Abstract:
In one aspect of the invention, a method for delivering drugs from an implantable medical device to an implantee is disclosed, comprising implanting the medical device having a receptacle configured to receive a drug release capsule, the drug release capsule having at least one drug disposed thereon, placing the drug release capsule in the receptacle subsequent to the implanting, and permitting the release of the at least one drug from the drug release capsule to the recipient

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation-In-Part Application of application Ser. No. 10/416,634, filed on Nov. 10, 2003, entitled “Apparatus For Delivery of Pharmaceuticals To The Cochlear”, which is a National Phase Application of International Application No. PCT/AU01/01479, filed Nov. 14, 2001, entitled “Apparatus For Delivery of Pharmaceuticals To The Cochlear”, which claims priority from Australian Provisional Application No. PR 1484, filed Nov. 14, 2000. This application also claims priority from U.S. Provisional Patent Application No. 60/978,572, filed Oct. 9, 2007, entitled “Drug release Capsule For Implantation Into An Accessible Lumen Of An Implanted Medical Device. The above applications are hereby incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to implantable medical devices, and more particularly, to a drug release capsule for implantation into an accessible lumen of an implantable medical device. 
         [0004]    2. Related Art 
         [0005]    Medical devices having one or more partially or completely implantable components, generally referred to as implantable medical devices, have provided a wide range of therapeutic benefits to patients over recent decades. One type of implantable medical device that has provided substantial benefits to patients over the years is a prosthetic hearing device. Prosthetic hearing devices process ambient sound to provide hearing ability to a hearing impaired patient. 
         [0006]    Prosthetic hearing devices include a category of implantable devices known as cochlear™ implants (also referred to as cochlear™ devices, cochlear™ implant devices, and the like; “cochlear implants” herein). (COCHLEAR is a trademark of Cochlear Limited, Lane Cove, NSW, Australia.) Cochlear implants include an array of stimulation electrodes which is implanted in the cochlea of the patient (referred to herein as a recipient). The electrode array is controlled by an electronic system encased in a hermetically sealed, biocompatible housing implanted in the recipient. The electronic system, commonly referred to as a stimulator unit, essentially contains decoder and driver circuits for the stimulation electrodes. Acoustic sound reception and conversion of acoustic signals into electrical signals typically occurs in a sound processor typically worn by the recipient. The sound processor superimposes the preprocessed signals, properly coded, on a high frequency carrier signal which is transmitted transcutaneously to the stimulator unit through the closed skin. A sound input device such as a microphone converts ambient sound into representative electrical signals for processing by the sound processor. The sound input device is typically located outside of the recipient&#39;s body such as in a behind-the-ear housing worn on the auricle. 
         [0007]    Traditionally, there has been interest in delivering a bioactive substance, pharmaceutical or chemical (collectively and generally referred to as a “drug” herein) in conjunction with implantable medical devices for a variety of purposes. For example, in one conventional approach an implantable medical device is coated with a drug. This and other conventional approaches typically require the incorporation of the drug into the implantable medical device during the manufacturing process of the device. 
       SUMMARY 
       [0008]    In accordance with one aspect of the present invention, a drug delivery system comprising: an implanted component having an accessible lumen and one or more drug release ports fluidically coupling the lumen with an exterior environment of the implanted component; and a drug-delivery capsule that carries at least one drug and is configured to release the at least one drug, wherein the capsule and lumen are correspondingly configured such that the capsule may be introduced into the lumen so that when the drug-delivery capsule releases the at least one drug, the at least one drug may travel through the lumen and exit the implantable component via at least one of the one or more drug release ports. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]    Illustrative embodiments of the present invention are described herein with reference to the accompanying drawings, in which: 
           [0010]      FIG. 1  is a perspective view of an exemplary implantable medical device, a cochlear implant, in which embodiments of the drug release system of the present invention may be advantageously implemented; 
           [0011]      FIG. 2A  is a side view of an embodiment of the electrode assembly illustrated in  FIG. 1 , in accordance with embodiments of the present invention; 
           [0012]      FIG. 2B  is a cross-sectional view of the electrode assembly illustrated in  FIG. 2A  taken along section line  2 B- 2 B in  FIG. 2A ; 
           [0013]      FIG. 2C  is a cross-sectional view of the electrode assembly illustrated in  FIG. 2A  taken along section line  2 C- 2 C in  FIG. 2A ; 
           [0014]      FIG. 2D  is a cross-sectional view of the electrode assembly illustrated in  FIG. 2A  taken along section line  2 D- 2 D in  FIG. 2A ; 
           [0015]      FIG. 3  is a perspective view of a drug delivery capsule in accordance with one embodiment of the present invention; 
           [0016]      FIG. 4A  is a partial view of an electrode assembly in which retention tabs provide an interference retention to maintain a drug release capsule in a desired location inside the lumen of the implantable medical device component; 
           [0017]      FIG. 4B  is a cross-sectional view of the electrode assembly of  FIG. 4A  taken along section line  4 B- 4 B, in accordance with embodiments of the present invention; 
           [0018]      FIG. 5A  is a partial view of the cochlea and an embodiment of the electrode assembly illustrated in  FIG. 2A , in which the electrode assembly has a lumen with multiple portholes, in accordance with an embodiment of the present invention; 
           [0019]      FIG. 5B  is the perspective view of the electrode assembly of  FIG. 2A  with the drug release capsule of  FIG. 3  positioned within the lumen, in accordance with one embodiment of the present invention; and 
           [0020]      FIG. 5C  is an enlarged view of the cochlea and electrode assembly of  FIG. 5B  showing the releasing of drugs through multiple portholes disposed on the electrode assembly. 
