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Bhuckory MB, Wang BY, Chen ZC, Shin A, Pham-Howard D, Shah S, Monkongpitukkul N, Galambos L, Kamins T, Mathieson K, Palanker D. 3D electronic implants in subretinal space: Long-term follow-up in rodents. Biomaterials 2024; 311:122674. [PMID: 38897028 PMCID: PMC11298295 DOI: 10.1016/j.biomaterials.2024.122674] [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: 01/17/2024] [Revised: 06/12/2024] [Accepted: 06/15/2024] [Indexed: 06/21/2024]
Abstract
Clinical results with photovoltaic subretinal prosthesis (PRIMA) demonstrated restoration of sight via electrical stimulation of the interneurons in degenerated retina, with resolution matching the 100 μm pixel size. Since scaling the pixels below 75 μm in the current bipolar planar geometry will significantly limit the penetration depth of the electric field and increase stimulation threshold, we explore the possibility of using smaller pixels based on a novel 3-dimensional honeycomb-shaped design. We assessed the long-term biocompatibility and stability of these arrays in rats by investigating the anatomical integration of the retina with flat and 3D implants and response to electrical stimulation over lifetime - up to 32-36 weeks post-implantation in aged rats. With both flat and 3D implants, signals elicited in the visual cortex decreased after the day of implantation by more than 3-fold, and gradually recovered over the next 12-16 weeks. With 25 μm high honeycomb walls, the majority of bipolar cells migrate into the wells, while amacrine and ganglion cells remain above the cavities, which is essential for selective network-mediated stimulation of the retina. Retinal thickness and full-field stimulation threshold with 40 μm-wide honeycomb pixels were comparable to those with planar devices - 0.05 mW/mm2 with 10 ms pulses. However, fewer cells from the inner nuclear layer migrated into the 20 μm-wide wells, and stimulation threshold increased over 12-16 weeks, before stabilizing at about 0.08 mW/mm2. Such threshold is still significantly lower than 1.8 mW/mm2 with a previous design of flat bipolar pixels, confirming the promise of the 3D honeycomb-based approach to high resolution subretinal prosthesis.
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Affiliation(s)
- Mohajeet B Bhuckory
- Department of Ophthalmology, Stanford University, Stanford, CA, USA; Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA.
| | - Bing-Yi Wang
- Department of Physics, Stanford University, Stanford, CA, USA
| | - Zhijie C Chen
- Department of Electrical Engineering, Stanford University, Stanford, CA, USA
| | - Andrew Shin
- Department of Material Science, Stanford University, Stanford, CA, USA
| | - Davis Pham-Howard
- Department of Ophthalmology, Stanford University, Stanford, CA, USA; Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
| | - Sarthak Shah
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
| | - Nicharee Monkongpitukkul
- Department of Ophthalmology, Stanford University, Stanford, CA, USA; Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
| | - Ludwig Galambos
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
| | - Theodore Kamins
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA; Department of Electrical Engineering, Stanford University, Stanford, CA, USA
| | - Keith Mathieson
- Department of Physics, Institute of Photonics, University of Strathclyde, Glasgow, Scotland, UK
| | - Daniel Palanker
- Department of Ophthalmology, Stanford University, Stanford, CA, USA; Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
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2
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Bhuckory MB, Wang BY, Chen ZC, Shin A, Huang T, Galambos L, Vounotrypidis E, Mathieson K, Kamins T, Palanker D. Cellular migration into a subretinal honeycomb-shaped prosthesis for high-resolution prosthetic vision. Proc Natl Acad Sci U S A 2023; 120:e2307380120. [PMID: 37831740 PMCID: PMC10589669 DOI: 10.1073/pnas.2307380120] [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: 05/03/2023] [Accepted: 09/08/2023] [Indexed: 10/15/2023] Open
Abstract
In patients blinded by geographic atrophy, a subretinal photovoltaic implant with 100 µm pixels provided visual acuity closely matching the pixel pitch. However, such flat bipolar pixels cannot be scaled below 75 µm, limiting the attainable visual acuity. This limitation can be overcome by shaping the electric field with 3-dimensional (3-D) electrodes. In particular, elevating the return electrode on top of the honeycomb-shaped vertical walls surrounding each pixel extends the electric field vertically and decouples its penetration into tissue from the pixel width. This approach relies on migration of the retinal cells into the honeycomb wells. Here, we demonstrate that majority of the inner retinal neurons migrate into the 25 µm deep wells, leaving the third-order neurons, such as amacrine and ganglion cells, outside. This enables selective stimulation of the second-order neurons inside the wells, thus preserving the intraretinal signal processing in prosthetic vision. Comparable glial response to that with flat implants suggests that migration and separation of the retinal cells by the walls does not cause additional stress. Furthermore, retinal migration into the honeycombs does not negatively affect its electrical excitability, while grating acuity matches the pixel pitch down to 40 μm and reaches the 27 μm limit of natural resolution in rats with 20 μm pixels. These findings pave the way for 3-D subretinal prostheses with pixel sizes of cellular dimensions.
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Affiliation(s)
- Mohajeet B. Bhuckory
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA94305
- Department of Ophthalmology, Stanford University, Stanford, CA94305
| | - Bing-Yi Wang
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA94305
- Department of Physics, Stanford University, Stanford, CA94305
| | - Zhijie Charles Chen
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA94305
- Department of Electrical Engineering, Stanford University, Stanford, CA94305
| | - Andrew Shin
- Department of Material Science, Stanford University, Stanford, CA94305
| | - Tiffany Huang
- Department of Electrical Engineering, Stanford University, Stanford, CA94305
| | - Ludwig Galambos
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA94305
| | | | - Keith Mathieson
- Department of Physics, University of Strathclyde, G1 1XQGlasgow, Scotland, United Kingdom
| | - Theodore Kamins
- Department of Electrical Engineering, Stanford University, Stanford, CA94305
| | - Daniel Palanker
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA94305
- Department of Ophthalmology, Stanford University, Stanford, CA94305
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3
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Son Y, Chen ZC, Roh H, Lee BC, Im M. Effects on Retinal Stimulation of the Geometry and the Insertion Location of Penetrating Electrodes. IEEE Trans Neural Syst Rehabil Eng 2023; 31:3803-3812. [PMID: 37729573 DOI: 10.1109/tnsre.2023.3317496] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/22/2023]
Abstract
Retinal implants have been developed and implanted to restore vision from outer retinal degeneration, but their performance is still limited due to the poor spatial resolution. To improve the localization of stimulation, microelectrodes in various three-dimensional (3D) shapes have been investigated. In particular, computational simulation is crucial for optimizing the performance of a novel microelectrode design before actual fabrication. However, most previous studies have assumed a uniform conductivity for the entire retina without testing the effect of electrodes placement in different layers. In this study, we used the finite element method to simulate electric fields created by 3D microelectrodes of three different designs in a retina model with a stratified conductivity profile. The three electrode designs included two conventional shapes - a conical electrode (CE) and a pillar electrode (PE); we also proposed a novel structure of pillar electrode with an insulating wall (PEIW). A quantitative comparison of these designs shows the PEIW generates a stronger and more confined electric field with the same current injection, which is preferred for high-resolution retinal prostheses. Moreover, our results demonstrate both the magnitude and the shape of potential distribution generated by a penetrating electrode depend not only on the geometry, but also substantially on the insertion depth of the electrode. Although epiretinal insertions are mainly discussed, we also compared results for subretinal insertions. The results provide valuable insights for improving the spatial resolution of retinal implants using 3D penetrating microelectrodes and highlight the importance of considering the heterogeneity of conductivities in the retina.
