Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF MAKING VASO-OCCLUSIVE COILS
FIELD OF THE INVENTION
This invention is in the field of an implantable vaso-occlusive device. In
particular,
the invention includes methods of malting such devices by varying the tension
during
winding of a wire to produce a primary coil configuration. The primary coil
efficiently self
forms into a three-dimensional shape when deployed into a body cavity.
Further, the
variations in winding tension induce this three-dimensional formation in the
desired
directions and shapes.
BACKGROUND
Vaso-occlusion devices are surgical implements or implants that are placed
within the
vasculature of the human body, typically via a catheter, either to block the
flow of blood
through a vessel making up that portion of the vasculature through the
formation of an
embolus or to form such an embolus within an aneurysm stemming from the
vessel. One
widely used vaso-occlusive device is a helical wire coil having windings which
may be
dimensioned to engage the walls of the vessels. Other less stiff helically
coiled devices have
been described, as well as those involving woven braids.
U.S. Pat. No. 4,994,069, to Ritchart et al., describes a vaso-occlusive coil
that
assumes a linear helical configuration when stretched and a folded, convoluted
configw-ation
when relaxed. Vaso-occlusive coils having attached fibrous elements in a
variety of
secondary shapes are shown in U.S. Pat. No. 5,304,194, to Chee et al. Vaso-
occlusive coils
having little or no inherent secondary shape have also been described. For
instance, co-owned
U.S. Patent Numbers 5,690,666 and 5,826,587 by Berenstein et al., describes
coils having
little or no shape after introduction into the vascular space.
Further, there are a variety of ways of discharging shaped coils and linear
coils into
the human vasculature. In addition to those patents which apparently describe
only the
physical pushing of a coil out into the vasculature (e.g., Ritchart et al.),
there are a number of
other ways to release the coil at a specifically chosen time and site. U.S.
Pat. No. 5,354,295
and its parent, U.S. Pat. No. 5,122,136, both to Guglielini et al., describe
an electrolytically
detachable embolic device.
Production of vaso-occlusive coils typically involves winding an elongated
wire
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around a mandrel and annealing the wire-mandrel complex. Generally, during
winding the
wire is held stationary, for example, on a spool. The free end of the wire is
affixed to the
mandrel and the mandrel is tunied such that the wire is released from the
spool as it is wound
about the mandrel. During winding, the tension between the wire and the
mandrel does not
change.
Thus, none of these documents disclose methods of making vaso-occlusive
devices
which involve varying the tension on the wire as it is wound around mandrel to
form the
vaso-occlusive coil.
SUMMARY OF THE INVENTION
Thus, this invention includes novel methods of making vaso-occlusive devices
and
devices made by these methods.
In one aspect, the invention includes a method of making a vaso-occlusive
device
comprising winding an elongated wire around a mandrel, wherein the tension on
the wire is
varied during said winding. The tension can be varied automatically or
manually in a variety
of ways (e.g., by varying distance between the wire and mandrel; the rate of
winding, and/or
the angle of winding). Thus, in certain embodiments, the elongated wire is
held in a holder
and the tension is varied during winding of the wire by varying the distance
between the
holder and the mandrel. In other embodiments, the elongated wire is held in a
holder and the
tension is varied during winding of the wire by varying the rate of winding
around the
mandrel, for example using a magnetic brake or transducer. In yet other
embodiments, the
elongated wire is held in a holder and the tension is varied during winding of
the wire by
varying the angle between the wire and mandrel. One or more of these
parameters can be
varied in the methods described herein.
These and other embodiments of the subject invention will readily occur to
those of
skill in the art in light of the disclosure herein.
DESCRIPTION OF THE INVENTION
Vaso-occlusive devices, particularly coils, made by winding a wire around a
mandrel
at varying tensions are described herein. Varying the tension at which the
wire is wound
about the mandrel to form a primary coil can be achieved in any number of
ways, for example
by varying the angle between the wire and the mandrel; by varying the distance
between the
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wire holding device and the mandrel and/or by varying the rate at which the
wire is wound
about the mandrel (e.g., using magnetic brakes and/or transducers). These and
other
parameters can be varied manually or using automated systems, for example
using one or
more computer programs linked to a winding device. Primary coils that have
been produced
using variable winding tensions exhibit particular characteristics, for
example, the three-
dimensional shape and the efficiency with which the three-dimensional shape is
formed.
Thus, vaso-occlusive devices made using these methods and methods of using
these devices
also form an aspect of this invention.
Advantages of the present invention include, but are not limited to, (i)
ability to
induce different three-dimensional shapes upon deployment, depending on which
areas of the
device have been wound at what tension; (ii) less rotation of the coil upon
deployment; and
(iii) rapid formation of three dimensional structures upon deployment into a
body cavity.
