U.S. patent application number 11/089207 was filed with the patent office on 2005-08-04 for multi-layer coaxial vaso-occlusive device.
This patent application is currently assigned to MICROVENTION, INC.. Invention is credited to Martinez, George.
Application Number | 20050171572 11/089207 |
Document ID | / |
Family ID | 36577531 |
Filed Date | 2005-08-04 |
United States Patent
Application |
20050171572 |
Kind Code |
A1 |
Martinez, George |
August 4, 2005 |
Multi-layer coaxial vaso-occlusive device
Abstract
A vaso-occlusive device includes inner, intermediate, and outer
elements arranged coaxially. The inner element is a filamentous
element, preferably a microcoil. The intermediate element is made
of a non-metallic material, preferably an expansile polymer. The
outer element is substantially non-expansile and defines at least
one gap or opening through which the intermediate element is
exposed. In a preferred embodiment, when the intermediate element
is expanded, it protrudes through the at least one gap or opening
in the outer element and assumes a configuration with an
undulating, convexly-curved outer surface defining a chain of
arcuate segments, each having a diameter significantly greater than
the diameter of the outer element. The expanded configuration of
the intermediate element minimizes friction when the device is
deployed through a microcatheter, thereby reducing the likelihood
of buckling while maintaining excellent flexibility. The result is
a device with enhanced pushability and trackability when deployed
through a microcatheter.
Inventors: |
Martinez, George; (Brea,
CA) |
Correspondence
Address: |
KLEIN, O'NEILL & SINGH
2 PARK PLAZA
SUITE 510
IRVINE
CA
92614
US
|
Assignee: |
MICROVENTION, INC.
Aliso Viejo
CA
|
Family ID: |
36577531 |
Appl. No.: |
11/089207 |
Filed: |
March 24, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11089207 |
Mar 24, 2005 |
|
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10631981 |
Jul 31, 2003 |
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60400103 |
Aug 2, 2002 |
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Current U.S.
Class: |
606/200 |
Current CPC
Class: |
A61B 17/1215 20130101;
A61L 31/14 20130101; A61B 2017/0084 20130101; A61L 31/145 20130101;
A61B 17/12022 20130101; A61B 17/12177 20130101; A61B 17/12154
20130101; A61L 2430/36 20130101; A61B 2017/00867 20130101; A61B
17/12145 20130101; A61B 17/1219 20130101; A61B 2017/12054 20130101;
A61B 2017/00004 20130101 |
Class at
Publication: |
606/200 |
International
Class: |
A61M 029/00 |
Claims
1. A vaso-occlusive device, comprising: an elongate, flexible,
filamentous inner element; a non-metallic intermediate element
coaxially surrounding the inner element and in intimate contact
therewith; and an outer element coaxially surrounding the
intermediate element, the outer element defining an open area
through which the intermediate element is exposed; wherein along a
substantial predetermined portion of the length of the device, the
open area constitutes at least about 20 percent of the surface area
of device within the predetermined portion of its length.
2. The vaso-occlusive device of claim 1, wherein the intermediate
element includes an expansile polymeric material
3. The vaso-occlusive device of claim 1, wherein the outer element
includes a helical coil having a pitch that defines the open area
through which the intermediate element is exposed.
4. The vaso-occlusive device of claim 3, wherein the coil is formed
of a helically-wound filament, and wherein the pitch of the coil is
greater than the diameter of the filament.
5. The vaso-occlusive device of claim 4, wherein the pitch of the
coil is between about 5 percent and about 100 percent greater than
the diameter of the filament.
6. The vaso-occlusive device of claim 2, wherein the expansile
polymeric material comprises a hydrogel.
7. The vaso-occlusive device of claim 6, wherein the expansile
polymeric material consists essentially of a hydrogel.
8. The vaso-occlusive device of claim 7, wherein the hydrogel is of
a type that expands in response to a change in an environmental
parameter.
9. The vaso-occlusive device of claim 8, wherein the environmental
parameter is selected from the group consisting of temperature and
pH.
10. The vaso-occlusive device of claim 1, wherein the inner element
comprises at least two concentric microcoils.
11. The vaso-occlusive device of claim 1, wherein the inner element
defines a lumen containing a hollow, tubular core element.
12. The vaso-occlusive device of claim 1, wherein the inner element
defines a lumen containing a substantially solid core element.
13. The vaso-occlusive device of claim 1, wherein at least one of
the inner element and the intermediate element includes a material
selected from the group consisting of at least one of a drug, a
bioactive agent, a therapeutic compound, cellular material, genes,
collagen, and protein.