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4
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Bhuckory M, Wang BY, Chen ZC, Shin A, Pham-Howard D, Shah S, Monkongpitukkul N, Galambos L, Kamins T, Mathieson K, Palanker D. 3D electronic implants in subretinal space: long-term follow-up in rodents. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.25.550561. [PMID: 37546971 PMCID: PMC10402070 DOI: 10.1101/2023.07.25.550561] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/08/2023]
Abstract
Photovoltaic subretinal prosthesis (PRIMA) enables restoration of sight via electrical stimulation of the interneurons in degenerated retina, with resolution limited by the 100 μm pixel size. Since decreasing the pixel size below 75 μm in the current bipolar geometry is impossible, we explore the possibility of using smaller pixels based on a novel 3-dimensional honeycomb-shaped design. We assessed the long-term biocompatibility and stability of these arrays in rats by investigating the anatomical integration of the retina with flat and 3D implants and response to electrical stimulation over lifetime - up to 9 months post-implantation in aged rats. With both flat and 3D implants, VEP amplitude decreased after the day of implantation by more than 3-fold, and gradually recovered over about 3 months. With 25 µm high honeycomb walls, the majority of bipolar cells migrate into the wells, while amacrine and ganglion cells remain above the cavities, which is essential for selective network-mediated stimulation of the second-order neurons. Retinal thickness and full-field stimulation threshold with 40 µm-wide honeycomb pixels were comparable to those with planar devices - 0.05 mW/mm2 with 10ms pulses. However, fewer cells from the inner nuclear layer migrated into the 20 µm-wide wells, and stimulation threshold increased over 5 months, before stabilizing at about 0.08 mW/mm2. Such threshold is significantly lower than 1.8 mW/mm2 with a previous design of flat bipolar pixels, confirming the promise of the 3D honeycomb-based approach to high resolution subretinal prosthesis.
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Affiliation(s)
- Mohajeet Bhuckory
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
- Department of Ophthalmology, Stanford University, Stanford, CA, USA
| | - Bing-Yi Wang
- Department of Physics, Stanford University, Stanford, CA, USA
| | - Zhijie Charles Chen
- Department of Electrical Engineering, Stanford University, Stanford, CA, USA
| | - Andrew Shin
- Department of Material Science, Stanford University, Stanford, CA, USA
| | - Davis Pham-Howard
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
- Department of Ophthalmology, Stanford University, Stanford, CA, USA
| | - Sarthak Shah
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
| | - Nicharee Monkongpitukkul
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
- Department of Ophthalmology, Stanford University, Stanford, CA, USA
| | - Ludwig Galambos
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
| | - Theodore Kamins
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
- Department of Electrical Engineering, Stanford University, Stanford, CA, USA
| | - Keith Mathieson
- Department of Physics, Institute of Photonics, University of Strathclyde, Glasgow, Scotland, UK
| | - Daniel Palanker
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
- Department of Ophthalmology, Stanford University, Stanford, CA, USA
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5
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Vu QA, Seo HW, Choi KE, Kim N, Kang YN, Lee J, Park SH, Kim JT, Kim S, Kim SW. Structural changes in the retina after implantation of subretinal three-dimensional implants in mini pigs. Front Neurosci 2022; 16:1010445. [PMID: 36248640 PMCID: PMC9561346 DOI: 10.3389/fnins.2022.1010445] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Accepted: 09/16/2022] [Indexed: 11/30/2022] Open
Abstract
The retinal structural changes after subretinal implantation of three-dimensional (3D) microelectrodes were investigated in a mini pig. Three types of electrode were implanted into the subretinal spaces of nine mini pigs: 75-μm-high 3D electrodes on a 200-μm-thick right-angled polydimethylsiloxane (PDMS) substrate (group 1); a 140-μm-thick sloped PDMS substrate without electrodes (group 2); and a 140-μm-thick sloped PDMS substrate with 20-μm-high 3D electrodes (group 3). One mini pig was used as a control. Spectral domain–optical coherence tomography (SD–OCT) images were obtained at baseline and 2, 6, and 12 weeks post-surgery. Retinal specimens were immunostained using a tissue-clearing method 3 months post-implantation. The 75-μm-high 3D electrodes progressively penetrated the inner nuclear layer (INL) and touched the inner plexiform layer (IPL) 2 weeks post-surgery. At 6 weeks post-operatively, the electrodes were in contact with the nerve-fiber layer, accompanied by a severe fibrous reaction. In the other groups, the implants remained in place without subretinal migration. Immunostaining showed that retinal ganglion and bipolar cells were preserved without fibrosis over the retinal implants in groups 2 and 3 during the 12-week implantation period. In summary, SD–OCT and immunohistology results showed differences in the extent of reactions, such as fibrosis over the implants and penetration of the electrodes into the inner retinal layer depending on different types of electrodes. A sloped substrate performed better than a right-angled substrate in terms of retinal preservation over the implanted electrodes. The 20-μm-high electrodes showed better structural compatibility than the 75-μm-high 3D electrodes. There was no significant difference between the results of sloped implants without electrodes and 20-μm-high 3D electrodes, indicating that the latter had no adverse effects on retinal tissue.
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Affiliation(s)
- Que Anh Vu
- Department of Ophthalmology, Korea University School of Medicine, Seoul, South Korea
- Department of Ophthalmology, Hanoi Medical University, Hanoi, Vietnam
| | - Hee Won Seo
- Department of Robotics and Mechatronics Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, South Korea
| | - Kwang-Eon Choi
- Department of Ophthalmology, Korea University School of Medicine, Seoul, South Korea
| | - Namju Kim
- Department of Robotics and Mechatronics Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, South Korea
| | - Yoo Na Kang
- Department of Medical Assistant Robot, Korea Institute of Machinery and Materials (KIMM), Daegu, South Korea
| | - Jaemeun Lee
- R&D Center for Advanced Pharmaceuticals and Evaluation, Korea Institute of Toxicology, Daejeon, South Korea
| | - Sun-Hyun Park
- R&D Center for Advanced Pharmaceuticals and Evaluation, Korea Institute of Toxicology, Daejeon, South Korea
| | - Jee Taek Kim
- Department of Ophthalmology, Chung-Ang University College of Medicine, Seoul, South Korea
| | - Sohee Kim
- Department of Robotics and Mechatronics Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, South Korea
- *Correspondence: Sohee Kim,
| | - Seong-Woo Kim
- Department of Ophthalmology, Korea University School of Medicine, Seoul, South Korea
- Seong-Woo Kim,
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6
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Tringides CM, Mooney DJ. Materials for Implantable Surface Electrode Arrays: Current Status and Future Directions. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2022; 34:e2107207. [PMID: 34716730 DOI: 10.1002/adma.202107207] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Revised: 10/26/2021] [Indexed: 06/13/2023]
Abstract
Surface electrode arrays are mainly fabricated from rigid or elastic materials, and precisely manipulated ductile metal films, which offer limited stretchability. However, the living tissues to which they are applied are nonlinear viscoelastic materials, which can undergo significant mechanical deformation in dynamic biological environments. Further, the same arrays and compositions are often repurposed for vastly different tissues rather than optimizing the materials and mechanical properties of the implant for the target application. By first characterizing the desired biological environment, and then designing a technology for a particular organ, surface electrode arrays may be more conformable, and offer better interfaces to tissues while causing less damage. Here, the various materials used in each component of a surface electrode array are first reviewed, and then electrically active implants in three specific biological systems, the nervous system, the muscular system, and skin, are described. Finally, the fabrication of next-generation surface arrays that overcome current limitations is discussed.
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Affiliation(s)
- Christina M Tringides
- Harvard Program in Biophysics, Harvard University, Cambridge, MA, 02138, USA
- Harvard-MIT Division in Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, MA, 02138, USA
| | - David J Mooney
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, MA, 02138, USA
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA
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7
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Sharafkhani N, Kouzani AZ, Adams SD, Long JM, Lissorgues G, Rousseau L, Orwa JO. Neural tissue-microelectrode interaction: Brain micromotion, electrical impedance, and flexible microelectrode insertion. J Neurosci Methods 2022; 365:109388. [PMID: 34678387 DOI: 10.1016/j.jneumeth.2021.109388] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2021] [Revised: 10/17/2021] [Accepted: 10/17/2021] [Indexed: 10/20/2022]
Abstract
Insertion of a microelectrode into the brain to record/stimulate neurons damages neural tissue and blood vessels and initiates the brain's wound healing response. Due to the large difference between the stiffness of neural tissue and microelectrode, brain micromotion also leads to neural tissue damage and associated local immune response. Over time, following implantation, the brain's response to the tissue damage can result in microelectrode failure. Reducing the microelectrode's cross-sectional dimensions to single-digit microns or using soft materials with elastic modulus close to that of the neural tissue are effective methods to alleviate the neural tissue damage and enhance microelectrode longevity. However, the increase in electrical impedance of the microelectrode caused by reducing the microelectrode contact site's dimensions can decrease the signal-to-noise ratio. Most importantly, the reduced dimensions also lead to a reduction in the critical buckling force, which increases the microelectrode's propensity to buckling during insertion. After discussing brain micromotion, the main source of neural tissue damage, surface modification of the microelectrode contact site is reviewed as a key method for addressing the increase in electrical impedance issue. The review then focuses on recent approaches to aiding insertion of flexible microelectrodes into the brain, including bending stiffness modification, effective length reduction, and application of a magnetic field to pull the electrode. An understanding of the advantages and drawbacks of the developed strategies offers a guide for dealing with the buckling phenomenon during implantation.
