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Thomas WM, Zuniga SA, Sondh I, Leber M, Solzbacher F, Lenarz T, Lim HH, Warren DJ, Rieth L, Adams ME. Development of a feline model for preclinical research of a new translabyrinthine auditory nerve implant. Front Neurosci 2024; 18:1308663. [PMID: 38379760 PMCID: PMC10877721 DOI: 10.3389/fnins.2024.1308663] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Accepted: 01/02/2024] [Indexed: 02/22/2024] Open
Abstract
Cochlear implants are among the most successful neural prosthetic devices to date but exhibit poor frequency selectivity and the inability to consistently activate apical (low frequency) spiral ganglion neurons. These issues can limit hearing performance in many cochlear implant patients, especially for understanding speech in noisy environments and in perceiving or appreciating more complex inputs such as music and multiple talkers. For cochlear implants, electrical current must pass through the bony wall of the cochlea, leading to widespread activation of auditory nerve fibers. Cochlear implants also cannot be implanted in some individuals with an obstruction or severe malformations of the cochlea. Alternatively, intraneural stimulation delivered via an auditory nerve implant could provide direct contact with neural fibers and thus reduce unwanted current spread. More confined current during stimulation can increase selectivity of frequency fiber activation. Furthermore, devices such as the Utah Slanted Electrode Array can provide access to the full cross section of the auditory nerve, including low frequency fibers that are difficult to reach using a cochlear implant. However, further scientific and preclinical research of these Utah Slanted Electrode Array devices is limited by the lack of a chronic large animal model for the auditory nerve implant, especially one that leverages an appropriate surgical approach relevant for human translation. This paper presents a newly developed transbullar translabyrinthine surgical approach for implanting the auditory nerve implant into the cat auditory nerve. In our first of a series of studies, we demonstrate a surgical approach in non-recovery experiments that enables implantation of the auditory nerve implant into the auditory nerve, without damaging the device and enabling effective activation of the auditory nerve fibers, as measured by electrode impedances and electrically evoked auditory brainstem responses. These positive results motivate performing future chronic cat studies to assess the long-term stability and function of these auditory nerve implant devices, as well as development of novel stimulation strategies that can be translated to human patients.
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Affiliation(s)
- W. Mitchel Thomas
- Department of Biomedical Engineering, University of Utah, Salt Lake City, UT, United States
| | - Steven A. Zuniga
- Department of Otolaryngology-Head and Neck Surgery, University of Minnesota, Minneapolis, MN, United States
| | - Inderbir Sondh
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, United States
| | - Moritz Leber
- Blackrock Neurotech, Salt Lake City, UT, United States
| | - Florian Solzbacher
- Blackrock Neurotech, Salt Lake City, UT, United States
- Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, UT, United States
| | - Thomas Lenarz
- Department of Otorhinolaryngology, Medical University of Hannover, Hannover, Germany
| | - Hubert H. Lim
- Department of Otolaryngology-Head and Neck Surgery, University of Minnesota, Minneapolis, MN, United States
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, United States
| | - David J. Warren
- Department of Biomedical Engineering, University of Utah, Salt Lake City, UT, United States
- Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, UT, United States
| | - Loren Rieth
- Department Mechanical and Aerospace Engineering, West Virginia University, Morgantown, WV, United States
| | - Meredith E. Adams
- Department of Otolaryngology-Head and Neck Surgery, University of Minnesota, Minneapolis, MN, United States
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Trout MA, Harrison AT, Brinton MR, George JA. A portable, programmable, multichannel stimulator with high compliance voltage for noninvasive neural stimulation of motor and sensory nerves in humans. Sci Rep 2023; 13:3469. [PMID: 36859464 PMCID: PMC9977866 DOI: 10.1038/s41598-023-30545-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2022] [Accepted: 02/24/2023] [Indexed: 03/03/2023] Open
Abstract
Most neural stimulators do not have a high enough compliance voltage to pass current through the skin. The few stimulators that meet the high compliance voltage necessary for transcutaneous stimulation are typically large benchtop units that are not portable, and the stimulation waveforms cannot be readily customized. To address this, we present the design and validation of a portable, programmable, multichannel, noninvasive neural stimulator that can generate three custom bipolar waveforms at ± 150 V with microsecond temporal resolution. The design is low-cost, open-source, and validated on the benchtop and with a healthy population to demonstrate its functionality for sensory and motor stimulation. Sensory stimulation included electrocutaneous stimulation targeting cutaneous mechanoreceptors at the surface of the skin and transcutaneous nerve stimulation targeting the median nerve at the wrist. Both electrocutaneous stimulation on the hand and transcutaneous stimulation at the wrist can elicit isolated tactile percepts on the hand but changes in pulse frequency are more discriminable for electrocutaneous stimulation. Also, neuromuscular electrical stimulation of the flexor digiti profundus is evoked by applying electrical stimulation directly above the muscle in the forearm and to the median and ulnar nerves in the upper arm. Muscle and nerve stimulation evoked similar grip forces and force rise times, but nerve stimulation had a significantly slower fatigue rate. The development and validation of this noninvasive stimulator and direct comparison of common sensory and motor stimulation targets in a human population constitute an important step towards more widespread use and accessibility of neural stimulation for education and research.
