Patent Description:
Cochlear implant systems are used to provide, restore and/or improve hearing loss suffered by cochlear implant patients who use the cochlear implant systems. A key component of a cochlear implant system is an electrode lead that is inserted into a cochlea of the patient. A distal end portion of the electrode lead is provided with a plurality of stimulation electrodes for applying a stimulation current to auditory nerve tissue within the cochlea, which is supplied via electrode wires extending through the electrode lead and electrically connecting the respective stimulation electrode with a cochlear implant implanted within the patient at the proximal end of the electrode lead. A proximal portion of the electrode lead may be provided with one or more ground electrodes for providing a current return path for stimulation current applied by the stimulation electrodes; alternatively, the ground electrode(s) may be provided separate from the electrode lead. The ground electrode may be designed as a ring electrode, which is disposed on the electrode lead and is electrically connected via a ground wire extending within the proximal portion of the electrode lead to the cochlear implant. An example of such cochlear implant system is described in <CIT>.

Another example of a cochlear implant electrode lead with a ground ring electrode is known from <CIT>, wherein the ring electrode is provided on a large diameter tube, with the stimulation electrode wires being helically coiled through the interior of the tube which is backfilled with silicone; also the ground wire is helically coiled and passes through the center of the helically coiled stimulation wires. Each side of the ring electrode is provided with silicone tapers for smoothing the profile of the tube, for securing the ring electrode in place and for reducing the potential for kinking of the tube. The ring electrode has the shape of a hollow cylindrical cylinder. The ground wire passes out of an opening in the sidewall of the tube and is electrically connected to the ring electrode disposed over the tube.

<CIT> relates to a cochlear electrode lead with a fixed ring electrode which does not form an elevation. <CIT> relates to a cochlear electrode lead with a ring electrode which is not fixed onto a tube and wherein an outer sheath is pushed onto the ends of ring electrode. <CIT> and <CIT> relate to methods of manufacturing a cochlear electrode lead, wherein a mandrel is used.

The ring of the ground electrode and the ground wire may be susceptible to fluid ingress, especially if the electrode lead has been stressed near the ring or the device fantail; fluid ingress can lead to high electrode impedances over time. Further, silicone tapers at both sides of the ring electrode - due to lack of a consistent boundary of the applied silicone - may be susceptible to variants of silicone application.

It is an object of the invention to provide for a method of manufacturing an electrode lead for a cochlear implant system, having a ground electrode which is relatively resistant to fluid ingress, in a relatively consistent and efficient manner.

According to the invention, this object is achieved by a manufacturing method as defined in the single claim.

The manufacturing method defined is beneficial in that it allows for particularly consistent and efficient manufacturing of the electrode lead. In particular, the dual tube configuration, with a first tube portion and a second tube portion abutting each other within the interior of the ground ring electrode, allows for full assembly of a sub-assembly of the ground ring electrode and the ground wire attached to the ground ring electrode, with the ground wire extending through the gap between the first tube portion and the second tube portion, whereby the need for passing the ground wire through the inner diameter of the tub and pulling it out through an opening cut in the tube wall can be avoided.

According to one embodiment, the ground wire may be wound co-radially with the electrode wires. This improves manufacturability and decreases potential-process failures.

According to one embodiment, the ground wire may be made of Pt and coated with PPSU, whereby the bonding to the ground wire and a silicone backfill of the tube may be improved.

According to one embodiment, the outer surface of the central portion of the ground electrode is radially elevated relative to the outer surface of the first end portion and the outer surface of the second end portion of the ground electrode, so as to form a step at the boundary between the first end portion and the central portion and at the boundary between the second end portion and the central portion, respectively, and the silicone coating is applied to the outer surface of the first and second end portion of the ground electrode in such a manner that the outer surface of each of the silicone coatings is substantially flush with the outer surface of the central portion of the ground electrode.

According to one embodiment, each of the first end portion and the second end portion comprises a ring-like marker structure, and the silicone coating is applied to the outer surface of the first and second end portion of the ground electrode in such a manner that the silicone coating does not extend axially beyond the ring-like marker structures into the central portion.

