Flexible Electrode Array Research Articles

Wet‐Printed Stretchable and Strain‐Insensitive Conducting Polymer Electrodes: Facilitating In Vivo Gastric Slow Wave Mapping

AbstractWearable and implantable devices play a crucial role in clinical diagnosis, disease treatment, and fundamental research on the body's electrophysiology and biochemical processes. Conducting polymers are emerging as promising solutions to surpass the limitations of traditional metal‐based electrodes, offering enhanced conformability, and stretchability. However, current microfabrication techniques of CP electrodes have a number of limitations. In this study, a novel wet‐printing technique is developed for the fabrication of highly stretchable poly(3,4‐ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) microelectrodes. The wet‐printing, conducted in a liquid coagulation bath, has the advantages of being non‐contact, easy and fast to perform, and capable of printing low‐viscosity inks. Wet‐printing of PEDOT:PSS lines with a width of ≈20 µm is demonstrated. By adding D‐sorbitol as a plasticizer, an ultra‐high stretchability of PEDOT:PSS electrodes, of more than 720% is achieved while the electrodes remained conductive and strain‐insensitive up to high strains. The use of PEDOT:PSS wet‐printed electrode arrays for the electrophysiological recording from the stomach is demonstrated. The stretchable electrodes conformed swell to the tissue and recorded comparable electrophysiological signals to Au‐plated electrodes in porcine and rodent animal models. The wet‐printing approach to fabricating flexible and stretchable electrode arrays using low‐viscosity, conducting inks holds promise for applications in conformable electronics.

Improving Sensitivity and Longevity of In Vivo Glutamate Sensors with Electrodeposited NanoPt.

In vivo glutamate sensing has provided valuable insight into the physiology and pathology of the brain. Electrochemical glutamate biosensors, constructed by cross-linking glutamate oxidase onto an electrode and oxidizing H2O2 as a proxy for glutamate, are the gold standard for in vivo glutamate measurements for many applications. While glutamate sensors have been employed ubiquitously for acute measurements, there are almost no reports of long-term, chronic glutamate sensing in vivo, despite demonstrations of glutamate sensors lasting for weeks in vitro. To address this, we utilized a platinum electrode with nanometer-scale roughness (nanoPt) to improve the glutamate sensors' sensitivity and longevity. NanoPt improved the GLU sensitivity by 67.4% and the sensors were stable in vitro for 3 weeks. In vivo, nanoPt glutamate sensors had a measurable signal above a control electrode on the same array for 7 days. We demonstrate the utility of the nanoPt sensors by studying the effect of traumatic brain injury on glutamate in the rat striatum with a flexible electrode array and report measurements of glutamate taken during the injury itself. We also show the flexibility of the nanoPt platform to be applied to other oxidase enzyme-based biosensors by measuring γ-aminobutyric acid in the porcine spinal cord. NanoPt is a simple, effective way to build high sensitivity, robust biosensors harnessing enzymes to detect neurotransmitters in vivo.

Origami-inspired soft fluidic actuation for minimally invasive large-area electrocorticography

Electrocorticography is an established neural interfacing technique wherein an array of electrodes enables large-area recording from the cortical surface. Electrocorticography is commonly used for seizure mapping however the implantation of large-area electrocorticography arrays is a highly invasive procedure, requiring a craniotomy larger than the implant area to place the device. In this work, flexible thin-film electrode arrays are combined with concepts from soft robotics, to realize a large-area electrocorticography device that can change shape via integrated fluidic actuators. We show that the 32-electrode device can be packaged using origami-inspired folding into a compressed state and implanted through a small burr-hole craniotomy, then expanded on the surface of the brain for large-area cortical coverage. The implantation, expansion, and recording functionality of the device is confirmed in-vitro and in porcine in-vivo models. The integration of shape actuation into neural implants provides a clinically viable pathway to realize large-area neural interfaces via minimally invasive surgical techniques.

Preparation of W-N-C single atom catalyst and Cu3(HHTP)2 metal-organic framework dual-decorated graphene nanoplatelet flexible electrode arrays for the rapid detection of carbendazim in vegetables

It is highly desirable to develop a low-cost and rapid detection method for trace levels of carbendazim fungicide residues, which would be beneficial for improving human health and mitigating environmental issues. Herein, isolated single tungsten atoms were implanted onto well-organized metal–organic framework (MOF)-derived N-doped carbons to form W-N-C single-site heterojunctions with ultrahigh electrocatalytic activity. The coupling of W-N-C with Cu3(HHTP)2, an electronically conductive MOF with a large surface area and porous structure, exhibited enhanced electrocatalytic performance for the oxidation of carbendazim (CBZ) when they were used for decorating graphene nanoplatelet flexible electrode arrays fabricated via template-assisted scalable filtration. A wide linear range (3.0 nM–50 μM) with an ultra-low detection limit of 0.97 nM and fast response was achieved for CBZ analysis. Moreover, the sensing platform has been utilised to monitor CBZ levels in vegetable samples with satisfactory recovery rates of 97.2–102% and a low relative standard deviation of 1.9%.

