Abstract:
Disclosed is an electrode lead for a medical implant, and in one example, a cochlear implant. The electrode lead includes a lumen for receiving a stylet for assisting in implanting the device. The lumen of the electrode lead is removable from the electrode lead upon or after implantation.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present invention is a National Stage Application of International Application No. PCT/AU2008/001776, filed Dec. 1, 2008, which claims priority from Australian Patent Application No. 2007906554, filed Nov. 30, 2007, which is hereby incorporated herein by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Field of Invention 
         [0003]    The present invention relates generally to cochlear implants having a lumen for receiving a stylet, and more particularly, to a cochlear implant with an improved lumen arrangement. 
         [0004]    2. Related Art 
         [0005]    A cochlear implant allows for electrical stimulating signals to be applied directly to the auditory nerve fibres of the 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&#39;s cochlea. 
         [0006]    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. 
         [0007]    When inserting the implant into the patient&#39;s cochlea, great care must be taken to avoid damaging the delicate structure of the cochlea. Since the cochlea is a coiled structure, many cochlear implants are manufactured to have a natural curve to facilitate insertion and to fit more naturally in the cochlea once implanted. 
         [0008]    However, while inserting a cochlear implant into the cochlea, it is necessary to straighten portions of the implant as it is being inserted, and then to allow it to naturally reassume its curled state after insertion by extracting the stylet from the lumen. To provide a means for straightening the implant, a rigid or semirigid spike, known as a stylet is used as a “spine” for the implant as it is being inserted. A portion of the implant, known as a lumen, receives the stylet during the insertion process.  FIG. 1A  shows a side view of a cochlear implant electrode lead  10 , for supporting an array of electrode contacts (not shown) with lumen  30  and stylet  20 . Stylet  20  is shown inserted into lumen  30  to straighten the natural curve of the electrode lead  10 . 
         [0009]      FIG. 1B  is a cross-sectional view of the electrode  10  in  FIG. 1  along the line A-A′.  FIG. 1B  shows electrode lead  10  with lumen  30  and stylet  20  inserted in the lumen  30 .  FIG. 1B  also shows electrode conductive wires  11  and electrode contact  12 , associated with one of the electrode conductive wires. The plurality of electrode conductive wires  11  and respective electrode contacts  12  form the electrode array supported by electrode lead  10 . 
       SUMMARY 
       [0010]    According to one aspect of the present invention, an electrode lead for a medical implant is disclosed. The electrode lead comprises: a lumen portion at least partially defining a lumen for receiving a stylet; and a main portion configured to carry one or more electrodes, wherein the main portion is removably connected to the lumen portion. 
         [0011]    In accordance with another aspect of the preset invention, a cochlear implant is disclosed. The cochlear implant comprises a stimulator and an electrode lead supporting an array of electrode contacts, the electrode lead comprising: a lumen portion at least partially defining a lumen for receiving a stylet; and a main portion configured to carry one or more electrodes, wherein the main portion is removably connected to the lumen portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Various aspects and embodiments of the present invention will now be described in detail with reference to the following drawings in which: 
           [0013]      FIG. 1A  shows a prior art electrode lead for a cochlear implant; 
           [0014]      FIG. 1B  is a cross-sectional view of the electrode lead of  FIG. 1A ; 
           [0015]      FIG. 2  is a cross-sectional view of an electrode lead for a cochlear implant according to one embodiment of a first aspect of the present invention; 
           [0016]      FIG. 3A  is a cross-sectional view of another embodiment of an electrode lead for a cochlear implant according to the first aspect of the present invention; 
           [0017]      FIG. 3B  shows the arrangement of  FIG. 3A  after separation; 
           [0018]      FIG. 4A  is a cross-sectional view of an electrode lead for a cochlear implant according to another embodiment of the first aspect of the present invention; 
           [0019]      FIG. 4B  is a cross-sectional side view of the electrode lead of  FIG. 4A ; 
           [0020]      FIG. 5  is a cross-sectional view of a further embodiment of the electrode lead for a cochlear implant according to the first aspect of the invention; 
           [0021]      FIG. 6  is a perspective view of a further embodiment of the electrode lead according to the first aspect of the present invention; 
           [0022]      FIG. 7  is a side view of one embodiment of an electrode lead for a cochlear implant according to a second and third aspect of the present invention; 
           [0023]      FIG. 8  is a side view of another embodiment of an electrode lead for a cochlear implant according to the second and third aspects of the present invention; 