       
    
    
     DETAILED DESCRIPTION  
       [0021]    Aspects of the present invention are generally directed to a drug delivery system for delivering a drug in connection with an implanted component having an accessible lumen. The implantable component may be a component of an implantable medical device. For example, the component may be a cochlear implant electrode assembly that has a lumen for receiving a stylet. In addition to the lumen of the implantable component, the drug release system comprises a drug release capsule that carries a drug. The capsule and lumen are correspondingly configured such that the capsule may be introduced into the lumen, advanced to a desired position in the lumen, and securely retained within the lumen. Because the implantable component and the drug release capsule are physically distinct, the component and capsule may be independently-manufactured, and the drug release capsule may be joined with the implantable component subsequent to the device&#39;s manufacture and/or sterilization of the component, and prior to, concurrently with, or subsequent to the implantation of the implantable medical device component. 
         [0022]    Manufacturing a drug release capsule separately from the implantable medical device component provides flexibility in the applied therapy while reducing the undesirable aspects associated with integrating drugs in implantable medical devices. For example, embodiments of the present invention may enable manufacturing efforts to be focused solely on the successful manufacture of the medical device component rather than on manufacturing an integrated assembly of the component and drug-delivery mechanism. This may result in reduced manufacturing costs, reduced drug yield loss, reduced handling and contamination of drugs, and other benefits. Furthermore, this may allow for the manufacturing of the drug release capsule to be outsourced to specialist manufacturers. Such outsourcing may provide further benefits such as the reduction of the cost of research and development by outsourcing to manufacturers that already have regulatory approval for the desired drugs, thus allowing faster and better provision of the medical devices incorporating the drug release capsules to the relevant market. Additionally, by manufacturing the drug release capsule separately from the device itself, the implantable medical device may be utilized as a universal device having a standardized lumen that may be loaded with different embodiments of the drug release capsules. This advantageously enables a single implantable device to be manufactured and inventoried without being restricted to operating with a single drug or specific combination or dosage of drugs. This is particularly advantageous in those circumstances in which the drug to be delivered via the drug release capsule has a limited shelf life. 
         [0023]    As used herein, the term “drug” refers to any bioactive substance or chemical now or later developed, including, but not limited to, pharmaceuticals and other chemical compounds such as those intended to provide therapeutic benefits to, or other reactions in, an implant recipient, whether localized or distributed throughout the recipient. Such drugs may include, for example, steroids or other anti-inflammatory drugs to reduce inflammation at the implantation site. Other drugs that may be included in the drug release capsules are antibiotics to mitigate bacterial growth related to the implantation of the medical device component. It should be appreciated that as used herein the term “drug release capsule” refers to any mass of material suitable for carrying a desired one or more drugs for subsequent release into the recipient, and which is configured to be introduced into and securely positioned within a lumen of the implantable medical device component. The more common definition of a capsule in the field of pharmacology; that is, a gelatinous case enclosing a dose of medicine, is just one of a myriad of embodiments of the drug release capsule of the present invention. This is described in greater detail below. 
         [0024]      FIG. 1  is a perspective view of an exemplary implantable medical device in which embodiments of a drug release system of the present invention may be implemented. In fully functional human hearing anatomy, outer ear  101  comprises an auricle  105  and an ear canal  106 . A sound wave or acoustic pressure  107  is collected by auricle  105  and channeled into and through ear canal  106 . Disposed across the distal end of ear canal  106  is a tympanic membrane  104  which vibrates in response to acoustic wave  107 . This vibration is coupled to oval window or fenestra ovalis  110  through three bones of middle ear  102 , collectively referred to as the ossicles  111  and comprising the malleus  112 , the incus  113  and the stapes  114 . Bones  112 ,  113  and  114  of middle ear  102  serve to filter and amplify acoustic wave  107 , causing oval window  110  to articulate, or vibrate. Such vibration sets up waves of fluid motion within cochlea  115 . Such fluid motion, in turn, activates tiny hair cells (not shown) that line the inside of cochlea  115 . Activation of the hair cells causes appropriate nerve impulses to be transferred through the spiral ganglion cells and auditory nerve  116  to the brain (not shown), where they are perceived as sound. In certain profoundly deaf persons, there is an absence or destruction of the hair cells. Cochlear implants such a cochlear implant  120  is utilized to directly stimulate the ganglion cells to provide a hearing sensation to the recipient. 
