion of the shaft of the PTA catheter. The film tube was approximately 
25 cm in length. With the film tube over the PTA catheter and attached to 
the injection site, tension was applied manually to the free end of the 
film tube while the injection site was held fixed, causing the film tube 
to reduce in diameter and fit snugly onto the underlying segment of PTA 
catheter. Next, the film tube was ligated at the distal end of the PTA 
catheter shaft so that the balloon cover remained taut and snugly fit. 
At this point the now covered balloon was measured in a deflated state. The 
minimum dimension was found to be 2.33 mm and the maximum dimension 2.63 
mm. As before, these measurements were taken from approximately the center 
of the balloon, as defined by the midpoint between the radiopaque marker 
bands, and a Lasermike model 183, manufactured by Lasermike, (Dayton, 
Ohio) was used to make the measurements. The balloon, when inflated to 8 
atmospheres internal water pressure had a minimum dimension of 7.93 mm and 
a maximum dimension of 8.06 mm at the center of the balloon. When deflated 
by removing the entire volume of water introduced during the 8 atmosphere 
pressurization, the balloon at its mid-length, had a minimum dimension of 
1.92 mm and a maximum dimension of 11.17 mm. Next, tension was manually 
applied to the injection site causing the balloon cover to reduce the size 
of the underlying balloon, particularly along the plane of the 11.17 mm 
measurement taken previously. After the application of tension the covered 
balloon was measured again, and the minimum and maximum dimensions were 
found as 3.43 and 3.87 mm respectively. 
This example shows that the balloon cover can be used effectively to 
compact a PTA balloon which was inflated and subsequently deflated to 
approximately the geometry of the balloon in an unused state. The 
measurements taken on the balloon (in both the uncovered and covered 
states) after inflation and subsequent deflation show that rather than 
undergoing a uniform circular compaction, the balloon tended to flatten. 
This flattening can be quantified by calculating the ratio of the minimum 
dimension to the maximum dimension measured after inflation and subsequent 
deflation. This ratio is defined as the compaction efficiency ratio. Note 
that a circular cross section yields a compaction efficiency ratio of 
unity. For this example, the uncovered balloon had a compaction efficiency 
ratio of 1.75 divided by 11.52, or 0.15. The balloon, after being provided 
with the inventive balloon cover, had a compaction efficiency ratio of 
3.43 divided by 3.87, or 0.89. Additionally, the ratio of the maximum 
dimension prior to any inflation, to the maximum dimension after inflation 
and subsequent deflation, is defined as the compaction ratio. A balloon 
which has the same maximum dimension prior to any inflation, and after 
inflation and subsequent deflation, has a compaction ratio of unity. For 
this example, the uncovered balloon had a compaction ratio of 2.42 divided 
by 11.52, or 0.21. The balloon, after being provided with the inventive 
balloon cover, had a compaction ratio of 2.63 divided by 3.87, or 0.68. 
Example 2 
This example illustrates the use of a balloon cover over a commercially 
available latex embolectomy balloon. The balloon cover provides a defined 
limit to the growth of the embolectomy balloon, a substantial increase in 
burst strength, and the known chemical inertness and low coefficient of 
friction afforded by PTFE. 
The balloon used was a Fogarty.RTM. Thru-Lumen Embolectomy Catheter model 
12TL0805F manufactured by Baxter Healthcare Corporation (Irvine, Calf.). 
This natural rubber latex balloon when measured immediately after being 
removed from the protective sheath provided by the manufacturer had a 
minimum dimension of 1.98 mm and a maximum dimension of 2.02 mm. These 
measurements were taken from approximately the center of the balloon, as 
defined by the midpoint between the radiopaque marker bands. A Lasermike 
model 183, manufactured by Lasermike, (Dayton, Ohio) was used to make the 
measurements while the balloon was rotated about its longitudinal axis. 
The shaft onto which the balloon was attached had a minimum dimension of 
1.64 mm and a maximum dimension of 1.68 mm measured adjacent to the point 
of balloon attachment closest to the center of the length of the shaft. 
The balloon, when filled with 0.8 cubic centimeters of water had a minimum 
dimension of 10.71 mm and a maximum dimension of 10.77 mm at the center of 
the balloon. When deflated by removing the entire volume of water 
introduced, the balloon at its midlength, had a minimum dimension of 1.97 
mm and a maximum dimension of 2.04 mm. The balloon when tested using a 
hand-held inflation syringe had a burst strength of 60 psi. 
