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Title:
IN SITU MOULDING FOR IMPLANTABLE HEARING PROSTHESES
Document Type and Number:
WIPO Patent Application WO/2010/000028
Kind Code:
A1
Abstract:
A method of modifying in situ the shape and/or orientation of a manipulable portion of a component of a prosthesis or transducer comprising: heating the manipulable portion from a first temperature to at least a second temperature; relatively bringing a different shaping portion of the component into contact with the manipulable portion; allowing the manipulable portion to cool back towards the first temperature; and relatively withdrawing the shaping portion at least partially away from the manipulable portion to leave the manipulable portion having a different shape and/or orientation.

Inventors:
CHAMBERS JOHN (AU)
Application Number:
PCT/AU2009/000854
Publication Date:
January 07, 2010
Filing Date:
July 02, 2009
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
COCHLEAR LTD (AU)
CHAMBERS JOHN (AU)
International Classes:
A61F11/00; H04R25/02
Foreign References:
US4735759A1988-04-05
US6421569B12002-07-16
Attorney, Agent or Firm:
COCHLEAR LIMITED (Attn: Amy Laxton14 Mars Roa, Lane Cove New South Wales 2066, AU)
Download PDF:
Claims:
CLAIMS:

1. A method of modifying in situ the shape and/or orientation of a manipulable portion of a component of a prosthesis or transducer comprising: heating the manipulable portion from a first temperature to at least a second temperature; relatively bringing a different shaping portion of the component into contact with the manipulable portion; allowing the manipulable portion to cool back towards the first temperature; and relatively withdrawing said shaping portion at least partially away from said manipulable portion to leave the manipulable portion having a different shape and/or orientation.

2. The method of claim 1 wherein the heating of the manipulable portion occurs before, at the same time, or after said shaping portion is brought into contact with the manipulable portion.

3. The method of claim 1 or claim 2 wherein the step of relatively withdrawing the shaping portion occurs before the manipulable portion has reached the first temperature, when the manipulable portion has reached the first temperature, or after the temperature of the manipulable portion has fallen below the first temperature.

4. The method of any one of the preceding claims wherein the manipulable portion comprises a thermoplastic polymeric material.

5. The method of any one of claims 1 to 3 wherein the manipulable portion is an elastomeric material

6. The method of claim 4 wherein the material is polyethylene, polypropylene, polystyrene, polycarbonate, polyacrylate, polybutylene, polyamide, polyimide, polysulfone, acrylonitrile butadiene styrene, polyvinyl chloride, or polytetrafluoroethylene.

7. The method of any one of the preceding claims wherein the manipulable portion is biocompatible and/or bio-inert.

8. The method of any one of the preceding claims wherein the manipulable portion comprises a first material and has one or more layers of a second material provided thereon.

9. The method of claim 8 wherein the manipulable portion comprises a first thermoplastic material coated with one or more layers of polytetrafluoroethylene.

10. The method of any one of the preceding claims wherein the shaping portion comprises a member that is deflectable by differential air pressure.

11. The method of claim 10 wherein the member has a shape and/or thickness and/or configuration that allows the member to deflect if one side of the member is subject to a relatively higher pressure compared to the other side.

12. The method of any one of the preceding claims wherein the shaping portion is used to heat the manipulable portion by radiating or conducting heat into the manipulable portion.

13. The method of claim 12 wherein the shaping portion comprises a relatively electrically resistive material and/or has a shape and/or a configuration such that it undergoes Joule heating heats on application of a suitable voltage.

14. The method of any one of the preceding claims wherein the shaping portion comprises a metallic member.

15. The method of claim 14 wherein the metallic member is biocompatible.

16. The method of claim 14 or claim 15 wherein the metallic member is formed from titanium or a titanium alloy.

17. The method of any one of the preceding claims wherein the shaping portion is a diaphragm of a microphone assembly and the manipulable portion is a microphone coupling of a microphone assembly.

