4. Adhesion test method
Several techniques can be applied to measure cell adhesion force[117]. It can be divided into two main categories:
population cell and single-cell methods, as shown in Figure 7. Many of
them, including the simple washing assay, the spinning disk technique,
and flow chambers, are based on the hydrodynamic shear flow removing
cells from the surface. The adhesion force can be calculated from the
applied flow rate,e, and thus, the adhesion force of the cells can be
measured. However, these techniques do not enable single-cell targeting,
and cell shape strongly impacts the shear force, making it difficult to
calculate the exact adhesion force. Furthermore, only weakly adhered
cells can be probed due to the technically limited shear stress
magnitude.
In order to directly probe the adhesion of single cells, an AFM probe or
micropipette can be used as an option. [118-120]Single-cell adhesion assay techniques can be further classified
according to how they work. The micropipette aspiration uses a glass
micropipette to suck cells from the surface and calculates adhesion
forces by hydrodynamic simulation. AFM is combined with modified probes
or nanofluidic channels to study cell adhesion. Fluorescence resonance
energy transfer (FRET) sensors can also be used to detect transgenic
cell protein fluorescence signals to characterize the mechanical tension
of cells and to measure the traction force generated by adherent cells
in the substrate.