Flexible electrode assembly having variable pitch electrodes

An electrode assembly for use in a prosthetic hearing implant, the electrode assembly comprising: an elongate carrier member for implantation into the cochlea, the carrier member having a proximal end adapted to be positioned in a basal region of the cochlea, and a distal end adapted to be positioned in an apical region of the cochlea; and a plurality of electrodes disposed along a longitudinal surface of the carrier member, wherein the plurality of electrodes have a predetermined spacing to attain a desired flexibility along the length of the carrier member.

BACKGROUND

1. Field of the Invention

The present invention relates generally to stimulating medical devices and, more particularly, to a flexible implantable electrode assembly for a stimulating medical device.

2. Related Art

Hearing loss is generally of two types, namely conductive and sensorineural. The treatment of both of types of hearing loss has been quite different, relying on different principles to deliver sound signals to be perceived by the brain as sound. Conductive hearing loss occurs when the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded, for example, by damage to the ossicles. In such cases, hearing loss is often improved with the use of conventional hearing aids, which amplify the sound so that acoustic information reaches the cochlear hair cells. Such hearing aids utilize acoustic mechanical stimulation, whereby the sound is amplified according to a number of varying techniques, and delivered to the inner ear as mechanical energy. This may be through a column of air to the eardrum, or through direct delivery to the ossicles of the middle ear.

On the other hand, sensorineural hearing loss is due to the absence or destruction of the cochlear hair cells which are needed to transduce acoustic signals into auditory nerve impulses. Individuals suffering from this type of hearing loss are unable to derive any benefit from conventional hearing aid systems regardless of the volume of the acoustic stimulus. This is because the natural mechanisms for transducing sound energy into auditory nerve impulses are either absent or damaged. In such cases, Cochlear™ implants (also referred to as Cochlear™ devices, Cochlear™ prostheses, Cochlear™ implant systems, and the like; simply “cochlear implants” herein) have been developed to provide the sensation of hearing to such individuals. In cochlear implants, electrical stimulation is provided via stimulating electrodes positioned as close as possible to the nerve endings of the auditory nerve, essentially bypassing the hair cells in a normally functioning cochlea. The application of a stimulation pattern to the nerve endings causes impulses to be sent to the brain via the auditory nerve, resulting in the brain perceiving the impulses as sound.

More recently, there has been an increased interest in Electro-Acoustical Stimulation (EAS) in which electrical stimulation of the cochlea is used in conjunction with acoustical stimulation. It is relatively common in hearing impaired individuals to experience sensorineural hearing loss for sounds in the high frequency range, and yet still be able to discern sounds in the middle to low frequency range, through the use of a conventional hearing aid, or naturally. Traditionally, in the majority of such cases, the recipient would only receive treatment to preserve and improve the hearing for the middle to low frequency sounds, most probably via a conventional hearing aid, and little would be done to attempt to restore the hearing loss for the high frequency sounds. This is due to the potential trauma caused by the implantation of an electrode assembly into the cochlea. Only if the individual lost the ability to perceive middle to low frequency sounds would consideration then be given to restoring the hearing loss for the high frequency sounds, in which case a cochlear implant would be considered a possible solution.

SUMMARY

In one aspect of the invention, an electrode assembly for use in a prosthetic hearing implant, the electrode assembly comprising: an elongate carrier member for implantation into the cochlea, the carrier member having a proximal end adapted to be positioned in a basal region of the cochlea, and a distal end adapted to be positioned in an apical region of the cochlea; and a plurality of electrodes disposed along a longitudinal surface of the carrier member, wherein the plurality of electrodes have a predetermined spacing to attain a desired flexibility along the length of the carrier member.

In another aspect of the invention, an electrode assembly for use in a prosthetic hearing implant is disclosed, the electrode assembly comprising: an elongate carrier member for implantation into the cochlea, the carrier member having a proximal end adapted to be positioned in a basal region of the cochlea, and a distal end adapted to be positioned in an apical region of the cochlea; and a plurality of electrodes disposed along a longitudinal surface of the carrier member, wherein a pitch of the plurality of electrodes varies over at least one portion of the elongate carrier member to attain a desired carrier member flexibility along the length of the carrier member.

