Carbon and metal microelectrodes for recording of epileptic High Frequency Oscillations: A comparative study

International audienceHigh Frequency Oscillations (HFO: 80-600 Hz) and particularly Fast-Ripples (FRs: 200-600 Hz) gained increasing interest over the last decade as a biomarker of epileptogenic networks. FRs were shown to be generated by small clusters of weakly synchronized hyperexcitable neurons, the recording of which requires the use of intracerebral microelectrodes. Nonetheless, the detection of FRs recorded using classical metal microelectrodes is very challenging. This is due to their small size which increases the impedance resulting in poor signal-to-noise ratio (SNR) and distortion. Coating electrodes with Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is a promising approach that was found to reduce their impedance by several orders of magnitude. However, it is also associated with poor adhesion to metals, which severely impacts its stability for chronic usage. In this study, we compared the performances of novel carbon microelectrodes combined with PEDOT:PSS and gold electrodes with PEDOT:PSS coating to Stainless Steel electrodes for the recording and detection of in vivo FRs (mouse hippocampus, kainate model of epilepsy). Results suggest that carbon electrodes allow for better detectability of epileptiform events and, in particular FRs. Perspectives of this work include the design of clinical hybrid (micro-macro) electrodes for the pre-surgical evaluation of patients with Drug-Resistant Epilepsy (DRE) and the design of neural implants for other applications in which chronic recording over long periods of time is required. © 2023 IEEE

Tuning Microelectrodes’ Impedance to Improve Fast Ripples Recording

International audienceEpilepsy is a chronic neurological disorder characterized by recurrent seizures resulting from abnormal neuronal hyperexcitability. In the case of pharmacoresistant epilepsy requiring resection surgery, the identification of the Epileptogenic Zone (EZ) is critical. Fast Ripples (FRs; 200–600 Hz) are one of the promising biomarkers that can aid in EZ delineation. However, recording FRs requires physically small electrodes. These microelectrodes suffer from high impedance, which significantly impacts FRs’ observability and detection. In this study, we investigated the potential of a conductive polymer coating to enhance FR observability. We employed biophysical modeling to compare two types of microelectrodes: Gold (Au) and Au coated with the conductive polymer poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (Au/PEDOT:PSS). These electrodes were then implanted into the CA1 hippocampal neural network of epileptic mice to record FRs during epileptogenesis. The results showed that the polymer-coated electrodes had a two-order lower impedance as well as a higher transfer function amplitude and cut-off frequency. Consequently, FRs recorded with the PEDOT:PSS-coated microelectrode yielded significantly higher signal energy compared to the uncoated one. The PEDOT:PSS coating improved the observability of the recorded FRs and thus their detection. This work paves the way for the development of signal-specific microelectrode designs that allow for better targeting of pathological biomarkers

Tuning the Physically Induced Crystallinity of Microfabricated Bioresorbable Guides for Insertion of Flexible Neural Implants

International audienceDevices that safely interface with the brain are critical to advancing neuroengineering. Thin and flexible neural implants show great promise alongside established silicon technologies. They therefore require a physical stiffener to allow their insertion into brain tissue. Bioresorbable polymer shanks are novel transient guides enabling accurate implantation using biocompatible materials that will be absorbed by the body over time. The development of materials with optimized stiffness and degradation is needed to provide minimally invasive probes with precise insertion capability under surgical conditions. A microfabrication protocol for the patterning of polyvinyl alcohol and its physical cross-linking is presented, resulting in insertion guides with precise shapes and tunable degradation and stiffness. The results demonstrate a remarkable improvement in batch fabricating micro-scale neural shanks with designed crystallinity. It results in their prolonged degradation time, evaluated in agarose gel, and remarkably improved penetrability due to the increase in mechanical stiffness. In vitro and in vivo studies support the high acceptability of this combination in interfacing with neural cells and tissue. This work represents a novel approach to the material and process engineering of bioresorbable polymers for developing fully organic and safe implants