Biomedical Engineering Reference
In-Depth Information
initial attachment (Garcia
et al.
, 1998) and adhesion strengthening (Gallant
et al.
, 2005).
Although these systems function well for low to moderate rotational
speeds, unsteady and inertial effects limit the use of these devices at higher
speeds and require the experimental validation of the fl ow conditions.
Another disadvantage is that cell adhesion processes cannot be examined
in situ
because the substrate is moving. After spinning, the sample must
be removed from the device in order to quantify the cells that remain
adherent.
Radial fl ow
A device with similarities to both the parallel plate and rotating disks,
the radial fl ow chamber uses axisymmetric fl ow between parallel surfaces
to generate a gradient of shear stress. These systems produce a range of
shear stresses that varies inversely with radial distance on a single substrate
(Cozens-Roberts
et al.
, 1990; Goldstein and Dimilla, 1997; Sordel
et al.
,
2007). The magnitude of the shear stress also depends on the fl uid viscos-
ity, volumetric fl ow rate, and gap height between the surfaces. The major
disadvantages of the radial fl ow assay are related to the complex hydrody-
namic conditions generated at the central inlet and the diffi culty in validat-
ing regions of laminar fl ow.
3.4
Collective motility of cell populations
In general, these assays measure the leading edge or total number of cells
migrating (Table 3.2). These methods do not consider single cell locomotion
or distinguish between cell migration and cell growth, both of which may
contribute to the expansion of a population over a distance. Therefore, care
must be taken in the interpretation of these assays as purely cell movement.
In addition, these assays are generally based on dispersion from regions of
high cell concentration to low, and are therefore highly dependent on assay
chamber geometry and initial cell concentration. The primary advantage of
the assays is their simplicity and ease of implementation.
3.4.1 Cell migration in two dimensions
The simpler class of collective cell migration assays characterizes motility
within a single plane.The two-dimensional nature of these methods makes
them relevant to
in vitro
test platforms and biomaterials surface interac-
tions. In addition, they rely primarily on standard microscopy techniques,
underscoring their ease of use.
