U.S. patent number 4,686,765 [Application Number 06/855,084] was granted by the patent office on 1987-08-18 for method for making an intracochlear electrode array.
This patent grant is currently assigned to Regents of the University of California. Invention is credited to Charles L. Byers, Gerald E. Loeb, Michael M. Merzenich, Stephen J. Rebscher.
United States Patent |
4,686,765 |
Byers , et al. |
August 18, 1987 |
**Please see images for:
( Certificate of Correction ) ** |
Method for making an intracochlear electrode array
Abstract
A method is disclosed for making an intracochlear multielectrode
array having a spiral configuration, at least generally conforming
to the scala tympani of a cochlea. The array is formed in a
two-part mold and comprises an elastomeric carrier supporting a
plurality of metallic electrodes in fixed positions thereon. Each
electrode has an associated lead to provide a plurality of leads
and composite rib structure extending from a basal portion of the
array to an apical portion thereof. Each electrode and associated
lead is formed from a flattened metallic wire. The wire leads are
stacked in the mold to permit the wires to flex in the direction of
their spiral curvatures, facilitating insertion of the array into a
cochlear, but to prevent transverse flexing thereof.
Inventors: |
Byers; Charles L. (Vacaville,
CA), Loeb; Gerald E. (Clarksburg, MD), Merzenich; Michael
M. (San Francisco, CA), Rebscher; Stephen J. (San
Francisco, CA) |
Assignee: |
Regents of the University of
California (Berkeley, CA)
|
Family
ID: |
27085397 |
Appl.
No.: |
06/855,084 |
Filed: |
April 22, 1986 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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607019 |
May 3, 1984 |
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Current U.S.
Class: |
29/858;
264/272.16; 264/272.15 |
Current CPC
Class: |
A61N
1/0541 (20130101); G09B 21/009 (20130101); Y10T
29/49176 (20150115) |
Current International
Class: |
A61F
11/04 (20060101); A61F 11/00 (20060101); A61N
1/36 (20060101); G09B 21/00 (20060101); H04R
25/00 (20060101); H01R 043/00 () |
Field of
Search: |
;29/858 ;179/17FD,17E
;264/272.14,272.15,272.16,277 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Multichannel Cochlear Implants: Electrode Design Surgical
Considerations", pp. 258-260; R. A. Schindler et al., Artificial
Organs, 1981. .
"Cochlear Implants: Case Selection and Technique", pp. 55-62; B. F.
O'Reilly, Ear, Nose & Throat Journal, 1981. .
"Design and Fabrication of an Experimental Cochlear
Prosthesis"--pp. 241-254, G. E. Loeb et al, Medical &
Biological Engineering and Computing, distributed 1983..
|
Primary Examiner: Goldberg; Howard N.
Assistant Examiner: Arbes; Carl J.
Attorney, Agent or Firm: Phillips, Moore, Lempio &
Finley
Government Interests
BACKGROUND OF THE INVENTION
This invention was made with Government support under Contract No.
N01-NS-0-2337 awarded by the Department of Health and Human
Services. The Government has certain rights in this invention.
Parent Case Text
This is a division of Ser. No. 607,019, filed May 3, 1984, now
abandoned.
Claims
We claim:
1. A method for making an intracochlear multielectrode array,
having an apical portion and a basal portion and a spiral shape at
least generally conforming to the scala tympani of a cochlea, said
array comprising an elastomeric carrier having a plurality of
metallic electrodes, each having an associated lead to form a
plurality of leads extending from the basal portion into the apical
portion of said array, supported in fixed positions by said
carrier, said method comprising the steps of
fabricating each elctrode and associated lead from a flattened
metallic wire by forming said electrode on a first end of said wire
to have a covex outer surface.
2. The method of claim 1 wherein said fabricating step further
comprises forming a an electrical connector contact on a second end
of said wire.
3. The method of claim 2 wherein said last mentioned forming step
comprises forming said contact into a sphere.
4. The method of claim 1 further comprising covering said wire with
an adherent layer of non-toxic and non-bioreactive electrical
insulation prior to said fabricating step.
5. The method of claim 4 further comprising melting the first end
of said wire to form a spherical electrical contact.
6. The method of claim 4 further comprising coating said lead with
a second layer of insulation after said fabricating step.
7. The method of claim 1 further comprising coating the convex
outer surface of said electrode with iridum oxide.
8. The method of claim 1 wherein said fabricating step comprises
fabricating leads extending from the basal portion into the apical
portion of said array from wires having a heavier gauge than other
ones of said leads terminating short of the apical portion of said
array to form a rib structure for said array that flexes
substantially uniformly throughout the length thereof.
9. The method of claim 1 wherein said fabricating step further
comprises forming a skirt member around the convex outer surface of
said electrode.
10. A method of maufacturing an electrode array for implanting in a
human cochliea comprising the following steps:
providing a plurality of electrodes, each having an associated
electrode lead;
disposing said plurality of electrodes and associated leads in a
mold cavity defined in a mold to position said electrodes at
predetemined spaced positions relative to each other to effectively
stimulate auditiory nerves when said array is implanted in a human
cochlea and to form said leads into a rib structure for said
array,
securing said electrodes at said predetermined spaced positions in
the cavity of said mold utilizing an elastomer material; and
after securing said electrodes, casting a resilient carrier within
said cavity in encapsulating relationship about said leads to form
a rib structure for said array and to position and secure said
electrodes at said predetermined positions and to expose outer
surface portions thereof on said array.
