High-density cochlear implants with position sensing and control

Implants with Sensing Capabilities

Because of the aging human population and increased numbers of surgical procedures being performed, there is a growing number of biomedical devices being implanted each year. Although the benefits of implants are significant, there are risks to having foreign materials in the body that may lead to complications that may remain undetectable until a time at which the damage done becomes irreversible. To address this challenge, advances in implantable sensors may enable early detection of even minor changes in the implants or the surrounding tissues and provide early cues for intervention. Therefore, integrating sensors with implants will enable real-time monitoring and lead to improvements in implant function. Sensor integration has been mostly applied to cardiovascular, neural, and orthopedic implants, and advances in combined implant-sensor devices have been significant, yet there are needs still to be addressed. Sensor-integrating implants are still in their infancy; however, some have already made it to the clinic. With an interdisciplinary approach, these sensor-integrating devices will become more efficient, providing clear paths to clinical translation in the future.

Recent Advances in Cochlear Implant Electrode Array Design Parameters

Cochlear implants are neural implant devices that aim to restore hearing in patients with severe sensorineural hearing impairment. Here, the main goal is to successfully place the electrode array in the cochlea to stimulate the auditory nerves through bypassing damaged hair cells. Several electrode and electrode array parameters affect the success of this technique, but, undoubtedly, the most important one is related to electrodes, which are used for nerve stimulation. In this paper, we provide a comprehensive resource on the electrodes currently being used in cochlear implant devices. Electrode materials, shape, and the effect of spacing between electrodes on the stimulation, stiffness, and flexibility of electrode-carrying arrays are discussed. The use of sensors and the electrical, mechanical, and electrochemical properties of electrode arrays are examined. A large library of preferred electrodes is reviewed, and recent progress in electrode design parameters is analyzed. Finally, the limitations and challenges of the current technology are discussed along with a proposal of future directions in the field.

Real-Time Data-Driven Approach for Prediction and Correction of Electrode Array Trajectory in Cochlear Implantation

Cochlear implants provide hearing perception to people with severe to profound hearing loss. The electrode array (EA) inserted during the surgery directly stimulates the hearing nerve, bypassing the acoustic hearing system. The complications during the EA insertion in the inner ear may cause trauma leading to infection, residual hearing loss, and poor speech perception. This work aims to reduce the trauma induced during electrode array insertion process by carefully designing a sensing method, an actuation system, and data-driven control strategy to guide electrode array in scala tympani. Due to limited intra-operative feedback during the insertion process, complex bipolar electrical impedance is used as a sensing element to guide EA in real time. An automated actuation system with three degrees of freedom was used along with a complex impedance meter to record impedance of consecutive electrodes. Prediction of EA direction (medial, middle, and lateral) was carried out by an ensemble of random forest, shallow neural network, and k-nearest neighbour in an offline setting with an accuracy of 86.86%. The trained ensemble was then utilized in vitro for prediction and correction of EA direction in real time in the straight path with an accuracy of 80%. Such a real-time system also has application in other electrode implants and needle and catheter insertion guidance.

Characterization and Miniaturization of Silver-Nanoparticle Microcoil via Aerosol Jet Printing Techniques for Micromagnetic Cochlear Stimulation

According to the National Institute of Deafness and other Communication Disorders 2012 report, the number of cochlear implant (CI) users is steadily increasing from 324,000 CI users worldwide. The cochlea, located in the inner ear, is a snail-like structure that exhibits a tonotopic geometry where acoustic waves are filtered spatially according to frequency. Throughout the cochlea, there exist hair cells that transduce sensed acoustic waves into an electrical signal that is carried by the auditory nerve to ultimately reach the auditory cortex of the brain. A cochlear implant bridges the gap if non-functional hair cells are present. Conventional CIs directly inject an electrical current into surrounding tissue via an implanted electrode array and exploit the frequency-to-place mapping of the cochlea. However, the current is dispersed in perilymph, a conductive bodily fluid within the cochlea, causing a spread of excitation. Magnetic fields are more impervious to the effects of the cochlear environment due to the material properties of perilymph and surrounding tissue, demonstrating potential to improve precision. As an alternative to conventional CI electrodes, the development and miniaturization of microcoils intended for micromagnetic stimulation of intracochlear neural elements is described. As a step toward realizing a microcoil array sized for cochlear implantation, human-sized coils were prototyped via aerosol jet printing. The batch reproducible aerosol jet printed microcoils have a diameter of 1800 μm, trace width and trace spacing of 112.5 μm, 12 μm thickness, and inductance values of approximately 15.5 nH. Modelling results indicate that the coils have a combined depolarization–hyperpolarization region that spans 1.5 mm and produce a more restrictive spread of activation when compared with conventional CI.