DETAILED DESCRIPTION

Embodiments of the present invention are generally directed to an apparatus and method for facilitating implantation of a flexible electrode assembly of a stimulating medical device into a patient (also referred to herein as a recipient). Embodiments of the present invention are described below in connection with one type of stimulating medical device, a cochlear implant. Cochlear implants use direct electrical stimulation of auditory nerve cells to bypass absent or defective hair cells that normally transduce acoustic vibrations into neural activity. Such devices generally use multi-contact electrodes inserted into the scala tympani of the cochlea so that the electrodes may differentially activate auditory neurons that normally encode differential pitches of sound. Such devices are also used to treat a smaller number of patients with bilateral degeneration of the auditory nerve. For such patients, the cochlear implant provides stimulation of the cochlear nucleus in the brainstem. Such devices, therefore, are commonly referred to as auditory brainstem implants (ABIs).

Exemplary embodiments of a cochlear implant include a Contour™, Freedom™, Nucleus™ or Cochlear™ implant sold by Cochlear Limited, Australia. Such devices are described in U.S. Pat. Nos. 4,532,930, 6,537,200, 6,565,503, 6,575,894, and 6,697,674, the entire contents and disclosures of which are hereby incorporated by reference herein. It should be understood to those of ordinary skill in the art that embodiments of the present invention may be used in other stimulating medical devices such as neurostimulators, cardiac pacemakers/defibrillators, etc. as well as other medical devices which utilize an elongate carrier member to temporarily or permanently implant, deliver or otherwise introduce a therapeutic agent, sensor, device, etc. into a recipient.

FIG. 1is a cut-away view of the relevant components of outer ear101, middle ear102and inner ear103, which are described next below. In a fully functional ear, outer ear101comprises an auricle105and an ear canal106. An acoustic pressure or sound wave107is collected by auricle105and channeled into and through ear canal106. Disposed across the distal end of ear cannel106is a tympanic membrane104which vibrates in response to acoustic wave107. This vibration is coupled to oval window, or fenestra ovalis,110through three bones of middle ear102, collectively referred to as the ossicles111.

Ossicles111comprises the malleus112, the incus113and the stapes114. Bones112,113and114of middle ear102serve to filter and amplify acoustic wave107, causing oval window110to articulate, or vibrate. Such vibration sets up waves of fluid motion within cochlea115. Such fluid motion, in turn, activates tiny hair cells (not shown) that line the inside of cochlea115. Activation of the hair cells causes appropriate nerve impulses to be transferred through the spiral ganglion cells (not shown) to auditory nerve116and, ultimately, to the brain where they are perceived as sound. In some persons experiencing sensorineural hearing loss, there is an absence or destruction of the hair cells. Cochlear implant120is utilized to directly stimulate the ganglion cells to provide a hearing sensation to such persons.

FIG. 1also shows how cochlear implant120is positioned in relation to outer ear101, middle ear102and inner ear103. Cochlear implant120comprises external component assembly122which is directly or indirectly attached to the body of the recipient, and an internal component assembly124which is temporarily or permanently implanted in the recipient. External assembly122comprises microphone125for detecting sound which is provided to a behind-the-ear (BTE) speech processing unit126that generates coded signals. The coded signals are provided to an external transmitter unit128, along with power from a power source (not shown) such as a battery. External transmitter unit128comprises an external coil130and, preferably, a magnet (not shown) secured directly or indirectly in external coil130.

Internal component assembly124comprises an internal receiver unit132having an internal coil (not shown) that transcutaneously receives power and coded signals from external assembly122, and provides such signals to a stimulator unit134. In response to the coded signals, stimulator134applies stimulation signals to cochlea115via an implanted electrode assembly140. Electrode assembly140enters cochlea115via a cochleostomy142or through oval window110, and has an array144of one or more electrodes150positioned to be substantially aligned with portions of tonotopically-mapped cochlea115. The delivery of stimulation signals at various locations along cochlea115causes a hearing percept representative of the received sound107.

While cochlear implant120is described as having external components, in another embodiment, the controller, including the microphone, speech processor and power supply, may also be implantable. In such embodiments, the controller may be contained within a hermetically sealed housing or the housing used for stimulator unit134.

Electrode assembly140preferably assumes an optimal electrode position in cochlea115upon or immediately following implantation into the cochlea. It is also desirable that electrode assembly140be configured such that the insertion process causes minimal trauma to the sensitive structures of cochlea115. Usually electrode assembly140is pre-curved, held in a straight configuration at least during the initial stages of the implantation procedure, conforming to the natural shape of the cochlea during and subsequent to implantation.