Cochlear implant electrode design for safe and effective treatment.

The optimal placement of a cochlear implant (CI) electrode inside the scala tympani compartment to create an effective electrode-neural interface is the base for a successful CI treatment. The characteristics of an effective electrode design include (a) electrode matching every possible variation in the inner ear size, shape, and anatomy, (b) electrically covering most of the neuronal elements, and (c) preserving intra-cochlear structures, even in non-hearing preservation surgeries. Flexible electrode arrays of various lengths are required to reach an angular insertion depth of 680° to which neuronal cell bodies are angularly distributed and to minimize the rate of electrode scalar deviation. At the time of writing this article, the current scientific evidence indicates that straight lateral wall electrode outperforms perimodiolar electrode by preventing electrode tip fold-over and scalar deviation. Most of the available literature on electrode insertion depth and hearing outcomes supports the practice of physically placing an electrode to cover both the basal and middle turns of the cochlea. This is only achievable with longer straight lateral wall electrodes as single-sized and pre-shaped perimodiolar electrodes have limitations in reaching beyond the basal turn of the cochlea and in offering consistent modiolar hugging placement in every cochlea. For malformed inner ear anatomies that lack a central modiolar trunk, the perimodiolar electrode is not an effective electrode choice. Most of the literature has failed to demonstrate superiority in hearing outcomes when comparing perimodiolar electrodes with straight lateral wall electrodes from single CI manufacturers. In summary, flexible and straight lateral wall electrode type is reported to be gentle to intra-cochlear structures and has the potential to electrically stimulate most of the neuronal elements, which are necessary in bringing full benefit of the CI device to recipients.

Electrically evoked compound action potentials are associated with the site of intracochlear stimulation

ObjectivesObjective measurements to predict the position of a cochlear electrode during cochlear implantation surgery may serve to improve the surgical technique and postoperative speech outcome. There is evidence that electrically evoked compound action potentials (ECAP) are a suitable approach to provide information about the site of stimulation. This study aims to contribute to the knowledge about the association between the intraoperative intracochlear ECAP characteristics and the site of stimulation.MethodsIn a retrospective cohort study, patients undergoing cochlear implant surgery with flexible lateral wall electrode arrays (12 stimulating channels) between 2020 and 2022 were analyzed. The CDL was measured using a CT-based clinical planning software. ECAP were measured for all electrode contacts and associated to the CDL as well as to the site of stimulation in degree.ResultsSignificant differences among the amplitudes and slopes for the individual stimulated electrode contacts at the stimulation sites of 90°, 180°, 270°, 360°, 450° and 540° were found. The values showed a trend for linearity among the single electrodes.ConclusionsECAP characteristics correlate with the electrode’s position inside the cochlea. In the future, ECAP may be applied to assess the intracochlear position inside the cochlea and support anatomy-based fitting.

Successful hearing preservation and improved subjective sound quality with the flexible 28-mm electrode array

IntroductionFlexible electrode arrays have shown to be an effective solution to ensure atraumatic insertion. However, flexible full-length electrodes are not suited for patients with smaller cochleae. Therefore, this study aimed to evaluate short-term and medium-term hearing preservation (HP) in patients with low-frequency residual hearing (LFRH) who were implanted with a flexible 28-mm electrode array and who did not meet the indication criteria for electric-acoustic stimulation (EAS).MethodsHP was determined based on the pure-tone audiogram of the implanted ear. A bisyllable sentence test was used to assess speech perception in quiet and in noise. The hearing implant sound quality index (HISQUI19) evaluated self-reported hearing quality. The tests were conducted pre- and post-operatively, at first fitting, and at 1, 3, 6, and 12 months after first fitting.ResultsAt 12 months post first fitting, 2 patients had complete HP; 4 patients had partial HP. Speech perception scores improved in all patients of the study. The mean scores on the bisyllable sentence test in noise significantly increased from 30% pre-operatively to 62% 6 months post first-fitting and to 68% 12 months post first-fitting. The mean score of the HISQUI19 improved from 40.56 (poor) pre-operatively to 72.56 (moderate) 1 month post first-fitting and to 90.29 (good) 12 months post first-fitting.ConclusionThe 28-mm flexible electrode array facilitates atraumatic surgery and HP and results in improved speech perception and subjective sound quality scores.