           [0024]      FIG. 9  is a side view of a further embodiment of an electrode lead for a cochlear implant according to the second and third aspects of the present invention; 
           [0025]      FIG. 10  is a side view of yet a further embodiment of an electrode lead for a cochlear implant according to both the first and the second aspects of the present invention combined; 
           [0026]      FIG. 11  is a side view of yet a further embodiment of an electrode lead for a cochlear implant according to both the first and the second aspects of the present invention combined; 
           [0027]      FIG. 12A  is a cross-sectional view of one embodiment of an electrode lead for a cochlear implant according to a fourth aspect of the present invention; 
           [0028]      FIG. 12B  shows the electrode lead of  FIG. 12A  showing swelling of the swelling polymer; and 
           [0029]      FIG. 12C  shows the electrode lead of  FIGS. 12A and 12B  showing further swelling of the swelling polymer; 
           [0030]      FIG. 12D  shows the electrode lead of  FIGS. 12A ,  12 B and  12 C showing even further swelling; 
           [0031]      FIG. 13A  shows an electrode lead according to another embodiment of the present invention; 
           [0032]      FIG. 13B  shows the electrode lead of  FIG. 13  A with the lumen removed; and 
           [0033]      FIG. 14  shows an example of a cochlear implant with an electrode lead to which one or more of the various aspects of the present invention may be applied. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    The various aspects of the present invention will now be described in detail with reference to one or more embodiments of the invention, examples of which are illustrated in the accompanying drawings. The examples and embodiments are provided by way of explanation only and are not to be taken as limiting to the scope of the invention. Furthermore, features illustrated or described as part of one embodiment may be used with one or more other embodiments to provide a further new combination. 
         [0035]    It will be understood that the present invention will cover these variations and embodiments as well as variations and modifications that would be understood by the person skilled in the art. 
         [0036]    During the following description, the term “lumen” will be used to refer to the cavity formed within the electrode lead or a portion of the electrode lead for receiving an insert such as a stylet. 
         [0037]    While the various aspects of the present invention will be described with specific reference to a cochlear implant, it will be understood that the principles of the various aspects of the present invention may be applied to other types of medical implants. For example: 
         [0038]    ABI (Auditory Brainstem Implant, electrode for hearing, placed in the brainstem) such as Cochlear Corporation&#39;s Nucleus 24 [R] Multichannel Auditory Brainstem Implant (Multichannel ABI) 
         [0039]    The auditory brainstem implant consists of a small electrode that is applied to the brainstem where it stimulates acoustic nerves by means of electrical signals. The stimulating electrical signals are provided by a signal processor processing input sounds from a microphone located externally to the user. This allows the user to hear a certain degree of sound. 
         [0040]    FES (Functional Electrical Stimulation) is a technique that uses electrical currents to activate muscles and/or nerves, restoring function in people with paralysis-related disabilities. 
         [0041]    Injuries to the spinal cord interfere with electrical signals between the brain and the muscles, which can result in paralysis. 
         [0042]    This SCS (Spinal Cord Stimulator) system delivers pulses of electrical energy via an electrode in the spinal area and may be used for pain management. An example of a commercially available system is the RESTOREPRIME system by Medtronic, Inc, USA. 
         [0043]      FIG. 2  shows a cross-sectional view of an electrode lead  10  according to one embodiment of the present invention. Shown is the electrode lead  10  provided as two separate parts—a lumen portion  13  and a main electrode lead portion  14 . Lumen portion  13  defines the lumen  30 , for receiving stylet  20 , while main electrode lead portion  14  contains the plurality of electrode contacts  12  and respective conductive pathways or electrode conductive wires  11 , which convey stimulation signals to respective electrode contacts  12  for stimulation of the patient&#39;s or recipient&#39;s tissue. 
         [0044]    Connecting lumen portion  13  to main electrode lead portion  14  is a temporary connector  40 . Temporary connector  40  may be a polymer, and in one example, a resorbable polymer, such as Polyacrylic acid (PAA), Polyvinyl alcohol (PVA), Polyactic acid (PLA) or Polyglycolic acid (PGA), (or any combination thereof) which, after a preset time lapse, or upon contact with fluid, begins to soften or dissolve, allowing lumen portion  13  to be separated from main electrode lead portion  14 . After implantation of the implant into the patient&#39;s cochlea, the surgeon can pull out both the stylet  20  and the lumen portion  13 , leaving only the main electrode lead portion  14  in the cochlea. The result is an implant of reduced bulk, and no easy path for passage of fluid to cause infection. 