18. A microphone assembly when formed using the method of claim 17.

19. A hearing prosthesis comprising a housing having a microphone assembly of claim 18 mounted thereto.

20. The hearing prosthesis of claim 19 wherein the prosthesis is totally implantable within an implantee.

21. A component of a transducer and/or for use in conjunction with an implantable device, the component comprising: a first member; a drivable actuator member having an end distal the first member; a drive for moving the actuator member relative to said first member over a range of oscillating movement about a set neutral position; and one or more biasing members that also controls movement of the actuator member and adjusts the set neutral position of the actuator member; wherein the biasing member comprises a shape memory alloy or a ferromagnetic shape memory alloy that changes shape, configuration and/or dimension on a change in temperature or applied magnetic field.

22. The component of claim 21 wherein the transducer or implantable device is a prosthesis, such as a hearing prosthesis.

23. The component of claim 22 wherein the hearing prosthesis is a hearing aid and the component of the hearing aid is positionable within the middle ear of a recipient.

24. The component of claim 23 wherein the actuator member is arranged in use to contact the ossicular chain of the recipient.

25. The component of any one of claims 21 to 24 wherein the first member comprises a base having a first fixation member, the base housing at least some components of the drive.

26. The component of claim 25 wherein the drive is an electromagnetic drive and the actuator member extends from the electromagnetic drive.

27. The component of claim 26 wherein the actuator member comprises a linear member extending from a proximal end, that is positionable within the electromagnetic drive, to the distal end.

28. The component of any one of claims 21 to 27 wherein the distal end of the actuator member has a second fixation member to assist in fixation of the distal end to a desired location on the ossicular chain of the recipient.

29. The component of claim 27 wherein the electromagnetic drive comprises a ferromagnetic armature mounted to the actuator member at and/or adjacent its proximal end and one or a plurality of solenoid coils within which the armature is positionable.

30. The component of claim 29 wherein a biasing member is positioned on each side of the armature and which separately undergo changes in shape, configuration and/or dimension on change in temperature.

31. The component of claim 29 or claim 30 wherein one or both biasing members comprise a spring member.

32. The component of claim 31 wherein a suitable applied voltage is delivered across the spring member to cause the spring member to undergo Joule heating, this Joule heating in turn resulting in the spring member relatively contracting or expanding depending on the shape memory that has previously been applied to the spring.

33. The component of any one claims 21 to 32 wherein the shape memory alloy comprises a copper-zinc-aluminium-nickel, copper-aluminium-nickel, or nickel-titanium alloy or Nitinolâ„¢ or other material exhibiting two or more allotropic states of differing morphology.

34. A method of modifying in situ the shape of a first portion of a component of a transducer or prosthesis comprising: heating the first portion from a first temperature to at least a second temperature; applying a physical, magnetic or electrical force to the first portion to modify the shape of the first portion; relatively removing the physical, magnetic or electrical force from the first portion to leave the first portion having a different shape or orientation.

35. A component of an implantable device comprising: an orientable first member; a drivable actuator member having an end distal the first member; and a drive for moving the actuator member relative to said first member over a range of movement about a set neutral position; wherein the orientation of said first member is controllable from a first position to at least a second position.

36. The steps, features, integers, compositions and/or compounds disclosed herein or indicated in the specification of this application individually or collectively, and any and all combinations of two or more of said steps or features.

Description:
IN SITU MOULDING FOR IMPLANTABLE HEARING

PROSTHESES

Field of the Invention

The present invention relates to a method for forming relatively small implantable components, including components of hearing prostheses, such as cochlear implants.

Background of the Invention

While cochlear implants have typically relied upon use of both an external component, such as a speech processor unit, and an implantable component, such as a receiver/stimulator unit, fully implantable systems have been proposed. Such fully implantable systems have a number of potential advantages, including being usable in circumstances where a traditional system cannot be used.

Successful use of a fully implantable system does require use of devices that would normally be used in or on an external component to be implanted in a biocompatible housing within a recipient. These devices potentially include a microphone and a power source.