         [0025]      FIG. 1  also shows the positioning of cochlear implant  120  relative to outer ear  101 , middle ear  102  and inner ear  103 . Cochlear implant  120  comprises external component assembly  122  which is directly or indirectly attached to the body of the recipient, and an internal component assembly  124  which is temporarily or permanently implanted in the recipient. External assembly  122  comprises microphone  125  for detecting sound which is outputted to a behind-the-ear (BTE) speech processing unit  126  that generates coded signals which are provided to an external transmitter unit  128 , along with power from a power source  129  such as a battery. External transmitter unit  128  comprises an external coil  130  and, preferably, a magnet (not shown) secured directly or indirectly in external coil  130 . 
         [0026]    Internal component assembly  124  comprise an internal coil  132  of a stimulator unit  134  that receives and transmits power and coded signals received from external assembly  122  to other elements of stimulator unit  134  which apply the coded signal to cochlea  115  via an implanted electrode assembly  140 . Electrode assembly  140  enters cochlea  115  at cochleostomy region  152  and has one or more electrodes  150  positioned on an electrode array  144  to be substantially aligned with portions of tonotopically-mapped cochlea  115 . Signals generated by stimulator unit  134  are typically applied by an array  144  of electrodes  150  to cochlea  115 , thereby stimulating auditory nerve  116 . 
         [0027]    Given the coiled shape of cochlea  115 , electrode carrier member  142  is typically constructed using a material, or combination of materials, which curls or is capable of being curled in a manner which follows the curvature of cochlea  115 . The portion of electrode assembly  140  intended to be inserted into cochlea  115  will often have a stiffening stylet (not shown) inserted into a channel, for example a lumen (not shown), which extends distally from the proximate end of electrode carrier member  142 . During implantation of electrode assembly  140 , the stylet contained in the lumen of carrier member  142  is removed from the proximate end of the carrier member as the carrier member is inserted into cochlea  115 . The act of removing the stiffening stylet from the lumen allows electrode carrier member  142  to curl. In further embodiments of cochlear implant  120 , the stiffness of the stylet decreases in response to fluids and/or body temperature allowing electrode carrier member  142  to curl in order to follow the curvature of the inner walls of cochlea  115 . In other embodiments of cochlear devices, electrode carrier member  142  is naturally straight without the assistance of a stylet inserted into the lumen. Such embodiments of electrode carrier member  142  are constructed using a flexible material, or is constructed so as to flex upon a fixed amount of force being exerted on the tip or body of electrode carrier member  142  as it is being inserted into cochlea  115 . 
         [0028]    As one of ordinary skill in the art will appreciate, embodiments of the present invention may be advantageously implemented in a variety of implantable components. In the exemplary application above of cochlear implant  120 , the implantable component is electrode carrier member  142  which is permanently implanted in cochlea  115  of a recipient. 
         [0029]    Embodiments of a drug release system of the present invention is described next below with reference to  FIGS. 2A through 2D .  FIG. 2A  is a side view of an embodiment of electrode carrier member  142 , referred to herein as electrode assembly  200 .  FIGS. 2B-2D  are cross-sectional views of electrode assembly  200  taken along their respective cross-sectional lines shown in  FIG. 2A . A perspective view of an exemplary embodiment of a drug-delivery capsule of the present invention is illustrated in  FIG. 3 . 
         [0030]    Drug-delivery capsule  300  is substantially cylindrical in shape and is constructed and may take on any form to retain and release one or more drugs into lumen  224 . In one embodiment, drug-delivery capsule  300  may be formed by impregnating the drug in a ceramic or a polymer material that is configured to release the drug at a predetermined rate. 
         [0031]    Electrode assembly  200  comprises an elongate carrier member  220  on which an electrode array  244  of electrodes  250  is disposed. As noted, each electrode  250  is constructed and arranged to deliver a stimulating signal to a particular region of cochlea  115 . 
