In-air activity recording from neuronal spheroids embedded in collagen gel

Cultured neuronal networks are promising biological information-processing units for biohybrid systems. While these systems must ultimately work under atmospheric conditions, the neuronal activity is difficult to sustain outside an incubator. Here, by comparing neuronal spheroids with and without collagen, we show that collagen gel embedding enables microelectrode array recording of their spontaneous activity in air. Although the embedding increased the distance between the spheroids and electrodes and thereby reduced the recorded signal amplitude, the collagen-embedded spheroids retained detectable activity for approximately 30 min under atmospheric conditions. In contrast, spheroids without collagen showed a more rapid decline in activity. These findings suggest that collagen gel preserves a hydrated microenvironment around the spheroids and could extend the window for extracellular recording outside an incubator without requiring bulky temperature- and humidity-control systems.