14. A vaso-occlusive device comprising: a filamentous inner
element; a non-metallic intermediate element coaxially surrounding
the inner element and in intimate contact therewith; and an outer
element coaxially surrounding the intermediate element and having
an open area through which the intermediate element is exposed, the
outer element comprising a helically-wound filament defining a
helical coil having a pitch that is greater than the diameter of
the filament.
15. The vaso-occlusive device of claim 14, wherein at least one of
the inner and intermediate elements is made at least in part of a
non-metallic biocompatible material.
16. The vaso-occlusive device of claim 15, wherein the pitch of the
coil is between about 5 percent and about 100 percent greater than
the diameter of the filament.
17. The vaso-occlusive device of claim 14, wherein the inner
element comprises a microcoil made of a biocompatible material
selected from the group consisting of metal wire and polymeric
filament, and wherein the intermediate element is formed of a
biocompatible polymeric material
18. The vaso-occlusive device of claim 14, wherein the intermediate
element includes an expansile polymeric material
19. The vaso-occlusive device of claim 14, wherein along a
substantial predetermined portion of the length of the device, the
open area constitutes at least about 20 percent of the surface area
of device within the predetermined portion of its length.
20. The vaso-occlusive device of claim 18, wherein the expansile
polymeric material comprises a hydrogel.
21. The vaso-occlusive device of claim 20, wherein the expansile
polymeric material consists essentially of a hydrogel.
22. The vaso-occlusive device of claim 21, wherein the hydrogel is
of a type that expands in response to a change in an environmental
parameter.
23. The vaso-occlusive device of claim 22, wherein the
environmental parameter is selected from the group consisting of
temperature and pH.
24. The vaso-occlusive device of claim 14, wherein the inner
element has proximal and distal ends, and wherein the outer element
comprises an open-wound helical coil portion extending between
proximal and distal end sections that are respectively attached to
the inner element adjacent to the proximal and distal ends of the
inner element, wherein the open-wound portion defines the open
area.
25. The vaso-occlusive device of claim 14, wherein at least one of
the inner element and the intermediate element includes a material
selected from the group consisting of at least one of a drug, a
bioactive agent, a therapeutic compound, cellular material, genes,
collagen, and protein.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation-in-Part of co-pending
application Ser. No. 10/631,981; filed Jul. 31, 2003, which prior
application claims the benefit, under 35 U.S.C. Section 119(e), of
provisional application No. 60/400,103, filed Jul. 31, 2002, the
disclosure of which is incorporated herein by reference.
FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable
BACKGROUND
[0003] This invention relates to vaso-occlusive devices, such as
vaso-occlusive coils and the like, for the embolization of vascular
aneurysms and similar vascular abnormalities. Specifically, the
invention is an improvement over existing two layer or two element
coaxial vaso-occlusive devices, particularly those having a polymer
coating or covering. In particular, the present invention is a
three layer or three element coaxial vaso-occlusive device that
provides improved durability, pushability, and trackability inside
a microcatheter. The characteristic termed "trackability" relates
to the ease of advancing one interventional device within or over
another, and it is related to friction and flexibility.
[0004] Vaso-occlusive devices are typically used within the
vasculature of the human body to block the flow of blood through a
vessel through the formation of an embolus. Vaso-occlusive devices
are also used to form an embolus within an aneurysm stemming from
the vessel. Vaso-occlusive devices can be formed of one or more
elements, generally delivered into the vasculature via a catheter
or similar mechanism.
[0005] The embolization of blood vessels is desired in a number of
clinical situations. For example, vascular embolization has been
used to control vascular bleeding, to occlude the blood supply to
tumors, and to occlude vascular aneurysms, particularly
intracranial aneurysms. In recent years, vascular embolization for
the treatment of aneurysms has received much attention. Several
different treatment modalities have been employed in the prior art.
One approach that has shown promise is the use of thrombogenic
microcoils. These microcoils may be made of a biocompatible metal
alloy (typically platinum and tungsten) or a suitable polymer. If
made of metal, the coil may be provided with Dacron fibers to
increase thrombogenicity. The coil is deployed through a
microcatheter to the vascular site. Examples of microcoils are
disclosed in the following U.S. Pat. No. 4,994,069--Ritchart et
al.; U.S. Pat. No. 5,133,731--Butler et al.; U.S. Pat. No.
5,226,911--Chee et al.; U.S. Pat. No. 5,312,415--Palermo; U.S. Pat.