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Affiliation(s)
- Marshall A Trout
- Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, USA.
| | - Abigail T Harrison
- Department of Biomedical Engineering, University of Utah, Salt Lake City, USA
| | - Mark R Brinton
- Department of Engineering and Physics, Elizabethtown College, Elizabethtown, USA
| | - Jacob A George
- Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, USA.
- Department of Biomedical Engineering, University of Utah, Salt Lake City, USA.
- Department of Physical Medicine and Rehabilitation, University of Utah, Salt Lake City, USA.
- Department of Mechanical Engineering, University of Utah, Salt Lake City, USA.
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Thomas WM, Leber M, Crew J, Warren DJ. Evaluation of Pneumatic Insertion Stability of Utah Slanted Electrode Arrays in Rat Sciatic Nerve. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2022; 2022:5099-5102. [PMID: 36086163 DOI: 10.1109/embc48229.2022.9871237] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The Utah Electrode Array (UEA) and its variants (e.g., the Utah Slanted Electrode Array, or USEA) have been prominent contributors to advances in the field of neural engineering over the past decade. The most common means of inserting UEA and USEA devices into neural tissue is pneumatic insertion performed by an insertion wand and a pneumatic controller. As design changes from the well-established standards occur to better suit specialized surgical applications, it becomes essential to verify that the alterations do not compromise the structural integrity of the device during insertion. This paper characterizes and demonstrates the reliability of specialized USEAs and insertion wands designed for auditory nerve implants following pneumatic insertion into a rat sciatic nerve. The results show that proposed changes in the USEA form factor and pneumatic insertion ergonomics do not compromise implant stability and device structural viability.
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Shin H, Hawari MA, Hu X. Activation of Superficial and Deep Finger Flexors Through Transcutaneous Nerve Stimulation. IEEE J Biomed Health Inform 2021; 25:2575-2582. [PMID: 33259310 DOI: 10.1109/jbhi.2020.3041669] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
OBJECTIVE Functional electrical stimulation (FES) is a common technique to elicit muscle contraction and help improve muscle strength. Traditional FES over the muscle belly typically only activates superficial muscle regions. In the case of hand FES, this prevents the activation of the deeper flexor muscles which control the distal finger joints. Here, we evaluated whether an alternative transcutaneous nerve-bundle stimulation approach can activate both superficial and deep extrinsic finger flexors using a high-density stimulation grid. METHODS Transverse ultrasound of the forearm muscles was used to obtain cross-sectional images of the underlying finger flexors during stimulated finger flexions and kinematically-matched voluntary motions. Finger kinematics were recorded, and an image registration method was used to capture the large deformation of the muscle regions during each flexion. This deformation was used as a surrogate measure of the contraction of muscle tissue, and the regions of expanding tissue can identify activated muscles. RESULTS The nerve-bundle stimulation elicited contractions in the superficial and deep finger flexors. Both separate and concurrent activation of these two muscles were observed. Joint kinematics of the fingers also matched the expected regions of muscle contractions. CONCLUSIONS Our results showed that the nerve-bundle stimulation technique can activate the deep extrinsic finger flexors, which are typically not accessible via traditional surface FES. SIGNIFICANCE Our nerve-bundle stimulation method enables us to produce the full range of motion of different joints necessary for various functional grasps, which could benefit future neuroprosthetic applications.
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Moleirinho S, Whalen AJ, Fried SI, Pezaris JS. The impact of synchronous versus asynchronous electrical stimulation in artificial vision. J Neural Eng 2021; 18. [PMID: 33900206 DOI: 10.1088/1741-2552/abecf1] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2020] [Accepted: 03/09/2021] [Indexed: 11/12/2022]
Abstract
Visual prosthesis devices designed to restore sight to the blind have been under development in the laboratory for several decades. Clinical translation continues to be challenging, due in part to gaps in our understanding of critical parameters such as how phosphenes, the electrically-generated pixels of artificial vision, can be combined to form images. In this review we explore the effects that synchronous and asynchronous electrical stimulation across multiple electrodes have in evoking phosphenes. Understanding how electrical patterns influence phosphene generation to control object binding and perception of visual form is fundamental to creation of a clinically successful prosthesis.
