In the latest years, several attempts to develop extracellular microtransducers to record electrophysiological activity of excitable cells have been done. In particular, many efforts have been oriented to increase the coupling conditions, and, thus, improving the quality of the recorded signal. Gold mushroom-shaped microelectrodes (GMμE) are an example of nano-devices to achieve those requirements. In this study, we developed an equivalent electrical circuit of the neuron-microelectrode system interface to simulate signal recordings from both planar and engulfed micro-nano-electrodes. To this purpose, models of the neuron, planar, gold planar microelectrode, and GMμE, neuro-electronic junction (microelectrode-electrolyte interface, cleft effect, and protein-glycocalyx electric double layer) are presented. Then, neuronal electrical activity is simulated by Hspice software, and analyzed as a function of the most sensitive biophysical models parameters, such as the neuron-microelectrode cleft width, spreading and seal resistances, ion-channel densities, double-layer properties, and microelectrode geometries. Results are referenced to the experimentally recorded electrophysiological neuronal signals reported in the literature.
Microtransducer arrays, both metal microelectrodes and silicon-based devices, are widely used as neural interfaces to measure, extracellularly, the electrophysiological activity of excitable cells. Starting from the pioneering works at the beginning of the 70's, improvements in manufacture methods, materials, and geometrical shape have been made. Nowadays, these devices are routinely used in different experimental conditions (both in vivo and in vitro), and for several applications ranging from basic research in neuroscience to more biomedical oriented applications. However, the use of these micro-devices deeply depends on the nature of the interface (coupling) between the cell membrane and the sensitive active surface of the microtransducer. Thus, many efforts have been oriented to improve coupling conditions. Particularly, in the latest years, two innovations related to the use of carbon nanotubes as interface material and to the development of micro-structures which can be engulfed by the cell membrane have been proposed. In this work, we review what can be simulated by using simple circuital models and what happens at the interface between the sensitive active surface of the microtransducer and the neuronal membrane of in vitro neurons. We finally focus our attention on these two novel technological solutions capable to improve the coupling between neuron and micro-nano transducer.
The purpose of this paper is to characterize the neuron-microelectrode junction, based on the equivalent electric-circuit approach. As a result, recording of action potentials can be simulated with a general-purpose circuit simulation program such as HSPICE. The response of the microelectrode was analyzed as a function of parameters such as sealing resistance and adhesion conditions. The models of the neuron and microelectrode implemented in HSPICE were first described. These models were used to simulate the behavior of the junction between a patch of neuronal membrane (described by the compartmental model) and a microelectrode.
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