FIGS. 2A and 2Bare side views of one embodiment of electrode assembly140, referred to herein as electrode assembly200. InFIG. 2A, electrode assembly200is shown in a typical configuration prior to insertion into cochlea115, while inFIG. 2Belectrode assembly200is shown after insertion into cochlea115.FIGS. 2C-2Eare cross-sectional views of electrode assembly200taken along their respective section lines inFIG. 2A.

Electrode assembly200comprises a carrier member202, a collar member204, a holding member213and one or more leads214. Carrier member202has a distal end210and a proximal end228connected to the distal end of laterally-extending collar member204. The opposing proximal end of collar member204is connected to holding member213. Lead214physically and electrically connects electrode assembly200and electrodes212disposed thereon with receiver/stimulator unit134.

The surface of carrier member202which faces the interior of cochlea115when carrier member202is implanted in a recipient, is referred to herein as the medial surface216of carrier member202. The opposing side of carrier member202, referred to herein as lateral surface218, faces the external wall and bony capsule (not shown) of cochlea115when carrier member202is implanted in a recipient. It should be understood that the terms medial surface, medial direction, and the like, are generally used herein to refer to the surfaces, features and directions toward the center of cochlea115, while the terms lateral surface, lateral direction, and the like, are generally used herein to refer to surfaces, features and directions toward the exterior of cochlea115.

A plurality of spaced-apart electrodes212are mounted on or in carrier member202. The array of electrodes212is referred to herein as electrode array230. Electrodes212may be disposed in a linear or non-linear array230on or in carrier member202, and may be positioned to align with predetermined regions of tonotopically mapped cochlea115. In alternative embodiments, electrodes212are implemented as described in the U.S. Provisional Patent Application 60/748,217, 60/748,273 and 60/748,314, which are hereby incorporated by reference herein. Such arrangements allow for individual electrodes212to be utilized to stimulate selected regions of cochlea115.

In one embodiment, electrodes212are half-band electrodes disposed in or on medial surface216of carrier member202. It should be appreciated, however, that any electrodes now or later developed suitable for a particular application may be used in alternative embodiments of the invention. For example, in one alternative embodiment, electrodes212are banded electrodes extending substantially around the circumference of carrier member202. In another embodiment, electrodes212do not laterally extend to or around the edges of carrier member202. Typically, each electrode212is arranged such that its exposed surface is substantially parallel to a longitudinal axis224of carrier member202. It should be appreciated, however, that electrode212may be implemented at other locations and orientations in alternative embodiments. It should further be appreciated that the quantity of electrodes212may vary from as few as one or two to as many as twenty-four or more.

In certain embodiments, at least one electrode212has a surface that is at least adjacent medial surface216of carrier member202. Preferably, one or more electrodes212has a surface that is collocated with medial surface216of carrier member202. In another embodiment, the surfaces of electrodes212are raised above or recessed into medial surface216of carrier member202.

Electrodes212may be manufactured from a biocompatible conductive material such as platinum, although other materials or combinations of materials may be used. Alternatively, electrodes212may be coated with a biocompatible covering that does not interfere with transfer of stimulation signals to cochlea115.

In this illustrative embodiment, each electrode212is electrically connected to at least one multi- or single-filament wire252(FIGS. 2C and 2D) that is embedded within flexible carrier member202, collar member204, handle member213and lead214. In one embodiment, wires252are embedded in a volumetric core254of carrier member202and collar member204. In an alternative embodiment, wires252may be located at or near surface216and/or surface218of carrier member202. In other embodiments, wires252are embedded in different regions of carrier member202to facilitate curvature or to maintain orientation of carrier member202once it is implanted. It is through wires252that stimulator/receiver unit134(FIG. 1) provides electrical stimuli to selected electrodes212. In one embodiment, wires252are connected to electrodes212by welding, although any suitable electrical connections now or later developed may be used.

It should be appreciated that the quantity of wires252connected to each electrode212may vary. For example, in one embodiment, at least two electrically conducting wires252are connected to each electrode212. It should also be appreciated that suitable transmission means other than wires may be used to communicably couple receiver/stimulator unit134with electrodes212. For example semiconductors or wireless technologies may be used.

