Percutaneous Connector Research Articles

Magnetically coupled percutaneous connector for chronic electrical peripheral nerve stimulation and recording in awake rats.

Here we aimed to develop and validate a chronic magnetic percutaneous connector designed for placement on the dorsal-lumbar aspect of the spine of awake, freely moving rats. A pedestal and external connector was developed, bench tested to assess for continuity, durability and disconnection forces, and validated in awake rats chronically implanted with an abdominal vagus nerve electrode array. The implanted pedestal and external connector were designed with custom PCBs, spring-loaded pins, magnets and biocompatible 3D printed housing. The magnetic coupling mechanism allowed disconnection with minimal force, was highly reliable in maintaining electrical connection in awake rats and allowed recording of electrically evoked compound action potentials after chronic implantation. In conclusion, this percutaneous connector is a useful research tool for peripheral nerve stimulation studies. The connector described will allow investigation into the safety and efficacy of emerging neuromodulation therapies for the treatment of disease.

EEG-based diagnostics of the auditory system using cochlear implant electrodes as sensors

The cochlear implant is one of the most successful medical prostheses, allowing deaf and severely hearing-impaired persons to hear again by electrically stimulating the auditory nerve. A trained audiologist adjusts the stimulation settings for good speech understanding, known as “fitting” the implant. This process is based on subjective feedback from the user, making it time-consuming and challenging, especially in paediatric or communication-impaired populations. Furthermore, fittings only happen during infrequent sessions at a clinic, and therefore cannot take into account variable factors that affect the user’s hearing, such as physiological changes and different listening environments. Objective audiometry, in which brain responses evoked by auditory stimulation are collected and analysed, removes the need for active patient participation. However, recording of brain responses still requires expensive equipment that is cumbersome to use. An elegant solution is to record the neural signals using the implant itself. We demonstrate for the first time the recording of continuous electroencephalographic (EEG) signals from the implanted intracochlear electrode array in human subjects, using auditory evoked potentials originating from different brain regions. This was done using a temporary recording set-up with a percutaneous connector used for research purposes. Furthermore, we show that the response morphologies and amplitudes depend crucially on the recording electrode configuration. The integration of an EEG system into cochlear implants paves the way towards chronic neuro-monitoring of hearing-impaired patients in their everyday environment, and neuro-steered hearing prostheses, which can autonomously adjust their output based on neural feedback.

Perceptual interactions between electrodes using focused and monopolar cochlear stimulation.

In today's cochlear implant (CI) systems, the monopolar (MP) electrode configuration is the most commonly used stimulation mode, requiring only a single current source. However, with an implant that will allow simultaneous activation of multiple independent current sources, it is possible to implement an all-polar (AP) stimulation mode designed to create a focused electrical field. The goal of this experiment was to study the potential benefits of this all-polar mode for reducing uncontrolled electrode interactions compared with the monopolar mode. The five participants who took part in the study were implanted with a research device that was connected via a percutaneous connector to a benchtop stimulator providing 22 independent current sources. The perceptual effects of the AP mode were tested in three experiments. In Experiment 1, the current level difference between loudness-matched sequential and simultaneous stimuli composed of 2 spatially separated pulse trains was measured as function of the electrode separation. Results indicated a strong current-summation interaction for simultaneous stimuli in the MP mode for separations up to at least 4.8 mm. No significant interaction was found in the AP mode beyond a separation of 2.4 mm. In Experiment 2, a forward-masking paradigm was used with fixed equally loud probes in AP and MP modes, and AP maskers presented on different electrode positions. Results indicated a similar spatial masking pattern between modes. In Experiment 3, subjects were asked to discriminate between across-electrode temporal delays. It was hypothesized that discrimination would decrease with electrode separation faster in AP compared to MP modes. However, results showed no difference between the two modes. Overall, the results indicated that the AP mode produced less current spread than MP mode but did not lead to a significant advantage in terms of spread of neuronal excitation at equally loud levels.

Chronic, percutaneous connector for electrical recording and stimulation with microelectrode arrays.

The translation of advances in neural stimulation and recording research into clinical practice hinges on the ability to perform chronic experiments in awake and behaving animal models. Advances in microelectrode array technology, most notably flexible polymer arrays, have significantly improved reliability of the neural interface. However, electrical connector technology has lagged and is prone to failure from non-biocompatibility, large size, contamination, corrosion, and difficulty of use. We present a novel chronic, percutaneous electrical connector system that is suitable for neural stimulation and recording. This system features biocompatible materials, low connect and disconnect forces, passive alignment, and a protective cap during non-use. We have successfully designed, assembled, and tested in vitro both a 16-channel system and a high density 64-channel system. Custom, polyimide, 16-channel, microelectrode arrays were electrically assembled with the connector system and tested using cyclic voltammetry and electrochemical impedance spectroscopy. This connector system is versatile and can be used with a variety of microelectrode array technologies for chronic studies.

