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OBJECTIVE The present study sought to 1) characterize insertion forces resulting from a flexible straight electrode array (EA) inserted at slow and ultra-slow insertion velocities, and 2) evaluate if ultra-slow velocities decrease insertion forces independent of other variables. BACKGROUND Low insertion forces are desirable in cochlear implant (CI) surgery to reduce trauma and preserve hearing. Recently, ultra-slow insertion velocities (lower than manually feasible) have been shown to produce significantly lower insertion forces using other EAs. METHODS Five flexible straight EAs were used to record insertion forces into an inelastic artificial scala tympani model. Eleven trial recordings were performed for each EA at five predetermined automated, continuous insertion velocities ranging from 0.03 to 1.6 mm/s. RESULTS An ultra-slow insertion velocity of 0.03 mm/s resulted in a median insertion force of 0.010 N at 20 mm of insertion depth, and 0.026 N at 24.3 mm-the final insertion depth. These forces represent only 24 to 29% of those measured using 1.6 mm/s. After controlling for insertion depth of the EA into the artificial scala tympani model and trial insertion number, decreasing the insertion velocity from 0.4 to 0.03 mm/s resulted in a 50% decrease in the insertion forces. CONCLUSION Using the tested EA ultra-slow velocities can decrease insertion forces, independent of variables like insertion depth. Our results suggest ultra-slow velocities can reduce insertion forces at least 60%, compared with humanly feasible continuous velocities (≥0.9 mm/s).

Detailed knowledge about the three-dimensional morphology of the human cochlea and its intra-cochlear bony and soft-tissue structures is essential for development of new cochlear implant electrode carriers. A manual cross-sectional preparation and imaging technique, hereinafter referred to as “microgrinding”, uses human temporal bone samples embedded in epoxy resin. This process was automated to shorten the time needed for preparation and to increase reproducibility. In this study, reconstruction accuracy of the automated microgrinding technique was determined. Four assemblies of LEGO® bricks were used as artificial samples to analyze the resulting reconstruction accuracy of the whole procedure including embedding, preparation and image registration. The outer surfaces of the samples were measured using a portable coordinate measuring machine by manually choosing points on each surface. After embedding the samples in epoxy resin, following the protocol for human temporal bone samples, preparation using the automated microgrinding was performed with a slice thickness of 50μm. Pixel-spacing within an image was 11.5μm/px. The samples were identified within the dataset using threshold segmentation. Subsequently, points were manually chosen on each surface of the segmented samples. Planes, angles between planes and distances between corners were calculated for the physical and the digital samples. Deviation of the digitally derived measures compared to the physically derived ones describe the reconstruction accuracy of the automated microgrinding process. Parallel planes had a deviation of 0.5° ± 0.5° (range: 0 - 2.9°). Orthogonal planes, whose line of intersection is parallel to the direction of milled abrasion, had a deviation of 0.8 ° ± 0.5 ° (range: 0 - 2.1°), whereas such orthogonal planes whose line of intersection is parallel to the documented sample surface had a deviation of 0.4° ± 0.3 ° (range: 0 - 1.7 °). Distances between corners had an absolute deviation of 0.1 mm ± 0.1mm (range: 0 - 0.6mm), which corresponds to a relative deviation of 1% ± 1% (range: 0 - 6.5%). This study shows a highly accurate sample preparation using an automated microgrinding technique as an essential prerequisite for three-dimensional morphological imaging.

The present study sought to 1) characterize insertion forces resulting from a flexible straight electrode array (EA) inserted at slow and ultra-slow insertion velocities, and 2) evaluate if ultra-slow velocities decrease insertion forces independent of other variables.Low insertion forces are desirable in cochlear implant (CI) surgery to reduce trauma and preserve hearing. Recently, ultra-slow insertion velocities (lower than manually feasible) have been shown to produce significantly lower insertion forces using other EAs.Five flexible straight EAs were used to record insertion forces into an inelastic artificial scala tympani model. Eleven trial recordings were performed for each EA at five predetermined automated, continuous insertion velocities ranging from 0.03 to 1.6 mm/s.An ultra-slow insertion velocity of 0.03 mm/s resulted in a median insertion force of 0.010 N at 20 mm of insertion depth, and 0.026 N at 24.3 mm-the final insertion depth. These forces represent only 24 to 29% of those measured using 1.6 mm/s. After controlling for insertion depth of the EA into the artificial scala tympani model and trial insertion number, decreasing the insertion velocity from 0.4 to 0.03 mm/s resulted in a 50% decrease in the insertion forces.Using the tested EA ultra-slow velocities can decrease insertion forces, independent of variables like insertion depth. Our results suggest ultra-slow velocities can reduce insertion forces at least 60%, compared with humanly feasible continuous velocities (≥0.9 mm/s).

