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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to coated guidewire for use in catheters. The
guidewires are coated with organosiloxane copolymer.
Guidewires for catheters have been coated with lubricants such as Teflon
prior to winding the guidewire into a coiled form. When the coated wire
has been tightly wound into an elongated coil, a safety core wire is
inserted into the coil and is welded to the respective ends of the
guidewire. The safety core wire generally takes the form of a cylindrical
wire having a uniform main body which is smoothly tapered into a very
flexible flattened tip so that one end of the guidewire exhibits the
property of being rigid and the other end of the guidewire remains very
flexible.
In inserting a catheter into the vascular system of a patient, the
guidewire is initially inserted through a cannula into the vascular
system, the cannula is removed, and the catheter is inserted over the
guidewire. The catheter is then moved along the guidewire to the desired
position within the vascular system and the guidewire is removed. Once the
guidewire has been removed, the catheter is in condition for use.
Accordingly, the guidewire must be extremely flexible at the distal end so
that the guidewire may be initially moved through the vascular system to a
position where it is desired to insert the cannula. The proximal end of
the guidewire should remain relatively rigid so that the position of the
guidewire may be controlled upon insertion of the guidewire within the
vascular system. It is, therefore, desirable that the guidewire have a
flexible distal tip and a relatively stiff body portion. In addition, the
guidewire should have a very smooth and lubricious outer surface.
Guidewires generally take the form of a tightly wound spring which is
constructed of a very fine wire tightly wrapped to form a coil in which
all of the turns contact adjacent turns. It is important that the
guidewire surface be as smooth as possible so that the internal walls of
the vascular system are not traumtized or damaged during movement of the
guidewire through the vascular system.
As is apparent, any material introduced into the bloodstream has the
potential of initiating blood clots. Since blood clots are an undesirable
side effect of known angiographic guidewires, it is desirable to utilize
materials which eliminate the probability of the formation of blood clots
and include a surface which is as lubricious as possible thereby
preventing trauma to the blood vessel.
One approach to preventing blood clot formation is the use of a guidewire
surface which is coated with Teflon prior to winding to provide a
relatively smooth antithrombogenic surface. Such a Teflon coated
angiographic guidewire is disclosed in U.S. Pat. No. 4,003,369.
While Teflon coated guidewires provided a substantial improvement over
previously developed guidewires, the guidewire of the present invention
has with improved lubricity with reduced trauma to the blood vessel
system.
As will be described in greater detail hereinafter, the guidewire of the
present invention is coated with an organisiloxane copolymer to provide
the enhanced lubricity with reduced trauma to a blood vessel system. Such
a copolymer has been proposed for use as a coating for a fine cutting edge
in U.S. Pat. No. 3,574,673. However, heretofore, such a copolymer has not
been proposed as a coating for an angiographic guidewire.
SUMMARY OF THE INVENTION
Briefly, the present invention is directed toward a guidewire having a
wound outer casing which is coated with an organosiloxane copolymer. The
guidewire also includes an integral core wire for insuring structural
integrity of the guidewire without substantially reducing the flexibility
of the distal tip of the guidewire. The invention also relates to a method
of manufacturing the guidewire of the present invention.
As a final operation after the guidewire is completely fabricated, the core
wire is then inserted into the outer casing and is attached to the casing
at the distal and proximal ends. The distal tip of the core wire is
tapered to a very small cylindrical cross-sectional area in order to make
the guidewire very flexible at the distal tip.
The smooth outer surface of the wound guidewire is developed by coating the
coiled guidewire with copolymers of methylsiloxane and aminoalkylsiloxane
units, such as
##STR1##
Accordingly, the present invention produces a smooth guidewire which is
very lubricious and which includes an integral core wire which is
relatively rigid at the proximal end and is very flexible at the distal
end.
Accordingly, the primary object of the present invention is to provide a
guidewire having an ultrasmooth exterior surface.
A further object of the present invention is to provide a wire wound
guidewire having an outer surface which is coated with a lubricating
material which is biocompatible with blood.
Still a further object of the present invention is to provide a method of
fabricating a guidewire with an improved coating.
These and other objects of the present invention, as well as the attendant
advantages thereof, will become more readily apparent when reference is
made to the following description taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an embodiment of the guidewire of the
present invention; and
FIG. 2 is a cross-sectional view of a portion of the guidewire shown in
FIG. 1 and illustrates the lubricating coating in more detail.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An elongated guidewire 10 constructed in accordance with the teachings of
the present invention is illustrated in FIG. 1. The guidewire 10 includes
an elongated body with a proximal tip portion 12 and a distal tip portion
14. A core wire 16 extends from the proximal end 12 to the distal end 14
of the guidewire 10. The outer core of the guidewire takes the form of a
coil spring 18, which is wound from thin wire with each of the coils in
direct contact with adjacent coils. The core 16 is welded to the proximal
tip portion 12 and is welded to the distal tip portion 14. The tip
portions 12, 14 serve to retain the respective ends of the wound body of
the coil spring 18.
As is illustrated, the core wire 16 is of an elongated cylindrical
configuration and tapers from the proximal end to the distal end of the
guidewire. As is apparent, the core wire 16 serves to impart rigidity to
the guidewire at the proximal end of the guidewire, however, the core wire
16 does not substantially reduce the flexibility of the coil spring 18 at
the distal end of the guidewire.
