ELECTRODE ARRAY ASSEMBLY

TECHNICAL FIELD

The present invention relates to electrode array assemblies for use in medical implants and to methods for forming them.

PRIORITY CLAIM

The present application claims priority from Australian Provisional Patent Application No. 2007906988 entitled "Electrode Array Assembly".

The entire content of this provisional application is hereby incorporated by reference.

INCORPORATION BY REFERENCE

The following documents are referred to in the present specification:

- US Patent No. 6,421,569 entitled "Cochlear Implant Electrode Array";

- International Patent Application No. PCT/AU2008/001712 entitled "Lead For A Cochlear Implant";

- International Patent Application No. PCT/AU2008/001718 entitled "Electrode Array for a Cochlear Implant"

- Australian Provisional Patent Application No. 2007906282 entitled "Electrode Array and Method"; and

- Australian Provisional Patent Application No. 2007906688 entitled "Stylet For a Medical Implant".

The entire content of each of these documents is hereby incorporated by reference.

BACKGROUND

A variety of medical implants apply electrical energy to tissue of a patient to stimulate that tissue. Examples of such implants include pace makers, auditory brain stem implants (ABI), devices using Functional Electrical Stimulation (FES) techniques, Spinal Cord Stimulators (SCS) and cochlear implants (CI).

A cochlear implant allows for electrical stimulating signals to be applied directly to the auditory nerve fibres of a patient, allowing the brain to perceive a hearing sensation approximating the natural hearing sensation. These stimulating signals are applied by an array of electrodes implanted into the patient's cochlea.

The electrode array is connected to a stimulator unit which generates the electrical signals for delivery to the electrode array. The stimulator unit in turn is operationally connected to a signal processing unit which also contains a microphone for receiving audio signals from the environment, and for processing these signals to generate control signals for the stimulator.

The electrode array is typically manufactured by placing a plurality (for example 22) of electrode contacts into a welding die, welding a conductive pathway such as a wire to those contacts and then removing the structure from the welding die for further processing, such as placing the structure in a moulding die to form a silicone carrier.

Due to the fragile components used in the construction of the electrode array, it is extremely difficult to perform the removal of the partially assembled electrode array from the welding die without damaging the conductive pathways, electrode contacts, or welded connections. It is also difficult not to disrupt the relative positioning of the electrode contacts while handling the electrode array during further processing.

This may lead to increased complexity in manufacturing, an increase in manufacturing costs, and may result in damaged and reject product, further adding to costs.

SUMMARY According to a first aspect of the present invention, there is provided a method of forming an electrode contact sub-assembly for use in a medical implant, the method comprising: placing at least two electrode contacts in a spaced relationship; and applying at least one permanent bridging material to connect the at least two electrode contacts.

In one form, the method further comprises applying a further material to the at least two electrode contacts prior to applying the at least one permanent bridging material.

In one form, the method further comprises connecting at least one conductive pathway to each of the at least two electrode contacts.

According to a second aspect of the present invention, there is provided a method of forming an electrode array sub-assembly for use in a medical implant, the method comprising:

obtaining an electrode array comprising at least two electrode contacts with at least one respective conductive pathway; and applying at least one permanent bridging material to connect the at least two electrode contacts.

In one form, the method further comprises applying a further material to the at least two electrode contacts prior to applying the at least one permanent bridging material.

In one form, the at least one permanent bridging material is silicone.

In one form, the further material is a silicone adhesive.

According to a third aspect of the present invention, there is provided a method of forming an electrode lead for a medical implant, the method comprising: placing an electrode array sub-assembly comprising at least two electrode contacts with at least one respective conductive pathway, and at least one permanent bridging material connecting the at least two electrode contacts in a die; adding a carrier material to the die; and allowing the carrier material to cure.

In one form, the method further comprises curving the electrode array sub-assembly prior to placing the electrode array sub-assembly in the die.

In one form, the die is a curved die.

In one form, the method further comprises placing a production stylet in the die prior to adding the carrier material to form a lumen.

According to a fourth aspect of the present invention, there is provided an electrode contact sub-assembly for use in a medical implant, comprising at least two electrode contacts and at least one permanent bridging material connecting the at least two electrode contacts.