Techniques for forming such implantable devices are often difficult to perform and/or relatively expensive due to the often intricate nature of the devices, their relatively small size of the devices, and the requirements for robustness and hermaticity so that they are suitable for implantation.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

Summary of the Invention Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

According to one aspect, the present invention is a method of modifying in situ the shape and/or orientation of a manipulable portion of a component of a prosthesis or transducer comprising: heating the manipulable portion from a first temperature to at least a second temperature; relatively bringing a different shaping portion of the component into contact with the manipulable portion; allowing the manipulable portion to cool back towards the first temperature; and relatively withdrawing said shaping portion at least partially away from said manipulable portion to leave the manipulable portion having a different shape and/or orientation.

According to a second aspect, the present invention is a method of modifying in situ the shape and/or orientation of a first portion of a component of a prosthesis or transducer comprising: heating the first portion from a first temperature to at least a second temperature; applying a physical, magnetic or electrical force to the first portion to modify the shape of the first portion; and relatively removing the physical, magnetic or electrical force from the first portion to leave the first portion having a different shape and/or orientation.

In these aspects, the prosthesis or transducer can comprise a hearing prosthesis.

In one embodiment, the manipulable portion can comprise a mouldable portion. The manipulable portion or the first portion can comprise a microphone coupling of a microphone assembly. In this or other embodiments, the shaping portion can comprise a diaphragm of a microphone assembly.

According to a third aspect, the present invention comprises a component of a prosthesis or transducer when formed using one of the methods as defined herein. In the third aspect, the component can be a microphone assembly of a prosthesis or a transducer.

The prosthesis can be a hearing prosthesis, including a totally implantable prosthesis. In further embodiments, the hearing prosthesis can be a cochlear implant or hearing aid.

According to a fourth aspect, the present invention is a component of a transducer and/or for use in conjunction with an implantable device, the component comprising: a first member; a drivable actuator member having an end distal the first member; a drive for moving the actuator member relative to said first member over a range of movement about a set neutral position; and one or more biasing members that also controls movement of the actuator member and adjusts the set neutral position of the actuator member; wherein the biasing member comprises a shape memory alloy that changes shape, configuration and/or dimension on a change in temperature or applied magnetic field.

According to a fifth aspect, the present invention is a component of an implantable device comprising: an orientable first member; a drivable actuator member having an end distal the first member; and a drive for moving the actuator member relative to said first member over a range of movement about a set neutral position; wherein the orientation of said first member relative to said actuator member is controllable from a first position to at least a second position.

In the fourth and fifth aspects, the drive can be an electromagnetic drive.

In the fifth aspect, the orientation of the first member can be adjusted in situ during or immediately following manufacture of the transducer. In another embodiment, the orientation of the first member can be adjusted in situ during or post- placement of the transducer. In the fifth aspect, the implantable device can comprise a transducer that can further comprise one or more biasing members that also controls movement of the actuator member and adjusts the set neutral position of the actuator member. The biasing member can comprise a spring member, for example a helical compression spring.

In another embodiment, the component of the fifth aspect can have one or more features of the component of the fourth aspect as described herein.

According to a sixth aspect, the present invention is a component for use in conjunction with a implantable transducer or other implantable device, the component having an orientable first member and wherein the orientation of the first member is adjustable in situ during or immediately following manufacture of the component and/or during or post-placement of the component within an implantee.

In one embodiment of the sixth aspect, the orientable first member can have a first end positioned within a container that is at least partially filled with a liquid/particulate material solution having a density that at least partially supports the first member within the container. In one embodiment, the liquid/particulate solution can undergo a relative increase in its degree of liquefaction through application of a vibratory stimulus. This increase in relative liquefaction can allow relatively more ready orientation of the first member within the container on application of a force to the first member.

In a further embodiment, the particulate material can be a ferromagnetic material that relatively binds together through magnetic attraction on application of a magnetic field to the material within the container. This can in turn serve to relatively increase the frictional engagement between the material and the first member so holding it in a relatively fixed position relative to the container.

