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Shah DD, Carter P, Shivdasani MN, Fong N, Duan W, Esrafilzadeh D, Poole-Warren LA, Aregueta Robles UA. Deciphering platinum dissolution in neural stimulation electrodes: Electrochemistry or biology? Biomaterials 2024; 309:122575. [PMID: 38677220 DOI: 10.1016/j.biomaterials.2024.122575] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2024] [Revised: 03/28/2024] [Accepted: 04/13/2024] [Indexed: 04/29/2024]
Abstract
Platinum (Pt) is the metal of choice for electrodes in implantable neural prostheses like the cochlear implants, deep brain stimulating devices, and brain-computer interfacing technologies. However, it is well known since the 1970s that Pt dissolution occurs with electrical stimulation. More recent clinical and in vivo studies have shown signs of corrosion in explanted electrode arrays and the presence of Pt-containing particulates in tissue samples. The process of degradation and release of metallic ions and particles can significantly impact on device performance. Moreover, the effects of Pt dissolution products on tissue health and function are still largely unknown. This is due to the highly complex chemistry underlying the dissolution process and the difficulty in decoupling electrical and chemical effects on biological responses. Understanding the mechanisms and effects of Pt dissolution proves challenging as the dissolution process can be influenced by electrical, chemical, physical, and biological factors, all of them highly variable between experimental settings. By evaluating comprehensive findings on Pt dissolution mechanisms reported in the fuel cell field, this review presents a critical analysis of the possible mechanisms that drive Pt dissolution in neural stimulation in vitro and in vivo. Stimulation parameters, such as aggregate charge, charge density, and electrochemical potential can all impact the levels of dissolved Pt. However, chemical factors such as electrolyte types, dissolved gases, and pH can all influence dissolution, confounding the findings of in vitro studies with multiple variables. Biological factors, such as proteins, have been documented to exhibit a mitigating effect on the dissolution process. Other biological factors like cells and fibro-proliferative responses, such as fibrosis and gliosis, impact on electrode properties and are suspected to impact on Pt dissolution. However, the relationship between electrical properties of stimulating electrodes and Pt dissolution remains contentious. Host responses to Pt degradation products are also controversial due to the unknown chemistry of Pt compounds formed and the lack of understanding of Pt distribution in clinical scenarios. The cytotoxicity of Pt produced via electrical stimulation appears similar to Pt-based compounds, including hexachloroplatinates and chemotherapeutic agents like cisplatin. While the levels of Pt produced under clinical and acute stimulation regimes were typically an order of magnitude lower than toxic concentrations observed in vitro, further research is needed to accurately assess the mass balance and type of Pt produced during long-term stimulation and its impact on tissue response. Finally, approaches to mitigating the dissolution process are reviewed. A wide variety of approaches, including stimulation strategies, coating electrode materials, and surface modification techniques to avoid excess charge during stimulation and minimise tissue response, may ultimately support long-term and safe operation of neural stimulating devices.
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Affiliation(s)
- Dhyey Devashish Shah
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, Australia
| | - Paul Carter
- Cochlear Ltd, Macquarie University, NSW, Australia
| | | | - Nicole Fong
- Cochlear Ltd, Macquarie University, NSW, Australia
| | - Wenlu Duan
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, Australia
| | - Dorna Esrafilzadeh
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, Australia
| | - Laura Anne Poole-Warren
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, Australia; The Tyree Foundation Institute of Health Engineering, University of New South Wales, Sydney, Australia.
