WO2024261557A1

WO2024261557A1 - Implant electrodes with electrolyte-filled region bounded by a barrier

Info

Publication number: WO2024261557A1
Application number: PCT/IB2024/055045
Authority: WO
Inventors: Wolfram Frederik DUECK; Mattheus Johannes Petrus KILLIAN
Original assignee: Cochlear Limited
Priority date: 2023-06-21
Filing date: 2024-05-23
Publication date: 2024-12-26

Abstract

An apparatus includes a housing configured to be implanted on or within a recipient's body and at least one chamber within the housing, the at least one chamber configured to contain a fluid. The apparatus further includes at least one barrier configured to separate the at least one chamber from tissue and/or body fluid of the recipient. The at least one barrier is configured to allow transport of electrical charge, electrons, ions, and/or predetermined molecules through the at least one barrier and to prevent transport of at least one organic species from the tissue and/or body fluid into the at least one chamber. The apparatus further includes at least one electrode within the housing and spaced from the at least one barrier. The at least one electrode is configured to be in electrical communication with the fluid within the at least one chamber.

Description

IMPLANT ELECTRODES WITH ELECTROLYTE-FILLED REGION BOUNDED

BY A BARRIER

BACKGROUND

Field

[0001] The present application relates generally to electrodes configured to be implanted on or within a recipient’s body.

Description of the Related Art

[0002] Medical devices have provided a wide range of therapeutic benefits to recipients over recent decades. Medical devices can include internal or implantable components/de vices, external or wearable components/devices, or combinations thereof (e.g., a device having an external component communicating with an implantable component). Medical devices, such as traditional hearing aids, partially or fully-implantable hearing prostheses (e.g., bone conduction devices, mechanical stimulators, cochlear implants, etc.), pacemakers, defibrillators, functional electrical stimulation devices, and other medical devices, have been successful in performing lifesaving and/or lifestyle enhancement functions and/or recipient monitoring for a number of years.

[0003] The types of medical devices and the ranges of functions performed thereby have increased over the years. For example, many medical devices, sometimes referred to as “implantable medical devices,” now often include one or more instruments, apparatus, sensors, processors, controllers or other functional mechanical or electrical components that are permanently or temporarily implanted in a recipient. These functional devices are typically used to diagnose, prevent, monitor, treat, or manage a disease/injury or symptom thereof, or to investigate, replace or modify the anatomy or a physiological process. Many of these functional devices utilize power and/or data received from external devices that are part of, or operate in conjunction with, implantable components.

SUMMARY

[0004] In one aspect disclosed herein, an apparatus comprises a housing configured to be implanted on or within a recipient’s body. The apparatus further comprises at least one chamber within the housing, the at least one chamber configured to contain a fluid. The apparatus further comprises at least one barrier configured to separate the at least one chamber from tissue and/or body fluid of the recipient. The at least one barrier is configured to allow transport of electrical charge, electrons, ions, and/or predetermined molecules through the at least one barrier and to prevent transport of at least one organic species from the tissue and/or body fluid into the at least one chamber. The apparatus further comprises at least one electrode within the housing and spaced from the at least one barrier. The at least one electrode is configured to be in electrical communication with the fluid within the at least one chamber.

[0005] In another aspect disclosed herein, an apparatus comprises a first portion of a body configured to be implanted on or within a recipient. The first portion is configured to be in fluidic communication with tissue and/or body fluid outside the body. The first portion is permeable to ions and/or molecules and impermeable to biological cells. The apparatus further comprises a region within the body. The region is configured to contain an electrolytic fluid and is at least partially bounded by the first portion. The apparatus further comprises an electrically conductive surface within the body and configured to contact the electrolytic fluid. The electrolytic fluid is between the surface and the first portion.

[0006] In another aspect disclosed herein, a method comprises providing a cavity implanted on or within a recipient. The cavity contains a liquid and is at least partially bounded by a partition in fluidic communication with an environment outside the cavity. The partition is permeable to at least one constituent of the liquid and not permeable to at least one type of biological cells. The method further comprises applying electrical signals to an electrode spaced from the partition and in fluidic communication with the cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Implementations are described herein in conjunction with the accompanying drawings, in which:

[0008] FIG. 1 is a perspective view of an example cochlear implant auditory prosthesis implanted in a recipient in accordance with certain implementations described herein;

[0009] FIG. 2 is cross-sectional view of the cochlea illustrating the stimulating assembly partially implanted therein in accordance with certain implementations described herein; [0010] FIG. 3 schematically illustrates a simplified side view of an example internal component comprising at least one stimulation electrode in accordance with certain implementations described herein;

[0011] FIGs. 4A-4C schematically illustrate cross-sectional views of various example apparatus in accordance with certain implementations described herein;

[0012] FIG. 5A schematically illustrates an example apparatus in which the at least one chamber comprises a lumen filled with a fluid in accordance with certain implementations described herein;

[0013] FIG. 5B schematically illustrates another example apparatus in which the at least one chamber comprises a lumen filled with a fluid in accordance with certain implementations described herein;

[0014] FIG. 5C shows plots of example concentrations of an example specific biomarker molecule in the tissue and/or body fluid, a first chamber, and a second chamber in accordance with certain implementations described herein;

[0015] FIGs. 6A and 6B schematically illustrates a cross-sectional view of an example apparatus at different times after implantation in accordance with certain implementations described herein; and

[0016] FIG. 7 is a flow diagram of an example method in accordance with certain implementations described herein.

DETAILED DESCRIPTION

[0017] The electrodes of certain implementations described herein are protected or hidden from biofouling-caused electrical impedance changes by placing the electrodes within a lumen filled with an electrolytic fluid in ionic contact with target tissue and/or body fluid through a permeable (e.g., semi-permeable) barrier spaced from an outer surface of the electrode. The barrier keeps the electrolytic fluid within the lumen substantially free of organic constituents (e.g., proteins; cells) to reduce or avoid biofouling-caused electrical impedance changes, keeping the electrode impedance substantially low and substantially stable over time. The electrolytic fluid can comprise a medicament which can be delivered (e.g., actively pumped; passively diffused) from a reservoir along the lumen and through the barrier into the target tissue and/or body fluid. [0018] The teachings detailed herein are applicable, in at least some implementations, to any type of implantable medical device (e.g., implantable sensory prostheses) configured to apply stimulation signals to a portion of the recipient’s body. For example, the implantable medical device can comprise an auditory prosthesis system configured to generate and apply stimulation signals that are perceived by the recipient as sounds (e.g., evoking a hearing percept). Merely for ease of description, apparatus and methods disclosed herein are primarily described with reference to an illustrative auditory prosthesis system, namely a cochlear implant. Examples of other auditory prosthesis systems compatible with certain implementations described herein include but are not limited to: acoustic hearing aids, bone conduction devices (e.g., active and passive transcutaneous bone conduction devices; percutaneous bone conduction devices), middle ear auditory prostheses, direct acoustic stimulators, other electrically simulating auditory prostheses (e.g., auditory brain stimulators), and/or combinations or variations thereof. Examples of other sensory prosthesis systems that are configured to evoke other types of neural or sensory (e.g., sight, tactile, smell, taste) percepts and are compatible with certain implementations described herein include but are not limited to: vestibular devices (e.g., vestibular implants), visual devices (e.g., bionic eyes), visual prostheses (e.g., retinal implants), somatosensory implants, and chemosensory implants.

[0019] The teachings detailed herein and/or variations thereof can also be used with a variety of other medical devices that provide a wide range of therapeutic benefits to recipients, patients, or other users. In some implementations, the teachings detailed herein and/or variations thereof can be utilized in other types of implantable medical devices beyond sensory prostheses. For example, apparatus and methods disclosed herein and/or variations thereof can be used with one or more of the following: sensors; cardiac pacemakers; drug delivery systems; defibrillators; functional electrical stimulation devices; catheters; brain implants; seizure devices (e.g., devices for monitoring and/or treating epileptic events); sleep apnea devices; pain relief devices; etc. Implementations can include any type of medical device that can utilize the teachings detailed herein and/or variations thereof. In addition, the teachings detailed herein and/or variations thereof can also be used with a variety of other nonimplantable and/or non-medical devices. [0020] FIG. 1 is a perspective view of an example cochlear implant auditory prosthesis 100 implanted in a recipient in accordance with certain implementations described herein. The example auditory prosthesis 100 is shown in FIG. 1 as comprising an implanted stimulator unit 120 (e.g., an actuator) and an external microphone assembly 124 (e.g., a partially implantable cochlear implant). An example auditory prosthesis 100 (e.g., a totally implantable cochlear implant) in accordance with certain implementations described herein can replace the external microphone assembly 124 shown in FIG. 1 with a subcutaneously implantable assembly comprising an acoustic transducer (e.g., microphone), as described more fully herein.

[0021] As shown in FIG. 1, the recipient normally has an outer ear 101, a middle ear 105, and an inner ear 107. In a fully functional ear, the outer ear 101 comprises an auricle 110 and an ear canal 102. An acoustic pressure or sound wave 103 is collected by the auricle 110 and is channeled into and through the ear canal 102. Disposed across the distal end of the ear canal 102 is a tympanic membrane 104 which vibrates in response to the sound wave 103. This vibration is coupled to oval window or fenestra ovalis 112 through three bones of middle ear 105, collectively referred to as the ossicles 106 and comprising the malleus 108, the incus 109, and the stapes 111. The bones 108, 109, and 111 of the middle ear 105 serve to filter and amplify the sound wave 103, causing the oval window 112 to articulate, or vibrate in response to vibration of the tympanic membrane 104. This vibration sets up waves of fluid motion of the perilymph within the cochlea 140. Such fluid motion, in turn, activates tiny hair cells (not shown) inside the cochlea 140. Activation of the hair cells causes appropriate nerve impulses to be generated and transferred through the spiral ganglion cells (not shown) and auditory nerve 114 to the brain (also not shown) where they are perceived as sound.

[0022] The human skull is formed from a number of different bones that support various anatomical features. Illustrated in FIG. 1 is the temporal bone 115 which is situated at the side and base of the recipient’s skull (covered by a portion of the recipient’s skin/muscle/fat, collectively referred to herein as tissue). For ease of reference, the temporal bone 115 is referred to herein as having a superior portion and a mastoid portion. The superior portion comprises the section of the temporal bone 115 that extends superior to the auricle 110. That is, the superior portion is the section of the temporal bone 115 that forms the side surface of the skull. The mastoid portion, referred to herein simply as the mastoid bone 119, is positioned inferior to the superior portion. The mastoid bone 119 is the section of the temporal bone 115 that surrounds the middle ear 105.

