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Description  |
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BACKGROUND OF THE INVENTION
Balloon catheters are commonly used, particularly the Foley catheter which
finds major use in uninary tract surgery. The catheter is inserted into
the urethra until the catheter head extends into the bladder. Then a
balloon adjacent the head is inflated to retain the catheter for usually a
period of days. However, a catheter may be inserted for an indefinite
period of time in chronic situations.
The early designs of balloon catheters were made of natural rubber latex.
As is known, the latex causes a reaction in the tissues which are adjacent
to it, which can be quite uncomfortable for the patient, and which is
medically undesirable.
In more recent times, balloon catheters have been fabricated out of
silicone rubber, or out of latex which is coated with a film of silicone
rubber, to avoid the tissue reaction problem. However, these catheters are
considerably more expensive than the latex catheters, and they share with
the latex catheters the disadvantage that they are somewhat difficult to
fabricate, because both latex and silicone rubber are generally not
thermoplastic materials, and thus must be cured over a period of time in
order to obtain the desired physical properties.
Another type of balloon catheter has a polyvinyl chloride tubular shank,
attached to a natural rubber latex balloon, because of the unsuitability
of vinyl as a balloon material. Thus, the latex balloon remains as an
irritant. Also, vinyl catheters have exhibited an undesirable "feel" to
the patient.
In accordance with this invention, a new catheter is provided which can
exhibit an extremely low toxicity so that little or no irritation is felt
by the patient. The balloon of the catheter of this invention exhibits
particularly good elastomeric recovery, with low creep, so that there is
little "pruning" upon deflation of the balloon, i.e. the formation of
wrinkles in the balloon.
While the material of the catheter of this invention, on a cost basis, is
similar to natural rubber latex and the like, it is as non-toxic as
silicone rubber, thereby combining the advantages of the two types of
catheters.
Also, as a further advantage, the tubular shaft of the catheter of this
invention may be formed by simple extrusion, without a post cure time,
since the material of the catheter may be thermoplastic, but also of a
softening temperature which permits autoclaving of the catheter if
desired.
Also, parts of the catheter may be thermoformed or injection molded as
desired. The tubing of the catheter of this invention may be kink and
collapse resistant upon aspiration and normal use, and it may be
fabricated by heat sealing, without separate adhesives.
Also, the cost of fabrication of the catheters of this invention may be
further reduced by the fact that scrap materials from the production of
the catheter may be reused in molding or extrusion, since the material is
of thermoplastic rather than of the thermoset type.
The catheters of this invention are also stable under radiation
sterilization.
DESCRIPTION OF THE INVENTION
In accordance with this invention, a balloon type catheter is provided with
a tubular shaft and an inflatable balloon member, carried by said
catheter, said shank and balloon member each being made of elastic
compositions which comprise: at least 40 percent by weight of a block
copolymer having thermoplastic rubber characteristics with a central block
of ethylene-butylene copolymer and terminal blocks of polystyrene; from 0
to 45 percent by weight of polypropylene; at least one of said shank and
balloon member containing from 5 to 30 percent by weight of tackifying
agent comprising a low molecular weight polystyrene; said elastic
compositions being mixed with sufficient hydrophobic oil-type plasticizer
to provide the desired physical properties to said shaft and balloon
member, i.e. low modulus, softness and resistance to creep.
However, if the molecular weight of the block copolymer formulations is of
an average of about 80,000 or less an adhesive or tackifying agent may not
be needed to seal the parts together. Specifically, the block copolymers
having thermoplastic rubber characteristics described above are
commercially available under the trademark KRATON from the Shell Chemical
Company, or SOLPRENE from the Phillips Petroleum Company. Other rubbery
block copolymers which are available under these trademarks utilize a
central block including butadiene or isoprene, rather than the ethylene
butylene copolymer units preferably utilized herein. These substitute
materials may be contemplated for use as equivalents to the
ethylene-butylene copolymer block.
These block copolymer materials preferably have a Brookfield viscosity of
10 to 2000 cps. as a ten weight percent toluene solution, measured at
25.degree. C. for the purposes of this invention. These materials exhibit
the characteristics of a thermoplastic rubber, due to the combined effects
of the central block of the molecule, which is typically a rubbery,
polyolefin material, and the terminal blocks of thermoplastic polystyrene.
Mixtures of the above-described block copolymers of different molecular
weight also may be desirable for use. An advantage of such mixtures is
that a component of the mixture may include the block copolymer as
described above with a molecular weight which is in itself too high to
permit extrusion, with the extrudability being facilitated by a component
of lower molecular weight block copolymer, to obtain an advantage in
physical properties from the high molecular weight component (for example,
a solution viscosity as calculated above of 1000 cps. The lower molecular
weight components of the block copolymer described above may preferably
have similar solution viscosities on the order of 20 to 100 cps.
Preferably, in the block copolymers described above, the central block of
ethylene-butylene units may comprise 50 to 85 percent by weight of the
copolymer molecule, while the terminal blocks of polystyrene or equivalent
material comprise the balance of the compound.
