J. Biomedical Science and Engineering, 2011, 4, 158-163 JBiSE
doi:10.4236/jbise.2011.43022 Published Online March 2011 (http://www.SciRP.org/journal/jbise/).
Published Online March 2011 in SciRes. http://www.scirp.org/jour nal/JBiSE
Recent promising technological developments on hearing
Murat Haluk Ozkul1, Tarik Ozkul2
1Haseki Teaching and Research Hospital, ENT Clinic, Istanbul, Turkey;
2American University of Sharjah, Department of Computer Scien ce and Engineering, Sharjah, UAE.
Email: mhalukozkul@superonline.com; tozkul@aus.edu
Received 6 January 2011; revised 23 February 2011; accepted 1 March 2011.
The purpose of this paper is to review some of the
promising technological developments related to hear-
ing restoration part of ENT practice. If successfully
implemented in product or procedure form, these
technologies are likely to simplify surgical procedures
related to hearing restoration and improve the condi-
tion of patients. The developments are compiled from
scientific sources as well as from recent patent docu-
ments and they are not yet commercially available.
Keywords: Ear Nose and Throat; ENT; Ossicular
Replacement Prosthesis, ORP; Ossiculoplasty;
Active Os s icular Prosthesis; Cochlear Im plant
It is very well known in medical community that tech-
nological developments benefit surgical and medical
procedures directly. Many technological innovations in
medical field eventually find its way into a product or a
procedure that affects the well being of human beings.
Due to this, technical innovations are eagerly awaited by
medical community more than any other field [1,2].
Ear nose and throat (ENT) related ailments plague a
very high percentage of society and as a result, any tech-
nological improvements in this arena find reflections into
the well being of many millions of patients in the world
[3]. In this study authors r eview some of the technologi-
cal developments in the area of hearing restoration which
looks promising and may find their ways into surgical
procedures and medical products duri ng the com ing years.
A word of warning may be necessary at this stage. Ob-
viously good ideas do not necessarily guarantee suc-
cessful products; as success of a product is as much to
do with marketing process as the innovative aspects of
the product. Engineering community know too well that
the best selling processor in the market may not neces-
sarily be the best processor technically. Sometimes suc-
cessful products are doomed because of marketing errors
and on the same token, some mediocre products may
turn into commercial successes because of successful
marketing [4]. Walking along this line of thought, it is
not possible to claim that the technologies reviewed in
this study will definitely be successful. But they cer-
tainly have potential to be successful if the products are
designed and marketed properly.
The technological developments reviewed in this pa-
per are categorized in the following groups;
1) Developments related to reconstruction of the
sound bridge inside the middle ear.
2) Cochlear implant related technological develop-
The middle ear contains chain of three bones which are
linked to each other extending from tympanic membrane
to oval window of the inner ear. These bones are known
commonly as the malleus, incus and stapes. This chain
of bones is called ossicular chain or auditory ossicles [5].
The Figure 1 shows the bones of the osscicular chain
which starts with malleus which engages the ear drum
(membrane tympani) and transfers the vibrations of tym-
panic membrane through incus and stapes bones. These
bones are connected to each other through joints and
transfer vibrational movement from one bone to the
other. Stapes is the last bone of this ossicular chain and
transfers vibrations to the cochlea of the inner ear which
is located in the vestibule.
When movement of the ossicular bones is impeded for
some reason which may be due to deterioration of one of
the bones or the joints, the chain is reconstructed using
artificial bone which is called Ossicular Replacement
Prosthesis ( ORP) [6] .
M. H. Ozkul et al. / J. Biomedical Science and Engineering 4 (2011) 158-163
Copyright © 2011 SciRes. JBiSE
wind o w
Figure 1. Structure of the middle ear and ossicular chain com-
Ossicular chain reconstruction surgery involves re-
constitution of sound conduction bridge of osscicular
bones by removing the dysfunctional elements of the
chain and replacing it by Ossicular Replacement Pros-
thesis (ORP) [7].
Ossiculoplasty is the type of the surgical operation
where ORP prosthesis is implanted into the middle ear
cavity using a surgical procedure where an incision is
made through the ear canal and prosthesis is placed. Re-
placement of incus and stapes in the chain is called Total
ORP (TORP), and replacement incus bone is called Par-
tial ORP (PORP) [8,9]. Both prosthesis touches the
remnant of tympanic membrane or newly created tym-
panic membrane. Ossicular Replacement Prosthesis is
expected to have low mechanical inertia, low mechanical
damping, as well as being durable and biocompatible
[10]. Currently ORP’s are attached to the ossicular chain
using wires, springs and cement. Since size of the os-
sicular chain components may be different for different
individuals, manufacturers usually manufacture several
different sizes to accommodate whole range of patients.