These advantages are achieved without the necessity of varying the diameter of
the wire
making up the coil. The devices described herein are useful whether the coils
have
mechanical or electrolytic detachment links at one or both ends.
All publications, patents and patent applications cited herein, whether supra
or infra,
are hereby incorporated by reference in their entirety.
It must be noted that, as used in this specification and the appended claims,
the
singular forms "a", "an", and "the" include plural referents unless the
content clearly dictates
otherwise. Thus, for example, reference to "a coil" includes a mixture of two
or more such
devices and the like.
Vaso-occlusive devices are typically formed by winding a wire (e.g., a
metallic wire)
axound a mandrel, for example winding the wire into a primary configuration,
for example a
helical coil. The primary coil can be wound into a secondary form or may self
form into a
three-dimensional structure. The pattern and tension during winding on the
mandrel provides
the three dimensional shape of the invention at deployment. Once wotmd onto a
mandrel, the
assembly of mandrel and coil is typically heat treated. The secondary form is
one which,
when ejected from a delivery catheter, forms a generally three-dimensional
shape, filling first
the outer periphery of the three-dimensional shape and then the center region.
Desirably, the
vaso-occlusive device is of a size acid shape suitable for fitting snugly
within a vascular
cavity (e.g., an aneurysm, or perhaps, a fistula).
Suitable winding mandrels may be a variety of shapes (e.g., cylindrical,
square,
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spherical, circular, rectangular, etc.) and may be solid or hollow. Some
exemplary shapes of
mandrels are shown in co-owned U.S. Patent No. 5,957,948 to Mariant et al. As
noted above,
the winding mandrel is typically of sufficient heat resistance to allow a
moderate annealing
step. The mandrel may be made of a refractory material such as alumina or
zirconia (for
heat-treating devices made of purely metallic components) or may be made of a
metallic
material. Composite mandrels (e.g., composites of conductive and non-
conductive materials)
described in co-owned U.S. Serial No. 09/637,470 may also be employed.
As noted above, varying the tension between the wire and the mandrel during
winding
can be achieved in any number of ways, including, but not limited to, varying
the rate at
which the wire is wound onto the mandrel and/or varying the distance between
the mandrel
and the wire-holder. In addition the angle between the wire and the mandrel
can be used to
vary the tension. Further, the use of magnetic brakes and/or transducers
during winding can
also be used to vary the tension of winding. Tension can be measured using
standard
techniques, for example using a force gauge, a transducer or the like. Such
techniques are
known to those of skill in the art. The variation in tension during winding
can be anywhere
from 2 gm to the deformation strength of the wire. The specific tensions will
depend on the
wire (e.g., diameter, composition, etc.) and can readily be determined using
known
techniques in view of the teachings herein. For example, a 0.002 inch wire can
be wound at
tensions varying between about 5 gm to about 500 gm (and any integer
therebetween), more
preferably, between about 5 gm and 250 gm (and any integer therebetween).
Thus, the wire may be held stationary, for example, on a spool. The wire-
holder can
comprise any device which allows the wire to be fed onto a mandrel, for
example a spool or
other threading device. One end of the wire is then attached to a mandrel. The
mandrel
and/or the wire-holding device can rotate in any direction and both can
optionally move
laterally. In certain embodiments, rotation of the mandrel pulls the wire off
the spool as the
wire is wound around the mandrel. The pattern of winding is achieved by moving
the
mandrel and/or spool laterally during rotation of the mandrel. Moreover, the
tension during
winding may be varied by manually adjusting the rate at which the mandrel
rotates. In
addition, the tension can be varied automatically, for example by using a
programmable
device which drives rotation of the mandrel and/or unwinding of the wire from
the spool.
Suitable programmable microprocessors will be known to those of skill in the
art.
Alternatively, the rate at which the mandrel rotates can be adjusted manually.
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In other embodiments, the tension is varied during winding by varying the
distance
between the wire-holder (e.g. spool) and the mandrel. In this way, tension can
be increased
by moving the wire-holder aild the mandrel farther apart and decreased by
moving the
mandrel and wire-holder closer together. As above, the distance can be varied
manually or
using a microprocessor, e.g., programmable device. One of skill in the art
could readily vary
these and other parameters to determine both the tension of winding and the
winding pattern
useful to achieve the desired coil type.
After winding, the mandrel and attached coil are typically annealed (e.g., by
heating).
A typical annealing step for a platinum/tungsten alloy coil would involve a
1100 °F heating
step in air for about between about 15-20 minutes to about 6 hours. The
primary coil is
typically linear after it has been wound and aimealed.