Design, Fabrication, and Evaluation of a Parylene Thin-Film Electrode Array for Cochlear Implants

OBJECTIVE

To improve the existing manually assembled cochlear implant electrode arrays, a thin-film electrode array (TFEA) was microfabricated having a maximum electrode density of 15 sites along an 8-mm length, with each site having a 75 μm × 1.8 μm (diameter × height) disk electrode.

METHODS

The microfabrication method adopted photoresist transferring, lift-off, two-step oxygen plasma etching, and fuming nitric acid release to reduce lift-off complexity, protect the metal layer, and increase the release efficiency.

RESULTS

Systematic in vitro characterization showed that the TFEA's bending stiffness was 6.40 × 10-10 N·m2 near the base and 1.26 × 10-10 N·m2 near the apex. The TFEA electrode produced an average impedance of 16 kΩ and a maximum current limit of 800 μA, measured with 1-kHz sinusoidal current using monopolar stimulation in saline. A TFEA prototype was implanted in a cat cochlea to obtain in vivo measurements of electrically evoked auditory brainstem and inferior colliculus responses to monopolar stimulation with 41-μs/phase biphasic pulses. Both physiological responses produced a threshold of ∼300 μA and a dynamic range of 5-8 dB above the threshold. Compared with existing arrays, the present TFEA had 104 times less bending stiffness, 97% less electrode area, and comparable physiological thresholds.

CONCLUSION

Using a simplified structure and stable fabrication method, the present TEFA produced physical and physiological performance comparable to existing commercial devices.

SIGNIFICANCE

The present TFEA represents a step closer toward an automated process replacing the labor-intensive and expensive manual assembly of the cochlear implant electrode arrays.

Optimization of cochlear implant stimulation resolution using an intracochlear electric potential model

Designing an electrode array with a high stimulation resolution (SR) is the main challenge in cochlear implant development. In this work, a thin-film electrode array (TFEA) and partial tripolar (pTP) mode were combined in the design stage to optimize the SR. A finite-element model of the intracochlear electric potential V_e incorporating a TFEA and pTP mode was built and validated using previous experimental measurements. Based on this model, the SR was analyzed by using a defined stimulation factor V_s, which takes both the amplitude and bandwidth of V_e into account. A co-simulation method integrating the model and genetic algorithm was employed to maximize V_s with an optimized parameter set including the electrode diameter d, electrode interval g, and compensation coefficient σ. The results indicated that a TFEA combined with pTP mode outperforms their individual utilization to improve the SR and that d has an independent negative correlation with the SR, but it is more effective and feasible to consider all three parameters in the design stage with the proposed model and co-simulation optimization method. In our design, the optimized parameters were d = 150 μm, g = 200.5 μm, and σ = 0.746.

Materials for microfabricated implantable devices: a review

The application of microfabrication to the development of biomedical implants has produced a new generation of miniaturized technology for assisting treatment and research. Microfabricated implantable devices (μID) are an increasingly important tool, and the development of new μIDs is a rapidly growing field that requires new microtechnologies able to safely and accurately function in vivo. Here, we present a review of μID research that examines the critical role of material choice in design and fabrication. Materials commonly used for μID production are identified and presented along with their relevant physical properties and a survey of the state-of-the-art in μID development. The consequence of material choice as it pertains to microfabrication and biocompatibility is discussed in detail with a particular focus on the divide between hard, rigid materials and soft, pliable polymers.

Thin-film micro-electrode stimulation of the cochlea in rats exposed to aminoglycoside induced hearing loss

The multi-channel cochlear implant (CI) provides sound and speech perception to thousands of individuals who would otherwise be deaf. Broad activation of auditory nerve fibres when using a CI results in poor frequency discrimination. The CI also provides users with poor amplitude perception due to elicitation of a narrow dynamic range. Provision of more discrete frequency perception and a greater control over amplitude may allow users to better distinguish speech in noise and to segregate sound sources. In this research, thin-film (TF) high density micro-electrode arrays and conventional platinum ring electrode arrays were used to stimulate the cochlea of rats administered sensorineural hearing loss (SNHL) via ototoxic insult, with neural responses taken at 434 multiunit clusters in the central nucleus of the inferior colliculus (CIC). Threshold, dynamic range and broadness of response were used to compare electrode arrays. A stronger current was required to elicit CIC threshold when using the TF array compared to the platinum ring electrode array. TF stimulation also elicited a narrower dynamic range than the PR counterpart. However, monopolar stimulation using the TF array produced more localised CIC responses than other stimulation strategies. These results suggest that individuals with SNHL could benefit from micro stimulation of the cochlea using a monopolar configuration which may provide discrete frequency perception when using TF electrode arrays.