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Affiliation(s)
- Susana Moleirinho
- Department of Neurosurgery, Massachusetts General Hospital, Boston, MA, United States of America.,Department of Neurosurgery, Harvard Medical School, Boston, MA, United States of America
| | - Andrew J Whalen
- Department of Neurosurgery, Massachusetts General Hospital, Boston, MA, United States of America.,Department of Neurosurgery, Harvard Medical School, Boston, MA, United States of America
| | - Shelley I Fried
- Department of Neurosurgery, Massachusetts General Hospital, Boston, MA, United States of America.,Department of Neurosurgery, Harvard Medical School, Boston, MA, United States of America.,Boston VA Healthcare System, Boston, MA, United States of America
| | - John S Pezaris
- Department of Neurosurgery, Massachusetts General Hospital, Boston, MA, United States of America.,Department of Neurosurgery, Harvard Medical School, Boston, MA, United States of America
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Eladly A, Del Valle J, Minguillon J, Mercadal B, Becerra-Fajardo L, Navarro X, Ivorra A. Interleaved intramuscular stimulation with minimally overlapping electrodes evokes smooth and fatigue resistant forces. J Neural Eng 2020; 17:046037. [PMID: 32717730 DOI: 10.1088/1741-2552/aba99e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVE It is known that multi-site interleaved stimulation generates less muscle fatigue compared to single-site synchronous stimulation. However, in the limited number of studies in which intramuscular electrodes were used, the fatigue reduction associated with interleaved stimulation could not consistently be achieved. We hypothesize that this could be due to the inability to place the intramuscular electrodes used in interleaved stimulation in locations that minimize overlap amongst the motor units activated by the electrodes. Our objective in the present study was to use independent intramuscular electrodes to compare fatigue induced by interleaved stimulation with that generated by synchronous stimulation at the same initial force and ripple. APPROACH In the medial gastrocnemius muscle of an anesthetized rabbit (n = 3), ten intramuscular hook wire electrodes were inserted at different distances from the nerve entry. Overlap was measured using the refractory technique and only three electrodes were found to be highly independent. After ensuring that forces obtained by both stimulation modalities had the same ripple and magnitude, fatigue induced during interleaved stimulation across three independent distal electrodes was compared to that obtained by synchronously delivering pulses to a single proximal electrode. MAIN RESULTS Contractions evoked by interleaved stimulation exhibited less fatigue than those evoked by synchronous stimulation. Twitch force recruitment curves collected from each of the ten intramuscular electrodes showed frequent intermediate plateaus and the force value at these plateaus decreased as the distance between the electrode and nerve entry increased. SIGNIFICANCE The results indicate that interleaved intramuscular stimulation is preferred over synchronous intramuscular stimulation when fatigue-resistant and smooth forces are desired. In addition, the results suggest that the large muscle compartments innervated by the primary intramuscular nerve branches give rise to progressively smaller independent compartments in subsequent nerve divisions.
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Affiliation(s)
- Ahmed Eladly
- Department of Information and Communication Technologies, Universitat Pompeu Fabra, Barcelona, Spain. Author to whom any correspondence should be addressed
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Zheng Y, Hu X. Elicited upper limb motions through transcutaneous cervical spinal cord stimulation. J Neural Eng 2020; 17:036001. [DOI: 10.1088/1741-2552/ab8f6f] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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8
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Wang J, Wang H, He T, He B, Thakor NV, Lee C. Investigation of Low-Current Direct Stimulation for Rehabilitation Treatment Related to Muscle Function Loss Using Self-Powered TENG System. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2019; 6:1900149. [PMID: 31380204 PMCID: PMC6662055 DOI: 10.1002/advs.201900149] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2019] [Revised: 03/13/2019] [Indexed: 05/19/2023]
Abstract
Muscle function loss is characterized as abnormal or completely lost muscle capabilities, and it can result from neurological disorders or nerve injuries. The currently available clinical treatment is to electrically stimulate the diseased muscles. Here, a self-powered system of a stacked-layer triboelectric nanogenerator (TENG) and a multiple-channel epimysial electrode to directly stimulate muscles is demonstrated. Then, the two challenges regarding direct TENG muscle stimulation are further investigated. For the first challenge of improving low-current TENG stimulation efficiency, it is found that the optimum stimulation efficiency can be achieved by conducting a systematic mapping with a multiple-channel epimysial electrode. The second challenge is TENG stimulation stability. It is found that the force output generated by TENGs is more stable than using the conventional square wave stimulation and enveloped high frequency stimulation. With modelling and in vivo measurements, it is confirmed that the two factors that account for the stable stimulation using TENGs are the long pulse duration and low current amplitude. The current waveform of TENGs can effectively avoid synchronous motoneuron recruitment at the two stimulation electrodes to reduce force fluctuation. Here, after investigating these two challenges, it is believed that TENG direct muscle stimulation could be used for rehabilitative and therapeutic purpose of muscle function loss treatment.
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Affiliation(s)
- Jiahui Wang
- Department of Electrical and Computer EngineeringNational University of Singapore4 Engineering Drive 3117576Singapore
- Singapore Institute for Neurotechnology (SINAPSE)National University of Singapore28 Medical Drive, #05‐COR117456Singapore
- Hybrid‐Integrated Flexible (Stretchable) Electronic Systems ProgramNational University of Singapore5 Engineering Drive 1117608Singapore
| | - Hao Wang
- Department of Electrical and Computer EngineeringNational University of Singapore4 Engineering Drive 3117576Singapore