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Affiliation(s)
- Naser Sharafkhani
- School of Engineering, Deakin University, Geelong, VIC 3216, Australia.
| | - Abbas Z Kouzani
- School of Engineering, Deakin University, Geelong, VIC 3216, Australia
| | - Scott D Adams
- School of Engineering, Deakin University, Geelong, VIC 3216, Australia
| | - John M Long
- School of Engineering, Deakin University, Geelong, VIC 3216, Australia
| | | | | | - Julius O Orwa
- School of Engineering, Deakin University, Geelong, VIC 3216, Australia.
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8
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Shim S, Eom K, Jeong J, Kim SJ. Retinal Prosthetic Approaches to Enhance Visual Perception for Blind Patients. MICROMACHINES 2020; 11:E535. [PMID: 32456341 PMCID: PMC7281011 DOI: 10.3390/mi11050535] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Revised: 05/22/2020] [Accepted: 05/22/2020] [Indexed: 12/14/2022]
Abstract
Retinal prostheses are implantable devices that aim to restore the vision of blind patients suffering from retinal degeneration, mainly by artificially stimulating the remaining retinal neurons. Some retinal prostheses have successfully reached the stage of clinical trials; however, these devices can only restore vision partially and remain insufficient to enable patients to conduct everyday life independently. The visual acuity of the artificial vision is limited by various factors from both engineering and physiological perspectives. To overcome those issues and further enhance the visual resolution of retinal prostheses, a variety of retinal prosthetic approaches have been proposed, based on optimization of the geometries of electrode arrays and stimulation pulse parameters. Other retinal stimulation modalities such as optics, ultrasound, and magnetics have also been utilized to address the limitations in conventional electrical stimulation. Although none of these approaches have been clinically proven to fully restore the function of a degenerated retina, the extensive efforts made in this field have demonstrated a series of encouraging findings for the next generation of retinal prostheses, and these could potentially enhance the visual acuity of retinal prostheses. In this article, a comprehensive and up-to-date overview of retinal prosthetic strategies is provided, with a specific focus on a quantitative assessment of visual acuity results from various retinal stimulation technologies. The aim is to highlight future directions toward high-resolution retinal prostheses.
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Affiliation(s)
- Shinyong Shim
- Department of Electrical and Computer Engineering, College of Engineering, Seoul National University, Seoul 08826, Korea;
- Inter-university Semiconductor Research Center, College of Engineering, Seoul National University, Seoul 08826, Korea
| | - Kyungsik Eom
- Department of Electronics Engineering, College of Engineering, Pusan National University, Busan 46241, Korea
| | - Joonsoo Jeong
- School of Biomedical Convergence Engineering, College of Information and Biomedical Engineering, Pusan National University, Yangsan 50612, Korea
| | - Sung June Kim
- Department of Electrical and Computer Engineering, College of Engineering, Seoul National University, Seoul 08826, Korea;
- Inter-university Semiconductor Research Center, College of Engineering, Seoul National University, Seoul 08826, Korea
- Institute on Aging, College of Medicine, Seoul National University, Seoul 08826, Korea
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9
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Lyu Q, Lu Z, Li H, Qiu S, Guo J, Sui X, Sun P, Li L, Chai X, Lovell NH. A Three-Dimensional Microelectrode Array to Generate Virtual Electrodes for Epiretinal Prosthesis Based on a Modeling Study. Int J Neural Syst 2020; 30:2050006. [DOI: 10.1142/s0129065720500069] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Despite many advances in the development of retinal prostheses, clinical reports show that current retinal prosthesis subjects can only perceive prosthetic vision with poor visual acuity. A possible approach for improving visual acuity is to produce virtual electrodes (VEs) through electric field modulation. Generating controllable and localized VEs is a crucial factor in effectively improving the perceptive resolution of the retinal prostheses. In this paper, we aimed to design a microelectrode array (MEA) that can produce converged and controllable VEs by current steering stimulation strategies. Through computational modeling, we designed a three-dimensional concentric ring–disc MEA and evaluated its performance with different stimulation strategies. Our simulation results showed that electrode–retina distance (ERD) and inter-electrode distance (IED) can dramatically affect the distribution of electric field. Also the converged VEs could be produced when the parameters of the three-dimensional MEA were appropriately set. VE sites can be controlled by manipulating the proportion of current on each adjacent electrode in a current steering group (CSG). In addition, spatial localization of electrical stimulation can be greatly improved under quasi-monopolar (QMP) stimulation. This study may provide support for future application of VEs in epiretinal prosthesis for potentially increasing the visual acuity of prosthetic vision.
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Affiliation(s)
- Qing Lyu
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Zhuofan Lu
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Heng Li
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Shirong Qiu
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Jiahui Guo
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Xiaohong Sui
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Pengcheng Sun
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Liming Li
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Xinyu Chai
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Nigel H. Lovell
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, NSW 2052, Australia
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10
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Losada PG, Rousseau L, Grzeskowiak M, Valet M, Nguyen D, Dégardin J, Dubus E, Picaud S, Lissorgues G. Protuberant Electrode Structures for Subretinal Electrical Stimulation: Modeling, Fabrication and in vivo Evaluation. Front Neurosci 2019; 13:885. [PMID: 31507363 PMCID: PMC6718636 DOI: 10.3389/fnins.2019.00885] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2018] [Accepted: 08/07/2019] [Indexed: 11/13/2022] Open
Abstract
Many neural interfaces used for therapeutic applications are based on extracellular electrical stimulation to control cell polarization and thus functional activity. Amongst them, retinal implants have been designed to restore visual perception in blind patients affected by photoreceptor degeneration diseases, such as age-related macular degeneration (AMD) or retinitis pigmentosa (RP). While designing such a neural interface, several aspects must be taken into account, like the stimulation efficiency related to the current distribution within the tissue, the bio-interface optimization to improve resolution and tissue integration, and the material biocompatibility associated with long-term aging. In this study, we investigate the use of original microelectrode geometries for subretinal stimulation. The proposed structures combine the use of 3D wells with protuberant mushroom shaped electrode structures in the bottom, implemented on a flexible substrate that allows the in vivo implantation of the devices. These 3D microelectrode structures were first modeled using finite element analysis. Then, a specific microfabrication process compatible with flexible implants was developed to create the 3D microelectrode structures. These structures were tested in vivo to check the adaptation of the retinal tissue to them. Finally, preliminary in vivo stimulation experiments were performed.
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Affiliation(s)
| | - Lionel Rousseau
- Laboratory ESYCOM, University Paris Est-ESIEE-MLV, Noisy-le-Grand, France
| | | | - Manon Valet
- INSERM, CNRS, Institut de la Vision, Sorbonne Université, Paris, France
| | - Diep Nguyen
- INSERM, CNRS, Institut de la Vision, Sorbonne Université, Paris, France
| | - Julie Dégardin
- INSERM, CNRS, Institut de la Vision, Sorbonne Université, Paris, France
| | - Elisabeth Dubus
- INSERM, CNRS, Institut de la Vision, Sorbonne Université, Paris, France
| | - Serge Picaud
- INSERM, CNRS, Institut de la Vision, Sorbonne Université, Paris, France
| | - Gaelle Lissorgues
- Laboratory ESYCOM, University Paris Est-ESIEE-MLV, Noisy-le-Grand, France
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11
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Fadeel B, Bussy C, Merino S, Vázquez E, Flahaut E, Mouchet F, Evariste L, Gauthier L, Koivisto AJ, Vogel U, Martín C, Delogu LG, Buerki-Thurnherr T, Wick P, Beloin-Saint-Pierre D, Hischier R, Pelin M, Candotto Carniel F, Tretiach M, Cesca F, Benfenati F, Scaini D, Ballerini L, Kostarelos K, Prato M, Bianco A. Safety Assessment of Graphene-Based Materials: Focus on Human Health and the Environment. ACS NANO 2018; 12:10582-10620. [PMID: 30387986 DOI: 10.1021/acsnano.8b04758] [Citation(s) in RCA: 302] [Impact Index Per Article: 50.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Graphene and its derivatives are heralded as "miracle" materials with manifold applications in different sectors of society from electronics to energy storage to medicine. The increasing exploitation of graphene-based materials (GBMs) necessitates a comprehensive evaluation of the potential impact of these materials on human health and the environment. Here, we discuss synthesis and characterization of GBMs as well as human and environmental hazard assessment of GBMs using in vitro and in vivo model systems with the aim to understand the properties that underlie the biological effects of these materials; not all GBMs are alike, and it is essential that we disentangle the structure-activity relationships for this class of materials.
