Barbed channels enhance unidirectional connectivity between neuronal networks cultured on multi electrode arrays

Abstract

Cultured neurons on multi electrode arrays (MEAs) have been widely used to study various aspects of neuronal (network) functioning. A possible drawback of this approach is the lack of structure in these networks. At the single cell level, several solutions have been proposed to enable directed connectivity, and promising results were obtained. At the level of connected sub-populations, a few attempts have been made with promising results. First assessment of the designs' functionality, however, suggested room for further improvement. We designed a two chamber MEA aiming to create a unidirectional connection between the networks in both chambers (“emitting” and “receiving”). To achieve this unidirectionality, all interconnecting channels contained barbs that hindered axon growth in the opposite direction (from receiving to emitting chamber). Visual inspection showed that axons predominantly grew through the channels in the promoted direction. This observation was confirmed by spontaneous activity recordings. Cross-correlation between the signals from two electrodes inside the channels suggested signal propagation at ≈2 m/s from emitting to receiving chamber. Cross-correlation between the firing patterns in both chambers indicated that most correlated activity was initiated in the emitting chamber, which was also reflected by a significantly lower fraction of partial bursts (i.e., a one-chamber-only burst) in the emitting chamber. Finally, electrical stimulation in the emitting chamber induced a fast response in that chamber, and a slower response in the receiving chamber. Stimulation in the receiving chamber evoked a fast response in that chamber, but no response in the emitting chamber. These results confirm the predominantly unidirectional nature of the connecting channels from emitting to receiving chamber.

Multichannel activity propagation across an engineered axon network

“…Notably, with shorter distances between nodes, neuritogenesis led to the formation of new inter-modular connections, thereby converting the culture to a uniform network (Pan et al, 2015). Furthermore, in contrast to the segregation of axon fibers formed via patterned channels in previous modular cultures (Peyrin et al, 2011; le Feber et al, 2015; Pan et al, 2015), the axon tract of the connectome unit was composed of a near-continuous array of naturally fasciculated axons (Figure S5). The mean conduction velocity across the engineered axons of 0.26 m/s likely underestimates the actual value, since the calculation method did not remove the temporal effect of synaptic activity within the remote node.…”

Asymmetric axonal edge guidance: a new paradigm for building oriented neuronal networks

“…An alternative consists in using only geometrical constraints to passively control the direction of axonal growth. 7,8 So far, the most characterized and efficient design consists in tapered microchannels, acting like axon diodes. It uses the differential entrance probability of axons at either the wide or the narrow opening of the channels to promote unidirectional connectivity.…”

Reconstruction of directed neuronal networks in a microfluidic device with asymmetric microchannels

“…The first proof of concept that neuronal populations could be connected in a directional manner came from studies aiming at controlling axonal outgrowth through physical constraints using asymmetrical microchannels to guide axons (Peyrin et al, 2011). The use of asymmetric microchannels shapes has then been further extended (Gladkov et al, 2017;Le Feber, Postma, De Weerd, Weusthof, & Rutten, 2015), and some of these designs allowed good performances regarding axonal filtration, reaching a selectivity ratio as high as 10 between the forward and reverse directions.…”