Satellite spheroid formation in deep hemicylindrical channels. (a) Schematic illustration of neural cell seeding (i) and satellite spheroid formation (ii-iii) on the deep HCWN system. Type I satellite spheroids are generated from the host spheroid (ii), whereas type II spheroids are generated by self-aggregation of residual cells (iii). (b) An optical microscope image of a satellite spheroid formed by migration from a host spheroid (type I, red arrowhead). (c) Satellite spheroids in the center of deep hemicylindrical channels spontaneously self-aggregated from residual cells (type II, white arrowheads). (d) Optical microscope image of type I and type II satellite spheroids formed simultaneously around the host spheroid on deep hemicylindrical channels. (e) Network formation between host spheroids (black arrowheads), type I spheroids (red arrowheads), and type II spheroids (white arrowheads) was observed in the deep HCWN system. (f) Multi-neurite connections between the host spheroid and satellite spheroids (blue arrowheads) in the deep HCWN system. (g) Direction and length of neurite outgrowth from satellite spheroids in a hemicylindrical channel at day 5. Orange lines indicate the edges of the deep hemicylindrical channel.