Patent Publication Number: US-2021177314-A1

Title: Modular implantable medical device

Description:
RELATED APPLICATIONS 
     This application is a continuation of PCT/EP2019/073078, filed Aug. 29, 2019, which claims priority to EP 18 191 878.0, filed Aug. 31, 2018, the entire disclosures of both of which are hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     This disclosure teaches an implantable medical device with an implantable medical unit and an implantable supply unit. This disclosure further relates to an implantable supply unit for electric power supply of an implantable medical unit as well as to a method for powering an implantable medical unit. One field of application is in implantable continuous glucose meters. 
     Implantable medical devices are widely known, for example, as heart pace makers, brain pacemakers, implantable infusion pumps, cochlea implants, or implantable measurement devices for body parameters such as glucose. 
     In the field of diabetes therapy, continuous glucose meters are being used in increasing numbers since they offer a number of advantages over so-called spot measurement devices based on test strips. Continuous glucose meters typically rely on an electrochemical measurement principle with a set of, e.g., three measurement electrodes that are placed in the tissue, and associated circuitry. In contrast to spot measurement devices, they provide glucose information continuously or quasi-continuously, e.g., every few minutes, and/or on demand. 
     Some available glucose meters are generally placed on the skin outside the body and comprise a subcutaneous or transcutaneous element that carries the electrodes. For such design, the power supply in the form of a battery is arranged together with circuitry in the portion outside the body, typically as a skin-adhesive patch. Since a continuous glucose meter is generally carried by a Person with Diabetes (PwD, also referred to as user) substantially continuously night and day, the skin of the user is permanently pierced by the transcutaneous element. This is known to cause side effects such as itching, eczema and in some cases even severe inflammation. 
     In order to avoid such drawbacks, fully implantable continuous glucose meters have been developed. 
     For such implantable continuous glucose meters as well as for other types of implantable medical devices, e.g., brain pacemakers or cochlea implants, powering the device by way of electric energy supply is a critical issue. For implantable devices with a built-in battery, the battery capacity is often the limiting factor for the lifetime of the overall device and accordingly determines the time after which the device needs to be explanted and replaced, even if other components are still intact and functional. If, on the other hand, the battery has a longer lifetime as compared to other components, the battery capacity cannot be fully exploited. This is particularly critical in devices where the costs of the battery are comparatively high in comparison to the total device costs, as it is the case, e.g., for typical implantable continuous glucose meters. 
     In order to improve the situation regarding the power supply, implantable medical devices have been developed that do not have an autonomous power supply in form of a battery, but are continuously powered transcutaneously by way of inductive coupling via an extracorporeal supply unit that is placed on the skin. Since, however, the location of the implanted device is determined by the implantation site and accordingly fixed, the supply unit also needs to be arranged on the skin at a corresponding fixed position, typically as adhesive patch. This continuous attachment of the supply unit also causes effects such as itching, eczema and in some cases inflammation. 
     EP 3 010 415 discloses a measurement system wherein a sensor and a transmitter are fully implantable and are connected via cable. The sensor and the transmitter are positioned in different regions of the body. This has the drawback that implantation and explanation of the system requires a surgery at at least two positions of the patient&#39;s body. Also, the cable can cause inconvenience for the patient and there is a risk of a cable failure. 
     EP 2 234 666 discloses a fully implantable medical device comprising a transmitter module with a cable and a battery module that is detachably connected with the transmitter module via the cable. This allows the battery module to be easily disconnected from the transmitter module and, therefore, to be easily exchanged. However, there is a risk of a failure of the cable. 
     U.S. Publication No. 2018/0028825 discloses an implantable hearing system wherein the main implant module which comprises a battery and a transceiver is implanted, as well. The main implant module is connected to the receiver coil and the stimulating assembly via cable. Thus, there is a risk of a failure of the cable. Also, the data and energy transfer is of comparatively low efficiency. 
     WO 2015/023291 A1 concerns the powering of cochlear implants. In an embodiment, a cochlear implant module and a separate battery module are provided. A junction connector provides a non-galvanic and releasable coupling via inductive power transfer. In a further embodiment, an implantable overmold comprises an implantable sound processor and a battery and is coupled with an implantable cochlea implant module via a connector junction and a cable. 