According to one embodiment, the ground wire is wound co-radially with the electrode wires onto the mandrel.

Hereinafter, examples of the invention will be illustrated by reference to the attached drawings, wherein:.

As used hereinafter, the term "distal" refers to portions or components that are farther away from the cochlear implant (hermitically sealed enclosure) or the surgeon implanting the cochlear implant, and the term "proximal" refers to portions or components that are closer to the cochlear implant or the surgeon implanting the cochlear implant. As used hereinafter, the term "substantially" should be understood as "within ± <NUM>%".

The terms "ground electrode", "ring electrode" and "ground ring electrode" are used in an interchangeable manner hereinafter to designate a ring-shaped ground electrode.

<FIG> illustrates an exemplary cochlear implant system <NUM>. As shown, cochlear implant system <NUM> may include a microphone <NUM>, a sound processor <NUM>, a headpiece <NUM> having a coil disposed therein, a cochlear implant <NUM>, and an electrode lead <NUM>.

Electrode lead <NUM> includes an array of stimulating electrodes <NUM> (also referred to as intracochlear electrodes) disposed on a distal portion of electrode lead <NUM> and that are configured to be located within and to stimulate the cochlea after the distal portion of electrode lead <NUM> is inserted into the cochlea. As shown, electrode lead <NUM> also includes a ground electrode <NUM> (also referred to as a ring electrode) disposed on a proximal portion of electrode lead <NUM> and that is configured provide a current return path for stimulation current generated by stimulation electrodes <NUM> and to remain external to the cochlea after electrode lead <NUM> is inserted into the cochlea. While a single ground electrode <NUM> is shown in <FIG>, it will be recognized that multiple ground electrodes <NUM> may be disposed on the proximal portion of electrode lead <NUM> as may serve a particular implementation. As shown, electrode lead <NUM> may be pre-curved so as to properly fit within the spiral shape of the cochlea. Additional or alternative components may be included within cochlear implant system <NUM> as may serve a particular implementation.

As shown, cochlear implant system <NUM> may include various components configured to be located external to a patient including, but not limited to, microphone <NUM>, sound processor <NUM>, and headpiece <NUM>. Cochlear implant system <NUM> may further include various components configured to be implanted within the patient including, but not limited to, cochlear implant <NUM> and electrode lead <NUM>.

Microphone <NUM> may be configured to detect audio signals presented to the user. Microphone <NUM> may be implemented in any suitable manner. For example, microphone <NUM> may include a microphone that is configured to be placed within the concha of the ear near the entrance to the ear canal, such as a T-MIC™ microphone from Advanced Bionics. Such a microphone may be held within the concha of the ear near the entrance of the ear canal by a boom or stalk that is attached to an ear hook configured to be selectively attached to sound processor <NUM>. Additionally, or alternatively, microphone <NUM> may be implemented by one or more microphones disposed within headpiece <NUM>, one or more microphones disposed within sound processor <NUM>, one or more beam-forming microphones, and/or any other suitable microphone as may serve a particular implementation.

Sound processor <NUM> (i.e., one or more components included within sound processor <NUM>) may be configured to direct cochlear implant <NUM> to generate and apply electrical stimulation (also referred to herein as "stimulation current") representative of one or more audio signals (e.g., one or more audio signals detected by microphone <NUM>, input by way of an auxiliary audio input port, input by way of a clinician's programming interface ("CPI") device, etc.) to one or more stimulation sites associated with an auditory pathway (e.g., the auditory nerve) of the patient. Exemplary stimulation sites include, but are not limited to, one or more locations within the cochlea, the cochlear nucleus, the inferior colliculus, and/or any other nuclei in the auditory pathway. To this end, sound processor <NUM> may process the one or more audio signals in accordance with a selected sound processing strategy or program to generate appropriate stimulation parameters for controlling cochlear implant <NUM>. Sound processor <NUM> may be housed within any suitable housing (e.g., a behind-the-ear ("BTE") unit, a body worn device, headpiece <NUM>, and/or any other sound processing unit as may serve a particular implementation).

