Biomedical Engineering Reference
In-Depth Information
1997; Finger
et al.
, 1996). An advantage of using fl ow chambers for adhe-
sion assays is that they produce well-defi ned forces, in contrast to the static
sedimentation and wash method. Another advantage is that cell adhesion
events can be visualized under a microscope in fl ow chambers constructed
of transparent materials such as glass and PDMS. This permits the detection
of rapidly occurring processes such as tethering and rolling or adhesive con-
tact remodeling (Smith
et al.
, 1999).
3.3 Cell adhesion strength
The following assays specifi cally quantify the strength of cell adhesion by
characterizing the capacity to resist forces applied to detach the cells (Table
3.1). Several quantitative adhesion assays have been developed to apply
controlled detachment forces to adherent cells. These methods are gener-
ally classifi ed according to the type of force applied to detach the cells and
can be divided into the subcategories of (1) micromanipulation, (2) centri-
fugation and (3) hydrodynamic force.
3.3.1 Micromanipulation
Micromanipulation encompasses several techniques which apply either nor-
mal or tangential detachment forces with a micropipette, microprobe, AFM
cantilever, or laser tweezers (Marshall
et al.
, 2003; Tozeren
et al.
, 1989; Evans
et al.
, 1991; McKeever, 1974; Prechtel
et al.
, 2002; Shao and Hochmuth, 1999;
Litvinov
et al.
, 2002). The major advantage of these techniques is that they
provide sensitive (pN range) real-time force-displacement measurements
of single or low-number receptor-ligand interactions. However, the upper
range of forces that can be applied by these techniques (~ 10 nN) is not
suffi cient to examine long-term integrin-mediated adhesion strengthening.
Furthermore, these methodologies require specialized calibrated equip-
ment and the measurements are time- and skill-intensive as cells are probed
one at a time.
3.3.2 Centrifugation
The centrifugation approach is a simple technique that employs standard
laboratory equipment to provide reproducible measurements of cell adhe-
sion for a large cell population (Chu
et al.
, 1994; Giacomello
et al.
, 1999;
McClay
et al.
, 1981; Reyes and Garcia, 2003). In this assay, a substrate (e.g.
ECM-coated multi-well plate) containing adherent cells is spun at a speci-
fi ed speed to apply a controlled detachment force perpendicular to the cell
adhesive area. This confi guration exploits the difference in density between
cells and the culture medium to exert a body force on the cell. Typically, the