     U.S. Publication No. 2017/173345 A1 concerns the powering of a long term implantable medical device. The disclosed arrangement includes an implantable functional unit, an implantable secondary power unit and an extracorporeal primary power unit. From the primary power unit, power is provided to the secondary power unit and from the secondary power unit to the functional unit via inductive coupling. 
     WO 2016/16178817 A1 discloses an implantable system with a battery package and an electronic device that may both be implanted into the body and be coupled via a magnetic alignment structure. The electronic device is powered from the battery package via wireless power transceivers with inductive coupling. 
     SUMMARY 
     This disclosure teaches improvements regarding the power supply of implantable devices. Favorably, the before-mentioned drawbacks of the state of the art can be reduced or avoided. 
     An implantable supply unit for use in combination with an implantable medical unit in accordance with the present disclosure may include:
     a) a hermetically sealed supply unit housing;   b) a battery;   c) a supply unit power coupler, the supply unit power coupler being configured for powering the medical unit from the battery by way of non-galvanic coupling;   d) a supply unit data coupler, the supply unit data coupler being configured for non-galvanic data communication with the medical unit;   e) a supply unit communication interface, the supply unit communication interface being configured for non-galvanic data communication with a non-implanted remote device;   f) a supply unit coupling arrangement, the supply unit coupling arrangement being configured for releasable mechanical coupling the medical unit to the supply unit.   

     The battery, the supply unit power coupler, the supply unit data coupler and the supply unit communication interface are enclosed by the supply unit housing. 
     The expression “implantable” in the context of a device or unit refers to the device or unit being designed and adapted to be fully located within in a human or animal body in a way that it is fully enclosed by tissue and without any part of the device or unit being located outside the body and in particular without piercing the skin. The expressions “implantable” and “fully implantable” are accordingly to be understood as synonyms where not explicitly stated differently. 
     The term “non-galvanic” refers to a power and/or data transmission that does not rely on a galvanic respectively conductive coupling by wiring or electrical contacts. It is therefore to be understood as equivalent to “wireless.” 
     The supply unit power coupler is operatively coupled with the battery, typically by way of galvanic coupling respectively wiring directly or via further circuitry. In a situation of use, the medical unit power coupler receives power from the supply unit power coupler by way of non-galvanic coupling and electrically powers the medical unit with the received power. 
     For purposes of this disclosure, the terms “supply unit,” “supply,” “implantable supply” and “implantable supply unit” are used interchangeably. The supply unit typically further includes a control circuit. The control circuit is designed to control the overall operation of the supply unit and a medical unit that is coupled to the supply unit in an operable state. The control circuit typically includes one or more programmable components, such as microcomputers and/or microprocessors running a corresponding firmware code, application specific integrated Circuits (ASICs), and/or further electronics components as generally known in the art. 
     In a situation of use, the supply unit data coupler operatively couples with a medical unit data coupler of a medical unit as counter element. The data communication may be unidirectional or bidirectional. In embodiments where the medical unit includes a diagnostic module for acquiring one or more body parameters such as a glucose value in case of the medical unit including a continuous glucose meter module, data reflecting the one or more body parameters may be transmitted from the medical unit to the supply unit. In embodiments where the medical unit includes a therapeutic module or stimulation module, such as a cochlea stimulation implant module, a brain pacemaker module, or a retinal implant module, data corresponding to the required stimulation may be transmitted from the supply unit to the medical unit. Data communication between the supply unit and the medical unit may be continuously or non-continuously respectively sporadic. By way of example, data corresponding to a glucose value may be transmitted within a predetermined time interval for the medical unit being or including a continuous glucose meter, and/or upon a corresponding request by the supply unit. 
     The supply unit communication interface serves for the purpose of wireless data communication with a non-implanted remote device in a situation of use. A remote device communication interface of the remote device serves as counter element for the supply unit communication interface. Data communication between the supply unit communication interface and the remote device communication interface may be based on any wireless technology that is suited for data communication through skin and tissue, such as Near Filed Communication (NFC), Bluetooth, Wi-Fi and/or a proprietary Radio Frequency (RF) coupling. A remote device may be a general-purpose device, such as a Smart Phone, that includes a suited remote device communication interface and hosts a corresponding application, or may be a dedicated special-purpose device. 