In one embodiment, lead214extends from handle member213to stimulator134or at least the housing thereof. In one particular embodiment, lead214is continuous with no intermediate electrical connectors external the housing of stimulator unit134; that is, there are no external connectors required to electrically connect electrode assembly200to stimulator134. One advantage of this arrangement is that there is no requirement for a surgeon implanting electrode assembly200to make the necessary electrical connection between wires252extending from electrodes214and stimulator134. Stimulator134is preferably encased within a housing that is implantable within the recipient, such as within a recess in the bone behind the ear posterior to the mastoid.

Returning toFIG. 2A, holding member213is configured to provide improved manual control of electrode assembly200, and to identify electrode orientation. In alternative embodiments, holding member213may be configured as described in U.S. patent application Ser. No. 10/825,360, which is hereby incorporated by reference herein.

In certain embodiments, a profiled tip or tip region211is used to guide electrode assembly200during implantation in a manner that reduced friction. Alternative embodiments of tip region211are described in International Application PCT/US06/34010 entitled, “Elongate Implantable Carrier Member Having An Embedded Stiffener,” and filed Aug. 31, 2006; U.S. patent application entitled “Prosthetic Hearing Implant Electrode Assembly Having Optimal Length for Atraumatic Implantation,” filed concurrently under Ser. No. 11/605,952; and U.S. patent application entitled “Promoting Curvature and Maintaining Orientation of an Electrode Carrier Member of a Stimulating Medical Device,” filed concurrently under Ser. No. 11/605,951 all of which are hereby incorporated by reference herein. In alternative embodiments, tip region211may be as described in U.S. patent application Ser. Nos. 10/825,358 and 11/125,171, which are also hereby incorporated by reference herein.

In certain embodiments, carrier member202also includes a stiffening member208permanently embedded in at least proximal region228of carrier member202. Stiffening member208is embedded, for example, during the manufacture of carrier member202. As shown inFIG. 2A, the illustrative embodiment of stiffening member208extends from an extra-cochlear position through collar member204and into carrier member202. It should be appreciated that in alternative embodiments, stiffening member208need not be embedded in collar member204, and may longitudinally extend further through carrier member202to terminate at any desired location along the length of electrode assembly200. As best shown inFIG. 2B, the distance that stiffening member208extends into carrier member202is such that the stiffening member terminates just before the lateral wall of the first turn of cochlea115when carrier member202is completely inserted into cochlea115.

Stiffening member208is configured to increase the stiffness of carrier member202in the region(s) of carrier member202in which stiffness member208is located. As such, stiffening member208assists in the prevention of buckling and/or deformation of carrier member202in such regions during insertion into cochlea115. In particular, stiffener member208assists in maintaining proximal region228of carrier member202in a sufficiently straight configuration when subjected to the forces typically experienced during implantation. This allows carrier member202and electrodes212to be fully implanted into cochlea115without being subject to insertion forces that may damage the delicate structures of the cochlea.

Additionally, stiffening member208causes electrodes212to be positioned closer to the inner wall of cochlea115, as generally a straight electrode will take a more lateral position in the basal region. As a result, the distance from the stimulating surface of carrier member202to the auditory nerve endings is substantially less than would be the case if stiffening element208were not embedded in electrode assembly200. It is anticipated that this will provide similar benefits in the basal region as a perimodiolar electrode, such as the perimodiolar electrode described in U.S. Pat. No. 6,421,569, which is hereby incorporated by reference herein. It should also be appreciated that the stiffness of member208may be less than, the same, or greater than the stiffness of carrier member202, so long as the presence of stiffening member202in regions of carrier member202results in at least one of such regions having a reduced likelihood of deformation.

FIGS. 3A through 3Care side views of different embodiments of stiffening element208, referred to herein as stiffening element302A,302B, and302C, respectively (generally and collectively referred to as stiffening elements302). Stiffening elements302are configured to be embedded in embodiments of electrode assembly200, as noted above. In these embodiments, the stiffness or malleability of stiffening member208is longitudinally varied so that, for example, that portion of carrier member202toward distal end210is more flexible than that portion of carrier member202toward proximal end228. Such variability may be attained, for example, by annealing (FIG. 3A), tapering (FIG. 3B) or stepped reduction (FIG. 3C). In these and other embodiments, there preferably is a gradual transition between adjacent segments of stiffening member208. It should be appreciated that the implemented stiffness is a function of the particular application of cochlear implants and may be different in other applications.