Some manufacturers make the components of ORP in
such a way that the size of the components can be al-
tered by cutting down the size of the components.
Ossicular chain of bones has a complex mechanism of
connection which transmits vibrations of the eardrum to
the inner ear. However, in case of large displacement
which is due to unusually loud sound or pressure differ-
ences, the joints absorb the excessive mechanical dis-
placement, so that neither the ossicular bones nor the
sensitive inner ear cochlea is damaged during the proc-
ess. Current state of the art ORP prosthesis use spring
elements to absorb these additional shocks due to pres-
sure differences or loud sounds although many experts
find their performances unsatisfactory. In technical lan-
guage, the vibrations due to sound are called dynamic
sound pressure variations; whereas vibrations due to
ambient pressures change or changes due to loud sounds
are called static and quasi-static sound pressure varia-
tions respectively. Displacements due to static and quasi-
static sound pressure variations may be 10,000 times
more than the typical displacements encountered with
conversational dynamic sound pressure variations [11].
Such high energy and displacement generated by static
and quasi-static sound pressures are likely to damage
sensitive inner ear components of hearing. Although cur-
rent state of the art ORP prosthesis perform satisfactorily
under dynamic sound pressure variations, their perform-
ance under static and quasi-static sound pressure varia-
tions has been less than ideal.
There are several promising developments in the area
of ORP prosthesis which addresses these complicated
issues. One such invention is disclosed in a recent patent
document where ORP prosthesis is designed with de-
formable joints in such a way that normal vibrations are
transmitted from eardrum to the oval window without
hindrance with minimal acoustic attenuatio n [12].
In this particular design, the deformable coupling be-
tween the ossicular components is designed to absorb the
additional changes under ambient pressure. The compo-
nents act rigid during regular dynamic load circumstances
but become soft under large static or quasi-static loads.
The design uses non-Newtonian fluids between the
couplings of the ossicular chain prosthesis components.
There is a special category of non-Newtonian fluids
which are called thixotropic fluids. Thixotropy is the
property of certain gels or fluids that are thick (viscous)
under normal conditions, but flow (become thin, less
viscous) over time when shaken, agitated, or otherwise
stressed. These fluids are also called “shear thinning
fluid” which displays decreasing viscosity with increas-
ing shear r ate [13].
There are some fluids used in industry which make
use of this property of thixotropic fluids. The drilling
mud is an example of thixotropic fluid which becomes
fluid under pressure, yet thickens when pressure is re-
moved. It is the ideal fluid to be pumped to the depth of
thousands of meters through drilling pipe to cool down
the drill tip as well as removing rock cuttings from the
locality of the drill tip. Since drilling mud becomes flu-
idic under pressure, it can be pumped to immense depth
with reasonable pressure.
The state of the art prosthesis designed with this
technology uses an artificial synovial fluid between the
joints of the prosthesis to achieve the similar affect.
Figure 2 shows the principle of operation of the com-
ponent. The device resembles a piston and cylinder as-
M. H. Ozkul et al. / J. Biomedical Science and Engineering 4 (2011) 158-163
Copyright © 2011 SciRes. JBiSE
sembly where the piston fits loosely having a gap be-
tween the piston and the cylinde r wall. The cavity inside
the cylinder is filled with thixotropic fluid which is
forced to move as the piston inside the cylinder moves.
The piston and the cylinder are covered by a spring like
casing which not only confines the thixotropic fluid
within the cylinder but also acts like a spring when the
piston is moved.
The operation of the unit can be described as follows.
Under regular dynamic vibration conditions, the thixo-
tropic liquid inside container is viscous enough to force
the piston and the cylinder to act as one rigid unit with
no relative movement between the two parts. Under these
conditions, the prosthesis acts like a rigid rod. When a
loud sound is encountered, the piston is pushed with
higher force toward the cylinder which increases the
pressure on the thixotropic fluid contained inside the cyl-
inder. Under increased pressure, the viscosity of the
thixotropic fluid decreases and becomes more fluid. As a
result of this, the fluid can escape through the loose fit-
ting between the piston and the cylinder. Under these
conditions, the piston and the cylinder is not rigid any-
more and movement of the piston is absorbed by the
prosthesis. When pressure is removed, the spring like
outer casing returns the piston and the cylinder to their
original position. In this sense, the device acts like a
special shock absorber similar to shock absorbers con-
nected to wheels of a vehicle.
