U.S. patent application number 10/825358 was filed with the patent office on 2004-12-02 for electrode array with bendable tip.
Invention is credited to Dadd, Fysh, Gibson, Peter, Treaba, Claudiu.
Application Number | 20040243212 10/825358 |
Document ID | / |
Family ID | 31500905 |
Filed Date | 2004-12-02 |
United States Patent
Application |
20040243212 |
Kind Code |
A1 |
Dadd, Fysh ; et al. |
December 2, 2004 |
Electrode array with bendable tip
Abstract
The present invention provides a tip member for inserting into
the cochlea, a device comprising: an elongate member including at
least one electrode mounted thereon; and a tip member extending
distally from a distal end of the elongate member, the tip member
comprising a tapered portion tapering distally and a blunt end
portion at a distal end of the tapered portion, wherein the tip
member is resiliently flexible, and a method for making such a
device.
Inventors: |
Dadd, Fysh; (Meadowbank,
AU) ; Treaba, Claudiu; (Wollstonecraft, AU) ;
Gibson, Peter; (South Coogee, AU) |
Correspondence
Address: |
JAGTIANI + GUTTAG
10363-A DEMOCRACY LANE
FAIRFAX
VA
22030
US
|
Family ID: |
31500905 |
Appl. No.: |
10/825358 |
Filed: |
April 16, 2004 |
Current U.S.
Class: |
607/137 |
Current CPC
Class: |
A61N 1/0541
20130101 |
Class at
Publication: |
607/137 |
International
Class: |
A61N 001/05 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 17, 2003 |
AU |
2003901868 |
Claims
What is claimed is:
1. A device comprising: an elongate member including at least one
electrode mounted thereon; and a tip member extending distally from
a distal end of said elongate member, said tip member comprising a
tapered portion tapering distally and a blunt end portion at a
distal end of said tapered portion, wherein said tip member is
resiliently flexible.
2. The device of claim 1, wherein said tip member further comprises
a barrel portion at a proximal end of said tip member and wherein
said tapered portion extends distally from a distal end of said
barrel portion.
3. The device of claim 2, wherein said barrel portion is
substantially cylindrical in shape.
4. The device of claim 3, wherein said elongate member distal end
has a greater diameter or minimum width than the diameter of said
barrel portion, wherein a liquid silicone rubber adhesive is used
to adhere said tip member to said elongate member, and wherein said
liquid silicone rubber adhesive is used to form a tapered region in
a gap formed by said elongate member distal end and said barrel
portion.
5. The device of claim 3, wherein said barrel portion is about 0.4
mm in length.
6. The device of claim 3, wherein said barrel portion is about 0.45
mm in diameter.
7. The device of claim 1, wherein said tapered portion is
substantially frusto-conical in shape.
8. The device of claim 7, wherein said tapered portion tapers
continuously.
9. The device of claim 7, wherein said tapered portion is about
0.76 mm.
10. The device of claim 7, wherein said diameter of said tapered
portion decreases from about 0.45 mm at a proximal end of said
tapered portion to about 0.2 mm at said distal end of said tapered
portion.
11. The device of claim 7, wherein the angle between notional
diametrically opposed sides of said tapered portion is about
18.9.degree..
12. The device of claim 1, wherein said blunt end portion has a
part-ellipsoidal shape.
13. The device of claim 1, wherein said blunt end portion has a
part-spherical shape.
14. The device of claim 1, wherein said tip member is integral with
said elongate member.
15. The device of claim 1, wherein said tip member is mounted on
said distal end of said elongate member.
16. The device of claim 1, wherein said tip member includes a lumen
therein.
17. The device of claim 16, wherein elongated member includes a
lumen therein for allowing a stiffening element to be inserted
through said elongate member and for allowing a distal end of said
stiffening element extends into said lumen in said tip member.
18. The device of claim 17, further comprising said stiffening
element inserted through said elongate member and into said tip
member.
19. The device of claim 1, wherein said device has a shape and size
that allows said device to be inserted in a human cochlea.
20. The device of claim 1, wherein said tip member has
substantially uniform bending stress distribution in an axial
direction.
21. The device of claim 1, wherein said tip member is adhered to
said elongate member using a liquid silicone rubber adhesive.
22. The device of claim 1, wherein said electrode is part of a
means for applying a tissue stimulation.
23. A tip member comprising: a barrel portion; a tapered portion at
a distal end of said barrel portion, said tapered portion tapering
distally; and a blunt end portion at a distal end of said tapered
portion, wherein said tip member has a substantially uniform
bending stress distribution in an axial direction and wherein said
tip member has a shape and size that allows said tip member to be
inserted in a human cochlea.
24. A method for making a device comprising the steps of: (a)
providing an elongate member; and (b) mounting a tip member on said
elongate member, wherein said tip member comprises a barrel
portion, a tapered portion tapering distally from at distal end of
said barrel portion and a blunt end portion at a distal end of said
tapered portion, wherein said tip member has a substantially
uniform bending stress distribution in an axial direction and
wherein said tip member has a shape and size that allows said tip
member to be inserted in a human cochlea.
25. The method of claim 24, wherein step (a) comprises adhering
said tip member to said elongate member using a liquid silicone
rubber adhesive.
26. The method of claim 25, wherein said elongate member distal end
has a greater diameter or minimum width than the diameter of said
barrel portion, and wherein said method further comprises using
said liquid silicone adhesive to form a tapered region in a gap
formed by said elongate member distal end and said barrel
portion.
27. The method of claim 24, wherein said elongate member includes
at least one electrode mounted thereon.