Referring toFIG. 3A, stiffening element302A is formed of, for example, glass or metal, which is annealed, i.e., subject to a process of heating and slow cooling to toughen and reduce brittleness. In the embodiment shown inFIG. 3A, longitudinally adjacent regions308(only one is identified for simplicity) of stiffening member302A are subject to different annealing process, resulting in regions308having a different hardness. In particular, longitudinally successive regions308have incrementally greater or less flexibility, depicted inFIG. 3Aby successively increasing and decreasing widths of regions308.

Referring toFIG. 3B, stiffening element302B is, in this illustrative embodiment, a unitary member that is tapered from its proximal end306B toward its distal end304B. The reduced volume of material along successive regions of stiffening element302B results in a successively decreasing stiffness. It should be appreciated that the rate of taper will dictate the rate of change in flexibility of carrier member202.

Referring toFIG. 3C, stiffening element302C is an integrated element comprised of a plurality of elongate strips310A-310D of differing lengths. Strips310may be formed of the same or different material, and may be manufactured to have the same or different stiffness. Strips310may be secured to each other or any manner now or later developed. As shown inFIG. 3C, stiffening member302C has a stepped configuration, due to the different lengths of strips310. As such, the stiffness provided by stiffening member302C varies due to the cumulative contribution of each strip310, which varies along its length. As one of ordinary skill in the art would appreciate, strips310need not be arranged to form a continuous series of steps. For example, in embodiments in which the desired flexibility of carrier member202does not vary continuously, strips310may be configured such that, for example, strip310B is longer than strip310C.

Advantageously, stiffening member208provides electrode carrier member202with sufficient stiffness to allow it to be effectively inserted into cochlea115, particularly once carrier member202encounters some resistance beyond the first turn of the cochlea. A further advantage of the variation in stiffness is to ensure that electrode assembly200is suitable for all cochlea sizes. Cochlea sizes, and therefore the basal length, from the round window to the lateral wall of cochlea115, vary slightly between recipients. The basal length is generally a straight path and is usually in the order of approximately 4 mm to 7 mm. The more flexible distal end of stiffening member208ensures that the distal tip of the stiffening member does not impact with the fragile structures of the cochlea. Rather, the distal end deforms allowing carrier member202to curve whilst still ensuring the proximal region of the electrode array200does not buckle or deform. Preferably, the variable stiffness also ensures that carrier member202forms a gradual curve rather than a sharp bend that could result by having a sudden change in mechanical stiffness.

In addition to the embodiments illustrated inFIGS. 3A-3C, the variable stiffness can be achieved by utilizing any number of the following alone or in combination with each other or the embodiments described above: varying the pitch of electrodes212as discussed herein; a plurality of stiffening members spaced at various pitches to provide a variable stiffness; use of different materials at various intervals along the length of stiffening member208; varying dimensions of stiffening element208or its component elements, etc. It should also be appreciated that stiffening member208may be of any manufacturable cross-section, including round, square, rectangular, oval etc., and use any manufacturable method to provide variable stiffness along its length.

In alternative embodiments, stiffening element208extends further into carrier member202, providing regions of enhanced stiffness where desired. It should be appreciated that the regions of stiffness in the embodiments illustrated inFIGS. 3A-3C, or otherwise, need not vary regularly or consistently. Other embodiments of stiffening member208are described in International Application. No. PCT/US06/34010; filed Aug. 31, 2006, which is hereby incorporated by reference herein.

Collar member204may serve as a region for grasping electrode assembly200. Preferably, collar member204is constructed and arranged to prevent insertion of carrier member202beyond a predetermined maximum depth. This reduces the risk of the surgeon over-inserting electrode assembly200, which could cause trauma to the delicate structures of cochlea115. In one preferred embodiment, the predetermined maximum insertion depth230B of carrier member202is approximately 16 mm+/−2 mm.

In the embodiment shown inFIGS. 2A-2E, collar member204has a diameter greater than that of carrier member202. As one of ordinary skill in the art should appreciate, the configuration, orientation and dimensions of collar member204can vary depending on the intended implant location and, more generally, on the application of electrode assembly200. In one embodiment, collar member204extends substantially at right angles to longitudinal axis224of carrier member202. In one embodiment, collar member204has a length of between about 1.5 mm and about 2.0 mm. In another embodiment, collar member204has a length of between about 1.5 mm and about 2.5 mm. Alternatively, collar member204may be constructed and arranged generally as described in U.S. patent application Ser. Nos. 10/518,811 and 11/125,171, which are hereby incorporated by reference herein. In certain embodiments, carrier member202also includes stiffening member208, as described above.

