11

BIOMATERIALSBIOMATERIALSANDAND

COCHLEARCOCHLEAR IMPLANTSIMPLANTS

AttiaAttia QamarQamar & Paolo & Paolo SabatiniSabatini

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CochleaCochlea

Middle Ear

Tympanic

MembraneVibrationVibrationVibration

External Ear

Inner Ear

CN VIIIBony LabyrinthBony LabyrinthBony LabyrinthCoclear DuctCoclearCoclear DuctDuct

To round windowTo round window

From oval windowFrom oval windowFrom oval window

PerilymphPerilymphPerilymph

Vibrations transmitted through the Vibrations transmitted through the perilymphperilymph in thein thebony labyrinth will be transmitted to the bony labyrinth will be transmitted to the endolymphendolymph in in

the cochlear ductthe cochlear duct

vestibule

EAR ANATOMY & MECHANICSEAR ANATOMY & MECHANICS

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Perilymph inscala vestibuli

Perilymph inscala tympani

Endolymph inCochlear Duct /scala media

Organ of Organ of CortiCorti

Vibrations ofTectorial Membrane Stimulation of

cilia on hair cells

Transmission of stimulus along CN VIIITransmission of stimulus along CN VIII

TectorialTectorial Membrane

Membrane

Basilar membrane

Vestib

ular m

embran

e

Vibrations conveyed toVibrations conveyed toOrgan of Organ of CortiCorti

Tension of Basilar membranedampens vibration

From oval windowFrom oval window

To round windowTo round window

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Low Frequency

High Frequency

The Basilar Membrane in ActionThe Basilar Membrane in Action::http://www.hhmi.org/biointeractive/animations/cochlea/coc_mov2.hhttp://www.hhmi.org/biointeractive/animations/cochlea/coc_mov2.htmtm

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Hearing ImpairmentHearing ImpairmentTwo types of hearing impairment:Two types of hearing impairment:

•• Conductive hearing lossConductive hearing loss: Damaged apparatus that : Damaged apparatus that transmits sound energy to cochlea. (transmits sound energy to cochlea. (EgEg/ Damaged / Damaged eardrum, bone tissue encrusted ossicles)eardrum, bone tissue encrusted ossicles)

Treatment:Treatment: Hearing Aid or SurgeryHearing Aid or Surgery

•• Sensorineural hearing lossSensorineural hearing loss: Damaged/destroyed hair : Damaged/destroyed hair cells within organ of cells within organ of CortiCorti or destroyed auditory nerve or destroyed auditory nerve (can be caused by a tumor).(can be caused by a tumor).

Treatment:Treatment: Cochlear implant in case of viable auditory Cochlear implant in case of viable auditory nerve, direct stimulation of sound centre in brain nerve, direct stimulation of sound centre in brain required otherwise.required otherwise.

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Main Causes of Hearing LossMain Causes of Hearing Loss

•• HeredityHeredity•• Infections:Infections: egeg. rubella, bacterial meningitis. rubella, bacterial meningitis

•• Acoustic TraumaAcoustic Trauma: : due to acute or chronic exposure due to acute or chronic exposure to loud soundsto loud sounds

•• Prescription drugsPrescription drugs (streptomycin. (streptomycin. tobramycintobramycin, , cisplatincisplatin –– a chemotherapy agent)a chemotherapy agent)

•• PresbycusisPresbycusis: : due to old age, acoustic trauma and due to old age, acoustic trauma and age hardening of microscopic blood vessels in inner ear. age hardening of microscopic blood vessels in inner ear.

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Candidate CriteriaCandidate Criteria

•• Profound sensorineural hearing loss of cochlea Profound sensorineural hearing loss of cochlea site. site.

•• Extremely poor word recognition in openExtremely poor word recognition in open--set set paradigms.paradigms.

•• A patent cochlea and viable auditory nerve.A patent cochlea and viable auditory nerve.

•• Good health to withstand anesthesia and Good health to withstand anesthesia and surgery.surgery.