No. 5,382,259--Phelps et al.; U.S. Pat. No. 5,382,260--Dormandy,
Jr. et al.; U.S. Pat. No. 5,476,472--Dormandy, Jr. et al.; U.S.
Pat. No. 5,578,074--Mirigian; U.S. Pat. No. 5,582,619--Ken; U.S.
Pat. No. 5,624,461--Mariant; U.S. Pat. No. 5,645,558--Horton; U.S.
Pat. No. 5,658,308--Snyder; and U.S. Pat. No. 5,718,711--Berenstein
et al.
[0006] A specific type of microcoil that has achieved a measure of
success is the Guglielmi Detachable Coil ("GDC"), described in U.S.
Pat. No. 5,122,136--Guglielmi et al. The GDC employs a platinum
wire coil fixed to a stainless steel delivery wire by a solder
connection. After the coil is placed inside an aneurysm, an
electrical current is applied to the delivery wire, which
electrolytically disintegrates the solder junction, thereby
detaching the coil from the delivery wire. The application of the
current also creates a positive electrical charge on the coil,
which attracts negatively-charged blood cells, platelets, and
fibrinogen, thereby increasing the thrombogenicity of the coil.
Several coils of different diameters and lengths can be packed into
an aneurysm until the aneurysm is completely filled. The coils thus
create and hold a thrombus within the aneurysm, inhibiting its
displacement and its fragmentation.
[0007] The advantages of the GDC procedure are the ability to
withdraw and relocate the coil if it migrates from its desired
location, and the enhanced ability to promote the formation of a
stable thrombus within the aneurysm.
[0008] A more recent development in the field of microcoil
vaso-occlusive devices is exemplified in U.S. Pat. No.
6,299,619--Greene, Jr. et al. and U.S. Pat. No. 6,602,261--Greene,
Jr. et al., both assigned to the assignee of the subject invention.
These patents disclose vaso-occlusive devices comprising a
microcoil with one or more expansile elements disposed on the outer
surface of the coil. The expansile elements may be formed of any of
a number of expansile polymeric hydrogels, or alternatively,
environmentally-sensitive polymers that expand in response to a
change in an environmental parameter (e.g., temperature or pH) when
exposed to a physiological environment, such as the blood
stream.
[0009] While the microcoils with expansile elements have exhibit
great promise in, for example, embolizing aneurysms of a wide
variety of sizes and configurations, the expansile elements
increase the frictional forces between the vaso-occlusive device
and a microcatheter through which the device is deployed.
Furthermore, depending on the configuration and material of the
expansile elements, the flexibility of the device may be reduced.
These factors may result in a device that has less than optimal
pushability (resistance to buckling) and reduced trackability (as
defined above).
[0010] There has thus been a long-felt, but as yet unsatisfied need
for a microcoil vaso-occlusive device that has all the advantages
of the expansile element type of device, and that also exhibits
enhanced pushability and trackability, with good durability
characteristics.
SUMMARY OF THE INVENTION
[0011] Broadly, the present invention is a vaso-occlusive device,
comprising three coaxial elements: an elongate, flexible,
filamentous inner element; a non-metallic intermediate element
coaxially surrounding the inner element and in intimate contact
therewith; and an outer element coaxially surrounding the
intermediate element and in intimate contact therewith, the outer
element including one or more openings or gaps through which the
intermediate element is exposed.
[0012] In one preferred embodiment of the invention, the inner
element is in the form of a helical coil made of a biocompatible,
radiopaque metal, and the intermediate element is a conformal
coating or layer on the inner element, the conformal coating or
layer being made of a soft polymeric material that is preferably an
expansile polymer. Advantageously, the polymeric hydrogel is an
environmentally-responsive hydrogel that expands upon exposure to
the physiological environment, for example, of the blood stream.
The polymer may advantageously be bio-absorbable or
biodegradable.
