WO2010000026A1

WO2010000026A1 - Removable components for implantable devices

Info

Publication number: WO2010000026A1
Application number: PCT/AU2009/000852
Authority: WO
Inventors: Werner Meskens; Charles Roger Aaron Leigh; Kames William Leith Dalton; Dirk Fiedler
Original assignee: Cochlear Limited
Priority date: 2008-07-02
Filing date: 2009-07-02
Publication date: 2010-01-07

Abstract

An arrangement for simple replacement of components of implantable devices, such as batteries, is disclosed. The component is formed as a removable unit which is mechanically secured to the outside of the unit, for example as a screw fitting within a recess of the implantable device.

Description

REMOVABLE COMPONENTS FOR IMPLANTABLE DEVICES

TECHNICAL FIELD

The present invention relates to implantable devices, and to batteries and other components for such devices.

BACKGROUND TO THE INVENTION

Implantable devices of various types rely upon an implanted power supply.

Generally, external power is supplied periodically to such devices via a transcutaneous link, and a rechargeable battery is used to store power between the charging periods. Whilst such batteries will be typically capable of operation for long periods of time, eventually they will require replacement. The batteries may also fail prematurely. Technology may also advance, providing greater capacity or other features, and so replacement may be desirable. All these situations require replacement of the battery. Existing systems typically incorporate the battery device within the implanted medical device. A problem with this approach is that it requires the whole medical device to be removed, even if only temporarily, in order to replace the battery. For some devices, explantation is not a simple procedure. For example, for an intracochlear implant, tissue growth typically occurs around the electrode array, and removal of a well established implant may damage the structures of the cochlea, and create a risk of infection.

Another alternative which has been proposed is to provide a separate power unit for the medical device, connected via a direct cable connection or an inductive link. It is an object of the present invention to provide an arrangement which facilitates relatively simple replacement of implanted batteries and other components.

SUMMARY OF THE INVENTION

In a broad form, the present invention provides a battery element or other component housed in a removable fitting which mechanically mates with a corresponding element in an implantable device, so as to facilitate removal and replacement. According to one aspect, the present invention provides a component assembly for an implantable device, the assembly being adapted to be releasably mechanically retained in a recess of the implantable device, such that the component assembly operatively forms a sealed structure with the implantable device.

According to another aspect, the present invention provides an implantable device, including a component assembly and a component recess, wherein the component assembly is removably retained within the component recess such that the component assembly operatively forms a sealed structure with the implantable device.

According to another aspect, the present invention provides a method of replacing a removable component assembly within an implantable device, including the steps of accessing the implantable device, mechanically releasing an old component assembly from the exterior of the implantable device, so as to expose recess in said implantable device; cleaning the recess; correctly positioning any separate seals; and retaining the new component assembly in the recess of the implantable device.

Accordingly, implementations of the present invention provide an arrangement whereby components requiring replacement can be readily replaced, without requiring major surgery or explantation. BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present invention will now be described with reference to the accompanying figures, in which:

Figure 1 is a sectional view illustrating one implementation of a battery unit of the present invention;

Figure 2a is a planar view of an implant system adapted to use one implementation of the present invention;

Figure 2b is a planar sectional view of the implant system shown in Figure 2a; Figure 3 is a detailed view of another implementation in section;

Figure 4 is a view of the implementation of Figure 3, showing the whole battery unit in section;

Figure 5a is a more general view of the implementation of Figure 3; Figure 5b is a sectional view of the implementation shown in Figure 5a;

Figure 6a is a general view of another implementation;

Figure 6b is a sectional view of the implementation shown in 6a;

Figure 7 illustrates another alternative implementation; Figure 8 illustrates rotation of the battery unit within the implant body;

Figure 9 illustrates alternative mechanisms to permit rotation of the battery unit; and