         [0032]    It has been found that the magnitude of the currents flowing from electrodes  250 , and the intensity of the corresponding electric fields, are a function of the distance between electrodes  250  and the modiolus (not shown) of cochlea  115 . If this distance is relatively great, the threshold current magnitude must be larger than if this distance is relatively small. Moreover, the current from each electrode  250  may flow in a number of directions, and the electrical fields corresponding to adjacent electrodes may overlap, thereby causing cross-electrode interference. To reduce such adverse effects, it is advisable to maintain a minimal distance between carrier member  220  and the modiolus. This is best accomplished by providing carrier member  220  in a shape which generally follows the shape of the modiolus, or inside wall of cochlea  115  ( FIG. 1 ). This increases the effectiveness of the delivery of electrical stimulation to auditory nerve  116  ( FIG. 1 ). 
         [0033]    In this exemplary application, to position electrodes  250  adjacent the inside wall of cochlea  115 , carrier member  220  adopts a curled or spiral position immediately following implantation into cochlea  115 . It is also desirable that carrier member  220  be shaped such that the insertion process causes minimal trauma to the sensitive structures of cochlea  115 . As such, carrier member  220  is manufactured to be pre-curved. Specifically, carrier member  220  is manufactured to have a spiral configuration; that is, one or more concentric circles that approximate the curvature of cochlea  115  as shown in  FIG. 2A . 
         [0034]    Usually carrier member  220  is held in a generally straight configuration at least during the initial stages of the insertion procedure, conforming to the natural shape of cochlea  115  once implantation is complete. To have carrier member  220  assume a generally straight configuration, a lumen  224  is provided in the carrier member. In the illustrative application of carrier member  220 , lumen  224  extends through a substantial length of a lower extension  205  of carrier member  220 . 
         [0035]    Lumen  224  is configured to receive a stiffening element  230  commonly referred to in the context of prosthetic hearing implants as a stylet. Although such reference is used in connection with prosthetic hearing devices, it should be appreciated that the term “stylet” is not limiting to any particular application or configuration. 
         [0036]    Prior to implanting carrier member  220 , stylet  230  is inserted into lumen  224  to maintain the carrier member in a relatively straight configuration. While electrode assembly  200  is inserted through cochleostomy  152  (or the oval window of the cochlea, not shown), a surgeon biases forward carrier member  220  on stylet  230  to allow carrier member  220  to return to its spiral configuration and, in doing so, to follow the curvature of cochlea  115 . In other words, during insertion, stylet  230  is withdrawn from lumen  224  thereby allowing carrier member  220  to return to its pre-curved configuration. 
         [0037]    In one embodiment, the technique for implanting electrode assembly  200  is the Advance Off-Stylet™ technique for the Contour™ Advance electrode (previously referred to as the Contour™ Electrode with Softip). In a another embodiment, electrode assembly  200  includes a Contour™ Advance Electrode, also described as Contour™ Electrode with Softip, Modified Tip, or Ski Tip. In another embodiment, the stylet is an Arrow Stylet, Surgical Stylet, or Surgical Ball Stylet. In these and other stylets and electrode carrier members, the stylet is removably inserted into lumen  224  of the carrier member prior to implantation, and is removed from the carrier member during implantation. 
         [0038]      FIGS. 2C and 2D  are cross-sectional views of electrode assembly  200  taken along cross-sectional lines  2 C- 2 C and  2 D- 2 D in  FIG. 2A .  FIGS. 2C and 2D  are schematic representations of two exemplary embodiments of drug release ports  240  which may be implemented in carrier member  220  to fluidically couple lumen  224  with an exterior environment of electrode assembly  200 . In the illustrative application shown in  FIG. 1 , for example, such external environment is one of the ducts of cochlea  115 . In the exemplary embodiments illustrated in  FIGS. 2C and 2D , drug release ports  240  are in the form of a narrow channel or opening in carrier member  220 . For example, in the embodiment illustrated in  FIG. 2C , a drug release port  240  extends from lumen  224  with the exterior surface of carrier member  220  which opposes the side of carrier member  220  on which electrodes  250  are disposed. As such, drug release port  240  fluidically couples lumen  224  with the exterior environment of electrode assembly  200  toward the lateral wall of cochlea  115  when electrode assembly  200  is implanted in the cochlea. As another example, in the embodiment illustrated in  FIG. 2D , two drug release ports  240 A and  240 B are formed in carrier member  220  on laterally-opposing sides of lumen  224 . It should be appreciated that the location, configuration, dimensions, and quantity of drug release ports  240  may vary depending on the particular application, type, configuration and quantity of the drug-delivery capsule and other factors such as the rate at which the capsule releases the drug, the molecular characteristics of the drug, and so on. 