11. A method for making an intracochlear multielectrode array,
having an apical portion and a basal portion and a spiral shape at
least generally conforming to the scala lympani of a cochlea, said
array comprising an elastomeric carrler havlng a plurality of
metallic electrodes, each having an associated lead to form a
plurality of leads extending from the basal portion into the apical
portion of said array, supported in fixed positions on said carrier
to expose an outer surface of each said electrode on said array,
said method comprising the steps of
fabricating each of said electrodes and associated leads,
placing said electrodes and associated leads in first cavities,
defined in a first mold member, conforming to the shape of said
array.
positioning said leads to form a central rib structure for said
array that is flexible to permit uncurling of said rib structure,
but is relative inflexible in a direction transverse to the
direction of such uncurling,
securing a second mold member, having second cavities at least
generally conforming to said first cavities, to said first mold
member to superimpose said first and second cavities which jointly
conform to the shape of said array,
filling said first and second cavities with an uncured elastomer,
and
curing said elastomer to form said carrier and said array.
12. The method of claim 11 wherein said fabricating step comprises
forming each said electrode on a first end of a wire and further
comprising forming an electrical connector contact on a second end
of said wire with said wire thus connected directly between said
electrode and said contact, placing said contact in a contact pad
cavity defined in said first mold member, filling said contact pad
cavity with said uncured elastomer, and curing the elastomer in
said contact pad cavity to form a contact pad connected to said
array by said associated wire.
13. The method of claim 11 wherein said first and second cavities
define a spiral-shaped cavity, conforing to the spiral shape of
said array, and a plurality of bores, each having a cross-sectional
areas essentially the same as that of the exposed outer surface of
a respective electrode, formed in spaced apart relationship
relative to each other in wall portions defining said spiral-shaped
cavity, and wherein said placing step comprises positioning the
exposed outer surface of each said electrode in a respective one of
said bores.
14. The method of claim 12 further comprising forming an
elastomeric gasket adjacent to each said bore and holding a said
electrode at said bore by said gasket, prior to said filling
step.
15. The method of claim 14 further comprising fixing said electrode
in position and simultaneously sealing said bore by applying a
small quantity of elastomer over said electrode and gasket, prior
to said filling step.
16. The method of claim 12 wherein said fabricating step comprises
forming a skirt member around the outer surface of said electrode
and said fixing step comprises encapsulating said skirt member with
said small quantity of elastomer.
17. The method of claim 15 further comprising arranging a plurality
of removable pins in said first cavities to define a pathway for
said leads, positioning said leads in said pathway between said
pins to form said rib structure, and removing said pins, subse-uent
to said applying step and prior to said securing step.
18. A method for making an intracochlear multielectrode array,
having an apical portion an a basal portion and a spiral shape at
least generally conforming to the scala tympani of a cochlea, said
array comprsiing an elastomeric carrier having a plurality of
metallic electrodes, each having an associated lead to form a
plurality of leads extending from the basal portion into the apical
portion of said array, supported in fixed positions on said carrier
to expose an outer surface of said electrode on said method
comprising the steps of
fabricating each electrode and associated lead from a flattened
metallic wire, including fabricating a first group of said leads
from wires having a heavier gauge than a second group of said
leads,
placing said electrodes and associated leads in a mold defining
cavities conforming to the shape of said array, including extending
only said first group of leads into an apical end of said cavities
to form a central rib structure for said array that flexes
substantially uniformly throughout the length thereof,
filling said cavities with an uncured elastomer, and
curing said elastomer to form said carrier and said array.
19. A method for making an intracochlear multielectrode array,
having an apical portion and a basal portion and a spiral shape at
least generally conforming to the scala tympani of a cochlea, said
array comprising an elastomeric carrier having a plurality of
metallic electrodes, each having an associated lead to form a
plurality of leads extending from the basal portion into the apical
portion of said array, supported in fixed positions on said carrier
to expose an outer surface of each of said elctrodes on said array,
said method comprising the steps of
fabricating each of said electrodes and associated lead from a
flattened wire of rectangular cross-section having a width
substantially large than its thickness,
placing said electrodes and associated leads in a mold defining
cavities conforming to the shape of said array, including stacking
substantial portions of at least some of said leads in stacked
alignment relative to each other to form a rib structure in said
array flexible in a horizontal plane containing the full spiral
shape of said array, but relatively inflexible in a vertical plane
perpendicular to said horizontal plane,
filling said cavities with an uncured elastomer, and
curing said elastomer to form said carrier and said array.
Description
FIELD OF THE INVENTION
The present invention relates generally to hearing prostheses and
more specifically to an electrode array for implanting in the
cochlea of an ear.
BACKGROUND ART
Cochlear prosthesis devices are currently being developed to
restore hearing in the profoundly deaf. Such prostheses utilize an
electrode array which is inserted in the scala tympani of the
cochlea and is used to stimulate the auditory nerves. Exemplary
arrays are described and referred to in various publications
including R.A. Schindler, et al., "Multichannel Cochlear Implants:
Electrode Design Surgical Considerations," Proceedings of the Third
Meeting of ISAO printed in Artificial Organs (Suppl.), pp. 258-260,
1981 and M.M. Merzenich, et al., "Cochlear Implant Prostheses:
Strategies and Progress," Annals of Biomedical Enqineering, Vol. 8,
pp. 361-368, 1980.