In one form, the electrode contact sub-assembly further comprises a further material disposed between the at least two electrode contacts and the at least one permanent bridging material.

In one form, the at least one permanent bridging material is silicone.

In one form, the further material is a silicone adhesive.

According to a fifth aspect of the present invention, there is provided an electrode lead for a medical implant, comprising: an electrode array sub-assembly comprising at least two electrode contacts with at least one respective conductive pathway and at least one permanent bridging material connecting the at least two electrode contacts; and a carrier material supporting the electrode array sub-assembly.

In one form, the electrode lead is curved.

In one form, the electrode lead further comprises a lumen.

According to a sixth aspect of the present invention, there is provided a medical implant comprising: a stimulator for generating stimulation signals for stimulating tissue of an implantee; and an electrode lead connected to the stimulator for applying the stimulation signals to the tissue, wherein the electrode lead comprises an electrode array sub-assembly comprising at least two electrode contacts with at least one respective conductive pathway and at least one permanent bridging material connecting the at least two electrode contacts; and a carrier material supporting the electrode array sub-assembly.

In one form, the medical implant is a cochlear implant.

DRAWINGS

The various aspects of the present invention are described in detail with reference to the following drawings in which: Figure IA - shows a perspective view of a distal end of an electrode array for use in the various aspects of the present invention;

Figure IB - shows a perspective view of a distal end of an alternative electrode array for use in the various aspects of the present invention;

Figure 1C - shows a perspective view of a distal end of yet another alternative electrode array for use in the various aspects of the present invention;

Figure 2- shows a perspective view of a medial section of an electrode array;

Figure 3 - shows the electrode array of Figure 2 with the bridging material forming an electrode array sub-assembly;

Figure 4 - shows an end view of the sub-assembly of Figure 3; Figure 5 - shows a perspective view of an alternative form of bridge;

Figure 6 - shows a perspective view of a further alternative form of bridge;

Figure 7 A - shows a perspective view of yet a further alternative form of bridge;

Figure 7B - shows a cross-section along the line A-A of Figure 7 A;

Figure 8 A - shows a partial electrode contact sub-array according to one aspect of the present invention;

Figure 8B - shows an electrode contact sub-array according to one aspect of the present invention;

Figure 8C - shows the electrode contact sub-array of Figure 8 A with conductive pathways attached; Figure 9A - is a flow chart of the broad steps of one method of forming an electrode contact sub- assembly;

Figure 9B - is a flow chart of the steps in a method of forming an electrode array sub-assembly according to an aspect of the present invention;

Figure 10A- is a flow chart showing the broad steps of another method of forming an electrode contact sub-assembly;

Figure 1OB - is a flowchart of more detailed steps of the method of Figure 9B;

Figure 11 - is a flow chart of the steps in a method to form an electrode lead according to an aspect of the present invention;

Figure 12 - is a flow chart showing the steps of a modified method of forming an electrode lead; Figure 13 - shows a perspective view of an electrode array in place in a die during the manufacture of an electrode array sub-assembly;

Figure 14 - shows a perspective view of the arrangement of Figure 13 with a bridging material applied;

Figure 15A - shows a cross-section of the electrode array sub-assembly along the line A-A of Figure 14;

Figure 15B - shows a cross-section of the electrode array sub-assembly along the line B-B of Figure 14; Figure 16 - shows the electrode sub-assembly in a curving die to form an electrode array lead;

Figure 17A - shows an electrode array lead formed by the method of Figure 12;

Figure 17B - shows a cross-section of the electrode array lead of Figure 17A along the line A-A; and

Figure 18 - shows a cochlear implant having a stimulator and electrode array lead attached thereto.

DETAILED DESCRIPTION

Throughout the following description, the term "electrode array" will be understood to mean a collection of two or more electrode contacts and their respective conductive pathways. It should be appreciated however, that in the literature and prior art, the term "electrode array" may also be used to refer to the combination of contacts, pathways and carrier members or materials in which the electrode contacts and conductive pathways are disposed.

