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(Color online) (a) Schematics of the experimental setup. Cells were placed and cultured on PDMS microposts, on which fibronectin was coated. A fibronectin-coated colloidal bead attached on the apex of the AFM tip was bound to the apical cell surface with an initial loading force less than 500 pN for a few tens of minutes. The oscillatory pulling force was applied in the frequency range of 0.01–0.5 Hz for three periods (0 < t < 3T) while the deflection of the micropost was measured by phase-contrast or bright-field microscopy. (b) Optical microscopic image of the AFM experiment. An objective lens (60×) with a long working distance was focused on the tops of the microposts. Red arrows indicate cell prestress, estimated from the deflection of microposts (letters A–D).
(a) Typical time series of the displacement of the z-piezo stage for moving the cantilever base z and loading force F at 0.1 Hz (T = 10 s). (b) The magnitude of elastic modulus normalized by that at f = 0.01 Hz. The magnitude follows a single power law, which is approximately proportional to f 0.17.
(Color online) Time series of lateral force magnitude applied to microposts during external modulation at different frequencies by AFM. Letters correspond to those in Fig. 1.
Typical traces of the lateral force vector, subtracting the prestress from the total lateral force applied to a micropost, in response to external force. Arrows represent the direction of prestress applied to the micropost.
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