     In a situation of use, the remote device serves as user interface and controls operation of the implanted medical device and/or receives data from the medical device. By way of example, the remote device may receive data reflecting measured glucose levels in case of the medical unit including a continuous glucose meter module. Communication between the implantable medical device respectively its supply unit and the remote device may be unidirectional or bidirectional. Further, the communication may be continuous or non-continuous or sporadic, for example initiated by a user command. 
     In a situation of use, the supply unit coupling arrangement mechanically couples with corresponding mechanical unit coupling arrangement of a medical unit as counter element such that the supply unit and the medical unit form a common compact assembly that can be implanted into and removed from the body. In the coupled state, the supply unit and the medical unit are favorable rigidly connected, at least held in a relative position to each other with limited possibility of movement. The expression “releasable mechanical coupling” refers to a coupling that may be separated with or without the use of additional tools such that at least one of the medical supply unit and the medical unit stays intact (i.e., is not destroyed or damaged) and can accordingly be subsequently reused. In some embodiments, both of the supply unit and the medical units stay intact. The supply unit coupling arrangement and the corresponding medical unit coupling arrangement may, by way of example, be realized by or include a bayonet, a threaded coupling, a snap-fit, or a force fit. If desired, either of both of the supply unit coupling arrangement and/or the medical unit coupling arrangement may include elastically or plastically deformable elements, such as deformable ribs, fingers, bars, a sleeve, or the like. 
     A supply unit of the above-described type provides, in combination with a corresponding medical unit, a particular favorable architecture for an implantable medical device. In the context of an overall design where the therapeutic and/or diagnostic functional modules or units have a longer lifetime as compared to other units or elements, in particular the battery, one and the same medical unit may be used in combination with a number of supply units in sequence. If, to the contrary, the supply unit has a longer lifetime as compared to the medical unit, one and the same supply unit may be used in combination with a number of medical units in sequence. This latter scenario is typical for example where the medical unit includes sensing and/or stimulation electrodes that degrade over time and/or are encapsulated by tissue in a way that functionality is reduced or even lost. Further advantages of particular embodiments are discussed below in context. 
     In a particular embodiment of the implantable supply unit, the supply unit power coupler is formed integrally with the supply unit data coupler. In such embodiments, a common coupling device, e.g., in form of a coil, serves as both supply unit power coupler and supply unit data coupler for both wireless power transmission to the medical unit and wireless data communication with the medical unit. Typically, the operative coupling is realized as inductive coupling in such embodiments. 
     Alternatively, however, the supply unit power coupler and the supply unit data coupler are distinct. In such embodiments, the supply unit power coupler is designed for coupling with a medical unit power coupler as counter element for power transmission purposes. The supply unit data coupler is designed for separate coupling with a medical unit data coupler for data transmission purposes. In such embodiments, power and data transmission are accordingly realized separately. Power transmission and data transmission may, for example, be realized via inductive capacitive, or optic. The type of coupling may be identical or different for power transmission and data transmission. 
     In a particular embodiment of the implantable supply unit, the battery is a rechargeable battery and the implantable supply unit includes a charging coupler for non-galvanic charging the battery in an implanted state of the supply unit. 
     This type of embodiment is particularly favorable since it allows a use of medical device over an extended time period of, e.g., a number of years, without the need for a corresponding extracorporeal charging device being permanently attached adjacent to respectively in proximity to the body. A charging device for transcutaneous powering an implantable device in the implanted state is typically attached to the skin by way of adhesive. While a variety of generally skin-friendly adhesives is available, the long-term use of such adhesives at one and the same position is an issue of concern and may cause skin moderate or severe skin-irritations, itching, eczema, or the like as explained before. In this context it is noted that transcutaneous power supply of an implanted device requires the charging device to be placed on the skin in substantially the same position. 
     For the above-described type of embodiment, a charging device needs to be attached to the body only temporarily and occasionally and for a limited time period for charging the battery. By way of example, the battery may be dimensioned such that recharging is only occasionally required. Intervals between a week and a month are most practical, but even daily is possible. In a typical technical implementation, the charging coupler is realized by a charging coil that couples with a supply coil of a charging device for charging the battery by way of transcutaneous inductive coupling. 
     In a particular embodiment of the implantable supply unit, the charging coupler is formed integrally with the supply unit communication interface. In such embodiment, the supply unit communication interface serves additionally as charging coupler, typically by way of inductive coupling. In further embodiments, the supply unit communication interface and the charging coupler are distinct from each other. 
