Abstract:
An electromechanical actuator for an implantable hearing aid device including a mechanical output structure that has a first portion and a second portion, wherein the first portion is a mechanical attachment structure to attach a stapes prosthesis, and wherein the second portion is a wire-like member coupling the mechanical attachment structure to a magnetically permeable armature shaft assembly.

Description:
RELATED APPLICATIONS 
       [0001]    The present application is related to U.S. Provisional Patent Application No. 60/631,512 entitled “Implantable Fixation System for Anchorage of Medical Devices,” filed 30 Nov. 2004, which is hereby incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to treatments for hearing loss. In a particular form, the present invention relates to an implantable actuator capable of direct stimulation of the middle and inner ear auditory systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    Today state-of-the-art conventional hearing aids are able to treat hearing loss, in particular sensorineural hearing loss, very efficiently but still have some major disadvantages such as occlusion of the auditory canal, feedback at high amplification levels and stigmatization of the patients with hearing loss. Further they are rather ineffective in the treatment of conductive and mixed hearing loss. Whilst the present invention is described in relation to the treatment of hearing loss it will be appreciated that the invention will have other applications consistent with the principles described in the specification. 
         [0004]    It is an object of the present invention to provide a stimulation device capable of being included in an implantable hearing aid device that addresses one or more of the disadvantages of conventional hearing aid devices. 
       SUMMARY OF THE INVENTION 
       [0005]    In a first aspect the present invention accordingly provides an electromechanical actuator comprising:
       first and second magnets arranged to provide a biasing field in a field region between two substantially opposed pole faces of said first and second magnets;   a magnetically permeable armature located in said biased field region between said opposed pole faces, the location of the magnetically permeable armature defining a first and second working gap between the magnetically permeable armature and respective opposed pole faces of the first and second magnets;   a magnetically permeable armature shaft assembly supporting said magnetically permeable armature, said magnetically permeable armature shaft assembly arranged to allow movement of said magnetically permeable armature between said opposed pole faces in a longitudinal direction defined by the movement of said armature shaft assembly;   biasing means for providing a biasing force to said magnetically permeable armature shaft assembly to bias said magnetically permeable armature to a predetermined location between said opposed pole faces; and   magnetic flux generating means responsive to an input signal to generate a signal flux to modulate said biasing field in said field region thereby providing an unbalanced force to said magnetically permeable armature causing actuation of said magnetically permeable armature shaft assembly.       
 
         [0011]    Preferably, said first and second magnets are supported by a magnet support assembly and wherein said magnet support assembly, said magnetically permeable armature and said first and second working gaps form a first magnetic circuit. 
         [0012]    Preferably, said magnetic flux generating means is supported by a flux generating means support assembly and wherein said flux generating means support assembly, said magnetically permeable armature, said magnetically permeable armature shaft assembly and one of said first and second working gaps forms a second magnetic circuit. 
         [0013]    Preferably, said magnetic flux generating means comprises an electrical coil. 
         [0014]    Preferably, said flux generating means support assembly comprises a magnetically permeable structure having a recess to receive a shaft of said magnetically permeable armature shaft assembly, thereby forming a transverse air gap between said shaft and the walls of said recess. 
         [0015]    Preferably, said recess is substantially cylindrical in shape. 
         [0016]    Preferably, said transverse air gap is minimized to reduce the reluctance of said second magnetic circuit. 
         [0017]    Preferably, said biasing means includes a first biasing member and a second biasing member. 
         [0018]    Preferably, said flux generating means support assembly comprises said first biasing member and wherein said first biasing member further comprises a magnetically permeable spring in mechanical contact with a shaft of said magnetically permeable armature shaft assembly. 
         [0019]    Preferably, said second biasing member comprises a diaphragm in mechanical contact with said shaft. 