The material used in constructing the vaso-occlusive member having enhanced
areas
of softness may be any of a wide variety of materials; preferably, the wire is
a radio-opaque
material such as a metal. Suitable metals and alloys for the wire making up
the primary coil
include the Platinum Group metals, especially platinum, rhodium, palladium,
rhenium, as
well as tungsten, gold, silver, tantalum, and alloys of these metals. These
metals have
significant radiopacity and in their alloys may be tailored to accomplish an
appropriate blend
of flexibility and stiffiless. They are also largely biologically inert.
Highly preferred is a
platinum/tungsten alloy.
The wire may also be of any of a wide variety of stainless steels if some
sacrifice of
radiopacity may be tolerated. Very desirable materials of construction, from a
mechanical
point of view, are materials which maintain their shape despite being
subjected to high stress.
Certain "super-elastic alloys" include nickel/titanium alloys (48-58 atomic %
nickel and
optionally containing modest amounts of iron); copper/zinc alloys (38-42
weight % zinc);
copper/zinc alloys containing 1-10 weight % of beryllium, silicon, tin,
aluminum, or gallium;
or niclcel/aluminum alloys (36-38 atomic % aluminum). Particularly preferred
are the alloys
described in U.S. Pat. Nos. 3,174,851; 3,351,463; and 3,753,700. Especially
preferred is the
titaniurn/nickel alloy known as "nitinol". These are very sturdy alloys which
will tolerate
significant flexing without deformation even when used as a very small
diameter wire. If a
superelastic alloy such as nitinol is used in the device, the diameter of the
coil wire may be
significantly smaller than that used when the relatively more ductile platinum
or
platintun/tungsten alloy is used as the material of construction.
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Generally speaking, when the device is formed of a metallic coil and that coil
is a
platinum alloy or a superelastic alloy such as nitinol, the diameter of the
wire used in the
production of the coil will be in the range of 0.0005 and 0.006 inches. The
wire of such
diameter is typically then wound into a primary coil having a primary diameter
of between
0.005 and 0.035 inches. For most neurovascular indications, the preferable
diameter is 0.010
to 0.018 inches. We have generally found that the wire may be of sufficient
diameter to
provide a hoop strength to the resulting device sufficient to hold the device
in place within
the chosen body cavity without distending the wall of the cavity and without
moving from the
cavity as a result of the repetitive fluid pulsing found in the vascular
system.
The axial length of the primary coil will usually fall in the range of 0.5 to
100 cm,
more usually 2.0 to 40 cm. Depending upon usage, the coil may well have 100-
400 turns per
centimeter, preferably 200-300 turns per centimeter. All of the dimensions
here are provided
only as guidelines and are not critical to the invention. However, only
dimensions suitable for
use in occluding sites within the human body are included in the scope of this
invention.
The overall diameter of the device as deployed is generally between 2 and 20
millimeters. Most aneurysms within the cranial vasculature can be treated by
one or more
devices having those diameters. Of course, such diameters are not a critical
aspect of the
invention.
The primary coil may include or be made entirely from radiolucent fibers or
polymers
(or metallic threads coated with radiolucent or radiopaque fibers) such as
Dacron (polyester),
polyglycolic acid, polylactic acid, fluoropolymers (polytetrafluoro-ethylene),
Nylon
(polyamide), or even silk. Polymer materials may be filled with some amount of
a known
radiopaque material such as powdered tantalum, powdered tungsten, bismuth
oxide, barium
sulfate, and the lilce. Also contemplated in this invention is the attachment
of various fibrous
materials to the inventive coil for the purpose of adding thrombogenicity to
the resulting
assembly. The fibrous materials may be attached in a variety of ways. A series
of looping
fibers may be looped through or tied to coil and continue axially down the
coil. Another
variation is by tying the tuft to the coil. Tufts may be tied at multiple
sites through the coil to
provide a vast area of embolus forming sites. The primary coil may be covered
by a fibrous
braid. The method for producing the former variation is described in U.S. Pat.
Nos.
5,226,911 and 5,304,194 to Chee. The method of producing the fibrous braid is
described in
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U.S. Pat. No. 5,382,259, issued Jan. 17, 1995, to Phelps and Van.
The coils described herein can also include additional additives, for example,
any
material that exhibits biological activity ih vivo. Non-limiting examples of
suitable bioactive
materials are known to those of skill in the art. Preferably, these materials
are added after
annealing.