     In a particular embodiment of the implantable supply unit, the supply unit power coupler includes a supply unit power coupler coil. In such embodiments, a medical unit includes a medical unit power coupler coil as counter element and wireless power supply of the medical unit is realized by way of inductive coupling. In other embodiments, wireless power supply of the medical unit is realized by way of capacitive coupling. In such embodiments, the supply unit power coupler includes corresponding supply unit power coupler electrodes and the medical unit may include corresponding medical unit power coupler electrodes as counter element. In still further embodiments, wireless power supply of the medial unit is realized by way of optical coupling, using, e.g., IR radiation. In such embodiment, a Light Emitting Diode (LED) in the supply unit may serve as supply unit power coupler and a photo diode in the medical unit may serve as medical unit power coupler. In accordance with the present disclosure, the medical unit is in any case passive in that it does not comprise its own power supply but is designed to by powered from the supply unit. 
     In a particular embodiment of the implantable supply unit, the supply unit coupling arrangement includes a receiving recess in the supply unit housing for receiving at least part of the medical unit. This type of arrangement allows a particularly compact and robust overall design and provides options for a favorable arrangement of the supply unit data coupler and supply unit power coupler as well as their corresponding counter elements in the medical unit, such that efficient and reliable coupling is achieved. 
     In a particular embodiment with a supply unit power coupler coil and a receiving recess as explained before, the supply unit power coupler coil is arranged circumferentially around the receiving recess. This type of arrangement allows a design where, in a coupled state of the supply unit and a medical unit respectively in a situation of use, the supply unit power coupler coil and a medical unit power coupler coil are cylinder coils, with the supply unit power coupler coil being arranged around the medical unit power coupler coil in a coaxial manner with or without axial offset. 
     An implantable medical device in accordance with the present disclosure may include an implantable supply unit and an implantable medical unit. The supply unit of the implantable medical device may generally be designed according to any embodiment as discussed above and/or further below. The implantable supply unit includes:
     a. a hermetically sealed supply unit housing;   b. a battery;   c. a supply unit power coupler, the supply unit power coupler being configured for powering the implantable medical unit from the battery by way of non-galvanic coupling;   d. a supply unit data coupler, the supply unit data coupler being configured for non-galvanic data communication with the medical unit;   e. a supply unit communication interface, the supply unit communication interface being configured for non-galvanic communication with a non-implanted remote device;   f. a supply unit coupling arrangement, the supply unit coupling arrangement being configured for releasable mechanical coupling the medical unit to the supply unit.   

     The battery, the supply unit power coupler, the supply unit data coupler and the supply unit communication interface are enclosed by the supply unit housing. 
     The medical unit of the implantable medical device includes:
     a. a hermetically sealed medical unit housing;   b. a functional medical module;   c. a medical unit power coupler, the medical unit power coupler being configured to receive power from the supply unit power coupler by way of non-galvanic coupling, thereby powering the medical unit;   d. a medical unit data coupler, the medical unit data coupler being configured for non-galvanic data communication with the supply unit;   e. a medical unit coupling arrangement, the medical unit coupling arrangement being configured as counter element for the supply unit coupling arrangement.   

     Both the supply unit and the medical unit may be of any design as discussed above and/or further below in the general description as well as exemplary embodiments. 
     The hermetically sealed medical unit housing generally encloses the components of the medical unit, in particular the medical unit power coupler and the medical unit data coupler, as well as any further medical unit circuitry. The functional medical module typically includes circuitry that is also enclosed by the medical unit housing. The functional medical module, however, typically has some interface to the outside, e.g., in the form of sensing and/or stimulation electrodes. 
     In a particular embodiment of the implantable medical device, the supply unit power coupler includes a supply unit power coupler coil and the medical unit power coupler includes a corresponding medical unit power coupler coil. In a typical realization, the supply unit power coupler coil and medical unit power coupler coil are NFC coils. 