- Hybrid‐Integrated Flexible (Stretchable) Electronic Systems ProgramNational University of Singapore5 Engineering Drive 1117608Singapore
| | - Tianyiyi He
- Department of Electrical and Computer EngineeringNational University of Singapore4 Engineering Drive 3117576Singapore
- Hybrid‐Integrated Flexible (Stretchable) Electronic Systems ProgramNational University of Singapore5 Engineering Drive 1117608Singapore
- NUS Suzhou Research Institute (NUSRI)SuzhouIndustrial Park, Suzhou215123P. R. China
| | - Borong He
- Department of Electrical and Computer EngineeringNational University of Singapore4 Engineering Drive 3117576Singapore
- Hybrid‐Integrated Flexible (Stretchable) Electronic Systems ProgramNational University of Singapore5 Engineering Drive 1117608Singapore
| | - Nitish V. Thakor
- Department of Electrical and Computer EngineeringNational University of Singapore4 Engineering Drive 3117576Singapore
- Singapore Institute for Neurotechnology (SINAPSE)National University of Singapore28 Medical Drive, #05‐COR117456Singapore
- Hybrid‐Integrated Flexible (Stretchable) Electronic Systems ProgramNational University of Singapore5 Engineering Drive 1117608Singapore
| | - Chengkuo Lee
- Department of Electrical and Computer EngineeringNational University of Singapore4 Engineering Drive 3117576Singapore
- Singapore Institute for Neurotechnology (SINAPSE)National University of Singapore28 Medical Drive, #05‐COR117456Singapore
- Hybrid‐Integrated Flexible (Stretchable) Electronic Systems ProgramNational University of Singapore5 Engineering Drive 1117608Singapore
- NUS Suzhou Research Institute (NUSRI)SuzhouIndustrial Park, Suzhou215123P. R. China
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Effects of Synchronous Electrode Pulses on Neural Recruitment During Multichannel Microstimulation. Sci Rep 2018; 8:13067. [PMID: 30166583 PMCID: PMC6117337 DOI: 10.1038/s41598-018-31247-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Accepted: 08/09/2018] [Indexed: 11/22/2022] Open
Abstract
The recent proliferation of high-density microelectrode arrays has inspired several new applications of electrical microstimulation, including restoration of sensory functions in the visual, auditory, and somatosensory systems. In each case, the goal is to achieve precisely targeted activation of neurons, while patterning the location and timing of stimulation across the array to mimic naturalistic patterns of neural activity. However, when two or more electrodes deliver stimulation pulses at the same time, the electric fields created by each electrode interact. The effects of field interactions on neuronal recruitment depend on several factors, which have been studied extensively at the macro-scale but have been overlooked in the case of high density arrays. Here, we report that field interactions can significantly affect neural recruitment, even with low amplitude stimulation. We created a computational model of peripheral nerve axons to estimate stimulation parameters sufficient to generate neural recruitment during synchronous and asynchronous stimulation on two microelectrodes located within the peripheral nerve. Across a range of stimulus amplitudes, the model predicted that synchronous stimulation on adjacent electrodes (400 µm separation), would recruit 2–3 times more neurons than during asynchronous stimulation. Our results suggest that field interactions should not be ignored when designing multichannel microstimulation paradigms, even at threshold-level stimulus amplitudes.
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Exploration of Hand Grasp Patterns Elicitable Through Non-Invasive Proximal Nerve Stimulation. Sci Rep 2017; 7:16595. [PMID: 29185474 PMCID: PMC5707381 DOI: 10.1038/s41598-017-16824-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Accepted: 11/16/2017] [Indexed: 11/19/2022] Open
Abstract
Various neurological conditions, such as stroke or spinal cord injury, result in an impaired control of the hand. One method of restoring this impairment is through functional electrical stimulation (FES). However, traditional FES techniques often lead to quick fatigue and unnatural ballistic movements. In this study, we sought to explore the capabilities of a non-invasive proximal nerve stimulation technique in eliciting various hand grasp patterns. The ulnar and median nerves proximal to the elbow joint were activated transcutanously using a programmable stimulator, and the resultant finger flexion joint angles were recorded using a motion capture system. The individual finger motions averaged across the three joints were analyzed using a cluster analysis, in order to classify the different hand grasp patterns. With low current intensity (<5 mA and 100 µs pulse width) stimulation, our results show that all of our subjects demonstrated a variety of consistent hand grasp patterns including single finger movement and coordinated multi-finger movements. This study provides initial evidence on the feasibility of a proximal nerve stimulation technique in controlling a variety of finger movements and grasp patterns. Our approach could also be developed into a rehabilitative/assistive tool that can result in flexible movements of the fingers.
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Downey RJ, Cheng TH, Bellman MJ, Dixon WE. Switched Tracking Control of the Lower Limb During Asynchronous Neuromuscular Electrical Stimulation: Theory and Experiments. IEEE TRANSACTIONS ON CYBERNETICS 2017; 47:1251-1262. [PMID: 27076479 DOI: 10.1109/tcyb.2016.2543699] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Neuromuscular electrical stimulation (NMES) induces muscle contractions via electrical stimuli. NMES can be used for rehabilitation and to enable functional movements; however, a fundamental limitation is the early onset of fatigue. Asynchronous stimulation is a method that can reduce fatigue by utilizing multiple stimulation channels to segregate and switch between different sets of recruited motor units. However, switching between stimulation channels is challenging due to each channel's differing response to stimulation. To address this challenge, a switched systems analysis is used in the present work to design a controller that allows for instantaneous switching between stimulation channels. The developed controller yields semi-global exponential tracking of a desired angular trajectory for a person's knee-joint. Experiments were conducted in six able-bodied individuals. Compared to conventional stimulation, the results indicate that asynchronous stimulation with the developed controller yields longer durations of successful tracking despite different responses between the stimulation channels.
