WO2011029960A2

WO2011029960A2 - Hearing instrument for round window stimulation

Info

Publication number: WO2011029960A2
Application number: PCT/EP2011/050056
Authority: WO
Inventors: Pierre-Yves Clair; Mohammad Imad Saffarini
Original assignee: Advanced Bionics Ag
Priority date: 2011-01-04
Filing date: 2011-01-04
Publication date: 2011-03-17
Also published as: WO2011029960A3

Abstract

The application relates to a hearing instrument comprising an audio signal source, an audio signal processing unit for processing the audio signals provided by the audio signal source and an implantable stimulation assembly for stimulating the round window membrane (24) of a patient according to the processed audio signals, wherein the stimulation assembly comprises an electromechanical actuator (20) to be driven according to the processed audio signals, a contact element (62) to be mechanically driven by the actuator and to be in direct contact with the round window for making the round window membrane vibrate according to the processed audio signals, and a support element (68) comprising a proximal portion (70) to be fixed (69) at the cortical part of the patient's temporal bone and a distal portion (66) angled with regard to the proximal portion, wherein the actuator is provided at a distal end of the distal portion of the support element, and wherein the contact element is driven by a distal end of the actuator in an axial direction with regard to the distal portion of the support element.

Description

Hearing instrument for round window stimulation

The present invention relates to a hearing instrument comprising an audio signal source (typically a microphone arrangement), an audio signal processing unit for processing the audio signals provided by the audio signal source and an implantable assembly for stimulation of the round window of the cochlea according to the processed audio signals.

Besides the stapes footplate and the oval window, the cochlea provides a second natural window for mechanical stimulation, namely the round window. In contrast to the oval window, the round window is closed by a compliant membrane and, besides other purposes, may serve for compensation of static pressures on the inner ear. Mechanical stimulation of the round window membrane is an approach particularly suitable in cases where normal middle ear structures are absent or are severely damaged and cannot be used.

US 2009/0306458 A l relates to a partially implantable hearing aid comprising an electromechanical actuator acting via a coupling element on the round window. The coupling element may have an angled configuration, and it may include a ball and socket joint which can be locked in order to adjust the angle formed by the coupling element.

WO 2009/062172 A2 relates to a fully implantable hearing aid comprising an electromechanical actuator acting via a coupling element on the round window. The coupling element comprises a first rod being driven by the actuator in reciprocating manner, a second rod being fixedly connected to a stationary portion of the middle ear anatomy and a third rod touching the round window, with the three rods being connected to each other in a star-like fashion at a central joint which may be a mechanical joint, such as a hinge, or a flexible joint, such as an elastomeric member. The first and the third rod thereby are angled with regard to each other.

US 2009/0131742 Al relates to a round window actuator comprising a piezoelectric stack driving a membrane which, in turn, drives a vibration transmitting member touching the round window membrane or which directly touches the round window membrane, wherein the actuator is mounted in the round window niche by fixing pins which may be made of a shape memor material in such a manner that the pins are straight below body temperature and are bent at body temperature.

WO 2008/139225 A2 relates to an actuator comprising a piezo-stack transducer, one end of which is coupled to the temporal bone of the skull and the other end of which is coupled to the round window.

WO 99/08480 A2 relates to a floating mass transducer comprising a piezoelectric element which may be coupled to the round window.

Several examples concerning the use of shape memory materials in hearing device components are known. US 2004/0078057 Al and US 2004/01 16995 Al relate to a shape memory stiffening element for a cochlea implant electrode. US 2007/0142697 Al relates to the use of a shape memory alloy in a detachable coupler of an electromechanical actuator for an ossicle. DE 10 2005 034 103 Bl and DE 10 2007 041 539 Al relate to the use of a shape memory alloy in an ossicle prosthesis. US 2009/0043149 Al relates to an electromechanical actuator comprising a stapes clip and an incus clip which are made of a shape memory alloy. WO 2004/100608 A2 relates to the use of a shape memory material in a self-expanding earplug. US 6,695,093 Bl relates to the use of a shape memory polymer material in an earplug.