[0013] The outer element is advantageously a helical "over-coil"
that is loosely wound ("open-wound") over the intermediate element,
except at proximal and distal end sections, where it is tightly
wound ("close-wound"). The close-wound proximal and distal end
sections support the inner element, protecting it from damage
during deployment and any necessary repositioning, while also
securely binding the intermediate element to the inner element at
the proximal and distal ends of the device and restraining the
hydrogel of the intermediate element from expanding at the
respective ends of the device. The open-wound section between the
proximal and distal end sections creates a single, continuous
helical opening through which the intermediate element expands. The
helical configuration of the opening forces the expanded polymeric
intermediate element to assume the configuration of a chain of
arcuate segments protruding radially outwardly between the coils of
the over-coil, rather than that of a continuous polymeric layer
having a continuous, uninterrupted exterior surface. Because each
of the arcuate segments contacts the interior surface of a
microcatheter (e.g., during deployment) primarily at or near a
tangential contact point, the total contact area of the
intermediate element is reduced as compared to a continuous axial
polymeric element. This reduced contact area correspondingly
reduces the aggregate friction between the polymeric layer and the
microcatheter, thereby decreasing the resistance to manipulation of
the device. The open-wound section also creates hinge points
between the arcuate segments of the polymeric intermediate element,
thereby increasing the overall flexibility of the device.
[0014] It has been confirmed experimentally that the reduced
friction and increased flexibility afforded by the outer element,
and by the interaction between the outer and intermediate elements,
enhances the both the pushability and trackability of a device made
in accordance with the present invention, as compared, for example,
with prior art microcoil devices having expansile polymeric
coatings or elements on or along their exterior surfaces.
[0015] The invention thus provides a microcoil vaso-occlusive
device with an expansile element that allows the device to embolize
very efficiently a wide variety of vascular abnormalities, e.g.,
aneurysms of a wide variety of shapes, sizes, and locations, and
yet that exhibits enhanced pushability and trackability as compared
to the prior art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a perspective view of a vaso-occlusive device in
accordance with a preferred embodiment of the present
invention;
[0017] FIG. 2 is an axial cross-sectional view of the device of
FIG. 1;
[0018] FIG. 3 is a perspective view, similar to that of FIG. 1,
showing the expansile polymeric intermediate element in its
expanded state;
[0019] FIG. 4 is an axial cross-sectional view of FIG. 3;
[0020] FIG. 5 is a cross-sectional view taken along line 5-5 of
FIG. 2, but showing a first variant form of the invention, in which
the inner element comprises two coaxial helical microcoils;
[0021] FIG. 6 is a cross-sectional view similar to that of FIG. 5,
but showing a second variant form of the invention, in which the
inner element comprises three coaxial helical microcoils;
[0022] FIG. 7 is a cross-sectional view similar to that of FIG. 5,
but showing a third variant form of the invention, in which the
inner element comprises a helical microcoil defining a lumen
containing a solid coaxial core;
[0023] FIG. 8 is a cross-sectional view similar to that of FIG. 5,
but showing a fourth variant form of the invention, in which the
inner element comprises a helical microcoil defining a lumen
containing a hollow, tubular coaxial core; and
[0024] FIG. 9 is a perspective view of an alternative embodiment of
the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Referring to FIGS. 1-4, a vaso-occlusive device 10, in
accordance with a preferred embodiment of the invention, comprises
three elongate, coaxial elements: an inner element 11, a
non-metallic intermediate element 12, and a non-expansile outer
element 13 that covers at least a portion of the intermediate
element. The intermediate element 12 is in intimate contact with
both the inner element 11 and the outer element 13.
[0026] The inner element 11 is formed of a flexible, elongate
filament or wire that is preferably made of a material that allows
visualization under various medical imaging means, such as X-ray,
MRI, or ultrasound. Preferably, the inner element 11 is formed from
a length of wire made of any of various biocompatible, radiopaque
metals, such as platinum, tantalum, tungsten, gold, titanium,
nitinol, stainless steel, Elgiloy (cobalt-chromium-nickel), or
other suitable alloys known in the art. Alternatively, it can be
made from or include non-metallic materials, such as polymers,
collagen, proteins, drugs, biologic materials (e.g., cellular
material and genes), bioactive agents, therapeutic compounds, or
combinations of these materials. If made of a non-radiopaque
material, it should advantageously be doped or impregnated or
chemically modified to be visible with one or more imaging
techniques. Alternatively, it can be made of a material that is
highly visible by means of MRI or ultrasound. The inner element 11
can be formed in various configurations, including, but not limited
to, coils, rods, tubes, cables, braids, cut tubes, or other
elongate, flexible forms. As shown, it is in the form of a helical
coil, which may be preferred. In one specific embodiment, it is
formed at least in part of a multi-filar coil configuration, as
described in the co-owned U.S. Patent Application Publication No.
2004/0006362, the disclosure of which is incorporated herein by
reference.
[0027] The intermediate element 12 may be formed as a coating,
wrapping, tubular sleeve, or other construction to create a
substantially continuous surface coaxially around the inner element
11. Alternatively, it can be formed into a cylinder and then
skewered onto the inner core element 11, as described in the
co-owned and co-pending U.S. Patent Application Publication No.