28. The method of claim 27, wherein said electrode is part of a
means for applying a tissue stimulation.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application makes reference to and claims priority from
the following co-pending Australian Provisional Specification:
Australian Provisional Application No. 2003901868, entitled
"Electrode Array with Bendable Tip" filed Apr. 17, 2003. The entire
disclosure and contents of the above applications are hereby
incorporated by reference.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to electrode arrays for use
with prostheses, such as hearing prostheses in which an electrode
array is implanted in a cochlea of a recipient.
[0004] 2. Related Art
[0005] Electrode array devices, such as cochlear implant electrode
array devices, generally consist of a plurality of electrode
elements which are adapted to apply electrical stimulation to
surrounding tissue to stimulate the surrounding nerves. In cochlear
implant applications, the electrode array device is implanted
within the cochlea of a recipient and applies stimulation to the
auditory nerves via a series of electrode elements, in accordance
with a set stimulation pattern, controlled by an implanted
stimulator unit.
[0006] The implanted stimulator unit typically applies the
stimulation in a manner which is representative of a detected
acoustic signal, such that the stimulation pattern applied by the
electrode array device stimulates the auditory nerves and elicits a
sensation that closely resembles the natural sensation of the
detected acoustic signal.
[0007] In this regard, it is important that when implanting
electrode arrays in sensitive regions of the body, such as the
cochlea, that the electrode array be designed in such a manner as
to be flexible enough to reduce damage to the sensitive structures
of the surrounding tissue, and yet be rigid enough to ensure that
the general shape and form of the electrode array is maintained
during the insertion procedure such that the electrode array can
perform as intended.
[0008] In electrode arrays of the type used for implantation in the
cochlea, it has been found that the tip of the array plays an
important role during the insertion procedure. In this regard,
there have been attempts to design the tip of the electrode array
in a manner that reduces the possibility of the tip of the
electrode array from puncturing or abrading the sensitive tissues
of the cochlea and causing damage to the nerve structures which the
implant is attempting to stimulate.
[0009] One such early attempt is described in Australian Patent No.
582264 to Clark et al. This patent discloses the provision of tip
or distal end of the electrode array being provided with at least
one discontinuity that increases the flexibility of the tip. The
tip is generally an extension of the existing electrode array and
is made from the same material, but is extending beyond the most
distal electrode element.
[0010] One problem with such a design is that the tips were
typically relatively too flexible such that during the insertion
process the tip would catch on the wall of the cochlea and cause
the array to bend back on itself, thereby potentially causing more
damage to the cochlea than would ordinarily be the case should the
flexible tip not be provided. Such a situation can also result in
an implant being incorrectly positioned from the auditory nerve
potentially reducing the effectiveness of the array in capturing
and stimulating the appropriate nerves. Further, such a situation
where the array folds upon itself can cause unwanted interaction or
shorting between electrode elements that may be touching, thereby
reducing the number of electrodes that may be operational for
stimulation.
[0011] Other designs have also considered providing an extended
flexible tip of a lead or electrode array to aid in insertion, such
as that described in EP 0 919 254 to Bakels et al. However, as
mentioned above, such tips have all been designed with flexibility
in mind rather than stability of the tip, hence all suffer from
similar problems as identified above.
SUMMARY
[0012] It is therefore an object of the present invention to
provide a tip member for an electrode array that is designed to
provide stability and flexibility to the electrode array and to
assist in guiding the electrode array during insertion thereof.
[0013] According to a first broad aspect of the present invention,
there is provided a device comprising: an elongate member including
at least one electrode mounted thereon; and a tip member extending
distally from a distal end of the elongate member, the tip member
comprising a tapered portion tapering distally and a blunt end
portion at a distal end of the tapered portion, wherein the tip
member is resiliently flexible.
[0014] According to a second broad aspect of the present invention,
there is provided a tip member comprising: a barrel portion; a
tapered portion at a distal end of the barrel portion, the tapered
portion tapering distally; and a blunt end portion at a distal end
of the tapered portion, wherein the tip member has a substantially
uniform bending stress distribution in an axial direction and
wherein the tip member has a shape and size that allows the tip
member to be in inserted in a human cochlea.
[0015] According to a third broad aspect of the present invention,
there is provided a method for making a device comprising the steps
of: (a) providing an elongate member; and (b) mounting a tip member
on the elongate member, wherein the tip member comprises a barrel
portion, a tapered portion tapering distally from at distal end of
the barrel portion and a blunt end portion at a distal end of the
tapered portion, wherein the tip member has a substantially uniform
bending stress distribution in an axial direction and wherein the
tip member has a shape and size that allows the tip member to be in
inserted in a human cochlea.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The invention will be described in conjunction with the
accompanying drawings, in which:
[0017] FIG. 1 is a force diagram of a prior art tip member used in
electrode arrays;
[0018] FIG. 2 is a force diagram of another prior art tip member
used in electrode arrays;
[0019] FIG. 3A is a side view of a tip member in accordance with an
embodiment of the present invention;
[0020] FIG. 3B is cross-sectional view of the tip member of FIG.
3A, taken along line B-B.
[0021] FIG. 4A is a cross-sectional view of an electrode array
device in accordance with one embodiment of the present invention
in which tip member of FIGS. 3A and 3B are mounted on an elongate
member with only a portion of the elongate member being shown for
simplicity;
[0022] FIG. 4B is an end-on view of the electrode array device of
FIG. 4A;
[0023] FIG. 5 is a simplified side elevational view of the
electrode array device of FIGS. 4A and 4B of the present invention
depicted in an intermediate orientation;
[0024] FIG. 6 is a simplified part sectional, part side elevational
view of the electrode array device of FIGS. 4A and 4B depicted in
its pre-formed orientation following insertion in the cochlea;
[0025] FIG. 7 is a simplified side elevation view of an electrode
array device in accordance with another embodiment of the present
invention depicted in an intermediate orientation; and
[0026] FIG. 8 is a cross-sectional view of an electrode array
device in accordance with one embodiment of the present invention
in which tip member of FIGS. 3A and 3B are mounted on an elongate
member with only a portion of the elongate member being shown for
simplicity.