Another embolectomy catheter of the same type was covered using a porous 
PTFE film tube made as described in Example 1. The method used to cover 
the embolectomy catheter was the same as that used to cover the PTA 
catheter in Example 1. 
At this point, the now covered balloon was measured in a pre-inflated 
state. The minimum dimension was found to be 2.20 mm and the maximum 
dimension 2.27 mm. As before, these measurements were taken from 
approximately the center of the balloon, as defined by the midpoint 
between the radiopaque marker bands, and a Lasermike model 183, 
manufactured by Lasermike (Dayton, Ohio) was used to make the 
measurements. The balloon, when filled with 0.8 cubic centimeters of water 
had a minimum dimension of 8.29 mm and a maximum dimension of 8.34 mm at 
mid-length. When deflated by removing the entire volume of water 
introduced, the balloon at its mid-length, had a minimum dimension of 3.15 
mm and a maximum dimension of 3.91 mm. Next, tension was manually applied 
to the injection site causing the balloon cover to reduce in size. After 
the application of tension the covered balloon was measured again, and the 
minimum and maximum dimensions were found as 2.95 and 3.07 mm 
respectively. The covered balloon was determined to have a burst strength 
of 188 psi, failing solely due the burst of the underlying embolectomy 
balloon. The inventive balloon cover exhibited no indication of rupture. 
This example shows that the inventive balloon cover effectively provides a 
limit to the growth, and a substantial increase in the burst strength of 
an embolectomy balloon. The measurements taken on the uncovered balloon 
show that when filled with 0.8 cubic centimeters of water the balloon 
reached a maximum dimension of 10.77 mm. Under the same test conditions, 
the covered balloon reached a maximum dimension of 8.34 mm. The burst 
strength of the uncovered balloon was 60 psi while the burst strength of 
the covered balloon was 188 psi when inflated until rupture using a 
hand-operated liquid-filled syringe. This represents more than a three 
fold increase in burst strength. 
Example 3 
This example illustrates the use of a composite material in a balloon 
application. A balloon made from the composite material described below 
exhibits a predictable inflated diameter, high strength, exceptional 
compaction ratio and compaction efficiency ratio, as well as the known 
chemical inertness and low coefficient of friction afforded by PTFE. 
A length of SILASTIC.RTM.R.times.50 Silicone Tubing manufactured by Dow 
Corning Corporation (Midland, Mich.) having an inner diameter of 1.5 mm 
and an outer diameter of 2.0 mm was fitted coaxially over a 1.1 mm 
stainless steel mandrel and secured at both ends. The silicone tubing was 
coated with a thin layer of Translucent RTV 108 Silicone Rubber Adhesive 
Sealant manufactured by General Electric Company (Waterford, N.Y.). An 8 
mm inner diameter film tube made in the same manner described in Example 1 
was fitted coaxially over the stainless steel mandrel and the silicone 
tubing. Tension was manually applied to the ends of the film tube causing 
it to reduce in diameter and fit snugly onto the underlying segment of 
silicone tubing secured to the stainless steel mandrel. With the film tube 
in substantial contact with the silicone tubing, this composite tube was 
gently massaged to ensure that no voids were present between the silicone 
tube and the porous PTFE film tube. Next the entire silicone-PTFE 
composite tube was allowed to cure in an air convection oven set at 
35.degree. C. for a minimum of 12 hours. Once cured, the composite tube 
was removed from the stainless steel mandrel. One end of the composite 
tube was then fitted coaxially over a section of 5 Fr catheter shaft taken 
from a model B507-412 MATCH 35.RTM. Percutaneous Transluminal Angioplasty 
(PTA) Catheter, manufactured by SCHNEIDER (Minneapolis, Minn.) and clamped 
to the catheter shaft using a model 03.3 RER Ear Clamp manufactured by 
Oetiker (Livingston, N.J.) such that a watertight seal was present. The 
distal end of the balloon was closed using hemostats for expediency, 
however, a conventional ligature such as waxed thread may be used to 
provide a suitable closure. In this manner a balloon catheter was 
fashioned, utilizing the silicone-PTFE composite tube as the balloon 
material. 