         [0039]    Drug release ports  240  may be passageways or channels within carrier member  202  as shown in  FIGS. 2C and 2D . It should be appreciated, however, that in other embodiments, drug release ports  240  are implemented as a permeable structure within a membrane which makes up at least a part of electrode carrier member  202 . Such drug release ports  240  allow drugs to move into cochlea  115  in the absence of a gross movement of fluid. In addition to permitting the flow of drugs into cochlea  115 , drug release ports  240  may be configured to control the rate of drug flow into cochlea  115 . In alternative embodiments, drug release ports  240  may be controllable. For example, in one specific embodiment, drug release ports  240  are responsive heat, adjusting the permeability in response to an applied heat source. 
         [0040]      FIG. 5A  is a partial view of cochlea  115  implanted with an embodiment of electrode assembly  200  illustrated in  FIG. 2A . in which the electrode assembly has a lumen with multiple portholes  240 , in accordance with embodiments of the present invention.  FIG. 5B  is the same view of electrode assembly  200  shown in the same implanted position as in  FIG. 5A  with a drug release capsule  300  positioned within the lumen, in accordance with embodiments of the present invention.  FIG. 5C  is an enlarged view of cochlea  115  and electrode assembly  200  showing the release of drugs through multiple portholes  240  disposed on the electrode assembly. 
         [0041]    In the exemplary embodiment of electrode assembly  200  illustrated in  FIGS. 5A-5C , multiple portholes  240  are formed in carrier member  200  circumferentially around lumen  224 , providing a passageway from lumen  224  to locations exterior of electrode assembly  200 . It is to be understood, however, that drug delivery ports  240  may be disposed along any portion of the perimeter or circumference of electrode carrier member  202 . 
         [0042]    Electrode assembly  200  is implanted in a recipient by inserting electrode carrier member  202  through, for example, cochleostomy region  152  which is formed in a portion of the recipient&#39;s cochlea  115 . Lumen  224 , as noted, is manufactured as a hollow channel inside electrode carrier member  202  and terminates at an opening  404  at or near cochleostomy region  152 , inside cochlea  115 . Lumen  224  is configured to receive and securely retain a correspondingly-configured drug release capsule  300  ( FIG. 3 ) as shown in  FIG. 2C . 
         [0043]    Although lumen  224  is depicted in  FIG. 5A  as starting from a location which is inside cochlea  115  just beyond cochleostomy region  152 , and which extends along a substantial length of electrode assembly  200 , it is to be understood that lumen  224  may extend along electrode carrier member  202  starting from and ending at any point along electrode carrier member  202 . For example, in one embodiment, lumen  224  extends along electrode assembly  200  from outside cochlea  115  to inside the cochlea when the device is implanted in the cochlea. As such, electrode carrier member  202  may be configured so that opening  404  for lumen  224  is located outside cochlea  115  when the carrier member is implanted in cochlea  115 . In such an embodiment, a plug or other type of seal may be used to provide an impermeable obstruction to prevent cochlea fluids from leaking out of cochlea  115 . It is also to be understood that electrode assembly  200  may be of various lengths and extend into cochlea  115  to different depths. It is also to be understood that although it is noted above that electrode carrier member  202  is preferably configured to be adjacent to the perimodiolar wall of cochlea  115  upon insertion, or may be configured to follow the lateral wall of cochlea  115 . 
         [0044]    As best illustrated in  FIG. 2D , as drug release capsule  300  releases the drug it is carrying, the drug travels through lumen  224  and exists the lumen through one or more ports  240 , as illustrated by arrows  502 . 
         [0045]    It should be appreciated  FIG. 2D  also depicts a recess  208  configured to receive and securely retain a drug release capsule  202  inserted into lumen  203 . Drug release capsule  240  is inserted inside lumen  224  of electrode carrier member  202  through opening  404  of lumen  224 . As shown in  FIG. 2D , a plurality of ports  240  are disposed in various regions of electrode carrier member  202  to provide a path of travel for bodily fluids (not shown), heat energy (not shown), and drugs disposed on drug release capsule  300  to travel between lumen  224  and inner areas of cochlea  115 , indicated by arrows  502  in  FIG. 5D . In one embodiment, drug release capsule  300  interacts with fluids present in cochlea  115 , which enters lumen  224  through ports  240 , to release drugs carrier by drug release capsule  300  into the fluids. The resulting fluid and drug mixture travels out of lumen  224  through ports  240  into cochlea  115 . In addition to providing localized benefits to the recipient&#39;s cochlea, it is to be understood that the drugs carrier by drug release capsule  300  and released into the recipient in the manner described above may also provide general benefits or benefits to other parts of the recipient&#39;s body remote from cochlea  115 . 