DETAILED DESCRIPTION
[0027] It is advantageous to define several terms before describing
the invention. It should be appreciated that the following
definitions are used throughout this application.
[0028] Definitions
[0029] Where the definition of terms departs from the commonly used
meaning of the term, applicant intends to utilize the definitions
provided below, unless specifically indicated.
[0030] For the purposes of the present invention the term "uniform
bending stress distribution" refers to the conventional meaning of
the term uniform bending stress distribution. For example, a tip
member that has uniform bending stress distribution may be
envisioned as a constant-strength cantilever beam where bending
stresses throughout the beam are equal to those at the fixed end,
that is, the junction of the tip member with the elongate member on
which the tip member is mounted.
[0031] For the purposes of the present invention, the term "distal"
refers to the end of a device or the end of a part of a device that
is to be inserted into a cochlea.
[0032] For the purposes of the present invention, the term
"tapering distally" refers to a device or part that is tapered and
in which the diameter of the device or part is smaller at the
distal end of the device or part than at the proximal end of the
device or part.
[0033] For the purposes of the present invention, the term
"proximal" refers to the end of a device or the end of a part of a
device that is at the opposite end of the device or the part of
device from the distal end.
[0034] For the purposes of the present invention, the term "axial
direction" refers to a line extending through a device between the
distal end of the device to the proximal end of the device in
either direction.
[0035] For the purposes of the present invention, the term "axis"
refers to the conventional meaning of the term "axis", i.e. a line
through the middle of a device or part of a device. The "long axis"
of a device or part of a device is the longest axis that may be
drawn through a device or part of device. In the devices of the
present invention, the long axis usually extends between the
proximal end and the distal end.
[0036] For the purposes of the present invention, the term
"cylindrical" refers to the general meaning of the term
"cylindrical". The term "substantially cylindrical" refers to any
part of a device having a generally cylindrical shape. For example,
a part of a device may be substantially cylindrical and still
include various raised or etched surface patterns and/or textures
and may vary in width throughout the length of the part as long as
the object has roughly the same diameter at the proximal and distal
ends of the part.
[0037] For the purposes of the present invention, the term
"frusto-conical" refers to the general meaning of the term
"frusto-conical". The term "substantially frusto-conical" refers to
any part of a device having a generally frusto-conical shape. A
part of a device may be substantially frusto-conical and still
include various raised or etched surface patterns and/or textures
and may taper non-continuously as the object has a proximal or
distal end that is narrower than the opposite end of the part.
[0038] For the purpose of the present invention, the term
"continuous taper" refers to a part that tapers at a set rate
throughout the length of the part. For example, a tapered portion
of a tip member that is frusto-conical has a continuous taper in
which the diameter of the tapered portion decreases at a fixed rate
from the proximal end of the tapered portion to the distal end of
the tapered portion. An example of a tapered portion of a tip
member of the present invention having a continuous taper is
illustrated in FIG. 5.
[0039] For the purposes of the present invention, the term
"non-continuous taper" refers to a part that does not taper at a
set rate throughout the length of the part. For example, a part
that is substantially frusto-conical may have regions where the
width of the part remains constant without tapering, but which,
viewed as a whole, tapers from one end to the other end of the part
in an axial direction.
[0040] For the purposes of the present invention, the term
"notional diametrically opposed sides" refers to the two opposing
angled edges formed by cutting a tapered portion of a tip member of
the present invention in half along the tapered portion's axis. The
angle between two notional diametrically opposed sides is the angle
formed by extending two lines from the opposed sides, one line from
each side, in a distal direction until the lines meet.
[0041] For the purposes of the present invention, the term "blunt"
refers to the usually meaning of the term blunt, i.e. not sharp.
The blunt end of a tip member of the present invention may be
convex or concave. The blunt end may be rounded, such as
part-spherical, part-ellipsoidal, part-paraboloidal, etc.
[0042] For the purposes of the present invention, the term
"part-spherical" refers to a shape formed by cutting through a
sphere to form two parts. For example, a hemisphere would be a
part-spherical shape formed by cutting a sphere in half to form two
parts.
[0043] For the purposes of the present invention, the term
"part-ellipsoidal" refers to a shape formed by cutting through an
ellipsoid. A part-ellipsoidal shape may be formed by cutting an
ellipsoid in half or by cutting an ellipsoid in two form two
unequally sized parts.
[0044] For the purposes of the present invention, the term
"part-paraboloidal" refers to a shape formed by cutting through a
paraboloid.
[0045] For the purposes of the present invention, the term
"resiliently flexible" refers to a flexible tip member than will
not undergo fold-over or bend backwards during insertion into a
cochlea when exposed to usual insertion forces necessary to insert
a tip member of an electrode array into a cochlea.
[0046] Description
[0047] In one embodiment, the present invention provides an
implantable tissue stimulating device, such as a electrode array
device, comprising: an elongate electrode carrier member (elongate
member) having a body having a first end, and a resiliently
flexible tip member extending distally from a distal end of the
body. The elongate member has at least one electrode mounted
thereon to apply a preselected tissue stimulation, such stimulation
of a nerve in a cochlea. The tip member includes a tapered portion
tapering distally and a blunt end at a distal end of the tapered
portion. In one embodiment of the present invention, the tip member
includes a barrel portion at a proximal end of the tip member and
the tapered portion extends distally from a distal end of the
barrel portion. In a preferred embodiment, the tip member has a
length of about 1.2 mm.