In this aspect, the first member can have an end positioned outside the container and an end inside the container. The outside end can have fixation member, for example a loop, that facilitates mounting of the end to a desired location following implantation. The inside end can be relatively enlarged, for example, a spiked bulb that serves to readily increase the frictional engagement between the inside end and the liquid/material combination within the container. In this sixth aspect, the component can have one, some or all of the features of the component according to the fourth and fifth aspects.

In the fourth, fifth and sixth aspects, the component can comprise a component, such as a transducer component, of a prosthesis. The prosthesis can comprise a hearing prosthesis. In one embodiment, the hearing prosthesis can comprise a hearing aid. The component of the hearing aid can be positionable within the middle ear. In this case, the actuator member can be arranged in use to contact the ossicular chain and can be located on the incus long process, the incodostapedial joint or the stapes. The component can be used in conjunction with any type of transducer or implantable device where it is necessary or desirable to adjust the position or shape of parts of the transducer or implantable device to suit the requirements of the recipient or implantee of the transducer or device.

Where present, the one or more biasing members can be used to provide relatively minor adjustment of the position of the actuator member. In particular, it can allow adjustment so that the actuator member can be moved to the desired set neutral position.

The ability to allow in situ modification of the transducer, such as the orientation on the first member, also provides a mechanism for ensuring the actuator member is moved to a desired set neutral position.

When in the neutral position, the transducer preferably does not exert, or at least only relatively minimally exerts, a static force on the ossicular chain when the prosthesis is turned off, deactivated or otherwise when the applied acoustic stimulation levels are relatively low or minimal in amplitude.

The present application, at least in part, describes herein various embodiments for modifying the shape and orientation or components of implantable devices during and/or following manufacture, including during or after placement in position within an implantee. Such variation to a desired shape and/or orientation can be difficult or at least expensive to achieve in what are typically relatively tiny components during and following manufacture. As used herein, the term "shape memory alloy" refers to a broad class of materials which, on possessing one particular shape or form, can, on being changed to a different shape or form through the application of an influencing agent, such as mechanical force, retain an ability to return, either partially or completely to the original form on application of a different agent, such as a temperature change. In this way, shape changes associated with the differing allotropic or crystallisation forms of an object are possible on changing their temperature.

Brief Description of the Drawings

By way of example only, the present invention is now described with reference to the accompanying drawings:

Fig. 1 is a simplified view of one embodiment of a microphone assembly mounted to an implantable housing;

Figs. 2 A to 2C depict steps in the formation of parts of one embodiment of a microphone assembly according to the present invention;

Fig. 3 is a simplified and not-to-scale depiction of one form of hearing prosthesis according to the present invention positioned within the middle ear of a recipient;

Figs. 4A to 4C depict use of a transducer of Fig. 3 to adjust the set neutral position of an actuator member;

Figs. 5A to 5D depict in a simplified and representational manner the steps for adjusting and then fixing the orientation of a member of a transducer following placement;

Fig. 6 depicts a further embodiment of the transducer of Fig. 5 but having ferromagnetic particles; and

Fig. 7 is a simplified representation of the member of Figs 5A to 6 mounted to another embodiment of a transducer for placement in the middle ear of a recipient. Preferred Mode of Carrying out the Invention

A totally implantable cochlear implant requires implantation of a relatively high quality microphone that will suitably meet the needs of the implantee to both hear and successfully engage in verbal communication.

Such a microphone needs to be mounted in a housing that is implantable within the implantee. This housing may also contain other componentry including a speech processor and stimulation circuitry to allow output of appropriate stimulation signals to an electrode assembly positioned within the cochlea of the implantee. The housing can be implantable in a recess of the temporal bone adjacent the ear of the implantee that is receiving the output of the implant system. The housing can be formed from a biocompatible material and/or have a biocompatible coating. The housing can be coated with a layer of silicone elastomer or parylene. While totally implantable, the housing may still need to, at least occasionally, communicate with an external component. As such, the implant will typically include an antenna for use as part of a bidirectional radio frequency magnetic induction link with an external antenna.