In some examples, sound processor <NUM> may wirelessly transmit stimulation parameters (e.g., in the form of data words included in a forward telemetry sequence) and/or power signals to cochlear implant <NUM> by way of a wireless communication link <NUM> between headpiece <NUM> and cochlear implant <NUM> (e.g., a wireless link between a coil disposed within headpiece <NUM> and a coil physically coupled to cochlear implant <NUM>). It will be understood that communication link <NUM> may include a bi-directional communication link and/or one or more dedicated uni-directional communication links.

Headpiece <NUM> may be communicatively coupled to sound processor <NUM> and may include an external antenna (e.g., a coil and/or one or more wireless communication components) configured to facilitate selective wireless coupling of sound processor <NUM> to cochlear implant <NUM>. Headpiece <NUM> may additionally or alternatively be used to selectively and wirelessly couple any other external device to cochlear implant <NUM>. To this end, headpiece <NUM> may be configured to be affixed to the patient's head and positioned such that the external antenna housed within headpiece <NUM> is communicatively coupled to a corresponding implantable antenna (which may also be implemented by a coil and/or one or more wireless communication components) included within or otherwise associated with cochlear implant <NUM>. In this manner, stimulation parameters and/or power signals may be wirelessly transmitted between sound processor <NUM> and cochlear implant <NUM> via a communication link <NUM> (which may include a bi-directional communication link and/or one or more dedicated uni-directional communication links as may serve a particular implementation).

Cochlear implant <NUM> may include any type of implantable stimulator that may be used in association with the systems and methods described herein. For example, cochlear implant <NUM> may be implemented by an implantable cochlear stimulator. In some alternative implementations, cochlear implant <NUM> may include a brainstem implant and/or any other type of cochlear implant that may be implanted within a patient and configured to apply stimulation to one or more stimulation sites located along an auditory pathway of a patient.

In some examples, cochlear implant <NUM> may be configured to generate electrical stimulation representative of an audio signal processed by sound processor <NUM> (e.g., an audio signal detected by microphone <NUM>) in accordance with one or more stimulation parameters transmitted thereto by sound processor <NUM>. Cochlear implant <NUM> may be further configured to apply the electrical stimulation to one or more stimulation sites (e.g., one or more intracochlear regions) within the patient via electrodes <NUM>, <NUM> disposed along electrode lead <NUM> (e.g., applying current by way of stimulating electrodes <NUM> that returns by way of ground electrode <NUM>). In some examples, cochlear implant <NUM> may include a plurality of independent current sources each associated with a channel defined by one or more of electrodes <NUM>. In this manner, different stimulation current levels may be applied to multiple stimulation sites simultaneously by way of multiple electrodes <NUM>.

The human cochlea is in the shape of a spiral beginning at a base and ending at an apex, and auditory nerve tissue resides within the cochlea resides. The auditory nerve tissue is organized within the cochlea in a tonotopic manner. Relatively low frequencies are encoded at or near the apex of the cochlea (referred to as an "apical region") while relatively high frequencies are encoded at or near the base (referred to as a "basal region"). Hence, electrical stimulation applied by way of electrodes disposed within the apical region (i.e., "apical electrodes") may result in the patient perceiving relatively low frequencies and electrical stimulation applied by way of electrodes disposed within the basal region (i.e., "basal electrodes") may result in the patient perceiving relatively high frequencies. The delineation between the apical and basal electrodes on a particular electrode lead may vary depending on the insertion depth of the electrode lead, the anatomy of the patient's cochlea, and/or any other factor as may serve a particular implementation.

An example of a ring-shaped ground electrode (hereinafter "ring electrode <NUM>") disposed on the electrode lead <NUM> is shown in <FIG>. The electrode lead <NUM> comprises a tube <NUM> having a first tube portion <NUM> and a second tube portion <NUM>, which are axially aligned to each other and which axially abut each other, thereby forming a circumferential gap <NUM>, which is filled with silicone adhesive and which is surrounded by the ring electrode <NUM>. The tube <NUM> may be formed, for example, from silicone with a shore A hardness of approximately <NUM> to <NUM>. The tube <NUM> has an interior volume <NUM>, which is backfilled with a fast-cure silicone adhesive, such as an adhesive available under the designation NuSil Technology MED2-<NUM> from the company Avantor located in Radnor, Pennsylvania, USA.

