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Tawakol O, Herman MD, Foxley S, Mushahwar VK, Towle VL, Troyk PR. In-vivo testing of a novel wireless intraspinal microstimulation interface for restoration of motor function following spinal cord injury. Artif Organs 2024; 48:263-273. [PMID: 37170929 DOI: 10.1111/aor.14562] [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: 02/17/2023] [Revised: 04/21/2023] [Accepted: 05/09/2023] [Indexed: 05/13/2023]
Abstract
BACKGROUND Spinal cord injury causes a drastic loss in motor and sensory function. Intraspinal microstimulation (ISMS) is an electrical stimulation method developed for restoring motor function by activating the spinal networks below the level of injury. Current ISMS technology uses fine penetrating microwires to stimulate the ventral horn of the lumbar enlargement. The penetrating wires traverse the dura mater through a transdural conduit that connects to an implantable pulse generator. OBJECTIVE A wireless, fully intradural ISMS implant was developed to mitigate the potential complications associated with the transdural conduit, including tethering and leakage of cerebrospinal fluid. METHODS Two wireless floating microelectrode array (WFMA) devices were implanted in the lumbar enlargement of an adult domestic pig. Voltage transients were used to assess the electrochemical stability of the interface. Manual flexion and extension movements of the spine were performed to evaluate the mechanical stability of the interface. Post-mortem 9T MRI imaging was used to confirm the location of the electrodes. RESULTS The WFMA-based ISMS interface successfully evoked extension and flexion movements of the hip joint. Stimulation thresholds remained stable following manual extension and flexion of the spine. CONCLUSION The preliminary results demonstrate the surgical feasibility as well as the functionality of the proposed wireless ISMS system.
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Affiliation(s)
- Omar Tawakol
- Department of Biomedical Engineering, Illinois Institute of Technology, Chicago, Illinois, USA
| | - Martin D Herman
- Department of Neurosurgery, University of Chicago, Chicago, Illinois, USA
| | - Sean Foxley
- Department of Radiology, University of Chicago, Chicago, Illinois, USA
| | - Vivian K Mushahwar
- Department of Medicine and Neuroscience, Mental Health Institute, University of Alberta, Edmonton, Alberta, Canada
- Sensory Motor Adaptive Rehabilitation Technology (SMART) Network, University of Alberta, Edmonton, Alberta, Canada
| | - Vernon L Towle
- Department of Neurology, University of Chicago, Chicago, Illinois, USA
| | - Philip R Troyk
- Department of Biomedical Engineering, Illinois Institute of Technology, Chicago, Illinois, USA
- Sensory Motor Adaptive Rehabilitation Technology (SMART) Network, University of Alberta, Edmonton, Alberta, Canada
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Butt E, Wang BY, Shin A, Chen ZC, Bhuckory M, Shah S, Galambos L, Kamins T, Palanker D, Mathieson K. Three-dimensional electro-neural interfaces electroplated on subretinal prostheses. J Neural Eng 2024; 21:016030. [PMID: 38364290 PMCID: PMC10884765 DOI: 10.1088/1741-2552/ad2a37] [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: 11/21/2023] [Revised: 01/26/2024] [Accepted: 02/16/2024] [Indexed: 02/18/2024]
Abstract
Objective.Retinal prosthetics offer partial restoration of sight to patients blinded by retinal degenerative diseases through electrical stimulation of the remaining neurons. Decreasing the pixel size enables increasing prosthetic visual acuity, as demonstrated in animal models of retinal degeneration. However, scaling down the size of planar pixels is limited by the reduced penetration depth of the electric field in tissue. We investigated 3-dimensional (3d) structures on top of photovoltaic arrays for enhanced penetration of the electric field, permitting higher resolution implants.Approach.3D COMSOL models of subretinal photovoltaic arrays were developed to accurately quantify the electrodynamics during stimulation and verified through comparison to flat photovoltaic arrays. Models were applied to optimize the design of 3D electrode structures (pillars and honeycombs). Return electrodes on honeycomb walls vertically align the electric field with bipolar cells for optimal stimulation. Pillars elevate the active electrode, thus improving proximity to target neurons. The optimized 3D structures were electroplated onto existing flat subretinal prostheses.Main results.Simulations demonstrate that despite exposed conductive sidewalls, charge mostly flows via high-capacitance sputtered iridium oxide films topping the 3D structures. The 24μm height of honeycomb structures was optimized for integration with the inner nuclear layer cells in the rat retina, whilst 35μm tall pillars were optimized for penetrating the debris layer in human patients. Implantation of released 3D arrays demonstrates mechanical robustness, with histology demonstrating successful integration of 3D structures with the rat retinain-vivo.Significance. Electroplated 3D honeycomb structures produce vertically oriented electric fields, providing low stimulation thresholds, high spatial resolution, and high contrast for pixel sizes down to 20μm. Pillar electrodes offer an alternative for extending past the debris layer. Electroplating of 3D structures is compatible with the fabrication process of flat photovoltaic arrays, enabling much more efficient retinal stimulation.
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Affiliation(s)
- Emma Butt
- Institute of Photonics, Department of Physics, University of Strathclyde, Glasgow, United Kingdom
| | - Bing-Yi Wang
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, United States of America
- Department of Physics, Stanford University, Stanford, CA, United States of America
| | - Andrew Shin
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, United States of America
| | - Zhijie Charles Chen
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, United States of America
- Department of Electrical Engineering, Stanford University, Stanford, CA, United States of America
| | - Mohajeet Bhuckory
- Department of Ophthalmology, Stanford University, Stanford, CA, United States of America
| | - Sarthak Shah
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, United States of America
| | - Ludwig Galambos
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, United States of America
- Department of Electrical Engineering, Stanford University, Stanford, CA, United States of America
| | - Theodore Kamins
- Department of Electrical Engineering, Stanford University, Stanford, CA, United States of America
| | - Daniel Palanker
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, United States of America
- Department of Ophthalmology, Stanford University, Stanford, CA, United States of America
| | - Keith Mathieson
- Institute of Photonics, Department of Physics, University of Strathclyde, Glasgow, United Kingdom
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