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Affiliation(s)
- Bengt Fadeel
- Nanosafety & Nanomedicine Laboratory, Institute of Environmental Medicine , Karolinska Institutet , 17777 Stockholm , Sweden
| | - Cyrill Bussy
- Nanomedicine Laboratory, Faculty of Biology, Medicine & Health , University of Manchester , Manchester M13 9PL , United Kingdom
| | - Sonia Merino
- Faculty of Chemical Science and Technology , University of Castilla-La Mancha , 13071 Ciudad Real , Spain
| | - Ester Vázquez
- Faculty of Chemical Science and Technology , University of Castilla-La Mancha , 13071 Ciudad Real , Spain
| | | | | | | | - Laury Gauthier
- CNRS, Université Paul Sabatier , 31062 Toulouse , France
| | - Antti J Koivisto
- National Research Centre for the Working Environment , 2100 Copenhagen , Denmark
| | - Ulla Vogel
- National Research Centre for the Working Environment , 2100 Copenhagen , Denmark
| | - Cristina Martín
- University of Strasbourg, CNRS , Immunology, Immunopathology and Therapeutic Chemistry , 67000 Strasbourg , France
| | - Lucia G Delogu
- Department of Chemistry and Pharmacy University of Sassari , Sassari 7100 , Italy
- Istituto di Ricerca Pediatrica , Fondazione Città della Speranza , 35129 Padova , Italy
| | - Tina Buerki-Thurnherr
- Swiss Federal Laboratories for Materials Science and Technology (EMPA) , 9014 St. Gallen , Switzerland
| | - Peter Wick
- Swiss Federal Laboratories for Materials Science and Technology (EMPA) , 9014 St. Gallen , Switzerland
| | | | - Roland Hischier
- Swiss Federal Laboratories for Materials Science and Technology (EMPA) , 9014 St. Gallen , Switzerland
| | - Marco Pelin
- Department of Life Sciences , University of Trieste , 34127 Trieste , Italy
| | | | - Mauro Tretiach
- Department of Life Sciences , University of Trieste , 34127 Trieste , Italy
| | - Fabrizia Cesca
- Center for Synaptic Neuroscience and Technology , Istituto Italiano di Tecnologia , 16132 Genova , Italy
| | - Fabio Benfenati
- Center for Synaptic Neuroscience and Technology , Istituto Italiano di Tecnologia , 16132 Genova , Italy
| | - Denis Scaini
- Scuola Internazionale Superiore di Studi Avanzati (SISSA) , 34136 Trieste , Italy
| | - Laura Ballerini
- Scuola Internazionale Superiore di Studi Avanzati (SISSA) , 34136 Trieste , Italy
| | - Kostas Kostarelos
- Nanomedicine Laboratory, Faculty of Biology, Medicine & Health , University of Manchester , Manchester M13 9PL , United Kingdom
| | - Maurizio Prato
- Department of Chemical and Pharmaceutical Sciences , University of Trieste , 34127 Trieste , Italy
- Carbon Nanobiotechnology Laboratory , CIC BiomaGUNE , 20009 San Sebastian , Spain
- Basque Foundation for Science, Ikerbasque , 48013 Bilbao , Spain
| | - Alberto Bianco
- University of Strasbourg, CNRS , Immunology, Immunopathology and Therapeutic Chemistry , 67000 Strasbourg , France
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12
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Fernandez E. Development of visual Neuroprostheses: trends and challenges. Bioelectron Med 2018; 4:12. [PMID: 32232088 PMCID: PMC7098238 DOI: 10.1186/s42234-018-0013-8] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2018] [Accepted: 07/27/2018] [Indexed: 02/06/2023] Open
Abstract
Visual prostheses are implantable medical devices that are able to provide some degree of vision to individuals who are blind. This research field is a challenging subject in both ophthalmology and basic science that has progressed to a point where there are already several commercially available devices. However, at present, these devices are only able to restore a very limited vision, with relatively low spatial resolution. Furthermore, there are still many other open scientific and technical challenges that need to be solved to achieve the therapeutic benefits envisioned by these new technologies. This paper provides a brief overview of significant developments in this field and introduces some of the technical and biological challenges that still need to be overcome to optimize their therapeutic success, including long-term viability and biocompatibility of stimulating electrodes, the selection of appropriate patients for each artificial vision approach, a better understanding of brain plasticity and the development of rehabilitative strategies specifically tailored for each patient.
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Affiliation(s)
- Eduardo Fernandez
- Institute of Bioengineering, University Miguel Hernández and CIBER-BBN, Avda de la Universidad, s/n, 03202 Alicante, Elche Spain.,2John A. Moran Eye Center, University of Utah, Salt Lake City, USA
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13
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Flores T, Lei X, Huang T, Lorach H, Dalal R, Galambos L, Kamins T, Mathieson K, Palanker D. Optimization of pillar electrodes in subretinal prosthesis for enhanced proximity to target neurons. J Neural Eng 2018; 15:036011. [PMID: 29388561 DOI: 10.1088/1741-2552/aaac39] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
OBJECTIVE High-resolution prosthetic vision requires dense stimulating arrays with small electrodes. However, such miniaturization reduces electrode capacitance and penetration of electric field into tissue. We evaluate potential solutions to these problems with subretinal implants based on utilization of pillar electrodes. APPROACH To study integration of three-dimensional (3D) implants with retinal tissue, we fabricated arrays with varying pillar diameter, pitch, and height, and implanted beneath the degenerate retina in rats (Royal College of Surgeons, RCS). Tissue integration was evaluated six weeks post-op using histology and whole-mount confocal fluorescence imaging. The electric field generated by various electrode configurations was calculated in COMSOL, and stimulation thresholds assessed using a model of network-mediated retinal response. MAIN RESULTS Retinal tissue migrated into the space between pillars with no visible gliosis in 90% of implanted arrays. Pillars with 10 μm height reached the middle of the inner nuclear layer (INL), while 22 μm pillars reached the upper portion of the INL. Electroplated pillars with dome-shaped caps increase the active electrode surface area. Selective deposition of sputtered iridium oxide onto the cap ensures localization of the current injection to the pillar top, obviating the need to insulate the pillar sidewall. According to computational model, pillars having a cathodic return electrode above the INL and active anodic ring electrode at the surface of the implant would enable six times lower stimulation threshold, compared to planar arrays with circumferential return, but suffer from greater cross-talk between the neighboring pixels. SIGNIFICANCE 3D electrodes in subretinal prostheses help reduce electrode-tissue separation and decrease stimulation thresholds to enable smaller pixels, and thereby improve visual acuity of prosthetic vision.
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Affiliation(s)
- Thomas Flores
- Department of Applied Physics, Stanford University, Stanford, CA, United States of America
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14
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Buchs G, Simon N, Maidenbaum S, Amedi A. Waist-up protection for blind individuals using the EyeCane as a primary and secondary mobility aid. Restor Neurol Neurosci 2018; 35:225-235. [PMID: 28157111 PMCID: PMC5366249 DOI: 10.3233/rnn-160686] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Background: One of the most stirring statistics in relation to the mobility of blind individuals is the high rate of upper body injuries, even when using the white-cane. Objective: We here addressed a rehabilitation- oriented challenge of providing a reliable tool for blind people to avoid waist-up obstacles, namely one of the impediments to their successful mobility using currently available methods (e.g., white-cane). Methods: We used the EyeCane, a device we developed which translates distances from several angles to haptic and auditory cues in an intuitive and unobtrusive manner, serving both as a primary and secondary mobility aid. We investigated the rehabilitation potential of such a device in facilitating visionless waist-up body protection. Results: After ∼5 minutes of training with the EyeCane blind participants were able to successfully detect and avoid obstacles waist-high and up. This was significantly higher than their success when using the white-cane alone. As avoidance of obstacles required participants to perform an additional cognitive process after their detection, the avoidance rate was significantly lower than the detection rate. Conclusion: Our work has demonstrated that the EyeCane has the potential to extend the sensory world of blind individuals by expanding their currently accessible inputs, and has offered them a new practical rehabilitation tool.