This formulation used herein may also contain a titanium dioxide pigment or
the like, for appropriate coloration of the catheter, as well as other
desired additives such as a stabilizing agents, plasticizers such as
mineral oil, and flow aid and hardener materials such as polypropylene.
Typically, a molded, branched connector such as a Y-site is attached at the
distal end of the tubular shaft of the catheter. The branched connector
may also be made of the elastic composition described above.
Either or both of the shaft and the balloon member (and the branched
connector when used) desirably may contain from 5 to 30 percent by weight
of tackifying agent such as low molecular weight polystyrene. When at
least one of the formulations contains this material, it facilitates the
adhesion of the balloon member and the Y-connector to the catheter shaft
without the use of adhesive by heat sealing or molding the balloon member
and connector in place on the shaft. The polystyrene material used may
preferably be of a molecular weight, for example, of 1000 to 6000, as a
tackifier.
Preferably up to 30 percent of the polypropylene may be used in the
oil-extended compound, both as a flow aid and as a surface finish,
depending on the molecular weight of the polypropylene. Generally, more
polypropylene is needed as a flow or extrusion aid when the block
copolymers used in this invention are of higher molecular weight. In
particular, from about one to five weight percent of polypropylene having
a melt flow of about 50 to 100, as tested under ASTM D1238-70, provides an
improved, smooth surface finish. Also, crystalline polypropylene is
believed to act as a diffusion barrier.
In the drawings,
FIG. 1 is a plan view of a typical Foley catheter which may be manufactured
in accordance with this invention.
FIG. 2 is a detailed view of the catheter of FIG. 1, taken partly in
section, showing the catheter balloon member adhered to the catheter shaft
.
Referring to the drawings, the catheter of this invention is shown defining
a double lumen tubular shaft 10 which may be extruded to define a drainage
lumen 12 and an inflation lumen 14 in accordance with conventional
technology. Tip member 16 may be conventionally thermoformed on the
catheter so that drainage lumen 12 communicates through aperture 18 to the
exterior, and inflation lumen 14 is closed off.
Aperture 20 is provided in the wall of shaft 10 to provide communication
between the inflation lumen 14 and the exterior of shaft 10. Balloon 22,
being a thin-walled tube, is sealed, for example by non-contact radiant
heat source, at ends 24 to the outer wall of shaft 10 about aperture 20.
Accordingly, when pressurized air or liquid is provided to inflate lumen
14, balloon 22 will expand.
Branched or Y-connector 26 comprises a pair of branching channels. Channel
28 is adapted to receive a pressure syringe, and communicates with the
inflation lumen 14. Valve 30 is provided to receive the luer of a syringe
and to allow it to pass to place pressurized fluid into the inflation
lumen 14. Valve 30 is also adapted to retain that pressure when the
syringe is withdrawn, and may be of conventional construction for a Foley
catheter. Branched tube 32 is adapted to communicate with the catheter
adapter of a urinary drainage bag or the like at its outer end 34, and
communicates with drainage lumen 12 within catheter shaft 10.
The following examples are provided to illustrate specific examples of
formulations which may be utilized in the catheter of this invention.
These specific examples are for illustrative purposes only, and are not
intended to limit the scope of the invention of this application, which is
as defined in the claims below.
EXAMPLE 1
A material for formulating extruded shaft 10 of the catheter of this
invention was prepared by mixing the following ingredients in a ribbon
blender: 100 parts by weight of a block copolymer of ethylene butylene
copolymer having terminal blocks of polystyrene (known as Kraton
G1651--Brookfield viscosity as a 10 weight percent solution in toluene at
25.degree. C.--1000 cps.; weight percent of the central block: 67
percent); and 40 parts by weight of polypropylene having a melt flow of 5
(ASTM D1238--70; Shell 5520). To this mixture was added 100 parts by
weight of U.S.P. light grade white mineral oil, manufactured by Witco
Chemical Company, Sonneborn Division, New York, New York; (viscosity at
100 degrees F. of 350 Saybolt seconds) as a plasticizer. To this
formulation was also added about 0.03 to 0.07 percent by weight of an
equal weight mixture of two stabilizers, one commercially available under
the trademark Irganox 1010 by the Ciba-Geigy Company, and the other being
dilauryl-thiodipropionate
One hundred parts by weight of the following formulation were blended with
one part by weight of a titanium dioxide pigment (Ti-Pure R-221,
manufactured by E. I. DuPont de Nemours).
After mixing of this formulation, it was extruded at 350-400 degrees F. in
a conventional extruder to form the double lumen catheter tube 10.
