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Abu Shihada J, Jung M, Decke S, Koschinski L, Musall S, Rincón Montes V, Offenhäusser A. Highly Customizable 3D Microelectrode Arrays for In Vitro and In Vivo Neuronal Tissue Recordings. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2024; 11:e2305944. [PMID: 38240370 PMCID: PMC10987114 DOI: 10.1002/advs.202305944] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2023] [Revised: 12/05/2023] [Indexed: 02/16/2024]
Abstract
Planar microelectrode arrays (MEAs) for - in vitro or in vivo - neuronal signal recordings lack the spatial resolution and sufficient signal-to-noise ratio (SNR) required for a detailed understanding of neural network function and synaptic plasticity. To overcome these limitations, a highly customizable three-dimensional (3D) printing process is used in combination with thin film technology and a self-aligned template-assisted electrochemical deposition process to fabricate 3D-printed-based MEAs on stiff or flexible substrates. Devices with design flexibility and physical robustness are shown for recording neural activity in different in vitro and in vivo applications, achieving high-aspect ratio 3D microelectrodes of up to 33:1. Here, MEAs successfully record neural activity in 3D neuronal cultures, retinal explants, and the cortex of living mice, thereby demonstrating the versatility of the 3D MEA while maintaining high-quality neural recordings. Customizable 3D MEAs provide unique opportunities to study neural activity under regular or various pathological conditions, both in vitro and in vivo, and contribute to the development of drug screening and neuromodulation systems that can accurately monitor the activity of large neural networks over time.
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Affiliation(s)
- J. Abu Shihada
- Institute of Biological Information Processing (IBI‐3) – BioelectronicsForschungszentrum52428JülichGermany
- RWTH Aachen University52062AachenGermany
| | - M. Jung
- Institute of Biological Information Processing (IBI‐3) – BioelectronicsForschungszentrum52428JülichGermany
- RWTH Aachen University52062AachenGermany
| | - S. Decke
- Institute of Biological Information Processing (IBI‐3) – BioelectronicsForschungszentrum52428JülichGermany
| | - L. Koschinski
- Institute of Biological Information Processing (IBI‐3) – BioelectronicsForschungszentrum52428JülichGermany
- RWTH Aachen University52062AachenGermany
- Helmholtz Nano Facility (HNF)Forschungszentrum Jülich52428JülichGermany
| | - S. Musall
- Institute of Biological Information Processing (IBI‐3) – BioelectronicsForschungszentrum52428JülichGermany
- RWTH Aachen University52062AachenGermany
- Faculty of MedicineInstitute of Experimental Epileptology and Cognition ResearchUniversity of Bonn53127BonnGermany
- University Hospital Bonn53127BonnGermany
| | - V. Rincón Montes
- Institute of Biological Information Processing (IBI‐3) – BioelectronicsForschungszentrum52428JülichGermany
| | - A. Offenhäusser
- Institute of Biological Information Processing (IBI‐3) – BioelectronicsForschungszentrum52428JülichGermany
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Vėbraitė I, Bar-Haim C, David-Pur M, Hanein Y. Bi-directional electrical recording and stimulation of the intact retina with a screen-printed soft probe: a feasibility study. Front Neurosci 2024; 17:1288069. [PMID: 38264499 PMCID: PMC10804455 DOI: 10.3389/fnins.2023.1288069] [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: 09/03/2023] [Accepted: 12/14/2023] [Indexed: 01/25/2024] Open
Abstract
Introduction Electrophysiological investigations of intact neural circuits are challenged by the gentle and complex nature of neural tissues. Bi-directional electrophysiological interfacing with the retina, in its intact form, is particularly demanding and currently there is no feasible approach to achieve such investigations. Here we present a feasibility study of a novel soft multi-electrode array suitable for bi-directional electrophysiological study of the intact retina. Methods Screen-printed soft electrode arrays were developed and tested. The soft probes were designed to accommodate the curvature of the retina in the eye and offer an opportunity to study the retina in its intact form. Results For the first time, we show both electrical recording and stimulation capabilities from the intact retina. In particular, we demonstrate the ability to characterize retina responses to electrical stimulation and reveal stable, direct, and indirect responses compared with ex-vivo conditions. Discussion These results demonstrate the unique performances of the new probe while also suggesting that intact retinas retain better stability and robustness than ex-vivo retinas making them more suitable for characterizing retina responses to electrical stimulation.
