[Why does a cell monolayer replicate the metal tray pattern of the thermostat?]

Cells freshly seeded into the closed culture flasks or dishes and placed on the metal tray with holes of the thermostat or incubator are seen to form the layer with uneven density: with high density corresponding to the flask bottom regions above the metal and low density corresponding to the flask bottom region above the holes in the tray. The effect was shown using several cell lines with different degrees of transformation and saturation density, including Swiss 3T3. The main cause of this effect is the difference between the temperature inside the thermostat and the lower temperature of the flasks with culture medium (rather than between the metal framework and the air), together with a high heat conduction of the metal. The reverse difference in the temperatures (higher temperature of the culture flasks) leads to the formation of the reverse pattern of the cell layer, with higher density corresponding to the holes. The temperature differences exert their influence presumably during the first 10-15 minutes after the cells seeding, when the process of cell sedimentation is involved possibly by creating the microcurrents in the medium.