At this point, the balloon was measured in a pre-inflated state. The 
minimum dimension was found to be 2.31 mm and the maximum dimension 2.42 
mm. As before, these measurements were taken from approximately the 
midpoint of the balloon, and a Lasermike model 183, manufactured by 
Lasermike, (Dayton, Ohio) was used to make the measurements while the 
balloon was rotated about its longitudinal axis. The balloon, when 
inflated to 8 atmospheres internal water pressure, had a minimum dimension 
of 7.64 mm and a maximum dimension of 7.76 mm at the center of the 
balloon. When deflated by removing the entire volume of water introduced 
during the 8 atmosphere pressurization, the balloon at its mid-length, had 
a minimum dimension of 2.39 mm and a maximum dimension of 2.57 mm. The 
silicone-PTFE composite balloon when tested using a hand-held inflation 
device had a burst strength of 150 psi, reaching a maximum dimension of 
about 7.9 mm prior to rupture. 
This example illustrates that the balloon made from the silicone-PTFE 
composite tube exhibited a predictable limit to its diametrical growth as 
demonstrated by the destructive burst strength test wherein the balloon 
did not exceed the 8 mm diameter of the porous PTFE film tube component. 
The compaction ratio as previously defined was 2.42 divided by 2.57, or 
0.94, and the compaction efficiency ratio as previously defined was 2.39 
divided by 2.57, or 0.93. 
Example 4 
This example describes the construction of a PTA balloon made by helically 
wrapping a porous PTFE film having a non-porous FEP coating over a thin 
porous PTFE tube. 
The FEP-coated porous expanded PTFE film was made by a process which 
comprises the steps of: 
a) contacting a porous PTFE film with another layer which is preferably a 
film of FEP or alternatively of another thermoplastic polymer; 
b) heating the composition obtained in step a) to a temperature above the 
melting point of the thermoplastic polymer; 
c) stretching the heated composition of step b) while maintaining the 
temperature above the melting point of the thermoplastic polymer; and 
d) cooling the product of step c). 
In addition to FEP, other thermoplastic polymers including thermoplastic 
fluoropolymers may also be used to make this coated film. The adhesive 
coating on the porous expanded PTFE film may be either continuous 
(non-porous) or discontinuous (porous) depending primarily on the amount 
and rate of stretching, the temperature during stretching, and the 
thickness of the adhesive prior to stretching. 
The FEP-coated porous PTFE film used to construct this example was a 
continuous (non-porous) film. The total thickness of the coated film was 
about 0.02 mm. The film was helically wrapped onto an 8 mm diameter 
stainless steel mandrel that had been coaxially covered with a porous 
expanded PTFE tube, made as taught by U.S. Pat. Nos. 3,953,566 and 
4,187,390. The porous PTFE tube was a 3 mm inside diameter tube having a 
wall thickness of about 0.10 mm and a fibril length of about 30 microns. 
Fibril length is measured as taught by U.S. Pat. No. 4,972,846. The 3 mm 
tube had been stretched to fit snugly over the 8 mm mandrel. The 
FEP-coated porous PTFE film was then wrapped over the outer surface of 
this porous PTFE tube in the same manner as described by Example 1, with 
the FEP-coated side of the film placed against the porous PTFE tube 
surface. The wrapped mandrel was placed into an air convection set at 
380.degree. C. for 2.5 minutes, removed and allowed to cool, at which time 
the resulting tube was removed from the mandrel. One end of this tube was 
fitted coaxially over the end of a 5 Fr catheter shaft taken from a model 
number B507-412 PTA catheter manufactured by Schneider (Minneapolis, 
Minn.), and clamped to the catheter shaft using a model 03.3 RER Ear Clamp 
manufactured by Oetiker (Livingston, N.J.) such that a watertight seal was 
present. The resulting balloon was packed into the protective sheath which 
was provided by Schneider as part of the packaged balloon catheter 
assembly. The balloon was then removed from the protective sheath by 
sliding the sheath proximally off of the balloon and over the catheter 
shaft. Prior to inflation, the minimum and maximum diameters of the 
balloon were determined to be 2.25 and 2.61 mm. The distal end of the 
balloon was then closed using hemostats for expediency, however, a 
conventional ligature such as waxed thread could have been used to provide 
a suitable closure. When inflated to a pressure of 6 atmospheres, the 
minimum and maximum diameters were 8.43 and 8.49 mm. After being deflated 
the minimum and maximum diameters were 1.19 and 12.27 mm. These diameters 
resulted in a compaction ratio of 0.21 and a compaction efficiency of 
0.10. 