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Azrad Leibovitch T, Farah N, Markus A, Mandel Y. A novel GCaMP6f-RCS rat model for studying electrical stimulation in the degenerated retina. Front Cell Dev Biol 2024; 12:1386141. [PMID: 38711618 PMCID: PMC11070775 DOI: 10.3389/fcell.2024.1386141] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2024] [Accepted: 03/25/2024] [Indexed: 05/08/2024] Open
Abstract
Background: Retinal prostheses aim to restore vision by electrically stimulating the remaining viable retinal cells in Retinal Degeneration (RD) cases. Research in this field necessitates a comprehensive analysis of retinal ganglion cells' (RGCs) responses to assess the obtained visual acuity and quality. Here we present a novel animal model which facilitates the optical recording of RGCs activity in an RD rat. This model can significantly enhance the functional evaluation of vision restoration treatments. Methods: The development of the novel rat model is based on crossbreeding a retinal degenerated Royal College of Surgeons (RCS) rat with a transgenic line expressing the genetic calcium indicator GCaMP6f in the RGCs. Characterization of the model was achieved using Optical Coherence Tomography (OCT) imaging, histology, and electroretinography (ERG) at the ages of 4, 8, and 12 weeks. Additionally, optical recordings of RGCs function in response to ex-vivo subretinal electrical stimulations were performed. Results: Histological investigations confirmed the high expression of GCaMP6f in the RGCs and minimal expression in the inner nuclear layer (INL). OCT imaging and histological studies revealed the expected gradual retinal degeneration, as evident by the decrease in retinal thickness with age and the formation of subretinal debris. This degeneration was further confirmed by ERG recordings, which demonstrated a significant decrease in the b-wave amplitude throughout the degeneration process, culminating in its absence at 12 weeks in the GCaMP6f-RCS rat. Importantly, the feasibility of investigating subretinal stimulation was demonstrated, revealing a consistent increase in activation threshold throughout degeneration. Furthermore, an increase in the diameter of the activated area with increasing currents was observed. The spatial spread of the activation area in the GCaMP6f-RCS rat was found to be smaller and exhibited faster activation dynamics compared with the GCaMP6f-LE strain. Conclusion: This novel animal model offers an opportunity to deepen our understanding of prosthetically induced retinal responses, potentially leading to significant advancements in prosthetic interventions in visual impairments.
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Affiliation(s)
- Tamar Azrad Leibovitch
- Bar Ilan Institute for Nanotechnology and Advanced Materials (BINA), Bar Ilan University, Ramat Gan, Israel
- Faculty of Life Sciences, School of Optometry and Visual Science, Bar Ilan University, Ramat Gan, Israel
| | - Nairouz Farah
- Bar Ilan Institute for Nanotechnology and Advanced Materials (BINA), Bar Ilan University, Ramat Gan, Israel
- Faculty of Life Sciences, School of Optometry and Visual Science, Bar Ilan University, Ramat Gan, Israel
| | - Amos Markus
- Bar Ilan Institute for Nanotechnology and Advanced Materials (BINA), Bar Ilan University, Ramat Gan, Israel
- Faculty of Life Sciences, School of Optometry and Visual Science, Bar Ilan University, Ramat Gan, Israel
| | - Yossi Mandel
- Bar Ilan Institute for Nanotechnology and Advanced Materials (BINA), Bar Ilan University, Ramat Gan, Israel
- Faculty of Life Sciences, School of Optometry and Visual Science, Bar Ilan University, Ramat Gan, Israel
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Zaidi M, Aggarwal G, Shah NP, Karniol-Tambour O, Goetz G, Madugula SS, Gogliettino AR, Wu EG, Kling A, Brackbill N, Sher A, Litke AM, Chichilnisky EJ. Inferring light responses of primate retinal ganglion cells using intrinsic electrical signatures. J Neural Eng 2023; 20:10.1088/1741-2552/ace657. [PMID: 37433293 PMCID: PMC11067857 DOI: 10.1088/1741-2552/ace657] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Accepted: 07/11/2023] [Indexed: 07/13/2023]
Abstract
Objective. Retinal implants are designed to stimulate retinal ganglion cells (RGCs) in a way that restores sight to individuals blinded by photoreceptor degeneration. Reproducing high-acuity vision with these devices will likely require inferring the natural light responses of diverse RGC types in the implanted retina, without being able to measure them directly. Here we demonstrate an inference approach that exploits intrinsic electrophysiological features of primate RGCs.Approach.First, ON-parasol and OFF-parasol RGC types were identified using their intrinsic electrical features in large-scale multi-electrode recordings from macaque retina. Then, the electrically inferred somatic location, inferred cell type, and average linear-nonlinear-Poisson model parameters of each cell type were used to infer a light response model for each cell. The accuracy of the cell type classification and of reproducing measured light responses with the model were evaluated.Main results.A cell-type classifier trained on 246 large-scale multi-electrode recordings from 148 retinas achieved 95% mean accuracy on 29 test retinas. In five retinas tested, the inferred models achieved an average correlation with measured firing rates of 0.49 for white noise visual stimuli and 0.50 for natural scenes stimuli, compared to 0.65 and 0.58 respectively for models fitted to recorded light responses (an upper bound). Linear decoding of natural images from predicted RGC activity in one retina showed a mean correlation of 0.55 between decoded and true images, compared to an upper bound of 0.81 using models fitted to light response data.Significance.These results suggest that inference of RGC light response properties from intrinsic features of their electrical activity may be a useful approach for high-fidelity sight restoration. The overall strategy of first inferring cell type from electrical features and then exploiting cell type to help infer natural cell function may also prove broadly useful to neural interfaces.