Figure 10 illustrates another alternative implementation. DETAILED DESCRIPTION The present invention will be described with reference to a particular illustrative example for use in a cochlear implant system. However, the present invention is broadly applicable to any implanted medical device having an implanted power supply. The power supply may be rechargeable or non- rechargeable. Such devices may include, for example, implanted neural stimulation devices, drug pumps, pacing and defibrillation devices, and monitoring devices. It will be appreciated that the present implementation is described for illustrative purposes, and its features are not intended to be limitative of the scope of the present invention. Many variations and additions are possible within the scope of the present invention. Figure 1 illustrates the general principle of a first implementation of the present invention. A battery unit 1000 is shown with a battery cell 100 encased within a battery body 102. A screw thread 104 is provided around the outer edge of the battery body 102. Positive and negative contacts 106, 108 are provided on the base of the battery body 102. As will be explained further below, the medical device includes a corresponding recess for receiving the battery unit 1000, with suitable matching contacts. Hence, the battery unit 1000 can be inserted and removed from the device, without requiring removal or replacement of the whole device, but with the efficiency advantages of direct contact between the battery and the device. The battery cell 100 must be encased in a protective, hermetically sealed, biocompatible casing. This is preferably a similar material to the casing for the medical device. It may be formed, for example, from a biocompatible metal, for example titanium, or a titanium alloy such as an aluminium vanadium titanium alloy. It is preferred that the material chosen for the battery body not exhibit an electrochemical reaction relative to the other components of the implantable device. Any suitable material may be used.

It is preferred that the recess in the medical device is formed into a part of the device which is convenient for access when the device is implanted. It is also preferred that the screw thread 104 is relatively fine and finely pitched, so as to obtain a minimal angle between the battery unit 1000 and the implant body and thereby provide maximal enclosure. It will be appreciated that the thread 104 should be carefully toleranced on both the battery unit 1000 and the recess, so as to minimise any potential fluid path, while not offering too high a torque when it is necessary to remove battery unit 1000. It is also noted that the thread alone should not be relied upon to provide a seal: other appropriate O-rings or other mechanical seals will in any case be preferably used to provide adequate sealing against fluid ingress. It is also noted that the thread needs to not be too tightly toleranced, so that removal and unscrewing (potentially after many years of implantation) does not require an excessive torque to be applied.

Implantable batteries for medical devices have different operational requirements, and the battery must be selected so as to be appropriate in output power and storage for the intended application. For some applications, it may be appropriate to use a non-rechargeable battery, for example a cell containing lithium-metal anodes. For other applications, for example left ventricular assistance devices, it is usual to use rechargeable batteries, which will only require replacement at the end of their operational lifetime.

For an implanted cochlear implant system, typically at least 10 hours of autonomous operation of the device is required. Current Li-ion cell designs relying on a liquid or even solid state electrolyte are efficient and suitable for an implanted system. According to current techniques, they can be reduced in size to a cell thickness of 4 mm and below, so that the cell can be as low-profile as many chip-sized components. Other technologies make it possible to create battery cell designs which are in the shape of a mat that can be rolled up and even form part of the protective housing. This type of Li-ion cells, commonly known as Li-polymer, exploit a polymer-style electrolyte. The polymer electrolyte provides the required electrode stack pressure making it possible to enclose the cell in a lightweight foil pouch.

One technology suitable for implantable devices are primary lithium cells. One type, Li-12, uses an iodine cathode (manufactured by i.e. Greatbatch), and a lithium anode. The electrolyte is a solid organic charge transfer complex (eg.poly- 2-vinylpyridine, P2VP). This type of cell has a solid electrolyte, very high reliability and has been used in medical applications. An advantage is that Lithium Iodine cells do not generate gas even under short circuit. However, it has limited short circuit current, and is suitable only for low-current applications. Another group of primary cell technologies are lithium silver technologies, such as Li-Ag₂V₄θn, Li-SVO, and Li-CSVO. In each case, the anode is lithium. The cathode in the case of Li-SVO is Silver oxide and vanadium pentoxide (SVO). The cathode for LI-CSVO includes copper (II) oxide. The electrolyte may be lithium hexafluorophosphate, or lithium hexafluoroarsenate in propylene carbonate with dimethoxyethane. These cells are used in medical applications, eg. implantable defibrillators, neurostimulators, and drug infusion systems.

They have a high energy density and long shelf life, and are capable of continuous operation at a nominal temperature of 37 ⁰C. They are also resistant to abuse. Another alternative is Li/CFx: Carbon Monofluoride (manufactured by e.g.

Quallion).The system uses a solid cathode (CFx), organic electrolyte and a lithium anode. A further alternative is SOCbLi: Lithium-thionyl chloride (manufactured by Eaglepicher).

The present invention may be used with any suitable primary cell, for example the following primary cells which are offered by Greatbatch for implants: model nos 8426, 8431 , 8711 , 8843 Lithium/Iodine cells (see http://www.greatbatchmedical.com/batteriesPrimary.aspx?s=product).

