U.S. patent application number 10/243633 was filed with the patent office on 2003-04-24 for intra-cochlear electrode with a partially detachable hydrophilic segment for deferred self-positioning.
Invention is credited to Abbasi, Farhang, Farhadi, Mohammad, Hochmair, Erwin S., Jolly, Claude, Mirzadeh, Hamid.
Application Number | 20030078516 10/243633 |
Document ID | / |
Family ID | 23253173 |
Filed Date | 2003-04-24 |
United States Patent
Application |
20030078516 |
Kind Code |
A1 |
Abbasi, Farhang ; et
al. |
April 24, 2003 |
Intra-cochlear electrode with a partially detachable hydrophilic
segment for deferred self-positioning
Abstract
A perimodiolar electrode for cochlear implantation includes an
electrode carrier having a front end and a back end. The electrode
carrier includes one or more contacts and a hydrophilic segment
that swells after insertion in a cochlea and detaches at least in
part from the carrier. In accordance with related embodiments, the
hydrophilic segment may detach from the electrode carrier between
the front end and the back end. The detached hydrophilic segment
may surround the modiolus of a scala tympani of the cochlea or the
inner wall of a scala tympani of the cochlea.
Inventors: |
Abbasi, Farhang; (Tehran,
IR) ; Jolly, Claude; (Voels, AT) ; Farhadi,
Mohammad; (Tehran, IR) ; Hochmair, Erwin S.;
(Axams, AT) ; Mirzadeh, Hamid; (Tehran,
IR) |
Correspondence
Address: |
BROMBERG & SUNSTEIN LLP
125 SUMMER STREET
BOSTON
MA
02110-1618
US
|
Family ID: |
23253173 |
Appl. No.: |
10/243633 |
Filed: |
September 13, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60322049 |
Sep 13, 2001 |
|
|
|
Current U.S.
Class: |
600/559 |
Current CPC
Class: |
A61N 1/0541
20130101 |
Class at
Publication: |
600/559 |
International
Class: |
A61B 005/00 |
Claims
What is claimed is:
1. A perimodiolar electrode for cochlear implantation comprising:
an electrode carrier having a front end and a back end, the carrier
including one or more contacts and a hydrophilic segment that
swells after insertion in a cochlea and detaches at least in part
from the carrier.
2. A perimodiolar electrode according to claim 1, wherein the
hydrophilic segment detaches from the electrode carrier between the
front end and the back end.
3. A perimodiolar electrode according to claim 1, wherein the
detached hydrophilic segment surrounds the modiolus of a scala
tympani of the cochlea.
4. A perimodiolar electrode according to claim 1, wherein the
detached hydrophilic segment surrounds the inner wall of a scala
tympani of the cochlea.
5. A perimodiolar electrode according to claim 1, wherein the
electrode carrier further comprises an elastomer.
6. A perimodiolar electrode according to claim 1, wherein the
hydrophilic segment comprises an elastomer and a metal-based
catalyst.
7. A perimodiolar electrode according to claim 6, wherein the
elastomer is silicone rubber.
8. A perimodiolar electrode according to claim 6, wherein the
elastomer is polyurethane.
9. A perimodiolar electrode according to claim 6, wherein the
catalyst is platinum-based.
10. A perimodiolar electrode according to claim 1, wherein the
hydrophilic segment includes a hydrogel.
11. A perimodiolar electrode according to claim 1, wherein the
hydrophilic segment includes a hydrogel and an elastomer.
12. A perimodiolar electrode according to claim 11, wherein the
elastomer is silicone rubber.
13. A method for forming a cochlear implant electrode, the method
comprising: preparing a hydrophilic segment; placing the
hydrophilic segment in a first section of an electrode mold;
placing electrical contacts in a second section of the electrode
mold; and injecting an elastomeric carrier into the mold.
14. A method according to claim 13, wherein preparing a hydrophilic
segment includes forming a hydrogel.
15. A method according to claim 13, wherein preparing a hydrophilic
segment includes a mixing a hydrogel and an elastomer.