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Affiliation(s)
- Moosa Zaidi
- Stanford University School of Medicine, Stanford University, Stanford, CA, United States of America
- Neurosurgery, Stanford University, Stanford, CA, United States of America
| | - Gorish Aggarwal
- Neurosurgery, Stanford University, Stanford, CA, United States of America
- Electrical Engineering, Stanford University, Stanford, CA, United States of America
| | - Nishal P Shah
- Neurosurgery, Stanford University, Stanford, CA, United States of America
| | - Orren Karniol-Tambour
- Princeton Neuroscience Institute, Princeton University, Princeton, NJ, United States of America
| | - Georges Goetz
- Neurosurgery, Stanford University, Stanford, CA, United States of America
| | - Sasidhar S Madugula
- Stanford University School of Medicine, Stanford University, Stanford, CA, United States of America
- Neurosciences, Stanford University, Stanford, CA, United States of America
| | - Alex R Gogliettino
- Neurosciences, Stanford University, Stanford, CA, United States of America
| | - Eric G Wu
- Electrical Engineering, Stanford University, Stanford, CA, United States of America
| | - Alexandra Kling
- Neurosurgery, Stanford University, Stanford, CA, United States of America
| | - Nora Brackbill
- Physics, Stanford University, Stanford, CA, United States of America
| | - Alexander Sher
- Santa Cruz Institute for Particle Physics, University of California Santa Cruz, Santa Cruz, CA, United States of America
| | - Alan M Litke
- Santa Cruz Institute for Particle Physics, University of California Santa Cruz, Santa Cruz, CA, United States of America
| | - E J Chichilnisky
- Neurosurgery, Stanford University, Stanford, CA, United States of America
- Ophthalmology, Stanford University, Stanford, CA, United States of America
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Cojocaru AE, Corna A, Reh M, Zeck G. High spatial resolution artificial vision inferred from the spiking output of retinal ganglion cells stimulated by optogenetic and electrical means. Front Cell Neurosci 2022; 16:1033738. [PMID: 36568888 PMCID: PMC9780279 DOI: 10.3389/fncel.2022.1033738] [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: 08/31/2022] [Accepted: 11/10/2022] [Indexed: 12/13/2022] Open
Abstract
With vision impairment affecting millions of people world-wide, various strategies aiming at vision restoration are being undertaken. Thanks to decades of extensive research, electrical stimulation approaches to vision restoration began to undergo clinical trials. Quite recently, another technique employing optogenetic therapy emerged as a possible alternative. Both artificial vision restoration strategies reported poor spatial resolution so far. In this article, we compared the spatial resolution inferred ex vivo under ideal conditions using a computational model analysis of the retinal ganglion cell (RGC) spiking activity. The RGC spiking was stimulated in epiretinal configuration by either optogenetic or electrical means. RGCs activity was recorded from the ex vivo retina of transgenic late-stage photoreceptor-degenerated mice (rd10) using a high-density Complementary Metal Oxide Semiconductor (CMOS) based microelectrode array. The majority of retinal samples were stimulated by both, optogenetic and electrical stimuli using a spatial grating stimulus. A population-level analysis of the spiking activity of identified RGCs was performed and the spatial resolution achieved through electrical and optogenetic photo-stimulation was inferred using a support vector machine classifier. The best f1 score of the classifier for the electrical stimulation in epiretinal configuration was 86% for 32 micron wide gratings and increased to 100% for 128 microns. For optogenetically activated cells, we obtained high f1 scores of 82% for 10 microns grid width for a photo-stimulation frequency of 2.5 Hz and 73% for a photo-stimulation frequency of 10 Hz. A subsequent analysis, considering only the RGCs modulated in both electrical and optogenetic stimulation protocols revealed no significant difference in the prediction accuracy between the two stimulation modalities. The results presented here indicate that a high spatial resolution can be achieved for electrical or optogenetic artificial stimulation using the activated retinal ganglion cell output.