Wireless and battery-free wearable biosensing of riboflavin in sweat for precision nutrition

Nutrition assessment is crucial for dietary guidance and prevention of malnutrition. Recent endeavors in wearable biochemical sensors have enabled real-time, in situ analysis of nutrients in sweat. However, the monitoring of riboflavin, an indispensable vitamin B involved in energy metabolism, remains challenging due to its trace level and variations in the sweat matrix. Herein, we report a wireless, battery-free, and flexible wearable biosensing system for the in situ monitoring of sweat riboflavin. Highly sensitive and selective electrochemical voltammetric detection is realized based on the synergistic effect of electrodeposited reduced graphene oxide (rGO) and platinum nanoparticles (PtNPs) with a low detection limit of 1.2 nM. The fully integrated system is capable of sweat sampling with the microfluidic patch, real-time riboflavin analysis and pH calibration with the flexible electrode array, as well as wirelessly simultaneous near field communication (NFC) energy harvesting and data transmission with the flexible circuit and a smartphone. On-body human sweat analysis demonstrates high accuracy cross-validated with gold-standard measurements, and reveals a strong correlation between sweat and urine riboflavin levels. The proposed wearable platform opens up attractive possibilities for noninvasive nutrient tracking, providing strong potential for personalized dietary guidance towards precision nutrition.

Shape-changing electrode array for minimally invasive large-scale intracranial brain activity mapping

Large-scale brain activity mapping is important for understanding the neural basis of behaviour. Electrocorticograms (ECoGs) have high spatiotemporal resolution, bandwidth, and signal quality. However, the invasiveness and surgical risks of electrode array implantation limit its application scope. We developed an ultrathin, flexible shape-changing electrode array (SCEA) for large-scale ECoG mapping with minimal invasiveness. SCEAs were inserted into cortical surfaces in compressed states through small openings in the skull or dura and fully expanded to cover large cortical areas. MRI and histological studies on rats proved the minimal invasiveness of the implantation process and the high chronic biocompatibility of the SCEAs. High-quality micro-ECoG activities mapped with SCEAs from male rodent brains during seizures and canine brains during the emergence period revealed the spatiotemporal organization of different brain states with resolution and bandwidth that cannot be achieved using existing noninvasive techniques. The biocompatibility and ability to map large-scale physiological and pathological cortical activities with high spatiotemporal resolution, bandwidth, and signal quality in a minimally invasive manner offer SCEAs as a superior tool for applications ranging from fundamental brain research to brain-machine interfaces.

Magnetically Compatible Brain Electrode Arrays Based on Single-Walled Carbon Nanotubes for Long-Term Implantation

Advancements in brain–machine interfaces and neurological treatments urgently require the development of improved brain electrodes applied for long-term implantation, where traditional and polymer options face challenges like size, tissue damage, and signal quality. Carbon nanotubes are emerging as a promising alternative, combining excellent electronic properties and biocompatibility, which ensure better neuron coupling and stable signal acquisition. In this study, a new flexible brain electrode array based on 99.99% purity of single-walled carbon nanotubes (SWCNTs) was developed, which has 30 um × 40 um size, about 5.1 kΩ impedance, and 14.01 dB signal-to-noise ratio (SNR). The long-term implantation experiment in vivo in mice shows the proposed brain electrode can maintain stable LFP signal acquisition over 12 weeks while still achieving an SNR of 3.52 dB. The histological analysis results show that SWCNT-based brain electrodes induced minimal tissue damage and showed significantly reduced glial cell responses compared to platinum wire electrodes. Long-term stability comes from SWCNT’s biocompatibility and chemical inertness, the electrode’s flexible and fine structure. Furthermore, the new brain electrode array can function effectively during 7-Tesla magnetic resonance imaging, enabling the collection of local field potential and even epileptic discharges during the magnetic scan. This study provides a comprehensive study of carbon nanotubes as invasive brain electrodes, providing a new path to address the challenge of long-term brain electrode implantation.