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Cochlear Implant MechanicsCochlear Implant Mechanics

BRIEF OVERVIEW OF THE IMPLANT:BRIEF OVERVIEW OF THE IMPLANT:http://www.cochlearimplant.com/mov/coch_anim.htmlhttp://www.cochlearimplant.com/mov/coch_anim.html

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Cochlear Implant Processing StrategiesCochlear Implant Processing Strategies

Processing Strategy Electrode Type

Max. # of Channels

Feature extraction Longitudinal bipolar 21

Bipolar 15Compressed analog(Simultaneous

Stimulation) Monopolar 4

Interleaved pulsatile Radial bipolar 8

(Digital) Longitudinal bipolar 21

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Multichannel vs. Single ChannelMultichannel vs. Single Channel(Prosthesis Audio Samples)(Prosthesis Audio Samples)

•• Speech: increasing channels 1, 2, 4, 8, 16Speech: increasing channels 1, 2, 4, 8, 16(more tolerant of degradation)(more tolerant of degradation)

http://www.hei.org/research/depts/aip/increase_channels.mp3http://www.hei.org/research/depts/aip/increase_channels.mp3

•• Music (instrumental, complex): increasing Music (instrumental, complex): increasing channels 4, 8, 16, 32channels 4, 8, 16, 32

(requires fine processing to achieve melody (requires fine processing to achieve melody recognition)recognition)

http://www.hei.org/research/depts/aip/rhapsodydemo.mp3http://www.hei.org/research/depts/aip/rhapsodydemo.mp3

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Goals•• Transmit coded frequency intensities through electrode Transmit coded frequency intensities through electrode

array to CNS (Central Nervous System) via multiarray to CNS (Central Nervous System) via multi--channel electrical stimulation of hearing nerves.channel electrical stimulation of hearing nerves.

•• Insert electrode array into correct location in cochlea, to Insert electrode array into correct location in cochlea, to minimize tissue and auditory nerve damage.minimize tissue and auditory nerve damage.

•• Non toxic and biocompatible materials to prevent injury Non toxic and biocompatible materials to prevent injury to cochlea and auditory nerve.to cochlea and auditory nerve.

•• Minimize current and charge density build up to prevent Minimize current and charge density build up to prevent damage to surrounding tissue.damage to surrounding tissue.

•• Proper electrode geometry for localizing current to Proper electrode geometry for localizing current to separate nerve fibers.separate nerve fibers.

•• Proper implant procedure to prevent infections from Proper implant procedure to prevent infections from spreading to inner ear from middle ear (spreading to inner ear from middle ear (egeg. meningitis). meningitis)

•• Sealed electronics to prevent corrosive body fluids from Sealed electronics to prevent corrosive body fluids from entering and causing device failureentering and causing device failure

•• Durable enough to not result in damage due to head Durable enough to not result in damage due to head impact or result in fatigue or fracture due to acute impact or result in fatigue or fracture due to acute movements.movements.

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BiomaterialsBiomaterials

External ComponentsExternal Components Internal ComponentsInternal Components

••Microphone Microphone -- directionaldirectional••Speech Processor Speech Processor ––Platinum Platinum (strong, light, one (strong, light, one quartzquartz--crystal oscillator)crystal oscillator)

••TransmitterTransmitter

••ReceiverReceiver••StimulatorStimulator••Electrode Array Electrode Array ••ElectrodesElectrodes

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Receiver/ Stimulator PackageReceiver/ Stimulator Package(side by side placement, cylindrical)(side by side placement, cylindrical)

RequirementRequirement MaterialMaterial•• Impervious to body Impervious to body fluidsfluids•• RobustRobust•• No corrosion No corrosion •• No leaks No leaks

•• Sintered Ceramics SealSintered Ceramics Seal(AlO(AlO22, SiO, SiO22, , MgOMgO))••Titanium case (bonds Titanium case (bonds with ceramic material)with ceramic material)•• Seal container halves Seal container halves by welding (Ti to Ti)by welding (Ti to Ti)•• Helium Helium

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Receiver specificallyReceiver specifically

RequirementRequirement MaterialMaterial•• Efficient Signal Efficient Signal TransmissionTransmission•• RobustRobust•• No Migration No Migration

•• coil wrapped around coil wrapped around rare earth magnetrare earth magnet••Titanium capsuleTitanium capsule•• Seal container halves Seal container halves by welding (Ti to Ti)by welding (Ti to Ti)

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Electrode ArrayElectrode Array

RequirementRequirement MaterialMaterial•• No Migration No Migration ••Easy insertion/ limited Easy insertion/ limited traumatrauma••Not an infection carrierNot an infection carrier••OsseointegrationOsseointegration••InsulativeInsulative

•• SilasticSilastic MDXMDX--44--42104210(Graded stiffness)(Graded stiffness)

••Fascia homograft, Fascia homograft, titanium collar, with titanium collar, with hydroxyapatitiehydroxyapatitie coatcoat••SilasticSilastic type A type A (biocompatible glue)(biocompatible glue)