Batteries Not Included: A Mat-Based Wireless Power Transfer System for Implantable Medical Devices As a Moving Target

Implantable devices have become increasingly popular in modern medicine. These devices have a wide range of applications, such as health monitoring, disease prevention, delivery of a therapeutic regimen, and biomimetic prosthesis. For example, electrical stimulation of nerve tissue and recording of neural electrical activity are the basis of emerging prostheses and treatments for spinal cord injury, stroke, sensory deficits, and neurological disorders [1]-[5]. Being able to record neural activity from awake animals with observable behavior has greatly advanced our understanding of the neural mechanisms that mediate behavior. Conventional microelectrode recording techniques typically require a percutaneous connector, which is associated with infection risks. Generally, in order to obtain stable recordings, animals must be trained to accept some degree of restraint (e.g., head fixation). Not only is the mobility of the animal subject limited, but the results obtained under such restricted conditions may not reflect the full repertoire of brain activity that occurs during natural behaviors [2]. This issue can be addressed with implantable electronics to record neural activity and wirelessly transmit this data through the skin to an external device. A wireless technique is then required to transmit both data and power, connecting the external system and the implanted devices.

A Three-Dimensional 64-Site Folded Electrode Array Using Planar Fabrication

Neuroscience and neuroprosthetic devices are increasingly in need of more compact less invasive 3-D electrode arrays for interfacing with neural tissue. To meet these needs, a folding 64-site 3-D array architecture has been developed. The microstructure, in which four probes and two platforms are fabricated as a single planar unit, results in a low-profile <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(&lt; 350\hbox{-}\mu\hbox{m})$</tex></formula> narrow-platform (0.604- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{mm}^{2}$</tex></formula> silicon footprint) implant for cortical use. Signals are routed from 177- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}^{2}$</tex></formula> iridium sites through polysilicon lines to the probe back end and then across 4- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$ \mu\hbox{m}$</tex></formula> -thick parylene-encased electroplated-gold folding lead transfers to the associated platform. Three levels of interconnect with a 10- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula> minimum pitch are utilized for the 32 leads that traverse the platforms. After rapid microassembly, micromachined latches are used to fasten the folded device. Two flexible parylene cables with gold leads at a 20- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula> pitch are monolithically integrated with the probes to minimize tethering and avoid any need for lead bonding within the array, and these cables carry the neural signals to a remote circuit module or percutaneous connector. With thin <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(\sim\! \! 15\hbox{-}\mu\hbox{m})$</tex></formula> boron-doped shanks at a <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\sim\!\! 200 \hbox{-}\mu\hbox{m}$</tex></formula> pitch, the array displaces only 1.7% of the 0.64- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\hbox{mm}^{2}$</tex></formula> instrumented tissue area, assuming a 100- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$ \mu\hbox{m}$</tex></formula> recording range. Neural signals were recorded in vivo from the guinea pig auditory cortex. <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hfill$</tex></formula> [2010-0200]

High channel-count neural interfaces for multiple degree- of-freedom neuroprosthetics

We have designed, fabricated, and tested an advanced neural interface based on the Utah Electrode Array (UEA) integrated with a custom ASIC that is currently able to acquire 200 channels of neural recordings. The Active Arrays are designed to acquire more neural data with the goal of controlling advanced prosthetic devices with as many as 17 degrees of freedom (DoF). The system is comprised of two modified UEAs, a custom ASIC, SMD capacitors, a Neu- roport™ (Blackrock Microsystems) percutaneous connector, 44 wires, and encapsulation materials. A photograph of the final device is presented in Fig. 1. The device has been tested in-vitro through soak testing in 0.15M PBS with synthetic neural signals applied to measure lifetime and recording fidelity. In-vivo measurements were collected using non-human primate (NHP) models.

