Abstract:
An implantable tissue-stimulating device for an implantee. The device comprising gate member having at least one electrode. At least a portion of the surface of the member having a configuration that at least partially controls any tissue growth on round the elongate member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the priority of co-pending Australian Patent No. 2004903436 entitled “Patterning of the Surface of Implantable Devices For Tissue Growth Management,” filed Jun. 23, 2004. The entire disclosure and contents of the above application is hereby incorporated by reference herein.  
       BACKGROUND  
       [0002]     1. Field of the Invention  
         [0003]     The present application relates to an implantable apparatus, such as a hearing implant, that delivers electrical stimulation to an implantee.  
         [0004]     2. Related Art  
         [0005]     During insertion of an electrode array into the cochlea there is the potential for damage to be caused to the sensitive cochlear tissues. Such damage may not prevent useful safe working of the device but may result in tissue growth occurring within the cochlea following implantation.  
         [0006]     The power consumption and efficiency of a hearing implant depends on the impedance of its electrodes. The deposition of material on the electrodes following implantation will in most instances increase that impedance. Studies have demonstrated that a build up of tissue growth occurs on and/or around electrode following implantation due to deposition of organic molecules from the perilymph within the cochlea. Tissue growth may also occur as result of an injury to the body caused by the implantation or some other interaction between the body and the implant.  
         [0007]     Tissue growth in other circumstances may though be beneficial. For example, tissue growth is desirable to ensure closing of the cochleostomy and so creating a barrier to bacteria and viruses entering the cochlea.  
         [0008]     Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.  
       SUMMARY  
       [0009]     Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.  
         [0010]     According to a first aspect, the present invention is an implantable tissue-stimulating device for an implantee comprising an elongate member having at least one electrode, wherein at least a portion of the surface of the elongate member has a configuration that at least partially controls tissue growth on and/or around the elongate member.  
         [0011]     In one embodiment, the configuration may be a pattern formed in the portion of the surface of the elongate member. The surface pattern can be adapted to direct tissue growth away from said at least one electrode following implantation. In another embodiment, the surface pattern may be adapted to enhance tissue growth in one or more particular locations. In a still further embodiment, the surface pattern may be adapted to at least partially suppress tissue growth in one or more particular locations.  
         [0012]     According to a second aspect, the present invention is an implantable tissue-stimulating device for an implantee comprising an elongate member having at least one electrode, wherein at least a portion of the surface of the elongate member has a coating of a molecule adsorption promoting material that at least partially controls any tissue growth on and/or around the elongate member.  
         [0013]     In one embodiment of this aspect, the molecule adsorption promoting material is myosin and is coated on the surface of the elongate material in a patterned arrangement to direct tissue growth away from the at least one electrode following implantation. In another embodiment, the patterned arrangement of the molecule adsorption promoting material may be adapted to enhance tissue growth in one or more particular locations. In a still further embodiment, the patterned arrangement of the molecule adsorption promoting material may be adapted to at least partially suppress tissue growth in one or more particular locations.  
         [0014]     According to a third aspect, the present invention is an implantable tissue-stimulating device for an implantee comprising an elongate member having at least one electrode, at least a portion of the surface of the elongate member having a configuration that at least partially controls tissue growth on and/or around the elongate member, said portion of the surface of the elongate member further having a coating of a molecule adsorption promoting material that assists in at least partially controlling tissue growth on and/or around the elongate member. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     By way of example only, the invention is now described with reference to the accompanying drawings:  
         [0016]      FIG. 1  is a pictorial representation of a hearing implant system;  
         [0017]      FIG. 2  depicts an implantable component of a hearing implant system;  
         [0018]      FIGS. 3   a - 3   c  depict an electrode array having a surface pattern;  
         [0019]      FIG. 4  is a cross-section of one example of a surface pattern;  
         [0020]      FIGS. 5   a - 5   c  depict another example of an electrode array;  
         [0021]      FIG. 6  depicts a still further example of an electrode array; and  
         [0022]      FIGS. 7   a  and  7   b  depict yet another example of an electrode array. 
     
    
     DETAILED DESCRIPTION  
       [0023]     The power consumption and efficiency of a tissue-stimulating device, such as a Cochlear™ implant, depends on the impedance of the electrodes positioned on the intracochlear electrode array. Factors that are thought to increase the impedance of the electrodes include adsorption of organic molecules onto the electrodes and subsequent growth of fibrous tissue on the electrodes or on the surrounding elongate member supporting them.  
         [0024]     Embodiments of a hearing implant are depicted in  FIGS. 1 and 2 . While for the purposes of this description, a Cochlear™ implant is depicted, it will be appreciated that other devices for stimulating other locations of an implantee can be envisaged and are encompassed within the present application.  
         [0025]     The hearing implant of  FIG. 1  comprises two main components, namely an external component including an external housing containing a speech processor  29 , and an internal component including an implanted receiver and stimulator unit  22 . The external component includes a microphone  27 . The speech processor  29  is, in this illustration, constructed and arranged so that it can be mounted on and fit behind the outer ear  11 . It will be understood that in an alternative version, the housing for the speech processor  29  and/or the microphone  27  may be worn on the body. Attached to the speech processor  29  is an external antenna coil  24  which transmits electrical signals to the implanted unit  22  via a frequency modulated (FM) radio frequency (RF) link.  
