Using the photo-thermal etching method, microstructures can be formed within the agar layer on the chip by melting a portion of the agar layer at the spot of a focused infrared laser beam as shown in Figure 2A [7,23]. This method can be applied even during cultivation, so the network pattern of nerve cells can be changed during cultivation by adding microchannels between two adjacent microchambers in a step-by-step fashion. This helps us to understand the meaning of the spatial pattern of a neuronal network by comparing the changes in signals before and after the network shape is changed. For example, an agar microchamber placed on top of an MEA can be used to record the long-term electronic properties of topographically controlled neuronal networks with precise fixation of cell positions and flexible network pattern rearrangement through photo-thermal etching of the agar layer.