Figure 3 shows the three dimensional view of the cyl-
inder and the piston assembly where the spring-like
shroud with compliance capability is shown as wire
frame for clarity. Figure 4 shows the three dimensional
view of the middle ear with incus bone is replaced by the
prosthesis (PORP).
Another promising technological development is the
development of active ossicular prosthesis concept [14].
Ossicular prosthesis replaces one of the ossicular bones in
the ossicular chain which transmits vibration of the sound
signal received by ear drum to the oval window of the
inner ear which converts the vibrations to sound signals.
As it is explained in the previous section in detail, re-
placement of one of the bones or the whole ossicular chain
is ossicular replacement prosthesis operation. In this
particular innovation, one of the bones of the ossicular
chain is replaced by an active ossicular replacement
component which not only carries vibrations forward
just like an ordinary ossicular bone, but also can actively
amplify the vibrations through a tiny actuator built inside
the prosthesis. Because of its active nature, this active
component can not only amplify vibrations but can also
Thixotropic fluid container
Outer casin
Spring like
Inner piston
Figure 2. Cross sectional view of the prosthesis member.
Figure 3. Perspective view of the cylinder and the piston
Figure 4. State of the art OSP prosthesis incorporating
shock absorbing ossicular elements.
dampen them in case it is required.
Active ossicular replacement prosthesis is not in-
tended to replace the whole chain of ossicular bones but
replace one of them. Having more than one active os-
sicular prosthesis in the ossicular chain is not recom-
mended. In this particular case, any one of the ossicular
bones can be replaced by the active component. How-
ever, the developers of the technology recommend re-
placement of the incus bone by the active component
M. H. Ozkul et al. / J. Biomedical Science and Engineering 4 (2011) 158-163
Copyright © 2011 SciRes. JBiSE
more than any other bone in the chain. Incus bone is
located between malleus and stapes ossicles and it is the
most suitable bone to be replaced by this prosthetic bone
since connection of prosthesis to bones is easier surgi-
cally than connection to tissue. The prosthesis is sup-
posed to be surgically placed in the ossicular chain
through an incision made in the ear drum. The prosthesis
is a self contained unit w ith no wire co ming out or going
into the unit. The prosthetic device receives its signal
and energy through optical connection from a transmitter
placed in the outer ear canal. Figure 5 shows the loca-
tion of the transmitter which transmits its signal and en-
ergy via optical means.
The design details of the prosthesis are shown in Fig-
ure 6. The unit is a self-contained one which receives its
energy through a photovoltaic cell placed in front of the
device facing eardrum. The same source that transmits
power through light spectrum also transmits the signals
in a different frequency of the spectrum. The sound sig-
nals are received by a microphone placed in the outer ear
canal, processed by a special processor and converted
into optical spectrum. The processor is expected to filter
out loud noises and other unwanted signals during the
processing phase and transmit only what is valuable. The
power and the signal are transmitted in photonic spectrum
in the form of light and can pass through the eardrum
which is translucent. Even though the signal is attenu-
ated partially, the experiments indicated that what is re-
ceived by the unit inside the middle ear is sufficient to
power the prosthesis to operate.
Behind the ear controller
with PV cell
Optic head and microphone
Figure 5. Placement of controller and optic head inside the
outer ear canal.
Photovoltaic ce ll to receive
power and signals
Piezoelectric or solenoid
actuator inside
Figure 6. Active prosthesis and its parts.
Actuation of the prosthesis is achieved by piezoelec-
tric or solenoid actuators. Piezoelectric actuators contain
crystals which can change shape under electric field. The
crystals used in commercial piezoelectric actuators are
optimized to change shape along one axis which causes
the crystal to elongate lengthwise. Solenoid actuators are
made up of a solenoid coil and a suitable core material
which can be magnetic or nonmagnetic. As current
passes through the so lenoid coil, the magnetic field gen-
erated inside the coil moves the core in and out. The
signal received by the prosthesis is converted into volt-
age or current form to activate the actuator, which in
return vibrates the ossicular chain components and oval
window which carries the signals to the brain.