While it is a benefit of round window stimulation that it does not involve opening of the inner ear, so that the risk of infections resulting from implantation of the hearing aid is lower compared to oval window stimulation which requires opening of the stapes footplate, the round window is a technically difficult area to be accessed and transducers in this area are difficult to be stabilized. In particular, when an electromechanical actuator is fixed in the usual way within a cavity of the mastoid region, the direction in which the mechanical output member is reciprocating does not coincide with the direction in which reciprocating movement of the coupling element would be desirable for achieving efficient and save vibration/stimulation of the round window membrane.

It is an object of the invention to provide for a hearing aid for direct mechanical stimulation of the round window, wherein the electromechanical actuator can be implanted and mounted in a relatively simple manner while nevertheless efficient mechanical stimulation of the round window should be achieved. It is a further object of the invention to provide for a corresponding method of providing hearing assistance.

According to the invention, these objects are achieved by a hearing aid as defined in claim 1 and a method as defined in claim 21 , respectively.

The invention is beneficial in that, by providing the electromechanical actuator at the distal end of the distal port ion of the support element fixed at the cortical part of the temporal bone, with the round window contact clement being driven by the distal end of the actuator in an axial direction with regard to the distal portion of the support element and with the distal portion of the support element being angled with regard to the proximal portion fixed at the patient's skull, the actuator can be implanted and mounted in a relatively simple manner while nevertheless, due to the angled configuration of the support element, efficient mechanical stimulation of the round window can be achieved, i.e. the vibration direction of the actuator can be adjusted by selecting the angle of the support element in an appropriate manner. Preferably, the support element is made of a shape memory material, so that the support element has an essentially straight configuration at temperatures below the transition temperature of the shape memory material and an angled configuration above the transition temperature, wherein the transition temperature is on the order of the body temperature.

Preferably, the actuator comprises a piezoelectric stack. Preferably, the contact element has a rounded contact surface made of a pyrocarbon material for touching the round window membrane.

Further preferred embodiments are defined in the dependent claims.

Hereinafter, examples of the invention will be illustrated by reference to the attached drawings, wherein: Fig. 1 is a schematic cross-sectional view of an example of a hearing instrument according to the invention after implantation; Fig. 2 is a block diagram of the hearing aid of Fig. I ;

Figs. 3 to 5 are schematic views of an example of a stimulation assembly of a hearing instrument according to the invention, wherein different stages of the implantation of the stimulation assembly are shown;

Fig. 6 is a more detailed view of the actuator tip of the stimulation assembly of Figs. 3 to 5;

Fig. 7 is an enlarged view of the contact element used in the example of Fig.6; and

Figs. 8 to 10 are schematic views of another example of a stimulation assembly of a hearing instrument according to the invention, wherein different stages of the implantation of the stimulation assembly are shown.

Fig. 1 shows a cross-sectional view of the mastoid region, the middle ear and the inner ear of a patient after implantation of an example of a hearing aid according to the invention, wherein the hearing aid is shown only schematically. The system comprises an external unit 10 which is worn outside the patient's body at the patient's head, typically close to the ear, and an implantable unit 12 which is implanted under the patient's skin 14, usually in an artificial cavity created in the user's mastoid. The implantable unit 12 is connected, via a cable assembly 16, to a stimulation assembly 18 comprising an electromechanical actuator 20 for stimulating the round window 24 of the cochlea 26, wherein the actuator 20 is located at the proximal end of a bent support element 68 fixed with its proximal end via a fixation element 69 at the cortical part of the temporal bone 72 (hereinafter, "distal" designates directions from the skin towards the round window 24, and "proximal" designates directions away from the round window 24 towards the skin, i.e. the skin is considered as a reference point).

The external unit 10 is fixed at the patient's skin 14 in a position opposite to the implantable unit 12, for example, by magnetic forces created between at least one fixation magnet provided in the external unit 10 and at least one co-operating fixation magnet provided in the implantable unit 12 (the magnets are not shown in Fig. 1). An example of a block diagram of the system of Fig. 1 is shown in Fig. 2. The external unit 10 includes a microphone arrangement 28, which typically comprises at least two spaced-apart microphones 30 and 32 for capturing audio signals from ambient sound, which audio signals are supplied to an audio signal processing unit 34, wherein they undergo, for example, acoustic beam forming. The processed audio signals are supplied to a transmission unit 36 connected to a transmission antenna 38 in order to enable transcutaneous transmission of the processed audio signals via an inductive link 40 to the implantable unit 12 which comprises a receiver antenna 42 connected to a receiver unit 44 for receiving the transmitted audio signals. The received audio signals are supplied to a driver unit 48 which drives the actuator 20. The external unit 10 also comprises a power supply 50 which may be a replaceable or rechargeable battery, a power transmission unit 52 and a power transmission antenna 54 for transmitting power to the implantable unit 12 via a wireless power link 56. The implantable unit 12 comprises a power receiving antenna 58 and a power receiving unit 60 for powering the implanted electronic components with power received via the power link 56. Preferably, the audio signal antennas 38, 42 are separated from the power antennas 54, 58 in order to optimize both the audio signal link 40 and the power link 56. However, if a particularly simple design is desired, the antennas 38 and 54 and the antennas 42 and 58 could be physically formed by a single antenna, respectively.