[0023] As shown in FIG. 1, the example auditory prosthesis 100 comprises one or more components which are temporarily or permanently implanted in the recipient. The example auditory prosthesis 100 is shown in FIG. 1 with an external component 142 which is directly or indirectly attached to the recipient’s body, and an internal component 144 which is temporarily or permanently implanted in the recipient (e.g., positioned in a recess of the temporal bone 115 adjacent auricle 110 of the recipient). The external component 142 typically comprises one or more input elements/devices for receiving input signals at a sound processing unit 126. The one or more input elements/devices can include one or more sound input elements (e.g., one or more external microphones 124) for detecting sound and/or one or more auxiliary input devices (not shown in FIG. l)(e.g., audio ports, such as a Direct Audio Input (DAI); data ports, such as a Universal Serial Bus (USB) port; cable ports, etc.). In the example of FIG. 1, the sound processing unit 126 is a behind-the-ear (BTE) sound processing unit configured to be attached to, and worn adjacent to, the recipient’s ear. However, in certain other implementations, the sound processing unit 126 has other arrangements, such as by an GTE processing unit (e.g., a component having a generally cylindrical shape and which is configured to be magnetically coupled to the recipient’s head), a mini or micro-BTE unit, an in-the-canal unit that is configured to be located in the recipient’s ear canal, a body-worn sound processing unit, etc.

[0024] The sound processing unit 126 of certain implementations includes a power source (not shown in FIG. l)(e.g., battery), a processing module (not shown in FIG. l)(e.g., comprising one or more digital signal processors (DSPs), one or more microcontroller cores, one or more application-specific integrated circuits (ASICs), firmware, software, etc. arranged to perform signal processing operations), and an external transmitter unit 128. In the illustrative implementation of FIG. 1, the external transmitter unit 128 comprises circuitry that includes at least one external inductive communication coil 130 (e.g., a wire antenna coil comprising multiple turns of electrically insulated single-strand or multi-strand platinum or gold wire). The external transmitter unit 128 also generally comprises a magnet (not shown in FIG. 1 ) secured directly or indirectly to the at least one external inductive communication coil 130. The at least one external inductive communication coil 130 of the external transmitter unit 128 is part of an inductive radio frequency (RF) communication link with the internal component 144. The sound processing unit 126 processes the signals from the input elements/devices (e.g., microphone 124 that is positioned externally to the recipient’s body, in the depicted implementation of FIG. 1, by the recipient’s auricle 110). The sound processing unit 126 generates encoded signals, sometimes referred to herein as encoded data signals, which are provided to the external transmitter unit 128 (e.g., via a cable). As will be appreciated, the sound processing unit 126 can utilize digital processing techniques to provide frequency shaping, amplification, compression, and other signal conditioning, including conditioning based on recipient-specific fitting parameters.

[0025] The power source of the external component 142 is configured to provide power to the auditory prosthesis 100, where the auditory prosthesis 100 includes a battery (e.g., located in the internal component 144, or disposed in a separate implanted location) that is recharged by the power provided from the external component 142 (e.g., via a transcutaneous energy transfer link). The transcutaneous energy transfer link is used to transfer power and/or data to the internal component 144 of the auditory prosthesis 100. Various types of energy transfer, such as infrared (IR), electromagnetic, capacitive, and inductive transfer, may be used to transfer the power and/or data from the external component 142 to the internal component 144. During operation of the auditory prosthesis 100, the power stored by the rechargeable battery is distributed to the various other implanted components as needed.

[0026] The internal component 144 comprises an internal receiver unit 132, a stimulator unit 120, and an elongate stimulation assembly 118. In some implementations, the internal receiver unit 132 and the stimulator unit 120 are sealed within a biocompatible housing, sometimes collectively referred to as a stimulator/receiver unit. The internal receiver unit 132 comprises at least one internal inductive communication coil 136 (e.g., a wire antenna coil comprising multiple turns of electrically insulated single-strand or multi-strand platinum or gold wire), and generally, a magnet (not shown in FIG. 1) fixed relative to the at least one internal inductive communication coil 136. The at least one internal inductive communication coil 136 receives power and/or data signals from the at least one external inductive communication coil 130 via a transcutaneous energy transfer link (e.g., an inductive RF link). The stimulator unit 120 generates stimulation signals (e.g., electrical stimulation signals) based on the data signals, and the stimulation signals are delivered to the recipient via the elongate stimulation assembly 118.

[0027] The elongate stimulation assembly 118 has a proximal end connected to the stimulator unit 120, and a distal end implanted in the cochlea 140. The stimulation assembly 118 extends from the stimulator unit 120 to the cochlea 140 through the mastoid bone 119. In some implementations, the stimulation assembly 118 can be implanted at least in the basal region 116, and sometimes further. For example, the stimulation assembly 118 can extend towards an apical end of the cochlea 140, referred to as the cochlea apex 134. In certain circumstances, the stimulation assembly 118 can be inserted into the cochlea 140 via a cochleostomy 122. In other circumstances, a cochleostomy can be formed through the round window 121, the oval window 112, the promontory 123, or through an apical turn 147 of the cochlea 140.

[0028] The elongate stimulation assembly 118 comprises a longitudinally aligned and distally extending array 146 (e.g., electrode array; contact array) of stimulation electrodes 148 (e.g., electrical contacts). The stimulation electrodes 148 are longitudinally spaced from one another along a length of the elongate body of the stimulation assembly 118. For example, the stimulation assembly 118 can comprise an array 146 comprising twenty-two (22) stimulation electrodes 148 that are configured to deliver stimulation signals to the cochlea 140. Although the stimulation electrodes 148 of the array 146 can be disposed on the stimulation assembly 118, in most practical applications, the array 146 is integrated into the stimulation assembly 118 (e.g., the stimulation electrodes 148 of the array 146 are disposed in the stimulation assembly 118). As noted, the stimulator unit 120 generates stimulation signals (e.g., electrical signals) which are applied by the stimulation electrodes 148 to the cochlea 140, thereby stimulating the auditory nerve 114.

[0029] While FIG. 1 schematically illustrates an auditory prosthesis 100 utilizing an external component 142 comprising an external microphone 124, an external sound processing unit 126, and an external power source, in certain other implementations, one or more of the microphone 124, sound processing unit 126, and power source are implantable on or within the recipient (e.g., within the internal component 144). For example, the auditory prosthesis 100 can have each of the microphone 124, sound processing unit 126, and power source implantable on or within the recipient (e.g., encapsulated within a biocompatible assembly located subcutaneously), and can be referred to as a totally implantable cochlear implant (“TICI”). For another example, the auditory prosthesis 100 can have most components of the cochlear implant (e.g., excluding the microphone, which can be an in-the-ear-canal microphone) implantable on or within the recipient, and can be referred to as a mostly implantable cochlear implant (“MICI”).

[0030] FIG. 2 is cross-sectional view of the cochlea 140 illustrating the stimulating assembly 118 partially implanted therein in accordance with certain implementations described herein. Only a subset of the stimulation electrodes 148 of the stimulation assembly 118 is shown in FIG. 2. The cochlea 140 is a conical spiral structure that comprises three parallel fluid-filled canals or ducts, collectively and generally referred to herein as canals 236. Canals 236 comprise the tympanic canal 237, also referred to as the scala tympani 237, the vestibular canal 238, also referred to as the scala vestibuli 238, and the median canal 239, also referred to as the scala media 239. The cochlea 140 includes the modiolus 240 which is a conical shaped central region around which the cochlea canals 236 spiral. The modiolus 240 consists of spongy bone in which the cochlea nerve cells, sometimes referred to herein as the spiral ganglion cells, are situated. The cochlea canals 236 generally turn 2.5 times around the modiolus 240.

[0031] In normal hearing, sound entering the auricle 110 (see, e.g., FIG. 1) causes pressure changes in the cochlea 140 that travel through the fluid-filled tympanic and vestibular canals 237, 238. The organ of Corti 242, which is situated on the basilar membrane 244 in scala media 239, contains rows of hair cells (not shown) which protrude from its surface. Located above the hair cells is the tectoral membrane 245 which moves in response to pressure variations in the fluid-filled tympanic and vestibular canals 237, 238. Small relative movements of the layers of the tectoral membrane 245 are sufficient to cause the hair cells to move, thereby causing the creation of a voltage pulse or action potential which travels along the associated nerve fibers that connect the hair cells with the auditory nerve 114. The auditory nerve 114 relays the impulses to the auditory areas of the brain (not shown) for processing.

[0032] Typically, in cochlear implant recipients, some portion of the cochlea 140 (e.g., the hair cells) is damaged such that the cochlea 140 cannot transduce pressure changes into nerve impulses for relay to the brain. As such, the stimulating electrodes 148 of the stimulating assembly 118 are used to directly stimulate the cells to create nerve impulses resulting in perception of a received sound (e.g., to evoke a hearing precept).

[0033] To insert the intra-cochlear stimulating assembly 118 into the cochlea 140, an opening (facial recess) is created through the recipient's mastoid bone 119 (see, e.g., FIG. 1) to access the recipient's middle ear cavity 105 (see, e.g., FIG. 1). An opening is then created from the middle ear 105 into the cochlea 140 through, for example, the round window 121, oval window 112, the promontory 123, etc. of the cochlea 140. The stimulating assembly 118 is then gently advanced (e.g., pushed) forward into the cochlea 140 until the stimulating assembly 118 achieves the implanted position. As shown in FIGs. 1 and 2, the stimulating assembly 118 follows the helical shape of the cochlea 140. That is, the stimulating assembly 118 spirals around the modiolus 240.

[0034] The effectiveness of the stimulation by the stimulation assembly 118 depends, at least in part, on the place along the basilar membrane 244 where the stimulation is delivered. That is, the cochlea 140 has characteristically been referred to as being "tonotopically mapped," in that regions of the cochlea 140 toward the basal end are more responsive to high frequency signals, while regions of cochlea 140 toward the apical end are more responsive to low frequency signals. These tonotopical properties of the cochlea 140 are exploited in a cochlear implant by delivering stimulation within a predetermined frequency range to a region of the cochlea 140 that is most sensitive to that particular frequency range. However, this stimulation relies on the particular stimulation electrodes 148 having a final implanted positioned adjacent to a corresponding tonotopic region of the cochlea 140 (e.g., a region of the cochlea 140 that is sensitive to the frequency of sound represented by the stimulation element 148).

[0035] To achieve a selected final implanted position, the apical (e.g., distal end/tip) portion 250 of the array 146 is placed at a selected angular position (e.g., angular insertion depth). As used herein, the angular position or angular insertion depth refers to the angular rotation of the apical portion 250 of the array 146 from the cochleostomy 122 (e.g., round window 121) through which the stimulation assembly 118 enters the cochlea 140. In certain implementations, while the stimulation assembly 118 is being implanted (e.g., during a surgical procedure conducted by an operator, such as a medical professional, surgeon, and/or an automated or robotic surgical system), a location and/or an orientation of the array 146 relative to the cochlea 140 (e.g., collectively referred to as the pose of the array 146) is adjusted as the array 146 is advanced and placed into position within the cochlea 140. The goal of the implantation is that the fully-implanted array 146 has an optimal pose in which the array 146 is positioned such that the stimulation electrodes 148 are adjacent to the corresponding tonotopic regions of the cochlea 140. To achieve the optimal pose, the array 146 can follow a trajectory in the cochlea 140 whereby (i) the stimulation electrodes 148 are distributed linearly along an axis of the cochlear duct 239, (ii) the array 146 does not make contact with the basilar membrane 244, and (iii) the stimulation electrodes 148 are in close proximity to the modiolar wall (e.g., if the array 146 is pre-curved) or the stimulation electrodes 148 are distant from the modiolar wall (e.g., if the array 146 is not pre-curved).