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Wurth S, Capogrosso M, Raspopovic S, Gandar J, Federici G, Kinany N, Cutrone A, Piersigilli A, Pavlova N, Guiet R, Taverni G, Rigosa J, Shkorbatova P, Navarro X, Barraud Q, Courtine G, Micera S. Long-term usability and bio-integration of polyimide-based intra-neural stimulating electrodes. Biomaterials 2017; 122:114-129. [PMID: 28110171 DOI: 10.1016/j.biomaterials.2017.01.014] [Citation(s) in RCA: 92] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Revised: 12/21/2016] [Accepted: 01/10/2017] [Indexed: 10/20/2022]
Abstract
Stimulation of peripheral nerves has transiently restored lost sensation and has the potential to alleviate motor deficits. However, incomplete characterization of the long-term usability and bio-integration of intra-neural implants has restricted their use for clinical applications. Here, we conducted a longitudinal assessment of the selectivity, stability, functionality, and biocompatibility of polyimide-based intra-neural implants that were inserted in the sciatic nerve of twenty-three healthy adult rats for up to six months. We found that the stimulation threshold and impedance of the electrodes increased moderately during the first four weeks after implantation, and then remained stable over the following five months. The time course of these adaptations correlated with the progressive development of a fibrotic capsule around the implants. The selectivity of the electrodes enabled the preferential recruitment of extensor and flexor muscles of the ankle. Despite the foreign body reaction, this selectivity remained stable over time. These functional properties supported the development of control algorithms that modulated the forces produced by ankle extensor and flexor muscles with high precision. The comprehensive characterization of the implant encapsulation revealed hyper-cellularity, increased microvascular density, Wallerian degeneration, and infiltration of macrophages within the endoneurial space early after implantation. Over time, the amount of macrophages markedly decreased, and a layer of multinucleated giant cells surrounded by a capsule of fibrotic tissue developed around the implant, causing an enlargement of the diameter of the nerve. However, the density of nerve fibers above and below the inserted implant remained unaffected. Upon removal of the implant, we did not detect alteration of skilled leg movements and only observed mild tissue reaction. Our study characterized the interplay between the development of foreign body responses and changes in the electrical properties of actively used intra-neural electrodes, highlighting functional stability of polyimide-based implants over more than six months. These results are essential for refining and validating these implants and open a realistic pathway for long-term clinical applications in humans.
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Affiliation(s)
- S Wurth
- Bertarelli Foundation Chair in Translational Neuroengineering, Center for Neuroprosthetics and Institute of Bioengineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland; International Paraplegic Foundation Chair in Spinal Cord Repair, Center for Neuroprosthetics and Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - M Capogrosso
- Bertarelli Foundation Chair in Translational Neuroengineering, Center for Neuroprosthetics and Institute of Bioengineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland; The Biorobotics Institute, Scuola Superiore Sant'Anna, Pisa, Italy
| | - S Raspopovic
- Bertarelli Foundation Chair in Translational Neuroengineering, Center for Neuroprosthetics and Institute of Bioengineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland; The Biorobotics Institute, Scuola Superiore Sant'Anna, Pisa, Italy
| | - J Gandar
- International Paraplegic Foundation Chair in Spinal Cord Repair, Center for Neuroprosthetics and Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - G Federici
- Bertarelli Foundation Chair in Translational Neuroengineering, Center for Neuroprosthetics and Institute of Bioengineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - N Kinany
- Bertarelli Foundation Chair in Translational Neuroengineering, Center for Neuroprosthetics and Institute of Bioengineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - A Cutrone
- The Biorobotics Institute, Scuola Superiore Sant'Anna, Pisa, Italy
| | - A Piersigilli
- Laboratory Animals Pathology Unit, Institute of Animal Pathology, University of Bern, Bern, Switzerland
| | - N Pavlova
- International Paraplegic Foundation Chair in Spinal Cord Repair, Center for Neuroprosthetics and Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland; Pavlov Institute of Physiology, St Petersbourg, Russia
| | - R Guiet
- Bioimaging and Optics Platform, Faculty of Life Sciences, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - G Taverni
- The Biorobotics Institute, Scuola Superiore Sant'Anna, Pisa, Italy
| | - J Rigosa
- Bertarelli Foundation Chair in Translational Neuroengineering, Center for Neuroprosthetics and Institute of Bioengineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland; SAMBA Lab, International School for Advanced Studies, Trieste, Italy
| | - P Shkorbatova
- International Paraplegic Foundation Chair in Spinal Cord Repair, Center for Neuroprosthetics and Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland; Pavlov Institute of Physiology, St Petersbourg, Russia
| | - X Navarro
- Institute of Neurosciences, Department of Cell Biology, Physiology, and Immunology, Universitat Autònoma de Barcelona, and CIBERNED, Bellaterra, Spain
| | - Q Barraud
- International Paraplegic Foundation Chair in Spinal Cord Repair, Center for Neuroprosthetics and Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - G Courtine
- International Paraplegic Foundation Chair in Spinal Cord Repair, Center for Neuroprosthetics and Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - S Micera
- Bertarelli Foundation Chair in Translational Neuroengineering, Center for Neuroprosthetics and Institute of Bioengineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland; The Biorobotics Institute, Scuola Superiore Sant'Anna, Pisa, Italy.
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13
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Frankel MA, Mathews VJ, Clark GA, Normann RA, Meek SG. Control of Dynamic Limb Motion Using Fatigue-Resistant Asynchronous Intrafascicular Multi-Electrode Stimulation. Front Neurosci 2016; 10:414. [PMID: 27679557 PMCID: PMC5020091 DOI: 10.3389/fnins.2016.00414] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2016] [Accepted: 08/25/2016] [Indexed: 11/28/2022] Open
Abstract
Asynchronous intrafascicular multi-electrode stimulation (aIFMS) of small independent populations of peripheral nerve motor axons can evoke selective, fatigue-resistant muscle forces. We previously developed a real-time proportional closed-loop control method for aIFMS generation of isometric muscle force and the present work extends and adapts this closed-loop controller to the more demanding task of dynamically controlling joint position in the presence of opposing joint torque. A proportional-integral-velocity controller, with integrator anti-windup strategies, was experimentally validated as a means to evoke motion about the hind-limb ankle joint of an anesthetized feline via aIFMS stimulation of fast-twitch plantar-flexor muscles. The controller was successful in evoking steps in joint position with 2.4% overshoot, 2.3-s rise time, 4.5-s settling time, and near-zero steady-state error. Controlled step responses were consistent across changes in step size, stable against external disturbances, and reliable over time. The controller was able to evoke smooth eccentric motion at joint velocities up to 8 deg./s, as well as sinusoidal trajectories with frequencies up to 0.1 Hz, with time delays less than 1.5 s. These experiments provide important insights toward creating a robust closed-loop aIFMS controller that can evoke precise fatigue-resistant motion in paralyzed individuals, despite the complexities introduced by aIFMS.