The subject electrode array is superior to the electrode arrays of
the type disclosed or referred to in the above-referenced
publications and is capable of providing improved performance under
safer operating conditions. In addition, the array can be implanted
in the cochlea with reduced likelihood of injury.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is an exploded view of an exemplary intracochlear
electrical stimulation system utilizing the subject electrode
array.
FIG. 1B is an illustration generally depicting the manner in which
the FIG. 1A system is positioned in a patient.
FIG. 2 is a cross-section schematic representation of the cochlea
with an exemplary electrode array implanted in the scala
tympani.
FIG. 3 is a plan view of a preferred embodiment of the subject
electrode array.
FIG. 4 is a graph illustrating the dimensions of the preferred
embodiment of the subject electrode array with respect to the
typical range of height dimensions for the human scala tympani.
FIG. 5 is a cross-sectional elevation view of the preferred
embod,iment electrode array.
FIGS. 6A and 6B are schematic cross-sectional views of the
preferred embodiment electrode array of FIG. 3 and FIG. 6c is a
cross-sectional view of one portion of the central rib structure of
the array.
FIG. 7 is an elevational view of a casting fixture used in the
fabrication of the subject electrode array.
FIG. 8 is a sectional view of the lower removable mold member of
the FIG. 7 casting fixture for forming the cochlea section of the
subject electrode array.
FIGS. 9A through 9E depict the method by which individual
electrodes are installed in the lower removable mold member of FIG.
8.
FIG. 10 is a fragmentary cross-sectional view of the upper and
lower removable mold member which form the cochlea section of the
electrode array prior to the injection of the elastomer.
FIG. 11 is a cross-sectional view of the hammer and anvil sections
of the swaging tool used to form the individual electrodes of the
subject electrode array.
SUMMARY OF THE DISCLOSURE
An electrode array is disclosed for implantation in a human
cochlea. The array includes a spiral-shaped resilient carrier and a
plurality of electrodes, with each electrode including an
associated electrode lead. The electrodes are supported in the
carrier, with the leads extending down the center of said carrier
so as to form a central rib structure. The leads have an elongated
cross-section and are individually vertically aligned in the rib
structure so as to limit flexing of the array in a vertical
direction.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE
INVENTION
Referring now to the drawings, the FIG. 1A system utilizes an
implanted assembly which includes a surgical disconnect/receiver,
generally designated by the numeral 16, coupled to an intracochlear
electrode array, generally designated by the numeral 18. The
external components of the system include a speech
processor/transmitter 20 which drives an antenna coil 22. The
electrode array is of the general type referred to in Loeb, G.E.,
et al., "Design and Fabrication of an Experimental Cochlear
Prosthesis" Medical and Biological Engineering and Computing, Vol.
21, pp. 241-254, 1983 and Merzenich, M. M., et al., "The UCSF
Cochlear Implant Project" Advances in Audiology, Vo. 2, pp. 119-144
(1984) the contents of which are both hereby fully incorporated
herein by reference.
Surgical disconnect/receiver 16 comprises a lid 24 which contains
the passive radio receiver and associated antenna coil. Lid 24 also
includes an elastomer pad with a pair of electrical contact strips
coupled to the output of the receiver. Receiver 16 further includes
a base 26 and a pair of elastomer contact pads 28 and 30
intermediate the base and lid 24. Elastomer contact pad 28 is
connected to electrode array 18 and contact pad 30 is connected to
a percutaneous cable 36 which is, in turn, connected to an external
connector 34.
When lid 24 is secured to base 26 with contact pads 28 and 30
disposed there between, the output of the receiver is electrically
connected through the pad to electrode array 18. In addition,
external connector 34 is connected to the array and receiver
output. Connector 34 may be used either to monitor the output of
the receiver or to stimulate the electrode array.
Speech processor/transmitter 20 includes a pocket-size sound
processor and transmitter box contains conventional components of a
high quality hearing aid (microphone, batteries, thresh hold and
volume control) plus an R.F. generator and internally adjustable
compressors and filters which are set during clinical testing to
optimize speech intelligibility.
Referring now to FIG. 1B, the surgical disconnect/receiver 16 is
mounted behind the ear of the patient with the receiver coil being
affixed to the mastoid bone. As will be subsequently described in
greater detail, the spiral-shaped intracochlear section of
electrode array 18 is implanted in the scala tympani of the cochlea
and is coupled to surgical disconnect/receiver 16 by way of the
elongated lead section of the array. The surgical implant procedure
involves exposure of the mastoid cortex and external auditory canal
of the implanted ear via elevation of a postauricular skin flap. A
shallow (2 mm deep) circular depression is drilled into the mastoid
cortex using a specially designed trephine. Disconnect/receiver 16
will later be seated in this depression. A continuous narrow,
shallow undercut grove is cut into the boney ear canal and over the
mastoid from the disconnect/receiver site into the middle ear
cavity. The round window of the cochlea is exposed and removed. The
window is then enlarged by about 3 mm to provide an unrestricted
view of the first turn of the scala tympani. The electrode is then
carefully inserted into the opening. Antenna coil 22 will be
positioned on the skin directly over the receiver coil when the
incision has healed.
