Abstract:
An implantable device is provided. The device is constructed from an open body containing electronic components, a heat-sensitive component, and a sealing component. The device is formed in a moisture controlled environment, such that the heat-sensitive component is attached to the open enclosure after the enclosure has been heated. The sealing component is subsequently affixed to the open enclosure to form a sealed enclosure.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a National Stage of PCT/AU2008/000570, filed Apr. 23, 2008, entitled “IMPLANT ASSEMBLY”, which claims priority from Australian Provisional Patent Application No. 2007902123 entitled “IMPLANT ASSEMBLY,” filed Apr. 23, 2007. The contents of these applications are hereby incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to implantable devices, and particularly to the construction and assembly of such devices. 
         [0004]    2. Related Art 
         [0005]    The present invention relates to devices intended to be implanted in the human body, particularly those having internal batteries, or other temperature-sensitive components. 
         [0006]    For example, active medical devices typically require a source of electrical power. This may be achieved by passing power transcutaneously via an inductive link, or by providing an implanted power source such as an internal battery. Battery power has the advantage of reducing the need for external components, and also avoids the power losses associated with an RF link. Also, batteries which are rechargeable via an inductive link may provide a degree of independent operation. 
         [0007]    A number of precautions are necessary to ensure the highest level of reliability of the electronics in an active medical device. One such precaution is ensuring the electronics are enclosed in a hermetically sealed enclosure with a very low moisture level, typically less than 0.5%. To achieve this low moisture level it is necessary to bake the assembly before final sealing of the enclosure. A typical bake would be 125° C. under vacuum for 16 hours. The final seal is typically achieved by sealing a “bake out hole,” which is a hole in the enclosure, of about 0.15 mm diameter left open to allow the escape of moisture, and which can be sealed by a laser pulse. 
         [0008]    While most electrical components can withstand the bake process, batteries often cannot withstand such temperatures. For example, lithium ion battery technology typically has an upper temperature limit of 60° C. When exposed to temperatures, such a battery is irreversibly damaged. Other temperature-sensitive components in implants may similarly be unable to withstand such bake temperatures. 
       SUMMARY 
       [0009]    In one aspect of the present invention, an implantable device constructed from an open body cochlear implant system is provided. The implantable device contains electronic components, a heat sensitive component, and a sealing component, the device being formed in a moisture controlled environment, such that the heat sensitive component is attached to the open body after the open body has been baked, and the sealing component is affixed to seal the enclosure. 
         [0010]    In a second aspect of the present invention, a method of forming an implantable device is provided. The method comprises, baking an open body containing electronic components so as to reduce the moisture content; connecting a heat sensitive component to said open body; and sealing the open body to form said device. 
         [0011]    In a third aspect of the present invention, a method of forming a sealed device is provided. The method comprises a sealed device, the device including electronic components and at least one heat sensitive component, the method comprising: baking an open body containing electronic components so as to reduce the moisture content; connecting a heat sensitive component to said open body; and sealing the open body to form said device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Illustrative embodiments of the present invention are described herein with reference to the accompanying figures, in which: 
           [0013]      FIG. 1  is a perspective view illustrating one implementation of the present invention; and 
           [0014]      FIG. 2  is a perspective view illustrating another implementation of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Embodiments of the present invention will now be described in detail. It will be appreciated that the embodiments are intended to be illustrative and not limiting. In particular, although the exemplary embodiments described herein are presented in the context of cochlear implants and batteries, embodiments of the present invention may be utilized in any implantable device having an enclosure housing heat-sensitive components. 
         [0016]      FIG. 1  shows a construction where electronics  12  are positioned in an implant enclosure  14 . Enclosure  14  is open on one side; that is, one side of enclosure  14  has an aperture that, in this illustrative embodiment, is the entire side. To reduce the moisture level in enclosure  14 , the enclosure  14  and electronics  12  may be heated such as by baking. In one embodiment, the package of enclosure  14  and electronics  12  is baked in the conventional way, for example at 125° C. under vacuum for 16 hours. One suitable approach is to bake electronics  12  in a vacuum oven attached to a glovebox (not shown) capable of controlling moisture content. Commercial gloveboxes capable of controlling moisture and oxygen levels to as low as a few ppm are appropriate. 