     In a particular embodiment with a supply unit power coupler coil and a corresponding medical unit coupler coil, the medical unit includes a ferromagnetic coupling member and the medical unit power coupler coil is arranged circumferentially around the ferromagnetic coupling member. The ferromagnetic coupling member is typically shaped as a rod or bar and is made of a material of high magnetic permeability, such as ferrite. In a coupled state of the supply unit and the medical unit respectively in a situation of use, the supply unit power coupler coil is favorable arranged circumferential around the medical unit power coupler coil. This results in a coaxial arrangement with the ferromagnetic coupling member in the center, the supply unit power coupler coil forming the periphery and the medical unit power coupler coil being arranged radially between the ferromagnetic coupling member and the supply unit power coupler coil. 
     Since the supply unit power coupler is enclosed by the supply unit housing and the medical unit power coupler is enclosed by the medical unit housing, corresponding wall elements of the supply unit housing and the medical unit housing are arranged, in a situation of use, between the supply unit power coupler and the medical unit power coupler. The wireless coupling and power transmission is accordingly effected through the wall elements of the supply unit housing and medical unit housing, respectively. 
     In a particular embodiment of the implantable medical device with a ferromagnetic coupling member, the medical unit housing includes an elongated medical unit housing member, wherein the ferromagnetic coupling member is enclosed by the elongated medical unit housing member, and wherein the supply unit housing includes a receiving recess, wherein the receiving recess is configured to receive at least part of the elongated medical unit housing member, and wherein the supply unit power coupler coil is arranged circumferentially around the receiving recess. 
     The arrangement of the elongated housing member and a corresponding receiving recess may also be reversed in alternative embodiments. That is, the supply unit housing may include an elongated supply unit housing member while the medical unit may include a corresponding receiving recess. Further in such embodiment, a ferromagnetic coupling member may be enclosed by the elongated supply unit housing member. 
     In accordance with this disclosure, the functional medical module is or includes a continuous glucose meter module. In an alternative embodiment of this disclosure, or additionally, the functional medical module is or includes a cochlea implant module, a brain pacemaker module or a retinal implant module. The present disclosure is, however not limited to these particular types of functional modules. 
     A method for powering an implantable medical unit in accordance with the present disclosure may include:
     a) releasable mechanical coupling the implantable medical unit and an implantable supply unit;   b) non-galvanic coupling a medical unit power coupler of the medical unit with a supply unit power coupler of the supply unit, thereby powering the medical unit from a battery of the supply unit.   

     The implantable medical unit and the implantable supply unit may be designed according to combination of corresponding respectively matching embodiments as discussed above and/or further below. 
     In a particular embodiment of the method, the non-galvanic coupling is an inductive coupling. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  shows an implantable medical device in a schematic functional view; 
         FIG. 2  shows an implantable medical device in a perspective view; 
         FIG. 3  shows a further perspective view of the medical device of  FIG. 2 ; 
         FIG. 4  shows a sectional view of the medical device of  FIG. 1 ; and 
         FIG. 5  shows a further sectional view of the medical device of  FIG. 1 . 
     
    
    
     DESCRIPTION 
     The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of this disclosure. 
       FIG. 1  shows an embodiment of an implantable medical device  1  in a schematic functional view and in an implanted state respectively in a situation of use. In  FIG. 1 , individual units or modules are shown as boxes. Operative couplings by way of galvanic coupling are shown as solid lines, while operative couplings by way of non-galvanic, particularly, wireless coupling, are shown as chain lines. It is noted that the shown functional units or modules are not necessarily structurally distinct from each other but may be realized in a fully or partly integral way. 
     The hermetically sealed implantable supply housing  21  encloses the control circuit  22 , the battery  23 , the implantable supply communication interface  24 , the implantable supply power coupler  26  and the implantable supply data coupler  27 . In embodiments where the battery  23  is rechargeable, the implantable supply  2  optionally further includes a charging coupler  25  for charging the battery  23  in the implanted state. As explained before in the general description, the implantable supply power coupler  26  and the implantable supply data coupler  27  may in some embodiments be realized integral with each other. Similarly, the implantable supply communication interface  24  and the optional charging coupler  25  may in some embodiments be formed integral with each other. 
     The hermetically sealed medical unit housing  31  encloses a functional medical module  32 , a medical unit power coupler  36  and a medical unit data coupler  37 . The functional medical module  32  is, by way of example, a continuous glucose meter module, but may additionally or alternatively also implement other medical functions as explained in the general description. The functional medical module  32  further includes sensing and/or stimulation electrodes that are separately shown as electrodes  32   a  in  FIG. 1  for clarity reasons. The electrodes  32   a  contact the surrounding tissue in an implanted state. The sensing arrangements alternatively may be of optical nature e.g. by sending light into the tissue and receiving the scattered or induced fluorescing light. 