Design of a Semi-Implantable Hearing Device for Direct Acoustic Cochlear Stimulation

A new hearing therapy based on direct acoustic cochlear stimulation was developed for the treatment of severe to profound mixed hearing loss. The device efficacy was validated in an initial clinical trial with four patients. This semi-implantable investigational device consists of an externally worn audio processor, a percutaneous connector, and an implantable microactuator. The actuator is placed in the mastoid bone, right behind the external auditory canal. It generates vibrations that are directly coupled to the inner ear fluids and that, therefore, bypass the external and the middle ear. The system is able to provide an equivalent sound pressure level of 125 dB over the frequency range between 125 and 8000Hz. The hermetically sealed actuator is designed to provide maximal output power by keeping its dimensions small enough to enable implantation. A network model is used to simulate the dynamic characteristics of the actuator to adjust its transfer function to the characteristics of the middle ear. The geometry of the different actuator components is optimized using finite-element modeling.

Chronic intracortical microstimulation (ICMS) of cat sensory cortex using the Utah Intracortical Electrode Array.

In an effort to assess the safety and efficacy of focal intracortical microstimulation (ICMS) of cerebral cortex with an array of penetrating electrodes as might be applied to a neuroprosthetic device to aid the deaf or blind, we have chronically implanted three trained cats in primary auditory cortex with the 100-electrode Utah Intracortical Electrode Array (UIEA). Eleven of the 100 electrodes were hard-wired to a percutaneous connector for chronic access. Prior to implant, cats were trained to "lever-press" in response to pure tone auditory stimulation. After implant, this behavior was transferred to "lever-presses" in response to current injections via single electrodes of the implanted arrays. Psychometric function curves relating injected charge level to the probability of response were obtained for stimulation of 22 separate electrodes in the three implanted cats. The average threshold charge/phase required for electrical stimulus detection in each cat was, 8.5, 8.6, and 11.6 nC/phase respectively, with a maximum charge/phase of 26 nC/phase and a minimum of 1.5 nC/phase thresholds were tracked for varying time intervals, and seven electrodes from two cats were tracked for up to 100 days. Electrodes were stimulated for no more than a few minutes each day. Neural recordings taken from the same electrodes before and after multiple electrical stimulation sessions were very similar in signal/noise ratio and in the number of recordable units, suggesting that the range of electrical stimulation levels used did not damage neurons in the vicinity of the electrodes. Although a few early implants failed, we conclude that ICMS of cerebral cortex to evoke a behavioral response can be achieved with the penetrating UIEA. Further experiments in support of a sensory cortical prosthesis based on ICMS are warranted.

Chronic recording capability of the Utah Intracortical Electrode Array in cat sensory cortex

The Utah Intracortical Electrode Array (UIEA) is an array of 100 penetrating silicon microelectrodes designed to focally electrically stimulate or record neurons residing in a single layer up to 1.5 mm beneath the surface of the cerebral cortex. Apart from its use as a unique tool to study parallel processing in the central nervous system, this array could form the platform for a cortical neuroprosthetic system. Although the UIEA has been used extensively in acute neural recording and stimulation experiments, its long-term performance in a chronic application has yet to be demonstrated. As an initial investigation into the feasibility of long-term cortical recording with an array of microelectrodes, we have hard-wired a subset of 11 electrodes of the UIEA to a percutaneous connector. This chronic UIEA assembly was then implanted into the cerebral cortices of ten cats for durations ranging from 2 to 13 months; over which time, both random and stimulus-evoked single and multiple unit action potentials were periodically recorded. On average, after a 6-month implant period, 60% of implanted arrays could still record some type of activity. Post-sacrifice dissections revealed a fibrous encapsulation of the UIEA. Although most implanted cortex was histologically normal, evidence of a chronic astroglial response was seen in a few cases. The results of the reported experiments indicate that the UIEA can be successfully used for limited times in a chronic recording application.

Design for an inexpensive but effective cochlear implant

Widespread application of cochlear implants is limited by cost, especially in developing countries. In this article we present a design for a low-cost but effective cochlear implant system. The system includes a speech processor, four pairs of transmitting and receiving coils, and an electrode array with four monopolar electrodes. All implanted components are passive, reducing to a minimum the complexity of manufacture and allowing high reliability. A four-channel continuous interleaved sampling strategy is used for the speech processor. The processor and transmission link have been evaluated in tests with a subject previously implanted with the Ineraid electrode array and percutaneous connector. A prototype of the link, consisting of four pairs of transmitting and external receiving coils, was used, with the outputs of the receiving coils directed to four intracochlear electrodes through the percutaneous connector. The subject achieved speech reception scores with the prototype system that were equivalent to those achieved with a standard laboratory implementation of a continuous interleaved sampling processor with current-controlled stimuli.