Throughout the following description, the term "conductive pathway" will be understood to mean any energy-carrying or guiding pathway that will carry or guide energy from one point to another, whether that energy is in the form of electricity, in which case the conductive pathway may be an electrically conductive wire made of any suitable material including platinum or Carbon Nanotubes, or if the energy is in the form of light, the conductive pathway may be for example, an optical fibre or a nanowire.

Throughout the following description, the term "electrode contact" will be understood to mean the element to which the stimulating energy is transferred by the conductive pathway, and through which the stimulating energy is applied to the tissue of the implantee. The electrode contact may be in the form of an electrically conductive element, or in other forms, an optical transmitter for applying light or optical energy to the tissue.

Throughout the following description, the term "electrode lead" will be used to mean the electrode array and the carrier material supporting the electrode array. The electrode lead may be connected to the stimulator to transfer stimulating energy to the tissue of the implantee.

Figures IA, IB and 1C show various forms of electrode arrays that may be used with the various aspects of the present invention. Figure Ia is a perspective view of a distal end of an electrode array 10, comprising a plurality of electrode contacts 11, 11' and 11 " and respective conductive pathways 12, 12' and 12". The conductive pathways may be connected to their respective electrode contacts by any suitable means including welding, adhering, crimping or knotting. In one embodiment, the conductive pathways 12 are provided by conductive wires. In other embodiments, the conductive pathways 12 could be provided by Carbon Nanotubes (CNTs) as described in International Patent Application No. PCT/AU2008/001718 previously incorporated by reference, hi other embodiments, the conductive pathways may be provided by optical fibres, nanowires or other wave guide to transport optical energy to the electrode contact for optical stimulation of the tissue.

Figure IB shows a perspective view of the distal end of an electrode array 10 made in this example, from a plurality of electrode contacts 11, 11 ' and 1 1 " with integral respective conductive pathways 12, 12' and 12". In one form, the electrode contact 11 and respective conductive pathway 12 may be formed by stamping from a sheet of suitable material such as platinum, or in another example, a sheet of CNTs.

Figure 1C shows a perspective view of yet another alternative form of an electrode array 10, with electrode contacts 11, 11 ' and 11 " and respective conductive pathways 12, 12' and 12" formed in this case by squashing platinum rings to a U-shape to form the electrode contact 11 and trapping the respective conductive pathway 12 therein.

Any other suitable form or arrangement of electrode array may also be used.

Figure 2 shows a perspective view of a medial section of an electrode array 10 with electrode contacts 11 and conductive pathways 12 of the form shown in Figure 1C. As shown in Figure 2, conductive pathways 12 are laid along the length of the electrode array 10 as defined by the layout of the electrode contacts 1 1.

In practice, each conductive pathway 12 is welded or otherwise electrically-connected to a respective electrode contact 11, and run in-line with subsequent electrode contacts 11.

As can be appreciated, the resulting assembly is very fragile, and the connections between the conductive pathways 12 and electrode contacts 11 may be easily damaged during further processing. Furthermore, the relative positions of the electrode contacts 11 with respect to each other may be disrupted.

According to one aspect of the present invention, a bridge between the electrode contacts is provided to provide stability between the different elements. In this aspect, the bridge is a permanent structure, in that the bridge is not removed during further assembly, and remains a part of the electrode assembly throughout its use.

Figure 3 shows the application of at least one permanent bridging material to form the bridge 20, forming an electrode array sub-assembly for further processing. In one form, the bridging material is silicone. In one form, the bridging material is a silicone adhesive, such as 3-1595 silicone adhesive provided by Dow Corning ®, or a High RTV silicone adhesive such as NuSiI MEDl 134 from NuSiI Technology LLC.

Alternative polymers include Liquid Silicone Rubber (LSR), (e.g. from Dow Corning® such as SILASTIC® 7-4860 BIOMEDICAL GRADE LSR or Nusil MED 4860), a Silicone Elastomer (e.g. from Nusil or Dow Corning®); or Parylene C (e.g. from Para Tech Coating, Inc.).

In one embodiment, a combination of the above, and/or other materials may be used. For example, the bridge 20 may be formed by layered silicone by forming the bridge with a combination of adhesive and LSR as will be described in more detail later.