In the embodiments illustrated herein, a band206is located adjacent collar member204, circumferentially surrounding carrier member202at the junction of carrier member202and collar member204. Band206is formed of a material designed to produce a tissue reaction that facilitates tissue attachment to the band, promoting sealing of cochlea115. In one embodiment, this material primarily contains platinum. This is especially important in preserving residual hearing as prompt sealing of cochlea115may greatly reduce the chances of infection of inner ear103due to implantation of electrode assembly200.

In one embodiment, electrodes212are half-band electrodes disposed on medial surface216of carrier member202, as shown inFIGS. 2D and 2E. It should be appreciated, however, that any electrode now or later developed suitable for a particular application may be used in alternative embodiments of the invention. For example, in one alternative embodiment, electrodes212are banded electrodes extending substantially around carrier member202. In another alternative embodiment, electrodes212do not laterally extend to or around the edges of carrier member202. Typically, each electrode212is arranged orthogonal to longitudinal axis250of carrier member202. It should be appreciated, however, that other relative positioning and orientation may be implemented in alternative embodiments. It should further be appreciated that the quantity of electrodes212may vary from as few as one or two to as many as twenty-four or more.

In certain embodiments, at least one electrode212has a surface that is at least adjacent medial surface216of carrier member202. Preferably, one or more electrodes212has a surface that is collocated with medial surface216of carrier member202, as shown inFIGS. 2D and 2E. In another embodiment, the surfaces of electrodes212are raised above or recessed into medial surface216of carrier member202.

Electrodes212may be manufactured from a biocompatible conductive material such as platinum, although other materials or combinations of materials may be used. Alternatively, electrodes212may be coated with a biocompatible covering that does not interfere with transfer of stimulation signals to cochlea115.

In the embodiments depicted inFIGS. 2A,2B and2F, the electrodes are variably spaced to improve flexibility of carrier member202. InFIGS. 2A and 2B, the electrodes212in the basal region are pitched more densely, and the pitch increases toward the center of carrier member202and then decreases toward distal end210of carrier member202. The rate of change in electrode pitch between proximal end228and the approximate center of carrier member202is greater than the more gradual decrease in pitch from the approximate center of carrier member202to distal end210of carrier member202.

This provides a distal region210that is more flexible that proximal region228of carrier member202, reducing insertion forces to achieve the optimal insertion depth. Furthermore, this also insures that the basal region or high frequency region, which is the area benefited by electrical stimulation in EAS patients, has a higher number, or denser array of stimulating surfaces, providing more specificity of stimulation, and also greater pitch matching of electrodes212.

FIG. 4Ais a graph illustrating the relationship between the variable electrode density and flexibility for the embodiment of the present invention illustrated inFIGS. 2A and 2B. InFIG. 4A, the horizontal axis represents carrier member length230B (FIG. 2B) and the position along cochlea115(FIG. 1). When implanted, proximal end228of carrier member202resides in the vicinity of basal end of cochlea115, while distal end210of carrier member202resides in the vicinity of apical end of cochlea115. The vertical axis represents the density of electrodes212and corresponding flexibility of carrier member202.

As noted, inFIGS. 2A and 2B, the pitch or spacing of electrodes212in the basal region is small; that is, the density of the electrodes is greater. The pitch increases toward the center of carrier member202and then decreases toward distal end210of carrier member202. Thus, the density decreases toward the center of carrier member202and increases toward the distal end, as shown by graph line402D. As shown inFIG. 4A, the rate of change in electrode pitch between proximal end228and the approximate center of carrier member202is greater than the more gradual decrease in pitch from the approximate center of carrier member202to distal end210of carrier member202.

Returning toFIG. 2Fis a side view of another embodiment of an electrode assembly of the present invention. In this embodiment, the electrode pitch continues to increase from proximal region228to distal region210. As shown in correspondingFIG. 4B, this provides a range of flexibility404F that increases steadily along the length of carrier member202, with proximal region228having increased density404D and decreased flexibility404F and distal region210having decreased density404D and increased flexibility404F.