Percutaneous cable 13 is intended for monitoring and testing and
may be removed by a simple surgical procedure wherein lid 24 is
disconnected from base 26. Percutaneous cable 36 is severed and
contact pad 30 is removed. Finally, cable 36 is pulled through the
opening in the skin, and the lid, and base are reconnected, thereby
coupling the output of the receiver directly to electrode array
contact pad 28. 20 It should be further noted that the receiver can
be easily replaced in the event of failure or the like in a similar
manner without removing electrode array 18 from the cochlea.
Although electrode array 18 is depicted in a single channel system,
the array is also suitable in multiple channel applications. An
exemplary multichannel application is disclosed in U.S. Pat. No.
4,400,590, the contents of which are fully incorporated herein by
reference.
The intracochlea section of electrode array 18 has a spiral shape
which generally corresponds to the shape of the scala tympani of
the cochlea as shown in FIG. 2. The array should loosly fit the
dimensions of the scala, and should bring the basilar electrodes
into very close proximity with the basilar membrane without
applying any pressure to this extremely delicate structure. As will
be subsequently described, array 18 should be also sufficiently
small to permit the perilymph in the cochlea to freely
circulate.
Array 18 preferably includes eight electrode pairs spaced along the
length of the cochlear section although a fewer or greater number
of pairs may be used. The pairs are imbedded in a resilient
elastomer carrier, molded to fit the Scala Tympani. An elastomer
sold by Dow Corning under the trademark Silastic MDX44210 has been
found to be suitable for the present application. Referring now to
FIG. 2, each electrode pair includes a basilar electrode 42, which
is positioned facing the basilar membrane and a modiolar electrode
44, which is positioned facing the modiolus (through which the
auditory nerve extends) at the center of the cochlear spiral. In
the embodiment depicted in FIG. 2, the basilar and modiolar
electrodes are positioned at right angles with respect to another.
Although both electrodes are visible in FIG. 2, it is preferred
that the electrodes of each pair be longitudinally displaced from
one another. As will be subsequently described, each electrode has
an integral lead which generally extends down the central portion
of carrier towards the lead section of the array. The grouped leads
form a central rib structure, generally designated by the numeral
48, which controls flexing of the array in a predetermined
manner.
Referring now to FIG. 3, the intracochlear section of a preferred
embodiment electrode array may be seen. This particular embodiment
preferably includes eight pairs of electrodes, with six pairs being
the minimum number required to achieve the full benefit of the
subject invention. The eight basilar electrodes 51B through 58B
extend generally along the upper surface of the array so as to face
the basilar membrane (FIG. 2). When implanted in the cochlea, the
eight modiolar electrodes 51M through 58M extend generally along
the inner periphery of the spiral and face the modiolus when
implanted.
Preliminary studies have indicated that the dimensions of the scala
tympani do not vary greatly from individual to individual,
including children and adults. The FIG. 4 graph shows the distance
from basilar membrane to floor of the scala tympani versus the
distance from the round window taken from Woods metal castings from
four adult temporal bones. The scala tympani depicted by curves 64
and 65 are believed to be of normal dimensions with curves 60 and
62 being somewhat unusually large and small, respectively.
In order to provide optimum performance, it is desirable for the
intracochlear array to extend approximately 24 mm into the scala
tympani from the round window. In order to achieve the desired
degree of insertion, the intracochlear section of the subject
electrode array is provided with a relatively large diameter basal
portion 66, a relatively small diameter apical portion 68 and a
tapered portion 70 intermediate the basal and apical portions.
FIG. 4 further includes a curve 61 which represents the diameter of
the intracochlea section of the subject array as measured from the
round window when the array has been implanted. The position of the
basilar electrodes 51B through 58B in the array are also
schematically depicted (the modiolar electrodes are not shown). As
can be seen from curve 61, the basal portion 66 of the array will
preferably extend into the scala tympani approximately 18 mm, with
the taper portion 70 being positioned at approximately 18-20 mm.
The apical portion 68 of the array typically extends from
approximately 20 mm to 24 mm.
As can be seen from curves 60, 62, 64 and 65, the scala tympani has
a constriction located at approximately 14 to 16 mm from the round
window. This constriction limits the maximum diameter of the basal
portion 66 of the array. Similarly, the cross-sectional area of the
scala tympani begins to diminish substantially in the apex region
of the cochlea at approximately 20 mm. The reduced cross-sectional
area of the apical portion 68 of the array is provided to
accommodate the reduced cochlear volume in this area and permit
free circulation of the perilymph contained in the scala
tympani.
The preferred embodiment electrode array is provided with a basal
portion 66 having a diameter of approximately lmm and an apical
portion 68 having a diameter of approximately 0.75 mm. These
dimension are believed to be suitable for most patients. A somewhat
smaller diameter electrode array would be appropriate for a patient
having a scala tympani as represented by curve 62 since the
preferred embodiment array would actually contact the basilar
membrane, this being undesirable.
FIG. 5 shows an exemplary cross-sectional view of the preferred
embodiment electrode array taken through a section located at
basilar electrode 57B. All electrodes include integral insulated
leads which extend through the central portion of the carrier to
form central rib structure 48.
Schematic representations of the cross-section of the FIG. 3 array
at various locations are shown in FIGS. 6A and 6B. By way of
example, cross-section 72 of FIG. 6A shows basilar electrode 51B
(the electrode array is inverted). Cross-section 74 shows modiolar
electrode 51M and the insulated lead 120 extending from electrode
51B towards the central portion of the carrier. Insulated lead 120
is seen partially rotated from the horizontal position as it curves
away from 51B, into the required vertical position in the central
rib. Cross-section 76 is taken between electrodes 51M and 52M. At
this position, lead 120 from electrode 51B and another lead from
electrode 51M are positioned within the central portion of the
carrier to form central rib structure 48.