A Bone-Anchored Percutaneous Connector System for Neural Prosthetic Applications

A percutaneous connector system has been developed for use in neural prosthetic applications. It is based on a skin-penetrating, bone-anchored titanium pedestal, housing an II-channel electrode array. Initial applications for the system are in audiology and as such, the proposed fixture site is in the temporal bone. The titanium pedestal is based on existing design features of the EPI Bioglass implant, developed by University College London (UCL), and the Brånemark System, employed by Nobel Biocare AB. The electrode array, consisting of platinum wires in a silicone carrier, can be custom designed to suit the application. The design features of the connector system are reviewed. Animal studies have been used to assess soft tissue reactions and the osseointegration of the pedestal. The histological data are presented. The pedestal, electrode array and the mating external connector are currently undergoing mechanical and electrical testing. The percutaneous connector system will undergo clinical trials, initially in the study of tinnitus (employing stimulation via an extracochlear electrode), and as part of a cochlear implant system (using a multichannel intracochlear electrode array and digital signal processing techniques.

Silicon ribbon cables for chronically implantable microelectrode arrays.

This paper describes the design, fabrication, and testing of miniature ultraflexible ribbon cables for use with micromachined silicon microprobes capable of chronic recording and/or stimulation in the central nervous system (CNS). These interconnects are of critical importance in reliably linking these microelectrodes to the external world through a percutaneous connector. The silicon cables allow the realization of multilead, multistrand shielded local interconnects that are extremely flexible and yet strong enough to withstand normal handling and surgical manipulation. Cables 5 microns thick, 1-5 cm long, and from 60 to 250 microns wide have been fabricated with up to eight leads. The series lead resistance is typically 4 k omega/cm for polysilicon and 500 omega/cm for tantalum, with shunt capacitance values of 5-10 pF/cm and an interlead capacitance below 10 fF/cm. Soak tests in buffered saline performed under electrical and mechanical stress have been underway for over three years and show subpicoampere leakage levels. Silicon microprobes with built-in ribbon cables have remained functional for up to one year in the guinea pig CNS, recording driven single-unit activity and maintaining impedance levels in the 1-7 M omega range.

Chronic skull-anchored percutaneous implants in non-human primates

Three groups of chronic, skull-anchored, percutaneous implants differing in materials, design and surgical procedures used for implantation, were tested in macaque monkeys in conjunction with studies of an inner ear stimulation device. Implants from the first two groups in which high-speed drilling methods and stainless steel materials were used, showed a high percentage of failures during the first 3 months after implantation of the percutaneous connector. Implants in the third group, in which measures were taken to preserve living bone tissue, all survived for greater than 7 months. Probable factors relating to implant survival are care of the bone during surgery, postsurgical mechanical trauma, materials and other details of the surgical procedure.

A speech processor with lateral inhibition for an eight channel cochlear implant and its evaluation.

A speech processor including the function of lateral inhibition was proposed to compensate for the wide current spread for an eight channel cochlear implant. Our cochlear implant system is composed of a speech processor, percutaneous connector and an eight channel electrode array made of Pt-Ir wires.

Auditory Prostheses Research with Multiple Channel Intracochlear Stimulation in Man

Although single-channel electrode arrays implanted in the scala tympani of deaf patients are useful as an aid to lip reading and for distinguishing some environmental sounds, they do not transmit intelligible speech. However, multichannel electrode arrays, which take advantage of the cochlea's tonotopic organization, may be capable of generating the complex patterns of neural activity necessary for speech discrimination. In this study, multichannel electrodes were implanted in the cochleas of four volunteers, with access to the connecting wires made through the skin via a percutaneous connector. The major portion of the data presented is from two of these subjects: one has been bilaterally deaf since birth and the other has been unilaterally deaf for 15 years. Preliminary results of experiments with two more recently implanted subjects are described as well as experiments with a fifth volunteer who was implanted with five electrodes by House in 1969. Data on pitch and loudness discrimination as well as the effects of stimulation parameters on threshold, impedance, and electrode interaction are presented. Place pitch and periodicity pitch were observed in all five volunteers. The results of pitch-matching experiments with the unilaterally deaf volunteer were consistent with tonotopic maps of the cochlea, and experiments indicated that a pitch continuum may be achieved by combining place and periodicity pitch modulation. Preliminary experiments in tune recognition with one subject demonstrate his ability to recognize simple melodies based on periodicity pitch cues. These results, coupled with the finding that subjective sensations remain stable over the long-term, support the feasibility of providing artificial hearing with a multichannel cochlear stimulation system.