         [0017]    Subsequently, a battery  16  is attached to electronics  12 , and enclosure  14  is hermetically sealed. Battery  16  is stored in the glovebox. Following baking, battery  16  is attached to the electronics package using, in this embodiment, a resistance weld  18 . This is a conventional process, which can be readily carried out by those of ordinary skill in the art. 
         [0018]    Alternatively the battery connections could be made as described in U.S. Pat. No. 5,103,818. Such an embodiment utilizes a plug and socket arrangement which is subsequently fusion welded. Following the electrical connection of the electronics package and battery  16  are hermetically sealed. Any other suitable connection arrangement could be used, being in mind the need to operate in the controlled environment. 
         [0019]    It is known that battery  16  itself can be suitably sealed so as to not provide a source of moisture within the package, and this can be controlled separately during the battery manufacture. One method of controlling battery moisture content is described in JP08343907, which is hereby incorporated by reference herein. This reference discloses manufacturing in a low moisture environment, and the use of a moisture absorbent powder. As such, battery  16  may then be sealed, separately from electronics  12 . 
         [0020]    In the embodiment illustrated in  FIG. 2 , battery  26  is shaped with a flange  28  so as to form the lid of electronics enclosure  24 . The outer surface of the battery structure will need to be formed from a suitable biocompatible material, for example titanium. Laser welding  30  around the edge of battery  26  then creates a hermetically-sealed enclosure. Such welding is a conventional process in the manufacture of implantable devices. 
         [0021]    Battery  26  may be connected by welds  18  to positive and negative terminals in device electronics  12 . However, it is preferred that the case of battery  26  provides one contact to battery  26 , and laser weld  30  then creates one electrical connection via implant enclosure  24 , so that only one resistance weld  18  is required, as shown in  FIG. 2 . Embodiments of this method of battery connection using enclosure  24  as a terminal is described in U.S. Pat. No. 5,814,091, which is incorporated by reference herein. Embodiments of the present invention may be conveniently used with a chassis design, such as disclosed in International Patent Application PCT/US2006/02794, which is hereby incorporated by reference herein. It is noted that as the device forms a complete metal enclosure with the other battery terminal inside the enclosure, there is no risk of a charge being delivered externally. 
         [0022]    Embodiments of the present invention may be deployed for any shape of device, and for devices made from any suitable material. Whilst the examples describe a metal enclosure, the invention may equally be employed with ceramic or other materials, with suitable modification to sealing techniques. Obviously, in such an arrangement the ceramic housing could not be used as a conductor. 
         [0023]    Battery energy is a function of the volume of the battery. By making the battery area most of, or the whole of, the area of the electrical enclosure the thickness of the battery can be minimized while obtaining an adequate volume. 
         [0024]    The constructions shown in  FIGS. 1 and 2  show a relatively shallow, wide construction with the seal applied to a large surface area. As such, a battery thickness of less than approximately 2 mm can be achieved. 
         [0025]    For example, the power required to power a typical cochlear implant is about 5 mW. Using current battery technology, energy density is typically about 0.15 mWh/mm 3 . Hence, to deliver about 5 mW with a 24 hour life requires a battery volume of about 800 mm 3 . Hence, according to this implementation of the present invention, with an implant electrical package measuring about 25 mm square, the thickness of the battery can be about 1.3 mm. Techniques may be used to minimize battery dimensions such as that described in U.S. Pat. No. 6,040,082. This in turn minimizes the thickness of the implant. 
         [0026]    In combination with PCT/US2006/02794, by the present applicant previously incorporated by reference herein, an overall implant thickness of less than 6 mm can be achieved. The positioning of the battery over the electronics also serves to provide additional protection to the electronics from impact. 
         [0027]    It will be appreciated that the present invention can be implemented in a variety of ways, in combination with existing and new construction techniques, and variations and additions are possible using the underlying principles of the present invention. 
         [0028]    All documents, patents, journal articles and other materials cited in the present application are hereby incorporated by reference. 
         [0029]    The invention described and claimed herein is not to be limited in scope by the specific preferred embodiments herein disclosed, since these embodiments are intended as illustrations, and not limitations, of several aspects of the invention. Any equivalent embodiments are intended to be within the scope of this invention. Indeed, various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims.