Abstract
The design of electrodes based on conductive polymers in brain-machine interface technology offers the opportunity to exploit variably manufactured materials to reduce gliosis, indeed the most common brain response to chronically implanted neural electrodes. In fact, the use of conductive polymers, finely tailored in their physical-chemical properties, might result in electrodes with improved adaptability to the brain tissue and increased charge-transfer efficiency. Here we interfaced poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) doped with different amounts of ethylene glycol (EG) with rat hippocampal primary cultures grown for 3 weeks on these synthetic substrates. We used immunofluorescence and scanning electron microscopy (SEM) combined to single cell electrophysiology to assess the biocompatibility of PEDOT:PSS in terms of neuronal growth and synapse formation. We investigated neuronal morphology, density and electrical activity. We reported the novel observation that opposite to neurons, glial cell density was progressively reduced, hinting at the ability of this material to down regulate glial reaction. Thus, PEDOT:PSS is an attractive candidate for the design of new implantable electrodes, controlling the extent of glial reactivity without affecting neuronal viability and function.
Highlights
Brain-machines interfaces are prosthetic devices designed to ameliorate the prognosis of neurological patients by targeting non-specific sensory/motor deficits in brain injuries, or more specific symptoms in Parkinson’s disease, chronic pain and epilepsy (Donoghue, 2002; Machado et al, 2010; Goodrick, 2014).Recording/stimulation electrodes are the core component of implanted interfaces and need to show excellent and stable electrical properties together with a good biocompatibility once chronically exposed to the biological environment.The most common cause of implant failure is the brain tissue reaction against the electrodes (Polikov et al, 2005)
When investigating the mean number of neuritis departing from the cell soma (Lovat et al, 2005) in these samples we found no significant differences between control and PEDOT:PSS substrates
PEDOT:PSS layers doped with different amounts of ethylene glycol (EG) were characterized for their physical and morphological properties before using them as growth substrates for culturing hippocampal cells
Summary
The most common cause of implant failure is the brain tissue reaction against the electrodes (Polikov et al, 2005). This reaction favors the glial-scar formation leading to devices with high impedance and poor electrical charge transfer (Lempka et al, 2009). CP electrodes are characterized by low impedance when interfaced to excitable tissues. Both these features improve the quality of the recorded signals (Ludwig et al, 2006) and are required in the design of high-performing electrodes
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