When the guidewire 10 has been assembled as illustrated in FIG. 1, a
lubricating coating 20 is applied to the coil spring 18. The coating may
be applied by simply dipping the guidewire in a solution of the
lubricating coating, by wiping the coating onto the external surface of
the guidewire or by spraying the guidewire with a lubricating coating.
As illustrated in FIG. 2, because of the low viscocity of the lubricating
coating 20, the coating passes between adjacent turns of the coil spring
18 and completely surrounds each of the turns of the coil spring 18. With
this smooth lubricious coating of the coil spring 18, the coating serves
the function of reducing the formation of blood clots because of the
smooth outer surface of both the outer portion and inner portion of the
coil spring 18.
The lubricating coating takes the form of an adherent coating consisting
essentially of at least a partially cured organosiloxane copolymer
consisting of:
(1) 5 to 20 weight of polymeric units of the formula
##STR2##
in which
R is a lower alkyl radical containing no more than 6 carbon atoms;
Y is selected from the group consisting of 13 OH and --OR' radicals, in
which R' is an alkyl radical of no more than 3 carbon atoms;
Q is selected from the group consisting of the hydrogen atom,
--CH.sub.3 and --CH.sub.2 CH.sub.2 NH.sub.2 ;
a has a value of 0 or 1; and
b has a value of 0 to 1; the sum of a+b being from 0 to 2; and
(2) 80 to 95 weight percent of polymeric units the formula
##STR3##
in which
R" is selected from the group consisting of --OH and --CH.sub.3 radicals,
and c has a value of 1 or 2.
As described above, the aminoalkyl siloxane unit can contain lower alkyl
substituents, such as methyl, ethyl, propyl, t-butyl and hexyl radicals.
In addition, those copolymers which are not fully condensed will contain
hydroxyl or alkoxy substituents, such as methoxy, ethoxy, and propinoxy
radicals. The Q substituents bonded to the nitrogen atom can be the same
or different. Thus the aminoalkysiloxane units include
##STR4##
and the like.
The methylsiloxane units of the copolymer include
##STR5##
The copolymers utilized in the practice of the invention are commercially
available and are prepared by well known methods, such as cohydrolysis and
co-condensation or equilibration of aminoalkyl-substituted aminoalkyl
polysiloxane with dimethylpolysiloxane in the presence of an alkaline
equilibration catalyst.
A preferred method of preparation is discussed in detail in U.S. 3,355,424,
the disclosure of which is incorporated herein by reference. In brief this
method comprises mixing the appropriate molar amounts of
(polyaminoalkyl)-alkoxysilane, Q.sub.2 N(CH.sub.2).sub.3 SiR.sub.a
(OR).sub.3-a with a conventional dimethylpolysiloxane which contains a
substantial amount of silicon-bonded hydrosyl groups, for example, 1 to 5
percent by weight .tbd. SiOH. The reaction to form new siloxane bonds is
illustrated as follows:
.tbd.SiOR'+HOSi.tbd..fwdarw..tbd.SiOSi.tbd.+R'OH
The reaction rate is accelerated by heating in the range of 100.degree. to
200.degree. C. Inert solvents can be present if desired. The alcohol which
is formed in this reaction can be removed by distillation, thus it is
certain that true copolymers are formed. It is apparent that the copolymer
can have unreacted (OR') and/or (OH) groups present, depending upon the
relative amounts of reactants and the amount of (OR') and (OH) present in
the reactants initially. If desired, excess (OR') groups can be hydrolyzed
by the addition of water to the system. Controlling the amount of water so
added controls the amount of such groups remaining in the copolymer.
Likewise, excess (OH) groups can be caused to condense, as for example by
heating the copolymer. Any or all of the alcohol formed by either the
reaction or by subsequent hydrolysis can be left in the reaction product
if desired.
The copolymeric coating is in the form of a stable material coating 20
which is adherent to the underlying surface of the coiled spring 18. As
used in this specification "at least partially cured copolymer" is defined
as a crosslinked or partially crosslinked copolymer which has insoluble,
infusible coherent three-dimensional structure, within which an uncured or
partially cured fluid copolymer is contained. The material is relatively
soft and waxy as contrasted to hard vitreous resins, which develop
fractures when coated onto a hard surface.
The liquid copolymer is applied to the guidewire 10 in any suitable manner,
for example by dipping brushing or spraying the material onto the coil
spring 18. The copolymer may be applied with a solvent carrier, such as
isopropyl alcohol. Prior to applying the copolymer, the coil spring 18
should be carefully cleaned so as to remove any oils which may have formed
on the surface. This cleaning process can be accomplished by use of any
suitable solvent.
When the copolymer has been applied to the surface, the copolymer may be
cured by heating the guidewire for a short period of time (e.g. 30 minutes
at 120.degree. C.) or by exposing the guidewire to room temperature and
50% relative humidity conditions for a longer period of time.
In evaluating the guidewire of the present invention, tests have shown that
the improved lubricating coating adheres satisfactorily to the coil spring
18 and that the coating exhibits improved lubricity over existing
guidewires and with reduced trauma to a blood vessel system.
Reasonable modifications and variations are within the teachings of the
invention as set forth in the following claims for an improved guidewire
for catheters and method of manufacturing such guidewires.
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