The following primary cells are offered commercially by Quallion LLC for implants: QL0020B, QL0230 Lithium/Carbon Monofluoride Cells (see http://www.quallion.com/sub-mm-implantable.asp).

The present invention is also applicable to devices using rechargeable cells, for example lithium ion cells. One available technology is LiCoO2, with a lithium anode, a lithium cobalt oxide cathode and a graphite electrolyte. An advantage of this technology is that it is very light and has an energy density, about three times higher than that of conventional rechargeable batteries. It is widely used as a power source for various portable or mobile IT devices, which benefit from a reduction of weight and volume. Other suitable rechargeable technologies include LiNixCoyAlzO2, which has a LiNixCoyAlzO2 cathode, graphite anodes and graphite electrolyte; and LiFePO4, with a LiFePO4 cathode, graphite anodes and graphite electrolyte.

All these lithium ion technologies have a porous separator, which is soaked with electrolytes. They are used as implantable power supplies, and available commercially from Greatbatch Inc, Quallion LLC and other suppliers.

Another rechargeable technology is the rechargeable solid state lithium or lithium ion cell. These cells have an anode of metallic lithium, eg, lithium foil, or a carbon or other anode capable of incorporating lithium ions, a solid or gelified polymeric or ceramic (eg, LiPON₁ Lithium Phosphoroxy nitride) electrolyte, and a cathode based on metal oxides, phosphates or otherwise which are capable of reversibly incorporating lithium ions in order to sustain the charge / discharge processes of such a battery. The solid state design offers advantages with respect to fabrication, ruggedness, safety and thin-profile. Any of these types of cell could be used to implement the present invention, or any suitable alternative technology may be used. The present invention could also be applied with alternative power supplies which may require replacement or which may be substituted for the existing devices. It will be appreciated that the present invention is primarily concerned with the mechanical arrangement, and that it is not limited to any particular battery cell or power supply technology. The present invention could equally be applied to other forms of electrical storage, such as super capacitors, batacitors, and the like.

Figures 2a and 2b illustrate a typical cochlear implant device 2000, adapted according to the present invention. The implant body 110, at one end, includes an RF coil 112 for communicating data and power from an external device (not shown) and a magnet 113 for positioning the external device. At the other end, a stimulation electrode array 114, and an extra-cochlear reference electrode 115. The implant body 110 includes a recess or slot 116 for receiving the battery unit 1000.

As can be seen from Figures 2a and 2b, the recess 116 includes an internal thread 118, indentations 120, 121 for one or more O-rings, and radially inwardly, a circular trace 122, 124 for receiving the negative and positive pole of the battery 1000. The O-ring arrangement can be seen more clearly in Figures 3 and 4. In this arrangement the O-rings 126, 128, 130 are placed between the contacts 106, 108, as well as at either end of the screw threads 104, 118. This should be effective, in this embodiment, to prevent biofilm and dendritic growth and ion transport between the battery contacts 106, 108 or poles 122, 124. The prevention of the formation of biofilms is highly desirable in any implementation, and the use of smooth surface around the O-rings 126, 128, 130 will assist.

The main O-ring 126, where the lip of the battery unit 1000 meets the body 110 of the implant, serves as a seal of the battery unit 1000 with the recess 116. It is important that the dimensions of O-ring 126 are controlled to ensure a good seal is achieved. Using a fine screw thread 104, 118 may provide an additional restriction on fluid ingress.

It is possible that the main O-ring material could allow some moisture through over time. In addition, it will be almost impossible to exclude all body fluids during battery replacement in vivo. The presence of such fluids could lead to shorts or electrical leakage currents between the contacts 106, 108. Therefore a second and third indentation is positioned further inwardly allowing placement for additional O-rings 128, 130. These face sealing o-rings require careful control of dimensions to ensure a good seal is obtained. It is important in practice to ensure that the extent of insertion is controlled, so that the correct degree of compression is provided to the O-rings, but so that they are not over-compressed. A preferred approach is to provide a step or the like at which the bottom of the battery unit 1000 bottoms out, and cannot be further compressed, at a point before further compression will damage or compromise the seal of the O-rings. O-ring 130 improves on electrical isolation between the positive and negative traces that are connected to the poles 122, 124 of the battery unit 1000. Both the positive and negative traces are circular, so that the angular end point upon rotation is not relevant to making an appropriate contact between the battery unit 1000 and the implant body 110.