A polymer-based multichannel cochlear electrode array

OBJECTIVE

Compared with conventional cochlear electrode arrays, which are hand assembled and wire-based, polymer-based implants have several advantages. They are very precise, and their fabrication is inexpensive because of the use of thin-film processes. In the present study, a cochlear electrode array based on a high-performance liquid crystal polymer material is devised. Furthermore, the device is encapsulated in silicone elastomer.

METHODS

The fabrication steps introduced here include thin-film processes with liquid crystal polymer (LCP) films and customized self-aligning molding processes for the electrode array. To assess the feasibility of the proposed electrode array, the charge storage capacitance and impedance were measured using a potentiostat. Vertical and horizontal deflection forces were measured using a customized fixture and a force sensor. Insertion and extraction forces were also measured using a transparent human cochlear plastic model, and five cases involving human temporal insertion trials were undertaken to assess the level of safety during the insertion process.

RESULTS

The charge storage capacity and impedance at 1 kHz were 33.26 mC/cm and 1.02 kΩ, respectively. Likewise, the vertical force and horizontal force of the electrode array were 3.15 g and 1.07 g. The insertion force into a transparent plastic cochlear model with displacement of 8 mm from a round window was 8.2 mN, and the maximum extraction force was 110.4 mN. Two cases of human temporal bone insertion showed no observable trauma, whereas 3 cases showed a rupture of the basilar membrane.

CONCLUSION

An LCP-based intracochlear electrode array was fabricated, and its electrical and mechanical properties were found to be suitable for clinical use.

Highly Flexible Silicone Coated Neural Array for Intracochlear Electrical Stimulation

We present an effective method for tailoring the flexibility of a commercial thin-film polymer electrode array for intracochlear electrical stimulation. Using a pneumatically driven dispensing system, an average 232 ± 64 μm (mean ± SD) thickness layer of silicone adhesive coating was applied to stiffen the underside of polyimide multisite arrays. Additional silicone was applied to the tip to protect neural tissue during insertion and along the array to improve surgical handling. Each array supported 20 platinum sites (180 μm dia., 250 μm pitch), spanning nearly 28 mm in length and 400 μm in width. We report an average intracochlear stimulating current threshold of 170 ± 93 μA to evoke an auditory brainstem response in 7 acutely deafened felines. A total of 10 arrays were each inserted through a round window approach into the cochlea's basal turn of eight felines with one delamination occurring upon insertion (preliminary results of the in vivo data presented at the 48th Annual Meeting American Neurotology Society, Orlando, FL, April 2013, and reported in Van Beek-King 2014). Using microcomputed tomography imaging (50 μm resolution), distances ranging from 100 to 565 μm from the cochlea's central modiolus were measured. Our method combines the utility of readily available commercial devices with a straightforward postprocessing step on the order of 24 hours.

Considering optogenetic stimulation for cochlear implants

Electrical cochlear implants are by far the most successful neuroprostheses and have been implanted in over 300,000 people worldwide. Cochlear implants enable open speech comprehension in most patients but are limited in providing music appreciation and speech understanding in noisy environments. This is generally considered to be due to low frequency resolution as a consequence of wide current spread from stimulation contacts. Accordingly, the number of independently usable stimulation channels is limited to less than a dozen. As light can be conveniently focused, optical stimulation might provide an alternative approach to cochlear implants with increased number of independent stimulation channels. Here, we focus on summarizing recent work on optogenetic stimulation as one way to develop optical cochlear implants. We conclude that proof of principle has been presented for optogenetic stimulation of the cochlea and central auditory neurons in rodents as well as for the technical realization of flexible μLED-based multichannel cochlear implants. Still, much remains to be done in order to advance the technique for auditory research and even more for eventual clinical translation. This article is part of a Special Issue entitled <Lasker Award>.