Figure 4 shows a cross sectional end view of the electrode array sub-assembly of Figure 3. There can be seen electrode contact 11 with a respective conductive pathway 12, connected thereto. Also shown are other conductive pathways 12' which are connected to other electrode contacts and which are passing over electrode contact 11. Also visible is bridge 20, which in this embodiment, substantially fills the region of the electrode contacts, covering the conductive pathways which in this case are in the form of platinum wires 12, 12'.

An advantage of the silicone bridge 20 is that it allows for further layering of the Silicone. Different Silicones have different properties. For example, in one embodiment, the silicon bridge is a Silicone Adhesive layer securely binding the contacts 11 and optionally, the conductive pathways 12 while having the remaining bulk of the electrode carrier needed to form the electrode lead being a Liquid Silicone Rubber (LSR).

A number of variations may be made to the various aspects of the invention described above. In one form, instead of injection moulding the silicone bridge 20, the bridge 20 could be made by a thin coating/layer. This could be made by , for example, spraying or brushing silicone over the electrode array 10. The silicone is may be diluted with N-heptane prior to applying a thin coating layer. An arrangement using this form is shown in Figure 5, in which the bridge 20 is provided as a thin layer over electrode contacts 11 and conductive pathways 12.

In yet another alternative, the bridge 20 could be made from a pre-moulded, or otherwise separately moulded, silicone bridge made and then attached (e.g. glued with silicone) to the electrode array 10. This strip would be permanent and become an integral part of the carrier. Such an arrangement is shown in figure 6, where the bridge 20 is provided by a thin strip of pre-made bridging material and then applied over the electrode contacts 11 and wires 12. The bridge 20 may be applied to the electrode contacts only, the conductive pathways only, or to both electrode contact and conductive pathway. In one embodiment, the LSR bridge is applied or connected to the electrode contacts only, using silicone adhesive.

In yet a further alternative, sparing use of a bridge may be made, as shown in Figure 7 A. As shown in this embodiment, the bridge 20 is made by applying a thin coating of material along the entire length of the electrode array 10 before it is removed from the welding die (not shown).

Figure 7B shows a cross sectional view along line A-A of the bridge 20 of Figure 7 A. The thin coating is made by, for example, spraying, brushing or drizzling silicone over the electrode array 10 while it is located in the welding die (not shown). The silicone may be diluted with N-heptane prior to its application to reduce the silicone's viscosity. Reducing the viscosity of the silicone allows it to be more evenly distributed over the electrode contacts 11 and conductive pathways 12 of the electrode array 10. In this way, it is possible to reduce the viscosity of the silicone such that it can flow over the contacts 11 and conductive pathways 12 to form a homogenous mass, while remaining sufficiently viscous to cling to the surface of the electrode array 10. Alternatively, the thin coating 25 may be made by spraying or brushing Parylene over the electrode array 10.

Figures 8 A to 8C show the construction of another aspect of the present invention, relating to an electrode contact sub-array. In this aspect, it will be appreciated that the electrode contacts may be connected by the bridge without any conductive pathways, to form an electrode contact sub-array. Figure 8A shows two electrode contacts 11 and 1 1 '. These may e of any form such as those shown in Figures IA to 1C. Figure 8B shows the two electrode contacts 11 and 11 ' connected by bridge 20 to form the electrode contact sub- array. In this embodiment, the bridge 20 is of the form shown in Figure 6, however, any other form of bridge as previously described may be used. In some embodiments, the bridge 20 may cover all or most of the electrode contacts 11 and 1 1 ' and holes may be formed in the bridge 20 to accommodate

conductive pathways that may be added at a later processing stage. Alternatively, the conductive pathways may be connected from underneath or on the edges of the electrode contact. Figure 8C shows the electrode contact sub-array with electrode contacts 11 and 11 ' with respective conductive pathway 12, 12'.

It will be appreciated therefore that the present invention may be applied to electrode contacts alone, to provide the relative support and stability for further processing, including the addition of conductive pathways.

Figure 9A shows the broad steps involved in constructing an electrode contact sub-array. In step 90, the electrode contacts are placed in a spaced relationship as shown in Figure 8 A. In step 91, the permanent bridging material is applied over the electrode contacts to form the electrode contact sub-array, ready for further processing.