As further cross-sections are taken through the electrode array
towards the basal end of the array, additional electrode leads are
added to center rib structure 48. As shown in the FIG. 6B
cross-section 118, and in FIG. 6c taken past the last electrode
58M, central rib structure 48 is comprised of sixteen separate
electrode leads.
The electrodes and electrode leads are fabricated from noble metals
which resist electrolytic corrosion. An alloy containing 90%
platinum and 10% iridium has been found to be ideal for the present
application. Junctions between dissimilar metals must be avoided.
It is preferred that the electrodes and leads form an integral
structure. A novel method of fabricating the electrodes and
associated leads will now be described. All fabrication takes place
in a Class 100 clean room.
The electrodes and leads are fabricated from flattened
platinum/iridium wires which are covered with a layer of
insulation. The insulation must be non-toxic and non-bioreactive. A
polyimide insulation sold under the trademark "Pyre ML" has been
found suitable for the present application. Such insulated
flattened wires may be obtained from California Fine Wire of Grove
City, Calif.
As will subsequently be explained, it is preferred that the
electrodes and leads positioned near the apical end of the array be
fabricated from a heavier gauge platinum/iridium wire than the
remainder of the electrodes and leads. In this regard, electrode
pairs 51B, 51M, 52B, and 52M and the associated leads are
fabricated from wires having a width of approximately 0.075 mm and
a thickness of approximately 0.025 mm (without insulation).
Electrode pairs 53B-58M are fabricated from wire having a somewhat
smaller cross-section of 0.055 mm by 0.020 mm.
The insulated platinum/iridium wires of the appropriate gauge are
cut into sixteen separate sections of approximately 11 cm.
Approximately 6 mm of each wire is burned back utilizing a micro
acetylene torch to melt the wire to form a sphere approximately
0.28 mm in diameter. The wire is then inserted in an electrode
forming swaging tool as depicted in FIG. 11.
The swaging tool, generally designated by the numeral 124, includes
a fixed lower steel anvil section 126 and a movable upper steel
hammer section 128. Anvil section 126 is provided with a pedestal
having a circular cross-section with a diameter of approximately
0.30 mm and a height of approximately 0.11 mm at the top and 0.33
mm at the base (not designated). A rectangular opening is provided
in the center of the pedestal for receiving the wire. Separate
anvil sections are utilized for the two gauges of wire.
Hammer section 128 is provided with a recess having a circular
cross-section, which is approximately 0.20 mm deep in the central
portion. The recess includes a central concave section which is
approximately 0.35 mm in diameter surrounded by a skirt section
which extends from the periphery of the concave section to the
bottom of the hammer section where the diameter of the recess is
approximately 0.38 mm.
Hammer section 128 is retained in a guiding assembly (not shown)
which permits the section to move freely in the vertical direction
while maintaining the section centered over the anvil section. In
operation, the hammer section is lifted to permit the end of the
wire to be inserted in the opening in the anvil section pedestal
with the sphere resting on the upper surface of the pedestal. The
hammer is then manually lifted a predetermined distance, typically
2 cm, and then released. The force of the hammer striking the
sphere causes a general mushroom-shaped electrode 130 to be formed
from the sphere.
It is important to maintain a relatively constant surface on each
of the electrodes used in the subject electrode array. The FIG. 11
swaging tool will provide a constant covex surface area even though
the volume of the sphere formed on the end of the wire may vary.
The preferred embodiment electrode is provided with a relatively
vertical skirt member which extends around the convex upper surface
of the electrode. The skirt member, which does not form part of the
final electrode surface, is formed between the side of the pedestal
of the anvil section and the parallel skirt section of the hammer
and is approximately 0.05 mm thick. The length of the skirt section
will vary depending upon the volume of the original sphere, thereby
compensating for errors in the sphere diameter so as to maintin a
constant electrode surface area. The skirt section of the
electrodes are preferably disposed at approximately a 5 degree
angle from vertical to facilitate the forming and removal of the
electrode and integral lead from the swaging tool.
After the electrodes are formed they are cleansed in alcohol to
remove charred insulation and the like. The leads of the electrodes
are then coated with a second layer of insulation. An insulation
marketed by Union Carbide, Electronics Division of San Diego,
Calif., under the trademark Parylene C has been found suitable for
this application.
It is believed that performance of the electrodes may be improved
by coating the convex surface of the electrodes with a layer of
iridium oxide. This may be accomplished in various ways. First, a
solution may be prepared by dissolving Iridium chloride in a
solution of isopropanol and hydrochloric acid. A single droplet of
the solution is deposited on the convex surface of the electrode
and then the electrode is placed in a 320.degree. C. oven until the
droplet has completely dried and the iridium chloride is converted
to iridium oxide. This procedure is repeated three or four times
thereby causing a layer of iridium oxide to be formed on the
surface of the electrode. Alternatively, an iridium oxide layer may
be sputtered directly onto the electrode using an iridium target in
an argon and oxygen plasma. Also, the electrode may be
sputter-coated or electroplated with pure iridium, and then baked
in an oxygenated furnace to oxidize the iridium film.