Example 5 
This example describes a balloon constructed by impregnating silicone 
dispersion into a porous PTFE tube with helically applied porous PTFE 
film. A balloon made in this way exhibits a very small initial diameter, 
predictable inflated diameter, high strength, exceptional compaction ratio 
and compaction efficiency ratio, as well as the known chemical inertness 
and low coefficient of friction afforded by PTFE. The impregnation with 
silicone dispersion enables the construction of a thinner balloon. The use 
of a thin porous PTFE tube as a substrate provides longitudinal strength 
to resist elongation of the balloon at high pressures. 
A longitudinally extruded and expanded porous PTFE substrate tube was 
obtained. The substrate tube was 1.5 mm inside diameter, having a wall 
thickness of about 0.17 mm and a fibril length of about 45 microns. The 
tube was fitted coaxially onto a 1.5 mm diameter stainless steel mandrel. 
Next, a length of porous expanded PTFE film was obtained that had been cut 
to a width of 2.54 cm. This film had a thickness of about 0.02 mm, a 
density of about 0.2 g/cc, and a fibril length of about 70 microns. 
Thickness was measured using a Mitutoyo snap gauge model No. 2804-10. The 
film bulk density was calculated based on dimensions and mass of a film 
sample. Density of non-porous PTFE was considered to be 2.2 g/cc. Fibril 
length of the porous PTFE film used to construct the example was estimated 
from scanning electron photomicrographs of an exterior surface of samples 
of the film. 
This film was helically wrapped directly onto the bare metal surface of a 7 
mm diameter stainless steel mandrel at about 65.degree. with respect to 
the longitudinal axis of the mandrel so that about two overlapping layers 
of film covered the mandrel. Both edges of the film were colored with 
black ink in order to measure the pitch angles of the film during the 
construction or use of the completed balloon. Following this, another 
approximately two layers of the same film were helically wrapped over the 
first two layers. The second two layers were applied at the same bias 
angle with respect to the longitudinal axis, but in the opposite 
direction. This procedure was repeated three times, providing 
approximately 16 total layers of film. The film-wrapped mandrel was then 
placed into a convection oven set at 380.degree. C. for 10 minutes to 
heat-bond the adjacent layers of film, then removed and allowed to cool. 
The resulting 7 mm inside diameter film tube formed from the helically 
wrapped layers of films was then removed from the mandrel. 
This 7 mm inside diameter porous PTFE film tube was then fitted coaxially 
over the 1.5 mm inside diameter PTFE substrate tube and mandrel. The film 
tube was then tensioned longitudinally to cause it to reduce in diameter 
to the extent that it fit snugly over the outer surface of the 1.5 mm 
tube. The ends of this reinforced tube were then secured to the mandrel in 
order to prevent longitudinal shrinkage during heating. The combined tube 
and mandrel assembly was placed into an air convention oven set at 
380.degree. C. for 190 seconds to heat bond the film tube to the outer 
surface of the substrate tube. The reinforced tube and mandrel assembly 
was then removed from the oven and allowed to cool. 
Additional porous PTFE film was then helically applied to outer surface of 
the reinforced tube to inhibit wrinkling of the tube in the subsequent 
step. The tube was then compressed in the longitudinal direction to reduce 
the tube length to approximately 0.6 of the length just prior to this 
compression step. Care was taken to ensure a high degree of uniformity of 
compression along the length of the tube. Wire was used to temporarily 
affix the ends of the tube to the mandrel. The mandrel-loaded reinforced 
tube with the additional helically applied film covering was then placed 
into a convention oven set at 380.degree. C. for 28 seconds, removed from 
the oven and allowed cool. 
The additional outer film was removed from the reinforced tube, followed by 
removing the reinforced tube from the mandrel. The reinforced tube was 
then gently elongated by hand to a length of about 0.8 of the length just 
prior to the compression step. 
The reinforced tube was then ready for impregnation with silicone 
dispersion (Medical Implant Grade Dimethyl Silicone Elastomer Dispersion 
in Xylene, Applied Silicone Corp., PN 40000, Ventura, Calif.). The 
silicone dispersion was first prepared by mixing 2.3 parts n-Heptane (J. 
T. Barker, lot #J07280) with one part silicone dispersion. Another mixture 
with n-Heptane was prepared by mixing 0.5 parts with 1 part silicone 
dispersion. Each mixture was loaded into an injection syringe. 