The choice of a cochlear implant electrode carrier for the individual patient is influenced by cochlear size, as this parameter has an impact on the risk of scala dislocations. Therefore, size and morphology should be represented in artificial cochlear models too, since these are generally used for insertion studies evaluating newly developed cochlear implant electrode carriers and insertion techniques, before human temporal bone studies are applied for. Within this study custom-made electrode carrier test samples were inserted into nine artificial cochlear models of different shape. To fabricate them, four human temporal bone samples have been processed by a serial cross-sectioning technique; the other four samples have been scanned with micro computed tomography. The cochlea was segmented on this data using rotating, midmodiolar slice planes, followed by the generation of a three-dimensional digital model, which finally was projected on a plane and 2D models were milled out of PTFE. The ratios of length to width of the cochlear basal turn of our samples were found to be within previously reported range. For comparative reasons a model used in previous studies was included in this study too. The maximal insertion forces per cochlear model followed a normal distribution. The insertion depth at initial insertion force increase is correlated to the length of cochlear basal turn. Using the here presented cochlear models with varying anatomical measures may help to increase the clinical relevance of insertion studies in artificial cochlear models.

For the treatment of deafness or severe hearing loss cochlear implants (CI) are used to stimulate the auditory nerve of the inner ear. In order to produce an electrode array which is both atraumatic and reaches a perimodiolar final position a design featuring shape memory effect was proposed. A Nitinol wire with a diameter of 100 μm was integrated in a state of the art lateral wall electrode array. The wire serves as an actuator after it has been ‘trained’ to adopt the spiral shape of an average human cochlea. Three small diameter platinum-iridium wires (each 20 μm) were crimped to the Nitinol wire in order to produce thermal energy. An insertion test was pursued using a human temporal bone specimen. The prototype electrode array was cooled down by means of immersion in ice water and freeze spray to enable sufficient straightening. Thereafter, insertion into the cochlea through the round window as performed. Insertion was feasible but difficult as premature curling of the electrode occurred during the movement towards the inner ear while passing the middle ear cavity. Therefore, the insertion had to be performed faster than usual. The shape memory actuator was subsequently activated with 450mA current at 5V for 3 seconds. After insertion the specimen was embedded in epoxy resin, microgrinded and all histological slices were assessed for trauma. Perimodiolar position was achieved. No insertion trauma was observed and there were no indications of thermal damage caused by the electrical heating. To the best of our knowledge, this is the first histological evaluation of the insertion trauma caused by an electrically activated shape memory electrode array. These promising results support further research on shape memory CI electrode arrays.

Hearing restoration using a cochlear implant requires a surgical access to the inner ear. In order to enhance patient safety, reduce trauma, and shorten the patient’s time under anaesthesia current research focusses on minimally invasive cochlear implantation surgery by drilling only a single bore hole. This demands a highly accurate surgical assistance device to guide the drill along a predetermined trajectory planned in patient’s image data. In this study a recently developed surgical targeting system was evaluated for the first time in a human cadaver trial. After screwing a reference frame on a temporal bone specimen and imaging of both, a trajectory through the facial recess was planned in order to reach the middle ear. Based on this plan a patient specific surgical template including a linear guide for the surgical drill was composed utilizing bone cement. After the hardening of the bone cement the surgical template was mounted on top of the reference frame. The drilling could be performed as previously planned without harming facial nerve and chorda tympani. The deviation of the actual drill hole to the planned trajectory was 0.17 mm at the level of the facial recess. The minimal distance of the drill hole to the facial nerve was 0.59 mm. This proof-of-concept study demonstrates the feasibility of performing the access to the middle ear in a minimally invasive manner using the mouldable surgical targeting system. The presented process allows the patient specific individualization of a drill guide under sterile conditions. This might facilitate its integration into clinical routine.