Once the electrodes have been formed, a sphere is formed on the
opposite end of the electrode lead with a final lead length of
approximately 75 mm. It will be necessary to add additional
platinum/iridium wire to form the desired sphere diameter of
approximately 0.5 mm. The spheres at the ends of the electrode
leads serve as the electrode contacts of contact pad 30 (FIG. 1A).
Once the electrodes and leads have been cleansed in alcohol, they
are ready for assembly in the electrode array.
The elastomer carrier which supports the electrodes and associated
leads are preferably cast using injection molding techniques. The
casting fixture shown in FIG. 7 includes an upper main mold member,
generally designated by the numeral 132 and a separate lower main
mold member, generally designated by the numeral 134. The upper and
lower mold members, which are machined stainless steel, each are
provided with a transverse notch (not designated) having an
inclined surface 170.
A lower removable intracochlear mold member 136 is positioned
within the transverse notch of lower main mold member 134. Member
136 has an inclined surface (not designated) which abuts and
slidably engages inclined surface 170 of member 134. A pair of
mounting blocks are disposed on opposite sides of mold member 136
in the notch and are spaced apart from the member. Adjustment
screws (not designated) extend through threaded openings in block
140 so as to engage mold member 136. The adjustment screws are used
to alter the lateral position of member 136 on the lower main mold
member 134. A third screw extends through the end of the main mold
member 134 and engages mold member 136 so as to force the member
against inclined surface 170. A similar arrangement is used to
secure an upper intracochlear mold member 138 in a notch machined
in upper main mold member 132.
Lower intracochlear member 136 has a spiral-shaped cavity 144
(FIG.10) which generally corresponds to the intracochlear section
of the electrode array of FIG. 3. A corresponding spiral-shaped
cavity 142 is machined into the upper intracochlear mold member
138. Mold members 136 and 138 are removable to facilitate the
machining of cavities 144 and 142 and other fabrication steps.
An elongated lead cavity 148 is machined down the central portion
of lower main mold member 134 which terminates in a contact pad
cavity 158. Cavity 158 is used to form contact pad 28 (FIG. 1A).
Upper main mold member 132 is machined to provide an elongated
upper lead cavity 146 which terminates by gently tapering to the
surface at the same distance from 170 that corresponding cavity 148
intersects the edge of cavity 158.
Upper main mold member 132 is provided with four downward
projecting alignment studs 154 which are received by corresponding
bore 156 machined in the lower main mold member 134. When the
alignment studs are positioned within the corresponding bores, the
upper and lower lead cavities are in registration. The adjustment
screws of blocks 140 are used to alter the position of the two
intracochlear mold members 136 and 138 so that the upper and lower
spiral cavities 142 and 144 are in registration.
Upper main mold member 132 carries eight screws 150 which are
positioned in openings 164. The screws are retained in the openings
by set screws 160. The set screws have central openings to provide
access to the heads of screws 150. Lower main mold member 134 is
provided with eight threaded bores 152 for receiving screws
150.
Although not depicted, an elastomer reservoir is formed in upper
main mold member 132. A series of small openings extend from the
reservoir into the upper lead cavity 146. In addition, a channel is
provided in the surface of upper intracochlear mold member 138
which couples the reservoir to spiral-shaped cavity 142.
Prior to the casting of the elastomer, the mold sections are
cleansed. Next, the electrodes and associated leads are installed
within the lower spiral cavity 144 and lead cavity 148. FIG. 8 is a
cross-sectional schematic view of a portion of lower intracochlear
mold member 136, with a top section removed. Some of the electrodes
and associated leads are shown installed in cavity 144 prior to the
casting of the elastomer carrier.
It is necessary to precisely align the various electrode within the
mold prior to casting. A series of bores 166 are drilled in cavity
144 at each desired electrode position. The cross-sectional area of
bores will be essentially the same as the exposed electrode area,
which is preferably 0.1 mm.
An elastomer gasket is formed over each bore 166 to hold the
electrodes in place. The sequence for forming the gaskets and
securing the electrodes is depicted in FIGS. 9A through 9E. As
shown in FIG. 9A, a temporary pin 174 is positioned within each
positioning bore 166. Pins 174 have a diameter approximately equal
to the bore diameter. Next, a small quantity of uncured elastomer
material 176 such as Silastic brand elastomer, is deposited around
each pin using a syringe or the like. Mold member 136 is preferably
resting on a hot plate which heats the member to approximately
250.degree. F. to 300.degree. F. The heated mold member causes the
elastomer to cure within a few seconds.
Once the elastomer has cured, pins 174 are removed as depicted in
FIG. 9C. Prior to removal, a short length of metal tubing having an
inside diameter slightly larger than that of pins 174 is positioned
over the pin with the bottom of the tubing resting against the
elastomer material 176. The pins are then extracted through the
tubing, with the tubing serving to retain the elastomer material in
place around bore 166.
The electrode 51 to be installed is then positioned over the
appropriate bore 166 and forced downward causing the electrode to
enter the opening formed in the gasket comprising material 176 and
become positioned adjacent the periphery of bore 166. Next, an
additional small quantity of elastomer is injected over the
electrode, thereby securing the electrode in place and sealing the
positioning bore 166.
FIG. 10 is a further cross-sectional view of a portion of
intracochlear mold member 136 in the region of electrodes 51M and
51B prior to the casting of the elastomer carrier. The two
electrodes are depicted as having the same longitudinal position,
although the electrodes are actually longitudinally spaced
apart.