The dispensing needle of each of the injection syringes was inserted inside 
one end of the reinforced tube. Wire was used to secure the tube around 
the needles. One of the dispensing needles was capped and the syringe 
containing the 2.3:1 silicone dispersion solution was connected to the 
other. The solution was dispensed inside the reinforced tube with about 6 
psi pressure. Pressure was maintained for approximately one minute, until 
the outer surface of the tube started to become wetted with the solution, 
indicating that the dispersion entered the pores of the PTFE material. It 
was ensured that the silicone dispersion coated the inside of the PTFE 
tube. At this point, the syringe was removed, the cap was removed from the 
other needle, and the syringe containing the 0.5:1 silicone dispersion 
solution was connected to the previously-capped needle. This higher 
viscosity dispersion was then introduced into the tube with the syringe, 
displacing the lower viscocity dispersion through the needle at the other 
end, until the higher viscosity dispersion began to exit the tube through 
the needle. After ensuring that the tube was completely filled with 
dispersion, both needles were capped. Curing of the silicone dispersion 
was effected by heating the assembly in a convection oven set at 
150.degree. C. for a minimum of one hour. The solvent evaporated during 
the curing process, thereby recreating the lumen in the tube. The 
impregnated reinforced tube was removed from the oven and allowed to cool. 
Both ends of the tube were opened and the 0.5:1 silicone dispersion 
solution was injected in one end to again fill the lumen, the needle ends 
were then capped, then the dispersion was cured in the same manner as 
described above. At this point the balloon construction was complete. 
The above-described process preserved PTFE as the outermost surface of the 
balloon. Alternatively, longer impregnation times or higher injection 
pressures during the initial impregnation could cause more thorough 
wetting of the PTFE structure with the silicone dispersion, thereby 
driving more dispersion to the outermost surface of the balloon. 
The balloon was then ready for mounting on a 5 Fr catheter shaft obtained 
from a balloon dilatation catheter (Schneider Match 35 PTA Catheter, 6 mm 
dia., 4 cm length, model no. B506-412) This balloon was mounted on the 
1.67 mm diameter catheter shaft as described by FIG. 8. Both ends of the 
balloon were mounted to the shaft. The catheter tip portion plus the 
balloon of the balloon dilatation catheter were cut off in the dual lumen 
portion of the shaft leaving only the catheter shaft 24. Guidewires 
serving as mandrels (not shown) were inserted into both lumens of the 
shaft. A 0.32 mm mandrel was inserted into the inflation lumen 87 and a 
0.6 mm mandrel was inserted into the wire lumen 83. The portion 24A of the 
shaft 24 containing the inflation lumen 87 was shaved off longitudinally 
to a length approximately 1 cm longer than the length of the balloon to be 
placed on the shaft; therefore, this portion 24A of the shaft 24 then 
contained only the wire lumen 83 which possessed a semi-circular exterior 
transverse cross section. (The extra 1 cm length accommodates room for a 
tip portion of the catheter, without a balloon covering, in the final 
assembly.) With the mandrels still in place, portion 24B of the shaft 24 
was inserted for about 30 seconds into a heated split die containing 1.5 
mm diameter bore when the dies were placed together. The dies were heated 
to a temperature of 180.degree. C. to form the semicircular cross 
sectional shape of the portion of the shaft into a round 1.5 mm cross 
section and to create a landing 91 in the area proximal to the distal end 
of the inflation lumen 87. Next, the balloon 10 (having circumferentially 
oriented film layers 14 and 16, and longitudinally oriented substrate tube 
81) was slipped over the modified distal end of the shaft 24 such that the 
proximal end of the balloon 10 was approximately 0.5 cm from the end of 
the landing 91. This approximately 0.5 cm segment of the landing 91 
adjacent to the abutment was primed for fifteen seconds (Loctite Prism.TM. 
Primer 770, Item #18397, Newington, Conn.) and then cyanoacrylate glue 
(Loctite 4014 Instant Adhesive, Part #18014, Rocky Hill, Conn.) was 
applied to that segment. The balloon 10 was moved proximally such that the 
proximal end of the balloon abutted against the end of the landing 91 and 
the glue was allowed to set. The distal end of the balloon 10 was attached 
in the same manner, while ensuring against wrinkling of the balloon during 
the attachment. At this point, a radiopaque marker could have been fitted 
at each end of the balloon. The last step in the mounting process involved 
securing the ends of the balloon with shrink tubing 93 (Advanced Polymers, 
Inc., Salem, N.H., polyester shrink tubing - clear, item #085100CST). 