The inventive coils described herein may be associated with other materials,
such as
radioactive isotopes, bioactive coatings, polymers, fibers, etc., for example
by winding,
braiding or coating onto the device one or more of these materials, typically
prior to
introduction into the subject. Methods of associating polymeric materials with
a solid
substrate such as a coil are known to those of skill in the art, for example
as described in U.S.
Patent Nos. 5,522,822 and 5,935,145. In yet other embodiments, the solid
substrate itself is
made to be radioactive for example using radioactive forms of the substrate
material (e.g.,
metal or polymer). Thus, the solid substrates can be made to be radioactive
after formation
by deposition (e.g., coating, winding or braiding), impregnantion (e.g., ion-
beam or
electrodeposition) or other techniques of introducing or inducing
radioactivity.
In addition one or more metals, the occlusive devices may optionally include a
wide
variety of synthetic and natural polymers, such as polyurethanes (including
copolymers with
soft segments containing esters, ethers and carbonates), ethers, acrylates
(including
cyanoacrylates), olefins (including polymers and copolymers of ethylene,
propylene, butenes,
butadiene, styrene, and thermoplastic olefin elastomers), polydimethyl
siloxane-based
polymers, polyethyleneterephthalate, cross-linked polymers, non-cross linked
polymers,
rayon, cellulose, cellulose derivatives such nitrocellulose, natural rubbers,
polyesters such as
lactides, glycolides, caprolactones and their copolymers and acid derivatives,
hydroxybutyrate and polyhydroxyvalerate and their copolymers, polyether esters
such as
polydioxinone, anhydrides such as polymers and copolymers of sebacic acid,
hexadecandioic
acid and other diacids, orthoesters may be used. In a preferred embodiment,
the polymeric
filament comprises the materials of the present invention or other suture
materials that have
already been approved for use in wound heating in humans.
Methods of Use
The coils prepared by varying the tension during winding as described above
are
typically removed from the winding mandrel and loaded into a carrier for
introduction into
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the delivery catheter. The devices are preferably first introduced to the
chosen site using the
procedure outlined below. This procedure maybe used in treating a variety of
maladies. For
instance, in treatment of an aneurysm, the aneurysm itself may be filled with
the mechanical
devices prior to introducing the inventive composition. Shortly after the
devices are placed
within the aneurysm, an emboli begins to form and, at some later time, is at
least partially
replaced by neovascularized collagenous material formed around the vaso-
occlusive devices.
In using the occlusive devices, a selected site is reached through the
vascular system
using a collection of specifically chosen catheters and guide wires. It is
clear that should the
site be in a remote site, e.g., in the brain, methods of reaching this site
are somewhat limited.
One widely accepted procedure is found in U.S. Patent No. 4,994,069 to
Ritchart, et al. It
utilizes a fine endovascular catheter such as is found in U.S. Patent No.
4,739,768, to
Engelson. First of all, a large catheter is introduced through an entry site
in the vasculature.
Typically, this would be through a femoral artery in the groin. Other entry
sites sometimes
chosen are found in the neck and are in general well known by physicians who
practice this
type of medicine. Once the introducer is in place, a guiding catheter is then
used to provide a
safe passageway from the entry site to a region near the site to be treated.
For instance, in
treating a site in the human brain, a guiding catheter would be chosen which
would extend
from the entry site at the femoral artery, up through the large arteries
extending to the heart,
around the heart through the aortic arch, and downstream through one of the
arteries
extending from the upper side of the aorta. A guidewire and neurovascular
catheter such as
that described in the Engelson patent are then placed through the guiding
catheter as a unit.
Once the tip of the guidewire reaches the end of the guiding catheter, it is
then extended
using fluoroscopy, by the physician to the site to be treated using the vaso-
occlusive devices
of this invention. During the trip between the treatment site and the guide
catheter tip, the
guidewire is advanced for a distance and the neurovascular catheter follows.
Once both the
distal tip of the neurovascular catheter and the guidewire have reached the
treatment site, and
the distal tip of that catheter is appropriately situated, e.g., within the
mouth of .
an aneurysm to be treated, the guidewire is then withdrawn. The neurovascular
catheter then
has an open lumen to the outside of the body. The devices of this invention
are then pushed
through the lumen to the treatment site. They are held in place variously
because of their
shape, size, or volume. These concepts are described in the Ritchart et al
patent as well as
others. Once the vaso-occlusive devices are situated in the vascular site, the
embolism forms.
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The mechanical or solid vaso-occlusion device may be used as a lit with the
inventive
polymeric composition.
Modifications of the procedure and device described above, and the methods of
using
them in keeping with this invention will be apparent to those having slcill in
this mechanical
and surgical art. These variations are intended to be within the scope of the
claims that
follow.
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