Feasibility of Energy-Autonomous Wireless Microsensors for Biomedical Applications: Powering and Communication

In this review, biomedical-related wireless miniature devices such as implantable medical devices, neural prostheses, embedded neural systems, and body area network systems are investigated and categorized. The two main subsystems of such designs, the RF subsystem and the energy source subsystem, are studied in detail. Different application classes are considered separately, focusing on their specific data rate and size characteristics. Also, the energy consumption of state-of-the-art communication practices is compared to the energy that can be generated by current energy scavenging devices, highlighting gaps and opportunities. The RF subsystem is classified, and the suitable architecture for each category of applications is highlighted. Finally, a new figure of merit suitable for wireless biomedical applications is introduced to measure the performance of these devices and assist the designer in selecting the proper system for the required application. This figure of merit can effectively fill the gap of a much required method for comparing different techniques in simulation stage before a final design is chosen for implementation.

Silicone-coated thin film array cochlear implantation in a feline model

OBJECTIVES

Some limitations of cochlear implants can be attributed to a restricted spectral representation of sound provided by contemporary electrode arrays. Microfabricated high-density thin film array (TFA) technology enables a greater density of stimulating sites and, thus, a more complete spectral representation. Previous pilot cadaveric studies have documented insertion characteristics, although not electrical characteristics.

STUDY DESIGN

Electrode evoked auditory brainstem response (ABR) testing in a feline model.

METHODS

Six healthy, normal hearing cats were unilaterally deafened and implanted with a silicone coated TFA, measuring 27.8 × 0.4 × 80μm (L × W × H). Monopolar stimulation of single electrodes was used to evoke a triple peaked ABR. Thresholds to evoke a minimal ABR were determined.

RESULTS

All 6 cats underwent successful full insertion and activation. Thresholds to evoke minimal ABR's varied among implants ranging from 75 to 450 μA. Over the basal portion of the array, thresholds were either larger or unable to evoke an ABR.

CONCLUSION

Two-thirds of the implants showed ABR's along the entire array, whereas the others evoked ABR's at the apical end and less robustly more basally. This may reflect increased distance of the electrodes from the modiolus, as the basal half of the array is narrower relative to the width of the scala. A tapered design to ensure array distance to modiolus is minimized may enable the basal half of the arrays to stimulate more consistently.

Low-power sensing for vestibular prostheses

This paper describes a novel sensing approach for reducing power requirements of implantable vestibular prostheses. A passive, microfabricated polymeric inertial sensor for detecting angular head rotations based on the biomechanics of the human semicircular canal is described. Angular head motion is coded by deflection of a highly compliant capacitor plate placed in parallel with a rigid reference electrode. This capacitance change serves to detect instantaneous angular velocity along a given axis of rotation. Designed for integration with a microelectromechanical systems-based fully implantable vestibular prosthesis, this sensing method can provide substantial power savings when compared with contemporary gyroscopes.

Midbrain responses to micro-stimulation of the cochlea using high density thin-film arrays

A broader activation of auditory nerve fibres than normal using a cochlear implant contributes to poor frequency discrimination. As cochlear implants also deliver a restricted dynamic range, this hinders the ability to segregate sound sources. Better frequency coding and control over amplitude may be achieved by limiting current spread during electrical stimulation of the cochlea and positioning electrodes closer to the modiolus. Thin-film high density microelectrode arrays and conventional platinum ring electrode arrays were used to stimulate the cochlea of urethane-anaesthetized rats and responses compared. Neurophysiological recordings were taken at 197 multi-unit clusters in the central nucleus of the inferior colliculus (CIC), a site that receives direct monaural innervation from the cochlear nucleus. CIC responses to both the platinum ring and high density electrodes were recorded and differences in activity to changes in stimulation intensity, thresholds and frequency coding of neural activation were examined. The high density electrode array elicited less CIC activity at nonspecific frequency regions than the platinum ring electrode array. The high density electrode array produced significantly lower thresholds and larger dynamic ranges than the platinum ring electrode array when positioned close to the modiolus. These results suggest that a higher density of stimulation sites on electrodes that effectively 'aim' current, combined with placement closer to the modiolus would permit finer control over charge delivery. This may equate to improved frequency specific perception and control over amplitude when using future cochlear implant devices.