In addition to being biocompatible, the housing also needs to have a level of hermaticity to ensure preservation of the components within the housing while ensuring the safety of the implantee, potentially for the entire lifetime of the implantee.

In this regard, the microphone needs to be able to perform at a suitable level to meet the needs of the implantee while being mounted in a housing that must meet the requirements defined herein.

One example of an implantable housing 21 having a microphone diaphragm assembly 10 mounted thereto formed according to the present invention is depicted in

Fig. 1. The housing 21 is depicted implanted in surrounding tissue 20. The assembly 10 includes a substantially planar diaphragm 11 and a microphone coupling 12 that defines an air or gas-filled cavity.

The assembly 10 can be formed from one material or two or more materials. In one embodiment, the assembly 10, including the diaphragm 11, can be formed from titanium or a titanium alloy. Other suitable biocompatible materials can be envisaged. As depicted in Fig. 1, the assembly 10 further includes a microphone 13 that is positioned within a microphone housing 14. In the depicted embodiment, the diaphragm 11 can be appropriately welded to the housing 21 at or adjacent the perimeter 15 thereof. The diaphragm also has an outer surface 16 and an inner surface 17.

One embodiment of a method for forming part of the microphone diaphragm assembly 10 is now described with reference to Fig. 2.

In this method, the microphone coupling 12 is manipulable, here mouldable, into a desired shape by another portion of the prosthesis itself, namely the diaphragm 11. The method comprises heating the microphone coupling 12 from a first temperature to or towards at least a second elevated temperature relative to the first temperature.

Before, during or after heating of the coupling 12, the diaphragm 11 can be brought into contact with the coupling 12 so as to mold the coupling 12 to a desired shape. In this regard, it will be understood that the heated coupling 12 can at least partially or fully adopt the shape of the diaphragm 11 when contact occurs.

In one embodiment, the diaphragm 11 can undergo an increase in temperature by exposing the said metal diaphragm to an intense, high oscillatory frequency, magnetic field, which through the action of induced current flow and associated Joule heating, raises the temperature of the diaphragm 11 and in turn the coupling 12.

The microphone coupling 12 can then be cooled, or allowed to cool, back to, towards or beyond the first temperature. Before, when or after the coupling 12 has reached the first temperature, the diaphragm 11 can be relatively withdrawn at least partially away from the coupling 12 so leaving the coupling 12 in its new configuration.

In considering this method, it will be appreciated that the steps need not necessarily occur in a particular order. For example, heating of the microphone coupling 12 can occur before, at the same time, or after the diaphragm 11 is brought into contact with the coupling 12. Still further, the step of relatively withdrawing the diaphragm 11 may not occur until the coupling 12 has reached the first temperature or even a temperature below the first temperature. In yet another embodiment, the step of relatively withdrawing the diaphragm 11 could occur before the first temperature is reached.

In one embodiment of the method, the microphone coupling 12 can comprise a thermoplastic polymeric material. Examples of suitable thermoplastic materials include polyethylene, polypropylene, polystyrene, polycarbonate, polyacrylate, polybutylene, polyamide, polyimide, polysulfone, acrylonitrile butadiene styrene, polyvinyl chloride, and polytetrafluoroethylene. In another embodiment, the coupling 12 can comprise an elastomeric material. The material preferably does soften or become more readily deformable when heated. In one embodiment, the material can be biocompatible and/or bio-inert. In a further embodiment, the coupling 12 can comprise a first material and have one or more layers of a second material provided thereon. In one embodiment, the coupling 12 can comprise a first thermoplastic material coated with one or more layers of polytetrafluoroethylene. The layer or layers of polytetrafluoroethylene can serve to assist in ensuring the diaphragm 11 does not become permanently adhered to the coupling 12 during the method. Other suitable linings than polytetrafluoroethylene can be envisaged.

