title: Mechanical failure modes of chronically implanted planar silicon-based neural probes for laminar recording.
abstract: Penetrating intracortical electrode arrays that record brain activity longitudinally are powerful tools for basic neuroscience research and emerging clinical applications. However, regardless of the technology used, signals recorded by these electrodes degrade over time. The failure mechanisms of these electrodes are understood to be a complex combination of the biological reactive tissue response and material failure of the device over time. While mechanical mismatch between the brain tissue and implanted neural electrodes have been studied as a source of chronic inflammation and performance degradation, the electrode failure caused by mechanical mismatch between different material properties and different structural components within a device have remained poorly characterized. Using Finite Element Model (FEM) we simulate the mechanical strain on a planar silicon electrode. The results presented here demonstrate that mechanical mismatch between iridium and silicon leads to concentrated strain along the border of the two materials. This strain is further focused on small protrusions such as the electrical traces in planar silicon electrodes. These findings are confirmed with chronic in vivo data (133-189 days) in mice by correlating a combination of single-unit electrophysiology, evoked multi-unit recordings, electrochemical impedance spectroscopy, and scanning electron microscopy from traces and electrode sites with our modeling data. Several modes of mechanical failure of chronically implanted planar silicon electrodes are found that result in degradation and/or loss of recording. These findings highlight the importance of strains and material properties of various subcomponents within an electrode array.
authors.affiliation: Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States; Center for Neural Basis of Cognition, Pittsburgh, PA, United States; McGowan Institute for Regenerative Medicine, Pittsburgh, PA, United States. Electronic address: tdk18@pitt.edu.
authors.forename: Takashi D Y
authors.initials: TD
authors.lastname: Kozai
authors.affiliation: Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States.
authors.forename: Kasey
authors.initials: K
authors.lastname: Catt
authors.affiliation: Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States.
authors.forename: Xia
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States; Division of Biology and Biological Engineering, California Institute of Technology, United States.
authors.forename: Zhannetta V
authors.initials: ZV
authors.lastname: Gugel
authors.affiliation: Neuroscience Imaging Center, University of Pittsburgh, Pittsburgh, PA, United States.
authors.forename: Valur T
authors.initials: VT
authors.lastname: Olafsson
authors.affiliation: Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States; Department of Radiology, University of Pittsburgh, Pittsburgh, PA, United States.
authors.forename: Alberto L
authors.initials: AL
authors.lastname: Vazquez
authors.affiliation: Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States; Center for Neural Basis of Cognition, Pittsburgh, PA, United States; McGowan Institute for Regenerative Medicine, Pittsburgh, PA, United States. Electronic address: xic11@pitt.edu.
authors.forename: X Tracy
authors.initials: XT
authors.lastname: Cui
mesh_terms: D000818:Animals; D001921:Brain / Q000033:anatomy & histology / Q000502:physiology*; D002428:Cebus; D017097:Electric Impedance; D004567:Electrodes, Implanted; D020342:Finite Element Analysis; D006801:Humans; D008279:Magnetic Resonance Imaging; D008810:Mice, Inbred C57BL; D008855:Microscopy, Electron, Scanning; D023421:Models, Animal; D011475:Prosthesis Failure; D012825:Silicon / Q000737:chemistry*; D013314:Stress, Mechanical
chemical_list: D012825:Silicon
keywords: Abiotic Failure; Intracortical electrode; Magnetic resonance imaging; Material failure; Neural interface; Structural failure