[0036] FIG. 3 schematically illustrates a simplified side view of an example internal component 144 comprising at least one stimulation electrode 148 in accordance with certain implementations described herein. The internal component 144 comprises an internal receiver unit 132 which receives encoded signals from an external component 142 of the auditory prosthesis 100 (e.g., cochlear implant system). The internal component 144 terminates in the stimulation assembly 118 that comprises an extra-cochlear region 310 and an intra-cochlear region 312. The intra-cochlear region 312 is configured to be implanted in the recipient’s cochlea 140 and has disposed thereon the longitudinally aligned and distally extending array 146 (e.g., electrode array; contact array) comprising a plurality of stimulation electrodes 148. In the example schematically illustrated in FIG. 3, the plurality of stimulation electrodes 148 are configured to apply electrical stimulation to the recipient’s body.

[0037] In certain implementations, the stimulation assembly 118 comprises a lead region 320 coupling the internal receiver unit 132 to the array 146. In certain implementations, electrical stimulation signals generated by the internal receiver unit 132 are delivered to the array 146 via the lead region 320. The lead region 320 comprises a first portion 322 configured to accommodate movement (e.g., is flexible) and a second portion 324 configured to connect the first portion 322 to the array 146. The first portion 322 of certain implementations is configured to prevent the stimulation assembly 118, the lead region 320 and its connection to the internal receiver unit 132, and the array 146 from being damaged due to movement of the internal component 144 (or part of the internal component 144) which may occur, for example, during mastication. In certain implementations, the second portion 324 comprises a distinct connection to the first portion 322 and/or the array 146, while in certain other implementations, the second portion 324 is blended into the first portion 322 and/or the array 146. The relative lengths of the stimulation assembly 118, the lead region 320, the first portion 322, the second portion 324, the extra-cochlear region 310, the intra-cochlear region 312, and the array 146 are not shown to scale in FIG. 3.

[0038] In certain implementations, the lead region 320 comprises a body 326 and a plurality of signal conduits (e.g., electrical wire leads; not shown) within the body 326. For example, the body 326 can comprise silicone or other biocompatible material in which the signal conduits are embedded (e.g., the body 326 is molded around the signal conduits) or the body 326 can comprise a tube in which the signal conduits are contained (e.g., the tube backfilled with silicone). The signal conduits of certain implementations comprise wires (e.g., platinum; platinum-iridium alloys) having outer diameters that are wavy or helixed around an axis substantially parallel to the longitudinal direction 321 of the lead region 320 (e.g., within the first portion 322) and/or are substantially straight and substantially parallel to the longitudinal direction 321 (e.g., within the second portion 324). In certain implementations, each of the signal conduits is connected to a corresponding one of the plurality of stimulation electrodes 148 of the array 146.

[0039] In certain implementations, the extra-cochlear region 310 is located in the middle ear cavity of the recipient after implantation of the intra-cochlear region 312 into the cochlea 140. Thus, the extra-cochlear region 310 corresponds to a middle ear cavity subsection of the array 146. In certain implementations, an outer surface of the extra-cochlear region 310 comprises nubs 314 configured to aid in the manipulation of the stimulation assembly 118 during insertion of the intra-cochlear region 312 into the cochlea 140.

[0040] Various types of stimulation assemblies 118 are compatible with certain implementations described herein, including short, straight, and peri-modiolar. In certain implementations, the stimulation assembly 118 is a peri-modiolar stimulation assembly 118 having an intra-cochlear region 312 that is configured to adopt a curved configuration during and or after implantation into the recipient’s cochlea 140. For example, the intra-cochlear region 312 of the stimulation assembly 118 can be pre-curved to the same general curvature of a cochlea 140. Such peri-modiolar stimulation assemblies 118 are typically held straight by, for example, a stiffening stylet (not shown) or sheath which is removed during implantation, or alternatively by varying material combinations or the use of shape memory materials, so that the stimulation assembly 118 can adopt its curved configuration when in the cochlea 140. Other methods of implantation, as well as other stimulation assemblies 118 which adopt a curved configuration, can also be used.

[0041] In certain implementations, the stimulation assembly 118 is a non- perimodiolar (e.g., straight) stimulation assembly 118 or a mid-scala assembly which assumes a mid-scala position during or following implantation. Alternatively, the stimulation assembly 118 of certain implementations comprises a short electrode implanted into at least the basal region. The stimulation assembly 118 can extend towards the apical end of the cochlea 140, referred to as the cochlea apex. In certain implementations, the stimulation assembly 118 is configured to be inserted into the cochlea 140 via a cochleostomy. In certain other implementations, a cochleostomy is formed through the oval window 112, the round window 121, the promontory 123, or through an apical turn of the cochlea 140.

[0042] Conventional implantable stimulating electrodes and recording electrodes can suffer from biofouling and tissue encapsulation which cause complex impedance changes over time and which can reduce the performance of these electrodes. For example, an electrode can be implanted to be in direct contact with an electrolytic body fluid (e.g., perilymph) comprising water molecules, ions (e.g., sodium (Na⁺) and chloride (Cl ) at physiological concentrations, such as 9 grams per liter NaCl equivalent), and other constituents, examples of which include but are not limited to: metabolites (e.g., urea; glucose; carbon dioxide; oxygen); proteins (e.g., albumin; hormones; amino acids; antibodies; cytokines), and cells (e.g., immune cells; blood cells; monocytes; T and B lymphocytes; neutrophils; eosinophils; basophils; leucocytes; macrophages; erythrocytes, platelets).

[0043] The proteins and cells of the body fluid generally take part in the response of the recipient body to an implanted foreign body, such as an electrode. For example, proteins can absorb onto a surface of the foreign body and can trigger immune cells (e.g., macrophages) to biodegrade the foreign body. For non-biodegradable foreign bodies, the proteins and cells can instead form a fibrotic sheath (e.g., connective tissue capsule) that eventually substantially encapsulates the foreign body, effectively separating the foreign body from the recipient’s body. In response to an electrode in direct contact with the body fluid (e.g., establishing an electrode-to-electrolyte interface that allows transition from electron-based charge transport through the bulk material of the electrode to ion-based charge transport in the electrolytic body fluid), the proteins and fibrotic sheath can cause biofouling and/or tissue encapsulation that result in complex impedance changes that reduce the performance of the electrode. For example, the bulk impedance of the environment adjacent to the electrode can change as highly conductive saline is displaced by the cellular networks and the electrical impedance of the electrode-to-electrolyte interface can change due to capacitive, pseudo-faradaic, and faradaic electrochemical redox reactions which are introduced and change over time. This immune response driven encapsulation mechanism can cause the electrical impedance of an implanted electrode to significantly increase over the first 4 to 6 weeks after implantation (e.g., as evident in clinical impedance data recorded of intra-cochlear electrodes (ICEs)). In addition, unpredictable and fast moving impedance fluctuations have been observed at random times over the lifetime of implanted electrodes. The onset of electrical stimulation can also cause a temporary impedance decrease due to disturbances of the complex electrode-to-tissue interface. These complex impedance changes can overlay one another and can be difficult to interpret and compensate for.

[0044] Certain implementations described herein provide an apparatus 400 that comprises at least a portion of a medical device (e.g., sensory prosthesis) configured to be implanted on or within a predetermined portion of a recipient’s body 405. For example, the apparatus 400 can be configured to be implanted to be in fluid communication with an electrolytic body fluid. The apparatus 400 of certain implementations is configured to create a substantially stable electrode-to-electrolyte interface (e.g., having a substantially constant electrical impedance over time).

[0045] FIGs. 4A-4C, 5A, 5B, 6A, and 6B schematically illustrate cross-sectional views of portions of various example apparatus 400 in accordance with certain implementations described herein. The cross-sections of FIGs. 4A-4C and 5A-5B are in a plane extending substantially parallel to a longitudinal direction of the portion of the apparatus 400 and the cross-sections of FIGs. 6A and 6B are in a plane extending substantially perpendicular to the longitudinal direction (see, e.g., FIG. 3). Other configurations of the apparatus 400 besides those schematically illustrated in FIGs. 4A-4C, 5 A, 5B, 6A, and 6B are also compatible with certain implementations described herein. [0046] The apparatus 400 comprises a housing 410 configured to be implanted on or within the recipient’s body 405. The apparatus 400 further comprises at least one chamber 420 within the housing 410, the at least one chamber 420 configured to contain a fluid 422. The apparatus 400 further comprises at least one barrier 430 configured to separate the at least one chamber 420 from tissue and/or body fluid of the recipient’s body 405. The at least one barrier 430 is configured to allow transport of electrons, ions, and/or predetermined molecules through the at least one barrier 430 and to prevent transport of at least one organic species from the tissue and/or body fluid into the at least one chamber 420. The apparatus 400 further comprises at least one electrode 440 within the housing 410 and spaced from the at least one barrier 430. The at least one electrode 440 is configured to be in electrical communication with the fluid 422 within the at least one chamber 420 (e.g., the at least one electrode 440 is configured to contact the fluid 422 within the at least one chamber 420 such that electrical charge can be transferred across the electrode/fluid interface).

[0047] In certain implementations, the housing 410 (e.g., a body configured to be implanted on or within a recipient) comprises at least one biocompatible first material. For example, the at least one biocompatible first material can comprise an electrically insulative (e.g., non-electrically conductive) material selected from the group consisting of: polymer; plastic; polyether ether ketone (PEEK); elastomer; silicone; rubber; polydimethylsiloxane (PDMS); ceramic; titanium oxide; zirconium oxide. For another example, the at least one biocompatible first material can comprise an electrically conductive material (e.g., metal; titanium; titanium alloy) that is electrically isolated from the at least one electrode 440 (e.g., by an electrically insulative spacer or layer). In certain implementations, the biocompatible first material is substantially non-permeable to the fluid 422 and/or the body fluid, while in certain other implementations, the biocompatible first material is permeable to at least one component of the body fluid (e.g., silicone rubber or PDMS which are permeable to water) or semi-permeable (e.g., permeable to ions and/or molecules without fluid transfer). For example, the portions of the housing 410 bounding the at least one chamber 420 (e.g., separating the fluid 422 within the at least one chamber 420 from the tissue and/or body fluid of the recipient’s body) can be composed of the same material as the at least one barrier 430.

[0048] In certain implementations, the at least one chamber 420 (e.g., reservoir; lumen; tubular cavity; region within the implantable housing 410) is at least partially bounded by the at least one barrier 430. The at least one chamber 420 can comprise a single chamber 420 configured to contain the fluid 422 in electrical communication (e.g., in contact) with a single electrode 440 (see, e.g., FIG. 4A) or with a plurality of electrodes 440 (see, e.g., FIGs. 4B and 5). The at least one chamber 420 can comprise a plurality of chambers 420, each chamber 420 of the plurality of chambers 420 configured to contain the fluid 422. For example, each chamber 420 of the plurality of chambers 420 can be in electrical communication (e.g., in contact) with a corresponding single electrode 440 (see, e.g., FIG. 4C), and the number of chambers 420 can be the same as the number of electrodes 440. For another example, at least one chamber 420 of the plurality of chambers 420 is in contact with a corresponding plurality of electrodes 440 (e.g., the number of chambers 420 can be less than the number of electrodes 440). In certain implementations, the plurality of chambers 420 are not in direct fluidic communication with one another (e.g., the housing 410 comprises walls that are impermeable to the fluid 422 between adjacent chambers 420), while in certain other implementations, at least two chambers 420 of the plurality of chambers 420 are in direct fluidic communication with one another (e.g., via a channel or fluid conduit extending within the housing 410).