In the depicted method, the diaphragm 11 can be deflectable by differential fluidic pressure, for example differential air pressure. It should also be appreciated that agents other than air can be used to differentially apply coercive force to the diaphragm. Such agents might include, but are not limited to, liquid or gaseous substances such as hydrocarbons, water, nitrogen, argon, helium etc. The diaphragm

11 can have a shape and/or thickness and/or configuration that allows it to deform if one side of the member is subject to a relatively higher pressure compared to the other side.

An example of how this can occur is depicted in Fig. 2. Fig. 2 is a simplified depiction of a microphone diaphragm 11 supported around a perimeter 15. In Fig. 2A, there is no difference in the air pressure adjacent each side (16 and 17) of the diaphragm 11. In Fig. 2B, the air pressure adjacent the outer surface 16 has increased relative to the air pressure adjacent the inner surface 17, so causing the diaphragm 11 to bend relatively inwardly. In Fig. 2C 9 the difference in air pressure has been removed so allowing the diaphragm 11 to return back or close to its original position. With reference to Fig. 2, it will be appreciated that particular gases could be used to constitute the particular atmosphere that is present adjacent the outer and/or inner surface of the diaphragm 11. Still further, while in Figs. 2A and 2C, the air pressure adjacent each surface is shown as equal, it will be appreciated that relatively small differences may exist with such differences being of a magnitude that no appreciable if any impact is caused to the shape or position of the diaphragm 11.

In the method depicted in Fig. 2, the diaphragm 11 is caused to undergo Joule heating by applying a suitable voltage across the diaphragm 11. In another embodiment, the coupling can be exposed to a relatively intense, high oscillatory frequency, magnetic field, which through the action of induced current flow and associate Joule heating raises the temperature of the diaphragm 11. The heat generated in the diaphragm 11 is then radiated and/or conducted to the microphone coupling 12 which also undergoes an increase in temperature. In one embodiment, the temperature of the coupling 12 can be increased to somewhere between about 8O 0 C and about 14O 0 C.

When heated, the microphone coupling 12 more readily undergoes deformation or reshaping due to applied pressure from the diaphragm 11 (see Fig. 2B). The voltage can then be removed, by removing the voltage source or disconnecting a switch, so allowing the diaphragm 11 to cool and so also allowing the coupling 12 to cool. Once the coupling 12 is below a suitable temperature at which it will retain its new shape, the differential pressure can be removed so allowing the diaphragm 11 to move back and away from the molded coupling 12 (see Fig. 2C).

By use of careful control of the applied heat and pressure in combination with knowledge of the coupling and diaphragm characteristics allows the shape of the coupling member to be precisely modified in relation to that of the diaphragm.

While Fig. 2 depicts a microphone assembly having a mouldable portion or component (ie the coupling 12) shaped by in situ moulding using a shaping portion (i.e. the diaphragm 11), it will be appreciated that the method defined herein could be used to shape other components within prostheses, including hearing prostheses.

Further, while Fig. 2 relied on heating of the diaphragm 11 to modify the coupling 12, in another embodiment, the coupling 12 could be modified through the application of a suitable physical, magnetic or electrical force to the coupling 12 so as to modify the shape of that component. Once it has been modified, the application of the physical, magnetic or electrical force could be removed.

While Figs. 1 and 2 are directed to an implantable cochlear implant, Figs. 3 to 4C depict one example of an alternative type of hearing prosthesis or hearing aid that provides a hearing sensation by using an electromagnetic transducer to convey sound vibrations to the relatively tiny and delicate bone structures of a recipient's middle ear.

During the surgical attachment and use of such a transducer, it is desirable that there is no or relatively little static or excessive force applied to these bones, since doing may lead to injury and destroy any benefit inferred by the prosthesis.

While not intended to be surgically accurate, Fig. 3 illustrates the approximate position and scale of a transducer, depicted generally as 30, attached to the stapes, one of the middle ear bones. It will be appreciated that the transducer 30 can be arranged to contact the ossicular chain in any appropriate location, including the incus long process, the incodostapedial joint or the stapes.