[0048] In one embodiment of the present invention, the tip member
may be formed of the same material as the body of the elongate
member. In another embodiment, the tip member may be formed of a
different material to that of the body of the elongate member.
[0049] The tip member may be formed separately to the body of the
elongate member and mounted thereto. For example, the tip member
may be adhered using an adhesive to the first end of the body of
the elongate member. Alternatively, the tip member may be mounted
on the tip member by other means such as by snapping the tip member
over a mating distal end portion of the elongate member, screwing
the tip member onto the end a threaded distal end of the elongate
member, hot welding together the tip member and the elongate
member, etc. In another embodiment, the tip member may be
integrally formed with the body of the elongate member. The tip
member may be formed from a silicone material. In another
embodiment, the tip member may be formed of an elastomeric
material, such as polyurethane. In general, the tip member is made
of any material that allows the tip member to be resiliently
flexible.
[0050] In some embodiments the barrel portion of the tip member may
be part of a separate tip member that is joined to an elongate
member, such as the embodiment of the present invention illustrated
in FIGS. 5. In other embodiments, the tip member may be formed as
part of an elongate member, such as the embodiment illustrated in
FIG. 7. The elongate member may also have a taper, but the tapered
portion of the tip member will taper at a faster rate than the
overall taper of the elongate member. Examples of tapered elongate
members are illustrated in FIGS. 5 and 7.
[0051] In one embodiment of the present invention, the barrel
portion of a tip member may be substantially cylindrical in form
for a portion of its length. In another embodiment, the barrel
portion may be substantially cylindrical in form. In other
embodiments the barrel portion may be various shapes and include
various types of contouring. The barrel portion also may have
various types of cross-section besides the circular cross-section
of a cylindrical barrel. For example, the barrel portion may be
elliptical in cross-section, rectangular with rounded comers in
cross-section, triangular with rounded comers in cross-section,
etc.
[0052] The barrel portion in some embodiments may be slightly
tapered, but in such embodiments the tapered portion tapers at a
faster rate than the barrel portion.
[0053] In one embodiment of the present invention, the barrel
portion is about or exactly 0.4 mm in length from the proximal end
of the barrel portion to the distal end of the barrel portion where
the tapered portion begins. In one preferred embodiment where the
barrel portion is cylindrical, the diameter of the barrel portion
may be exactly or about 0.45 mm.
[0054] In one embodiment for use with a tip member having a barrel
portion with a 0.45 mm diameter the elongate member on which the
tip member is mounted is slightly tapered and has a maximum
diameter at its proximal end of about 0.80 mm and a minimum width
or diameter at its distal end of about 0.5 mm. When the diameter of
the distal end of the elongate member is larger diameter of the
barrel portion or a different cross-sectional shape, such as
illustrated in the embodiment of FIGS. 4A and 4B, various means may
be used to ensure a smooth transition between the distal end of the
elongate member and the barrel portion. For example, when a
silicone adhesive is used to adhere the tip member to the elongate
member, some of the silicone adhesive may be used on the surface of
the barrel portion to taper to form tapered region filling the gap
between the edges of the elongate member and the edges of the
barrel portion as shown in FIG. 4A.
[0055] The barrel portion preferably includes a lumen therein that
extends for some or all of its length of the barrel portion. An
example of such lumen is shown in the embodiment of the present
invention illustrated in FIG. 3B. In one preferred embodiment, the
lumen may be about 0.3 mm and have a diameter of about 0.125 mm.
The lumen may be adapted to receive the distal end of a stiffening
element, such as a stylet of the type typically used with cochlear
implants. An example of a distal end of a stiffening element being
received by a lumen is shown in the embodiment of the invention
illustrated in FIG. 4A. The barrel portion preferably has a lumen
therein that extends for some or all of its length. In one
embodiment of the present invention, the lumen may be about 0.3
mm.
[0056] In one embodiment of the present invention, the tapered
portion may be substantially frusto-conical in shape. In another
embodiment, the tapered portion is frusto-conical in shape. In
other embodiments, the tapered portion may be various tapered
shapes that are continuously tapered or non-continuously
tapered.
[0057] In one preferred embodiment, the tapered portion of the tip
member may be frusto-conical and has a length of about 0.76 mm and
the diameter of tapered portion decreases from about 0.45 mm to
exactly or about 0.2 mm. In one embodiment, the angle between
notional diametrically opposed sides of a tapered portion that is
frusto-conical is about or exactly about 18.9.degree.. In another
embodiment the frusto-conical tapered portion may have a length of
about 0.76 mm. Over this length, the diameter of the frusto-conical
portion decreases from 0.45 mm to 0.2 mm.
[0058] Although one type of tapered portion of the present
invention is described above, the tapered portion of the present
invention may have a shape other than frusto-conical and taper
portions that are frusto-conical or substantially frusto-conical
may have an angle between notional diametrically opposed sides that
is greater or less than 18.9.degree..
[0059] In one embodiment of the present invention, the blunt end of
the tip member is round in shape. In another embodiment, the blunt
end of the tip member is part-spherical for a portion of its
length. In other embodiments the blunt end may have various blunt
shapes, both convex and concave, such as part-ellipsoidal,
part-paraboloidal, etc.
[0060] In one preferred embodiment, the blunt end is part-spherical
in shape and has length of about 0.04 mm and a maximum diameter of
about 0.2 mm where the blunt end meets the distal end of the
tapered portion.