2002/0177855, the disclosure of which is incorporated herein by
reference. The intermediate element 12 preferably covers all of the
length of the inner element 11, except for short proximal and
distal sections.
[0028] The intermediate element 12 may be made of any of various
suitable, substantially non-metallic, biocompatible materials,
including polymers, biopolymers, biologic materials, and
combinations of these materials. Suitable polymers include
cellulose, polypropylene, polyvinylpyrrolidone, polyacrylics,
polylactides, polyamides, polyvinyl alcohol (PVA), polyester,
polyurethane, polyglycolic acid, polyfluorocarbons (e.g., PTFE),
nylon, polymethylmethacrylate (PMMA), hydrogels, and silicones.
Exemplary biologic materials include alginates, hyaluronic acid,
fibrin, collagen and silk. Optionally, the intermediate element 12
can be impregnated, grafted, bound, or modified to deliver
therapeutic compounds, drugs, collagen, proteins, genes, bioactive
agents, or cellular material. See, e.g., U.S. Pat. No. 5,658,308
and International Publications Nos. WO 99/65401 and WO 00/27445,
the disclosures of which are incorporated herein by reference. In
one preferred embodiment, the intermediate element 12 is made of a
state-of-the-art bioabsorbable or biodegradable polymer, such as,
for example, those described in U.S. Patent Application
Publications Nos. 2002/0040239 and 2002/0020417, the disclosures of
which are incorporated herein by reference. In another preferred
embodiment, the intermediate element 12 is made of a soft conformal
material, and more preferably of an expansile material such as a
hydrogel.
[0029] The most preferred material is an environmentally responsive
hydrogel, such as that described in U.S. Patent Application
Publication No. 2002/0176880, the disclosure of which is
incorporated herein by reference. Specifically, the hydrogels
described in U.S. Patent Application Publication No. 2002/0176880
are of a type that undergoes controlled volumetric expansion in
response to changes in such environmental parameters as pH or
temperature. These hydrogels are prepared by forming a liquid
mixture that contains (a) at least one monomer and/or polymer, at
least a portion of which is sensitive to changes in an
environmental parameter; (b) a cross-linking agent; and (c) a
polymerization initiator. If desired, a porosigen (e.g., NaCl, ice
crystals, or sucrose) may be added to the mixture, and then removed
from the resultant solid hydrogel to provide a hydrogel with
sufficient porosity to permit cellular ingrowth. The controlled
rate of expansion is provided through the incorporation of
ethylenically unsaturated monomers with ionizable functional groups
(e.g., amines, carboxylic acids). For example, if acrylic acid is
incorporated into the crosslinked network, the hydrogel is
incubated in a low pH solution to protonate the carboxylic acids.
After the excess low pH solution is rinsed away and the hydrogel
dried, the hydrogel can be introduced through a microcatheter
filled with saline at physiological pH or with blood. The hydrogel
cannot expand until the carboxylic acid groups deprotonate.
Conversely, if an amine-containing monomer is incorporated into the
crosslinked network, the hydrogel is incubated in a high pH
solution to deprotonate amines. After the excess high pH solution
is rinsed away and the hydrogel dried, the hydrogel can be
introduced through a microcatheter filled with saline at
physiological pH or with blood. The hydrogel cannot expand until
the amine groups protonate.
[0030] More specifically, in a preferred formulation of the
hydrogel, the monomer solution is comprised of ethylenically
unsaturated monomers, an ethylenically unsaturated crosslinking
agent, a porosigen, and a solvent. At least a portion, preferably
10%-50%, and more preferably 10%-30%, of the monomers selected must
be pH sensitive. The preferred pH sensitive monomer is acrylic
acid. Methacrylic acid and derivatives of both acids will also
impart pH sensitivity. Since the mechanical properties of hydrogels
prepared exclusively with these acids are poor, a monomer to
provide additional mechanical properties should be selected. A
preferred monomer for providing mechanical properties is
acrylamide, which may be used in combination with one or more of
the above-mentioned pH sensitive monomers to impart additional
compressive strength or other mechanical properties. Preferred
concentrations of the monomers in the solvent range from 20% w/w to
30% w/w.
[0031] The crosslinking agent can be any multifunctional
ethylenically unsaturated compound, preferably
N,N'-methylenebisacrylamide. If biodegradation of the hydrogel
material is desired, a biodegradable crosslinking agent should be
selected. The concentrations of the crosslinking agent in the
solvent should be less than about 1% w/w, and preferably less than
about 0.1% w/w.