Approximately 0.25 cm of the proximal end of the balloon and approximately 
0.75 cm of the shaft adjacent to the end of the balloon were treated with 
the same primer and glue as described above. Approximately 1 cm length of 
shrink tubing 93 was placed over the treated regions of the shaft 24 and 
balloon 10. The same process was followed to both prepare the distal end 
the balloon and the adjacent modified shaft portion and to attach another 
approximately 1 cm length of shrink tubing 93. The entire assembly was 
then placed into a convection oven set at 150.degree. C. for at least 
about 2 minutes in order to shrink the shrink tubing. 
The pre-inflation balloon possessed 2.03 mm and 2.06 mm minimum and maximum 
dimensions, respectively, the balloon catheter was tested under pressure 
as described in Example 1. The inflated balloon possessed 5.29 mm and 5.36 
mm minimum and maximum dimensions, respectively. The deflated balloon 
possessed 2.19 mm and 3.21 mm minimum and maximum dimensions, 
respectively. The resulting compaction efficiency and the compaction ratio 
were 0.68 and 0.64, respectively. 
The pitch angles of the film were also measured pre-inflation, at inflation 
(8 atm), and at deflation, yielding values of about 20.degree., 
50.degree., and 25.degree., respectively. The balloon was reinflated with 
10 atm and the pitch angles of the film were measured for the inflation 
and deflation conditions. The angles were the same for both inflation 
pressures. 
The balloon was subjected to even higher pressures to determine the 
pressure at failure. The balloon withstood 19.5 atm pressure prior to 
failure due to breakage of the shrink tubing at the distal end of the 
balloon. Another balloon catheter was made using a piece of the same 
balloon material, following the same procedures described in this example. 
This balloon catheter was used to distend a 3 mm GORE-TEX Vascular Graft 
(item no. V03050L, W. L. Gore and Associates, Inc., Flagstaff Ariz.) from 
which the outer reinforcing film had been removed. The graft was placed 
over the balloon such that the distal end of the graft was positioned 
approximately 1 cm from the distal end of the balloon. The balloon was 
inflated to 8 atm, the graft distended uniformly without moving in the 
longitudinal direction with respect to the balloon. Another piece of the 
same graft was tested in the same manner using a 6 mm diameter, 4 cm long 
Schneider Match 35 PTA Catheter (model no. B506-412). In this case, the 
graft slid along the length of the balloon proximally during the balloon 
inflation; the distal end of the graft was not distended. 
Example 6 
A balloon catheter was made following all of the steps of Example 5 with 
one exception in order to provide a balloon that bends during inflation. 
All of the same steps were followed as in Example 5 with the exception of 
eliminating the manual elongation step that immediately followed the 
longitudinal compression step. That is, at the point of being impregnated 
with silicone dispersion, the film-covered porous PTFE tube was 0.6 of its 
initial length (instead of 0.8 as in Example 5). 
A balloon catheter was constructed using this balloon. The length of the 
balloon was 4.0 cm. The bend of the balloon was tested by inflating the 
balloon to 8 atm and measuring the bend angle created by inflation. 
Measurements were made via the balloon aligned coincident with the 
0.degree. scribe line of a protractor, with the middle of the balloon 
positioned at the origin. The bend angle was 50.degree.. The balloon was 
then bent an additional 90.degree. and allowed to relax. No kinking 
occurred even at 140.degree.. The angle of the still inflated, relaxed 
balloon stabilized at 90.degree.. 
The balloon of an intact 6 mm diameter, 4 cm long Schneider Match 35 PTA 
Catheter (model no. B506-412) was tested in the same manner. The bend 
angle under 8 atm pressure was 0.degree.. The inflated balloon was then 
bent to 90.degree., which created a kink. The inflated balloon was allowed 
to relax. The balloon bend angle stabilized at 25.degree.. The bending 
characteristics of an article of the present invention should enable the 
dilatation of a vessel and a side branch of the same vessel 
simultaneously. The inventive balloon is easily bendable without kinking. 
Kinking is defined as wrinkling of the balloon material. 
While particular embodiments of the present invention have been illustrated 
and described herein, the present invention should not be limited to such 
illustrations and descriptions. It should be apparent that changes and 
modifications may be incorporated and embodied as part of the present 
invention within the scope of the following claims.