While not limited to any particular configuration, the embodiment of the invention depicted in Figs. 3 to 4C employs the use of two shape memory alloy spring members 31, 32 as biasing members to control the set neutral position of the linear actuator 33 of the electromagnetic transducer for use within the middle ear as depicted in Fig. 3.

Presetting the neutral, or at rest, position of the transducer, during or after surgical placement of the transducer, minimises the static force that is applied to the stapes and associated bone and tissue structures when little or no sound is required to be conveyed to the recipient or at times when the hearing prosthesis is de-activated or switched off.

The shape memory alloy that can comprise the spring members 31, 32 can comprise a nickel-titanium alloy or Nitinolâ„¢. This composite material makes uses of differing allotropic characteristics to bring about shape changes on exposure to specified temperatures or temperature ranges. For example, the material can be set to undergo a change in shape, configuration or dimension on being exposed to a particular temperature or temperature range. In one embodiment, such a change can occur when the temperature is increased to 45 0 C or higher. As depicted in Figs. 4A to 4C, application of a voltage across the spring member 31,32 can induce an electric current in the spring member leading to Joule heating of the spring member and so a predetermined variation in the relative compression or expansion of the spring member. For example, if the spring member has been initially fashioned at a relatively higher temperature in the shape of a tightly compressed helical spring, then stretched to have an expanded shape, application of an electrical current from a power source such as a battery, for a relatively short time can cause the temperature of the spring to increase to said relatively higher temperature so causing the spring to contract and remain so, when the current is removed.

While clinical safety standards preclude raising the temperature of internal body tissue by more than I 0 C, the relatively short heating of the shape memory springs is still possible in vivo. This is because the heat energy applied to affect shape changes in these relatively small components is relatively low and needs only to be applied for periods of a few seconds or so. As a consequence, this heat energy soon disperses into the relatively high thermal mass of adjacent members and body tissue so that any increase in the temperature of surrounding body tissue remains below stipulated safety limits.

It will be appreciated that the transducer 30 depicted in Figs. 3 to 4C has been depicted in a simplified form for reasons of clarity, and does not, for example, depict many details such as necessary wiring, hermetic seals, a housing, and an armature supporting structures nor the specific structure of any actual transducer 30. It does, however, illustrate the principal of use of the invention and how it might be applied in this example. Where used as part of a hearing aid, it will be appreciated that the hearing aid will likely have a microphone, amplifier and a signal processor that converts the detected sound into amplified signals that in turn are used to control the operation of the transducer.

An electromagnetic drive comprising two solenoid coils 34,35 is mounted to a first or base member 36 having a first fixation member 37. It will be appreciated that one coil could be used. The base member 36 houses at least some of the components of the electromagnetic drive and surrounds a moveable ferromagnetic armature 38 which is in turn attached to a drivable linear actuator 33. As depicted, the actuator 33 has a distal stapes fixation structure 39. Sound vibrations are conveyed by changes in the flow of electric current applied to coils 34,35. The resultant changing magnetic field associated with these coils produces a linear to and fro motion of the armature 38, actuator 33, and fixation structure 39 with respect to the first fixation member 37.

The two spring members 31,32 are helical and apply a biasing force so as to centralise the position of the armature 38 within the two coils 34,35 when no coil current is applied. While this may seem ideal, surgical access and other factors can influence the final location of the transducer in such a manner that it applies an undesirably continuous static force to the stapes. Adjustment to the neutral position of the armature 38 so as to reduce static force upon the stapes or other bones in the ear is achieved with the present invention by using an electrical system of the prosthesis so as to cause it to momentarily apply an electric current to either shape memory spring 31 and/or 32.

The resultant Joule heating effect when current is applied to spring 32 for example (see Fig. 4B), causes it to contract thereby allowing the armature 38 to which it is attached to move to the right (as depicted) under the influence of spring 31. As such, the armature 38 moves to a new neutral position with the stapes fixation member 39 being in the new position depicted in Fig. 4B instead of at its original position as depicted in Fig. 4A.