Cochlear infrastructure for electrical hearing

Although the cochlear implant is already the world's most successful neural prosthesis, opportunities for further improvement abound. Promising areas of current research include work on improving the biological infrastructure in the implanted cochlea to optimize reception of cochlear implant stimulation and on designing the pattern of electrical stimulation to take maximal advantage of conditions in the implanted cochlea. In this review we summarize what is currently known about conditions in the cochlea of deaf, implanted humans and then review recent work from our animal laboratory investigating the effects of preserving or reinnervating tissues on psychophysical and electrophysiological measures of implant function. Additionally we review work from our human laboratory on optimizing the pattern of electrical stimulation to better utilize strengths in the cochlear infrastructure. Histological studies of human temporal bones from implant users and from people who would have been candidates for implants show a range of pathologic conditions including spiral ganglion cell counts ranging from approximately 2% to 92% of normal and partial hair cell survival in some cases. To duplicate these conditions in a guinea pig model, we use a variety of deafening and implantation procedures as well as post-deafening therapies designed to protect neurons and/or regenerate neurites. Across populations of human patients, relationships between nerve survival and functional measures such as speech have been difficult to demonstrate, possibly due to the numerous subject variables that can affect implant function and the elapsed time between functional measures and postmortem histology. However, psychophysical studies across stimulation sites within individual human subjects suggest that biological conditions near the implanted electrodes contribute significantly to implant function, and this is supported by studies in animal models comparing histological findings to psychophysical and electrophysiological data. Results of these studies support the efforts to improve the biological infrastructure in the implanted ear and guide strategies which optimize stimulation patterns to match patient-specific conditions in the cochlea.

Cochlear implantation using thin-film array electrodes

OBJECTIVE

Current limitations in language perception may stem from an inability to provide high-resolution sound input. Thin-film array technology allows for a greater density of stimulating sites within the limited diameter of the scala tympani. This study examines the use of a flexible carrier to achieve adequate depth of insertion.

STUDY DESIGN

A prospective human cadaveric temporal bone insertion analysis.

SETTING

Academic otolaryngology department and school of electrical and computer engineering collaboration.

METHODS

A prototype thin-film array electrode coupled with an insertion test device (ITD) was manufactured and inserted into 10 human cadaveric temporal bones. As controls, 2 additional temporal bones were implanted with the ITD only and 2 were unimplanted. Radiologic and histologic data were collected.

RESULTS

Ten thin-film array electrodes were successfully implanted into 10 individual temporal bones via round window (5) and cochleostomy (5) approaches. Seventeen millimeters of insertion was noted for each device, with an average angular insertion depth of 292° by radiographic measurements and 392° by histologic sectioning. Electrode distance to the modiolus averaged 0.88 mm by computed tomography and 0.67 mm by histologic measurements. Average percentage trauma was 26% for the ITD-backed arrays compared with 15% and 29% for ITD only and unimplanted temporal bones, respectively.

CONCLUSION

Thin-film array electrodes coupled with an ITD were successfully inserted into the human cochlea with limited trauma. With continued development and testing of this electrode design, the thin-film array may improve the language perception achieved through cochlear implantation.

From cleanroom to desktop: emerging micro-nanofabrication technology for biomedical applications

This review is motivated by the growing demand for low-cost, easy-to-use, compact-size yet powerful micro-nanofabrication technology to address emerging challenges of fundamental biology and translational medicine in regular laboratory settings. Recent advancements in the field benefit considerably from rapidly expanding material selections, ranging from inorganics to organics and from nanoparticles to self-assembled molecules. Meanwhile a great number of novel methodologies, employing off-the-shelf consumer electronics, intriguing interfacial phenomena, bottom-up self-assembly principles, etc., have been implemented to transit micro-nanofabrication from a cleanroom environment to a desktop setup. Furthermore, the latest application of micro-nanofabrication to emerging biomedical research will be presented in detail, which includes point-of-care diagnostics, on-chip cell culture as well as bio-manipulation. While significant progresses have been made in the rapidly growing field, both apparent and unrevealed roadblocks will need to be addressed in the future. We conclude this review by offering our perspectives on the current technical challenges and future research opportunities.

Current steering and current focusing with a high-density intracochlear electrode array

Creating high-resolution or high-density, intra-cochlear electrode arrays may significantly improve quality of hearing for cochlear implant recipients. Through focused activation of neural populations such arrays may better exploit the cochlea's frequency-to-place mapping, thereby improving sound perception. Contemporary electrode arrays approach high-density stimulation by employing multi-polar stimulation techniques such as current steering and current focusing. In our procedure we compared an advanced high-density array with contemporary arrays employing these strategies. We examined focused stimulation of auditory neurons using an activating function and a neural firing probability model that together enable a first-order estimation of an auditory nerve fiber's response to electrical stimulation. The results revealed that simple monopolar stimulation with a high-density array is more localized than current steering with a contemporary array and requires 25-30% less current. Current focusing with high-density electrodes is more localized than current focusing with a contemporary array; however, a greater amount of current is required. This work illustrates that advanced high-density electrode arrays may provide a low-power, high-resolution alternative to current steering with contemporary cochlear arrays.