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Affiliation(s)
- Galit Buchs
- Department of Cognitive Science, Faculty of Humanities, Hebrew University of Jerusalem, Hadassah Ein-Kerem, Jerusalem, Israel
| | - Noa Simon
- The Edmond and Lily Safra Center for Brain Research, Hebrew University of Jerusalem, Hadassah Ein-Kerem, Jerusalem, Israel
| | - Shachar Maidenbaum
- Department of Medical Neurobiology, Institute for Medical Research Israel-Canada, Faculty of Medicine, Hebrew University of Jerusalem, Hadassah Ein-Kerem, Jerusalem, Israel
| | - Amir Amedi
- Department of Cognitive Science, Faculty of Humanities, Hebrew University of Jerusalem, Hadassah Ein-Kerem, Jerusalem, Israel.,The Edmond and Lily Safra Center for Brain Research, Hebrew University of Jerusalem, Hadassah Ein-Kerem, Jerusalem, Israel.,Department of Medical Neurobiology, Institute for Medical Research Israel-Canada, Faculty of Medicine, Hebrew University of Jerusalem, Hadassah Ein-Kerem, Jerusalem, Israel.,Sorbonne Universités UPMC Univ Paris 06, Institut de la Vision, Paris, France
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15
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Yue L, Weiland JD, Roska B, Humayun MS. Retinal stimulation strategies to restore vision: Fundamentals and systems. Prog Retin Eye Res 2016; 53:21-47. [DOI: 10.1016/j.preteyeres.2016.05.002] [Citation(s) in RCA: 173] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2016] [Revised: 05/13/2016] [Accepted: 05/21/2016] [Indexed: 11/28/2022]
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Abstract
OBJECTIVE High resolution visual prostheses require dense stimulating arrays with localized inputs of individual electrodes. We study the electric field produced by multielectrode arrays in electrolyte to determine an optimal configuration of return electrodes and activation sequence. APPROACH To determine the boundary conditions for computation of the electric field in electrolyte, we assessed current dynamics using an equivalent circuit of a multielectrode array with interleaved return electrodes. The electric field modeled with two different boundary conditions derived from the equivalent circuit was then compared to measurements of electric potential in electrolyte. To assess the effect of return electrode configuration on retinal stimulation, we transformed the computed electric fields into retinal response using a model of neural network-mediated stimulation. MAIN RESULTS Electric currents at the capacitive electrode-electrolyte interface redistribute over time, so that boundary conditions transition from equipotential surfaces at the beginning of the pulse to uniform current density in steady state. Experimental measurements confirmed that, in steady state, the boundary condition corresponds to a uniform current density on electrode surfaces. Arrays with local return electrodes exhibit improved field confinement and can elicit stronger network-mediated retinal response compared to those with a common remote return. Connecting local return electrodes enhances the field penetration depth and allows reducing the return electrode area. Sequential activation of the pixels in large monopolar arrays reduces electrical cross-talk and improves the contrast in pattern stimulation. SIGNIFICANCE Accurate modeling of multielectrode arrays helps optimize the electrode configuration to maximize the spatial resolution, contrast and dynamic range of retinal prostheses.
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Affiliation(s)
- Thomas Flores
- Department of Applied Physics, Stanford University, Stanford, CA 94305, USA
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Fabbro A, Scaini D, León V, Vázquez E, Cellot G, Privitera G, Lombardi L, Torrisi F, Tomarchio F, Bonaccorso F, Bosi S, Ferrari AC, Ballerini L, Prato M. Graphene-Based Interfaces Do Not Alter Target Nerve Cells. ACS NANO 2016; 10:615-623. [PMID: 26700626 DOI: 10.1021/acsnano.5b05647] [Citation(s) in RCA: 96] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Neural-interfaces rely on the ability of electrodes to transduce stimuli into electrical patterns delivered to the brain. In addition to sensitivity to the stimuli, stability in the operating conditions and efficient charge transfer to neurons, the electrodes should not alter the physiological properties of the target tissue. Graphene is emerging as a promising material for neuro-interfacing applications, given its outstanding physico-chemical properties. Here, we use graphene-based substrates (GBSs) to interface neuronal growth. We test our GBSs on brain cell cultures by measuring functional and synaptic integrity of the emerging neuronal networks. We show that GBSs are permissive interfaces, even when uncoated by cell adhesion layers, retaining unaltered neuronal signaling properties, thus being suitable for carbon-based neural prosthetic devices.
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Affiliation(s)
- Alessandra Fabbro
- International School for Advanced Studies (SISSA/ISAS) , Trieste 34136, Italy
- Department of Chemical and Pharmaceutical Sciences, University of Trieste , Trieste 34127, Italy
| | - Denis Scaini
- International School for Advanced Studies (SISSA/ISAS) , Trieste 34136, Italy
- Life Science Department, University of Trieste , Trieste 34127, Italy
- NanoInnovation Laboratory, ELETTRA Synchrotron Light Source , Trieste 34149, Italy
| | - Verónica León
- Department of Organic Chemisty, University of Castilla-La Mancha , Ciudad Real 13071, Spain
| | - Ester Vázquez
- Department of Organic Chemisty, University of Castilla-La Mancha , Ciudad Real 13071, Spain
| | - Giada Cellot
- International School for Advanced Studies (SISSA/ISAS) , Trieste 34136, Italy
| | - Giulia Privitera
- Cambridge Graphene Centre, University of Cambridge , Cambridge CB3 0FA, United Kingdom
| | - Lucia Lombardi
- Cambridge Graphene Centre, University of Cambridge , Cambridge CB3 0FA, United Kingdom
| | - Felice Torrisi
- Cambridge Graphene Centre, University of Cambridge , Cambridge CB3 0FA, United Kingdom
| | - Flavia Tomarchio
- Cambridge Graphene Centre, University of Cambridge , Cambridge CB3 0FA, United Kingdom
| | - Francesco Bonaccorso
- Cambridge Graphene Centre, University of Cambridge , Cambridge CB3 0FA, United Kingdom
- Istituto Italiano di Tecnologia, Graphene Labs , Genova 16163, Italy
| | - Susanna Bosi
- Department of Chemical and Pharmaceutical Sciences, University of Trieste , Trieste 34127, Italy
| | - Andrea C Ferrari
- Cambridge Graphene Centre, University of Cambridge , Cambridge CB3 0FA, United Kingdom
| | - Laura Ballerini
- International School for Advanced Studies (SISSA/ISAS) , Trieste 34136, Italy
- Life Science Department, University of Trieste , Trieste 34127, Italy
| | - Maurizio Prato
- Department of Chemical and Pharmaceutical Sciences, University of Trieste , Trieste 34127, Italy
- Carbon Nanobiotechnology Laboratory, CIC biomaGUNE , Paseo de Miramón 182, 20009 Donostia-San Sebastian, Spain
- Basque Foundation for Science, Ikerbasque , Bilbao 48013, Spain
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18
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Cao X, Sui X, Lyu Q, Li L, Chai X. Effects of different three-dimensional electrodes on epiretinal electrical stimulation by modeling analysis. J Neuroeng Rehabil 2015; 12:73. [PMID: 26311232 PMCID: PMC4551567 DOI: 10.1186/s12984-015-0065-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Accepted: 08/19/2015] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Epiretinal prostheses have been greatly successful in helping restore the vision of patients blinded by retinal degenerative diseases. The design of stimulating electrodes plays a crucial role in the performance of epiretinal prostheses. The objective of this study was to investigate, through computational modeling analysis, the effects on the excitation of retinal ganglion cells (RGCs) when different three-dimensional (3-D) electrodes were placed in the epiretinal space. METHODS 3-D finite element models of retinal electrical stimulation were created in COMSOL using a platinum microelectrode, a vitreous body, multi-layered retinal tissue, and retinal pigment epithelium (RPE). Disk and non-planar electrodes with different 3-D structures were used in the epiretinal electrical stimulation. In addition, a multi-RGC model including ionic mechanisms was constructed in NEURON to study the excitability of RGCs in response to epiretinal electrical stimulation by different types of electrodes. Threshold current, threshold charge density, and the activated RGC area were the three key factors used to evaluate the stimulating electrode's performance. RESULTS As the electrode-retina distance increased, both threshold current and threshold charge density showed an approximately linear relationship. Increasing the disk electrode's diameter resulted in an increase in threshold current and a decrease in threshold charge density. Non-planar electrodes evoked different activation responses in RGCs than the disk electrode. Concave electrodes produced superior stimulation localization and electrode safety while convex electrodes performed relatively poorly. CONCLUSIONS Investigation of epiretinal electrical stimulation using different 3-D electrodes would further the optimization of electrode design and help improve the performance of epiretinal prostheses. The combination of finite element analysis in COMSOL and NEURON software provides an efficient way to evaluate the influences of various 3-D electrodes on epiretinal electrical stimulation. Non-planar electrodes had larger threshold currents than disk electrodes. Of the five types of electrodes, concave hemispherical electrodes may be the ideal option, considering their superior stimulation localization and electrode safety.