16. A method according to claim 15, wherein mixing a hydrogel and
an elastomer includes mixing a hydrogel and liquid silicone
rubber.
17. A method according to claim 13, wherein preparing a hydrophilic
segment includes mixing an elastomer and a metal-based
catalyst.
18. A method according to claim 17, wherein the mixing an elastomer
and a metal-based catalyst includes mixing liquid silicone rubber
and a platinum-based catalyst.
19. A method for preparing a hydrophilic segment, the method
comprising: adding a metal-based catalyst to an elastomer;
mechanically mixing the metal-based catalyst and the elastomer to
form a crossed linked product; de-gasing the mixture; curing the
mixture in a segment mold; immersing the mixture in a
polymerization solution; and suspending the mixture in a sealed
glass reactor.
20. A method according claim 19, further comprising: raising the
temperature to allow monomer, initiator, and cross-linker to react;
and removing the monomers and unreacted hompolymers by soxlet
extraction in distilled water.
Description
[0001] The present application claims priority from U.S.
Provisional Application No. 60/322,049 which is incorporated
herein, in its entirety, by reference.
TECHNICAL FIELD
[0002] The present invention relates to cochlear implants, and more
particularly to a perimodiolar electrode designed for cochlear
implantation.
BACKGROUND
[0003] It is known to provide implants containing electrodes for
stimulation of nerve tissue. Such implants include, for example,
pacemakers, oral implants for stimulating muscle tissue in the
mouth of a subject or patient as well as nerve tissue associated
with a subject's sinus cavity and cochlear implants for stimulating
the tissues of the inner ear. In the case of cochlear implants, the
dynamic range of stimulation is often limited and channel
interaction often interferes with the effectiveness of the implant.
Channel interaction may be caused by the temporal integration of
charges at the membrane level or by the field overlap from
individual electrodes.
[0004] Another problem associated with cochlear implants, is a
tendency for the electrode to move after placement in the ear. Such
movement decreases the control of place stimulation, and
consequently lowers the hearing performance of the subject.
Movement of the electrode of a cochlear implant may also contribute
to unwanted and unnecessary nerve stimulation such as facial nerve
stimulation.
[0005] Recently, polydimethylsiloxane (PDMS)-based elastomers have
been used in a wide range of biomedical applications. Due to their
physiological inertness, good blood compatibility, low toxicity,
good thermal and oxidative stability, low modulus and anti-adhesive
properties. There has been an increasing interest in silicone
rubber/hydrogels multi-component systems for various biomedical
applications.
SUMMARY
[0006] In accordance with a first embodiment of the invention, a
perimodiolar electrode for cochlear implantation includes an
electrode carrier having a front end and a back end. The carrier
includes one or more contacts and a hydrophilic segment that swells
after insertion in a cochlea and detaches at least in part from the
carrier. In accordance with related embodiments, the hydrophilic
segment may detach from the electrode carrier between the front end
and the back end. The detached hydrophilic segment may surround the
modiolus of a scala tympani of the cochlea or the inner wall of a
scala tympani of the cochlea. In accordance with further related
embodiments, the electrode carrier may include an elastomer.
Similarly, the hydrophilic segment may include an elastomer and a
metal-based catalyst. The elastomer may be silicone rubber or the
elastomer may be polyurethane. The catalyst may be platinum-based.
In accordance with further related embodiments, the hydrophilic
segment may include a hydrogel or the hydrophilic segment may
include a hydrogel and an elastomer.
[0007] In accordance with another embodiment of the invention, a
method for forming a cochlear implant electrode includes preparing
a hydrophilic segment and placing the hydrophilic segment in a
first section of an electrode mold. Electrical contacts are placed
in a second section of the electrode mold and an elastomeric
carrier is injected into the mold. In accordance with related
embodiments, preparing a hydrophilic segment may include forming a
hydrogel. Similarly, preparing a hydrophilic segment may include
mixing a hydrogel and an elastomer. In addition, mixing a hydrogel
and an elastomer may include mixing a hydrogel and liquid silicone
rubber. In accordance with other related embodiments preparing a
hydrophilic segment may include mixing an elastomer and a
metal-based catalyst, and mixing an elastomer and a metal-based
catalyst may include mixing liquid silicone rubber and a
platinum-based catalyst.