Flexible switch matrix addressable electrode arrays with organic electrochemical transistor and pn diode technology

Due to their effective ionic-to-electronic signal conversion and mechanical flexibility, organic neural implants hold considerable promise for biocompatible neural interfaces. Current approaches are, however, primarily limited to passive electrodes due to a lack of circuit components to realize complex active circuits at the front-end. Here, we introduce a p-n organic electrochemical diode using complementary p- and n-type conducting polymer films embedded in a 15-μm -diameter vertical stack. Leveraging the efficient motion of encapsulated cations inside this polymer stack and the opposite doping mechanisms of the constituent polymers, we demonstrate high current rectification ratios (105\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${10}^{5}$$\\end{document}) and fast switching speeds (230 μs). We integrate p-n organic electrochemical diodes with organic electrochemical transistors in the front-end pixel of a recording array. This configuration facilitates the access of organic electrochemical transistor output currents within a large network operating in the same electrolyte, while minimizing crosstalk from neighboring elements due to minimized reverse-biased leakage. Furthermore, we use these devices to fabricate time-division-multiplexed amplifier arrays. Lastly, we show that, when fabricated in a shank format, this technology enables the multiplexing of amplified local field potentials directly in the active recording pixel (26-μm diameter) in a minimally invasive form factor with shank cross-sectional dimensions of only 50×8 μm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mu m}^{2}$$\\end{document}.

Wireless facial biosensing system for monitoring facial palsy with flexible microneedle electrode arrays

Facial palsy (FP) profoundly influences interpersonal communication and emotional expression, necessitating precise diagnostic and monitoring tools for optimal care. However, current electromyography (EMG) systems are limited by their bulky nature, complex setups, and dependence on skilled technicians. Here we report an innovative biosensing approach that utilizes a PEDOT:PSS-modified flexible microneedle electrode array (P-FMNEA) to overcome the limitations of existing EMG devices. Supple system-level mechanics ensure excellent conformality to the facial curvilinear regions, enabling the detection of targeted muscular ensemble movements for facial paralysis assessment. Moreover, our apparatus adeptly captures each electrical impulse in response to real-time direct nerve stimulation during neurosurgical procedures. The wireless conveyance of EMG signals to medical facilities via a server augments access to patient follow-up evaluation data, fostering prompt treatment suggestions and enabling the access of multiple facial EMG datasets during typical 6-month follow-ups. Furthermore, the device’s soft mechanics alleviate issues of spatial intricacy, diminish pain, and minimize soft tissue hematomas associated with traditional needle electrode positioning. This groundbreaking biosensing strategy has the potential to transform FP management by providing an efficient, user-friendly, and less invasive alternative to the prevailing EMG devices. This pioneering technology enables more informed decision-making in FP-management and therapeutic intervention.

Monitoring Contractility of Junctional Zone Endometrium across Menstrual Cycle Using the ElectroUteroGraph (EUG): A Clinical Evaluation

(1) Background: Abnormal uterine contractility for nonpregnant women has been associated with gynecological pathologies and infertility. The objective of this study was to evaluate the ability of a novel monitoring technique to assess the contractility of the nongravid uterus using a simple, standardized, direct, in vivo methodology during the different phases of the menstrual cycle. (2) Methods: Twenty-six healthy women of reproductive age (28–48 years) were recruited. An ElectroUteroGraph (EUG) was used to measure the electrical activity from the contractility of the junctional zone endometrium (JZE) across the menstrual cycle. Derived recordings were separated into the early proliferative (EP) (n = 10), late proliferative (LP) (n = 31), early luteal (EL) (n = 27), and late luteal (LL) (n = 12) phases of the menstrual cycle. EUG recordings were performed by inserting a flexible electrode array into the endometrial cavity. (3) Results: Waveforms that were measured from the electrode closer to the fundus (1 cm distance) were processed. The Root-Mean-Square (RMS) Voltage Amplitude (VJZE-RMS) (in μV) and the Mean Frequency (fJZE-mean) (in cycles/min) of the JZE’s electrical activity, as direct indicators of the intensity and frequency changes in the JZE’s contractions, were extracted from the recorded waveforms. There was a trend in the median values of the VJZE-RMS decreasing from the EP to the LP phase (247–158 μV). During the EL phase, an upward trend was observed (158–374 μV, p < 0.05), reaching its highest value during the LL phase (374–477 μV, p < 0.05) when compared to the LP phase. The fJZE-mean showed the opposite trend, increasing from 2.5 cycles/min during the EP phase to 2.96 cycles/min during the LP phase. During the EL phase, a downward trend was observed (2.96–2.37 cycles/min), continuing to fall to 1.33 cycles/min, in the LL phase, with p < 0.05 when compared to the previous three phases. (4) Conclusions: The novel in vivo monitoring technique has shown clinically, for the first time, significant electrical activity differences in the different sub-phases of the menstrual cycle, recorded in a safe and painless way.