         [0020]    In a second aspect the present invention accordingly provides an electromechanical actuator for an implantable hearing aid device comprising:
       a hermetic housing of tubular shape closed on one side with a diaphragm and on the other side, with a hermetic feedthrough;   first and second magnets located in said hermetic housing arranged to provide a biasing field in a field region between two substantially opposed pole faces of said first and second magnets;   a magnetically permeable armature located in said biased field region between said opposed pole faces, the location of the magnetically permeable armature defining a first and second working gap between the magnetically permeable armature and respective opposed pole faces of the first and second magnets;   a magnetically permeable armature shaft assembly supporting said magnetically permeable armature, said magnetically permeable armature shaft assembly arranged to allow movement of said magnetically permeable armature between said opposed pole faces in a longitudinal direction defined by the movement of said magnetically permeable armature shaft assembly;   biasing means to provide a biasing force to said magnetically permeable armature shaft assembly to bias said magnetically permeable armature to a predetermined location between said opposed pole faces;   magnetic flux generating means including an electrical signal coil responsive to an input signal delivered by an electrical connection to said hermetic feedthrough to generate a signal flux to modulate the biasing field in said field region thereby providing an unbalanced force to said magnetically permeable armature causing actuation of said magnetically permeable armature shaft assembly;   a mechanical output structure including stimulation means to stimulate the inner ear auditory system responsive to actuation of said magnetically permeable armature shaft assembly; and   a lead electrically connected to outer pins of said hermetic feedthrough and mechanically attached to said titanium housing.       
 
         [0029]    In a third aspect the present invention accordingly provides an implantable stimulation device for stimulating an inner ear of a patient, said stimulation device including an electromechanical actuator responsive to an auditory signal for providing mechanical stimulation to said inner ear in response to said auditory signal. 
         [0030]    Preferably, said stimulation device further includes a middle ear prosthetic, said middle ear prosthetic reproducing in part or in full the function of the middle ear, wherein said electromechanical actuator includes actuation means to actuate said middle ear prosthetic thereby stimulating said inner ear in response to said auditory signal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    A preferred embodiment of the present invention will be discussed with reference to the accompanying drawings wherein: 
           [0032]      FIG. 1  is a perspective view of the interior components of an implantable hearing aid device incorporating an electromechanical actuator in accordance with a first embodiment of the present invention; 
           [0033]      FIG. 2  is a composite view of the implantable hearing aid device illustrated in  FIG. 1 ; 
           [0034]      FIG. 3  is an elevation view in longitudinal diametric section of the electromechanical actuator illustrated in  FIG. 1  having a low reluctance transverse gap; 
           [0035]      FIG. 4  is an elevation view in longitudinal diametric section of a second embodiment of an electromechanical actuator of the present invention having a flux conducting spring member; 
           [0036]      FIG. 5  is a lower elevation view in longitudinal diametric section of the electromechanical actuator illustrated in  FIG. 1 , showing the attachment of coil wires and lead; 
           [0037]      FIG. 6  is an elevation view in longitudinal diametric section of the electromechanical actuator illustrated in  FIG. 1 , showing the mechanical output structure; 
           [0038]      FIG. 7  is a side view of the mechanical output structure illustrated in the above figures, with an attached stapes prosthesis; 
           [0039]      FIG. 8  is a side view of the mechanical output structure illustrated in the above figures, having a ball joint between coupling rod and artificial incus; 
           [0040]      FIG. 9  is a side view of the mechanical output structure illustrated in the above figures, having a bendable coupling rod; 
           [0041]      FIG. 10  is a side view of the mechanical output structure illustrated in the above figures, having a partially bendable coupling rod; 
           [0042]      FIG. 11  is a side view of the mechanical output structure illustrated in the above figures, having a ball joint between artificial incus and stapes prosthesis; and 
           [0043]      FIG. 12  is a perspective view of a cochlear implant system showing one exemplary application of the electromechanical actuator of the present invention. 
       
    
    
       [0044]    In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. 
       DESCRIPTION OF PREFERRED EMBODIMENT 
       [0045]    Referring now to  FIGS. 1 and 2 , there are shown perspective and composite views depicting the components of an implantable hearing aid device  100  incorporating an electromechanical actuator  50  according to a first embodiment of the present invention. Hearing aid device  100  includes a housing  1  formed from titanium tubing that is substantially cylindrical and of circular cross section. Hearing aid device  100  further comprises a titanium diaphragm  6 , a titanium ring  21  and a multi-pin feedthrough  9  which are joined by hermetic laser welds. Coupling rod  7 , which is part of the moving mechanical output structure of electromechanical actuator  50 , is placed in ring  21  and is hermetically welded to it. This assembly provides a hermetically closed housing  1  that is suitable for implantation in the human body. 