[0032] The porosity of the hydrogel material is provided by a
supersaturated suspension of a porosigen in the monomer solution. A
porosigen that is not soluble in the monomer solution, but is
soluble in the washing solution can also be used. Sodium chloride
is the preferred porosigen, but potassium chloride, ice, sucrose,
and sodium bicarbonate can also be used. It is preferred to control
the particle size of the porosigen to less than about 25 microns,
more preferably less than about 10 microns. The small particle size
aids in the suspension of the porosigen in the solvent. Preferred
concentrations of the porosigen range from about 5% w/w to about
50% w/w, more preferably about 10% w/w to about 20% w/w, in the
monomer solution. Alternatively, the porosigen can be omitted and a
non-porous hydrogel can be fabricated.
[0033] The solvent, if necessary, is selected based on the
solubilities of the monomers, crosslinking agent, and porosigen. If
a liquid monomer (e.g. 2-hydroxyethyl methacrylate) is used, a
solvent is not necessary. A preferred solvent is water, but ethyl
alcohol can also be used. Preferred concentrations of the solvent
range from about 20% w/w to about 80% w/w, more preferably about
50% w/w to about 80% w/w.
[0034] The crosslink density substantially affects the mechanical
properties of these hydrogel materials. The crosslink density (and
hence the mechanical properties) can best be manipulated through
changes in the monomer concentration, crosslinking agent
concentration, and solvent concentration. The crosslinking of the
monomer can be achieved through reduction-oxidation, radiation, and
heat. Radiation crosslinking of the monomer solution can be
achieved with ultraviolet light and visible light with suitable
initiators or ionizing radiation (e.g. electron beam or gamma ray)
without initiators. A preferred type of crosslinking initiator is
one that acts via reduction-oxidation. Specific examples of such
red/ox initiators that may be used in this embodiment of the
invention are ammonium persulfate and
N,N,N',N'-tetramethylethylenediamine.
[0035] After the polymerization is complete, the hydrogen is washed
with water, alcohol or other suitable washing solution(s) to remove
the porosigen(s), any unreacted, residual monomer(s) and any
unincorporated oligomers. Preferably this is accomplished by
initially washing the hydrogel in distilled water.
[0036] As discussed above, the control of the expansion rate of the
hydrogel is achieved through the protonation/deprotonation of
ionizable functional groups present on the hydrogel network. Once
the hydrogel has been prepared and the excess monomer and porosigen
have been washed away, the steps to control the rate of expansion
can be performed.
[0037] In embodiments where pH sensitive monomers with carboxylic
acid groups have been incorporated into the hydrogel network, the
hydrogel is incubated in a low pH solution. The free protons in the
solution protonate the carboxylic acid groups on the hydrogel
network. The duration and temperature of the incubation and the pH
of the solution influence the amount of control on the expansion
rate. Generally, the duration and temperature of the incubation are
directly proportional to the amount of expansion control, while the
solution pH is inversely proportional. It has been determined that
the water content of the treating solution also affects the
expansion control. In this regard, the hydrogel is able to expand
more in the treating solution and it is presumed that an increased
number of carboxylic acid groups are available for protonation. An
optimization of water content and pH is required for maximum
control on the expansion rate. After the incubation is concluded,
the excess treating solution is washed away and the hydrogel
material is dried. The hydrogel treated with the low pH solution
has been observed to dry down to a smaller dimension than the
untreated hydrogel. This is a desired effect since delivery of
these hydrogel materials through a microcatheter is desired.
[0038] If pH sensitive monomers with amine groups were incorporated
into the hydrogel network, the hydrogel is incubated in high pH
solution. Deprotonation occurs on the amine groups of the hydrogel
network at high pH. The duration and temperature of the incubation,
and the pH of the solution, influence the amount of control on the
expansion rate. Generally, the duration, temperature, and solution
pH of the incubation are directly proportional to the amount of
expansion control. After the incubation is concluded, the excess
treating solution is washed away and the hydrogel material is
dried.
[0039] For the embodiment of the vaso-occlusive device having an
intermediate element formed of an expansile polymeric hydrogel,
when the intermediate element 12 expands, the areas of the soft,
conformal intermediate element 12 that are not covered or
constrained by the outer element 13 extend radially outward through
the openings or gaps, or between the coils of the outer element 13
(as described below) to form an undulating outer surface comprising
a chain of arcuate segments, as a result of the constraint imposed
by the outer element 13. Because the arcuate segments of the
undulating outer surface contact the interior wall surface of a
microcatheter through which the device is deployed only at or near
tangential contact points proximate the apex of each segment, this
undulating or arcuate configuration provides reduced friction as
compared to a continuous or smooth surface of the same
material.