Insertion studies in artificial cochlea models (aCM) are used for the analysis of insertion characteristics of different cochlear implant electrode carrier (EC) designs by measuring insertion forces. These forces are summed forces due to the measuring position which is directly underneath the aCM. The current hypothesis is that they include dynamic friction forces during the insertion process and the forces needed to bend an initially straight EC into the curved form of the aCM. For the purposes of the present study, straight EC substitutes with a constant diameter of 0.7 mm and 20.5 mm intracochlear length were fabricated out of silicone in two versions with different stiffness by varying the number of embedded wires. The EC substitutes were inserted into three different models made of polytetrafluoroethylene (PTFE), each model showing only one constant radius. Three different insertion speeds were used (0.11 / 0.4 / 1.6 mm/s) with an automated insertion test bench. For each parameter combination (curvature, speed, stiffness) twelve insertions were conducted. Measurements included six full insertions and six paused insertions. Paused insertions include a ten second paused time interval without further insertion movement each five millimetres. Measurements showed that dynamic and static components of the measured summed forces can be identified. Dynamic force components increase with increased insertion speeds and also with increased stiffness of the EC substitutes. Both force components decrease with larger radius of the PTFE model. After the insertion, the EC substitutes showed a curved shape, which indicates a plastic deformation of the embedded wires due to the insertion into the curved models. The results can be used for further research on an analytical model to predict the insertions forces of a specific combination of selected parameters as insertion speed and type of EC, combined with given factors such as cochlear geometry.

The bend and free recovery (BFR) test according to ASTM F2082 is a standard method to determine the transition temperatures of Nitinol shape memory alloys (SMAs). Unfortunately, this standard method is limited to SMA wires which are straight in its trained shape. Thus, the standard BFR test is not suitable for thermomechanical characterization of curved Nitinol SMA wires which should serve as actuators in cochlear implants in future. We developed a modified BFR measurement setup to determine the active austenite finish (AF) temperature of these very thin wires (Ø100 μm). The active AF temperature specifies the completion of the shape recovery upon heating. A parametric study of the measurement setup was carried out to investigate the influence of the heating rate on the observed active AF temperature and to verify the repeatability of the measurement setup. First, the curved wire was straightened in a cold water bath before inserting it into a water bath that is gradually heated from 5 °C to 45 °C. The shape change of the previously straightened wire was then recorded throughout the experiment using a digital microscope. Five different heating rates were employed: 0.25 K/min, 0.33 K/min, 0.5 K/min, 1 K/min as well as an unregulated maximum heating rate achievable of approximately 1.5 K/min. Furthermore, an investigation on the test-retest reliability was performed with three wires by repeating the experiment ten times with each wire. The results of this study revealed no influence of the heating rate on the thermomechanical response of the wires. Based on data from this study, a regulated heating rate of 1 K/min is suggested for future investigations, as this reduces the duration of the measurement from four hours to less than an hour. The values obtained from each wire through the test-retest reliability investigation showed a standard deviation of 1.9 K, 1.1 K and 2.1 K respectively. Our developed measurement setup demonstrates appropriate repeatability of the measurements.

Restoration of hearing is a demanding surgical task which requires the insertion of a cochlear implant electrode array into the inner ear while preserving the delicate basilar membrane inside the cochlea for an atraumatic insertion. Already shortly after the first clinical success with early versions of cochlear implants the desire for a controlled insertion of the electrode array arose. Such a steerable electrode should be in its shape adaptable to the individual path of the helical inner ear in order to avoid any contact between the implant and the surrounding tissue. This article provides a short overview of concepts and actuator mechanisms investigated in the past and present with the objective of developing a steerable electrode array for an individualized insertion process. Although none of these concepts has reached clinical implementation, there are promising experimental results indicating that insertion forces can be reduced up to 60% compared to straight and not steerable electrodes. Finally, related research topics are listed which require considerable further improvements until steerable electrodes will reach clinical applicability.