[0008] In accordance with a further embodiment of the invention, a
method for preparing a hydrophilic segment includes adding a
metal-based catalyst to an elastomer and mechanically mixing the
metal-based catalyst and the elastomer to form a cross-linked
product. The mixture is de-gassed and cured in a segment mold. The
mixture is then immersed in a polymerization solution and suspended
in a sealed glass reactor. In accordance with related embodiments,
the method may also include raising the temperature to allow a
monomer, initiator, and cross-linker to react and removing monomers
and unreacted hompolymers by soxlet extraction in distilled
water.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The features of the invention will be more readily
understood by reference to the following detailed description,
taken with reference to the accompanying drawings, in which:
[0010] FIG. 1 is a graphical illustration of an electrode with a
hydrophylic segment prior to insertion into a cochlea in accordance
with one embodiment of the invention;
[0011] FIG. 2 is a pictorial illustration of the electrode of FIG.
1;
[0012] FIG. 3 is a pictorial illustration of the electrode of FIG.
2 showing initial swelling of the hydrophilic segment;
[0013] FIG. 4 is a pictorial illustration of an electrode in
accordance with an embodiment of the invention after insertion in a
scala tympani model;
[0014] FIG. 5 is a pictorial illustration of the electrode of FIG.
4 after the hydrophilic segment swells;
[0015] FIG. 6 is a flow chart illustrating a method for making a
perimodiolar electrode in accordance with another embodiment of the
invention; and
[0016] FIG. 7 is a flow chart illustrating a method for making a
hydrophilic segment in accordance with a further embodiment of the
invention.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0017] The present application pertains to the formation of
implantable apparatuses such as pacemakers, cochlear implants, and
other nerve stimulating devices. In accordance with the invention,
polydimethylsiloxane (PDMS)-based elastomers are used to aid in the
positioning of the implantable device subsequent to insertion into
the body of a subject or patient.
[0018] Modeling of intra-cochlear stimulation and animal EABR data
indicates that an electrode (or electrode array) positioned close
to the inner wall of the scala tympani would be beneficial to the
neuro-stimulation of cochlea implants (hence the name perimodiolar
electrode). There is a consensus that such a perimodiolar electrode
would lower psyco-accoustic threshold, increase the dynamic range
of stimulation, and reduce channel interaction. Other potential
benefits expected from a perimodiolar electrode array include
reduced power consumption to drive the implant, reduced side
effects for the subject or patient, implementation of innovative
stimulation schema, and better place coding of frequency. Further,
a perimodiolar electrode would allow a larger number of electrodes
to be used effectively. It is hoped that an increase in the control
of place stimulation would contribute toward raising the level of
subjects or patients with poor hearing performance. An additional,
potential benefit expected from a perimodiolar electrode is the
side effect of unwanted and unnecessary stimulation would be
reduced (especially reduced facial nerve stimulation).
[0019] FIGS. 1 and 2 illustrate a perimodiolar electrode with a
hydrophylic segment prior to insertion into a cochlea in accordance
with one embodiment of the invention. In accordance with this
embodiment, the perimodiolar electrode 101 is designed for
implantation into the cochlea of a subject and includes an
electrode which can surround the modiolus or the inner wall (also
called the medial wall) of the scala tympani. The electrode 101
includes a front end 104 and a back end 105. The electrode 101 also
includes a hydrophilic segment 102 that is initially substantially
fully connected to an electrode carrier 103. The cross sectional
shape of the electrode 101 may be ellipsoid, round, somewhat
rectangular, or any combination of the above. Similarly, the
electrode 101 may be tapered or un-tapered along its length. When
the hydrophilic segment 102 is substantially fully connected to the
electrode carrier 103, the overall electrode 101 appears as a
single unit, as shown in cross section A-A' of FIG. 1. When the
electrode 101 is fully or partially introduced in the scala tympani
spiral, it lays against the outer wall of the lumen.