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Affiliation(s)
- Xun Cao
- School of Biomedical Engineering, Shanghai Jiao Tong University, No.800 Dongchuan Road, Shanghai, People's Republic of China.
| | - Xiaohong Sui
- School of Biomedical Engineering, Shanghai Jiao Tong University, No.800 Dongchuan Road, Shanghai, People's Republic of China.
| | - Qing Lyu
- School of Biomedical Engineering, Shanghai Jiao Tong University, No.800 Dongchuan Road, Shanghai, People's Republic of China.
| | - Liming Li
- School of Biomedical Engineering, Shanghai Jiao Tong University, No.800 Dongchuan Road, Shanghai, People's Republic of China.
| | - Xinyu Chai
- School of Biomedical Engineering, Shanghai Jiao Tong University, No.800 Dongchuan Road, Shanghai, People's Republic of China.
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Synthetic 3D diamond-based electrodes for flexible retinal neuroprostheses: Model, production and in vivo biocompatibility. Biomaterials 2015. [PMID: 26210174 DOI: 10.1016/j.biomaterials.2015.07.018] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Two retinal implants have recently received the CE mark and one has obtained FDA approval for the restoration of useful vision in blind patients. Since the spatial resolution of current vision prostheses is not sufficient for most patients to detect faces or perform activities of daily living, more electrodes with less crosstalk are needed to transfer complex images to the retina. In this study, we modelled planar and three-dimensional (3D) implants with a distant ground or a ground grid, to demonstrate greater spatial resolution with 3D structures. Using such flexible 3D implant prototypes, we showed that the degenerated retina could mould itself to the inside of the wells, thereby isolating bipolar neurons for specific, independent stimulation. To investigate the in vivo biocompatibility of diamond as an electrode or an isolating material, we developed a procedure for depositing diamond onto flexible 3D retinal implants. Taking polyimide 3D implants as a reference, we compared the number of neurones integrating the 3D diamond structures and their ratio to the numbers of all cells, including glial cells. Bipolar neurones were increased whereas there was no increase even a decrease in the total cell number. SEM examinations of implants confirmed the stability of the diamond after its implantation in vivo. This study further demonstrates the potential of 3D designs for increasing the resolution of retinal implants and validates the safety of diamond materials for retinal implants and neuroprostheses in general.
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20
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Xiang Z, Yen SC, Sheshadri S, Xue N, Lee SH, Wang J, Thakor NV, Lee C. Flexible and self-adaptive neural ribbon with three-dimensional electrodes for sciatic nerve recording. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2015; 2015:3157-3160. [PMID: 26736962 DOI: 10.1109/embc.2015.7319062] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Various peripheral nerve interfaces have been developed in the last decades and transferred into neuroscientific researches or clinical applications. In this study, we present a novel flexible neural ribbon electrode that can achieve self-adaption to nerves in various diameters and have three dimensional (3D) contacts. Impedance spectroscopy of the neural ribbon electrode was carried out to determine its electrochemical characteristics during the recording. The recording capability of the neural ribbon on sciatic nerves with different diameter was demonstrated by successful signal acquisitions.
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Hébert C, Scorsone E, Bendali A, Kiran R, Cottance M, Girard HA, Degardin J, Dubus E, Lissorgues G, Rousseau L, Mailley P, Picaud S, Bergonzo P. Boron doped diamond biotechnology: from sensors to neurointerfaces. Faraday Discuss 2014; 172:47-59. [PMID: 25259508 DOI: 10.1039/c4fd00040d] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Boron doped nanocrystalline diamond is known as a remarkable material for the fabrication of sensors, taking advantage of its biocompatibility, electrochemical properties, and stability. Sensors can be fabricated to directly probe physiological species from biofluids (e.g. blood or urine), as will be presented. In collaboration with electrophysiologists and biologists, the technology was adapted to enable structured diamond devices such as microelectrode arrays (MEAs), i.e. common electrophysiology tools, to probe neuronal activity distributed over large populations of neurons or embryonic organs. Specific MEAs can also be used to build neural prostheses or implants to compensate function losses due to lesions or degeneration of parts of the central nervous system, such as retinal implants, which exhibit real promise as biocompatible neuroprostheses for in vivo neuronal stimulations. New electrode geometries enable high performance electrodes to surpass more conventional materials for such applications.
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Affiliation(s)
- C Hébert
- CEA, LIST, Diamond Sensors Laboratory, F-91191, Gif-sur-Yvette, France.
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22
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Heimler B, Weisz N, Collignon O. Revisiting the adaptive and maladaptive effects of crossmodal plasticity. Neuroscience 2014; 283:44-63. [PMID: 25139761 DOI: 10.1016/j.neuroscience.2014.08.003] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2014] [Revised: 08/01/2014] [Accepted: 08/06/2014] [Indexed: 11/15/2022]
Abstract
One of the most striking demonstrations of experience-dependent plasticity comes from studies of sensory-deprived individuals (e.g., blind or deaf), showing that brain regions deprived of their natural inputs change their sensory tuning to support the processing of inputs coming from the spared senses. These mechanisms of crossmodal plasticity have been traditionally conceptualized as having a double-edged sword effect on behavior. On one side, crossmodal plasticity is conceived as adaptive for the development of enhanced behavioral skills in the remaining senses of early-deaf or blind individuals. On the other side, crossmodal plasticity raises crucial challenges for sensory restoration and is typically conceived as maladaptive since its presence may prevent optimal recovery in sensory-re-afferented individuals. In the present review we stress that this dichotomic vision is oversimplified and we emphasize that the notions of the unavoidable adaptive/maladaptive effects of crossmodal reorganization for sensory compensation/restoration may actually be misleading. For this purpose we critically review the findings from the blind and deaf literatures, highlighting the complementary nature of these two fields of research. The integrated framework we propose here has the potential to impact on the way rehabilitation programs for sensory recovery are carried out, with the promising prospect of eventually improving their final outcomes.
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Affiliation(s)
- B Heimler
- Center for Mind/Brain Sciences (CIMeC), University of Trento, Italy.
| | - N Weisz
- Center for Mind/Brain Sciences (CIMeC), University of Trento, Italy
| | - O Collignon
- Center for Mind/Brain Sciences (CIMeC), University of Trento, Italy
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Bendali A, Agnès C, Meffert S, Forster V, Bongrain A, Arnault JC, Sahel JA, Offenhäusser A, Bergonzo P, Picaud S. Distinctive glial and neuronal interfacing on nanocrystalline diamond. PLoS One 2014; 9:e92562. [PMID: 24664111 PMCID: PMC3963931 DOI: 10.1371/journal.pone.0092562] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Accepted: 02/25/2014] [Indexed: 11/20/2022] Open
Abstract
Direct electrode/neuron interfacing is a key challenge to achieve high resolution of neuronal stimulation required for visual prostheses. Neuronal interfacing on biomaterials commonly requires the presence of glial cells and/or protein coating. Nanocrystalline diamond is a highly mechanically stable biomaterial with a remarkably large potential window for the electrical stimulation of tissues. Using adult retinal cell cultures from rats, we found that glial cells and retinal neurons grew equally well on glass and nanocrystalline diamond. The use of a protein coating increased cell survival, particularly for glial cells. However, bipolar neurons appeared to grow even in direct contact with bare diamond. We investigated whether the presence of glial cells contributed to this direct neuron/diamond interface, by using purified adult retinal ganglion cells to seed diamond and glass surfaces with and without protein coatings. Surprisingly, these fully differentiated spiking neurons survived better on nanocrystalline diamond without any protein coating. This greater survival was indicated by larger cell numbers and the presence of longer neurites. When a protein pattern was drawn on diamond, neurons did not grow preferentially on the coated area, by contrast to their behavior on a patterned glass. This study highlights the interesting biocompatibility properties of nanocrystalline diamond, allowing direct neuronal interfacing, whereas a protein coating was required for glial cell growth.