The cochlear implant, consisting of an electrode carrier and embedded electrodes, is an auditory neuroprosthesis surgically inserted into the cochlea in order to create an auditory impression in deaf or profoundly hearing-impaired patients. This contribution presents a fluidically actuated electrode carrier with a changeable curvature to simplify insertion. Targeted deformation of the carrier is accomplished by applying pressure internally as well as using a non-stretchable thin fibre embedded in its wall. An analytical examination of the scaled model shows that enlarged geometrically similar systems can be studied in place of actual systems, reducing the effort required for measurements. The geometry of the electrode carrier was determined using model-based synthesis combining the finite element method with an analytical model. The material parameters for the finite element model were found experimentally and fitted by using a third-order Ogden material model. The result of the synthesis yielded a conical shape for the carrier. Synthesis of other forms is also possible and one form is shown which was calculated using a polynomial approach. Demonstrators (3:1-scale) were manufactured and measured. The difference between the measured and calculated pressures was less than 0.6 bar for the cylindrical form and less than 0.78 bar for the conical form.

Das Cochlea-Implantat, bestehend aus einem nachgiebigen Elektrodentrager (ET) und den eingebetteten Elektroden mit Kontaktdrahten. Sie ist eine auditorische Neuroprothese, die operativ in die Cochlea eingefuhrt wird, um einen Horeindruck bei horgeschadigten Patienten zu ermoglichen. Zur Insertionserleichterung wird ein fluidisch aktuierter Elektrodentrager mit veranderbarer Krummung vorgestellt. Seine Verformung wird durch Druckbeaufschlagung im Innenraum sowie einen in die Wand eingebetteten Faden gezielt manipuliert. Eine analytische Betrachtung der Skalierungseigenschaften erlaubt skalierte Strukturen fur Modelle und Messungen zu verwenden. Zur Ermittlung der Geometrie des ETs wird eine modellbasierte Synthese durchgefuhrt: FE-Methode kombiniert mit analytischer Modellbildung. Eine konische Form des ETs mit einseitig geschlossenem, zylindrischem Hohlraum und dazu parallel verlaufendem Faden ist ein Ergebnis der Synthese. Experimentelle Untersuchungen einer Testgeometrie zeigen maximale Abweichungen von 0,6 bar bei einem maximalen Innendruck von 6 bar. Die Untersuchungen zeigen, dass die vorgestellte Methode fur die Entwicklung chirurgischer Instrumentarien mit veranderlicher Krummung geeignet ist.

Latest research on cochlear implantations focuses on hearing preservation during insertion of the implant’s electrode array by reducing insertion trauma. One parameter which may influence trauma is insertion speed. The objective of this study was to extend the range of examined insertion speeds to include ultra-low velocities, being lower than manually feasible, and investigate whether these reduce insertion forces. 24 custom-made cochlear implant test samples were fabricated and inserted into an artificial scala tympani model using 12 different insertion speeds while measuring the resulting insertion forces. Three commercially available slim straight electrode carriers were inserted using the same setup to analyze whether the results are comparable. Insertions of the test samples using high insertion speeds (2.0/2.8 mm/s) showed significantly higher insertion forces than insertions done with low insertion speeds (0.2 mm/s) or ultra-low insertion speeds (

The aim of the study was to evaluate insertion forces during manual insertion of a straight atraumatic electrode in human temporal bones, and post-implantation histologic evaluation of the samples to determine whether violation of intracochlear structures is related to insertion forces. In order to minimize intracochlear trauma and preserve residual hearing during cochlear implantation, knowledge of the insertion forces is necessary. Ten fresh frozen human temporal bones were prepared with canal wall down mastoidectomy. All samples were mounted on a one-axis force sensor. Insertion of a 16-mm straight atraumatic electrode was performed from different angles to induce “traumatic” insertion. Histologic evaluation was performed in order to evaluate intracochlear trauma. In 4 of 10 samples, dislocation of the electrode into scala vestibuli was observed. The mean insertion force for all 10 procedures was 0.003 ± 0.005 N. Insertion forces measured around the site of dislocation to scala vestibuli in 3 of 4 samples were significantly higher than insertion forces at the same location of the cochleae measured in samples without trauma (p