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Affiliation(s)
- Ieva Vėbraitė
- School of Electrical Engineering, Tel Aviv University, Tel Aviv, Israel
- Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
| | - Chen Bar-Haim
- School of Electrical Engineering, Tel Aviv University, Tel Aviv, Israel
- Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
| | - Moshe David-Pur
- School of Electrical Engineering, Tel Aviv University, Tel Aviv, Israel
- Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
| | - Yael Hanein
- School of Electrical Engineering, Tel Aviv University, Tel Aviv, Israel
- Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
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Kauth A, Mildner AK, Hegel L, Wegener J, Ingebrandt S. Development of Specialized Microelectrode Arrays with Local Electroporation Functionality. Ann Biomed Eng 2024; 52:12-21. [PMID: 37326946 PMCID: PMC10761456 DOI: 10.1007/s10439-023-03268-0] [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: 12/27/2022] [Accepted: 05/31/2023] [Indexed: 06/17/2023]
Abstract
When a cell or tissue is exposed to a pulsed electric field (100-1000 V/cm), the cellular membrane permeabilizes for biomolecules that cannot pass an intact cellular membrane. During this electropermeabilization (EP), plasmid deoxyribonucleic acid sequences encoding therapeutic or regulatory genes can enter the cell, which is called gene electrotransfer (GET). GET using micro-/nano technology provides higher spatial resolution and operates with lower voltage amplitudes compared to conventional bulk EP. Microelectrode arrays (MEAs), which are usually used for the recording and stimulation of neuronal signals, can be utilized for GET as well. In this study, we developed a specialized MEA for local EP of adherent cells. Our manufacturing process provides a most flexible electrode and substrate material selection. We used electrochemical impedance spectroscopy to characterize the impedance of the MEAs and the impact of an adherent cellular layer. We verified the local EP functionality of the MEAs by loading a fluorophore dye into human embryonic kidney 293T cells. Finally, we demonstrated a GET with a subsequent green fluorescent protein expression by the cells. Our experiments prove that a high spatial resolution of GET can be obtained using MEAs.
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Affiliation(s)
- Andrea Kauth
- Institute of Materials in Electrical Engineering 1, RWTH Aachen University, Sommerfeldstr. 18-24, 52074, Aachen, Germany
| | - Anne-Kathrin Mildner
- Institute of Analytical Chemistry, Universitaet Regensburg, Universitaetsstr. 31, 93053, Regensburg, Germany
| | - Lena Hegel
- Institute of Materials in Electrical Engineering 1, RWTH Aachen University, Sommerfeldstr. 18-24, 52074, Aachen, Germany
| | - Joachim Wegener
- Institute of Analytical Chemistry, Universitaet Regensburg, Universitaetsstr. 31, 93053, Regensburg, Germany
- Fraunhofer Research Institution for Microsystems and Solid State Technologies EMFT, Universitaetsstr. 31, 93053, Regensburg, Germany
| | - Sven Ingebrandt
- Institute of Materials in Electrical Engineering 1, RWTH Aachen University, Sommerfeldstr. 18-24, 52074, Aachen, Germany.
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Halfmann C, Rüland T, Müller F, Jehasse K, Kampa BM. Electrophysiological properties of layer 2/3 pyramidal neurons in the primary visual cortex of a retinitis pigmentosa mouse model ( rd10). Front Cell Neurosci 2023; 17:1258773. [PMID: 37780205 PMCID: PMC10540630 DOI: 10.3389/fncel.2023.1258773] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2023] [Accepted: 08/25/2023] [Indexed: 10/03/2023] Open
Abstract
Retinal degeneration is one of the main causes of visual impairment and blindness. One group of retinal degenerative diseases, leading to the loss of photoreceptors, is collectively termed retinitis pigmentosa. In this group of diseases, the remaining retina is largely spared from initial cell death making retinal ganglion cells an interesting target for vision restoration methods. However, it is unknown how downstream brain areas, in particular the visual cortex, are affected by the progression of blindness. Visual deprivation studies have shown dramatic changes in the electrophysiological properties of visual cortex neurons, but changes on a cellular level in retinitis pigmentosa have not been investigated yet. Therefore, we used the rd10 mouse model to perform patch-clamp recordings of pyramidal neurons in layer 2/3 of the primary visual cortex to screen for potential changes in electrophysiological properties resulting from retinal degeneration. Compared to wild-type C57BL/6 mice, we only found an increase in intrinsic excitability around the time point of maximal retinal degeneration. In addition, we saw an increase in the current amplitude of spontaneous putative inhibitory events after a longer progression of retinal degeneration. However, we did not observe a long-lasting shift in excitability after prolonged retinal degeneration. Together, our results provide evidence of an intact visual cortex with promising potential for future therapeutic strategies to restore vision.
