Time-lapse viscoelastic imaging of living fibroblasts using force modulation mode in AFM

Using the force modulation mode in atomic force microscopy, we have succeeded in capturing time-lapse viscoelastic images of living mouse fibroblasts (NIH3T3) for several hours in a physiological condition without damaging the fibroblasts. Elongation of the lamellipodia and swelling of blebs were observed in time-lapse topographic images, which were taken every 10 min. The corresponding viscoelastic responses at a frequency of 600 Hz were visualized as consecutive images. The stiffer part of the cell body was fairly stable and did not show morphological changes for over 1 h. This is probably due to excess condensation of the actin network, hardening the cell cortex, and lowering the cytoskeletal activity. The nuclear portion of the cell body seems to be slightly less viscous than the peripheral region.