According to the example shown in Figs. 3 to 7, the stimulation assembly 18 comprises a contact element 62 supported by a distal end 64 of an actuator 20 which, in turn, is provided at the distal end of a distal portion 66 of a support element 68 which also has a proximal portion 70 which is fixed at the patient's skull 72. The distal portion 66 of the support element 68 is angled with regard to the proximal portion 70, wherein the angle preferably is from 10 to 80 degrees. The actuator 20 comprises a rigid housing 74 which is closed on its distal end by a vibration membrane 76 driven by piezoelectric element, preferably a piezoelectric stack 78 which comprises a plurality of piezoelectric layers 80 having a thickness of preferably 10 to 100 μιη. The contact element 62 is mounted via a shaft portion 82 at the membrane 76 which serves to make the actuator 20 fluid-tight. The contact element 62 is thus driven by the distal end of the piezoelectric stack 78 for vibrating along a vibration axis 84.

Preferably, the support element 68 is made of a shape memory material having a transition temperature below body temperature, i.e. 37 °C, with the support element 68 having an essentially straight (or rod-like) configuration at temperatures below the transition temperature (see Fig. 3) and an angled configuration at temperatures above the transition temperature (see Fig. 5). Preferably, the shape memory material is an alloy, in particular a NiTi alloy, such as nitinol.

According to one example, the support element 68 may be manufactured by the following process. The support element 68 is heated to a first temperature above the transition temperature of the shape memory material and is worked into a first configuration, namely the angled configuration of Fig. 5, wherein the distal portion 66 is angled with regard to the proximal portion 70. Then the support element 68 is cooled to a second temperature below the transition temperature and is worked into a second configuration, namely the straight configuration of Fig. 3, wherein the distal portion 66 is substantially straight with regard to the proximal portion 70.

For implantation of the stimulation assembly 18, the surgeon creates a cavity providing for an access to the round window, and the stimulation assembly 18 is inserted into the cavity, with the support clement 68 bein in the straight configuration, i.e. the temperature of the support element 68 is below the transition temperature when being inserted into the cavity, see Fig. 3. Then the support element 68 is warmed to a third temperature above the transition temperature, for example by using an appropriate tool, such as a bipolar forceps 86 (see Fig. 4); this third temperature preferably is above 40 °C. Since the third temperature is above the transition temperature, the support element 68 will "remember" its "warm" shape, so that the distal portion 66 will bend with regard to the fixed proximal portion 70, thereby moving the contact element 62 towards the round window 24 (Fig. 5). The proximal portion 70 of the support element 68 is fixed at the patient's skull 72 via the fixation element 69. Preferably, some final adjustment of the position of the proximal portion 70 of the support element 68 is carried out after bending of the support element 68 in order to bring the contact element 62 finally into the desired position at the round window 24 (to this end, the fixation element 69 should be adjustable). Since the transition temperature is below body temperature, the support element 68 will remain in the "warm", i.e. angled, configuration after implantation.

Due to this temperature-induced bending of the support element 68 after having been inserted into the cavity at the patient's head, a particularly easy access to the round window 24 is created, since the support element 68 may be inserted as a straight member, while nevertheless the round window 24 can be contacted by the contact element 62 in such a manner that the vibration direction 84 of the contact element 62 (and the actuator 20) is essentially normal to the round window membrane, thereby providing for high stimulation efficiency.