A helically wound or coiled ground wire <NUM> extends from the cochlear implant <NUM> through the interior volume <NUM> of the second tube portion <NUM> to the ring electrode <NUM>, to which it is electrically connected, typically via laser welding. As can be seen in <FIG>, an end portion <NUM> of the ground wire <NUM> extends through the gap <NUM>, which thus forms an opening in the tube <NUM>, to the ring electrode <NUM>. The ground wire <NUM>, in one example, may be coated with PPSU and may be made of Pt. This provides for a good bonding between the ground wire <NUM> and the silicone backfill in the interior volume <NUM> of the tube <NUM>. A backfill of with a silicone adhesive, such as one available under the designation NuSil Technology MED2-<NUM> from the company Avantor located in Radnor, Pennsylvania, USA, in the interior volume <NUM> provides for a good bonding to the PPSU coated ground wire <NUM> and the wall of the tube <NUM>. In some implementations, the ground wire may be solid; alternatively, it may be multi-stranded.

The preferred materials for the coating of the ground wire <NUM> and the backfill of the tube <NUM> provide for good fluid resistance and increased adhesion.

As shown in <FIG>, a plurality of electrode wires <NUM> extends in a helically wound/coiled configuration through the backfilled interior volume <NUM> of the tube <NUM>, wherein each of the electrodes wires <NUM> connects one of the stimulation electrodes <NUM> to the cochlear implant <NUM>. As can be seen in <FIG>, the ground wire <NUM> is co-radially wound with regard to the electrode wires <NUM>. Typically, the ground wire <NUM> has a larger diameter than each one of the electrode wires <NUM>, so that it is able to carry the sum of the stimulation currents produced by the electrodes <NUM>. The ground wire <NUM> may be multi-strand to reduce the stiffness resulting from the larger diameter.

The ring electrode <NUM> comprises a first end portion <NUM>, a central portion <NUM> axially adjacent to the first end portion <NUM> and a second end portion <NUM> axially adjacent to the central portion <NUM>. The outer surface <NUM> of the central portion <NUM> is radially elevated relative to the outer surface <NUM> of the first end portion <NUM> and the outer surface <NUM> of the second end portion <NUM>, so as to form a step <NUM> at the boundary between the first end portion <NUM> and the second end portion <NUM> and a step <NUM> at the boundary between the second end portion <NUM> and the central portion <NUM>, respectively. The outer surface <NUM> of the central portion <NUM> may be highly polished for best biofilm resistance or it may be laser textured to increase the surface area.

In the example shown in <FIG>, the outer diameter of the central portion <NUM> of the ring electrode <NUM> is axially substantially constant over the entire length of the central portion <NUM>, so that the outer surface <NUM> of the central portion <NUM> is substantially cylindrical. Also, the outer diameter of the first end portion <NUM> and the second end portion <NUM> is substantially constant over the entire length of the respective end portion, so that the outer surface <NUM>, <NUM> of the first end portion <NUM> and the second end portion <NUM> is substantially cylindrical, with the first end portion <NUM> and the second end portion <NUM> having substantially the same outer diameter. Further, the ring electrode <NUM> may be symmetric in the axial direction, i.e., the axial dimension of the first end portion <NUM> is substantially the same as the axial dimension of the second end portion. Also, the first end portion <NUM>, the second end portion <NUM> and the central portion <NUM> may have the same inner diameter, so that the inner surface <NUM> of the ring electrode <NUM> is circular cylindrical.

The ring electrode <NUM> may be made of Pt, Ti, a Ptlr alloy or a Ti alloy or any other biocompatible conductor.

As can be seen in <FIG>, at least part of the inner surface <NUM> of the ring electrode is provided with a silicone adhesive coating <NUM>, such as one available under the designation NuSil Technology MED3-<NUM> from the company Avantor located in Radnor, Pennsylvania, USA, which is located between the outer surface <NUM> of the tube <NUM> and the inner surface <NUM> of the ring electrode <NUM>, so as to attach the ring electrode <NUM> to the tube <NUM>.