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Affiliation(s)
- Claas Halfmann
- Systems Neurophysiology, Institute of Zoology, RWTH Aachen University, Aachen, Germany
| | - Thomas Rüland
- Systems Neurophysiology, Institute of Zoology, RWTH Aachen University, Aachen, Germany
- Molecular and Cellular Physiology, Institute of Biological Information Processing (IBI-1), Forschungszentrum Jülich GmbH, Jülich, Germany
- Research Training Group 2416 MultiSenses-MultiScales, RWTH Aachen University, Aachen, Germany
| | - Frank Müller
- Molecular and Cellular Physiology, Institute of Biological Information Processing (IBI-1), Forschungszentrum Jülich GmbH, Jülich, Germany
- Research Training Group 2416 MultiSenses-MultiScales, RWTH Aachen University, Aachen, Germany
- Research Training Group 2610 Innoretvision, RWTH Aachen University, Aachen, Germany
| | - Kevin Jehasse
- Systems Neurophysiology, Institute of Zoology, RWTH Aachen University, Aachen, Germany
| | - Björn M. Kampa
- Systems Neurophysiology, Institute of Zoology, RWTH Aachen University, Aachen, Germany
- Research Training Group 2416 MultiSenses-MultiScales, RWTH Aachen University, Aachen, Germany
- Research Training Group 2610 Innoretvision, RWTH Aachen University, Aachen, Germany
- JARA BRAIN, Institute of Neuroscience and Medicine (INM-10), Forschungszentrum Jülich, Jülich, Germany
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Forró C, Musall S, Montes VR, Linkhorst J, Walter P, Wessling M, Offenhäusser A, Ingebrandt S, Weber Y, Lampert A, Santoro F. Toward the Next Generation of Neural Iontronic Interfaces. Adv Healthc Mater 2023; 12:e2301055. [PMID: 37434349 DOI: 10.1002/adhm.202301055] [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: 04/03/2023] [Revised: 05/23/2023] [Indexed: 07/13/2023]
Abstract
Neural interfaces are evolving at a rapid pace owing to advances in material science and fabrication, reduced cost of scalable complementary metal oxide semiconductor (CMOS) technologies, and highly interdisciplinary teams of researchers and engineers that span a large range from basic to applied and clinical sciences. This study outlines currently established technologies, defined as instruments and biological study systems that are routinely used in neuroscientific research. After identifying the shortcomings of current technologies, such as a lack of biocompatibility, topological optimization, low bandwidth, and lack of transparency, it maps out promising directions along which progress should be made to achieve the next generation of symbiotic and intelligent neural interfaces. Lastly, it proposes novel applications that can be achieved by these developments, ranging from the understanding and reproduction of synaptic learning to live-long multimodal measurements to monitor and treat various neuronal disorders.