The rounded contact element 62 preferably has a mushroom-like spherical head 88, with the front surface area of the head being substantially equal to the area of the round window membrane 24. The contact element 62 is made of or coated with a biocompatible material having an elastic modulus between 5 and 40 GPa, preferably between 15 and 25 GPa. and density of 1.5 to 3 g/cm³, preferably 1.7 to 2.3 g/cm³. The prefered material of the contact surface is a pyrocarbon material. The pyrocarbon material typically has a Vickers hardness of 150 to 250. Preferably, the surface roughness Ra of the contact element 62 is less than 0.02 μηι.

An alternative example of a stimulation assembly is shown during implantation in Figs. 8 to 10, wherein the support element 168, in contrast to the embodiment shown in Figs. 3 to 5, is not made of a shape memory material, but rather of a "conventional" material, such a titanium. Prior to implantation the support element 168 has an essentially straight (or rod-like) configuration, as shown in Fig. 8, wherein an intermediate portion between the distal portion 66 carrying the actuator 20 and the proximal portion 70 connected to the fixation element 69 is provided with bending structure 90 which allows the surgeon to bend the distal portion 66 relative to the proximal portion 70 during implantation in order to achieve an angled configuration of the support element 168. The bending structure 90 may be some kind of fold line, indent or recess provided at given axial position of the support element 168 in order to promote bending of the support element 168 at that axial position. The bending structure 90 is such in the region of the bending structure 90 the flexural resistance of the support element 168 is lower than than in adjacent regions. When the support element 168 has been inserted into the cavity created by the surgeon for providing acces to the round window 24, the surgeon will use an appropriate bending tool 92 for bending the support element 168 by applying a bending force 94 to the distal portion 66 relative to proximal portion 70 in a manner so as to achieve a desired angled configuration, see Fig. 9. To this end, the distal portion 66 of the support element 168 may be provided with an appropriate engagement structure 96, such as an eyelet, allowing the bending tool 92 to engage with the distal portion 66. The bending tool 92 may be, for example, a hook or some kind of rope which may be handled by using a forceps or other surgical tool.

The desired final angled configuration of the support element 168 is illustrated in Fig. 10, wherein the contact element 62 touches the round window 24. During the bending process the support element 168 is plastically deformed, so that the angled configuration is permanent.

Claims

1. A hearing instrument comprising an audio signal source (28), an audio signal processing unit (34) for processing the audio signals provided by the audio signal source and an implantable stimulation assembly (18) for stimulating the round window membrane (24) of a patient according to the processed audio signals, wherein the stimulation assembly comprises an electromechanical actuator (20) to be driven according to the processed audio signals, a contact element (62) to be mechanically driven by the actuator and to be in direct contact with the round window for making the round window membrane vibrate according to the processed audio signals, and a support element (68, 168) comprising a proximal portion (70) to be fixed at the cortical part of the patient's temporal bone (72) and a distal portion (66) angled with regard to the proximal portion, wherein the actuator is provided at a distal end of the distal portion of the support element, and wherein the contact element is driven by a distal end of the actuator in an axial direction (84) with regard to the distal portion of the support element.

2. The hearing instrument of claim 1 , wherein the support element (68) is made of a shape memory material, such as a NiTi alloy.

3. The hearing instrument of claim 2, wherein the transition temperature of the shape memory material is below 37°C.

4. The hearing instrument of claim 3, wherein the support element (68) has an essentially straight configuration at temperatures below the transition temperature and an angled configuration above the transition temperature.

5. The hearing instrument of claim 1 , wherein the support element (168) is provided with a bending structure (90) between the distal portion (66) and the proximal portion (70) for promoting bending of the distal portion relative to the proximal portion.

6. The hearing instrument of one of the preceding claims, wherein the proximal portion (70) and the distal portion (66) of the support element (68) form an angle of from 10 to 80 degrees, when the support element is above the transition temperature.

7. The hearing instrument of one of the preceding claims, wherein the actuator (20) comprises a piezoelectric stack (78).

8. The hearing instrument of claim 7, wherein the actuator (20) comprises a rigid housing (74) closed on its distal end by a vibration diaphragm (76) driven by the piezo-electric stack (78).

9. The hearing instrument of one of claims 7 and 8, wherein the piezoelectric stack (78) comprises a plurality of piezoelectric layers (80) having a thickness of 10 to 100 pm.

10. The hearing instrument of one of claims 8 and 9, wherein the contact element (62) is supported by the vibration diaphragm (76) and the piezo-electric stack (78).