     As user interface for controlling operation of the implantable medical device  1  and/or displaying and further processing data that are acquired or measured by the implantable medical device  1 , a remote device (also referred to as a “remote” or “remote control”)  5  is provided. The remote device  5  is not part of the implantable medical device. The remote device  5  and the supply unit communication interface  24  may operatively couple and exchange data transcutaneously, with the skin being schematically shown as “S”. It is noted that the remote device  5  does not need to be present continuously and/or continuously couple with the supply unit communication interface  24 , but only in situations where data need to be exchanged. In particular in embodiments where the functional medical module is or includes a measuring module for a body parameter, such as a continuous glucose measurement module, the supply unit  2  and/or the medical unit  3  may be designed to store measured data, e.g., measured glucose data, and transmit them to the remote device  5  from time to time, e.g., upon user command. 
     In embodiments with a charging coupler  25  as explained before, an external charging device  4  may be provided that is designed to transmit power transcutaneous to the charging coupler  25 , e.g., by way of inductive coupling. The charging device  4  is placed on the skin in close proximity to the supply unit  2  and in particular the charging coupler  25  from time to time for charging the battery  23 , e.g., during night time. 
       FIG. 2  shows an embodiment of an implantable medical device  1  in a perspective view. The implantable device may for example correspond to the embodiment of  FIG. 1 . In  FIG. 2 , the supply unit  2  and the medical unit  3  are shown in a relative orientation that corresponds to a situation of use. However, the medical unit  3  is shown as uncoupled with respect to the supply unit  2 . 
     In this example, the supply unit  2  and the medical unit  3  both extend along a common longitudinal axis A. Opposing directions along the longitudinal axis A are referred to as proximal (towards the supply unit  2 , indicated as “P”), respectively distal (towards the medical unit  3 , indicated as “D”). 
     The hermetically sealed supply unit housing  21  of the supply unit  2  comprises an exemplary substantially cylindrical receiving recess  213  that exemplarily extends along the longitudinal axis A. A distal end section of the receiving recess  213  is formed by a circumferential resilient sleeve  212 . In this example, the hermetically sealed medical unit housing  31  is also substantially cylindrical. The medical unit housing  31  includes an elongated medical unit housing member  31   a  as proximal portion. At least a portion of the elongated medical unit housing member  31  is received by the receiving recess  213  in a coupled state. The outer diameter of the elongated medical unit housing member  31   a  corresponds to the inner diameter of the receiving recess  213  such that it is insertable into the receiving recces  213  with little or substantially no play by displaying the medical unit  3  in proximal direction along the longitudinal axis A. Due to its resilient properties, the sleeve  212  fixes the medical unit  3  by way of force locking. The receiving recess  213  and the sleeve  212  accordingly serve as supply unit coupling arrangement, while the corresponding elongated medical unit housing member  31   a  serves as medical unit coupling arrangement. 
     In this embodiment, the sleeve  212  does not need to hermetically seal the receiving recess  213  against the entry of body liquids. In typical application scenarios where the supply unit  2  has a longer lifetime as compared to the medical unit  3 , body liquids may enter the receiving recess  213  when the medical unit is explanted for the purpose of replacement, while the supply unit  2  remains implanted. The sleeve  212  may be provided with openings that allow fluidic communication of the receiving recess  213  with the exterior, such body liquids are displaced out of the receiving recess  213  when a new medical unit  3  is connected. In the shown embodiment, openings are exemplary realized by longitudinal channels (not individually referenced) in the circumferential inner contact surface  212   a  that contacts the elongated medical unit housing member  31   a  in the coupled state. 
     Further in this example, the supply unit housing  21  comprises optional fixing elements that are realized by fixing eyes  211  on opposite sides of the supply unit housing  21 . The fixing eyes  211  serve for fixing the supply unit  2  in the tissue by sewing it to solid tissue structures to prevent it from drifting around in the subcutaneous fat tissue. In this way, the supply unit provides a solid basis for the medical unit  3 . Further, the fixing allows a simple location of the supply unit  2  at the end of its lifetime since it cannot move within the body during its application time. 