Translational nanomedicine: status assessment and opportunities

Nano-enabled technologies hold great promise for medicine and health. The rapid progress by the physical sciences/engineering communities in synthesizing nanostructures and characterizing their properties must be rapidly exploited in medicine and health toward reducing mortality rate, morbidity an illness imposes on a patient, disease prevalence, and general societal burden. A National Science Foundation-funded workshop, "Re-Engineering Basic and Clinical Research to Catalyze Translational Nanoscience," was held 16-19 March 2008 at the University of Southern California. Based on that workshop and literature review, this article briefly explores scientific, economic, and societal drivers for nanomedicine initiatives; examines the science, engineering, and medical research needs; succinctly reviews the US federal investment directly germane to medicine and health, with brief mention of the European Union (EU) effort; and presents recommendations to accelerate the translation of nano-enabled technologies from laboratory discovery into clinical practice.

FROM THE CLINICAL EDITOR

An excellent review paper based on the NSF funded workshop "Re-Engineering Basic and Clinical Research to Catalyze Translational Nanoscience" (16-19 March 2008) and extensive literature search, this paper briefly explores the current state and future perspectives of nanomedicine.

Cochlear implants: a remarkable past and a brilliant future

The aims of this paper are to (i) provide a brief history of cochlear implants; (ii) present a status report on the current state of implant engineering and the levels of speech understanding enabled by that engineering; (iii) describe limitations of current signal processing strategies; and (iv) suggest new directions for research. With current technology the "average" implant patient, when listening to predictable conversations in quiet, is able to communicate with relative ease. However, in an environment typical of a workplace the average patient has a great deal of difficulty. Patients who are "above average" in terms of speech understanding, can achieve 100% correct scores on the most difficult tests of speech understanding in quiet but also have significant difficulty when signals are presented in noise. The major factors in these outcomes appear to be (i) a loss of low-frequency, fine structure information possibly due to the envelope extraction algorithms common to cochlear implant signal processing; (ii) a limitation in the number of effective channels of stimulation due to overlap in electric fields from electrodes; and (iii) central processing deficits, especially for patients with poor speech understanding. Two recent developments, bilateral implants and combined electric and acoustic stimulation, have promise to remediate some of the difficulties experienced by patients in noise and to reinstate low-frequency fine structure information. If other possibilities are realized, e.g., electrodes that emit drugs to inhibit cell death following trauma and to induce the growth of neurites toward electrodes, then the future is very bright indeed.

Penetrating multichannel stimulation and recording electrodes in auditory prosthesis research

Microelectrode arrays offer the auditory systems physiologists many opportunities through a number of electrode technologies. In particular, silicon substrate electrode arrays offer a large design space including choice of layout plan, range of surface areas for active sites, a choice of site materials and high spatial resolution. Further, most designs can double as recording and stimulation electrodes in the same preparation. Scala tympani auditory prosthesis research has been aided by mapping electrodes in the cortex and the inferior colliculus to assess the CNS responses to peripheral stimulation. More recently silicon stimulation electrodes placed in the auditory nerve, cochlear nucleus and the inferior colliculus have advanced the exploration of alternative stimulation sites for auditory prostheses. Multiplication of results from experimental effort by simultaneously stimulating several locations, or by acquiring several streams of data synchronized to the same stimulation event, is a commonly sought after advantage. Examples of inherently multichannel functions which are not possible with single electrode sites include (1) current steering resulting in more focused stimulation, (2) improved signal-to-noise ratio (SNR) for recording when noise and/or neural signals appear on more than one site and (3) current source density (CSD) measurements. Still more powerful are methods that exploit closely-spaced recording and stimulation sites to improve detailed interrogation of the surrounding neural domain. Here, we discuss thin-film recording/stimulation arrays on silicon substrates. These electrode arrays have been shown to be valuable because of their precision coupled with reproducibility in an ever expanding design space. The shape of the electrode substrate can be customized to accommodate use in cortical, deep and peripheral neural structures while flexible cables, fluid delivery and novel coatings have been added to broaden their application. The use of iridium oxide as the neural interface site material has increased the efficiency of charge transfer for stimulation and lowered impedance for recording electrodes.