Microfluidic-MEA hybrid systems for electrophysiological recordings of neuronal co-cultures

The study of brain development and degeneration is frequently observed in the scope of in vivo studies. However, newly developed in vitro models offer better precision and specificity in the investigation of neuronal networks. For example, the use of microfluidic microchannels, which have proven to be a successful method of isolating axons and directing their growth. Building upon the axon diode microchannel shape initially proposed by Peyrin et al. in 2011, I developed a µFluidic-MEA device with integrated microchannel structures on a recording platform. The microchannels were fabricated using photostructurable polymer, i.e. HD-8820, with the goal of improving the precision of aligning the compartmentalized microfluidic on top and facilitating the co-culturing of cortical and striatal neuronal cells. The primary objective of this thesis was to characterize the electrophysiological activity of a cortico-striatal co-culture in a µFluidic-MEA device, with variation of axon diode microchannel lengths. A secondary objective was to enhance the unidirectionality of the device and recordable activity yield by modifying the microelectrode array layout and the number of electrically active microchannels. The co-culture is then observed in a newly proposed design µFluidic-r16MEA device following the same conditions of reversible (RB) and irreversible (IRB) final device assembly. The analysis of recorded electrophysiological activity was focused on action potential spike shapes classification, microchannel amplification effect, and measuring of the signal propagation velocities over the long-term cell culture maintenance (up to DIV 35).One of the main findings in this thesis is the definition and characterization of small in peak-to-peak amplitude monophasic spike shapes that, to the best of our knowledge, have not been reported previously. The significance of these results lies in the comprehensive understanding of axonal dynamics within the microchannel area. The occurrence of this shape is associated with the boundary microchannel electrodes, indicating that the axon-electrode coupling is less effective and results in a less visible signal. Depending on the electrode pair and the length of the microchannel observed for this type of analysis, the signal propagation velocities range from 0.14 to 1.7 m/s. The size of the microchannels allows multiple axons to pass through, making it challenging to determine with certainty whether a given spike pair is correct. This can be observed in recordings where the directionality of signal propagation is atypical, with both forward and backward spike pairs being detected in a train of spikes that are labeled as belonging to the same axon. In conclusion, the successful application of a novel fabrication approach for microchannels on top of an MEA has been demonstrated. The following effects of final device assembly (RB vs. IRB) were observed on electrophysiological activity from cortico-striatal co-culture. The introduced changes in the overall microfluidic design have brought benefits in terms of microchannel activity yield and unidirectionality of axonal growth.