[0061] In one embodiment the tip member of is designed so that when
the tip member is subject to a bending force, the moment of that
force may be evenly distributed along the tip member and the
bending stresses on the tip member are constant throughout its
length. This even distribution provides a tip member that is
resiliently flexible, i.e. that is not subject to foldover when the
tip member is subject to a bending force, such as may occur during
insertion of the tip member into a recipient of the device.
[0062] In one embodiment the tissue-stimulating device may be a
prosthetic hearing implant, such as a Cochlear.TM. implant made by
Cochlear Limited, with the elongate member comprising a carrier
member for a plurality of electrodes. The tip member in this
embodiment may be constructed to assist in the guiding of the
elongate member into the cochlea, particularly into the scala
tympani of the cochlea.
[0063] In another embodiment the elongate member may have a first
configuration selected to allow the elongate member to be inserted
into a recipient's body and at least a second configuration wherein
the elongate member is adapted to apply the preselected tissue
stimulation. In one embodiment of the present invention, the
elongated member in the first configuration is straight or
substantially straight. However, in other embodiments, the
elongated member in the first configuration may be curved.
[0064] In one embodiment of the present invention, the second
configuration of the elongate member is curved. In another
embodiment, the elongate member adopts a spiral configuration when
in the second configuration. The body of the elongate member may be
preformed from a plastic or rubber material with memory that is
preformed to the second configuration.
[0065] The elongate member may be formed from a resiliently
flexible material. In a further embodiment, the tip member is
resiliently flexible. In one embodiment of the present invention,
the tip member may be formed of a material having substantially the
same or the same flexibility as the material used to form the body
of the elongate member that encapsulates the electrode element(s)
and wires.
[0066] In one embodiment of the present invention, the tip member
may be formed of the same material as the body of the elongate
member. In another embodiment, the tip member may be formed of a
different material to that of the body of the elongate member. For
example, the tip member may be formed of a material having a
relatively lesser stiffness than a portion of the body of the
elongate member. In another embodiment, the tip member may be
formed of a material that undergoes a change in stiffness,
preferably a decrease in stiffness, on insertion into the body,
such as the cochlea.
[0067] The tip member may be made as a separate unit and then
mounted on to a distal end of the elongate member. For example, the
tip member may be adhered to the distal end of the body of the
elongate member or be molded thereto in a secondary molding step.
In one embodiment of the present invention, the tip member may be
formed of an elastomeric material, such as polyurethane. The tip
member may also be formed from a silicone material. In general the
tip member may be made from any material such as plastic or rubber
that allows the tip member to be resiliently flexible.
[0068] In one embodiment of the present invention, the body of the
elongate member may be formed from a suitable biocompatible
material. In one embodiment of the present invention, the material
may be a silicone. In another embodiment, the body may be formed
from a suitable elastomeric material, such as a polyurethane or
other biocompatible rubbers or plastics.
[0069] In another embodiment, the elongate member may have a
receiving portion into which a stiffening element may be inserted.
The device may also further include a removable stiffening element
positionable within the receiving portion of the elongate member
and having a configuration selected for biasing the elongate member
into the first configuration, described above. The stiffening
element is preferably relatively stiffer than the elongate
member.
[0070] In one embodiment of both aspects, the receiving portion may
comprise a lumen extending at least into, and more preferably
through, the body of the elongate member. The lumen for the stylet
may be cylindrical and also may have an opening formed therein
proximal to the tip member. In the case of a metal stylet, the
stylet may extend out of the opening allowing the stylet to be
manipulated and removed from the lumen during or following
insertion of the device.
[0071] In one embodiment the stiffening element is formed of a
bioresorbable material which dissolves on exposure to a fluid. The
stiffening element may dissolve on exposure to a saline solution or
a body fluid of the implantee, such as cochlear fluid. In another
embodiment, the bioresorbable material of the stiffening element is
selected from the group consisting of polyacrylic acid (PAA),
polyvinyl alcohol (PVA), polylactic acid (PLA) and polyglycolic
acid (PGA).
[0072] In one embodiment of the present invention, the stiffening
element may comprise a stiffening element formed from a
non-bioresorbable material. In this embodiment, the stiffening
element may comprise a metallic stylet extending through the
receiving portion of the body of the elongate member. In one
embodiment of the present invention, the wire may be formed from a
biocompatible metal or metallic alloy. In one embodiment of the
present invention, the stylet may be formed from platinum. Other
suitable stiffening elements and stylets for use in the present
invention are also described in U.S. Pat. No. 6,421,569, U.S.
patent application Ser. No. 10/070,102 filed Jul. 8, 2002, and U.S.
patent application Ser. No. 10/203,279 filed Oct. 17, 2001, the
entire disclosures and contents of which are hereby incorporated by
reference.
[0073] In one embodiment of the present invention, the stiffening
element may be formed from a shape memory or heat sensitive
material. For example, the stiffening element may be formed from a
bimetallic element (such as nickel/titanium) and shaped to take a
straight or substantially straight configuration at room
temperature but bends into another shape once it is exposed to body
temperature.
[0074] The construction of the electrode array device of the
present invention may be adapted to minimize the likelihood of
trauma to the cochlea caused by insertion of the electrode array
device. The construction of the tip member is envisaged by the
present inventors to assist in guiding the electrode down the lumen
of the scala tympani of the cochlea. It is also envisaged that the
construction of the tip member will minimize the potential for the
tip member of the electrode to perforate the basilar membrane of
the cochlea or damage other sensitive structures in the
cochlea.