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Affiliation(s)
- Csaba Forró
- Institute for Biological Information Processing - Bioelectronics IBI-3, Wilhelm-Johnen-Straße, 52428, Jülich, Germany
- Institute of Materials in Electrical Engineering 1, RWTH Aachen, Sommerfeldstr. 24, 52074, Aachen, Germany
| | - Simon Musall
- Institute for Biological Information Processing - Bioelectronics IBI-3, Wilhelm-Johnen-Straße, 52428, Jülich, Germany
- Institute for Zoology, RWTH Aachen University, Worringerweg 3, 52074, Aachen, Germany
| | - Viviana Rincón Montes
- Institute for Biological Information Processing - Bioelectronics IBI-3, Wilhelm-Johnen-Straße, 52428, Jülich, Germany
| | - John Linkhorst
- Chemical Process Engineering, RWTH Aachen, Forckenbeckstr. 51, 52074, Aachen, Germany
| | - Peter Walter
- Department of Ophthalmology, University Hospital RWTH Aachen, Pauwelsstr. 30, 52074, Aachen, Germany
| | - Matthias Wessling
- Chemical Process Engineering, RWTH Aachen, Forckenbeckstr. 51, 52074, Aachen, Germany
- DWI Leibniz Institute for Interactive Materials, RWTH Aachen, Forckenbeckstr. 50, 52074, Aachen, Germany
| | - Andreas Offenhäusser
- Institute for Biological Information Processing - Bioelectronics IBI-3, Wilhelm-Johnen-Straße, 52428, Jülich, Germany
| | - Sven Ingebrandt
- Institute of Materials in Electrical Engineering 1, RWTH Aachen, Sommerfeldstr. 24, 52074, Aachen, Germany
| | - Yvonne Weber
- Department of Epileptology, Neurology, RWTH Aachen, Pauwelsstr. 30, 52074, Aachen, Germany
| | - Angelika Lampert
- Institute of Neurophysiology, Uniklinik RWTH Aachen, Pauwelsstrasse 30, 52074, Aachen, Germany
| | - Francesca Santoro
- Institute for Biological Information Processing - Bioelectronics IBI-3, Wilhelm-Johnen-Straße, 52428, Jülich, Germany
- Institute of Materials in Electrical Engineering 1, RWTH Aachen, Sommerfeldstr. 24, 52074, Aachen, Germany
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Zhang K, Liu Y, Song Y, Xu S, Yang Y, Jiang L, Sun S, Luo J, Wu Y, Cai X. Exploring retinal ganglion cells encoding to multi-modal stimulation using 3D microelectrodes arrays. Front Bioeng Biotechnol 2023; 11:1245082. [PMID: 37600306 PMCID: PMC10434521 DOI: 10.3389/fbioe.2023.1245082] [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: 06/23/2023] [Accepted: 07/21/2023] [Indexed: 08/22/2023] Open
Abstract
Microelectrode arrays (MEA) are extensively utilized in encoding studies of retinal ganglion cells (RGCs) due to their capacity for simultaneous recording of neural activity across multiple channels. However, conventional planar MEAs face limitations in studying RGCs due to poor coupling between electrodes and RGCs, resulting in low signal-to-noise ratio (SNR) and limited recording sensitivity. To overcome these challenges, we employed photolithography, electroplating, and other processes to fabricate a 3D MEA based on the planar MEA platform. The 3D MEA exhibited several improvements compared to planar MEA, including lower impedance (8.73 ± 1.66 kΩ) and phase delay (-15.11° ± 1.27°), as well as higher charge storage capacity (CSC = 10.16 ± 0.81 mC/cm2), cathodic charge storage capacity (CSCc = 7.10 ± 0.55 mC/cm2), and SNR (SNR = 8.91 ± 0.57). Leveraging the advanced 3D MEA, we investigated the encoding characteristics of RGCs under multi-modal stimulation. Optical, electrical, and chemical stimulation were applied as sensory inputs, and distinct response patterns and response times of RGCs were detected, as well as variations in rate encoding and temporal encoding. Specifically, electrical stimulation elicited more effective RGC firing, while optical stimulation enhanced RGC synchrony. These findings hold promise for advancing the field of neural encoding.
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Affiliation(s)
- Kui Zhang
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing, China
- School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing, China
| | - Yaoyao Liu
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing, China
- School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing, China
| | - Yilin Song
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing, China
- School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing, China
| | - Shihong Xu
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing, China
- School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing, China
| | - Yan Yang
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing, China
- School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing, China
| | - Longhui Jiang
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing, China
- School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing, China
| | - Shutong Sun
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing, China
- School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing, China
| | - Jinping Luo
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing, China
- School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing, China
| | - Yirong Wu
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing, China
- School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing, China
| | - Xinxia Cai
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing, China
- School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing, China
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Vėbraitė I, David-Pur M, Rand D, Głowacki ED, Hanein Y. Electrophysiological investigation of intact retina with soft printed organic neural interface. J Neural Eng 2021; 18. [PMID: 34736225 DOI: 10.1088/1741-2552/ac36ab] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2021] [Accepted: 11/04/2021] [Indexed: 12/26/2022]
Abstract
Objective.Understanding how the retina converts a natural image or an electrically stimulated one into neural firing patterns is the focus of on-going research activities.Ex vivo, the retina can be readily investigated using multi electrode arrays (MEAs). However, MEA recording and stimulation from an intact retina (in the eye) has been so far insufficient.Approach.In the present study, we report new soft carbon electrode arrays suitable for recording and stimulating neural activity in an intact retina. Screen-printing of carbon ink on 20µm polyurethane (PU) film was used to realize electrode arrays with electrodes as small as 40µm in diameter. Passivation was achieved with a holey membrane, realized using laser drilling in a thin (50µm) PU film. Plasma polymerized 3.4-ethylenedioxythiophene was used to coat the electrode array to improve the electrode specific capacitance. Chick retinas, embryonic stage day 13, both explanted and intact inside an enucleated eye, were used.Main results.A novel fabrication process based on printed carbon electrodes was developed and yielded high capacitance electrodes on a soft substrate.Ex vivoelectrical recording of retina activity with carbon electrodes is demonstrated. With the addition of organic photo-capacitors, simultaneous photo-electrical stimulation and electrical recording was achieved. Finally, electrical activity recordings from an intact chick retina (inside enucleated eyes) were demonstrated. Both photosensitive retinal ganglion cell responses and spontaneous retina waves were recorded and their features analyzed.Significance.Results of this study demonstrated soft electrode arrays with unique properties, suitable for simultaneous recording and photo-electrical stimulation of the retina at high fidelity. This novel electrode technology opens up new frontiers in the study of neural tissuein vivo.
