Figure 1: Pattern design mask and examples of patterned embryonic hippocampal neurons. A: In this design, a line/gap topology is used to promote neuronal polarity in feed-forward architecture between horizontal layers of soma interconnected by vertical segments. The mask consisted of four 50 μm wide lines that were oriented over every other row of electrodes on an MEA to provide a primary attachment point for neural soma. Each line contained 8 vertical 5 μm wide narrow extensions that terminated 10 μm before the next layer in the series to guide neuronal polarity and produce directional connectivity proceeding from the bottom layer upward in a feed-forward architecture. B: Phase contrast images of simple patterned neuronal networks on a Multichannel Systems microelectrode array that utilize gaps to promote neuronal polarity (image is at 7 days in vitro. Electrode distance 200 μm) consisting of two short arcs, interconnected layers, and grid patterns.