         [0046]    As depicted in  FIG. 4A , in some embodiments of the present invention, the interior walls of electrode carrier member  202  that define lumen  224  may have one or more tabs  402 A,  402 B configured to receive and securely retain drug release capsule  300  inserted into lumen  224 . For example, in one embodiment, drug release capsule  300  is securely retained in the lumen between tabs  402  due to the respective dimensions of the tabs and capsule. Alternatively, drug release capsule  300  is securely retained in lumen  224  due to a compression fit. Alternatively, a recess, rough edges, and the link may be formed in lumen  224  to facilitate retaining capsule  300  in a desired position in lumen  224 . In such embodiments the drugs carried by drug release capsule  300  interact with body fluids and/or temperature so that the drugs are carried out through various portholes  240 . Inserting drug release capsules  300  so as to be positioned securely at a desired location within recesses  208  inside lumen  224  of electrode carrier member  202  may be beneficial for keeping lumen  24  free of any objects while allowing drugs to escape from lumen  224 , through ports  240 . 
         [0047]    In other embodiments of the present invention, ports  240  may be dimensioned and/or arranged along electrode carrier member  202  to attain a desired outcome with or without a specialized drug release capsule configuration. For example, ports  240  disposed closer to drug release capsule  300 , when drug release capsule  300  is inserted into lumen  224 , may be configured to be smaller than ports  240  that will be further from the implanted position of drug release capsule  202 . Such a configuration may beneficially direct the same amount of drugs to escape from those ports  240  that are further away from drug release capsule  300  as would escape from ports  240  that are closer to drug release capsule  300 . Alternatively, by dimensioning all portholes along electrode carrier member  202  to be of the same size, more drugs may be delivered to ports  240  that are nearer to drug release capsule  300  as compared to ports  240  that are further from drug release capsule  300 . Additionally, ports  240  may generally be designed to be smaller in one embodiment of drug release system  200  than in other embodiments of the present invention for the purpose of reducing the amount of drugs released from drug release system  200 , as described above. For example, as part of a miniaturization effort for making these implantable devices more sophisticated or smaller for better suited for implantation in a recipient, drug release capsule  300  is highly concentrated with the drugs disposed thereon. Depending on the amount or rate of discharge desired, portholes  204  may be configured to have larger or smaller openings, or to have thicker or thinner sidewall thicknesses, which will impact the rate, volume or type of interaction permitted between drug release capsule  300  and body fluids or heat energy, in order to achieve the desired amount or rate of discharge from drug release system  200 . 
         [0048]    In certain embodiments of the present invention, drug release capsule  300  is maintained in place after being inserted into lumen  224  by retention tab  402 , as shown in  FIGS. 4A and 4B .  FIG. 4A  is a partial view of an embodiment in which retention tabs  404 A and  207 B maintain drug release capsule  300  in place inside electrode assembly  200 .  FIG. 4B  is a cross-sectional view of electrode assembly  200  taken along section line  4 B- 4 B showing retention tab  402 B. Drug release capsule  300  is shown inserted through lumen opening  404  into lumen  224  of electrode assembly  200 . Retention tab  402 B projects inwardly into lumen  224  from electrode assembly  140  and prevents drug release capsule  202  from further entering lumen  224  by interfering with that path of travel. Retention tab  207 B also projects inwardly into lumen  224  from electrode assembly  140  and prevents drug release capsule  202  from escaping out of electrode assembly  140  through lumen opening  404 . Retention tabs  402 A,  40207 B may be integrally formed with electrode assembly  140 , or may be separately formed attached to electrode assembly, and may be resilient to some degree. Drug release capsule  202  is inserted into lumen  203  through lumen opening  205 . During insertion, when sufficient force is applied to drug release capsule  202 , resiliently formed interference tab  207 B compresses or bends sufficiently to permit the continued insertion of drug release capsule  202  into lumen  203  towards interference tab  207 A. When fully inserted, drug release capsule  202  may be positioned in lumen  203  aligned with either or both interference tabs  207 A and  207 B such that one or both are compressed by drug release capsule  202 . Alternatively, interference tabs  207 A and  207 B may be positioned apart from one another such that drug release component  202  is situated between and apart from both interference tabs  207 A and  207 B. 
         [0049]    Although an interference retention is described above with regard to  FIGS. 2E and 2F , it is to be understood that other types of retention are possible to maintain the position of drug release capsule  202  when inserted into lumen  203 . For example, a compression retention, bonded retention, sutures, screws, clips, a combination of the above, or others may be used for such a purpose. In a compression retention, drug release capsule  202  is manufactured to be resilient to some degree and slightly larger than lumen  203  along at least a portion of lumen  203 . Alternatively, drug capsule  202  may be manufactured to be rigid and electrode assembly  140  having lumen  203  therein may be manufactured to be resilient to some degree. When inserted into lumen  203 , drug release component  202  will compress, electrode assembly  140  will expand, or a combination of the two will occur, so that a compression force is created between drug release capsule  202  and electrode assembly  140 , thereby securely retaining drug release capsule  202  in that position. 