[0040] The outer element 13 is a flexible, elongate, substantially
tubular member, at least a substantial portion of the length of
which, and preferably most of the length of which, includes or
defines at least one opening or gap to allow the exposure and/or
protrusion of the intermediate element 12. Suitable configurations
for the outer element 13 include helical coils, braids, and slotted
or spiral-cut tubes. The outer element 13 may be made of any
suitable biocompatible metal or polymer, including those listed
above for the inner element 11. For those embodiments using a soft,
conformal intermediate element 12, the outer element 13 should have
sufficient radial strength to compress or restrain the intermediate
element 12.
[0041] Preferably, the openings in the outer element 13 are such
that, along a substantial portion of the length of the device, the
open area of the outer element 13 is at least about 20%, and more
preferably, more than about 40%, of the total external surface area
of the device between the proximal and distal limits of that
portion of the device length. For example, near the ends of the
device, the outer element 13 may have a relatively low percentage
of open area (i.e., less than about 20%), while for the greater
part of the length of the device between the end portions thereof,
a greater percentage (i.e., at least about 20%, and preferably more
than about 40%) of the outer element 13 may be open, allowing a
greater exposure of the intermediate element 12 through the outer
element 13. Preferably, the portion of the outer element 13
covering at least about 75% of the overall length of the device
will have the greater percentage of open area.
[0042] In the most preferred embodiment, the device comprises an
inner element 11 formed of a tightly-wound ("close-wound") helical
coil of a biocompatible metal wire (e.g., platinum alloy), an
intermediate element 12 of a hydrophilic expansile polymer (e.g.,
hydrogel), and an outer element 13 in the form of a biocompatible
metal or polymer helical coil that is open-wound for most of its
length, with a close-wound proximal end section 14 and a
close-wound distal end section 15. The open-wound portion of the
outer element 13 defines a single, continuous, helical opening or
gap. The coil is preferably made from a wire that has a diameter of
no more than about 0.15 mm. The pitch of the coil of which the
outer element 13 is comprised may be up to ten times the diameter
of filament from which the coil is wound, and preferably between
about 5 percent and about 100 percent greater than the diameter of
the filament.
[0043] A coupling element 16 is advantageously attached to the
proximal end of the inner element 11 for detachable attachment to a
deployment device (not shown). A rounded obturator tip 17 may be
attached to the distal end of the inner element 11.
[0044] In the above-described most preferred embodiment, the
hydrogel of the intermediate element 12 expands or swells upon
exposure to an aqueous environment (e.g., blood). Preferably, the
hydrogel expands to between about two times and about 20 times its
original volume. As shown in FIGS. 3 and 4, the swollen or expanded
intermediate element 12 protrudes through the helical opening or
gap defined between the coils of the open-wound section of the
outer element 13 to form an undulating, convexly-curved surface
defining a chain of arcuate or rounded segments, each having a
diameter that is substantially greater than the diameter of the
outer element 13.
[0045] The helical outer element 13 described above may be
considered as defining a single, helical opening or gap, or it may
be viewed as defining a plurality of connected openings or gaps,
each defined between an adjacent pair of windings of the coil of
the outer element 13. Alternatively, if the outer element 13 is
formed as a slotted tube, for example, the outer element 13 will be
seen to define a plurality of discrete openings or gaps in its
axial middle section that are functionally equivalent to the
helical opening(s) defined in the illustrated embodiment.
[0046] The device 10 can be constructed with various radial
thickness of each coaxial element to provide different handling
characteristics. Preferably, the inner element 11 has a diameter of
between about 0.075 mm and 0.75 mm; the intermediate element 12 has
a thickness of between about 0.025 mm and 1.00 mm; and the outer
element 13 has a thickness of between about 0.025 mm and 0.25 mm.
For the embodiments that use an expansile intermediate element 12,
these thicknesses are measured in the non-expanded state.
Preferably, the outer diameter of the outer element 13 is actually
somewhat less than the expanded or swollen diameter of the
intermediate element 12, so that the latter will readily expand
through the openings or gaps in the outer element 13.