As can be seen in <FIG>, the first end portion <NUM> and the second end portion <NUM> of the ring electrode <NUM> are covered, on the respective outer surface <NUM>, <NUM>, by a silicone coating (which also may be labelled "taper") <NUM>, <NUM>, which extends from the outer surface <NUM> of the tube <NUM> to the step <NUM>, <NUM> at the boundary between the central portion <NUM> and the respective first end portion <NUM> or second end portion <NUM>. The silicone coatings <NUM>, <NUM> serve to stabilize attachment of the ring electrode <NUM> to the tube <NUM> and to seal the edges <NUM>,<NUM> of the first and second end portions <NUM>, <NUM> to the tube <NUM>, so as to prevent ingress of fluid into the space between the inner surface <NUM> of the ring electrode <NUM> and the outer surface <NUM> of the tube <NUM>. The silicone coatings <NUM>, <NUM> may be made of, for example, NuSil Technology MED3-<NUM>, like the attachment layer <NUM> between the tube <NUM> and the inner surface <NUM> of the ring electrode <NUM>. In some examples, the ring electrode <NUM> may be mode of Ti, with a primer compound being used to promote adhesion of the silicone material to the Ti surface of the ring electrode <NUM>.

As can be seen in <FIG>, the silicone coatings <NUM> or <NUM> are applied in such a manner that the outer surface of each of the silicone coatings <NUM>, <NUM> is radially substantially flush with the outer surface <NUM> of the central portion <NUM> of the ring electrode <NUM>. In particular, the silicone coatings <NUM>, <NUM> terminate at the steps <NUM>, <NUM>, respectively, so that the entire outer surface <NUM> of the central portion <NUM> of the ring electrode <NUM> remains exposed for contact with tissue when implanted. Thereby, the manufacturing process results in a reproducible and well-defined exposed surface area of the ring electrode <NUM>. In particular, the steps <NUM>, <NUM> prevent inconsistency of silicone application when producing the silicone coatings <NUM>, <NUM>.

As illustrated by the examples shown in <FIG>, the first end portion <NUM> and/or the second end portion <NUM> may be provided with features for attachment of the ground wire <NUM> to the ring electrode <NUM> and/or with features for improving adhesion of the silicone coating <NUM>, <NUM> at the first and second end portions <NUM>, <NUM>. Alternatively, the central portion <NUM> may be provided with a feature for attachment of the ground wire <NUM>.

In some embodiments, the ring electrode <NUM> comprises at least one opening for receiving an end portion <NUM> of the ground wire <NUM>, which is to be welded to the ground electrode <NUM>. For example, as illustrated in <FIG> and <FIG>, at least one opening may comprise at least one slot for receiving the end portion <NUM> of the ground wire <NUM>. As illustrated in <FIG>, at least one slot <NUM> may be provided on the edge <NUM> of the second end portion <NUM>. For example, as shown in <FIG>, two slots <NUM> may be provided on the edge <NUM>, which are circumferentially spaced apart by <NUM> degrees, so that the two slots <NUM> are opposite to each other. As can be seen in <FIG>, the end of the end portion <NUM> of the ground wire <NUM> may be inserted into one of the two slots <NUM>, so as to weld, for example by laser welding, the ground wire <NUM> to the ring electrode <NUM>.

In the examples shown in <FIG> and <FIG>, the central portion <NUM> of the ring electrode <NUM> may be provided with at least one slot <NUM> for receiving an end of the ground wire <NUM>, so as to weld the ground wire <NUM> to the ring electrode <NUM>. Also, in these examples, two of the slots <NUM> may be provided circumferentially spaced apart by <NUM> degrees (only one of these slots <NUM> is visible in the Figures).

Various features for enhancing attachment of the silicone coatings <NUM> or <NUM> to the ring electrode <NUM> are illustrated in <FIG>.

For example, the first end portion <NUM> and/or the second end portion <NUM> of the ring electrode <NUM> may comprise at least one opening for ingress of silicone during manufacturing for anchoring the silicone coating <NUM>, <NUM> to the respective first or second end portion <NUM>, <NUM>. For example, as shown in <FIG>, the first and second end portion <NUM>, <NUM> may be provided with a plurality of holes, in particular circular holes <NUM>, which are circumferentially spaced apart. Alternatively, as shown in <FIG>, the edges <NUM>, <NUM> of the first and second end portions <NUM>, <NUM> may be provided with circumferentially spaced apart slots <NUM>.