Figure 9B shows the general steps of a method of forming an electrode array sub-assembly (which includes the conductive pathways) according to one aspect of the present invention. In step 100 an electrode array of contacts with respective conductive pathways such as wires is obtained. In step 102, a permanent bridging material such as silicone is applied to the electrode array to support and retain the electrode contacts and respective conductive pathways in relative position to each other. As will be described in more detail later, this sub-assembly may then be processed in any desired way, including curving or moulding.

Figure 1OA shows the broad steps of forming an electrode contact sub-assembly according to another aspect of the invention. In step 92, the electrode contacts are placed in a spaced relationship with respect to each other. In step 93, the electrode contacts are coated with a permanent bridging material. In step 94, the bridging material is cured or otherwise allowed to cure. This forms the electrode contact sub- assembly, ready for further processing. One form of further processing is shown in step 95, which is to connect one or more respective conductive pathways to the electrode contacts, thus forming an electrode array sub-assembly.

Figure 1OB is a more detailed flowchart of the steps used in the method of manufacturing an electrode array sub-assembly (which includes the electrode pathways) according to one aspect of the present invention. In this method, an electrode array consisting of a plurality of electrode contacts with respective conductive pathways or wires connected thereto is obtained at step 200. This electrode array is then coated with the bridging material such as silicone in step 201 , and in step 202, the bridging material is cured, or allowed to cure, in accordance with the specifications of the manufacturer of the material.

If a layered bridge is used each layer may need to be cured (or partially cured) prior to the addition of the next layer as will be described in more detail further below. In some embodiments however, depending upon the choice of silicones used, some may be cured together.

Figure 11 shows the steps involved in a full method of forming an electrode array lead using within it, the method as described in relation to Figures 8 and 9. This method describes the forming of one example only and it will be appreciated that various variations may be made in relation to one or more of the steps described. In this method, the first part is the connection of the conductive pathways or wires 12 to respective electrode contacts 11, for example by welding. Such a process is described in US Patent No. 6,421, 569, previously incorporated by reference. In step 300 the electrode contacts are formed by slicing 0.3mm wide sections of platinum tube. The formed contacts are then placed in a welding jig and squashed to a U shape in step 301. In step 302, a bundle of 22 conductive wires is placed in the welding jig and in step 303, each wire is connected to a respective contact (e.g. by welding). The wire strand travels from the contact proximally in the bottom of all the proximal U-shaped contacts. It will be appreciated of course that in some embodiments, the conductive pathways will already be connected to their respective electrode contacts such as in the arrangement shown in Figure IB.

The method as previously described with reference to Figure 9B is now used to continue the process. In step 304, the welding die lid is placed on the welding jig and then in step 305, bridging material such as silicone is injected into the die. In step 306, the die is placed in an oven to cure the silicone, or otherwise allowed to cure on its own in accordance with the manufacturer's specifications. The curing of silicone is well known to the person skilled in the art and need not be described further.

The next stage involves using the formed electrode array sub-assembly to manufacture an electrode array lead as follows. In step 307, the sub-assembly is removed from the die and then in step 308, it is carefully curved to match the shape of a moulding die. The following steps used in moulding of the electrode array are also described in previously referred to and incorporated, US Paten No. 6,421,569.

In step 309, the sub-assembly is then placed in the moulding die (curved) with the electrode contacts being located closer to the medial side (inside of the curve). This is to form a carrier about the electrode array sub-assembly. The space in the die is then packed with a carrier material such as silicone material in step 310. In step 311, a matching die cover is placed over the assembly and pressed down. The die is then placed in an oven to cure the silicone in step 312 (or otherwise allowed to cure on its own, in accordance with the manufacturer's specifications) and then in step 313, the die is opened to allow the resulting electrode array lead to be removed from the die.

Note that a variety of moulding dies may be utilised, including straight and partially curved.

Figure 12 shows the various steps in yet a further exemplary method of forming an electrode array lead.

The various steps are described and further illustrated in Figures 12 to 16B.