[0075] The tip member of the present invention is useful for those
elongate members inserted in the cochlea using an Advance
Off-Stylet.TM. (AOSM) mode of implantation. In this mode, the
elongate member while mounted on a stylet is inserted through a
cochleostomy until the tip member is positioned just short of the
basal turn of the cochlea. Once the tip member has reached this
position, the elongate member may be advanced or moved off the
stylet and further into the scala tympani. As the elongate member
is advanced off the stylet, the elongate member is also free to
begin to adopt its preferential spiral curvature. The construction
of the tip member of the present invention prevents foldover of the
tip member as the tip member is moved off the stylet. The length of
the tip member, however, is also sufficiently short to ensure that
the tip member does not damage the walls of the scala tympani once
the elongate member has reached its desired final insertion
position in the cochlea.
[0076] FIGS. 1 and 2 represent force diagrams of typical tip
members of known prior art electrode array carriers. It is possible
from a review of these two diagrams to identify the problems with
such prior art tip members.
[0077] FIG. 1 illustrates a prosthetic hearing implant device 100
including a tip member 102 is essentially an extension of an
electrode array carrier member 104. For simplicity, only a portion
of electrode array carrier member 104 is illustrated in FIG. 1.
Electrode 106 is the most distal electrode of electrode array
carrier member 104. Tip member 102 has a bulbous distal end 108 a
relatively narrow diameter neck section 112 which is designed to
provide increased flexibility to tip member 102. As is shown,
during insertion a force, (represented by arrow 122) is applied to
tip member 102 when electrode array carrier member 100 comes into
contact with the wall of the cochlea (not shown) during insertion.
Due to the force represented by arrow 122, tip member 102 will flex
about neck section 112 causing distal end 108 to undergo excessive
deflection, indicated by ghost lines 124, greatly increasing the
possibility of tip member 102 folding over upon itself during
insertion.
[0078] FIG. 2 illustrates a prosthetic hearing implant device 200
including a tip member 202 having a constant cross-sectional
diameter d2 along the length of tip member 202. Similarly tip
member 102 shown in FIG. 1, tip member 202 is essentially an
extension a carrier member 204 for the electrode array (not shown)
beyond the position of the most distal electrode (not shown). As is
shown, when a force represented by arrow 222 is applied to a distal
end 228 of tip member 202, tip member 202 will flex about a
location 230 where tip member 202 joins carrier member 204.
[0079] The design of the implant device illustrated in FIG. 2
increases flexibility due to the long arm of the impact force and
as such there is an increased risk of such a tip member design
causing array foldover and potential damage to the sensitive
structures of the cochlea.
[0080] FIGS. 3A and 3B represents one embodiment of a tip member
302 of the present invention. Tip member 302 includes a cylindrical
barrel portion 304, a frusto-conical tapered portion 306 at a
distal end 308 of barrel portion 304 and a part-spherical blunt end
310 at distal end 312 of tapered portion 306. Blunt end 310
terminates at tip member distal end 314. Within cylindrical barrel
portion 304 is a lumen 314 for receiving a stiffening element (not
shown). Cylindrical barrel portion 304 has diameter 318 that is
constant. In contrast, tapered portion 306 has a diameter that
continuously decreases along the length of tapered portion 306, as
illustrated by exemplary diameters 320 and 322. Tip member 302 is
attached to a carrier member (not shown in FIG. 3) at a proximal
end 330 of tip member 302. An angle 332 between notional
diametrically opposed sides 334 and 336 of tapered portion 306 is
18.9.degree.. Lumen 314 has a constant diameter 342.
[0081] In the embodiment depicted in FIGS. 3A and 3B, the tip
member is constructed separately from the carrier member carrying
the electrode array. This allows the tip member to more easily be
constructed in a manner that ensures the parameters of the tip
member are appropriately controlled to ensure that the tip member
fulfils its designed purpose.
[0082] The tip member depicted in FIGS. 3A and 3B, may be
constructed of any material that allows the tip member to be
resiliently flexible.
[0083] The dimensions and shape of tip member shown in FIGS. 3A and
3B allows for smooth insertion of an electrode array to which the
tip member is attached while preventing tip member foldover.
[0084] In one embodiment of the present invention, the barrel
portion of the tip member shown in FIGS. 3A and 3B may be exactly
or about 0.4 mm in length and the diameter of the barrel portion
may be exactly or about 0.45 mm for all or at least some of its
length.
[0085] In one embodiment, the lumen in the tip member of FIGS. 3A
and 3B has a diameter of about 0.125 mm and a length of about 0.3
mm.
[0086] In one embodiment of the present invention, the tapered
portion of the tip member of FIGS. 3A and 3B has a length of about
0.76 mm and over this length the diameter of the tapered portion
decreases from about 0.45 mm to 0.2 mm.
[0087] In one embodiment of the present invention, the length of
the part-spherical blunt end has a length of about 0.04 mm and over
this length blunt end decreases from about 0.2 mm to 0.0 mm at the
very distal end of the blunt end.
[0088] FIGS. 4A and 4B illustrates a electrode array device 400 in
accordance with one embodiment of the present invention. Electrode
array device 400 includes tip member 302 mounted on an elongate
member 402, only a portion of which is shown in FIG. 4A. Elongate
member 402 includes a lumen 404 extending therethrough. Tip member
302 is held on elongate member 402 by means of a liquid silicone
rubber adhesive 406. Filler portions 408 of adhesive 406 smooth the
transition from elongate member 402 to tip member 302, because in
this embodiment a distal end 410 of elongate member 402 has a
larger diameter than tip member proximal end 330. For illustration
purposes, the amount of adhesive 406 between elongate member distal
end 410 and tip member proximal end 330 is exaggerated in the
depiction in FIG. 4A. A stylet 422 inserted into elongate member
extends through lumen 404 and into lumen 314 of tip member 302.
Elongate member 402 is slightly tapered, but the taper is of
elongate member 402 is not as great as the taper of tapered portion
306 of tip member 302. Elongate member 402 includes electrodes 432
on one side of elongate member 402. During insertion into a cochlea
(not shown), tip member 302 may be subject to a impact/deflection
force represented by arrow 442. As illustrated in FIG. 4B, elongate
member 402 has a rounded corner square shaped cross-section having
a minimum width 452.
[0089] As illustrated in FIG. 4A, the tip member provides a smooth
transition of flexibility from the relatively stiff portion of the
carrier member containing the electrode elements and wires (not
shown) to the more flexible blunt end of the tip member.
[0090] Although the elongate member shown in FIG. 4B has a rounded
corner square shaped cross-section, the elongate member of the
present invention may have various cross-sectional shapes such as
circular, elliptical, rectangular, etc. and the cross-sectional
shape of the elongate member may vary over the length of the
elongate member.
[0091] FIG. 5 illustrates electrode array device 400 in a curved
orientation. Upon insertion of electrode array device 400 into the
scala tympani of the cochlea (not shown), the exposure of electrode
array device 400 to body temperature (about 37.degree. C.) results
in stylet 422 adopting a curved orientation. As stylet 422 adopts a
curved orientation, elongate member 402 is free to also adopt the
curved orientation as is depicted in FIG. 5.
[0092] As the elongate member 402 curls, the surgeon may continue
to further insert electrode array device 400 into scala tympani 622
of a cochlea 624 as illustrated in FIG. 6. During the further
insertion process, the surgeon may commence withdrawal of stylet
422 from lumen 404 of elongate member 402. Alternatively, the
surgeon may withdraw stylet 422 following complete insertion of
electrode array device 400 into its final position, this decision
being dependent of the surgeon's preferences. Upon withdrawal of
stylet 422, elongate member 402 is free to adopt its pre-formed
spiral orientation, as depicted in FIG. 6, with electrodes 432 (not
visible in FIG. 6) facing the modiola (not visible in FIG. 6)
within cochlea 624 so that electrodes 432 are positioned as close
as possible to the spiral ganglia thereof.
[0093] FIG. 7 illustrates a electrode array device 702 of the
present invention including a tip member 704 that is integral with
an elongate member 706. A stylet 708 is inserted through a lumen in
elongate member 706 and into a lumen in tip member 704. Electrode
array device 702 is essentially similar to electrode array device
400 in both structure and function, except that tip member 704 is
integral with elongate member 706 whereas in electrode array device
402 tip member 302 is mounted on elongate member 402. As
illustrated in FIG. 7, electrode array device 702 is in a curved
orientation, similar to the curved orientation of electrode array
device 400 in FIG. 5.
[0094] While an elongate member of the present invention, such as
the elongate members of FIG. 5 and FIG. 7, may be manufactured with
a preformed curved orientation, the device is typically delivered
to a surgeon with the stylet in place. The stylet, while at room
temperature, holds the elongate member in a straight orientation. A
useful stylet for the purposes of the present invention may be a
Nitinol wire.
[0095] FIG. 8 illustrates an electrode array device 800 in
accordance with one embodiment of the present invention. Electrode
array device 800 includes tip member 302 mounted on an elongate
member 802, only a portion of which is shown in FIG. 8. Elongate
member 802 includes a lumen 804 extending therethrough. A distal
end 810 of elongate member 802 has the same size diameter and is
the same shape as tip member proximal end 330, so there is a smooth
transition between elongate distal end 810 and tip member proximal
end 330. A stylet 822 inserted into elongate member extends through
lumen 804 and into lumen 314 of tip member 302. Elongate member 802
is slightly tapered, but the taper is of elongate member 802 is not
as great as the taper of tapered portion 306 of tip member 302.
Elongate member 802 includes electrodes 832 on one side of elongate
member 802. During insertion into a cochlea (not shown), tip member
302 may be subject to an impact/deflection force represented by
arrow 842.
[0096] In the electrode array device of the present invention, such
as the cochlear implant devices illustrated in FIGS. 5, 6 and 7 the
stylet may have a preferred direction of curl on exposure to body
temperature within the cochlea. In one embodiment, the device may
have an indicia means that provides an indication to a user, such
as a surgeon, of the preferred direction of curl of the device on
implantation. This may be important as the device is preferably
oriented in the cochlea such that the direction of curl results in
the device being able to be moved into the scala tympani. The
indicia means may comprise a loop formed in the wire at or adjacent
a distal end thereof. The loop as well as acting as an indicia
means may act as a means of engaging with and withdrawing the
stylet from the lumens in the elongate member and tip member during
or following implantation. In one embodiment, the loop may be in
the same plane as the preferred direction of curl of the stylet.
The loop may extend away from the preferred direction of curl of
the stylet.
[0097] In one embodiment of the present invention, it is possible
to provide a sheath of bioresorbable and lubricious material,
similar to the sheath described and shown in U.S. patent
application Ser. No. 10/203,079, the entire disclosure and contents
of which is hereby incorporated by reference. The bioresorbable
material of stiffening sheath may be polyacrylic acid (PAA) that is
adapted to dissolve on exposure to cochlear fluids. Other suitable
bioresorbable materials may be envisaged and such materials need
not necessarily dissolve on exposure to fluids. For example, the
sheath may be made of a material that softens upon exposure to
fluids but does not get absorbed.
[0098] As mentioned above, in one embodiment of the present
invention, the tip member may be constructed separately from the
elongate member of electrode array device. In this regard, the tip
member may be constructed out of a similar material to the body of
the electrode array carrier such as silicone. To aid in fixing the
tip member to the elongate member during production, the tip member
lumen may be used to fit over a production stylet positioned within
the lumen of the elongate member of the electrode array device
during its manufacture. Such a production stylet may be placed in a
mold, along with the electrodes, and a suitable quantity of
silicone is then poured into the mould around the stylet and
electrodes to form the elongate member. In the present embodiment,
the distal end of the production stylet would preferably extend a
relatively short distance out of the distal end of the molded
carrier member and act as a support for the tip member lumen of the
tip member when the tip member is subsequently securely mounted on
the distal end of the elongate member. A suitable production stylet
and a method of manufacturing the elongate member of the electrode
array device of the present invention is described in more detail
in U.S. Pat. No. 6,421,569, the entire disclosure and contents of
which is hereby incorporated by reference.
[0099] Suitable elongate members for use with the tip member of the
present invention and methods for inserting a device of the present
invention into a cochlear are described in U.S. Pat. No. 6,421,569,
U.S. patent application Ser. No. 10/070,102 filed Jul. 8, 2002, and
U.S. patent application Ser. No. 10/203,279 filed Oct. 17, 2001,
the entire disclosures and contents of which are hereby
incorporated by reference.
[0100] The present invention provides a specifically designed tip
of a electrode array device that is shaped and dimensioned in a
manner to optimize the flexibility of the array such that the tip
will not undergo fold-over during insertion when exposed to usual
insertion forces. This invention is a significant improvement over
prior art attempts at providing such a flexible tip as embodiments
of the present invention overcome the problem of the tip being too
flexible at a critical section and becoming too flexible to enable
smooth insertion of the array.
[0101] The present invention will now be described by way of
example:
EXAMPLE
[0102] In one embodiment of the tip member of the present invention
having a shape such as shown in FIGS. 3A and 3B, the design of the
tip member may be based upon establishing the dimensions of three
main parameters:
[0103] D1 is the diameter of the proximal end of the tip member
that is connected to the elongate member;
[0104] D2 is the diameter of the distal end of the frusto-conical
tapered portion; and
[0105] L is the length of the tip member.
[0106] The diameter D1 of the tip member in this embodiment at its
proximal end that is connected to the end of the elongate member is
preferably exactly or about 0.45 mm. This diameter allows the tip
member to be easily fitted onto the end of a conventional electrode
array device, such as the Contour electrode array device
manufactured by Cochlear Limited of Lane Cove, New South Wales,
Australia.
[0107] The diameter D2 of the distal end of the frusto-conical
tapered portion of the tip member in this embodiment is preferably
exactly or about 0.2 mm. This diameter has been determined based
upon studies and experimental measurements of human cochlea and the
sizes of the diameter of the outer wall of the cochlea as a
dimension most likely to minimize the chance of the tip member
penetrating the outer wall.
[0108] The length L of the tip member in this embodiment is
preferably exactly or about 1.2 mm. Again, this dimension has been
determined as being suitable for ensuring the tip fits within the
appropriate region inside the cochlea for a range of initial
electrode array insertion depths. It has been found that such a
length of the tip member minimizes the likelihood of, and more
preferably avoids, tip foldover for typical forces associated with
electrode array insertion.
[0109] Having determined the important parameters of the tip of the
present invention, namely D1, D2 and L, the shape of the tip in
this embodiment provides great flexibility whilst providing smooth
mechanical interaction between the tip and the cochlea thereby
providing a smooth insertion procedure. The shape of the tip member
in this embodiment takes into consideration the mechanical design
requirements of the tip member. The shape and dimensions of the tip
member of this embodiment is based on the idea of treating the tip
member as a cantilever beam and determining the dimensions of a
constant-strength cantilever beam where bending stresses throughout
the beam are equal to those at the fixed end, that is, the junction
of the tip member with the elongate member.
[0110] In this regard, the general stress formula for such a
cantilever beam (assuming a rectangular cross-section) is:
.sigma.=6FL/(bh.sup.2)
[0111] where .sigma. is the stress;
[0112] F is the deflection/impact force; and
[0113] L,b,h are the beam length, fixed end width, and height,
respectively.
[0114] Assuming that the tip member is attached to a substantially
tubular elongate member, the preferred cross-section of the tip is
circular, so that there is maximum alignment between the elongate
member and the tip member when the tip is attached to the elongate
member during production. In this regard, for a circular beam the
constant stress formula may be written as:
.sigma.=k(const.).times.((F.x)/D.sup.3)
[0115] where x is arm of force F (see FIG. 4A); and
[0116] D is the diameter for the circular beam.
[0117] Therefore, for a given impact/deflection force F (constant),
in order to achieve uniform strength the following formula may be
found:
X/D.sup.3=k'(const.)
[0118] Therefore the formula for D as a function of x is:
D=k"(const.).times.cube root (x)
[0119] Given the abovementioned established parameters of the tip,
namely D1 D2 and L, the following equations may be determined:
0.2=k"(const).times.cube root(x)
0.45=k"(const).times.cuberoot (x=1.2)
[0120] As a result, in order to control the distribution of the
force over the length of the tip, the shape of the tip member of
this embodiment may be approximated to the partially frusto-conical
tapered shape as depicted in FIG. 3A.
[0121] All documents, patents, journal articles and other materials
cited in the present application are hereby incorporated by
reference.
[0122] Although the present invention has been fully described in
conjunction with several embodiments thereof with reference to the
accompanying drawings, it is to be understood that various changes
and modifications may be apparent to those skilled in the art. Such
changes and modifications are to be understood as included within
the scope of the present invention as defined by the appended
claims, unless they depart therefrom.
* * * * *