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

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