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Affiliation(s)
- Ieva Vėbraitė
- School of Electrical Engineering, Tel Aviv University, Tel Aviv, 699780, Israel
| | - Moshe David-Pur
- School of Electrical Engineering, Tel Aviv University, Tel Aviv, 699780, Israel
| | - David Rand
- School of Electrical Engineering, Tel Aviv University, Tel Aviv, 699780, Israel
| | - Eric Daniel Głowacki
- Central European Institute of Technology, Brno University of Technology, Brno, 61200, Czech Republic
| | - Yael Hanein
- School of Electrical Engineering, Tel Aviv University, Tel Aviv, 699780, Israel.,Sagol School of Neuroscience, Tel Aviv University, Tel Aviv 699780, Israel
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Rincón Montes V, Gehlen J, Ingebrandt S, Mokwa W, Walter P, Müller F, Offenhäusser A. Development and in vitro validation of flexible intraretinal probes. Sci Rep 2020; 10:19836. [PMID: 33199768 PMCID: PMC7669900 DOI: 10.1038/s41598-020-76582-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Accepted: 10/28/2020] [Indexed: 12/01/2022] Open
Abstract
The efforts to improve the treatment efficacy in blind patients with retinal degenerative diseases would greatly benefit from retinal activity feedback, which is lacking in current retinal implants. While the door for a bidirectional communication device that stimulates and records intraretinally has been opened by the recent use of silicon-based penetrating probes, the biological impact induced by the insertion of such rigid devices is still unknown. Here, we developed for the first time, flexible intraretinal probes and validated in vitro the acute biological insertion impact in mouse retinae compared to standard silicon-based probes. Our results show that probes based on flexible materials, such as polyimide and parylene-C, in combination with a narrow shank design 50 µm wide and 7 µm thick, and the use of insertion speeds as high as 187.5 µm/s will successfully penetrate the retina, reduce the footprint of the insertion to roughly 2 times the cross-section of the probe, and induce low dead cell counts, while keeping the vitality of the tissue and recording the neural activity at different depths.
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Affiliation(s)
- V Rincón Montes
- Bioelectronics, Institute of Biological Information Processing-3, Forschungszentrum Jülich, Jülich, Germany
- RWTH Aachen University, Aachen, Germany
| | - J Gehlen
- Molecular and Cellular Physiology, Institute of Biological Information Processing-1, Forschungszentrum Jülich, Jülich, Germany
| | - S Ingebrandt
- Institute of Materials in Electrical Engineering 1, RWTH Aachen University, Aachen, Germany
| | - W Mokwa
- Institute of Materials in Electrical Engineering 1, RWTH Aachen University, Aachen, Germany
| | - P Walter
- Department of Ophthalmology, RWTH Aachen University, Aachen, Germany
| | - F Müller
- Molecular and Cellular Physiology, Institute of Biological Information Processing-1, Forschungszentrum Jülich, Jülich, Germany
| | - A Offenhäusser
- Bioelectronics, Institute of Biological Information Processing-3, Forschungszentrum Jülich, Jülich, Germany.
- RWTH Aachen University, Aachen, Germany.
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