In other examples, the outer surface <NUM>, <NUM> of the first and second end portions <NUM>, <NUM> are provided with surface structures for improving the adhesion of the silicone coating <NUM>, <NUM>. For example, as shown in <FIG>, circumferential ribs <NUM> (see <FIG>) or circumferential grooves <NUM> forming a partial thread may be provided on the outer surfaces <NUM>, <NUM> of the first and second end portions <NUM>, <NUM>.

Alternatively, or in addition, the outer surfaces <NUM>, <NUM> of the first and second end portions <NUM>, <NUM> may be roughened for improving adhesion of the silicone coating <NUM>, <NUM>, such as by bead blast treatment, laser treatment or chemical etch; this is schematically illustrated by the darker color in <FIG>.

In some examples, the step <NUM>, <NUM> between the first and second end portion <NUM>, <NUM> and the central portion <NUM>, respectively, may be provided with recesses <NUM>, which are circumferentially spaced apart and which are provided in the outer surface <NUM> of the central portion <NUM> and extend axially into the elevated part of the central portion <NUM>. The recesses <NUM> are configured to allow ingress of silicone during manufacturing for anchoring the silicone coatings <NUM>, <NUM> in the respective first or second end portion <NUM>, <NUM> at the steps <NUM>, <NUM> (see <FIG>).

An example of a method for manufacturing the electrode lead <NUM> illustrated in <FIG> is shown in <FIG>.

In a first step illustrated in <FIG>, the ring electrode <NUM> is provided and an end of a ground wire <NUM> is electrically connected to the ring electrode <NUM>, for example at a slot <NUM> (in the method illustrated in <FIG> the ring electrode <NUM> is of the type shown in <FIG>); preferably, a laser welding process is used.

In the example of <FIG> the welding slot <NUM> is provided in the first end portion <NUM> of the ring electrode <NUM>, and the ground wire <NUM> extends through the interior volume of the ring electrode <NUM> out of the second end portion <NUM>.

In the step shown in <FIG> the sub assembly formed by the ring electrode <NUM> and the ground wire welded thereto is fit to one end 152A of a first tube portion <NUM>, wherein first a silicone adhesive, such as NuSil Technology MED3-<NUM>, is applied to the inner surface <NUM> of the ring electrode <NUM>, so as to form the layer <NUM> shown in <FIG>, and the first end portion <NUM> of the ring electrode is slid over the outer surface <NUM> of the end 152A of the first tube portion <NUM>, so as to attach the ring electrode <NUM> to the first tube portion <NUM>. Thereby, the end portion <NUM> of the ground wire <NUM> is sandwiched between the outer surface <NUM> of the first tube <NUM> and the inner surface <NUM> of the ring electrode <NUM>, as illustrated in <FIG>. After the step shown in <FIG> the end 152A of the first tube portion <NUM> extends into the ring electrode <NUM> from one side along a part of the axial length of the ring electrode <NUM>.

In a next step, a plurality of parallel stimulation electrode wires <NUM> is helically wound/coiled onto a mandrel <NUM>. As illustrated in <FIG>, the mandrel <NUM> with the stimulation electrode wires <NUM> is inserted into the interior of the ring electrode <NUM> and the interior volume <NUM> of the first tube portion <NUM>. Thereafter, the ground wire <NUM> is wound co-radially with the electrode wires <NUM> onto the mandrel <NUM>.

In a next step, as illustrated in <FIG>, a second tube portion <NUM> is slid over the mandrel <NUM> with the stimulation electrode wires <NUM> and the ground wire <NUM>, and one end 155A of the second tube portion <NUM> is inserted into the interior of the ring electrode <NUM>, so that the end 154A of the second tube portion <NUM> abuts the end 152A of the second tube portion, thereby forming a circumferential gap <NUM> through which the end portion <NUM> of the ground wire passes towards the interior surface <NUM> of the ring electrode <NUM>. In this step, the ring electrode <NUM> is attached on the second tube portion <NUM> via silicone adhesive applied to the interior surface <NUM> of the ground electrode, resulting in the adhesive layer <NUM>. The dual tube concept is also illustrated in <FIG>, wherein it is shown by arrows that the first tube portion <NUM> and the second tube portion <NUM> are slid over the mandrel <NUM> towards each other, so as to meet in the interior of the ring electrode <NUM>.