A flexible electrode Array for genetic transfection of different layers of the retina by electroporation.

Electroporation (in which the permeability of a cell membrane is increased transiently by exposure to an appropriate electric field) has exhibited great potential of becoming an alternative to adeno-associated virus (AAV)-based retina gene delivery. Electroporation eliminates the safety concerns of employing exogenous viruses and exceeds the limit of AAV cargo size. Unfortunately, several concerns (e.g., relatively high electroporation voltage, poor surgical operability and a lack of spatial selectivity of retina tissue) have prevented electroporation from being approved for clinical application (or even clinical trials). In this study, a flexible micro-electrode array for retina electroporation (FERE) was developed for retina electroporation. A suitably shaped flexible substrate and well-placed micro-electrodes were designed to adapt to the retina curvature and generate an evenly distributed electric field on the retina with a significantly reduced electroporation voltage of 5 V. The FERE provided (for the first time) a capability of controlled gene delivery to the different structural layers of retina tissue by precise control of the distribution of the electrical field. After ensuring the surgical operability of the FERE on rabbit eyeballs, the FERE was verified to be capable of transfecting different layers of retina tissue with satisfactory efficiency and minimum damage. Our method bridges the technical gap between laboratory validation and clinical use of retina electroporation.

Multiplexed Surface Electrode Arrays Based on Metal Oxide Thin-Film Electronics for High-Resolution Cortical Mapping.

Electrode grids are used in neuroscience research and clinical practice to record electrical activity from the surface of the brain. However, existing passive electrocorticography (ECoG) technologies are unable to offer both high spatial resolution and wide cortical coverage, while ensuring a compact acquisition system. The electrode count and density are restricted by the fact that each electrode must be individually wired. This work presents an active micro-electrocorticography (µECoG) implant that tackles this limitation by incorporating metal oxide thin-film transistors (TFTs) into a flexible electrode array, allowing to address multiple electrodes through a single shared readout line. By combining the array with an incremental-ΔΣ readout integrated circuit (ROIC), the system is capable of recording from up to 256 electrodes virtually simultaneously, thanks to the implemented 16:1 time-division multiplexing scheme, offering lower noise levels than existing active µECoG arrays. Invivo validation is demonstrated acutely in mice by recording spontaneous activity and somatosensory evoked potentials over a cortical surface of ≈8×8mm2 . The proposed neural interface overcomes the wiring bottleneck limiting ECoG arrays, holding promise as a powerful tool for improved mapping of the cerebral cortex and as an enabling technology for future brain-machine interfaces.

Large-scale fully printed “Lego Bricks” type wearable sweat sensor for physical activity monitoring

Wearable sweat sensors are becoming increasingly popular for their robust capabilities in non-invasive, dynamic, and continuous real-time monitoring of biological information. Real-time monitoring of large-scale samples is crucial for realizing intelligent health. A major bottleneck for enabling large-scale sweat elucidation is the fabrication of wearable sensors equipped with microfluidic devices and flexible electrodes in a cost-effective, homogeneous performance and rapid large-scale way. Herein, a “Screen+Wax”-printing technique was introduced to prepare these components and construct “Lego Bricks” type wearable sweat sensor sensor to monitor sweat Na+ and K+. Flexible electrode arrays and paper-based microfluidic layers (they act as building blocks) were fabricated on polyethylene terephthalate and paper surfaces, respectively, using screen printing and wax printing. Gold nanoparticles and Na+/K+ ion-selective membranes were modified on the electrode surfaces by electrodeposition and drop coating, respectively. In this work, we highlight the excellent performance of the “Lego Bricks” type wearable sweat sensor in testing the Na+ and K+ imbalance of sweat from different body regions during exercise and, more significantly, to track the physical activity during prolonged exercise under different interventions. Furthermore, the prepared “Lego Bricks” wearable sweat ion electrochemical sensor is demonstrated to be capable of large-scale samples elucidation with outstanding performance and cost-effectiveness, which is expected to deeply integrate sweat monitoring into physical activity, providing an important tool for intelligent health.