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Affiliation(s)
- Mitchell A Frankel
- Department of Mechanical Engineering, University of Utah Salt Lake City, UT, USA
| | - V John Mathews
- School of Electrical Engineering and Computer Science, Oregon State University Corvallis, OR, USA
| | - Gregory A Clark
- Department of Bioengineering, University of Utah Salt Lake City, UT, USA
| | - Richard A Normann
- Department of Bioengineering, University of Utah Salt Lake City, UT, USA
| | - Sanford G Meek
- Department of Mechanical Engineering, University of Utah Salt Lake City, UT, USA
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Downey RJ, Cheng TH, Bellman MJ, Dixon WE. Closed-Loop Asynchronous Neuromuscular Electrical Stimulation Prolongs Functional Movements in the Lower Body. IEEE Trans Neural Syst Rehabil Eng 2015; 23:1117-27. [PMID: 25935038 DOI: 10.1109/tnsre.2015.2427658] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Ethier C, Miller LE. Brain-controlled muscle stimulation for the restoration of motor function. Neurobiol Dis 2015; 83:180-90. [PMID: 25447224 PMCID: PMC4412757 DOI: 10.1016/j.nbd.2014.10.014] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2014] [Revised: 10/14/2014] [Accepted: 10/20/2014] [Indexed: 12/21/2022] Open
Abstract
Loss of the ability to move, as a consequence of spinal cord injury or neuromuscular disorder, has devastating consequences for the paralyzed individual, and great economic consequences for society. Functional electrical stimulation (FES) offers one means to restore some mobility to these individuals, improving not only their autonomy, but potentially their general health and well-being as well. FES uses electrical stimulation to cause the paralyzed muscles to contract. Existing clinical systems require the stimulation to be preprogrammed, with the patient typically using residual voluntary movement of another body part to trigger and control the patterned stimulation. The rapid development of neural interfacing in the past decade offers the promise of dramatically improved control for these patients, potentially allowing continuous control of FES through signals recorded from motor cortex, as the patient attempts to control the paralyzed body part. While application of these 'brain-machine interfaces' (BMIs) has undergone dramatic development for control of computer cursors and even robotic limbs, their use as an interface for FES has been much more limited. In this review, we consider both FES and BMI technologies and discuss the prospect for combining the two to provide important new options for paralyzed individuals.
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Affiliation(s)
- Christian Ethier
- Department of Physiology, Feinberg School of Medicine, Northwestern University, 303 E. Chicago Ave., Chicago, IL 60611, USA
| | - Lee E Miller
- Department of Physiology, Feinberg School of Medicine, Northwestern University, 303 E. Chicago Ave., Chicago, IL 60611, USA; Department of Biomedical Engineering, Northwestern University, 2145 Sheridan Road Evanston, IL 60208, USA; Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, 345 E. Superior Ave., Chicago, IL 60611, USA.
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Thompson AC, Stoddart PR, Jansen ED. Optical Stimulation of Neurons. ACTA ACUST UNITED AC 2015; 3:162-177. [PMID: 26322269 PMCID: PMC4541079 DOI: 10.2174/2211555203666141117220611] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2014] [Revised: 09/26/2014] [Accepted: 10/20/2014] [Indexed: 01/01/2023]
Abstract
Our capacity to interface with the nervous system remains overwhelmingly reliant on electrical stimulation devices, such as electrode arrays and cuff electrodes that can stimulate both central and peripheral nervous systems. However, electrical stimulation has to deal with multiple challenges, including selectivity, spatial resolution, mechanical stability, implant-induced injury and the subsequent inflammatory response. Optical stimulation techniques may avoid some of these challenges by providing more selective stimulation, higher spatial resolution and reduced invasiveness of the device, while also avoiding the electrical artefacts that complicate recordings of electrically stimulated neuronal activity. This review explores the current status of optical stimulation techniques, including optogenetic methods, photoactive molecule approaches and infrared neural stimulation, together with emerging techniques such as hybrid optical-electrical stimulation, nanoparticle enhanced stimulation and optoelectric methods. Infrared neural stimulation is particularly emphasised, due to the potential for direct activation of neural tissue by infrared light, as opposed to techniques that rely on the introduction of exogenous light responsive materials. However, infrared neural stimulation remains imperfectly understood, and techniques for accurately delivering light are still under development. While the various techniques reviewed here confirm the overall feasibility of optical stimulation, a number of challenges remain to be overcome before they can deliver their full potential.