[0049] In certain implementations, the at least one chamber 420 has a substantially parallelepiped shape with the at least one barrier 430 and the at least one electrode 440 positioned at opposite faces of the parallelepiped shape (see, e.g., FIGs. 4A-4C). For example, the at least one barrier 430 can comprise a wall portion of the at least one chamber 420. In certain other implementations, the at least one chamber 420 has a substantially cylindrical shape with the at least one barrier 430 comprising an end portion (e.g., end face) of the cylindrical shape and the at least one electrode 440 at a side face (e.g., perimeter) of the cylindrical shape (see, e.g., FIGs. 5A-5B). For example, as shown in FIGs. 5A-5B, the housing 410 can comprise a tube (e.g., having a width in a range of 0.05 micron to 5 microns) encircling an elongated substantially cylindrically-shaped lumen chamber 420 with an end of the chamber 420 capped by the barrier 430 and the at least one electrode 440 at an inner wall of the tube. Other shapes and configurations of the at least one barrier 430 and the at least one electrode 440 are also compatible with certain implementations described herein.

[0050] In certain implementations, the fluid 422 comprises an electrolytic fluid. For example, the fluid 422 can comprise a physiological NaCl solution placed within the at least one chamber 420 prior to implantation of the apparatus 400. For another example, the fluid 422 can comprise one or more components of the body fluid that are filtered by the at least one barrier 430 and enter the at least one chamber 420 after implantation of the apparatus 400. The at least one barrier 430 can filter the body fluid by allowing passage of water and small ions (e.g., sodium; chloride, potassium) of the body fluid into the at least one chamber 420 while preventing passage of some or all organic matter (e.g., amino acids, proteins, cells) of the body fluid into the at least one chamber 420. The osmolarity of the fluid 422 within the at least one chamber 420 can be substantially equal to the osmolarity of the body fluid outside the apparatus 400. The composition of the fluid 422 within the at least one chamber 420 can be substantially stable over time, or can be modified by concentration changes of at least one body fluid constituents outside the apparatus 400 that can pass through the at least one barrier 430 to the at least one chamber 420.

[0051] In certain implementations, the fluid 422 comprises at least one medicament (e.g., a drug; a drug-containing substance; a liquid) configured to pass through the at least one barrier 430 from the at least one chamber 420 to the tissue and/or body fluid of the recipient’s body 405. The at least one medicament can be configured to provide the recipient’s body 405 with a therapeutic benefit and/or to inhibit biofouling of the apparatus 400. Examples of medicaments compatible with certain implementations described herein include but are not limited to: a neurotrophin (e.g., neurotrophin-3 (NT-3); brain-derived neurotrophic factor (BDNF)); a steroid (e.g., dexamethasone). The neurotrophin can be used to promote neuron growth towards the apparatus 400 and to establish a strong neuroprosthetic interface with dendritic processes integrated into the apparatus 400 for improved sensitivity and spatial selectivity of the stimulation generated by the electrode 440. In certain implementations, the at least one chamber 420 contains the at least one medicament prior to implantation of the apparatus 400, while in certain other implementations, the apparatus 400 comprises a reservoir containing the at least one medicament and in fluidic communication with the at least one chamber 420, and the at least one medicament is configured to flow into the at least one chamber 420 from the reservoir (e.g., after implantation of the apparatus 400). For example, FIG. 5A schematically illustrates an apparatus 400 in which the at least one chamber 420 comprises a lumen filled with a fluid 422 comprising at least one medicament configured to pass through the at least one barrier 430 to be provided to the recipient’s body 405. [0052] In certain implementations, the at least one barrier 430 (e.g., first portion of the implantable housing 410) comprises a biocompatible second material which can be different from the biocompatible first material of the housing 410 or can be the same as the biocompatible first material of the housing 410. The biocompatible second material can comprise at least one porous material, at least one permeable material, or at least one electrically conductive material. In certain implementations, the at least one barrier 430 comprises an anti-inflammatory drug (e.g., dexamethasone) and/or a protective (e.g., antibiofouling) material.

[0053] Examples of porous materials compatible with certain implementations described herein include but are not limited to: polyvinylidene fluoride (PVDF); polydimethylsiloxane (PDMS); polytetrafluoroethylene (PTFE); polyethylene; nitrocellulose; polycarbonate; alumina; biocompatible metal, such as titanium. The pores can be sufficiently large to allow fluid transport through the at least one barrier 430 (e.g., in response to a pressure differential across the at least one barrier 430) while preventing transport of one or more organic species through the at least one barrier 430. For example, the pore sizes (e.g., widths in a direction substantially perpendicular to a longitudinal direction of the pores through the porous biocompatible material) can be in a range of less than 0.4 micron (e.g., less than 0.3 micron; less than 0.2 micron; less than 0.1 micron; less than 0.05 micron).

[0054] Examples of permeable materials compatible with certain implementations described herein include but are not limited to: polydimethylsiloxane (PDMS) membrane; hydrogel membrane; synthetic membrane; cellulosic membrane. The permeability of the at least one barrier 430 can be dependent on the degree of crosslinking molecules (e.g., the sizes of the molecular spaces within the permeable material) and/or the polarity of the permeable material. For example, the permeable material can be permeable (e.g., with fluid transfer in response to a pressure differential across the barrier 430) to at least one component of the body fluid (e.g., water) and/or to at least one medicament of the fluid 422. For another example, the permeable material can be semi-permeable (e.g., without fluid transfer) to at least one component of the body fluid (e.g., ions and/or molecules) and/or to at least one medicament of the fluid 422.

[0055] Examples of electrically conductive materials compatible with certain implementations described herein include, but are not limited to: electrically conductive hydrogels (e.g., electrically conductive polymers; polypyrrole (PPy); poly(3, 4-ethylenedioxythiophene) (PEDOT); hyaluronic acid (HA), gelatin methacryloyl (GelMA); chitosan. The electrically conductive hydrogels can be configured to allow transport of electrical charge through the at least one barrier 430 by conformal changes of the backbone of the electrically conductive polymer molecules (e.g., PEDOT) inside the hydrogel without actual mass transport from one side of the at least one barrier 430. For example, such electrically conductive hydrogels can be used in an apparatus 400 which is not configured for delivery of a medicament from the fluid 422 to the recipient’s body 405.

[0056] In certain implementations, the biocompatible second material is configured to substantially prevent transport of at least one organic species (e.g., at least one type of biological cells) from outside the apparatus 400, through the at least one barrier 430, into the at least one chamber 420. For example, the at least one barrier 430 can be configured to filter the electrolytic body fluid entering into the at least one chamber 420 to control the composition of the fluid 422 in direct contact with the at least one electrode 440. Examples of the at least one organic species prevented from entering the at least one chamber 420 include but are not limited to: amino acids, deoxyribonucleic acid (DNA), ribonucleic acid (RNA), proteins, enzymes, cytokines, viruses, bacteria, leucocytes, macrophages, and other biological cells. The biocompatible second material can be configured to be substantially impermeable to at least one organic species and substantially permeable to at least one other organic species (e.g., having material properties to be selectively permeable to a predetermined molecule or organic species of interest). For example, the biocompatible second material can have pore sizes configured to only allow transport of predetermined constituents of the body fluid through the at least one barrier 430 into the at least one chamber 420 (e.g., a pore size of 0.22 micron can be substantially impermeable to bacteria, cells, and some viruses but substantially permeable to DNA, amino acids, enzymes, and cytokines).

[0057] In certain implementations, the fluid 422 within the at least one chamber 420 is in fluidic communication (e.g., fluidic contact) with the tissue and/or body fluid outside the apparatus 400 via the at least one barrier 430 (e.g., the at least one barrier 430 allows mass transport of at least one component of the fluid 422 through the at least one barrier 430). In certain other implementations, the biocompatible second material is configured to substantially prevent mass transport through the at least one barrier 430 while allowing transport of electrical charge through the at least one barrier 430. For example, the biocompatible second material can comprise an electrically conductive hydrogel membrane (e.g., PEDOT) that is configured to substantially prevent mass transport through the at least one barrier 430 while allowing electrical charge transport through the at least one barrier 430 (e.g., by conformal changes of the backbone of the conductive polymer molecules inside the hydrogel).

[0058] In certain implementations, the at least one electrode 440 comprises at least one electrically conductive material selected from the group consisting of: metal; noble metal; non-noble metal; platinum; palladium; ruthenium; rhodium; osmium; iridium; titanium; gold; alloys comprising one or more of the foregoing (e.g., platinum- iridium); composites comprising one or more of the foregoing. For example, the electrically conductive material can comprise platinum-iridium alloy with an iridium content in a range of 10 wt% to 30 wt%. In certain implementations, the at least one electrode 440 comprises a plurality of electrically conductive materials and/or the composition of the at least one electrode 440 can vary through the at least one electrode 440. In certain implementations, the at least one electrode 440 is substantially flat (e.g., planar), while in certain other implementations, the at least one electrode 440 is curved or irregular (e.g., non-planar). For example, the housing 410 can comprise a metal tube and an inside wall portion of the metal tube can be used as the at least one electrode 440. The outside wall of the metal tube can be coated with a biocompatible, electrically insulative material (e.g., PDMS) that is used as the electrically insulating wall of the housing 410. In certain implementations, the at least one electrode 440 extends over an area in a range of 0.01 mm² to 1 mm² (e.g., in a range of 0.025 mm² to 0.5 mm²). In certain implementations, the at least one electrode 440 has a low electrical impedance to be used for tracking (e.g., sensing) electrical potential changes (e.g., broadband or DC intra-cochlear potentials; scalar potentials relevant to diagnosis, treatment, and/or management of Meniere’s disease).

[0059] In certain implementations, the at least one electrode 440 comprises a single electrode 440 in electrical communication with the fluid 422 within a chamber 420 (see, e.g., FIGs. 4A and 4C), while in certain other implementations, the at least one electrode 440 comprises a plurality of electrodes 440 in electrical communication with the fluid 422 within a common chamber 420 (see, e.g., FIGs. 4B and 5). In certain implementations, the at least one electrode 440 has one or more dimensions (e.g., width; length; height; thickness) in a range of 200 microns to 1 millimeter (e.g., in a range of 300 microns to 400 microns). In certain implementations in which the at least one electrode 440 comprises a plurality of electrodes 440, the electrodes 440 can be spaced from one another by a distance in a range of 0.5 to 5 times a width of at least one electrode 440 (e.g., adjacent electrodes 440 each having a width of 200 microns can be spaced from one another by a distance in a range of 100 microns to 1000 microns).

