(a) Scanning electron microscope (SEM) image of octagonal separators on the sensor platform. With the supporting parts for the 3D-printing process positioned at the top surface of the device, we were able to prepare a platform with a smooth bottom surface that contacted the glass bottom dish. (b) SEM image of the octagonal separator from the bottom side. Eight openings were created in an octagonal formation. (c) Fluorescence image of LIVE/DEAD staining cells in the octagonal sensor. (d) Temporal variation in the fluorescence intensity emitted from cells in reaction to muscarine depending on culture conditions: monolayered culture (red) and 3D culture (blue). The intensity was higher for the 3D-cultured cells inside the hydrogel than for the monolayered cells on the hydrogel. The intensity change was also clearly visible for the cells in the hydrogel when compared with the cells on the hydrogel.