         [0046]    Lead  11  which provides the input signal to electromechanical actuator  50  is connected to feedthrough  9 . To protect the connection site of the lead  11 , electromechanical actuator  50  may be covered by a silicone filled titanium cap  10 . In this embodiment directed to a hearing aid device, the titanium cap  10  provides multiple flat surface regions to allow secure manipulation of the device during implantation with surgical tweezers or little tongs. The titanium cap  10  also has a conical shape that provides mechanical transition between the small diameter of the lead  11  and larger diameter of the titanium tube  1 . 
         [0047]    Referring now to  FIG. 3 , there is shown an elevation view in longitudinal diametric section of the first embodiment of electromechanical actuator  50  of the present invention incorporating a low reluctance transverse gap. Armature  2 , shaft  12  and coupling rod  7  form the moving part of the actuator  50 . As armature  2  and shaft  12  form part of the magnetic circuits which drive electromechanical actuator  50  they are made of soft magnetic alloys. However, as would be understood by those skilled in the art, other suitable materials having the desired magnetic permeability properties may also be used. 
         [0048]    Shaft  12  is made of titanium to enable hermetic closing of the actuator by welding it to a ring  21 . The resulting moving structure is elastically supported at one side by a diaphragm  6 , which performs the function of a restoring spring. As such, diaphragm  6  prevents magnetic snap over. On the other side, shaft  12  is supported in the longitudinal direction by a spring bearing  5  having a spring constant sufficient to provoke, together with diaphragm  6 , the demanded dynamic characteristic of this spring-mass structure. 
         [0049]    The armature  2  is centred between two permanent magnets  3   a  and  3   b  thereby forming two working gaps  17   a  and  17   b . Both magnets  3   a  and  3   b  are polarized in the same direction substantially in parallel to the actuator axis and the direction of movement of shaft  12 , and provide polarizing flux in working gaps  17   a  and  17   b  that extends through the armature  2 . This first magnetic circuit is closed through the magnet supports  16   a  and  16   b  and the short sleeve  15  which are again fabricated from soft magnetic alloys. 
         [0050]    A second magnetic circuit comprises signal coil  4 , coil core  13 , long sleeve  14 , the magnet support  16   b , the armature  2  and the shaft  12 . Signal coil  4  includes two input coil wires  23  which are connected to lead  11  by virtue of feedthrough  9 . Preferably, all elements forming the second magnetic circuit other than the signal coil  4  are made of soft magnetic alloys to conduct the signal flux generated by coil  4 . This magnetic signal circuit includes two air gaps: the working gap  17   b  and a transverse gap  18  formed between the coil core  13  and the shaft  12 . The transverse gap  18  between the coil core  13  and shaft  12  has been minimized in order to provide a low reluctance thereby minimize losses in the magnetic circuit. 
         [0051]    In operation, the signal flux passing through the working gap  17   b  has the effect of modulating the polarizing flux generated by the magnets  3   a  and  3   b  in the process either increasing or decreasing the flux in the working gap  17   b  depending on the direction of the current passing through the signal coil  4 . This in turn increases or decreases the attractive force in gap  17   b  compared to the constant polarizing flux in gap  17   a  which results in a net force pulling the armature upwards or downwards. In this manner, small changes in the signal flux generated by coil  4  will result in corresponding actuation of shaft  12  thereby providing an electromechanical actuator of enhanced sensitivity. 
         [0052]    Referring now to  FIG. 4 , there is shown an elevation view in longitudinal diametric section of a second embodiment of an electromechanical actuator  55 . The main structure of the electromechanical actuator  55  is the same as shown in  FIG. 3 , however, the spring bearing  5  and the transverse gap  18  of the  FIG. 3  embodiment are replaced by flux conducting spring members  25  in this second embodiment. Flux conducting spring members  25  are preferably made of soft magnetic alloys providing reduced reluctance to overcome the losses resulting from the increased air gap  18  when compared to the air gap between the shaft  12  and coil core  13  in the first embodiment. 
         [0053]    The use of multiple spring members  25  separated by flux conducting spacers  26  increases the sectional area that can be passed by the magnetic flux to further reduce the overall reluctance of the magnetic circuit. Compared to one spring that is simply increased in thickness, the multiple springs provide higher compliance. 