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Affiliation(s)
- Alexander C Thompson
- Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Australia
| | - Paul R Stoddart
- Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Australia
| | - E Duco Jansen
- Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA
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Sharpe AN, Jackson A. Upper-limb muscle responses to epidural, subdural and intraspinal stimulation of the cervical spinal cord. J Neural Eng 2014; 11:016005. [PMID: 24654267 DOI: 10.1088/1741-2560/11/1/016005] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
OBJECTIVE Electrical stimulation of the spinal cord has potential applications following spinal cord injury for reanimating paralysed limbs and promoting neuroplastic changes that may facilitate motor rehabilitation. Here we systematically compare the efficacy, selectivity and frequency-dependence of different stimulation methods in the cervical enlargement of anaesthetized monkeys. APPROACH Stimulating electrodes were positioned at multiple epidural and subdural sites on both dorsal and ventral surfaces, as well as at different depths within the spinal cord. Motor responses were recorded from arm, forearm and hand muscles. MAIN RESULTS Stimulation efficacy increased from dorsal to ventral stimulation sites, with the exception of ventral epidural electrodes which had the highest recruitment thresholds. Compared to epidural and intraspinal methods, responses to subdural stimulation were more selective but also more similar between adjacent sites. Trains of stimuli delivered to ventral sites elicited consistent responses at all frequencies whereas from dorsal sites we observed a mixture of short-latency facilitation and long-latency suppression. Finally, paired stimuli delivered to dorsal surface and intraspinal sites exhibited symmetric facilitatory interactions at interstimulus intervals between 2–5 ms whereas on the ventral side interactions tended to be suppressive for near-simultaneous stimuli. SIGNIFICANCE We interpret these results in the context of differential activation of afferent and efferent roots and intraspinal circuit elements. In particular, we propose that distinct direct and indirect actions of spinal cord stimulation on motoneurons may be advantageous for different applications, and this should be taken into consideration when designing neuroprostheses for upper-limb function.
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Wark HAC, Mathews KS, Normann RA, Fernandez E. Behavioral and cellular consequences of high-electrode count Utah Arrays chronically implanted in rat sciatic nerve. J Neural Eng 2014; 11:046027. [DOI: 10.1088/1741-2560/11/4/046027] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Wark HAC, Sharma R, Mathews KS, Fernandez E, Yoo J, Christensen B, Tresco P, Rieth L, Solzbacher F, Normann RA, Tathireddy P. A new high-density (25 electrodes/mm²) penetrating microelectrode array for recording and stimulating sub-millimeter neuroanatomical structures. J Neural Eng 2013; 10:045003. [PMID: 23723133 DOI: 10.1088/1741-2560/10/4/045003] [Citation(s) in RCA: 112] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
OBJECTIVE Among the currently available neural interface devices, there has been a need for a penetrating electrode array with a high electrode-count and high electrode-density (the number of electrodes/mm(2)) that can be used for electrophysiological studies of sub-millimeter neuroanatomical structures. We have developed such a penetrating microelectrode array with both a high electrode-density (25 electrodes/mm(2)) and high electrode-count (up to 96 electrodes) for small nervous system structures, based on the existing Utah Slanted Electrode Array (USEA). Such high electrode-density arrays are expected to provide greater access to nerve fibers than the conventionally spaced USEA especially in small diameter nerves. APPROACH One concern for such high density microelectrode arrays is that they may cause a nerve crush-type injury upon implantation. We evaluated this possibility during acute (<10 h) in vivo experiments with electrode arrays implanted into small diameter peripheral nerves of anesthetized rats (sciatic nerve) and cats (pudendal nerve). MAIN RESULTS Successful intrafascicular implantation and viable nerve function was demonstrated via microstimulation, single-unit recordings and histological analysis. Measurements of the electrode impedances and quantified electrode dimensions demonstrated fabrication quality. The results of these experiments show that such high density neural interfaces can be implanted acutely into neural tissue without causing a complete nerve crush injury, while mediating intrafascicular access to fibers in small diameter peripheral nerves. SIGNIFICANCE This new penetrating microelectrode array has characteristics un-matched by other neural interface devices currently available for peripheral nervous system neurophysiological research.
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Affiliation(s)
- H A C Wark
- Department of Bioengineering, University of Utah, Salt Lake City, UT, USA
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Bruns TM, Wagenaar JB, Bauman MJ, Gaunt RA, Weber DJ. Real-time control of hind limb functional electrical stimulation using feedback from dorsal root ganglia recordings. J Neural Eng 2013; 10:026020. [PMID: 23503062 DOI: 10.1088/1741-2560/10/2/026020] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVE Functional electrical stimulation (FES) approaches often utilize an open-loop controller to drive state transitions. The addition of sensory feedback may allow for closed-loop control that can respond effectively to perturbations and muscle fatigue. APPROACH We evaluated the use of natural sensory nerve signals obtained with penetrating microelectrode arrays in lumbar dorsal root ganglia (DRG) as real-time feedback for closed-loop control of FES-generated hind limb stepping in anesthetized cats. MAIN RESULTS Leg position feedback was obtained in near real-time at 50 ms intervals by decoding the firing rates of more than 120 DRG neurons recorded simultaneously. Over 5 m of effective linear distance was traversed during closed-loop stepping trials in each of two cats. The controller compensated effectively for perturbations in the stepping path when DRG sensory feedback was provided. The presence of stimulation artifacts and the quality of DRG unit sorting did not significantly affect the accuracy of leg position feedback obtained from the linear decoding model as long as at least 20 DRG units were included in the model. SIGNIFICANCE This work demonstrates the feasibility and utility of closed-loop FES control based on natural neural sensors. Further work is needed to improve the controller and electrode technologies and to evaluate long-term viability.