For the catheter of this invention, balloon member 20 was extruded and
Y-connector 26 was conventionally molded out of a formulation containing
the following ingredients:
(a) 65 percent by weight of a mixture of 100 parts by weight of the block
copolymer described immediately above (Kraton G1651) and 85 parts by
weight of the mineral oil described above;
(b) 17 percent by weight of a mixture comprising 100 parts by weight of an
ethylene butylene block copolymer with polystyrene end blocks of lower
molecular weight (Kraton G1650; Brookfield viscosity as a 10 percent
toluene solution--60 cps. at 25 degrees C.; weight percent of the
ethylene-butylene block: 70 percent); 51 parts of polypropylene having a
melt flow of 12 according to ASTM D1238-70 (Shell 5820); 19 parts by
weight of a copolymer of alphamethyl styrene and vinyl toluene (Piccotex
120, sold by Hercules Chemical Company); and 100 parts by weight of the
mineral oil described previously.
(c) 15 percent by weight of a low molecular weight polystyrene having a
ring and ball softening point of about 100 degrees C. (Piccolastic E100,
sold by Hercules Chemical Company).
(d) 3 percent by weight of a high melting polypropylene (Tenite 4G7DP sold
by Eastman Chemical Products, Inc.) having a melt flow of 60 according to
ASTM D1238-70), as a surface finish improving agent.
To one hundred parts by weight of the above formulation was added one part
of the titanium dioxide pigment described above. The mixture was thorougly
mixed in a ribbon blender; the balloon 22 was heat sealed in position on
shaft 10, while Y-connector 26 was molded on the catheter, both without
adhesive. Tip 16 is thermoformed.
The formulation also contains from 0.03 to 0.07 percent by weight of the
stabilizers described earlier.
EXAMPLE 2
Another catheter may be prepared by extruding shaft 10 out of a formulation
of the following composition:
A. 60 percent by weight of a mixture of 100 parts by weight of Kraton G1651
(described above) and 85 parts by weight of the mineral oil described
above.
B. 5 percent by weight of polypropylene having a melt flow of 60 under the
test described above (Tenite 4G7DP).
C. 10 percent by weight of the low molecular weight polystyrene described
above (Piccolastic E100).
D. 5 percent by weight of polypropylene having a melt flow of approximately
2 according to ASTM D-1238 (condition L).
E. 20 percent by weight of the mineral oil described above.
One hundred parts of this formulation were mixed with two parts of the
titanium dioxide pigment described in Example 1, and blended for extrusion
at 350 degrees to 400 degrees F. into the double lumen shaft 10 of the
catheter of this invention.
The balloon 22 may, in this instance, be extruded from a formulation of the
block copolymer of ethylene-butylene with polystyrene end blocks, in which
the ethylene-butylene portion of the copolymer comprises about 70 percent
by weight of the copolymer molecule, having a Brookfield viscosity at 25
degrees C. of 20 cps. using a 10 weight percent solution in toluene, and
containing from 0.03 to 0.07 percent by weight of A0330 antioxidant
(Kraton G1662). To this is added 40 percent by weight of the mineral oil
described in Example 1 above. The composition is then blended.
One hundred parts by weight of this blended formulation was then mixed with
two parts by weight of the titanium dioxide pigment. Balloon 22 is made
from this formulation, and may be directly molded about and in contact
with shaft 10.
Y-connector site 26 may be formulated out of the same material as it was
formulated from in the previous example.
The distal end of catheter shaft 10 is inserted into an injection mold for
Y-site 26, with the Y-site being then molded about the distal end, with
good adhesion taking place between the molded Y-connector 26 and shaft 10
of the catheter without the need for an adhesive.
Valve 30 is then inserted into the Y-site to complete the construction of
the catheter which exhibits the advantages described previously.
EXAMPLE 3
In this example, shaft 10 for a catheter was made from a formulation
comprising 100 parts by weight of the following ingredients:
(a) 30 percent by weight of the block copolymer material utilized in the
balloon formulation in Example 2 (Kraton 1662).
(b) 20 percent by weight of the poly(ethylene-butylene)-polystyrene
copolymer of Example 1(b), and further containing an effective level of
the Example 1. antioxidant described previously (Kraton G1650).
(c) 5 percent of the polypropylene formulation having a melt flow of 60 as
described in Example 2.
(d) 5 percent by weight of a polypropylene material having a melt flow of
about 2.
(e) 40 percent by weight of the mineral oil described in Example 1.
To 100 parts by weight of this mixture was added 2 parts by weight of the
titanium dioxide pigment described previously. The mixture is processed as
previously described.
It is also contemplated as an alternative to utilize a single type of
antioxidant, either one or the other, in conjunction with the two types of
block copolymer.
This material was blended and extruded in the manner of the previous
examples to form shafts 10 of catheters made in accordance with this
invention.
The balloon was extruded of the same material as in Example 2, and sealed
onto the shaft, after punching aperture 20. The Y-connector site material
may be identical to the shaft material of Example 1 and may be molded on
to the shaft in the same manner as is described previously.
It is noted in this Example that, because of the relatively low average
molecular weight and Brookfield viscosity of the block copolymer utilized
herein, it is not necessary to provide a low melting polystyrene to the
balloon or the shaft formulations since adhesion between the materials
upon molding takes place spontaneously in this instance.
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Description |
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