[0020] FIGS. 3 and 5 illustrate that at some time after insertion
into the scala tympani, the hydrophilic segment 102 of the
electrode 101 begins swelling. The swelling of the hydrophilic
polymer causes an increase in diameter as well as an elongation of
the hydrophilic segment 102. Eventually, the swelling hydrophilic
segment 102 detaches itself from the electrode carrier 103, except
at the front end 104 and back end 105, as shown in FIGS. 3 and 5.
The swelling segment of the electrode stays in close contact with
the outer wall of the scala tympani. Elongation of the hydrophilic
segment 102 causes the electrode 101 to position itself against the
inner wall of the scala tympani as shown in FIG. 5.
[0021] The shape of the swelling hydrophilic segment 102 is
determined by the mold that receives the injection of the polymer
or other composition from which the segment it is formed. The shape
may be that of a half circle, an ellipsoid, a rectangle, or any
other shape which may promote or restrict the swelling properties
of the segment in relation to the electrode carrier. The increase
in volume of the swelling polymer is a control parameter and may
vary between 10% and 60% depending on the hydrophilic mixture. The
elongation of the swelling polymer may be anywhere between 10% and
50%. The relative size of the swelling polymer compared to the
electrode carrier may be arbitrary.
[0022] In its final state, the electrode 101 consists of two
connected branches and as shown in FIG. 3. The electrode carrier
103 and the hydrophilic segment 102 both have a front-end
connection 301 and a back-end connection 302. The front-end
connection 301 and back-end connection 302 consist of any means
which keeps the electrode carrier 103 and the hydrophilic segment
102 connected before, during, and after completion of swelling
while permitting detachment of the hydrophilic segment 102 over at
least part of the distance between the front-end connection 301 and
the back-end connection 302. Such a connection includes but is not
limited to polymer bonding, clip, pin-notch system, or any means as
deemed profitable.
[0023] In the embodiments described herein, the front-end
connection 301 is dis-connectable for the purpose of ex-plantation
of the electrode 101 when necessary. Thus, when the implant needs
replacement, the hydrophilic segment 102 is easily dis-connectable.
In order to achieve dis-connectibility, the hydrophilic segment 102
and the electrode carrier 103 may be joined by a bare PtIr ribbon
section, which comes out of the hydrophilic segment 102 and is
lodged snuggly or loosely in an oriented silicone cavity molded on
the electrode carrier 103. In case of revision surgery, the
hydrophilic segment 102 can be dislocated at the front-end
connection 301 by simply pulling back on the hydrophilic segment
102 with sufficient force. The front-end connection 301 may be any
other system known in the art and deemed advantageous. The back-end
connection 302 may be accomplished through polymer bonding.
Similarly, the back-end connection 302 may be accomplished through
a medical grade titanium clip such as those produced by Heinz Kurz
GmbH in Dusslingen, Germany. The branches may also be attached with
a PtIr wire, a silicone ring, or surgical sutures.
[0024] As can be seen in FIGS. 1, 2 and 3, the front end 104
generally projects beyond the hydrophilic segment 102 by some
distance. However, the length ratio between the front end 104 and
hydrophilic segment 102 may be anywhere from 0.3 to 3. The
electrode carrier 103 usually includes a single row of contacts 106
facing the modiolus and the number of contacts 106 may be
arbitrarily fixed. Further, the electrode 101 may have double or
more contacts to increase the surface area of the electrode and
reduce the impedance. The contact distribution between the front
end 104 and the rest of the electrode 101 can be arbitrary. For an
n contacts electrode, the front end 104 may receive anywhere from
0.1 n to 0.8 n of the contacts, as deemed advantageous for
stimulation. It may also be that the electrode 101 is built with no
front end 104 and that the hydrophilic segment 102 converges at the
tip of the electrode 101. In addition, the contact spacing on the
front end 104 may be equal, logarithmic, or equal and logarithmic.