[0060] In certain implementations, the at least one electrode 440 comprises at least one stimulating electrode configured to apply electrical stimulation signals to a portion of the recipient’s body 405 (e.g., tissue and/or body fluid) via the fluid 422 and the at least one barrier 430. For example, the electrical stimulation signals can be configured to evoke a neural, sensory, somatosensory, or chemosensory percept (e.g., hearing; sight; tactile; smell; taste; balance; pressure; pain; temperature) and/or to affect (e.g., control) the functioning of a portion of the recipient’s body (e.g., cardiac pacemaker or defibrillation signals; autonomic nervous system stimulation signals; brain stimulation signals; muscle stimulation signals). The at least one electrode 440 of certain implementations can comprise a longitudinally aligned and distally extending array 146 of intra-cochlea stimulation electrodes 148 each longitudinally spaced from one another along a length of the stimulation assembly 118 and configured to deliver stimulation signals to a corresponding portion of the recipient’s cochlea 140.

[0061] In certain other implementations, the at least one electrode 440 is configured to receive electrical signals from a portion of the recipient’s body (e.g., tissue and/or body fluid) via the fluid 422 and the at least one barrier 430. For example, the received electrical signals can be indicative of the functioning of a portion of the recipient’s body (e.g., electroencephalogram signals; electrocardiogram signals; electromyograph signals; electrocochleography signals; neural response telemetry signals; compound action potential signals; cochlea microphonics signals; neural tissue evoked electrical potential signals). In certain implementations, the at least one barrier 430 is substantially permeable to a constituent of the body fluid (e.g., a predetermined molecule) and the at least one electrode 440 is configured to generate electrical signals indicative of a concentration of the constituent in the fluid 422 (e.g., thereby monitoring the concentration of the constituent in the body fluid).

[0062] In certain other implementations, the at least one electrode 440 is configured to detect a presence and/or a concentration of specific biomarker molecules that have entered the at least one chamber 420 from the tissue and/or body fluid of the recipient’s body through the at least one barrier 430. For example, the at least one electrode 440 can be used to detect biomarker molecules in regions of the recipient’s body where the collection of samples can be challenging and typically utilizes invasive procedures (e.g., the cochlea 140). Examples of cochlea-specific biomarker molecules and uses of their concentration measurements in perilymph within the cochlea 140 compatible with certain implementations described herein include but are not limited to: glutamate (e.g., indicative of various inner ear disorders, such as noise-induced hearing loss and exci to toxicity); lactate (e.g., indicative of reduced oxygen availability, impaired metabolism in the inner ear, ischemia, noise exposure, or ototoxic drug exposure); reactive oxygen species (ROS) (e.g., indicative of oxidative stress, noise-induced hearing loss, ototoxicity, or age-related hearing loss); inflammatory markers including cytokines and chemokines (e.g., indicative of immune responses or inflammatory conditions, such as autoimmune inner ear disease or viral infections); neurotrophic factors such as brain- derived neurotrophic factor (BDNF) or nerve growth factor (NGF) (e.g., indicative of neurotrophic support and potential therapeutic targets for inner ear disorders).

[0063] Examples of other biomarker molecules and uses of their concentration measurements compatible with certain implementations described herein include but are not limited to: glucose (e.g., indicative of diabetes, metabolic disorders; to be measured in blood, interstitial fluid, or tears); lactate (e.g., indicative of metabolic activity; to be measured for sports medicine, critical care, and exercise physiology); pH (e.g., indicative of acidity or alkalinity; to be measured in blood, urine, or saliva); oxygen such as partial pressure of oxygen (pCF) (e.g., indicative of respiratory function, wound healing, or hypoxia detection; to be measured in blood, tissue, or gases); carbon dioxide (e.g., indicative of respiratory function; to be measured in blood or exhaled breath); electrolytes (e.g., sodium, potassium, or chloride ions; indicative of electrolyte imbalance, kidney function, and acid-base balance); cholesterol (e.g., total cholesterol, high-density lipoprotein (EDE) cholesterol, low-density lipoprotein (LDL) cholesterol; indicative of cardiovascular health and risk); hemoglobin (e.g., indicative of anemia and blood disorders; to be measured in blood); C-reactive protein (CRP) (e.g., indicative of inflammation); troponin (e.g., indicative of acute myocardial infarction; to be measured in blood); prothrombin time (PT) and international normalized ratio (INR) (e.g., indicative of blood clotting ability and efficacy of anticoagulant therapy); uric acid (e.g., indicative of various conditions such as gout; to be measured in blood or urine); creatinine (e.g., indicative of kidney function and renal health).

[0064] In certain other implementations, the at least one electrode 440 is configured to detect a presence and/or a concentration of at least one specific active pharmaceutical ingredient (API) (e.g., medicament; drug) in the at least one chamber 420. For example, the at least one specific API can be administered to the recipient’s body separately from the apparatus 400 (e.g., systemically) and can enter the at least one chamber 420 from the tissue and/or body fluid of the recipient’s body through the at least one barrier 430. For another example, the at least one specific API can be administered to the recipient’s body by the apparatus 400 (e.g., locally; from the at least one chamber 420 through the at least one barrier 430) and the signals generated by the at least one electrode 440 can be used for controlling the delivery of the API to the recipient’s body.

[0065] The outer surface 442 of the at least one electrode 440 can comprise or be coated with at least one recognition species configured to bond with a corresponding specific biomarker molecule in the fluid 422 and/or a specific API. The selection of the at least one recognition species can depend on the specific biomarker molecule to be detected and the desired sensitivity and specificity of the detection, as well as on availability, stability, and cost.

[0066] For example, the at least one recognition species can comprise at least one enzyme (e.g., protein that can catalyze specific biochemical reactions) having sufficiently high specificity and catalytic activity with a corresponding specific biomarker molecule to be sensed in the fluid 422. The at least one electrode 440 having an enzyme coating can recognize and interact with the specific biomarker molecule via a specific enzymatic reaction that generates a measurable signal (e.g., electrochemical signal; optical signal) that is indicative of the presence and/or concentration of the specific biomarker molecule. Examples of enzymes include, but are not limited to: glucose oxidase for detecting glucose levels and lactate dehydrogenase for detecting lactate levels.

[0067] For another example, the at least one recognition species can comprise antibodies (e.g., immunoglobulins; Y-shaped proteins produced by the immune system in response to foreign substances or antigens) having sufficiently high affinity and specificity with a corresponding specific antigen to be sensed in the fluid 422. The at least one electrode 440 can have the antibodies immobilized on the outer surface 442 of the at least one electrode 440, allowing the antibodies to bind specifically to the specific antigen. The binding can generate a signal (e.g., change in electrical properties) that is indicative of the presence and/or concentration of the specific antigen. Certain such implementations can be used for disease biomarker detection and/or therapeutic drug monitoring.

[0068] For another example, the at least one recognition species can comprise aptamers (e.g., short, single-stranded nucleic acid molecules, such as DNA and RNA) (e.g., selected through a systematic evolution of ligands by exponential enrichment (SELEX) process). The aptamers can bind to specific biomarker molecules with sufficient specificity and can have sufficient stability and ease of synthesis. The at least one electrode 440 can have the aptamers immobilized on the outer surface 442 of the at least one electrode 440, allowing the aptamers to bind specifically to the specific biomarker molecules, generating a corresponding signal. Certain such implementations can be used for detecting small molecules or complex targets in biosensing applications.

[0069] In certain implementations, the at least one electrode 440 comprises a molecularly imprinted polymer (MIP) coating configured to selectively bind to specific biomarker molecules. MIP coatings are synthetic polymers configured to have binding sites with specific shapes and functionalities that complement the target analyte and can provide sufficient stability, reproducibility, and cost-effectiveness for certain implementations described herein.

[0070] For example, the MIP coating can be configured to have selective binding by imprinting the polymer with a target molecule or a structurally similar template molecule, and the resulting MIP coating comprises cavities or binding sites that specifically bind the target molecule (e.g., allowing for sensitive detection and quantification of the target molecule in complex biological samples). For another example, the MIP coating can be configured to detect specific biomarker molecules in biological fluids or tissues. The MIP coating can be tailored to match the structural and chemical characteristics of the target biomarker molecules, enabling their specific capture from complex biological matrices (e.g., enabling early diagnosis and monitoring of diseases, including cancer biomarkers, infectious agents, or metabolic markers). For another example, the MIP coating can be configured to detect specific environmental pollutants, hazardous substances, and toxins (e.g., heavy metals; pesticides; chemical contaminants) allowing real-time monitoring. For another example, the MIP coating can be configured for screening and/or monitoring of specific drugs, medicaments, or therapeutic molecules (e.g., for therapeutic drug optimization or drug abuse detection) by binding and detecting the concentration of the specific molecules in biological samples (e.g., blood; urine). For another example, the MIP coating can be configured for point-of-care testing devices (e.g., at a patient’s bedside) to provide rapid and selective detection of target analytes (e.g., in resource-limited settings or in remote areas where access to advanced laboratory facilities is limited).

[0071] As shown in FIGs. 4A-4C, 5 A, 5B, 6A, and 6B, an electrically conductive outer surface 442 of the electrode 440 is in contact with the fluid 422 and is spaced from (e.g., behind) the at least one barrier 430 (e.g., the fluid 422 is between the outer surface 442 and the at least one barrier 430). The outer surface 442 of the at least one electrode 440 is protected from direct contact with the tissue and/or body fluid of the recipient’s body 405 by the at least one barrier 430 and the intervening fluid 422 (e.g., protecting the at least one electrode 440 from biofouling or biofouling-caused increases of electrical impedance). The surface area of the outer surface 442 in contact with the fluid 422 can be in a range of 2500 square microns (e.g., an outer surface having dimensions of 50 microns to 50 microns) to 40,000 square microns (e.g., an outer surface 442 having dimensions of 200 microns by 200 microns). In certain implementations, a ratio of the surface area of the at least one barrier 430 in contact with the fluid 422 to the surface area of the outer surface 442 of the underlying at least one electrode 440 can be in a range of 0.5 to 1000 (e.g., in a range of 0.5 to 5; in a range of 1 to 10; in a range of 10 to 1000).

[0072] As schematically illustrated by FIGs. 4A-4C and 6A-6B, the outer surface 442 of the at least one electrode 440 can be substantially parallel to the at least one barrier 430. The distance between the at least one barrier 430 and the outer surface 442 of the at least one electrode 440 in certain such implementations is at least 1 micron (e.g., in a range of 1 micron to 5 microns). As schematically illustrated by FIGs. 5A-5B, the outer surface 442 of the at least one electrode 440 can be substantially perpendicular to the at least one barrier 430. The distance between the at least one barrier 430 and a center point of at least one outer surface 442 of the at least one electrode 440 in certain such implementations is in a range of 1 micron to 5 microns. In certain implementations, the at least one barrier 430 is outside the Stern layer and/or outside the Helmholtz layer of the fluid 422 next to the outer surface 442 of the at least one electrode 440 such that electrical charge is transmitted between the at least one barrier 430 and the at least one electrode 440 by ionic transport.