[0047] FIGS. 5 and 6 illustrate variants of the preferred
embodiment of the invention, with multilayer structures for the
inner element. Specifically, FIG. 5 shows a first variant having an
inner element comprising first and second coaxial coils 110a, 110b,
respectively. FIG. 6 shows a second variant having an inner element
comprising first, second, and third coaxial coils 210a, 210b, and
210c, respectively. Suitable coaxial coil structures and their
methods of manufacture are disclosed in commonly owned and
co-pending U.S. Patent Application Publication No. 2004/0006363,
the disclosure of which is incorporated herein by reference. The
inner element may, in fact, comprise four or more coaxial layers.
Similarly, the outer element 13 may comprise multiple coaxial
helical coil layers, provided that a suitable percentage of the
surface area of the outer element remains open for the exposure of
the intermediate element, as explained above.
[0048] FIG. 7 illustrates a third variant of the present invention,
in which the inner element comprises a helical coil 310 defining an
axial lumen, at least a substantial portion of the length of which
is filled with a solid core member 320. The solid core member 320
may be impregnated with a therapeutic agent that can be absorbed
into the bloodstream.
[0049] FIG. 8 illustrates a fourth variant of the invention, in
which the inner element comprises a helical coil 410 defining an
axial lumen, at least a substantial portion of which contains a
hollow, tubular core member 420. The tubular core member 340
provides additional strength, and it may be filled with a liquid
therapeutic agent (not shown).
[0050] FIG. 9 shows a vaso-occlusive device 10' in accordance with
an alternative embodiment of the invention. This embodiment
includes an outer element 13' with a distal section 15' that is not
close wound, but is, instead, made with small gaps of approximately
5% to 100% of the diameter of the wire or filament of which the
outer element 13' is made. These gaps make the distal section 15'
of the device 10' more flexible in the area where the outer element
13' overlaps the inner element 11'.
[0051] In the embodiment shown in FIG. 9, the proximal ends of both
the inner element 11' and the outer element 13' are both
advantageously attached to a coupling element 16' by soldering or
welding. The attachment of both the inner element 11' and the outer
element 13' to the coupling element 16' makes the proximal end of
the device 10' more resistant to deformation during deployment and
implantation.
[0052] In any of the embodiments described above, a portion of the
outer element and/or a portion of the intermediate element may be
modified (as by coating, for example) to include structure that
promotes the adhesion of beneficial cells or growth factors. An
exemplary coating that be used for this purpose is disclosed in
U.S. Patent Application Publication No. 2002/0049495, the
disclosure of which is incorporated herein by reference.
[0053] As indicated above, the present invention provides good
trackability in a microcatheter. In other words, it is easily
advanced through a catheter without binding against or moving the
catheter. This advantage is achieved through reduced friction and
reduced buckling at the ends of the device. The force required to
advance the device through a typical microcatheter would normally
be less than about 0.7 lbs.
[0054] The device is preferably detachable from a flexible,
elongate delivery apparatus (not shown), such as a wire, a pusher
tube, or the like. Exemplary detachment systems known in the art
include electrolytic, mechanical, electromechanical, thermal,
ultrasonic, and hydraulic detachment mechanisms. The device may be
formed into a secondary configuration, such as a helical coil, a
sphere, an ovoid, or any other suitable two- or three-dimensional
shape known in the art of vaso-occlusive devices. Alternatively,
the device can be left in a relatively straight configuration with
or without a curvature at the end (such as a "J"
configuration).
[0055] In any of the above-described embodiments, either the inner
element or the intermediate element, or both, may be formed so as
to be substantially stretch-resistant, so as to limit the
stretching of the entire device (including the outer element) if
the device needs to be partially withdrawn for repositioning or the
like. It will be appreciated that a number of the materials
discussed above will be stretch-resistant to varying degrees.
[0056] The device is useful for the occlusion and/or embolization
of blood vessels, other vascular spaces such as aneurysms, and
other tubular or saccular organs or spaces throughout the body.
Specific applications where it may be useful include the occlusion
of cerebral aneurysms, aortic aneurysms, fistulas, fallopian tubes,
cardiac septal defects, patent foramen ovale, and the left atrial
appendage of the heart. For some of these applications, it may be
preferable to use devices with dimensions larger than those
specified above.
[0057] Although preferred embodiments of the invention have been
described in this specification and the accompanying drawings, it
will be appreciated that a number of variations and modifications
may suggest themselves to those skilled in the pertinent arts.
Thus, the scope of the present invention is not limited to the
specific embodiments and examples described herein, but should be
deemed to encompass alternative embodiments and equivalents, as
determined by a fair reading of the claims that follow.
* * * * *