         [0050]    In another embodiment, the drug release capsule may be configured to be bonded into the corresponding lumen of the implantable medical device thereby eliminating the need for a non-bonded retention means (e.g., compression retention, interference retention) between the drug release capsule and the lumen of the medical device. In one embodiment, such bonding is performed in a sterile field immediately prior to surgery, for example by inserting a ring-shaped drug release capsule around a stylet that has yet to be removed from an electrode array. Alternatively, such bonding is performed after the medical device is implanted in the patient. In another embodiment, such bonding is performed during manufacturing, such as one of the last few steps of manufacturing. 
         [0051]    In one embodiment, the above bonding is performed by disposing a glue layer on the lumen so that the drug release capsule may be pressed in prior to surgery. This may be performed manually or with a simple press-tool that aligns the two components and presses them together with a predefined amount of pressure. Alternatively, a liquid glue may be applied between the lumen surface and the drug release capsule. In one preferred embodiment, the liquid glue sets and/or cures rapidly. In another embodiment, a UV-cured glue is pre-applied to the component, or applied as a liquid, or is a separate component that is inserted between the drug release capsule and the lumen within the implantable medical device. In one embodiment, a liquid perfluoropol polymer such as that described in International Application WO 2007/021620 A2 may be utilized. International Application WO 2007/021620 A2 is hereby incorporated by reference herein. Other adhesives include, but are not limited to, fibrin glues, cyanoacrylates, polyurethane adhesives, silicone adhesives, and UC-cured acrylics. In another embodiment, chemical surface modification may be utilized to attain a desired bonding. For example, in one embodiment, covalently bonded proteins, or sulfonation may be performed to increase the wetability of the surface. 
         [0052]    It may be desirable for embodiments of the drug release capsule of the present invention to be constructed of a resorbable material, so that while drugs are being absorbed from the lumen, or after they are absorbed, the drug release capsule may be partially or completely resorbed by the tissue surrounding the implant site. In certain embodiments, the drug release capsule is comprised of a resorbable material that partially or completely degrades over time through interaction with various body fluids. In other embodiments, the drug release capsule is comprised of a resorbable material that partially or completely degrades over time through exposure to body temperatures. 
         [0053]    However, it may also be desirable for the drug release capsule to be constructed of a non-resorbable material. The use of a non-resorbable material may offer different benefits from the use of a resorbable material, such as the continued provision of a flush and gapless surface on one or more sides of the implantable medical device or tissue. For example, the drug release capsule may be made of a polymeric material configured to enable drugs to be embedded within the structure of the polymeric material, and to release the drugs either naturally or through the interaction of body fluids or body heat which may permeate the capsule. Furthermore, the drug release capsule may have micro-surface geometry, such as those possible through advances in nano-technologies, which may limit or inhibit bacteria growth. 
         [0054]    It should also be appreciated that the drug release capsules described above may be formed by one or more layers or sub-parts. In other words, each drug release capsule may be a composite of multiple layers or sub-parts. Each such layer or sub-part may serve a different function, for example, being configured to carry a different drug, releasing the same or different drug at the same or different rate, or having different concentrations of a drug across one or more portions of the drug release capsule. 
         [0055]    Furthermore, it is to be understood that drugs may be disposed on just a portion of a drug release capsule depending on the particular application. For example, it may be beneficial for a drug release capsule to have a drug disposed on only a portion of the capsule, with the remaining portion of the capsule configured merely as a carrier or supporting member for the medicated portion of the drug release capsule. 
         [0056]    According to a further embodiment of the present invention, the drug release capsule may be constructed of a polymeric material, in which molecules or other components of a drug are disposed within the chemical structure of the drug release capsule. One example of a polymeric material which may be used to construct an embodiment of a drug release capsule of the present invention is silicone. Drugs may be disposed within the silicone drug release capsule such that the drug is released from the drug release capsule. 
         [0057]    According to another embodiment of the present invention, the surface of the drug release capsule may be constructed to have microsurface geometry. Such a microsurface geometry may be constructed using nano-technologies, or may be constructed using other technologies presently known or developed in the future. Having a microsurface geometry may enable the drug release capsule to be useful in partially or completely inhibiting growth of bacteria and other biological organisms adjacent to the drug release capsule. 