[0073] In certain implementations, the outer surface 442 comprises the electrically conductive bulk material of the at least one electrode 440 (e.g., metal). In certain other implementations, the outer surface 442 comprises a coating comprising an anti-inflammatory drug (e.g., dexamethasone) and/or a protective (e.g., anti-biofouling) material, examples of which include, but are not limited to: plastic; polyethylene glycol (PEG); polyethylene terephthalate (PTE); polyvinylidene fluoride (PVDF); polytetrafluoroethylene (PTFE). For example, the coating can be configured to allow permeation and diffusion of at least one analyte of the fluid 422 to the bulk material of the at least one electrode 440, but not for other species which could otherwise interfere with the electrode functionality. For another example, the coating can be configured to inhibit cellular attachment through continuous, cyclic deswelling/reswelling in response to temperature fluctuations (see, e.g., A.K. Means et al., “A self-cleaning, mechanically robust membrane for minimizing the foreign body reaction: toward extending the lifetime of sub-Q glucose biosensors,” J. Mater. Sci.: Mater. Med. 30(7), 79 doi: 10.1007/sl0856-019-6282-2 (2019)). While the at least one barrier 430 provides protection of the at least one electrode 440 from biofouling and the concomitant degradation of the electrode functionality (e.g., electrical impedance changes), the coating of the outer surface 442 of the at least one electrode 440 can provide additional protection.

[0074] In certain implementations in which the at least one electrode 440 is configured to be used as a sensing electrode that detects the presence and/or concentration of specific molecules (e.g., as a biosensor of specific biomarker molecules). The at least one electrode 440 can be configured to respond to the specific molecules that have adsorbed onto the outer surface 442 of at least one electrode 440. Upon the at least one electrode 440 becoming saturated with the adsorbed specific molecules over time, an electrical current can be passed through the at least one electrode 440 to release the absorbed molecules from the at least one electrode 440, thereby resetting the at least one electrode 440 (e.g., cleaning the adsorbed molecules from the at least one electrode 440 to restore the sensing functionality).

[0075] For example, the at least one barrier 430 can be permeable to specific biomarker molecules to be detected while protecting the at least one electrode 440 from biofouling (e.g., the at least one barrier 430 impermeable to at least one organic species that contributes to biofouling). The biomarker molecules that reach the outer surface 442 of the at least one electrode 440 can be absorbed onto the outer surface 442 (e.g., can bind to the outer surface 442), causing characteristic impedance changes that are indicative of the presence of the biomarker molecules on the outer surface 442. For example, for at least one barrier 430 that is permeable to a single specific protein that is to be detected, the at least one electrode 440 can comprise bare platinum and impedance changes corresponding to the specific protein attaching to the outer surface 442 can be correlated with the concentration of the specific protein in the fluid 422. For another example, for at least one barrier 430 that is permeable to multiple proteins, one of which is a specific protein to be detected, the at least one electrode 440 can comprise a coating that specifically binds to the one specific protein to be detected (e.g., a molecular imprinted polymer (MIP) coating, an example of which is described by G. Wackers et al., “Electro-polymerized receptor coatings for the quantitative detection of histamine with a catheter-based, diagnostic sensor,” ACS Sens. Vol. 6, No. 1, 26 pages (2021)).

[0076] In certain implementations, the apparatus 400 further comprises at least one electrical conduit 450 (e.g., one or more wires or leads) in mechanical and electrical communication with the at least one electrode 440. In certain implementations, the at least one electrical conduit 450 comprises at least one material selected from the group consisting of: metal; noble metal; non-noble metal; platinum; palladium; ruthenium; rhodium; osmium; iridium; titanium; gold; alloys of one or more of the foregoing; composites of one or more of the foregoing. The at least one electrical conduit 450 can have a width (e.g., outer diameter) that is in a range of 0.05 millimeter to 0.3 millimeter (e.g., in a range of 0.1 millimeter to 0.2 millimeter). As schematically illustrated by FIGs. 4A-4C and 5, the at least one electrical conduit 450 can be within the housing 410 and can extend along the housing 410 in a longitudinal direction of the housing 410. The at least one electrical conduit 450 and the at least one electrode 440 can be parts of a single (e.g., unitary; integrated) element.

[0077] The at least one electrical conduit 450 can be configured to transmit electrical signals between the at least one electrode 440 and a controller (e.g., processor; digital signal processor; microcontroller core; application-specific integrated circuit; circuitry) of the apparatus 400. For example, the controller can be configured to generate electrical signals to be delivered by the at least one electrode 440 to the recipient’s body 405 and/or to receive electrical signals received by the at least one electrode 440 from the recipient’s body 405. [0078] In certain implementations, the apparatus 400 further comprises a return (e.g., ground) electrode 460 on an opposite side of the at least one barrier 430 from the at least one electrode 440. The return electrode 460 can be larger than each electrode 440 of the at least one electrode 440. The return electrode 460 can be in electrical communication with the controller, in electrical communication with the outer surface 442 of the at least one electrode 440 via the fluid 422, the at least one barrier 430, and the tissue and/or body fluid of the recipient’s body 405. The return electrode 460 can be configured to provide a return path for stimulating electrical current from the at least one electrode 440 through the tissue and/or body fluid of the recipient’s body 405 (e.g., the at least one electrode 440 can be configured to flow electrical current to the return electrode 460 via the fluid 422 and the at least one barrier 430).

[0079] In certain implementations, as shown in FIGs. 4A-4C, the return electrode 460 is in direct contact with the tissue and/or body fluid (e.g., perilymph; modiolus 240) of the recipient’s body 405. In certain other implementations, the return electrode 460 is not in direct contact with the tissue and/or body fluid of the recipient’s body 405. For example, the return electrode 460 can be in electrical communication with the same fluid 422 in the same chamber 420 as is the at least one electrode 440 (see, e.g., FIG. 5A in which one of the electrodes 440a, b can serve as a return electrode 460 for sensing electrical current from the other of the electrodes 440a, b). In certain such implementations, the electrodes 440a, b can be configured to generate electrical signals indicative of an amount (e.g., concentration) of the at least one medicament in the at least one chamber 420. For another example, the apparatus 400 can comprise a second chamber (not shown) in a second portion of the housing 410 configured to be in fluidic communication with the tissue and/or body fluid of the recipient’s body 405 and configured to contain an electrolytic fluid (e.g., same as the fluid 422 or different from the fluid 422). The second chamber can be at least partially bounded by a second barrier (not shown) permeable to at least one component (e.g., ions; molecules) of the electrolytic fluid, and the return electrode 460 can be configured to contact the electrolytic fluid with the electrolytic fluid between the return electrode 460 and the second barrier (e.g., the return electrode 460 within the second chamber and spaced from the second barrier). The second chamber and the second barrier can be configured to protect the return electrode 460 from biofouling and/or biofouling- caused increases of electrical impedance. [0080] In certain implementations, the return electrode 460 is on an opposite side of the at least one barrier 430 from the at least one electrode 440 and is configured to be used with the at least one electrode 440 to generate electric fields configured to perform electrophoresis to move molecules of interest (e.g., medicament molecules) from the at least one chamber 420, through the at least one barrier 430, to the tissue and/or body fluid of the recipient’s body 405 (e.g., electrophoretic drug delivery through an ion exchange membrane). In certain other implementations, the return electrode 460 and the at least one electrode 440 are configured to generate electric fields configured to perform electrophoresis to move molecules and/or biological matter from the tissue and/or body fluid of the recipient’s body 405, through the at least one barrier 430, into the at least one chamber 420.

[0081] FIG. 5B schematically illustrates another example apparatus 400 in accordance with certain implementations described herein. As shown in FIG. 5B, the at least one chamber 420 comprises a first chamber 420a and a second chamber 420b in series with one another and the at least one barrier 430 comprises a first barrier 430a that is permeable to a specific biomarker molecule and a second barrier 430b (e.g., permeable to the specific biomarker molecule; non-permeable or impermeable to the specific biomarker molecule). The first chamber 420a is separated from the tissue and/or body fluid of the recipient’s body by the first barrier 430a and the second chamber 420b is separated from the first chamber 420a by the second barrier 430b and from the tissue and/or body fluid of the recipient’s body by the first barrier 430a, the first chamber 420a, and the second barrier 430b. A first electrode 440a is in electrical communication with the fluid 422a within the first chamber 420a and is configured to detect a presence and/or concentration of the specific biomarker molecule. A second electrode 440b is in electrical communication with the fluid 422b in the second chamber 420b. Certain implementations can have three or more chambers 420 in series with one another and three or more barriers 430. In certain implementations, instead of the second barrier 430b, a narrow channel provides fluidic communication between the first and second chambers 420a, b.

[0082] In certain implementations in which the second barrier 430b is permeable to the specific biomarker molecule, the biomarker molecules reach the first electrode 440a before reaching the second electrode 440b. The second electrode 440b can be used as a reference electrode configured to maintain a substantially stable reference potential that is either unaffected or differently affected by the concentration of the biomarker molecules and that has a resting potential or impedance that is either unchanging or changing by a different amount in the presence of the biomarker molecules. For example, the second electrode 440b can have a size that is substantially larger (e.g., in a range of 10 to 1000 times) than the size of the first electrode 440a (e.g., comparable to the size of an extra-cochlear electrode (ECE)).

[0083] Measurements of the electrical signals (e.g., impedance and/or the electrical potential between the first and second electrodes 440a, b) can be used to track the concentration ci of the specific biomarker molecule in the first chamber 420a and therefore the concentration c_p of the biomarker molecule in the tissue and/or body fluid of the recipient’s body. For example, the concentration c_p can be indirectly measured using the first and second electrodes 440a, b which each provide a corresponding signal when the biomarker molecule has a concentration above a corresponding predetermined threshold concentration (e.g., detection limits of the electrodes 440a, b; Cthreshoid_i for the first electrode 440a and Cthreshoid_2 for the second electrode 440b) and employing Fick’s law. Such measurements can be easier to achieve and more reliable than measurements of an absolute biomarker molecule concentration in real time.

[0084] FIG. 5C shows plots of an example concentration c_p of an example specific biomarker molecule in the tissue and/or body fluid, an example concentration ci of the example specific biomarker molecule in the first chamber 420a, and an example concentration C2 of the example specific biomarker molecule in the second chamber 420b in accordance with certain implementations described herein. The first barrier 430a and the first chamber 420a can be configured so that ci closely follows c_p and the diffusion parameters (e.g., geometry of the first and second chambers 420a, b; the distance between the first and second electrodes 440a, b; diffusion coefficient of the biomarker molecule through the second barrier 430b) can be known. The second barrier 430b can have a thickness m, a cross-sectional area A, and a diffusion coefficient D for the biomarker molecules, and the diffusion time of the biomarker molecules through the second barrier 430b can dominate the total diffusion time from the first chamber 420a to the second chamber 420b. Measurements of the time between the first electrode 440a generating a first signal (e.g., indicative of the concentration ci being equal to Cthreshoidj) and the second electrode 440b generating a second signal (e.g., indicative of a concentration C2 of the specific biomarker molecule in the second chamber 420b being equal to cthreshoid_2) can be used to calculate an average concentration c_p of the biomarker molecule in the tissue and/or body fluid during time period dt.