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Affiliation(s)
- Amel Bendali
- INSERM U968, Institut de la Vision, Paris, France
- Sorbonne Universités, UPMC Univ Paris 06 UMR_S968, Institut de la Vision, Paris, France
- CNRS UMR7210, Institut de la Vision, Paris, France
| | - Charles Agnès
- CEA-LIST, Diamond Sensors Laboratory, Saclay, Gif-sur-Yvette, France
| | - Simone Meffert
- Institute of Bio- & Nanosystems - Bioelectronics (IBN2) Forschungszentrum, Juelich, Germany
| | - Valérie Forster
- INSERM U968, Institut de la Vision, Paris, France
- Sorbonne Universités, UPMC Univ Paris 06 UMR_S968, Institut de la Vision, Paris, France
- CNRS UMR7210, Institut de la Vision, Paris, France
| | | | | | - José-Alain Sahel
- INSERM U968, Institut de la Vision, Paris, France
- Sorbonne Universités, UPMC Univ Paris 06 UMR_S968, Institut de la Vision, Paris, France
- CNRS UMR7210, Institut de la Vision, Paris, France
- Centre Hospitalier National d'Ophtalmologie des Quinze-Vingts, Paris, France
- Fondation Ophtalmologique Adolphe de Rothschild, Paris, France
- Institute of Ophthalmology, University College of London, London, United Kingdom
- French Academy of Sciences, Paris, France
| | - Andreas Offenhäusser
- Institute of Bio- & Nanosystems - Bioelectronics (IBN2) Forschungszentrum, Juelich, Germany
| | - Philippe Bergonzo
- CEA-LIST, Diamond Sensors Laboratory, Saclay, Gif-sur-Yvette, France
| | - Serge Picaud
- INSERM U968, Institut de la Vision, Paris, France
- Sorbonne Universités, UPMC Univ Paris 06 UMR_S968, Institut de la Vision, Paris, France
- CNRS UMR7210, Institut de la Vision, Paris, France
- Fondation Ophtalmologique Adolphe de Rothschild, Paris, France
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Picaud S, Sahel JA. Retinal prostheses: clinical results and future challenges. C R Biol 2014; 337:214-22. [PMID: 24702848 DOI: 10.1016/j.crvi.2014.01.001] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2014] [Accepted: 01/06/2014] [Indexed: 12/30/2022]
Abstract
Retinal prostheses aim at restoring visual perception in blind patients affected by retinal diseases leading to the loss of photoreceptors, such as age-related macular degeneration or retinitis pigmentosa. Recent clinical trials have demonstrated the feasibility of this approach for restoring useful vision. Despite a limited number of electrodes (60), and therefore of pixels, some patients were able to read words and to recognize high-contrast objects. Face recognition and independent locomotion in unknown urban environments imply technological breakthroughs to increase the number and density of electrodes. This review presents recent clinical results and discusses future solutions to answer the major technological challenges.
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Affiliation(s)
- Serge Picaud
- Inserm, U968, Institut de la Vision, 17, rue Moreau, 75012 Paris, France; Sorbonne Universités, Université Pierre et Marie Curie (Paris-6), UMR S968, Institut de la Vision, 17, rue Moreau, 75012 Paris, France; CNRS, UMR 7210, Institut de la Vision, 17, rue Moreau, 75012 Paris, France; Fondation Ophtalmologique Adolphe de Rothschild, 75019 Paris, France.
| | - José-Alain Sahel
- Inserm, U968, Institut de la Vision, 17, rue Moreau, 75012 Paris, France; Sorbonne Universités, Université Pierre et Marie Curie (Paris-6), UMR S968, Institut de la Vision, 17, rue Moreau, 75012 Paris, France; CNRS, UMR 7210, Institut de la Vision, 17, rue Moreau, 75012 Paris, France; Fondation Ophtalmologique Adolphe de Rothschild, 75019 Paris, France; Centre Hospitalier National d'Ophtalmologie des Quinze-Vingts, 75012 Paris, France; Institute of Ophthalmology, University College of London, London EC1V 9EL, United Kingdom; Académie des sciences, Institut de France, 23, quai de Conti, 75006 Paris, France
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Maidenbaum S, Abboud S, Amedi A. Sensory substitution: closing the gap between basic research and widespread practical visual rehabilitation. Neurosci Biobehav Rev 2013; 41:3-15. [PMID: 24275274 DOI: 10.1016/j.neubiorev.2013.11.007] [Citation(s) in RCA: 89] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2013] [Revised: 10/06/2013] [Accepted: 11/08/2013] [Indexed: 11/25/2022]
Abstract
Sensory substitution devices (SSDs) have come a long way since first developed for visual rehabilitation. They have produced exciting experimental results, and have furthered our understanding of the human brain. Unfortunately, they are still not used for practical visual rehabilitation, and are currently considered as reserved primarily for experiments in controlled settings. Over the past decade, our understanding of the neural mechanisms behind visual restoration has changed as a result of converging evidence, much of which was gathered with SSDs. This evidence suggests that the brain is more than a pure sensory-machine but rather is a highly flexible task-machine, i.e., brain regions can maintain or regain their function in vision even with input from other senses. This complements a recent set of more promising behavioral achievements using SSDs and new promising technologies and tools. All these changes strongly suggest that the time has come to revive the focus on practical visual rehabilitation with SSDs and we chart several key steps in this direction such as training protocols and self-train tools.
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Affiliation(s)
- Shachar Maidenbaum
- Department of Medical Neurobiology, The Institute for Medical Research Israel-Canada, Faculty of Medicine, The Hebrew University of Jerusalem, Jerusalem 91220, Israel
| | - Sami Abboud
- Department of Medical Neurobiology, The Institute for Medical Research Israel-Canada, Faculty of Medicine, The Hebrew University of Jerusalem, Jerusalem 91220, Israel
| | - Amir Amedi
- Department of Medical Neurobiology, The Institute for Medical Research Israel-Canada, Faculty of Medicine, The Hebrew University of Jerusalem, Jerusalem 91220, Israel; The Edmond and Lily Safra Center for Brain Sciences (ELSC), The Hebrew University of Jerusalem, Jerusalem 91220, Israel.
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Bendali A, Lorach H, Djilas M, Marre O, Bensoman R, Rousseau L, Lissorgues G, Scorsone E, Bergonzo P, Garrido JA, Sahel JA, Picaud S. [Restoring vision in blind patients following photoreceptor degeneration: clinical results and future challenges]. Biol Aujourdhui 2013; 207:123-32. [PMID: 24103342 DOI: 10.1051/jbio/2013008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2013] [Indexed: 11/15/2022]
Abstract
Retinal prostheses aim at restoring vision in patients blind from photoreceptor degeneration by electrically stimulating the residual retinal tissue. Currently, the most efficient implants are either inserted in the subretinal space or on the vitreal side of the retina (epi-retinal). Although the residual tissue can partly degenerate, it was shown that acute stimulation of residual neurones can induce visual percepts. Recently, a clinical trial with the epiretinal Argus2 device (60 electrodes) from the company 2nd Sight enabled most patients to orient and find light targets, some even reading words. This device has received a CE mark. Surprisingly, when the subretinal implant from the company Retina Implant AG displaying many more electrodes (1500 electrodes) was evaluated in clinical trials, the patient visual performances were fairly similar. The restored visual performances of the patients demonstrate that blind patients can recover some visual function when their residual retina is properly stimulated. However, the resolution is not yet sufficient to perform complex tasks such as autonomous locomotion, face identification or text reading. Several challenges remain to generate an increase in pixel density corresponding to the increase in electrode number and density. These challenges include the stimulation modality, the tissue/implant interface design, the electrode materials, and the visual information encoder. This review will discuss these great challenges after introducing the major clinical results.
