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Matching the mechanical properties of the brain: histological performance of soft elastomeric wires designed for use in neural interface devices (651.15)

A number of factors contribute to the failure of microelectrodes implanted into the central nervous system and designed for therapeutic purposes. We hypothesized that more closely matching the mechanical properties of the microelectrode to those of the brain in combination with biomolecule coatings would promote a lower inflammatory response and less scar tissue encapsulation. In vitro cell culture studies were used to evaluate novel elastomeric wires with Young’s modulus lower than 1 MPa; the L1 protein coating was compared to laminin‐coated and uncoated microelectrodes. In vivo work included characterization of the tissue response associated with microelectrode implantation into the subthalamic nucleus of rats (n = 4/group) at acute and chronic time points. Commercial tungsten microelectrodes with Young’s modulus of 411,000 MPa were used as a standard (stiff control). The in vitro results indicate that soft wires had greater neuronal but less astrocyte and microglial attachment than stiff wires. Additional benefits were noted with the L1 protein coating. In vivo histological assessment indicates the superior performance of soft wires with the L1 protein coating: increased neuronal density (NF200 staining), decreased microglial presence (Iba1 staining), decreased astrocyte activation (GFAP staining) and decreased neuronal cell death (NeuN/Caspase‐3 colocalization) when compared to control stiff wires either with or without L1 coating and to soft wires without L1. This work contributes to evidence supporting the use of soft microelectrodes and the L1 protein coating.