In the step illustrated in <FIG>, silicone coatings <NUM>, <NUM> are applied to the outer surfaces <NUM>, <NUM> of the end portions <NUM>, <NUM> and to the outer surface <NUM> of the first tube portion <NUM> and the second tube portion <NUM> in a region adjacent to the ring electrode <NUM>, so as to seal the ring electrode <NUM> to the first tube portion <NUM> and the second tube portion <NUM>. The silicone coatings <NUM>, <NUM> are applied in such a manner that the outer surfaces of the silicone coatings <NUM>, <NUM> are flush with the outer surface <NUM> of the central portion <NUM> of the ring electrode <NUM>.

In some implementations the ratio of the outer surface area of the central portion <NUM> to the total outer surface area of the ring electrode <NUM> (formed by the sum of the outer surfaces of the central portion <NUM> and the first and second end portions <NUM>, <NUM>) is from <NUM> to <NUM>. The outer surface of the central portion <NUM> represents the exposed surface of the ring electrode <NUM>.

In <FIG> a side view of an example of a cochlear implant <NUM> connected to an electrode lead <NUM> having a ring electrode <NUM> is shown, wherein it is illustrated that the distance d in the axial direction between an end <NUM> of the housing / case <NUM> of the cochlear implant <NUM> from which the electrode lead <NUM> extends and a central cross sectional plane <NUM> extending through the center of the axial length of the ring electrode <NUM> (the plane <NUM> represents the axial center of the ring electrode <NUM>) may be from <NUM> to <NUM> to optimize surgical placement of the cochlear implant system and to achieve optimal electrical performance.

While in the above examples of the ring electrode <NUM> the central portion <NUM> is elevated so as to ensure proper placement of the silicone coating on the ring electrode120 by providing a boundary of the silicone application to the end portions of the ring electrode, in an alternative embodiment such boundary may be provided by a ring-like marker structure on each of the end portions of the ring electrode. Such ring-like marker structures serve to mark the axial boundary of the proper silicone application, so as to ensure that the operator applies a silicone coating to the outer surface of the first and second end portion of the ground electrode in such a manner that the silicone coating does not extend axially beyond the respective marker structure into the central portion.

Claim 1:
A method for manufacturing an electrode lead (<NUM>) for a cochlear implant system (<NUM>), comprising
providing a ring-shaped ground electrode (<NUM>) having an inner surface (<NUM>) and an outer surface (<NUM>, <NUM>, <NUM>) and comprising a first end portion (<NUM>), a central portion (<NUM>) axially adjacent to the first end portion, and a second end portion (<NUM>) axially adjacent to the central portion;
welding an end (<NUM>) of a ground wire (<NUM>) to the ground electrode;
applying a silicone based adhesive to the inner surface of the ground electrode and attaching the ground electrode over an end of a first tube portion (<NUM>) in such a manner that an end (152A) of the first tube portion extends from one side along a part of the axial length of the ground electrode into the interior of the ground electrode, wherein the ground wire extends from the other side of the ground electrode;
winding a plurality of parallel electrode wires (<NUM>) helically onto a mandrel (<NUM>);
inserting the mandrel with the electrode wires into the ground electrode and the first tube portion;
winding the ground wire onto the mandrel;
sliding a second tube portion (<NUM>) onto the mandrel and into the ground electrode so that an end (154A) of the second tube portion abuts the end of the first tube portion in the interior of the ground electrode;
applying a silicone coating (<NUM>, <NUM>) to the outer surface (<NUM>, <NUM>) of the first and second end portion of the ground electrode and to the outer surface (<NUM>) of the first tube portion and the second tube portion in a region adjacent to the ground electrode; and
removing the mandrel.