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Affiliation(s)
- Amel Bendali
- INSERM, U968, Institut de la Vision, 75012 Paris, France - UPMC Université Paris 06, UMR S968, Institut de la Vision, 75012 Paris, France - CNRS, UMR 7210, Institut de la Vision, 75012 Paris, France
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Bendali A, Hess LH, Seifert M, Forster V, Stephan AF, Garrido JA, Picaud S. Purified neurons can survive on peptide-free graphene layers. Adv Healthc Mater 2013; 2:929-33. [PMID: 23300024 DOI: 10.1002/adhm.201200347] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2012] [Revised: 10/25/2012] [Indexed: 01/07/2023]
Affiliation(s)
- Amel Bendali
- Institut de la Vision, INSERM, U968, UPMC Univ Paris, Paris, France
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Long-term in vivo impedance changes of subretinal microelectrodes implanted in dystrophic P23H rats. Int J Artif Organs 2013; 36:612-9. [PMID: 23918262 DOI: 10.5301/ijao.5000213] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/08/2013] [Indexed: 11/20/2022]
Abstract
Retinal prostheses are being developed to restore vision in blind patients with photoreceptor degeneration. Electrodes arrays were subretinally implanted in transgenic P23H rats with their photoreceptors degenerated. Electrical stability of the implants was evaluated by long-term monitoring of their impedance changes. Electrode impedances were found to increase by two log units over a three weeks period whereas no impedance increase was noted when the implants were located in the vitreous. In case of hemorrhage or major fibrous reactions, the impedance continued to increase steadily. After explantation, it recovered its initial value indicating no deterioration of the implant. Although the glial cell layer at the surface of the subretinal space was slightly larger, no major glial reaction was seen in direct contact to the implant. These results indicate that no functional testing should be considered before at least three weeks post implantation.
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Agudelo-Toro A, Neef A. Computationally efficient simulation of electrical activity at cell membranes interacting with self-generated and externally imposed electric fields. J Neural Eng 2013; 10:026019. [PMID: 23503026 DOI: 10.1088/1741-2560/10/2/026019] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVE We present a computational method that implements a reduced set of Maxwell's equations to allow simulation of cells under realistic conditions: sub-micron cell morphology, a conductive non-homogeneous space and various ion channel properties and distributions. APPROACH While a reduced set of Maxwell's equations can be used to couple membrane currents to extra- and intracellular potentials, this approach is rarely taken, most likely because adequate computational tools are missing. By using these equations, and introducing an implicit solver, numerical stability is attained even with large time steps. The time steps are limited only by the time development of the membrane potentials. MAIN RESULTS This method allows simulation times of tens of minutes instead of weeks, even for complex problems. The extracellular fields are accurately represented, including secondary fields, which originate at inhomogeneities of the extracellular space and can reach several millivolts. We present a set of instructive examples that show how this method can be used to obtain reference solutions for problems, which might not be accurately captured by the traditional approaches. This includes the simulation of realistic magnitudes of extracellular action potential signals in restricted extracellular space. SIGNIFICANCE The electric activity of neurons creates extracellular potentials. Recent findings show that these endogenous fields act back onto the neurons, contributing to the synchronization of population activity. The influence of endogenous fields is also relevant for understanding therapeutic approaches such as transcranial direct current, transcranial magnetic and deep brain stimulation. The mutual interaction between fields and membrane currents is not captured by today's concepts of cellular electrophysiology, including the commonly used activation function, as those concepts are based on isolated membranes in an infinite, isopotential extracellular space. The presented tool makes simulations with detailed morphology and implicit interactions of currents and fields available to the electrophysiology community.
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Affiliation(s)
- Andres Agudelo-Toro
- Max Planck Institute for Dynamics and Self-Organization, Göttingen, Germany.
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Neural stimulation for visual rehabilitation: advances and challenges. ACTA ACUST UNITED AC 2012; 107:421-31. [PMID: 23148976 DOI: 10.1016/j.jphysparis.2012.10.003] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2012] [Revised: 10/04/2012] [Accepted: 10/23/2012] [Indexed: 02/07/2023]
Abstract
Blindness affects tens of million people worldwide and its prevalence constantly increases along with population aging. In some pathologies leading to vision loss, prosthetic approaches are currently the only hope for the patient to recover some visual perception. Here, we review the latest advances in visual prosthetic strategies with their respective strength and weakness. The principle is to electrically stimulate neurons along the visual pathway. Ocular approaches target the remaining retinal cells whereas brain stimulation aims at stimulating higher visual structures directly. Even though ocular approaches are less invasive and easier to implement, brain stimulation can be applied to diseases where the connection between the retina and the brain is lost such as in glaucoma and could therefore benefit to patients with different pathologies. Today, numbers of groups are investigating these strategies and the first devices start being commercialized. However, critical bottlenecks still impair our scientific efforts towards efficient visual implants. These challenges include electrode miniaturization, material optimization, multiplexing of stimulation channels and encoding of visual information into electrical stimuli.
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O'Brien EE, Greferath U, Vessey KA, Jobling AI, Fletcher EL. Electronic restoration of vision in those with photoreceptor degenerations. Clin Exp Optom 2012; 95:473-83. [PMID: 22823954 DOI: 10.1111/j.1444-0938.2012.00783.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2011] [Revised: 06/06/2012] [Accepted: 06/11/2012] [Indexed: 11/27/2022] Open
Abstract
Complete loss of vision is one of the most feared sequelae of retinal disease. Currently, there are few if any treatment options available to patients that may slow or prevent blindness in diseases caused by photoreceptor loss, such as retinitis pigmentosa and age-related macular degeneration. Electronic restoration of vision has emerged over recent years as a safe and viable option for those who have lost substantial numbers of photoreceptors and who are severely vision impaired. Indeed, there has been a dramatic increase in our understanding of what is required to restore vision using an electronic retinal prosthesis. Recent reports show that for some patients, restoration of vision to the point of reading large letters is possible. In this review, we examine the types of implants currently under investigation and the results these devices have achieved clinically. We then consider a range of engineering and biological factors that may need to be considered to improve the visual performance of newer-generation devices. With added research, it is hoped that the level of vision achieved with newer generation devices will steadily improve, resulting in enhanced quality of life for those with severe vision impairment.
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Affiliation(s)
- Emily E O'Brien
- Department of Anatomy and Cell Biology, The University of Melbourne, Parkville, Victoria, Australia.
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Joucla S, Rousseau L, Yvert B. Focalizing electrical neural stimulation with penetrating microelectrode arrays: A modeling study. J Neurosci Methods 2012; 209:250-4. [DOI: 10.1016/j.jneumeth.2012.05.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2012] [Revised: 05/02/2012] [Accepted: 05/03/2012] [Indexed: 11/29/2022]
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Joucla S, Yvert B. Modeling extracellular electrical neural stimulation: from basic understanding to MEA-based applications. ACTA ACUST UNITED AC 2011; 106:146-58. [PMID: 22036892 DOI: 10.1016/j.jphysparis.2011.10.003] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2011] [Revised: 09/02/2011] [Accepted: 10/10/2011] [Indexed: 01/28/2023]
Abstract
Extracellular electrical stimulation of neural networks has been widely used empirically for decades with individual electrodes. Since recently, microtechnology provides advanced systems with high-density microelectrode arrays (MEAs). Taking the most of these devices for fundamental goals or developing neural prosthesis requires a good knowledge of the mechanisms underlying electrical stimulation. Here, we review modeling approaches used to determine (1) the electric potential field created by a stimulation and (2) the response of an excitable cell to an applied field. Computation of the potential field requires solving the Poisson equation. While this can be performed analytically in simple electrode-neuron configurations, numerical models are required for realistic geometries. In these models, special care must be taken to model the potential drop at the electrode/tissue interface using appropriate boundary conditions. The neural response to the field can then be calculated using compartmentalized cell models, by solving a cable equation, the source term of which (called activating function) is proportional to the second derivative of the extracellular field along the neural arborization. Analytical and numerical solutions to this equation are first presented. Then, we discuss the use of approximated solutions to intuitively predict the neuronal response: Either the "activating function" or the "mirror estimate", depending on the pulse duration and the cell space constant. Finally, we address the design of optimal electrode configurations allowing the selective activation of neurons near each stimulation site. This can be achieved using either multipolar configurations, or the "ground surface" configuration, which can be easily integrated in high-density MEAs. Overall, models highlighting the mechanisms of electrical microstimulation and improving stimulating devices should help understanding the influence of extracellular fields on neural elements and developing optimized neural prostheses for rehabilitation.
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Affiliation(s)
- Sébastien Joucla
- CNRS, Institut des Neurosciences Cognitives et Intégratives d’Aquitaine, UMR 5287, Bordeaux F-33000, France
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