         [0058]    According to yet another embodiment of the present invention, drug release capsule  202  may be formed to be resilient to some degree, for use in situations where it is desirable to insert a soft or flexible capsule into an implanted medical device. For example, where the medical device a cochlear implant comprising electrode array  144 , it may be desirable to advance drug release capsule  202  past the first curved portion inside cochlea  115 . In that case, having a resilient capsule  202  may be useful or even necessary for such an insertion such that the outer shape of electrode array  144  is not deformed or otherwise unacceptably altered so as to negatively impact the operation or durability of the electrode array  144  and surrounding anatomy. 
         [0059]    Conversely, drug release capsule  202  may be formed as a rigid capsule and used to provide or supplement the structural integrity of lumen  203 . For example, rigid drug release capsule  202  having a straight or other shape may be inserted into lumen  203  so that drug release capsule  202  provides or reinforces the shape of electrode array  144  surrounding lumen  203  through rigid drug release capsule  202 . 
         [0060]    Although various embodiments of the present invention have been described herein as a single capsule, it is to be understood that embodiments in which the drug release capsule  202  comprise multiple components, some of which may be drug release capsules and some of which may serve other functions, are also considered a part of the present invention. Examples include, but are not limited to, a drug release capsule component carrying drugs which promote tissue growth, for example to promote, cause or support the sealing of the cochleostomy region  152  or oval window  110 . Another example is a drug release capsule component carrying drugs which promote enhanced stimulation. These and other components may be inserted into lumen  203  of electrode array  144  as described above. Other embodiments may also have an additional lumen (not shown) disposed in a portion of electrode array  144  configured to remain outside cochlea  115  near cochleostomy region  152  into which a drug release capsule component which promotes tissue growth may be inserted. Other drug release capsule components in the same embodiment may be inserted inside cochlea  115  in lumen  203  to provide other therapeutic benefits such as promoting enhanced stimulation. Although the components of drug release capsule  202  are described above as being separate from one other, it is to be understood that in other embodiments, the various drug release components carrying different types of drugs may be joined or produced as a unitary body which is inserted into lumen  203 . 
         [0061]    In other embodiments, various drug release capsule components may be inserted in lumen  203  together and in a specific sequence so as to direct the various drugs being carried by one or more of those drug release capsule components to different locations within cochlea  115 . For example, a component carrying a stimulation enhancing drug may be inserted into lumen  203  prior to a component carrying a tissue growth promoting drug so that each drug may be directed to deeper regions in cochlea  115  or to cochleostomy region  152 , respectively, to provide the various therapeutic benefits afforded by each component. Intermediate to inserting each component into lumen  203 , one or more inert or other component not carrying any drugs may be inserted, to provide one or more spaces between components carrying drugs. Furthermore, one or more of these inert or other components may provide a sealing function, in order to segregate fluids, drugs and other materials from passing the sealing component in lumen  203 . The sealing components may be manufactured of a hygroscopic material which swells soon after being exposed to liquid so as to provide a seal inside lumen  203  thereby segregating the inner regions of lumen  203  from the portion outside the seal inside lumen  203 . In other embodiments, a shape memory polymer material may be used to manufacture a seal component. 
         [0062]      FIG. 3A  is a partial perspective view of cochlea  115  ( FIG. 1 ) and an embodiment of electrode assembly  140  of cochlear implant  120  ( FIG. 1 ). As noted, in this exemplary embodiment, electrode carrier member  202  has a lumen  204  with multiple portholes  206  disposed therein. 
         [0063]      FIG. 3B  is the same perspective view of cochlea  115  and electrode assembly  140  as shown in  FIG. 3A , with drug release capsule  210  positioned in lumen  204  of carrier member  202 . 
         [0064]      FIG. 3C  is an enlarged cross-sectional view of a portion of cochlea  115  and electrode assembly  140 . 
         [0065]    Similarly, in the exemplary application of a cochlear implant in which the implanted component that implements embodiments of the drug release system is a fully implanted component, it should be appreciated that the present invention may be implemented in implanted medical device components that are partially implanted. These alternative embodiments and applications of the present invention are described in greater detail below. 
         [0066]    Further features and advantages of the present invention are described in U.S. patent application Ser. No. 10/416,634, filed on Nov. 10, 2003, entitled “Apparatus For Delivery of Pharmaceuticals To The Cochlear”, which is a National Phase Application of International Application No. PCT/AU01/01479, filed Nov. 14, 2001, entitled “Apparatus For Delivery of Pharmaceuticals To The Cochlear”, which claims priority from Australian Provisional Application No. PR 1484, filed Nov. 14, 2000. This application also claims priority from U.S. Provisional Patent Application No. 60/978,572, filed Oct. 9, 2007, entitled “Drug release Capsule For Implantation Into An Accessible Lumen Of An Implanted Medical Device. The above applications are hereby incorporated by reference herein. 
         [0067]    While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. All patents and publications discussed herein are incorporated in their entirety by reference thereto.