CELLS AND MEMBRANES - Nanoindentation with Biological Applications - page 321

2.1. Cell poking

The “Cell-poking” technique developed by Daily et al. 7 and Zahalak
et al . 8 can be regarded as an extended depth-sensing indentation method.
Figure 10-1 is the schematic view of the instrumental set-up. The setup
mainly comprises a micro- and nano-size punch pressing a sample cell
against a rigid substrate. Applied force is measured as a function of
punch displacement during indentation loading. However, some serious
drawbacks are identified. For instance, there is a potential detachment of
cytoplasm from the thin lipid bilayer. The local mechanical properties of
the sample cell can be determined, provided the indentation depth is less
than roughly 10% of the cell wall thickness in order to avoid a “substrate
backing” effect. 9 Measurements with such fine displacement control are
technically difficult to control and to yield feasible data is challenging.

A Cell
B Petri Dish with Solvent
C Indenterr with Sharp Tip
D Force Transducer
E Arm
F Translational Stage

F

E

D

C

B B

A

Figure 10-1. Schematic of experimental setup of “cell-poking” test.

2.2. Atomic force microscope (AFM)

AFM, originally designed for surface topography mapping, is now
widely used for force measurement of cells. The instrument comprises a
sharp tip for scanning the sample surface with atomic resolution and
an ultra-sensitive cantilever beam for sensing topographical changes
and tip-surface interactions. Figure 10-2 shows a schematic of AFM
indentation of biomembranes (testing geometry for single cell is shown