     Further in this example, the medical unit housing  31  comprises an optional ring-shaped circumferential anti-inflammatory element  311  that is made from silicone rubber with an embedded anti-inflammatory agent. The anti-inflammatory element  311  is arranged in a distal section of the medical unit housing that is not inserted into the receiving recess  213 . Alternatively or additionally, the sleeve  212  may comprise an embedded anti-inflammatory agent, thereby serving as anti-inflammatory element. Anti-inflammatory elements prevent an undesired encapsulation by body tissue over an extended time period. 
     The electrodes  32   a  are arranged on the circumference of the medical unit housing  31  in the area that is not inserted into the receiving recess  213 . 
       FIG. 3  shows the implantable medical device  1  of  FIG. 2  in a further view. In  FIG. 3 , the medical unit  3  and the supply unit  2  are shown in the mechanically coupled state where a proximal portion of the medical unit housing  31  is located inside the receiving recess  313  as explained before. Further in  FIG. 3 , the supply unit housing  21  is removed. 
     The battery  23  which is in this example rechargeable is exemplarily arranged in a proximal section of the supply unit  2 . For transcutaneous battery charging, a charging coupler is  25  is provided in form of a flat coil. The coil  25  is favorably arranged on a side of the supply unit  2  that faces, in an implanted state, towards the skin and substantially parallel to the skin, thereby enabling good inductive coupling with an external charging device  4  as explained before. 
     Further, a medical unit NFC coil  26   a  is circumferentially arranged around a portion of the receiving recess  213 . The medical unit NFC coil  26   a  serves as both supply unit power coupler coil of the supply unit power coupler  26  and supply unit data coupler coil of the supply unit data coupler  27  in an integral way. 
     A printed circuit board with electronics component serves as control circuit  22  and carries, among others, the supply unit communication interface  24  as well as further circuitry for charging the battery  23 , providing power to and communicating with the medical unit  3 . 
       FIG. 4  shows the implantable medical device  1  in a sectional view and a corresponding configuration where the supply unit  2  and the medical unit  3  are uncoupled (like in  FIG. 2 ).  FIG. 5  is similar to  FIG. 4  and shows the medical device  1  in a configuration where the supply unit  2  and the medical unit  3  are coupled to each other, corresponding to a situation of use. The medical unit  3  comprises a rod-shaped ferrite core  38  that is arranged along the longitudinal axis A inside the medical unit housing  31 . The ferrite core  38  is positioned such that at least part of its length is located inside the receiving recess  213  in a coupled state of the supply unit  2  and the medical unit  3 . The medical unit power coupler  36  and the medical unit data coupler  37  are in this embodiment realized by a common NFC arrangement with a medical unit NFC coil  36   a  that is circumferentially arranged around the ferrite core  38  and serves as both medical unit power coupler coil and medical unit data coupler coil. The ferrite core  38  and the NFC coil  36   a  may form, in combination, a compact NFC module. In the coupled state of the supply unit  2  and the medical unit  3 , the ferrite core  38  ensures good inductive coupling between the supply unit NFC coil  26   a  and the medical unit NFC coil  36   a , respectively, thereby ensuring safe and efficient power transmission from the supply unit  2  to the medical unit  3  as well as data communication between the units. 
     While exemplary embodiments have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of this disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims. 
     LIST OF DESIGNATIONS 
     
         
           1  implantable medical device 
           2  implantable supply unit 
           21  supply unit housing 
           22  control circuit 
           23  battery 
           24  supply unit communication interface 
           25  charging coupler 
           26  supply unit power coupler 
           26   a  supply unit NFC coil 
           27  supply unit data coupler 
           211  fixing eye 
           212  sleeve 
           212   a  circumferential inner contact surface 
           213  receiving recess 
           3  implantable medical unit 
           31  medical unit housing 
           31   a  elongated medical unit housing member 
           32  functional medical module/continuous glucose meter module 
           32   a  electrodes 
           36  medical unit power coupler 
           36   a  medical unit NFC coil 
           37  medical unit data coupler 
           38  ferrite core 
           311  anti-inflammatory element 
           4  charging device 
           5  remote device 
         A longitudinal axis 
         S skin 
         D distal direction 
         P proximal direction