Myomatrix arrays for high-definition muscle recording

Neurons coordinate their activity to produce an astonishing variety of motor behaviors. Our present understanding of motor control has grown rapidly thanks to new methods for recording and analyzing populations of many individual neurons over time. In contrast, current methods for recording the nervous system’s actual motor output – the activation of muscle fibers by motor neurons – typically cannot detect the individual electrical events produced by muscle fibers during natural behaviors and scale poorly across species and muscle groups. Here we present a novel class of electrode devices (‘Myomatrix arrays’) that record muscle activity at unprecedented resolution across muscles and behaviors. High-density, flexible electrode arrays allow for stable recordings from the muscle fibers activated by a single motor neuron, called a ‘motor unit,’ during natural behaviors in many species, including mice, rats, primates, songbirds, frogs, and insects. This technology therefore allows the nervous system’s motor output to be monitored in unprecedented detail during complex behaviors across species and muscle morphologies. We anticipate that this technology will allow rapid advances in understanding the neural control of behavior and identifying pathologies of the motor system.

Myomatrix arrays for high-definition muscle recording.

Neurons coordinate their activity to produce an astonishing variety of motor behaviors. Our present understanding of motor control has grown rapidly thanks to new methods for recording and analyzing populations of many individual neurons over time. In contrast, current methods for recording the nervous system's actual motor output - the activation of muscle fibers by motor neurons - typically cannot detect the individual electrical events produced by muscle fibers during natural behaviors and scale poorly across species and muscle groups. Here we present a novel class of electrode devices ('Myomatrix arrays') that record muscle activity at unprecedented resolution across muscles and behaviors. High-density, flexible electrode arrays allow for stable recordings from the muscle fibers activated by a single motor neuron, called a 'motor unit,' during natural behaviors in many species, including mice, rats, primates, songbirds, frogs, and insects. This technology therefore allows the nervous system's motor output to be monitored in unprecedented detail during complex behaviors across species and muscle morphologies. We anticipate that this technology will allow rapid advances in understanding the neural control of behavior and identifying pathologies of the motor system.

Flexible multichannel electrodes for acute recording in nonhuman primates

Flexible electrodes have demonstrated better biocompatibility than rigid electrodes in relieving tissue encapsulation and long-term recording. Nonhuman primates are closer to humans in their brains’ structural and functional properties, thus making them more suitable than rodents as animal models for potential clinical usage. However, the application of flexible electrodes on nonhuman primates has rarely been reported. In the present study, a flexible multichannel electrode array for nonhuman primates was developed and implemented for extracellular recording in behaving monkeys. To minimize the window of durotomy for reducing possible risks, a guide-tube-compatible implantation solution was designed to deliver the flexible electrodes through the dura into the cortex. The proposed structure for inserting flexible electrodes was characterized ex vivo and validated in vivo. Furthermore, acute recording of multichannel flexible electrodes for the primates was performed. The results showed that the flexible electrodes and implantation method used in this study meet the needs of extracellular recording in nonhuman primates. Task-related neuronal activities with a high signal-to-noise ratio of spikes demonstrated that our whole device is currently a minimally invasive and clinically viable approach for extracellular recording.

Comparing linear and non-linear models to estimate the appropriate cochlear implant electrode array length—are current methods precise enough?

PurposeIn cochlear implantation with flexible lateral wall electrode arrays, a cochlear coverage (CC) range between 70% and 80% is considered ideal for optimal speech perception. To achieve this CC, the cochlear implant (CI) electrode array has to be chosen according to the individual cochlear duct length (CDL). Here, we mathematically analyzed the suitability of different flexible lateral wall electrode array lengths covering between 70% and 80% of the CDL.MethodsIn a retrospective cross-sectional study preoperative high-resolution computed tomography (HRCT) from patients undergoing cochlear implantation was investigated. The CDL was estimated using an otosurgical planning software and the CI electrode array lengths covering 70–80% of the CDL was calculated using (i) linear and (ii) non-linear models.ResultsThe analysis of 120 HRCT data sets showed significantly different model-dependent CDL. Significant differences between the CC of 70% assessed from linear and non-linear models (mean difference: 2.5 mm, p < 0.001) and the CC of 80% assessed from linear and non-linear models (mean difference: 1.5 mm, p < 0.001) were found. In up to 25% of the patients none of the existing flexible lateral wall electrode arrays fit into this range. In 59 cases (49,2%) the models did not agree on the suitable electrode arrays.ConclusionsThe CC varies depending on the underlying CDL approximation, which critically influences electrode array choice. Based on the literature, we hypothesize that the non-linear method systematically overestimates the CC and may lead to rather too short electrode array choices. Future studies need to assess the accuracy of the individual mathematical models.