Simulation of contour insertion

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Electrode ContactsElectrode ContactsRequirementRequirement MaterialMaterial•• ConductiveConductive•• No electrolysisNo electrolysis••Minimum toxic Minimum toxic electrochemical electrochemical reactionsreactions

•• PlatinumPlatinum•• IridiumIridium

A. Deaf, Stimulated B. Deaf, Unstimulated

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BiocompatibiltyBiocompatibiltyIssueIssue SolutionSolution

Channel Interaction Channel Interaction (conductive fluid in (conductive fluid in cochlea)cochlea)

Sequential Stimulation Sequential Stimulation (Interleaving)(Interleaving)

Charge density buildup Charge density buildup (tissue and implant (tissue and implant damage)damage)

Increase contact surface Increase contact surface area (mushroom shape)area (mushroom shape)

Spread of infections Spread of infections (meningitis and (meningitis and streptococousstreptococouspneumonia)pneumonia)

GraftinGraftin fascia about fascia about electrode entry point,electrode entry point,Prevent seeding bacteria Prevent seeding bacteria at time of surgeryat time of surgery

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MigrationMigration Fixation and Fixation and retrospective magnetretrospective magnet

Head growth and Head growth and electrode extractionelectrode extraction

Additional 20Additional 20--25 mm 25 mm loop in lead wire and loop in lead wire and fixing array to floor of fixing array to floor of mastoid mastoid atrumatrum

Electrode junction weekElectrode junction week Stress relief via spiral Stress relief via spiral electrodeselectrodes

MRI (implant damage)MRI (implant damage) Non magnetic versionNon magnetic version

2020

SurgerySurgeryPrecautions: Precautions: •• micromicro--clawclaw•• protocol to prevent seeding bacteriaprotocol to prevent seeding bacteria•• Flap < 6mm Flap < 6mm •• Bed depth approxBed depth approx

5mm, round5mm, round

Complications:Complications:•• Hemorrhage : mastoid emissary vein; control with diamond burr, Hemorrhage : mastoid emissary vein; control with diamond burr,

bone wax, crushed muscle, bone wax, crushed muscle, GelfoamGelfoam•• Facial Nerve and Facial Nerve and ChordaChorda Tympani InjuryTympani Injury•• Perilymph GusherPerilymph Gusher

Emplantedelectrode array

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Postoperative ComplicationsPostoperative Complications

•• Wound BreakdownWound Breakdown•• Pain: infection, Pain: infection, extracochlearextracochlear spread of spread of

current, excessively strong magnetscurrent, excessively strong magnets•• InfectionInfection•• LabyrinthitisLabyrinthitis and Meningitisand Meningitis

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The ManufacturesThe Manufactures

•• Advanced BionicsAdvanced Bionics -- ClarionClarionwww.cochlearimplant.comwww.cochlearimplant.com

•• Cochlear CorporationCochlear Corporation -- NucleusNucleuswww.cochlear.comwww.cochlear.com

•• MEDMED--ELEL -- CombiCombi 40+40+www.medel.comwww.medel.com

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The FutureThe Future

For those with destroyed auditory nervesFor those with destroyed auditory nerves-- Implantation of electrodes into cochlear Implantation of electrodes into cochlear

nucleusnucleus-- Implantation of Electrodes into auditory Implantation of Electrodes into auditory

cortexcortex

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RefrencesRefrences

•• www.cochlearimplant.comwww.cochlearimplant.com•• www.cochlear.comwww.cochlear.com•• www.medel.comwww.medel.com•• http://forms.gradsch.psu.edu/equity/sroppapers/2004/SeshadriSudhhttp://forms.gradsch.psu.edu/equity/sroppapers/2004/SeshadriSudh

arshana.pdfarshana.pdf•• http://http://www.phm.gov.au/hsc/cochlear/commercial.htmwww.phm.gov.au/hsc/cochlear/commercial.htm•• “Cochlear Implants”; Fundamentals and Applications, Graeme Clar“Cochlear Implants”; Fundamentals and Applications, Graeme Clarkk•• “Cochlear Implants”, Schindler & M. “Cochlear Implants”, Schindler & M. MerzenichMerzenich•• “Cochlear Implants”, Roger F. Gray“Cochlear Implants”, Roger F. Gray•• “Cochlear Implants in Adults and Children”, NIH Consensus “Cochlear Implants in Adults and Children”, NIH Consensus

Development Conference, May 15Development Conference, May 15--17, 199517, 1995•• “Practical Hearing Aid Selection and Fitting”, Henry Tobin“Practical Hearing Aid Selection and Fitting”, Henry Tobin

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The ENDThe END