QUANTIFYING CELL ADHESION USING SINGLE-CELL FORCE SPECTROSCOPY - Life at the Nanoscale: Atomic Force Microscopy of Live Cells - page 210

force is reached. After a deined contact time, the cell is withdrawn at
constant velocity. Bonds between cell and substrate sequentially break until
cell and substrate are completely separated ( Fig. 10.3 ). During the approach
and retract process, the force acting on the cantilever, which is proportional
to the cantilever delection, is recorded in a force-distance (F-D) curve.
Parameters inluencing the experimental results, such as contact force and
time, contact condition (constant height, constant force) and pulling velocity
can be precisely controlled.

10.3.3 Interpretaon of F-D Curves

When interpreting F-D curves, it must be considered that they contain
information about the established interactions between cell and substrate
and about mechanical properties of the cell. Often F-D curves ( Fig. 10.4 )

show characteristic complex interaction patterns. Approach F-D curves ( Fig.
10.4 , black) are characterized by a steep force increase occurring as soon as
the cell is in contact with the substrate. The slope of the F-D curve in this
contact region (dashed ellipse E) can be used to extract elastic properties of
the cell. The retraction F-D curve ( Fig. 10.4 , blue) is typically characterized
by the maximum force required to separate the cell from the substrate
referred to as the detachment force (

28,35,47

F D ). F D is followed by step-like events,

which are either preceded (jumps) or not preceded (tethers) by a ramp-like

increase in force.

(a) (b)

Figure 10.4. Information extracted from an F-D curve. (a) Schematic representation
of the F-D cycle and recorded F-D curves. The approach curve is shown in black,
retraction curve in blue. (b) Information that can be obtained from the F-D curves: F D

maximal force required to detach the cell from the substrate, E elastic properties, W D
adhesion work, d distance required for complete separation of cell from the substrate,
discrete force steps (jumps and tethers).