As shown in Figure 12, the manufacturing process begins with the initial stage 600 of assembling an electrode array. In step 700 an electrode contact 11 is placed in a straight welding die 14 (see Figure 13) such that it is located at a proximal end of the U-shaped channel 13. The next step 702 involves connecting each electrode contact 11 to its respective conductive pathway 12. In the embodiment shown in Figure 13, each electrode contact 11 is connected to its conductive pathway ( in this example, an electrically conductive wire) 12 by threading an end of the wire through a ring before squashing the ring down in the channel 13 of the welding die 14 to form the U-shaped trough 15 of the contact 11. The end of the wire is then folded over and welded to the bottom of the U-shaped trough 15 before placing subsequent rings along the channel 13 of the welding die 14 and drawing their respective wires over and through the trough 15 of each contact 11 previously formed. This process is repeated until all of the contacts 11 have been connected to their respective conductive pathways 12.

The next stage 602 of the manufacturing process involves forming a bridge 20 over the electrode array 10. As shown in Figure 14, this involves the step 706 of spraying or otherwise applying a first material 21 (providing the further material), such as silicone adhesive, to the surface of each electrode contact. In step 708, the first material 21 is cured by placing the welding die 14 into a heated oven over a period of time, or allowing the silicone to cure on its own in accordance with the manufacturer's specifications. After curing the silicone adhesive, a lid (not shown) is placed over the welding die 14 to cover the U- shaped channel 13 before a second material 22, (providing the at least one permanent bridging material) such as Liquid Silicone Rubber (LSR), is injected into the welding die 14 at step 710. In step 712, the welding die 14 is again placed in an oven to allow the second material 22 to cure (or otherwise allowing to cure on its own in accordance with the manufacturer's specifications) in order to form the bridge 20. This forms the electrode array sub-assembly.

As indicated by step 714, the electrode array sub-assembly may now be removed from the welding die 14. Figures 15A and 15B show cross-sections of the electrode array sub-assembly along the lines A-A and B- B respectively, hi Figure 15 A, it can be seen that the bridge 20 comprises a first material 21 and a second material 22, wherein the first material 21 is formed from silicone adhesive applied within the U-shaped trough 15 of each contact 11 as described above with respect to step 706. Forming the first material 21 from silicone adhesive allows a strong bond to be created between the contact 11 and the bridge 20 to prevent the contact detaching from the electrode array during explantation of the electrode array. The silicone adhesive also helps the conductive pathways 12 to remain seated in the U-shaped trough 15 of each contact 11 during further processing. The second material 22 is formed from Liquid Silicone Rubber (LSR) with a Shore hardness ranging between 10 to 80 Durometers. It will be appreciated that

while Figure 15A shows some of the bridging material filling the eyelets resulting from the squashing of the electrode ring, this need not necessarily occur, and forms no part of the invention. In some cases, the eyelets will have no material in them, in other cases, the eyelets may have a combination of materials in them, depending upon the characteristics of the materials used and the processing methods used.

Figure 15B shows a cross sectional view along line B-B of the bridge 20 of Figure 14, wherein only the second material 22 is applied between each contact (not shown). Forming the second material 22 from Liquid Silicone Rubber (LSR) having a Shore hardness ranging between 10 to 80 Durometers provides the bridge 20 with the required hardness and may also provide some protection to the conductive pathways 12 of the electrode array 10 while is being handled during further processing. It will be appreciated however, that the purpose of the bridge 20 is not necessarily to provide protection to the conductive pathways directly. The mere presence of the bridge in providing support to and between the electrode contacts and maintaining the relative positioning between the electrode contacts may also provide some incidental protection to the conductive pathways. Indeed, in some embodiments, the bridge 20 need not even contact or cover the conductive pathways at all. The second material of LSR also provides the bridge 20 with the required structural integrity so the electrode array 10 is adequately supported while it is handled during further processing. It is noted that using LSR with a Shore hardness ranging between 10 to 35 Durometers is particularly desirable as this range allows the bridge 20 to remain sufficiently flexible so as not to impede or "fight against" any curving force provided by any curved moulded silicone that may be later added, as will be described later.