[0085] Fick’s law can be expressed as: dn de

— = -DA — dt dx where de is the concentration gradient (e.g., diffusion driving force), dx is the diffusion distance (e.g., thickness m of the second barrier 430b), D is the diffusion coefficient for the biomarker molecules through the second barrier 430b, 5n is the number of biomarker molecules diffused along the distance dx, and dt is the diffusion time. At time tsi_gnai_2 (when the second electrode 440b generates the second signal), 5n can be calculated to be Cthreshoid_2*V2, with V2 being the known volume of the second chamber 420b and Cthreshoid_2 being a known value defined by the design of the second electrode 440b. The diffusion time dt is the time tsignaij of the first signal from the first electrode 440a and the time t_Signai_2 of the second signal from the second electrode 440b.

[0086] These quantities can be inserted into Fick’s law to calculate the average concentration of the biomarker molecule in the first chamber 420a: er molecule in

the first chamber 420a can be substantially equal to the average concentration c_p of the biomarker molecule in the tissue and/or body fluid during diffusion time dt (e.g., the biomarker concentration of physiological relevance) and can be the driving force for passive diffusion of the biomarker molecules across the second barrier 430b into the second chamber 420b.

[0087] In certain implementations, the at least one electrode 440 is protected (e.g., hidden) from the electrolytic body fluid (e.g., perilymph) of the recipient’s body 405 in that the at least one electrode 440 is not in direct contact with the electrolytic body fluid of the recipient’s body 405. The at least one barrier 430 can be sufficiently spaced from the at least one electrode 440 such that a substantially stable electrode-to-electrolyte interface is established between the fluid 422 and the at least one electrode 440, the substantially stable electrode-to-electrolyte interface providing a substantially stable electrode interface impedance. As used herein, “substantially stable” denotes a quantity or feature that does not change more than 20% over a relevant time period (e.g., over the time since implantation was performed). The substantially stable electrode-to-electrolyte interface can be established within seconds of implantation if the at least one barrier 430 is impermeable to all organic species, or can be established within hours if the at least one barrier 430 is permeable (e.g., semi-permeable) to proteins. For protected recording electrodes 440 configured to record bioelectric signals (e.g., compound action potentials (CAPs); auditory brainstem responses (ABRs); neural response telemetry (NRT); electrocochleography (EcochG)), the substantially stable electrode interface impedance can facilitate increased sensitivity and/or an increased signal-to-noise ratio (SNR) as compared to electrodes that are not protected. The substantially stable electrode interface impedance can also facilitate measurements of electrical impedance and/or electrical impedance changes over time (e.g., to characterize the status and/or changes of biological factors) by the protected recording electrodes 440. Examples of biological factors that can be monitored over time include but are not limited to: the fibrotic sheath that forms and encapsulates the implanted apparatus 400; naive tissue in the electrical current path between the two electrodes being used to measure electrical impedance, such as one ICE (e.g., electrode 440) and one ECE (e.g., return electrode 460).

[0088] In certain implementations in which the at least one barrier 430 triggers the foreign body response of the recipient’s body 405, a fibrotic sheath 470 can form over the at least one barrier 430. Since the at least one barrier 430 is spaced from the at least one electrode 440, the surface area of the outer surface 442 of the at least one electrode 440 remains available for low impedance and substantially stable charge transfer (e.g., in contrast to biosensor electrodes with semi-permeable coatings in physical contact with the electrode surface). For example, the at least one barrier 430 can have a surface area in a range of 10 to 1000 times the surface area of the outer surface 442 of the underlying at least one electrode 440, thereby reducing changes in the overall electrical impedance due to protein and cell attachment to the at least one barrier 430.

[0089] FIG. 6A schematically illustrates a cross-sectional view of an example apparatus 400 a brief time (e.g., hours) after implantation surrounded by perilymph and FIG. 6B schematically illustrates a cross-sectional view of the same example apparatus 400 a significantly longer time (e.g., weeks; years) after implantation during which the apparatus 400 has been subject to the foreign body response of the recipient’s body 405. While FIGs. 6A and 6B show the at least one barrier 430 extending substantially around a perimeter of the apparatus 400, in certain other implementations, the at least one barrier 430 extends only over the at least one chamber 420. The fluid 422 within the chamber 420 comprises saline with aqueous sodium (Na⁺) and chloride (Cl ) ions.

[0090] As shown in FIG. 6A, the at least one barrier 430 is configured to allow the sodium and chloride ions to pass between the perilymph and the fluid 422 within the chamber 420 while preventing proteins and cells from the perilymph from reaching the fluid 422 within the chamber 420. As shown in FIG. 6B, the foreign body response of the recipient’s body 405 results in the fibrotic sheath 470 forming on the apparatus 400, including over the at least one barrier 430. The ions are able to continue to pass between the perilymph and the fluid 422 within the chamber 420 through the fibrotic sheath 470 and the at least one barrier 430. The charge distribution of the electrode-to-electrolyte interface at the outer surface 442 of the electrode 440 (e.g., positively-charged sodium ions in the fluid 422 and electrons in the electrode 440) remain substantially constant (e.g., substantially unaffected by the fibrotic sheath 470) as does the electrical impedance of the electrode-to-electrolyte interface (e.g., the electrode-to-electrolyte interface is substantially maintained despite the foreign body response of the recipient’s body 405).

[0091] FIG. 7 is a flow diagram of an example method 500 in accordance with certain implementations described herein. While the method 500 is described by referring to some of the structures of the example apparatus 400 described herein, other apparatus and systems with other configurations of components can also be used to perform the method 500 in accordance with certain implementations described herein.

[0092] In an operational block 510, the method 500 comprises providing a cavity (e.g., chamber 420) implanted on or within a recipient, the cavity containing a liquid (e.g., fluid 422) and at least partially bounded by a partition (e.g., barrier 430) in fluidic communication with an environment (e.g., tissue and/or body fluid, such as perilymph) outside the cavity. The partition is permeable to at least one constituent of the liquid and is not permeable to at least one type of biological cells. For example, the liquid within the cavity can contain a medicament and the partition can be permeable to the medicament (e.g., for applying the medicament through the cavity to the tissue and/or body fluid within the environment). The medicament can be transmitted (e.g., actively pumped; passively diffused) from a reservoir, through the cavity, and through the partition to the environment outside the cavity. For another example, the partition can be permeable to leucocytes but impermeable to macrophages.

[0093] In an operational block 520, the method 500 further comprises applying electrical signals to an electrode (e.g., electrode 440) spaced from the partition and in fluidic communication with the cavity (e.g., within the cavity). For example, applying the electrical signals can comprise generating the electrical signals (e.g., by a controller in electrical communication with the electrode) and using the electrical signals to stimulate tissue within the environment outside the cavity (e.g., the electrode used as a stimulation electrode). For another example, the electrical signals are generated by tissue within the environment outside the cavity, and applying the electrical signals comprises exposing the electrode to the electrical signals (e.g., the electrode used as a sensing or recording electrode). For another example, the electrical signals are generated by binding biomarker molecules with an outer surface of the electrode 440.

[0094] In certain implementations, the at least one electrode 440 is configured to measure electrical impedance. For example, the two electrodes used for electrical impedance measurements can both be electrodes 440 (e.g., both protected ICEs) or one of the two electrodes can be an electrode 440 (e.g., a protected ICE) and the other of the two electrodes can be a return electrode 460 with a sufficiently large surface area and that is sufficiently far from the tissue of interest (e.g., an ECE). The electrode interface impedance of the two electrodes can be substantially stable over time and any measured change of electrical impedance can be attributed to changes of the intervening tissue of interest.

[0095] In certain other implementations, the at least one electrode 440 is configured to monitor a slowly changing electrical potential of tissue in contact with the at least one barrier 430 as compared to the electrical potential of tissue spaced from the at least one barrier 430. For example, the at least one electrode 440 can be configured to monitor an electrical potential difference between the at least one electrode 440 (e.g., a protected ICE) and a return electrode 460 (e.g., a large ECE). Shifts (e.g., positive or negative shifts) of the electrical potential of perilymph in the scala tympani 237 in which the protected ICE is positioned can be indicative of an inner ear disorder (e.g., Meniere’s disease) and can be used for diagnosis and treatment (e.g., management) of the disorder. [0096] For another example, the at least one electrode 440 can comprise a substantially stable reference electrode used for monitoring the resting electrical potential difference between the reference electrode and the return electrode 460. An increasing resting electrical potential difference between the reference electrode and the return electrode 460 can be indicative of a DC current between the reference electrode and the return electrode 460. In certain implementations, measurements of the electrical potential difference can be compared to a predetermined threshold potential difference value, and such measurements being above the threshold potential difference can be used to trigger actions intended to reduce the measured electrical potential difference. For example, to dissipate electrical charge build-up on at least one stimulation electrode, such actions can include electrically shorting the at least one stimulation electrode (e.g., between application of stimulation signal pulses) to one or more other stimulation electrodes, to the return electrode 460, or to a separate, low electrical impedance electrode (e.g., protected by a corresponding chamber 420 and barrier 430) dedicated to such shorting. For another example, to balance out an increasing electrical potential difference in a closed loop fashion, the amplitudes of the biphasic stimulation pulses can be adjusted and/or the polarity of the biphasic stimulation pulses can be switched (e.g., reversed).

[0097] In certain implementations in which the apparatus 400 is also used for medicament delivery, the apparatus 400 can be configured to use the monitored electrical potential difference as a feedback signal in a closed loop medicament delivery system (e.g., to avoid or reduce the severity of vertigo attacks and/or hearing loss related to Meniere’s disease).

[0098] In certain implementations, low electrical impedances of the at least one electrode 440 protected by the fluid 422 and the at least one barrier 430 can facilitate efficient (e.g., reduced) power consumption and/or improved performance compliance as compared to electrodes that are not protected from the foreign body response (e.g., in direct contact with the tissue and/or body fluid of the recipient’s body 405). For example, the at least one electrode 440 can comprise stimulation electrodes 148 of a cochlear implant auditory prosthesis 100 within at least one chamber 420 and spaced from (e.g., behind) at least one barrier 430 (e.g., within an electrolyte-filled lumen) inserted into the cochlea 140, the at least one electrode 440 protected from direct contact with the intra-cochlear perilymph. In a monopolar (MP) stimulation configuration, the return electrode 460 (e.g., extra-cochlear electrode (ECE)) is outside the at least one chamber 420 (see, e.g., FIGs. 4A-4C), with electrical charge transfer between the at least one electrode 440 and the return electrode 460. In a bipolar (BP) stimulation configuration, the electrical charge transfer occurs between one protected electrode 440 and one other protected electrode 440, and in a common ground (CG) stimulation configuration, the electrical charge transfer occurs between one protected electrode 440 and a plurality of other protected electrodes 440. In certain implementations, including the MP, BP, and CG stimulation configurations, the return electrode 460 is in direct contact with the tissue and/or body fluid of the recipient’s body 405, while in certain other implementations, the return electrode 460 is protected from direct contact with the tissue and/or body fluid of the recipient’s body 405 by a corresponding chamber 420 and barrier 430.