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Affiliation(s)
| | - Andrea Corna
- Institute of Biomedical Electronics, TU Wien, Vienna, Austria
| | - Miriam Reh
- Institute for Ophthalmic Research at the University of Tübingen, Tübingen, Germany
| | - Günther Zeck
- Institute of Biomedical Electronics, TU Wien, Vienna, Austria
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Abstract
Our sense of sight relies on photoreceptors, which transduce photons into the nervous system's electrochemical interpretation of the visual world. These precious photoreceptors can be disrupted by disease, injury, and aging. Once photoreceptors start to die, but before blindness occurs, the remaining retinal circuitry can withstand, mask, or exacerbate the photoreceptor deficit and potentially be receptive to newfound therapies for vision restoration. To maximize the retina's receptivity to therapy, one must understand the conditions that influence the state of the remaining retina. In this review, we provide an overview of the retina's structure and function in health and disease. We analyze a collection of observations on photoreceptor disruption and generate a predictive model to identify parameters that influence the retina's response. Finally, we speculate on whether the retina, with its remarkable capacity to function over light levels spanning nine orders of magnitude, uses these same adaptational mechanisms to withstand and perhaps mask photoreceptor loss.
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Affiliation(s)
- Joo Yeun Lee
- Department of Ophthalmology, University of California, San Francisco, California 94143, USA; , , ,
| | - Rachel A Care
- Department of Ophthalmology, University of California, San Francisco, California 94143, USA; , , ,
| | - Luca Della Santina
- Department of Ophthalmology, University of California, San Francisco, California 94143, USA; , , ,
- Bakar Computational Health Sciences Institute, University of California, San Francisco, California 94143, USA
| | - Felice A Dunn
- Department of Ophthalmology, University of California, San Francisco, California 94143, USA; , , ,
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Aydındoğan G, Kavaklı K, Şahin A, Artal P, Ürey H. Applications of augmented reality in ophthalmology [Invited]. BIOMEDICAL OPTICS EXPRESS 2021; 12:511-538. [PMID: 33659087 PMCID: PMC7899512 DOI: 10.1364/boe.405026] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Revised: 12/08/2020] [Accepted: 12/10/2020] [Indexed: 05/21/2023]
Abstract
Throughout the last decade, augmented reality (AR) head-mounted displays (HMDs) have gradually become a substantial part of modern life, with increasing applications ranging from gaming and driver assistance to medical training. Owing to the tremendous progress in miniaturized displays, cameras, and sensors, HMDs are now used for the diagnosis, treatment, and follow-up of several eye diseases. In this review, we discuss the current state-of-the-art as well as potential uses of AR in ophthalmology. This review includes the following topics: (i) underlying optical technologies, displays and trackers, holography, and adaptive optics; (ii) accommodation, 3D vision, and related problems such as presbyopia, amblyopia, strabismus, and refractive errors; (iii) AR technologies in lens and corneal disorders, in particular cataract and keratoconus; (iv) AR technologies in retinal disorders including age-related macular degeneration (AMD), glaucoma, color blindness, and vision simulators developed for other types of low-vision patients.