11. The hearing instrument of one of the preceding claims, wherein the contact element (62) has a rounded contact surface made of a pyrocarbon material for touching the round window membrane (24).

12. The hearing instrument of claim 1 1 , wherein the pyrocarbon material has a Vickers hardness of 150 to 250.

13. The hearing instrument of claim 11 or 12, wherein the surface roughness Ra of the contact surface of t he contact element (62) is less than 0.02μηι.

14. The hearing instrument of one of claims 1 1 to 13, wherein the material of the contact surface has an elastic modulus between 1 5 and 25 GPa.

15. The hearing instrument of one of claims 1 1 to 14, wherein the material of the contact surface has a density of 1.7 to 2.3 g/cm³.

16. The hearing instrument of one claims 1 1 to 15, wherein the contact surface of the contact element (62) forms part of a mushroom-like spherical head (88).

The hearing instrument of claim 16, wherein the spherical head (88) is made of the pyrocarbon material.

The hearing instrument of one of claims 11 to 17, wherein the area of the contact surface is substantially equal to the area of the round window membrane (24).

The hearing instrument of one of the preceding claims, wherein the audio signal source is formed by a microphone arrangement (28) for capturing audio signals from ambient sound.

The hearing instrument of claim 19, wherein the microphone arrangement (28) and the audio signal processing unit (34) form part of an external unit (10) to be fixed at the patient's head and comprising means (36, 38) for transmitting the processed audio signals via a wireless subcutaneous link (40) to the stimulation assembly (18).

A method of providing hearing assistance to a patient, comprising providing audio signals from an audio signal source (28) and processing the audio signals provided by the audio signal source, vibrating a contact element (62), which is in direct contact with the round window membrane (24) and which is driven by an electromechanical actuator (20), which is fixed at the cortical part of the patient's temporal bone (72), according to the processed audio signals, thereby stimulating the round window membrane according to the processed audio signals, wherein the actuator is provided at a distal end of a distal portion (66) of a support element (68, 168) comprising a proximal portion (70) fixed at the patient's skull, wherein the distal portion is angled with regard to the proximal portion, and wherein the contact element is driven by a distal end of the actuator.

A method of implanting an implantable stimulation assembly (18) for stimulating a round window membrane (24) of a patient, the stimulation assembly comprising an electromechanical actuator (20) to be driven according to processed audio signals, a contact element (62) to be mechanically driven by the actuator, a support element (68) comprising a proximal portion (70) and a distal portion (66) and being made of a shape memory material having a transition temperature below 37°C, wherein the actuator is provided at a distal end of the distal portion of the support element, and wherein the contact element is driven by a distal end of the actuator, the method comprising: working the support element at a first temperature above the transition temperature of the shape memory material into a first configuration, wherein the distal portion is angled with regard to the proximal portion, cooling the support element to a second temperature below the transition temperature and working the support element into a second configuration, wherein the distal portion is substantially straight with regard to the proximal portion, creating a cavity providing for an access to the round window, inserting the stimulation assembly into the cavity, with support element being in the second configuration, warming the support element to a third temperature above the transition temperature, thereby bringing the support element into the first configuration, and fixing the proximal portion of the support element at the patient's skull, whereby the contact element is brought in direct contact with the round window.

23. The method of claim 22, wherein the third temperature is above the body temperature of the patient.

24. A method of implanting an implantable stimulation assembly (18) for stimulating a round window membrane (24) of a patient, the stimulation assembly comprising an electromechanical actuator (20) to be driven according to processed audio signals, a contact element (62) to be mechanically driven by the actuator, a support element (68) comprising a proximal portion (70), a distal portion (66) and a bending structure (90) between the distal portion and the proximal portion for promoting bending of the distal portion relative to the proximal portion, wherein the actuator is provided at a distal end of the distal portion of the support element, and wherein the contact element is driven by a distal end of the actuator, the method comprising: providing the support element in a straight configuration, wherein the distal portion is substantially straight with regard to the proximal portion, creating a cavity providing for an access to the round window, inserting the stimulation assembly into the cavity, bending the distal portion relative to the proximal portion in order to achieve an angled configuration of the support element, wherein the distal portion is angled with regard to the proximal portion, and fixing the proximal portion of the support element at the patient's skull, whereby the contact element is brought in direct contact with the round window.