         [0045]      FIG. 3A  shows a variation of the electrode lead  10  of  FIG. 2 . Specifically, electrode lead  10  is still made up of the lumen portion  13  and the main electrode lead portion  14  with wires  11  and electrode contact  12 , however, instead of only a single temporary connector  40 , there is now a second temporary connector  50 . 
         [0046]    In this embodiment, temporary connector  40  may be a similar material to that used in the examples given with reference to  FIG. 2 , such that it will soften or dissolve after a preset time period and/or contact with fluid. This will be designed to allow relatively fast separation of lumen portion  13  from main electrode lead portion  14  to allow removal of lumen portion  13  as previously described. 
         [0047]      FIG. 3B  shows the lumen portion  13  with lumen  30  separated from main electrode lead portion  14  with both temporary and second temporary connectors dissolved. 
         [0048]    Second temporary connector  50  may be of a different material such as a resorbable polymer—for example Polyacrylic acid (PAA), Polyvinyl alcohol (PVA), Polyactic acid (PLA) or Polyglycolic acid (PGA). This material is designed to dissolve more slowly than temporary connector  40 , and may slowly release drugs such as antibiotics or neurotrophins into the cochlea to facilitate the healing and recovery process and reduce the likelihood of infection. 
         [0049]    In a further embodiment of this aspect of the invention, the lumen portion  13  defining lumen  30  may be made entirely of the dissolving material as previously mentioned.  FIG. 4A  shows electrode lead  10  made up of lumen portion  13  defining lumen  30 , and main electrode lead portion  14  containing wires  11  and electrode contact  12 . In this embodiment, lumen portion  13  is made substantially of the dissolving material and is disposed on top of main electrode lead portion  14 . Stylet  20  will in use, be received in lumen  30  during or prior to the implant procedure, and after a preset amount of time or contact with fluid, the entire lumen portion  13  will begin to dissolve, leaving stylet  20  completely separated from main electrode lead portion  14 , and able to be pulled out of the cochlea by the surgeon. Alternatively, the surgeon may remove the stylet during insertion, leaving the lumen portion  13  to dissolve over time. In this embodiment, the lumen portion  13  may also release drugs while dissolving. 
         [0050]      FIG. 4B  shows a side view of an electrode lead  10  according to this embodiment as shown in  FIG. 4A . In this view, stylet  20  is not shown. Shown is main electrode lead portion  14  supporting electrode contacts  12  and  12 ′ with respective electrode wires or conductors  11 ,  11 ′. Lumen portion  13  is shown, connected to main electrode portion  14 , and defines lumen  30 . After insertion, lumen portion  13  slowly dissolves, removing lumen  30  and leaving behind main electrode lead portion  14  with associated electrode array. 
         [0051]    In yet a further embodiment as shown in  FIG. 5 , main electrode lead portion  14  may be shaped to provide a channel in which at least a part of lumen portion  13  may be disposed. As in the embodiment described above in relation to  FIGS. 4A and 4B , lumen portion  13  is made up entirely of the dissolving material, which upon dissolving releases stylet  20  (not shown) from main electrode lead portion  14  allowing it to be removed. This particular design provides for an even less bulky main electrode lead portion that is left in the patient&#39;s cochlea. 
         [0052]      FIG. 6  shows a similar design as that shown in  FIG. 5 ; however, main electrode lead portion  14  defines a lower half of electrode lead  10 , while lumen portion  13  defines the upper half of electrode lead  10 . In this embodiment, lumen  30  is defined by both portions, and upon dissolving of the lumen portion  13  material, stylet  20  is freed to be removed by the surgeon. 
         [0053]    According to second and third aspects of the present invention, there is shown an embodiment of electrode lead  10  in which no stylet  20  and therefore no lumen  30  is required at all. 