Returning now to Figure 12, in order to complete the manufacture of the electrode array 10 lead, a number of further steps need to be taken. In order to form a lumen 32 in the carrier member 30 as shown in Figure 16, a production stylet 33 is attached to the bridge 20 in step 716. Various methods of attaching the production stylet 33 are described in US Patent No. 6,421,569 previously incorporated by reference. In step 718, the electrode array sub-assembly 10 is placed in the moulding die 31 such that the electrode contacts 11 are located on a medial side (i.e. inside) of the curve. After placement of the electrode array sub-assembly 10 inside the moulding die 31, a matching moulding cover 34 is placed over the moulding die 31 before a High Consistency Peroxide Cure (HCRP) silicone is injected into the moulding die 31 at step 720. In step 722, the moulding die 31 is placed in an oven to allow the HCRP silicone to cure (or otherwise allowed to cure in accordance with the manufacturer's specifications) in order to form the carrier member, resulting in the formation of the fully assembled electrode array lead.

The electrode array lead described above forms the distal end of an electrode array lead 30 as shown in Figure 17A that is adapted to be connected to an implantable cochlear stimulator (ICS) (not shown). The electrode array lead 30 includes the electrode array of electrode contacts 11 and respective conductive pathways 12, the carrier material 31 surrounding the electrode contacts 11 and the bridging material

inside. Figure 17B shows a cross-section view of Figure 17A along line A-A. In the embodiment shown, the carrier member 30 is formed from a High Consistency Peroxide Cure (HCRP) silicone with a Shore hardness ranging between about 10 to 80 Durometers. In this instance, it is noted that forming the carrier member 30 from HCRP silicone having a greater Shore hardness than the material/s 21, 22 of the bridge 20 allows the carrier member 30 to retain its pre-curved shape. However, it is to be appreciated that any suitable biocompatible material may be used to form the carrier member 30, including Liquid Silicone Rubber (LSR) and polyurethane rubber, and is not necessarily restricted to the specific example given above.

As previously described, the formed electrode array lead may be attached to a stimulator to form a medical implant, such as a cochlear implant. Figure 18 shows a cochlear implant 400 having stimulator 410 with electrode array lead 30.

The various aspects of the present invention may be used in relation to any type of electrode array lead, including straight and curved, peri-modiolar electrodes, short/basilar electrodes, as well as electrode arrays with or without lumens or stylets. The various aspects of the present invention are also usable with aspects of electrode arrays described in International Patent Application No. PCT/AU2008/001712 entitled "Lead For A Cochlear Implant"; Australian Provisional Patent Application No. 2007906282 entitled "Electrode Array and Method"; and Australian Provisional Patent Application No. 2007906688 entitled "Stylet For a Medical Implant", all previously incorporated by reference.

The various aspects of the present invention are also applicable to other implantable electrode arrays, including auditory brain stem implant (ABI) electrode arrays, Functional Electrical Stimulation (FES) electrode arrays, and Spinal Cord Stimulator (SCS) electrode arrays.

One particular advantage of the various aspects of the present invention is that as it facilitates the holding of the electrode contacts more securely during assembly, more than typical number of contacts may be used as part of this invention. The number of electrode contacts may vary between 2 contacts and 256 contacts, or even more. Typically, the number of contacts would be 22 as described above.

Yet a further advantage is that more than one conductive pathway or wire 12 may be connected to a single electrode contact 11. Multiple wires provide redundancy in case one of them breaks, and furthermore, also provide greater mechanical flexibility for a given electrical resistance.

It will also be appreciated that the various aspects of the present invention have been described in relation to specific embodiments, various modifications and variations may be made. For example, while a bridge comprising two different materials has been described, it will be appreciated that any number of materials

may be used to construct the bridge. It is also envisaged that the bridge may consist of different materials blended together to form an admixture. Alternatively, each material may be applied along the length of the electrode array to form a distinct layer, or to only particular sections of the electrode array, as described in the above embodiment. Furthermore, different materials may be applied along the length of the electrode array in order to vary the physical properties along the length of the bridge. For example, the bridge may be made softer and more flexible along a distal portion of the electrode array than at a proximal portion of the electrode array to minimise the risk of insertion trauma and resulting damage to residual hearing.

Throughout the specification and the claims that follow, unless the context requires otherwise, the words "comprise" and "include" and variations such as "comprising" and "including" will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.