         [0054]    Referring now to  FIG. 5 , there is shown an elevation view in longitudinal diametric section of the first embodiment of the electromechanical actuator  55  showing the attachment of the coil wires  23  and lead  11 . Coil wires  23  are attached to feedthrough pins  24  by, for example, brazing, welding or gluing with an electrically conductive glue. To prevent coil wires  23  from coming into contact with moving shaft  12  or spring bearing  5 , a cover  20  is placed between the coil wires and the shaft. 
         [0055]    The terminals  27  of lead  11  are inserted in a crimping tube  31  that is welded to the feedthrough pin  24 . Crimping the tube  31  mechanically attaches lead terminal  27  and establishes a low-impedance electrical connection. In this embodiment, a cap  10  protects the whole connection site. The cavity  32  formed by the cap  10  is filled up with silicone to provide a firm mechanical attachment of the lead  11 . To enable proper sterilization of the silicone, the cap  10  provides multiple openings  28 . 
         [0056]    Referring now to  FIG. 6 , there is shown an elevation view in longitudinal diametric section of the moving mechanical output structure  110  forming part of the implantable hearing aid device  100  illustrated in  FIGS. 1 and 2 . Mechanical output structure  110  comprises a coupling rod  7  and an artificial incus  8 , both made of titanium and, in this embodiment, welded together. A silicone coating  38  covers artificial incus  8 . The artificial incus  8  closely emulates the long process of the incus of the human middle ear, and is placed next to it during implantation. 
         [0057]    The length of the coupling rod  7 , measured from the outer surface of the diaphragm  6  to the end of the coupling rod  7 , is chosen in the range from approximately 3 mm to approximately 20 mm, and preferably in the range from approximately 5 mm to approximately 8 mm, to place the artificial incus  8  in the intended location. The angle formed by the axis of the coupling rod  7  and the axis of the artificial incus  8  is chosen in the range from 80° to 150°, preferably in the range from 115° to 125°, in order to correctly orientate the artificial incus  8  according to the anatomical conditions in the human middle ear. 
         [0058]    The cross sectional profile of the artificial incus  8  is elliptical with a numeric eccentricity in the range from 0 to 0.5 in order to provide reliable mechanical connection of the stapes prosthesis by crimping. Additionally, the artificial incus  8  is covered with a silicone coating  38  that has a thickness chosen in the range from 0.05 mm to 0.2 mm in order to allow proper stapes prosthesis attachment and crimping. It should be appreciated that the above dimensions and distances are approximate and that other dimensions may be established in alternative embodiments. 
         [0059]    Referring now to  FIG. 7 , there is shown a schematic diagram of one embodiment of the mechanical output structure of  FIG. 6  with an attached stapes prosthesis  33 . 
         [0060]    Referring now to  FIG. 8 , there is shown another embodiment of the mechanical output structure having a ball joint  35  between coupling rod  39  and artificial incus  40  to allow intra-operative adjustment of the angle between the coupling rod  39  and the artificial incus  40 . 
         [0061]    Referring now to  FIG. 9 , there is shown yet another embodiment of the mechanical output structure having a bendable coupling rod  41  to allow intra-operative adjustment of the orientation and the location of the artificial incus  8 .  FIG. 10  shows yet another embodiment of the mechanical output structure having a two part coupling rod, a stiff part  42  next to actuator  50 ,  55  and a bendable part  36  next to the artificial incus  8  to allow intra-operative adjustment of the orientation and the location of the artificial incus  8 . 
         [0062]    Referring now to  FIG. 11 , there is shown a further embodiment of the mechanical output structure having a stapes prosthesis  34  directly attached to the artificial incus  43  via a ball joint  37  to allow intra-operative adjustment of the insertion angle of the stapes prosthesis  34 . 
         [0063]    Referring now to  FIG. 12 , there is shown implantable hearing aid device  1200  implementing an electromechanical actuator  1210  according to a preferred embodiment of the present invention. In this preferred embodiment, implantable hearing aid device  1200  is a totally implantable Cochlear™ prosthesis (also referred to as a Cochlear™ implant system, Cochlear™ prosthetic device and the like) which functions as an implantable stimulation device for stimulating the inner ear by employing an electromechanical actuator responsive to an auditory signal. As would be apparent to those skilled in the art, the electromechanical actuator of the present invention can be utilized in current or future implantable medical devices. These implantable medical devices can be either partially or totally implanted in an individual, and such implantation may be temporary or permanent. 