         [0054]      FIG. 7  shows electrode lead  10  having electrode contacts  12 ,  12 ′ and  12 ″ with a layer of swelling material  60  which upon contact with fluid such as saline or water, or by some other trigger such as humidity, begins to swell. This causes a positive pressure on the surface of electrode lead  10 , causing it to bend or curl. This allows the electrode lead  10  to be manufactured without an inherent curl, providing a much more simplified manufacturing and handling process, and removes the need for a lumen and stylet. 
         [0055]    The function of this aspect of the invention may be enhanced by designing electrode lead  10  to have one or more grooves  15  which are filled with the swelling material  60 . This further enhances the curling action of electrode  10  as material  60  swells. 
         [0056]    Examples of suitable materials for swelling material  60  include any type of suitable water-expanding material. One example is Silastic A™ silicone polymer, mixed for example with a finely-ground NaCl as will be known to the person skilled in the art. The curling effect can be even further enhanced by proving a layer of dissolvable material  70  on the side opposite the swelling material. Dissolving material  70  provides a counter force to swelling material  60  when it is present; however this counter force disappears once material  70  has dissolved. This allows more precise design of curling parameters. 
         [0057]      FIG. 8  shows a further alternative of the embodiment shown in  FIG. 7 , in which electrode lead  10  also has slits or grooves  16  on the side opposite to slits or grooves  15 , and filled with the dissolving material  70 . Having material  70  in slits or grooves  16  provides a greater counter curling force to the curling force provided by swelling material  60 ; however, the presence of slits or grooves  16  when devoid of dissolving material  70  facilitates the curling caused by swelling material  60 . Examples of suitable dissolving materials include those previously mentioned. 
         [0058]      FIG. 9  shows electrode lead  10  in its curled position as slits or grooves  15  are made larger by swelling material  60 , while slits or grooves  16  are made smaller by the disappearance of dissolving material  70  (not shown in this view). 
         [0059]    The degree of curling of electrode  10  can also be controlled by controlling the shape and volume of slits or grooves  15  and  16  during the manufacturing process for example. These may be balanced by the strength or resilience of the electrode  10 . 
         [0060]    In these embodiments, the dissolving layers of material  70  may also contain antibiotics, neurotrophins or other drug compounds. 
         [0061]    It will of course be understood that any other combination of the layers, materials and slits or grooves may be used and will not be limited to only those illustrated. 
         [0062]    While the embodiments described with reference to  FIGS. 7 to 9  may not require a lumen and stylet, it will be appreciated that such can be provided if required. 
         [0063]      FIG. 10  shows a side cross-sectional view of an electrode lead  10  supporting electrode contacts  12  having slits or grooves  15  and dissolving material  70  in which stylet  20  may be embedded. Upon material  70  dissolving, stylet  20  is released to be removed from the cochlea, while also “emptying” slits or grooves  15  to allow them to “open” or expand, thereby causing electrode  10  to curl. In this embodiment, the dissolving material  70  may act to “pull together” the slits or grooves  15 , and upon dissolving, release them to promote curving. 
         [0064]    In another embodiment, the portion of lumen portion  13  above the lumen  30  as seen in  FIGS. 10 and 11  may be made from a dissolving material while a lower portion (below lumen  30 ) may be made from a swelling material. Upon contact with fluid after insertion, the top portion dissolves, removing lumen  30 , while the lower portion swells, to provide even greater curving forces as described above with reference to  FIGS. 7-9 . 
         [0065]      FIG. 11  shows a similar embodiment to that of  FIG. 10 , except that dissolving material  70  is provided in discrete portions, retaining stylet  20  only at discrete points for release upon dissolving. 
         [0066]    According to a fourth aspect of the present invention, electrode lead  10  may be shaped to define a partial lumen  30  or at least a portion of the lumen  30 , to retain stylet  20  in place, and a swelling material may then be used to eject stylet  20  from electrode lead  10  as required after insertion.  FIG. 12A  shows electrode lead  10  shaped so as to provide a recess (which could be referred to as a partial lumen  30 ) for retaining stylet  20 . Electrode lead  10  also supports wires  11  and electrode contacts  12 . 