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Affiliation(s)
- Tim M Bruns
- Department of Physical Medicine and Rehabilitation, University of Pittsburgh, Pittsburgh, PA, USA
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Abstract
Regaining motor function is of high priority to patients with spinal cord injury (SCI). A variety of electronic devices that interface with the brain or spinal cord, which have applications in neural prosthetics and neurorehabilitation, are in development. Owing to our advancing understanding of activity-dependent synaptic plasticity, new technologies to monitor, decode and manipulate neural activity are being translated to patient populations, and have demonstrated clinical efficacy. Brain-machine interfaces that decode motor intentions from cortical signals are enabling patient-driven control of assistive devices such as computers and robotic prostheses, whereas electrical stimulation of the spinal cord and muscles can aid in retraining of motor circuits and improve residual capabilities in patients with SCI. Next-generation interfaces that combine recording and stimulating capabilities in so-called closed-loop devices will further extend the potential for neuroelectronic augmentation of injured motor circuits. Emerging evidence suggests that integration of closed-loop interfaces into intentional motor behaviours has therapeutic benefits that outlast the use of these devices as prostheses. In this Review, we summarize this evidence and propose that several known plasticity mechanisms, operating in a complementary manner, might underlie the therapeutic effects that are achieved by closing the loop between electronic devices and the nervous system.
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Weber DJ, Friesen R, Miller LE. Interfacing the Somatosensory System to Restore Touch and Proprioception: Essential Considerations. J Mot Behav 2012; 44:403-18. [DOI: 10.1080/00222895.2012.735283] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Ledbetter NM, Ethier C, Oby ER, Hiatt SD, Wilder AM, Ko JH, Agnew SP, Miller LE, Clark GA. Intrafascicular stimulation of monkey arm nerves evokes coordinated grasp and sensory responses. J Neurophysiol 2012; 109:580-90. [PMID: 23076108 DOI: 10.1152/jn.00688.2011] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
High-count microelectrode arrays implanted in peripheral nerves could restore motor function after spinal cord injury or sensory function after limb loss. In this study, we implanted Utah Slanted Electrode Arrays (USEAs) intrafascicularly at the elbow or shoulder in arm nerves of rhesus monkeys (n = 4) under isoflurane anesthesia. Input-output curves indicated that pulse-width-modulated single-electrode stimulation in each arm nerve could recruit single muscles with little or no recruitment of other muscles. Stimulus trains evoked specific, natural, hand movements, which could be combined via multielectrode stimulation to elicit coordinated power or pinch grasp. Stimulation also elicited short-latency evoked potentials (EPs) in primary somatosensory cortex, which might be used to provide sensory feedback from a prosthetic limb. These results demonstrate a high-resolution, high-channel-count interface to the peripheral nervous system for restoring hand function after neural injury or disruption or for examining nerve structure.
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Affiliation(s)
- Noah M Ledbetter
- Department of Bioengineering, University of Utah, Salt Lake City, Utah 84112, USA
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Abaya T, Diwekar M, Blair S, Tathireddy P, Rieth L, Clark G, Solzbacher F. Characterization of a 3D optrode array for infrared neural stimulation. BIOMEDICAL OPTICS EXPRESS 2012; 3:2200-19. [PMID: 23024914 PMCID: PMC3447562 DOI: 10.1364/boe.3.002200] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2012] [Revised: 08/08/2012] [Accepted: 08/10/2012] [Indexed: 05/03/2023]
Abstract
This paper characterizes the Utah Slant Optrode Array (USOA) as a means to deliver infrared light deep into tissue. An undoped crystalline silicon (100) substrate was used to fabricate 10 × 10 arrays of optrodes with rows of varying lengths from 0.5 mm to 1.5 mm on a 400-μm pitch. Light delivery from optical fibers and loss mechanisms through these Si optrodes were characterized, with the primary loss mechanisms being Fresnel reflection, coupling, radiation losses from the tapered shank and total internal reflection in the tips. Transmission at the optrode tips with different optical fiber core diameters and light in-coupling interfaces was investigated. At λ = 1.55μm, the highest optrode transmittance of 34.7%, relative to the optical fiber output power, was obtained with a 50-μm multi-mode fiber butt-coupled to the optrode through an intervening medium of index n = 1.66. Maximum power is directed into the optrodes when using fibers with core diameters of 200 μm or less. In addition, the output power varied with the optrode length/taper such that longer and less tapered optrodes exhibited higher light transmission efficiency. Output beam profiles and potential impacts on physiological tests were also examined. Future work is expected to improve USOA efficiency to greater than 64%.
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Affiliation(s)
- T.V.F. Abaya
- Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112,
USA
| | - M. Diwekar
- Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112,
USA
| | - S. Blair
- Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112,
USA
- Department of BioEngineering, University of Utah, Salt Lake City, Utah 84112,
USA
| | - P. Tathireddy
- Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112,
USA
| | - L. Rieth
- Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112,
USA
| | - G.A. Clark
- Department of BioEngineering, University of Utah, Salt Lake City, Utah 84112,
USA
| | - F. Solzbacher
- Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112,
USA
- Department of BioEngineering, University of Utah, Salt Lake City, Utah 84112,
USA
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