         [0064]    Hearing aid device  1200  comprises external component assembly  1242  which is directly or indirectly attached to the body of the recipient, and an internal component assembly  1244  which is temporarily or permanently implanted in the recipient. External assembly  1242  typically comprises audio pickup devices  1220  for detecting sound, a speech processing unit  1216 , a power source (not shown), and an external transmitter unit  1206  comprising an external coil  1208 . Speech processing unit  1216  processes the output of audio pickup devices  1220  that are positioned by the ear  1222  of the recipient. Speech processing unit  1216  generates coded signals which are provided to external transmitter unit  1206  via cable  1218 . 
         [0065]    Internal components  1244  comprise an internal receiver unit  1212 , a stimulator unit  1226 , and a moving electromechanical actuator  1210  according to a preferred embodiment of the present invention. Internal receiver unit  1212 , which comprises an internal transcutaneous transfer coil  1224 , and stimulator unit  1226  are hermetically sealed within a housing  1228 . Collectively, transmitter antenna coil  1208  and receiver antenna coil  1224  form an inductively-coupled coil system used to transfer data and power via a radio frequency (RF) link  114 . A cable  1230  extends from stimulator unit  1226  to actuator  1210 . 
         [0066]    Actuator  1210  is coupled to the inner ear fluids via artificial incus  8  extending through a cochleostomy. Signals generated by stimulator unit  1226  are applied by mechanical actuator  1210  to inner ear fluids. It should be appreciated that the arrangement shown in  FIG. 12  is a schematic representation only, and that embodiments of the electromechanical actuator  1210  of the present invention may be positioned in a variety of locations to provide the desired stimulative effect. For example, in the embodiment shown in  FIG. 12 , actuator  1210  is coupled to the inner ear fluids via artificial incus  8 . However, a variety of stapes prostheses may be attached to artificial incus  8  in alternative embodiments, as described above. 
         [0067]    It should also be appreciated that electromechanical actuator  1210  may be secured to the recipient utilizing a variety of techniques now or later developed. In one embodiment, electromechanical actuator  1210  is configured to be implanted in a recipient utilizing an embodiment of a fixation system described in commonly owned U.S. Provisional Patent Application No. 60/631,512 entitled “Implantable Fixation System for Anchorage of Medical Devices,” filed 30 Nov. 2004, which is hereby incorporated by reference herein in its entirety. 
         [0068]    A brief consideration of the above described embodiments will indicate that the invention may be employed to remedy any source of conductive hearing loss. Additionally, these embodiments of the electromechanical actuator may be configured to provide sufficiently high output levels to treat severe sensorineural hearing loss while being sufficiently small to completely fit into a human mastoid. 
         [0069]    It should also be appreciated that Cochlear™ implant system  1200  described above is just one exemplary system in which the electromechanical actuator of the present invention may be implemented. The electromechanical actuator of the present invention may be implemented in a myriad of embodiments of a cochlear implant system, hearing aid or other medical devices or systems now or later developed. 
         [0070]    Advantageously, the dimensions and shape of embodiments of the electromechanical actuator of the present invention may be selected to take into account the anatomy of the implantation site. For example, for an actuator that is to be placed in a hole drilled into the human mastoid, an elongated cylindrical shape such as that described above has been found to be advantageous. In addition, in the above or other application, embodiments of the actuator may have a diameter and a length which are sufficiently small to allow placement of the actuator in narrow anatomical locations as required. A further advantage of embodiments of the present invention directed to hearing aid devices is that they are able to deliver sufficiently high output levels to manage progressive hearing loss in order to prevent revision surgeries. A still further advantage is that certain embodiments of the actuator are highly energy efficient thereby minimizing power consumption and facilitating autonomy. 
         [0071]    Although a preferred embodiment of the method and system of the present invention has been described in the foregoing detailed description, it will be understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims. 
         [0072]    It will be understood that the term “comprise” and any of its derivatives (eg. comprises, comprising) as used in this specification is to be taken to be inclusive of features to which it refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.