         [0067]    Once electrode lead  10  is inside the cochlea of the patient, a swelling material  80  coating a lower portion of partial lumen  30  begins to swell as shown in  FIG. 12B . This results in stylet  20  being urged out of partial lumen  30 .  FIG. 12C  shows the swelling material  80  even more swollen, further expelling stylet  20  from partial lumen  30 , and able to be removed by the surgeon.  FIG. 12D  shows the electrode lead  10  after the swelling material  80  has swelled to the extent that it entirely, or almost entirely, fills the cavity that was once lumen  30 , thereby effectively removing lumen  30  from electrode lead  10 . This embodiment will reduce the likelihood of fluids entering a cavity within electrode lead  10  that may subsequently promote infection. 
         [0068]    In a further variation of this embodiment, as shown in  FIG. 13A , the electrode lead  10  can define the entire lumen  30 , which has disposed therein, a material  80  that swells upon contact with fluid. In this arrangement, the stylet may be removed manually by the surgeon during or after the implantation, to leave lumen  30 , which then is effectively removed, as material  80  begins to swell. 
         [0069]      FIG. 13B  shows electrode lead  10  without lumen  30 , as material  80  has swelled to fill the cavity. Again, this embodiment will reduce the likelihood of fluids entering a cavity within electrode lead  10  that may subsequently promote infection. 
         [0070]      FIG. 14  shows a cochlear implant  100  having stimulator  90  and electrode lead  10 . Electrode lead  10  could have any one or more of the features described above. 
         [0071]    The various forms of electrode lead  10  described above may be made in any manner known as would be apparent to the person skilled in the art. For example, in manufacturing the electrode lead  10  shown in  FIG. 2 , the following method may be used. 
         [0072]    In order to form the electrode array, the electrode contacts  12 ,  12 ′,  12 ″ are placed in a U-shaped holding die. In this case, the electrode contacts  12 ,  12 ′,  12 ″ may be welded or otherwise electrically connected to their respective electrode wires or conductors  11 ,  11 ′,  11 ″ in sequential order, starting from the most proximal electrode contact. Once all of the wires  11 ,  11 ′,  11 ″ have been connected to their respective electrode contacts  12 ,  12 ′,  12 ″, a droplet of adhesive  41 , such as adhesive silicone, is placed in the trough of each electrode contact in order to secure the wires in place. 
         [0073]    A production stylet (for example, a PTFE coated wire) is suspended or otherwise placed over the electrode array before filling each trough with more silicone. The production stylet is used to hold the electrode contacts in spaced relationship to each other and provide further support to the electrode array, and is later removed to form a lumen in the lead. The holding die is then placed in an oven to cure the silicone. 
         [0074]    The formed electrode lead in one form, could then be split into two portions—the main lead portion  14  and the lumen portion  13 , and then reconnected by applying an amount of material  40  between them and allowing this to set. 
         [0075]    In an alternative method, prior to the step of introducing the production stylet, silicone may be poured into the trough to a level just above the electrode contacts and wires, allowed to cure, and then applying a layer of material  40  over the partially-constructed electrode lead. This partially-constructed electrode lead may then have the remainder of the silicone applied over the layer of material  40  using a production stylet to form the lumen, to form the 2-part electrode lead as shown in  FIG. 2 , with material  40  therebetween. 
         [0076]    In a further alternative method, the two parts  14  and  13  may be formed separately and then combined using material  40  as described above. 
         [0077]    In forming the arrangement shown in  FIG. 4A , the main lead portion  14  could be formed by conventional means, and then lumen portion  13  could be either formed separately and adhered to portion  14 , or by pouring and allowing to set on top of portion  14 , material  40 , using a production stylet to form the lumen. 
         [0078]    In forming the electrode lead as shown in  FIG. 12A , the silicone could be poured up to about halfway up to the top of the production stylet. The production stylet could then be removed, and an amount of material  80  could be placed in the semi-lumen thus created, and then cured. The production stylet could then be reintroduced and the silicone continued to be poured to cover the production stylet to form the full lumen, and then processed as described above. 
         [0079]    Once formed, the electrode lead  10  may then be removed from the U-shaped holding die and placed in a curved moulding die, if a curved electrode lead is desired, as will be known to the person skilled in the art. These methods may also be combined with appropriate parts or appropriately modified parts of methods as described in International Patent Application No. PCT/AU99/00391 (WO 00/71063) to the present applicant, previously incorporated by reference. 
         [0080]    It will be understood that the above has been described with reference to particular embodiments and that many variations and modifications may be made within the scopes of the different aspects of the present invention. 
         [0081]    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. 
         [0082]    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.