Dosimetry of Microelectrodes Array Chips for Electrophysiological Studies Under Simultaneous Radio Frequency Exposures

Abstract

Studying the response of neuronal networks to radiofrequency signals requires the use of a specific device capable of accessing and simultaneously recording neuronal activity during electromagnetic fields (EMF) exposure. In this study, a Microelectrode Array (MEA) that records the spontaneous activity of neurons is coupled to an open transverse electromagnetic (TEM) cell which propagates EMF. We characterize this system both numerically and experimentally at 1.8 GHz. Two MEA versions were compared, for the first time, to determine the impact of their design dissimilarities on the response to EMF. Macroscopic and microscopic measurements using respectively a fiber-optic probe and a temperature-dependent fluorescent dye (Rhodamine-B) were carried out. Results indicate that one MEA shows more stability toward the changes of the surrounding environment compared to the other MEA. Using a fiber-optic thermometer, the measured specific absorption rate (SAR) probe value in the center of the more stable MEA was 5.5±2.3 W/kg. Using a Rhod-B microdosimetry technique, the measured SAR value at the level of the MEA electrodes was 7.0±1.04 W/kg. SAR values are normalized per 1-W incident power. Due to the additional metallic planes and a smaller chip aperture, this new recording chip is steadier in terms of SAR and temperature stability allowing high exposure homogeneity as required during biological experiments. A typical neuronal activity recording under EMF exposure is reported.

Comparative study between radiofrequency-induced and muscimol-induced inhibition of cultured networks of cortical neuron

“…Indeed a recent re-evaluation of the dosimetry (Nefzi et al, 2022) indicated estimated SAR values per Watt of incident power of 5.5 ± 2.3 W/kg and 40.3 ± 5.3 W/kg respectively for the present and former MEA version (El Khoueiry et al, 2018 andMoretti et al, 2013). This reevaluation was made possible thanks to the continuous progress in experimental and numerical dosimetry and better assessment of influencing environmental factors (Nefzi et al, 2022). The SAR level of 28.6 W/kg is however higher than local basic safety restriction fixed at 2.0 W/kg (ICNIRP, 2020).…”

“…This new design shared the main characteristic of these MEAs namely the amplifier contact pads placed underneath the printed circuit board but presented as main evolutions a reduced chip aperture to the limits of the recording zone and several ground planes in the multi-layered PCB. These evolutions allowed this device to be steadier in terms of Specific Absoption Rate (SAR) and temperature stability during EMF exposure (see Nefzi et al, 2022, for numerical and experimental dosimetry of the device). In this modified MEA, SAR values normalized per 1 Watt of incident power was estimated at 5.5 ± 2.3 W/kg.…”

“…The experimental setup for simultaneous electrophysiological recordings and exposure to RF or pharmacological agents comprised a MEA coupled to an open transverse electromagnetic cell (TEM) (Merla et al, 2011, Soueid et al 2014, Nefzi et al, 2022) and a perfusion system allowing continuous fresh medium exchange with minimal disturbances. RF CW signal at 1800 MHz was delivered to the open TEM cell with a signal generator-amplifier (RFPA, Artigues-près-Bordeaux, France).…”

“…Signaling at this receptor is well understood thus making it a solid reference for comparative studies aiming to infer potential mechanisms of actions of particular drugs or treatments. Experiments were carried on a new MEA device with improved stability during EMF exposure (Nefzi et al, 2022) and changes in spiking, bursting activity and action potential (AP) waveform in response to RF fields or MU were analyzed and compared. This comparative approach allowed us to identify similarities and dissimilarities between these two forms of inhibition and to employ them as a basis for unravelling a potential mechanism of action of the inhibitory effect of RF fields on cultured neural networks.…”

Comparative study between radiofrequency- and muscimol-induced inhibition of cultured net5 works of cortical neuron

“…To enable simultaneous recording and exposure to RF fields, MEAs were maintained “sandwiched” between the TEM bottom plate and the preamplifier (MEA1060-Inv, Multi-Channel Systems, MCS, Reutlingen, Germany), as described in previous publications (El Khoueiry et al, 2018; Merla et al, 2011; Moretti et al, 2013; Nefzi et al, 2022). Once installed on the MEA amplifier, a perfusion holder (MEA-MEM-PL5, ALA Scientific Instruments Inc. USA) was inserted into the MEA chamber.…”