A new exposure system for the in vitro detection of GHz field effects on neuronal networks

Dosimetric Characteristics of an EMF Delivery System Based on a Real-Time Impedance Measurement Device

In this paper, the dosimetric characterization of an EMF exposure setup compatible with real-time impedance measurements of adherent biological cells is proposed. The EMF are directly delivered to the 16-well format plate used by the commercial xCELLigence apparatus. Experiments and numerical simulations were carried out for the dosimetric analysis. The reflection coefficient was less than -10 dB up to 180 MHz and this exposure system can be matched at higher frequencies up to 900 and 1800 MHz. The specific absorption rate (SAR) distribution within the wells containing the biological medium was calculated by numerical finite-difference time domain simulations and results were verified by temperature measurements at 13.56 MHz. Numerical SAR values were obtained at the microelectrode level where the biological cells were exposed to EMF including 13.56, 900, and 1800 MHz. At 13.56 MHz, the SAR values, within the cell layer and the 270-μL volume of medium, are 1.9e3 and 3.5 W/kg/incident mW, respectively.

In-vitro exposure of neuronal networks to the GSM-1800 signal

The central nervous system is the most likely target of mobile telephony radiofrequency (RF) field exposure in terms of biological effects. Several electroencephalography (EEG) studies have reported variations in the alpha-band power spectrum during and/or after RF exposure, in resting EEG and during sleep. In this context, the observation of the spontaneous electrical activity of neuronal networks under RF exposure can be an efficient tool to detect the occurrence of low-level RF effects on the nervous system. Our research group has developed a dedicated experimental setup in the GHz range for the simultaneous exposure of neuronal networks and monitoring of electrical activity. A transverse electromagnetic (TEM) cell was used to expose the neuronal networks to GSM-1800 signals at a SAR level of 3.2 W/kg. Recording of the neuronal electrical activity and detection of the extracellular spikes and bursts under exposure were performed using microelectrode arrays (MEAs). This work provides the proof of feasibility and preliminary results of the integrated investigation regarding exposure setup, culture of the neuronal network, recording of the electrical activity, and analysis of the signals obtained under RF exposure. In this pilot study on 16 cultures, there was a 30% reversible decrease in firing rate (FR) and bursting rate (BR) during a 3 min exposure to RF. Additional experiments are needed to further characterize this effect.

Investigation of cell-substrate interactions by focused ion beam preparation and scanning electron microscopy

Cell-substrate interactions, which are an important issue in tissue engineering, have been studied using focused ion beam (FIB) milling and scanning electron microscopy (SEM). Sample cross-sections were generated at predefined positions (target preparation) to investigate the interdependency of growing cells and the substrate material. The experiments focus on two cell culturing systems, hepatocytes (HepG2) on nanoporous aluminum oxide (alumina) membranes and mouse fibroblasts (L929) and primary nerve cells on silicon chips comprised of microneedles. Cross-sections of these soft/hard hybrid systems cannot be prepared by conventional techniques like microtomy. Morphological investigations of hepatocytes growing on nanoporous alumina membranes demonstrate that there is in-growth of microvilli from the cell surface into porous membranes having pore diameters larger than 200 nm. Furthermore, for various cell cultures on microneedle arrays contact between the cells and the microneedles can be observed at high resolution. Based on FIB milled cross-sections and SEM micrographs cells which are only in contact with microneedles and cells which are penetrated by microneedles can be clearly distinguished. Target preparation of biological samples by the FIB technique especially offers the possibility of preparing not only soft materials but also hybrid samples (soft/hard materials). Followed by high resolution imaging by SEM, new insights into cell surface interactions can be obtained.

Modular glass chip system measuring the electric activity and adhesion of neuronal cells--application and drug testing with sodium valproic acid

We developed a modular neurochip system by combining a small (16x16 mm2) glass neurochip (GNC) with a homemade head stage and commercial data acquisition hardware and software. The system is designed for the detection of the electric activity of cultivated nerve or muscle cells by a 52-microelectrode array (MEA). In parallel, cell adhesion can be registered from the electric impedance of an interdigitated electrode structure (IDES). The GNC was tested with various cell lines and primary cells. It is fully autoclavable and re-useable. Murine embryonic primary cells were used as a model system to correlate the electric activity and adhesion of neuronal networks in a drug test with sodium valproic acid. The test showed the advantage of the parallel IDES and MEA measurements, i.e. the parallel detection of cytotoxic and neurotoxic effects. Toxic exposure of the cells during neuronal network formation allows for the characterization of developmental neurotoxic effects even at drug concentrations below the EC50-value for acute neurotoxic effects. At high drug concentrations, the degree of cytotoxic damage can still be assessed from the IDES data in the event that no electric activity develops. The GNC provides optimal cell culture conditions for up to months in combination with full microscopic observability. The 4'' glass wafer technology allows for a high precision of the GNC structures and an economic production of our new system that can be applied in general and developmental toxicity tests as well as in the search for neuro-active compounds.

Electronic interfacing with living cells

The direct interfacing of living cells with inorganic electronic materials, components or systems has led to the development of two broad categories of devices that can (1) transduce biochemical signals generated by biological components into electrical signals and (2) transduce electronically generated signals into biochemical signals. The first category of devices permits the monitoring of living cells, the second, enables control of cellular processes. This review will survey this exciting area with emphasis on the fundamental issues and obstacles faced by researchers. Devices and applications that use both prokaryotic (microbial) and eukaryotic (mammalian) cells will be covered. Individual devices described include microbial biofuel cells that produce electricity, bioelectrical reactors that enable electronic control of cellular metabolism, living cell biosensors for the detection of chemicals and devices that permit monitoring and control of mammalian physiology.