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Affiliation(s)
- Güneş Aydındoğan
- Koç University, Department of Electrical Engineering and Translational Medicine Research Center (KUTTAM), Istanbul 34450, Turkey
| | - Koray Kavaklı
- Koç University, Department of Electrical Engineering and Translational Medicine Research Center (KUTTAM), Istanbul 34450, Turkey
| | - Afsun Şahin
- Koç University, School of Medicine and Translational Medicine Research Center (KUTTAM), Istanbul 34450, Turkey
| | - Pablo Artal
- Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo, E-30100 Murcia, Spain
| | - Hakan Ürey
- Koç University, Department of Electrical Engineering and Translational Medicine Research Center (KUTTAM), Istanbul 34450, Turkey
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Shivdasani MN, Evans M, Burns O, Yeoh J, Allen PJ, Nayagam DAX, Villalobos J, Abbott CJ, Luu CD, Opie NL, Sabu A, Saunders AL, McPhedran M, Cardamone L, McGowan C, Maxim V, Williams RA, Fox KE, Cicione R, Garrett DJ, Ahnood A, Ganesan K, Meffin H, Burkitt AN, Prawer S, Williams CE, Shepherd RK. In vivo feasibility of epiretinal stimulation using ultrananocrystalline diamond electrodes. J Neural Eng 2020; 17:045014. [PMID: 32659750 DOI: 10.1088/1741-2552/aba560] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
OBJECTIVE Due to their increased proximity to retinal ganglion cells (RGCs), epiretinal visual prostheses present the opportunity for eliciting phosphenes with low thresholds through direct RGC activation. This study characterised the in vivo performance of a novel prototype monolithic epiretinal prosthesis, containing Nitrogen incorporated ultrananocrystalline (N-UNCD) diamond electrodes. APPROACH A prototype implant containing up to twenty-five 120 × 120 µm N-UNCD electrodes was implanted into 16 anaesthetised cats and attached to the retina either using a single tack or via magnetic coupling with a suprachoroidally placed magnet. Multiunit responses to retinal stimulation using charge-balanced biphasic current pulses were recorded acutely in the visual cortex using a multichannel planar array. Several stimulus parameters were varied including; the stimulating electrode, stimulus polarity, phase duration, return configuration and the number of electrodes stimulated simultaneously. MAIN RESULTS The rigid nature of the device and its form factor necessitated complex surgical procedures. Surgeries were considered successful in 10/16 animals and cortical responses to single electrode stimulation obtained in eight animals. Clinical imaging and histological outcomes showed severe retinal trauma caused by the device in situ in many instances. Cortical measures were found to significantly depend on the surgical outcomes of individual experiments, phase duration, return configuration and the number of electrodes stimulated simultaneously, but not stimulus polarity. Cortical thresholds were also found to increase over time within an experiment. SIGNIFICANCE The study successfully demonstrated that an epiretinal prosthesis containing diamond electrodes could produce cortical activity with high precision, albeit only in a small number of cases. Both surgical approaches were highly challenging in terms of reliable and consistent attachment to and stabilisation against the retina, and often resulted in severe retinal trauma. There are key challenges (device form factor and attachment technique) to be resolved for such a device to progress towards clinical application, as current surgical techniques are unable to address these issues.
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Affiliation(s)
- Mohit N Shivdasani
- Graduate School of Biomedical Engineering, University of New South Wales, Kensington, NSW 2033, Australia. The Bionics Institute of Australia, East Melbourne, VIC 3002, Australia
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Ho E, Boffa J, Palanker D. Performance of complex visual tasks using simulated prosthetic vision via augmented-reality glasses. J Vis 2019; 19:22. [PMID: 31770773 PMCID: PMC6880846 DOI: 10.1167/19.13.22] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Accepted: 10/05/2019] [Indexed: 11/29/2022] Open
Abstract
Photovoltaic subretinal prosthesis is designed for restoration of central vision in patients with age-related macular degeneration (AMD). We investigated the utility of prosthetic central vision for complex visual tasks using augmented-reality (AR) glasses simulating reduced acuity, contrast, and visual field. AR glasses with blocked central 20° of visual field included an integrated video camera and software which adjusts the image quality according to three user-defined parameters: resolution, corresponding to the equivalent pixel size of an implant; field of view, corresponding to the implant size; and number of grayscale levels. The real-time processed video was streamed on a screen in front of the right eye. Nineteen healthy participants were recruited to complete visual tasks including vision charts, sentence reading, and face recognition. With vision charts, letter acuity exceeded the pixel-sampling limit by 0.2 logMAR. Reading speed decreased with increasing pixel size and with reduced field of view (7°-12°). In the face recognition task (four-way forced choice, 5° angular size) participants identified faces at >75% accuracy, even with 100 μm pixels and only two grayscale levels. With 60 μm pixels and eight grayscale levels, the accuracy exceeded 97%. Subjects with simulated prosthetic vision performed slightly better than the sampling limit on the letter acuity tasks, and were highly accurate at recognizing faces, even with 100 μm/pixel resolution. These results indicate feasibility of reading and face recognition using prosthetic central vision even with 100 μm pixels, and performance improves further with smaller pixels.
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Affiliation(s)
- Elton Ho
- Department of Physics, Stanford University, Stanford, CA, USA
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
| | - Jack Boffa
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
| | - Daniel Palanker
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
- Department of Ophthalmology, Stanford University, Stanford, CA, USA
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