Conversely, by temporarily applying an electric heating current to spring 31, spring 31 contracts, which in turn allows the armature 38 to move to the left (as depicted) and so resulting in the stapes fixation member 39 being in the new position depicted in Fig. 4C. Arrows A and B illustrate one example of the potential range of surgical adjustment available to the implanting surgeon afforded by the depicted embodiment of the transducer 30.

A component according to the present invention for use in conjunction with and for modifying in situ the neutral position of a transducer during or following surgical placement of the transducer is depicted generally as 40 in Figs. 5A to 7.

As depicted in Figs. 5A, 5B, 5C and 5D, the component 40 has a movable or orientable rod-shaped first member 41. The member 41 has a fixation facilitating loop

42 at one end and a substantially spherical spiked-member 43 at its other end and is further located within a sealed container 44. A corrugated compliant membrane 45 is joined to the member 41 between the loop 42 and the spiked-member 43.

Partially filling the container 44 is a liquid 46 and a quantity of non-soluble, finely divided, particulate material 47. Through the action of gravity of other means, the particulate material can settle into a state of frictional engagement with the interior walls of the container 44 and the member 41. This frictional engagement acts to relatively hold the member 41 in a fixed position relative to that of the container 44.

By suppling a high frequency alternating voltage to an ultrasonic transducer or shaker 48 (see Fig. IB), a vibratory force 49 is applied to the liquid 46 and particulate material 47 in such a manner as to perturb the liquid and particles into a state of liquefaction whereby a significant majority of the particles become suspended or surrounded by liquid so as to lose at least some of their frictional engagement with each other, the walls of the container 44 and member 41.

This at least partial reduction of the frictional engagement allows member 41 to be manoeuvred or oriented relatively freely into a desired position with respect to the container 44 on application of a relatively small force 51 (see arrow 51 in Fig. 5C). Subsequent removal of the alternating current (as depicted by Fig. 5D), allows the particles 47 to settle back into a position of frictional engagement that secures member 41 in the new desired position.

Fig. 6 demonstrates how, through the use of a ferromagnetic particulate material 52, inter-particle cohesion and frictional engagement can be relatively increased so as to relatively increase the degree of frictional fixation friction that occurs between the settled particulate material and the member 41.

In the embodiment depicted in Fig. 6, un-magnetised ferromagnetic material 52 in suspension allows the member 41 to be oriented to the desired position where it is held in place by the particulate material 52 when it settles into frictional engagement with the walls of the container 44 and member 41 on removal of the agitation provided by the ultrasonic transducers or shaker 48, as previously described

Engagement friction is then relatively substantially increased following the temporary application of a magnetic field when switch 54 is momentarily closed so as to connect a source of electric current 55 to solenoid coil 53. This temporary application of a magnetic field permanently magnetises the ferromagnetic particles 52 in a manner that creates a force of mutual attraction so as to bind the particles 52 together.

It will be appreciated that this magnetic field could be applied locally from within the body. In another embodiment, the magnetic field can be applied transcutaneously. In this latter embodiment, such an arrangement may minimise the size and complexity of the implanted part.

Fig. 7 depicts how the component 40 can be used in conjunction with a modified in situ fixation system 60. The system 60 can be placed so as to provide acoustic excitation of the ossicular bones of the middle ear.

Like the embodiment depicted in Figs. 3 and 4, the arrangement depicted in Fig.

7 provides a mechanism for adjusting the location of an actuator 63 and a fixation structure 69 so as to minimise static loading as described previously. In this embodiment, the fixation system 60 uses a single helical compression spring 61 in conjunction with an electromagnetic drive comprising two solenoid coils 64,65 to control the movement of the actuator 63. Component 40 (as depicted for example in Fig. 6) provides a mechanism for adjusting (e.g. during surgical placement) the neutral set position of the fixation structure 69.

It will be appreciated that the embodiments depicted in Figs. 5A to 7 are not intended to accurately represent all of the features of a particular device but instead are provided as an aid to the descriptions given herein.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the scope of the invention as broadly described.

The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.