         [0026]     The implanted component includes a receiver antenna coil  23  for receiving power and data from the transmitter coil  24 . A cable  21  extends from the implanted receiver and stimulator unit  22  to the cochlea  12  and terminates in an electrode array  20 . The signals thus received are applied by the array  20  to the basilar membrane  8  thereby stimulating the auditory nerve  9 .  
         [0027]     An enlargement of one example of the array  20  is provided in  FIGS. 3   a  to  3   c.  In this embodiment, the array  20  comprises a series of longitudinally extending platinum half-bend electrodes  32  that are recessed into the silicone elongate body  31 . As depicted in  FIG. 3   b,  the array has a lumen  37  and a plurality of wires extending therethrough to the electrodes  32 . The surface of the elongate member  31 , at least in the location of the electrodes  32 , is provided with a series of grooves that are designed to direct any tissue growth that may occur on the array  20  away from the electrodes  32 . It is to be understood that the aim of the grooves is not to necessarily prevent tissue growth on the array  20 . Rather, the purpose of the grooves is to minimize tissue growth extending over the electrodes  32  and so causing an increase in the impedance of the array  20 .  
         [0028]     The outer or under surface  33  of the elongate member  31  is provided with a series of parallel longitudinally extending grooves  34 . The grooves  34  are designed to facilitate tissue growth along the outer surface of the array  20  and so away from the electrodes  32 . This arrangement not only reduces the impedance and related power consumption of the electrodes  32  by reducing the amount fibrous tissue growth on and around the electrodes, but as the arrangement facilitates tissue growth in regions away from the auditory nerve  9 , it will increase the impedance in that area and hence direct current away from that area and towards the auditory nerve  9 .  
         [0029]     As depicted in  FIGS. 3   a - 3   c,  the inner surface  36  of the array  20  is provided with a series of transverse grooves  35  between each of the electrodes  32 . Again, these grooves  35  preferably direct any tissue growth that may occur away from the electrodes  32 .  
         [0030]     In the embodiment depicted in  FIGS. 3   a - 3   c,  the grooves  34  and  35  are parallel and each of identical width, depth and spacing. The grooves (see  FIG. 4 ) are 5 μm deep and have a width and spacing of between 1 and 10 μm. It will be appreciated that other depths, widths and spacings might be utilized. It will be further appreciated that the width, depth and spacing need not be identical for all grooves.  
         [0031]      FIGS. 5   a - 5   c  depicts an alternative arrangement in which the array  20  comprises a substantially cylindrical silicone elongate member  41  supporting a series of ring electrodes  42 . In this arrangement, the surface has a series of annular grooves  43  positioned between each of the electrodes  42 . Again, the grooves  43  preferably direct any tissue growth away from the electrodes  42  following implantation of the array  20 .  
         [0032]      FIG. 6  depicts an arrangement in which the electrodes are longitudinal. In this embodiment, the grooves are also longitudinal.  
         [0033]      FIGS. 7   a  and  7   b  depict an electrode array  20  having an inner surface  51  having  32  electrodes thereon, an outer surface having  17  electrodes supported thereon and two sidewalls. For the sake of clarity, not all of the electrodes are depicted in  FIGS. 7   a  and  7   b.  On the inner surface  51 , the array has 4 longitudinally extending electrodes  53  closest to the distal end  52  while the remaining  28  electrodes  54  extend transversely. The  17  electrodes  58  on the outer surface  55  extend longitudinally. The electrodes on both surfaces of the array are positioned substantially within the plane of the array.  
         [0034]     In this arrangement, the outer surface  55  and the sidewalls have a plurality of longitudinally extending grooves  56 . On the inner surface  51 , a series of transverse grooves  57  are provided between the transverse electrodes  54  and a series of longitudinally extending grooves  59  are provided between the tip electrodes  53 . Again, the orientation of the grooves preferably directs any tissue growth that may occur following implantation away from the electrodes of the array.  
         [0035]     Other orientations and combinations of orientations of grooves and/or other surface features can be envisaged that are directed to meeting the requirement of minimizing tissue growth over the electrodes of the array. In one embodiment, the surface pattern can comprise an array of relatively small pillars. Such pillars or other surface features may have a height ranging between less than a micron to tens of microns to utilize the properties of cytoskeletal molecules to bond in differing degrees to surface with different surface structures.  
         [0036]     The patterned elongate members can be used in conjunction with other techniques to minimize or inhibit tissue growth. Other possible techniques include coating the array, or a portion thereof, with a material that inhibits or promotes organic molecular deposition. In this regard, those regions of the array where tissue growth is unwanted, namely on and around the electrodes, can be coated with an organic growth inhibitor, whilst those regions of the array, such as those regions remote from the electrodes, can be coated with am organic growth promoter to promote tissue growth in these regions.  
         [0037]     In this regard, one type of material that tends to promote the adsorption of organic molecules is myosin, a molecule that is attracted to actin. By coating the array with a compound such as myosin in a patterned fashion, as discussed above, the cytoskeletal molecules will be attracted and deposited on the array in a patterned fashion which assists in directing the growth of tissue in the region.  
         [0038]     The depicted elongate members can be formed from a suitable biocompatible material. As already described, that material can be a silicone, such as Silastic MDX 4-4210. In another embodiment, the elongate member can be formed from a polyurethane.  
         [0039]     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.