The cross-sectional area of the cavity formed between the lower and
upper intracochlear mold members 136 and 138 is fixed at one value
between the positions for electrodes 51B and 53M and anther larger
value between the positions for electrodes 54B and the remainder of
the electrodes as indicated by curve 61 of FIG. 4. The taper
between the two cross-sections occurs between the positions for
electrodes 53M and 54B.
Returning to FIG. 10, for the small cross-sectional area cavity 144
has a center depth of 0.5 mm and cavity 142 has a center depth of
0.25 mm. The average width of the two cavities is 0.75 mm, with the
sidewalls of cavity 144 being slightly tapered. The four
cross-sectional corners of the cavities have a radius of 0.25 mm.
The center axis for the modiolar electrode positioning bores 166
for the small cross-sectional portion is displaced below the
horizontal axis by 40.degree. with the distance between the upper
most periphery of bores 166 and the top surface of the mold being
approximately 0.2 mm so as to provide sufficient area for the
elastomer material 176. Bores 166 for the basal electrodes have a
vertical central axis which is offset from the center of cavity 144
by 0.10 mm so as to provide clerance for the electrode leads.
For the larger cross-sectional area of array, cavity 144 has a
center depth of 0.625 mm and cavity 142 has a center depth of 0.375
mm. The average width of the two cavities is 1.0 mm, and the
sidewalls of the cavity are slightly tapered. The four
cross-sectional corners of the cavities have a radius of 0.375 mm,
and the center axis for the modiolar electrode positioning bores
166 for the large cross-sectional portion is displaced below the
horizontal axis by 30.degree.. The distance between the uppermost
periphery of bores 166 and the top surface of the mold is again
approximately 0.2 mm and the basilar electrode bore is offset from
the center of cavity by 0.100 mm.
Prior to the installation of the electrodes over bores 166 in the
elastomer gasket, the insulated electrode leads must be positioned
generally down the center of cavity 144. A series of guide pins
168, arranged in spaced-apart pairs, are disposed along the length
of the lower spiral cavity 144 and the lead cavity 148. The bottom
portion of the cavities are provided with openings (not designated)
for temporarily receiving the guide pins. In cavity 144, the guide
pins are positioned generally intermediate adjacent electrode
pairs, or about every 2 mm. The guide pin pairs may be spaced
significantly further apart along the generally linear portion of
cavity 144 and along cavity 148.
The electrodes and associated leads are first positioned between
the guide pin pairs 168 along the linear portion of cavities 144
and 148 with the connector spheres (not shown) being positioned
generally over contact pad cavity 158. The relative position of the
large and small gauge leads are preferably as shown in FIG. 6C
although other lead arrangements may be used. As indicated by
cross-section 118 of FIG. 6B, the relative spacing of guide pins
168 in this region should be great enough to snugly receive three
horizontally-positioned small-gauge leads, with the individual
leads aligned vertically between the guide pins. By way of further
example, cross-section 106 of FIG. 6B indicates that the guide pins
168 positioned between electrodes 56M and 57B should be spaced
apart to snugly receive two horizontally-positioned large-gauge
leads, with the individual lead aligned vertically between the
pins.
It is important that all of the electrode leads be individually
vertically aligned between the guide pins. Once all of the leads
are in position, the individual electrodes are inserted in the
elastomer gaskets 144 (FIG. 9D) as previously described. Since the
electrode leads are individually vertically aligned, it will be
necessary to twist the electrode leads, as depicted in FIG. 10, in
order to insert the electrodes into the gaskets.
Once the electrodes have been inserted and secured in place using
additional elastomer material, the connector spheres are positioned
in the appropriate openings in the contact pad cavity 158. It is
important to note that the path taken by each electrode lead for a
given contact pad cavity opening to the associated positioning bore
166 is constant, therefore the electrode leads may be of a single
length and interchangeable (except for the large and small gauge
leads) thereby greatly simplifying assembly of the array.
Once the electrodes have been tacked in position with a quantity of
elastomer, small quantities of elastomer are deposited at various
points along the electrode lead path to secure the leads together
and to the surface of the mold cavity. Next, the guide pins 168 are
removed from their respective bores. The assembly is now ready for
injecting the uncured elastomer so as to form the carrier.
The carrier may be cast either using injection molding, centrifugal
molding or a combination of both. First the upper main mold member
132 is installed on the lower main mold member 134. The two members
are secured together by tightening screws 150. Next, a suitable
quantity of elastomer is mixed with the appropriate catalyst and
centrifuged in a vacuum environment to remove any air bubbles. The
elastomer is then added to the reservoir of the casting fixture.
The fixture is then installed on a centrifuge utilizing mounting
bore 162 and returned to a vacuum environment. The fixture is then
centrifuged for approximately fifteen minutes at three G's so as to
propel the uncured elastomer from the reservoir through the
numerous small openings into the mold cavity.
After centrifuging, the fixture is removed from the vacuum
environment and placed in a curing oven or hotplate set at
approximately 200.degree. F. for several hours. Once the elastomer
is cured, screws 150 are unscrewed causing the upper main mold
member 132 to separate from the lower member 134. The formed
electrode array is then carefully removed from the lower mold
member and the flash is removed using nippers.