Cochlear implant has been a very valuable innovation
for patients who suffer hearing loss due to neurological
problems in the inner ear [15]. A typical cochlear im-
plant has electrode implanted on the cochlea and con-
trolling electronics placed in the temporal bone. Elec-
tronic unit receives its power and signal through an RF
coil placed under the skin. Using a suitable power source,
power is delivered to the electronics embedded inside
the temporal bone through wireless means. The sound
signal is picked up by an external microphone and sound
signal is processed and converted into electrical form
which is suitable for feeding into the cochlear electrode
in contact with the cochlea. Cochlear implant has pro-
vided a solution to thousands of severely hearing im-
paired who otherwise, would not have an idea about
hearing sense whatsoever. A typical cochlear implant is
M. H. Ozkul et al. / J. Biomedical Science and Engineering 4 (2011) 158-163
Copyright © 2011 SciRes. JBiSE
shown in Figure 7 belo w.
Although cochlear implant has been a wonderful de-
vice, there are some aspects of the device and the im-
plementation which are less than desirable. The exis-
tence of RF coils and electronics either prevents or makes
it difficult for the cochlear implant patients to go through
MRI imaging process. And other undesirable aspect of
the current costlier implant is the level of invasiven ess of
the surgical procedure. Part of the temporal bone has to
be cut out or emptied to make room for the electronics
which in return weakens the temporal bone. Making
wire connections from temporal bone to cochlear elec-
trode is not an easy process. Yet another difficulty is
maintaining connection with the internal RF coil placed
under the skin and external unit placed over the skin.
External microphone unit that picks up the signal pro-
vides little information about the direction where the
sound comes from [16].
Currently there is a significant innovation which may
get rid of many undesirable aspects of the classical co-
chlear implant system [17,18]. This system uses optically
energized electronics as well as optically provided signals.
A simple behind the ear external unit picks up sound
signals through the microphone placed inside the exter-
nal auditory canal. This technique provides highly direc-
tional sound signals. The sound signals are processed
and converted into optical signals in the light spectrum.
The processor unit which is located inside the behind the
ear unit generates signals which are suitable for feeding
into the cochlear electrode. The electronic signal is con-
verted into photonic signal by an ordinary LED, light
emitting diodes which is placed inside the external
Figure 7. Typical cochlear implant and location of processor.
auditory canal in clo se prox imity to th e microph one. Th e
light signals penetrate and pass-through the translucent
eardrum with little impairment. The internal unit of the
cochlear implant is located inside the middle ear cavity.
This unit has a photovoltaic sensor facing eardrum for
receiving power which is transmitted in the form of light
by the external unit placed in the ear canal.
In addition to the photovoltaic sensor, there are addi-
tional light sensors mounted on the middle ear unit of the
optical cochlear implant to receive excitation signals
transmitted in different light wavelengths. The optical
signals are encoded using suitable optical techniques to
provide signals with adequ ate fidelity to the internal unit
of the optical cochlear implant.
This new way of implementation of cochlear implant
is likely to simplify the su rgical process since it does not
require placement in the temporal bone. The internal
electronic part of the cochlear implant is implemented
using suitable nonmagnetic material which causes no
interaction with the MRI imaging process. Since excita-
tion of the cochlea through the cochlear electrode re-
quires very little power, power transmitted through photo-
voltaic means is likely to be sufficient for powering the
internal electronics. The placement location of the inter-
nal unit is the middle ear which is normally occupied by
ossicular bone chain. Placement surgery most probably
requires making an incision on the eardrum and empty-
ing the middle ear cavity to house the inner unit of the
cochlear implant. The Figure 8 indicates the location of
the inner and outer units of the optical cochlear implant.
We presented several new promising technologies re-
lated hearing restoration in this study. The technologies
Figure 8. Optically coupled cochlear implant.
M. H. Ozkul et al. / J. Biomedical Science and Engineering 4 (2011) 158-163
Copyright © 2011 SciRes. JBiSE
are invented quite recently and it may take some time for
the products to appear on the commercial market. The
information about the technological developments is
compiled from scientific documents as well as patent
filings. Authors have neither commercial interest nor
connections to any of developers of the technologies
whatsoever. Authors are not responsible for the accuracy
of claims in the referenced documents.
The information is collected and presented in good
faith for the purpose of informing ENT community
about the recent developments and encouraging practi-
tioners’ and inventors to think and invent out of the box.
Disclaimer: The information about the technological
developments is compiled from scientific documents as
well as patent filings and authors have neither commer-
cial interest nor connections to any of the applicants/
inventors/developers of the technologies whatsoever. The
technologies reviewed are selected by authors on the basis
of their merit and information is collected from patent
filing documents as well as scientific publications. Au-
thors are not responsible for the accuracy of claims in
the referenced documents.
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