Figures 5a and 5b illustrate the implementation of Figures 3 and 4, with the battery unit 1000 positioned within the implant housing 110. It is preferred that the electrical contacts 106, 108 between the battery

1000 and the recess 116 are in the form of gold plated spring contacts, attached to the battery body 102. This enables an effective electrical connection with minimal losses between the battery unit 1000 and the implant body 110. Having the spring contacts on the battery allows for a simpler, smoother internal surface on the implant to facilitate cleaning during surgical replacement of the battery. In addition, the battery could include a coating or cover for spring terminals, which is removed, pierced or worn through as the battery is inserted. This would provide an additional level of protection against bodily fluids being trapped within the recess during replacement of the battery. Additionally, the spring contacts may be made replaceable. Of course, the present invention can be implemented with alternative contact arrangements.

It is preferred that the interior of recess 116 be kept as smooth and simple as possible. This area will need to cleaned out during surgery to fit the replacement unit, and any projections, cavities, etc will make this more difficult. An aspect of implantable device design is to avoid providing areas which may serve as a reservoir for disease after implantation. In order to avoid slowly developing infections 'from the inside out¹, it is preferred that antimicrobial / antibacterial coatings are applied to the inside surface of the sealed-off areas. Such coatings are well known in the art, and may include silver coated nanometre sized dots, or other suitable antimicrobial / antibacterial coatings.

In one alternative implementation, the replacement battery 1000 is placed in a separate implanted module 3000, an 'upgrade module¹ shown in Figures 6a and 6b. In this case, the battery 1000 is placed in a separate implantable module 3000 connected by a cable 132 to the main cochlear stimulation module 4000. This module 3000 may include other components, for example an implantable microphone, as will be discussed below. This module 3000 is directly connected by cable 132 to the main implant unit 4000, so no implantable connectors are required. The module 3000 would generally be positioned close to the skin, which will assist in simplifying any required surgery. As the upgrade module 3000 is only indirectly connected to the stimulation components, this arrangement further reduces the possibility of disturbing the implanted electrode array 114. It is also highly likely that an implantable microphone will require replacement in a fully implantable hearing prosthesis. Figure 7 illustrates an implementation similar to Figure 4, but in which a microphone unit 134 is included in the battery body 102. This allows for the microphone unit 134 to be replaced easily at the same time the battery 1000 is replaced. It is likely that the performance of implantable microphones will improve, and the time of battery replacement is likely to be an opportune time to replace the microphone. The same traces may be used for the microphone signal as well as the DC power from the battery.

An alternative to placing the microphone in the battery body is to provide a mechanically retained microphone unit, similar to the battery unit, which can be readily removed from the implant body, using a similar mechanical mechanism and electrical contacts to that used for the battery unit. The same arrangement of traces to permit connection may be used as for the battery, with the spring contacts attached, in this case, preferably to the microphone unit. It will be appreciated that the microphone could be associated with the implant body, or with an upgrade module.

It will be understood that this mechanical retention mechanism may be used for other components which may require replacement, as appropriate for the medical device in question. Figure 8 illustrates one way of removing the battery unit 1000 from the implanted body 110. A recess 136 for an Allen key or lnbus key may be provided, and the surgeon can insert a suitable tool 138 and rotate to remove the battery unit 1000. Figure 9 illustrates in plan view some suitable structures to receive various tools such as an Allen or hex key 138, a screwdriver 140, or a two- pronged release tool 142.

It is contemplated that the top cover at least of the battery unit could have an alternative shape, for example oval. In this case, a corresponding shaped tool could be attached to the top cover to release or insert the unit. In order to minimise biofilm formation, it is important to ensure that the O-rings are correctly positioned. Figure 10 illustrates an arrangement in which indentations 144 are provided to seat the O-rings 128, 130 in the battery unit 1000. It is preferred that the indentations 144 have a depth of about 2/3 of the diameter of the O-ring to effect a good planar seal. An adapted indentation depth equalizes frictions and pressure over the O-ring surface and prevents cracks of the O-ring during the locking and unlocking phase of the removable battery body from the implant device.

The advantage of this implementation over figure 5 is that the cleaning of a smoother implant surface is easier for the surgeon during replacement.