[0099] In certain implementations, the at least one electrode 440 is used as a low electrical impedance and substantially stable reference electrode for monitoring slowly changing neural activity, such as slow wave electrical afterpotential (e.g., M.J.P. Killian, “Excitability of the electrically stimulated auditory nerve,” Ph.D. thesis, University of Utrecht, Utrecht, the Netherlands (1994)). For example, since the amplitude of the electrical afterpotential can depend on the health of the stimulated neural tissue (e.g., and on the parameters of the stimulation signals), such measurements can be used to facilitate diagnosis of the health of the neural tissue and to monitor changes over time (e.g., due to application of a neurotrophic medicament). For another example, such measurements can be used to optimize the stimulation signal parameters for an individual recipient.

[0100] In certain implementations, the at least one electrode 440 is used as a low electrical impedance and substantially stable reference electrode for cyclic voltammetry, electrical impedance spectroscopy, or other electrophysiological measurements (e.g., as a biosensing electrode as described herein). The at least one electrode 440 can be used in place of non-biocompatible reference electrodes (e.g., Ag/AgCl; electrodes available from SME, Inc. of Wilmington, NC) used in in-vitro or acute in-vivo measurements. For example, the at least one electrode 440 can comprise a coating configured to reduce the electrical impedance of the at least one electrode 440 (e.g., to facilitate ion-to-electron charge transfer; to increase stability).

[0101] Although commonly used terms are used to describe the systems and methods of certain implementations for ease of understanding, these terms are used herein to have their broadest reasonable interpretations. Although various aspects of the disclosure are described with regard to illustrative examples and implementations, the disclosed examples and implementations should not be construed as limiting. Conditional language, such as, among others, “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain implementations include, while other implementations do not include, certain features, elements and/or steps. Thus, such conditional language is not generally intended to imply that features, elements and/or steps are in any way required for one or more implementations or that one or more implementations necessarily include logic for deciding, with or without user input or prompting, whether these features, elements and/or steps are included or are to be performed in any particular implementation. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a nonexclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced.

[0102] It is to be appreciated that the implementations disclosed herein are not mutually exclusive and may be combined with one another in various arrangements. In addition, although the disclosed methods and apparatuses have largely been described in the context of conventional cochlear implants, various implementations described herein can be incorporated in a variety of other suitable devices, methods, and contexts. More generally, as can be appreciated, certain implementations described herein can be used in a variety of implantable medical device contexts that can benefit from having at least a portion of the received power available for use by the implanted device during time periods in which the at least one power storage device of the implanted device unable to provide electrical power for operation of the implantable medical device.

[0103] Language of degree, as used herein, such as the terms “approximately,” “about,” “generally,” and “substantially,” represent a value, amount, or characteristic close to the stated value, amount, or characteristic that still performs a desired function or achieves a desired result. For example, the terms “approximately,” “about,” “generally,” and “substantially” may refer to an amount that is within ± 10% of, within ± 5% of, within ± 2% of, within ± 1 % of, or within ± 0.1% of the stated amount. As another example, the terms “generally parallel” and “substantially parallel” refer to a value, amount, or characteristic that departs from exactly parallel by ± 10 degrees, by ± 5 degrees, by ± 2 degrees, by ± 1 degree, or by ± 0.1 degree, and the terms “generally perpendicular” and “substantially perpendicular” refer to a value, amount, or characteristic that departs from exactly perpendicular by ± 10 degrees, by ± 5 degrees, by ± 2 degrees, by ± 1 degree, or by ± 0.1 degree. The ranges disclosed herein also encompass any and all overlap, sub-ranges, and combinations thereof. Language such as “up to,” “at least,” “greater than,” less than,” “between,” and the like includes the number recited. As used herein, the meaning of “a,” “an,” and “said” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “into” and “on,” unless the context clearly dictates otherwise.

[0104] While the methods and systems are discussed herein in terms of elements labeled by ordinal adjectives (e.g., first, second, etc.), the ordinal adjective are used merely as labels to distinguish one element from another (e.g., one signal from another or one circuit from one another), and the ordinal adjective is not used to denote an order of these elements or of their use.

[0105] The invention described and claimed herein is not to be limited in scope by the specific example implementations herein disclosed, since these implementations are intended as illustrations, and not limitations, of several aspects of the invention. Any equivalent implementations are intended to be within the scope of this invention. Indeed, various modifications of the invention in form and detail, in addition to those shown and described herein, will become apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the claims. The breadth and scope of the invention should not be limited by any of the example implementations disclosed herein, but should be defined only in accordance with the claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. An apparatus comprising: a housing configured to be implanted on or within a recipient’s body; at least one chamber within the housing, the at least one chamber configured to contain a fluid; at least one barrier configured to separate the at least one chamber from tissue and/or body fluid of the recipient’s body, the at least one barrier configured to allow transport of electrical charge, electrons, ions, and/or predetermined molecules through the at least one barrier and to prevent transport of at least one organic species from the tissue and/or body fluid into the at least one chamber; and at least one electrode within the housing and spaced from the at least one barrier, the at least one electrode configured to be in electrical communication with the fluid within the at least one chamber.

2. The apparatus of claim 1, wherein the housing comprises a biocompatible first material and the at least one barrier comprises a biocompatible second material.

3. The apparatus of any preceding claim, wherein the at least one organic species is selected from the group consisting of: amino acids, deoxyribonucleic acid (DNA), ribonucleic acid (RNA), proteins, enzymes, cytokines, viruses, bacteria, leucocytes, macrophages, and other biological cells.

4. The apparatus of any preceding claim, wherein the at least one barrier comprises at least one biocompatible porous material, at least one biocompatible permeable material, or at least one biocompatible electrically conductive material.

5. The apparatus of any preceding claim, wherein the at least one barrier comprises at least one biocompatible porous material selected from the group consisting of: polyvinylidene fluoride (PVDF); polydimethylsiloxane (PDMS); polytetrafluoroethylene (PTFE); polyethylene; nitrocellulose; polycarbonate; alumina; metal; titanium.

6. The apparatus of any preceding claim, wherein the at least one barrier comprises at least one biocompatible permeable material selected from the group consisting of: polydimethylsiloxane (PDMS); hydrogel; synthetic membrane; cellulosic membrane.

7. The apparatus of any preceding claim, wherein the at least one barrier comprises at least one biocompatible electrically conductive material comprising an electrically conductive hydrogel.

8. The apparatus of claim 7, wherein the electrically conductive hydrogel is configured to substantially prevent mass transport through the at least one barrier while allowing electrical charge transport through the at least one barrier.

9. The apparatus of any preceding claim, wherein the at least one electrode is configured to apply electrical signals to the recipient’s body via the fluid and the at least one barrier.

10. The apparatus of any preceding claim, wherein the at least one electrode is configured to receive electrical signals from the tissue of the recipient’s body via the fluid and the at least one barrier.

11. The apparatus of any preceding claim, wherein the at least one electrode is configured to detect a presence and/or a concentration of specific biomarker molecules that have entered the at least one chamber from the tissue and/or body fluid of the recipient’s body through the at least one barrier.

12. The apparatus of any preceding claim, wherein the at least one electrode is configured to detect a presence and/or a concentration of at least one specific active pharmaceutical ingredient which is administered to the recipient’s body and that have entered the at least one chamber from the tissue and/or body fluid of the recipient’s body through the at least one barrier.

13. The apparatus of any preceding claim, wherein the at least one chamber comprises a first chamber and a second chamber and the at least one barrier comprises a first barrier and a second barrier, the first chamber separated from the tissue and/or body fluid of the recipient’s body by the first barrier and the second chamber separated from the first chamber by the second barrier and from the tissue and/or body fluid of the recipient’s body by the first barrier, the first chamber, and the second barrier, the at least one electrode comprising a first electrode and a second electrode, the first electrode in electrical communication with the fluid within the first chamber, the second electrode in electrical communication with the fluid in the second chamber.

14. The apparatus of any preceding claim, further comprising a return electrode, the at least one electrode configured to flow electrical current to the return electrode via the fluid and the at least one barrier.

15. The apparatus of any preceding claim, wherein the fluid comprises at least one medicament and the at least one electrode is configured to generate electrical signals indicative of an amount of the at least one medicament in the at least one chamber.

16. An apparatus comprising: a first portion of a body configured to be implanted on or within a recipient, the first portion configured to be in fluidic communication with tissue and/or body fluid outside the body, the first portion permeable to ions and/or molecules and impermeable to biological cells; a region within the body, the region configured to contain an electrolytic fluid and at least partially bounded by the first portion; and an electrically conductive surface within the body and configured to contact the electrolytic fluid, the electrolytic fluid between the surface and the first portion.

17. The apparatus of claim 16, wherein the first portion and the electrolytic fluid are configured to protect the surface from biofouling-caused increases of electrical impedance.

18. The apparatus of claim 16 or claim 17, wherein the surface and the first portion are spaced from one another by at least one micron.

19. The apparatus of any of claims 16 to 18, wherein the region is substantially cylindrical lumen.

20. The apparatus of claim 19, wherein the first portion comprises an end portion of the lumen.

21. The apparatus of any of claims 16 to 19, wherein the first portion comprises a wall portion of the region.

22. The apparatus of any of claims 16 to 21, further comprising a return electrode configured to be in electrical communication with the surface via the electrolytic fluid the first portion, and the tissue and/or body fluid.

23. The apparatus of claim 22, wherein the return electrode is in contact with the tissue and/or body fluid.

24. The apparatus of claim 22, further comprising: a second portion of the body configured to be in fluidic communication with the tissue and/or body fluid, the second portion permeable to the ions and/or molecules and impermeable to the biological cells; and a second region within the body, the second region at least partially bounded by the second portion and configured to contain the electrolytic fluid, the return electrode configured to contact the electrolytic fluid with the electrolytic fluid between the return electrode and the second portion.

25. The apparatus of claim 24, wherein the second portion and the electrolytic fluid are configured to protect the return electrode from biofouling-caused increases of electrical impedance.

26. A method comprising: providing a cavity implanted on or within a recipient, the cavity containing a liquid and at least partially bounded by a partition in fluidic communication with an environment outside the cavity, the partition permeable to at least one constituent of the liquid and not permeable to at least one type of biological cells; and applying electrical signals to an electrode spaced from the partition and in fluidic communication with the cavity.

27. The method of claim 26, wherein said applying electrical signals comprises generating the electrical signals and using the electrical signals to stimulate tissue within the environment outside the cavity.

28. The method of claim 26, wherein the electrical signals are generated by tissue within the environment outside the cavity and said applying electrical signals comprises exposing the electrode to the electrical signals.

29. The method of any of claims 26 to 28, wherein the liquid contains a medicament and the partition is permeable to the medicament.

30. The method of claim 29, further comprising actively pumping the medicament from a reservoir, through the cavity, and through the partition to the environment outside the cavity.

31. The method of claim 29, further comprising passively diffusing the medicament from a reservoir, through the cavity, and through the partition to the environment outside the cavity.

32. The method of claim 26, wherein said applying electrical signals comprises generating the electrical signals by binding biomarker molecules with an outer surface of the electrode.

33. The method of any of claims 26 to 32, further comprising detecting a presence and/or a concentration of biomarker molecules that have entered the cavity from the environment outside the cavity.

34. The method of any of claims 26 to 33, further comprising detecting a presence and/or a concentration of at least one active pharmaceutical ingredient in the cavity.