The greater flexibility in distal region210As compared with proximal region228reduces the insertion forces required to achieve the optimal insertion depth. This also insures that the basal (high frequency) region of cochlea115, which is the area benefited by electrical stimulation in EAS patients, has a greater density of electrodes, providing more specificity of stimulation, and also greater pitch matching of electrodes212.

As one of ordinary skill in the art would appreciate, the type, dimensions and other characteristics of electrodes212and other elements of the electrode carrier member may be altered in concert with the electrode spacing or pitch to achieve a desired level of flexibility along the length of electrode carrier202.

The increased density of electrodes212in proximal region228of electrode carrier member202provides additional stiffness sufficient to assist in the prevention of buckling of carrier member202during insertion into cochlea115. This allows carrier member202and electrodes212to be introduced into cochlea115without deformation, thereby enabling full insertion without application of unnecessary force which may damage the delicate structures of the cochlear.

Additionally, the density of electrodes212in proximal region228of carrier member202causes the basal electrode contacts212to be positioned closer to the inner wall of cochlea115, as generally a straight electrode will take a more lateral position in the basal region. As a result, the distance from the stimulating surface of carrier member202to the cochlear nerve is shorter. It is anticipated that this will provide similar benefits in the basal region as a perimodiolar electrode, such as the perimodiolar electrode described in U.S. Pat. No. 6,421,569.

As noted, in certain embodiments, carrier member202also includes a stiffening member208as described above. In certain embodiments, stiffening member208may be longitudinally varied in concert with the variable pitch of electrodes212to achieve a desired flexibility along the length of carrier member202.

An advantage of the variation in stiffness is to ensure that electrode assembly200is suitable for all sizes of cochleas. Cochlea sizes, and therefore the basal length, from the round window to the lateral wall of cochlea115, vary slightly between patients. The basal length is generally a straight path and is usually in the order of 4 mm to 7 mm. The more flexible distal end210of carrier member202ensures that the distal tip of the stiffening member does not impact with the fragile structures of the cochlear. Rather, the distal end deforms allowing the carrier member202to curve whilst still ensuring the proximal region of the electrode array200does not buckle or deform. Preferably, the variable stiffness also ensures that carrier member202forms a gradual curve rather than a sharp bend that could result by having a sudden change in mechanical stiffness.

Returning toFIG. 2A, collar member212serves as both a region for grasping electrode assembly200and also acts to prevent insertion of carrier member202beyond a predetermined maximum depth to reduce the risk of the surgeon over-inserting electrode assembly200, which could otherwise cause trauma to the delicate structures of cochlea115. In one embodiment described in the noted concurrently-filed US Provisional Patent Applications, incorporated by reference elsewhere herein, the predetermined maximum depth is approximately 16 mm+/−2 mm.

In the embodiment shown inFIG. 2A, collar member212has a diameter slightly greater than that of carrier member202. As one of ordinary skill in the art should appreciate, the configuration, orientation and dimensions of collar member212can vary depending on the intended application of electrode assembly200. In one embodiment, collar member212extends substantially at right angles to longitudinal axis224of carrier member202. In another embodiment of the present invention, collar member212has a length of between about 1.5 and about 2.0 mm. Alternatively, collar member204may be constructed and arranged generally as described in U.S. patent application Ser. Nos. 10/518,811 and 11/125,171, which are hereby incorporated by reference herein in their entireties.

Referring toFIGS. 2A,2B,2D and2E, in certain embodiments, electrode carrier member202is longitudinally-tapered. As such, the dimensions of carrier member202at section line2D-2D are greater that the dimensions of carrier member202at section line2E-2E, as shown inFIGS. 2D and 2E. This tapered configuration may, in certain embodiments, result in a continuous gradual taper to tip region210. Tip region210facilitates the insertion of carrier member202into a recipient's cochlea115. In one embodiment, tip member region210comprises a taper which slopes from a lateral surface218rearward and inward toward the medial surface216. Such a tapered tip region210aids the coiling of carrier member200and further helps prevent damage to the delicate structures of the cochlea.FIG. 2C, which is a cross-sectional view of collar member212, shows a marker304to facilitate orientation and a lumen through which wires252and stiffening element208extend.

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.

All documents, patents, journal articles and other materials cited in the present application are hereby incorporated by reference.