Dummy contacts or markers can be placed between the last contact on
the electrode (most basal) and for a distance of up to 15 mm. Dummy
contact or marker separation is arbitrary. The role of the dummy
contact or marker is to give an indication of the insertion depth
of the electrode to the surgeon. The dummy contact or marker may be
shape coded to indicate distance along the array without having to
count the number of interval between the contacts.
[0025] FIG. 6 is a flow chart illustrating a method for making a
perimodiolar electrode in accordance with another embodiment of the
invention. In process 601 a hydrophilic segment is prepared and
then placed 602 in a first section of an electrode mold. Preparing
a hydrophilic segment may include forming a hydrogel. (For purposes
of the present application, the term "hydrogel" refers to a
coherent three-dimensional polymeric network that can imbibe large
quantities of water without the dissolution of the polymer
network.) Preparing a hydrophilic segment may further include a
mixing a hydrogel and an elastomer. In addition, mixing a hydrogel
and an elastomer may include mixing a hydrogel and liquid silicone
rubber. Similarly, preparing a hydrophilic segment may include
mixing an elastomer and a metal-based catalyst, and mixing an
elastomer and a metal-based catalyst may include mixing liquid
silicone rubber and a platinum-based catalyst. Electrical contacts
are placed 603 in a second section of the electrode mold and an
elastomeric carrier is injected 604 into the mold.
[0026] As discussed above, the hydrophilic segment can be prepared
from a hydrogel or a multi-component system of hydrogel and
elastomer (silicone rubber or polyurethane). The multi-component
system may be fabricated by co-polymerization, grafting, blending,
simultaneous interpenetrating polymer network, and sequential
interpenetrating polymer network. An interpenetrating polymer
network ("IPN") is defined as an intimate combination of two or
more polymers, at least one of which is synthesized or cross-linked
in the immediate presence of the other. The cross linking of at
least one of the polymer systems distinguishes an IPN from an
ordinary blend or a co-polymer.
[0027] FIG. 7 is a flow chart illustrating a method for making a
hydrophilic segment in accordance with a further embodiment of the
invention. In accordance with this embodiment, the hydrophilic
segment is prepared by adding, in process 701, a metal-based
catalyst to an elastomer. For example, liquid silicone rubber
("LSR") may be mixed with a platinum-based catalyst. The
metal-based catalyst and the elastomer are mechanically mixed 702
to form a cross-linked product. The mixture is de-gassed in process
703 and injected into a mold with a pre-designed cavity shaped for
the hydrophilic segment. After a curing (and optionally,
post-curing) the mixture in the segment mold in process 704, the
product is immersed 705 for approximately twenty-four hours at room
temperature in a polymerization solution that may include acrylic
acid or acrylamide monomer. The swollen hydrophilic segment samples
are suspended 706 in a sealed glass reactor. The temperature is
raised 707 and kept at a definite temperature to allow the monomer,
initiator, and cross-linker to react. The monomers and unreacted
hompolymers are removed 708 by soxlet extraction in distilled
water. As described above with respect to the embodiment of FIG. 6,
the hydrophilic segment is placed in a first part of a mold, and,
after fixation of wires inside a second part of the mold, LSR is
injected in to the mold to produce the final electrode.
[0028] There are several advantages of the design disclosed in the
present application over prior art: a) the electrode carrier and
hydrophilic polymer are and remain attached during the insertion
process; b) a surgeon does not have to perform any additional
positioning since the electrode is self positioning post
operatively; c) the connection to the electrode modiolus is
independent of morphology; d) the front end of the electrode has
less of a tendency to perforate the basilar membrane during the
positioning process; e) no special tools are needed for insertion
or positioning; f) the electrode and the insertion aperture on the
bony promontory may remain small in diameter; and g) a section of
the electrode (e.g., the front end) may be deeply inserted in the
cochlear.
[0029] While the invention has been described in connection with
specific embodiments thereof, it will be understood that it is
capable of further modification. This application is intended to
cover any variation, uses, or adaptations of the invention and
including such departures from the present disclosure as come
within known or customary practice in the art to which invention
pertains.
* * * * *