Alternatively, indentations could be provided in both the battery unit 1000 and the implant body 110 to receive the O-ring.

It is preferred in any case that at least one of the seals is of the planar, flange type, as this is not prone to rolling out of position in the same way as a circumferential seal.

Another alternative would be to use metal seals formed from a suitable material. It is noted that the material should be carefully selected so that there is no electro negativity difference between the implant body 110 and the battery casing 102 to create an electrochemical reaction. Yet another alternative is to use two types of biocompatible materials each having different mechanical properties such as hardness or stiffness. The removable fitting that mechanically mates with a corresponding implant element is made out of a softer material. This would allow a better and firmer sealing between the mating devices. One example of this is to manufacture the battery casing 102 or its exterior screw thread 104 using a softer material. During the first insertion the battery casing 102 or screw thread 104 would adapt itself for the best mating with the corresponding implant recess 116. In a more extreme case, the screw thread may not be required. It is noted that any unwanted deformation of the removable battery casing 102 during replacement is not a concern, as it is being removed.

Another alternative would be to construct the engagement between the battery casing and the recess to form a labyrinth seal. In such a structure, for example using a particular 3D structure for the corresponding housing materials instead of additional parts, a seal is created by a long, tortuous path for fluid travel, which in effect creates a seal.

It will be appreciated that a particular advantage of the present invention is that the implant battery, microphone or other components may be conveniently replaced, without the need to cut wires or use implantable connectors. For a device such as a cochlear implant, there is no need to explant or interfere in any way with the electrode array.

Whilst a screw thread type arrangement has been illustrated, any other suitable mechanical releasable structure may be used. For example, a bayonet- type junction between the battery cell body and the implant body may be employed in order to facilitate fewer turns when joining the two members. Any other suitable mechanical retention may be used.

Claims

CLAIMS:

1. A component assembly for an implantable device, the assembly being adapted to be releasably mechanically retained in a recess of the implantable device, such that the component assembly operatively forms a sealed structure with the implantable device.

2. A component assembly according to claim 1 , wherein the component assembly includes a battery unit including one or more battery cells.

3. A component assembly according to claim 1 , wherein the component assembly includes a battery unit and a microphone unit.

4. A component assembly according to claim 2 or 3, wherein the battery unit is rechargeable.

5. A component assembly according to any one of claims 2 to 4, wherein an electrical contact between the battery unit and the recess is a spring contact.

6. A component assembly according to any one of the preceding claims, wherein the assembly includes an exterior screw thread, adapted to be received by a corresponding thread in the recess.

7. A component assembly according to claim 6, wherein the exterior screw thread of the component assembly is made of a softer material than the material of the corresponding thread in the recess.

8. A component assembly according to any one of the preceding claims, wherein a plurality of seals are provided between the component assembly and the recess, positioned so as to provide overlapping seals between the component assembly and the recess.

9. An implantable device, including a component assembly and a component recess, wherein the component assembly is removably retained within the component recess such that the component assembly operatively forms a sealed structure with the implantable device.

10. A device according to claim 9, wherein the component assembly includes a battery unit including one or more battery cells.

11. A device according to claim 9, wherein the component assembly includes a battery unit and a microphone unit.

12. A device according to any one of claims 9 to 11 , wherein at least part of the exterior of the component assembly is made of a softer material than the material of the corresponding component recess.

13. A device according to any one of claims 9 to 12, wherein the assembly includes an exterior screw thread, adapted to be received by a corresponding thread in the recess.

14. A device according to any one of claims 9 to 13, wherein a plurality of seals are provided between the component assembly and the recess, positioned so as to provide overlapping seals between the component assembly and the recess.

15. A device according to any one of claims 9 to 14, wherein the device includes a main implant unit and an upgrade unit, the upgrade unit being electrically connected to the main implant unit, the upgrade unit including the component recess and the component assembly.

16. A method of replacing a removable component assembly within an implantable device, including the steps of accessing the implantable device, mechanically releasing an old component assembly from the exterior of the implantable device, so as to expose a recess in said implantable device; cleaning the recess; correctly positioning any separate seals; and retaining the new component assembly in the recess of the implantable device.

17. A method according to claim 16, wherein the component assembly is mechanically retained by a screw fitting into the recess of the implantable device.

18. A method according to claim 16 or 17, further including providing one or more seals between the component assembly and the recess prior to mechanically retaining the new component assembly in the recess of the implantable device.