The elastomer carrier is elastic and retains a memory of the
original shape of the mold. The grouped electrode leads which form
the central rib structure 48 have some tendency to straighten the
intracochlear portion of the array so as to cause the array
depicted in FIG. 3 to uncurl approximately one-quarter turn.
The surgical handling properties of the intracochlear portion of
the electrode array are governed by the central rib structure and
the elasticity of the carrier. There tends to be a sharp decrease
in the stiffness of a conventional central rib structure at the
position of each electrode pair when flexed from the basal portion
of the array and moving toward the tip of the array, since there
are progressively fewer electrode leads present in the rib
structure. However, by utilizing a relatively large gauge wire or
otherwise stiffer wire in the leads extending into the apical
portion of the array, the flexibility of the array becomes more
uniform.
The apical tip of conventional electrode arrays also had a tendency
to curl upward and out of the plane of the cochlear spiral during
the implantation procedure, so as to cause damage to the basilar
membrane. The disclosed central rib structure 48 greatly reduces
the tendency of the tip to deflect out of the plane of the cochlear
spiral, but provides an anisotropic and longitudinally consistent
stiffness which permits the array to flex smoothly in the plane.
This is achieved by virtue of the use of electrode leads having an
elongated cross-section which are individually aligned vertically,
i.e., the major axis of the cross-section is transverse to the
plane of the spiral.
In addition, the relative placement of the electrode leads in the
central rib structure contributes to the desired physical
properties of the array. It is preferred that the leads be stacked
in a vertical arrangement with respect to the spiral plane, as
opposed to a horizontal arrangement, to the extent possible. This
further enhances the stiffness of central rib structure 48 in the
vertical direction yet allows for the desired flexing in the
horizontal plane. Given the height restrictions of the scala
tympani, and therefore the maximum thickness of the electrode
array, it is not possible to stack all of the lead vertically
throughout the length of the electrode array as shown in
cross-section 82 of FIG. 6A. For example, at cross-section 94 of
FIG. 6A, it is necessary to position some of the leads horizontally
so as to limit the height of central rib structure 48. Similarly,
FIG. 6C shows a preferred lead stacking arrangement in the area of
the array where central rib structure 48 includes all sixteen
leads, such as in the region between the basal end of the array and
electrode 58M. Other suitable lead stacking arrangements can be
used to achieve the desired results.
It is generally desirable to maximize the exposed surface area of
the individual electrodes so as to reduce the current densities and
thereby to minimize the possibility of tissue damage and the like.
The preferred exposed electrode area may range from approximately
0.08 mm.sup.2 to approximately 0.12 mm.sup.2 with the preferred
approximate area being 0.1 mm.sup.2 as previously noted.
In view of current spread between electrode pairs which tends to
cause channel interaction, approximately 2.0 mm has been found to
be ideal electrode pair spacing for patients with good auditory
nerve survival in the basilar membrane, although spacing of
approximately 1.6 mm would be adequate and provide meaningful
channel resolution. This measurement is made from the center of one
basilar electrode to the center of the adjacent basilar electrode.
For patients having poor nerve survival, the pair spacing should be
increased from 2.0 mm to enable the patient to resolve the
individual channels. The objective for most patients is to space
the electrode pairs a sufficient distance so as to achieve channel
resolution, yet not too great a distance so as to be unable to
stimulate a portion of surviving nerves between the electrode
pairs. It has been found that the maximum pair spacing for such
patients is approximately 2.4 mm.
In order to more effectively stimulate the auditory nerves in the
basilar membrane, it has been found that the modiolar electrode
should be positioned as near to the basilar membrane as possible
without causing severe current shunting between the electrodes. The
angle of inclination of the modiolar electrode should be displaced
above the plane of the electrode array spiral by at least
20.degree. and not more than 50.degree..
The center-to-center spacing of the basilar and modiolar electrodes
within a pair should be at least 0.650 mm, measured from center to
center, with a spacing of 0.800 mm being found to be optimal, and
1.00 mm being the maximum value. The longitudinal offset of the
electrodes within a pair should be approximate 0.20 mm to 0.60 mm,
with 0.40 being found to be optimum.
It is important that the intracochlear portion of the electrode
array rest within the scala tympani in a relaxed condition without
exerting force against any structures within the scala tympani.
Therefore, the intracochlear portion of the array must have a
spiral form which matches the spiral of the cochlea and which
generally correspondes to the following equation:
Where R is the radius of the spiral in milimeters and .0. is the
angle in radians.
As previously noted, the intracochlear portion of the subject
electrode array includes a basal portion and an apical portion
having differing cross-sectional dimensions. It has been found for
most patients that the basal portion should not have a height which
exceeds approximately 1 mm (measured vertically with respect to the
spiral plane) and should not exceed approximately 18 mm in length.
Further it has been found that the apical portion should not have a
height which exceeds approximately 0.80 mm and should preferably
not extend beyond 8 mm from the basal portion of the array.
The electrode leads associated with the electrodes positioned in
the apical portion of the array should be relatively stiffer than
the remaining electrode leads. At least the most apical three
electrode pairs, and preferably only the most apical two pairs
should have relatively stiff leads in comparison to the remaining
leads.
Thus a novel electrode array and method of manufacturing same has
been disclosed. Although preferred embodiments of the subject array
and method have been described in some detail, it is to be
understood that various changes can be made by persons skilled in
that art without departing from the spirit and scope of the
invention as defined by the appended claims.
* * * * *